Effects of Endocrine Disrupting Chemicals (EDCs) on Skeletal System Development: A Review

INTRODUCTION

Endocrine-disrupting chemicals (EDCs) are exogenous substances that alter endocrine function and cause adverse effects on an organism. EDC interference with the endocrine system leads to chronic autoimmune disorders, abnormal osteogenesis, infertility, and reproductive, neurological, cardiovascular, and metabolic disorders. Among the adverse effects of EDCs are their impact on developing fetuses and neonates. EDCs like bisphenol A (BPA), pesticides, and lead interfere with or alter sex steroid hormone synthesis and metabolism, leading to developmental delay, infertility, and urogenital carcinoma in both sexes.

OBJECTIVE

This review article examines the most harmful EDC, BPA, which affects the skeletal system during the embryonic period. The literature investigates the effects of BPA on various systems in our body, but the mechanism behind skeletal system development during the embryonic period is still unknown.

MATERIALS AND METHODS

In the present review, 25 articles were reviewed through multiple windows like PubMed, Scopus, and Web of Science. Many articles mention the effects of BPA on the skeletal system after birth and also examine reproductive system abnormalities, hereditary characteristics, excretory system malfunctions, and physical and mental illness in various mechanisms.

DISCUSSION

The impact of BPA on the skeletal system causes morphological and physiological changes in developing embryos. The general ideology regarding skeletal system development and its mechanism is as follows: the formation of bone (osteocytes) is reduced by the apoptosis of precursor bone cells (osteoblasts) by the effect of BPA.

CONCLUSION

EDC exposure induces the apoptosis of bone cells and inhibits the formation of osteoblasts, and long-term exposure to these chemicals will also impact immune system development.

Chromatin Landscape Governing Murine Epidermal Differentiation

Chromatin landscape and regulatory networks are determinants in lineage specification and differentiation. To define the temporospatial differentiation axis in murine epidermal cells in vivo, we generated datasets profiling expression dynamics (RNA sequencing), chromatin accessibility (assay for transposase-accessible chromatin using sequencing), architecture (Hi-C), and histone modifications (chromatin immunoprecipitation followed by sequencing) in the epidermis. We show that many differentially regulated genes are suppressed during the differentiation process, with superenhancers controlling differentiation-specific epigenomic changes. Our data shows the relevance of the Dlx/Klf/Grhl combinatorial regulatory network in maintaining correct temporospatial gene expression during epidermal differentiation. We determined differential open compartments, topologically associating domain score, and looping in the basal cell and suprabasal cell epidermal fractions, with the evolutionarily conserved epidermal differentiation complex region showing distinct suprabasal cell-specific topologically associating domain and loop formation that coincided with superenhancer sites. Overall, our study provides a global genome-wide resource of chromatin dynamics that define unrecognized regulatory networks and the epigenetic control of Dlx3-bound superenhancer elements during epidermal differentiation.

The banned sunscreen ingredients and their impact on human health: a systematic review

Recent evidence of high systemic absorption of sunscreen ingredients has raised concerns regarding the safety of sunscreen products. Oxybenzone (BP-3) and octinoxate (OMC), two common sunscreen ingredients, were recently banned in Key West and Hawaii owing to their toxic effects on marine ecosystems. Their impact on human health requires a careful assessment. To summarize the current evidence on the association between the systemic level of BP-3 or OMC and its health impact, a primary literature search was conducted using PubMed database in February 2019. There are 29 studies that address the impact of these ingredients on human health. Studies show that elevated systemic level of BP-3 has no adverse effect on male and female fertility, female reproductive hormone level, adiposity, fetal growth, child's neurodevelopment, and sexual maturation. However, the association of BP-3 level on thyroid hormone, testosterone level, kidney function, and pubertal timing has been reported and prompts further investigations to validate a true association. The systemic absorption of OMC has no reported effect on thyroid and reproductive hormone levels. In conclusion, current evidence is not sufficient to support the causal relationship between the elevated systemic level of BP-3 or OMC and adverse health outcomes. There are either contradictory findings among different studies or an insufficient number of studies to corroborate the observed association. To accurately evaluate the long-term risk of exposure to BP-3 and OMC from sunscreen, a well-designed longitudinal randomized controlled trial needs to be conducted.

Transgenerational effects of obesogens and the obesity epidemic

In the last three decades there has been a dramatic, worldwide increase in the incidence of obesity, particularly in Western societies. This trend has required a significant economic investment to treat obesity-related disorders such as type 2 diabetes, cardiovascular disease, and non-alcoholic fatty liver disease. There is an urgent need to understand the factors that contribute to this increase in obesity in order to find new tools that will improve quality of life in affected individuals and to avoid the propagation of obesity to future generations. Endocrine disrupting chemicals have become an important piece of the obesity epidemic puzzle but little is known about the mechanism underlying their effects. In this commentary, we highlight recent work showing that the consequences of ancestral exposure to obesogenic chemicals results in the transmission of obesity-related phenotypes through at least three generations.

Adipogenic effects of a combination of the endocrine-disrupting compounds bisphenol A, diethylhexylphthalate, and tributyltin

OBJECTIVE

The food contaminants bisphenol A (BPA), diethylhexylphthalate (DEHP), and tributyltin (TBT) are potent endocrine-disrupting compounds (EDC) known to interfere with adipogenesis. EDC usually act in mixtures and not as single compounds. The aim of this study was to investigate the effects of a simultaneous exposure of BPA, DEHP, and TBT on mesenchymal stem cell differentiation into adipocytes.

METHODS

Multipotent murine mesenchymal stem cells (C3H10T1/2) were exposed to EDC mixtures in high concentrations, i.e. MIX-high (10 µmol/l BPA, 100 µmol/l DEHP, 100 nmol/l TBT), and in environmentally relevant concentrations, i.e. MIX-low (10 nmol/l BPA, 100 nmol/l DEHP, 1 nmol/l TBT). The exposure was performed either for the entire culture time (0-12 days) or at distinct stages of adipogenic differentiation. At day 12 of cell culture, the amount of adipocytes, triglyceride content (TG), and adipogenic marker gene expression were analyzed.

RESULTS

MIX-high increased the development of adipocytes and the expression of adipogenic marker genes independently of the exposure window. The total TG amount was not increased. The low-concentrated EDC mixture had no obvious impact on adipogenesis.

CONCLUSION

In EDC mixtures, the adipogenic effect of TBT and DEHP predominates single effects of BPA. Mixture effects of EDC are not deducible from single compound experiments.

Disruption of androgen receptor signaling in males by environmental chemicals

Androgen-disruptors are environmental chemicals in that interfere with the biosynthesis, metabolism or action of endogenous androgens resulting in a deflection from normal male developmental programming and reproductive tract growth and function. Since male sexual differentiation is entirely androgen-dependent, it is highly susceptible to androgen-disruptors. Animal models and epidemiological evidence link exposure to androgen disrupting chemicals with reduced sperm counts, increased infertility, testicular dysgenesis syndrome, and testicular and prostate cancers. Further, there appears to be increased sensitivity to these agents during critical developmental windows when male differentiation is at its peak. A variety of in vitro and in silico approaches have been used to identify broad classes of androgen disrupting molecules that include organochlorinated pesticides, industrial chemicals, and plasticizers with capacity to ligand the androgen receptor. The vast majority of these synthetic molecules act as anti-androgens. This review will highlight the evidence for androgen disrupting chemicals that act through interference with the androgen receptor, discussing specific compounds for which there is documented in vivo evidence for male reproductive tract perturbations. This article is part of a Special Issue entitled 'Endocrine disruptors'.

Endocrine disrupting chemicals and the developmental programming of adipogenesis and obesity

Obesity and related disorders are a burgeoning public health epidemic, particularly in the U.S. Currently 34% of the U.S. population is clinically obese (BMI > 30) and 68% are overweight (BMI > 25), more than double the worldwide average and 10-fold higher than Japan and South Korea. Obesity occurs when energy intake exceeds energy expenditure; however, individuals vary widely in their propensity to gain weight and accrue fat mass, even at identical levels of excess caloric input. Clinical, epidemiological, and biological studies show that obesity is largely programmed during early life, including the intrauterine period. The environmental obesogen hypothesis holds that prenatal or early life exposure to certain endocrine disrupting chemicals can predispose exposed individuals to increased fat mass and obesity. Obesogen exposure can alter the epigenome of multipotent stromal stem cells, biasing them toward the adipocyte lineage at the expense of bone. Hence, humans exposed to obesogens during early life might have an altered stem cell compartment, which is preprogrammed toward an adipogenic fate. This results in a higher steady state number of adipocytes and potentially a lifelong struggle to maintain a healthy weight, which can be exacerbated by societal influences that promote poor diet and inadequate exercise. This review focuses on the developmental origins of the adipocyte, the relationship between adipocyte number and obesity, and how obesogenic chemicals may interfere with the highly efficient homeostatic mechanisms regulating adipocyte number and energy balance.

Epigenetic effects of endocrine-disrupting chemicals on female reproduction: an ovarian perspective

The link between in utero and neonatal exposure to environmental toxicants, such as endocrine-disrupting chemicals (EDCs) and adult female reproductive disorders is well established in both epidemiological and animal studies. Recent studies examining the epigenetic mechanisms involved in mediating the effects of EDCs on female reproduction are gathering momentum. In this review, we describe the developmental processes that are susceptible to EDC exposures in female reproductive system, with a special emphasis on the ovary. We discuss studies with select EDCs that have been shown to have physiological and correlated epigenetic effects in the ovary, neuroendocrine system, and uterus. Importantly, EDCs that can directly target the ovary can alter epigenetic mechanisms in the oocyte, leading to transgenerational epigenetic effects. The potential mechanisms involved in such effects are also discussed.