Endocrine-disrupting chemicals, epigenetics, and skeletal system dysfunction: exploration of links using bisphenol A as a model system

Understanding risk and causal mechanisms for developing obesity in infants and young children: A National Institutes of Health workshop

Obesity in children remains a major public health problem, with the current prevalence in youth ages 2-19 years estimated to be 19.7%. Despite progress in identifying risk factors, current models do not accurately predict development of obesity in early childhood. There is also substantial individual variability in response to a given intervention that is not well understood. On April 29-30, 2021, the National Institutes of Health convened a virtual workshop on "Understanding Risk and Causal Mechanisms for Developing Obesity in Infants and Young Children." The workshop brought together scientists from diverse disciplines to discuss (1) what is known regarding epidemiology and underlying biological and behavioral mechanisms for rapid weight gain and development of obesity and (2) what new approaches can improve risk prediction and gain novel insights into causes of obesity in early life. Participants identified gaps and opportunities for future research to advance understanding of risk and underlying mechanisms for development of obesity in early life. It was emphasized that future studies will require multi-disciplinary efforts across basic, behavioral, and clinical sciences. An exposome framework is needed to elucidate how behavioral, biological, and environmental risk factors interact. Use of novel statistical methods may provide greater insights into causal mechanisms.

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.

Recruitment of CTCF to an Fto enhancer is responsible for transgenerational inheritance of BPA-induced obesity

The mechanisms by which environmentally-induced epiphenotypes are transmitted transgenerationally in mammals are poorly understood. Here we show that exposure of pregnant mouse females to bisphenol A (BPA) results in obesity in the F2 progeny due to increased food intake. This epiphenotype can be transmitted up to the F6 generation. Analysis of chromatin accessibility in sperm of the F1-F6 generations reveals alterations at sites containing binding motifs for CCCTC-binding factor (CTCF) at two cis-regulatory elements (CREs) of the Fto gene that correlate with transmission of obesity. These CREs show increased interactions in sperm of obese mice with the Irx3 and Irx5 genes, which are involved in the differentiation of appetite-controlling neurons. Deletion of the CTCF site in Fto results in mice that have normal food intake and fail to become obese when ancestrally exposed to BPA. The results suggest that epigenetic alterations of Fto can lead to the same phenotypes as genetic variants.

Effects of bone marrow-derived mesenchymal stem cells exposed to endocrine-disrupting chemicals on the differentiation of umbilical cord blood hematopoietic stem cells

Endocrine-disrupting chemicals (EDCs), a class of peripheral toxic substances, can cause many environmental and clinical side effects, particularly on the human body's endocrine system. Bisphenol A (BPA) and diethylhexyl phthalate (DEHP) are two well-known EDCs in the medicine industry. However, there are no comprehensive studies on their effects on hematopoiesis. Hence, this study aimed to investigate the effect of these two aforementioned substances on the clonogenic capacity of umbilical cord blood hematopoietic stem cells (CB-HSCs). The HSCs which express CD34 + were isolated from umbilical cord blood by the magnetic-activated cell sorting (MACS) system. To investigate the effects of different optimized concentrations of BPA and DEHP, CB-CD34⁺ HSCs were exposed to EDCs in semisolid medium. For evaluation of coexposures, CB-CD34⁺ HSCs were cocultured with bone marrow-derived mesenchymal stem cells (BM-MSCs) in the presence of BPA and DEHP. Finally, the number and types of colonies were evaluated after 14 days. Statistical analysis was performed by GraphPad Prism through ANOVA. CB-HSC treated by BPA and DEHP showed a lower absolute colony count than the control group (P < 0.05). Decrease in clonogenic potential of HSCs was more significant in coculture condition by MSCs. In particular, there was a significant decrease in the BFU-E colonies in comedicated-derived fractions (P < 0.0001). In the presence of EDCs such as BPA and DEHP, the patterns of differentiation in CD34⁺ CB-HSCs changed from suppressed erythroid differentiation toward stimulated myelogenesis pathways.

Gestational and lactational exposure to BPA or BPS has minimal effects on skeletal outcomes in adult female mice

Bisphenol-A (BPA) and bisphenol-S (BPS) are estrogen disrupting chemicals (EDCs) found in the environment and common household items. Estrogen is a primary hormonal regulator of bone growth and development; however, the impact of gestational BPA or BPS exposure on skeletal health of offspring remains relatively unknown. In this longitudinal study, adult female mice were randomized into three groups: 200 μg BPA/kg BW (BPA), 200 μg BPS/kg BW (BPS) or control (CON). Animals in each group were further randomized to exercise treatment (EX) or sedentary (SED) control, resulting in six overall groups. BPA/BPS/CON and EX/SED treatment were initiated prior to mating and continued through mating, gestation, and lactation. One female offspring from each dam (n = 6/group) was assessed at 17 weeks of age to evaluate effects of EDC exposure on the adult skeleton. Cortical geometry of the mid-diaphysis and trabecular microarchitecture of the distal femur were assessed via micro-computed tomography. Biomechanical strength and mineral apposition rate of the femoral diaphysis were assessed via three-point bending and dynamic histomorphometry, respectively. Sclerostin expression was measured using immunohistochemistry. Two-factor ANOVA or ANCOVA were used to determine the effects of maternal exercise and BPA or BPS exposure on trabecular and cortical bone outcomes, respectively. Consistent with prior studies, there were no significant differences in body weight, femoral length, cortical geometry, trabecular microarchitecture, or biomechanical strength between groups in female offspring. In conclusion, gestational BPA exposure and maternal exercise have minimal impact on skeletal outcomes in female adult offspring.

Endocrine-Disrupting Chemicals and Child Health

While definitions vary, endocrine-disrupting chemicals (EDCs) have two fundamental features: their disruption of hormone function and their contribution to disease and disability. The unique vulnerability of children to low-level EDC exposures has eroded the notion that only the dose makes the thing a poison, requiring a paradigm shift in scientific and policy practice. In this review, we discuss the unique vulnerability of children as early as fetal life and provide an overview of epidemiological studies on programming effects of EDCs on neuronal, metabolic, and immune pathways as well as on endocrine, reproductive, and renal systems. Building on this accumulating evidence, we dispel and address existing myths about the health effects of EDCs with examples from child health research. Finally, we provide a list of effective actions to reduce exposure, and subsequent harm that are applicable to individuals, communities, and policy-makers. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Developmental low-dose exposure to bisphenol A induces chronic inflammation, bone marrow fibrosis and reduces bone stiffness in female rat offspring only

BACKGROUND

Developmental exposure to low doses of the endocrine disruptor bisphenol A (BPA) is known to alter bone tissue in young rodents, although how bone tissue is affected in aged animals is not well known. We have recently shown that low-dose developmental exposure to BPA increases procollagen type I N-terminal propeptide (P1NP) levels, a peptide formed during type 1 collagen synthesis, in plasma of 5-week-old female rat offspring while male offspring showed reduced bone size.

OBJECTIVE

To analyze offspring bone phenotype at 52 weeks of age and clarify whether the BPA-induced increase in P1NP levels at 5 weeks is an early sign of bone marrow fibrosis development.

METHODS

As in our 5-week study, pregnant Fischer 344 rats were exposed to BPA via drinking water corresponding to 0.5 μg/kg BW/day (BPA0.5), which is in the range of human daily exposure, or 50 μg/kg BW/day (BPA50) from gestational day 3.5 until postnatal day 22. Controls were given only vehicle. The offspring were sacrificed at 52 weeks of age. Bone effects were analyzed using peripheral quantitative and micro-computed tomography (microCT), 3-point bending test, plasma markers and histological examination.

RESULTS

Compared to a smaller bone size at 5 weeks, at the age of 52 weeks, femur size in male offspring had been normalized in developmentally BPA-exposed rats. The 52-week-old female offspring showed, like the 5-week-old siblings, higher plasma P1NP levels compared to controls but no general increasing bone growth or strength. However, 2 out of 14 BPA-exposed female offspring bones developed extremely thick cortices later in life, discovered by systematic in vivo microCT scanning during the study. This was not observed in male offspring or in female controls. Biomechanical testing revealed that both doses of developmental BPA exposure reduced femur stiffness only in female offspring. In addition, histological analysis showed an increased number of fibrotic lesions only in the bone marrow of female rat offspring developmentally exposed to BPA. In line with this, plasma markers of inflammation, Tnf (in BPA0.5) and Timp1 (in BPA50) were increased exclusively in female offspring.

CONCLUSIONS

Developmental BPA exposure at an environmentally relevant concentration resulted in female-specific effects on bone as well as on plasma biomarkers of collagen synthesis and inflammation. Even a dose approximately eight times lower than the current temporary EFSA human tolerable daily intake of 4 μg/kg BW/day, appeared to induce bone stiffness reduction, bone marrow fibrosis and chronic inflammation in female rat offspring later in life.

Impact of prenatal exposure to bisphenol A on pregnant rats: Fetal bone development and immunohistochemistry implications

BACKGROUND:

Bisphenol A (BPA) is one of the most commonly produced chemicals in the world. BPA is used in products such as food packaging, personal care products, detergents, and plastic bottles. This study was conducted to determine the effect of BPA on fetal bone development.

MATERIAL AND METHODS:

In this study, 16 pregnant female Sprague-Dawley rats were used. The rats were divided into four groups: the control group and 0.5 mg/kg/day, 5 mg/kg/day, and 50 mg/kg/day dose BPA groups. The skeletal system development of fetuses was examined with double skeletal and immunohistochemistry (IHC) staining (tartrate resistant acid phosphatase (TRAP) and the alkaline phosphatase (AP) expressions) methods.

RESULTS:

The highest ossification rates in the humerus, radius, and ulna were detected as 41.05%, 39.25%, and 37.26% in the control group, respectively. The highest ossification rates in the femur, tibia, and fibula were detected as 23.04%, 30.73%, and 32.78% in the control group, respectively. Statistically significant differences were found between control and experimental groups in the TRAP and AP expression of the femur by IHC staining ( p < 0.001).

CONCLUSION:

Exposure to BPA during pregnancy adversely affected ossification and bone growth. A dose-dependent decrease was observed in the rate of ossification.