Abstract
Interleukin (IL)-5 is a chemotactic factor of eosinophils, and promotes the growth and survival of eosinophils, which plays an important role in the eosinophilia-associated allergic inflammation. In this study, luteolin 4′-O-glucopyranoside was identified as the IL-5 inhibitor from Kummerowia striata Thunb. (Leguminosae) by activity-guided fractionation followed by structural analysis compared with reported spectral data. The flavone compound exhibited dose-dependent inhibitory effect on IL-5 bioactivity with 95% inhibition at 30 µM, 79% at 15 µM, 60% at 7.5 µM, 54% at 3.8 µM and 29% at 1.9 µM, where 50% of inhibition (IC50) value was shown at the concentration of 3.7 µM. Furthermore, the inhibitory effect on IL-5 bioactivity by other flavonoid compounds available was estimated. In view of the IC50 values, the inhibitory potency on IL-5 bioactivity was in order of luteolin 4′-O-glucopyranoside > cosmosiin (14.2 µM) ≅ apigenin (16.4 µM) ≅ luteolin (18.7 ≅M) > quercimeritrin (27.3 µM)≅kaempferol (30.0 µM).
