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Vitamin B6 (pyridoxine) :
Pyridoxine is not a single substance but consist of 3 closely related naturally occurring pyridine derivatives
compounds with similar physiological actions(pyridoxine, pyridoxal, and pyridoxamine .Its resistant to
moderate heat but destroyed by exposuring to U.V light .Daily requirement is 1.6 - 2mg for adults .
Stability in foods :- Considerable losses during cooking. •
•Function :
•Pyridoxal phosphate(PLP) as a coenzyme in transamination and decarboxylation reactions.
•Function of (PLP):
•1-It is a co-enzyme to decarboxylate certain amino acids such as tyrosine, arginine and glutamic acid, it
act as co-decarboxylase . decarboxylation to yield biologically active amines , e.g, neurotransmitters
2-it is act as a coenzyme for deaminase of serine and therionine .
3-it is act as a coenzyme for aminotrasferase which are involve in amino acid metabolism(protein
metabolism), Transamination of amino acids to produce Ketoacids and synthesis of non –essential amino
acids .
4-it is act coenzyme for enzyme involved in metabolism of tryptophan .
5-it is transfer of sulfur group from methionine to serine to form cysteine(TRANSULFURATION) ALSO act as
a coenzyme for desulfhydrase(loss of H2S) WHICH CATALYSE AND REMOVE OF SULFUR FROM CYSTEINE OR
HOMOCYSTEINE .
6- It is involved in the absorption of A.A from intestine .
7-it is involved in biosynthetic pathway of porphyrins and synthesis of hemoglobin(RBC formation).
8-IT IS ACT AS CO-FACTOR IN THE ACTIVITY OF PHOSPHORYLASE AND IN THE METABOLISM OF
UNSATURATED F.A and cholesterol .
9- it is involved in the maintenance and integrity of nervous system .
10-Vitamin B6 is also involved in the conversion of glycogen to glucose in muscle, hormone metabolism &
synthesis of Ab to support of immune system .
•Deficiency :
•Sever deficiency of vitamin B6 is rare . patient suffering
malabsorption , receiving dialysis or alcoholic are at risk to deficiency .
•clinical signs include :
•Lesion of the lips and corners of the mouth and inflammation of the
tongue , irritability and infantile convulsion, peripheral Neuropathy,
hypo chromic microcytic anemia with high serum iron (due to poor
haemsynthesis) .
•Appearance of Xanthurenic acid in the urine of pregnant woman due
to B6 deficiency as aresult of increase fetal demand for vitamin (give
10 gm of D,L tryptophan) in pregnancy .
•Hyperoxaluria: increased excretion of oxalate in urine, this is
attributed to defective transamination of glyoxylic acid to form glycine
•Due to the importance of vitaminB6 in amino acid metabolism
requirement are linked to protein intake ..
•Diagnosis of B6 deficiency :
•Tryptophan loading dose
•Gutamic-oxalo-acetic acid…transaminase test
treatment :
•Infantile convulsion: should be treated by 4 mg of
pyridoxine/kg B.W .
•In peripheral neuritis result from antitubercle drug
isoniazid(INH) isonicotinic acid hydrozide, which lead to B6
deficiency should be prevented by prophylactic dose of B6
10mg/day . INH is forms a hydrazone complex with pyridoxal
that promote excretion in urine
INH +pyridoxal
pyridoxal hydrazone .
•Other form of deficiencies can be treated with 50-100 mg/day
•Good food sources of vitamin B6:
Rich: meat, fish, potatoes, bananas .
Important: vegetables, intestinal micro flora synthesis .
•Folate (folic acid ), (folacin), (vitamin B9) :
Exist in nature in over 100 forms which are all derivatives of
folic acid . its absorbed in duodenum and jejunum .Its easily
destroyed by storage, cooking and other processing.
It helps the body make healthy new cells. Everyone needs
folic acid. For women who may get pregnant, it is really
important. Getting enough folic acid before and during
pregnancy can prevent major birth defects of her baby's
brain or spine.
Folic acid antagonist is methotrexate which bind s
strongly to dihydro folate reductase and ihibite
formation of tetrahydrofolate(H4 folate) this folate
antagonist is important for treatment of infection
and cancer.
Function:
•it is involved in the DNA & RNA synthesis , and requirements
increase during embryonic development. women who have
experienced a pregnancy affected by a neural tube defect should
take 5 mg of folic acid daily from before conception and through
out the first trimester because supplementation of folate in
advanced of conception and during the first trimester reduces
the incidence of neural tube defect by about 70% .
•folate aids in the production of RBC,
•folate works with B12 and vitamin C to help the body digest and
utilize proteins .
•lowers homocystein levels and thus coronary heart disease risk.
folate deficiency :
•deficiency of folate lead to megaloblastic anemia and atrophic
changes of tongue(smooth tongue) .
•megaloblastic anemia(large size of bone marrow cells primitive RBC)
due to dietary deficiency of vitamin B12 is rare but it is common in
case of dietary deficiency of folate which develop in 4-5 months of
Causes of folate deficiency:
1.Poor intake of vegetables.
2.Malabsorption: example coeliac disease .
3.Increased demand in haemolysis and
pregnancy .
4.Drugs example phenytoin, contraceptive
pill, Methotrexate .
Treatment of folate deficiency:
by giving 5-10 mg of folate by mouth but avoid to give folate in
addisonnians (primary adrenal insufficiency) associated with
increased adrenocorticotropic hormone (ACTH) production, or other
vitamin B12 deficiencies because it precipitate or exaggerate
neurological menifestations of vitamin B12 deficiency .
Overconsumption symptoms :- May mask vitamin B12deficiency
(pernicious anemia).
Good food sources of folate : Rich: liver
Importance: green leafy vegetables, fortified breakfast
cereals .
RDA 2oo Mg\day for adults .
to prevent NTD in pregnancy = 400Mg\day until 12 week of
pregnancy . to prevent recurrence of NTD =5000Mg
Cobalamin B12:
Normal daily requirement is 2 mcg/day . several years should
be passed before deficiency to be manifested .
Molecules of vitamin B12 are large molecules absorbed in
terminal ileum in presence of gastric intrinsic factor(IF)
Function:
1- as coenzyme to form succinyl-coA .
2- Vitamin B12 and folate both of them as coenzymes are
involved in methylation of homocysteine to methionine in the
cellular cytoplasm(Synthesis of methionine from homocystein)
3-Normal myelination of nerves
4- vitamin B12 and folate are particularly important in DNA
synthesis in red blood cells .
Vitamin B12 deficiency seen in the following conditions :
•Lacking of gastric intrinsic factor (IF) in case of addisonnians
pernicious anemia or after gastrectomy .
•Colonization of bacteria in small intestine .
•Diseases of ileum resulting in malabsorption of vitamin B12 .
•Deficiency lead to :
•pernicious anaemia & or neurologic disorders; degeneration of
peripheral nerves that may cause parasthesia, numbness, tingling in
fingers and toes.
•Red-sore-tongue .
•Amenorrhea.
•Homocystein-urea.
•Sub acute combined degeneration of spinal cord .
•dysfunction of spinal cord occur in association with addisonian
pernicious anemia commonly after gastrectomy or other causes of
vitamin B12 deficiencies, rarely result from lack of vitamin B12 in diet .
The most common cause of deficiency is mal absorption due
to atrophy of the gastric mucosa
Good food sources of vitamin B12:
vitamin B12 does not found in
plant foods . meat ,liver, kidney poultry, eggs ,milk and dairy products ,oysters,
shellfish ,yeast products . bacterial synthesis of vitamin B12 in human intestine not
absorbed, and excreted in faeces .
Absorption:(by diffusion).
It is absorbed in the ileum after combination with intrinsic factor IF ( glycoprotein
secreted by gastric mucosa) in a ratio of 2:1 to form a complex, this complex is
resistant to intestinal digestion and bacterial attack .
Transport:
Cobalamin is transported in the plasma by binding of two proteins.
•Transcobalamin I :this is strong binder in the liver(it provides an effective storage
form of cobalamin).
•Transcobalamin II:this is weak binder(delivery of cobalamine to the tissues ).
The major form of vitamin B12 in the plasma is methylcobalamine.
70% of vitamin B12 is stored in the liver as 5-deoxy cobalamine.
27% of vitamin B12 as hydroxyl cobalamine .
3% of vitamin B12 as methyl cobalamine .
The total amount of vitamin B12 in the body of adult is 2.5 mg(1.5 mg is present in
the liver)
RDA: 3mcg/day .