Content and Activities of UGT2B7 in Human Liver In Vitro and Predicted In Vivo: A Bottom-Up Approach

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 maximum velocity (V) and intrinsic clearance (CL), in human liver at isoform, microsomal, liver tissue, and liver levels and identified the factors that influence expression. We determined absolute protein content by liquid chromatography-tandem mass spectroscopy 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 maximum velocity (V) had a median (range) of 7.5 (2-24) pmol/min per picomole of 2B7, and the CL was 0.08 (0.02-0.31) l/min per picomole of 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, , may lead to decreased protein content and increased intrinsic CL; and 3) the transcription factor pregnane X receptor mRNA expression level was positively associated with the measured protein content. In all, we showed that protein content and activities at different levels and the factors that influence content provide valuable information for UGT2B7 research and clinically individualized medication.

Intraindividual Variation and Correlation of Cytochrome P450 Activities in Human Liver Microsomes

“…The mechanism underlying the good correlation between two CYP450 activities is still unknown, but a possible hypothesis is that they share higher homology with other genes. Another speculation may be that they use the same control mechanism for CYP450 activity or expression as other related proteins, such as POR, CYPb5, and UGT2B7 . However, investigation of the precise mechanism underlying this is still in progress.…”

“…Another speculation may be that they use the same control mechanism for CYP450 activity or expression as other related proteins, such as POR, 10 CYPb5, 9 and UGT2B7. 28 However, investigation of the precise mechanism underlying this is still in progress. A third clade comprised CYP1A2, 2E1, 2A6, and 2C19.…”

Pharmacokinetics, Pharmacodynamics, and Side Effects of Midazolam: A Review and Case Example

“…The influence of the ligand-activated transcription factors PXR and CAR extends beyond CYP3A4, as they serve as transcriptional activators for at least 40 genes involved in drug transport and phase I/II metabolism [ 94 ]. These factors have been implicated in the transcriptional activation of genes crucial to the pharmacokinetics of midazolam, including cytochrome P450 oxidoreductase ( POR ) [ 118 ], CYP3A4 [ 119 ], CYP3A5 [ 120 ], UGT1A4 [ 121 ], and UGT2B7 [ 122 ]. PXR is activated by a wide range of xenobiotics, including antibiotics, antimycotics, herbal components [ 123 ], and benzodiazepines such as medazepam and midazolam [ 124 ].…”

Analysis of in vitro and in vivo metabolism of zidovudine and gemfibrozil in trans‐chromosomic mouse line expressing human UGT2 enzymes

“…A recent study suggested a bottom‐up approach for predicting hepatic clearance in vivo by using protein contents and activity of UGT2B7 in human liver microsomes. 12 However, predicting the involvement of human UGT2 enzymes in in vivo drug disposition from in vitro data remains challenging.…”

“…Human liver microsomes and recombinant UGT isoforms are useful for clarifying the contribution of UGT2 enzymes to the metabolism of interest drug and also for examining the interactions with other substrates. A recent study suggested a bottom‐up approach for predicting hepatic clearance in vivo by using protein contents and activity of UGT2B7 in human liver microsomes 12 . However, predicting the involvement of human UGT2 enzymes in in vivo drug disposition from in vitro data remains challenging.…”