18-Hydroxylase activity in the Y1 adrenal cell line

Structure-activity relationship for inhibition of CYP11B1-dependent glucocorticoid synthesis in Y1 cells by aryl methyl sulfones

The effects of xenobiotics on CYP11B1-dependent corticosterone synthesis (11 beta-hydroxylase) in mouse adrenocortical Y1 cells were studied. 3-Methylsulfonyl-2,2-bis(4-chlorophenyl)-1,1-dichloroethene (MeSO2-DDE) and some methylsulfonyl polychlorinated biphenyls (MeSO2-PCB) inhibited the corticosterone synthesis, whereas PCBs or DDE did not. This indicates a crucial role of the methyl sulfone group for this inhibitory effect. Kinetic analyses of MeSO2-DDE and the two most potent MeSO2-PCBs were conducted using Lineweaver-Burk double-reciprocal plots. The data showed a competitive inhibition of CYP11B1 by the compounds, with apparent inhibitory constants (Ki) of 1.6, 4.6, and 6.7 microM for MeSO2-DDE, 4-MeSO2-2,3,6,4'-tetrachlorobiphenyl, and 4-MeSO2-2,3,6,3',4'-pentachlorobiphenyl, respectively. For comparison, the substrate K(m) was 3.5 microM in the cells, and metyrapone and ketoconazole had apparent Ki-values of 0.8 and 0.04 microM, respectively. In contrast to all previously known inhibitors of CYP11B1, the aryl methyl sulfones are the first examples of CYP11B1 inhibitors not being heterocyclic amines or steroids. The aryl methyl sulfones are widespread environmental pollutants and their inhibition of CYP11B1 constitutes another potential mechanism for endocrine disruption. Their influence on the synthesis of adrenocortical hormones thus merits further interest.

Aldosterone synthase activity in the Y-1 adrenal cell line

The Y-1 adrenal cell line was shown to produce 20 alpha-dihydroaldosterone from deoxycorticosterone. This compound was identified by GC-MS by comparison with the previously synthesized reference compound. Two other 18-hydroxylated metabolites were identified as 11 beta,18-dihydroxy-20 alpha-dihydroprogesterone from endogenous cholesterol and 18-hydroxy-20 alpha-dihydro-11-dehydrocorticosterone from DOC. The conditions necessary for the synthesis of these compounds are culturing in 20% serum-supplemented medium and repeated incubations with the substrate. The production of 11 beta-hydroxylated steroids and that of 18-oxygenated steroids is stimulated differently by ACTH and angiotensin II suggesting the expression of two different enzymes, cytochrome P-450(11)beta and cytochrome P-450aldo. The Y-1 cell line can secrete either 11 beta-hydroxylated steroids characteristic of the glucocorticoid pathway or 18-oxygenated steroids characteristic of the mineralocorticoid pathway, which in vivo are generally produced in two different zones of the adrenal cortex. This cell line should be an interesting model for the study of the molecular mechanisms regulating the expression of these two enzymes involved in the final steps of the steroidogenic pathways.

18-hydroxylation in the Y-1 adrenal cell line: response to ACTH and to culture conditions

The 18-hydroxylation of deoxycorticosterone in the Y-1 adrenal cell line was studied under various incubation and cell culture conditions and compared to 11 beta-hydroxylation. Repeated incubation of the substrate increased both 18- and 11 beta-hydroxylation in the Y-1 cells. Furthermore, both 18- and 11 beta-hydroxylation were increased with increased serum concentration and prolonged incubation time. While the increase in 11 beta-hydroxylation seemed to be independent of the type of serum, 18-hydroxylation was much more important in cells cultured in fetal or newborn calf serum supplemented medium than in those cultured in horse serum supplemented medium. As expected, ACTH treatment increased 11 beta-hydroxylation; however, it decreased 18-hydroxylation. The different regulation of these two hydroxylating pathways by ACTH, point to a heterogeneity of the cytochrome P-450(11) beta of the Y-1 cell line.

Chromatographic and mass spectrometric characteristics of 20-dihydroaldosterone

The 20 alpha-reduced derivative of aldosterone, 20 alpha-dihydroaldosterone, was needed as reference compound in order to continue the studies on 18-hydroxylation in the Y-1 adrenal cell line. It was obtained by reduction of aldosterone with sodium borohydride. Analysis of the products of the reaction as methoxime trimethylsilyl (MO-TMS) derivatives by gas chromatography (GC) and GC-mass spectrometry (GC-MS) showed three possible forms of the compound. Their identification was confirmed by comparison with the products obtained by stereospecific reduction of aldosterone using 3 alpha,20 beta-hydroxysteroid dehydrogenase. Chromatographic behavior and mass spectra are given for the three forms of 20 alpha-dihydroaldosterone as the MO-TMS derivatives; that is, the 18-aldehyde, the 18,11 beta-hemiacetal, and the 11 beta:18,18:20 alpha-acetal. The possible origin of these different forms is discussed as a function of these results and of the results obtained by complementary analysis on high-performance liquid chromatography.

19-Hydroxylated steroids, new metabolites produced by the Y1 adrenal cell line

The expression of 19-hydroxylase activity in the Y1 adrenal cell line is reported here for the first time. Two new metabolites from the incubation of deoxycorticosterone (DOC) with these cells, 19-hydroxy-20 alpha-dihydroDOC and 19-hydroxy-20 alpha-dihydrocorticosterone, have been identified. The most important of the two is the 11 beta,19-dihydroxylated metabolite, which is produced in smaller amounts than 18-hydroxy-20 alpha-dihydrocorticosterone. A third 19-hydroxylated metabolite was identified as 19-hydroxy-20 alpha-dihydroprogesterone, produced from the cholesterol in the serum supplemented medium. These results show that the cytochrome P-450(11)beta of this cell line expresses 19-hydroxylase activity in addition to 11 beta- and 18-hydroxylase activities, as do those of other species.