Niacin Flashcards
INFO
niacin and nicotinic acid are synonyms
niacinamide - active form of vitamin in tissues
previously called as coenzyme-1 , diphosphopyrisine nucleotide (DNP) later changed to NAD+
NIACIN DEFICIENCY
deficiency leads to pellagra
also caused by tryptophan def.
more in women bcs :- estrogen metabolites inhibits tryptophan metabolites
1) DERMATITIS - bright red erythema in feet ankles face
- increased pigmentation around neck :- CASSAL’S necklace
2)DIARRHEA - mild/severe with blood , mucous . lead to weight loss , nausea and vomiting may also be present
3)DEMENTIA - seen in chronic cases , delirium is seen in acute pellagra , Irritability , loss of concentration , memory loss , Ataxia and spasticity may also be present
NIACIN SYNTHESIS FROM TRYPTOPHAN
60mg tryptophan – 1mg of niacin
quinolinolate phosphoribosyltransferase – rate limitting enzyme of niacin →NAD+
CAUSES OF NIACIN DEFICIENCY
1.dietary def. :- people with staple food of maize and sorghum
maize has niacin in unbound form and is not available
sorghum has high levels of leucine which inhibits QPRT enzyme hence niacin does not convert to NAD+
2.Isoniazid(INH) - anti-tuberculous drug , prevents pyroxidal phosphate formation , blocks tryptophan to NAD+
3.Deficient synthesis - kynureninase involved in tryptophan pathway , dependent on pyrodixal phosphate
4.Hartnup’s disease - congenital disease , inhibited absorption of tryptophan from intestine .
5.Carcinoid syndrome - - tryptophan is used for serotonin and not left for niacin synthesis
THERAPEUTIC USE OF NIACIN
inhibits flux of free fatty acids from adipose tissue and acetyl CoA levels are reduced and serum cholesterol is lowered
high doses - helps to reduce lipoproteinA levels
TOXICITY OF NIACIN
when given orally or parenterally :-
transient vasodialtion of cutaneous vessels and histamine release + itching burning tingling
>50mg/day intake – liver damage
SOURCES AND RDA
Richest - fish eggs meat whole cereals legumes liver dried yeast rice
half is obtained from tryptophan conversion
RDA:-
adults :-15-20mg/day
children:- 10-15mg/day
lactation - +5mg
