Mechanism of Cinnamaldehyde in Alleviating Staphylococcus aureus-Induced Mammary Inflammatory Response

CA, a major bioactive component of cinnamon essential oil, possesses broad-spectrum antibacterial, anti-inflammatory, and antioxidant activities and is widely recognized as a safe food additive. In the context of exploring natural plant extracts for the prevention and alleviation of bovine mastitis, it is noteworthy that research and clinical reports on the use of cinnamon essential oil for bovine mastitis are relatively limited. In this study, S. aureus isolates recovered from subclinical bovine mastitis were used to establish a mastitis infection model, and the antioxidant and anti-inflammatory effects of CA were preliminarily investigated in both mouse mastitis models and mammary epithelial cells (MAC-T). Studies have demonstrated that in a mouse model of mastitis, CA reduces inflammatory cell infiltration, decreases myeloperoxidase (MPO) activity, and inhibits S. aureus colonization in mammary tissue. CA alleviates oxidative stress by lowering malondialdehyde (MDA) levels, enhancing superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities, and activating the Nrf2/HO-1/xCT antioxidant pathway. In addition, CA suppresses the activation of the TLR4/NF-κB signalling pathway and modulates the expression of Bax and Bcl-2, accompanied by reduced levels of pro-inflammatory cytokines, including tumour necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6), ultimately ameliorating mastitis in mice. In the MAC-T cell infection model, CA significantly inhibited S. aureus adhesion and invasion and decreased the production of pro-inflammatory cytokines and mediators. CA also activated the Nrf2/HO-1/xCT antioxidant pathway, which led to decreased intracellular reactive oxygen species (ROS), concurrently inhibited the TLR4/NF-κB pathway, and downregulated apoptotic protein expression, ultimately attenuating inflammation in MAC-T cells. Collectively, these findings demonstrate that CA exerts protective effects against inflammation and oxidative damage in both mammary tissues and epithelial cells infected with S. aureus. Thus, this study provides a theoretical and practical basis for further exploring CA as a candidate therapy for bovine mastitis.