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Antioxidant enzymes and human health

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Antioxidant enzymes and human health

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Antioxidant enzymes and human health

  1. 1. 1 Antioxidant Enzymes and Human Health By Muhammad Z. Naji
  2. 2. 2 • An antioxidant is a molecule that inhibits the oxidation of other molecules. • Oxidation is a chemical reaction that can produce free radicals, leading to chain reactions that may damage cells.
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  4. 4. 4 Free radicalsFree radicals • Is a highly reactive compounds form during normal metabolic functions and may be introduced from the environment. • These molecules are unstable because of lone pair of electrons make it become highly reactive. • They react with cellular molecules such as proteins, lipids and carbohydrates, and denature them. RISK • As a result of this, vital cellular structures andAs a result of this, vital cellular structures and functions are lost and resulting a pathologicalfunctions are lost and resulting a pathological conditions.conditions.
  5. 5. 5 • The main role of antioxidant enzymes are stabilizing, or deactivating free radicals before they attack cellular components. • They act by reducing the energy of the free radicals by giving up some electrons to become stable
  6. 6. 6 • Many studies shows causes by more than sixty different health conditions, including the aging process, cancer, diabetes, Alzheimer’s disease, strokes, heart attacks and atherosclerosis.
  7. 7. 7 Free radicals and their scavengers • Free radicals are electrically charged molecules, i.e., they have an unpaired electron, which causes them to seek out and capture electrons from other substances in order to neutralize themselves.
  8. 8. • Oxygen is a highly reactive atom that is capable of becoming part of potentially damaging molecules commonly called free radical or reactive oxygen species (ROS).
  9. 9. About 5% or more of the inhaled O2 is converted to ROS such as superoxide, hydrogen peroxide, and hydroxyl radicals by univalent reduction of O2.
  10. 10. • This antioxidant system includes :- • antioxidant enzymes:- (SOD, and reductase, etc.), • nutrient-derived antioxidants:- (ascorbic acid, tocopherols and tocotrienols, carotenoids), • metal binding proteins:- (ferritin, lactoferrin, albumin, and ceruloplasmin) • and numerous other antioxidant phytonutrients present in a wide variety of plant foods
  11. 11. • Reactive Oxygen Species:- Reactive oxygen species (ROS) is a term that encompasses all highly reactive, oxygen containing molecules, including free radicals • Types of ROS include the hydroxyl radical, the superoxide anion radical, hydrogen peroxide, singlet oxygen, nitric oxide radical, hypochlorite radical, and various lipid peroxides
  12. 12. 12 Pathways of ROS generation:-Pathways of ROS generation:- • A consequence of normal aerobic metabolism:A consequence of normal aerobic metabolism: approximately 90% of the oxygen utilized byapproximately 90% of the oxygen utilized by the cell is consumed by the mitochondrialthe cell is consumed by the mitochondrial electron transport system.electron transport system. • Oxidative burst from phagocytes (white bloodOxidative burst from phagocytes (white blood cells) as part of the mechanism by whichcells) as part of the mechanism by which bacteria and viruses are killed, and by whichbacteria and viruses are killed, and by which foreign proteins (antigens) are denatured.foreign proteins (antigens) are denatured. • Xenobiotic metabolism, i.e., detoxification ofXenobiotic metabolism, i.e., detoxification of toxic substances.toxic substances.
  13. 13. 13 Consequences of generation of ROS • O2 can behave like a radical (a diradical) owing to presence of two unpaired electrons of parallel spin Its electronic structure result in formation of water by reduction with four electrons, i.e.: O2 + 4H+ + 4e- 2H2O
  14. 14. 14 • O2 undergoes reduction, several reactive • intermediates are formed, such as superoxide (O2 - ), hydrogen peroxide (H2O2), and the • extremely reactive hydroxy radical (°OH): collectively termed as the reactive oxygen • species, the process can be represented as:
  15. 15. Finally, for the production of reactive hydroxy radical ºOH, except during abnormal exposure to ionization radiation, generation of ºOH in vivo requires the presence of trace amount of H2O2 and Fe2+ salt forms ºOH, as given following reaction :
  16. 16. 17 Antioxidant protection system To protect the cells and organ systems of the body against reactive oxygen species (ROS), humans have evolved a highly complex antioxidant protection system. It involves a variety of components, both endogenous and exogenous in origin,
  17. 17. 18 A.A. Endogenous AntioxidantsEndogenous Antioxidants  BilirubinBilirubin  Thiols, e.g., glutathione, lipoic acid, N-acetyl ysteineThiols, e.g., glutathione, lipoic acid, N-acetyl ysteine  NADPH and NADHNADPH and NADH  Ubiquinone (coenzyme Q10)Ubiquinone (coenzyme Q10)  Uric acidUric acid  Enzymes:Enzymes: - copper/zinc and manganese-dependent superoxide- copper/zinc and manganese-dependent superoxide dismutasedismutase - iron-dependent catalase- iron-dependent catalase - selenium-dependent glutathione peroxidase- selenium-dependent glutathione peroxidase
  18. 18. 19 b. Dietary Antioxidants  Vitamin C  Vitamin E  Beta carotene and other carotenoids and oxycarotenoids, e.g., lycopene and lutein  Polyphenols, e.g., flavonoids, flavones, flavonol’s, and Proanthocyanidins c. Metal Binding Proteins  Albumin (copper)  Ceruloplasmin (copper)  Metallothionein (copper)  Ferritin (iron)  Myoglobin (iron)  Transferrin (iron)
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  20. 20. 21 Defence mechanisms against free radical-inducedDefence mechanisms against free radical-induced oxidative damage include the following:oxidative damage include the following: i.i.catalytic removal of free radicals and reactivecatalytic removal of free radicals and reactive species by factors such as CAT, SOD, GPx and thiol-species by factors such as CAT, SOD, GPx and thiol- specific antioxidants;specific antioxidants; ii.ii. binding of proteins (e.g., transferrin,binding of proteins (e.g., transferrin, metallothionein, haptoglobins, caeroplasmin) tometallothionein, haptoglobins, caeroplasmin) to pro-oxidant metal ions, such as iron and copper;pro-oxidant metal ions, such as iron and copper; iii.iii. protection against macromolecular damage byprotection against macromolecular damage by proteins such as stress or heat shock proteins;proteins such as stress or heat shock proteins; iviv. reduction of free radicals by electron donors, such. reduction of free radicals by electron donors, such as GSH, vitamin E (as GSH, vitamin E (α-α- tocopherol), vitamin C (ascorbictocopherol), vitamin C (ascorbic acid), bilirubin, and uric acidacid), bilirubin, and uric acid
  21. 21. 22 THANK YOU FOR ATTENTIONTHANK YOU FOR ATTENTION

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