Niacin (B3)

Question 1

what are the multiple molecules that make up Niacin (B3)?

Answer 1

• nicotinic acid
• nicotinamide
• nicotinamide nucleotides

Question 2

what are the active forms of niacin (B3)?

Answer 2

NAD(H), NADP(H) – nicotinamide nucleotides

Question 3

what does NAD stand for?

Answer 3

nicotinamide ADP-ribose

Question 4

how does NAD/NADP change to NADH/NADPH?

Answer 4

hydride ion (H-) attaches to the molecule

Question 5

what two of the three molecules that make up niacin are absorbed in the small intestine and transported through circulation to tissue cells?

Answer 5

nicotinic acid and nicotinamide

Question 6

what are the three structures that make up NAD?

Answer 6

nicotinamide, ribose, and adenosine

Question 7

what are the sources of niacin in the diet?

Answer 7

• nicotinamide & NAD+/NADPH: fish and meats
• nicotinic acid: plants
• supplements are nicotinamide

Question 8

how are niacin sources from the diet synthesized?

Answer 8

via tryptophan

Question 9

how is niacin digested, absorbed, transported and stored in the body?

Answer 9

1. NAD/NADP are hydrolyzed in the intestine to make nicotinamide (free form)
2. nicotinic acid and nicotinamide (free form) are absorbed in the small intestine (via sodium-dependent, carrier-mediated diffusion or by passive diffusion)
3. nicotinic acid and nicotinamide (free form) are then transported in the blood and move across cell membranes via simple diffusion
4. NAD(P) is then synthesized from the free form in the liver (or other tissues)
5. excess NAD(P) is converted back to the free form as storage and available for transport to other tissues when needed

Question 10

what are the functions and mechanisms of the coenzyme form of niacin?

Answer 10

• oxidative reactions
• reductive biosynthesis
• electron donor

Question 11

what are the functions and mechanisms of the non-coenzyme form of niacin?

Answer 11

• donor of ADP-ribose for protein modification
• formation of cyclic ADP-ribose

Question 12

what are the mechanisms of action of NAD+?

Answer 12

• electron acceptor (2e and H+ or hydride H-)
• de-hydrogen reactions (dehydrogenases)
• oxidative catabolism and electron transport chain to generate ATP (TCA cycle, glycolysis, beta-oxidation) – good for cell and DNA growth

Question 13

what are the mechanisms of action of NADPH?

Answer 13

• electron donor
• reducing agents in reductive biosynthesis (reductases)

Question 14

how is NADPH generated?

Answer 14

via glucose 6-phosphate dehydrogenases in pentose-phosphate pathway

Question 15

what is the common niacin deficiency and how is it caused?

Answer 15

• pellagra “rough skin”: lack of nicotinic acid or its precursor tryptophan in the diet
• causes: poor nutritional intake, medication, malabsorptive conditions/disorders

Question 16

what are the 4 D’s severe symptoms of pellagra?

Answer 16

dermatitis, dementia, diarrhea, and death

Question 17

what are the outcomes of large dosages of niacin?

Answer 17

• treat hypercholesterolemia
• lowering serum LDL and VLDL lipoproteins
• increase HDL lipoproteins

Question 18

what are the common signs of toxicity of niacin?

Answer 18

• flushing/redness
• GI problems (heartburn, nausea, vomiting)
• liver injury
• glucose intolerance (elevated levels)

Question 19

how do we find the nutritional status of niacin in the body?

Answer 19

• measurement of urinary metabolites
• erythrocyte NAD concentrations

Question 20

what is the non-redox role of NAD+?

Answer 20

serves as a donor of adenosine diphosphate ribose (ADP-ribose) for posttranslational modification of proteins or formation of cyclic ADP-ribose

Question 21

what are the key enzymes niacin is involved with?

Answer 21

• NADH dehydrogenase
• glyceraldehyde-3-phosphate dehydrogenase

Question 22

what physiological processes is niacin involved with?

Answer 22

• electron transport chain
• cholesterol and fatty acid synthesis