Molecular mechanisms of tributyltin‐induced alterations in cholesterol homeostasis and steroidogenesis in hamster testis: In vivo and in vitro studies

Abstract

Tributyltins (TBT) are ubiquitous and persistent environmental contaminants that disturb normal endocrine function including gonadal function in humans and marine organisms. TBT was administered through oral route to male Syrian hamsters at daily doses of 50, 100, and 150 ppm/kg for 65 days. Changes in testis morphology, immunohistochemistry of iNOS, 3β-HSD, and 17β-HSD, cholesterol transport receptor, nuclear receptors, and transcription factors were analyzed. TBT treatment affected each of these parameters to significant levels in a dose-dependent manner compared to vehicle treated control. Real-time PCR and protein analyses revealed that expression levels of ApoE and LDL-R mRNA were up-regulated in the testis of TBT-treated animals while the expression levels of SR-B1, LXR, PPARs α, β, and γ, SCAP, SREBP 1 and 2, 3β-HSD, 17β-HSD, CYP17A1, and P450 were down-regulated. Leydig cells were isolated and separated adopting percoll gradient centrifugation under aseptic condition. The viability of Leydig cell was affected by TBT treatment in a dose- and time-dependent manner. Further, the mechanism of action of TBT was ascertained by siRNA transfection of ApoE, which was upregulated, and SREBP, which was down-regulated. These observations led us to infer that exposure to TBT hinders intracellular cholesterol transport resulting in abnormal sex steroid biosynthesis and alteration of steroidogenic enzyme activities. Finally, we could recognize ApoE and SREBP as the major factors regulating genes that control cholesterol biosynthesis and steroidogenesis that ultimately inhibit the synthesis of testosterone. Therefore, ApoE is one of the important molecular targets that can be intercepted in context of male infertility/male contraception.

Multispecies study: low-dose tributyltin impairs ovarian theca cell cholesterol homeostasis through the RXR pathway in five mammalian species including humans

“…Because cholesterol is the precursor for sex hormone production, we predicted that the reduction in intracellular cholesterol upon TBT exposure would reduce theca cell steroid hormone production. In support of this hypothesis, in vivo studies have demonstrated that TBT exposure inhibits steroidogenic enzymes' transcription, and reduces serum testosterone production in mouse (Kim et al 2008) and hamster (Kanimozhi et al 2018) testes. In these studies, however, intracellular cholesterol was not assessed.…”

“…Exposure to endocrine disrupting chemicals (EDCs) can impair fertility and ovarian cell function (Craig and Ziv-Gal 2018;Mlynarcikova et al 2014), specifically altering steroidogenesis in vitro (Romani et al 2013;Romani et al 2014) and in vivo (Li et al 2012;Melzer et al 2011). TBT's steroidogenic effects have been reported in Leydig cells and testis (Kanimozhi et al 2018;Kariyazono et al 2015;Mitra et al 2014;Nakajima et al 2005). However, TBT's effect on ovarian steroidogenic cells has been restricted to granulosa cells.…”

Triphenyltin Chloride Delays Leydig Cell Maturation During Puberty in Rats

“…As shown in the present study, TPT downregulated many steroidogenic gene expression such as Lhcgr , Scarb1 , Star , Cyp11a1 , Hsd3b1 , Cyp17a1 , and Hsd17b3 . A recent study using another organotin tributyltin also showed that the expression levels of SCARB1, CYP11A1, HSD3B1, CYP17A1, and HSD17B3 were downregulated in the adult male hamster testes after 65-day treatment ( Kanimozhi et al, 2017 ). Secondly, TPT directly inhibited steroidogenic enzyme activities.…”

Effects of Tributyltin Exposure in the Male Mammal’s Reproductive System: A Systematic Review

“…In the study by Grote et al (32) , one animal receiving 15 mg TBT/kg body weight died, but no signs of general toxicity were observed. Regarding the male reproductive organs, most studies have shown no changes in testes weight among the groups treated with TBT over a wide range of doses (33,34,35,32,36,24,37) .…”

“…Steroidogenic acutely regulated proteins (StAR) and other hamster steroidogenic enzymes (expressions of Cypscc, Hsd 3β1 and Cyp17α1) were studied by real-time PCR, which revealed significantly decreased mRNA expression of StAR, Cypscc, Hsd 3β1 and Cyp17α1, all involved in normal testicular function and steroidogenesis. Immunoblotting research showed that the expression of StAR, 3β-HSD, Cypscc, Hsd 3β1 and Cyp17α1 was also significantly down-regulated in hamsters treated with TBT in a dose-dependent manner compared to control (37) (Table 4).…”