Human hepatic UGT2B15 developmental expression

Abstract

Human hepatic UGT2B15 developmental expression changes may alter the metabolism of important drugs and toxicants such as bisphenol A (BPA). Previously, UGT2B15 ontogeny knowledge consisted of transcript data, a dubious surrogate for protein expression. Herein, UGT2B15 protein content was determined in human hepatic microsomes (n = 236, 8 weeks gestation to 18 years). The impact of a common, functional single nucleotide polymorphism (g.253G>T), present in UGT2B15*2 and *5 alleles, was also tested. UGT2B15 expression began during late fetal life, at about 18% of mature values (medians = 48, 267 pmoles/mg of microsomal protein, respectively; p < 0.001). UGT2B15 neonatal (n = 39) and late fetal (≥28 weeks, n = 10) content was similar, but lower than that of infants between 3 and 15 weeks age (n = 46; medians = 38, 48, 404 pmoles/mg microsomal protein, respectively; p < 0.001). Values for the latter group were higher compared with the remaining age group (15 weeks to 18 years; n = 82, p < 0.001). UGT2B15 expression varied 31-fold across the entire sample, and within groups, ranged from 4- to 27-fold. Among postnatal samples, age group, the presence of g.253T and male gender were each significantly associated with greater UGT2B15 expression (p < 0.001, <0.01, and <0.05, respectively; stepwise linear regression). In summary, hepatic UGT2B15 protein onset begins in late gestation; however, the greatest rate of change occurs during the first few weeks after birth. We speculate that the fetus and neonate may have lower clearance of some UGT2B15 substrates, such as BPA, compared with older individuals.

Keywords: SNP; UGT; hepatic liver microsomes; ontogeny; single nucleotide polymorphism; uridine diphosphate glucuronosyltransferase.

FIG. 1.

Western blot analysis of UGT2B15 developmental expression pattern in human liver microsomes: Western blot depicts fractionated microsomal samples from differing age groups representing both fetal and postnatal ages (random order) along with UGT2B15 supersome standards. Electrophoresis and immunodetection using UGT2B15-specific antibody were conducted as described in Materials and Methods.

FIG. 2.

Human hepatic UGT2B15-specific content as a function of gestational age in 71 fetal hepatic microsomal samples. UGT2B15 content was quantified by Western blotting, densitometry, and comparison with known standards.

FIG. 3.

Human hepatic UGT2B15-specific protein content as a function of postnatal age in 165 hepatic microsomal samples. UGT2B15 content was quantified by Western blotting, densitometry, and comparison with known standards.

FIG. 4.

Human hepatic UGT2B15 developmental expression pattern in 97 samples from individuals from birth through the first six postnatal months.

FIG. 5.

The developmental expression of human hepatic UGT2B15 categorized into four age brackets using CRT analysis. Each of the four major groups differed in UGT2B15 content from every other group. UGT2B15 protein expression was not significantly different among samples between 28 weeks gestational age (GA) and 3 weeks postnatal age. This group, group II, is shown separated into two statistically similar subparts connected by a bracket to visually illustrate the event of birth. The boxes represent the 25th and 75th percentiles, the horizontal bar within the box represents the median, and the vertical bars represent the 5th and 95th percentiles. Outliers (•) were defined as having specific protein content 1.5-fold from the 25th and 75th percentiles. Significant differences between groups were determined by Kruskal-Wallis testing (*** p < 0.001, all between group comparisons).

FIG. 6.

The effect of UGT2B15 genotypes on hepatic UGT2B15-specific content. (A) UGT2B15 protein content in microsomal samples that were homozygous reference (GG), heterozygous (GT), or homozygous variant (TT) for g.253G>T (D85Y). (B) UGT2B15 protein content in microsomal samples that were homozygous reference (AA), heterozygous (AC), or homozygous variant (CC) for g.23490A>C (K523T). The data are represented as box and whisker plots, in which the boxes represent the 25th and 75th percentiles, the horizontal bar within the box represents the median of the data, and the vertical bars represent the 5th and 95th percentiles (N = 225, p = 0.089 and not significant (NS), for D85Y and K523T, respectively; One-way ANOVA).