Effect of diisobutyl adipate on the expression of biomarker genes that respond to endocrine disruption and on gonadal sexual differentiation in Japanese medaka (Oryzias latipes).

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.

Influence of phthalate and non-phthalate plasticizers on reproductive endocrine system-related gene expression profiles in Japanese medaka (Oryzias latipes).

Plasticizers containing phthalates have the potential to alter endocrine function in vertebrates. While non-phthalate plasticizers were previously considered to be environmentally friendly and safe, our research team discovered that bis-(2-ethylhexyl) adipate (DEHA) and acetyl tributyl citrate (ATBC) disrupt thyroid hormones in Japanese medaka (Oryzias latipes). We assessed reproductive- and estrogen-responsive gene expression patterns in Japanese medaka to determine whether the phthalate plasticizers bis-(2-ethylhexyl) phthalate (DEHP, positive control) and the non-phthalate plasticizers DEHA and ATBC disrupt endocrine signaling. The results showed that the levels of choriogenin H (chgH) and vitellogenin (vtg) genes increased after exposure to DEHP and ATBC, suggesting that these plasticizers may have estrogenic activity. Exposure to DEHP and DEHA resulted in the upregulation of kisspeptin (kiss), gonadotropin-releasing hormone (gnrh), and follicle-stimulating hormone beta (fshß) genes, suggesting that these plasticizers may interfere with reproductive function. To the best of our knowledge, this is the first study to demonstrate that the non-phthalate plasticizers DEHA and ATBC can disrupt reproduction-related hormonal activity in fish.

Impact of acetyl tributyl citrate on gonadal sex differentiation and expression of biomarker genes for endocrine disruption in Japanese medaka.

Plasticizers are broadly classified as phthalate or nonphthalate. Recently, acetyl tributyl citrate (ATBC), an environmentally friendly nonphthalate plasticizer, was revealed to have the ability to disrupt thyroid hormone activity in fish species. Therefore, we aimed to assess whether ATBC exhibits any sex hormone (i.e., androgenic or estrogenic) activities. First, we examined the effects of ATBC on gonadal sex differentiation. Subsequently, we analyzed the different expression of biomarker genes that respond to endocrine-disrupting chemicals (EDCs) with sexual hormone activity in the liver. We observed normal testes and ovaries after both XX and XY medakas were exposed to ATBC, indicating that ATBC is not an EDCs with strong sex hormone activity and that it does not induce intersex (testis-to-ova or ovo-to-testis) or sex changes in Japanese medaka. The vitellogenin 1 (vtg1) and vitellogenin 2 (vtg2) mRNA expression levels in the liver of XX medakas were significantly reduced compared with those in the control group, whereas the expression levels of these genes in the liver of XY medakas remained unchanged. Finally, we examined the changes in the expression of biomarker genes that respond to EDCs with sex hormone activity in the gonads. The expression levels of biomarker genes did not differ significantly from that of the control group, although the expression levels of gsdf mRNA tended to increase while that of aromatase mRNA tended to decrease in the ovary of XX medakas following ATBC exposure. Conversely, the expression levels of gsdf and aromatase mRNAs in the testis of XY medakas remained unchanged. These results suggest that ATBC does not exhibit estrogenic activity, although it may have weak androgenic activity or no sexual hormone activity.