Ischemia-Reperfusion Injury - SACCM 8, SAER 158 Flashcards
Define free radicals
reactive atoms with one or more unpaired electrons
technically O2 has 2 free unpaired electrons in the outer shell - but not highly reactive becasue the unpaired electrons orbit in parallel around the oxygen atom
Describe the stages of oxygen reduction in health
95% in health reduced to water H2O
* O2 –> reduced to superoxide anion (O-2)
* superoxide dismutase (SOD) –> H2O2 (hydrogen peroxide) –> catalase/glutathione peroxidase –> 2 x H2O + O2
5% –> will undergo only partial reduction and cause odixative injuries
What is the name of the most cytotoxic reaction of the oxidative pathways?
Fenton/Haber-Weiss reaction
Describe the Fenton/Haber-Weiss reaction
Name explanation
* Fenton describes the reduction of Ferrous (Fe2+) ion back to Ferric (Fe3+) ion
* Haber-Weiss describes the whole process/net summary
Picture => see bottom is just the summary of the 2 equations on top
Ferric ion + superoxide ion –> Ferrous ion + + O2
Ferrous ion + hydrogen peroxide –> ferric ion + hydroxyl free radial + hydroxyl anion
net summary
superoxide + hydrogen peroxide –> O2 + hydroxy free radical + hydroxyl anion
Describe the myoloperoxidase reaction
Occurs in phagocytic vesicles of neutrophils - important for killing bacteria
H2O2 reacting with chloride –> hypochlorous acid (ROS)
Describe three functions of nitric oxide (NO) in health
vasodilator
platelet inhibitor
cell messanger
What is the most common reactive nitrogen species and how is it produced?
peroxynitrite (ONO-2)
NO + O2- (superoxide) –> ONO2-
Describe the steps happening during the ischemic phase of ischemia-reperfusion injury
- anaerobic metabolism –> H+ ion accumulation –> intracellular acidosis –> enzyme dysfunction + damage to regulatory membrane channel proteins
- ATP depletion –> dysfunction of ATP-dependent ion pumps –> influx of Na+, Ca++, Cl- and efflux of K+
- IC Na accumulation –> water influx –> cellular swelling
- cytoplasmic Ca++ accumulation –> faciliates ROS formation, initiates apoptosis and necrosis
- ATP degradation to adenosine –> inosine –> hypoxanthine
- Ca++ –> activates calpain –> converts xanthine dehydrogenase to xanthine oxidase
- xanthine oxidase requires O2, so xanthine oxidase and hypoxanthine accumulate
Describe the steps during the reperfusion phase of ischemia reperfusion injury
- xanthine oxidase and hypoxanthine accumulated –> O2 now available –> oxidases hypoxanthine to xanthine, then urate + superoxide anion
- superoxide anion (O2-) –> superoxide dismutase –> H2O2 (hydrogen peroxide)
- superoxide anion + nitric oxide (NO) –> peroxynitrite (ONO-2)
- if free iron present: Fenton/Haber-Weiss reaction –> hydroxyl free radial + hydroxyl anion
What are the two main radicals causing lipid peroxidation?
- peroxynitrite
- hydroxyl free radical
What type of lipids are the major target for lipid peroxidation?
polyunsaturated free fatty acids (PUFA)
What are the most susceptible amino acid residues to oxidative stress?
- cysteine and methionine
- oxidation of the sulfhydryl groups –> forms disulphide bridges –> inactivate a range of proteins –> impairment of cellular signaling and metabolism
Fill in the blanks
catalase + glutathione peroxidase
Fill in the blanks
What cofactors are needed for xanthine-oxidase to metabolize hypoxanthine to uric acid?
NAD+ and O2
Fill in the blanks
What are the 4 damaging effects peroxynitrite and hydroxyl radicals have?
- lipid peroxidation
- oxidative damage to DNA/RNA
- loss of membrane selective permeability
- protein degradation
What are the clinical consequences seen in patients with ischemia reperfusion injuries?
- hyperkalemia
- acidemia
- cardiac arrhythmias
- “no flow” phenomenom
- myocardial stunning
- central nervous system changes
- GI signs
- MODS
Describe the “no flow” phenomenon in ischemia reperfusion injury
diminished or absent blood flow despite resolution of the vascular occlusion
neutrophil adhering to the endothelium –> induces endothelial swelling, platelet adhesion, thrombus formation + further neutrophil recruitment
Describe the immunologic pathways of ischemia reperfusion injury
- NF-kappa-B activation –> increase in inflammatory mediators + adhesion molecules (especially intracellular adhesion molecule-1 and E-selectin)
- COX-2 activation –> proinflammatory prostaglandin formation + arachidonic acid + phospholipase A2 actrivation –> ROS
- cell death –> DAMPs –> stimulates TLRs
name 3 DAMPs released during cell death
cell-free DNA
histones
high mobility group box 1
Name 8 antioxidant molecules
- haptoglobin
- ferritin
- ceruloplasmin
- vitamin C/ascorbic acid
- glutathion
- vitamin E/alpha-tocopherol
- vitamin A/beta-carotene
- ubiquinol-10
how is arginine implicated in arterial thromboembolism formation?
low arginine levels –> increased platelet aggregation
What are 3 ways to identify ischemia reperfusion injury?
- measurement of reaction products, e.g., meondialdehyde (MDA) or isoprostanes
- measurement of low levels of endogenous antioxidants, e.g., glutathione or tocopherol
- measurement of biomarkers of injury, e.g., TNF-alpha, IL-1, IL-6, IL-8, transforming growth factor-beta, cell-free DNA
What are effects of lidocaine besides Na-channel antagonism?
- free radical scavenger (superoxide and hydroxyl radicals)
- antagonist of ATP-sensitive potassium channels
- inflammatory modulator
- inhibitor of granulocytes
Describe the evidence of lidocaine administration to reduce ischemia-reperfusion injury in dogs with GDV
- study administering lidocaine before surgery but after medical treatment (decrompression included) –> no benefit
- study administering lidocaine before decompression –> decreased incidence of AKI, cardiac arrhythmias, coag disorders and shortened hospitalization time
List 7 proposed treatments for ischemia-reperfusion injuries
- lidocaine
- N-acetylcysteine
- Ischemic preconditioning
- deferoxamine
- allopurinol
- cyclosporine
- remifentanil
How is NAC proposed to help in ischemia-reperfusion injury?
Glutathione precursor that can penetrate into cells –> replenishes IC glutathione concentrations
What is the mechanism of action of Deferoxamine in ischemia reperfusion injury?
Iron chelator
ischemia –> ferritin releases its bound Fe3+
superoxide + H2O2 –> mobilize iron from ferritin and heme
free iron –> Fenton/Haber-Weiss reaction
What is the mechanism of action of Allopurinol in ischemia-reperfusion injury?
Xanthine-oxidase inhibtor
How could cyclosporine help in ischemia-reperfusion injury?
calcineurin inhibitor
Calcineurin likely mediates Ca-trigger apoptosis in IRI
What are the co-factors needed to convert H2O2 to hydroxyl free radicals?
Fenton/Haber-Weiss reaction!
Fe2+ (Ferrous ion)
