Dichlorodiphenyltrichloroethane impairs follicle-stimulating hormone receptor-mediated signaling in rat Sertoli cells

In Vitro and In Vivo Models for Drug Transport Across the Blood-Testis Barrier

The blood-testis barrier (BTB) is a selectively permeable membrane barrier formed by adjacent Sertoli cells (SCs) in the seminiferous tubules of the testes that develops intercellular junctional complexes to protect developing germ cells from external pressures. However, due to this inherent defense mechanism, the seminiferous tubule lumen can act as a pharmacological sanctuary site for latent viruses (e.g., Ebola, Zika) and cancers (e.g., leukemia). Therefore, it is critical to identify and evaluate BTB carrier-mediated drug delivery pathways to successfully treat these viruses and cancers. Many drugs are unable to effectively cross cell membranes without assistance from carrier proteins like transporters because they are large, polar, and often carry a charge at physiologic pH. SCs express transporters that selectively permit endogenous compounds, such as carnitine or nucleosides, across the BTB to support normal physiologic activity, although reproductive toxicants can also use these pathways, thereby circumventing the BTB. Certain xenobiotics, including select cancer therapeutics, antivirals, contraceptives, and environmental toxicants, are known to accumulate within the male genital tract and cause testicular toxicity; however, the transport pathways by which these compounds circumvent the BTB are largely unknown. Consequently, there is a need to identify the clinically relevant BTB transport pathways in in vitro and in vivo BTB models that recapitulate human pharmacokinetics and pharmacodynamics for these xenobiotics. This review summarizes the various in vitro and in vivo models of the BTB reported in the literature and highlights the strengths and weaknesses of certain models for drug disposition studies. SIGNIFICANCE STATEMENT: Drug disposition to the testes is influenced by the physical, physiological, and immunological components of the blood-testis barrier (BTB). But many compounds are known to cross the BTB by transporters, resulting in pharmacological and/or toxicological effects in the testes. Therefore, models that assess drug transport across the human BTB must adequately account for these confounding factors. This review identifies and discusses the benefits and limitations of various in vitro and in vivo BTB models for preclinical drug disposition studies.

Impact of environmental toxin exposure on male fertility potential

Idiopathic infertility is the most common individual diagnosis in male infertility, representing nearly 44% of cases. Research studies dating over the last half-century consistently demonstrate a decline in male fertility that is incompletely explained by obesity, known genetic causes, or diet and lifestyle changes alone. Human exposures have changed dramatically over the same time course as this fertility decline. Synthetic chemicals surround us. Some are benevolent; however, many are known to cause disruption of the hypothalamic-pituitary-gonadal axis and impair spermatogenesis. More than 80,000 chemicals are registered with the United States National Toxicology Program and nearly 2,000 new chemicals are introduced each year. Many of these are known toxins, such as phthalates, polycyclic aromatic hydrocarbons, aromatic amines, and organophosphate esters, and have been banned or significantly restricted by other countries as they carry known carcinogenic effects and are reproductively toxic. In the United States, many of these chemicals are still permissible in exposure levels known to cause reproductive harm. This contrasts to other chemical regulatory legislature, such as the European Union’s REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) regulations which are more comprehensive and restrictive. Quantification of these diverse exposures on an individual level has proven challenging, although forthcoming technologies may soon make this data available to consumers. Establishing causality and the proportion of idiopathic infertility attributable to environmental toxin exposures remains elusive, however, continued investigation, avoidance of exposure, and mitigation of risk is essential to our reproductive health. The aim of this review is to examine the literature linking changes in male fertility to some of the most common environmental exposures. Specifically, pesticides and herbicides such as dichlorodiphenyltrichloroethane (DDT), dibromochloropropane (DBCP), organophosphates and atrazine, endocrine disrupting compounds including plastic compounds phthalates and bisphenol A (BPA), heavy metals, natural gas/oil, non-ionizing radiation, air and noise pollution, lifestyle factors including diet, obesity, caffeine use, smoking, alcohol and drug use, as well as commonly prescribed medications will be discussed.

In Vitro Effects of the Endocrine Disruptor p,p'-DDT on Human Follitropin Receptor

BACKGROUND

1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene (p,p'-DDT) is a persistent environmental endocrine disruptor (ED). Several studies have shown an association between p,p'-DDT exposure and reproductive abnormalities.

OBJECTIVES

To investigate the putative effects of p,p'-DDT on the human follitropin receptor (FSHR) function.

METHODS AND RESULTS

We used Chinese hamster ovary (CHO) cells stably expressing human FSHR to investigate the impact of p,p'-DDT on FSHR activity and its interaction with the receptor. At a concentration of 5 μM p,p'-DDT increased the maximum response of the FSHR to follitropin by 32 ± 7.45%. However, 5 μM p,p'-DDT decreased the basal activity and did not influence the maximal response of the closely related LH/hCG receptor to human chorionic gonadotropin (hCG). The potentiating effect of p,p'-DDT was specific for the FSHR. Moreover, in cells that did not express FSHR, p,p'-DDT had no effect on cAMP response. Thus, the potentiating effect of p,p'-DDT was dependent on the FSHR. In addition, p,p'-DDT increased the sensitivity of FSHR to hCG and to a low molecular weight agonist of the FSHR, 3-((5methyl)-2-(4-benzyloxy-phenyl)-5-{[2-[3-ethoxy-4-methoxy-phenyl)-ethylcarbamoyl]-methyl}-4-oxo-thiazolidin-3-yl)-benzamide (16a). Basal activity in response to p,p'-DDT and potentiation of the FSHR response to FSH by p,p'-DDT varied among FSHR mutants with altered transmembrane domains (TMDs), consistent with an effect of p,p'-DDT via TMD binding. This finding was corroborated by the results of simultaneously docking p,p'-DDT and 16a into the FSHR transmembrane bundle.

CONCLUSION

p,p'-DDT acted as a positive allosteric modulator of the FSHR in our experimental model. These findings suggest that G protein-coupled receptors are additional targets of endocrine disruptors.

CITATION

Munier M, Grouleff J, Gourdin L, Fauchard M, Chantreau V, Henrion D, Coutant R, Schiøtt B, Chabbert M, Rodien P. 2016. In vitro effects of the endocrine disruptor p,p'-DDT on human follitropin receptor. Environ Health Perspect 124:991-999; http://dx.doi.org/10.1289/ehp.1510006.

Occupational exposure to pesticides and consequences on male semen and fertility: a review

Exposure to pesticides affects many body organs including reproductive system. Disorder of the reproductive system leads to infertility and therefore has been in the center of attention within the recent decades. Pesticides are one of the compounds that might reduce the semen quality in the exposed workers according to current knowledge. Although many underlying mechanisms have been proposed, the mechanisms of action are not clarified yet. The object of the present review was to criticize all the results of studies which evaluated the pesticide effects on male reproductive system. Results indicate that semen changes are multifactorial in the workers exposed to pesticides as there are numerous factors affecting sperm quality in occupational exposures. Majority of pesticides including organophosphoruses affect the male reproductive system by mechanisms such as reduction of sperm density and motility, inhibition of spermatogenesis, reduction of testis weights, reduction of sperm counts, motility, viability and density, and inducing sperm DNA damage, and increasing abnormal sperm morphology. Reduced weight of testes, epididymis, seminal vesicle, and ventral prostate, seminiferous tubule degeneration, change in plasma levels of testosterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH), decreased level and activity of the antioxidant enzymes in testes, and inhibited testicular steroidogenesis are other possible mechanisms. Moreover, DDT and its metabolites have estrogenic effects on males. Although effect of pesticides on sperm quality is undeniable, well-designed long-term studies are needed to elucidate all the possible affecting variables such as socioeconomic, cultural, nutritional, occupational, physical, and clinical characteristics alongside pesticides.

Effects of p,p'-DDE on the mRNA and protein expressions of vimentin, N-cadherin and FSHR in rats testes: an in vivo and in vitro study

To elucidate the mechanism underlying the testicular effects of 1,1-dichloro-2,2bis(p-chlorophenyl)ethylene (p,p'-DDE), the expressions of vimentin, neural cadherin and follicle-stimulating hormone receptor mRNA and proteins were measured in vivo and in vitro. Sprague-Dawley rats were dosed with p,p'-DDE at 0, 20, 60 and 100 mg/kg every other day by intraperitoneal injection for 10 days, and Sertoli cells were treated with p,p'-DDE (0, 10, 30, and 50 μM) for 24 h. Results indicated that the survival rate of Sertoli cells was decreased with increasing doses of p,p'-DDE. In vitro and in vivo studies, p,p'-DDE could increase the expression of neural cadherin, follicle-stimulating hormone receptor mRNA, while decrease the levels of vimentin, neural cadherin and follicle-stimulating hormone receptor proteins. Moreover, immunohistochemistry analysis revealed that the protein expressions of vimentin, neural cadherin and follicle-stimulating hormone receptor in pubertal rat testes were disrupted by treatment with p,p'-DDE. Taken together, these results suggested that p,p'-DDE exposure could induce testicular toxicity through the changes of the mRNA and protein expressions of vimentin, neural cadherin and follicle-stimulating hormone receptor in vitro and in vivo.

Protective effects of ginsenosides against Bisphenol A-induced cytotoxicity in 15P-1 Sertoli cells via extracellular signal-regulated kinase 1/2 signalling and antioxidant mechanisms

Numerous studies have demonstrated that Bisphenol A (BPA) can cause reproductive toxicity. Ginseng has wide range of pharmacological actions and, more importantly, has proven its worth with respect to reproductive function in several reports. We have suggested that ginsenosides, the main active components of ginseng, may protect against BPA-induced cell damage. Therefore, an in vitro culture model of 15P-1 Sertoli cells was employed to investigate whether ginsenosides have protective effects on BPA-stimulated 15P-1 Sertoli cells. The results revealed that ginsenosides (75 μg/ml) significantly inhibited BPA-induced decreases in cell viability and increases in apoptosis. Immunofluorescence staining showed that BPA exposure-induced collapse of vimentin intermediate filaments was prevented by the application of ginsenosides. Ginsenosides also inhibited extracellular signal-regulated kinase (ERK1/2) phosphorylation and BPA-induced alterations of Bcl-2 and Bax protein expression in 15P-1 Sertoli cells. Furthermore, the alterations of T-AOC, superoxide dismutase, glutathione peroxidase, glutathione reductase, glutathione and malondialdehyde levels in BPA-stimulated cells were partially prevented with pre-treatment with ginsenosides. Taken together, these results suggest that ginsenosides have protective effects against BPA-induced cell damage and that these effects are mediated by preventing ERK1/2 phosphorylation and through the enhancement of cellular antioxidant capacity. Ginsenosides may therefore be beneficial in the prevention of environmental BPA-induced, reproduction-related toxicity.

Developmental regulation of p70 S6 kinase by a G protein-coupled receptor dynamically modelized in primary cells

The mechanisms whereby G protein-coupled receptors (GPCR) activate signalling pathways involved in mRNA translation are ill-defined, in contrast to tyrosine kinase receptors (TKR). We compared a GPCR and a TKR, both endogenously expressed, for their ability to mediate phosphorylation of 70-kDa ribosomal S6 kinase p70S6K in primary rat Sertoli cells at two developmental stages. In proliferating cells stimulated with follicle-stimulating hormone (FSH), active p70S6K was phosphorylated on T389 and T421/S424, through cAMP-dependent kinase (PKA) and phosphatidyl-inositide-3 kinase (PI3K) antagonizing actions. In FSH-stimulated differentiating cells, active p70S6K was phosphorylated solely on T389, PKA and PI3K independently enhancing its activity. At both developmental stages, insulin-induced p70S6K regulation was consistent with reported data. Therefore, TKR and GPCR trigger distinct p70S6K active conformations. p70S6K developmental regulation was formalized in a dynamic mathematical model fitting the data, which led to experimentally inaccessible predictions on p70S6K phosphorylation rate.

Accelerated internalization of junctional membrane proteins (connexin 43, N-cadherin and ZO-1) within endocytic vacuoles: an early event of DDT carcinogenicity

Stability of cell-to-cell interactions and integrity of junctional membrane proteins are essential for biological processes including cancer prevention. The present study shows that DDT, a non-genomic carcinogen used at a non-cytotoxic dose (1 microM), rapidly disrupted the cell-cell contacts and concomitantly induced the formation of cytoplasmic vacuoles close to the plasma membrane in the SerW3 Sertoli cell line. High-resolution deconvolution microscopy reveals that this vacuolization process was clathrin-dependent since a hyperosmotic media (0.2 M sucrose) blocked rhodamine-dextran endocytosis. In response to DDT, junctional proteins such as Cx43, N-Cadherin and ZO-1 were internalized and present in vacuoles. In Cx43-GFP transfected cells, time lapse videomicroscopy demonstrates that DDT rapidly enhanced fragmentation of the gap junction plaques and abolished the gap junction coupling without major modification of Cx43 phosphorylation status. Repeated exposure to DDT resulted in chronic gap junction coupling injury. The present results demonstrate that one of the early effect of DDT is to interfere with the plasma membrane and to perturb its function, specifically its ability to establish cell-cell junctions that are essential for tissue homeostasis and control of cell proliferation and differentiation. Such an alteration may play a specific role during carcinogenesis.