Brief maternal exposure of rats to the xenobiotics dibutyl phthalate or diethylstilbestrol alters adult-type Leydig cell development in male offspring

Influence on the adult male Leydig cell biomarker insulin‐like peptide 3 of maternal exposure to estrogenic and anti‐androgenic endocrine disrupting compound mixtures: A retrospective study

Insulin-like peptide 3 (INSL3) is a peptide biomarker secreted specifically by the mature Leydig cells of the testes. It is constitutive, has low within-individual variance, and effectively measures the functional capacity of Leydig cells to make testosterone. In young adult men there is a large 10-fold range of serum INSL3 concentration, persisting into old age, and implying that later hypogonadal status might be programmed in early life. To determine whether maternal exposure to environmental endocrine disrupting compounds (EDCs) influences adult serum INSL3 concentration, using a retrospective paradigm, INSL3 was measured in young adult male rats (80-90 days) from the F1 generation of females maternally exposed to varied doses of bisphenol A (BPA), butylparaben, epoxiconazole, and fludioxonil as single compounds, as well as estrogenic and anti-androgenic mixtures of BPA and butylparaben, and di(2-ethylhexyl) phthalate and procymidone respectively. A mixture of BPA and butylparaben significantly reduced circulating INSL3 concentration in adult male progeny. The remaining compounds or mixtures tested, though sufficient to induce other effects in the F1 generation were without significant effect. Maternal exposure to low concentrations of some EDCs may be a contributing factor to the variation in the Leydig cell biomarker INSL3 in young adulthood, though caution is warranted translating results from rats to humans.

Expression and Role of INSL3 in the Fetal Testis

Insulin-like peptide 3 (INSL3) is a small peptide hormone of the insulin-relaxin family which is produced and secreted by the fetal Leydig cells in the testes only. It appears to be undetectable in female fetuses. In the human fetus INSL3 synthesis begins immediately following gonadal sex determination at weeks 7 to 8 post coitum and the peptide can be detected in amniotic fluid 1 to 2 weeks later. INSL3 acts through a unique G-protein-coupled receptor, called RelaXin-like Family Peptide receptor 2 (RXFP2), which is expressed by the mesenchymal cells of the gubernacular ligament linking the testes to the inguinal wall. The role of INSL3 in the male fetus is to cause a thickening of the gubernaculum which then retains the testes in the inguinal region, while the remainder of the abdominal organs grow away in an antero-dorsal direction. This represents the first phase of testis descent and is followed later in pregnancy by the second inguino-scrotal phase whereby the testes pass into the scrotum through the inguinal canal. INSL3 acts as a significant biomarker for Leydig cell differentiation in the fetus and may be reduced by maternal exposure to endocrine disrupting chemicals, such as xenoestrogens or phthalates, leading to cryptorchidism. INSL3 may have other roles within the fetus, but as a Leydig cell biomarker its reduction acts also as a surrogate for anti-androgen action.

Antioxidative Molecules in Human Milk and Environmental Contaminants

Breastfeeding provides overall beneficial health to the mother-child dyad and is universally recognized as the preferred feeding mode for infants up to 6-months and beyond. Human milk provides immuno-protection and supplies nutrients and bioactive compounds whose concentrations vary with lactation stage. Environmental and dietary factors potentially lead to excessive chemical exposure in critical windows of development such as neonatal life, including lactation. This review discusses current knowledge on these environmental and dietary contaminants and summarizes the known effects of these chemicals in human milk, taking into account the protective presence of antioxidative molecules. Particular attention is given to short- and long-term effects of these contaminants, considering their role as endocrine disruptors and potential epigenetic modulators. Finally, we identify knowledge gaps and indicate potential future research directions.

Developmental, behavioral and endocrine alterations in male rats at early and late postnatal life following in utero exposure to low dose di-n-butylphthalate

Environmental chemical pollutants that interfere with hormonal homeostasis or hormone signaling are the relevant agents inducing congenital or postnatally developed reproductive abnormalities in human beings, wild and domestic animals. In this study, we are examining reproductive effects of prenatal exposure of male rats to a low dose di-n-butylphthalate (DBP). Wistar female rats were given intragastrically DBP at a daily dose of 100 mg/kg b.w. during 15th-21st days of pregnancy. Anogenital distance (AGD) in male offspring decreased on postnatal day (PND) 2 followed by its normalization on PND 7 and 10. There were no other visible teratogenic lesions in the newborns. The testicle descent into scrotum of control males occurred on PND 38.5 ± 0.1, while in DBP group it accelerated by 5.3 days on the average. At the age of 6 months, DBP-exposed animals exhibited double increase of blood plasma testosterone level as compared to controls, and hyperactive male sexual behavior in the presence of receptive female. The duration of latent periods of the first mount and the first intromission, as well as post-ejaculatory refractory period, have been shortened; the number of mounts with intromission and the number of ejaculations increased significantly. Histological examination of the testes indicated activation of Leydig cells. The female-type sexual behavior as evaluated by appearance of lordosis of orchidectomized and primed with estradiol and progesterone 10-month-old males in response to mount or approach of sexually active normal male was enhanced in DBP-group. Both 10-month-old and aging males (18 months), castrated and hormone-primed, displayed homosexual type of behavior. Prenatal low dose DBP caused in 18-month-old males premature atrophy of the testes and accessory sexual glands, increased number of Leydig cell adenomas, a twice decrease of plasma testosterone level and exhausting of sexual potency. We concluded that prenatal exposition of male rats to low dose DBP determines epigenetic alterations of programming of sex brain differentiation and regulation of testicular steroidogenesis that leads to reproductive disorders and accelerated aging of reproductive system.

RXFP2 as novel potential biomarker for abnormal differentiation induced by diethylstilbestrol in the gubernaculum of fetal mice

Environmental estrogens (EEs) have been correlated with abnormalities in the male urogenital system. However, the mechanism underlying the effect of these molecules remains unclear. In vitro and in vivo experiments were performed to examine the expression level and mechanism of relaxin family peptide receptor 2 (RXFP2) in the gubernaculum of fetal mice following diethylstilbestrol (DES) treatment. The in vivo results demonstrate that DES treatment increased the stillbirth rate gradually, decreased the gubernacular cone volume significantly, and disrupted the tissue structure, leading to incomplete testicular descent. In vitro experiments reveal that DES administration resulted in abnormal cellular morphology and structural disorder of gubernacular cells, which lost their original morphology in a dose-dependent manner. Moreover, DES-induced F-actin rearrangement and stress fiber formation in cultured cells. Protein quantitative analysis showed that the RXFP2 level in each experimental group was significantly lower than that of the normal group. In conclusion, DES affects the morphology and alters the gubernaculum structure, as well as the expression of RXFP2 protein. These data demonstrate that DES is toxic to gubernaculum in fetal mice, and that RXFP2 is associated with the abnormal gubernaculum morphology induced by DES. Taken together, these data suggest that RXFP2 may be a novel potential biomarker for abnormal differentiation of the gubernaculum.

A strategy to validate a selection of human effect biomarkers using adverse outcome pathways: Proof of concept for phthalates and reproductive effects

Human biomonitoring measures the concentrations of environmental chemicals or their metabolites in body fluids or tissues. Complementing exposure biomarkers with mechanistically based effect biomarkers may further elucidate causal pathways between chemical exposure and adverse health outcomes. We combined information on effect biomarkers previously implemented in human observational studies with mechanisms of action reported in experimental studies and with information from published Adverse Outcome Pathways (AOPs), focusing on adverse reproductive effects of phthalate exposure. Phthalates constitute a group of chemicals that are ubiquitous in consumer products and have been related to a wide range of adverse health effects. As a result of a comprehensive literature search, we present an overview of effect biomarkers for reproductive toxicity that are substantiated by mechanistic information. The activation of several receptors, such as PPARα, PPARγ, and GR, may initiate events leading to impaired male and female fertility as well as other adverse effects of phthalate exposure. Therefore, these receptors appear as promising targets for the development of novel effect biomarkers. The proposed strategy connects the fields of epidemiology and toxicology and may strengthen the weight of evidence in observational studies that link chemical exposures to health outcomes.

Isolation and molecular characterization of spermatogonia from male Sprague-Dawley rats exposed in utero and postnatally to dibutyl phthalate or acrylamide

The increased incidence of testicular disorders in young men and the possible influence of environmental chemicals, such as dibutyl phthalate (DBP) and acrylamide (AA), requires experimental models for identifying modes of action. Most published reproductive toxicologic studies use RNA samples from the total testis to evaluate testicular gene expression; however, analyses of isolated cell types could provide a more specific tool. Among testicular germ cells, spermatogonia are critical since they represent the onset of spermatogenesis. This study aimed, (1) to establish a technique for spermatogonia isolation; (2) to apply this isolation technique to verify possible gene expression alterations (Pou5f1, Kitlg, Mki-67, Bak1 and Spry4) in prepubertal post-natal day, (PND24) and pubertal (PND45) testes after in utero and postnatal exposure to DBP or AA. The technique was efficient for isolation of a majority of spermatogonia. In utero DBP exposure led to reduced litter body weight at birth, reduced anogenital distance of male pups on PND4, and increased frequency of male nipple retention on PND14 compared to controls. DBP-exposed relative testes weights were reduced only at PND24 compared to control but they did not differ at PND45. DBP-exposed animals showed reduced expression levels of Pou5f1 and Mki67 on PND24, and reduced expression of Pou5f1 and Spry4 on PND45. AA exposure reduced expression of Pou5f1, Mki67, and Spry4 at PND45 although not significantly. Our results suggest that DBP acts by reducing cell proliferation and impairing differentiation in prepubertal and pubertal testes.

Diethylstilbestrol induces morphological changes in the spermatogonia, Sertoli cells and Leydig cells of adult rat

It is now established that diethylstilbestrol (DES) has damaging effects on the male reproductive system. However, to date there have been no studies morphological analysis of adult rat testes upon treatment with DES. Here, we examined whether DES has any significant morphological effect on steroidogenesis and spermatogenesis. DES was injected subcutaneously at 3 μg/day and 30 μg/day in adult male Sprague-Dawley (SD) rats for two different treatment lengths (1 or 3 weeks), after which rats were necropsied. TUNEL labeling, cell counting, and morphological analysis were used to evaluate the effects of DES. A high dose of DES and longer exposure severely affected the cellular development of the testis. Specifically, DES treatment disrupted both steroidogenesis and spermatogenesis by decreasing the number of spermatogonia, Sertoli cells, and Leydig cells in a dose- and time-dependent manner. Thus, DES may account for decreases in the number of spermatogenic cells, Sertoli cells and Leydig cells, which in turn may lead to reduced fertility in males.

Amniotic Fluid INSL3 Measured During the Critical Time Window in Human Pregnancy Relates to Cryptorchidism, Hypospadias, and Phthalate Load: A Large Case-Control Study

The period of the first to second trimester transition in human pregnancy represents a sensitive window for fetal organogenesis, particularly in regard to the development of the male reproductive system. This is a time of relative analytical inaccessibility. We have used a large national biobank of amniotic fluid samples collected at routine amniocentesis to determine the impacts of exogenous endocrine disruptor load on specific fetal biomarkers at this critical time. While adrenal and testicular steroids are highly correlated, they are also mostly positively influenced by increasing phthalate load, represented by the metabolites 7cx-MMeHP and 5cx-MEPP, by perfluorooctane sulfonate (PFOS) exposure, and by smoking, suggesting an adrenal stress response. In contrast, the testis specific biomarkers insulin-like peptide 3 (INSL3) and androstenedione are negatively impacted by the phthalate endocrine disruptors. Using a case-control design, we show that cryptorchidism and hypospadias are both significantly associated with increased amniotic concentration of INSL3 during gestational weeks 13-16, and some, though not all steroid biomarkers. Cases are also linked to a specifically increased variance in the Leydig cell biomarker INSL3 compared to controls, an effect exacerbated by maternal smoking. No influence of phthalate metabolites or PFOS was evident on the distribution of cases and controls. Considering that several animal and human studies have shown a negative impact of phthalate load on fetal and cord blood INSL3, respectively, the present results suggest that such endocrine disruptors may rather be altering the relative dynamics of testicular development and consequent hormone production, leading to a desynchronization of tissue organization during fetal development. Being born small for gestational age appears not to impact on the testicular biomarker INSL3 in second trimester amniotic fluid.

Perturbation of epigenetic processes by doxorubicin in the mouse testis

Epigenetic processes play a major role in normal mammalian development, particularly during gametogenesis and early embryogenesis. Thus, perturbation of epigenetic processes in the testis by xenobiotics could have a major impact on testicular function and fertility, and potentially affect the development and health of subsequent generations. There has been substantial research into the epigenetic toxicity of environmental exposures over the last decade. However, few studies have focussed on pharmaceutical drugs, which due to the nature of their use are typically found at much higher concentrations within exposed individuals than environmental chemicals. Here, we investigated genome-wide changes in testicular mRNA transcription, microRNA expression and DNA methylation to assess the contribution of epigenetic mechanisms to the testicular toxicity induced by doxorubicin (DOX) as a representative, widely used and well-characterised anti-cancer drug. We demonstrated that DOX is able to induce transcriptional, microRNA and DNA methylation changes, which perturb pathways involved in stress/cell death and survival and testicular function and lead to germ cell loss and reproductive organ damage. This identified potential novel mechanisms of DOX-induced testicular toxicity for further focussed investigations. Such work is required to fully assess the role of epigenetics in toxicity, determine whether single and/or multigenerational epigenetic toxicity is a real public health concern, and begin to develop and incorporate relevant epigenetic endpoints into regulatory toxicology.

Male rats exposed in utero to di(n-butyl) phthalate: Age-related changes in Leydig cell smooth endoplasmic reticulum and testicular testosterone-biosynthesis enzymes/proteins

This study investigated the age-related (i.e., weeks 5, 7, 9, 14 and 17) morphological changes of Leydig cell smooth endoplasmic reticulum (LCs-ER) and testicular testosterone biosynthesis/protein expression in rats in utero exposed to di(n-butyl) phthalate (DBP) (intragastrically; 100mg/kg/day) on days 12-21 post-conception. Ultrastructural observations revealed the LCs-ER of the DBP group were non-dilated until peri-puberty, and thereafter decreased and disappeared. RT-PCR and Western blotting analyses revealed that StAR and P450scc levels in the DBP group were significantly lower at 5 and 7 weeks compared with the vehicle group but became similar during weeks 9-17. Although 3β-HSD, P450c17, and 17β-HSD levels of mRNA and protein in the DBP group were similar to the vehicle control group at 5 and 7 weeks of age, they were significantly lower during weeks 9-17. In utero DBP exposure results in age-related LCs-ER changes corresponding to reduction of testicular testosterone biosynthesis enzymes/associated proteins.

The mechanism underlying dibutyl phthalate induced shortened anogenital distance and hypospadias in rats

PURPOSE

The purpose of this study was to investigate the mechanism of dibutyl phthalate (DBP) induced hypospadias and shortened anogenital distance (AGD).

METHODS

AGD, hypospadias, and cryptorchidism incidence was observed in male offspring of DBP treated pregnant Wistar rats. Testicular development and testosterone levels of normal and DBP-treated rat embryos were compared.

RESULTS

Male offspring of 300mg and 900mg DBP-treated pregnant Wistar rats exhibited shortened average AGD compared with the control group. A 22.7% hypospadias incidence was observed in the 300mg group, but no offspring with cryptorchidism were identified. In the 900mg group, hypospadias and cryptorchidism incidence reached 43.5% and 17.4%, respectively. Between E15.5 and E17.5, the 300mg group exhibited delayed testicular development and testosterone secretion. However, testicular development and testosterone secretion subsequently recovered. The 300mg treated and control groups had similar measures after E19.5. Contrastingly, testicular development and testosterone secretion were significantly diminished throughout development in the 900mg group. Exogenous testosterone partially counteracted DBP-induced changes in the reproductive organs of male offspring of DBP-treated rats.

CONCLUSIONS

High-dose DBP exposure may induce testicular dysgenesis in rat embryos. Additionally, low-dose DBP may delay testicular development and testosterone secretion during urethral development. This disruption may result in hypospadias.

The INSL3 gene is a direct target for the orphan nuclear receptor, COUP-TFII, in Leydig cells

Insulin-like 3 (INSL3), a hormone produced by Leydig cells, regulates testicular descent during foetal life and bone metabolism in adults. Despite its importance, little is known about the molecular mechanisms controlling INSL3 expression. Reduced Insl3 mRNA levels were reported in the testis of mice deficient for chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), an orphan nuclear receptor known to play critical roles in cell differentiation and lineage determination in several tissues. Although COUP-TFII-deficient mice had Leydig cell dysfunction and impaired fertility, it remained unknown whether Insl3 expression was directly regulated by COUP-TFII. In this study, we observed a significant decrease in Insl3 mRNA levels in MA-10 Leydig cells depleted of COUP-TFII. Furthermore, a -1087 bp mouse Insl3 promoter was activated fourfold by COUP-TFII in MA-10 Leydig cells. Using 5' progressive deletions, the COUP-TFII-responsive element was located between -186 and -79 bp, a region containing previously uncharacterised direct repeat 0-like (DR0-like) and DR3 elements. The recruitment and direct binding of COUP-TFII to the DR0-like element were confirmed by chromatin immunoprecipitation and DNA precipitation assay respectively. Mutation of the DR0-like element, which prevented COUP-TFII binding, significantly decreased COUP-TFII-mediated activation of the -1087 bp Insl3 reporter in CV-1 fibroblast cells but not in MA-10 Leydig cells. Finally, we found that COUP-TFII cooperates with the nuclear receptor steroidogenic factor 1 (SF1) to further enhance Insl3 promoter activity. Our results identify Insl3 as a target for COUP-TFII in Leydig cells and revealed that COUP-TFII acts through protein-protein interactions with other DNA-bound transcription factors, including SF1, to activate Insl3 transcription in these cells.