医学教学课件：Ischemia-Reperfusion Injury

1、Ischemia-Reperfusion Injury In 1955，Sewell et al., reported that ventricular fibrillation occurred in dogs when sudden return of blood flow to the coronary artery that was ligated Myocardial reperfusion injury was first postulated in 1960 by Jennings et al. in their description of the histologic fea

2、tures of reperfused ischemic canine myocardium. The injury of ischemic cardiac muscles was more severe after reperfusion than before. 1967，Bulkley and Hutchins found that reflow of blood induced necrosis of cardiac myocytes after coronary artery bypass graft surgery. 1981, Greenberg confirmed that r

3、eperfusion induced severe damage of the intestinal mucosal cells of cat after 3 hours of ischemia. Clinic:Clinic: Shock, DIC microcirculation reperfusion Coronary reperfusion、artery bypass graft Restoration of blood supply in reimplantation of limb, transplantation of organs. The restoration of bloo

4、d flow after transient ischemia may be associated with further reversible or irreversible cell damage, which is called ischemia-reperfusion injury or reperfusion injury. What is ischemia-reperfusion injury? In the definition of ischemia- reperfusion injury 3 3 Key points are:Key points are: Ischemia

5、 for a long time Reestablishment of blood flow More severe injury Characteristics of ischemia- reperfusion injury: 1. Reversible Irreversible injury 2. Having reported in heart, kidney, liver, lung, brain, intestine, skeletal muscles Calcium paradox Oxygen paradox pH paradox Etiology of ischemia-rep

6、erfusion injury Cause Ischemia followed by reperfusion Which factors are involved in reperfusion injury Generally speaking, 1. Duration of ischemia the longer period of ischemia, the more severe injury 2. Severity of ischemia the more grievous ischemia, the more severe injury 3. Speed of reperfusion

7、 the faster reperfusion of blood, the more severe injury 4. Ischemia preconditioning increasing tolerance to reperfusion injury Why are more severe injury induced by reestablishment of blood flow after ischemia? Vaso-endothelial edema ATP depletion decreased Na+-K+ pump function Na+ and water enteri

8、ng cell endothelial edema Vaso-endothelial damage WBC adherence OFR (Oxygen Free Radical) increase and NO decrease Microvascular obstruction Squeeze of the coronary arteries induced by ischemic myocardium and by interstitial edema of myocardium Adherence, Aggregation and Activation of WBC MICROVASCU

9、LAR DAMAGENO-Reflow Phenomenon Pathogenesis of ischemia- reperfusion injury 1. Injury of free radicals O2 (1) Free radical Free radicalatoms, molecules or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are like

10、ly to take part in chemical reactions. 1)Oxygen free radical 2)Lipid radical (2) Oxygen free radical, OFR Types： (1)the superoxide anion (O2-) (2)the hydroxyl radical (OH ) (3)singlet oxygen (1O2 ) (4)hydrogen peroxide (H2O2) (3) Lipid free radicals： The interaction of oxygen free radicals with poly

11、unsaturated fatty acids in the phospholipids of cell membrane leads to the formation of lipid free radicals. Types： 1) Fatty acid radical (L) 2) Lipid peroxide（LOO） (4) Others: Cl, CH3, NO (5) Generation and elimination of oxygen free radicals 1) Origin of O-2： a. Mitochondria b. Oxidation of some c

12、hemicals in body. c. Catalysis by enzymes d. Stimulation of cells with toxins (6) Generation of OFR O2 + e O2 O2+ 2e + 2H+ H2O2 H2O2 O2 + 3 e + 3H+HO + H2O O2 + 4 e + 4H+2 H2O Cytaa3 SOD SOD, Superoxide dismutase Cytochrome aa3 Haber-Weiss reaction (without Fe 3 ) O O2 2 + H + H2 2O O2 2 O O2 2 + OH

13、 + OH +OH +OH SLOW hydroxyl radical; ferrum Fenton-Haber-Weiss reaction Fe Fe 3 3 O O2 2 + H + H2 2O O2 2 O O2 2 + OH + OH +OH +OH FAST (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 Cata

14、lase (CAT) Peroxydase （H2O2） Superoxide dismutase MnSOD CuZnSOD (7) The mechanisms of increased generation of oxygen free radicals during ischemia-reperfusion 1) Mitochondria pathway1) Mitochondria pathway CaCa2+ 2+entering MT entering MT O O2 2+e+e nO-2 Hypoxia Mn-SOD Superoxide dismutase Mn SOD +

15、O-2 Mn+ SOD + O2 2) Xanthine oxidase pathway Xanthine oxidase (XO) 10% Xanthine dehydrogenase (XD) 90% Ca+2 Ischemia: ATP comsumption Hypoxanthine Reperfusion: (1) Ca2+ overload activating protein kinase XO (2) Restoration of O2 supply xanthine + O-2+ H2O2 O-2+ H2O2 +Uric acid O2 O2 XD OH Effect of

16、XO on formation of OFR 3) Neutrophil pathway NADH(I)NADH(I) NADPH(II)NADPH(II)+ O2 NADPH oxidase H+ + O-2+H2O2 NADH oxidase C3, LTB4 (Complement C3 Leukotriene B4 ) Activating neutrophil Hexose shunt activity cellular respiration 4) Catecholamines Adr Methyl transferase vanillylmandelic acid (normal

17、) Remove Stress 80% OStress 80% O2 2 adrenochrome O O- -2 2 monoamine oxidase (8) Alterations induced by OFR 1) lipid peroxidation a.Alteration of membrane lipid b.Function inhibition of membrane proteins c.Enhance of arachidonic acid metabolism d.Blockage of ATP production in mitochondria membrane

18、2) Injury of chromosome and nuclear acid 80% induced by OH 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

19、 membrane cell death Destroying proteins decreased enzyme activity metabolic disorder Destructive effects of OFR:Destructive effects of OFR: Calcium Overload Intracellular calcium concentration abnormally increases and leads to cell and tissue damages HowHow to maintain Intracellular calcium at norm

20、al level? Ca2+ Pump on cell membrance Na+ - Ca2+ exchage pump Ca2+ Pump on mitochondrial membrane Ca2+ Pump on endoplasmic reticulum 2. Calcium overload Na + -Ca 2+ exchanger Ca2+ Binding proteins Mt SR Ca 2+ Ca 2+ Ca2+pumpCa2+ channel Ca2+ (1) Mechanisms of calcium overload 1)Disorder of Na+ -Ca2+

21、exchange Intracellular Na+, H+, NE- 1R- PLC-PKC 2)Activation of Na+-H+ exchanger 3)Cellular membrane injury permeability, membrane phospholipid degradation, OFR 4)Injury of mitochondria 5)Catecholamines -R WhyWhy dose calcium overload occur during reperfusion v Depleted energe v Increased permeabili

22、ty of cellular membrance v Increased intracellular sodium (2) Alterations induced by calcium overload 1)Mitochondria functionATP production 2)Activation of membrane phosphatidasemembrane damage 3)Cardiac arrhythmia 4)OFR 5)Myofibril contracture, rupture, cell damage WhatWhat are effects of calcium o

23、verloadare effects of calcium overload v Damage mitochondria ATP production decrease v Cause myocardial injury contraction weakness v promote OFR formation damage aggravation 3. The Role of Leukocyte3. The Role of Leukocyte Blocking microvasculature in the region of reperfusion Adhering to microvasc

24、ular endothelium through interaction between L-selectin on surface of WBC and ICAM-1 (cell adhesion molecules) on surface of endothelium Damaging tissues and cells in the region of reperfusion through releasing arachidonic acid (AA) TXA2 (thromboxane A ), lysosomal enzymes etc. And producing OFR in

25、“respiratory burst”. Accumulation of WBC SELECTINS Progressive Activation INTEGRINS Capture Slow Rolling Firm Adhesion Transmigration Rolling Chemotactic factor Adhesion molecule) Vascular endothelial cells and neutrophil injury 1. Microvessel injury (1) no-reflow phenomenon (2) Change in blood flow

26、, diameter and permeability of vessel 2. Cell injury OFR, lysoome, cell factors Cell adhesion, accumulation, flow blockage vessel permeabilityedema No reflow Damaged endothelium NO decrease CAMs upregulation L-selectin ICAM-1 WBC ADHERENCE to ENDOTHELIUM Releasing OFR, TXA2, lysosomal enzymes Blocki

27、ng blood flow Damaging tissues and cell NO, nitric oxide; CAM, cell adhesion molecules; TXA2, thromboxane A2 OFR Ca overload endothelia- neutrophil ？ Alterations in metabolism and energy Ca overload is common way of irreversible death of cells Mechanisms of IRI Excess oxygen Neutrophil Free radicals

28、 infiltration ISCHEMIAREPERFUSION INJURY Microvascular damage Calcium overload Major mechanisms of ischemia- reperfusion injury Alterations of metabolism and function during ischemia- reperfusion injury Heart 1. Cardiac function-heart pump 2. Electrocardiogram-Reperfusion arrhythmia 3. Energy metabo

29、lism change in heart 4. Change in cardiac microstructure Brain 1. Alterations of brain metabolism (energy, acidosis, FFA, transmitters) cAMP / cGMP PL 2. Abnormal electroencephalogram (EEG) (Slow wave, excitatory transmitters inhibitory transmitters) 3. Alterations in brain structure (edema, necrosi

30、s) Ischemia-reperfusion injury in other organs (intestine, kidney, bone) Excess oxygen Neutrophil Free radicals infiltration ISCHEMIAREPERFUSION INJURY Microvascular damage Calcium overload Major mechanisms of ischemia- reperfusion injury 1.Vasomotor Responses OFR Calcium Overload WBC Damaged endothelium NO, PGI2 release TXA2, ET release VASOCONSTRICTION Aggravating injury OFR Calcium Overload WBC Damaged endothelium Vascular Sticking WBC Liable to form permeability platelets to endothelium thrombosis Edema Releasing OFR Blocking blood proteolytic enzymes flow