Vinclozolin: A feasibility and sensitivity study of the ILSI-HESI F1-extended one-generation rat reproduction protocol

Azole fungicides inhibit human and rat gonadal 3β-hydroxysteroid dehydrogenases: Structure-activity relationship and in silico docking analysis

Azole fungicides are widely used in the agricultural industry to control fungal infections in crops. However, recent studies have shown that some azole fungicides inhibit the activity of 3β-hydroxysteroid dehydrogenases (3β-HSDs) in the gonads. Out of the 16 azole fungicides tested, 8 were found to inhibit human KGN cell 3β-HSD2 with IC50 values of less than 100 μM. The strongest inhibitor was difenoconazole, with an IC50 value of 1.88 μM. In contrast, only 3 of the azole fungicides inhibited rat testicular 3β-HSD1, which was less sensitive to inhibition. Azole fungicides potently inhibited progesterone secretion by KGN cells under basal and forskolin stimulated conditions at ≥ 5 μM. The inhibitory strength of azole fungicides was determined by their lipophilicity (LogP), molecular weight, pKa, and binding energy. A pharmacophore analysis revealed that the hydrogen bond acceptor-lipid group was a critical feature required for inhibition. Overall, these findings suggest that the use of azole fungicides have unintended consequences on reproductive health due to their inhibition of gonadal 3β-HSDs. Key words: Azole fungicides; steroid hormones; 3β-hydroxysteroid dehydrogenase; docking analysis; lipophilicity.

Long exposure to a mixture of endocrine disruptors prediposes the ventral prostate of rats to preneoplastic lesions

Endocrine disruptors (ED) are compounds dispersed in the environment that modify hormone biosynthesis, affecting hormone-dependent organs such as the prostate. Studies have only focused on evaluating the effects of ED alone or in small groups and short intervals and have not adequately portrayed human exposure. Therefore, we characterized the prostate histoarchitecture of rats exposed to an ED mixture (ED Mix) mimicking human exposure. Pregnant females of the Sprague-Dawley strain were randomly distributed into two experimental groups: Control group (vehicle: corn oil, by gavage) and ED Mix group: received 32.11 mg/kg/day of the ED mixture diluted in corn oil (2 ml/kg), by gavage, from gestational day 7 (DG7) to post-natal day 21 (DPN21). After weaning at DPN22, the male pups continued to receive the complete DE mixture until they were 220 days old when they were euthanized. The ED Mix decreased the epithelial compartment, increased the fractal dimension, and decreased glandular dilation. In addition, low-grade prostatic intraepithelial neoplasia was observed in addition to regions of epithelial atrophy in the group exposed to the ED Mix. Exposure to the mixture decreased both types I and III collagen area in the stroma. We concluded that the ED Mix was able to cause alterations in the prostatic histoarchitecture and induce the appearance of preneoplastic lesions.

AOP key event relationship report: Linking androgen receptor antagonism with nipple retention

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A full AOP KER description linking AR antagonism with nipple retention in rodents.

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Described KER 2133 is a non-adjacent KER of an intended AOP delineating anti-androgenicity as a mode for nipple retention.

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A case study for developing and publishing independent units of information under the AOP framework.

In rat developmental and reproductive toxicity studies, nipple/areola retention (NR) in male offspring is a biomarker for reduced androgen signaling during development. This is because nipples normally regress in male rats in response to androgen signaling during critical stages of development. NR is thus included as a mandatory endpoint in several OECD test guidelines for assessment of chemicals, particularly as a readout for anti-androgenic effects relevant for reproductive toxicity. With the growing interest in developing Adverse Outcome Pathways (AOPs) to aid in chemical risk assessment, a more pragmatic approach has been proposed, whereby essential units of knowledge could be developed independently of complete AOPs, not least emergent key event relationships (KERs). Herein, we have developed a KER linking “androgen receptor antagonism” and “increased areola/nipple retention”. The KER is based on a literature review conducted in a transparent semi-systematic manner in peer-reviewed databases with pre-defined inclusion criteria. Twenty-seven papers were included for development of the KER. The results support a qualitative relationship between the two key events (KEs) with a high weight of evidence; i.e., a causal relationship between androgen receptor (AR) antagonism and nipple retention in male rats exists.

A mixture of 15 phthalates and pesticides below individual chemical no observed adverse effect levels (NOAELs) produces reproductive tract malformations in the male rat

Humans carry residues of multiple synthetic chemicals at any given point in time. Research has demonstrated that compounds with varying molecular initiating events (MIE) that disrupt common key events can act in concert to produce cumulative adverse effects. Congenital defects of the male reproductive tract are some of the most frequently diagnosed malformations in humans and chemical exposures in utero can produce these effects in laboratory animals and humans. Here, we hypothesized that in utero exposure to a mixture of pesticides and phthalates, each of which produce male reproductive tract defects individually, would produce cumulative effects even when each chemical is present at a no observed adverse effect level (NOAEL) specific for male reproductive effects. Pregnant Sprague-Dawley rats were exposed via oral gavage to a fixed-ratio dilution mixture of 5 pesticides (vinclozolin, linuron, procymidone, prochloraz, pyrifluquinazon), 1 pesticide metabolite (dichlorodiphenyldichloroethylene (DDE)), and 9 phthalates (dipentyl, dicyclohexyl, di-2-ethylhexyl, dibutyl, benzyl butyl, diisobutyl, diisoheptyl, dihexyl, and diheptyl) during the critical window of rat fetal masculinization (gestation day 14-18). The top dose (100% dose) contained each compound at a concentration 2-fold greater than the individual chemical NOAEL followed by a dilution series that represented each chemical at NOAEL, NOAEL/2, NOAEL/4, NOAEL/8, NOAEL/15, NOAEL/100, NOAEL/1000. Reduced fetal testis gene expression occurred at NOAEL/15, reduced fetal testis testosterone production occurred at NOAEL/8, reduced anogenital distance, increased nipple retention, and delayed puberty occurred at NOAEL/4, and severe effects including genital malformations and weight reductions in numerous reproductive tissues occurred at NOAEL/2. This study demonstrates that these phthalates and pesticides acted cumulatively to produce adverse effects at doses below which any individual chemical had been shown to produce an effect alone and even though they have different MIEs.

On the Use and Interpretation of Areola/Nipple Retention as a Biomarker for Anti-androgenic Effects in Rat Toxicity Studies

Areola/nipple retention (NR) is an established biomarker for an anti-androgenic mode of action in rat toxicity studies. It is a mandatory measurement under several OECD test guidelines and is typically assessed in combination with anogenital distance (AGD). Both NR and AGD are considered retrospective biomarkers of insufficient androgen signaling during the masculinization programming window in male fetuses. However, there are still aspects concerning NR as a biomarker for endocrine disruption that remains to be clarified. For instance, can NR be regarded a permanent adverse effect? Is it a redundant measurement if AGD is assessed in the same study? Is NR equally sensitive and specific to anti-androgenic chemical substances as a shortening of male AGD? In this review we discuss these and other aspects concerning the use of NR as a biomarker in toxicity studies. We have collected available literature from rat toxicity studies that have reported on NR and synthesized the data in order to draw a clearer picture about the sensitivity and specificity of NR as an effect biomarker for an anti-androgenic mode of action, including comparisons to AGD measurements. We carefully conclude that NR and AGD in rats for the most part display similar sensitivity and specificity, but that there are clear exceptions which support the continued assessment of both endpoints in relevant reproductive toxicity studies. Available literature also support the view that NR in infant male rats signifies a high risk for permanent nipples in adulthood. Finally, the literature suggests that the mechanisms of action leading from a chemical stressor event to either NR or short AGD in male offspring are overlapping with respect to canonical androgen signaling, yet differ with respect to other mechanisms of action.

Multi- and Transgenerational Outcomes of an Exposure to a Mixture of Endocrine-Disrupting Chemicals (EDCs) on Puberty and Maternal Behavior in the Female Rat

BACKGROUND

The effects of endocrine-disrupting chemicals (EDCs) on fertility and reproductive development represent a rising concern in modern societies. Although the neuroendocrine control of sexual maturation is a major target of EDCs, little is known about the potential role of the hypothalamus in puberty and ovulation disruption transmitted across generations.

OBJECTIVES

We hypothesized that developmental exposure to an environmentally relevant dose of EDC mixture could induce multi- and/or transgenerational alterations of sexual maturation and maternal care in female rats through epigenetic reprograming of the hypothalamus. We investigated the transmission of a disrupted reproductive phenotype via the maternal germline or via nongenomic mechanisms involving maternal care.

METHODS

Adult female Wistar rats were exposed prior to and during gestation and until the end of lactation to a mixture of the following 13 EDCs: di-n-butyl phthalate (DnBP), di(2-ethylhexyl) phthalate (DEHP), bisphenol A (BPA), vinclozolin, prochloraz, procymidone, linuron, epoxynaxole, dichlorodiphenyldichloroethylene, octyl methoxynimmate, 4-methylbenzylidene camphor (4-MBC), butylparaben, and acetaminophen. Perinatally exposed offspring (F1) were mated with unexposed males to generate germ cell (F2) and transgenerationally exposed (F3 and F4) females. Sexual maturation, maternal behavior, and hypothalamic targets of exposure were studied across generations.

RESULTS

Germ cell (F2) and transgenerationally (F3) EDC-exposed females, but not F1, displayed delayed pubertal onset and altered folliculogenesis. We reported a transgenerational alteration of key hypothalamic genes controlling puberty and ovulation (Kiss1, Esr1, and Oxt), and we identified the hypothalamic polycomb group of epigenetic repressors as actors of this mechanism. Furthermore, we found a multigenerational reduction of maternal behavior (F1-F3) induced by a loss in hypothalamic dopaminergic signaling. Using a cross-fostering paradigm, we identified that the reduction in maternal phenotype was normalized in EDC-exposed pups raised by unexposed dams, but no reversal of the pubertal phenotype was achieved.

DISCUSSION

Rats developmentally exposed to an EDC mixture exhibited multi- and transgenerational disruption of sexual maturation and maternal care via hypothalamic epigenetic reprogramming. These results raise concerns about the impact of EDC mixtures on future generations. https://doi.org/10.1289/EHP8795.

Effects of the endocrine disruptor vinclozolin in male reproduction: a systematic review and meta-analysis†

Endocrine-disrupting chemicals have become an issue of scientific and public discussion. Vinclozolin (VNZ) is a fungicide that competitively antagonizes the binding of natural androgens to their receptor, disturbing the function of tissues that are sensitive to these hormones, as is the case of the male reproductive organs. A systematic review with meta-analyses of rodent studies was conducted to answer the following question: Does exposure to VNZ affect sperm parameters and testicular/epididymal weight? The methodology was prespecified according to the Cochrane Handbook for Systematic Reviews and PRISMA recommendations. Sixteen articles met the inclusion criteria, comprising a total of 1189 animals. The risk of publication bias was assessed using the Trim and Fill adjustment, funnel plot, and Egger regression test. Heterogeneity and inconsistency across the findings were tested using the Q-statistic and I2 of Higgins, respectively. Sensitivity was also analyzed. Statistical analysis was performed on Comprehensive Meta-Analysis software (Version 2.0), using random models and weighted mean differences along with a 95% confidence interval. Sperm motility, counts, daily sperm production (evidence of publication bias), and epididymis weight were decreased in VNZ-treated animals. Exposure length and dose, as well as the time point of exposure, influenced the obtained results. Despite the moderate/high heterogeneity observed, the sensitivity analysis overall demonstrated the robustness of the findings. The quality scores of the included studies were superior to 4 in a total of 9, then classified as good. The obtained data corroborate the capability of VNZ exposure to disrupt spermatogenic output and compromise male fertility.

Prenatal EDCs Impair Mate and Odor Preference and Activation of the VMN in Male and Female Rats

Environmental endocrine-disrupting chemicals (EDCs) disrupt hormone-dependent biological processes. We examined how prenatal exposure to EDCs act in a sex-specific manner to disrupt social and olfactory behaviors in adulthood and underlying neurobiological mechanisms. Pregnant rat dams were injected daily from embryonic day 8 to 18 with 1 mg/kg Aroclor 1221 (A1221), 1 mg/kg vinclozolin, or the vehicle (6% DMSO in sesame oil). A1221 is a mixture of polychlorinated biphenyls (weakly estrogenic) while vinclozolin is a fungicide (anti-androgenic). Adult male offspring exposed to A1221 or vinclozolin, and females exposed to A1221, had impaired mate preference behavior when given a choice between 2 opposite-sex rats that differed by hormone status. A similar pattern of impairment was observed in an odor preference test for urine-soaked filter paper from the same rat groups. A habituation/dishabituation test revealed that all rats had normal odor discrimination ability. Because of the importance of the ventrolateral portion of the ventromedial nucleus (VMNvl) in mate choice, expression of the immediate early gene product Fos was measured, along with its co-expression in estrogen receptor alpha (ERα) cells. A1221 females with impaired mate and odor preference behavior also had increased neuronal activation in the VMNvl, although not specific to ERα-expressing neurons. Interestingly, males exposed to EDCs had normal Fos expression in this region, suggesting that other neurons and/or brain regions mediate these effects. The high conservation of hormonal, olfactory, and behavioral traits necessary for reproductive success means that EDC contamination and its ability to alter these traits has widespread effects on wildlife and humans.

A Conflicted Tale of Two Novel AR Antagonists In Vitro and In Vivo: Pyrifluquinazon Versus Bisphenol C

Chemicals that disrupt androgen receptor (AR) function in utero induce a cascade of adverse effects in male rats including reduced anogenital distance, retained nipples, and reproductive tract malformations. The objective of this study was to compare the in vitro and in utero activities of two novel AR antagonists, bisphenol C (BPC) and pyrifluquinazon (PFQ). In vitro, BPC was as potent an AR antagonist as hydroxyflutamide. Furthermore, BPC inhibited fetal testis testosterone production and testis gene expression ex vivo. However, when BPC was administered at 100 and 200 mg/kg/d in utero, the reproductive tract of the male offspring was minimally affected. None of the males displayed reproductive malformations. For comparison, in utero administration of flutamide has been shown to induce malformations in 100% of males at 6 mg/kg/d. In vitro, PFQ was several orders of magnitude less potent than BPC, vinclozolin, or procymidone. However, in utero administration of 12.5, 25, 50, and 100 mg PFQ/kg/d on GD 14-18 induced antiandrogenic effects at all dosage levels and 91% of the males displayed reproductive malformation in the high dose group. Overall, BPC was ∼380-fold more potent than PFQ in vitro, whereas PFQ was far more potent than BPC in utero. Incorporating toxicokinetic and toxicodynamic data into in vitro to in vivo extrapolations would reduce the discordance between the in vitro and in utero effects of PFQ and BPC and combining in vitro results with a short-term Hershberger assay would reduce the uncertainty in predicting the in utero effects of antiandrogenic chemicals.

Perfluorohexane Sulfonate (PFHxS) and a Mixture of Endocrine Disrupters Reduce Thyroxine Levels and Cause Antiandrogenic Effects in Rats

The developmental toxicity of perfluorohexane sulfonate (PFHxS) is largely unknown despite widespread environmental contamination and presence in human serum, tissues and milk. To thoroughly investigate PFHxS toxicity in developing rats and to mimic a realistic human exposure situation, we examined a low dose close to human relevant PFHxS exposure, and combined the dose-response studies of PFHxS with a fixed dose of 12 environmentally relevant endocrine disrupting chemicals (EDmix). Two reproductive toxicity studies in time-mated Wistar rats exposed throughout gestation and lactation were performed. Study 1 included control, two doses of PFHxS, and two doses of PFHxS + EDmix (n = 5-7). Study 2 included control, 0.05, 5, or 25 mg/kg body weight/day PFHxS, EDmix-only, 0.05, 5, or 25 mg PFHxS/kg plus EDmix (n = 13-20). PFHxS caused no overt toxicity in dams and offspring but decreased male pup birth weight and slightly increased liver weights at high doses and in combination with the EDmix. A marked effect on T4 levels was seen in both dams and offspring, with significant reductions from 5 mg/kg/day. The EDmix caused antiandrogenic effects in male offspring, manifested as slight decreases in anogenital distance, increased nipple retention and reductions of the weight of epididymides, ventral prostrate, and vesicular seminalis. PFHxS can induce developmental toxicity and in addition results of the co-exposure studies indicated that PFHxS and the EDmix potentiate the effect of each other on various endpoints, despite their different modes of action. Hence, risk assessment may underestimate toxicity when mixture toxicity and background exposures are not taken into account.

Maternal care modulates transgenerational effects of endocrine-disrupting chemicals on offspring pup vocalizations and adult behaviors

Endocrine-disrupting chemicals (EDCs) can act upon a developing organism to change its endocrine health and behavior in adulthood. Beyond actions on the exposed individuals, transgenerational effects of several EDCs have been reported. This study assessed the combinatorial impact of EDC-altered maternal care and transgenerational inheritance on F3 male and female offspring. Pregnant rats were exposed to EDCs with different modes of action: the weakly estrogenic polychlorinated biphenyl (PCB) mixture Aroclor 1221, the anti-androgenic fungicide vinclozolin (VIN), or the vehicle (6% dimethylsulfoxide in sesame oil; VEH) during embryonic development. The F1 male and female offspring were bred through the paternal- or maternal-lineage with untreated partners to generate F2 offspring. This process was repeated through both maternal and paternal lineages to create the F3 generation. Maternal care of F2 dams towards their F3 offspring was altered in a lineage-dependent manner, particularly in PCB paternal-lineage animals. When F3 pups were recorded for ultrasonic vocalizations (USVs) following separation from the mother, the rate of neonatal USVs in F3 offspring were decreased in PCB paternal-lineage pups. In adulthood, anxiety-like behaviors of the F3 rats were tested, with only small effects of EDCs detected. These interactions of maternal behaviors and EDC effects across generations, especially via the paternal lineage, has implications for health and environmental responses in wildlife and humans.

Anogenital distance as a toxicological or clinical marker for fetal androgen action and risk for reproductive disorders

Male reproductive development is intricately dependent on fetal androgen action. Consequently, disrupted androgen action during fetal life can interfere with the development of the reproductive system resulting in adverse effects on reproductive function later in life. One biomarker used to evaluate fetal androgen action is the anogenital distance (AGD), the distance between the anus and the external genitalia. A short male AGD is strongly associated with genital malformations at birth and reproductive disorders in adulthood. AGD is therefore used as an effect readout in rodent toxicity studies aimed at testing compounds for endocrine activity and anti-androgenic properties, and in human epidemiological studies to correlate fetal exposure to endocrine disrupting chemicals to feminization of new-born boys. In this review, we have synthesized current data related to intrauterine exposure to xenobiotics and AGD measurements. We discuss the utility of AGD as a retrospective marker of in utero anti-androgenicity and as a predictive marker for male reproductive disorders, both with respect to human health and rodent toxicity studies. Finally, we highlight four areas that need addressing to fully evaluate AGD as a biomarker in both a regulatory and clinical setting.

Investigations on the dose-response relationship of combined exposure to low doses of three anti-androgens in Wistar rats

The current investigation examines whether combined exposure to three anti-androgens (flutamide, prochloraz, vinclozolin) result in interference with endocrine homeostasis when applied at very low dose levels, and whether the results of combined exposure are more pronounced than to the individual compounds. A pre-post-natal in vivo study design was chosen with more parameters than regulatory testing protocols require (additional endpoints addressing hormone levels, morphology and histopathological examinations). Dose levels were chosen to represent the lowest observed adverse effect level (LOAEL), the no observed adverse effect level (NOAEL), and the acceptable daily intake for each individual substance. Anti-androgenic changes were observable at the effect level (LOAEL) but not at lower exposures. Nipple/areola counts appeared to be a sensitive measure of effect, in addition to male sex organ weights at sexual maturation, and finally gross findings. The results indicate the absence of evidence for effects at low or very low dose levels. No (adverse) effects were seen at the NOAEL dose. A non-monotonic dose-response relationship was not evident. Combined exposure at LOAEL level resulted in enhanced responses for anogenital index, number of areolas/nipples, delayed preputial separation and reduced ventral prostate weight in comparison to the individual compounds.

Differentiating true androgen receptor inhibition from cytotoxicity-mediated reduction of reporter-gene transactivation in-vitro

In vitro effect-based reporter assays are applied as biodetection tools designed to address nuclear receptor mediated-modulation. While such assays detect receptor modulating potential, cell viability needs to be addressed, preferably in the same well. Some assays circumvent this by co-transfecting a second constitutively-expressed marker gene or by multiplexing a cytotoxicity assay. Some assays, such as the CALUX®, lack this feature. The cytotoxic effects of unknown substances can confound in vitro assays, making the interpretation of results difficult and uncertain, particularly when assessing antagonistic activity. It's necessary to determine whether the cause of the reporter signal decrease is an antagonistic effect or a non-specific cytotoxic effect. To remedy this, we assessed the suitability of multiplexing a cell viability assay within the CALUX® transcriptional activation test for anti-androgenicity. Tests of both well-characterized anti-androgens and cytotoxic compounds demonstrated the suitability of this approach for discerning between the molecular mechanisms of action without altering the nuclear receptor assay; though some compounds were both cytotoxic and anti-androgenic. The optimized multiplexed assay was then applied to an uncharacterized set of polycyclic aromatic compounds. These results better characterized the mode of action and the classification of effects. Overall, the multiplexed protocol added value to CALUX test performance.

Investigations of putative reproductive toxicity of low-dose exposures to vinclozolin in Wistar rats

The current investigation examines whether the fungicide vinclozolin, which has an anti-androgenic mode of action, is capable of disrupting endocrine homeostasis at very low doses. The data generated clarify whether a non-monotonic dose-response relationship exists to enhance the current debate about the regulation of endocrine disruptors. Moreover, it is part of a series of investigations assessing the dose-response relationship of single and combined administration of anti-androgenic substances. A pre-postnatal in vivo study design was chosen which was compliant with regulatory testing protocols. The test design was improved by additional endpoints addressing hormone levels, morphology and histopathological examinations. Doses were chosen to represent an effect level (20 mg/kg bw/d), the current NOAEL (4 mg/kg bw/d), and a dose close to the "ADI" (0.005 mg/kg bw/d) for the detection of a possible non-monotonic dose-response curve. Anti-androgenic changes were observable at the effect level but not at lower exposures. Nipple/areola counts appeared to be the most sensitive measure of effect, followed by male sex organ weights at sexual maturation, and finally gross and histopathological findings. The results indicate the absence of evidence for effects at low or very low dose levels. A non-monotonic dose-response relationship was not evident.

Reproductive and developmental toxicity testing: Examination of the extended one-generation reproductive toxicity study guideline

An important aspect of safety assessment of chemicals (industrial and agricultural chemicals and pharmaceuticals) is determining their potential reproductive and developmental toxicity. A number of guidelines have outlined a series of separate reproductive and developmental toxicity studies from fertilization through adulthood and in some cases to second generation. The Extended One-Generation Reproductive Toxicity Study (EOGRTS) is the most recent and comprehensive guideline in this series. EOGRTS design makes toxicity testing progressive, comprehensive, and efficient by assessing key endpoints across multiple life-stages at relevant doses using a minimum number of animals, combining studies/evaluations and proposing tiered-testing approaches based on outcomes. EOGRTS determines toxicity during preconception, development of embryo/fetus and newborn, adolescence, and adults, with specific emphasis on the nervous, immunological, and endocrine systems, EOGRTS also assesses maternal and paternal toxicity. However, EOGRTS guideline is complex, criteria for selecting doses is unclear, and monitoring systemic dose during the course of the study for better interpretation and human relevance is not clear. This paper discusses potential simplification of EOGRTS, suggests procedures for relevant dose selection and monitors systemic dose at multiple life-stages for better interpretation of data and human relevance.

Do endocrine disruptors cause hypospadias?

Introduction

Endocrine disruptors or environmental agents, disrupt the endocrine system, leading to various adverse effects in humans and animals. Although the phenomenon has been noted historically in the cases of diethylstilbestrol (DES) and dichlorodiphenyltrichloroethane (DDT), the term “endocrine disruptor” is relatively new. Endocrine disruptors can have a variety of hormonal activities such as estrogenicity or anti-androgenicity. The focus of this review concerns on the induction of hypospadias by exogenous estrogenic endocrine disruptors. This has been a particular clinical concern secondary to reported increased incidence of hypospadias. Herein, the recent literature is reviewed as to whether endocrine disruptors cause hypospadias.

Methods

A literature search was performed for studies involving both humans and animals. Studies within the past 5 years were reviewed and categorized into basic science, clinical science, epidemiologic, or review studies.

Results

Forty-three scientific articles were identified. Relevant sentinel articles were also reviewed. Additional pertinent studies were extracted from the reference of the articles that obtained from initial search results. Each article was reviewed and results presented. Overall, there were no studies which definitely stated that endocrine disruptors caused hypospadias. However, there were multiple studies which implicated endocrine disruptors as one component of a multifactorial model for hypospadias.

Conclusions

Endocrine disruption may be one of the many critical steps in aberrant development that manifests as hypospadias.

Investigations of putative reproductive toxicity of low-dose exposures to flutamide in Wistar rats

The current investigation examines whether the model anti-androgenic substance flutamide is capable of disrupting endocrine homeostasis at very low doses. The data generated clarify whether a non-monotonic dose-response relationship exists to enhance the current debate about the regulation of endocrine disruptors. Moreover, it is part of a series of investigations assessing the dose-response relationship of single and combined administration of anti-androgenic substances. A pre-postnatal in vivo study design was chosen, which was compliant with regulatory testing protocols. The test design was improved by additional endpoints addressing hormone levels, morphology, and histopathological examinations. Doses were chosen to represent a clear effect level (2.5 mg/kg bw/d), a low endocrine effect level (LOAEL, 0.25 mg/kg bw/d), a NOAEL for endocrine effects (0.025 mg/kg bw/d), a further dose at 0.0025 mg/kg bw/d flutamide, as well as an "ADI" (0.00025 mg/kg bw/d or 100-fold below the NOAEL) for the detection of a possible non-monotonic dose-response curve. Anti-androgenic changes were observable at LOAEL and the clear effect dose level but not at lower exposures. Nipple retention appeared to be the most sensitive measure of anti-androgenic effects, followed by age at sexual maturation, anogenital distance/anogenital index and male sex organ weights, as well as gross and histopathological findings. The results of all five doses indicate the absence of evidence for effects at very low dose levels. A non-monotonic dose-response relationship was not evident for the anti-androgenic drug flutamide.

Regulatory acceptance and use of the Extended One Generation Reproductive Toxicity Study within Europe

The two-generation study (OECD TG 416) is the standard requirement within REACH to test reproductive toxicity effects of chemicals with production volumes >100 tonnes. This test is criticized in terms of scientific relevance and animal welfare. The Extended One Generation Reproductive Toxicity Study (EOGRTS), incorporated into the OECD test guidelines in 2011 (OECD TG 443) has the potential to replace TG 416, while using only one generation of rats and being more informative. However, its regulatory acceptance proved challenging. This article reconstructs the process of regulatory acceptance and use of the EOGRTS and describes drivers and barriers influencing the process. The findings derive from literature research and expert interviews. A distinction is made between three sub-stages; The stage of Formal Incorporation of the EOGRTS into OECD test guidelines was stimulated by retrospective analyses on the value of the second generation (F2), strong EOGRTS advocates, animal welfare concern and changing US and EU chemicals legislation; the stage of Actual Regulatory Acceptance within REACH was challenged by legal factors and ongoing scientific disputes, while the stage of Use by Industry is influenced by uncertainty of registrants about regulatory acceptance, high costs, the risk of false positives and the manageability of the EOGRTS.

A critical appraisal of the process of regulatory implementation of novel in vivo and in vitro methods for chemical hazard and risk assessment

Regulatory toxicology urgently needs applicable alternative test systems that reduce animal use, testing time, and cost. European regulation on cosmetic ingredients has already banned animal experimentation for hazard identification, and public awareness drives toward additional restrictions in other regulatory frameworks as well. In addition, scientific progress stimulates a more mechanistic approach of hazard identification. Nevertheless, the implementation of alternative methods is lagging far behind their development. In search for general bottlenecks for the implementation of alternative methods, this manuscript reviews the state of the art as to the development and implementation of 10 diverse test systems in various areas of toxicological hazard assessment. They vary widely in complexity and regulatory acceptance status. The assays are reviewed as to parameters assessed, biological system involved, standardization, interpretation of results, extrapolation to human hazard, position in testing strategies, and current regulatory acceptance status. Given the diversity of alternative methods in many aspects, no common bottlenecks could be identified that hamper implementation of individual alternative assays in general. However, specific issues for the regulatory acceptance and application were identified for each assay. Acceptance of one-in-one replacement of complex in vivo tests by relatively simple in vitro assays is not feasible. Rather, innovative approaches using test batteries are required together with metabolic information and in vitro to in vivo dose extrapolation to convincingly provide the same level of information of current in vivo tests. A mechanistically based alternative approach using the Adverse Outcome Pathway concept could stimulate further (regulatory) acceptance of non-animal tests.

Vinclozolin exposure throughout pregnancy and its developmental toxicity

Vinclozolin administration effects: placenta, fetal tissues and skeletal measurements during pregnancy.

Vinclozolin: a case study on the identification of endocrine active substances in the past and a future perspective

In the late 1980s vinclozolin was tested for prenatal developmental toxicity in rats for registration purposes in USA. At 1000mg/kgbw, 95% of all fetuses were female upon visual inspection (ano-genital distance determination). Anti-androgenic effects (AA) were also noted in a subsequent 2-generation study. These findings triggered mechanistic investigations at BASF and at US-EPA. Results published by the latter were the starting point of the endocrine disruption (ED) discussion in the 1990s. AA effects of vinclozolin are mediated by two metabolites, which have an antagonistic effect on the androgen receptor. Currently, determination of ED has become a major end-point in toxicology testing and the US-EPA has set up an elaborated testing paradigm to fulfill this requirement. Future screening for ED can be improved making use of new technologies. ED modes of action can be determined by three alternative (3R) methods. Steroid synthesis in H295R cells (1), androgen-receptor binding in modified yeast (2) and metabolomics (3). Using vinclozolin as a case study, results indicate: (1) an effect on steroid synthesis in vitro, (2) an antagonistic effect on the androgen receptor and (3) that the metabolome profile of vinclozolin is similar to that of other receptor mediated anti-androgens (e.g. flutamide).

Human infertility: are endocrine disruptors to blame?

Over recent decades, epidemiological studies have been reporting worrisome trends in the incidence of human infertility rates. Extensive detection of industrial chemicals in human serum, seminal plasma and follicular fluid has led the scientific community to hypothesise that these compounds may disrupt hormonal homoeostasis, leading to a vast array of physiological impairments. Numerous synthetic and natural substances have endocrine-disruptive effects, acting through several mechanisms. The main route of exposure to these chemicals is the ingestion of contaminated food and water. They may disturb intrauterine development, resulting in irreversible effects and may also induce transgenerational effects. This review aims to summarise the major scientific developments on the topic of human infertility associated with exposure to endocrine disruptors (EDs), integrating epidemiological and experimental evidence. Current data suggest that environmental levels of EDs may affect the development and functioning of the reproductive system in both sexes, particularly in foetuses, causing developmental and reproductive disorders, including infertility. EDs may be blamed for the rising incidence of human reproductive disorders. This constitutes a serious public health issue that should not be overlooked. The exposure of pregnant women and infants to EDs is of great concern. Therefore, precautionary avoidance of exposure to EDs is a prudent attitude in order to protect humans and wildlife from permanent harmful effects on fertility.