Ischemia-Reperfusion InjuryIschemia-Reperfusion Injury

(IRI)(IRI)

Department of PathophysiologyDepartment of Pathophysiology

Shanghai Jiao-Tong University School of MedicineShanghai Jiao-Tong University School of Medicine

What is ischemia-reperfusion injury?What is ischemia-reperfusion injury?

In majority situations, blood reperfusion can In majority situations, blood reperfusion can

reduce ischemia-induced tissue and organ injury, reduce ischemia-induced tissue and organ injury,

resulting in the structural and functional recovery. resulting in the structural and functional recovery.

In some circumstances, however, blood In some circumstances, however, blood

reperfusion may induce or aggravate the further reperfusion may induce or aggravate the further

reversible even irreversible cell damage and reversible even irreversible cell damage and

tissue or organ injury, especially for a prolonged tissue or organ injury, especially for a prolonged

ischemia. This phenomenon has been termed ischemia. This phenomenon has been termed

IRI.IRI.

CHAPTER 1CHAPTER 1

Etiology and FactorsEtiology and Factors

• InfluencingInfluencing factorsfactors

• EtiologyEtiology

EtiologyEtiology

Recovery of blood supplementation following ischemiaRecovery of blood supplementation following ischemia

Microcirculation revascularization during shock treatment Coronary artery convulsion relief

Application of new medical technologiesApplication of new medical technologies

PTCA, Thrombolytic therapy

Cardiac bypass surgeryCardiac bypass surgery

Cardiopulmonary resuscitationCardiopulmonary resuscitation in sudden arrest of heart beatin sudden arrest of heart beat

Others: organ transplantationOthers: organ transplantation

FactorsFactors

Duration of ischemia

Collateral circulation formation

Dependency on oxygen supply

Condition of reperfusion

The speed of reperfusion

The components of reperfusion solution

Experimental study showedExperimental study showed

Calcium paradox

Oxygen paradox

PH paradox

CHAPTER 2CHAPTER 2

The pathogenesis of IRIThe pathogenesis of IRI

•IntracellularIntracellular calcium overloadcalcium overload

•The increase of free radicalsThe increase of free radicals

•Neutrophil activationNeutrophil activation

■■Conception and properties

Free radicalsFree radicals

Free radicals are a highly reactive group of atoms, Free radicals are a highly reactive group of atoms,

molecules or radicals, which carry unpaired electron in out molecules or radicals, which carry unpaired electron in out

orbital. The properties of these radicals are as following: orbital. The properties of these radicals are as following:

short life time and powerful oxidative ability.short life time and powerful oxidative ability.

Oxygen free radicals (OFR)

Nitrogen free radicals (NFR)

Lipid free radicals (LFR)

Others: chlorine radicals (Cl.), methyl radicals (CH3.)

■■Classification

▲▲ Reactive oxygen species (ROS)

ROS are composed of oxygen-derived free radicals

(OFR), and non free radical substances such as hydrogen

peroxide and singlet oxygen.

H2O2 、 1O2Non free radical ROSNon free radical ROS

Free radical ROSFree radical ROSRO

S

OFROFR

（（ OO22 、、 OO

H•H•））

.

●Oxygen free radicals (OFR)

OFR is referred to oxygen-derived free radicals.

Nitrogen free radicals (NFR)(NFR)

NFR is defined as nitrogen-derived free radicals (also identified as reactive nitrogen species, RNS).

NONO••

ONOO , NOONOO , NO22

RNSRNS

Lipid free radicals (LFR) Lipid free radicals (LFR)

Lipid free radicals are referred to middle metabolic products resulting from the chain reaction of lipid peroxidation, which is produced by interaction of OFR and non-saturated fatty acid.

L•L•

LO•LO•

LOO•LOO•

LFRLFR

■■Metabolism of the free radicals

O2 O2̄·e

O2 OH· + H2O 3e3H+

2eO2 H2O2 2H+

4eO2 2H2O4H+

● Production of oxygen free radicalProduction of oxygen free radical

Sources of OH•OH• ▲▲

Fe2+ + HH22OO22 OO22 + OH• + OH + OH• + OH++·OO22

HH22O OH• + H• O OH• + H• ； ； HH22O HO H++ + OH + OH‒‒heterolysisheterolysishomolysishomolysis

▲▲ ·OO2 2

Sources of

autoxidationautoxidation Enzyme Enzyme oxidationoxidation

poison

O2

e-

MitochondriaMitochondriaO2

·

ionic ionic irradiationirradiation

Scavenge the free radicalScavenge the free radical

Enzymes

superoxide dismutase (SOD)

catalase (CAT)

gluthione peroxidase (GSH-Px)

▲▲

2O2 + 2H+ H2O2 + O2.- SOD

2H2O2 2H2O + O2

CAT

H2O2 + 2GSH 2H2O + O2GSH-Px

vitamin-E, -A, and -C; cysteine; glutathione; albumin; allopurinol; ceruloplasmin

Non-enzyme substances ▲▲

■ ■ Mechanisms of free radical increase

The increase of xanthine oxidase (XO) formation in VECThe increase of xanthine oxidase (XO) formation in VEC

ischemia ATP↓ calcium overload

calcium-dependent proteasescalcium-dependent proteases↑ ↑

Neutrophil respiratory burstNeutrophil respiratory burst

IRI induces the activation of complement and endothelial IRI induces the activation of complement and endothelial cells and the increase of chemokine such as cells and the increase of chemokine such as C3a and leukotriene, which further attract and activate neutrophils. This activa, which further attract and activate neutrophils. This activation of neutrophils then intakes large amounts of molecular oxtion of neutrophils then intakes large amounts of molecular oxygen and produce OFR by respiratory burst.ygen and produce OFR by respiratory burst.

The increase of one electron deoxidization in The increase of one electron deoxidization in mitochondriamitochondria

95%O95%O2 2 Cytochrome C oxidasesCytochrome C oxidases OO2 2 H H22O O

【【 NormalNormal 】】4e4e--

OO22 OFR OFR

【【 ischemiaischemia 】】

2%O2%O2 2 respiratory chain enzyme↓respiratory chain enzyme↓

4e4e--

95%O95%O2 2 respiratory chain enzyme↓respiratory chain enzyme↓OO2 2 HH22O↓ O↓ 【【 reperfusionreperfusion 】】

ee--

Transferring the electrons↓↓

╳

The increase of catecholamine and its oxidazitioThe increase of catecholamine and its oxidazitionn

sympathetic-adrenal medulla ()

vanilmandelic acid (normal)

monoamine oxidase

adrenochrome

ischemia and hypoxia

CA release

OFR

■ ■ Mechanisms of free radical-induced IRI

The increase of membrane lipid peroxidation (MIP)The increase of membrane lipid peroxidation (MIP)

OFR interacts with non-saturated fatty acids from membrane lipids and further induce lipid peroxidation reaction, which results in the structural alteration and dysfunction of membrane.

ROS induces oxidation of lips, proteins and nucleic acid.ROS induces oxidation of lips, proteins and nucleic acid.

OFR are extremely reactive to interact with lipids, proteins and nucleic acids.

Membrane structural damage

MIP leads to the abnormal state of membrane non-saturation, which results in the decreases of membrane fluidity and permeability.

▲▲

Membrane protein function inhibition

MIP induces the deactivation and malfunction of membrane receptors and ionic pumps, which produces the signal pathway blockage.

▲▲

Mitochondrial function damage

MIP induces mitochondrial dysfunction and further decreases ATP generation.

▲▲

Protein denaturalization and decreased enzyme activityProtein denaturalization and decreased enzyme activity

Nucleic acid damage and chromosome aberrationNucleic acid damage and chromosome aberration

Others: Others:

Mediation of a series of reaction important for IRI, such aMediation of a series of reaction important for IRI, such as releasing inflammatory factors; decreasing nitric oxide; pros releasing inflammatory factors; decreasing nitric oxide; promoting the expression of adhesion molecules and the adhermoting the expression of adhesion molecules and the adherence between neutrophils and vessels.ence between neutrophils and vessels.

Intracellular calcium overloadIntracellular calcium overload

Calcium overloadCalcium overload

The phenomenon of cellular structure damage and dysfunction caused by intracelluar calcium increasing abnormally is termed “calcium overload”.

■ ■ Mechanisms of IRI-induced calcium overload

Disorder of NaDisorder of Na++/Ca/Ca2+2+ exchange exchange

Na+/Ca2+ exchange protein▲▲

Na+/H+ exchange protein▲▲

Protein kinase C (PKC)▲▲

Membrane permeability damageMembrane permeability damage

The integrity and permeability of membrane is impaired during ischemia-reperfusion. These damages do not occur only in sarcoplasmic reticulum (SR) but also in mitochondria, lysosomes and other cellular membranes. Therefore, Ca2+ can flow into the cytoplasm through damaged membrane according to the gradient.

Mitochondrial injuryMitochondrial injury

CA increase CA increase

■ ■ Mechanisms of calcium overload-induced IRI

Promotion of OFR generationPromotion of OFR generation

Aggravation of acidosisAggravation of acidosis

Damage of cellular membraneDamage of cellular membrane

Mitochondrial dysfunctionsMitochondrial dysfunctions

Activation of other enzymes Activation of other enzymes (proteinases, nucleases)(proteinases, nucleases)

Neutrophil activationNeutrophil activation

It has been manifested that the capillary damage and dysfunction which mediated by neutrophil activation play an important role in IRI.

Cell adhesion molecule (CAM) increase

Activated neutrophils can increase the expression of CAMs, which including the selectins, integrins (CD11/CD18) and immunoglobulin superfamily (ICAM-1, VCAM-1).

■ ■ Leukecyte accumulation induced by IRI

Inflammatory factors or chemokines increaseInflammatory factors or chemokines increase

Activated neutrophils can adhere to endothelial cells or blood cells, then to release the inflammatory factors after margination and aggregation, such as TXA2, leukotrienes, prostaglandin and so on, to increase the permeability of endothelial cell monolayer.

■ ■ Mechanism of leukecyte-mediated IRI

Microvascular damageMicrovascular damage

The ischemia region could not be reperfused sufficiently after relieving the occlusion to recover the blood flow.

-No-reflow phenomenon

microvessel hemorheological alteration

Abnormal regulation of inflammatory reactionsAbnormal regulation of inflammatory reactions

Machinery blockage action

CHAPTER 3CHAPTER 3

The alterations of function and metabolism The alterations of function and metabolism induced by IRIinduced by IRI

•The alteration of IRI in brainThe alteration of IRI in brain

•The alteration of IRI in heartThe alteration of IRI in heart

•The alteration of IRI in other organsThe alteration of IRI in other organs

Myocardial IRIMyocardial IRI

The major IRI in heart includes arrhythmia, reversible contractile dysfunction, alterations of myocardium untrastructure and metabolism.

■■Lower myocardial diastolic & contractility functionLower myocardial diastolic & contractility function

●Myocardium stunningMyocardium stunning

▲▲A form of IRI to reversible loss of myocardial contractility

▲▲Its mechanism is associated with OFR and Ca2+ overload

Myocardium stunning is termed that cardiac contractile function is impaired temporarily but reversibly for a period of hours to days after ischemia-reperfusion.

■ ■ Reperfusion arrhythmiaReperfusion arrhythmia

Ventricular tachycardia and fibrillation are the Ventricular tachycardia and fibrillation are the major manifestation of reperfusion arrhythmias.major manifestation of reperfusion arrhythmias.

● The occurrence of reperfusion arrhythmiaThe occurrence of reperfusion arrhythmia

▲▲Ischemia period before reperfusion

▲▲Ischemia degree

▲▲The cardiac myocytes with recoverable capability existed

▲▲The speed of reperfusion blood

● The mechanism of reperfusion arrhythmiaThe mechanism of reperfusion arrhythmia▲▲OFR and calcium disturbance

▲▲Sodium and potassium homeostasis

▲▲The ununiformity of action potential duration (APD)

■ ■ Alterations of myocardium metabolism Alterations of myocardium metabolism

● Decreased generation of ATP and CPDecreased generation of ATP and CP

● Mitochondrial functional lossMitochondrial functional loss

■ ■ Alterations of myocardium ultrastructure Alterations of myocardium ultrastructure

● Cellular membrane damageCellular membrane damage

● Myofibrils break down and contractile bands occurMyofibrils break down and contractile bands occur

● Mitochondria swellingMitochondria swelling

Cristae fragmentation and solutionCristae fragmentation and solution

Cerebral IRICerebral IRI

Cerebral IRI includes cytotoxic edema and apoptosis or death of brain, which causes the manifestation of intracranial hypertension such as vomiting and coma.

■■The alteration of cerebral energy metabolismThe alteration of cerebral energy metabolism

●Enhancing lipid peroxidation reactionEnhancing lipid peroxidation reaction

During IRI, the accumulation of free fatty acids such as arachidonic acid and stearic acid as substrates produces OFR and peroxidative lipids by lipid peroxidation, due to the increased degradation of cerebral phospholipid.

■■The alteration of cerebral amino acid metabolismThe alteration of cerebral amino acid metabolism

●Stimulant amino acid decreaseStimulant amino acid decrease

●Repressive amino acid increaseRepressive amino acid increase

▲▲Glutamic acid

▲▲Aspartic acid

▲▲Alanine

▲▲-Aminobutyric acid

▲▲Taurine

▲▲Glycine

■■The alteration of cerebral histologyThe alteration of cerebral histology

▲▲Cerebral edema

▲▲Cerebral cellular necrosis

IRI in other organsIRI in other organs

The IRI also can occur in other organs besides heart and brain. For example, liver and kidney are the organs which studied extensively in IRI. It has been implicated in the pathogenesis of a variety of clinical conditions including trauma, hypovolemic and endotoxic shock, transplantation, etc.

CHAPTER 4CHAPTER 4

Pathophysiological basis of prevention anPathophysiological basis of prevention and treatment for IRId treatment for IRI

•Scavenge the free radicalsScavenge the free radicals

•Control the reperfusion conditionsControl the reperfusion conditions

•Relieve calcium overloadRelieve calcium overload

•Improve the metabolismImprove the metabolism

Control the reperfusion conditionsControl the reperfusion conditions

■■Shorten the ischemia periodShorten the ischemia period

●Lower pressureLower pressure

■■Improve the reperfusion conditionsImprove the reperfusion conditions

●Lower flow speedLower flow speed

●Lower temperatureLower temperature

●Lower pHLower pH●Lower concentration of calcium and sodiumLower concentration of calcium and sodium

Scavenge the free radicalsScavenge the free radicals

■■EnzymesEnzymes

■■Non-enzyme substancesNon-enzyme substances

Relieve calcium overloadRelieve calcium overload

■■Calcium antagonistsCalcium antagonists

■■Calcium channel blockersCalcium channel blockers

Improve the metabolismImprove the metabolism

■■Energy supplementationEnergy supplementation

■■Cell protector applicationCell protector application

Ischemic preconditioning (IPC)

IPC is defined as short period-ischemic stress can significantly led to the protection of tissue and organs with subsequent longer IRI, which is also an adaptive mechanism.