Chapter 10
Ischemia-reperfusion
injury (IRI)
Yuxia Zhang
Department of Pathophysiology, Anhui Medical University
Contents
 Concepts: IRI, oxygen/calcium/pH paradox
 Causes and conditions of IRI
 Mechanisms of IRI injury
 Metabolic and functional alterations
 Prevention and treatment principle
Introduction
• at 1960，Jenning:MI/R I
• 1968, brain；1972, kindey；1978, lung；1981,
intestinal；and so on
• Clinical phenomenon: bypass surgery,shock
treatment,organ transplantation, thrombolysis,
recovery of hearts after ischemic arrest，
Percutanueous Transluminal Coronary Angioplasty
(PTCA)
• I/R I is a common phenomenon
•
paradoxical phenomenon
1.Concept
IRI
the reestablishment of blood flow
after prolonged ischemia aggravates
the tissue damage.
pH paradox
ischemia
acidosis , disorder of
function and metbolism on cell severe
IRI
pH paradox
calcium paradox
pre-perfuse rat heart with no calcium
perfusion for 2min
perfuse
calcium perfusion, cell release enzyme
myofibril over-constract, electron signals
abnormal，
calcium paradox
Oxygen paradox
Hypoxia liquid perfuse organ or culture
without oxygen
injury
restore perfusion
severe injury
2. Cause of ischemia-reperfusion
injury and affecting factor
Recover from cardiac arrest
（1）cause Organ transplantation
Lysing thrombi
（2）Affecting
factor
small animals
Duration of
ischemia
big animals
5-10min: arrhythmia
20-30min: ventricular
tremor
20-40min: reversible injury
40-60min:irreversible injury
diversity between small and big animal
Branch circulation：chronic
O2 consumption rate
condition of
reperfusion
T, pressure,pH,Na+,Ca2+
[K+ ], [Mg2+]
T, pressure,Na+,Ca2+
protection
damage
3. Mechanisms of IRI
• role of oxygen free radical
• calcium overload
• role of leukocyte
(1)Role of oxygen free radical
concept and classification of free radical
Free radical: Any atom or molecule possessing unpaired electrons
Oxygen free
radicals(OFR)
Free radicals Lipid peroxide
radical ˉ
Others
:
Superoxide anion (O2.-),
Hydroxyl radical (OH.)
: L LO LOO
oxide (NO )Peroxynitrite（ONOO )
: Nitric
Cl 、CH 、NO
Reactive oxygen species (ROS)
•
•
•
.
•
:
-
•
3
O2•
OH•
1O
2
H2O2
 formation of oxygen free radical
nature oxidation of Hb , Cyt C
O2
O ‾∙2
O ‾∙2
H2O2
OH∙
H2O
H2O
oxidation of enzyme :XO
normal: O2+4e+4H+→H2O+ATP
Mitochondria: abnormal :O +e→ O·- +e +2H+
2
2
→H202+e+H+→ OH· +e+H+
→H20
Production of OH·
SOD
O·-2+ O·-2+2H+
O·-2+H2O2
H2O2+O2
OH· + OH·+O2
Fenton Haber-Weiss：
SOD
O·-2
Fe2+
H2O2
Fe3+
OH· + OH-
Mechanism of increased OFR generation
Xanthine oxidase pathway：XO↑
normal： Endothelial cell，XO 10% ，XD 90%
ischemia
ATP
XD
Ca2+
ADP
XO
AMP
– 2 •+H2O2
xanthine+O
hypoxanthine
reperfusion
O2
Uric acid+O2 –• +H2O2
O2
OH•
The effects of leucocyte：respiratory burst
reperfusion：oxygen consumption of infiltrated
WBC:↑70-90% O2
NADPH +2O2
NADH+O2
NADPH oxidase
NADH oxidase
2O·-2 +NADP++H+
H2O2+NAD+ + 2H+
Disfunction of mitochondria
normal: O2+4e+4H+→H2O+ATP
abnormal :O2+e→ O·-2 +e +2H+→H202+e+H+
→OH· +e+H+→H20
catecholamine autooxidation
AD MAO
adsenale+ O·-2
Damage of oxygen-derived free radicals
membrane lipid peroxidation
cellular membrane
lipid peroxidation
permeability↑
fluidity↓
calcium
overload
lipid cross-linked
inhibition of
Na+-pump and
Ca 2+ -pump
[Ca2+] i
[Na+] i , [Ca2+] i
membrane lipid
peroxidation
phospholipase C
phospholipase D
damage of mitochondria
membrane
ATP
PGs , LTs
TXA2
inhibition of protein function
enzymes ：
channels:
destruction of nuclear acid
base hydroxylation 、
breakdown of DNA
HEALTHY CELL (left) | FREE RADICAL DAMAGE (right)
(2) Calcium overload
Concept
The abnormal increase of intracellular calcium
which causes cell injury
Metabolic pathway of [Ca2+]i
Ca 2+ pump in the cell membrane;

Na+-Ca2+ exchange pump in the cell membrane ;

Ca 2+ pump in the mito. membrane ;

Ca 2+ pump in endoplasmic reticulum

mechanism of calcium overload
Abnormal Na+-Ca2+ exchange
Reperfusion
Ischemia
3Na+
ATP↓
Na+↑ Ca2+
K+
Ca2+↑
Na+
direct activation：intracellular sodium↑
H+
Ischemia
H+↑
H +↑
K+
Na+
Ca2+↑
Na+↑
Na+
Ca2+
Reperfusion
H+↓
3Na+
indirect activation（1）：intracellular 【H+】↑
ischemia
NE
α1 – receptor
NE
SR
myofilament
indirect activation（2）：activation of PKC
catecholamine
β – receptor
[Ca2+] i
L Ca2+- channel
β
Cellular
membrane
2+
Ca
↑
injury of biomembrane
damage
of cellular membrane:
[Ca2+ ] ↑
Damage
of mitochondria and sarcoplasmic
Damage of
mitochondria
Damage of
Sarcopasmic
ATP
Ca
2+
- ATPase
calcium
overload
Pathogenesis of calcium overload
promote OFR formation：damege aggravation
Damage mitochondria：ATP ↓
Stimulating the phospholipase ：injury of
membrane cell and cell organ
mitochondrial dysfunction
(3) role of leukocyte
activation,margination and aggregation of
PMNs after reperfusion
adhesion
molecule ;
chemotatic
mediators
factor;
of inflammation
Role of Neutrophil
Reperfusion
Neutrophil activation
ROS
Inflammatory
mediators
Cell injury
Injury of
Micro-vessels
No-reflow phenomenon
3. Changes of function and metabolism
Ischemia-reperfusion injury of heart
Changes in cardiac function
 Decrease of myocardial contractility ：myocardial stunning
 Eperfusion arrhythmia
Changes in myocardial metabolism: ATP↓,
ADP↑, AMP↑
Changes in myocardial structure: cell edma，
contraction band，apoptosis
Heart Injury
Ischemia-reperfusion injury
Calcium overload
Ca++ K+ Na+
Arrhythmia
Free radical
Destroy of contractile protein
Myocardial stunning
Cell death
 Ischemia-reperfusion injury of brain
ATP
Na+-pump
cellular edema
Hypoxia of cells
cellular acidosis
Excitability transmitter
inhibitive transmitter
cAMP↑ cGMP↓
activate
free fatty acid↑
lipid peroxidation↑
Hisconstructure:Edema , necrosis
4. Principles of prevention and treatment
(1) restoring normal perfusion of tissue in time
low temperature;
low pressure;
low flow;
low natrium(sodium);
low pH;
low calcium
(2) improve the metabolism of the tissues
ATP; cytochrome C;
(3) sweep away free radical:
VitE: lose e
VitC:
FR (lipid)
FR
clear OH∙
β-cartenoids: clear
GSH
(water)
1O
2
enzyme scavenger：
2 O‾∙2 +2H+
SOD
CAT
H 2O + O 2
H2O2
H2O+ O2
(4) relieve of calcium overload
Ca2+ ion blok agent
5. CoQ
Inhibit L • (lipid free radical)
2L+ CoQ
2LH+ CoQ
protein enzyme inhibitor:
ulinastatin