病理生理学：第12章 缺血-再灌注损伤（英）

1、Ischemia InjuryIschemia-Reperfusion InjuryIschemia InjuryIschemia-Reperfusion InjuryIschemia-Reperfusion InjuryCoronary artery bypass grafting (CABG) surgery Coronary artery bypass grafting (CABG) surgery The surgery grafts a healthy artery or vein from another part of the body to the blocked corona

2、ry artery, and bypasses the blocked portion of the coronary artery. This new passage routes oxygen-rich blood around the blockage to the heart muscle. Ischemia is a restriction in blood supply, generally due to factors in the blood vessels.Ischemia-Reperfusion Injury is the cell and tissue damage ca

3、used when blood supply returns to the tissue after a period of ischemia or lack of oxygen. Ischemia-Reperfusion InjuryDefinitionIschemia-reperfusion injury can occurin many pathological conditions: Stroke Shock Organ transplantation Myocardial infarction Sudden reopening of the occluded vessel by th

4、rombolytic therapy. Sudden reopening of the occluded coronary artery by PTCANote: not all of the ischemia organs suffer from reperfusion injury.Factors that influent the occurrence of ischemia-reperfusion (I-R) injury1.Duration of ischemia In general, longer for ischemia, more chance to develop the

5、I-R injury. However, if ischemia sustains for too long and causes necrosis of the cells, the chance of the I-R injury decreases.2. Dependency on oxygen supply Some organs, i.e. heart and brain, demand higher oxygen supply, which may, in turn, create reactive oxygen species (ROS) and causes I-R injur

6、y. Factors that influence the occurrence of ischemia-reperfusion (I-R) injury3. The condition of reperfusionbetterworseReperfusion speed gradual rapidTemperaturelowerhigherpHlowerhigherCa2+lowerhigherNa+lowerhigherK+higherlowerMg2+higherlower Mechanisms of ischemia-reperfusion injury1. Free radical-

7、caused injury2. Calcium overload3. Endothelial injury and neutrophil activationWhy reperfusion of an ischemic organor tissue causes injury?Mechanisms of ischemia-reperfusion injury1. Free radical-caused injury2. Calcium overload3. Endothelial injury and neutrophil activationWhy reperfusion of an isc

8、hemia organor tissue causes injury?Free radical-caused injury2. How are free radicals generated?1. What are free radicals?3. What alterations are caused by oxygen free radicals?What are free radicals?Free radicals are atoms or molecules with unpaired electrons in their outer orbital. The unpaired el

9、ectrons cause free radicals to be highly chemically reactive.Normal oxygen atomLoss of electronFree radicalFree radicals are generated in small amounts during the normal metabolism of cells, andare inactivated by endogenous scavenging systems.Oxygen free radicalsFree radicals derived originally from

10、 oxygen are called oxygen free radicals.Reactive oxygen species (ROS)ROS are chemically reactive molecules containing oxygen. 1Free radicals, Oxygen free radicals, and Reactive oxygen species (ROS) Free radicalsGeneration of free radicals1. Mitochondria pathway2. Xanthine oxidase pathway3. Neutrophi

11、l pathway (NADPH Oxidase) How are free radicals generated? Generation of free radicals1. Mitochondria pathway2. Xanthine oxidase pathway3. Neutrophil pathway (NADPH Oxidase) How are free radicals generated? 95% - 98% of O2 in mitochondria is reducedto water: O2 + 4e- + 4H+ H2O Tetravalent reduction2

12、% - 5% of O2 in mitochondria is reduced via univalent pathway to produce free radicals: O2 + e- O2 Univalent reduction.superoxideUnivalent reductionO2 + e- O2 Univalent reduction.Generation of hydroxyl radicalFerric Ferrous Fenton s reaction-2O2 + 2H+ H2O2 + O2.Superoxide dismutase-Generation of oxy

13、gen radicals usually peaks within 5 minutes after reperfusion. Reperfusion1orChanges inmitochondria membranefluidity and rigidity(Triggering ROS)Electron transport inhibitedElectrons are passed to O2Burst of ROS formationGeneration of free radicals1. Mitochondria pathway2. Xanthine oxidase pathway3.

14、 Neutrophil pathway (NADPH Oxidase) How are free radicals generated? Adenosine triphosphate (ATP) Adenosine Adenosine monophosphate (AMP) Adenosine diphosphate (ADP) Hypoxanthine Xanthine oxidase (XO) Xanthine uric acid IschemiaXanthine oxidase pathwayATP ADP AMPAdenosine Hypoxanthine Cytosol Ca2+ C

15、a2+-dependentProteases activation Xanthine oxidase Xanthine dehydrogenase Xanthine + uric acid + Ischemia phaseReperfusion phaseO2O2O2Generation of free radicals1. Mitochondria pathway2. Xanthine oxidase pathway3. Neutrophil pathway (NADPH Oxidase) How are free radicals generated? The NADPH oxidase

16、(nicotinamide adenine dinucleotide phosphate-oxidase) is a membrane-bound enzyme complex.NADPH oxidase Under normal circumstances, the complex is inactive in neutrophils. Once the neutrophilsare stimulated, NADPH oxidase is assembledand activated. Generation of free radicals1. Mitochondria pathway2.

17、 Xanthine oxidase pathway3. Neutrophil pathway (NADPH Oxidase) How are free radicals generated? Respiratory burst (or oxygen burst) Is the rapid release of ROS from the cells, especially, from neutrophils. Respiratory burst plays an important role in the immune system. It is a crucial reaction that

18、occurs in phagocytes to degrade internalized particles and bacteria. Oxidative stress Is defined as an imbalance between pro-oxidants and antioxidants and in favor of the former, resulting in cellular damages. Two concepts:What alterations are caused by oxygen free radicals?1. Membrane lipid peroxid

19、ation2. Inhibition of protein function3. DNA disruption and chromosome aberration4. Alteration of biochemical factorsWhat alterations are caused by oxygen free radicals?1. Membrane lipid peroxidation2. Inhibition of protein function3. DNA disruption and chromosome aberration4. Alteration of biochemi

20、cal factorsMembrane lipid peroxidationLipid peroxidation refers to the oxidative degradation of lipids. It is the process in which free radicals steal electrons from the lipids in cell membrane. Lipid peroxidation is proceeded by a free radical chain reaction. It most often affects polyunsaturated f

21、atty acids. polyunsaturated fatty acids are fatty acids in which more than one carboncarbon double bond exists within the molecule.Linoleic acid Membrane lipid peroxidation free radical chain reaction(LH)(L. & secondary L .)(free radical R.)(LOO.)(LOOH)Membrane lipid peroxidationAlters membrane

22、fluidity and permeabilityDestroys transmembrane ion gradientsDamagesmembraneembedded enzymeAlters cellfunctionInhibits acylation of phospholipidsInterferesmembranerepairingDestroy membraneCell deathAcylation is the process of adding an acyl group to a compound. Acylationacyl groupWhat alterations ar

23、e caused by oxygen free radicals?1. Membrane lipid peroxidation2. Inhibition of protein function3. DNA disruption and chromosome aberration4. Alteration of biochemical factorsInhibition of protein functionOxidation of two thiol groups to form disulfide bond 1. Direct effect Breakage or formation of

24、new disulfide bonds changesprotein tertiary structure,and therefore changesprotein function. Protein structureSecondary structure(alpha helix or beta sheet)Tertiary structure(three-dimensional)Quaternary structure(complex of protein molecules)Primary structure(amino acid sequence)SSdisulfide bondsIn

25、hibition of protein function1. Direct effect2. Indirect effect Membrane lipid peroxidationDamages membraneembedded enzyme and receptorWhat alterations are caused by oxygen free radicals?1. Membrane lipid peroxidation2. Inhibition of protein function3. DNA disruption and chromosome aberration4. Alter

26、ation of biochemical factorsDNA disruption and chromosome aberrationDNA oxidation is the process of oxidative damage on deoxyribonucleic acid. It mostly occurs at guanine residues due to the high oxidation potential of this base relative to other bases. 80% of DNA oxidation is mediated by hydroxyl r

27、adical.DNA oxidation can cause DNA disruption and chromosome aberration.What alterations are caused by oxygen free radicals?1. Membrane lipid peroxidation2. Inhibition of protein function3. DNA disruption and chromosome aberration4. Alteration of biochemical factorsAlteration of biochemical factors1

28、. Superoxide impairs NO formation;2. Hydrogen peroxide induces neutrophil- endothelial cell adhesion;3. Free radicals induce tissue factor synthesis and release. 4. Free radicals promote inflammatory factors expression and release. SummaryFree radical-caused injury2. How are free radicals generated?

29、 1) Mitochondria pathway2) Xanthine oxidase pathway3) Neutrophil pathway 1. What are free radicals, oxygen free radicals, and ROS? What is respiratory burst (or oxygen burst)? What is oxidative stress? 3. What alterations are caused by oxygen free radicals?1) Membrane lipid peroxidation2) Inhibition

30、 of protein function3) DNA disruption and chromosome aberration4) Alteration of biochemical factorsMechanisms of ischemia-reperfusion injury1.Free radical-caused injury2.Calcium overload3.Endothelial injury and neutrophil activationMechanisms of ischemia-reperfusion injury1.Free radical-caused injur

31、y2.Calcium overload3.Endothelial injury and neutrophil activationWhat is Calcium Overload?Calcium overload refers to a significant increase in intracellular calcium and resulted impairment of cellular structure and function. Normally, extracellular Ca2+ is 10,000-foldhigher than intracellular Ca2+.

32、Extracellular Ca2+Intracellular Ca2+100 nM1 mM= Ca2+How is a huge difference between extracellular and intracellular Ca2+ maintained?1. Intact cell membrane2. Ca2+ is removed from cell by Na+/Ca2+ exchanger (NCX)3. Ca2+ is removed from cell by plasma membrane Ca2+ ATPase (PMCA) 4. Ca2+ is uptaken by

33、 sarcoplasmic reticulum and endoplasmic reticulum through sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) 5. Ca2+ binds with other molecules to form complex, and thus reduces free Ca2+.Calcium-bindingproteinCa2+ 0.1 MEndoplasmic reticulumNCXPMCACa2+ 1 mMHow does calcium overload occur?1. Disorder of

34、 Na+/Ca2+ exchanger2. Defects in membrane permeability Mechanism of calcium overloadCalcium-bindingproteinCa2+ 0.1 MEndoplasmic reticulumNCXPMCACa2+ 1 mMDisorder of Na+/Ca2+ exchanger1. Intracellular Na+ increaseNa+/K+-ATPaseNa+/Ca2+ exchangerNa+K+Na+Ca2+I/RATPXForward modeDisorder of Na+/Ca2+ excha

35、nger1. Intracellular Na+ increaseNa+/K+-ATPaseNa+/Ca2+ exchangerNa+K+Na+Ca2+I/RATPXNa+Na+Na+Na+Reverse modeDisorder of Na+/Ca2+ exchanger1. Intracellular Na+ increaseNa+/K+-ATPaseNa+/Ca2+ exchangerNa+K+Na+Ca2+I/RATPXReverse modeCa2+Ca2+Ca2+Ca2+Ca2+Disorder of Na+/Ca2+ exchanger2. Intracellular H+ in

36、creaseNa+/H+exchangerNa+/Ca2+ exchangerH+Na+Ca2+Forward modeI/RIntracellularacidosisH+H+Disorder of Na+/Ca2+ exchanger2. Intracellular H+ increaseNa+/H+exchangerNa+/Ca2+ exchangerNa+H+Na+Ca2+Forward modeI/RIntracellularacidosisH+H+Na+Na+Disorder of Na+/Ca2+ exchanger2. Intracellular H+ increaseNa+/H

37、+exchangerNa+/Ca2+ exchangerNa+H+Na+Ca2+I/RIntracellularacidosisH+H+Reverse modeCa2+Ca2+Ca2+Ca2+Ca2+3. Activation of Na+/H+ exchanger by protein kinase C Disorder of Na+/Ca2+ exchangerG proteinGqa ag gb bGPCRGDPGTPPLCb b(a1(a1-adrenergic receptor) PIP2IP3receptorEndoplasmicreticulumCa+Disorder of Na

38、+/Ca2+ exchanger caused by PKC(Page 146)G proteing gb bGPCRGqa aGTP(a1(a1-adrenergic receptor) PLCb bPIP2IP3receptorEndoplasmicreticulumCa+Disorder of Na+/Ca2+ exchanger caused by PKC(Page 146)G proteing gb bGPCRGqa aGTP(a1(a1-adrenergic receptor) PLCb bIP3receptorIP3DAGEndoplasmicreticulumCa+Disord

39、er of Na+/Ca2+ exchanger caused by PKC(Page 146)G proteing gb bGPCR(a1(a1-adrenergic receptor) PLCb bprotein kinase CEndoplasmicreticulumCa+IP3receptorGqa aGTPDisorder of Na+/Ca2+ exchanger caused by PKC(Page 146)G proteing gb bGPCR(a1(a1-adrenergic receptor) PLCb bProtein kinase CEndoplasmicreticul

40、umCa+IP3receptorGqa aGTPDAGNa+/H+exchangerNa+H+Na+Na+Na+Ca2Na+/Ca2+ exchangerCa2Ca2Ca2Ca2Disorder of Na+/Ca2+ exchanger caused by PKCHow does calcium overload occur?1. Disorder of Na+/Ca2+ exchanger2. Defects in membrane permeability Mechanism of calcium overload2. Defects in membrane permeability2.

41、 Defects in membrane permeabilitySummary1.Disorder of Na+/Ca2+ exchanger1) ATP intracellular Na+ increase2) Intracellular acidosis H+i Na+i 3) catcholamine a a1 receptor PKC Na+/H+ exchanger Na+i Mechanism of calcium overload2. Defects in membrane permeability Na+/Ca2+ Exchangerruns in reverse modeA

42、lterations induced by calcium overload1. Activation of Ca2+-dependent enzymes1. ATPases ATP2. Phospholipases membrane damage3. Proteases break down membrane & protein4. Endonucleases chromatin fragmentation CytosolCa2+2. Mitochondria dysfunctionCa2+i interrupts oxidative phosphorylation in mitoc

43、hondria ATP productionIschemiaXanthine oxidase pathwayATP ADP AMPAdenosine Hypoxanthine Cytosol Ca2+ Ca2+-dependentProteases activation Xanthine oxidase Xanthine dehydrogenase Xanthine + uric acid + Ischemia phaseReperfusion phaseO2O2O2Mechanisms of ischemia-reperfusion injury1.Free radical-caused i

44、njury2.Calcium overload3.Endothelial injury and neutrophil activation EndotheliumArteryVeinCapillary bedEndothelial injury and neutrophil activationNeutrophil activationEndothelial injurycausemanifestationPlugcapillariesAdhere &activate EC ReleaseROS,Proteolytic Enzymes,Inflammatory mediatorsEnd

45、othelium1. Impaired endothelium- dependent dilation in arteriole 2. Enhanced fluid filtration3. Neutrophil plugging in capillaries4. Protein & neutrophil extravasation Endothelium1. Impaired endothelium- dependent dilation in arteriole 2. Enhanced fluid filtration3. Neutrophil plugging in capill

46、aries4. Protein & neutrophil extravasation XXX No-reflow phenomenon is the failure of blood to reperfuse an ischemic area after the physical obstruction has been removed. Mechanisms of ischemia-reperfusion injury1.Free radical-caused injury2.Calcium overload3.Endothelial injury and neutrophil ac

47、tivationAlterations of function and metabolismduring I/R injury1.Myocardial I-R injury2.Cerebral I-R injury3.Hepatic I-R injury4.Renal I-R injury2. Alterations induced by oxygen free radicals3. Alterations induced by calcium overloadAlterations induced by oxygen free radicals1. Membrane lipid peroxi

48、dation2. Inhibition of protein function3. DNA disruption and chromosome aberration4. Alteration of biochemical factors2. Alterations induced by oxygen free radicals3. Alterations induced by calcium overloadAlterations induced by calcium overload1. Activation of Ca2+-dependent enzymes:ATP , membrane

49、damage, protein break down,and chromatin fragmentation 2. Mitochondria dysfunction ATP3. Xanthine oxidase pathway activation ROS2. Alterations induced by oxygen free radicals3. Alterations induced by calcium overloadEndothelium1. Impaired endothelium- dependent dilation in arteriole 2. Enhanced flui

50、d filtration3. Neutrophil plugging in capillaries4. Protein & neutrophil extravasation XXX2. Alterations induced by oxygen free radicals3. Alterations induced by calcium overloadMyocardial I-R injuryHeart weight / body weight = 0.3%Heart O2 consumption / body O2 consumption = 7%1. High metabolis

51、m and energy2. Normal rhythm3. Normal contractilityI-R:O2 , ATPArrhythmiasMyocardial stunning & hypercontractureReperfusion ArrhythmiasVentricular tachycardia and fibrillationNormal sinus rhythmMyocardial I-R injuryVentricular tachycardia and fibrillation1. Ionic channels dysfunction arrhythmias

52、 Reperfusion ArrhythmiasMyocardial I-R injuryVentricular tachycardia and fibrillation1. Ionic channels dysfunction arrhythmias Reperfusion ArrhythmiasMyocardial I-R injury2. Reduction of conduction velocity 3. Heterogeneity of myocardial responsesMyocardial stunning & hypercontractureMyocardial I-R injuryMyocardial stunning is the reversible reduction of heart contraction after reperfusion.Low ATP production, ROS release, Ca