Maternal phthalate exposure during pregnancy and testis function of young adult sons

Foetal Exposure to Phthalates and Endocrine Effects on the Leydig Cell

This review examines the association between early life exposure to phthalates in human males and Leydig cell endocrine function. A systematic search was performed in PubMed and EMBASE, identifying 17 studies for analysis. Association scores weighted for number of phthalates and subjects were calculated for luteinizing hormone (LH), testosterone, testosterone/LH ratio and insulin-like factor 3 (INSL3). The scores ranges from full consistency of positive (score = 1), through inconsistent (score = 0), to negative/inverse (score = -1) associations. LH and early life phthalate exposure showed a statistically significant weighted phthalate association score of 0.18. Testosterone showed largely null results, whereas testosterone/LH ratio showed a negative association, both not statistically significant. A rise in LH, and decrease of testosterone/LH ratio, indicates that early life phthalate exposure results in a demand for a larger LH stimulus to produce the same amount of testosterone, and perhaps a decreased function of the Leydig cells, that manifests with the onset of high testosterone production in puberty and adulthood. A statistically non-significant decrease in INSL3 with a weighted phthalate association score of -0.29 supports this finding. An early life phthalate exposure-induced decline in Leydig cell function could possibly impact the spermatogenesis and adult male fertility.

Fetal exposure to a mixture of endocrine-disrupting chemicals and biomarkers of male fecundity: A population-based cohort study

BACKGROUND

Fetal exposure to endocrine-disrupting chemicals (EDCs) has been associated with reduced male fecundity, but with few studies considering chemical mixtures.

OBJECTIVES

We assessed the association between fetal exposure to a mixture of EDCs and biomarkers of male fecundity in young adulthood.

MATERIALS AND METHODS

The study population comprised 841 young adult males enrolled in the Fetal Programming of Semen Quality cohort, established as a male offspring sub-cohort within the Danish National Birth Cohort. Maternal blood samples were analyzed for concentrations of per- and polyfluoroalkyl substances (PFAS), phthalate metabolites, and triclosan. We used quantile g-computation to estimate the change in semen characteristics, testicular volume, and reproductive hormone levels with 95% confidence intervals (CI) per one-quartile increase in all chemicals within three chemical mixtures; an overall chemical mixture, a PFAS mixture, and a non-persistent chemical mixture.

RESULTS

Fetal exposure to a one-quartile increase in the overall chemical mixture was associated with 4.0 million/mL lower sperm concentration (95% CI: -9.1, 1.1), 16.1 million lower total sperm count (95% CI: -33.8, 1.6), 0.5 mL smaller testicular volume (95% CI: -1.2, 0.3), 5% higher proportion of non-progressive and immotile spermatozoa (95% CI: 0.99, 1.11), and 7% higher concentration of FSH (95% CI: 0.99, 1.16), but with limited precision. Effect sizes were greatest in magnitude for sperm concentration and total sperm count. We observed somewhat similar associations for the PFAS mixture and no associations for the non-persistent chemical mixture.

DISCUSSION

Results suggest that fetal exposure to an overall mixture of EDCs may be adversely associated with several biomarkers of male fecundity, but findings are also compatible with null associations. These associations, if true, appeared to be driven by PFAS, but misclassification due to a single measurement of the phthalate metabolites and triclosan may have attenuated the results.

Down-regulation of TET2 inhibits testosterone synthesis in offspring mice exposed to DBP during pregnancy through LH/cAMP/PKA/StAR signaling mediated by LHR

Exposure to di-n-butyl phthalate (DBP) during embryo development or lactation has been linked to reproductive toxicity. The ten-eleven translocation (TET) protein family plays a role in various pathological processes; however, its involvement in reproductive dysfunction in offspring mice exposed to DBP during gestation remains sparsely reported. In this study, SPF C57BL/6 pregnant mice were intragastrically administered DBP at doses of 0.5, 5, and 75 mg/kg body weight, or corn oil as a control, from gestational days 5-19. Following weaning, the offspring mice were maintained on a standard diet for 5 weeks. Additionally, mono-n-butyl phthalate (MBP)-induced TM3 cells were utilized to explore the underlying mechanisms in vitro. The results showed that in utero exposure to DBP resulted in diminished sperm quality, testicular damage, decreased reproductive hormone levels, and reduced expression of testosterone synthesis proteins in male offspring mice. Moreover, DBP exposure influenced the expression of steroidogenic acute regulatory protein (StAR) via the cAMP/PKA signaling pathway, associated with luteinizing hormone receptor (LHR)-mediated suppression of testosterone synthesis. Notably, DBP exposure led to decreased expression of TET methylcytosine dioxygenase 2 (TET2) in the progeny, and overexpression or silencing of TET2 affected the levels of proteins involved in the LHR-mediated testosterone synthesis pathway. Further investigations revealed that TET2 downregulation inhibits testosterone synthesis through the LHR-mediated LH/cAMP/PKA/StAR signaling pathway, ultimately impairing reproductive function in DBP-exposed offspring mice during gestation. This study provides a novel perspective for identifying molecular markers that may be more sensitive indicators of male reproductive damage from an epigenetic standpoint.

Reproductive and Metabolic Health Following Exposure to Environmental Chemicals: Mechanistic Insights from Mammalian Models

The decline in human reproductive and metabolic health over the past 50 years is associated with exposure to complex mixtures of anthropogenic environmental chemicals (ECs). Real-life EC exposure has varied over time and differs across geographical locations. Health-related issues include declining sperm quality, advanced puberty onset, premature ovarian insufficiency, cancer, obesity, and metabolic syndrome. Prospective animal studies with individual and limited EC mixtures support these observations and provide a means to investigate underlying physiological and molecular mechanisms. The greatest impacts of EC exposure are through programming of the developing embryo and/or fetus, with additional placental effects reported in eutherian mammals. Single-chemical effects and mechanistic studies, including transgenerational epigenetic inheritance, have been undertaken in rodents. Important translational models of human exposure are provided by companion animals, due to a shared environment, and sheep exposed to anthropogenic chemical mixtures present in pastures treated with sewage sludge (biosolids). Future animal research should prioritize EC mixtures that extend beyond a single developmental stage and/or generation. This would provide a more representative platform to investigate genetic and underlying mechanisms that explain sexually dimorphic and individual effects that could facilitate mitigation strategies.

Short-Half-Life Chemicals: Maternal Exposure and Offspring Health Consequences-The Case of Synthetic Phenols, Parabens, and Phthalates

Phenols, parabens, and phthalates (PPPs) are suspected or known endocrine disruptors. They are used in consumer products that pregnant women and their progeny are exposed to daily through the placenta, which could affect offspring health. This review aims to compile data from cohort studies and in vitro and in vivo models to provide a summary regarding placental transfer, fetoplacental development, and the predisposition to adult diseases resulting from maternal exposure to PPPs during the gestational period. In humans, using the concentration of pollutants in maternal urine, and taking the offspring sex into account, positive or negative associations have been observed concerning placental or newborn weight, children's BMI, blood pressure, gonadal function, or age at puberty. In animal models, without taking sex into account, alterations of placental structure and gene expression linked to hormones or DNA methylation were related to phenol exposure. At the postnatal stage, pollutants affect the bodyweight, the carbohydrate metabolism, the cardiovascular system, gonadal development, the age of puberty, sex/thyroid hormones, and gamete quality, but these effects depend on the age and sex. Future challenges will be to explore the effects of pollutants in mixtures using models and to identify the early signatures of in utero exposure capable of predicting the health trajectory of the offspring.

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

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

Endocrine disruption and male reproductive disorders: unanswered questions

Maternal exposure to endocrine-disrupting chemicals (EDCs) in human pregnancy is widely considered as an important cause of adverse changes in male reproductive health due to impaired foetal androgen production/action. However, the epidemiological evidence supporting this view is equivocal, except for certain phthalates, notably diethyl hexyl phthalate (DEHP). Maternal phthalate exposure levels associated with adverse reproductive changes in epidemiological studies are several thousand-fold lower than those needed to suppress foetal androgen production in rats, and direct studies using human foetal testis tissue show no effect of high phthalate exposure on androgen production. This conundrum is unexplained and raises fundamental questions. Human DEHP exposure is predominantly via food with highest exposure associated with consumption of a Western style (unhealthy) diet. This diet is also associated with increased exposure to the most common EDCs, whether persistent (chlorinated or fluorinated chemicals) or non-persistent (phthalates, bisphenols) compounds, which are found at highest levels in fatty and processed foods. Consequently, epidemiological studies associating EDC exposure and male reproductive health disorders are confounded by potential dietary effects, and vice versa. A Western diet/lifestyle in young adulthood is also associated with low sperm counts. Disentangling EDC and dietary effects in epidemiological studies is challenging. In pregnancy, a Western diet, EDC exposure, and maternal living in proximity to industrial sites are all associated with impaired foetal growth/development due to placental dysfunction, which predisposes to congenital male reproductive disorders (cryptorchidism, hypospadias). While the latter are considered to reflect impaired foetal androgen production, effects resulting from foetal growth impairment (FGI) are likely indirect. As FGI has numerous life-long health consequences, and is affected by maternal lifestyle, research into the origins of male reproductive disorders should take more account of this. Additionally, potential effects on foetal growth/foetal testis from the increasing use of medications in pregnancy deserves more research attention.

Deteriorating Semen Quality: The Role of the Environment

Since the end of the last century, several reports have suggested that semen quality is declining, especially in Western countries. Furthermore, cross-sectional studies using similar protocols have suggested regional differences in semen quality of young and fertile men. Reasons for these regional differences and local adverse trends in semen quality are unknown, but environmental factors are suspected to have a role. Besides adulthood environmental exposures, those occurring during testicular development may also affect semen quality. Longitudinal follow-up studies and mixture risk analyses are needed to study the effect of fetal, childhood, and adult life environment on semen quality.