VIMAMIN E and Free Radicals

1. FREE RADICALS AND
VITAMIN E
BY: DR. MAYUR MAKADIA
RESIDENT,
BIOCHEMISTRY DEPARTMENT
PRAMUKHSWAMI MEDICAL COLLEGE
KARAMSAD

2. Definition
• A free radical is a molcule or molecular
fragment that contains one or more
unpaired electrons in its outer orbital.
• Represented by a superscript dot, (R˙)

4. ROS
• Normally, 4e- are transferred to
complete reduction of O2 to form H2O.
• O2 + 4H⁺ + 4e- ―› 2 H2O
• The products of partial reduction of O2
are highly reactive and called Reactive
Oxygen Species(ROS), Reactive Oxygen
Intermediates, Oxygen free
radicals(OFR).

5. ROS (reactive oxygen species)
Free radicals
Superoxide =O2
·
Hydroxyl radical =OH ·
Lipid peroxyl =ROO ·
Hydroperoxyl =HOO·
Particals, which are not
free radicals
Hydrogen peroxide
(H2O2)
Hypochlorous
acid(HClO)
Ozone (O3)
Singlet oxygen (1
O2)

6. Reactive Oxygen Intermediates
• Superoxide Radical: single electron reduction product of oxygen
• Hydrogen Peroxide: two-electron reduction product of oxygen
 Dismutation
• Hydroxy Radical: three-electron reduction product of oxygen
 Fenton Reaction
 Haber- Weiss Reaction

8. Transition Metals
• Ferrous iron, and Cuprous copper can
react with hydrogen peroxide to yield
the hydroxy radical.
• They are referred to as the Transition
Metals.
• They never occur in free, unbound form
in the body.

9. Generation of Oxygen Free
Radicals
• 1) Electron Leakage: major source
Constantly produced due to leaks in ETC.
There is production of superoxide radicals
from interaction between CoQ and O2
in ETC.

10. Generation of Oxygen Free
Radicals
• 2) Normal Oxidation- Reduction
Reaction
• Auto-oxidation of certain compound:
Adrenaline, thiols, ascorbic acid
• Falvin coenzymes present in
peroxisomes are specially active in
generating H2O2.
• Enzymes: xanthine oxidase, aldehyde
oxidase.

11. Generation of Oxygen Free
Radicals
• 3) Exogenous Agents:
• Toxic compound, such as CCl4
• Ionizing Radiation
• Light of appropriate wavelengths
• Cigarette smoke
• Inhalation of air pollutants

13. Generation of Oxygen Free
Radicals
• 4) Respiratory Burst:
• Free radical production is sometimes
required in biological systems.

15. Damage Produced by Free
Radicals
• Extremely reactive
• Half life is only a few milliseconds
• Almost all biological macromolecule are
damaged
• Protein: fragmentation of proteins.
• Oxidation of sulfhydryl group containing
enzymes, loss of function.
• DNA: damaged by strand breaks, directly cause
inhibition of protein and enzyme synthesis and
indirectly cell death, mutation & carcinogenesis.

17. Lipid Peroxidation
• Lipids are most susceptible
• PUFA present in cell membrane
especially prone to damage.
• Initiation phase:
• Primary event is production of R˙ by
interaction of a PUFA with free radicals
generated by other means.
• RH + OH˙ ―› R˙ + H2O

18. Lipid Peroxidation
• Propagation phase:
• R˙ rapidly react with molecular O2 forming a Peroxyl
radical (ROO˙) which can attack another PUFA.
• R˙ + O2 ―› ROO˙
• ROO˙ + RH ―› ROOH + R˙
• Net result is the conversion of R˙ to ROOH
(Hydroperoxide).
• But simultaneous conversion of R˙ to ROO˙ which
lead to continuous production of Hydroperoxide.
• Chain reaction
• “Death kiss” by free radicals.

19. Lipid Peroxidation
• Termination phase:
• The chain reaction continue untill a
peroxyl radical react with another
peroxyl radical to form inactive
products.
• ROO˙ + ROO˙ ―› RO-OR + O2
• R˙ + R˙ ―› R-R
• ROO˙ + R˙ ―› RO-OR

21. Free radical scavenger systems
• Also called Antioxidant defence
mechanism

22. Free radical scavenger systems
• A) Preventive mechanism:
Prevent the generation of free radicals
• B) Interceptive mechanism:
Destroy the free radicals that are
generated

23. Preventive mechanism
• The efficacy of ETC
• Sequestration of transition metals
• Peroxide decomposing enzymes
– Glutathion peroxidase
– Catalase

24. Interceptive mechanism
• A)Enzyme : Superoxide dismutase
(SOD)
• Only enzyme that take a free radical as
its substrate.
• Different isoenzymes
• 1) mitochondrial SOD: Mg++ dependant
• 2)cytosoplasmic SOD: copper-zinc
dependant

26. Interceptive mechanism
• B) Non- enzyme substance:
• Vitamin E
• Retinoids
• Ascorbate
• Ceruloplasmin
• Uric acid

27. Vitamin E as antioxidant
• Most effective naturally occurring chain
breaking antioxidant in tissue.
• Alpha tocopherol (T-OH) intercept the
peroxyl free radical
• T-OH + ROO˙―› TO˙+ ROOH
• The tocoperoxyl radical formed is stable and
will not propagate the cycle any further
• TO˙+ ROO˙ ―› inactive products

28. Vitamin E
• Only traces of tocopherol are required to
protect considerable amounts of PUFA.
• 1 tocopherol per 1000 lipid molecule
• But as antioxidant, alpha tocopherol is
consumed, so it has to be replenished by
dietary supply

29. Vitamin E
• Isolated from wheat germ oil
• Earlier known as Anti-Sterility Vitamin
• Other name “tocopherol” derived from
greek word tokos (childbirth), pheros (to
bear) and ol(alcohol)
• Eight naturallly occurring tocophrols
• Most Important: Alpha tocopherol

30. Vitamin E
• Chemical structure:
• A chromane ring(tocol), with an
isoprenoid side chain

31. Vitamin E
• Absorption : along with other fats and need
bile salts
• Transport : as chylomicrons
• Store : adipose tissue
• Plasma concentration : 0.5-1 mg/dL
• Excretion : in feces via hepato-biliary route,
after chromane ring oxidation followed by
conjugation with glucuronic acid

32. Function of Vitamin E
• Most powerful natural antioxidant

34. Function of Vitamin E
• Reduce risk of Atherosclerosis by reducing
oxidation of LDL
• Boost immune response
• Protect RBC from haemolysis
• Keeps structural and functional integrity of all
cells
• Slows ageing process
• Protection against Alzheimer’s disease
• Act synergistically with Selenium to minimise
lipid peroxidation

35. Deficiency of Vitamin E
• Uncommon, due to adequate level in
average diet.
• Deficiency seen in :
– Cannot absorb dietary fat
– In premature infants
– In abetalipoproteinemia
– Mutation in the gene for tocopherol trasfer
protein

36. RDA
• Male : 10 mg/day
• Females : 8 mg/day
• Pregnancy : 10 mg/day
• Lactation: 12 mg/day
• 15 mg Vit. E = 33 IU
• Requirement increase with higher intake of PUFA
• Pharmacological dose= 200-400 IU/day
• Hypervitaminosis E: rarely occur
• Cause tendency to hemorrhage, bcz it is mild anti-
coagulant

38. Thank You