Quercetin alleviates Streptococcus agalactiae-induced mastitis in mice by inhibiting the NF-κB/NLRP3 signaling pathway and ferroptosis.

Mastitis is the most common dairy disease, impairing milk quality and yield. Quercetin (QUE), a natural compound with anti-inflammatory, antioxidant, and antimicrobial activities, lacks a clear mechanism against mastitis. This study evaluated QUE in a mouse model of Streptococcus agalactiae (commonly known as Group B Streptococcus (GBS))-induced mastitis. Mice (n = 25) were randomized into five groups (n = 5/group): control, GBS model, and QUE (25, 50, 100 mg/kg). QUE or vehicle was administered intraperitoneally 24 h before mammary duct injection of GBS. Pathohistological analysis demonstrated that QUE inhibited GBS-induced histopathological damage and myeloperoxidase activity in mouse mammary tissue (p < 0.01). Immunofluorescence experiments revealed that QUE upregulated the tight junction proteins Occludin and tight junction protein 1, thereby maintaining the integrity of the mammary blood-milk barrier. The results of qPCR and ELISA demonstrated that QUE was effective in reducing the gene expression and content of pro-inflammatory factors IL-6, IL-1β, and TNF-α (p < 0.01). Western blotting and qPCR demonstrated that QUE impeded the NF-κB pathway and diminished the activity of the NLRP3 inflammasome. Concurrently, QUE diminished the iron content of mouse mammary tissues induced by GBS, repressed TfR and ACSL4 protein expression, and FTH1, PTGS2, NCOA4 gene transcript levels, while elevating SLC7A11 and GPX4 protein expression (p < 0.01). These findings indicated that QUE mitigated GBS-induced mammary gland injury in mice by inhibiting the NF-κB/NLRP3 signaling pathway and ferroptosis. This study elucidated the potential mechanism of QUE on GBS-induced mastitis and enhanced the theoretical foundation for future prevention and treatment of mastitis.