1. Free radicals and Antioxidants

2. Objectives  Basics of Redox Chemistry.  Heterolytic and Homolytic fission.  Free Radical meaning.  Important characteristics of free radicals.  Types of Free Radicals.  Sources of Free Radicals.

3. Objectives  Roles of Free Radicals in Biological Systems.  Mechanism of radical reactions.  lipid peroxidation.  Antioxidant meaning.  Oxidative stress.  Antioxidant System in our body.  What do antioxidants do?

4. Basics of Redox Chemistry Term Definition Oxidation Gain in oxygen Loss of hydrogen Loss of electrons Reduction Loss of oxygen Gain of hydrogen Gain of electrons Oxidant Oxidizes another chemical by taking electrons, hydrogen, or by adding oxygen Reductant Reduces another chemical by supplying electrons, hydrogen, or by removing oxygen

5. When bonds break and one atom gets both bonding electrons- Pairs of Ions. Heterolytic and Homolytic fission Heterolytic fission:

6. When bonds break and the atoms get one electron each. Heterolytic and Homolytic fission Homolytic fission:

7. The breakage of covalent bond ‘homolytic fission’ A B A + B     H 2 O H + OH   Example : Radicals can be formed by…

8.  A free radical is an atom capable of independent existence (hence the term “free”) that contains one or more unpaired electrons in its outer orbital.  It is an electron-deficient species.  It is represented by a superscript dot to the right.(R ● ) Free Radical

9. Important characteristics of free radicals Free radicals are: – Highly reactive. – Unstable and try to become stable. – Short life span ( Short-lived ) as they tend to catch an electron from other molecules.

10. Types of Free Radicals  Oxygen free radicals (OFR)  Nitrogen free radicals (NFR)  Lipid free radicals (LFR)  Others: chlorine radicals(Cl ● ),carbon radicals(CCl 3 ● ), sulfur radicals (RS ● ).

11. Types of Free Radicals  Oxygen free radicals (OFR): OFR is referred to oxygen-derived free radicals. The unpaired electron is located on O such as superoxide radical and hydroxyl radical.  Reactive oxygen species (ROS): ROS is a collective term that includes both oxygen free radicals (OFR), and non radicals that are oxidizing agents and / or are easily converted into radicals such as hydrogen peroxide and singlet oxygen. H2O2、 1O2H2O2、 1O2 Non free radical ROS Free radical ROS ROSOFR （ O 2 、 OH ）.

12. Types of Free Radicals (NFR)  Nitrogen free radicals (NFR) NFR is defined as nitrogen-derived free radicals. RNS: NO NO ONOO, NO 2 RNS (LFR)  Lipid free radicals (LFR) Lipid free radicals are referred to middle metabolic products resulting from the chain reaction of lipid peroxidation, which is produced by interaction of OFR and unsaturated fatty acid.LLOLOO LFR

13. Sources of Free Radicals Exogenous sources of free radicals: – Ionizing radiation – Ultraviolet radiation – Chemicals, smoking – Pollution – Diet (fatty and processed foods) Endogenous sources of free radicals: Respiration Metabolism. Inflammation Phagocytosis

15. Roles of Free Radicals in Biological Systems Like two-edged sword: It can be beneficial. It can be harmful. They play an important role in a number of biological processes, many of which are necessary for life. But they also cause damage and disease.

16. Positive effects of free radicals The presence of low concentrations of free radicals is important for normal cellular redox status and immune function. Immune system: Free radicals are used by phagocytic cells to kill bacteria during infections. (Antimicrobial actions). Modify oxidation-reduction (redox) states. Nitric oxide (NO ● ) helps to regulate blood pressure.

17. Negative effects of free radicals  Free radicals attack the nearest stable molecule, "stealing" its electron.  When the "attacked" molecule loses its electron, it becomes a free radical itself, beginning a chain reaction.  Once the process is started, it can cascade, finally resulting in the disruption of a living cell.  Almost all biological macromolecules are damaged by the free radicals.

18. Negative effects of free radicals They attack sites of increased electron density such as: The nitrogen atom present in proteins and DNA predominantly Carbon-carbon double bonds present in polyunsaturated fatty acids and phospholipids to produce additional free radical, often reactive, intermediates.

19. Negative effects of free radicals However, excessive production can provoke inflammation or altered cellular functions through: lipid peroxidation. protein modification. DNA modification (DNA is damaged by strand breaks) The DNA damage may directly cause inhibition of protein and enzyme synthesis and indirectly cause cell death or mutation and carcinogenesis. Which compromises cell function leading to cell death.

20. Mechanism of radical reactions Radicals are highly reactive species Three distinct steps  Initiation (homolytic covalent bonds cleavage).  Propagation (chain propagation).  Termination.

21. Oxidative damage to lipids Lipid peroxidation  Peroxidation (auto-oxidation) of lipids exposed to oxygen is responsible not only for deterioration of foods (rancidity) but also for damage to tissues in vivo, where it may be a cause of cancer, inflammatory diseases, atherosclerosis, and aging.  The deleterious effects are considered to be caused by free radicals (ROO, RO, OH) produced during peroxide formation from fatty acids containing methylene-interrupted double bonds, ie, those found in the naturally occurring polyunsaturated fatty acids.  Lipid peroxidation is a chain reaction providing a continuous supply of free radicals that initiate further peroxidation.

22. Lipid peroxidation 1.Initiation: RH + X R + XH 2.Propagation: R + O 2 ROO ROO + RH R + ROOH, etc. 3.Termination: ROO + ROO ROOR + O 2 R + ROO ROOR R + R RR

23. Counteracting free radical damage  The human body has several mechanisms to counteract damage by free radicals and other reactive oxygen species.  One important line of defense against free radical damage is the presence of antioxidants.  Some such antioxidants, are produced during normal metabolism in the body.  Other lighter antioxidants are found in the diet.

24. Antioxidants  Substances that are able to neutralize reactive molecules and reduce oxidative damage.  Result of metabolic processes and environmental sources.

25. Sources of antioxidants in diet

27. Damage (Pro-oxidants) Defense (Antioxidants) Pro-oxidant & Antioxidant Balance Damage (Pro-oxidants) Defense (Antioxidants) Decrease of antioxidant defense system Oxidative damage

28.  It is an excess of free-radicals damages cells.  Oxidative stress has been identified as a causative factor in: – Cognitive performance. – Aging process. – Development of diseases such as cancer, arthritis, cataracts, and heart disease. Oxidative stress

29. Free Radical Diseases

30. Many of the changes associated with aging are actually due to the effects of free-radicals. As we age, the antioxidant enzyme systems work less efficiently. Free Radical Diseases

31. Antioxidant System in our body -Superoxide dismutase (SOD) eliminates the superoxide (O 2 -. ). -Catalase and the glutathione peroxidase eliminate hydrogen peroxide (H 2 O 2 ). The enzymatic antioxidants: The non enzymatic antioxidants: Vitamins E, C, A or Pro vitamin A(beta-carotene).

32. Vitamin C  Vitamin C, or ascorbic acid, is a water-soluble vitamin.  This vitamin is a free radical scavenger.  It is effective in protecting tissues against oxidative damage.  Its protective effects extend to cancer, coronary artery disease, arthritis and aging.

33. Vitamin E  Vitamin E is a fat-soluble substance  It is a principal antioxidant in the body and protects polyunsaturated fatty acids in cell membranes from peroxidation.

34. (1) - Preventative antioxidants: Reduce the rate of chain initiation. e.g.: catalase and other peroxidases that react with ROOH and chelators of metal ions such as EDTA. (2) - Chain-breaking Antioxidants: Which interfere with chain propagation. e.g.: In vivo, superoxide dismutase, which acts in the aqueous phase to trap superoxide free radicals (O2 −); perhaps urate ; and vitamin E, which acts in the lipid phase to trap ROO radicals. 2 types of Antioxidants

35. What do antioxidants do What do antioxidants do?  Provides key nutrients needed by the body to neutralize free radicals.  Aid the human body’s natural defenses.  Repair oxidative damage.  Slow or prevent damage to body cells.  May exhibit anti-aging benefits.  May improve immune function and lower risk for infection and cancer.

36. Reactive Oxygen Species and Antioxidants that reduce Them Reactive SpeciesAntioxidant Singlet oxygen 1 O 2 Vitamin A, vitamin E Superoxide radical (O 2 -  ) superoxide dismutase, vitamin C Hydrogen peroxide (H 2 O 2 )Catalase; glutathione peroxidase Peroxyl radical (ROO  ) Vitamin C, vitamin E Lipid peroxyl radical (LOO  ) Vitamin E Hydroxyl radical (OH  ) Vitamin C

37. Summary

38. Conclusion Antioxidant plays an important role to prevent cancer, and other disease. They also have role in slowing aging process and preventing heart disease. So antioxidant are very much necessary for our body.But our body can’t manufacture these chemicals, so they must be supplied through diet.