Structure-activity relationship and docking analysis of nature flavonoids as inhibitors of human and rat gonadal 3β-hydroxysteroid dehydrogenases for therapeutic purposes

The potential inhibitory effects of flavonoids on gonadal steroid biosynthesis have gained attention due to their widespread presence in natural plant sources. Specifically, our study focused on evaluating the inhibitory efficacy of these compounds on human 3β-hydroxysteroid dehydrogenase 2 (h3β-HSD2) and rat homolog r3β-HSD1, enzymes responsible for the conversion of pregnenolone to progesterone. Through our investigations, we observed that the potency of flavonoids was silymarin (IC50, 1.31 μM) > luteolin (4.63 μM) > tectorigenin > (5.86 μM), and rutin (44.12 μM) in inhibiting human KGN cell microsomal h3β-HSD2. Similarly, the potency of flavonoids was silymarin (9.50 μM) > luteolin (11.49 μM) > tectorigenin (14.06 μM), and rutin (145.71 μM) in inhibiting rat testicular r3β-HSD1. Silymarin, luteolin, and tectorigenin acted as mixed inhibitors of both human and rat 3β-HSDs. Luteolin and tectorigenin were able to penetrate human KGN cells to inhibit progesterone secretion. Furthermore, docking analysis and structure-activity relationship analysis highlighted the importance of hydrogen bond formation for the inhibitory efficacy of these compounds against h3β-HSD2 and r3β-HSD1. Overall, this study demonstrates that silymarin exhibits the most potent inhibition of human and rat gonadal 3β-HSDs, and significant SAR differences exist among the tested compounds.