Vit E Flashcards
What is the umbrella term for the Vitamin E family? what are the two main types?
Tocochromanols
-Tocopherols and tocotrienols
-structurally similar compounds which exhibit RRR-alpha-tocopherol activity
Which isomer of Vitamin E is the most bioactive?
RRR-α-tocopherol
What structural difference exists between tocopherols and tocotrienols?
Tocopherols have a saturated phytyl tail, while tocotrienols have an unsaturated tail (three double bonds)
What part of the Vitamin E molecule reacts with radicals?
The chromanol head
How does sythetic vs natural vit E structure differ?
The steriochemistry at various positions can be S or R, while in natural vit E it is always R (all methyl groups flipped up)
what 4 things impact biological activity of Vit E?
1) prescence of double bonds in phytyl tail
2) location of methyl groups on phenolic ring
3) configuration at the 3 chiral centers
4) esterification of the phenolic ring
How is tocochromanol digestion / absorption affected?
dependent on lipid digestion/absorption
-absorbed into entorocyte by facilitated and passive transport
How is tocopherol released from synthetic tocopherol?
Pancreatic esterase cleaves synthetic forms to free tocopherol
What 5 things impact bioavailibility of vit E?
1) food matrix
2) lipid content in meal
3) type of lipid
4) competition of alpha-TP with other isomers, micronutrients, or polyphenolics
5) alcohol consumption
What is the primary function of α-Tocopherol Transfer Protein (α-TTP)?
To selectively bind and transfer α-tocopherol between membranes and tissues
How is Vit E transported?
In chylomicrons
What condition is associated with mutations in the TTPA gene? what is the impact? what are symptoms?
Primary vit E deficiency :Ataxia with Isolated Vitamin E Deficiency (AVED)
-inadequate distribution of Vit E to peripheral tissues (absoprtion / lipoprotein transport of vit E is normal)
-impaired vibration sense, ataxia, dysarthria
What is a major pathway for Vitamin E catabolism? explain why tocochromanol metabolism is selective.
Tocopherol-ω-Oxidation
-metabolism is selective in order to conserve α-tocopherol and clear out excess /less active forms
-conjugated metabolites generated using CYP450 to increase clearance of other isomers
Where is 90% of body vitamin E stored? what does this mean for vit E utilization? where else is it stored and how does utilization differ?
Membranes (helps with stability)
-white adipose tissue
-very immobile pool; slow release
Vit E is also stored in the liver and in RBC membranes
-readily availible for redistribution to be able to maintain membrane levels + sequester free radicals
Why is Vit E storedin adrenal tissue?
Hormone synthesis causes oxidized species
-vit E present to act as antioxidant
how does the amount of dietary tocopherol isomers reflect plasma levels? what is the impact of suplements?
The diet has highest amounts of g-tocopherol, s-tocopherol, but it is lowest in plasma
20-30uM of a-tocopherol
-low amounts of other forms
Supplements show minimal plasma changes due to tight regulation
What is the primary role of Vitamin E as an antioxidant?
To quench free radicals and ROS made from metabolic pathways
Explain how oxidation of free radicals occurs. what are the steps?
1) lipid radicals are formed when OH reacts with FA
2) rxn of lipid radical with O2 generates a lipid peroxide radical
3) radicals abstract H from other molecules, forming more radicals
what is a lipophilic antioxidant?
antioxidant localized in lipid-bilayer (donates its H to quench unpaired e- radical)
-stabilizes cell membrane
Tocopherol reacts w peroxyl lipid radicals
How does vit E work as a lipophillic antioxidant?
Vit E has a way higher affinity for LOO * / LOOH than cholesterol and FA
- effective at [low]
-recycled by carotenoids and vit C
What other vitamins can help recycle vit E?
glutathione, vit C, carotenoids
- carotenoids step in when vit C is low
what is a physiological role of tocochromanols?
1) antioxidant in steroid synthesis
2) spermatogenesis
3) placenta development
What are rich dietary sources of Vitamin E (tocochromanols)?
Oil seeds and vegetable oils, processed products made from these oils, leafy green vegetables, fortified breakfast cereals
Examples include olive, sunflower, and canola oil; almonds, hazelnuts, red pepper/broccoli, mangoes / papaya
In what portion of food are tocopherols predominantly found?
In the lipid portion of membranes
This suggests a close tie to fat content in food.
