Thymol improves barrier function and attenuates inflammatory responses in porcine intestinal epithelial cells during lipopolysaccharide (LPS)-induced inflammation

Abstract

It is well known that essential oil thymol exhibits anti-bacterial activity. The protective effects of thymol on pig intestine during inflammation is yet to be investigated. In this study, an in vitro (LPS)-induced inflammation model using IPEC-J2 cells was established. Cells were pre-treated with thymol for 1 h and then exposed to LPS for various assays. Interleukin 8 (IL-8) secretion, the mRNA abundance of cytokines, ROS, nutrient transporters, and tight junction proteins was measured. The results showed that LPS stimulation increased IL-8 secretion, reactive oxygen species (ROS) production, and tumor necrosis factor alpha (TNF-α) mRNA abundance (P < 0.05), but the mRNA abundance of sodium-dependent glucose transporter 1 (SGLT1), excitatory amino acid transporter 1 (EAAC1) and H+/peptide cotransporter 1 (PepT1) were decreased (P < 0.05). Thymol blocked ROS production (P < 0.05) and tended to decrease the production of LPS-induced IL-8 secretion (P = 0.0766). The mRNA abundance of IL-8 and TNF-α was reduced by thymol pre-treatment (P < 0.05), but thymol was unable to improve the gene expression of nutrient transporters (P > 0.05). The transepithelial electrical resistance (TEER) was reduced and cell permeability increased by LPS treatment (P < 0.05), but these effects were attenuated by thymol (P < 0.05). Moreover, thymol increased zonula occludens-1 (ZO-1) and actin staining in the cells. However, the mRNA abundance of ZO-1 and occludin-3 was not affected by either LPS or thymol treatments. These results indicated that thymol can enhance barrier function and reduce ROS production and pro-inflammatory cytokine gene expression in the epithelial cells during inflammation. The regulation of barrier function by thymol and LPS may be at post-transcriptional or post-translational levels.