Cobalamin is also called vitamin b12. Group of compounds called corrinoids (a group of cobalamin)- Coenzyme form: methylcobalamin and 5-deoxyadenosylcobalamin are forms of vitamin B12 in the human body- Humans can convert most of the other cobalamins into an active coenzyme form. Once absorbed, cobalamin travels in the portal blood to the liver, and then to the rest ofthe body, bound to the transport protein, transcobalamin Methionine synthase- converts homocysteine to methionine. Reduces blood homocysteine concentrations (reduces CVD).

1. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
COBALAMIN (VITAMIN B12)

2. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Inroduction:
• Synonyms are cobalamin, extrinsic factor (EF) of Castle and antipernicious
anemia factor.
• In 1849, Thomas Addison described pernicious anemia.
• William Murphy and George Minot showed that liver therapy is very
effective to treat pernicious anemia (Nobel prize, 1934).
• Dorothy Hodgkin suggested the structure by X-ray diffraction studies (Nobel
Prize, 1964).
• Later Robert Woodward synthesized B12 and proved the structure (Nobel
prize, 1965).

3. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Chemistry Of Vitamin B12:
• Vitamin B12 is the only vitamin with a complex structure.
• The structure of vitamin B12 consists of a corrin ring with a central cobalt
atom.
• Four pyrrole rings coordinated with a cobalt atom is called a Corrin ring.
• The 5th valency of the cobalt is covalently linked to a substituted
benzimidazole ring. This is then called cobalamin.
• The 6th valency of the cobalt is satisfied by any of the following groups:
cyanide, hydroxyl, adenosyl or methyl.

4. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences

5. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences

6. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Different forms of vitamin B12
1. Cyanocobalamin
• When cyanide is added at the R position, the molecule is called
cyanocobalamin.
• During the isolation procedure, cyanide is added to get stable crystals.
• The CN group has no physiological function, it is only a laboratory artefact.
• Oral preparations are in this form.
2. Hydroxy Cobalamin
• When hydroxyl group is attached at the R position, it is called hydroxy
cobalamin or vitamin B12a.
• Injectable preparations are in this form.

7. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
3. Adenosyl Cobalamin
• When taken up by the cells, these groups are removed and deoxy
adenosyl cobalamin or Ado-B12 is formed.
• This is the major storage form, seen in liver.
• When the methyl group replaces adenosyl group, it is known as methyl
cobalamin.
• This is the major form seen in blood circulation as well as in cytoplasm of
cells.
• The Ado-B12 and methyl B12 are the functional co-enzymes in the body.
4. Methyl Cobalamin

8. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Absorption of Vitamin B12:
• Absorption of vitamin B12 requires two binding proteins. First is the
intrinsic factor (IF) of Castle. Intrinsic factor is secreted by the gastric
parietal cells. It is a glycoprotein.
• The second factor is cobalophilin, secreted in the saliva.
• Gastric pepsin release the vitamin from proteins of the food, and then B12
binds with cobalophilin.
• In duodenum, cobalophilin is hydrolyzed by trypsin of pancreatic juice;
vitamin is released, and then vitamin binds to intrinsic factor.
• In pancreatic insufficiency (absence of trypsin), the vitamin may not be
released. Then vitamin-cobalophilin complex is excreted, resulting in
vitamin deficiency.

9. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
(A) =Intrinsic factor secreted from stomach reaches intestine;
(B) = Vitamin B12 absorbed with the help of intrinsic factor;

10. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
• One molecule of IF can combine with two molecules of B12.
• This IF-B12 complex is attached with specific receptors on mucosal cells
(mediated by Ca2+ ions). The whole IF-B12 complex is internalized.
• It may be noted that B12 is absorbed from ileum, while folic acid is from
jejunum.
Transport and Storage
• In the blood, methyl B12 form is predominant. Transcobalamin, a
glycoprotein, is the specific carrier. Physiologically Transcobalamine II is
more important.
• It is stored in the liver cells, as ado-B12 form, in combination with transcorrin.
Generally, B complex vitamins are not stored in the body, B12 is an exception.
• Whole liver contains about 2 mg of B12, which is sufficient for the
requirement for 2–3 years.

11. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Functional Role of B12
Methyl Malonyl CoA Isomerase:
• L-Methyl malonyl CoA is isomerized by methylmalonyl CoA mutase
(containing Ado-B12) to succinyl CoA, which enters into citric acid cycle.
• In B12 deficiency, methylmalonyl CoA accumulates and methyl malonic
aciduria occurs.
• The metabolism of odd chain fatty acids, valine, isoleucine, methionine
and threonine leads to the production of methylmalonyl CoA.

12. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Homocysteine Methyl Transferase:
• Step 2 in Figure is catalyzed by the enzyme
methionine synthase or homocysteine
methyl transferase.
• The steps marked as 1 and 2 in Figure need
the activity of vitamin B12 (methyl cobalamin).
Methyl Folate Trap and Folate Deficiency:
• The production of methyl THFA is an irreversible step. Therefore, the only way
for regeneration of free THFA is step No. 1 in Figure.
• When B12 is deficient, this reaction cannot take place. This is called the methyl
folate trap. This leads to the associated folic acid scarcity in B12 deficiency.
• Thus folic acid deiecency can cause hyperhomocysteinemia and heart
problems.

13. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Causes of B12 Deficiency
Nutritional:
• Nutritional vitamin B12 deficiency is very common among vegetarians of
low socioeconomic group.
• The only source for B12 in vegetarian diet is curd/milk, and lower income
group may not be able to afford it.
Decrease in Absorption:
• Absorptive surface is reduced by gastrectomy, resection of ileum and
malabsorption syndromes.
Addisonian Pernicious Anemia:
• It is an autoimmune disease in which
antibodies are generated against IF.
• So, IF becomes deficient, leading to defective
absorption of B12. (C) = In pernicious anemia, antibody against IF is produced;
(D) = In presence of antibody, absorption is not taking place

14. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Deficiency Manifestations
1. Folate trap:
• Vitamin B12 deficiency causes simultaneous folate deficiency due to the
folate trap.
• Therefore all the manifestations of folate deficiency are also seen.
2. Megaloblastic anemia:
• In the peripheral blood, megaloblasts and immature RBCs are observed.
• The peripheral blood picture in folate deficiency is described as macrocytic,
and in cobalamin deficiency as megaloblastic. In B12 deficiency, there are
additional neurological symptoms.
Macrocytic anemia
THFA dificiency
Megaloblastic anemia with
nucleated RBCs in vitamin B12
deficiency

15. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
3. Abnormal homocysteine level:
• In vitamin B12 deficiency, step No. 2 is blocked, so that
homocysteine is accumulated, leading to
homocystinuria.
• Homocysteine level in blood is related with myocardial
infarction. So, B12 and folic acid are protective against
ischemic heart disease.
4. Demyelination:
• In vitamin B12 deficiency, homocysteine levels are high and active
methionine (methyl donor to various acceptors) is not formed.
• Therefore methylation of phosphatidyl ethanolamine to phosphatidyl
choline is not adequate.
• This leads to deficient formation of myelin sheaths of nerves, demyelination
and neurological lesions.

16. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Requirement of Vitamin B12
Normal daily requirement is 1–2 mg/day.
During pregnancy and lactation, this is increased to 2 mg/day.
Dietary Sources:
• Vitamin B12 is not present in vegetables.
• Liver is the richest source but also present in meat, fish and eggs.
• Curd is a good source, because lactobacillus can synthesize B12.
Products available in the market:
Methecobal
Cobalmin
Bevidox
Sangobion
Nerobion

17. Abbottabad University Of Science And Technology
Department Of Pharmaceutical Sciences
Extra stuff