oxidative stress

knowlege

1. Presentation on OXIDATIVE STRESS SHAILY MEHRA M.PHARM

2. Contents Introduction Causes of oxidative stress Free radicals Free radicals nomenclature Types of free radicals Roles of free radicals in biological system Effect of oxidative stress Molecular Vascular

3. Common diseases caused by Oxidative stress Measurement of Oxidative stress Protective measures for Oxidative stress

4. What is oxidative stress? A disturbance in the balance between reactive species or free radicals and antioxidants. Under normal conditions, cells are able to balance the production of oxidants and antioxidants. Oxidative stress occurs when there is imbalance in our cells due to either an increase in free radicals or a decrease in antioxidants.

5. Oxidative stress leads to the structural changes of the cell wall and hamper the process of maturation of cellular structures. Its also lead to the change in the function and death eventually.

6. ENDOGENOUS SOURCE Body's normal use of oxygen such as respiration and some cell mediated immune functions Immune cell activation Inflammation Mental stress etc. EXOGENOUS SOURCE Environmental pollutants Cigarette smoke Radiations etc.

7. Free Radicals any species capable of independent existent that contains one or more unpaired electrons. These are highly reactive chemical entities that have a single unpaired electron in their outer most orbit. Under certain conditions can be highly toxic to the cells. Generally unstable and try to become stable, either by accepting or donating an electron .

8. Example of free radicals

9. Radicals can be formed by … The loss of a single electron from a non-radical, or by the gain of a single electron by a non-radical. The breakage of covalent bond ‘hemolytic fission’.

10. Free Radical Nomenclature A free radical is denoted by a superscript dot to the oxygen (or carbon) e.g., HO  , NO  ,  CH 3 If a free radical is a charged species, the dot is put and then the charge e.g., O 2  -

11. TYPES OF FREE RADICALS Superoxide radical Hydroxide radical Nitric oxide radical Peroxide radicals H2O2(non radical)..etc.

12. SUPEROXIDE RADICAL Generation of superoxide (O 2  - ) The addition a single electron to the ground-state molecule (O 2 + e - O 2  - ) Biological generation of O 2  - Mitochondrial electron transport chain Enzymatic reduction of oxygen (O 2 ) Xenobiotic metabolisms (redox cycling) Respiratory burst (phagocytes)

13. Biological Generation of Superoxide Enzymatic reduction of oxygen Xanthine/hypoxanthine Uric acid Redox cycling : Paraquat (Xenobiotic) XOD N • N CH 3 H 3 C + N N CH 3 H 3 C + Oxidized cytochomre P450 reductase Reduced cytochomre P450 reductase NADPH NADP O 2 O 2  - Paraquat e - +

14. Respiratory Burst Myeloperoxidase Oxidizes Cl - to hypochlorous acid Chronic granulomatous disease NADPH oxidase enzyme. • • NADPH NADP + O 2 O 2  - NADPH NADP + O 2 O 2  - outside inside . . . . Phagocytic vacuole (phagosome)

15. Hydrogen Peroxide Not a free radical but ROS(reactive oxygen species) Formed in the cell by dismutation reactions by : Spontaneously during respiratory burst. By enzymes e.g. : Superoxide dismutase.

16. Hydroxyl Radical (HO  ) Highly reactive oxygen radicals Formation of hydroxyl radicals in biological systems : Ionizing radiation Reaction of metal ions with hydrogen peroxide (Fenton reaction) Formation of hydroxyl radical from ozone (O 3 )

17. Fenton Reaction Discovered by Fenton (1894) “A mixture of hydrogen peroxide and an iron(II) salts causes the formation of hydroxyl radical ” Fe 2+ + H 2 O 2 intermediate complex Fe 3+ + OH - + HO  Fe 3+ + H 2 O 2 intermediate complex Fe 2+ + O 2  - + 2H +

18. Haber-Weiss reaction Fe 2+ + H 2 O 2 Fe 3+ + OH - + HO  Fe 3+ + O 2  - Fe 2+ + O 2 Net : O 2  - + H 2 O 2 O 2 + HO  + OH -

19. Nitrogen-Centered Radicals Nitric oxide (NO  ) Endothelial derived-relaxing factor (EDRF) Generated from the catalysis of L-arginine by nitric oxide synthase (NOS) enzymes Functions Vascular function, platelet aggregation, immune response, neurotransmitter, signal transduction Cytotoxicity. NO  + O 2  - ONOO - (highly toxic)

20. L- arginine L-citrulline + NO  NOS In the absence of L-arginine and BH 4 (tetrahydrobiopterin), the activation of molecular by NOS results in a divalent reduction of O 2 to yield superoxide anions and hydrogen peroxide. BH4

21. Roles of Free Radicals in Biological Systems Enzyme-catalyzed reactions Electron transport in mitochondria Signal transduction & gene expression Activation of nuclear transcription factors Oxidative damages of molecules, cells, tissues Antimicrobial actions Aging & diseases

22. Molecular effects of oxidative stress Lipid peroxidation DNA damage Protein oxidation Inactivation of enzymes Release of ca ions from intracellular stores Cytoskeletal damage Chemotaxis

23. Vascular effects altered vascular tone increased endothelial permeability

24. Common diseases caused by oxidative stress

25. Measurement of Oxidative Stress Oxygen consumption Oxidative markers Lipid peroxidation products (TBARs, lipid hydroperoxides, etc.) DNA hydroxylation products Protein hydroxylation products (nitration products)

26. Free radical detection Single photon counting Chemiluminescence Fluorescent probe Electron paramagnetic resonance spectroscopy (EPR)

27. Protection Against ROS Damage Direct protection against ROS Superoxide dismutase, Glutathione peroxidase, Catalase Non-specific reduction system Glutathione, Vitamin C Protection against lipid peroxidation Glutathione peroxidase, Vitamin E,  -Carotene

28. Sequestration of metals Transferrin, Lactoferrin, Ferritin, Metallothionein Repair systems DNA repair enzymes, Macroxyproteinases, Glutathione transferase