US EPA

4091172 

Journal Article 

Role Of Mouse CYP2E1 In The O-Hydroxylation Of P-Nitrophenol: Comparison Of Activities In CYP2E1 (-/-) And Wildtype Mice 

Wolf, KK; Wood, SG; Bement, JL; Sinclair, PR; Wrighton, SA; Jeffery, E; Gonzalez, FJ; Sinclair, JF 

2004 

1 

Toxicologist
ISSN: 0731-9193 

TOX/4001957 

78 

1-S 

English 

Selective enzymatic activities are used to identify the role of an individual form of CYP in a particular biotransformation. p-Nitrophenol O-hydroxylation (PNPH) has been widely used as a measure of CYP2E1. However, rat and human forms of CYP3A have also been shown to catalyze this activity. In mice, the contribution of CYP3As and CYP2E1 to PNPH is not known. Here we compared hepatic microsomes from Cyp2e1 (-/-) and wild type mice to investigate the contribution of constitutive and alcohol-induced levels of murine CYP2E1 and CYP3A to PNPH. In untreated mice, hepatic levels of PNPH were much greater in wildtype mice compared to Cyp2e1 (-/-) mice, suggesting a major role of CYP2E1 in catalyzing PNPH. Hepatic levels of PNPH were not significantly different between males and females, even though females have dramatically higher levels of CYP3A. Treatment with ethanol in combination with isopentanol resulted in induction of CYP3A proteins in wildtype and knockout mice, and CYP2E1 protein in wildtype mice. The alcohol treatment increased PNPH in hepatic microsomes from wildtype mice but not from knockout mice. Our findings suggest that constitutive and alcohol-induced forms of mouse CYP3A have little to no role in PNPH. Therefore, in untreated and alcohol-treated mice, PNPH can be used as an unambiguous assay for CYP2E1.