Niacin (4 questions)

Question 1

What are the oxidized forms of niacin?

Answer 1

NAD/NADP

Question 2

What are the reduced forms of niacin?

Answer 2

NADH/NADPH

Question 3

The term niacin is a generic term for?

Answer 3

Nicotinic acid and Nicotinamide

Question 4

(T/F) The adequate intake for infants is based solely on niacin intake, because from birth to 6 months, the tryptophan that is going to be consumed by an infant is going to be used strictly for protein synthesis. They will not be converting tryptophan to niacin, as we see in older children and adults.

Answer 4

TRUE

Question 5

How is NE defined?

Answer 5

NE = niacin equivalents.

FNB defines 1 NB as 1 mg niacin or 60 mg of the AA tryptophan (secondary source, which the body can convert to niacin)

Question 6

What are food sources of niacin?

Answer 6

1. Beef liver
2. Chicken breast
3. Marinara sauce
4. Turkey
5. Salmon
6. Tuna

…fortified breakfast cereals, pasta

Question 7

Poultry, beef, and fish provide XXXX mg niacin per serving, primarily in what form?

Answer 7

5-10 mg niacin

in the highly bioavailable forms of NAD and NADP

Question 8

Plant-based foods, such as nuts, legumes, and grains provide XXX mg niacin per serving, in what form?

Answer 8

2-5 mg niacin, mainly as nicotinic acid

Question 9

In some grain products, naturally present niacin is largely bound to polysaccharides and glycopeptides which makes it only about X% bioavailable.

Answer 9

30%

Question 10

What form of niacin is provided in fortified foods?

Answer 10

NICOTINAMIDE; therefore, highly bioavailable bc its the free form

Question 11

What organ can synthesize niacin from tryptophan?

Answer 11

The liver

Question 12

How much tryptophan is converted to niacin?

Answer 12

~3%

60 mg of tryptophan yields 1 mg of niacin

Question 13

What is Hartnup disease?

Answer 13

Autosomal recessive; individuals have defects in their ability to convert tryptophan to niacin; shown to have niacin deficiencies

Question 14

How is niacin absorbed?

Answer 14

Once in nicotinamide form, it can be absorbed in the S.I. via sodium-dependent carrier-mediated diffusion

For pharmacological doses, it is absorbed by passive diffusion

In the colon, some can be absorbed via sodium-independent, high affinity carrier

Question 15

How is niacin transported in the blood?

Answer 15

Majority is free niacin form

15-30% is bound to proteins

Question 16

How does nicotinamide/nicotinic acid move across cell membranes?

Answer 16

Simple diffusion

EXCEPT for kidney tubules and RBCs require carrier transport; Brain uptake requires ATP

Question 17

Where is the majority of excess niacin stored?

Answer 17

In the liver, excess tryptophan is converted to niacin and then to NAD, and very limited amounts are stored here.

Question 18

Over 200 enzymes, primarily XXXX, require the coenzymes NAD and NADP.

Answer 18

Dehydrogenases

Act as hydrogen donors or electron acceptors, and enable nutrient metabolism and energy production

Question 19

What is the major role of NADH?

Answer 19

NADH = Reduced form of NAD

To transfer its electrons from metabolic intermediates through the ETC to produce ATP; at Complex I

Question 20

What is the major role for NADPH?

Answer 20

NADPH acts as a reducing agent in many biosynthetic pathways
—–Pentose Phosphate Pathway
—–Mito membrane malate aspartate shuttle

Question 21

What are 3 nonredox activities of NAD derivatives?

Answer 21

1. DNA repair of strand breaks
2. Acts as second messengers involved in control of mobilization of calcium from intracellular stores, especially in neurons (one-way cells communicate via calcium-flux in and out of the cell)
3. SIRTUINS (enzyme deactylases), catalyze the removal of acetyl groups from the target proteins containing actylated lysine residues

Question 22

Explain how SIRTUINS affect the function of many enzymes. What are some of the functions affected?

Answer 22

Sirtuins (enzyme deactylases) catalyze the removal of acteyl groups from proteins. Typically, these proteins are actylated on lysine residues. The removal of the acetyled lysine residues is going to affect numerous functions of many enzymes including:

—enzyme activity
—cell signaling
—gene expression (DNA deacetylation)

Question 23

What role does NADH have in the ETC?

Answer 23

NADH acts as a vehicle for getting electrons to the ETC; donated electrons at complex I

Question 24

What happens once NADH drops off it’s electrons at XXXXXX?

Answer 24

Complex I.

The electrons will be passed from complex I and enter the intermembrane, this energy is going to pump 4 protons into the intermembrane space; and again in complex III; and 2 protons are pumped in Complex IV.

Question 25

The pumping of protons in the ETC, generates….?

Answer 25

IONIC GRADIENT; which will power the enzymes that is embedded in the membrane, allowing it to make ATP from ADP + phosphate.

Question 26

What enzyme is embedded in the membrane of the ETC? What is its function?

Answer 26

ATP synthase; takes protons generated from ETC, and generates ATP from ADP + phosphate

Question 27

What is glutathione? Which form is the active form?

Answer 27

An endogenous antioxidant; important in terms of neutralizing pro-oxidic compounds, such as hydrogen peroxide.

The reduced form is the active form that is able to act as an antioxidant

Question 28

What needs to happen so glutathione can carry out its functions?

Answer 28

NADPH will donate it’s electrons to RIBOFLAVIN (FAD —> FADH), then those electrons will be passed to glutathione. This will convert the oxidized form of glutathione to the reduced (active) form.

Question 29

What enzyme does glutathione use for neutralizing pro-oxidants?

Answer 29

Glutathione peroxidase enzyme

Question 30

For folate metabolism, NADP/NADPH is required for which 5 reactions?

Answer 30

1. 5, 10-methylene THF —-> 5-methyl THF
2. 5, 10-methenyl THF —-> 5, 10-methylene THF
3. 10-formyl THF —-> THF
4. THF —-> DHF
5. Folic acid —–> DHF

Question 31

What form of niacin has been used to treat hyperlipidemia?

Answer 31

NICOTINIC ACID; large doses up to 6g/day in divided doses has been shown to:

—lower total cholesterol
—lower LDLs
—increase HDLs
—reduce lipoprotein A concentrations

Question 32

(T/F) Nicotinamide in large doses also reduces blood lipids.

Answer 32

FALSE; only nicotinic acid form

Question 33

What form of niacin (in large doses) can be used topically to reduce inflammation associated with acne vulgaris?

Answer 33

NICOTINAMIDE

Question 34

What dose of nicotinamide can reduce the rates of new nonmelanoma skin cancers and actinic keratosis?

Answer 34

500 mg doses BID

Question 35

Niacin Deficiency

Answer 35

Pellagra, is characterized by the 4 D’s:

D: Dermatitis (similar to sunburn; hyperpigmented and scaly; changes in oral cavities)
D: Diarrhea (can lead to a reduced absorption of other nutrients)
D: Dementia
D: Death

Question 36

What is the treatment for niacin deficiency?

Answer 36

Treatment requires oral intakes of ~300 mg of NICOTINAMIDE daily (usually divided into 3 doses), for about 1 month

Question 37

What is the upper tolerable limit of niacin?

Answer 37

35 mg/day in adults for the general population

Toxicity presents as flushing of the skin

Question 38

How is niacin status assessed, in clinical settings?

Answer 38

Urinary excretion of methyl nicotinamide (~0.8 mg/day)

2-pyridone in plasma