Exemestane induces a reduction in hematopoietic stem cells and immunotoxicity in zebrafish larvae by downregulating Wnt signaling pathway.

Exemestane is a third-generation aromatase inhibitor commonly prescribed for estrogen-dependent breast cancer. Given the widespread clinical use of exemestane, various adverse reactions have been reported. However, there are only a limited number of reports on the effects on the immune system. Therefore, it is essential to examine its potential toxicity and mechanism of action. In this research, zebrafish were employed as a model organism to examine the impact of exemestane on embryonic development and immune function. The larvae that were fertilized 8 hours post-fertilization (hpf) were respectively exposed to exemestane solutions of different concentrations (0.9, 1.8 and 2.7 mg/L).The results demonstrated that exemestane exposure induced a concentration-dependent reduction in larval body length and an increase in yolk sac area, indicative of developmental toxicity. Subsequently, exemestane was administered to the corresponding transgenic fish lines, and it was observed that the numbers of hematopoietic stem cells (HSCs), neutrophils, macrophages, and thymic T cells exhibited dose dependent decreases during exposure. Concurrently, exemestane-exposed zebrafish exhibited significantly elevated oxidative stress levels and an increased incidence of apoptotic cells. Gene expression analysis demonstrated that the immune-related gene NF-kB was downregulated, whereas tlr2 and tlr3 were upregulated in response to treatment. Notably, no significant alterations were observed in the expression levels of il-1b, prl, or lakros. . The use of astaxanthin (AS) and the wnt signaling pathway activator BML-284 can alleviate the embryonic immunotoxicity caused by exemestane. In conclusion, our study represents the first comprehensive evaluation of the immunomodulatory effects of exemestane on zebrafish larvae. These effects are likely associated with exemestane-induced elevation of oxidative stress and suppression of the Wnt signaling pathway.