NIACIN

By V. S Deepika raniM.Sc. 1st year student

DISCOVERY• Pellagra was first observed in 1900’s in U.S –

families whose diet is largely based on corn.• Children – no pellagra seen- high intakes of

meat and milk.• Pellagra related to food factor.• Goldberg experiment – 12 convicts – corn meal,

corn starch, rice, sweet potato and pork fat.• Administration of dried meat or liver cured

pellagra. Thus niacin was discovered by Goldberger in 1928.• Other names are nicotinic acid, P.P, anti

pellagra vitamin, and vitamin-B 3.

CHEMISTRYExists in 2 forms Nicotinic acid Nicotinamide mol wt is 123 mol wt. is 122

• Niacin is a pyridine derivative.• Structurally it is pyridine 3 – carboxylic acid.• Water soluble, stable to acid and heat.• White powder when crystallized.• Coenzymes NAD and NADP – oxidation – reduction rxn’s - enzymes oxidoreductases

Nicotinic acid

Precursor role of tryptophanQ 1. Why did milk, which is low in niacin cure or prevent pellagra?Q 2. Why was pellagra so common in families subsisting on diets high in corn?

Key discovery – tryptophan can be used by the body to make niacin.

Corn based diet- low in both tryp and niacinMilk – high in tryptophan

• Nicotinamide – niacin

• PRPP ( phospho ribosyl pyro phosphate) – ribose phosphate

• ATP – AMP moiety

• Glutamine – amide group

NAD and NADHelectron acceptor hydrogen donorCatabolism rxn’s + A + NADH +

Example

ETC

ATP

NADP and NADPH• Anabolism or bio synthesis rxn’s Examples – biosynthesis of fatty acids and steroids.

Eg. 1

Eg. 2

NADP - hydrogen donor

Digestion absorption and storage

• NAD / NADP are digested by nucleotide pyrophosphatases present in pancreatic and intestinal secretion.

• Nicotinamide and niconitate are absorbed from stomach and small intestine - transported in blood - uptake by cells.

Excretion : Excreted as N methyl nicotinamide, nicotinic acid N-oxide, N1 – methyl- 2- pyridone -5 – carboxamide etc

Storage sites : Liver, Kidney, Heart, and skeletal muscles – high concentrations of NAD

RDIVery often niacin equivalents are used while expressing RDA

1 NE = 60 mg of tryptophanAdequate intake = 15 – 20 mg

GROUP CATEGORY/ AGE N . E (mg/d)

MEN 16-21

WOMEN 12-16

Pregnant +2

Lactating 0-6 m 6-12m

+4+3

INFANTS 0-6m 710µg/kg

6-12 650µg/kg

CHILDREN 1-9 yr 8-13

BOYS 10-17yr 15-17

GIRLS 10-17yr 13-14

Food Sources• Meat, liver, fish, yeast and

diary products – major sources of niacin and tryptophan.

Other are peanuts, dried beans, and peas, whole grains, treated millets like corn, roasted coffee beans( trigonelline), enriched breads an cereals.

DEFICIENCY• Deficiency of niacin causes Pellagra( Italian : rough skin).• This disease involves skin, gastrointestinal tract, and

central nervous system.

Symptoms : 4 D’s Dermatitis, Diarrhea, Dementia if not treated Death.

Risk of deficiency :Mostly seen among people whose staple diet is corn and maize.

OTHER EFFECTS

Pharmacological use : Niacin and its related derivatives when given in daily doses of 1 to several gm treats hyperlipidemia

Possible effects stated are:• Lowers LDL cholesterol and Lp(a) conc.

• Increases HDL cholesterol.

HYPERVITAMINOSIS• At intake levels of 1000 to

2000mg leads to skin flushing and itching as nicotinic acid acts as vasodilator.

• Other effects are G.I upset, hyperglycemia, liver damage, etc.

• So medical supervision is very important.