PDE inhibition by Gloriosa superba and its main alkaloid colchicine

The use of Gloriosa superba against a variety of degenerative and inflammatory diseases in Ethiopi- an traditional medicine is mainly attributed to its alkaloid colchicine [1], which reduces neutrophil migration, causing an anti-inflammatory effect. However, the traditional indications cannot be ex- plained by this single pharmacological action alone. It seems to have an additional phosphodiesterase (PDE) inhibiting activity. G. superba rhizomes from north-western Ethiopia were mashed and ex- tracted with 50% MeOH. The resulting raw extract was partitioned between water and CH₂Cl₂ by serial liquid-liquid extraction, removing Dragendorff-positive components from the aqueous phase. The remaining plant material was boiled in MeOH for 30min. The PDE inhibiting potential of all four extracts was tested in an in vitro system on equine bronchial fibroblasts according to [2] with pure colchicine and 3-isobutyl-1-methylxanthine as positive controls. Already the G. superba raw extract exhibited a significant PDE inhibiting activity that was enhanced more than twofold in the CH₂Cl₂ alkaloid phase. Conversely, the aqueous phase and the final boiling MeOH extract were largely inactive. A remarkable effect surpassing that of the raw extract but not on the same level as the CH₂Cl₂ phase could be observed for isolated colchicine. The PDE-inhibiting activity of G. su- perba cannot thus be explained with this single constituent alone, indicating the presence of further natural compounds with PDE inhibiting activity in this traditional Ethiopian medicinal plant.

References: 1. Neuwinger HD (1996) African Ethnobotany. Chapman and Hall. London. 2. Werner, C. et al. (1997)J Auton Pharmacol 17: 237–242.