Epigallocatechin gallate (EGCG) inhibits lipopolysaccharide-induced inflammation in RAW 264.7 macrophage cells via modulating nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) signaling pathway

Abstract

Epigallocatechin-3-gallate (EGCG) is a major bioactive compound in tea polyphenol extract. After ingestion, EGCG reaches the intestine and may commence anti-inflammation in the intestinal organ. Thus, in this paper, the anti-inflammatory effect of EGCG was studied using lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 cells. LPS induction instigated morphological deformation extensively which was normalized by EGCG. In LPS-induced macrophage cells, EGCG was found to lower cellular nitric oxide (32% of LPS group) and intercellular ROS level (45.4% of LPS group). It also suppressed the expression of IL-1β (LPS 132.6 ± 14.6, EGCG 10.67 ± 3.65), IL-6 (LPS 2994.44 ± 178.5, EGCG 408.33 ± 52.34), TNF-α (LPS 27.11 ± 2.84, EGCG 1.22 ± 0.03), and iNOS (LPS 40.45 ± 11.17, EGCG 10.24 ± 0.89). The GO function analysis identified that these differential genes involved 24 biological processes, 18 molecular functions, and 19 cellular component-related processes. KEGG pathway enrichment analysis revealed that LPS significantly affects NF-κB, TNF, and TLR signaling pathways. Western blotting revealed that EGCG diminished P-IκB/IκB ratio by 75% and p-p65/p65 by 50% compared to the LPS group. Finally, Arg-1 and CD-206 mRNA expression were determined by RT-PCR, which was consistent with the RNA-Seq result. These findings indicate that EGCG exerts an anti-inflammatory effect by reducing NO and ROS production, suppressing TLR4 protein expression, and inhibiting IκB and p65 phosphorylation.