Free Radical Injury by prof dr naseer ppt

lecture from robbin

1. Free Radical Injury

2. Free radicals are chemical species that have single unpaired electron in their outer orbit. Examples of pathological conditions due to free radical: Chemical and radiation injury Ischemic reperfusion injury Cellular aging Microbial killing by phagocytes

3. Free radicals usually attacks: Proteins , Lipids, Carbohydrate, Nucleic acids Characteristic of free radicals: they initiate autocatalytic reaction. Molecules with which they reacts are themselves converted into free radicals. They propagate chain damage reactive oxygen species are a type of oxygen derived free radicals.

4. Normally free radicals(ROS) are produced normally in all cells during mitochondrial respiration. Which are degraded by cellular defense system. So Ros are presents in low concentration and do not damage the cell. Oxidative stress: when production of ROS increase or scavenging system are ineffective leads to excess of free radicals  called Oxidative stress which play role in cell injury.

5. Cancer. Aging. some degenerative disease like Alzheimer. Ros also produced in large amount by neutrophil and macrophages for destroying microbes, dead tissue and other un wanted substances. Injury caused by free radicals often accompanies inflammatory reaction.

6. 1. Reduction oxidative reaction: During normal metabolic process normally O2 reduced by four electron to H2 to generate water molecule during this process small amount of physically reduced intermediate product are produced. These include : O2 ( one electron) H2O2 (two electron) OH (three electron) Generation of free radical

7. 2. Absorption of radiant energy: Ultraviolet rays , X-rays( ionizing radiation  can hydrolyze water into H and OH free radical. 3. Rapid burst of ROS: Produced in activated leukocytes during inflammation . uses NAPDPH oxidase for redox reaction – in addition in some xanthine oxidase generate O2. 4. Enzymatic metabolism of chemical drugs: Generate free radicals e.g. from CCL4 –> CCL3 are produced.

8. 5. Transition metals: As iron and copper donates or accept free electron during intracellular reactions and catalyze free radicals formations. As in Fenton reaction H202 + Fe (2+) Fe(3+)+OH+OH- As most of intracellular free iron in ferric(Fe3+) must be reduced to ferrous form for Fenton reaction  this reduction enhanced by O2. So O2 and iron co operate in oxidative cell damage.

9. 6. Nitric Oxide (NO): Important chemical meditator generalised by – Endothelial cells, macrophages, neuron. Act as free radical Can also be converted to reactions peroxynitrate(ONOO-)as well NO2 and NO3+

10. Three reactions relevant to cell injury Lipid peroxidation in membrane: Free radicals cause peroxidadtion of lipids in membrane . Lipids are attacked by O2 derivatives particularly off to double bond-- yields lipid peroxide as they are unstable and reactive so autocatalytic reaction ensues causes extensive membrane damage. Pathological effects of free radicals

11. 2. Oxidative modification of protein: Free radical promote oxidation of amino acids. Formation of protein – protein ion kafe (disulphide bond) and oxidation protein backbone. Oxidative modification: Damage the active site of enzyme. Disrupt the structural protein Enhance proteo somal degradation of unfolded protein. Raising havoc throughout cell.

12. Lesion in DNA: Free radical react with thymine in nuclear and mitochondrial DNA . Produced single and double strands breaks in DNA and then cross linking of DNA and formation of adduce implicated in Cell aging Malignant transformation

13. Removal of free radicals: Free radicals are there and unstable so decay spontaneous . Cells have developed – Non enzymatic & enzymatic mechanism to remove free radicals. Antioxidants: Either block the initiation of free radical formation or inactive them. Vitamin E,A and ascorbic acid and glutathione in cytoplasm act as auto oxidant. Transport protein like: Transferrin ,ferritin lacto ferritin and ceruplasmin – binds with iron and copper and minimizing free radical formation .

14. Scavenging system: Series of enzyme breakdown free radicals into H2O2, O2. Catalase: Present in peroxisomes decompose H2O2. 2. Superoxide dismutase(SOD) Convert O2 to H2O2 2O2+2H H2O2+O2 This group include magnese SOD localised in mitochondria and copper zinc SOD found in cytosol.

15. Glutathione peroxidase: Catalyse free radicals breakdown. H2O2+2GSH GSSG + 2H2O 2OH + 2GSHGSSG + 2H2O Ratio of oxidised glutathione GSSG to reduced glutathione GSH is important.

16. More cell injury and inflammation Chemical Toxic injury Chemical injury remained as frequent problem in clinical medicine is major limitation to drug therapy. Drugs are metabolised in liver so the organ is frequent target of drug toxicity . Toxic liver injury the most frequent reason for terminating the therapeutic use or development of a drug. Two general mechanism of chemical injury are: Direct Toxicity Cyanide poisoning Clinico pathological correlation of cell injury and Necrosis

17. Direct Toxicity: Mercury chloride poisoning --- mercury binds to sulphidial groups of cell membrane .protein causing increased membrane permeability and inhibition of ion transport. The poison cells that absorb, excrete or concentrate the chemicals so cells of GIT & Kidneys . Cyanide poisoning: Mitochondrial cytochrome oxidase is poisoned by Cyanide. It inhibits oxidation phosphorylation Cellular response to stress and toxic insult

18. Conversion to toxic metabolic : Most toxic chemicals are not biologically toxic