lecture 15: vitamin E

Question 1

vitamin E

Answer 1

lipid soluble, trapping of lipophilic free radicals
all structurally related tocopherols and tocotrienols

Question 2

vitamin E deficiency

Answer 2

species-specific abnormalities

a-TTP or lipoprotein deficiencies, lipid malabsorption, doesn’t have to do with vitamin E itself

Question 3

a-tocopherol

Answer 3

primary form, major lipid-soluble antioxidant in plasma, RBCs, tissues

Question 4

absorption and transport

Answer 4

follows transport of cholesterol absorption
incorporated in chylomicrons, eventually transported by other lipoproteins
excreted through urine after being metabolized to water-soluble compounds

Question 5

plasma concentrations

Answer 5

linearly related to intake from foods, intake possible from diet
nonlinearly related to higher intakes (supplements), saturation only increases plasma concentrations slightly

Question 6

secretion of a-tocopherol from liver

Answer 6

repackaged and sent out via VLDLs, crucial to maintaining normal plasma vitamin E levels
a-TTP facilitates secretion of a-tocopherol in plasma lipoprotein pool

Question 7

a-tocopherol transfer protein (a-TTP)

Answer 7

predominantly in liver
preferentially binds a-tocopherol relative to other forms, high affinity
transfers a-tocopherol from one membrane to another

Question 8

cytochrome P450

Answer 8

involved in vitamin E metabolism
stronger affinity for all forms of vitamin E OTHER than a-tocopherol > initiates its breakdown
post-absorptive metabolism for these other forms

pathway: selective tissue deposition of a-tocopherol

OVERALL: takes other forms of vitamin E for breakdown

Question 9

antioxidant activity

Answer 9

vitamin E protects lipids from free-radical induced oxidative damage

reaction of a-tocopherol with peroxyl radicals to prevent uncontrolled lipid peroxidation, terminate chain reaction of radicals

Question 10

tocopherol oxidation pathway

Answer 10

all forms of vitamin E except a-tocopherol are degraded via cytochrome P450
relative proportions of tocopherols in body lie in stark contrast to those found in foods

Question 11

free radical initiators

Answer 11

free Fe2+, UV, ionizing radiation, free electrons etc can produce carbon-centered lipid radicals

Question 12

lipid peroxidation process

Answer 12

1) initiation: initiator forms free radical, reacts with O2 to form peroxyl radical
2) propagation: ROO. reacts with unsaturated FA to form ROOH and a new radical R’.
3) propagation process occurs until antioxidant quenches free radical

Question 13

6-hydroxyl group

Answer 13

reactive portion of vitamin E
hydroxyl donates hydrogen atom > tocopheroxyl radical, which is stable due to resonance/delocalized electrons

Question 14

tocopheroxyl radical

Answer 14

stable due to resonance/delocalized electrons, relatively unreactive

tocopherols react more rapidly with peroxyl radicals than do polyunsaturated FAs (protects polyunsaturated FAs from being oxidized)

radical reduced back to tocopherol by vitamin C (see diagram) > REPLENISHED

Question 15

reversible reaction

Answer 15

single electron oxidation is reversible, e can be replenished by vitamin C, full oxidation is irreversible

Question 16

storage of vitamin E

Answer 16

no storage organ
accumulate in adipose tissue, but mobilization from this tissue is slow and insufficient to prevent vitamin E deficiency

Question 17

fetal circulation

Answer 17

concentration of tocopherols in fetal blood are considerably lower than those in maternal system

Question 18

health effects of Vitamin E

Answer 18

increased vitamin E: increased immune response, reduced risk of diseases, antioxidant properties

Question 19

food sources

Answer 19

y-tocopherol: soybean and corn oil
a-tocopherol: sunflower, safflower, olive oil

Question 20

tomato as vitamin E source

Answer 20

low in fat, fat-soluble vitamin in something with no fat, must be consumed with fats in order for the vitamin to absorb, non-heme iron prone to oxidation, but there is vitamin C to help with absorption