| Cytochrome P450 (CYP) 2E1 is considered the sole CYP responsible for APAP bioactivation leading to hepatotoxicity. CYP2E1 is also considered the alcohol-inducible CYP and therefore, the sole CYP responsible for alcohol-mediated increases in APAP hepatotoxicity. However, we previously found that alcohol increased APAP hepatotoxicity in Cyp2e1(-/-) mice, showing that CYP2E1 is not essential. The current studies examined the hypothesis that CYP1A2, CYP2E1 and CYP3A, which are highly active in the conversion of APAP to its toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI), all contribute to the development of APAP hepatotoxicity and to alcohol-mediated increases in this response. Here we used Cyp2e1 (-/-) and wild-type mice to investigate the roles of CYP3A and CYP2E1 in APAP hepatotoxicity. Alcohol-mediated increases in APAP hepatotoxicity occurred at a lower APAP dose in wild-type mice compared to Cyp2e1 (-/-) mice, suggesting CYP2E1 has a role in the different susceptibilities of the two mouse lines. Alcohol increased CYPs 3A, 2E1, and 1A2 in wild-type mice, but only CYP3A in Cyp2e1(-/-) mice. At the time of APAP administration, only increases in CYP3A were sustained and CYP3A activity was greater in wild-type mice than in Cyp2e1(-/-) mice. In vivo treatment with triacetyloleandomycin (TAO) inhibited CYP3A activity without effecting CYP1A2 or CYP2E1 activities. TAO decreased APAP hepatotoxicity in alcohol-treated wild-type and Cyp2e1(-/-) mice, and surprisingly, control wild-type mice, indicating CYP3A is an important contributor to APAP hepatotoxicity in untreated and alcohol-treated mice. Deletion of the pregnane X receptor (PXR) results in increased CYP3A protein and enzymatic activity, a finding anticipated to increase APAP hepatotoxicity. However, APAP hepatotoxicity was lower in PXR(-/-) mice compared to wild-type mice. Hepatic levels of CYP1A2 were greater in wild-type mice than in PXR(-/-) mice. Caffeine, an inhibitor of CYP1A2 and enhancer of CYP3A, protected wild-type mice against APAP hepatotoxicity. Wild-type mice had greater absorption and exposure to APAP than PXR(-/-) mice. These results suggest that PXR is an important modulator of APAP hepatotoxicity through the regulation of CYP1A2 and APAP transport. Overall, these studies indicate that, in mice, CYP1A2, CYP2E1, and CYP3A each contribute to APAP hepatotoxicity. Decreases in any one of these three CYPs will decrease toxicity. |
