Niacin Flashcards
How can niacin status be determined?
- amount of Trp, pyridoxine, Leu
- whole blood NAD/NADP + urine breakdown metabolites.
What are the non-cofactor roles of niacin?
- ADP-ribosylation (its a substrate) - cell signalling and protein modifications
- Reduction of cholesterol and TG (super high doses of nicotinic acid = anti-lipolytic effect)
What compounds does niacin participate in the catabolism of?
glucose, FAs, AAs, and ketones.
What are the niacin requirements?
- 7mg NE/1000kcal
- around 15mg for adults
- UL = 35mg/d (liver damage)
What are niacin’s properties?
White crystal
Water + alcohol soluble
What increases deficiency risk?
Poor diet + high E requirements
Certain drugs
Alcoholism
Cancer
Genetic disorders (hartnups - Trp transporter deficiency)
What form is niacin in in the blood?
Unbound forms of acid and amide
What is the process of niacin absorption?
- Coenzyme (NAD) hydrolyzed to nicotinamide in intestinal lumen.
- Absorbed in SI by facilitated and passive diffusion.
**nicotinic acid can also be absorbed in stomach by passive diffusion - Metabolic trapping to NAD(P)
_______ can result from niacin deficiency, and what is it?
Pellagra - 3D’s (dermatitis, diarrhea, dementia)
Where is niacin first sent to? And where does the excess go?
to the liver and converted to NAD, surplus NAD is hydrolyzed and released into circulation.
How is niacin reabsorbed?
Active Na-dependent mechanism
Which coenzyme is involved in redox status regulation? Explain how?
NADP
NADPH + H donates the protons so glutathione reductase can replenish 2 GSH to reduced form
What is the active form of niacin?
Pyridine nucleotide coenzymes.
NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate)
What is reactions are NAD and NADP involved in?
NAD - catabolic reactions (Box of fatty acyl CoAs, degradation of CHO)
NADP - biosynthetic reactions (PPP, synthesis of fats)
What are 2 sources other than Trp and preformed?
- Nicotinic acid from roasted coffee
- niacin present as trigonelline
How does limewater or wood ash affect niacin bioavailability?
It’s an alkaline substance that liberates the nicotinic acid
What are some food sources of niacin?
preformed - meat, legumes, enriched grains
Tryptophan (eggs)
Describe the bioavailability of niacin in cereals and why?
Not available since present as nicotinic acid bound to complex CHO proteins.
How is NAD/NADP involved in redox reactions?
Acts as a H acceptor in oxidation and H-donor in reduction.
How can niacin be made in the body?
De novo synthesis from tryptophan which is oxidatively cleaved.
60mg Trp = 1mg niacin
Normal Trp intakes adequate to meet niacin requirements w/o need for preformed niacin.
What 3 vitamins are involved in niacin synthesis?
Vit C, B2, and B6
Do we store lots of niacin? And where is most of it stored?
No we don’t have a lot.
Most stored in cytoplasm bound to protein (inside cells).
What is the difference between niacin and nicotinamide?
Niacin has a COOH group whereas nicotinamide has an amide group (O=C-NH2)
