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Vitamin B12

Vitamin B12. By:Zahra Mahboob. Outline …. Introduction Structure Synthesis Sources Absorbtion Function Deficiencies Treatment Vitamin B12 and Cancer. Introduction a water-soluble vitamin

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Vitamin B12

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  1. Vitamin B12 By:ZahraMahboob

  2. Outline… • Introduction • Structure • Synthesis • Sources • Absorbtion • Function • Deficiencies • Treatment • Vitamin B12 and Cancer

  3. Introduction • a water-soluble vitamin • a group of cobalt-containing vitamer compounds known as cobalamins • is the largest and most structurally complicated vitamin • 3 forms:cyanocobalamin, hydroxocobalamin, and cofactor forms of B12: adenosylcobalamin, methylcobalamin • Rols:in brainand nervous system function, and the formation of blood. • Produced by: bacteria and archaea

  4. Structure • corrinring • The central metal ion: cobalt • six coordination sites Four sites: corrin ring fifth site: dimethylbenzimidazolegroup sixth site: is variable -CN, -OH, -CH3or a 5'-deoxyadenosyl group

  5. Synthesis • Only bacteria and archaea have the enzymes required for its biosynthesis • Neither plants nor animals are independently capable of constructing vitamin B12but conversion between different forms of the vitamin can be accomplished in the human body

  6. How much vitamin B12 do I need? The amount of vitamin B12 you need each day depends on your age.

  7. What foods provide vitamin B12? • Vitamin B12 is found naturally in a wide variety of animal foods and some fortified foods. • Plant foods have no vitamin B12 unless they are fortified. • Beef liver and clams • Fish, meat, poultry, eggs, milk.

  8. Absorption of Vitamin B12 • first mechanism: Intrinsic factor • second mechanism: transcobalamin II Vitamin B12 IF B12-IF complex Stomach Transcobalamin II Parietal cell IF receptor Epithelial cells of terminal ileum Ileum Epithelial cells

  9. function • Cyanocobalamin • Hydroxocobalamin • two cofactor forms of B12 in the human body: 1) adenosylcobalamin(AdoB12) the cofactor of Methylmalonyl Coenzyme A mutase (MUT) and L-αleucinemutase. 2) methylcobalamin (MeB12), the cofactor of enzyme Methioninesynthase.

  10. function

  11. Vitamin B12 Deficiency DNA synthesis vitamin B12 roles neurologic function. Deficiency of vitamin B12 macrocytic anemia neuropsychiatric disorders

  12. Clinical Manifestations of Vitamin B12 Deficiency • Hematologic:Megaloblastic anemia, Pancytopenia (leukopenia, thrombocytopenia)

  13. Neurologic: Paresthesias, Peripheral neuropathy Combined systems disease (demyelination of dorsal columns and corticospinal tract) • Psychiatric: Irritability, personality change Mild memory impairment, dementia, Depression Psychosis • Cardiovascular: Possible increased risk of myocardial infarction and stroke

  14. Diagnosis of Vitamin B12 Deficiency • Serum B12:Normal range 200-900 (pg ml-1) • B12 deficiency < 100 • Methylmalonicacid:Normal range 1.5-2.0 (mg per 24 h urine) • measurements of metabolites such as methylmalonic acid and homocysteine have been shown to be more Sensitive(%99.8) than measurement of serum B12 levels alone.

  15. Causes of Vitamin B12 Deficiency • nutritional deficiency • malabsorption syndromes • gastrointestinal causes

  16. Schedule for Vitamin B12 Therapy

  17. Medical uses • vitamin B12 deficiency • cyanide poisoning • hereditary deficiency of transcobalamin II. • High vitamin B12 level: protect against brain atrophy or shrinkage associated with Alzheimer's disease • High-dose administration of Vitamin B12 : stimulate the activity of the body's TH1 suppressor T-Cells.

  18. Vitamin B12 and Cancer • Evidence indicates that deficiencies of iron and zinc, and the vitamins folate, B12, B6 and C, can cause DNA damage and lead to cancer. • Reduced folate intake has been associated with cancer. Folate, B6 and B12 deficiencies cause the incorporation of deoxyuracil into DNA, leading to DNA breakage, and could promote tumorigenesis.

  19. Folate and vitamin B6 were inversely associated and vitamin B12 was positively associated with Oesophageal and gastric cancers in a case–control study. • Dietary intakes of folate, B6 and B12 were inversely related to the risk of developing cervical dysplasia • No statistically significant association between folate, B12 and cervical cancer was found

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