Anti-inflammatory function of sudachitin and demethoxysudachitin from <i>Citrus sudachi</i>

It has been recognized that chronic inflammation, which differs in mechanism from acute inflammation triggered by normal immune responses, induces various diseases, including lifestyle-related diseases. Sudachitin (4’,5,7-trihydroxy-3’,6,8-trimethoxyflavone) and demethoxysudachitin (4’,5,7-trihydroxy-6,8-dimethoxyflavone) are types of polymethoxyflavones found in the peel of sudachi ( Citrus sudachi ). This study focused on evaluation of the anti-inflammatory effects of these compounds, their mode of action, and their effect in vivo . Mouse macrophage cell line RAW264.7 cells and primary peritoneal macrophages (P-mac) were cultured with sudachitin or demethoxysudachitin, followed by stimulation with lipopolysaccharide (LPS) to induce an inflammatory response. Sudachitin and demethoxysudachitin suppressed IL-6, TNF-α, nitric oxide (NO) and MCP-1 production by RAW264.7 cells without cytotoxicity. Regarding their mode of action, they downregulated the activation of the MAPK and NF-κB pathways activated by LPS, thereby inhibiting the gene expression of inflammatory factors and suppressing the inflammatory response. Similarly, both compounds suppressed the production of inflammation mediators of in P-mac. Sudachitin exhibited a stronger inhibitory effect than demethoxysudachitin, suggesting that the methoxy group at the 3’ position of sudachitin enhances its anti-inflammatory effect. To examine the anti-inflammatory effects in vivo , mice were orally administered samples for seven days and then subjected to LPS-induced systemic inflammation. Oral administration in the systemic inflammation model mice resulted in reduced blood levels of inflammatory cytokines. These findings confirm the efficacy of sudachitin and demethoxysudachitin in exerting anti-inflammatory effect.