Glucuronidation of bile acids by rat liver 3-OH androgen UDP-glucuronyltransferase

The glucuronidation of bile acids is an important pathway for the detoxification and elimination of retained bile acids during cholestasis. A 3-OH-specific androgen UDP-glucuronyltransferase was purified from solubilized female rat liver microsomes using Chromatofocusing and UDP- hexanolamine -Sepharose 4B affinity chromatography. The purified 3-OH androgen UDP-glucuronyltransferase is reactive towards bile acids, including lithocholic acid, deoxycholic acid, and ursodeoxycholic acid, in addition to the androgenic steroids etiocholanolone and androsterone. The highest activity towards bile acids is seen with lithocholic acid-24-methyl ester, and no activity is seen with lithocholic acid-3 alpha-sulfate or 5 beta- cholanic acid-3-one. No glucuronidation activity towards bile acids was observed with either a purified 17-OH steroid UDP-glucuronyltransferase or a p-nitrophenol-UDP-glucuronyltransferase. Lithocholic acid competitively inhibits etiocholanolone glucuronidation by the purified 3-OH androgen isoenzyme. These results suggest that a UDP-glucuronyltransferase isoenzyme is present in female rat liver which is capable of specifically glucuronidating the 3-OH group of bile acids and androgenic steroids.