RESUMEN
Abstract Free-living amoebae of the genus Acanthamoeba are the causative agents of granulomatous encephalitis and keratitis, severe human infections. Bioactive compounds from plants are recognized as an alternative source for the development of new drugs. The Amaryllidaceae is a botanical family able to synthesize a very specific and consistent group of biologically active isoquinoline-like alkaloids. The alkaloidal fractions from the Brazilian species Hippeastrum canastrense, H. diniz-cruziae, H. puniceum, and Crinum x amabile, along with the alkaloid lycorine, were investigated against Acanthamoeba castellanii. The in vitro assays were performed with distinct concentrations of lycorine and alkaloidal fractions, while the cell viability was evaluated by the MTT method upon MDCK cells. Chlorhexidine 0.02% was used as the positive control. The effect of alkaloid fractions was concentration dependent, and 2000 µg mL-1 of H. canastrense and H. diniz-cruziae provided a 100% inhibition. At concentrations of 250, 500, and 1000 µg mL-1, the H. diniz-cruziae alkaloidal fraction showed the lowest cytotoxic effect (5%-7%) and remarkable anti-amoebic activity, demonstrating values of IC50 285.61 µg mL-1, low cytotoxicity (5%-7%), and selectivity index (7.0). Taken together, the results are indicative of the great potential that the alkaloids from H. diniz-cruziae have as new candidates for anti-amoebicidal compounds