Abstract: Purpose: The aim of this study was to evaluate the inhibition effects of six flavonoids (luteolin, quercetin, myricetin, apigenin, kaempferol and chrysin) on M1 polarization in RAW264.7 macrophages and to delineate the structural determinants involved in their activity. Methods: 100 ng/mL of lipopolysaccharide (LPS) was used to stimulate RAW264.7 macrophages to establish an inflammatory model. Macrophages were divided into 8 groups: control, LPS, LU, QU, MY, AP, KA and CH groups. Cell proliferation activity was detected by MTT assay. The expressions of CD274 and CD38 were detected by flow cytometry. The expression of related protein in the inflammatory signaling pathway was detected by western blot. The levels of M1-type macrophage marker genes were detected by real-time PCR. Results: These flavonoids were no significant effect on cell proliferation at 20 μM. All the six flavonoids showed inhibition effects on the expression of CD274 and CD38, of which the effects of luteolin, apigenin and chrysin were significantly stronger than that of quercetin, myricetin and kaempferol. The inhibitory activity of luteolin on NF-κB signaling pathway was stronger than that of apigenin and quercetin. The effects of luteolin, apigenin and chrysin in inhibiting the expression of Nos2 mRNA was stronger than that of the other three compounds, and the effects of luteolin, quercetin and apigenin in inhibiting the expression of IL-1β and MCP1 mRNA was stronger than that of others. Conclusions: Hydroxylation at position 3 on ring C is not conducive to its activity on macrophage polarization, while the hydroxylations at positions 3' and 4' on the B ring are beneficial to enhance its activity.

Key words: flavonoids, macrophages, polarization, inflammation, structure-activity relationship