Abstract
Bile acids (BA) are essential modulators of lipid, glucose and cholesterol homeostasis, but exert cytotoxic effects in the cholestatic liver. Glucuronidation, catalyzed by the UDP-glucuronosyltransferase (UGT) enzymes is a pharmacologically-relevant BA detoxification process. The present study aimed at characterizing the BA-conjugating activity of the little-studied human UGTs of subfamily 2A, UGT2A1, 2A2 and 2A3. Recombinant UGT2As, expressed in baculovirus-infected insect cells, were assayed for the glucuronidation of 6 major bile acids, chenodeoxycholic (CDCA), cholic (CA), lithocholic (LCA), deoxycholic (DCA), hyocholic (HCA) and hyodeoxycholic (HDCA) acids. UGT2A3 exhibited detectable, but very low, activity with all the tested BAs substrates. UGT2A1 was highly efficient in forming LCA-3 and -24G, CDCA-24, DCA-24, HCA-24 and HDCA-24G, while UGT2A2 was the most active enzyme for CA-24G and CDCA-24G formation, and was also able to generate HDCA-6G, HDCA-24G, LCA-24G and HCA-24G. The Km values of UGT2A1 varied between 102.2 ± 14.3 μM and 2.4 ± 1.2 mM. With the exception of CA-24G, a low affinity substrate for UGT2A2, all the Km values for UGT2A2 were in the 100 to 400 μM range. In conclusion, the present study demonstrates the high reactivity of the human UGT2A1 and UGT2A2 for bile acid glucuronidation.
- analytical chemistry
- bile acid metabolism
- enzyme kinetics
- glucuronidation
- HPLC
- mass spectrometry
- UDP glucuronyltransferases
- The American Society for Pharmacology and Experimental Therapeutics