Journal of Pharmacognosy & Natural Products

In Vitro Anti-onchocercal Activity, Phytochemical Analysis and Toxicity Studies of Extracts of Azadirachta indica

Abstract

Irene Memeh Tumanjong, Tobias Obejum Apinjoh, Faustin Pascal Tsague Manfo, Evans Ngandung Mainsah, Stanley Dobgima Gamua and Fidelis Cho-Ngwa*

Ivermectin and moxidectin are the only recommended drugs for the treatment of onchocerciasis, with the former being the most widely used. However, both drugs are not suitable in eliminating the disease. There is the need to identify novel anti-onchocercal agents including from plant sources. This project investigated the anti-onchocercal activity of extracts of Azadirachta indica that could eventually yield new drug leads for the cure of onchocerciasis. Organic extracts were obtained from the leaves and seeds of Azadirachta indica using solvents of different polarities and tested in vitro against two developmental stages of the bovine model parasite, Onchocerca ochengi. Both microfilariae (mf) and adult male worm viabilities were assessed by motility reduction, while adult female worm viability was evaluated using the standard MTT/formazan assay. Toxicity of active extracts was assessed on monkey kidney epithelial cells (LLC-MK2) and in BALB/c mice. The methylene chloride extract of the leaves was the most active against the adult female worms and the mf with IC_50s of 55.61 μg/ml and 8.048 μg/ml respectively. The hexane extract of the leaves was the most active against the adult male worms with an IC₅₀ of 16.34 μg/ml. Selectivity indices for the most active extracts were 1.12 for adult females, 7.77 for the mf and 7.35 for adult males indicating that the extracts are selectively active on the parasites. The most active extracts showed no acute toxicity to Balb/c mice and had no significant effect on the liver enzymes, alanine aminotransferase and aspartate aminotransferase and markers of kidney function, urea and creatinine (p<0.05). Phytochemical analysis revealed the presence of saponins, flavonoids, steroids, tannins, alkaloids, polyphenols and terpenoids. The anti-onchocercal activity and selectivity indices of A. indica extracts suggest the plant is a potential source of new anti-onchocercal drug leads justifying further investigations for the identification and isolation of the bioactive compounds.