Investigation on the antimalarial properties of Plumeria alba Linn (apocynaceae) cultivated in Nigeria
Many of the African antimalarial ethno medicinal plants are good sources of promising antimalarial compounds. The stem bark of Plumeria alba Linn, was evaluated for in vivo chemosuppressive antimalarial activities in order to identify the most active solvent fraction from which antimalarial constituents can be isolated. The stem-bark of Plumeria alba Linn, family Apocynaceae was collected, air-dried, powdered, macerated in methanol and the extract concentrated in vacuo. The acute toxicity study was performed on the extract using Lorke’s method. The extract was thereafter tested for chemosuppressive antiplasmodial activities against Plasmodium berghei berghei NK65- infected mice using Peter’s four-day test at doses 100-800 mg /kg with normal saline (0.2 ml) and chloroquine (10 mg/kg) as negative and positive control drugs respectively. The average percentage parasitaemia, percentage chemosuppression and effective doses (ED50 and ED90), the survival times and percentage survivors elicited in all the mice were determined as indices of antimalarial activity. The active extract was subsequently partitioned successively into n-hexane, dichloromethane, ethyl acetate and butanol. The respective partitioned fractions with the aqueous phase were also tested as above at doses 0-80 mg/kg. All results were subjected to statistical analysis using ANOVA with Student Newman Keul’s post hoc test. Crude extracts of P. alba gave considerable reduction of percentage parasitaemia up to 200 mg/kg. The percentage chemosuppression at all doses, were significantly higher (p<0.05) than the negative but lower than the positive control with 200 mg/kg dose showing the highest activity of 65.88 %. The effective doses, ED50 and ED90 were 305.82±9.99 and 389.74± 9.60, respectively. The most active n-hexane partitioned fraction elicited a percentage chemosuppression of 67.75 and a significantly lower (p<0.05) ED50 and ED90 of 31.27±0.85 and 54.80±1.75 mg/kg. The butanol and ethyl acetate partitioned fractions gave significantly higher (p<0.05) survival time value than those of the crude extract, other partition fractions and the positive control, while the n-hexane, dichloromethane and the aqueous, just like chloroquine, gave high percentage survivors. The study concluded that Plumeria alba stem-bark extract was active as an antimalarial drug with its antiplasmodial and the survival time–enhancing activity concentrated in the n-hexane and ethyl acetate with butanol partitioned fractions respectively, thus confirming and justifying its ethnomedical application in malaria.