Modulation of ERs/Nrf2–Keap1 Signaling Pathway by Ethinylestradiol in Juvenile Common Carp ( Cyprinus carpio ): Implications for Oxidative Stress and Estrogenic Effects

This study investigates the acute effects of ethinylestradiol (EE2) on oxidative stress markers and key genes involved in the estrogen receptors (ERs)/Nrf2–Keap1 signaling pathway, which is crucial for managing oxidative stress. Juvenile common carp were exposed to nominal EE2 concentrations of 10, 50, and 100 ng/L for 7 days. Liver tissue was harvested for biochemical analyses, including assays for enzymatic antioxidant activities, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), concentrations of glutathione (GSH) and its oxidized form (GSSG), malondialdehyde (MDA) as an index of lipid peroxidation, and gene expression analysis of ERα , Vtg , Keap1 , Nrf2 , and HO‐1 . The study found that EE2 exposure at higher concentrations (50 and 100 ng/L) significantly reduced the activity of key antioxidant enzymes in the liver of juvenile carp, indicating a compromised antioxidant defense system. This reduction was accompanied by increased oxidative stress, as showed by increased MDA values. Additionally, the expression of Vtg , Keap1 , and ERα genes significantly increased in response to EE2 exposure, whereas dose‐dependent decreases in the expression of Nrf2 and HO‐1 genes were observed. The findings provide evidence that EE2 induces significant oxidative stress in the liver of juvenile common carp, disrupting key antioxidant defense mechanisms and altering gene expression in the ERs/Nrf2–Keap1 pathway. These findings underscore the potential risks posed by EE2 and similar endocrine‐disrupting compounds (EDCs) to aquatic organisms.