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© 1997 Oxford University Press

research-article

Differences in Caffeine 3-Demethylation Activity among Inbred Mouse Strains: A Comparison of Hepatic Cyp 1a2 Gene Expression between Two Inbred Strains1

William L. Casley*,{dagger},2, Allan Menzies*, Michel Girard*, Lyse Larocque*, Nicole Mousseau*, Larry W. Whitehouse* and Thomas W. Moon{dagger}

*Bureau of Drug Research, Therapeutic Products Directorate, Health Canada, Banting Research Centre Ottawa, Ontario, Canada, KIA 0L2 {dagger}Departmnent of Biology, University of Ottawa Ottawa, Ontario, Canada, KIN 6N5

Received May 28, 1997; accepted October 15, 1997

The 3-demethylation of caffeine can be used as an index of cytochrome P450 CYP1A2 activity in vivo. We compared the plasma levels of caffeine and the 3-demethylated metabolite, 1,7-dimethylxanthine, in six common inbred strains (A/J, P/J, BALB/cJ, C3H/HeJ, AKR/J, and SWR/J) and one inbred strain (APN) derived in our laboratory from outbred Swiss-Webster mice on the basis of its relative susceptibility to acetaminophen-induced hepatotoxicity. We found significant variations between a number of the common strains, all of which produced significantly higher caffeine 3-demethylation indices than our APN strain. In three of the six common strains, there was a significant difference between males and females, with the females having consistently lower 1,7-xanthine/caffeine ratios. Hepatic Cyp1a2 expression was compared between APN and C3H/HeJ males. Microsomal methoxyresorufin O-demethylation, acetanilide 4-hydroxylation, and CYP1A2 immunoreactive protein levels were significantly higher in C3H/HeJ relative to APN mice, as were hepatic CYP1A2 mRNA levels. These results indicate the importance of strain and gender to the outcome of pharmacological or toxicological studies involving CYP1A2-mediated metabolism, as well as the suitability of the plasma 1,7-dimethylxanthine/caffeine ratio as a marker of CYP1A2 activity in the mouse. The striking differences observed between the APN and C3H/HeJ mice suggest that these strains may be suitable for a genetic analysis of the regulation of the basal expression of CYP1A2, a key enzyme In procarcinogen activation.

Key Words: 1,3,7-trimethylxanthine; caffeine; metabolism; mice; inbred strains; CYP1A2; genetics.


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