1. Haemopoietic Functions- Related Vitamins
HMIM224

2. Objectives of the Lectures
Introduction to the role of vitamins
Types of vitamins
Biochemistry of water soluble vitamins
Importance of water soluble vitamins in red blood cells formation
Biochemistry of the fat soluble vitamins
Role of vitamin K in blood coagulation

3. Vitamins are chemically unrelated organic compounds that cannot be
synthesized by humans & therefore must be supplied by diet

4. Nutritional deficiency of many vitamins may lead to different types of anemia

5. Water-soluble vitamins
Types of water-soluble vitamins:
Non B – Complex :
Vitamin C
B-Complex:
Thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), cobalamin (B12) & folic acid
Water-soluble vitamins:
Not significantly stored in the body
Must be supplied regularly in the diet
Excess than need is excreted in urine .

6. B-Complex vitamins
Available in small quantities in different types of food
Important for growth & good health
Help in various biochemical processes in cell as many of them are precursors of coenzymes

7. Water-soluble vitamins related to the haemopoeitic system
Folic acid
Cobalamin (vitamin B12)
Ascorbic Acid (vitamin C)

8. Biochemistry of Folic Acid

9. So, folic acid is essential for cell division including haemopoetic
Synthesized by: microorganisms (not synthesized by humans)
Active form : Tetrahydrofolate (activation occurs in human cells)
Function:
Active form of folic acid receives one-carbon fragments from donors
such as serine, glycine, and histidine & transfers them to intermediates
This function is required in synthesis of purines & TMP.
Purines & TMP are required for DNA synthesis that is essential
for cell division.
So, folic acid is essential for cell division including haemopoetic
cells (as RBCS)

10. Folic acid is synthesized by microorganisms (as bacteria)
Humans can not synthesize folic acid.
Humans obtain folic acid by diet & converts it to the active form tetrahydrofolate.
Tetrahydrofolate is required for synthesis of purines & TMP
Purines & TMP are required for DNA synthesis (required during cell division)

11. Folic Acid & Anemia
Inadequate serum levels of folic acid is caused by:
increased demand (pregnancy & lactation)
poor absorption caused by pathology of the small intestine
drugs for example, methotrexate (inhibit activation of folic acid)
A folate-free diet (rare) can cause a deficiency within a few weeks.
Effect of folic acid deficiency:
A primary result of folic acid deficiency is megaloblastic anemia caused by
diminished synthesis of purines & TMP (required for DNA molecules synthesis in
the nucleus & hence no division of cells)

12. Folic Acid & Anemia (cont.)
It is important to evaluate the cause of the megaloblastic anemia prior to instituting therapy because also vitamin B12 deficiency indirectly causes symptoms of this disorder.
Deficiency of folic acid leads to neural tube defects in fetus.

13. Biochemistry of Vitamin B12 (Cobalamin)

14. Vitamin B12 (Cobalamin)

15. Forms of vitamin B12 Cyanocobalamin (commercial preparation)
Hydroxycobalamin
Adenosylcobalamin (major storage form in the liver)
Methylcobalamin (mostly found in blood circulation)

16. Coenzyme forms of B12 Adenosylcobalamin Methylcobalamin
Body can convert other forms of cobalamins into active coenzymes

17. Sources & absorption of vitamin B12
Vitamin B12 is Not synthesized in the body (synthesized only by microorganism)
Humans obtain vitamin B12:
- performed by natural bacterial flora
- or/ supplied in the diet (animal sources of diet – not in plants)
Vitamin B12 binds to intrinsic factor and absorbed by intestine.
Intrinsic factor is a protein secreted by cells in the stomach

18. Sources & absorption of vitamin B12 (cont.)

19. Functions of vitamin B12 Two reactions require B12 Reaction 1:
Conversion of methylmalonyl-CoA to succinyl-CoA
Methylmalonyl CoA is produced during the
degradation of fatty acids with odd numbers of
carbon atoms.
When vitamin B12 is deficient, abnormal fatty
acids accumulate & become incorporated to cell
membranes including those of nervous system
leading to neurological manifestations.

20. Functions of vitamin B12 (cont.)
Reaction 2:
Conversion of homocysteine to methionine
Methionine synthase requires B12 in converting
homocysteine to methionine.
When vitamin B12 is deficient, homocysteine accumulates
leading to neurological manifestations.
Also, tetrahydrofolate will not be available for formation of
purine & TMP leading to megaloblastic anemia.

21. Vitamin B12 Deficiency Causes of vitamin B12 deficiency:
1- Deficiency of vitamin B12 in diet (rare)
2- Deficiency of absorption of vitamin B12 from intestine, called pernicious
anemia (more common)
due to:
- Autoimmune destruction of gastric parietal cells (that synthesizes intr. f).
- Partial or total gastrectomy
N.B. As liver stores 4-5 mg of vitamin B12 (in contrast to other water soluble
vitamins), clinical symptoms develop in several years after gastrectomy.

22. Clinical manifestations of vitamin B12 deficiency
Block of reaction 1 & 2:
B12 deficiency causes accumulation of homocysteine and methylmalonic acid which are harmful for nervous tissue leading to neurological manifestations
Block of reaction 1:
Methyl tetrahydrofolate cannot be converted to tetrahydrofolate
Hence folate is trapped as N5-methyltetrahydrofolate (folate trap)
This leads to folate deficiency (not available for purine synthesis).
So, vitamin B12 deficiency (indirectly) causes megaloblastic anemia.
TREATMENT OF THIS CASE BY FOLIC ACID ONLY CURES ANAEMIA ONLY BUT NERVOUS MANIFESTATIONS ARE NOT CURED (masking of B12 def.)

23. Neurological manifestations of vitamin B12 deficiency
Demyelination
Myelin sheath of neurons is chemically unstable and damaged
Neuropathy
Peripheral nerve damage
Causes of neurological manifestations:
Deficiency of vitamin B12 leads to accumulation of methylmalonyl CoA
High levels of methylomalonyl CoA is used instead of acetyl CoA for fatty acid synthesis resulting in synthesis of abnormal fatty acids.
Myelin sheath is synthesized with these abnormal fatty acids is unstable and degraded causing neuropathy

24. Treatment of vitamin B12 deficiency
Caution:
Administration of high levels of folic acid can mask vitamin B12 deficiency. So, therapy is initiated with folic acid and vitamin B12 until the cause of the anemia can be determined (either due to folic acid def. or vit.B12 def.).
Therapy with vitamin B12 :
1- Route:
Oral: High doses
or/ IM injection of cyanocobalamin)
2- Duration: must be continued life-long

25. Biochemistry of Vitamin C (Ascorbic Acid)

26. Vitamin C (Ascorbic acid)
Function of ascorbic acid:
1- Reducing agent in several different reactions
2- Coenzyme in hydroxylation reactions:
as hydroxylation of lysine & proline amino acids of collagen.
Thus, vitamin C is required for the maintenance of normal connective
tissue & wound healing.
3- Helps absorption of dietary iron from the intestine.
4- One of the antioxidants available in diet
Consumption of diets rich in vitamin C (& other antioxidants as vitamin E &
b-carotenes) is associated with a decreased incidence of some chronic
diseases as coronary heart disease & certain cancers.

27. Vitamin C (Ascorbic acid)
Proline is hydroxylated by
prolyl hydroxylase enzyme
which requires
ascorbic acid (vitamin C)
as a coenzyme

28. Vitamin C (Ascorbic acid)
Deficiency of ascorbic acid (Scurvy)
Hydroxylation of collagen is deficient resulting in weakness of collagen present in connective tissue & blood vessels.
This results in fragile blood vessels that causes hemorrhage which if severe & prolonged may lead to anemia.
Also, absorption of iron is low which may end in iron deficiency anemia.
Clinical manifestations:
Sore, spongy gums
Loose teeth
Fragile blood vessels
Swollen joints
Anemia

29. Bruises in lower limb in a case of scurvy

30. Fat Soluble Vitamins

31. Fat Soluble Vitamins
They are vitamin A, vitamin D, vitamin K & vitamin E
Characteristics of fat-soluble vitamins:
Absorbed & transported with fat of diet.
Not excreted in the urine (but excreted in bile)
Significant quantities are stored in the liver & adipose tissue.
Toxicity due to overdose is more common than water-soluble vitamins.

32. Biochemistry of Vitamin K

33. Types of vitamin K Vitamin K occurs in several forms:
Vitamin K1 (Phylloquinone)
Vitamin K2 (Menaquinone)
Vitamin K3 (Menadione)

34. Sources of vitamin K Vitamin K1 (Phylloquinone):
Vitamin K1 is available in green leafy vegetables
Vitamin K2 (Menaquinone):
Vitamin K2 is produced by intestinal bacteria.
Intestinal bacterial synthesis meets the daily requirement of vitamin K even without dietary supplement
Vitamin K3 (Menadione):
Synthetic form (for therapy)

35. Function of vitamin K (cont.)
Vitamin K is a Coenzyme essential for the carboxylase enzyme involved for the synthesis of prothrombin & blood clotting factors in the liver
Synthesis of prothrombin & clotting factors II, VII, IX, X require carboxylation of their glutamic acid (Glu) at Ɣ-carbon by carboxylase enzyme .
Prothrombin & clotting factors that get Ɣ-carboxyglutamate are capable of subsequent activation ending in coagulation (formation of blood clot).

38. Functions of vitamin K (cont.)
Prothrombin – platelets interaction:
Carboxylated prothrombin contains two carboxylate groups (COO–)
These groups bind to Ca2+ forming prothrombin-calcium complex
The complex then binds to phosholipids on the surface of platelets (important for blood clotting)
This will convert prothrombin to thrombin and thus blood coagulation process is proceeded ending in blood clot formation.

40. Anticoagulant drugs (warfarin & dicoumarol) are structural
analogs of vitamin K.
Hence, prothrombin and clotting factors are not carboxylated
resulting in stopping of the coagulation process (no blood clot formation).
Blood coagulation time increases upon injury
Analogs of vitamin K

41. Functions of vitamin K in other proteins
Synthesis of g-carboxyglutamate in osteocalcin:
Osteocalcin is a bone protein
May have a role in bone formation & mineralization
g-carboxyglutamate is required for its binding to hydroxyapatite (a mineral) in the bone
The function of bone osteocalcin is unclear

42. other causes are in next slide….
Vitamin K Deficiency
Causes of vitamin K deficiency:
1- Actual deficiencies are rare as it is synthesized by the intestinal bacteria
in addition to being obtained by diet.
2- Malabsorption of lipids leads to vitamin K deficiency
3- Deficiency most common in newborns (first month of life) as:
Newborns lack intestinal flora
Human milk cannot provide enough vitamin K.
So, supplements are given by single IM injection of vitamin K
to all newborns to protect them against hemorrhagic diseases
other causes are in next slide….

43. Vitamin K Deficiency (cont.)
Causes of vitamin K deficiency (cont.):
4- Destruction of the normal bacterial flora due to:
- Prolonged antibiotic therapy
- Gastrointestinal infections with diarrhea
Both of above cause destroy the bacterial flora and can also lead to vitamin
K deficiency.
5- Second generation cephalosporins cause warafarin-like action

44. Vitamin K Deficiency (cont.)
Effects of vitamin K deficiency:
1- Hypoprothrombinemia: increased blood coagulation time
2- Deficiency may affect bone growth and mineralization

45. Vitamin K Deficiency (cont.)
Clinical manifestations of vitamin K deficiency:
Hemorrhagic disease of the newborn
Bruising tendency, ecchymotic patches, mucus membrane hemorrhage
post-traumatic bleeding
Internal bleeding
Prolongation of the prothrombin time

46. References
Lippincott’s Illustrated Biochemistry
Harper’s Biochemistry