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.This project has received funding from the European Unions' Horizon 2020 research and innovation Programme under grant agreement No 733032 HBM4E

Environmental contaminants and male infertility: Effects and mechanisms

The escalating prevalence of male infertility and decreasing trend in sperm quality have been correlated with rapid industrialisation and the associated discharge of an excess of synthetic substances into the environment. Humans are inevitably exposed to these ubiquitously distributed environmental contaminants, which possess the ability to intervene with the growth and function of male reproductive organs. Several epidemiological reports have correlated the blood and seminal levels of environmental contaminants with poor sperm quality. Numerous in vivo and in vitro studies have been conducted to investigate the effect of various environmental contaminants on spermatogenesis, steroidogenesis, Sertoli cells, blood–testis barrier, epididymis and sperm functions. The reported reprotoxic effects include alterations in the spermatogenic cycle, increased germ cell apoptosis, inhibition of steroidogenesis, decreased Leydig cell viability, impairment of Sertoli cell structure and function, altered expression of steroid receptors, increased permeability of blood–testis barrier, induction of peroxidative and epigenetic alterations in spermatozoa resulting in poor sperm quality and function

EFFECT OF TRANSLOCATOR PROTEIN (TSPO) STIMULATION OF STEROIDOGENESIS BY TSPO-SPECIFIC DRUG LIGAND: IMPLICATIONS FOR HYPOGONADISM AND SPERMATOGENESIS

The Leydig cells, localized in the interstitial compartment of the mammalian testis, produce testosterone (T) in response to luteinizing hormone (LH) released from the anterior pituitary. As most men age, serum T levels decrease, which is clinically referred to as hypogonadism. Fatigue, erectile dysfunction, and reduced bone density and muscle mass are some of the symptoms linked to these declining T levels. Age-related decline in T also occurs in aging Brown Norway rats. Previous studies reported that with aging, LH levels do not change, but Leydig cells become less responsive to LH, resulting in reduced T production. Currently, the only readily available treatment for hypogonadism is T replacement therapy (TRT). However, exogenous T administration has been shown to suppress LH release and thus Leydig cell T production. This results in reduced intratesticular T levels and therefore in suppressive effects on spermatogenesis to the point of azoospermia. Thus, TRT is an inadequate therapy for men who wish to father children. We wished to develop a method by which to elevate serum T levels without affecting intratesticular T levels. To accomplish this, we used the current understanding of the T biosynthetic pathway to pharmacologically stimulate a key protein in this pathway called Translocator Protein (18-kDa TSPO) using a TSPO-specific drug ligand. We compared the effects on serum and intratesticular T levels of administering the TSPO-specific ligand with administering exogenous T. Old (18-24 mo) rats have significantly reduced serum T levels compared to young (3-6 mo) rats. We administered the TSPO drug ligand, N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide (FGIN-1-27), via daily ip injection to aged rats at a concentration of 1 mg/kg body weight over the course of 10 days. Control rats received vehicle for the same time period. Another group of aged rats were given exogenous T via T-containing Silastic implants. Serum T levels were significantly lower in old control rats than in young control rats. When administering FGIN-1-27, serum T levels in old rats rose significantly, and administering exogenous T rose to the level of young rats. Administering exogenous T to old rats reduced intratesticular T levels significantly from control levels. In striking contrast, administering FGIN-1-27 to old rats resulted in a significant increase in intratesticular T levels. Taken together, these results show that administering FGIN-1-27 can increase serum T in hypogonadal old rats, as can administering exogenous T. However, in contrast to exogenous T, administering FGIN-1-27 can do so without reducing intratesticular T levels, suggesting that this approach would not suppress spermatogenesis and might even enhance this process

Reprod Toxicol

Known endocrine disruptor bisphenol A (BPA) has been shown to be a reproductive toxicant in animal models. Its structural analogs: bisphenol S (BPS), bisphenol F (BPF), bisphenol AF (BPAF), and tetrabromobisphenol A (TBBPA) are increasingly being used in consumer products. However, these analogs may exert similar adverse effects on the reproductive system, and their toxicological data are still limited. This mini-review examined studies on both BPA and BPA analog exposure and reproductive toxicity. It outlines the current state of knowledge on human exposure, toxicokinetics, endocrine activities, and reproductive toxicities of BPA and its analogs. BPA analogs showed similar endocrine potencies when compared to BPA, and emerging data suggest they may pose threats as reproductive hazards in animal models. While evidence based on epidemiological studies is still weak, we have utilized current studies to highlight knowledge gaps and research needs for future risk assessments.R21 OH010473/OH/NIOSH CDC HHS/United StatesR43 ES027374/ES/NIEHS NIH HHS/United StatesR44 ES027374/ES/NIEHS NIH HHS/United States2019-08-11T00:00:00Z29925041PMC6689411655

Effects of endocrine disrupting chemicals on gonad development: Mechanistic insights from fish and mammals

Over the past century, evidence has emerged that endocrine disrupting chemicals (EDCs) have an impact on reproductive health. An increased frequency of reproductive disorders has been observed worldwide in both wildlife and humans that is correlated with accidental exposures to EDCs and their increased production. Epidemiological and experimental studies have highlighted the consequences of early exposures and the existence of key windows of sensitivity during development. Such early in life exposures can have an immediate impact on gonadal and reproductive tract development, as well as on long-term reproductive health in both males and females. Traditionally, EDCs were thought to exert their effects by modifying the endocrine pathways controlling reproduction. Advances in knowledge of the mechanisms regulating sex determination, differentiation and gonadal development in fish and rodents have led to a better understanding of the molecular mechanisms underlying the effects of early exposure to EDCs on reproduction. In this manuscript, we review the key developmental stages sensitive to EDCs and the state of knowledge on the mechanisms by which model EDCs affect these processes, based on the roadmap of gonad development specific to fish and mammals.The authors are grateful to the Intersectoral Centre for Endocrine Disruptor Analysis (ICEDA)'s researcher network that facilitated this Special Issue. LNM was supported by a H2020-Marie Skłodowska-Curie Action MSCA-IF-RI- 2017 awarded by the European Commission (ref. 797725-EpiSTOX).With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Peer reviewe

Mode of action studies with phthalate acid monoesters: pharmacokinetic and pharmacodynamic factors affecting steroidogenesis

The use of phthalate esters in plastics and resulting human exposure has led to concern over potential adverse effects in fetal development. This project provided data and quantitative tools to improve phthalate risk assessments. In vivo, in vitro and in silico experiments evaluated pharmacokinetic and pharmacodynamic factors responsible for anti-androgenic effects of phthalate esters. For pharmacokinetics, plasma and tissue metabolite levels were measured in maternal and fetal rats following DBP administration. A physiologically based pharmacokinetic (PBPK) model was developed for DBP distribution in rat gestation, tested against a variety of data across life-stages, doses and exposure routes, and accurately predicted maternal and fetal plasma MBP levels for acute and repeated dosing. The validated model permitted direct correlation of testes phthalate concentrations and testosterone. When extended to DEHP, the model also predicted MEHP kinetics. For pharmacodynamic evaluation, monoester concentrations were measured in the fetal testes after repeated doses of BBP, DEP, DBP, DEHP, and DMP. An in vitro assay tested the effect of inhibition of steroidogenesis directly in the Leydig cell. The differential ability of the monoesters to cause developmental toxicity was found to result from differences in their pharmacodynamic potency. Finally, we attempted to identify the molecular target for the phthalates in the Leydig cell. The phospholipase A2 (PLA2) inhibitor CQ and MEHP had a similar ability to inhibit testosterone production, steroidogenic gene expression and AA release in the LH-stimulated (MA-10) Leydig cell. Both compounds interfered with translocation of fluorescently tagged cPLA2 in human HEK-cells after activation by a calcium ionophore, providing at least indirect evidence that inhibition of AA release by cPLA2 is likely to be involved in phthalate anti-androgenic effects. When CQ was administered to the pregnant rat, fetal testes testosterone levels were reduced in a dose-dependent manner. CQ also down-regulated steroidogenic genes as noted with active phthalate administration. Our results strongly indicate that cPLA2 is a key target of these phthalates in relation to decreased testosterone production. The improved understanding of phthalate dose-response and mechanism of action, together with in vitro derived potencies of phthalates for testosterone inhibition, should greatly improve cumulative risk assessments for the phthalates

The Mechanisms and Management of Age-Related Oxidative Stress in Male Hypogonadism Associated with Non-communicable Chronic Disease

Androgens have diverse functions in muscle physiology, lean body mass, the regulation of adipose tissue, bone density, neurocognitive regulation, and spermatogenesis, the male repro- ductive and sexual function. Male hypogonadism, characterized by reduced testosterone, is com- monly seen in ageing males, and has a complex relationship as a risk factor and a comorbidity in age-related noncommunicable chronic diseases (NCDs), such as obesity, metabolic syndrome, type 2 diabetes, and malignancy. Oxidative stress, as a significant contributor to the ageing process, is a common feature between ageing and NCDs, and the related comorbidities, including hypertension, dyslipidemia, hyperglycemia, hyperinsulinemia, and chronic inflammation. Oxidative stress may also be a mediator of hypogonadism in males. Consequently, the management of oxidative stress may represent a novel therapeutic approach in this context. Therefore, this narrative review aims to discuss the mechanisms of age-related oxidative stress in male hypogonadism associated with NCDs and discusses current and potential approaches for the clinical management of these patients, which may include conventional hormone replacement therapy, nutrition and lifestyle changes, ad-herence to the optimal body mass index, and dietary antioxidant supplementation and/or phyto-medicines.O