1. Folic Acid and Vitamin B 12Dr. Abhishek Roy JR I, MD (Biochemistry), GGMC & JJH, Mumbai Email: mail@abhishek.roDr. Abhishek Roy1

2. Dealing with the topic Introduction Types and basic biochemistry Dietary Sources Absorption, Transport, Metabolism & Excretion RDA Deficiency and Clinical Manifestations Laboratory Assessments of Status Toxicity Dr. Abhishek Roy2 3. Types and forms: Folate (most oxidized form) Dihydrofolate (FH2) Tetrahydrofolate (FH4) (most reduced form)Basic Structure of Folate 1. Bicyclic Pteridine Ring 2. PABA( Para-amino-benzoic acid) 3. Polyglutamate Tail Dr. Abhishek Roy3 4. Salient Points: N5-Methyl-FH4 once formed, the step is irreversible.Dr. Abhishek Roy4 5. Folate from food Sources Small degradation LiverUrineFolate Entero-hepatic circulation(through bile)Monoglutamates (Absorbed)Folate ConjugasesDuodenumFolateN5-methyl FH4Dr. Abhishek RoyWithin Intestinal Cell5 6. Vitamin B12 Structure Contains a CORRIN ring. Two of the four pyrrole rings are joined directly rather than joined by methylene bridges(heme) Unusual feature- Cobalt coordinated with Corrin ring. In the body, Co reacts with the carbon of a methyl group, forming methylcobalamin, or with the 5carbon of 5-deoxyadenosine, forming 5-deoxyadenosylcobalamin. The form of Vit B12 found in supplements is Cyanocobalamin.Dr. Abhishek Roy6 7. Absorption and Transport of Vitamin B12Dr. Abhishek Roy7 8. RDA of FOLATE Age Male 0-6months* 65g DFE* 7-12months* 80g DFE* 1-3 years 150g DFE 4-8 years 200g DFE 9-13 years 300g DFE 14-18 years 400g DFE 19+ years 400g DFE *Adequate Intake (AI)Female Pregnant Lactating 65g DFE* 80g DFE* 150g DFE 200g DFE 300g DFE 400g DFE 600g DFE 600g DFE 400g DFE 600g DFE 600g DFEDr. Abhishek Roy8 9. 1 DFE(Dietary Folate Equivalent) = 1 g of Folic acid in dietary food. 1DFE = 0.6g of Folic acid when consumed along with dietary food. 1 DFE= 0.5g of Folic Acid when consumed in empty stomach.Dr. Abhishek Roy9 10. RDA OF VITAMIN B12 Age Male 0-6months* 0.4g 7-12months* 0.5g 1-3 years 0.9g 4-8 years 1.2g 9-13 years 1.8g 14+ years 2.4g *Adequate Intake (AI)Female 0.4g 0.5g 0.9g 1.2g 1.8g 2.4gDr. Abhishek RoyPregnantLactating2.6g2.8g10 11. Dietary Sources of Folate Spinach Green Leafy Vegetables Liver Yeast Legumes Natural Dietary Sources- Reduced Co-enzyme form Vitamin Supplements/Fortified Foods-Abhishek Roy Oxidized form of Pteridine Ring Dr.11 12. Dietary Sources of Vitamin B12Dr. Abhishek Roy12 13. One Carbon Pool The collection of one-carbon groups attached to FH4 is known as the one-carbon pool. While attached to FH4, these one-carbon units can be oxidized and reduced. The most oxidized form is N10-formyl FH4. The most reduced form is N5-methyl-FH4. Once the methyl group is formed, it is not readily reoxidized back to N5, N10 methylene FH4, and thus N5-methyl-FH4 will tend to accumulate in the cell.Dr. Abhishek Roy13 14. Salient points of Serine as Carbon donor Serines hydroxyl-methyl group is transferred to FH4 in a reversible reaction, catalyzed by the enzyme serine hydroxymethyltransferase. This reaction produces glycine and N5, N10-methylene-FH4. Because serine can be synthesized from 3-phosphoglycerate, an intermediate of glycolysis, dietary carbohydrate can serve as a source of carbon for the one-carbon pool. The glycine that is produced may be further degraded by donation of a carbon to folate Dr. Abhishek Roy14 15. The chief carbon donator is SERINE. Methionine metabolism is dependent both on the Vitamin B12 as well as Folate.Dr. Abhishek Roy15 16. A deficiency of folate results in the accumulation of FIGLU, which is excreted in the urine. A histidine load test can be used for detecting folate deficiencies. Patients were given a test dose of histidine (a histidine load), and the amount of FIGLU that appeared in the urine was measured.Dr. Abhishek Roy16 17. Dr. Abhishek Roy17 18. Dr. Abhishek Roy18 19. Methyl GroupWhat do you think the structure of Methotrexate resembles to?Folic Acid. Binds to DHFR 1000 times more strongly Dr. Abhishek Roy19 20. Two main reactions of Vitamin B12 The transfer of a methyl group from N5-methyl FH4 to homocysteine to form methionine. The rearrangement of the methyl group of L-methylmalonyl CoA to form succinyl CoADr. Abhishek Roy20 21. The Methyl-Trap Hypothesis The equilibrium lies in the direction of the N5-methyl FH4 form. This appears to be the most stable form of carbon attached to the vitamin. However, in only one reaction can the methyl group be removed from N5-methyl FH4, and that is the methionine synthase reaction, which requires vitamin B12. Therefore if there is Vitamin B12 deficiency, then most folate forms in body is trapped in N5-methyl FH4 form- Functional Folate Deficiency. This is the Methyl-Trap Hypothesis. Dr. Abhishek Roy21 22. How Folate, Vitamin B12 and SAM are related?Dr. Abhishek Roy22 23. Tests done Serum Cobalamin normal range- 160-200ng/L to 1000ng/L. If megaloblastic anemia then levels are