Comparison of motility, recovery, and methyl-thiazolyl-tetrazolium reduction assays for use in screening plant products for anthelmintic activity

The primary objective of these experiments was to compare the effectiveness of motility, recovery, and methyl-thiazolyl-tetrazolium (MTT) reduction assays for determining anthelmintic activity of plant extracts and purified compounds from these extracts. Caenorhabditis elegans was used as the test organism. High-performance liquid chromatography (HPLC) grade water and M9 medium were used as the solvents. Copper, a common metal pollutant, and the anthelmintic drug levamisole were used as reference compounds. Extracts from the West African plant Anogeissus leiocarpus, which is used to treat worm infections, as well as two active compounds found in this plant, gallic and gentisic acids, were included in this comparison. MTT assay results for viability of worms were significantly lower (p < 0.01) than motility and recovery assay results. However, both gallic acid and the plant extract, in the absence of worms, caused reduction of MTT. Worm survival for levamisole using M9 medium was significantly (p < 0.01) higher than for HPLC grade water for all three methods. On the other hand, gallic acid showed significant (p < 0.05) activity in M9 medium but no activity in HPLC grade water, whereas gentisic acid was effective in HPLC grade water but had no activity in M9 medium. Activity of the A. leiocarpus extract also varied with solvent. In conclusion, plant extracts can be screened using motility assays that include both HPLC grade water and M9 salts.