Abstract
Background: The purpose of this study was to investigate cytochrome P450-7B1 (CYP7B1) in the human and rat testes to regulate 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity. We hypothesized that dehydroepiandrosterone (DHEA) and its product 7α-hydroxydehydroepiandrosterone (7αOHD) after catalysis of CYP7B1 played a critical role in driving the direction of 11β-HSD1, because 7αOHD is an alternative substrate for 11β-HSD1.Methods: We examined the influence of DHEA and 7αOHD on 11β-HSD1 activities in both intact Leydig cells and microsomes using radioactive substrates and identified the location of CYP7B1 in Leydig cells using immunohistochemical staining, Western blot, and qPCR.Results: We found that DHEA stimulated 11β-HSD1 oxidase activity in intact cells (EC50 = 0.97 ± 0.11 μM) and inhibited its reductase activity (IC50 = 1.04 ± 0.06 μM). In microsomes, DHEA was a competitive inhibitor of the reductase activity. The 11β-HSD1 oxidase activity in intact cells was inhibited by 7αOHD (IC50 = 1.18 ± 0.12 μM), and the reductase activity was enhanced (EC50 = 0.7 ± 0.04 μM). 7αOHD was a competitive inhibitor of 11β-HSD1 oxidase. CYP7B1 was present in rat Leydig cells, as shown by immunohistochemistry, Western blotting, and qPCR analysis.Conclusion: Our results are consistent with a conclusion that DHEA in the circulation driving 11β-HSD1 toward an oxidase in Leydig cells mainly through inhibiting the reductase of the enzyme, while 7αOHD (CYP7B1 catalytic product of DHEA) drives the enzyme toward the opposite direction.
Highlights
The purpose of this study was to investigate cytochrome P450-7B1 (CYP7B1) in the human and rat testes to regulate 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity
The IC50 value of DHEA of inhibiting 11βHSD1 reductase activity was 1.04 μM (Table 1). This indicates that DHEA is a potent inhibitor of 11β-HSD1 reductase in intact adult Leydig cells (ALCs)
We measured the rates of oxidase reactions in ALC microsomes in presence of different 7αOHD concentrations (0, 1, and 10 μM) in order to evaluate the mode of action. 7αOHD was a competitive inhibitor of 11β-HSD1 oxidase (Figure 7B)
Summary
The purpose of this study was to investigate cytochrome P450-7B1 (CYP7B1) in the human and rat testes to regulate 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity. The goal of the present study was to investigate each of these possibilities
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