Vit A & E: E

Question 1

What is the structure of vitamin E?

Answer 1

8 vitamers which contain a phenolic functional group on a chromanol/chromane ring with a phytyl side chain
(antioxidants)

Question 2

What are the classes of vitamin E?

Answer 2

2 classes:
1. tocopherols: only RRR alpha-tocopherol has biologic activity

2. tocotrienols

body cant interconvert vitamers

Question 3

What is the structure of Tocopherols?

Answer 3

ring and fully saturated side chain (16 carbons)

4 types of tocopherol: alpha, beta, gamma, delta

3 spots (R1...): different routes
each consider chiral centers

Question 4

What are some sources of vitamin E (food)?

Answer 4

found primarily in plant foods:
nuts, some vegetable oils, green leafy veg.

susceptible to destruction during food preparation (heat) and storage

Question 5

What are the supplements for vitamin E?

Answer 5

usually provided as alpha-tocopherol (often esterified to prolong shelf-life)

synthetically produced alpha-tocopherol contains equal amounts of all 8 possible sterioisomers

a given amount of synthetic alpha-tocopherol (all rac-alpha-tocopherol, DL or dl): half as active as natural forms of alpha tocopherol
(RRR-alpha-tocopherol, D or d)

Question 6

Digestion, absorption, metabolism and storage of vitamin E?

Answer 6

-Tocopherols found free in foods

-Tocotrienols: found esterified and must be hydrolyzed prior to digestion
(little known for mech. of their absorption)

-vit E absorbed primarily in jejunum by passive diffusion (duodenum)

absorption improved with dietary lipids

chylomicrons for transport

liver re-circulates some in VLDL

stored mostly in adipose tissues (unesterified form in lipid droplets)
release from adipose slow

-rest stored in liver and other tissues (skeletal muscles): better sources in times of need

Question 7

What is the function of vitamin E? Antioxidant

Answer 7

tocopherol and tocotrienols

maintains membrane integrity of body cells via prevention of the oxidation of unsaturated fatty acids contained in the phospholipids of membranes

Question 8

What is the function of vitamin E? Antioxidant

Answer 8

free radical termination

singlet molecular oxygen destruction:
vitamin E has oxygen quenching abilities related to its hydroxyl group in position 6 of vitamin E’s chromane ring
-alpha-tocopherol most effective

Question 9

Vitamin E: antioxidative function in heart disease?

Answer 9

Heart disease: oxidation of LDL–> plaque formation + accumulation of lipid laden foam cells in blood

vitamin E enables body to inhibit oxidation of LDL + prevent blood clot formation + helps suppress release of inflammatory cytokines

while many observational studies: favorable
recent RCTs: not protective

Question 10

Vitamin E: antioxidative function in cancer?

Answer 10

Vit E: blocks formation of nitrosamines formed in the stomach from nitrates in food

free radical damage: trigger cancer through activation of certain signaling pathways, alterations in gene expression…etc.

Studies: NOT found higher dietary intakes/supp. vit.E protective
–>increased use–>increased risk of prostate cancer

Question 11

Vitamin E: antioxidative function in eye health?

Answer 11

the etiology of age-related macular degeneration and cataracts: poorly understood

radical-induced damage?

studies INCONSISTENT about whether vitamin E taken alone or in combination w/ other antioxidants might be effective

possible combination: vitamin E (400 IU), vitamin C (500 mg), Beta-carotene (15 mg), zinc (80 mg), and copper (2 mg)

Question 12

What are some other functions of vitamin E?

Answer 12

diabetes: improve plasma membrane structure to increase glucose uptake

Alzheimer;s, other degenerative condition

scar formation

cell signaling molecule

gene expression

tocotrienols function in cell signaling (estrogen, insulin receptors): act as antioxidants, hypercholesterolemic (lower HMG-CoA reductase activity), inhibit platelet aggregation, anticancer roles

no evidence to support supp.

Question 13

What nutrients do vitamin E interacts with?

Answer 13

1. ) selenium, vitamin C: higher level of one of these antioxidants may reduce effect of others
   - vit C involved in vit E regeneration
2. )polyunsaturated FAs: enhance
3. )high intake of vit E can interfere w/ other fat-soluble vitamins (e.g. beta-carotene and ivt K absorption and metabolism)

Question 14

Metabolism and excretion of vitamin E

Answer 14

hepatic metabolism requires cytochrome p450

several metabolites excreted in urine

Question 15

What are the effects of vitamin E deficiency?

Answer 15

deficiency is rare

but risk will increased with fat malabsorption, genetic defects in lipoproteins and fat absorption

Question 16

What is the toxicity of vitamin E?

Answer 16

UL = 1000 mg alpha-tocopherol
(set based on risk of bleeding and anti-coagulation)

toxicity rare but may cause GI distress, bleeding, hemorrhagic toxicity

Question 17

What are some ways to assess vitamin E?

Answer 17

plasma vitamin E

Erythrocyte hemolysis test (amount of hemoglobin released following incubation of red blood cells w/ hydrogen peroxide)

possible future: urinary metabolite: alpha-carboxy-ethyl-hydroxychromanol (a-CEHC)
-excretion was reflective of adequcy when its excretion exceed 1.39 mmol/g creatinine

Question 18

What are some common sources of vitamin E in the US?

Answer 18

ready to eat cereals, cakes, cookies, pies, oils, salad dressings, white bread, beef, nuts and seeds