Anti-Acanthamoeba castellanii activity of alkaloid-enriched extracts and lycorine from the Amaryllidaceae species

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.

摘要：棘阿米巴属（Acanthamoeba）的自由生活阿米巴是引发肉芽肿性脑炎与角膜炎这两种严重人类感染性疾病的致病菌。植物来源的生物活性化合物被视作新药研发的替代资源。石蒜科（Amaryllidaceae）是一类能够合成特异性且稳定的生物活性类异喹啉生物碱的植物科属。本研究针对巴西物种朱顶红（Hippeastrum canastrense）、H. diniz-cruziae、H. puniceum以及杂交文珠兰（Crinum x amabile）的生物碱组分，连同生物碱石蒜碱（lycorine），开展了抗卡氏棘阿米巴（Acanthamoeba castellanii）的活性测试。实验采用不同浓度的石蒜碱与生物碱组分进行体外实验，并通过MTT法检测其对MDCK细胞的细胞活力，以0.02%的氯己定作为阳性对照。结果显示，生物碱组分的抗阿米巴活性呈浓度依赖性：当浓度为2000 μg·mL⁻¹时，H. canastrense与H. diniz-cruziae的提取物可实现100%的抑制率。在250、500与1000 μg·mL⁻¹浓度下，H. diniz-cruziae的生物碱组分展现出最低的细胞毒性（5%~7%）与显著的抗阿米巴活性，其半数抑制浓度（IC50）为285.61 μg·mL⁻¹，细胞毒性极低（5%~7%），选择性指数为7.0。综上，本研究结果表明，H. diniz-cruziae中的生物碱类成分具备开发为抗阿米巴候选药物的巨大潜力。