Cloning , Expression , and Regulation of Lithocholic Acid G @ - Hydroxylase

We have isolated a hamster liver cDNA whose expression is induced upon feeding hamsters with a cholic acid-rich diet. It was identified as a cytochrome P460 family 3 protein, by sequence homology, and named CYP3AlO. The activity of CYP3AlO was determined by transient expression of its cDNA in transfected COS cells and was found to hydroxylate lithocholic acid at position 68. CYP3A10 RNA is 50-fold higher in males than in female hamsters. In males, it appears to be regulated by age with expression highest after puberty. Shortly after weaning (28 days), cholic acid feeding of male hamsters elevates the level of message over that of hamsters fed with normal laboratory chow. Females do not exhibit regulation by cholic acid. In hamster liver, murideoxycholic acid, the 68-metabolite of lithocholic acid, is the major hydroxylated product of lithocholic acid. Lithocholic acid 68hydroxylase (68-hydroxylase) activity is greatly diminished in hamster female liver microsomes as would be expected due to the lack of CYP3A10 mRNA in females. Additionally, male liver microsomal 6B-h~droxylase activity was increased by cholic acid feeding, consistent with the cholic acid-mediated induction of its RNA. These results indicate that, in male hamsters, 68-hydroxylation is the major pathway for detoxification of lithocholate and that, likely, CYP3A10 is responsible for that activity.