Thyroid hormones (THs) are essential for normal brain development, influencing neural cell differentiation, migration, and synaptogenesis. Multiple endocrine-disrupting chemicals (EDCs) are found in the environment, raising concern for their potential effects on thyroid hormone signaling and the consequences on neurodevelopment and behavior. While most research on EDCs investigates the effects of individual chemicals, human health may be adversely affected by a mixture of chemicals. Many compounds belonging to a wide range of chemical classes have been identified as EDCs, notably those affecting thyroid hormone signaling. We hypothesized that embryonic exposure to a mixture of chemicals (containing phenols, phthalates, pesticides, heavy metals, perfluorinated -, polychlorinated, and polybrominated compound) commonly found in the human amniotic fluid could lead to altered brain development to assess its effect on thyroid hormone signaling and neurodevelopment in an amphibian model (Xenopus laevis), highly sensitive to thyroid disruption. Newly hatched tadpoles were exposed for eight days to either TH (thyroxine, T4 10nM) or the amniotic mixture (1x concentration) and gene expression was analyzed in the brains of exposed tadpoles using both RT-qPCR and RNA sequencing. Results indicate that whilst some overlap on TH-dependent genes exist, T4 and the mixture have different gene signatures. Immunohistochemistry showed increased proliferation in the brains of T4-treated animals whereas no difference was observed for the amniotic mixture. Further, we demonstrated diminished tadpoles’ motility in response to T4 and mixture exposure. As the individual chemicals composing the mixture are considered safe, these results highlight the importance of examining the effects of mixtures to improve risk assessment

Humans are often exposed to various environmental contaminants, among which phthalates are prevalent due to their extensive use as plasticizers in various consumer goods. Di(2-ethylhexyl) phthalate (DEHP), a widely used phthalate, is recognized as an endocrine disruptor chemical (EDC). DEHP is reported to affect various organs. Few studies have addressed the effects of phthalates on bone. However, the effects of DEHP on the bone forming cells (osteoblasts) are obscure. The present study was peformed to determine the cytotoxic effects of DEHP on human osteoblasts in vitro and to delineate the mechansims. In this study, we exposed the human osteo-blastic cell line MG-63 to various concentrations of DEHP (1, 25, 50 and 100 µM) for 24, 48 and 72 h. Cell viability was assessed by MTT assay. Total RNA and protein were collected after 48 h treatment with 1 and 100 µM DEHP and determined for the mRNA and/or protein expression of alkaline phosphatase (ALP), sex steroid receptors (androgen and estrogen receptors), receptor activator of nuclear factor kappa-Β ligand (RANKL), runt-related transcription factor 2 (RUNX2) and peroxisome proliferator-activated receptor alpha (PPARα). The mRNA expression was stud-ied by real-time RT-PCR analysis and the protein expression was determined by western blot analysis. Statistical analyses were done by one-way analysis of variance (ANOVA) followed by the Students–Newman–Keuls (SNK) test. The exposure of MG-63 cells to DEHP caused a signifi-cant decrease in osteoblast viability in all the treatment groups and at all the time points stud-ied. Interestingly, DEHP exposure decreased the mRNA expression of ALP, a bone formation marker. DEHP had differential effects on estrogen receptor alpha (ERα) mRNA and protein ex-pression. However, DEHP treatment downregulated the mRNA and protein expression of ERβ, and androgen receptor (AR). Surprisingly, DEHP downregulated the RANKL mRNA expression. DEHP decreased the protein expression of RUNX2, the key transcription factor and master regu-lator of bone formation. Furthermore, DEHP increased the PPARα protein expression in the os-teoblasts. Importantly, DEHP increased the reactive oxygen species (ROS) molecules and thus oxidative stress in osteoblasts, as observed by increased hydrogen peroxide, hydroxyl radical levels and lipid peroxidation. On the other hand, it decreased the enzymatic and non-enzymatic antioxidant levels namely catalase, superoxide dismutase, glutathione peroxidase activity and reduced glutathione. Our study demonstrated that in vitro exposure to DEHP reduces the osteo-blast viability possibly through alterations in the oxidant-antioxidant system and modulation of the key genes involved in bone formation, highlighting the cytotoxic effects of DEHP on bone forming cells.