Role of CYP450 enzymes in toxicology and provide an example of a toxic consequence.

• A. They metabolize xenobiotics; some metabolites are more toxic or reactive; example: acetaminophen metabolized to NAPQI, causing hepatotoxicity at high doses.
• B. They detoxify every xenobiotic without toxic metabolites.
• C. They are not involved in toxicology.
• D. They always detoxify xenobiotics, reducing risk.

Answer: (A)

CYP450 enzymes act as gatekeepers in toxicology by oxidizing many foreign compounds (xenobiotics) to more polar metabolites that can be excreted. But this same oxidation can create reactive or more toxic intermediates, a process called bioactivation. A classic example is acetaminophen: it is normally processed by CYP enzymes (notably CYP2E1, along with contributions from CYP1A2 and CYP3A4) to a reactive metabolite called NAPQI. At therapeutic doses, NAPQI is quickly neutralized by glutathione and the toxin is safely eliminated. In an overdose, glutathione stores are overwhelmed or depleted, allowing NAPQI to accumulate and bind to cellular proteins in liver cells, causing oxidative stress and hepatotoxicity. This illustrates why the role of CYP enzymes in toxicology is dual: they help detoxify many compounds, but they can also convert some into more hazardous forms.