Volume 12, Issue 4 (July 2010) 12, 519–526; 10.1038/aja.2010.18
Effects of genistein and equol on human and rat testicular 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase 3 activities
Guo-Xin Hu1,2,*, Bing-Hai Zhao3,*, Yan-Hui Chu3, Hong-Yu Zhou2, Benson T. Akingbemi4, Zhi-Qiang Zheng5 and Ren-Shan Ge1,5
1 Population Council, New York, NY 10065, USA
2 School of Pharmacy, Wenzhou Medical College, Wenzhou 325000, China
3 Heilongjiang Key Laboratory of Anti-fibrosis Biotherapy, Mudanjiang Medical University, Mudanjiang 157001, China
4 Departments of Anatomy, Physiology and Pharmacology, Auburn University, Auburn, AL 36849, USA
5 The Second Affiliated Hospital, Wenzhou Medical College, Wenzhou 325000, China
*These two authors contributed equally to this work.
Correspondence: Dr Ren-Shan Ge,email@example.com Dr Zhi-Qiang Zheng firstname.lastname@example.org
Received 9 December 2009; Revised 22 January 2010; Accepted 25 February 2010; Published online 10 May 2010.
The objective of the present study was to investigate the effects of genistein and equol on 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase 3 (17β-HSD3) in human and rat testis microsomes. These enzymes (3β-HSD and 17β-HSD3), along with two others (cytochrome P450 side-chain cleavage enzyme and cytochrome P450 17α-hydroxylase/17-20 lyase), catalyze the reactions that convert the steroid cholesterol into the sex hormone testosterone. Genistein inhibited 3β-HSD activity (0.2 μmol L−1 pregnenolone) with half-maximal inhibition or a half-maximal inhibitory concentration (IC50) of 87 ± 15 (human) and 636 ± 155 nmol L−1 (rat). Genistein's mode of action on 3β-HSD activity was competitive for the substrate pregnenolonrge and noncompetitive for the cofactor NAD+. There was no difference in genistein's potency of 3β-HSD inhibition between intact rat Leydig cells and testis microsomes. In contrast to its potent inhibition of 3β-HSD, genistein had lesser effects on human and rat 17β-HSD3 (0.1 μmol L−1 androstenedione), with an IC50 ≥ 100 μmol L−1. On the other hand, equol only inhibited human 3β-HSD by 42%, and had no effect on 3β-HSD and 17β-HSD3 in rat tissues. These observations imply that the ability of soy isoflavones to regulate androgen biosynthesis in Leydig cells is due in part to action on Leydig cell 3β-HSD activity. Given the increasing intake of soy-based food products and their potential effect on blood androgen levels, these findings are greatly relevant to public health.
Keywords: 3β-hydroxysteroid dehydrogenase; 17β-hydroxysteroid dehydrogenase 3; enzyme inhibition; equol; genistein