Thiazolidinediones but Not Metformin Directly Inhibit the Steroidogenic Enzymes P450c17 and 3β-Hydroxysteroid Dehydrogenase

Richard J. Auchus,Walter L. Miller,Wiebke Arlt

doi:10.1074/jbc.m100040200

Abstract

Androgen biosynthesis requires 3beta-hydroxysteroid dehydrogenase type II (3betaHSDII) and the 17alpha-hydroxylase and 17,20-lyase activities of cytochrome P450c17. Thiazolidinedione and biguanide drugs, which are used to increase insulin sensitivity in type 2 diabetes, lower serum androgen concentrations in women with polycystic ovary syndrome. However, it is unclear whether this is secondary to increased insulin sensitivity or to direct effects on steroidogenesis. To investigate potential actions of these drugs on P450c17 and 3betaHSDII, we used "humanized yeast" that express these steroidogenic enzymes in microsomal environments. The biguanide metformin had no effect on either enzyme, whereas the thiazolidinedione troglitazone inhibited 3betaHSDII (K(I) = 25.4 +/- 5.1 microm) and both activities of P450c17 (K(I) for 17alpha-hydroxylase, 8.4 +/- 0.6 microm; K(I) for 17,20-lyase, 5.3 +/- 0.7 microm). The action of troglitazone on P450c17 was competitive, but it was mainly a noncompetitive inhibitor of 3betaHSDII. The thiazolidinediones rosiglitazone and pioglitazone exerted direct but weaker inhibitory effects on both P450c17 and 3betaHSDII. These differential effects of the thiazolidinediones do not correlate with their effects on insulin sensitivity, suggesting that distinct regions of the thiazolidinedione molecule mediate these two actions. Thus, thiazolidinediones inhibit two key enzymes in human androgen synthesis contributing to their androgen-lowering effects, whereas metformin affects androgen synthesis indirectly, probably by lowering circulating insulin concentrations.

Highlights

The first and rate-limiting step in the biosynthesis of all steroid hormones is the conversion of cholesterol to pregnenolone by the mitochondrial cholesterol side chain cleavage enzyme, P450scc, which is the quantitative regulator of steroidogenesis [1]
To determine whether metformin or troglitazone inhibits either P450c17 or 3␤-hydroxysteroid dehydrogenase type II (3␤HSDII), and if so by what mechanism, we examined the actions of these two drugs using our humanized yeast expression system [8, 21], in which individual human steroidogenic enzymes are examined in native microsomal environments without interfering factors that are often present in whole-cell experiments
Insulin-sensitizing drugs increase insulin sensitivity and decrease hyperandrogenemia in women with Polycystic ovary syndrome (PCOS) [11,12,13,14], and it has been suggested that metformin decreases P450c17 activity in PCOS [12, 31, 32], but this suggestion has been based on serum hormone values rather than on direct biochemical study

Summary

Introduction

The first and rate-limiting step in the biosynthesis of all steroid hormones is the conversion of cholesterol to pregnenolone by the mitochondrial cholesterol side chain cleavage enzyme, P450scc, which is the quantitative regulator of steroidogenesis [1]. The biguanide metformin had no effect on either enzyme, whereas the thiazolidinedione troglitazone inhibited 3␤HSDII (KI ‫؍‬ 25.4 ؎ 5.1 ␮M) and both activities of P450c17 (KI for 17␣-hydroxylase, 8.4 ؎ 0.6 ␮M; KI for 17,20-lyase, 5.3 ؎ 0.7 ␮M).

Results

Conclusion