Formation of three types of glucuronides of 6-hydroxy bile acids by rat liver microsomes.
The glucuronidation of 6-hydroxylated bile acids by rat liver microsomes was studied in vitro; for comparison, several major bile acids lacking a hydroxyl group in position 6 were also investigated. The highest reaction rates were found for lithocholic and deoxycholic acid (10.2 +/- 0.2 and 7.3 +/- 1.4 nmol/mg.min, respectively); our results for these substrates agree well with published values. Glucuronidation rates for the 6 beta-hydroxylated bile acids 3 alpha, 6 beta-dihydroxy-5 beta-cholanoate (murideoxycholate) and 3 alpha, 6 beta, 7 beta-trihydroxy-5 beta-cholanoate (beta-muricholate) were only slightly lower (3.7 +/- 0.3 and 3.6 +/- 0.3 nmol/mg.min). 6 alpha-Hydroxylated bile acids were glucuronidated at rates that were lower than those for their 6 beta-hydroxy counterparts. Rigorous product identification by high-field proton NMR of methyl/acetyl derivatives revealed that while bile acids lacking a 6-hydroxyl group gave rise exclusively to the typical 3-O-glucuronide, the presence of a hydroxyl group in position 6 led to the formation, in ratios depending on the substrate, of three types of conjugate: the 3-O-, the 6-O-, and the carboxyl-linked (acyl-) glucurnide. The latter is the first example of an acyl glucuronide of a bile acid of conventional (C24) size.
Zimniak
P
P
Department of Internal Medicine, University of Texas Medical School, Houston 77225.
Radominska
A
A
Zimniak
M
M
Lester
R
R
D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005965:Glucuronates / Q000096:biosynthesis*; D006900:Hydroxylation; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
D001647:Bile Acids and Salts; D005965:Glucuronates