ACMT Board Review 2012: Molecular Mechanisms 1.3 Apoptosis: Programmed Cell Death Homeostatic...

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Transcript of ACMT Board Review 2012: Molecular Mechanisms 1.3 Apoptosis: Programmed Cell Death Homeostatic...

  • ACMT Board Review 2012: Molecular Mechanisms

    Russ Kerns, MD, FACMT Carolinas Medical Center

    Charlotte, NC

  • Objectives: Cover Core Content

      1.2 Molecular components/mechanisms   1.2.1 Glycolysis & oxidative phosphorylation   1.2.2 Other metabolic pathways (β-oxidation)   1.2.4 Transport proteins (hemoglobin)   1.2.5 Channels

      1.3 Cytotoxic mechanisms   Provide key example toxins

  • 1.2.1 Glycolysis & Oxidative Phosphorylation

  • Oxidative Phosphorylation

      Energy is released when ATP → P + ADP   Restoration of ATP (energy stores) involves

    phosphorylation of ADP via coupling of oxidation of H+ to form H20.

  • Oxidative Phosphorylation

    carbohydrate/fatty acid

    acetyl-CoA

    TCA

    NADH/FADH2

    electron transport chain

    H+ + e-

    P

    ADP ATP H2O ADP antiporter

    H+

    e- + O2- + H+

    ATP synthase

    H+ H+

  •   Main carb metab path   Cytosolic process   6C cmpd → 2 X 3 C cmpd   Net 2 ATP molecules   Make pyruvate for Kreb’s

    Glycolysis glucose

    glucose-6-P

    fructose-6-P

    glyceraldehyde-3-P + DHA-P

    2 [pyruvate]

    fructose-1,6-diP

    2 [glyceraldehyde-3-P]

    2 [1,3-diphosphoglycerate]

    2 [P intermediates]

    ATP

    ATP

    ATP

    ATP

  •   Arsenic (V)   Substitutes for P   Fail to make 1,3-diP intermed   Fail to make ATP   Fail to make pyruvate

    Glycolysis: Toxins

    glyceraldehyde-3-P + DHA-P

    2 [glyceraldehyde-3-P]

    2 [1,3-diphosphoglycerate]

    2 [P intermediates]

    ATP

    2NAD+ + 2 P As5+ X

  • Glycolysis

    CH3CO-CoA acetyl-CoA

    NADH

    CH3COCOOH

    CoA, NAD+

    CH3CH2OCOOH

    NAD+

    lactate

    pyruvate

    NADH, CO2

  • Glycolysis: Toxins

    CH3CO-CoA acetyl-CoA

    CH3COCOOH

    lipoamide

    pyruvate

    dihydrolipoamide

    As3+

    X

  • Kreb’s TCA Cycle pyruvate acetyl-CoA

    NADH NAD+

    citrate

    Succinyl-CoA

    oxalosuccinate

    isocitrate

    oxaloacetate

    succinate

    maleate cis-aconitate

    α-ketoglutarate

    fumarate

    NAD+

    NADH

    NAD+ NADH

    FADH FADH2

  • Kreb’s TCA Cycle: Toxins

    Rodenticides   Sodium monofluoroacetate   Fluoroacetamide

    acetyl-CoA

    fluorocitrate

    isocitrate

    oxaloacetate

    cis-aconitate monofluoroacetate

    fluoroacetamide

  • Electron Transport Chain   Mitochondrial process   Series of oxidation-reduction reactions

      Cytochrome enzymes   FADH2 and NADH electron sources   Produce H2O and ATP

  • ETC: Toxins   Enzyme inhibitors   Uncouplers

    X X

    cytochrome oxidase aa3 NADH-CoQ reductase

    X

  • Cytochrome Oxidase Inhibitors

    acetyl CoA

    lactate

    glucose

    pyruvate

    TCA cycle

    ATP H +

    e- transport X X X

    lactate

    lactate lactate

    lactate

    lactate lactate

    lactate

  • ETC: Toxins   Uncouplers

      Salicylate   Dinitrophenol (explosives & wood preservative)   Pentachlorophenol (fungicide)

      Cytochrome aa3 inhibitors   Cyanide   H2S   CO   Methanol   Phosphine gas   Sodium azide (propellant in airbags)

      NADH-CoQ reductase   Rotenone (plant derived fish poison)

  • 1.2.2 β-Oxidation of FFA

    fatty acyl-CoA

    CoA carnitine

    fatty acylcarnitine fatty acyl-CoA

    carnitine-palmitoyltransferase

    CoA

    (CH)nCO-CoA (CH)n-2CO-CoA + CH3CO-CoA acetyl-CoA

    NADH, FADH2

    CoA

    (CH)nCOOH (CH)nCO-CoA acyl-CoA synthetase

    ATP

    fatty acyl-CoA

    ADP + P CoA

  • β-Oxidation of FFA: Toxins

    fatty acyl-CoA

    CoA carnitine

    fatty acylcarnitine fatty acyl-CoA

    CoA

    (CH)nCO-CoA (CH)n-2CO-CoA + CH3CO-CoA acetyl-CoA

    NADH, FADH2

    CoA

    etoh, hypoglycin

    valproate

  • β-Oxidation of FFA: Toxins   ↑ NADH/NAD+ ratio

      ethanol   Hypoglycin(?)

      Carnitine   Valproate

      Undefined mechanism   Aflatoxin   Amiodarone   cereulide   dimethylformamide   tetracycline

    www.australianprescriber.com

  • Mitochondrial DNA: NRTIs

      Nucleoside reverse transcriptase inhibitors   Mechanism

      Inhibit mitochondrial DNA replication   Inhibit ADP/ATP antiporter(?)

      Result   Lactic acidosis ± steatosis

      Agents   Stavudine   Didandosine   Zalcitobine   Zidovudine   Tenofovir (nucleotide)

    X

  • 1.2.4 Transport Proteins

  • Hemoglobin   iron-based tetrameric protein   α- and β-globin chains (2 each)   Heme complex in each chain (4 total)

      protoporhyrin ring   central iron atom

  • Hemoglobin: Toxins

     Site of action of toxins  Heme synthesis  Erythropoiesis  Hemorrhage  Oxidant stress  Competition for oxygen binding

  • Heme Synthesis: Direct Toxin

    Harrison’s On-Line

  • Heme Synthesis: Indirect Toxins

      Acute Intermittent Porphyria   Hepatic   Autosomal dominant   Reduced HMB synthase activity   Some drugs may exacerbate AIP by

    increasing ALA-synthase activity   Poorly defined mechanism

  • Heme Synthesis: AIP

      Barbiturates   Carisoprodol   Danazol   Ethchlorvinyl   Meprobamate   Primidone   Pyrazolones   Trimethadione

    dark red urine

    www.porphyriafoundation.com

  • Hemoglobin: Toxins

      Erythropoiesis  Nephrotoxins - ↓ erythropoietin  Pure rbc aplasia – rare

     INH  Hypoglycemics (chlorpropamide, tolbutamide)  Phenytoin  Sulfasalazine  Valproate (single case report)

  • Hemoglobin: Aplastic Anemia aplastic marrow normal marrow

    www.hopkinsmedicine.org

  • Hemoglobin: Aplastic Anemia

      Immune mediated   T lymphocytes release cytokines

      Suppress hematopoietic stem cells   Apoptosis (↑ Fas receptors on stem cells)

    TNF

    interferon-γ

  • Hemoglobin: Aplastic Anemia

      DNA injury   Direct DNA injury

      Ionizing radiation   Inhibition of DNA replication

      Folate inhibitors (methotrexate)   Intermediary metabolite that binds DNA

      Benzene (quinone + free radicals)   Tubulin inhibition during cell replication

      Antimitotics (colchicine, vincristine, vinblastin)

    metaphase arrest

    metaphase.wordpress.com

  • Hemoglobin: Aplastic Anemia   Antibiotics

      Chloramphenicol   Anti-convulsants

      Carbamazepine, phenytoin   Anti-inflammatory agents

      Diclofenac, D-penicilamine, gold salts, indomethicin, phenylbutazone

      Anti-neoplastic agents   Alkylating agents (nitrogen mustards)   Antibiotics (danorubicin, adriamycin)   Antimitotics (colchicine, vinblastin, vincristine)   Antimetabolites (purine and pyrimidine analogues)

      Antipsychotics   Chlorpromazine, clozapine

  • Hemoglobin: Aplastic Anemia   Chemicals

      Benzene, lindane   Metals

      Arsenic   Miscellaneous

      Acetazolamide, captopril, cimetidine, chlorpromazine, dapsone, fluoxetine, meprobamate, nifedipine, PTU, ticlopidine, tocainide

      Radiation

  • Hemoglobin: Toxins

    www.pathology.vcu.edu

  • Hemoglobin: Toxins

      Megaloblastic anemia   ↓ Vit B12 absorption

      Colchicine, metformin, neomycin   ↓ folate absorption

      Etoh   Impaired dihydrofolate reductase

      Methotrexate   Pyrimethamine   Pyridium   Trimethoprim

  • Hemoglobin: Oxidant Stress

      Heme: deoxyhgb → Methgb (Fe2+→Fe3+)   Prophyrin ring by sulfur: Sulfhgb   Globin: Heinz body hemolytic anemia

  • Hemoglobin: Oxidant Stress

      Protection from oxidant stress   Ascorbic acid (Vit C)   Glutathione (intact HMP, G6PD)   Enzymatic

      NADH-dependent reductase (Cytochrome b5 reduc)   NADPH-dependent reductase (intact HMP, G6PD)   Catalase   Hydrogen peroxidase

  • Hemoglobin: Methemoglobin

      Fe2+ state: deoxyhemoglobin carries oxygen 