Sex hormones differentially regulate isoforms of UDP-glucuronosyltransferase.

PURPOSE: To investigate the role of sex hormones in the regulation of UDP-glucuronosyltransferase (UGT). METHODS: We examined liver from adult, prepubertal, gonadectomised and gonadectomised plus hormone replaced rats of both sexes. Immunohistochemistry and immunoblots were performed using a polyclonal UGT antibody to a number of family 1 and family 2 UGT isoforms. Northern blot analysis was performed utilising cDNA probes to family 1 and family 2 isoforms. RESULTS: Immunohistochemistry demonstrated variations in intensity and distribution of staining in the hormonally manipulated rats. Immunoblots showed variations in individual band intensity between rat groups. Immunoblots using a more specific antibody (anti-17 beta-hydroxysteroid UGT, which recognises UGT2B3 and UGT2B2) demonstrated marked differences between male and female rats and significant alterations after gonadectomy and testosterone replacement in the male rats. In northern analysis, UGT2B3 and 2B1 mRNA were significantly higher in adult males than females, and in prepubertal males compared to prepubertal females. In male rats, gonadectomy resulted in a 45-53% reduction in UGT2B3 and 2B1 levels respectively, which increased significantly with testosterone treatment to greater than normal adult levels. No change in UGT2B3 or 2B1 occurred after gonadectomy in females. In contrast, UGT1*1 mRNA tended to be higher in adult female and prepubertal female rats than in their male counterparts. In females, gonadectomy resulted in significant up-regulation of UGT1*1, while gonadectomy plus oestradiol treatment resulted in markedly reduced levels. UGT1*1 mRNA was not significantly altered by gonadectomy in males. CONCLUSIONS: This study demonstrates the differential effects of sex hormones on the expression of isoforms from the two phylogenetically distinct UGT families.

UDP-glucuronosyltransferase in the regenerating rat liver.

In both acute and chronic liver disease in man, elimination of drugs metabolized by the cytochrome P450 (CYP) enzymes is impaired. In contrast, those drugs metabolized by UDP-glucuronosyltransferase (UGT) have a relatively normal elimination. Studies in rats with experimentally induced liver injury also show this relative preservation of glucuronidation. In liver disease, a number of factors, including inflammation, fibrosis and regeneration, may be associated with this differential effect on drug metabolism. Partial hepatectomy provides a model in which to isolate the effects of liver regeneration on drug metabolism. Partial hepatectomy or sham operation was performed in 24 male Sprague-Dawley rats and three rats from each group were studied at days 1, 2, 4 and 6. Comparison between CYP and UGT was made at the protein level using immunohistochemistry and immunoblotting probed with a polyclonal antibody to UGT, identifying both family 1 and family 2 isoforms, and an antibody to the CYP isoform CYP2C11. Steady state messenger RNA levels of four isoforms of UGT were assessed by northern blot analysis. By both immunohistochemistry and immunoblotting, the level of CYP protein decreased from day 2 to 6 after hepatectomy. In contrast, the UGT protein level was not altered by partial hepatectomy. Northern blot analysis of UGT isoforms demonstrated differential regulation of isoforms from the two major families. The UGT family 1 isoforms were initially markedly depressed following partial hepatectomy and then steadily rose over 6 days to greater than the level in controls. In contrast, there was an apparent increase in UGT2B1 mRNA (not significant) on day 2, while UGT2B3 mRNA was maintained over the six days. These results demonstrate that during hepatic regeneration the protein content of total UGT is normal, while CYP2C11 protein is markedly reduced. Northern blot analysis suggests that individual isoforms of UGT are differentially regulated during the regeneration process.