Inhibitory effect of rice (Oryza sativa) polyphenols on degranulation of rat basophilic leukemia cell line RBL-2H3

Abstract

The effects of polyphenol compounds isolated from young rice plants (Oryza sativa) on IgE-mediated degranulation of rat basophilic leukemia RBL-2H3 cells were investigated. Five polyphenol fractions were obtained by solid-phase extraction column chromatography (SPE) followed by reversed-phase HPLC from water extract of dried young rice plants. LC-MS/MS analysis indicated that these fractions contained flavone-C-glycosides, three of which were determined to be neocarlinoside (6-C-β-D-glucopyranosyl-8-C-β-L- arabinopyranosylluteolin), carlinoside (6-C-β-D-glucopyranosyl-8-C-α- L-arabinopyranosylluteolin) and isoorientin-2″-O-β-glucopyranoside by the NMR analysis. LC-MS/MS analysis of another fraction suggested the presence of an isomer of neocarlinoside or carlinoside. The fifth fraction appeared to consist of two compounds that had a C-glycoside, an O-glycoside and an organic acid bound to aglycone. The polyphenol-rich SPE fraction and the five HPLC fractions inhibited the degranulation of RBL-2H3 cells. The five HPLC fractions inhibited the degranulation in similar dose-dependent manner regardless of the kind of sugar bound to the aglycone and the presence of organic acid ester. Removal of polyphenols from the SPE fraction significantly decreased the degranulation inhibitory activity. These results suggested that the inhibitory activity should be derived from polyphenols.