Hepatic Abundance and Activity of Androgen- and Drug-Metabolizing Enzyme UGT2B17 Are Associated with Genotype, Age, and Sex

Abstract

The major objective of this study was to investigate the association of genetic and nongenetic factors with variability in protein abundance and in vitro activity of the androgen-metabolizing enzyme UGT2B17 in human liver microsomes ( = 455). UGT2B17 abundance was quantified by liquid chromatography-tandem mass spectrometry proteomics, and enzyme activity was determined by using testosterone and dihydrotestosterone as in vitro probe substrates. Genotyping or gene resequencing and mRNA expression were also evaluated. Multivariate analysis was used to test the association of UGT2B17 copy number variation, single nucleotide polymorphisms (SNPs), age, and sex with its mRNA expression, abundance, and activity. UGT2B17 gene copy number and SNPs (rs7436962, rs9996186, rs28374627, and rs4860305) were associated with gene expression, protein levels, and androgen glucuronidation rates in a gene dose-dependent manner. UGT2B17 protein (mean ± S.D. picomoles per milligram of microsomal protein) is sparsely expressed in children younger than 9 years (0.12 ± 0.24 years) but profoundly increases from age 9 years to adults (∼10-fold) with ∼2.6-fold greater abundance in males than in females (1.2 vs. 0.47). Association of androgen glucuronidation with UGT2B15 abundance was observed only in the low UGT2B17 expressers. These data can be used to predict variability in the metabolism of UGT2B17 substrates. Drug companies should include UGT2B17 in early phenotyping assays during drug discovery to avoid late clinical failures.

Characterization of the Ontogeny of Hepatic UDP‐Glucuronosyltransferase Enzymes Based on Glucuronidation Activity Measured in Human Liver Microsomes

“…Increases in activities of UGT1A4 (1.6‐fold) and UGT1A6 (2.7‐fold) from infants (n = 6) to adults (n = 29) are consistent than the results of previous publications where significant 4.1‐ and 3.8‐fold increase in UGT1A4 and UGT1A6 activity were detected between infants (n = 17) and adults (n = 16) . In addition, the slow maturation of the UGT2B17 glucuronidation pathway with adult levels reached at adolescence which we found when using testosterone as a probe substrate, was in agreement with literature . However, Bhatt et al .…”

“…We also reported discrepancies in maturation of UGT1A1, UGT1A9, UGT2B7, and UGT2B15 with the results of published ontogeny . With our HLM donor panel, no significant age‐associated changes in activity of UGT1A1, UGT1A9, UGT2B7, and UGT2B15 were observed between infants and adults (<1.3‐fold, P > .05).…”

“…To characterize the ontogeny of 10 hepatic UGT isoforms, the UGT activity was transformed to fractions of adult UGT activity ( F activity ) by defining the median UGT activity measured ( F adult ) in the adult population (range, 19‐65 years) as 1 and recalculating all individual UGT activity relative to this number. The resulting ontogeny data were used to calculate kinetic parameters by either linear regression using the age‐independent relationship (equation ) and nonlinear regression using the 1‐phase decay equation (equation ) and the sigmoid equation equation ) using GraphPad Prism version 7.3 for Windows (GraphPad Software, La Jolla, California). where F birth and Plateau represent the fraction of adult UGT activity at birth, F max and Y0 indicate the maximal fraction of adult UGT activity, and Age 50 , g , and k indicate the age at which half the maximal fraction of adult UGT activity is reached, the Hill exponent, and the developmental rate, respectively.…”

“…In addition, protein abundance‐activity correlations for those UGT isoforms was demonstrated recently by Bhatt et al . Distinct maturation of activity or protein expression levels between those UGT isoforms and across different age categories were demonstrated with maximum UGT‐mediated metabolic capacity achieved at different times after birth . The ontogeny pattern of other major hepatic UGT isoforms, including UGT1A3, UGT2B4, and UGT2B10, remained to be elucidated.…”

“…To date, the ontogeny of 7 hepatic UGT isoforms (UGT1A1, UGT1A4, UGT1A6, UGT1A9, UGT2B7, UGT2B15, and UGT2B17) has been evaluated based on glucuronidation activity or protein abundance determined in human liver microsomes (HLMs) in independent studies . In addition, protein abundance‐activity correlations for those UGT isoforms was demonstrated recently by Bhatt et al .…”