In vitro anti-parasitic effects of sesquiterpene lactones from chicory against cattle nematodes

Chicory (Cichorium intybus) has the potential as an anti-parasitic crop for ruminants. However, the mechanisms behind observed in vivo effects are poorly understood but it is likely that plant secondary metabolites like sesquiterpene lactones (SL) play a role. In this study we tested the effect of SL-rich extracts from 2 chicory cultivars on the viability of first-stage larvae (L1) of Ostertagia ostertagi, a pathogenic cattle nematode. Chicory Spadona and Puna II were grown at the same farm and leaves were sampled the same day. 1 g of freeze-dried leaves was extracted in methanol/water. Resulting extracts were incubated with cellulase enzymes, recovered in ethyl acetate and purified by normal solid-phase extraction. Obtained extracts were dissolved in 100% dimethyl sulfoxide (DMSO). A calf infected with O. ostertagi served as donor of nematode eggs. Eggs were hatched and L1 obtained were incubated in 8 extract concentrations for each cultivar (in duplicates) ranging from 2000 μg to 16 μg dry matter (DM) extract/ml (final concentration 1% DMSO in phosphate buffered saline-PBS). Ivermectin (1 mg/ml) and 1% DMSO in PBS were used as positive and negative controls, respectively. Viability of L1 was evaluated morphologically after 12 h of incubation (25°C) and was expressed as the number of live L1 to the total number of L1. Spadona-SL dramatically decreased the survival of O. ostertagi L1, with a mortality of 99% at concentrations ≥500 μg/ml and EC₅₀ of 132.8 μg/ml (CI=117.5-150.2 μg/ml). Conversely, Puna-SL induced a larval mortality of only 37% at the highest concentration tested (2,000 μg/ml), thus estimation of EC50 was not possible. Results showed a marked difference in the anti-parasitic activity of SL-rich extracts from 2 different chicory cultivars. Further biochemical analyses of the extracts may reveal the responsible compounds.