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Anti-pruritic effect of baicalin and its metabolites, baicalein and oroxylin A, in mice

Anti-pruritic effect of baicalin and its metabolites, baicalein and oroxylin A, in mice

Hien-trung TRINH1, Eun-ha JOH1, Ho-young KWAK2, Nam-in BAEK2, Dong-hyun KIM1, *
1Department of Pharmaceutical Science and Department of Life and Pharmaceutical Sciences, Kyung Hee University, 1, Hoegi, Dongdaemun-ku, Seoul 130–701, Korea; 2Graduate School of Biotechnology and PMRC, Kyung Hee University, 1, Seochunri, Suwon, Kyunggi-Do 449–701, Korea
Aim: To explore whether intestinal micro ora plays a role in anti-pruritic activity of baicalin, a main constituent of the rhizome of Scutellaria baicalensis (SB).
Methods: Baicalin was anaerobically incubated with human fecal micro ora, and its metabolites, baicalein and oroxylin A, were isolated. The inhibitory effect of baicalin and its metabolites was accessed in histamine- or compound 48/80-induced scratching behavior in mice.
Results: Baicalin was metabolized to baicalein and oroxylin A, with metabolic activities of 40.2±26.2 and 1.2±1.1 nmol·h-1·mg-1 wet weight of human fecal micro ora, respectively. Baicalin (20, 50 mg/kg) showed more potent inhibitory effect on histamine-induced scratching behavior when orally administered than intraperitoneally. In contrast, baicalein and oroxylin A had more potent inhibitory effect when the intraperitoneally administered. The anti-scratching behavior activity of oral baicalin and its metabolites was in proportion to their inhibition on histamine-induced increase of vascular permeability with oroxylin A more potent than baicalein and baicalin. In Magnus test using guinea pig ileum, oroxylin A is more potent than baicalein and baicalin in inhibition of histamine-induced contraction. The anti-scratching behavioral effect of oral baicalin was signi cantly reduced when oral antibiotics were simultaneously administered, whereas the effect of baicalein and oroxylin A were not affected.
Conclusion: Oral baicalin may be metabolized by intestinal micro ora into baicalein and oroxylin A, which ameliorate pruritic reactions through anti-histamine action.
Keywords: Scutellaria baicalensis; baicalin; baicalein; oroxylin A; scratching behavior; metabolism; histamine Acta Pharmacologica Sinica (2010) 31: 718–724; doi: 10.1038/aps.2010.42; published online 10 May 2010