Abstract
UDP-glucuronosyltransferase 2B7 (UGT2B7) is one of the most significant isoforms of UGTs in human liver. This research measured UGT2B7 protein content and activities including Vmax and CLint in human liver at isoform, microsomal, liver tissue, and liver levels and identified the factors that influence expression. We determined absolute protein content by LC-MS/MS and activities using the probe drug Zidovudine in 82 normal human liver microsomes. Using a bottom-up method for derivation, we showed UGT2B7 content at the microsomal, liver tissue, and liver levels, as well as activities at the isoform, microsomal, liver tissue, and liver levels in vitro, and predicted hepatic clearance in vivo, with median, range, variation, and 95 and 50% prediction intervals. With regard to the intrinsic activities, the Vmax had a median (range) of 7.5 (2-24) pmol/min/pmol 2B7 and the CLint was 0.08 (0.02-0.31) µl/min/pmol 2B7. Determinations at liver level showed larger variations than at microsomal level, so it was more suitable for evaluating individual differences. By analyzing factors that affect UGT2B7, we found that: 1) the content at the liver tissue and liver levels correlated positively with activities; 2) the mutant heterozygotes of -327G>A, -900A>G, -161C>T may lead to decreased protein content and increased intrinsic CLint; and 3) the transcription factor pregnane X receptor (PXR) mRNA expression level was positively associated with the measured protein content. In all, we showed protein content and activities at different levels and the factors that influence content to provide valuable information for UGT2B7 research and clinically individualized medication.
- enzyme kinetics
- gene regulation/transcription
- glucuronidation/UDP-glucuronyltransferases/UGT
- human/clinical
- in vitro-in vivo prediction (IVIVE)
- liver/hepatic
- mass spectrometry/MS
- pregnane X receptor/PXR/SXR
- The American Society for Pharmacology and Experimental Therapeutics