Free Radicals: Injury induced by free radicals O2

(1) Free radical Free radical——atoms, molecules or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions. Oxygen free radical Lipid radical

(2) Oxygen free radical, OFR Types： the superoxide anion (O2-) the hydroxyl radical (OH ·) singlet oxygen (1O2 ) hydrogen peroxide (H2O2)

(3) Lipid free radicals： The interaction of oxygen free radicals with polyunsaturated fatty acids in the phospholipids of cell membrane leads to the formation of lipid free radicals. Types： Fatty acid radical (L·) Lipid peroxide（LOO·） (4) Others: Cl·, CH3·, NO· 氧化还原过程中产生的具有高活性的一系列中间产物

(5) Generation and elimination of oxygen free radicals 1) Origin of O·-2： a. Mitochondria b. Oxidation of some chemicals in body. c. Catalysis by enzymes d. Stimulation of cells with toxins

O2  SOD (6) Generation of OFR O2 + e Cytaa3 O2 + 3 e + 3H+ 2 H2O HO + H2O H2O2 Cytochrome aa3 2 H2O O2 + 4 e + 4H+ SOD, Superoxide dismutase

Haber-Weiss reaction (without Fe3 ) O2－ + H2O2 O2 + OH +OH  SLOW hydroxyl radical; ferrum

Fenton-Haber-Weiss reaction O2－ + H2O2 O2 + OH +OH  FAST

Cysteine, Vit C, glutathione (6) Elimination of oxygen free radicals 1）Small MW scavenging agents Dihydrocoenzyme II Cysteine, Vit C, glutathione Vit E、 Vit A

2）Enzymatic scavenging agents Catalase (CAT) Superoxide dismutase MnSOD CuZnSOD Peroxydase （H2O2）

(7) The mechanisms of increased generation of oxygen free radicals during ischemia-reperfusion

1) Mitochondria pathway Ca2+entering MT O2+e↑ Mn− SOD + O-2 Mn+ − SOD + O2 O-2↑ · Hypoxia Mn-SOD  Superoxide dismutase Pm O2 呼吸链受抑 NADH蓄积供电子

2) Xanthine oxidase pathway Xanthine oxidase (XO) 10% Xanthine dehydrogenase (XD) 90% Ca+2

Effect of XO on formation of OFR Ischemia: ATP comsumption↑ Hypoxanthine ↑ (1) Ca2+ overload→ activating protein kinase O2 Reperfusion: xanthine + O·-2+ H2O2 XD XO (2) Restoration of O2 supply O2 O·-2+ H2O2 +Uric acid Effect of XO on formation of OFR OH ·

H+ + O-2·+H2O2 3) Neutrophil pathway NADH(I) NADPH(II) + O2 Activating C3, LTB4 (Complement C3 Leukotriene B4 ) Hexose shunt activity↑ cellular respiration ↑ NADH oxidase NADH(I) NADPH(II) H+ + O-2·+H2O2  + O2 NADPH oxidase

4) Catecholamines  Adr Remove O-2· adrenochrome Methyl transferase vanillylmandelic acid (normal) monoamine oxidase Stress 80% O2 Remove O-2· adrenochrome

(8) Alterations induced by OFR 1) lipid peroxidation Alteration of membrane lipid Function inhibition of membrane proteins Enhance of arachidonic acid metabolism Blockage of ATP production in mitochondria membrane 4造成生物膜损害

2) Injury of chromosome and nuclear acid 80% induced by OH

Destructive effects of OFR: Attacking membrane structure such as mitochondria membrane  interfering with energy metabolism Attacking DNA  changing genetic information  cell death Initiating lipid peroxidation  increasing permeability of membrane and inducing destruction of membrane  cell death Destroying proteins  decreased enzyme activity  metabolic disorder