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Ischemia-Reperfusion Injury
(IRI)
Department of Pathophysiology
Shanghai Jiao-Tong University School of Medicine
What is ischemia-reperfusion injury?
In majority situations, blood reperfusion can
reduce ischemia-induced tissue and organ injury,
resulting in the structural and functional recovery.
In some circumstances, however, blood
reperfusion may induce or aggravate the further
reversible even irreversible cell damage and
tissue or organ injury, especially for a prolonged
ischemia. This phenomenon has been termed
IRI.
CHAPTER 1
Etiology and Factors
• Etiology
• Influencing factors
Etiology
 Recovery of blood supplementation following ischemia
 Microcirculation revascularization during shock treatment
 Coronary artery convulsion relief
 Application of new medical technologies
PTCA, Thrombolytic therapy
 Cardiac bypass surgery
 Cardiopulmonary resuscitation in sudden arrest of heart beat
 Others: organ transplantation
Factors
 Duration of ischemia
 Collateral circulation formation
 Dependency on oxygen supply
 Condition of reperfusion
 The speed of reperfusion
 The components of reperfusion solution
Experimental study showed
 Calcium paradox
 Oxygen paradox
 PH paradox
CHAPTER 2
The pathogenesis of IRI
•The increase of free radicals
•Intracellular calcium overload
•Neutrophil activation
Free radicals
Conception and properties
■
Free radicals are a highly reactive group of atoms,
molecules or radicals, which carry unpaired electron in out
orbital. The properties of these radicals are as following:
short life time and powerful oxidative ability.
■
Classification
 Oxygen free radicals (OFR)
 Nitrogen free radicals (NFR)
 Lipid free radicals (LFR)
 Others: chlorine radicals (Cl.), methyl radicals (CH3.)
●Oxygen
free radicals (OFR)
OFR is referred to oxygen-derived free radicals.
▲ 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.
Free radical ROS
ROS
Non free radical ROS
OFR
（O .、OH•）
2
H2O2、 1O2
Nitrogen free radicals (NFR)
NFR is defined as nitrogen-derived free radicals
(also identified as reactive nitrogen species, RNS).
RNS
NO•
ONOO , NO2
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•
LFR
LO•
LOO•
Metabolism of the free radicals
■
● Production
O2 e
O2
3e
3H+
of oxygen free radical
Oˉ2·
OH· + H2O
O2
O2
2e
2H+
4e
4H+
H2O2
2H2O
▲ Sources

of O2·
e
O2
autoxidation
▲Sources
-
Mitochondria
Enzyme
oxidation
poison
O2·
ionic
irradiation
of OH•
O2· + H2O2
Fe2+
O2 + OH• + OH+
H2O homolysis OH• + H• ； H2O heterolysis H+ + OH‒
Scavenge the free radical
▲Enzymes
-.
superoxide dismutase (SOD)
2O2 + 2H+
catalase (CAT)
2H2O2
CAT
SOD
H2O2 + O2
2H2O + O2
gluthione peroxidase (GSH-Px) H2O2 + 2GSHGSH-Px 2H2O + O2
▲Non-enzyme
substances
vitamin-E, -A, and -C; cysteine; glutathione; albumin;
allopurinol; ceruloplasmin
■
Mechanisms of free radical increase
The increase of xanthine oxidase (XO) formation in VEC
ischemia
ATP↓
calcium overload
calcium-dependent proteases↑
Neutrophil respiratory burst
IRI induces the activation of complement and endothelial
cells and the increase of chemokine such as C3a and
leukotriene, which further attract and activate neutrophils.
This activation of neutrophils then intakes large amounts of
molecular oxygen and produce OFR by respiratory burst.
The increase of one electron deoxidization in mitochondria
O2
O2
O2
e-
95%O2
Cytochrome C oxidases
4e-
2%O2 respiratory chain enzyme↓
Transferring the electrons↓
95%O2 respiratory chain enzyme↓
4e-
╳
H2O
【Normal】
OFR 【ischemia】
H2O↓ 【reperfusion】
The increase of catecholamine and its oxidazition
ischemia and hypoxia
sympathetic-adrenal
medulla ()
CA release
monoamine oxidase
vanilmandelic acid (normal)
OFR
adrenochrome
■
Mechanisms of free radical-induced IRI
OFR are extremely reactive to interact with
lipids, proteins and nucleic acids.
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.
▲ Membrane
structural damage
MIP leads to the abnormal state of membrane nonsaturation, 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.
Intracellular calcium overload
Protein denaturalization and decreased enzyme activity
Nucleic acid damage and chromosome aberration
Others:
Mediation of a series of reaction important for IRI, such
as releasing inflammatory factors; decreasing nitric oxide;
promoting the expression of adhesion molecules and the
adherence between neutrophils and vessels.
Calcium 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 Na+/Ca2+ exchange
▲ Na+/Ca2+
exchange protein
▲ Na+/H+
exchange protein
▲ Protein
kinase C (PKC)
Membrane 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 injury
CA increase
■
Mechanisms of calcium overload-induced IRI
Promotion of OFR generation
Aggravation of acidosis
Damage of cellular membrane
Mitochondrial dysfunctions
Activation of other enzymes (proteinases, nucleases)
Neutrophil activation
It has been manifested that the capillary
damage and dysfunction which mediated by
neutrophil activation play an important role in
IRI.
■
Leukecyte accumulation induced by IRI
Inflammatory 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.
Cell adhesion molecule (CAM) increase
Activated neutrophils can increase the expression
of CAMs, which including the selectins, integrins
(CD11/CD18) and immunoglobulin superfamily (ICAM1, VCAM-1).
■
Mechanism of leukecyte-mediated IRI
Microvascular damage
microvessel hemorheological alteration
-No-reflow phenomenon
The ischemia region could not be reperfused
sufficiently after relieving the occlusion to recover
the blood flow.
Abnormal regulation of inflammatory reactions
Machinery blockage action
CHAPTER 3
The alterations of function and metabolism
induced by IRI
•The alteration of IRI in heart
•The alteration of IRI in brain
•The alteration of IRI in other organs
Myocardial IRI
The major IRI in heart includes arrhythmia,
reversible contractile dysfunction, alterations of
myocardium untrastructure and metabolism.
■
Lower myocardial diastolic & contractility function
●Myocardium
stunning
Myocardium stunning is termed that cardiac contractile
function is impaired temporarily but reversibly for a period
of hours to days after ischemia-reperfusion.
▲A
form of IRI to reversible loss of myocardial contractility
▲Its
mechanism is associated with OFR and Ca2+ overload
■
Reperfusion arrhythmia
Ventricular tachycardia and fibrillation are the
major manifestation of reperfusion arrhythmias.
● The
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 arrhythmia
▲OFR
and calcium disturbance
▲Sodium and potassium homeostasis
▲The ununiformity of action potential duration (APD)
■
Alterations of myocardium metabolism
● Decreased
generation of ATP and CP
● Mitochondrial
■
functional loss
Alterations of myocardium ultrastructure
● Cellular
●
membrane damage
Mitochondria swelling
Cristae fragmentation and solution
● Myofibrils
break down and contractile bands occur
Cerebral 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 metabolism
●Enhancing
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 metabolism
●Stimulant
amino acid decrease
▲Glutamic
▲Aspartic
acid
acid
●Repressive
amino acid increase
▲Alanine
▲-Aminobutyric
acid
▲Taurine
▲Glycine
■
The alteration of cerebral histology
▲Cerebral
edema
▲Cerebral
cellular necrosis
IRI 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 4
Pathophysiological basis of prevention
and treatment for IRI
•Control the reperfusion conditions
•Scavenge the free radicals
•Relieve calcium overload
•Improve the metabolism
Control the reperfusion conditions
■
Shorten the ischemia period
■
Improve the reperfusion conditions
●Lower
pressure
●Lower flow speed
●Lower temperature
●Lower pH
●Lower concentration of calcium and sodium
Scavenge the free radicals
■
Enzymes
■
Non-enzyme substances
Relieve calcium overload
■
Calcium antagonists
Calcium channel blockers
■
Improve the metabolism
■
Energy supplementation
Cell 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.