Synthesis of 6- and 7-hydroxyestradiol 17-sulfates: the potential metabolites of estradiol 17-sulfate by female rat liver microsomes

On the structures of hydroxylated metabolites of estradiol 17-sulfate by rat liver microsomes

The metabolism of estradiol 17-sulfate (ES) by hepatic microsomes of female rats produced four new metabolites in addition to 2- and 4-hydroxyestradiol 17-sulfates (2- and 4-OH-ES), which were detected on an HPLC chromatogram. By comparison with synthetic specimens, three of these compounds were identified as 6alpha-, 6beta-, and 7beta-hydroxyestradiol 17-sulfates. To elucidate the structure of the remaining metabolite, a large-scale incubation of ES was carried out, followed by isolation using preparative HPLC to give the single material, which was assigned as 15beta-hydroxyestradiol 17-sulfate by instrumental analyses. On the other hand, when ES was incubated with the microsomes of male rats, 2-OH-ES was produced accompanied by two minor products: 4-OH-ES and a metabolite of unknown structure. The results show clearly that the metabolism of ES by rat hepatic microsomes is remarkably different between the sexes.

Cholesterol and hydroxycholesterol sulfotransferases: identification, distinction from dehydroepiandrosterone sulfotransferase, and differential tissue expression

In humans, the biotransformation of cholesterol and its hydroxylated metabolites (oxysterols) by sulfonation is a fundamental process of great importance. Nevertheless, the sulfotransferase enzyme(s) that carries out this function has never been clearly identified. Cholesterol is a relatively poor substrate for the previously cloned hydroxysteroid sulfotransferase (HST), i.e. dehydroepiandrosterone (DHEA) sulfotransferase (HST1). Recently, cloning of a single human gene that encodes for two proteins related to HST1 was reported. These newly cloned sulfotransferases (HST2a and HST2b), while exhibiting sequence similarity to other members of the soluble sulfotransferase superfamily, also contain unique structural features. This latter aspect prompted an examination of their substrate specificity for comparison with HST1. Thus, HST1, HST2a, and HST2b were overexpressed as fusion proteins and purified. Furthermore, a novel procedure for the isolation of cholesterol and oxysterol sulfonates was developed that was used in association with HPLC to resolve specific sterol sulfonates. HST1 preferentially sulfonated DHEA and, to a lesser extent, oxysterols; whereas cholesterol was a negligible substrate. The reverse, however, was the case for the HST2 isoforms, particularly HST2b, which preferentially sulfonated cholesterol and oxysterols, in contrast to DHEA, which served as a poor substrate for this enzyme. RT-PCR analysis revealed distinct patterns of HST1, HST2a, and HST2b expression. It was particularly notable that both HST2 isoforms, but not HST1, were expressed in skin, a tissue where cholesterol sulfonation plays an important role in normal development of the skin barrier. In conclusion, substrate specificity and tissue distribution studies strongly suggest that HST2a and HST2b, in contrast to HST1, represent normal human cholesterol and oxysterol sulfotransferases. Furthermore, this study represents the first example of the sulfonation of oxysterols by a specific human HST.