Anti-inflammatory action and associated intracellular signaling of Centella asiatica extract on lipopolysaccharide-stimulated RAW 264.7 macrophage

Centella asiatica (CA) has been reported to exert pharmacological effects on inflammatory diseases. In particular, CA possesses anti-inflammatory effects on macrophages; however, the precise intracellular mechanisms remain unclear. This study aimed to investigate the anti-inflammatory activity and intracellular signaling mechanism of a CA-active extract in a LPS-induced macrophage model of inflammation. In addition, FTIR spectra and RP-HPLC were used to analyze the centelloid compounds with known anti-inflammatory activity. We found that 70% EtOH extract (CA-70E) from CA alleviated oxidative damage and inflammation by reducing intracellular ROS formation and the secretion of pro-inflammatory factors (NO, TNF-α, MCP-1, and IL-6). CA-70E inhibited the mRNA expression of inflammatory factors (iNOS, TNF-α, MCP-1, IL-6, IL-12, and COX-2) as well as phagocytic activity. Additionally, it suppressed the phosphorylation cascade of pro-inflammatory proteins and nuclei translocation of activated p65 protein in MAPK and NF-κB signaling system. The antagonistic study using anti-PRRs revealed that CA-70E decreased the secretion of TNF-α, MCP-1, and IL-6 by binding to TLR4, CR3, CD14, and dectin-1 receptors. Meanwhile, FTIR spectra and RP-HPLC analyses showed that among the major centelloids, asiaticoside was the most abundant in CA-70E. We suggest that 70% EtOH extract of C. asiatica, with asiaticoside as a major compound, suppresses the phosphorylation in MAPK and NF-κB signaling pathways primarily via its action on TLR4, CR3, CD14, and dectin-1 receptors, thus decreasing the secretion of TNF-α, IL-6, and MCP-1.