Metabolism of cyanidin-3-O-beta-D-glucoside isolated from black colored rice and its antiscratching behavioral effect in mice.

Black-colored rice (BCR), the main constituent of which is cyanidin-3-O-beta-D-glucoside (C3G), exhibits an anti-allergic effect, and orally administered C3G is mainly metabolized to protocatechuic acid in rats. Therefore, to understand the relationship between the metabolism of C3G and its pharmacological effect, we isolated C3G from BCR, anaerobically incubated it with fecal microflora, investigated its metabolite(s) by LC-MS/MS, and measured the antiscratching behavioral effects of C3G and its metabolites. C3G was metabolized to protocatechuic acid via cyanidin. Protocatechuic acid and cyanidin were identified as the metabolites. The activities transforming C3G to protocatechuic acid and cyanidin were 28.2 +/- 11.7 and 21.8 +/- 5.2 nmol/h/mg fecal microflora, respectively. C3G and its metabolites showed inhibitory effects against histamine- or compound 48/80-induced scratching behaviors in mice. C3G more potently inhibited scratching behaviors following oral administration than following intraperitoneal administration. However, protocatechuic acid and cyanidin showed more potent inhibition when administered intraperitoneally than when administered orally. These metabolites also inhibited the expression of allergic cytokines, IL-4 and TNF-alpha, and the activation of their transcription factor, NF-kappaB, in RBL-2H3 cells stimulated with IgE-antigen. These findings suggest that C3G-rich BCR may be a beneficial food for diseases involving scratching behaviors, such as chronic dermatitis, rhinitis, and psoriasis.