α-Melanocyte-Stimulating Hormone and Related Tripeptides: Biochemistry, Antiinflammatory and...

�-Melanocyte-Stimulating Hormone and RelatedTripeptides: Biochemistry, Antiinflammatory andProtective Effects in Vitro and in Vivo, and FuturePerspectives for the Treatment of Immune-MediatedInflammatory Diseases

Thomas Brzoska,* Thomas A. Luger, Christian Maaser, Christoph Abels, and Markus Bohm*

Department of Dermatology (T.B., T.A.L., M.B.), University of Munster, Munster, Germany; Wolff Arzneimittel (T.B., C.A.),Bielefeld, Germany; and Department of Internal Medicine (C.M.), University of Munster, Munster, Germany

�-MSH is a tridecapeptide derived from proopiomelanocortin.Many studies over the last few years have provided evidencethat �-MSH has potent protective and antiinflammatory ef-fects. These effects can be elicited via centrally expressedmelanocortin receptors that orchestrate descending neuro-genic antiinflammatory pathways. �-MSH can also exert an-tiinflammatory and protective effects on cells of the immunesystem and on peripheral nonimmune cell types expressingmelanocortin receptors. At the molecular level, �-MSH affectsvarious pathways implicated in regulation of inflammationand protection, i.e., nuclear factor-�B activation, expressionof adhesion molecules and chemokine receptors, productionof proinflammatory cytokines and mediators, IL-10 synthesis,T cell proliferation and activity, inflammatory cell migration,expression of antioxidative enzymes, and apoptosis. The an-tiinflammatory effects of �-MSH have been validated in ani-

mal models of experimentally induced fever; irritant and al-lergic contact dermatitis, vasculitis, and fibrosis; ocular,gastrointestinal, brain, and allergic airway inflammation; andarthritis, but also in models of organ injury. One obstaclelimiting the use of �-MSH in inflammatory disorders is itspigmentary effect. Due to its preserved antiinflammatory ef-fect but lack of pigmentary action, the C-terminal tripeptideof �-MSH, KPV, has been delineated as an alternative for an-tiinflammatory therapy. KdPT, a derivative of KPV corre-sponding to amino acids 193–195 of IL-1�, is also emerging asa tripeptide with antiinflammatory effects. The physiochemi-cal properties and expected low costs of production renderboth agents suitable for the future treatment of immune-me-diated inflammatory skin and bowel disease, fibrosis, allergicand inflammatory lung disease, ocular inflammation, andarthritis. (Endocrine Reviews 29: 581–602, 2008)

I. IntroductionII. Biochemistry of �-MSH and Related Peptides

A. Biosynthesis of �-MSHB. Structure of �-MSH and related tripeptidesC. Melanocortin receptors—obligatory structures mediat-

ing the inflammatory effects of �-MSH and relatedtripeptides?

III. Antiinflammatory and Protective Spectrum of �-MSHA. Antiinflammatory effects in vitroB. Antiinflammatory effects in vivoC. Cytoprotective effects in vitroD. Protective effects against organ damage

IV. Antiinflammatory Effects of �-MSH-Related Tripeptides inVitro and in Vivo

V. Therapeutic Potential of �-MSH-Related Tripeptides in Hu-man Immune-Mediated Inflammatory Diseases

I. Introduction

�-MSH has fascinated researchers since its discovery andinitial characterization as a pigment-inducing (mela-

notropic) peptide more than 50 yr ago. Enabled with a pleth-ora of biological activities far beyond pigment regulation, theantiinflammatory effects of �-MSH have received particularattention in the last few years due to the potential to bring�-MSH and related peptides into clinical practice, i.e., to treathuman inflammatory disorders with such novel agents (1–3).This paper summarizes our current knowledge on the im-munomodulatory spectrum of �-MSH, the parental peptidehormone based on which �-MSH tripeptides and derivativeshave subsequently been developed. The emphasis of thisreview is on antiinflammatory effects of �-MSH and its de-rived tripeptides. Because antiinflammatory and protectiveeffects are, however, closely related and often employ similareffector pathways, we included a separate section on theprotective spectrum of �-MSH in models of cell and tissueinjury/toxicity. To facilitate understanding of the text, the

First Published Online July 8, 2008* T.B. and M.B. contributed equally to this work.Abbreviations: AP1, Activator protein 1; AQP, aquaporin; BAL, bron-

choalveolar lavage; CNS, central nervous system; DNP, dinitrophenol;DRG, dorsal root ganglia; DSS, dextran sodium sulfate; EAE, experi-mental autoimmune encephalitis; FasL, Fas ligand; HO-1, heme oxy-genase-1; ICAM-1, intercellular adhesion molecule-1; IFN, interferon;I�B�, inhibitory subunit of NF-�B; iNOS, inducible NO synthase; KC,keratinocyte-derived chemokine; MC-R, melanocortin receptor; MMP,matrix metalloproteinase; MPO, myeloperoxidase; MW, molecularweight; NDP-MSH, [Nle4,d-Phe7]�-MSH; NF-�B, nuclear factor-�B;NO, nitric oxide; PBMC, peripheral blood mononuclear cells; PC, pro-hormone convertase; PG, prostaglandin; POMC, proopiomelanocortin.Endocrine Reviews is published by The Endocrine Society (http://www.endo-society.org), the foremost professional society serving theendocrine community.

0163-769X/08/$20.00/0 Endocrine Reviews 29(5):581–602Printed in U.S.A. Copyright © 2008 by The Endocrine Society

doi: 10.1210/er.2007-0027

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basic biochemistry of �-MSH and its principal mechanism ofaction via melanocortin receptors are also described.

II. Biochemistry of �-MSH and Related Peptides

A. Biosynthesis of �-MSH

�-MSH is naturally generated from a precursor hormonecalled proopiomelanocortin (POMC) (4). This approximately31-kDa protein molecule is the source for several bioactivepeptide hormones including ACTH, �-, �-, and �-MSH, andthe endogenous opioids including �-endorphin (Fig. 1A).Proteolytic cleavage of POMC is catalyzed by prohormoneconvertases (PCs), which are serine proteases of the subtili-sin/kexin type. PC1 and PC2 are currently considered themajor processing enzymes of POMC, although other mem-bers of the PC family, in particular PACE4 and furin con-vertase, may also process POMC (5). In contrast to ACTH,further processing of �-MSH via the action of C-terminalcarboxypeptidase, �-amidating monooxygenase, and

N-acetyltransferase is required for full biological activity ofthe peptide. ACTH, �-, �-, and �-MSH are the bona fidemelanocortins, a term describing the stimulatory effects ofthese peptides on pigment cells and cells of the zona fas-ciculata and glomerulosa of the adrenal gland. As will beoutlined below, the natural melanocortins elicit their biolog-ical effects via binding to specific surface receptors expressedon target cells. These receptors are distinct from receptors of�-endorphin, which belong to the family of opioid receptors.Although POMC peptides were originally considered asneuropeptides, it is now well established that many periph-eral tissues including the skin (6, 7) autonomously expressPOMC and process it via expression of distinct PCs toPOMC-derived peptides. Proinflammatory cytokines as wellas corticotropin releasing hormone have been identified asthe prototypical stimuli that regulate POMC expression andprocessing in both central and peripheral tissues (6).

B. Structure of �-MSH and related tripeptides

As illustrated in Fig. 1B, the tridecapeptide sequence of�-MSH [molecular weight (MW), 1664.91] is containedwithin ACTH. The core amino acid sequence HFRW (�-MSH6–9) is moreover common in �-, �-, and �-MSH andACTH. Pharmacological studies using the frog (Rana pipiens)skin pigmentation bioassay disclosed that the minimal se-quence of �-MSH required for the melanotropic effect of�-MSH resides in this core amino acid sequence (8). Effortshave been made to create protease-stable �-MSH analogscontaining this core sequence with superpotent melanogeniceffects such as [Nle4, d-Phe7]�-MSH (NDP-MSH) (9). C- andN-terminal fragments of �-MSH, on the other hand, wereshown to have no melanotropic effect in frog and lizard skinbioassays (9). Surprisingly, C-terminal peptide fragments of�-MSH, however, possess similar or even pronounced anti-inflammatory effects as full-length �-MSH, as will be out-lined in detail below. These small molecular weight peptidesinclude the N-acetylated and C-amidated tripeptide KPV(MW, 383.49) and several stereoisomers, i.e., dKPV, KPdV,KdPV, and dKPdV. A structurally related derivate is KdPT(MW, 344.41) in which the hydrophobic amino acid valine ofKPV is substituted by the more polar amino acid threonine.Recent evidence indicates that KdPT has likewise potentantiinflammatory effects.

C. Melanocortin receptors—obligatory structures mediatingthe inflammatory effects of �-MSH and related tripeptides?

The natural melanocortins �-, �-, and �-MSH and ACTHbind to melanocortin receptors (MC-Rs), which are ex-pressed on the cell surface and belong to the superfamily ofG protein-coupled receptors with seven transmembrane do-mains (10, 11). Five MC-R subtypes, MC-1R to MC-5R, havebeen cloned. They have a sequence homology of 39 to 61%to one another on the amino acid level and bind the naturalmelanocortin peptides with differential affinity (Table 1).Human MC-1R and MC-4R discriminate poorly betweenACTH, whereas �-MSH in murine Mc-1r appears more po-tent than ACTH. MC-2R is selective for ACTH. �-MSH is thepreferred, though not exclusive, MC-5R ligand, whereas

POMC

DNA

Pro-hormone

5‘- -3‘

RNA

3 noxE1 noxE Exon 2

Transcription

Translation

N- -C

ACTHJP PC1

PC2/7B2

α-MSH

β-LPH

CLIP β-ENDNT

γ-MSH γ-LPH

β-END1 27

A

B

1 6 10 13-------------39

ACTH NH2-SYSMEHFRWGKPV------------F-OHα-MSH Ac-SYSMEHFRWGKPV-NH2α-MSH(6-9) Ac-HFRW-NH2α-MSH (11-13) /KPV Ac-KPV-NH2α-MSH (11-12)-T/KPT H-KPT-OH

β-MSH NH2-AEKKDEGPYRMEHFRWGSPPKD-OHγ-MSH NH2-YVMGHFRWDRGR-OH

Peptide Amino Acid Sequence

β-MSH

FIG. 1. A, Biosynthesis of POMC peptides and natural melanocort-ins. Posttranslational processing of POMC by PC1 and PC2 (togetherwith its cofactor 7B2) at specific cleavage sites (arrow tips) yieldspeptide hormones such as ACTH, �-MSH, �-MSH, and �-endorphin(�-ED) peptides with less-defined functions (�- and �-LPH) and frag-ments (NT, JP, CLIP). LPH, Lipotropic hormone; NT, N-terminalpeptide; JP, junctional peptide; CLIP, corticotropin-like intermediatelobe peptide. B, Peptide sequences of the natural melanocortins, thecentral melanotropic pharmacophor of �-MSH, and the �-MSH-re-lated C-terminal tripeptides. Structural homologies are depicted inred.

582 Endocrine Reviews, August 2008, 29(5):581–602 Brzoska et al. • �-MSH and Related Tripeptides


MC-3R is the least selective receptor of the family. The corepeptide HFRW binds MC-1R, MC-3R, MC-4R, and MC-5Rbut with less MC-R subtype specificity than the full lengthnatural melanocortins (12). Ligand stimulation of all MC-Rsleads to activation of adenylate cyclase with increase of in-tracellular cAMP but other signaling events, e.g., calciumfluxes (13) or activation of MAPKs (14), can also occur de-pending on the studied cell type.

Expression and functional analysis by many independentresearch groups has provided evidence that MC-Rs are muchmore widely expressed than originally thought (Table 1). Ofnote, there are species-specific differences in the expressionof MC-R subtypes, and one particular cell type can alsoexpress concomitantly multiple MC-Rs. Therefore, blockingexperiments with natural and pharmacological MC-R antag-onists or MC-R-specific gene knockdown may be required toprecisely define the functional relevance of a specific MC-Rsubtype expressed (15). Moreover, it should be pointed outthat MC-R expression analysis has been performed in a num-ber of studies only in immortalized cell lines and at RNAlevel, making interpretation of such data difficult, even in thepresence of additional in vivo experiments.

With regard to MC-1R, it has been shown that this MC-Rsubtype is expressed not only in melanocytes but also in themajority of nonmelanocytic cutaneous human cell types (7),in mucosal cells of the human gastrointestinal tract (16), andin various cell types of the immune system including humanmonocytes (17, 18), lymphocytes (19), and neutrophils (20).The majority of antiinflammatory effects of �-MSH in vitrohave been linked to the detection of MC-1R. It is of note thatthe antiinflammatory effects of �-MSH have been observedin the presence of extremely low, i.e., subpicomolar, concen-trations where, based upon the ligand binding affinity ofMC-1R, only a few if any receptors would be occupied. It istherefore possible that the antiinflammatory effects of�-MSH are mediated not only by MC-Rs but also by addi-tional effector pathways. In fact, previous studies could in-deed demonstrate that �-MSH potently and selectively re-duces surface binding of radiolabeled IL-1� to the T cellsubclone EL4–6.1 (21). The latter findings are supported byin vivo findings in rats demonstrating an antagonistic effect

of �-MSH on the hyperalgesic response induced by IL-1�(22). Further support for a non-MC-R-mediated effectorpathway involved in the antiinflammatory action of �-MSHcomes from ex vivo studies from patients with nonfunctionalMC-1R (i.e., individuals with the red hair phenotype) (18) aswell as from animal studies using signal-deficient MC-1Rmice (recessive yellow e/e mice) (23, 24). However, thesefindings are complicated by a recent observation demon-strating that recessive yellow e/e mice have a significantlyaggravated inflammatory response in a model of inflamma-tory bowel disease (123).

Whether KPV and its stereoisomers bind to MC-Rs andutilize the identical signaling pathways as the natural ligandsis controversial. Early studies using in vitro binding assaysand autoradiography in frozen rat brain tissue sections failedto demonstrate replacement of binding of [125]NDP-MSH byKPV at concentrations of up to 100 �m (26). Competitivebinding analysis of radiolabeled full-length �-MSH and KPVin murine B16 melanoma cells furthermore did not revealany surface binding (27). In addition, KPV even in concen-trations up to 1 �m did not compete with radioligand NDP-MSH binding in murine RAW 264.7 macrophages that ex-press MC-1R (28). In the same cell line, KPV failed to increasecAMP levels. Like �-MSH, KPV displaced surface binding ofradio-labeled IL-1� to the T cell subclone EL4–6.1 and in-hibited the hyperalgesic effect of IL-1� in vivo (21, 22). Othermore functional in vitro and in vivo studies in the murinesystem failed to show an involvement of MC-1R, MC-3R, andMC-4R in the antiinflammatory mechanism of KPV andrather suggested an inhibition of IL-1� functions by thispeptide (23). On the other hand, intracellular induction ofcAMP representing the prototypical signal transductionpathway elicited by �-MSH has been observed in murinemicroglial cells (29). In addition, it has been reported that�-MSH, KPV, KPdV, and ACTH have similar pharmacolog-ical potency on elicitation of intracellular calcium fluxes asdemonstrated in human keratinocytes expressing the MC-1R. Stable transfection of Chinese hamster ovary cells withthe MC-1R demonstrated that �-MSH and its related C-terminal peptide elevated intracellular calcium (13). Lately,there is evidence that a H�-coupled oligopeptide transporter

TABLE 1. Characteristics of MC-R subtypesa

Subtype Agonist profile Tissue expressionb Identified cell typeb

MC-1R �-MSH�ACTH��-MSH Skin, brain, immune system, gut, testis, ovary,placenta, lung, liver, adrenal gland, skeletal muscle

Melanocytes, keratinocytes, fibroblastic cells,endothelial cells, secretory epithelia, microglia,astrocytes, monocytes/macrophages, lymphocytes,neutrophils, mast cells, intestinal epithelia, Leydig’scells, lutein cells, trophoblastic cells, skeletal musclecells

MC-2R ACTH Adrenal glands, testis, skin, adipose tissue, pancreas Cells of the zona fasciculata and glomerulosa,adipocytes, keratinocytes, lymphocytes, �-pancreascells

MC-3R �-MSH � ACTH��-MSH Brain, heart, immune system, skeletal muscle Macrophages, intestinal epithelial cells, lymphocytesMC-4R �-MSH � ACTH��-

MSHBrain, skin, skeletal muscle Dermal papilla cells, skeletal muscle cells, lymphocytes

MC-5R �-MSH�ACTH��-MSH Skeletal muscle, brain, skin, exocrine glands, lung,heart, spleen, immune system, kidney, adipose tissue,adrenal gland, uterus, ovary, placenta, bone marrow,skeletal muscle

Adipocytes, mast cells, secretory epithelia, macrophages,skeletal muscle cells, intestinal epithelial cells,lymphocytes

a Including immortalized cell lines and tumor cells.b As detected in the murine or human system.

Brzoska et al. • �-MSH and Related Tripeptides Endocrine Reviews, August 2008, 29(5):581–602 583


(PepT1) is involved in the antiinflammatory effects of trun-cated �-MSH peptides such as KPV (30). This issue will bediscussed in detail in Section IV.

III. Antiinflammatory and Protective Spectrum of�-MSH

A. Antiinflammatory effects in vitro

�-MSH has been found to exert multiple antiinflammatoryeffects in a variety of in vitro cell culture systems. Table 2summarizes the majority of antiinflammatory effects of�-MSH in vitro.

1. �-MSH, a suppressor of proinflammatory cytokine production.Early studies addressing the antiinflammatory effect of�-MSH at the cellular level focused on the suppressive effectof the peptide on expression of proinflammatory cytokines,interferon-� (IFN-�) and TNF-�. Taylor et al. (31, 32) detected�-MSH in picomolar levels in the aqueous humor of the eyeand found that such naturally occurring doses of the peptidehad suppressive effects on the production of IFN-� by an-tigen-stimulated primed murine lymph node cells. In mito-gen-stimulated human peripheral blood mononuclear cells(PBMC), �-MSH likewise suppressed IFN-� expression dose-dependently (33). The suppressive effect of �-MSH on TNF-�expression and secretion has been studied mainly in neuralcell tissue and cells derived from the central nervous system(CNS) but also in a number of cell types from other tissues(29, 34–39). For example, in activated human astrocytes andmicroglia �-MSH suppressed TNF-� production presumablyvia the MC-1R (34). Similarly, lipopolysaccharide (LPS)-in-duced TNF-� expression could be blocked by �-MSH in thehuman monocyte/macrophage cell line THP-1 (37). Remark-ably, �-MSH was effective here at doses from 10�17 to 10�12

m. The stimulatory effect of IgE/dinitrophenol (DNP)-serumalbumin on bone marrow-cultured murine mast cells onmRNAs for IL-1�, TNF-�, and lymphotactin was likewisesuppressed by �-MSH (38). Other proinflammatory cyto-kines suppressed by �-MSH, when coincubated with a proin-flammatory stimulus, include the chemokines IL-8 and Gro�(40–42). Accordingly, �-MSH suppressed IL-8 productioninduced by IL-1� in human sebocytes and dermal fibroblasts(40, 42). Other proinflammatory cytokines regulated by�-MSH are IL-1, IL-6, and the keratinocyte-derived chemo-kine (KC) (23, 113). The impact of �-MSH on chemokines isfurther supported by recent findings demonstrating that theIL-8 receptor in human neutrophils is also down-regulatedby �-MSH (44). Moreover, chemotaxis induced by IL-8 inboth human neutrophils and monocytic cells is suppressedby �-MSH (20, 44), indicating that the function of thesephagocytic cell types during inflammatory responses isblocked by the peptide via multiple effector pathways.

2. �-MSH induces the cytokine suppressor IL-10. In contrast tothe suppressive effects of �-MSH on several proinflamma-tory mediators, the peptide was also identified as an inducerof IL-10, a cytokine with potent immunosuppressive activ-ities. Stimulation of PBMC with �-MSH increased both IL-10mRNA and protein at a concentration of 10�10 and 10�12 m(45). Analogous inductive effects were reported in nonim-

mune cells, e.g., in human epidermal keratinocytes (46). Aswill be outlined, induction of IL-10 has been demonstratedto be a key mediator of the antiinflammatory effects of�-MSH in vivo.

3. �-MSH inhibits expression of intercellular adhesion molecules.Studies on various cell types of human skin including pig-ment cells, fibroblastic cells, and dermal microvascular en-dothelial cells as well as murine mast cells have demon-strated that �-MSH is capable of suppressing the expressionof intercellular adhesion molecule-1 (ICAM-1) induced byproinflammatory stimuli such as IFN-�, LPS, or TNF-� (47–52). Other surface molecules modulated by �-MSH are CD86and CD40, which are required for antigen presentation bymonocytes and dendritic cells. In LPS-treated human mono-cytes, �-MSH suppressed expression of CD86 but not CD80(17). In human peripheral blood-derived dendritic cells,�-MSH at 10�12 m likewise down-regulated surface expres-sion of CD86 in nonstimulated cells (53). The modulatoryeffect of �-MSH on another important surface molecule or-chestrating immune responses was recently highlighted inan organ model of the human hair follicle. �-MSH potentlysuppressed ectopic MHC class I expression in the constitu-tively MHC class I-negative hair matrix epithelium of organ-cultured anagen hair bulbs (54).

4. �-MSH—a suppressor of proinflammatory noncytokine medi-ators. An inhibitory effect of �-MSH on prostaglandins (PGs)was demonstrated many years ago. Accordingly, �-MSHsuppressed PGE synthesis in fetal human lung fibroblastsstimulated with IL-1 (55). The effect of �-MSH on PGE syn-thesis appears to be cell type-specific because TNF-�-in-duced PGE2 production in FM55 melanoma cells but not inHaCaT keratinocytes was blocked by �-MSH (56). Inductionof inducible NO synthase (iNOS) and release of the gaseousvasodilator nitric oxide (NO) after stimulation of cells withvarious proinflammatory stressors, e.g., LPS, �-IFN, and�-amyloid can also be suppressed by �-MSH (29, 36, 57–61).The immunomodulatory effects of �-MSH via NO may bemore important in rodent cells than in human monocyticcells, which are known to express only marginal amounts ofthis gaseous mediator. However, �-MSH suppressed inTHP-1 cells the IFN-�/TNF-�-mediated production of ne-opterin, a primate homolog of NO in lower animals (62).Regarding reactive oxygen species, it was recently demon-strated that �-MSH inhibits the production of superoxideradicals in rat neutrophils treated with LPS or phorbolester(63). Similarly, �-MSH reduced the amount of oxidative burstin HL-60 cells, a human monocytic cell line (44). Althoughthere is no evidence that �-MSH is a true radical scavengerby itself, these findings are in accordance with other reportsindicating an effect of the peptide on the cellular redox bal-ance as well as on apoptosis pathway, as will be outlinedbelow. Regarding the release of histamine by mast cells,different effects of �-MSH have been reported which areprobably related to species-specific differences, type of mastcells, and experimental conditions. In murine bone marrow-derived mast cells, �-MSH inhibited antigen-induced hista-mine release along with suppression of other proinflamma-tory cytokines (38).



TABLE 2. Antiinflammatory effects of �-MSH in vitro

Target molecule/process Effect of �-MSH Cell type tested Ref.

Proinflammatorycytokines

Antigen-stimulated �-IFN production 2 Murine lymph node T cells Taylor et al., 1992 (31)

�-IFN production induced by Con A 2 Human PBMC Luger at al., 1993 (33)Anti-IL-4 induced �-IFN production 2 Murine lymph node T cells Taylor et al., 1994 (32)LPS/PMA-induced TNF-� expression 2 Human astrocytoma cell line A-172; murine

fibroblast cell line L292Wong et al., 1997 (34)

TNF-� induction by LPS treatment 2 Murine brain tissue Rajora et al., 1997 (35)LPS/IFN-�-induced TNF-� and IL-6 expression 2 Murine microglial cell line (N9 clone) Delgado et al., 1998 (29)

LPS-induced TNF-� expression 2 THP-1 cell line Taherzadeh et al., 1999 (37)IgE/DNP-HSA-stimulated PMA-induced IL-1�, TNF-

� and lymphotactin expression 2Bone marrow murine mast cells Adachi et al., 1999 (38)

IL-1�-induced IL-8 expression 2 Human dermal fibroblasts, HaCaT cells Böhm et al., 1999 (40);Brzoska et al., 1999 (41)

IL-1�-induced Gro� expression 2 HaCaT cells Brzoska et al., 1999 (41)�A/IFN-�-induced TNF-� expression 2 Murine microglia cell line (N9 clone) Galimberti et al., 1999 (36)

IL-1�-induced IL-8 secretion 2 Human sebocyte cell line SZ95 Böhm et al., 2002 (42)Gliadin-stimulated IL-6 release 2 Duodenal mucosa from patients with celiac

diseaseColombo et al., 2002 (16)

MSU-crystal-induced IL-1� and KC release 2 Murine peritoneal macrophages Getting et al., 2002 (113);Getting et al., 2003 (23)

PMA/ionomycin-induced IL-1� and TNF-� 2 Rat PBMC Jung et al., 2007 (61)Cytokine receptors IL-8 receptor and CXCR type I and II expression 2 Human monocytic cell line HL-60 Manna et al., 2006 (44)Inflammatory cell

migrationFMLP- or IL-8-induced chemotaxis 2 Human neutrophils Catania et al., 1996 (20)

IL-8-induced migration 2 Human monocytic cell line HL-60 Manna et al., 2006 (44)Lymphocyte

proliferation andactivation

Regulatory T cell activity 1 Primed murine T cells Nishida and Taylor, 1999(64)

SK/SD-induced proliferation 2 Human lymphocytes Cooper et al., 2005 (18)Cytokine suppressors IL-10 production 1 Human monocytes Bhardwaj et al., 1996 (45)

Human keratinocytes Redondo et al., 1998 (46)Adhesion molecules LPS-induced CD86 expression 2 Human monocytes Bhardwaj et al., 1997 (17)

TNF-�-induced ICAM-1 expression 2 Human normal and malignant melanocytes Morandini et al., 1998 (47)Basal CD80 suppression 2 Human monocyte-derived dendritic cells Becher et al., 1999 (53)

LPS-induced E-selectin and VCAM-1 expression 2 HMEC-1 cell line Kalden et al., 1999 (48)Serum-activated/LPS-ICAM-1 induction 2 Murine mast cell line MC-9 Sarkar et al., 2003 (52)

LPS and TNF-�-induced ICAM-1, VCAM-1, and E-selectin expression 2

HDMECs Scholzen et al., 2003 (49)

IFN-�-induced MHC class I expression 2 Whole organ cultures of human hair follicles Ito et al., 2004 (54)IFN-�-induced ICAM-1 expression 2 Human dermal papilla cells Böhm et al., 2005 (50)TNF-�-induced ICAM-1 expression 2 Human dermal fibroblasts Hill et al., 2006 (51)

Noncytokineproinflammatorymediators

IL-1-induced secretion of PGE 2 Human lung fibroblast cell line MRC5 Cannon et al., 1986 (55)

IFN-�/LPS-induced NO2� production and iNOS

expression 2RAW 264.7 cell line Star et al., 1995 (57)

IL-4/anti-CD23 receptor/IFN-�/TNF-�-induced NO2�

and neopterin synthesis 2THP-1 cell line Rajora et al., 1996 (62)

IFN-�/LPS-induced NO2� production 2 Murine microglial cell line (N9 clone) Delgado et al., 1998 (29)

IFN-�/LPS-induced NO2� 2 Mouse cortical tubule cells Raw 264.7 cell line Chiao et al., 1998 (39)

IgE/DNP-HSA-stimulated histamine release 2 Bone-marrow-derived murine mast cells Adachi et al., 1999 (38)�A1/IFN-�-induced NO2

� production and iNOSexpression 2

Murine microglial cell line (N9 clone) Galimberti et al., 1999 (36)

LPS-induced production of NO2� 2 Human melanoma cell line FM55 Tsatmali et al., 2000 (58)

LPS/ IFN-�-induced NO2� production 2 RAW 264.7 murine macrophage cell line Mandrika et al., 2001 (28)

Basal PGF2� and TNF-� induced PGE2 secretion 2,basal PGF2� secretion 2

Human melanoma cell line FM55, HaCaTcells

Nicolaou et al., 2004 (56)

IFN-�/LPS-induced iNOS promoter activity 2 RAW 264.7 cell line Gupta et al., 2000 (59)LPS/PMA-induced superoxide anion production 2 Rat peritoneal neutrophils Oktar et al., 2004 (63)

IL-8-induced oxidative burst 2 Human monocytic cell line HL-60 Manna et al., 2006 (44)IFN-�/LPS-induced PGE2 and NO release 2 Rat astrocytes Caruso et al., 2007 (60)

PMA-induced NO2� 2 Rat PBMC Jung et al., 2007 (61)

Transcription factorNF-�B

TNF-�, IL-1�, LPS, ceramide or okadeic acid-inducedNF-�B activation 2

U937, HeLa, Jurkat, H4 cell lines Manna et al., 1998 (70)

TNF-�-induced NF-�B activation 2 Human melanocytes and melanoma cell lines Haycock et al., 1999 (71)LPS-induced NF-�B activation 2 HMEC-1 cell line Kalden et al., 1999 (48)

LPS-induced NF-�B 2 A-172 human glioma cells Ichiyama et al., 1999 (74)IL-1�-induced NF-�B activation 2 HaCaT cells Brzoska et al., 1999 (41)

LPS/ IFN-�-induced NF-�B activation 2 RAW 264.7 murine macrophage cell line Mandrika et al., 2001 (28)TNF-�-induced NF-�B activation 2 HaCaT cells Moustafa et al., 2002 (72)

LPS-induced NF-�B activation 2 HDMECs Scholzen et al., 2003 (49)Serum-activated/LPS-NF-�B and promoter gene

activation 2Murine mast cell line MC-9 Sarkar et al., 2003 (52)

TNF-� and IFN-j-induced NF-�B activation 2 Rat Schwann cells Teare et al., 2004 (73)TNF-�-induced NF-�B activation 2 Rat small intestinal IEC-6 cells Zou et al., 2004 (75)

IL-8-induced NF-�B activation 2 Human monocytic cell line HL-60; humanmacrophage cell line THP1

Manna et al., 2006 (44)

TNF-�-induced NF-�B activation 2 Human dermal fibroblasts Hill et al., 2006 (51)TNF-�-induced NF-�B activation 2 Human HTB-94 chondrosarcoma cells Yoon et al., 2007 (76)

�A, �-Amyloid protein; Con A, concanavalin A; fMLP, formyl-Met-Leu-Phe; HDMECs, human dermal microvascular endothelial cells;HMEC-1, human microvascular endothelial cell line-1; HSA, human serum albumin; MHC, major histocompatibility complex; MSU, monoso-dium urate; PMA, phorbol-12-myristate-13-acetate; SK/SD, streptokinase/streptodornase; VCAM, vascular cell adhesion molecule; 2, de-creased; 1, increased.



5. �-MSH modulates lymphocyte activity and proliferation. Untilnow, comparatively few studies have investigated the effectof �-MSH on lymphocyte function, probably because theoverall expression of MC-Rs is low or undetectable in severallymphocyte subsets (19). The detection of �-MSH in theimmune-privileged microenvironment of the anterior eyechamber and its effect on production of �-IFN by antigen-stimulated primed lymph node cells prompted further stud-ies on the effect of �-MSH on effector T cells (31). Aqueoushumor-treated T cells were capable of suppressing inflam-mation induced by delayed-type hypersensitivity T cells. Theinduction of regulatory T cells was mostly pronounced whenprimed T cells were activated in vitro first in the presence of�-MSH, followed by TGF-�2 (64). The effector T cells pro-duced increased levels of TGF-�2, whereas their productionof �-IFN, IL-4, and IL-10 was suppressed (66, 114). The reg-ulatory T cells induced by �-MSH exhibited the CD25 andCD4 markers and suppressed the in vitro production of �-IFNby other inflammatory T cells. In the human system, �-MSHalso exhibited modulatory effects on T cells. Cooper et al. (18)could recently demonstrate that �-MSH suppresses prolif-eration of human T lymphocytes stimulated with streptoki-nase/streptodornase. Streptokinase/streptodornase is a po-tent bacterial antigen to which most individuals mount a Tcell-mediated response. Interestingly, this inhibitory effect of�-MSH was independent of the MC-1R genotype which ishighly polymorphic, with more than 35 genetic variants be-ing identified (67). In particular, the Arg151Cys, Arg160Trp,and Asp294His variants are associated with red hair andfaint skin due to impaired cAMP signaling in melanocytesresulting in an increased phaeomelanin/eumelanin ratio (68,69). Although a single variant allele leads to a fairer skin,compound heterozygous or homozygous alleles result in redhair. In the study by Cooper et al. (18), however, the sup-pressive effect of �-MSH was similar in activated lympho-cytes from donors carrying wild-type MC-1R and in thosefrom donors being compound heterozygous or homozygousfor the Arg151Cys, Arg160Trp, and Asp294His variants.Here, it was suggested that �-MSH may utilize other sig-naling pathways than cAMP, i.e., calcium, to maintain itsimmunosuppressive effect. Of note, and as observed in sev-eral other studies addressing the immunomodulating effectof the peptide, �-MSH exhibited an unusual dose kinetics,being most effective at 10�13 m, which cannot be modeled bythe known MC-1R ligand affinity or a simple peptide recep-tor interaction.

6. NF-�B—a master regulator of inflammation suppressed by�-MSH. A key molecular mechanism underlying the antiin-flammatory effects of �-MSH, especially the modulation ofproinflammatory cytokine and adhesion molecule expres-sion, appears to be suppression of nuclear factor-�B (NF-�B)activation. Manna and Aggarwal (70) were the first whoreported that �-MSH at nanomolar doses inhibits activationof NF-�B in a number of cell types and in response to TNF-�,IL-1, LPS, okadeic acid, and ceramide. Subsequent studiescould confirm this observation in many different cell typesusing various proinflammatory stimuli (41, 44, 48, 49, 51, 52,71–75). Mechanistically, NF-�B deactivation by �-MSH ismediated by increased levels of cAMP and correlates with

inhibition of the degradation of the inhibitory subunit ofNF-�B, I�B�. As a consequence, nuclear translocation of thep65 subunit of NF-�B is suppressed. However, the precisemechanism by which �-MSH releases NF-�B from its cyto-plasmic anchor protein I�B� appears to be cell type-specific.In the rat small intestine cell line IEC-6, it was shown thatH2O2 resulted in NF-�B activation, which could be preventedby 100 nm of �-MSH (75). The overall I�B� protein levelswere similar in cells treated with H2O2 alone and in thosetreated with H2O2 plus �-MSH. In contrast, tyrosine phos-phorylation of Syk kinase and its downstream target I�B�were increased by H2O2, and these processes were attenu-ated by �-MSH or the Syk kinase inhibitor piceatannol (75).Interestingly, �-MSH also restored H2O2-induced inhibitionof scrape wounding of IEC-6 cells, suggesting a potential ofmelanocortin peptides in epithelial restitution. Recently, itwas reported that �-MSH (200 nm) inhibits TNF-�-inducedmatrix metalloproteinase (MMP)-13 expression by modulat-ing p38 kinase and NF-�B activation in the human chondro-sarcoma cell line HTB-94 (76). HTB-24 cells were found toexpress MC-1R. These findings are interesting with regard toMMP-13-mediated collagen degradation, which could beprevented by melanocortin peptides. Subsequent studies,however, will have to confirm the relevance of these findingsin primary human chondrocytes.

B. Antiinflammatory effects in vivo

The antiinflammatory effects of �-MSH in vitro have beensubstantiated in a variety of animal models, mostly in mousemodels. In many of these models, systemic or local inflam-mation is induced by application of endotoxin (LPS), proin-flammatory cytokines, or agents known to induce suchendogenous proinflammatory mediators. The proinflam-matory stimuli are typically given for a short period, usuallyonce or for several days, whereas in other models specificagents such as bleomycin or carbon tetrachloride are admin-istered over prolonged time periods, resulting in chronicinflammation and tissue fibrosis (Table 3).

1. �-MSH in experimentally induced fever and brain inflamma-tion. One of the earliest findings pointing toward a futurepotential of �-MSH as an antiinflammatory agent was thedemonstration of its potent antipyretic activity in experi-mental fever. In such models, fever is induced by centralapplication of endogenous or exogenous pyrogen, and theefficacy of a coinjected antipyretic substance is subsequentlymeasured (77–86). Nanogram doses of �-MSH injected in-tracerebroventricularly were found to be sufficient to sup-press the pyrogenic effect induced by central application ofbacterial endotoxin (LPS) or PGE2. Similar results were ob-tained when exogenous pyrogen or IL-1 was injected iv. Theantipyretic effect of �-MSH was operational not only whenthe peptide was administered centrally but also when givensystemically or even intragastrically, albeit in much higherdoses. It is also of interest that this antipyretic effect of�-MSH was confirmed in several rodent models but not incats (87). Mechanistically, the antipyretic effect of centrallyadministered �-MSH is mediated by MC-Rs, most likely viaMC-3Rs/MC-4Rs, which are expressed in autonomic sites in



TABLE 3. Antiinflammatory in vivo effects of �-MSH in animal modelsa

Type of model Effect of �-MSH Application routeof �-MSH Species Ref.

Fever Hyperthermia induced by iv and icv injection of LP 2 icv Rabbit Glyn and Lipton, 1981 (77)Hyperthermia induced by iv injection of LP 2 icv, iv,

intragastricRabbit Murphy and Lipton, 1982, (79)

Murphy et al., 1983 (80)Hyperthermia induced by iv injection of LP 2 Intraseptally Rabbit Glyn-Ballinger et al., 1983 (78)

Hyperthermia induced by injection of LPS and PGE2 2 icv Guinea pig Kandasamy and Williams, 1984 (81)Hyperthermia induced by iv injection of LPS 2 iv Squirrel monkey Shih and Lipton, 1985 (82)

Hyperthermia induced iv injection of IL-1 2 Preoptic Rabbit Feng et al., 1987 (86)Hyperthermia induced iv injection of IL-1� 2 iv Mouse Daynes et al., 1987 (83)

Hyperthermia induced by iv administration of EP 2 icv Rabbit Deeter et al., 1989 (84)Hyperthermia induced by iv injection of LPS 2 iv Rabbit Martin and Lipton, 1990 (85)

Systemic inflammation Survival after induction ofperitonitis/endotoxemia/septic shock by cecal ligation 2

ip Mouse Lipton et al., 1994 (97)

Respiratory distress (as measured by number of whiteblood cells in BAL fluid) induced by intratracheal

infusion of endotoxin 2

ip Rats Lipton et al., 1994 (97)

Induction of TNF-� and IL-1� serum levels by ipinjection of LPS 2

iv, sc Mouse Gonindard et al., 1996 (96)

Brain inflammation Induction of TNF-� in the brain and in plasma bycentral injection of LPS 2

icv, ip Mouse Rajora et al., 1997 (35)

Activation of NF-�B in brain induced by centralinjection of LPS 2

ip Mouse Ichiyama et al., 1999 (94)

Adoptive transfer EAE-induced CNS inflammation, 2,chemokine expression 2, Th1/Th2 imbalance 2

icv Mouse Han et al., 2007 (95)

Arthritis Periarticular inflammation induced by M. tuberculosis2

ip Rat Ceriani et al., 1994 (105)

Ocular inflammation Autoimmune uveitis induced by immunization withhuman interphotoreceptor retinoid binding proteinpeptide, Freund’s adjuvants and M. tuberculosis 2

iv Mouse Taylor et al., 2000 (114)

Traumatic ocular inflammation with edema,hyperemia, increased protein content and number ofinflammatory cells induced by a corneolimbal cut 2

im, topically Rabbit Naveh and Marshall, 2001 (116)

LPS-induced uveitis with inflammatory infiltrate,increased protein and levels of NO, TNF-�, IL-6, MCP-

1 and MIP2 in the anterior chamber 2

iv Rat Nishida et al., 2004 (115)

Contact dermatitis andcutaneous vasculitis

Hind paw inflammation induced by sc injection of uratecrystals 2

sc Rats Denko and Gabriel, 1985 (98)

IL-1, TNF-� and C5a-induced neutrophil migration insc transplanted sponges 2

ip Mouse Mason and Van Epps, 1989 (99)

Contact dermatitis induced by DNFB and oxazalone 2 Epicutanously Mouse Rheins et al., 1989 (106)Contact dermatitis of the ear induced by topical

application of DNFB 2ip Mouse Hiltz and Lipton, 1990 (100)

Hind paw edema induced by injection of �-carrageenan2

ip Mouse Hiltz and Lipton, 1990 (100)

Ear swelling induced by intradermal injection of IL-1�,IL-6 and TNF-� 2

ip Mouse Hiltz et al., 1992 (101)

IL-1�-induced neutrophil accumulation into air pouches2

sc Mouse Perretti et al., 1993 (102)

Ear swelling induced by intradermal injection of IL-1�2

ip Mouse Watanabe et al., 1993 (103)

Ear swelling induced by intradermal IL-1� injection 2 icv Mouse Macaluso et al., 1994 (104)Hind paw edema induced by injection of �-carrageenan

2icv, (ip) Mouse

Ear edema induced by intradermal injection of IL-1�and PAF 2

icv Mouse Ceriani et al., 1994 (105)

Ear edema induced by intradermal injection of IL-8and LTB4 2

icv, ip Mouse

Contact dermatitis of the ear induced by TNCBapplication 2

iv Mouse Grabbe et al., 1996 (107)

NF-�B activation of the foot pad induced by injection ofTNF-� 2

icv Mouse Ichiyama et al., 1999 (94)

LPS-induced cutaneous vasculitis (hemorrhage,inflammatory infiltration) and E-selectin expression 2

ip Mouse Scholzen et al., 2003 (49)

Fibrosis Cutaneous collagen induction, and myofibroblastaccumulation induced by repetitive dermal injection of

TGF-�1 2

sc Mouse Böhm et al., 2004 (110)

Carbon tetrachloride-induced liver fibrosis, TGF-�1 andadhesion molecule expression 2

im Mouse Lee et al., 2006 (111)

Bleomycin-induced skin fibrosis 2 sc Mouse Kokot et al., 2008 (109)Allergic airway

inflammationAirway influx of inflammatory cells (eosinophils), IL-4,-5 and -13, production of allergen-specific IgE and IgG

induced by ip OVA injection 2

iv Mouse Raap et al., 2003 (117)

Acute pancreatitis Cerulein-induced pancreatic leukocyte infiltration andmyeoloperoxidase activity 2

ip Rat Jahovic et al., 2004 (118)

Gastrointestinalinflammation

DSS-induced colitis inflammation with fecalhemorrhage, weight loss, NO2

� and TNF-� production2

ip Mouse Rajora et al., 1997 (121)

Hepatic inflammation with increased TNF-�, KC/IL-8,MCP-1 and NO production induced by LPS after

pretreatment with C. parvum 2

iv Mouse Chiao et al., 1996 (120)

icv, Intracerebroventricularly; DNFB, 2,4- dinitrofluorobenzene; EP, endogenous pyrogen; LTB4, leukotriene B4; LP, leukocyte pyrogens;OVA, ovalbumin; PAF, platelet-activating factor. TNCB, 2,4,6-trinitrochlorobenzene; 2, decreased.

a Excluding in vivo studies with NDP-MSH.



the hypothalamus and brain stem (88, 89). Interestingly, al-though intracerebroventricular coinjection of the MC-3R/MC-4R antagonist SHU9119 at equimolar concentration in-hibited the antipyretic effect of exogenous �-MSH (180pmol), selective activation of central MC-4Rs by the MC-4R-selective agonist MRLOB-001 suppressed LPS-induced fever.Intracerebroventricular coinjection of LPS, MRLOB-001, andthe selective MC4R antagonist HS014 blocked the antipyreticeffects of MRLOB-0001 (90). Of note, central MC4-R blockadeby coinjected HS014 not only prevented but also reversed theeffect of �-MSH on body core temperature leading to anaugmented LPS-induced fever response presumably viaMC-Rs other than MC-4R (91). �-MSH injected iv is likewiseantipyretic and may act similarly as centrally administered�-MSH due to crossing the blood-brain barrier (92). How-ever, the downstream of MC-3R or MC-4R mediating theantipyretic action of �-MSH is still unclear. Surprisingly,targeted disruption of MC-3R or MC-4R does not alter thepyrogenic response of LPS or IL-1�, suggesting that the roleof melanocortins and MC-3R/MC-4R in thermoregulation iscomplex (93).

In accordance with the inhibitory effect of �-MSH onNF-�B activation and cytokine production in vitro, �-MSHalso preserved expression of I�B� protein and TNF-� ex-pression in murine brain after injection of mice with LPS (35,74, 94). The potent antiinflammatory effects of �-MSH invarious cell types of the CNS have resulted in attempts totreat experimental autoimmune encephalomyelitis (EAE), acommonly used animal model for multiple sclerosis, with aspecial �-MSH delivery system. EAE is induced in mice byeither immunizing susceptible animals with myelin antigens,e.g., myelin basic protein, or by transfer with activated my-elin antigen-specific T lymphocytes (adoptive transfer EAE)resulting in paralysis and often demyelinization of the CNS.Using adenovirus-associated, virus-mediated �-MSH-trans-duced proteolipid 139–151-specific T cells, it could be shownthat these cells secreted high levels of �-MSH and displayedan altered Th1-like cytokine as well as a high frequency ofCD4�CD25� regulatory T cells (95). Transfer of the �-MSH-transduced cells into animals with EAE resulted in decreasedinflammatory cell infiltrates within the CNS, higher IL-10and TGF-� levels, decreased IL-2 and IFN-� content, andreduced chemokine expression. Moreover, the �-MSH-trans-duced cells not only suppressed the induction of adoptivetransfer EAE but also had preventive effects on active re-lapse-remitting EAE, indicating a novel therapeutic ap-proach to treat autoimmune diseases of the CNS.

2. Inhibition of systemic inflammation by �-MSH. In models ofsystemic inflammation, sepsis, and acute respiratory dis-tress, �-MSH proved to be a potent agent. Systemic or scinjection of �-MSH reduced the circulating levels of IL-1�and TNF-� (96). Lipton et al. (97) could further show that ina model of peritonitis/endotoxemia induced by cecal liga-tion and puncture, systemic �-MSH administration (100 �g)improved the survival rate of the mice. Interestingly, theeffect of �-MSH in this model was similar to systemic ad-ministration of the broad-spectrum antibiotic gentamycin,and both �-MSH and gentamycin even increased the survivalcompared with both agents alone. The authors could further

show that systemically administered �-MSH attenuated thenumber of white blood cell bronchoalveolar lavage (BAL)fluids of mice exposed to intratracheal endotoxin from Sal-monella typhosa (97).

3. �-MSH in experimentally induced contact dermatitis and cu-taneous vasculitis. Central, systemic, and topical (sc, epicuta-neous) application of �-MSH has been evaluated in a varietyof inflammatory skin models. Earliest studies focused onirritant agents, e.g., sodium urate crystals, topically appliedto shaved skin of rodents resulting in acute contact dermatitis(98). The effect of locally injected �-MSH, however, alreadysuggested that the antiinflammatory mechanism of the pep-tide can be mediated via mechanisms different from activa-tion of centrally expressed MC-Rs. Subsequent studies fo-cused on the characterization of the antiinflammatoryefficacy of various routes of �-MSH application and on ad-ditional models of skin inflammation induced by proinflam-matory cytokines and mediators such as IL-1�, IL-6, IL-8,TNF-�, platelet-activating factor, and leukotriene B4 (24, 99–105). Of note, central administration of �-MSH alone wascapable of inhibiting skin inflammation induced by localinjection of irritants or proinflammatory cytokines, and thiseffect could be prevented by spinal cord transection sup-porting the role of descending antiinflammatory neurogenicpathways elicited by �-MSH in such models (104).

The effect of �-MSH was further characterized in exper-imental allergic contact dermatitis. Today, epicutaneous sen-sitization of mice (typically on the ears) with contact aller-gens such as dinitrofluoro-benzene or oxazalone followed bychallenges with these substances is the most commonly usedmodel to study immunosuppressive agents as well as theinduction of tolerance in contact dermatitis. Application of�-MSH suppressed both the sensitization and elicitationlimbs of the cutaneous immune response (106). Later studiesusing iv administered �-MSH (75 �g/kg) extended thesefindings by demonstrating that the peptide induces hapten-specific tolerance. Importantly, in vivo tolerance induction by�-MSH could be abrogated by application of an antibodyagainst the cytokine suppressor IL-10 (107), strongly sug-gesting that this cytokine is a key player in the molecularmechanism of antiinflammation by �-MSH. There is prelim-inary evidence that �-MSH topically applied in a cream mayalso reduce contact eczema in man (6).

One of the classical models to study vasculitis is the so-called Shwartzman reaction. In the local Shwartzman reac-tion, mice are primed with sc injections of LPS followed bysystemic challenges whereupon perivascular inflammatorycell infiltrates, vasculitis, and hemorrhage develop. A singleip injection of �-MSH suppressed this vascular damage andhemorrhage by inhibiting the sustained expression of vas-cular E-selectin and vascular cellular adhesion molecule-1,two adhesion molecules orchestrating diapedesis and acti-vation of leukocytes, which subsequently leads to hemor-rhagic vascular damage (49). The antiinflammatory activityof �-MSH in this model is in accordance with the detectionof MC-Rs in endothelial cells in vitro in which the peptide alsodown-regulates adhesion molecule expression.

4. �-MSH in experimentally induced organ fibrosis. There isaccumulating evidence that �-MSH also has antifibrogenic/



antifibrotic effects in animal models of fibrosis. One of themost extensively used models especially for experimentallung fibrosis is the bleomycin model in which this anticancerchemotherapeutic is intratracheally instilled and leads topulmonary fibrosis within several weeks. The use of thisexperimental model for fibrosis is emphasized by the well-known side effect of bleomycin in cancer patients in whicha scleroderma-like disease of the lung and skin can develop.A cutaneous scleroderma-like model was also established byinjecting fibrosis-susceptible mice sc for 3 wk with bleomycin(108). Using this model we could recently demonstrate that10 �g of coinjected �-MSH significantly attenuated skin fi-brosis. Histological analysis, immunohistochemistry, real-time RT-PCR, and pepsin digestion with SDS-PAGE of skinsamples revealed that �-MSH reduced collagen type Iamounts compared with bleomycin-alone injected animals(109). Interestingly, this salutary effect of �-MSH was asso-ciated with increased in vivo levels of sodium dismutase 2and heme oxygenase-1 (HO-1), two enzymes involved inoxidative stress defense and tissue protection. In vitro,�-MSH at doses of 10�6 to 10�10 m reduced bleomycin-in-duced collagen type I �1/�2 and type III �1 synthesis inhuman dermal fibroblasts and up-regulated the expressionof the above enzymes (109). The observed antifibrogeniceffects of �-MSH are in accordance with our previous find-ings in which 25 �g of �-MSH suppressed cutaneous fibrosisinduced by repetitive injections of high amounts of TGF-�1in newborn mice (110). It is unknown whether �-MSH has aphysiological role in collagen metabolism because the dosesof the peptide used to induce antifibrogenic effect appearsupraphysiological. However, fibroblastic cells of humanskin express functional MC-1Rs (50, 110), and in vitro colla-gen synthesis can be reduced at nanomolar amounts of�-MSH (109, 110).

Using another �-MSH delivery approach, Lee et al. (111)recently showed that �-MSH gene therapy reversed an es-tablished liver fibrosis induced in mice by administeringcarbon tetrachloride for a total of 10 wk. After 6 wk of carbontetrachloride administration, electroporative gene therapywith �-MSH in frame with a four-amino acid extension(ACTH 14–17) was started. �-MSH attenuated liver fibrosisand reduced hepatic levels of collagen type I �1, TGF-�1, andelevated adhesion molecules. Moreover, �-MSH gene ther-apy led to increased MMP1, -2, and -8 expression and/oractivity. Collectively, these findings indicate a novel thera-peutic approach to treat fibrotic diseases of man with �-MSHand related peptides.

5. �-MSH and models of experimentally induced arthritis. It hasbeen known for some time that �-MSH has antiinflammatoryeffects in experimental arthritis. More than 10 yr ago it wasshown that repeated administration of 50 �g of �-MSH iptwice daily significantly attenuated the clinical and histo-logical signs of adjuvant-induced arthritis in the rat usingMycobacterium tuberculosis. �-MSH was similarly effective as100 mg/kg prednisolone but did not cause significant andprogressive weight loss (112). Currently, collagen-inducedexperimental arthritis is a more commonly used experimen-tal arthritis model in rats and mice, but we are unaware ofany study investigating the effect of melanocortins in such

models. However, in a rat model of gouty arthritis elicited byintraarticular administration of monosodium urate mono-hydrate crystals, the MC-3R antagonist SHU9119 blocked theantiinflammatory action of the �-MSH precursor and struc-turally related peptide ACTH (113). Local, but not systemic,administration of very high amounts of ACTH (100 �g) re-duced neutrophil migration, arthritis score, joint size, andcytokine levels at doses that did not alter circulating corti-costerone. Moreover, the antiinflammatory effect of ACTHwas operational in adrenalectomized rats. The precise mech-anism of action of �-MSH and the relevance of locally ex-pressed MC-Rs, in particular those expressed in the synovia,remains speculative. The observations on the use of SHU9119in the gouty arthritis model and the presence of functionalMC-3Rs on rat knee joint macrophages may suggest an an-tiinflammatory action of ACTH (and possibly other mela-nocortins) at the locoregional level.

6. �-MSH and experimental ocular inflammation. One of themost commonly used animal models for human autoim-mune inflammatory eye diseases such as a uveitis or retinitisis experimental autoimmune uveitis. Here, uveitis is inducedby immunizing mice with human interphotoreceptor retin-oid binding protein peptide emulsified with Freund’s adju-vant and M. tuberculosis antigen. �-MSH (50 �g) given iv 10and 12 d after immunization suppressed the mean uveitisscores (114). Similarly, iv application of �-MSH (250–1000 �gper injection) dose-dependently reduced endotoxin-induceduveitis as determined by the number of infiltrating cells in theanterior chamber and the amounts of protein, NO, TNF-�,IL-6, monocyte chemoattractant protein-1, and macrophageinhibitory protein-2 in the aqueous humor (115). The anti-inflammatory mechanism of �-MSH in these models appearsto be linked to induction of regulatory T cells because adop-tively transferred T cells generated by �-MSH and TGF-�2 invitro suppressed experimental autoimmune uveoretinitis(66). It remains to be determined whether �-MSH present inthe aqueous humor (31) plays a physiological role as anendogenous immunomodulator because the doses of �-MSHused in the above studies were supraphysiological.

In another model of corneal trauma and inflammation,�-MSH furthermore turned out to act equipotently with cor-ticosteroids. Treatment with �-MSH, either topically (10�8 m)or im (50 mg/kg�d), markedly reduced edema, hyperemia,aqueous protein levels, and aqueous inflammatory cell num-ber (116). In light of the other biological effects of �-MSH (e.g.,its antimicrobial action) and the simple route of topical ap-plication based on this model, MSH peptides may be ex-ploited in future for the treatment of external eye disease.

7. �-MSH in experimentally induced airway inflammation.�-MSH was further shown to inhibit allergic airway inflam-mation in mice. A well-established murine model to inves-tigate the impact of immunomodulators in allergic asthma isovalbumin-induced airway inflammation model. Accord-ingly, airway inflammation is induced by aerosol sensitiza-tion of ovalbumin followed by subsequent challenges. Mi-crogram doses of ip injected �-MSH reduced peribronchialairway inflammation as measured by cell numbers and dis-tribution of leukocyte subpopulations in BAL fluid and the



extent of the peribronchial and perivascular inflammatorycell infiltrate of lung sections (117). Of note, levels of both IL-4and IL-13, two important proallergic cytokines, were sup-pressed in BAL of allergic mice treated with �-MSH. Inter-estingly and in accordance with the impact of proinflamma-tory signals on the POMC system in other tissues,endogenous levels of �-MSH were rapidly and strongly in-duced in BAL fluids after aerosol challenges in nonsensitizedmice but not in allergic animals. In accordance with the keyrole of IL-10 in �-MSH-mediated suppression of experimen-tal contact dermatitis, the antiinflammatory action of thepeptide in allergic airway inflammation was dependent onthe presence of IL-10 because IL-10 knockout mice wereresistant to treatment with �-MSH (117).

8. �-MSH in experimentally induced acute pancreatitis. Acutepancreatitis is a severe human disorder that can be fatal.Using an animal model for experimentally induced acutepancreatitis, it could be shown that �-MSH injected ip (50 �g)attenuated cerulein-induced organ inflammation and dam-age. Cerulein is a potent stimulant of pancreas exocrine se-cretion when injected sc into fasted rats. �-MSH before in-jection of cerulein reduced plasma amylase levels, pancreaticweight, and inflammation as demonstrated by measure-ments of myeloperoxidase (MPO) activity and inflammatorycell infiltrates (118). The precise mechanism by which �-MSHattenuates this form of experimental acute pancreatitis isunclear. Exocrine secretory epithelia are known to expressthe MC-5R. Moreover, it was recently shown that MC-2R isexpressed in mouse primary islet tissue and in the MIN6mouse insulinoma cell line (119). Interestingly, ACTH atnanomolar concentration increased insulin secretion in per-fusion experiments with MIN6 pseudo-islets and in mono-layer cultures. Using a coculture approach of rat PBMC andpancreas islet cells in a transwell system, it was shown that�-MSH (50 nm) reduces PMA/ionomycin-induced IL-1�,TNF-�, and NO release by PBMC and subsequently atten-uates pancreas islet cell apoptosis (61). Functional studieswith MC-R knockout animals and expression analysis inhuman pancreas tissue are needed to clarify the precise roleof MC-Rs in the pancreas physiology.

9. �-MSH in experimental liver inflammation and colitis. Chiaoet al. (120) originally demonstrated that acute hepatitis in-duced by LPS and Corynebacterium parvum pretreatmentcould be prevented by �-MSH when given ip 30 min afterLPS administration (120). �-MSH suppressed systemic NOproduction, hepatic neutrophil infiltration, and increased he-patic mRNA levels of TNF-� and the chemokines IL-8 andmonocyte chemoattractant protein-1 (120). The same authorsshowed expression of MC-1R suggesting that the immuno-modulatory effect of �-MSH could be related to direct effectson the liver.

Increasing evidence exists that �-MSH has potent antiin-flammatory activity in experimentally induced colitis. In amouse model of dextran sodium sulfate (DSS)-induced co-litis, 50 �g of �-MSH daily profoundly reduced the appear-ance of fecal blood, inhibited weight loss, and preventeddisintegration of the general condition of the animals (121).In a rat model of trinitrobenzene sulfonic acid-induced co-

litis, ip injection of �-MSH likewise reduced the colonic mac-roscopic lesions compared with untreated ones in both acuteand chronic colitis groups (122). Further studies with phar-macological NO donors and cyclooxygenase inhibitors em-phasized the role of reduced levels of NO and PGs as im-portant players in the mechanism of antiinflammation by�-MSH (122). A modulatory role for �-MSH in the gut isunderscored by the suppressing effect of the peptide on IL-6release in ex vivo samples from patients with celiac disease asoutlined above (16). Interestingly, the latter authors detectedimmunostaining for �-MSH, MC-1R, and MC-5R in the du-odenal mucosa of celiac patients, suggesting the presence ofa localized POMC system in the intestinal mucosa. Recently,definitive evidence was provided for an important role of theMC-1R in the regulation of inflammatory responses of thegut using the DSS model of experimental colitis. Maaser et al.(123) examined the inflammatory intestinal response of micewith a frameshift mutation in the MC-1R gene (MC-1Re/e),C57BL/6 wild-type mice, and MC-1Re/e-C57BL/6 bonemarrow chimeras. DSS-induced colitis in MC1Re/e mice wasaggravated with higher weight loss, and marked histologicalchanges compared with C57BL/6WT, eventually leading todeath of all MC1Re/e mice. Similar observations were madein a transmissible murine colitis model induced by Citrobacterrodentium in which infected MC1Re/e mice showed delayedclearance of infection. Aggravation of intestinal inflamma-tion in MC1Re/e mice was not due to lack of hematopoieticcells expressing MC-1R because the course of colitis wassimilar between MC1Re/e-C57BL/6 bone marrow chimerasand MC1Re/e mice (123). Moreover, the authors could alsoidentify MC-1R expression in murine intestinal epithelia sup-porting the view that MC-1R may be an important regulatorof the mucosal innate host defense (Fig. 2).

C. Cytoprotective effects in vitro

The following section is dedicated to the protective effectsof �-MSH against cellular toxicity and cell-death-inducingsignals in vitro. Whereas early studies focused on the pro-tective effect of melanocortins on neuronal cell types, morerecent studies have lately extended our knowledge towardother nonneuronal cell types with fascinating new functionalfacets of �-MSH as a potent modulator of apoptosis inducedby genotoxic stress (Table 4).

1. �-MSH protects against neuronal cell toxicity. A limited num-ber of studies addressed the protective effects of �-MSH oncellular neurotoxicity in vitro. These studies were performedin complementation of the wealth of previous in vivo findingsthat indicated a neurotrophic and neuroprotective effect ofmelanocortins against various forms of nerve damage suchas crush injury or neurotoxic drug damage (124–129). Ac-cordingly, cultured rat dorsal root ganglia (DRG) were par-tially protected against the growth-inhibitory effect of theneurotoxic drug cisplatin by 10 nm �-MSH (130) and thiseffect was found not to involve potentiation of nerve growthfactor action (131). Recent studies are focusing on the mo-lecular mechanism by which �-MSH and MC-Rs preventapoptosis in neuronal and related cell types. Using the im-mortalized hypothalamic tumor cell line GT1-1, it was shown



that NDP-MSH (10�6 m) inhibited serum deprivation-in-duced caspase-3 activation as a readout for apoptosis (132).The antiapoptotic effect of NDP-MSH was inhibited bySHU9119, suggesting that MC-4R expressed by GT1-1 cellsmediates the protective effect of NDP-MSH. Moreover, NDP-MSH induced phosphorylation of ERK1/2, and pharmaco-logical inhibition of these enzymes by the kinase inhibitorPD98059 attenuated the antiapoptotic effect of NDP-MSH inGT1-1 cells (132). These data suggest that NDP-MSH viaMC-4R activates ERK1/2 and thereby attenuates serum dep-rivation-induced apoptosis. In another report, �-MSH re-duced IFN-�/LPS-induced apoptosis of rat astrocytes, andthis effect could be abolished by HS024 (60). Here, �-MSHproduced a shift in the expression of the apoptotic regulatorsBax/Bcl2. Although these findings emphasize the roles of�-MSH and MC-4R in neuroprotection, the doses of �-MSHused in the latter two in vitro studies were 1–5 �m. It remainsto be shown whether �-MSH acts physiologically in the brainas an endogenous neuroprotective peptide.

2. �-MSH—a suppressor of apoptosis in nonneuronal cells. Oneof the earliest reports definitely linking the protective effectof �-MSH with inhibition of apoptosis was the work by Jo etal. (133). Using cyclosporine A as an in vitro model substanceto study nephrotoxicity, it was shown that this drug inducesexpression of the Fas/Fas ligand system in human kidney-2cells, an immortalized proximal tubular epithelial cell line.One micromole of �-MSH reduced cyclosporine A-induced

apoptosis and also attenuated the enhanced levels of Fas, Fasligand, and the Fas-associated protein with death domain.

Recently, our group demonstrated that apoptosis inducedby UVB irradiation, the most ubiquitous environmentalstressor for the skin, is significantly suppressed by �-MSH ina number of cutaneous cell types (134). This antiapoptoticeffect of �-MSH can be elicited by nanomolar to micromolardoses of the peptide in melanocytes (134, 135) and is linkedto reduced amounts of DNA photoproducts, i.e., cyclopyri-midine dimers. Because XPA fibroblasts carrying a grossdefect in the nucleotide excision repair do not respond to�-MSH with inhibition of UVB-induced apoptosis (134),these data point toward a modulatory effect of �-MSH in theDNA repair machinery that is currently under investigationin our laboratory. In light of the discovered protective effectof �-MSH on UVB-induced genotoxic stress tetrapeptide,�-MSH analogs have been suggested as a novel melanomapreventive strategy (136). Ac-His-D-Phe-Arg-Trp-NH2,n-pentadecanoyl- and 4-phenylbutyryl-His-D-Phe-Arg-Trp-NH2 were assessed for their in vitro capacity to stimulatetyrosinase (thus increasing melanogenesis), to reduce UVB-induced apoptosis and release of H2O2, and to enhance re-moval of cyclopyrimidine dimers after UVB exposure. Thelatter two peptides were more potent than the former or�-MSH at 1 nm, and their action could readily be reversed byagouti signaling protein, the physiological antagonist ofMC-1R (136).

In accordance with the inhibitory effect of �-MSH on UVB-induced apoptosis, it was further shown that the peptide cansuppress UVB-induced H202-, TNF-�-, and IL-1�-inducedcell death (135, 137). These findings create a link between theidentified cytoprotective effects of �-MSH and the deleteri-ous or cytotoxic effects of proinflammatory cytokines or re-active oxygen species released during inflammatoryresponses.

D. Protective effects against organ damage

Numerous studies have provided ample evidence for asignificant in vivo activity of �-MSH and related peptides invarious animal models of organ injury and damage (Table 5).In several cases it has become apparent that this protectiveactivity of �-MSH is linked to its antiinflammatory action andto common molecular effector pathways, e.g., modulation ofNF-�B activity. The following section therefore describes inbrief the spectrum of �-MSH as a protective peptide in vivowith focus on the more recent literature. It should be notedthat coverage of the full literature on the protective in vivoeffects of melanocortins is beyond the intention of this re-view. The interested reader is therefore referred to otherexpert reviews covering specific topics in this broad field(124–129, 138).

1. �-MSH and postlesional repair. A large number of in vivostudies have addressed the neuroprotective and neurotro-phic effects of melanocortins, especially ACTH and relatedtruncated ACTH peptides such as ORG 2766 [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH] (125–127). With regard to�-MSH, it has been known for years that local delivery of thepeptide can increase postlesional repair of nerve in rats (139,

IntestinalLumen

α-MSH

MC-1R

Epithelial Barrier

Lamina propria

Microvascular Endothelium

Circulating Leukocytes

NF-κB

Proinflammatory signal

NF-κB IL-8 α-MSH IL-8

FIG. 2. Hypothetic role of the melanocortin system in intestinal in-flammation. In response to a proinflammatory signal, e.g., bacterialinfection, NF-�B expression in intestinal epithelial cells is up-regu-lated leading to an increased expression and release of proinflam-matory cytokines such as IL-8 into the basolateral compartment. Theincreased IL-8 gradient then leads to an enhanced recruitment ofneutrophils to the site of inflammation. At the same time, these cellsas well as intestinal epithelial cells release �-MSH, which binds in anautocrine as well as paracrine fashion to its cognate receptor, MC-1R,with the effect of NF-�B down-regulation. This leads to a reduction ofproinflammatory cytokine expression and recruitment of leukocytesfrom the circulating pool of cells.



140). Interestingly, in the study by Vadoud Seyedi et al. (140),�-MSH reduced inflammation, hypervascularization, and fi-brosis, the latter recapitulated by the recent studies indicat-ing an antifibrogenic/antifibrotic potential of �-MSH (109–111). In the rat weight drop injury model, sc treatment with

�-MSH—either 75 �g/kg of body weight every 48 h for 3 wkafter trauma or a single 30 mg/kg dose, 30 min after injury—also led to significant neurological and electrophysiologicalimprovement in spinal cord function (141). Two other studiesconfirmed the neuroprotective effect of �-MSH by delivering

TABLE 5. Protective effects of �-MSH in vivoa

Type of model Effect of �-MSH Application routeof �-MSH Species Ref.

Postlesional repair Neural degeneration after crush 2 Perilesional delivery bychamber

Rat Edwards et al., 1984 (139)

Neural degeneration, fibrosis, inflammationafter incision 2

Perilesional delivery usinga chamber

Rat Vadoud Seyedi et al., 1993 (140)

Neurodegeneration after weight drop 2 sc Rat Van de Meent et al., 1997 (141)Neurodegeneration after spinal cord

contusion injury 2Intrathecally, by a mini

pumpRat Lankhorst et al., 1999 (142)

Neural degeneration after spinal cordtransection 2

Local delivery system by acollagen matrix

Rat Joosten et al., 1999 (143)

Drug-induced neuro- andototoxicity

Ototoxicity induced by cisplatin ip 2 sc Guinea pigs Heijmen et al., 1999 (145)

Ototoxicity induced by cisplatin givenintracochlear 2

sc Guinea pigs Wolters et al., 2003 (146)

Ototoxicity induced by cisplatin ip 2 sc Guinea Hamers et al., 2003 (147)Kainic acid-induced excitotoxic cell death

and IL-1� expression 2ip Rat Forslin Aronsson et al., 2007 (148)

Brain ischemia Brain stem auditory evoked potentials 2 iv Dog Huh et al., 1997 (149)Postischemic expression of TNF-� and IL-1�

2ip Mouse Huang and Tatro, 2002 (150)

Core and brain temperature 2 ip Rat Spulber et al., 2005 (151)No. of viable neurons 1, astrocyte

proliferation 2ip Rat Forslin Aronsson et al., 2006 (152)

Myocardial ischemia Infarct size 2, coronary and flow aorticflow, left ventricular pressure 1

sc Rat Vecsernyes et al., 2003 (156)

Mesenteric ischemia Intestinal injury 2, MPO activity and NF-�B activation 2

iv Rat Hassoun et al., 2002 (161)

Mucosal injury, MPO activity, IL-6 levelsand NF-�B activation 2

iv Rat Zou et al., 2003 (162)

Renal ischemia Tubule necrosis, neutrophil pluggingcapillary congestion 2, renal function 1,

renal IL-8, ICAM-1 and iNOS levels 2

iv Mouse Chiao et al., 1997 (164)

Rat Chiao et al., 1998 (39)Renal AQP1/2 expression 1 iv Rat Kwon et al., 1999 (166)

Renal function 1, tubular apoptosis, Fas/FasL and ICAM-1 expression 2

ip Rat Jo et al., 2001 (165)

Renal function 1, sodium transporter andAQP expression 1

iv Rat Gong et al., 2004 (167)

Renal function 1, leukocyte infiltration,MPO and NF-�B activity, AP1 binding, p38

phosphorylation 2

iv Mouse Deng et al., 2004 (171)

Renal toxicity Cyclosporine-induced inflammation,apoptosis, and fibrosis 2, Bax and TGF-�1

level 2, Bcl2 level 1

ip Rat Lee et al., 2004 (168)

Gentamycin-induced inflammation, MPOactivity and malondialdehyde 2, GSH 1

ip Rat Kolgazi et al., 2007 (169)

Ureteral obstruction Renal function 1, Na-K-ATPase and AQPexpression 1, renal tubular apoptosis 2

iv Rat Li et al., 2006 (170)

Lung injury Renal ischemia-induced lung injury,leukocyte infiltration, MPO and NF-�B

activity, AP1 binding, p38 phosphorylation,TNF-� and ICAM-1 expression 2

iv Mouse Deng et al., 2004 (171)

GSH, Glutathione; 2, decreased; 1, increased.a Excluding in vivo studies with NDP-MSH.

TABLE 4. Cytoprotective effects of �-MSH in vitro

Process Effect of �-MSH Cell type tested Ref.

Neuronal cell toxicity Cisplatin-induced growth inhibition2

Rat DRG Bär et al., 1993 (130)

Cisplatin-induced growth inhibition2

Rat DRG Windebank et al., 1994 (131)

Apoptosis Cyclosporine-A-induced Fas/FasLexpression and apoptosis 2

Human kidney-2 cells (HK-2) Jo et al., 2001 (133)

UVB-induced apoptosis and DNAdamage 2

Human melanocytes, (keratinocytes,fibroblasts)

Böhm et al., 2005 (134)

UVB-induced apoptosis and DNAdamage 2

Human melanocytes Kadekaro et al., 2005 (135)

TNF-�-, IL-1�- and LPS-inducedapoptosis 2

Human dermal fibroblasts Hill et al., 2005 (137)

Serum deprivation-induced apoptosisand caspase 3 activation 2

GT1-1 hypothalamic tumor cells Chai et al., 2006 (132)

IFN-�/LPS-induced apoptosis 2 Rat astrocytes Caruso et al., 2007 (60)

2, Decreased.



it with a mini pump to the cisterna magna in the well-characterized spinal cord contusion injury model (142) or byproviding it locally in a special collagen matrix in the spinalcord transection model of the rat (143). These promisingfindings have prompted additional studies using low mo-lecular weight nonpeptide compounds with varying affini-ties at MC-Rs in nerve injury models (144).

2. �-MSH in drug-induced neuro- and ototoxicity. Like theACTH-related peptide ORG 2766 (128), �-MSH was evalu-ated for its protective in vivo effect against cisplatin-inducedototoxicity (128, 145–147). These studies were performed inlight of the need for neuroprotective strategies in cancerpatients in which cisplatin can lead to severe neuro- andototoxicity as a limiting side effect. Initial studies with�-MSH were uncertain toward a clear-cut protective effect insystemically cisplatin-treated albino guinea pigs due to theexistence of responders and nonresponders and also becauseof a high interanimal variability (145). However, subsequentlongitudinal studies with intracochlear administration re-vealed that sc daily bolus injections of �-MSH (75 �g/kg)delay the threshold shift induced by cisplatin (146). In an-other study using chronically implanted round window elec-trodes, �-MSH was superior to ORG 2766 in the speed andextent of the recovery of the auditory nerve compound actionpotential threshold (147). Recently, the effect of �-MSH wasassessed in kainic acid-induced excitotoxicity of the rat rep-resenting a model for human temporal lobe epilepsy. Inter-estingly, the number of viable neurons in the hippocampusand hypothalamus was increased in animals receiving threetreatments of �-MSH (0.5 mg/kg body weight) after kainicacid administration (148). Moreover, �-MSH reduced kainicacid-induced astrocyte excitotoxicity and reduced elevatedIL-1� levels in this study. These data are interesting andcreate a link between epileptogenesis, inflammation, and theneuroprotection by �-MSH.

3. �-MSH in experimental ischemia. An increasing number ofreports highlight an intriguing protective property of �-MSH(and related peptides) in ischemic organ damage. Usingbrain stem auditory-evoked potential as a first readout forCNS damage, �-MSH (1 mg/kg) was shown to improve therecovery of these potentials especially when coadministeredbefore and during the 20-min ischemia (149). Subsequentstudies addressing the effect of �-MSH on postischemic ac-tivation of proinflammatory cytokines demonstrated that thepeptide (0.5 mg/kg) given before the start of the ischemiaand again 1 h after reperfusion significantly suppressed el-evated TNF-� levels in the cerebrocortical territory of themiddle cerebral artery after transient unilateral occlusion(150). The same authors could show that �-MSH likewisesuppressed intracerebral TNF-� protein after transient globalischemia. Therefore, not only the effect of �-MSH on core andbrain temperature (151) but also reduced cerebral levels ofproinflammatory cytokines appear to be involved in the pro-tective mechanism of �-MSH in ischemic brain damage (152).Using NDP-MSH as a related melanocortin peptide, theseneuroprotective effects in ischemic brain damage of �-MSHcould be confirmed in focal cerebral ischemia induced by thevasoconstrictor endothelin-1 in the rat (153) and in global

cerebral ischemia in the gerbil (154). Remarkably, in the lattertwo studies NDP-MSH was effective upon delayed systemicdelivery (3 or 9 h after endothelin-1 injection) and inducedlong-lasting protection (until 67 d after ischemia). Interest-ingly, the protective effect of NDP-MSH on ischemia-in-duced inflammatory, apoptotic pathways and hippocampusinjury in gerbils could be prevented by HS024, indicating apromising clinical potential of MC-4R agonists as a futuretherapeutic approach in ischemic stroke (138, 155)

As an extension to the above findings, �-MSH was shownto protect against ischemic heart injury as demonstrated inrats sc injected with 40–400 �g/kg of the peptide followedby isolation of hearts 12 h later, perfusion, ischemia for 30min, and 120-min reperfusion (156). All doses of �-MSHreduced infarct size, whereas only at 200 �g/kg of �-MSHwere coronary flow, aortic flow, and left ventricular devel-oped pressure significantly increased compared with non-�-MSH-treated animals. These findings are in accordancewith earlier findings that revealed beneficial effects of�-MSH as well as of ACTH peptides on cardiovascular func-tion and survival (157). Pharmacological blockade experi-ments using synthetic MC-3R agonists (158), the MC-4R an-tagonist HS059, and the MC-3R/MC-4R antagonist SHU9119 (159) indicate that MC-3R mediates the protective effectof �-MSH or ACTH (1–24) on myocardial ischemia/reper-fusion damage and arrhythmia. These data suggest a poten-tial for MC-3R agonists in the treatment of myocardial in-farction. Whether �-MSH exerts a physiological orpathophysiological role in myocardial function in man, how-ever, remains unclear. Recently, elevated levels of circulating�-MSH have been detected in patients with congestive heartfailure New York Heart Association class II, suggesting atleast a participation of melanocortins in distinct forms ofhuman heart disease (160).

In at least two other organ systems, �-MSH was examinedas a protective agent upon ischemia. Given either 30 minbefore or even 1–2 h after mesenteric ischemia, the peptide(50–100 �g) had salutary effects on intestinal damage, in-flammation, and NF-�B activation (161, 162). The delayedadministration of �-MSH, moreover, not only decreasedischemia-induced IL-6 tissue levels but also enhanced ex-pression of HO-1, a guardian of tissue injury (163). The latterobservation is in accordance with our data on the up-regu-lating effect of �-MSH on HO-1 in bleomycin-induced skinfibrosis (109). With regard to the kidney, Chiao et al. (164)were the first to report on a protective effect of �-MSH inrenal damage. Again, not only 25 �g of �-MSH during renalischemia (followed by multiple bolus injections of the pep-tide after ischemia) but also delaying administration for 6 hreduced ischemia-induced renal dysfunction, reduced tu-bule necrosis and inflammation, and attenuated ischemia-induced expression of KC/IL-8, ICAM-1 and iNOS (164).Interestingly, the protective effect of �-MSH was preservedin ICAM-1 knockout mice, indicating that �-MSH protectsagainst ischemia-induced renal damage by neutrophil-inde-pendent mechanisms (39). Because �-MSH attenuates NOproduction in activated murine cortical tubule cells, a directprotective effect of �-MSH on the kidney parenchyma islikely. This concept is supported by the regulatory effects of�-MSH on expression of Fas and Fas ligand (FasL) in isch-



emic kidney (165). Another interesting observation with re-gard to the possible mechanism of �-MSH against ischemickidney damage is its up-regulatory effect on the ischemia-induced repression of aquaporin (AQP) 1 and 2 as well as onthe sodium transporters Na, K-ATPase, and rat type 1 bu-metamide-sensitive Na-K-2Cl cotransporter (166, 167). It willbe very interesting to further decipher the exact protectivemechanism of �-MSH in ischemic kidney injury and to clarifywhich MC-R subtype in the kidney is involved in thisphenomenon.

4. �-MSH in experimental nephrotoxicity. Two other reportsfurther point toward a protective activity of �-MSH in thekidney. Using a model of chronic cyclosporine-induced ne-phropathy, it could be shown that daily ip injection of 50 �gof �-MSH reduces apoptosis in the tubules and the intersti-tium and attenuates tubulointerstitial fibrosis after 48 d ofcyclosporine treatment (168). Moreover, �-MSH attenuatedthe cyclosporine-induced expression of the proapoptotic reg-ulator Bax, increased the expression of the antiapoptotic Bcl2,and reduced TGF-� in the kidney. However, �-MSH in thismodel failed to improve renal function parameters. In an-other model of drug-induced nephrotoxicity, gentamycinwas administered for 7 consecutive days. �-MSH (25 �g) wasadministered daily into the peritoneal cavity. Although�-MSH reduced the severity of renal damage as determinedby histology, MPO activity, and concentration of renal glu-tathione levels, it again failed to improve renal functionalparameters (169).

5. �-MSH and experimental ureteral obstruction. Recently,�-MSH was tested in an animal model for obstructive ne-phropathy. Using a bilateral ureteral obstruction model, Li etal. (170) showed that iv administration of 50 �g of �-MSH (atthe onset and 12 h after the obstruction) almost completelyprevented the decrease in glomerular filtration rate andstrongly reduced tubular cell apoptosis. Analogous with theprotective effects of �-MSH in renal ischemia, the peptidepartially restored the reduced expression of AQP1 and Na-K-ATPase expression.

6. �-MSH and experimental acute lung injury. Finally, there isevidence that melanocortin peptides protect against acutelung injury. Using the renal ischemia-reperfusion model ofthe mouse, it was demonstrated that iv �-MSH (25 �g) notonly attenuated NF-�B and p38 activation, as well as DNAbinding of activator protein 1 (AP1) in the kidney, but alsohad similar distant protective effects, namely in the lung(171). Most recently, Catania and co-workers (172) furtherinvestigated the effect of NDP-MSH in rats exposed to bleo-mycin instilled into the lungs. Intraperitoneal injection of 100�g of NDP-MSH reduced bleomycin-induced acute lung in-jury as determined 8 and 24 h after treatment by reducedinterstitial pulmonary edema, less inflammatory cell infil-tration, and thinner alveolar walls. NPD-MSH not only at-tenuated bleomycin-induced IL-6, TNF-�, and TGF-�1 ex-pression but also prevented the up-regulation of genesinvolved in lung fluid homeostasis, e.g., Na�/K�-transport-ing ATPase or epithelial sodium channels. Interestingly,bleomycin treatment resulted in endogenous induction of�-MSH in the lung, presumably by monocytes or macro-

phages (172). These data point toward a clinical potential of�-MSH and related peptides in various forms of inflamma-tory lung disease.

IV. Antiinflammatory Effects of �-MSH-RelatedTripeptides in Vitro and in Vivo

There is clear evidence that KPV has potent antiinflam-matory actions in vitro and in vivo although the exact mech-anism by which these peptides exert their effects is stillpoorly understood. Until now most of the studies addressingthe antiinflammatory effect of C-terminal tripeptides of�-MSH have been performed in vitro and mainly concen-trated on the L-form of KPV, leaving it open as to whetherother stereoisomers are also effective (Table 6). KPV wasshown to reduce production of TNF-�, IL-6, and NO inducedby proinflammatory stressors (29, 34, 36). Suppression of NOproduction by RAW 264.7 cells was similarly as effective asfull-length �-MSH, whereas cyclic KPV derivatives wereweaker in their antiinflammatory activity (173). Similar to�-MSH, KPV reduced activation of NF-�B in human kera-tinocytes and monocytic cells (72, 174). In the former celltype, KPdV was similarly as effective as KPV in inhibition ofTNF-�-induced NF-�B activation. Pharmacological studiesin human keratinocytes interestingly revealed an unusualdose-response curve of KPV that extends over six orders ofmagnitude of dose and which cannot be explained by asimple peptide-receptor interaction (72). Interestingly, thestereoisomer of KPV, KdPV, which previously was shown tolack antipyretic activity in vivo (175), was able to suppressLPS-induced NF-�B activation in rat alveolar cells (176). Fi-nally, KPV and KdPV were shown to induce IL-10 in humanmonocytes at 10�13 m, albeit to a lesser extent than equimolaramounts of �-MSH (45). However, some modulatory effectsof �-MSH may not be replicated by KPV. We could not detectany cytoprotective effect of KPV on UVB-induced apoptosisin normal human melanocytes (134), suggesting cell typespecificity and/or an indispensable role for MC-1R in themodulatory effect of �-MSH in this action of the parentalneuropeptide. Recent observations from our laboratory fur-ther indicate that the structurally related tripeptide KdPT isalso capable of suppressing IL-1-mediated inflammatory ef-fects, e.g., IL-1�-induced, but not TNF-�-induced, NF-�B ac-tivation and IL-6 and IL-8 expression in human sebocytes atnano- and subnanomolar doses (177).

Regarding in vivo experiments, KPV and several stereo-isomers and derivatives have been evaluated in a limitednumber of studies, some of them more almost 20 yr ago(Table 7). KPV has antipyretic effects when administeredintracerebroventricularly or iv to rabbits made hyperthermicby systemic administration of IL-1 (178, 179). Truncationstudies of �-MSH indeed disclosed that the antipyretic mes-sage sequence resides in the C-terminal amino acids KPV.The antipyretic activity of KPV was higher upon central thanupon peripheral administration and overall lower than theantipyretic effect of full-length �-MSH (178). In accordancewith the effect of KPV on NF-�B activation in vitro, thepeptide suppressed activation of this transcription factor inthe brain of LPS-treated mice in vivo (94). In mouse models



of skin inflammation including irritant and allergic contactdermatitis, KPV exerted antiinflammatory effects as well(100, 101, 104, 105, 175, 180). Descending neurogenic path-ways are of less importance for the antiinflammatory mech-anism of KPV than for full-length �-MSH. In mice with

experimentally induced hind paw inflammation, KPV ad-ministered ip had marked antiinflammatory activity even inanimals with spinal cord transection (104). Interestingly, itcould be demonstrated that the L-configuration of the centralamino acid Pro of KPV is critical for the antiinflammatory

TABLE 7. Antiinflammatory effects of �-MSH tripeptide analogs and derivatives in vivo

Peptide Type of model Effect of �-MSH Application routeof �-MSH Species Ref.

KPV Fever Hyperthermia induced by iv injectionof LP 2

icv, iv Rabbit Richards and Lipton, 1984 (178)

KPV Hyperthermia-induced ivadministration of IL-1 2

icv Rabbit Deeter et al., 1989 (179)

KPV Skin inflammation Ear inflammation induced by topicalapplication of picrylic acid 2


KPV Hind paw edema induced byinjection of �-carrageenan 2


KPV Contact dermatitis of the ear inducedby topical application of DNFB 2


KPV, dKPV,KPdV,dKPdV

Ear swelling induced by topicalapplication of picryl acid 2


KPdV Ear swelling induced by intradermalinjection of IL-1�, IL-6, and TNF-�

2


KPV Ear edema induced by dermalinjection of IL-1� and PAF 2

icv, ip Mouse Ceriani et al., 1994 (105)

KPV Hind paw edema induced byinjection of �-carrageenan 2

ip Mouse Macaluso et al., 1994 (104)

KPV Brain inflammation Activation of NF-�B central injectionof LPS 2

ip Mouse Ichiyama et al., 1999 (94)

KPV Gastrointestinal inflammation Peritonitis with neutrophilaccumulation induced by ip injection

of MSU and IL-1� 2

sc Mouse Getting et al., 2003 (23)

KdPT DSS-induced colitis withinflammatory cell infiltration,

increased MPO activity 2

iv Mouse Maaser et al., 2006 (123)

KPV DSS-induced colitis withinflammatory cell infiltration,

increased MPO activity, and IL-1�levels 2

iv Mouse Kannengiesser et al., 2008 (181)

KPV DSS- and trinitrobenzene-sulfonicacid-induced colitis with

inflammatory cell infiltration,increased MPO activity, IL-1�, IL-6,IL-12, TNF-�, and IFN-� levels 2

Oral Mouse Dalmasso et al., 2008 (30)

icv, Intracerebroventricularly; DNFB, 2,4-dinitrofluorobenzene; LP, leukocyte pyrogen; MSU, monosodium urate; PAF, platelet-activatingfactor; 2, decreased.

TABLE 6. Antiinflammatory effects of �-MSH tripeptide analogs and derivatives in vitro

Target molecule/process Peptide Effect of �-MSH Cell type Ref.

Proinflammatory cytokines KPV LPS/PMA-induced TNF-�expression 2

Murine connective tissuefibroblasts cell line L292

Wong et al., 1997 (34)

KPV LPS/IFN-�-induced TNF-� and IL-6 expression 2

Murine microglial cellline (N9 clone)

Delgado et al., 1998 (29)

KPV �A/IFN-�-induced NO2�

production 2, iNOS expression 2Murine microglial cell

line (N9 clone)Galimberti et al., 1999 (36)

KPV IL-1�-induced IL-8 expression 2 Human colon, Jurkatcells

Dalmasso et al., 2008 (30)

KdPT IL-1�-induced IL-6 and IL-8expression 2

SZ95 human sebocytes Mastrofrancesco et al., 2007 (177)

Transcription factor NF-�B KPV TNF-�-induced NF-�B activation2

HIV-1-infectedpromonocytic U1 cell line

Barcellini et al., 2000 (174)

KdPV LPS-induced NF-�B activation 2 Rat alveolar type IIepithelial cells

Haddad et al., 2001 (176)

KPV LPS/IFN-�-induced NF-�Bactivation 2

RAW 264.7 murinemacrophage cell line

Mandrika et al., 2001 (28)

KPV, KPdV TNF-�-induced NF-�B activation2

HaCaT keratinocytes,human keratinocytes

Moustafa et al., 2002 (72)

KPV IL-1�-induced NF-�B activation 2 Human colon, Jurkatcells

Dalmasso et al., 2008 (30)

KdPT IL-1�-induced NF-�B activation 2 SZ95 human sebocytes Mastrofrancesco et al., 2007 (177)Non-cytokine pro-inflammatory

mediatorsKPV IFN-�/LPS-induced NO2

�

production 2Murine microglial cell

line (N9 clone)Delgado et al., 1998 (29)

KPV LPS/IFN-�-induced NO production2


Mandrika et al., 2001 (28)

Cyclic KPV,KPdV

derivatives

LPS/IFN-�-induced NO production2


Muceniece et al., 2003 (173)

Cytokine suppressors KPV IL-10 production 1 Human peripheral bloodmonocytes

Bhardwaj et al., 1996 (45)

�A, �-Amyloid protein; PMA, phorbol-12-myristate-13-acetate; 2, decreased; 1, increased.



action of stereoisomers of KPV, at least in the employedmouse model of picryl acid-induced skin inflammation (175).These in vivo findings are in some contrast to the recentlyreported immunomodulatory effects of KdPV in rat epithe-lial lung cells (176).

The potent in vivo antiinflammatory actions of KPV are fur-ther highlighted by its modulatory effect in crystal-inducedperitonitis of mice (23) in which full-length �-MSH, KPV, andthe �-MSH core peptide HFRW suppressed accumulation ofpolymorphonuclear leukocytes in the peritoneal cavity. In thismodel, administration of a MC-1R agonistic peptide, MS05, didnot have any antiinflammatory effect, and in mice with non-functional MC-1R KPV likewise had antiinflammatory effects.Recently, there is emerging evidence that both KPV and KdPThave potent antiinflammatory effects in models of inflamma-tory bowel disease (30, 181, 182). We could demonstrate that ivapplication of 100 ng of KPV leads to earlier recovery andsignificantly stronger regain of body weight (181). In accor-dance with these readouts, intestinal MPO activity was signif-icantly reduced in mice receiving KPV. KPV likewise acted asa potent antiinflammatory agent in the CD45Rbhi transfer colitismodel. During revision of this review, it was reported by Dal-masso et al. (30) that orally administered KPV (100 �mol/liter)also decreases both DSS-induced and trinitrobenzene sulfonicacid-induced intestinal inflammation. In DSS-induced colitis,KPV suppressed intestinal mRNA levels of IL-6 and IL-12,whereas in the latter model it furthermore suppressed TNF-�and IFN-� mRNA amounts. In an attempt to identify the po-tential antiinflammatory mechanism of KPV, two human im-mortalized colonic carcinoma cell lines, Caco2-BBE and HT29-CL.19A, were used. KPV at nanomolar amounts suppressedIL-1�-induced NF-�B activation and IL-8 mRNA expression inCaco2-BBE cells and also decreased TNF-�-induced NF-�B ac-tivation in Jurkat cells (30), a human T cell lymphoma cell line.Although both Caco2-BBE and Jurkat cells expressed multipleMC-Rs, KPV (as well as �-MSH) failed to increase intracellularcAMP levels. Interestingly, KPV did not reduce IL-1�-inducedNF-�B activation in HT29-CL.19A cells, which in contrast toCaco2-BBE and Jurkat cells lack expression of the PepT1, anH�-coupled oligopeptide transporter (183). Binding kinetics onboth Caco2-BBE and Jurkat cells revealed specific uptake ofradiolabeled KPV. These findings add a novel twist to ourunderstanding of how KPV and possibly related peptides couldmediate their antiinflammatory action. Whether KPV andKdPT act in a similar fashion in primary cells or via additionalmechanism, e.g., by competing with IL-1� binding to its recep-tor (184), remains to be determined.

V. Therapeutic Potential of �-MSH-RelatedTripeptides in Human Immune-Mediated

Inflammatory Diseases

KPV, its stereoisomers, and KdPT are attractive futurecandidates for pharmaceutical companies that wish to ex-ploit these peptides for the treatment of human immune-mediated inflammatory diseases. At present, evidence existsfor the antiinflammatory effects of KPV (Tables 6 and 7), butcompared with what is known about �-MSH (Tables 2 and3), more studies are urgently needed for KPV, its stereoiso-

mers, and especially for the �-MSH tripeptide derivativeKdPT.

The molecular effects underlying the antiinflammatoryactivity of KPV that have been identified so far are verysimilar to �-MSH and include major effector pathways ofinflammation, i.e., suppression of TNF-� production, induc-tion of IL-10, and inhibition of NF-�B activation. In manyimmune-mediated inflammatory diseases including inflam-matory bowel disease, rheumatoid arthritis, eczema, or al-lergic asthma, these effector pathways of inflammation arecrucially involved in their pathogenesis. Accordingly, anti-inflammatory strategies with the so-called “biologics” thattarget specifically the above effector pathways, e.g., anti-TNF-� therapy, have successfully emerged as novel andpowerful treatment avenues for such diseases (185). Based onthe homology of KPV with �-MSH and the homology ofKdPT with IL-1�[193–195], it would only be justified to callthese peptides “natural biologics” when used in the futurefor the treatment of immune-mediated inflammatorydiseases.

At present, no toxicity studies of KPV and KPT are avail-able, and thus we do not know the overall safety profile ofsuch tripeptides compared with the melanotropic superpo-tent �-MSH analog NDP-MSH. Previously, NDP-MSH atdoses of up to 0.16 mg/kg was injected into humans iv forevaluation of its effect on skin pigmentation. Adverse effectsconsisted of occasional gastrointestinal upset and facialflushing (186). Several recent studies investigating the in vivoeffect of NDP-MSH in humans for pigmentation confirmedno major adverse effects (187–189). In light of the well-knownspectrum of adverse effects encountered with almost all con-ventional immunosuppressive therapies (e.g., azathioprine,methotrexate, mycophonolate mofetil, cyclosporine, and cy-clophosphamide) but also with biologics, the safety profile of�-MSH and related tripeptides therefore appears to be high.

Regarding the future safety profile of �-MSH and relatedpeptides in man, another biological property of these agentsdeserves some attention: �-MSH and KPV were recentlyshown to possess antimicrobial activity against Staphylococ-cus aureus and Candida albicans, two major and representativepathogens (190). This antimicrobial activity of �-MSH pep-tides is linked to an increase in bacterial cAMP content.Moreover, �-MSH peptides increased in vitro killing of bothpathogens by human neutrophils. The direct and indirectantimicrobial actions of MSH peptides are in marked con-trast to virtually all established antiinflammatory and im-munosuppressive agents that typically increase the risk forinfection during prolonged treatment. It will be interesting toinvestigate whether the KPV-related KdPT tripeptide hassimilar antimicrobial actions as �-MSH and KPV.

A major advantage of KPV and its stereoisomers appearsto be the lack of any melanotropic effect based on the re-quired central message sequence of �-MSH to elicit such aneffect (8). We are currently unaware of any studies evaluatingthe effect of KdPT on melanogenesis, but it is unlikely thatthis peptide has a strong impact on pigmentation.

A definitive future task will also be the design of the mostsuccessful routes of administration of �-MSH and relatedtripeptides depending on the targeted immune-mediated in-flammatory disease. The half-life of iv administered full-



length �-MSH is only a few minutes, and thus the durationof the antipyretic effect of �-MSH is 1.5 h at most (191). Thisis probably due to the presence of several serum proteasesincluding aminopeptidase, angiotensin-converting enzyme,prolyl endopeptidase, �-chymotrypsin, trypsin, and neutralendopeptidase 24.11 (192–196). Neutral endopeptidase 24.11is also expressed by many cell types on the cell surface,thereby directly limiting the biological effects of full-length�-MSH at a cellular level (65, 196). Indeed, attempts havebeen successful to create protease-stable �-MSH analogssuch as NDP-MSH but with increased potency on pigmen-tation, while interestingly lacking a definitive effect on ex-perimental fever when injected iv (43). To the best of ourknowledge, no data exist on the precise pharmacokinetics ofKPV and related tripeptides in blood, and it is even unknownwhether such tripeptides are endogenously produced from�-MSH, ACTH, POMC, or other precursors. However, it maybe speculated that the d-enantiomers of KPV are more stableagainst peptidase activity than their stereochemical analogs.

On the other hand, the rapid degradation of �-MSH inserum may be related to the observed minimal side effectsafter systemic administration of �-MSH analogs in man andwill make this peptide and its derived tripeptides especiallyuseful for local delivery in a number of immune-mediatedinflammatory diseases. Such diseases include inflammatoryskin disorders like eczema, atopic dermatitis, alopecia areata,and several fibrosclerotic disorders (lichen sclerosus, sclero-derma, and fibrosing forms of inflammatory alopecia) inwhich both an antiinflammatory and antifibrogenic effect ofa given drug would be embraced. The smaller molecularweight of both KPV and KdPT, below 400 Da compared with�-MSH, may here be of particular advantage for the trans-epithelial delivery of the tripeptides. Disturbance of the skinbarrier, as present in atopic eczema, may further enhance therate of skin absorption of both KPV and KdPT. In other cases,e.g., in the treatment of corneal injury or keratitis, instillationsof �-MSH and related tripeptides may be possible, whereasin patients with inflammatory bowel diseases creation ofslow-release carriers suitable for oral administration of theagents may be desirable. In patients with allergic asthma,aerosolized �-MSH or related tripeptides may be envisioned.In patients with inflammatory arthritis, brain inflammation,or uveitis, however, delivery of effective concentrations of�-MSH or related tripeptides into inflamed target tissues vianondirect application may be more challenging. As demon-strated already in daily routine practice with pegylated IFNsor biologics, depot preparations of �-MSH or related trip-eptides may offer a perspective. Previous in vivo studies inguinea pigs using implants containing 4 mg of NDP-MSHcould demonstrate a marked and prolonged melanogenicskin response that lasted for 3 months (25). Promising phar-macokinetic observations have recently been made in humanvolunteers with depot formulations of NDP-MSH (20 mg) forstudies on pigmentation (189). The findings suggest thatdepot formulation of nonmelanotropic �-MSH-related trip-eptides is likewise possible.

In summary, �-MSH and related tripeptides have beenshown to possess promising antiinflammatory effects. Com-pared with the parental neuropeptide, �-MSH-related trip-eptides are: 1) small and inexpensive molecules, thus suitable

for large-scale pharmaceutical production; 2) expected tohave no melanogenic effect; 3) through their combined an-tiinflammatory and antimicrobial effects, have a lower riskfor infection compared with conventional immunosuppres-sive agents; 4) possibly limited in adverse effects, based onthe available toxicity and safety data of systemically admin-istered NDP-MSH; and 5) because of their molecular size,have advantages especially for local therapy of several in-flammatory disorders. The authors are thus confident that�-MSH-related tripeptides will find their way into clinicalpractice as novel weapons for the treatment of immune-mediated inflammatory diseases.

Acknowledgments

Received August 14, 2007. Accepted April 28, 2008.Address all correspondence and requests for reprints to: Markus

Bohm, M.D., Associate Professor Department of Dermatology, Univer-sity of Munster, Von Esmarch-Strasse 58, D-48149 Munster, Germany.E-mail: [email protected]

Disclosure Statement: C.M. and C.A. have nothing to declare. T.B. andT.A.L. are inventors on antiinflammatory tripeptides (PCT/EP02/01323;Europe, USA, Mexico, Canada; Japan, China, Australia, New Zealand).M.B. is an inventor on antioxidative tripeptides (EP070222401; Europe).

This work was supported by grants from the Deutsche Forschungs-gemeinschaff (DFG) to M.B. (BO 1075/5-3) and to C.M. and M.B. (MA2247/3-1).

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α-Melanocyte-Stimulating Hormone and Related Tripeptides: Biochemistry, Antiinflammatory and...

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