Thymol Inhibits LPS-Stimulated Inflammatory Response via Down-Regulation of NF-κB and MAPK Signaling Pathways in Mouse Mammary Epithelial Cells

Thymol is a natural monoterpene phenol primarily found in thyme, oregano, and tangerine peel. It has been shown to possess anti-inflammatory property both in vivo and in vitro. In the present paper, we studied the anti-inflammatory effect of thymol in lipopolysaccharide (LPS)-stimulated mouse mammary epithelial cells (mMECs). The mMECs were stimulated with LPS in the presence or absence of thymol (10, 20, 40 μg/mL). The concentrations of tumor necrosis factor α (TNF-α), interleukin (IL)-6, and IL-1β in the supernatants of culture were determined using enzyme-linked immunosorbent assay. Cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), nuclear factor-κB (NF-κB), and inhibitor protein of NF-κB (IκBα) were measured using western blot. The results showed that thymol markedly inhibited the production of TNF-α and IL-6 in LPS-stimulated mMECs. The expression of iNOS and COX-2 was also suppressed by thymol in a dose-dependent manner. Furthermore, thymol blocked the phosphorylation of IκBα, NF-κB p65, ERK, JNK, and p38 mitogen-activated protein kinases (MAPKs) in LPS-stimulated mMECs. These results indicate that thymol exerted anti-inflammatory property in LPS-stimulated mMECs by interfering the activation of NF-κB and MAPK signaling pathways. Thereby, thymol may be a potential therapeutic agent against mastitis.