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 (n = 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.

Fig. 1.

The UGT2B17 gene deletion is associated with its protein abundance (A), rates of testosterone- and DHT-glucuronide formation (B and C, respectively). UGT2B17 diplotypes (haplotype pairs on homologous chromosomes) are associated with UGT2B17 mRNA expression (D), protein abundance (E), testosterone-glucuronide formation (F), and DHT-glucuronide formation (G). Confounding factor, that is, samples from subjects aged younger than 12 years, were excluded from the subanalysis. *P < 0.05; **P < 0.01; ***P < 0.0001. Sample number in each group is shown in parentheses in the x-axis.

Fig. 2.

Categorical age-dependent UGT2B17 protein abundance (A–D), testosterone (T)-glucuronide formation (E–H), and DHT-glucuronide formation (I–L) data in all (A, E, and I), male (B, F and J) and female (C, G, and K) livers. The x-axis labels identifying data categories in the bottom panel (I–L) are also applicable to the corresponding top two panels (A–H). Number of samples is presented either as main label in the x-axis (A–H) or the x-axis parentheses (I–L). Donors with zero UGT2B17 gene copy were excluded from this analysis. Of 375 samples (male plus female), 205 were lower than the LOD of UGT2B17 protein measurement. For statistical analysis, samples <LOD (excluding zero copy number) were assigned a value of 0.06 pmol/mg of microsomal protein, which was one-third the LLOQ (0.17 pmol/mg of microsomal protein). UGT2B17 was sparsely (12 of 92 samples) detected in children younger than the age of 9 years. An association of age with UGT2B17 abundance or testosterone and DHT-glucuronide formation was more prominent in male versus. female. Mean UGT2B17 protein abundance and testosterone- and DHT-glucuronide formation in these samples was 2.8-, 1.9-, and 1.4-fold greater in male versus female donors aged ≥12 years, respectively (D). *P < 0.05; **P < 0.01; ***P < 0.0001.

Fig. 3.

The UGT2B15 SNP (rs1902023) is not associated with UGT2B15 protein abundance in low UGT2B17 expressers (A), but it is significantly associated with increased rates of testosterone-glucuronide (B) and DHT-glucuronide (C) formation (picomoles per milligram per minute microsomal protein). Only samples with UGT2B17 abundance <LOD (0.06 pmol/mg of microsomal protein) samples were included in this analysis.