Novel molecular targets associated with testicular dysgenesis induced by gestational exposure to diethylhexyl phthalate in the rat: a role for estradiol

Methodology for developing data-rich Key Event Relationships for Adverse Outcome Pathways exemplified by linking decreased androgen receptor activity with decreased anogenital distance

The Adverse Outcome Pathway (AOP) framework has gained widespread acceptance in toxicological disciplines as a tool for aiding chemical hazard assessment. Despite increased activity in AOP development, progress towards a high volume of fully endorsed AOPs has been slow, partly due to the challenging task of constructing complete AOPs according to the AOP Developer's Handbook. To facilitate greater uptake of new knowledge units onto the open-source AOP-wiki platform, a pragmatic approach was recently proposed. This approach involves considering Key Event Relationships (KERs) for individual development through systematic approaches, as they represent essential units of knowledge from which causality can be inferred; from low complexity test data to adverse outcomes in intact organisms. However, more broadly adopted harmonized methodologies for KER development would be desirable. Using the AOP Developer's Handbook as a guide, a KER linking 'decreased androgen receptor (AR) activity' with 'reduced anogenital distance (AGD)' was developed to demonstrate a methodology applicable for future developments of KERs requiring systematic literature retrieval approaches.

Gut microbiota may contribute to the postnatal male reproductive abnormalities induced by prenatal dibutyl phthalate exposure

Phthalate is an environmental endocrine disruptor that causes direct and intergenerational male reproductive damage. However, its mechanisms require further investigation. The role of gut microbiota in male reproductive function has been gradually revealed in the past. To explore the intergenerational testicular injury and the influence on offspring gut microbiota of the widely used phthalate dibutyl phthalate (DBP), we conducted a prenatal DBP exposure experiment with microbiota sequencing. We finally explained the gestational DBP exposure-induced gut dysbacteriosis, which is one of the mechanisms of testicular injury in the offspring. The occurrence of seminiferous atrophy and spermatogenic cells apoptosis showed a slight increase. Our study partially supported the results of previous research works on the characteristics of gut dysbacteriosis, which featured the increased relative abundance of Bacteroidetes, Prevotella and P. copri. Focusing on the role of gut microbiota in reproductive function is important. Future studies need to investigate the relationship between environmental pollution and human health.

Research progress on the effect of Di-(2-ethylhexyl) phthalate (DEHP) on reproductive health at different periods in life

Di-(2-ethylhexyl) phthalate (DEHP) is a representative endocrine-disrupting chemical (EDC) that has reproductive, developmental, neurological and immune toxicity in humans and rodents, of which damage to the reproductive system is the most serious. However, exposure to DEHP at different stages of life may produce different symptoms. Studies on this substance are also controversial. This review describes the reproductive effects of DEHP in males and females at different life stages, including infancy, childhood and adulthood.

Di-(2-ethylhexyl) phthalate induces testicular endoplasmic reticulum stress and germ cell apoptosis in adolescent mice

Di-(2-ethylhexyl) phthalate (DEHP) is a male reproductive toxicant. This research is aimed at investigating the effect of pubertal DEHP exposure on testicular endoplasmic reticulum (ER) stress and germ cell apoptosis. Five-week-old male mice were orally administered with DEHP (0, 0.5, 50, or 500 mg/kg/day) for 35 days. Testis weight and sperm count were reduced in mice exposed to 500 mg/kg/day DEHP. The number of seminiferous tubules in stages VII-VIII, mature seminiferous tubules, was reduced and the number of seminiferous tubules in stages IX-XII, immature seminiferous tubules, was elevated in mice treated with 500 mg/kg/day DEHP. Numerous apoptotic germ cells were observed in mouse seminiferous tubules exposed to 50 and 500 mg/kg/day DEHP. Moreover, cleaved caspase-3 was elevated in mouse testes exposed to 500 mg/kg/day DEHP. In addition, Bcl-2 was reduced and Bax/Bcl-2 was elevated in mouse testes exposed to 500 mg/kg/day DEHP. Additional experiment showed that GRP78, an ER molecular chaperone, was downregulated in mouse testes exposed to 500 mg/kg/day DEHP. Testicular p-IRE-1α, p-JNK, and CHOP, three markers of ER stress, were upregulated in mice exposed to 500 mg/kg/day DEHP. These results suggest that pubertal exposure to high doses of DEHP induces germ cell apoptosis partially through initiating ER stress in testes.

Gestational and pubertal exposure to low dose of di-(2-ethylhexyl) phthalate impairs sperm quality in adult mice

Di-(2-ethylhexyl)-phthalate (DEHP) is a compound widely used as a plasticizer, which can leach from plastics into the environment and thus influence human health. The aim of this study was to analyze whether exposure to an environmentally relevant dose of DEHP during mice fetal development or puberty can cause long-lasting changes detectable month/s after the last exposure. We used a DEHP concentration relevant to a daily human intake of 2.4-3 μg/kg of body weight/day. CD1 outbred mice were treated either in utero or postnatally during puberty and analyzed in adulthood. Analyzing fertility parameters using morphometric, histologic, genomic and proteomic methods we showed that DEHP exposure leads to decreased sperm concentration and quality, in both experimental groups. Moreover, the changes in anogenital distance, seminal vesicle weight, and testicular gene expression suggest a disturbance of androgen signaling in exposed animals. In conclusion, we hereby present, that the prenatal and pubertal exposure to a low dose of DEHP negatively influenced reproductive endpoints in male mice, and some of the effects were persistent until adulthood.

All-trans Retinoic Acid Disrupts Development in Ex Vivo Cultured Fetal Rat Testes. II: Modulation of Mono-(2-ethylhexyl) Phthalate Toxicity

Humans are universally exposed to low levels of phthalate esters (phthalates), which are used to plasticize polyvinyl chloride. Phthalates exert adverse effects on the development of seminiferous cords in the fetal testis through unknown toxicity pathways. To investigate the hypothesis that phthalates alter seminiferous cord development by disrupting retinoic acid (RA) signaling in the fetal testis, gestational day 15 fetal rat testes were exposed for 1-3 days to 10-6 M all-trans retinoic acid (ATRA) alone or in combination with 10-6-10-4 M mono-(2-ethylhexyl) phthalate (MEHP) in ex vivo culture. As previously reported, exogenous ATRA reduced seminiferous cord number. This effect was attenuated in a concentration-dependent fashion by MEHP co-exposure. ATRA and MEHP-exposed testes were depleted of DDX4-positive germ cells but not Sertoli cells. MEHP alone enhanced the expression of the RA receptor target Rbp1 and the ovary development-associated genes Wnt4 and Nr0b1, and suppressed expression of the Leydig cell marker, Star, and the germ cell markers, Ddx4 and Pou5f1. In co-exposures, MEHP predominantly enhanced the gene expression effects of ATRA, but the Wnt4 and Nr0b1 concentration-responses were nonlinear. Similarly, ATRA increased the number of cells expressing the granulosa cell marker FOXL2 in testis cultures, but this induction was attenuated by addition of MEHP. These results indicate that MEHP can both enhance and inhibit actions of ATRA during fetal testis development and provide evidence that RA signaling is a target for phthalate toxicity in the fetal testis.

Lactobacillus plantarum TW1-1 Alleviates Diethylhexylphthalate-Induced Testicular Damage in Mice by Modulating Gut Microbiota and Decreasing Inflammation

Diethylhexylphthalate (DEHP), acting as an endocrine disruptor, disturbed reproductive health. Here, we evaluated the effects of Lactobacillus plantarum TW1-1 (L. plantarum TW1-1) on DEHP-induced testicular damage in adult male mice. Results showed that oral supplementation of L. plantarum TW1-1 significantly increased the serum testosterone concentration, enhanced the semen quality, and attenuated gonad development defects in DEHP-exposed mice. L. plantarum TW1-1 also alleviated DEHP-induced oxidative stress and inflammatory responses by decreasing the mRNA expression and serum protein concentration of different inflammatory factors [tumor necrosis factor-α, interleukin (IL)-1β and IL-6]. Furthermore, L. plantarum TW1-1 significantly reduced DEHP-induced intestinal hyper-permeability and the increase in the serum lipopolysaccharide level. Gut microbiota diversity analysis revealed that L. plantarum TW1-1 shifted the DEHP-disrupted gut microbiota to that of the control mice. At phylum level, L. plantarum TW1-1 reversed DEHP-induced Bacteroidetes increase and Firmicutes decrease, and restored Deferribacteres in DEHP-exposed mice. Spearman's correlation analysis showed that Bacteroidetes, Deferribacteres, and Firmicutes were associated with DEHP-induced testicular damage. In addition, the ratio of Firmicutes to Bacteroidetes (Firm/Bac ratio) significantly decreased from 0.28 (control group) to 0.13 (DEHP-exposed group), which was restored by L. plantarum TW1-1 treatment. Correlation analysis showed that the Firm/Bac ratio was negatively correlated with testicular damage and inflammation. These findings suggest that L. plantarum TW1-1 prevents DEHP-induced testicular damage via modulating gut microbiota and decreasing inflammation.

Lactobacillus plantarum TW1-1 Alleviates Diethylhexylphthalate-Induced Testicular Damage in Mice by Modulating Gut Microbiota and Decreasing Inflammation

Diethylhexylphthalate (DEHP), acting as an endocrine disruptor, disturbed reproductive health. Here, we evaluated the effects of Lactobacillus plantarum TW1-1 (L. plantarum TW1-1) on DEHP-induced testicular damage in adult male mice. Results showed that oral supplementation of L. plantarum TW1-1 significantly increased the serum testosterone concentration, enhanced the semen quality, and attenuated gonad development defects in DEHP-exposed mice. L. plantarum TW1-1 also alleviated DEHP-induced oxidative stress and inflammatory responses by decreasing the mRNA expression and serum protein concentration of different inflammatory factors [tumor necrosis factor-α, interleukin (IL)-1β and IL-6]. Furthermore, L. plantarum TW1-1 significantly reduced DEHP-induced intestinal hyper-permeability and the increase in the serum lipopolysaccharide level. Gut microbiota diversity analysis revealed that L. plantarum TW1-1 shifted the DEHP-disrupted gut microbiota to that of the control mice. At phylum level, L. plantarum TW1-1 reversed DEHP-induced Bacteroidetes increase and Firmicutes decrease, and restored Deferribacteres in DEHP-exposed mice. Spearman's correlation analysis showed that Bacteroidetes, Deferribacteres, and Firmicutes were associated with DEHP-induced testicular damage. In addition, the ratio of Firmicutes to Bacteroidetes (Firm/Bac ratio) significantly decreased from 0.28 (control group) to 0.13 (DEHP-exposed group), which was restored by L. plantarum TW1-1 treatment. Correlation analysis showed that the Firm/Bac ratio was negatively correlated with testicular damage and inflammation. These findings suggest that L. plantarum TW1-1 prevents DEHP-induced testicular damage via modulating gut microbiota and decreasing inflammation.

A systematic review on the adverse health effects of di-2-ethylhexyl phthalate

Di (ethylhexyl) phthalate (DEHP) is a global environmental pollutant. This study aims to systematically review the literature on health effects of exposure to DEHP including effects on reproductive health, carcinogenesis, pregnancy outcome, and respiratory system. The literature search was done through Scopus, ISI Web of Science, Google Scholar, PubMed, Medline, and the reference lists of previous review articles to identify relevant articles published to June 2016 in each subject area. The inclusion criteria were as follows: original research, cross-sectional studies, case-control studies, cohort studies, interventional studies, and review articles. Both human and animal studies were included. The search was limited to English language papers. Conference papers, editorials, and letters were not included. The systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Overall, 152 of the 407 papers met the inclusion criteria. We provided an up-to-date comprehensive and critical assessment of both human and animal studies undertaken to explore the effects of DEHP. It revealed that in experimental studies, exposure to DEHP mainly targeted the reproductive, neurodevelopment, and respiratory systems. Human studies reported that exposure to this contaminant had carcinogenic effects and influenced neurodevelopment in early life. This systematic review underscored the adverse health effects of DEHP for pregnant women and the pediatric age group. It summarizes different response of humans and experimental animals to DEHP exposure, and some suggested underlying mechanisms.

Systems Toxicology of Male Reproductive Development: Profiling 774 Chemicals for Molecular Targets and Adverse Outcomes

BACKGROUND

Trends in male reproductive health have been reported for increased rates of testicular germ cell tumors, low semen quality, cryptorchidism, and hypospadias, which have been associated with prenatal environmental chemical exposure based on human and animal studies.

OBJECTIVE

In the present study we aimed to identify significant correlations between environmental chemicals, molecular targets, and adverse outcomes across a broad chemical landscape with emphasis on developmental toxicity of the male reproductive system.

METHODS

We used U.S. EPA's animal study database (ToxRefDB) and a comprehensive literature analysis to identify 774 chemicals that have been evaluated for adverse effects on male reproductive parameters, and then used U.S. EPA's in vitro high-throughput screening (HTS) database (ToxCastDB) to profile their bioactivity across approximately 800 molecular and cellular features.

RESULTS

A phenotypic hierarchy of testicular atrophy, sperm effects, tumors, and malformations, a composite resembling the human testicular dysgenesis syndrome (TDS) hypothesis, was observed in 281 chemicals. A subset of 54 chemicals with male developmental consequences had in vitro bioactivity on molecular targets that could be condensed into 156 gene annotations in a bipartite network.

CONCLUSION

Computational modeling of available in vivo and in vitro data for chemicals that produce adverse effects on male reproductive end points revealed a phenotypic hierarchy across animal studies consistent with the human TDS hypothesis. We confirmed the known role of estrogen and androgen signaling pathways in rodent TDS, and importantly, broadened the list of molecular targets to include retinoic acid signaling, vascular remodeling proteins, G-protein coupled receptors (GPCRs), and cytochrome P450s.

CITATION

Leung MC, Phuong J, Baker NC, Sipes NS, Klinefelter GR, Martin MT, McLaurin KW, Setzer RW, Darney SP, Judson RS, Knudsen TB. 2016. Systems toxicology of male reproductive development: profiling 774 chemicals for molecular targets and adverse outcomes. Environ Health Perspect 124:1050-1061; http://dx.doi.org/10.1289/ehp.1510385.

Developmental origins of male subfertility: role of infection, inflammation, and environmental factors

Male gamete development begins with the specification of primordial cells in the epiblast of the early embryo and is not complete until spermatozoa mature in the epididymis of adult males. This protracted developmental process involves extensive alteration of the paternal germline epigenome. Initially, epigenetic reprogramming in fetal germ cells results in removal of most DNA methylation, including parent-specific epigenetic information. The germ cells then establish sex-specific epigenetic information through de novo methylation and undergo spermatogenesis. Chromatin in haploid germ cells is repackaged into protamines during spermiogenesis, providing further widespread epigenetic reorganization. Finally, after fertilization, epigenetic reprogramming in the preimplantation embryo is necessary for regaining totipotency. These events provide substantial windows during which epigenetic errors either may be corrected or may occur in the germline. There is now increasing evidence that environmental factors such as exposure to toxicants, the parents' and individual's diet, and even infectious and inflammatory events in the male reproductive tract may influence epigenetic reprogramming. This, together with other damage inflicted on the germline chromatin, may result in negative consequences for fertility and health. Large epidemiological birth cohort studies have yielded insight into possible causative environmental factors. Together with experimental animal studies, a clearer view of environmental impacts on fetal development and their intergenerational and even transgenerational effects on reproductive health has emerged and is reviewed in this article.

Prenatal Exposures of Male Rats to the Environmental Chemicals Bisphenol A and Di(2-Ethylhexyl) Phthalate Impact the Sexual Differentiation Process

The increasing incidence of reproductive anomalies, described as testicular dysgenesis syndrome, is thought to be related to the exposure of the population to chemicals in the environment. Bisphenol A (BPA) and di(2-ethylhexyl)phthalate (DEHP), which have hormonal and antihormonal activity, have attracted public attention due to their presence in consumer products. The present study investigated the effects of BPA and DEHP on reproductive development. Timed-pregnant female rats were exposed to BPA and DEHP by gavage from gestational days 12 to 21. Results showed that prenatal exposures to test chemicals exerted variable effects on steroidogenic factor 1 and GATA binding protein 4 protein expression and increased (P < .05) sex-determining region Y-box 9 and antimüllerian hormone protein in the infantile rat testis compared with levels in the control unexposed animals. Pituitary LHβ and FSHβ subunit protein expression was increased (P < .05) in BPA- and DEHP-exposed prepubertal male rats but were decreased (P < .05) in adult animals relative to control. Exposure to both BPA and DEHP in utero inhibited (P < .05) global DNA hydroxymethylation in the adult testis in association with altered DNA methyltransferase protein expression. Together the present data suggest that altered developmental programming in the testes associated with chemical exposures are related to the disruption of sexual differentiation events and DNA methylation patterns. The chemical-induced effects impact the development of steroidogenic capacity in the adult testis.

In utero exposure to di-(2-ethylhexyl) phthalate induces testicular effects in neonatal rats that are antagonized by genistein cotreatment

Fetal exposure to endocrine disruptors (EDs) is believed to predispose males to reproductive abnormalities. Although males are exposed to combinations of chemicals, few studies have evaluated the effects of ED mixtures at environmentally relevant doses. Our previous work showed that fetal exposure to a mixture of the phytoestrogen genistein (GEN) and the plasticizer di-(2-ethylhexyl) phthalate (DEHP) induced unique alterations in adult testis. In this follow-up study, we examined Postnatal Day 3 (PND3) and PND6 male offspring exposed from Gestational Day 14 to parturition to corn oil, 10mg/kg GEN, DEHP, or their combination, to gain insight into the early molecular events driving long-term alterations. DEHP stimulated the mRNA and protein expression of the steroidogenic enzyme HSD3B, uniquely at PND3. DEHP also increased the mRNA expression of Nestin, a Leydig progenitor/Sertoli cell marker, and markers of Sertoli cell (Wt1), gonocyte (Plzf, Foxo1), and proliferation (Pcna) at PND3, while these genes were unchanged by the mixture. Redox (Nqo1, Sod2, Sod3, Trx, Gst, Cat) and xenobiotic transporter (Abcb1b, Abcg2) gene expression was also increased by DEHP at PND3, while attenuated when combined with GEN, suggesting the involvement of cellular stress in short-term DEHP effects and a protective effect of GEN. The direct effects of GEN and mono-(2-ethylhexyl) phthalate, the principal bioactive metabolite of DEHP, on testis were investigated in PND3 organ cultures, showing a stimulatory effect of 10 μM mono-(2-ethylhexyl) phthalate on basal testosterone production that was normalized by GEN. These effects contrasted with previous reports of androgen suppression and decreased gene expression in perinatal rat testis by high DEHP doses, implying that neonatal effects are not predictive of adult effects. We propose that GEN, through an antioxidant action, normalizes reactive oxygen species-induced neonatal effects of DEHP. The notion that these EDs do not follow classical dose-response effects and involve different mechanisms of toxicity from perinatal ages to adulthood highlights the importance of assessing impacts across a range of doses and ages.

Endocrine-disrupting Chemicals: Review of Toxicological Mechanisms Using Molecular Pathway Analysis

Endocrine disruptors are known to cause harmful effects to human through various exposure routes. These chemicals mainly appear to interfere with the endocrine or hormone systems. As importantly, numerous studies have demonstrated that the accumulation of endocrine disruptors can induce fatal disorders including obesity and cancer. Using diverse biological tools, the potential molecular mechanisms related with these diseases by exposure of endocrine disruptors. Recently, pathway analysis, a bioinformatics tool, is being widely used to predict the potential mechanism or biological network of certain chemicals. In this review, we initially summarize the major molecular mechanisms involved in the induction of the above mentioned diseases by endocrine disruptors. Additionally, we provide the potential markers and signaling mechanisms discovered via pathway analysis under exposure to representative endocrine disruptors, bisphenol, diethylhexylphthalate, and nonylphenol. The review emphasizes the importance of pathway analysis using bioinformatics to finding the specific mechanisms of toxic chemicals, including endocrine disruptors.

Serum phthalate levels and time to pregnancy in couples from Greenland, Poland and Ukraine

Phthalates are ubiquitous industrial chemicals that have been associated with altered reproductive function in rodents. Several human studies have reported an inverse association between male testosterone and phthalate levels. Our aim was to investigate time to pregnancy (TTP) according to serum levels of diethylhexyl phthalate (DEHP) and diisononyl phthalate (DiNP) metabolites in both partners. In 2002-2004 we enrolled 938 pregnant women and 401 male spouses from Greenland, Poland and Ukraine. Six oxidized metabolites of DEHP and DiNP were summarized for each of the two parent compounds to provide proxies of the internal exposure. We used Cox discrete-time models to estimate fecundability ratios (FR) and 95% confidence intervals (95% CIs) for men and women according to their proxy-DEHP or -DiNP serum levels adjusted for a fixed set of covariates.

The FR was slightly elevated among women with high levels of DEHP (FR=1.14, 95% CI 1.00;1.30) suggesting a shorter TTP in these women. The FR was unrelated to DiNP in women, whereas the results for men were inconsistent pointing in opposite directions. First-time pregnant women from Greenland with high serum DiNP levels had a longer TTP. This study spanning large contrast in environmental exposure does not indicate adverse effects of phthalates on couple fecundity. The shorter TTP in women with high levels of DEHP metabolites is unexplained and needs further investigation.

Interpreting histopathology in the epididymis

While most of this Special Issue is devoted to the testis (which is where most drug and chemically induced toxicity of the male reproductive tract is identified), being able to recognize and understand the potential effects of toxicants on the epididymis is immensely important and an area that is often overlooked. The epididymis is the organ where the post-testicular sperm differentiation occurs, through a complex and still not completely understood sperm maturation process, allowing them to fertilize the oocyte. Also in the epididymis, sperm are stored until ejaculation, while being protected from immunogenic reaction by a blood-epididymis barrier. From a toxicologic perspective the epididymis is inherently complicated as its structure and function can be altered both indirectly and directly. In this review we will discuss the factors that must be considered when attempting to distinguish between indirect and direct epididymal toxicity and highlight what is currently known about mechanisms of epididymal toxicants, using the rat as a reference model. We identify 2 distinguishable signature lesions - one representing androgen deprivation (secondary to Leydig cell toxicity in the testis) and another representing a direct acting toxicant. Other commonly observed alterations will also be shown and discussed. Finally, we point out that many of the key functions of the epididymis can be altered in the absence of a detectable change in tissue structure. Collectively, we hope this will provide pathologists with increased confidence in identification of epididymal toxicity and enable more informed guidance as mechanism of action is considered.

Nuclear receptors and endocrine disruptors in fetal and neonatal testes: a gapped landscape

During the last decades, many studies reported that male reproductive disorders are increasing among humans. It is currently acknowledged that these abnormalities can result from fetal exposure to environmental chemicals that are progressively becoming more concentrated and widespread in our environment. Among the chemicals present in the environment (air, water, food, and many consumer products), several can act as endocrine disrupting compounds (EDCs), thus interfering with the endocrine system. Phthalates, bisphenol A (BPA), and diethylstilbestrol (DES) have been largely incriminated, particularly during the fetal and neonatal period, due to their estrogenic and/or anti-androgenic properties. Indeed, many epidemiological and experimental studies have highlighted their deleterious impact on fetal and neonatal testis development. As EDCs can affect many different genomic and non-genomic pathways, the mechanisms underlying the adverse effects of EDC exposure are difficult to elucidate. Using literature data and results from our laboratory, in the present review, we discuss the role of classical nuclear receptors (genomic pathway) in the fetal and neonatal testis response to EDC exposure, particularly to phthalates, BPA, and DES. Among the nuclear receptors, we focused on some of the most likely candidates, such as peroxisome-proliferator activated receptor (PPAR), androgen receptor (AR), estrogen receptors (ERα and β), liver X receptors (LXR), and small heterodimer partner (SHP). First, we describe the expression and potential functions (based on data from studies using receptor agonists and mouse knockout models) of these nuclear receptors in the developing testis. Then, for each EDC studied, we summarize the main evidences indicating that the reprotoxic effect of each EDC under study is mediated through a specific nuclear receptor(s). We also point-out the involvement of other receptors and nuclear receptor-independent pathways.

Phthalate-induced pathology in the foetal testis involves more than decreased testosterone production

Foetal exposure to phthalates is known to adversely impact male reproductive development and function. Developmental anomalies of reproductive tract have been attributed to impaired testosterone synthesis. However, species differences in the ability to produce testosterone have been noted; e.g., following foetal exposure, abnormal clustering of Leydig cells or decreased production of testosterone that is manifested in rats does not occur in mice or humans. Nonetheless, other facets of testicular dysgenesis occur in both rats and mice as well as in some other species tested. We recently published a comprehensive evaluation of the foetal rat testis proteome, following in utero exposure to diethylhexyl phthalate (DEHP), which revealed changes in individual proteins that are known to be factors in cellular differentiation and migration or related to the capacity of the foetal Leydig cell to produce testosterone and fit a pathway network in which each is regulated directly or indirectly by oestradiol. Plasma oestradiol indeed was found to be elevated approximately twofold in 19-day-old DEHP-exposed foetal male rats. In this brief review, we discuss our new findings vis-à-vis ‘oestrogen hypothesis’ as a cause for testicular dysgenesis syndrome.

What should it take to describe a substance or product as 'sperm-safe'

BACKGROUND

Male reproductive potential continues to be adversely affected by many environmental, industrial and pharmaceutical toxins. Pre-emptive testing for reproductive toxicological (side-)effects remains limited, or even non-existent. Many products that come into direct contact with spermatozoa lack adequate testing for the absence of adverse effects, and numerous products that are intended for exposure to spermatozoa have only a general assumption of safety based on the absence of evidence of actual harm. Such assumptions can have unfortunate adverse impacts on at-risk individuals (e.g. couples who are trying to conceive), illustrating a clear need for appropriate up-front testing to establish actual 'sperm safety'.

METHODS

After compiling a list of general areas within the review's scope, relevant literature and other information was obtained from the authors' personal professional libraries and archives, and supplemented as necessary using PubMed and Google searches. Review by co-authors identified and eliminated errors of omission or bias.

RESULTS

This review provides an overview of the broad range of substances, materials and products that can affect male fertility, especially through sperm fertilizing ability, along with a discussion of practical methods and bioassays for their evaluation. It is concluded that products can only be claimed to be 'sperm-safe' after performing objective, properly designed experimental studies; extrapolation from supposed predicate products or other assumptions cannot be trusted.

CONCLUSIONS

We call for adopting the precautionary principle, especially when exposure to a product might affect not only a couple's fertility potential but also the health of resulting offspring and perhaps future generations.

Transgenerational effects of di-(2-ethylhexyl) phthalate on testicular germ cell associations and spermatogonial stem cells in mice

Recent evidence has linked human phthalate exposure to abnormal reproductive and hormonal effects. Phthalates are plasticizers that confer flexibility and transparency to plastics, but they readily contaminate the body and the environment. In this study, timed pregnant CD1 outbred mice were treated with di-(2-ethylhexyl) phthalate (DEHP) from Embryonic Day 7 (E7) to E14. The subsequent generation (F1) offspring were then bred to produce the F2, F3, and F4 offspring, without any further DEHP treatment. This exposure scheme disrupted testicular germ cell association and decreased sperm count and motility in F1 to F4 offspring. By spermatogonial transplantation techniques, the exposure scheme also disrupted spermatogonial stem cell (SSC) function of F3 offspring. The W/W(V) recipient testes transplanted with F3 offspring germ cells from the DEHP-treated group had a dramatically lower percentage of donor germ cell-derived spermatogenic recovery in seminiferous tubules when compared to the recipient testes transplanted with CD1 control germ cells. Further characterization showed that the major block of donor germ cell-derived spermatogenesis was before the appearance of undifferentiated spermatogonia. Interestingly, the testes transplanted with the F3 offspring germ cells from the DEHP-treated group, when regenerated, replicated testis morphology similar to that observed in the testes from the F1 to F3 offspring of the DEHP-treated group, suggesting that the germ cell disorganization phenotype originates from the stem cells of F3 offspring. In conclusion, embryonic exposure to DEHP was found to disrupt testicular germ cell organization and SSC function in a transgenerational manner.