Water pollution due to plasticizers is one of the most severe environmental problems worldwide. Phthalate plasticizers can act as endocrine disruptors in vertebrates. In this study, we investigated whether the non-phthalate bis(2-ethylhexyl) sebacate (DEHS) plasticizer can act as an endocrine disruptor by evaluating changes in the expression levels of thyroid hormone-related, reproduction-related, and estrogen-responsive genes of Japanese medaka (Oryzias latipes) exposed to the plasticizer. Following the exposure, the gene expression levels of thyroid-stimulating hormone subunit beta (tshβ), deiodinase 1 (dio1), and thyroid hormone receptor alpha (trα) did not change. Meanwhile, DEHS suppressed dio2 expression, did not induce swim bladder inflation, and eventually reduced the swimming performance of Japanese medaka. These findings indicate that DEHS can potentially disrupt the thyroid hormone-related gene expression and metabolism of these fish. However, exposure to DEHS did not induce changes in the gene expression levels of kisspeptin 1 (kiss1), gonadotropin-releasing hormone (gnrh), follicle-stimulating hormone beta (fshβ), luteinizing hormone beta (lhβ), choriogenin H (chgH), and vitellogenin (vtg) in a dose-dependent manner. This is the first report providing evidence that DEHS can disrupt thyroid hormone-related metabolism in fish.
Plasticizer pollution of the water environment is one of the world's most serious environmental issues. Phthalate plasticizers can disrupt endocrine function in vertebrates. Therefore, this study analyzed thyroid-related, reproduction-related, and estrogen-responsive genes in Japanese medaka (Oryzias latipes) to determine whether non-phthalate diisobutyl adipate (DIBA) plasticizer could affect endocrine hormone activity or not. Developmental toxicity during fish embryogenesis was also evaluated. At a concentration of 11.57 mg/l, embryonic exposure to DIBA increased the mortality rate. Although abnormal development, including body curvature, edema, and lack of swim bladder inflation, was observed at 3.54 and 11.57 mg/l DIBA, growth inhibition and reduced swimming performance were also observed. In addition, DIBA exposure increased the levels of thyroid-stimulating hormone beta-subunit (tshβ) and deiodinase 1 (dio1) but decreased the levels of thyroid hormone receptor alpha (trα) and beta (trβ). These results suggest that DIBA has thyroid hormone-disrupting activities in fish. However, kisspeptin (kiss1 and kiss2), gonadotropin-releasing hormone (gnrh1), follicle-stimulating hormone beta (fshβ), luteinizing hormone beta (lhβ), choriogenin H (chgH), and vitellogenin (vtg1) expression did not change dose-dependently in response to DIBA exposure, whereas gnrh2 and vtg2 expression was elevated. These results indicate that DIBA has low estrogenic activity and does not disrupt the endocrine reproduction system in fish. Overall, this is the first report indicating that non-phthalate DIBA plasticizer is embryotoxic and disrupt thyroid hormone activity in fish.
Phthalate and non-phthalate plasticizers are used in polymer materials, such as plastic and rubber. It has recently been found that diisobutyl adipate (DIBA), which is considered an environmentally safe non-phthalate plasticizer, potentially acts as a thyroid disruptor in fish. Here, we investigated the sexual hormone effects of DIBA based on the expression levels of genes that respond to endocrine disruption and sexual hormone activity in the livers and gonads, and on gonadal sexual differentiation in Japanese medaka. Compared with the control group, the mRNA expression of chgH, vtg1, vtg2, and esr1 was significantly suppressed in the livers of DIBA exposed XX individuals. Furthermore, the mRNA expression of gsdf was significantly upregulated and downregulated in the gonads of XX and XY individuals, respectively. The mRNA expressions of esr1 and esr2b were significantly suppressed by DIBA exposure in the gonads of both XX and XY individuals. These observations suggest that DIBA has potential androgenic activity in Japanese medaka. However, normal testes and ovaries were observed in respective XY and XX medaka after DIBA exposure; therefore, these results suggest that DIBA may have weak androgenic activity.