The metabolism of testosterone by the periwinkle (Littorina littorea) in vitro and in vivo: Effects of tributyl tin
The metabolism of testosterone by the periwinkle (Littorina littorea) in vitro and in vivo: Effects of tributyl tin
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DOI：
10.1016/0141-1136(95)00069-0
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发表时间：
1996-06-01
影响因子：
3.3
通讯作者：
Mason, AZ
中科院分区：
文献类型：
--
作者：
Ronis, MJJ;Mason, AZ
暴露于低至0.5纳克/升的三丁基锡(TBT)与40-50种海洋腹足动物的性生理紊乱(性畸变)有关。性畸变是假性两性畸形的一种状态，在这种状态下，女性表现出无功能的次级男性特征。有人认为，性畸变的机制涉及内源性性激素代谢的紊乱，特别是抑制细胞色素P450依赖的雄激素到雌激素的芳构化。本研究在体外和体内研究了TBT对长春花(Littorina Littorea)代谢雄激性类固醇睾酮能力的影响。从消化腺(包括性腺在内的内脏复合体)以及肾和鳃的组合部分中制备微粒体。共连接的还原差谱在459 nm处有峰，计算出P450的含量分别为0.3和0.05nmol/mg。在NADPH存在或不存在的情况下，消化腺微体都能够进行睾酮的氧化代谢。在没有NADPH的情况下，睾酮被代谢成雄烯二酮、6β-、6α和15β-羟睾酮、17-β-雌二醇和一种未知的代谢物，可能是3-α-雄烯-17-β-二醇。在NADPH存在下，同样的产物以更高的速率产生，但形成的主要产物是NADPH依赖的类固醇5α-还原酶-3α(β)羟基类固醇脱氢酶途径的产物；二氢睾酮(DHT)和3α(β)雄烷-17β二醇(DHTdiol)。TBT在体外对依赖于P450的睾酮代谢只有轻微的影响，即使在高达100 mU M的浓度下，也只能增加雄烯二酮的形成，对芳香酶的抑制只有30-40%。在体内，将[C-14]睾酮直接注射到成年蜗牛和动物的头足窦中，在0、0.5和5 mM TBT的存在下，在15℃的海水中饲养42小时。在此期间，睾酮几乎完全代谢，主要代谢为睾酮、5α-还原产物和6α-羟基睾酮的水溶性硫结合物。然而，随着TBT浓度的增加，更多的放射性被保留在动物体内，并与有机可提取的未代谢的睾酮及其I相产物雄烯二酮、二氢雄烯二酮(DHA)、DHT和DHT-二醇越来越相关。因此，在体内，TBT似乎抑制了睾酮及其I相代谢物的硫结合和它们的排泄，导致药理活性雄激素在组织中的积聚。这一数据与TBT在敏感腹足类动物(如狭舌)中诱导的性畸变可能起因于性类固醇代谢紊乱的假设是一致的。然而，TBT的主要生化目标似乎是类固醇结合和排泄转运机制，而不是P450依赖的氧化途径作为芳香酶燃料。版权所有(C)1996爱思唯尔科学有限公司
Exposure to tributyl tin (TBT) at concentrations as low as 0.5 ng/liter has been associated with disrupted sexual physiology (imposex) in 40-50 species of marine gastropod. Imposex is a state of pseudohemaphrodism in which females exhibit nonfunctional secondary male characteristics. It has been suggested that the mechanism underlying imposex involves disrupted metabolism of endogenous sex hormones and in particular inhibition of cytochrome P450-dependent aromatization of androgens to estrogens. In the current study, the effects of TBT on the ability of the Periwinkle (Littorina littorea) to metabolize the androgenic sex steroid testosterone was examined in vitro and in vivo. Microsomes were prepared from 'digestive gland' (visceral complex including the gonads) and combined kidney and gill fractions. CO-ligated reduced difference spectra contained peaks at 459 nm and calculated P450 contents of 0.3 and 0.05 nmol/mg. Digestive gland microsomes were found to be capable of oxidative metabolism of testosterone in either the presence or absence of NADPH. In the absence of NADPH, testosterone was metabolized to androstenedione, 6 beta-, 6 alpha- and 15 beta-hydroxytestosterone, 17 beta-estradiol and an unidentified metabolite possibly 3 alpha-androstene-17 beta-diol. In the presence of NADPH the same products were produced at a higher rate but the major products formed were the products of the NADPH-dependent steroid 5 alpha-reductase-3 alpha (beta) hydroxysteroid dehydrogenase pathway; dihydrotestosterone (DHT) and 3 alpha (beta) androstane-17 beta-diols (DHT diols). TBT, even at high concentrations up to 100 mu M, had only, modest effect on P450-dependent testosterone metabolism in vitro, producing increases in androstenedione formation and only 30-40% inhibition of aromatase. In vivo, [C-14] testosterone was injected directly into the cephalopedal sinus of adult snails and animals maintained in sea water at 15 degrees C for 42 h in the presence of 0, 0.5 and 5 mM TBT. Testosterone was almost completely metabolized during this time, predominantly to water-soluble sulfur conjugates of testosterone, the 5 alpha-reduced products and 6 alpha-hydroxytestosterone. However, with increasing concentrations of TBT, more radioactivity was retained within the animal and was increasingly associated with organic extractable unmetabolized testosterone and its phase I products androstenedione, dihydroandrostenedione (DHA), DHT and DHT-diols. Thus it appears that, in vivo, TBT inhibits sulfur conjugation of testosterone and its phase I metabolites and their excretion resulting in a build-up of pharmacologically active androgens in the tissues. This data are consistent with the hypothesis that TBT-induced imposex in sensitive gastropods, such as stenoglossans, may arise from perturbations in sex steroid metabolism. However, the major biochemical targets of TBT appear to be steroid conjugation and excretory transport mechanisms rather than P450-dependent oxidative pathways fuel as aromatase. Copyright (C) 1996 Elsevier Science Ltd