Inhibitory Effect of Baicalein, a Flavonoid in Scutellaria Root, on Eotaxin Production by Human Dermal Fibroblasts

Abstract

Eotaxin is an eosinophil-specific chemokine associated with the recruitment of eosinophils to sites of allergic inflammation. "Saiboku-to" (Formula magnoliae et bupleuri) is a kampo herbal medicine used for the treatment of bronchial asthma in Japan. In this study, we investigated the effects of Scutellaria Root, a major herb in Saiboku-to and its components such as baicalein and baicalin on eotaxin production by IL-4 plus TNF-alpha-stimulated human fibroblasts. An extract of Scutellaria Root markedly inhibited eotaxin production. Four major flavonoids from Scutellaria Root were found to show inhibitory activity on eotaxin production at a concentration of 10 micrograms/ml in the order of baicalein > oroxylin A > baicalin > skullcapflavon II. The inhibitory effect of baicalein was expressed in a dose-dependent manner, and almost 50% inhibition was observed at 1.8 micrograms/ml. Furthermore, baicalein prevented human eotaxin mRNA expression in IL-4 plus TNF-alpha-stimulated human fibroblasts. These results help explain the pharmacological efficacy of Scutellaria Root in the treatment of bronchial asthma since it would suppress eotaxin associated recruitment of eosinophils.