Chemical and toxicological study of extracts from the stem bark of Uapaca thouarsii Baill. (Phyllanthaceae), a medicinal plant endemic to Madagascar

The aim of this study was to assess on different organisms the toxicity of extracts from the stem bark of Uapaca thouarsii, a medicinal plant endemic to Madagascar. An aqueous crude extract (CE) was prepared from bark powder. CE was successively dialysed and fractionated with n-butanol. A partially purified toxic extract (E2) was obtained with a yield of 0.13%. The bitter-tasting toxic principles were thermostable, precipitable by neutral lead acetate and adsorbed by activated charcoal. Phytochemical screening of the bark powder revealed the presence of triterpenes, leucoanthocyanins, unsaturated sterols and a small amount of saponins. By intraperitoneal (i.p.) route, the LD50 (24 h) was between 396.12 mg/kg and 398.56 mg/kg of body weight (b.w.). No symptoms were observed when E2 was administered by gavage. CE and E2 caused sheep erythrocyte lysis. They were toxic to frog tadpoles with LC50 of 35 µg/ml and 25 µg/ml respectively and to carp alvins by an action following the all-or-nothing law. CE significantly inhibited seed germination of lettuce, tomato, zucchini, basil and onion, while no inhibition of germination was observed for pea, cowpea, rice and maize. In the antibiogram test, of the 14 strains tested, Shigella sonnei, Escherichia coli and Listeria ivanovii were very sensitive to CE and sensitive to E2, while Listeria seeligeri was very sensitive to CE but resistant to E2.