Background Recent advances in understanding the toxic effects of inorganic arsenic have revealed that arsenic exposure impacts multiple endocrine organs, thereby altering their functions. However, the mechanisms underlying arsenic-induced thyroid injury remain unclear. Objective To investigate the mechanisms by which sodium arsenite (NaAsO₂) affects the proliferation and apoptosis of normal thyroid cells (Nthy-ori3-1) through the estrogen receptor (ER)-phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. Methods Nthy-ori3-1 cells were cultured in vitro and divided into the following groups: a control group (complete medium without drugs, 0 μmol·L⁻¹), and NaAsO₂-treated groups at 1, 2, and 4 μmol·L⁻¹. Additionally, 1 μmol·L⁻¹ of the ER inhibitor ICI182780 was used to intervene in the NaAsO₂ exposure groups, resulting in the following combinations: 1 μmol·L⁻¹ NaAsO₂ + ICI182780, 2 μmol·L⁻¹ NaAsO₂ + ICI182780, and 4 μmol·L⁻¹ NaAsO₂ + ICI182780. The median lethal concentration of NaAsO₂ was determined using cell viability assay. Cell viability was assessed at 24, 36, and 48 h using Cell Counting Kit-8 (CCK-8) assay. Colony formation ability was evaluated via plate cloning assay. Apoptosis was detected using Hoechst 33342 staining. Protein and mRNA expression levels of ERα, ERβ, c-MYC, Bax, Bcl-2, PI3K, p-PI3K, AKT, and p-AKT were measured using Western blot (WB) and real-time quantitative PCR (qRT-PCR), respectively. Results The median lethal concentration of NaAsO₂ was determined to be 4.034 μmol·L⁻¹. CCK-8 assay at 24, 36, and 48 h revealed that, compared with the control group, the 1, 2, and 4 μmol·L⁻¹ NaAsO₂ groups significantly inhibited Nthy-ori3-1 cell proliferation (P < 0.001). The plate cloning assays demonstrated a concentration-dependent reduction in colony formation ability (P < 0.001). Following the ICI182780 intervention, the cell viability and colony formation ability in the 1, 2, and 4 μmol·L⁻¹ NaAsO₂ groups were significantly restored compared with the corresponding NaAsO₂-only groups (P < 0.001, P < 0.01). The Hoechst 33342 staining indicated that compared with the control group, the nuclear staining intensity and apoptosis levels in the 1, 2, and 4 μmol·L⁻¹ NaAsO₂ groups increased in a concentration-dependent manner (P < 0.001). However, the ICI182780 intervention reduced the apoptosis levels in the NaAsO₂-treated groups compared with their NaAsO₂-only counterparts (P < 0.001). The WB analysis showed that, compared with the control group, the protein expression of ERα, ERβ, c-MYC, Bcl-2, p-PI3K, and p-AKT in the 1, 2, and 4 μmol·L⁻¹ NaAsO₂ groups decreased manner (P < 0.001, P < 0.01), while the Bax expression increased in a concentration-dependent (P < 0.001); the PI3K and AKT protein levels showed no significant differences (P > 0.05). In the ICI182780-treated NaAsO₂ groups, the ERα, ERβ, c-MYC, Bcl-2, p-PI3K, and p-AKT protein expression increased (P < 0.001, P < 0.01), the Bax expression decreased (P < 0.001), and the PI3K and AKT levels remained unchanged (P > 0.05) compared with the corresponding NaAsO₂-only groups. The mRNA expression patterns of ERα, ERβ, c-MYC, Bcl-2, and Bax were consistent with the WB results. Conclusion NaAsO₂ inhibits proliferation and promotes apoptosis in Nthy-ori3-1 cells in a dose-dependent manner. The underlying mechanism likely involves NaAsO₂-mediated suppression of the ER-PI3K/AKT signaling pathway, which subsequently regulates downstream proliferation- and apoptosis-related genes.

Background Arsenic can enter the hypothalamus to induce estrogen effect and interfere with the function of the neuroendocrine system. The thyroid endocrine system (hypothalamic-pituitary-thyroid axis) is one of the main endocrine systems, and the mechanism of arsenic-induced thyroid endocrine toxicity is still unclear. Objective To investigate the effects of different arsenic exposure levels on estradiol (E2), hypothalamic thyrotropin-releasing hormone (TRH), and their receptor (ERα, ERβ, and TRHR) mRNAs in rats and the possible hypothalamic toxic pathway and mechanism. Methods Seventy Wister rats were randomly divided a control group (sterile water); low-, medium-, and high-dose arsenic exposure groups [0.8, 4.0, and 20.0 mg·kg⁻¹ sodium arsenite (NaAsO₂)]; estrogen receptor inhibitor (ICI182780) intervention + low-, medium-, and high-dose arsenic exposure groups; with 10 animals in each group, half male and half female. Rats in the arsenic exposure groups were exposed to NaAsO₂ by drinking water for 19 weeks, and rats in the intervention groups were injected with 0.5 mg·kg⁻¹ ICI182780 via tail vein at week 9, 3 times a week. The levels of E2 and TRH in serum of rats were detected by ELISA. The expression levels of estrogen receptor α (ERα), estrogen receptor β (ERβ), and TRH receptor (TRHR) mRNAs in hypothalamus of rats were detected by real-time PCR (RT-PCR). Results (1) E2 and its receptor mRNA: Compared with the control group, the serum E2 level of female rats was increased in the low-dose and the medium-dose arsenic exposure groups (P<0.05), and the serum E2 level of male rats was increased in the low-dose, the medium-dose, and the high-dose arsenic exposure groups (P<0.05), and the change of female E2 was greater than that of male rats. Compared with the control group, the relative expression levels of ERα mRNA and ERβ mRNA in female rats were increased in the low-dose, the medium-dose, and the high-dose arsenic exposure groups (P<0.05), so were the relative expression levels of ERα mRNA in male rats (P<0.05). (2) TRH and its receptor mRNA: Compared with the control group, the serum TRH level of female rats was increased in the high-dose arsenic group (P<0.05), the relative expression level of TRHR mRNA was increased in the low-dose, the medium-dose, and the high-dose arsenic exposure groups (P<0.05). Results (1) and results (2) suggested that females were more likely than males to have abnormal changes in E2, TRH, and related receptor genes after arsenic exposure. (3) Compared with female rats in the medium-high dose arsenic exposure group, the expressions of TRH and TRHR induced by arsenic exposure were inhibited after the intervention of ICI182780 (P<0.05), suggesting that arsenic in the hypothalamus may have toxic effects on TRH and TRHR by inducing estrogen-like effects. Conclusion Arsenic exposure can induce estrogen-like effects in the hypothalamus, interfere with thyroid function, and show dose-dependent and sex differences. E2 and TRH and their receptors may be the toxic pathway of arsenic-related estrogen-like effect.