Essential oils for the discovery of new anthelmintic compounds tested on the nematode Caenorhabditis Elegans

Abstract

Parasitic nematodes of humans and animals cause dis- eases of major socio-economic importance globally. Con- trol of infections in both human and veterinary medicine currently relies mainly on chemotherapy, but resistance is an increasing problem, so there is an urgent need for discovery of novel drugs. As parasitic nematodes are not ideal laboratory animals, the free-living nematode C. ele- gans was demonstrated to be an excellent model system for the discovery of new anthelmintics and for character- izing their mechanisms of action and resistance. Essen- tial oils (EOs) are natural products produced by aromatic plants. EOs are complex mixtures that contain 2 or 3 ma- jor phytochemicals, which can be terpenes or aromatic compounds. We used paralysis assays of wild-type and mutant C. elegans strain to identify EOs with potential anthelmintic activities, reveal the active components, the target sites and the mechanisms of action. We found that EOs belonging to six different orders produced rap- id paralysis of C. elegans and we established the half maximal effective concentration values between 0.02-1.2 percent of EOs. All EOs tested also inhibited egg hatch- ing, a property related to anthelmintic ability. Thus, EOs mediate both rapid and long-term anthelmintic effects. We determined that trans-cinnamaldehyde (TC), a ma- jor component of C. verum EO, produces both paralysis and egg-hatching inhibition. By testing mutant worms, we identified the muscle L-AChR and GABA receptors as EOs and TC targets in vivo. Thus, by modulating two receptors with key roles in worm motility, these EOs emerge as novel sources of anthelmintic compounds. Likewise, the N-AChR mutant strain is slightly resistant to TC, thus revealing a third target receptor for terpenes. Due to the potential of EOs as sources of novel antipara- sitic compounds, additional studies will be carried out to determine in more detail the molecular mechanisms of action and structure-activity relationships of their active compounds.