Evaluation of the Antiandrogenic Effects of Flutamide, DDE, and Linuron in the Weanling Rat Assay Using Organ Weight, Histopathological, and Proteomic Approaches

Prenatal exposure to Di(2-ethylhexyl) phthalate and high-fat diet synergistically disrupts gonadal function in male mice†

Prenatal exposure to Di (2-ethylhexyl) phthalate (DEHP) impairs the reproductive system and causes fertility defects in male offspring. Additionally, high-fat (HF) diet is a risk factor for reproductive disorders in males. In this study, we tested the hypothesis that prenatal exposure to a physiologically relevant dose of DEHP in conjunction with HF diet synergistically impacts reproductive function and fertility in male offspring. Female mice were fed a control or HF diet 7 days prior to mating and until their litters were weaned on postnatal day 21. Pregnant dams were exposed to DEHP or vehicle from gestational day 10.5 until birth. The male offspring's gross phenotype, sperm quality, serum hormonal levels, testicular histopathology, and testicular gene expression pattern were analyzed. Male mice born to dams exposed to DEHP + HF had smaller testes, epididymides, and shorter anogenital distance compared with those exposed to HF or DEHP alone. DEHP + HF mice had lower sperm concentration and motility compared with DEHP mice. Moreover, DEHP + HF mice had more apoptotic germ cells, fewer Leydig cells, and lower serum testosterone levels than DEHP mice. Furthermore, testicular mRNA expression of Dnmt1 and Dnmt3a was two to eight-fold higher than in DEHP mice by qPCR, suggesting that maternal HF diet and prenatal DEHP exposure additively impact gonadal function by altering the degree of DNA methylation in the testis. These results suggest that the combined exposure to DEHP and high-fat synergistically impairs reproductive function in male offspring, greater than exposure to DEHP or HF diet alone.

An Experimental Approach to Study the Effects of Realistic Environmental Mixture of Linuron and Propamocarb on Zebrafish Synaptogenesis

The reasons behind the extensive use of pesticides include the need to destroy vector organisms and promote agricultural production in order to sustain population growth. Exposure to pesticides is principally occupational, even if their persistence in soil, surface water and food brings the risk closer to the general population, hence the demand for risk assessment, since these compounds exist not only as individual chemicals but also in form of mixtures. In light of this, zebrafish represents a suitable model for the evaluation of toxicological effects. Here, zebrafish embryos were exposed for 96 h post fertilization (hpf) to sublethal concentrations (350 µg/L) of linuron and propamocarb, used separately and then combined in a single solution. We investigated the effects on morphological traits and the expression of genes known to be implicated in synaptogenesis (neurexin1a and neuroligin3b). We observed alterations in some phenotypic parameters, such as head width and interocular distance, that showed a significant reduction (p < 0.05) for the mixture treatment. After individual exposure, the analysis of gene expression showed an imbalance at the synaptic level, which was partially recovered by the simultaneous administration of linuron and propamocarb. This preliminary study demonstrates that the combined substances were responsible for some unpredictable effects, diverging from the effect observed after single exposure. Thus, it is clear that risk assessment should be performed not only on single pesticides but also on their mixtures, the toxicological dynamics of which can be totally unpredictable.

Prenatal Exposure to DEHP Induces Premature Reproductive Senescence in Male Mice

Di-(2-ethylhexyl) phthalate (DEHP) is the most commonly used phthalate, and it is an endocrine-disrupting chemical. This study tested a hypothesis that prenatal exposure to DEHP lays the foundation for premature gonadal dysfunction and subsequent reproductive senescence in male mice. Pregnant female CD-1 mice were orally dosed with vehicle control (tocopherol-stripped corn oil) or with 20 μg/kg/day, 200 μg/kg/day, 500 mg/kg/day, or 750 mg/kg/day of DEHP from gestational day 11 to birth. Overall, the prenatal DEHP exposure did not cause any overt physical health problems in male offspring, as no significant differences in their body nor gonadal weight were seen up to the age of 23 months. However, an age- and dose-dependent gonadal dysfunction was observed. As early as 7 months of age, the 750 mg/kg/day group of mice exhibited significantly reduced fertility. At 19 months of age, 86% of the 750 mg/kg/day mice became infertile, whereas only 25% of the control mice were infertile. At this age, all of the DEHP-exposed mice had lower serum testosterone levels, higher serum estradiol levels, and higher LH levels compared with control mice. Histological evaluations showed that mice prenatally exposed to DEHP displayed a wide array of gonadal and epididymal abnormalities such as increased germ cell apoptosis, degenerative seminiferous tubules, oligozoospermia, asthenozoospermia, and teratozoospermia in comparison to age-matching control mice. In summary, this study shows that prenatal exposure to DEHP induces premature reproductive senescence in male mice.

Assessing the antiandrogenic properties of propyl paraben using the Hershberger bioassay

Propyl paraben is a widely used preservative in pharmaceuticals, cosmetics, and foods preventing microbial and fungal contamination. This study was designed to investigate antiandrogenic profiles of propyl paraben following oral doses at 10, 250, and 750 mg kg-1 day to immature male rats using the Hershberger Bioassay. Rats were divided into six groups including solvent control, negative control (0.4 mg kg-1 day testosterone propionate = TP), positive control (3 mg kg-1 day flutamide = FLU) and treatment groups (10, 250, and 750 mg kg-1 day testosterone propionate + Propyl paraben). Propyl paraben (PP) significantly decreased all accessory sex organ weights at each dose of 250 and 750 mg kg-1 day compared to control groups. Thus, we found that propyl paraben had antiandrogenic activity within the supported results of increasing LH levels and histopathologic results such atrophy, hyalinization, and anastomosis on androgenic tissues.

Effects of anti-androgens cyproterone acetate, linuron, vinclozolin, and p,p'-DDE on the reproductive organs of the copepod Acartia tonsa

The study was performed to detect the effects of anti-androgenic compounds on the reproduction. In this paper alterations observed in the marine calanoid copepod Acartia tonsa exposed to environmental concentrations of cyproterone acetate (CPA), linuron (LIN), vinclozolin (VIN), and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE) for 21 days covering a full life cycle are described. Histological alterations were studied with a focus on reproductive organs, gonad and accessory sexual glands. Exposure to ≥1.2 µg L(-1) CPA caused degeneration of spermatocytes and deformation of the spermatophore in males. In a single male exposed to 33 µg L(-1) CPA, an ovotestis was observed. In CPA exposed females, enhancement of oogenesis, increase in apoptosis and a decrease in proliferation occurred. Exposure of males to ≥12 µg L(-1) LIN caused degenerative effects in spermatogonia, spermatocytes and spermatids, and at 4.7 µg L(-1) LIN, the spermatophore wall displayed an irregular formation. In LIN exposed females, no such structural alterations were found; however, the proliferation index was reduced at 29 µg L(-1) LIN. At an exposure concentration of ≥100 µg L(-1) VIN, distinct areas in male gonad were stimulated, whereas others displayed a disturbed spermatogenesis and a deformed spermatophore wall. In VIN exposed female A. tonsa, no effects were observed. Male A. tonsa exposed to p,p'-DDE displayed an impairment of spermatogenesis in all stages with increased degrees of apoptosis. In p,p'-DDE-exposed females, a statistical significant increase of the proliferation index and an intensification of oogenesis were observed at 0.0088 µg L(-1).

Steroid Androgen Exposure during Development Has No Effect on Reproductive Physiology of Biomphalaria glabrata

Gastropod mollusks have been proposed as alternative models for male reproductive toxicity testing, due to similarities in their reproductive anatomy compared to mammals, together with evidence that endocrine disrupting chemicals can cause effects in some mollusks analogous to those seen in mammals. To test this hypothesis, we used the freshwater pulmonate snail, Biomphalaria glabrata, for which various genetic tools and a draft genome have recently become available, to investigate the effects of two steroid androgens on the development of mollusk secondary sexual organs. Here we present the results of exposures to two potent androgens, the vertebrate steroid; 5α-dihydrotestosterone (DHT) and the pharmaceutical anabolic steroid; 17α-methyltestosterone (MT), under continuous flow-through conditions throughout embryonic development and up to sexual maturity. Secondary sexual gland morphology, histopathology and differential gene expression analysis were used to determine whether steroid androgens stimulated or inhibited organ development. No significant differences between tissues from control and exposed snails were identified, suggesting that these androgens elicited no biologically detectable response normally associated with exposure to androgens in vertebrate model systems. Identifying no effect of androgens in this mollusk is significant, not only in the context of the suitability of mollusks as alternative model organisms for testing vertebrate androgen receptor agonists but also, if applicable to other similar mollusks, in terms of the likely impacts of androgens and anti-androgenic pollutants present in the aquatic environment.

The fetal ovary exhibits temporal sensitivity to a 'real-life' mixture of environmental chemicals

The development of fetal ovarian follicles is a critical determinant of adult female reproductive competence. Prolonged exposure to environmental chemicals (ECs) can perturb this process with detrimental consequences for offspring. Here we report on the exposure of pregnant ewes to an environmental mixture of ECs derived from pastures fertilized with sewage sludge (biosolids): a common global agricultural practice. Exposure of pregnant ewes to ECs over 80 day periods during early, mid or late gestation reduced the proportion of healthy early stage fetal follicles comprising the ovarian reserve. Mid and late gestation EC exposures had the most marked effects, disturbing maternal and fetal liver chemical profiles, masculinising fetal anogenital distance and greatly increasing the number of altered fetal ovarian genes and proteins. In conclusion, differential temporal sensitivity of the fetus and its ovaries to EC mixtures has implications for adult ovarian function following adverse exposures during pregnancy.

Application of omics data in regulatory toxicology: report of an international BfR expert workshop

Advances in omics techniques and molecular toxicology are necessary to provide new perspectives for regulatory toxicology. By the application of modern molecular techniques, more mechanistic information should be gained to support standard toxicity studies and to contribute to a reduction and refinement of animal experiments required for certain regulatory purposes. The relevance and applicability of data obtained by omics methods to regulatory purposes such as grouping of chemicals, mode of action analysis or classification and labelling needs further improvement, defined validation and cautious expert judgment. Based on the results of an international expert workshop organized 2014 by the Federal Institute for Risk Assessment in Berlin, this paper is aimed to provide a critical overview of the regulatory relevance and reliability of omics methods, basic requirements on data quality and validation, as well as regulatory criteria to decide which effects observed by omics methods should be considered adverse or non-adverse. As a way forward, it was concluded that the inclusion of omics data can facilitate a more flexible approach for regulatory risk assessment and may help to reduce or refine animal testing.

Assessment of three approaches for regulatory decision making on pesticides with endocrine disrupting properties

Recent EU legislation has introduced endocrine disrupting properties as a hazard-based "cut-off" criterion for the approval of active substances as pesticides and biocides. Currently, no specific science-based approach for the assessment of substances with endocrine disrupting properties has been agreed upon, although this new legislation provides interim criteria based on classification and labelling. Different proposals for decision making on potential endocrine disrupting properties in human health risk assessment have been developed by the German Federal Institute for Risk Assessment (BfR) and other regulatory bodies. All these frameworks, although differing with regard to hazard characterisation, include a toxicological assessment of adversity of the effects, the evaluation of underlying modes/mechanisms of action in animals and considerations concerning the relevance of effects to humans. Three options for regulatory decision making were tested upon 39 pesticides for their applicability and to analyze their potential impact on the regulatory status of active substances that are currently approved for use in Europe: Option 1, based purely on hazard identification (adversity, mode of action, and the plausibility that both are related); Option 2, based on hazard identification and additional elements of hazard characterisation (severity and potency); Option 3, based on the interim criteria laid down in the recent EU pesticides legislation. Additionally, the data analysed in this study were used to address the questions, which parts of the endocrine system were affected, which studies were the most sensitive and whether no observed adverse effect levels were observed for substance with ED properties. The results of this exercise represent preliminary categorisations and must not be used as a basis for definitive regulatory decisions. They demonstrate that a combination of criteria for hazard identification with additional criteria of hazard characterisation allows prioritising and differentiating between substances with regard to their regulatory concern. It is proposed to integrate these elements into a decision matrix to be used within a weight of evidence approach for the toxicological categorisation of relevant endocrine disruptors and to consider all parts of the endocrine system for regulatory decision making on endocrine disruption.

Androgenic effect of honeybee drone milk in castrated rats: roles of methyl palmitate and methyl oleate

ETHNOPHARMACOLOGICAL RELEVANCE

Numerous honeybee (Apis mellifera) products have been used in traditional medicine to treat infertility and to increase vitality in both men and women. Drone milk (DM) is a relatively little-known honeybee product with a putative sexual hormone effect. The oestrogenic effect of a fraction of DM has recently been reported in rats. However, no information is available on the androgenic effects of DM. The purpose of the present study was to determine the androgen-like effect of DM in male rats and to identify effective compounds.

MATERIALS AND METHODS

A modified Hershberger assay was used to investigate the androgenic effect of crude DM, and the plasma level of testosterone was measured. The prostatic mRNA and protein expression of Spot14-like androgen-inducible protein (SLAP) were also examined with real-time PCR and Western blot techniques. GC-MS and NMR spectroscopic investigations were performed to identify the active components gained by bioactivity-guided fractionation.

RESULTS

The crude DM increased the relative weights of the androgen-dependent organs and the plasma testosterone level in castrated rats and these actions were flutamide-sensitive. DM increased the tissue mRNA and protein level of SLAP, providing further evidence of its androgen-like character. After bioactivity-guided fractionation, two fatty acid esters, methyl palmitate (MP) and methyl oleate (MO), were identified as active compounds. MP alone showed an androgenic effect, whereas MO increased the weight of androgen-sensitive tissues and the plasma testosterone level only in combination.

CONCLUSION

The experimental data of DM and its active compounds (MO and MP) show androgenic activity confirming the traditional usage of DM. DM or MP or/and MO treatments may project a natural mode for the therapy of male infertility.

Estrogenic endocrine-disrupting chemicals: molecular mechanisms of actions on putative human diseases

Endocrine-disrupting chemicals (EDC), including phthalates, bisphenol A (BPA), phytoestrogens such as genistein and daidzein, dichlorodiphenyltrichloroethane (DDT), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are associated with a variety of adverse health effects in organisms or progeny by altering the endocrine system. Environmental estrogens, including BPA, phthalates, and phytoestrogens, are the most extensively studied and are considered to mimic the actions of endogenous estrogen, 17β-estradiol (E2). Diverse modes of action of estrogen and estrogen receptors (ERα and ERβ) have been described, but the mode of action of estrogenic EDC is postulated to be more complex and needs to be more clearly elucidated. This review examines the adverse effects of estrogenic EDC on male or female reproductive systems and molecular mechanisms underlying EDC effects that modulate ER-mediated signaling. Mechanisms of action for estrogenic EDC may involve both ER-dependent and ER-independent pathways. Recent findings from systems toxicology of examining estrogenic EDC are also discussed.

OECD validation of phase-3 Hershberger assay using the stimulated weanling male rat in Korea

The OECD has proposed a new, validated test guideline with the stimulated weanling male Hershberger assay to avoid the surgical castration step. In the present study, we assessed the relevance and reliability of the stimulated weanling Hershberger assay in four stages. All chemicals except for testosterone propionate (TP) were orally administered to sexually immature male rats of 22 days old for 10 days. The weights of four mandatory accessory sex organs, two additional reproductive tissues and optional systemic organs were evaluated. At the first two stages, TP, as reference androgen, significantly increased the weights of epididymides and accessory sex organs (ASO) at 1.0 mg kg(-1) and flutamide (FLU), as a positive anti-androgen control, decreased the TP-stimulated organ weights at 3.0 mg kg(-1). At stage 3, trenbolone (40 mg kg(-1)), an anabolic steroid, significantly increased ASO weights, and weak anti-androgens (DDE and linuron) decreased the TP-stimulated ASO weights at each high dose. The above results were confirmed in a blind test with coded substances provided by OECD. Compared with results from our previous castrated male assay, the intact weanling version is less sensitive than the castrated male version, in terms of a smaller response at the reference dose of TP or FLU. However, this study suggests that the stimulated weanling Hershberger assay can detect the effects of both potent and weak anti-androgens on androgen-producing and androgen-dependent tissues.

Modified expression of several sperm proteins after chronic exposure to the antiandrogenic compound vinclozolin

Little is known about the molecular impact of in vivo exposure to endocrine disruptors (EDs) on sperm structures and functions. We recently reported that the lifelong exposure of rats to the antiandrogenic compound vinclozolin results in low epididymal weight, changes in sperm kinematic parameters, and immature sperm chromatin condensation, together with the impairment of several fertility end points. These results led us to focus specifically on possible molecular abnormalities in sperm. Sperm samples were recovered from the frozen epididymides of rats exposed during the previous study. The proteins present in the samples from six exposed and six control rats were analyzed in pairs, by two-dimensional fluorescence difference gel electrophoresis, to investigate possible exposure-induced changes to sperm protein profiles. Twelve proteins, from the 380 matched spots observed in at least five gels, were present in larger or smaller amounts after vinclozolin exposure. These proteins were identified by mass spectrometry, and several are known to play a crucial role in the sperm fertilizing ability, among which, two mitochondrial enzymes, malate dehydrogenase 2 and aldehyde dehydrogenase (both of which were present in smaller amounts after treatment) and A-kinase anchor protein 4 (larger amounts of precursor after treatment). Finally, Ingenuity Pathway Analysis revealed highly significant interactions between proteins over- and underexpressed after treatment. This is the first study to show an association between in vivo exposure to an ED and changes to the sperm protein profile. These modifications may be at least partly responsible for the reproductive abnormalities and impaired fertility recently reported in this rat model of vinclozolin exposure.

Di-(2 ethylhexyl) phthalate and flutamide alter gene expression in the testis of immature male rats

We previously demonstrated that the androgenic and anti-androgenic effects of endocrine disruptors (EDs) alter reproductive function and exert distinct effects on developing male reproductive organs. To further investigate these effects, we used an immature rat model to examine the effects of di-(2 ethylhexyl) phthalate (DEHP) and flutamide (Flu) on the male reproductive system. Immature male SD rats were treated daily with DEHP and Flu on postnatal days (PNDs) 21 to 35, in a dose-dependent manner. As results, the weights of the testes, prostate, and seminal vesicle and anogenital distances (AGD) decreased significantly in response to high doses of DEHP or Flu. Testosterone (T) levels significantly decreased in all DEHP- treated groups, whereas luteinizing hormone (LH) plasma levels were not altered by any of the two treatments at PND 36. However, treatment with DEHP or Flu induced histopathological changes in the testes, wherein degeneration and disorders of Leydig cells, germ cells and dilatation of tubular lumen were observed in a dose-dependent manner. Conversely, hyperplasia and denseness of Leydig, Sertoli and germ cells were observed in rats given with high doses of Flu. The results by cDNA microarray analysis indicated that 1,272 genes were up-regulated by more than two-fold, and 1,969 genes were down-regulated in response to DEHP, Flu or both EDs. These genes were selected based on their markedly increased or decreased expression levels. These genes have been also classified on the basis of gene ontology (e.g., steroid hormone biosynthetic process, regulation of transcription, signal transduction, metabolic process, biosynthetic process...). Significant decreases in gene expression were observed in steroidogenic genes (i.e., Star, Cyp11a1 and Hsd3b). In addition, the expression of a common set of target genes, including CaBP1, Vav2, Plcd1, Lhx1 and Isoc1, was altered following exposure to EDs, suggesting that they may be marker genes to screen for the anti-androgenic or androgenic effects of EDs. Overall, our results demonstrated that exposure to DEHP, Flu or both EDs resulted in a alteration of gene expression in the testes of immature male rats. Furthermore, the toxicological effects of these EDs on the male reproductive system resulted from their anti-androgenic effects. Taken together, these results provide a new insight into the molecular mechanisms underlying the detrimental impacts of EDs, in regards to anti-androgenic effects in humans and wildlife.