Short Lecture "Anthelmintic activities of the West African medicinal plants Combretum mucronatum and Phyllanthus urinaria against free-living and parasitic nematodes"

Tanniferous plants have been proposed as a sustainable control of helminth infections to overcome the problem of resistances to standard anthelmintics in livestock. Combretum mucronatum Schumach. & Thonn. (CM) and Phyllanthus urinaria L. (PU) which are used to treat soil-transmitted helminthiases in West Africa were therefore explored for their anthelmintic properties. The procyanidin-rich hydroethanolic leaf extract from CM inhibited larval migration in vitro against Ascaris suum, Ancylostoma caninum, Trichuris suis, Toxocara canis, Ostertagia ostertagi, Cooperia oncophora, Trichostrongylus colubriformis, T. axei and Haemonchus contortus (IC₅₀ 2.1–310.0 µg/mL). The activity was further evaluated in vivo in goats infected with Haemonchus contortus. In the free-living nematode Caenorhabditis elegans, lethal effects (LC₅₀ 1809 µg/mL) and moulting inhibition in all larval stages were observed. Functional studies indicated the cuticle to be the main binding site for procyanidins, causing an increased rigidity. Further, expression of unique proline-rich proteins for tannin defense was upregulated. Similar to CM, an acetone-water extract from PU aerial parts inhibited larval migration in A. suum, A. caninum, T. suis and T. canis with large variation in the nematodes’ susceptibility (IC₅₀ 24.3–1510 µg/mL). The major ellagitannins from PU were isolated and characterised by HR-MS and NMR. Geraniin was generally most active (IC₅₀ 0.6–804 µM), however, the activity of the respective isolated ellagitannins varied with different parasite species. In summary, the data supports the use of CM and PU as traditional remedies against helminthiases, reveal insights into their mode of action and underline strong species-specific differences in tannin susceptibility.