Sodium nitrite impairs reproduction in female mice by disrupting ovarian steroid hormone synthesis and lipid metabolic pathways

Sodium nitrite (NaNO₂) is a naturally occurring compound in the nitrogen cycle; however, it has become a widespread environmental pollutant due to human activities. It seriously threatens female reproductive health through chronic or acute toxicity, although its precise mechanism of action in female mice is not clear. In this study, ICR female mice were administered normal saline, low-dose NaNO₂ (60 mg/kg/day), or high-dose NaNO₂ (120 mg/kg/day) via oral gavage for three weeks to establish a NaNO₂-induced reproductive injury model. The presence of NO₂^- in the serum and tissues was measured to confirm that NaNO₂ was absorbed. Reproductive phenotypes were assessed by evaluating blood lipid levels, the estrous cycle, sex hormone levels, and ovarian morphology. Moreover, transcriptomic and metabolomic analyses, along with multiomics integration, were performed to elucidate the molecular and metabolic changes in the ovaries of NaNO₂-exposed mice. The results revealed that exposure to NaNO₂ led to the accumulation of NO₂^- in peripheral blood and ovaries, accompanied by significant reproductive dysfunction, including a decrease in E2, T, and AMH levels, disrupted estrous cycles, and impaired development of follicles. Additionally, NaNO₂-treated mice exhibited dyslipidemia. Metabolomic analysis revealed that ovarian lipid synthesis pathways were disrupted following exposure to NaNO₂. Transcriptomic analysis revealed that the primary enriched biological processes in the ovaries were related to reproduction and metabolism, with considerable disturbances in steroid biosynthesis and lipid metabolism. Integrated transcriptomic and metabolomic analyses revealed abnormalities in steroid hormone synthesis and lipid metabolism pathways in the ovaries. We found that NaNO₂ exerts detrimental effects on female reproductive ability in mice by disrupting the synthesis of ovarian steroid hormones and lipid metabolism.