The orl rat with inherited cryptorchidism has increased susceptibility to the testicular effects of in utero dibutyl phthalate exposure

Effects of bis(2-butoxyethyl) phthalate exposure in utero on the development of fetal Leydig cells in rats

Phthalates are plasticizers widely found in the environment. They are potential endocrine disruptors. Bis(2-butoxyethyl) phthalate (BBOP) is a unique phthalate that contains oxygen atoms in the carbon backbone. Little is known about its reproductive and developmental toxicity. The objective of this study was to determine the effect of BBOP on fetal Leydig cell development after in utero exposure to rats. Sprague Dawley pregnant dams were randomly allocated into 6 groups, and were gavaged with BBOP (0, 10, 100, 250, 500, and 1000 mg/kg body weight/day) from gestational day (GD) 14-21. Seven of the 8 dams in the 1000 mg/kg BBOP group died before giving birth. Twelve of the 20 dams in the 500 mg/kg BBOP group had whole litter loss. BBOP significantly reduced the body weight of dams and male offspring and serum testosterone level and anogenital distance of male fetus on GD 21 at 500 mg/kg. BBOP markedly increased fetal Leydig cell proliferation and number at 500 mg/kg while inducing their abnormal aggregation at 250 and 500 mg/kg. BBOP down-regulated the expression of Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Insl3, and Nr5a1 at various doses while up-regulating the expression of Sertoli cell gene Fshr and Sox9. The phosphorylation of AKT1, AKT2, and ERK1/2 was also markedly reduced by BBOP. In conclusion, BBOP in utero exposure can disrupt fetal Leydig cell development, possibly via the mechanism that may include inhibiting the phosphorylation of AKT1, AKT2, and ERK1/2.

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.

Validation of an automated counting procedure for phthalate-induced testicular multinucleated germ cells

In utero exposure to certain phthalate esters results in testicular toxicity, characterized at the tissue level by induction of multinucleated germ cells (MNGs) in rat, mouse, and human fetal testis. Phthalate exposures also result in a decrease in testicular testosterone in rats. The anti-androgenic effects of phthalates have been more thoroughly quantified than testicular pathology due to the significant time requirement associated with manual counting of MNGs on histological sections. An automated counting method was developed in ImageJ to quantify MNGs in digital images of hematoxylin-stained rat fetal testis tissue sections. Timed pregnant Sprague Dawley rats were exposed by daily oral gavage from gestation day 17 to 21 with one of eight phthalate test compounds or corn oil vehicle. Both the manual counting method and the automated image analysis method identified di-n-butyl phthalate, butyl benzyl phthalate, dipentyl phthalate, and di-(2-ethylhexyl) phthalate as positive for induction of MNGs. Dimethyl phthalate, diethyl phthalate, the brominated phthalate di-(2-ethylhexyl) tetrabromophthalate, and dioctyl terephthalate were negative. The correlation between automated and manual scoring metrics was high (r = 0.923). Results of MNG analysis were consistent with these compounds' anti-androgenic activities, which were confirmed in an ex vivo testosterone production assay. In conclusion, we have developed a reliable image analysis method that can be used to facilitate dose-response studies for the reproducible induction of MNGs by in utero phthalate exposure.

Maternal phthalate exposure during early pregnancy and at delivery in relation to gestational age and size at birth: A preliminary analysis

Epidemiologic studies of in utero phthalate exposure and birth outcomes have had conflicting findings. The objective of this study was to characterize maternal phthalate exposure across pregnancy, examine associations between maternal phthalate levels and infant size and gestational age at birth, and investigate relationships between concurrent bisphenol A (BPA) and phthalate exposure and birth outcomes. Women in the Michigan Mother-Infant Pairs cohort provided urine and blood samples during their first trimester and at delivery. Urinary phthalate metabolites and serum BPA were measured at both time points, and birth weight, length, head circumference, and gestational age were recorded from medical records. Maternal DEHP metabolite concentrations were significantly higher at delivery compared to the first trimester (p<0.05), suggesting increased DEHP exposure late in pregnancy. A number of phthalate metabolites were associated with birth size and gestational age in patterns that varied by sex and timing of exposure, independent of BPA exposure.

Maternal phthalate exposure during early pregnancy and at delivery in relation to gestational age and size at birth: A preliminary analysis

Epidemiologic studies of in utero phthalate exposure and birth outcomes have had conflicting findings. The objective of this study was to characterize maternal phthalate exposure across pregnancy, examine associations between maternal phthalate levels and infant size and gestational age at birth, and investigate relationships between concurrent bisphenol A (BPA) and phthalate exposure and birth outcomes. Women in the Michigan Mother-Infant Pairs cohort provided urine and blood samples during their first trimester and at delivery. Urinary phthalate metabolites and serum BPA were measured at both time points, and birth weight, length, head circumference, and gestational age were recorded from medical records. Maternal DEHP metabolite concentrations were significantly higher at delivery compared to the first trimester (p<0.05), suggesting increased DEHP exposure late in pregnancy. A number of phthalate metabolites were associated with birth size and gestational age in patterns that varied by sex and timing of exposure, independent of BPA exposure.

Expression of the Shh/Bmp4 signaling pathway during the development of anorectal malformations in a male rat model of prenatal exposure to di(n-butyl) phthalate

Sonic hedgehog (Shh)/bone morphogenetic protein 4 (Bmp4) is an androgen-regulated signaling pathway that has been shown to be crucial for embryonic development.

Phenotype specific association of the TGFBR3 locus with nonsyndromic cryptorchidism

PURPOSE

Based on a genome-wide association study of testicular dysgenesis syndrome showing a possible association with TGFBR3, we analyzed data from a larger, phenotypically restricted cryptorchidism population for potential replication of this signal.

MATERIALS AND METHODS

We excluded samples based on strict quality control criteria, leaving 844 cases and 2,718 controls of European ancestry that were analyzed in 2 separate groups based on genotyping platform (ie Illumina® HumanHap550, version 1 or 3, or Human610-Quad, version 1 BeadChip in group 1 and Human OmniExpress 12, version 1 BeadChip platform in group 2). Analyses included genotype imputation at the TGFBR3 locus, association analysis of imputed data with correction for population substructure, subsequent meta-analysis of data for groups 1 and 2, and selective genotyping of independent cases (330) and controls (324) for replication. We also measured Tgfbr3 mRNA levels and performed TGFBR3/betaglycan immunostaining in rat fetal gubernaculum.

RESULTS

We identified suggestive (p ≤ 1× 10(-4)) association of markers in/near TGFBR3, including rs9661103 (OR 1.40; 95% CI 1.20, 1.64; p = 2.71 × 10(-5)) and rs10782968 (OR 1.58; 95% CI 1.26, 1.98; p = 9.36 × 10(-5)) in groups 1 and 2, respectively. In subgroup analyses we observed strongest association of rs17576372 (OR 1.42; 95% CI 1.24, 1.60; p = 1.67 × 10(-4)) with proximal and rs11165059 (OR 1.32; 95% CI 1.15, 1.38; p = 9.42 × 10(-4)) with distal testis position, signals in strong linkage disequilibrium with rs9661103 and rs10782968, respectively. Association of the prior genome-wide association study signal (rs12082710) was marginal (OR 1.13; 95% CI 0.99, 1.28; p = 0.09 for group 1), and we were unable to replicate signals in our independent cohort. Tgfbr3/betaglycan was differentially expressed in wild-type and cryptorchid rat fetal gubernaculum.

CONCLUSIONS

These data suggest complex or phenotype specific association of cryptorchidism with TGFBR3 and the gubernaculum as a potential target of TGFβ signaling.

The orl rat is more responsive to methacholine challenge than wild type

BACKGROUND

This study presents an animal model of native airway hyperresponsiveness (AHR). AHR is a fundamental aspect of asthma and reflects an abnormal response characterized by airway narrowing following exposure to a wide variety of non-immunological stimuli. Undescended testis (UDT) is one of the most common male congenital anomalies. The orl rat is a Long Evans substrain with inherited UDT. Since boys born with congenital UDT are more likely to manifest asthma symptoms, the main aim of this study was to investigate the alternative hypothesis that orl rats have greater AHR to a methacholine aerosol challenge than wild type rats.

METHODS

Long Evans wild type (n = 9) and orl (n = 13) rats were anesthetized, tracheostomized, and mechanically ventilated at 4 weeks of age. Escalating concentrations of inhaled methacholine were delivered. The methacholine potency and efficacy in the strains were measured. Respiratory resistance was the primary endpoint. After the final methacholine aerosol challenge, the short-acting β2-adrenoceptor agonist albuterol was administered as an aerosol and lung/diaphragm tissues were assayed for interleukin (IL)-4, IL-6, and tumor necrosis factor (TNF)-α. Histological and histomorphometrical analyses were performed.

RESULTS

The methacholine concentration-response curve in the orl group indicated increased sensitivity, hyperreactivity, and exaggerated maximal response in comparison with the wild type group, indicating that orl rats had abnormally greater AHR responses to methacholine. Histological findings in orl rats showed the presence of eosinophils, unlike wild type rats. β2-Adrenoceptor agonist intervention resulted in up-regulation of IL-4 diaphragmatic levels and down-regulation of IL-4 and IL-6 in the lungs of orl rats.

CONCLUSION

orl rats had greater AHR than wild type rats during methacholine challenge, with higher IL-4 levels in diaphragmatic tissue homogenates. Positive immunostaining for IL-4 was detected in lung and diaphragmatic tissue in both strains. This model offers advantages over other pre-clinical murine models for studying potential mechanistic links between cryptorchidism and asthma. This animal model may be useful for further testing of compounds/therapeutics options for treating AHR.

Prenatal di-n-butyl phthalate exposure alters reproductive functions at adulthood in male rats

This study was aimed to investigate the reproductive health in adult male rats exposed to di-n-butyl phthalate (DBP) during embryonic development. Pregnant rats were injected with DBP and F1 male rats were weaned and on postnatal day 100, used for mating with normal cycling females to assess reproductive performance. After completion of cohabitation period, rats were analyzed for other reproductive end points. Transplacental exposure to DBP significantly decreased fertility in adult male rats. Prenatal exposure to DBP significantly decreased sperm density, number of motile sperms, viable sperms, and hypoosmotic swelling tail coiled sperms with an increase in morphological abnormalities in sperms. Testicular steroidogenic enzyme activity levels and serum testosterone levels were significantly decreased in rats exposed to DBP during embryonic development. In conclusion, transplacental exposure to DBP impairs male reproductive performance by decreasing steroidogenesis and spermatogenesis.

Pharmacokinetics of dibutyl phthalate (DBP) in the rat determined by UPLC-MS/MS

Dibutyl phthalate (DBP) is commonly used to increase the flexibility of plastics in industrial products. However, several plasticizers have been illegally used as clouding agents to increase dispersion of aqueous matrix in beverages. This study thus develops a rapid and validated analytical method by ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) for the evaluation of pharmacokinetics of DBP in free moving rats. The UPLC-MS/MS system equipped with positive electrospray ionization (ESI) source in multiple reaction monitoring (MRM) mode was used to monitor m/z 279.25→148.93 transitions for DBP. The limit of quantification for DBP in rat plasma and feces was 0.05 μg/mL and 0.125 μg/g, respectively. The pharmacokinetic results demonstrate that DBP appeared to have a two-compartment model in the rats; the area under concentration versus time (AUC) was 57.8 ± 5.93 min μg/mL and the distribution and elimination half-life (t_1/2,α and t_1/2,β) were 5.77 ± 1.14 and 217 ± 131 min, respectively, after DBP administration (30 mg/kg, i.v.). About 0.18% of the administered dose was recovered from the feces within 48 h. The pharmacokinetic behavior demonstrated that DBP was quickly degraded within 2 h, suggesting a rapid metabolism low fecal cumulative excretion in the rat.

Of mice and men (and rats): phthalate-induced fetal testis endocrine disruption is species-dependent

For over 15 years, reproductive toxicologists have explored the physiological outcomes and mechanism of fetal phthalate exposure to determine the risk posed to human male reproductive health. This review examines the fetal male reproductive system response to phthalate exposure across species including rat, mouse, and human, with emphasis on the testis. In the rat, in utero phthalate exposure causes male reproductive tract malformations, in large part, by targeting the testis and inhibiting fetal Leydig cell hormone production. Despite mouse phthalate pharmacokinetics being similar to the rat, inhibition of fetal Leydig cell hormone synthesis is not observed in the mouse. The species-specific differences in testicular response following in utero phthalate exposure and the discordant reaction of the rodent fetal testis when exposed to phthalates ex vivo versus in vivo have made determining risk to humans difficult, yet critically important. The recent use of fetal testis xenotransplants to study phthalate toxicity suggests that the human fetal testis responds like the mouse fetal testis; it appears refractory to phthalate-induced inhibition of testosterone production. Although this result is unfulfilling from the perspective of identifying environmental contributions to human reproductive maldevelopment, it has important implications for phthalate risk assessment.

Cryptorchidism and hypospadias as a sign of testicular dysgenesis syndrome (TDS): environmental connection

Cryptorchidism and hypospadias are common genital birth defects that affect 2-9% and 0.2-1% of male newborns, respectively. The incidence of both defects shows large geographic variation, and in several countries increasing trends have been reported. The conditions share many risk factors, and they are also interlinked to the risk of testis cancer and poor semen quality. Testicular Dysgenesis Syndrome (TDS) may underlie many cases of all these male reproductive health problems. Genetic defects in androgen production or action can cause both cryptorchidism and hypospadias, but these are not common. A monogenic reason for cryptorchidism or hypospadias has been identified only in a small proportion of all cases. Environmental effects appear to play a major role in TDS. Exposure to several persistent chemicals has been found to be associated with the risk of cryptorchidism, and exposure to anti-androgenic phthalates has been shown to be associated with hormonal changes predisposing to male reproductive problems. Despite progress in identification of endocrine-disrupting substances, we are still far from knowing all the risk factors for these birth defects, and advice for prevention must be based on precautionary principles.

Species-specific dibutyl phthalate fetal testis endocrine disruption correlates with inhibition of SREBP2-dependent gene expression pathways

Fetal rat phthalate exposure produces a spectrum of male reproductive tract malformations downstream of reduced Leydig cell testosterone production, but the molecular mechanism of phthalate perturbation of Leydig cell function is not well understood. By bioinformatically examining fetal testis expression microarray data sets from susceptible (rat) and resistant (mouse) species after dibutyl phthalate (DBP) exposure, we identified decreased expression of several metabolic pathways in both species. However, lipid metabolism pathways transcriptionally regulated by sterol regulatory element-binding protein (SREBP) were inhibited in the rat but induced in the mouse, and this differential species response corresponded with repression of the steroidogenic pathway. In rats exposed to 100 or 500 mg/kg DBP from gestational days (GD) 16 to 20, a correlation was observed between GD20 testis steroidogenic inhibition and reductions of testis cholesterol synthesis endpoints including testis total cholesterol levels, Srebf2 gene expression, and cholesterol synthesis pathway gene expression. SREBP2 expression was detected in all fetal rat testis cells but was highest in Leydig cells. Quantification of SREBP2 immunostaining showed that 500 mg/kg DBP exposure significantly reduced SREBP2 expression in rat fetal Leydig cells but not in seminiferous cords. By Western analysis, total rat testis SREBP2 levels were not altered by DBP exposure. Together, these data suggest that phthalate-induced inhibition of fetal testis steroidogenesis is closely associated with reduced activity of several lipid metabolism pathways and SREBP2-dependent cholesterologenesis in Leydig cells.

Gene-environment interaction and male reproductive function

As genetic factors can hardly explain the changes taking place during short time spans, environmental and lifestyle-related factors have been suggested as the causes of time-related deterioration of male reproductive function. However, considering the strong heterogeneity of male fecundity between and within populations, genetic variants might be important determinants of the individual susceptibility to the adverse effects of environment or lifestyle. Although the possible mechanisms of such interplay in relation to the reproductive system are largely unknown, some recent studies have indicated that specific genotypes may confer a larger risk of male reproductive disorders following certain exposures. This paper presents a critical review of animal and human evidence on how genes may modify environmental effects on male reproductive function. Some examples have been found that support this mechanism, but the number of studies is still limited. This type of interaction studies may improve our understanding of normal physiology and help us to identify the risk factors to male reproductive malfunction. We also shortly discuss other aspects of gene-environment interaction specifically associated with the issue of reproduction, namely environmental and lifestyle factors as the cause of sperm DNA damage. It remains to be investigated to what extent such genetic changes, by natural conception or through the use of assisted reproductive techniques, are transmitted to the next generation, thereby causing increased morbidity in the offspring.