Ethanol-induced inhibition of testosterone biosynthesis in rat leydig cells: Central role of mitochondrial NADH redox state

Arto K. Orpana , Mauri M. Orava , Reuo K. Vihko , Math Härkönen, C.J.Peter Eriksson
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引用次数: 15

Abstract

The mechanisms by which ethanol (EtOH) inhibits the human chorionic gonado-tropin (hCG)-stimulated testosterone synthesis was studied in isolated rat Leydig cells in vitro. EtOH inhibited steroidogenesis, but this inhibition was reversed by l-glutamate (Glu) and an uncoupler of the oxidative phosphorylation, 2,4-dinitrophenol (DNP). The mechanism of EtOH-induced inhibition was studied by measuring steroidogenic precursors and comparing them with the cytosolic and mitochondrial NADH redox states during uncoupling or in the presence of Glu. DNP had a dual effect. Low concentrations abolished the EtOH-induced inhibition of progesterone to testosterone formation suggesting that the inhibitory step was at or before progesterone formation. A large concentration led to an overall decrease in steroidogenesis indicating toxic effects on steroidogenesis. The mitochondrial NADH/NAD+ ratio, measured as the 3-hydroxybutyrate/acetoacetate ratio, decreased simultaneously when steroidogenesis was stimulated, either during uncoupling or in the presence of Glu, whereas cytosolic NADH/NAD+ ratio, measured as lactate/pyruvate ratio showed no response. These results demonstrate that the rise in the mitochondrial NADH/NAD+ ratio rather than in the cytosolic one is connected with the inhibition of testosterone synthesis by EtOH in isolated Leydig cells. The EtOH-induced high mitochondrial NADH/NAD+ ratio may deplete mitochondrial oxalacetate concentrations. This can decrease the activity of several transport shuttles and interrupt the flow of mitochondrial citrate into the smooth endoplasmic reticulum, which then reflects to decreased rate of steroidogenesis in the presence of ethanol.

乙醇诱导的大鼠间质细胞睾酮生物合成抑制:线粒体NADH氧化还原状态的中心作用
在离体大鼠间质细胞中研究了乙醇(EtOH)抑制人绒毛膜促性腺激素(hCG)刺激的睾酮合成的机制。EtOH抑制甾体生成,但这种抑制作用被l-谷氨酸(Glu)和氧化磷酸化解耦剂2,4-二硝基苯酚(DNP)逆转。通过测量甾体生成前体,并将其与解偶联或Glu存在时细胞质和线粒体NADH氧化还原状态进行比较,研究了etoh诱导的抑制机制。DNP有双重作用。低浓度etoh消除了黄体酮对睾酮形成的抑制作用,表明抑制作用发生在黄体酮形成时或之前。高浓度导致类固醇生成的整体减少,表明对类固醇生成有毒性作用。线粒体NADH/NAD+比值(以3-羟基丁酸/乙酰乙酸比值测量)在甾体生成刺激时同时下降,无论是在解偶联过程中还是在Glu存在的情况下,而细胞质NADH/NAD+比值(以乳酸/丙酮酸比值测量)则没有反应。这些结果表明,在分离的间质细胞中,线粒体NADH/NAD+比值的升高而不是细胞质内NADH/NAD+比值的升高与EtOH抑制睾酮合成有关。etoh诱导的高线粒体NADH/NAD+比值可能会耗尽线粒体草酸盐浓度。这可以降低几种运输穿梭体的活性,并中断线粒体柠檬酸盐进入光滑内质网的流动,这反映了乙醇存在时类固醇生成率的降低。
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