Niacin Flashcards
2 chemical name forms of niacin
i) Nicotinic acid [pyridine 3-carboxylic acid]
ii) Nicotinamide (also called niacinamide )
NAD=
nicotinamide adenine dicnucleotide
NADP
nicotinamide adenine dinucleotide phosphate
4 coenzyme functions of niacin
- Pyruvate dehydrogenase
- synthesis of fa
- Citric acid cycle
- regenerate antioxidants
niacin and pyruvate dehydrogenase reaction
pyruvate -> acetyl CoA +CO2
ECT: NADH + H+ = NAD+ in complex 1
a) FAD + 2H = FADH2
b) FADH2 + NAD+ = NADH + H+ + FAD
niacin and synthesis of fa
NADPH donates Hydrogens
citric acid cycle and niacin
malate + NAD+ = oxaloacetate + NADH === 3 ATP
niacin and regenerating antioxidants
dehydroascorbic acid (ox) + GSH/GSSG + NADH =ascorbic acid (reduced) + NAD+
non-coenzyme roles of niacin
- protein deacetylation
- histone deacetylation (gene silencing)
niacin in protein deacetylation
Catalysed by sirtuins (NAD-dependent deacetylases)
transfer protein acetyl to NAD+ = NAD+ cleavage
and O-acetyl-ADP-ribose
niacin in histone deacetylation
histone de-acetylation = more condensed DNA/ decreased expression
➜deficiency associated with cancer and DNA damage
2 ways to obtain niacin
- exogenous (from food)
- mainly protein foods fish, meat, grains, seeds
- some bound to carbs in cereal grains/corn (niacytin) needs digesting - endogenous = make in body from aa tryptophan
food sources of niacin
fish, meat, peanuts
endogenous synthesis of niacin from TRP
in liver:
TRP = nicotinamide
60mg TRP = 1 mg NE
* vitamin B6 PLP dependent enzyme and riboflavin dependent enzyme
milk is good source of NE because high in TRP
EAR niacin
M = 12 NE
W= 11NE
RDA niacin
M= 16 NE
W = 14 NE
*stated as NE even though most ppl meet from mg of exogenous niacin
niacin deficiency causes
pellagra
3Ms:
maize diet (corn binds niacin w niacytin)
molasses (high CHO, lack of sufficient protein)
meat (really pork fat, low niacin = low TRP)
symptoms of pellagra
3Ds:
diarrhea/ dehydration
dementia
dermatitis - rough scaly patches on sun exposed skin
what areas is pellagra a problem
corn based diet of US south, Africa
NOT: central America/mexico- quicklime
mechanism of why corn is a problem
- low in available niacin (bound to niacytin)
- can release niacin from corn using activated lime water = calcium hydroxide (Ca(OH)2)- lime is CaO/quicklime, activates when in water
- this is how corn flour is made in central and south americas so no pellagra
- corn is low in quality protein, 0.6% TRP (good is over 1%)
niacin UL
UL= 35mg from synthetic or fortified sources only- not niacin in food or TRP in food
nicotinic acid form causes flushing (release of histamine)
- severe itching and headaches
- at higher doses above UL= liver damage
why are people treated with such high doses of niacin
niacin-induced hepatitis-liver transplant
ppl take niacin supplements bc nicotinic acid form can effectively reduce blood cholesterol by increasing HDL and decreasing LDL
