IN VITRO SUSCEPTIBILITY OF ENTAMOEBA HISTOLYTICA TO FRAXINUS MICRANTHA LEAF EXTRACTS AND ITS ISOLATED CONSTITUENTS (TRITERPENES AND COUMARINS)

The activity of n-hexane, benzene, chloroform, ethyl acetate, acetone, n-butanol and crude methanolic extracts from the leaves of Fraxinus micrantha was tested against HM1: IMSS strain of Entamoeba histolytica. Results showed that benzene; ethyl acetate and n-butanol extracts were most active with an IC50 of 0.39g/ml, 0.41g/ml and 0.43g/ml, respectively. Chromatographic separation of these extracts led to the isolation of a pentacyclic triterpene acid (3β-hydroxy-urs-12en-28-oic acid), commonly known as ursolic acid, 6,7-dihydroxy-2H1-benzopyran-2-one (esculetin) and 6-(β-D-glucopyranosyloxy)-7hydroxy-2H-1-benzopyran-2-one (esculin). These compounds were derivatize to yield their methoxy and acetoxy derivatives and then subjected to in vitro antiamoebic activity. Ursolic acid, esculetin and esculin showed promising activity with an IC50 of 2.20 g/ml, 2.25g/ml and 2.97 g/ml, respectively. Methyl ursolate (IC50 = 3.11 μg/ml) and acetyl ursolic acid (IC50 = 2.87 μg/ml) showed less activity than ursolic acid. Methoxy derivative (6,7-dimethoxycoumarin) (IC50 = 1.95 μg/ml) showed higher activity whereas acetoxy derivative (6,7-diacetoxycoumarin) (IC50 = 2.74 μg/ml) showed less activity than the parent compound esculetin. These findings support the traditional use of Fraxinus micrantha leaves for the treatment of amoebic dysentery.