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A water extract of licorice root inhibits granuloma angiogenesis in adjuvant-induced chronic inflammation (Phytother. Res., 5, 195. 1991). The present study has investigated the effects of licorice-derived compounds on granuloma angiogenesis. Isoliquiritin (0.31-3.1 mg/kg), a licorice-derived flavonoid, inhibited the carmine content of granuloma tissue 50-fold greater than licorice extract. Glyeyrrhizin (20-80 mg/kg), a licorice-derived saponin, inhibited carmine content with a weak potency. The licorice extract (0.01-1 mg/ml) also inhibited tube formation from vascular endothelial cells in a concentration-dependent manner. From the chemical structure-activities of used licorice-derived flavonoids (0.1-100 microM), their potencies for anti-tube formation were in the order isoliquiritigenin > isoliquiritin > liquiritigenin >> isoliquiritin-apioside. Glycyrrhizin (0.1-100 microM) and glycyrrhetinic acid (0.1-10 microM) increased tube formation. A glycyrrhizin (82 micrograms/ml)-induced increase in tube formation was inhibited by isoliquiritin. The combined effect of a mixture of 82 micrograms/ml glycyrrhizin and 4.2 micrograms/ml isoliquiritin, a similar concentration ratio to their yield ratio in the licorice extract, corresponded to the effect of 100 micrograms/ml extract. In conclusion, the anti-angiogenic effect of licorice extract depended on the anti-tube formation effect of isoliquiritin.