Thymol mitigates lipopolysaccharide-induced endometritis by regulating the TLR4-and ROS-mediated NF-κB signaling pathways

The purpose of this study was to investigate the effects of thymol on lipopolysaccharide (LPS)-induced inflammatory responses and to clarify the potential mechanism of these effects. LPS-induced mouse endometritis was used to confirm the anti-inflammatory action of thymol in vivo. RAW264.7 cells were used to examine the molecular mechanism and targets of thymol in vitro. In vivo, thymol markedly alleviated LPS-induced pathological injury, myeloperoxidase (MPO) activity, and the production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) in mice. Further studies were performed to examine the expression of the Toll-like receptor 4 (TLR4) -mediated nuclear factor-kappa B (NF-kappa B) pathway. These results showed that the expression of the TLR4-mediated NF-kappa B pathway was inhibited by thymol treatment. In vitro, we observed that thymol dose-dependently inhibited the expression of TNF-alpha, IL-1 beta, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) in LPS-stimulated RAW264.7 cells. Moreover, the results obtained from immunofluorescence assays also indicated that thymol dose-dependently suppressed LPS-induced reactive oxygen species (ROS) production. Silencing of TLR4 inhibited NF-kappa B pathway activation. Furthermore, H2O2 treatment increased the phosphorylation of p65 and I.Ba, which were decreased when treated with N-acetyl cysteine or thymol. In conclusion, the anti-inflammatory effects of thymol are associated with activation of the TLR4 or ROS signaling pathways, contributing to NF-kappa B activation, thereby alleviating LPS-induced oxidative and inflammatory responses.