The antinociceptive and anti-inflammatory activities of Petasites formosanus Kitamura extract

Petasites formosanus Kitamura (Compositae) is native to Taiwan and is used in folk medicine to treat hypertension and asthma. Aqueous methanolic (50%) extracts of leaves of P. formosanus (Leaves-MeOH extract) showed the strongest inhibitory effect against NO production by lipopolysaccharide (LPS)-induced RAW 264.7 cells with an IC₅₀ of 22.85 μg/mL. In an in vivo assay, 200 mg/kg of the extract also significantly decreased the acetic acid-induced writhing response, increased the hot-plate latency, and significantly suppressed carrageenan-induced paw edema. The principle anti-inflammatory constituents of the leaf extract were isolated by column chromatography combined with bioassay-guided fractionation, and 4 compounds, isopetasin, S-isopetasin, S-petasin, and caffeic acid methyl ester, were obtained. S-Ispopetasin and S-petasin more significantly inhibited NO production, inducible nitric oxide synthase, and cyclooxygenase-2 expression in a dose-dependent manner in LPS-induced RAW 264.7 cells, and S-ispopetasin showed stronger potency than S-petasin. S-Isopetasin also showed stronger reductions in the acetic acid-induced writhing response and carrageenan- induced paw edema than S-petasin. Taken together, the results indicate that P. formosanus possesses both anti-inflammatory and anti-nociceptive activities, and S-isopetasin was the major constituent mediating those activities and may be used as a lead for new anti-inflammatory drug development.