In vivo and in vitro effects of PCB126 and PCB153 on rat testicular androgenesis

HBCDD-induced sustained reduction in mitochondrial membrane potential, ATP and steroidogenesis in peripubertal rat Leydig cells

Hexabromocyclododecane (HBCDD), a brominated flame retardant added to various consumer products, is a ubiquitous environmental contaminant. We have previously shown that 6-hour exposure to HBCDD disturbs basal and human chorionic gonadotropin (hCG)-induced steroidogenesis in rat Leydig cells. Reduction in mitochondrial membrane potential (ΔΨm) and cAMP production was also observed. Here, we further expanded research on the effect of HBCDD on Leydig cells by using a prolonged exposure scenario. Cells were incubated in the presence of HBCDD during 24h and then treated with HBCDD+hCG for additional 2h. Results showed that HBCDD caused a sustained reduction in ATP level after 24h of exposure, which persisted after additional 2-hour treatment with HBCDD+hCG. cAMP and androgen accumulations measured after 2h of HBCDD+hCG treatment were also inhibited. Real-time PCR analysis showed significant inhibition in the expression of genes for steroidogenic enzymes, luteinizing hormone receptor, regulatory and transport proteins, and several transcription factors under both treatment conditions. Western blot analysis revealed a decreased level of 30kDa steroidogenic acute regulatory protein (StAR) after HBCDD+hCG treatment. In addition, HBCDD decreased the conversion of 22-OH cholesterol to pregnenolone and androstenedione to testosterone, indicating loss of the activity of cytochrome P450C11A1 (CYP11A1) and 17β-hydroxysteroid dehydrogenase (HSD17β). Cell survival was not affected, as confirmed by cytotoxicity and trypan blue tests or DNA fragmentation analysis. In summary, our data showed that HBCDD inhibits ATP supply, most likely through a decrease in ΔΨm, and targets multiple sites in the steroidogenic pathway in Leydig cells.

Acute effects of hexabromocyclododecane on Leydig cell cyclic nucleotide signaling and steroidogenesis in vitro

Hexabromocyclododecane (HBCDD), an additive brominated flame retardant routinely added to various consumer products, was reported to have toxic effects upon biota, including endocrine disruption. In this study, the potential toxicity of HBCDD was tested in peripubertal rat Leydig cells in vitro during 6h exposure. HBCDD inhibited human chorionic gonadotropin- and forskolin-supported cAMP accumulation and steroidogenesis. It also inhibited basal cAMP production, but elevated basal steroidogenesis. The expression of several cAMP-dependent genes, including steroidogenic acute regulatory protein, cholesterol side chain cleavage enzyme, and 3β-hydroxysteroid dehydrogenase, was also inhibited by HBCDD treatment. Nevertheless, this was not accompanied by a decrease in steroidogenic acute regulatory protein expression, as documented by western blot analysis, and activity of steroidogenic enzymes, as documented by unaffected steroidogenesis in the presence of permeable 22(R)-hydroxycholesterol. However, HBCDD caused significant decrease in mitochondrial membrane potential in untreated and human chorionic gonadotropin-treated cells. This indicates that HBCDD acute toxicity in Leydig cells reflects changes in mitochondrial membrane potential-dependent cAMP production and basal and cAMP-regulated cholesterol transport. This in turn facilitates basal but inhibits cAMP-dependent steroidogenesis. Acute effects of HBCDD treatment on transcription are also indicative of its sustained effects on Leydig cell function.

Atrazine acts as an endocrine disrupter by inhibiting cAMP-specific phosphodiesterase-4

Atrazine, one of the most commonly used herbicides worldwide, acts as an endocrine disruptor, but the mechanism of its action has not been characterized. In this study, we show that atrazine rapidly increases cAMP levels in cultured rat pituitary and testicular Leydig cells in a concentration-dependent manner, but less effectively than 3-isobutyl-1-methylxanthine, a competitive non-specific inhibitor of phosphodiesterases (PDEs). In forskolin (an activator of adenylyl cyclase)- and probenecid (an inhibitor of cyclic nucleotide transporters)-treated cells, but not in 3-isobutyl-1-methylxanthine-treated cells, atrazine further increased cAMP levels, indicating that inhibition of PDEs accounts for accumulation of cAMP. In contrast to cAMP, atrazine did not alter cGMP levels, further indicating that it inhibits cAMP-specific PDEs. Atrazine-induced changes in cAMP levels were sufficient to stimulate prolactin release in pituitary cells and androgen production in Leydig cells, indicating that it acts as an endocrine disrupter both in cells that secrete by exocytosis of prestored hormones and in cells that secrete by de novo hormone synthesis. Rolipram abolished the stimulatory effect of atrazine on cAMP release in both cell types, suggesting that it acts as an inhibitor of PDE4s, isoforms whose mRNA transcripts dominate in pituitary and Leydig cells together with mRNA for PDE8A. In contrast, immortalized lacto-somatotrophs showed low expression of these mRNA transcripts and several fold higher cAMP levels compared to normal pituitary cells, and atrazine was unable to further increase cAMP levels. These results indicate that atrazine acts as a general endocrine disrupter by inhibiting cAMP-specific PDE4s.

Atrazine effects on antioxidant status and xenobiotic metabolizing enzymes after oral administration in peripubertal male rat

Previously, we reported that in vivo applied atrazine from postnatal day 23 to 50 induced strong inhibition of testicular steroidogenesis. Therefore, the aim of the present study was to investigate, in the same experimental model, the oxidative status in androgen-producing testicular interstitial compartment characterized by diminished steroidogenesis. In parallel, we determined activities of antioxidative and cytochrome P450 (CYP) xenobiotic-metabolizing enzymes in liver. To confirm the results on atrazine induced-inhibition of testicular androgenesis, we measured ex vivo production of androgen in Leydig cells. The results revealed decreased activity of antioxidant enzymes, especially glutathione S-transferase (GST), but also glutathione peroxidase (GSH-Px) and catalase (CAT) in testicular interstitial cells, in parallel with strongly diminished ex vivo basal and agonist-stimulated Leydig cell androgenesis. In liver, atrazine increased the activity of GSH-Px, GST, and CYP1A1/2 enzyme, but not lipid peroxidation. These results indicate that atrazine markedly affects both antioxidant status and androgenesis in peripubertal rats.

Upregulation of peripubertal rat Leydig cell steroidogenesis following 24 h in vitro and in vivo exposure to atrazine

Atrazine is currently one of the most widely used herbicides in the United States and elsewhere. Here we examined 24 h in vitro and in vivo effects of atrazine on androgen production and on expression and activity of steroidogenic enzymes and regulatory proteins involved in cyclic adenosine monophosphate (cAMP)-signaling pathway in peripubertal rat Leydig cells. When in vitro added, 1-50 μM atrazine increased basal and human chorion gonadotropin-stimulated testosterone production and accumulation of cAMP in the medium of treated cells. The stimulatory action of atrazine on androgen production but not on cAMP accumulation was abolished in cells with inhibited protein kinase A. Atrazine also stimulated the expression of mRNA transcripts for steroidogenic factor-1, steroidogenic acute regulatory protein, cytochrome P450 (CYP)17A1, and 17β-hydroxysteroid dehydrogenase (HSD), as well as the activity of CYP17A1 and 17βHSD. The stimulatory effects of atrazine on cAMP accumulation and androgen production were also observed during the first 3 days of in vivo treatment (200 mg/kg body weight, by gavage) followed by a decline during further treatment. These results indicate that atrazine has a transient stimulatory action on cAMP signaling pathway in Leydig cells, leading to facilitated androgenesis.

Atrazine oral exposure of peripubertal male rats downregulates steroidogenesis gene expression in Leydig cells

In the present study, we investigated the effects of oral dosing of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) to peripubertal male rats (50 and 200 mg/kg body weight daily from postnatal days 23-50) on ex vivo Leydig cell steroidogenesis. Leydig cells from treated rats were characterised by significant decline in mRNA transcripts of several genes responsible for steroidogenesis: luteinizing hormone receptor (LHR), scavenger receptor-B1, steroidogenic acute regulatory protein, translocator protein, steroidogenic factor-1, phosphodiesterase 4B, 3beta-hydroxysteroid dehydrogenase (HSD), CYP17A1, and 17betaHSD. In the presence of human chorion gonadotropin, the dose-dependent decrease in extracellular cAMP level and accordingly strong inhibition of androgenesis were obtained. The transcription of LHR gene in Leydig cells of atrazine-treated rats was downregulated in a dose-dependent manner, which could be the reason for reduction in cAMP level and expression of cAMP-dependent genes. To clarify the activity of the steroidogenic enzymes responsible for androgenesis, purified Leydig cells were challenged with different steroid substrates (22OH-cholesterol, pregnenolone, progesterone, and Delta(4)-androstenedione), and the obtained results indicated inhibition of androgen production in Leydig cells isolated from atrazine-treated animals in the presence of all those substrates. However, when Leydig cells were challenged with 22OH-cholesterol, the progesterone level in the incubation medium was unchanged, indicating that decrease in cholesterol transport and/or CYP17A1 and 17betaHSD activity are most probably responsible for inhibition of androgen production after the addition of different substrates. Our results demonstrated that in vivo exposure to atrazine affects Leydig cell steroidogenesis via the inhibition of steroidogenesis gene expression, which is accompanied by decreased androgenesis.