RESUMO
ETHNOPHARMACOLOGICAL RELEVANCE: Schistosomiasis (bilharzia) is an important, prevalent and neglected tropical disease for which new treatments are urgently required. In the DR Congo and other sub- and tropical countries, traditional medicines are widely used for the control of schistosomiasis. AIM OF STUDY: To evaluate 43 Congolese plant species used traditionally for the treatment of urogenital schistosomiasis against Schistosoma mansoni. MATERIALS AND METHODS: Methanolic extracts were screened against S. mansoni newly transformed schistosomula (NTS). Three of the most active extracts were evaluated for acute oral toxicity in guinea pigs and activity guided fractionation of the least toxic was carried out using S. mansoni NTS and adult stages. An isolated compound was identified by means of spectroscopic techniques. RESULTS: Thirty-nine of 62 extracts killed S. mansoni NTS at 100 µg/mL and 7 extracts were active at ≥ 90% at 25 µg/mL; 3 extracts were selected for acute oral toxicity evaluation; the least toxic of these, Pseudolachnostylis maprouneifolia leaf was then subjected to activity-guided fractionation. 173-ethoxyphaeophorbide a (1) was isolated as an active compound with 56% activity against NTS at 50 µg/mL and 22.5% activity against adult S. mansoni at 100 µg/mL but these activities are significantly less than those of the parent fractions suggesting that other active compounds are also present and/or that synergistic interactions are taking place. CONCLUSION: This study has identified 39 plant extracts with activity against S. mansoni NTS lending support to their traditional use in the treatment of schistosomiasis for which new treatments are urgently needed. P. maprouneifolia leaf extract was found to have potent anti-schistosomal activity and low in vivo oral toxicity in guinea pigs; activity-guided fractionation resulted in the isolation of an active compound, 173-ethoxyphaeophorbide a. Phaeophorbides may merit exploration as potential anti-schistosomal agents and further work on plant species shown to have potent activity against S. mansoni NTS in this study would be worthwhile.
