Caffeic acid phenethyl ester attenuates pro-inflammatory and fibrogenic phenotypes of LPS-stimulated hepatic stellate cells through the inhibition of NF-kB signaling

Abstract

Hepatic stellate cells (HSCs) are the major cell type involved in liver fibrosis. Lipopolysaccharide (LPS)-mediated signaling through koll-like receptor 4 (TLR4) in HSCs has been identified as a key event in liver fibrosis, and as the molecular link between inflammation and liver fibrosis. In this study, we investigated the effects of caffeic acid phenethyl ester (CAPE), one of the main medicinal components of propolis, on the pro-inflammatory and fibrogenic phenotypes of LPS-stimulated HSCs. HSCs from rats were isolated and cultured in Dulbecco's modified Eagle's medium (DMEM). Following treatment with LPS, HSCs showed a strong pro-inflammatory phenotype with an upregulation of pro-inflammatory mediators, and a fibrogenic phenotype with enhanced collagen synthesis, mediated by transforming growth factor-β1 (TGF-β1). CAPE significantly and dose-dependently reduced LPS-induced nitrite production, as well as the transcription and protein synthesis of monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS), as determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), western blotting and enzyme-linked immunosorbent assays (ELISA). CAPE further reduced the TGF-β1-induced transcription and translation (protein synthesis) of the gene coding for collagen type I a1 (col1A1), in LPS-stimulated HSCs. Following LPS stimulation, the phosphorylation of the nuclear factor-kB (NF-kB) inhibitor IkBa and consequently, the nuclear translocation of NF-kB, were markedly increased in the HSCs, and these changes were reversed by pre-treatment with CAPE. In conclusion, CAPE attenuates the pro-inflammatory phenotype of LPS-stimulated HSCs, as well as the LPS-induced sensitization of HSCs to fibrogenic cytokines by inhibiting NF-kB signaling. Our results provide new insight into the treatment of hepatic fibrosis through regulation of the TLR4 signaling pathway.