Pharmaceutical evaluation of liquorice before and after roasting in mice

Liquorice has been used for allergic-inflammatory and liver disorders in both traditional Chinese and modern medicine. In traditional Chinese formulations, it is mainly roasted liquorice that has been used rather than un-roasted liquorice. We have compared the pharmaceutical characteristics of liquorice before and after roasting to clarify the pharmaceutical significance of the roasting. Although roasted liquorice contained less glycyrrhizin (an anti-allergic component) than un-roasted liquorice, the inhibitory potency of roasted liquorice extract (200 mg kg¹) on immunoglobulin E (IgE)-mediated triphasic ear swelling in mice was much greater compared with un-roasted liquorice. To search for additional active ingredients, roasted liquorice extract was subjected to gel-chromatography to give an anti-allergic fraction (Fa) of molecular weight ranging from 15 000 to 200 000 or more, in which glycyrrhizin was not detected. By testing the activity of the various fractions, it was proved that the anti-allergic effect of roasted liquorice was due to glycyrrhizin, its metabolite glycyrrhetic acid, and the Fa fraction. The inhibitory potency of the Fa fraction (15 and 75 mg kg^-1) prepared from roasted liquorice was stronger than that prepared from un-roasted liquorice. Therefore, a pharmaceutical implication of roasting the liquorice seems to be associated with an increase in the anti-allergic property of the Fa fraction. It is notable that oral administration of the high molecular mass fraction (Fa) significantly inhibited IgE-mediated ear swelling six days after challenge at doses as low as 3, 15 or 75 mg kg^-1.