Role of free radicals in Ischemic reperfusion injury MCQs With Answer

Role of free radicals in Ischemic reperfusion injury MCQs With Answer — Introduction

Ischemia-reperfusion injury (I/R) occurs when blood flow returns to ischemic tissue, triggering an intense surge of free radicals and reactive oxygen species (ROS). Key sources include mitochondria, xanthine oxidase, NADPH oxidase and activated neutrophils that generate superoxide, hydrogen peroxide and hydroxyl radicals. Resulting oxidative stress causes lipid peroxidation, protein oxidation, DNA damage and mitochondrial permeability transition, promoting apoptosis and necrosis. Calcium overload, inflammation and reduced nitric oxide bioavailability amplify injury. Pharmacological approaches—antioxidants, xanthine oxidase inhibitors, iron chelators, SOD mimetics and thiol donors—are central to therapy. This focused review helps B. Pharm students link mechanisms to drug strategies. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which reactive oxygen species is produced first during the respiratory burst in ischemia-reperfusion?

• Hydroxyl radical (•OH)
• Hydrogen peroxide (H2O2)
• Superoxide anion (O2•−)
• Peroxynitrite (ONOO−)

Correct Answer: Superoxide anion (O2•−)

Q2. Which enzyme converts xanthine dehydrogenase to xanthine oxidase during ischemia, increasing ROS on reperfusion?

• Superoxide dismutase
• Proteolytic cleavage by calcium-activated proteases
• Cyclooxygenase
• Catalase

Correct Answer: Proteolytic cleavage by calcium-activated proteases

Q3. Which free radical formation mechanism involves iron and hydrogen peroxide producing the highly reactive hydroxyl radical?

• Fenton reaction
• Haber-Weiss antioxidant cycle
• Nitrosation
• Glutathione peroxidation

Correct Answer: Fenton reaction

Q4. Which biomarker is commonly measured as an index of lipid peroxidation following I/R injury?

• 8-OHdG (8-hydroxy-2′-deoxyguanosine)
• MDA (malondialdehyde)
• CRP (C-reactive protein)
• CK-MB (creatine kinase-MB)

Correct Answer: MDA (malondialdehyde)

Q5. Which antioxidant enzyme catalyzes dismutation of superoxide to hydrogen peroxide?

• Glutathione peroxidase
• Catalase
• Superoxide dismutase (SOD)
• NADPH oxidase

Correct Answer: Superoxide dismutase (SOD)

Q6. Glutathione peroxidase protects cells by reducing hydrogen peroxide using which cofactor?

• Glutathione (GSH)
• Vitamin C
• Iron
• NADH

Correct Answer: Glutathione (GSH)

Q7. Peroxynitrite (ONOO−) forms by the reaction of superoxide with which molecule?

• Hydrogen peroxide
• Nitric oxide (NO)
• Glutathione
• Carbon monoxide

Correct Answer: Nitric oxide (NO)

Q8. Activation of which immune cell contributes to ROS production in reperfusion through NADPH oxidase?

• Lymphocytes
• Neutrophils
• Erythrocytes
• Platelets

Correct Answer: Neutrophils

Q9. Opening of the mitochondrial permeability transition pore during reperfusion primarily leads to:

• Enhanced ATP synthesis
• Mitochondrial swelling and cell death
• Decreased ROS generation
• Activation of glutathione synthesis

Correct Answer: Mitochondrial swelling and cell death

Q10. Which drug is a xanthine oxidase inhibitor used to reduce ROS generation in I/R?

• Allopurinol
• Nifedipine
• Propranolol
• Warfarin

Correct Answer: Allopurinol

Q11. N-acetylcysteine (NAC) primarily protects against oxidative injury by:

• Directly inhibiting NADPH oxidase
• Scavenging hydroxyl radicals exclusively
• Replenishing intracellular glutathione (GSH)
• Blocking mitochondrial electron transport

Correct Answer: Replenishing intracellular glutathione (GSH)

Q12. Measurement of TBARS in tissue is commonly used to estimate levels of:

• Protein carbonyls
• Lipid peroxidation
• DNA strand breaks
• Calcium concentration

Correct Answer: Lipid peroxidation

Q13. Which NOS isoform is typically induced during inflammation and can contribute to reactive nitrogen species formation?

• eNOS (endothelial NOS)
• nNOS (neuronal NOS)
• iNOS (inducible NOS)
• mNOS (mitochondrial NOS)

Correct Answer: iNOS (inducible NOS)

Q14. Ischemic preconditioning reduces reperfusion injury mainly by:

• Eliminating neutrophils permanently
• Inducing brief, controlled ischemia to activate protective signaling
• Blocking all ROS formation
• Increasing iron availability

Correct Answer: Inducing brief, controlled ischemia to activate protective signaling

Q15. Which therapeutic approach chelates iron to limit hydroxyl radical formation in reperfusion?

• Deferoxamine
• Vitamin K
• Acetaminophen
• Insulin

Correct Answer: Deferoxamine

Q16. A small-molecule SOD mimetic that scavenges superoxide is an example of which strategy?

• Enzyme inhibition
• Antioxidant replacement therapy
• Pro-oxidant therapy
• Calcium channel blockade

Correct Answer: Antioxidant replacement therapy

Q17. Which event increases free radical production on reperfusion after myocardial ischemia?

• Restoration of oxygen to ischemic mitochondria
• Permanent oxygen deprivation
• Complete depletion of iron
• Increased GSH synthesis only

Correct Answer: Restoration of oxygen to ischemic mitochondria

Q18. Which pharmacological agent supplies thiol groups to scavenge free radicals and support antioxidant defenses?

• N-acetylcysteine
• Amiodarone
• Diclofenac
• Metoprolol

Correct Answer: N-acetylcysteine

Q19. Oxidative modification of which vascular molecule reduces nitric oxide bioavailability and promotes endothelial dysfunction?

• Low-density lipoprotein (LDL)
• Endothelial nitric oxide synthase (eNOS) cofactor tetrahydrobiopterin (BH4)
• Albumin exclusively
• Hemoglobin only

Correct Answer: Endothelial nitric oxide synthase (eNOS) cofactor tetrahydrobiopterin (BH4)

Q20. Which laboratory marker reflects oxidative DNA damage after reperfusion?

• MALDI-TOF mass spectra
• 8-OHdG (8-hydroxy-2′-deoxyguanosine)
• Troponin I
• Serum glucose

Correct Answer: 8-OHdG (8-hydroxy-2′-deoxyguanosine)

Q21. Which strategy describes ischemic postconditioning?

• Rapid full reperfusion without interruptions
• Pharmacological blockade of antioxidants
• Brief intermittent cycles of ischemia during early reperfusion
• Permanently occluding the vessel

Correct Answer: Brief intermittent cycles of ischemia during early reperfusion

Q22. Which enzyme family directly produces superoxide during the respiratory burst in phagocytes?

• NADPH oxidase (NOX) family
• Catalase family
• Glutathione S-transferases
• Cytochrome P450 reductases

Correct Answer: NADPH oxidase (NOX) family

Q23. Which of the following best describes the reperfusion paradox?

• Reperfusion always completely reverses ischemic damage
• Restoring blood flow can cause additional injury via ROS and inflammation
• Reperfusion prevents inflammation entirely
• Ischemia alone is more damaging than reperfusion in all tissues

Correct Answer: Restoring blood flow can cause additional injury via ROS and inflammation

Q24. Which vitamin is a water-soluble antioxidant that can scavenge ROS in plasma?

• Vitamin E (α-tocopherol)
• Vitamin A (retinol)
• Vitamin C (ascorbic acid)
• Vitamin D (calciferol)

Correct Answer: Vitamin C (ascorbic acid)

Q25. Which cellular consequence is a direct result of lipid peroxidation in reperfused membranes?

• Increased membrane fluidity and improved ion homeostasis
• Loss of membrane integrity and increased permeability
• Selective DNA repair enhancement
• Decreased calcium entry into the cell

Correct Answer: Loss of membrane integrity and increased permeability

Q26. Which pharmacological agent primarily reduces ROS by inhibiting xanthine oxidase activity?

• Deferoxamine
• Allopurinol
• Hydralazine
• Furosemide

Correct Answer: Allopurinol

Q27. Which measurement technique is most appropriate to quantify protein oxidation in tissues after reperfusion?

• TBARS assay
• Carbonyl content assay (protein carbonyls)
• Serum creatinine
• ELISA for troponin

Correct Answer: Carbonyl content assay (protein carbonyls)

Q28. ROS-mediated activation of which pathway commonly triggers apoptosis in reperfused cells?

• Intrinsic (mitochondrial) apoptotic pathway
• Extracellular matrix synthesis pathway
• Protein synthesis initiation pathway
• Glycolysis upregulation pathway

Correct Answer: Intrinsic (mitochondrial) apoptotic pathway

Q29. Therapeutic hypothermia protects against reperfusion injury mainly by:

• Increasing metabolic demand and ROS
• Reducing metabolic rate and ROS generation
• Activating NADPH oxidase
• Stimulating iron release

Correct Answer: Reducing metabolic rate and ROS generation

Q30. Which experimental antioxidant is a catalytic scavenger that mimics SOD activity and has been studied for I/R?

• Tempol
• Ibuprofen
• Atorvastatin
• Clopidogrel

Correct Answer: Tempol

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