Vitamin B12

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Transcript of Vitamin B12

  • Vitamin B 1

    Vitamin B

    Vitamin B12

    Systematic (IUPAC) name

    -(5,6-dimethylbenzimidazolyl)cobamidcyanide

    Clinical data

    AHFS/Drugs.com monograph [1]

    Pregnancy cat. ?

    Legal status POM (UK) OTC (US)

    Routes oral, IV, IM

    Pharmacokinetic data

    Bioavailability readily absorbed in distal half of the ileum

    Protein binding Very high to specific transcobalamins plasma proteinsBinding of hydroxocobalamin is slightly higher than cyanocobalamin.

    Metabolism hepatic

    Half-life Approximately 6 days(400 days in the liver)

    Excretion renal

    Identifiers

    CAS number 68-19-9 [2]

    ATC code B03BA01 [3]

    PubChem CID 5479203 [4]

    DrugBank DB00115 [5]

  • Vitamin B 2

    ChemSpider 10469504 [6]

    KEGG D00166 [7]

    ChEMBL CHEMBL1697777 [8]

    Chemical data

    Formula C63H88CoN14O14P

    Mol. mass 1355.37 g/mol

    (what is this?) (verify) [9]

    Vitamin B12

    , vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in thenormal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins.It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis andregulation, but also fatty acid synthesis and energy production. It is the largest and most structurally complicatedvitamin and can be produced industrially only through bacterial fermentation-synthesis.Vitamin B12 consists of a class of chemically related compounds (vitamers), all of which have vitamin activity. Itcontains the biochemically rare element cobalt. Biosynthesis of the basic structure of the vitamin is accomplishedonly by bacteria, but conversion between different forms of the vitamin can be accomplished in the human body. Acommon synthetic form of the vitamin, cyanocobalamin, does not occur in nature, but is used in manypharmaceuticals and supplements, and as a food additive, because of its stability and lower cost. In the body it isconverted to the physiological forms, methylcobalamin and adenosylcobalamin, leaving behind the cyanide, albeit inminimal concentration. More recently, hydroxocobalamin, methylcobalamin, and adenosylcobalamin can also befound in more expensive pharmacological products and food supplements. The extra utility of these is currentlydebated.Vitamin B12 was discovered from its relationship to the disease pernicious anemia, which is an autoimmune diseasein which parietal cells of the stomach responsible for secreting intrinsic factor are destroyed. Intrinsic factor iscrucial for the normal absorption of B12, so a lack of intrinsic factor, as seen in pernicious anemia, causes a vitaminB12 deficiency. Many other subtler kinds of vitamin B12 deficiency and their biochemical effects have since beenelucidated.[10]

    TerminologyThe names vitamin B12, vitamin B12, or vitamin B-12, and the alternative name cobalamin, generally refer to allforms of the vitamin. Some medical practitioners have suggested that its use be split into two different categories,however. In a broad sense, B12 refers to a group of cobalt-containing vitamer compounds known as cobalamins: these

    include cyanocobalamin (an artifact formed from using activated charcoal, which always contains trace cyanide,to purify hydroxycobalamin), hydroxocobalamin (another medicinal form, produced by bacteria), and finally, thetwo naturally occurring cofactor forms of B12 in the human body: 5'-deoxyadenosylcobalamin(adenosylcobalaminAdoB12), the cofactor of Methylmalonyl Coenzyme A mutase (MUT), andmethylcobalamin (MeB12), the cofactor of 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR).

    The term B12 may be properly used to refer to cyanocobalamin, the principal B12 form used for foods and in nutritional supplements. This ordinarily creates no problem, except perhaps in rare cases of eye nerve damage, where the body is only marginally able to use this form due to high cyanide levels in the blood due to cigarette smoking, and thus requires cessation of smoking, or else B12 given in another form, for the optic symptoms to abate. However, tobacco amblyopia is a rare enough condition that debate continues about whether or not it

  • Vitamin B 3

    represents a peculiar B12 deficiency which is resistant to treatment with cyanocobalamin.Finally, so-called pseudo-B12 refers to B12-like substances which are found in certain organisms, including Spirulina(a cyanobacterium) and some algae. These substances are active in tests of B12 activity by highly sensitiveantibody-binding serum assay tests, which measure levels of B12 and B12-like compounds in blood. However, thesesubstances do not have B12 biological activity for humans, a fact which may pose a danger to vegans and others ondiets who may not ingest sufficient quantities of B12 producing bacteria, but who nevertheless may show normal"B12" levels in the standard immunoassay which has become the normal medical method for testing for B12deficiency.[11] A number of vegan sources of Vitamin B12 do exist, however, including some meat analogues (foodsthat are vegan that are made to resemble meat), some soy-based products and some brands of fortified cereals(SOURCE: http:/ / www. vrg. org/ nutrition/ b12. htm).

    Medical usesVitamin B12 is used to treat vitamin B12 deficiency, cyanide poisoning, and hereditary deficiency of transcobalaminII.[12] It is also given as part of the Schilling test for detecting pernicious anemia.[12]

    For cyanide poisoning, a large amount may be given intravenously, and sometimes in combination with sodiumthiosulfate.[13] The mechanism of action is straightforward: the hydroxycobalamin hydroxide ligand is displaced bythe toxic cyanide ion, and the resulting harmless B12 complex is excreted in urine. In the United States, the Food andDrug Administration approved (in 2006) the use of hydroxocobalamin for acute treatment of cyanide poisoning.[14]

    High vitamin B12 level in elderly individuals may protect against brain atrophy or shrinkage associated withAlzheimer's disease and impaired cognitive function.[15]

    High-dose administration of Vitamin B12 has been additionally validated to stimulate the activity of the body's TH1suppressor T-Cells, which then down-regulates the over-production of the allergen antibody IgE in allergicindividuals.[16][17]

    Recommended intakeThe dietary reference intake for an adult ranges from 2 to 3g per day.[18]

    Vitamin B12 is believed to be safe when used orally in amounts that do not exceed the recommended dietaryallowance (RDA). There have also been studies that showed no adverse consequences of doses above the RDA.[19]

    The RDA for vitamin B12 in pregnant women is 2.6g per day and 2.8g during lactation periods.[20] There is

    insufficient reliable information available about the safety of consuming greater amounts of vitamin B12 duringpregnancy.The Vegan Society, the Vegetarian Resource Group, and the Physicians Committee for Responsible Medicine,among others, recommend that vegans either consistently eat foods fortified with B12 or take a daily or weekly B12supplement.[21][22][23] Fortified breakfast cereals are a particularly valuable source of vitamin B12 for vegetariansand vegans. In addition, adults age 51 and older are recommended to consume B12 fortified food or supplements tomeet the RDA, because they are a population at an increased risk of deficiency.[24]

  • Vitamin B 4

    DeficiencyVitamin B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervoussystem. At levels only slightly lower than normal, a range of symptoms such as fatigue, depression, and poormemory may be experienced.[10] However, these symptoms by themselves are too nonspecific to diagnosedeficiency of the vitamin.Vitamin B12 deficiency can also cause symptoms of mania and psychosis.

    [25][26] Vitamin B12 deficiency can becaused by the metabolic disorder pernicious anemia.

    Adverse effects Vitamin B12 has extremely low toxicity and even taking it in enormous doses appears not to be harmful to healthy

    individuals.[27][28]

    Hematologic: Peripheral vascular thrombosis has been reported. Treatment of vitamin B12 deficiency can unmaskpolycythemia vera, which is characterized by an increase in blood volume and the number of red blood cells. Thecorrection of megaloblastic anemia with vitamin B12 can result in fatal hypokalemia and gout in susceptibleindividuals, and it can obscure folate deficiency in megaloblastic anemia. Caution is warranted.

    Leber's disease: Vitamin B12 in the form of cyanocobalamin is contraindicated in early Leber's disease, which ishereditary optic nerve atrophy. Cyanocobalamin can cause severe and swift optic atrophy, but other forms ofvitamin B12 are available. However, the sources of this statement are not clear, while an opposing view

    [29]

    concludes: "The clinical picture of optic neuropathy associated with vitamin B12 deficiency shows similarity tothat of Leber's disease optic neuropathy. Both involve the nerve fibres of the papillomacular bundle. The presentcase reports suggest that optic neuropathy in patients carrying a primary LHON mtDNA mutation may beprecipitated by vitamin B12 deficiency. Therefore, known carriers should take care to have an adequate dietaryintake of vitamin B12 and malabsorption syndromes like those occurring in familial pernicious anaemia or aftergastric surgery should be excluded."

    AllergiesVitamin B12 supplements in theory should be avoided in people sensitive or allergic to cobalamin, cobalt, or anyother product ingredients. However, direct allergy to a vitamin or nutrient is extremely rare, and if reported, othercauses should be sought.

    Interactions Alcohol (ethanol): Excessive alcohol intake lasting lon