Suppression of lipopolysaccharide-induced upregulation of toll-like receptor 4 by emodin in mouse proximal tubular epithelial cells

The aim of this study was to investigate the effects of emodin, the major component of Rheum palmatum, on lipopolysaccharide (LPS)-induced toll-like receptor 4 (TLR4) expression in cultured mouse tubular epithelial cells (TECs). The TECs were obtained from mice and incubated with LPS and/or indicated concentrations of emodin for 24 h. Cytokeratin, alpha-SMA and vimentin were detected using immunohistochemistry. The TLR4 protein level was detected by flow cytometry. TNF alpha and IL-6 protein levels were measured using an enzyme-linked immunosorbent assay (ELISA). mRNA expression of TLR4, TNF alpha and IL-6 was detected using a reverse-transcription polymerase chain reaction (RT-PCR). Results showed that a concentration of 10(2) ng/ml LPS significantly upregulated TLR4 mRNA and protein levels. TNF alpha and IL-6 mRNA and protein levels were also increased. Emodin (at doses of 40,20 and 10 mu M) was able to inhibit LPS-induced TLR4 protein synthesis in cultured TECs. However, TNF alpha and IL-6 protein expression was decreased in cells treated with emodin at concentrations of 40 and 20 mu M. These results demonstrate that an elevated expression of inflammatory cytokines and TLR4 in cells stimulated with LPS, were simultaneously inhibited by emodin. Emodin is therefore able to inhibit the LPS-induced expression of TLR4 in order to downregulate TNF alpha and IL-6 synthesis in TECs, which may contribute to the protective effects of emodin in renal disease.