In vitro anti-Onchocerca ochengi activities of extracts and chromatographic fractions of Craterispermum laurinum and Morinda lucida

Onchocerciasis caused by Onchocerca volvulus is the world’s second leading infectious cause of blindness. There is currently no cure for the disease. Ivermectin, the current drug of choice is only microfilaricidal and suboptimal response to it is increasingly being reported. Thus, in contributing to the search for a cure, crude extracts and chromatographic fractions of Craterispermum laurinum and Morinda lucida were screened in vitro, against the bovine and most popular model of the parasite, Onchocerca ochengi.

Extracted parasites were cultured in RPMI-1640 based media for 05 days in the presence of control drugs, test drugs or drug diluents only. Microfilarial motility was scored using microscopy while adult worm viability was determined biochemically by MTT/formazan colorimetry. Cytotoxicity and acute toxicity of active fractions were tested on monkey kidney epithelial cells (LLCMK2) and in Balb/c mice, respectively.

Out of the 18 extracts screened, the methanolic extracts of the leaves of both plants recorded the highest activities against both the microfilariae (IC₁₀₀ of 125 μg/ml for both extracts) and adult worms (IC₁₀₀ of 250 μg/ml and 500 μg/ml for M. lucida and C. laurinum respectively). The most active chromatographic fraction was obtained from M. lucida and had an IC₅₀ of 7.8 μg/ml and 15.63 μg/ml on microfilariae and adult worms respectively, while the most active fraction from C. laurinum had an IC₅₀ of 15.63 μg/ml and 46.8 μg/ml, respectively on microfilariae and adult worms. The 50% cytotoxic concentration (CC_50s) on LLCMK2 cells ranged from 15.625 μg/ml to 125 μg/ml for the active fractions. No acute toxicity was recorded for the extracts from both plants. Phytochemical analysis of the most active fractions revealed the presence of sterols, alkaloids, triterpenes, saponins and flavonoids.