Antimalarial and Antioxidant Activities of the Leaf Exudate and a Naphthalene Derivative from Aloe otallensis Baker
Aloe otallensis Baker is endemic to Ethiopia where its leaf exudate is traditionally used in the southern part of the country for the treatment of malaria. The methanol-soluble portion of the leaf exudate which was subjected to preparative thin layer chromatography (PTLC) over silica gel led to the isolation of a naphthalene derivative identified as 2,8-O,O-di(β-D-gluco-pyranosyl)-1,2,8-trihydroxy-3-methylnaphtalene (plicataloside). The exudate and plicataloside were evaluated for their in vivo antimalarial activity using a 4- day Plasmodium berghei suppressive test method, and their in vitro antioxidant potential assessed by 2,2- diphenyl-1-picrylhydrazyl (DPPH) assay. The exudate (300 mg/kg) and plicataloside (100 mg/kg) inhibited parasite growth by 60.7% and 40.7%, respectively. They also exhibited comparable radical scavenging activity with an IC50 value of about 26 μg/ml. It was proposed that plicataloside may minimize oxidative stress thereby contributing to the antimalarial activity of the plant. The findings support the traditional use of A. otallensis in the treatment of malaria.
Keywords: Aloe otallensis; exudate, 2,8-O,O-di(β-D-glucopyranosyl)-1,2,8-trihydroxy-3-methylnaphtalene antimalarial, antioxidant