Antioxidants: protective activities and therapeutic uses MCQs With Answer

Introduction: This MCQ set on “Antioxidants: protective activities and therapeutic uses” is crafted for M.Pharm students studying Advanced Pharmacology-II. It covers fundamental mechanisms of reactive oxygen species (ROS) generation and the cellular antioxidant defense systems, including enzymatic and non-enzymatic antioxidants. Questions examine pharmacological actions, clinical indications, molecular targets such as Nrf2 and selenoproteins, biomarker evaluation, pro-oxidant risks, and therapeutic agents like NAC, vitamin E isoforms, SOD mimetics and metal chelators. Emphasis is placed on translational and therapeutic considerations, drug interactions, dosing, and evidence from clinical studies to prepare students for advanced exams and practical decision-making in oxidative stress–related therapies.

Q1. What is the primary biochemical event that initiates lipid peroxidation in biological membranes?

• Direct enzymatic oxidation by cyclooxygenase
• Hydrogen abstraction from polyunsaturated fatty acids by ROS
• Spontaneous hydrolysis of phospholipids
• Cross-linking of membrane proteins

Correct Answer: Hydrogen abstraction from polyunsaturated fatty acids by ROS

Q2. Which antioxidant enzyme catalyzes the dismutation of superoxide anion into hydrogen peroxide and oxygen?

• Glutathione peroxidase
• Catalase
• Superoxide dismutase
• Thioredoxin reductase

Correct Answer: Superoxide dismutase

Q3. N-acetylcysteine (NAC) primarily exerts its antioxidant effect by which mechanism?

• Direct scavenging of hydroxyl radicals with high affinity
• Serving as a precursor to intracellular glutathione synthesis
• Chelating free iron to prevent Fenton reactions
• Inhibiting NADPH oxidase enzymatic activity

Correct Answer: Serving as a precursor to intracellular glutathione synthesis

Q4. Which biomarker is most specific for oxidative damage to DNA?

• Malondialdehyde (MDA)
• Protein carbonyls
• 8-hydroxy-2′-deoxyguanosine (8-OHdG)
• F2-isoprostanes

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

Q5. Which vitamin can act as a pro-oxidant under conditions of high free transition metal availability?

• Vitamin K
• Vitamin C (ascorbate)
• Vitamin A (retinol)
• Vitamin B12

Correct Answer: Vitamin C (ascorbate)

Q6. Which class of antioxidants functions primarily by chelating catalytic metal ions to inhibit Fenton chemistry?

• Chain-breaking antioxidants (e.g., vitamin E)
• Metal chelators (e.g., deferoxamine)
• Enzymatic antioxidants (e.g., catalase)
• Peroxynitrite scavengers (e.g., uric acid)

Correct Answer: Metal chelators (e.g., deferoxamine)

Q7. Which selenoprotein is directly involved in reducing hydrogen peroxide and lipid hydroperoxides using glutathione?

• Thioredoxin
• Glutathione peroxidase
• Selenoprotein P
• Peroxiredoxin 6

Correct Answer: Glutathione peroxidase

Q8. Activation of the Nrf2 signaling pathway leads to increased expression of which type of genes?

• Pro-apoptotic caspases
• Phase II detoxification and antioxidant enzymes
• Pro-inflammatory cytokines
• Glycolytic enzymes only

Correct Answer: Phase II detoxification and antioxidant enzymes

Q9. Which of the following therapeutic uses of antioxidants is supported by strong clinical evidence?

• High-dose vitamin E for prevention of all-cause mortality
• N-acetylcysteine in acetaminophen (paracetamol) overdose
• Large-dose beta-carotene supplements for lung cancer prevention in smokers
• Vitamin C megadoses to cure the common cold

Correct Answer: N-acetylcysteine in acetaminophen (paracetamol) overdose

Q10. Which antioxidant is lipid-soluble and protects cell membranes from lipid peroxidation by donating a hydrogen atom to lipid radicals?

• Glutathione
• Ascorbic acid
• Alpha-tocopherol (vitamin E)
• Uric acid

Correct Answer: Alpha-tocopherol (vitamin E)

Q11. SOD mimetics used therapeutically primarily aim to replicate which biochemical activity?

• Reduction of hydrogen peroxide to water
• Dismutation of superoxide radicals to hydrogen peroxide and oxygen
• Direct scavenging of hydroxyl radicals
• Inhibition of nitric oxide synthase

Correct Answer: Dismutation of superoxide radicals to hydrogen peroxide and oxygen

Q12. In cardiovascular disease, which oxidative marker derived from arachidonic acid non-enzymatic peroxidation is considered a reliable in vivo indicator of lipid peroxidation?

• Malondialdehyde (MDA)
• F2-isoprostanes
• 8-OHdG
• Protein nitrotyrosine

Correct Answer: F2-isoprostanes

Q13. Which statement best describes the “redox cycling” property that can make some phenolic antioxidants act as pro-oxidants?

• Phenolics irreversibly bind to lipid radicals preventing regeneration
• Phenolics repeatedly donate and re-receive electrons in the presence of transition metals, generating ROS
• Phenolics are permanently oxidized and excreted without effect
• Phenolics activate catalase, increasing peroxide levels

Correct Answer: Phenolics repeatedly donate and re-receive electrons in the presence of transition metals, generating ROS

Q14. Which therapeutic antioxidant is an approved drug for reducing iron burden and preventing iron-catalyzed oxidative damage in thalassemia?

• Deferasirox
• Vitamin C
• Alpha-lipoic acid
• Glutathione

Correct Answer: Deferasirox

Q15. Which intracellular molecule provides the reducing equivalents for glutathione reductase to regenerate reduced glutathione (GSH) from oxidized glutathione (GSSG)?

• NADH
• NADPH
• FADH2
• ATP

Correct Answer: NADPH

Q16. Which clinical concern is most relevant when prescribing high-dose antioxidant supplements to patients undergoing chemotherapy?

• Antioxidants may enhance chemotherapy-induced oxidative damage
• Antioxidants may reduce efficacy of pro-oxidant chemotherapeutic agents by protecting tumor cells
• Antioxidants always increase chemotherapy toxicity in normal tissues
• Antioxidants cause irreversible DNA crosslinking with alkylating agents

Correct Answer: Antioxidants may reduce efficacy of pro-oxidant chemotherapeutic agents by protecting tumor cells

Q17. Which endogenous molecule is the most abundant intracellular non-enzymatic antioxidant and is critical for phase II conjugation reactions?

• Ascorbate
• Glutathione (GSH)
• Uric acid
• Coenzyme Q10

Correct Answer: Glutathione (GSH)

Q18. Which therapeutic antioxidant has been studied for preventing contrast-induced nephropathy due to its ROS-scavenging and vasodilatory properties?

• N-acetylcysteine (NAC)
• Vitamin B6
• Deferoxamine
• Alpha-tocopherol

Correct Answer: N-acetylcysteine (NAC)

Q19. Which method is most appropriate for quantifying protein oxidative damage in a biological sample?

• Measuring reduced glutathione by HPLC
• Assessing protein carbonyl content
• Assessing serum vitamin C levels
• Measuring activity of cytochrome P450 enzymes

Correct Answer: Assessing protein carbonyl content

Q20. Which pharmacological approach targets mitochondrial oxidative stress specifically to protect tissues from ischemia-reperfusion injury?

• Systemic high-dose vitamin E supplementation
• Mitochondria-targeted antioxidants (e.g., MitoQ)
• Oral iron chelation only
• Topical ascorbate application

Correct Answer: Mitochondria-targeted antioxidants (e.g., MitoQ)

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