Metformin Inhibits Human Androgen Production by Regulating Steroidogenic Enzymes HSD3B2 and CYP17A1 and Complex I Activity of the Respiratory Chain

Abstract

Metformin is treatment of choice for the metabolic consequences seen in polycystic ovary syndrome for its insulin-sensitizing and androgen-lowering properties. Yet, the mechanism of action remains unclear. Two potential targets for metformin regulating steroid and glucose metabolism are AMP-activated protein kinase (AMPK) signaling and the complex I of the mitochondrial respiratory chain. Androgen biosynthesis requires steroid enzymes 17α-Hydroxylase/17,20 lyase (CYP17A1) and 3β-hydroxysteroid dehydrogenase type 2 (HSD3B2), which are overexpressed in ovarian cells of polycystic ovary syndrome women. Therefore, we aimed to understand how metformin modulates androgen production using NCI-H295R cells as an established model of steroidogenesis. Similar to in vivo situation, metformin inhibited androgen production in NCI cells by decreasing HSD3B2 expression and CYP17A1 and HSD3B2 activities. The effect of metformin on androgen production was dose dependent and subject to the presence of organic cation transporters, establishing an important role of organic cation transporters for metformin's action. Metformin did not affect AMPK, ERK1/2, or atypical protein kinase C signaling. By contrast, metformin inhibited complex I of the respiratory chain in mitochondria. Similar to metformin, direct inhibition of complex I by rotenone also inhibited HSD3B2 activity. In conclusion, metformin inhibits androgen production by mechanisms targeting HSD3B2 and CYP17-lyase. This regulation involves inhibition of mitochondrial complex I but appears to be independent of AMPK signaling.

Metformin therapy for the reproductive and metabolic consequences of polycystic ovary syndrome

“…Further, in one recent study, metformin lowered testosterone levels in women with PCOS despite the absence of any improvement in insulin sensitivity, as quantified by a frequently sampled IVGTT [40]. In vitro studies using cultured ovarian theca cells support a direct inhibitory effect of metformin on ovarian steroidogenesis [35,41,42] through inhibition of mitochondrial Complex I [35], a mechanism which has also been implicated in metformin action in the liver and other tissues [29,31].…”

“…However, there is evidence that metformin directly inhibits ovarian steroidogenesis [33,34]. Inhibition of mitochondrial Complex I has been implicated as one potential mechanism for this action [35]. There is also evidence that metformin lowers androgen levels by an inhibitory effect on 3β-hydroxysteroid dehydrogenase/Δ 5 -Δ 4 isomerase type 2 [36].…”

Mutations inSDHDlead to autosomal recessive encephalomyopathy and isolated mitochondrial complex II deficiency

“…The OROBOROS oxygraph was used to measure oxygen consumption in permeabilised cells using a substrate-uncoupler-inhibitor titration regimen as previously described 21. The oxygen consumption rates were calculated and expressed as specific oxygen consumption rates (pmol O 2 /s/10 6 cells).…”

Metformin: From Mechanisms of Action to Therapies

“…Thus, the concept that members of the biguanide family, including phenformin and metformin, exert many of their actions though modulation of mitochondrial energetics is not a recent proposal. During the last decade, the specific inhibition of the mitochondrial respiratory-chain complex 1 by metformin was confirmed in many cellular models, including rat, mouse and human primary hepatocytes (El-Mir et al, 2000;Owen et al, 2000;Stephenne et al, 2011), hepatoma, and adrenocortical carcinoma immortalized cell lines (Guigas et al, 2004;Hirsch et al, 2012;Kim et al, 2013), skeletal muscle homogenates (Brunmair et al, 2004), endothelial cells (Detaille et al, 2005), pancreatic beta cells (Hinke et al, 2007), neurons (El-Mir et al, 2008), peripheral blood mononuclear cells and platelets (Piel et al, 2014), and more recently in cancer cells (Bridges et al, 2014;Janzer et al, 2014;Scotland et al, 2013;Wheaton et al, 2014). It has been reported that this transient inhibition of complex 1 induces a drop in cellular energy charge, a measure of the energetic state of the cell defined as ( (Foretz et al, 2010;Stephenne et al, 2011).…”