Background: The active ingredients of essential plant oils appear as potentially effective antinematodal drugs or substances that can potentiate the action of already-existing anthelmintics. So far, we have verified that, aside from the direct effect on the neuromuscular system of nematodes, some of them can potentiate the effects of drugs that are agonists or antagonists of nematode cholinergic receptors. Methods: In this study, the antinematodal effects of geraniol and carvacrol were compared, as well as their interaction in the experimental model Caenorhabditis elegans, on the contractile properties of Ascaris suum neuromuscular preparations and on the ACR-16 nicotinic acetylcholine receptor (nAChR) of A. suum expressed in Xenopus leavis oocytes. Results: The combination of geraniol and carvacrol showed a synergistic nematocidal effect in the tests on C. elegans, reducing the value of individual LC₅₀ by almost 10-times. This combination also exerted a synergistic inhibitory effect on the contractions of A. suum, significantly increased the EC₅₀ of ACh and reduced the maximal contractile effect. The synergistic interaction of these two monoterpenes on Asu-ACR-16 nAChR expressed in Xenopus oocytes resulted in a significant decrease in the maximum current, while the ACh EC₅₀ value remained unchanged. Conclusions: Our findings provide a better understanding of the mode of action of monoterpene plant compounds. The possible antiparasitic application of active ingredients of essential plant oils that exhibit a synergistic anthelmintic effect represents an important basis for the development of new drugs and new therapeutic procedures.

Background: The active ingredients of essential plant oils appear as potentially effective antinemtodal drugs or substances that can potentiate the action of already existing anthelmintics. So far, we have verified that, aside from the direct effect on the neuromuscular system of nematodes (by inhibiting or potentiating contractility), some of them can potentiate the effects of drugs that are agonists or antagonists of nematode cholinergic receptors. Methods: In this study the antinematodal effects of geraniol and carvacrol was compared, as well as their interaction in the experimental model Caenorhabditis elegans, on the contractile properties of Ascaris suum neuromuscular preparations and on the ACR-16 nicotinic acetylcholine receptor (nAChR) of A. suum expressed in Xenopus leavis oocytes. Results: Combination of geraniol and carvacrol, showed a synergistic nematocidal effect in the tests on C. elegans, reducing the value of individual LC50 for almost 10 times. This combination also exerted a synergistic inhibitory effect on the contractions of A. suum, and significantly increased the EC50 of ACh and reduced the maximal contractile effect. The synergistic interaction of these two monoterpenes on Asu-ACR-16 nAChR expressed in Xenopus oocytes resulted in a significant decrease of the maximum current while the ACh EC50 value remained unchanged. Conclusions: Our findings bring a better understanding on the mode of action of monoterpene plant compounds. The possible application of active ingredients of essential plant oils that exhibit a synergistic anthelmintic effect represents an important basis for the development of new drugs and new therapeutic procedures.

The parasitic nematode Ascaris suum is an economically significant worm that infects pigs and causes health issues and economic losses in pig farming. The intestine of A. suum is a long, straight tube that runs from the mouth to the anus and can be colonized by bacteria. Several bacteria have been studied for their potential antinematocidal effects. Bacillus thuringiensis (Bt), a soil bacterium known to produce many toxic crystal proteins (Cry), is emerging as a promising candidate for nematode control. Treatment of A. suum with all tested Bt strains (SS_26.2, SS_29.2, SS_35.1, SS_37.7) resulted in histopathological changes in the parasite intestine. Our research highlights the anthelmintic effect of Cry proteins and emphasizes the potential of Bt as an alternative tool for controlling parasitic nematodes of domestic animals. The studied strains are promising for the eradication of A. suum as a novel, environmentally friendly and cost-effective One Health approach, but further testing in pigs is needed to confirm these findings.

Caenorhabditis elegans is a nematode that is known as an alternative model for research. Adult forms are about 1mm long, while larvae reach a length of 0.25 mm. This nematode is easily grown in laboratories in a special nematode growth medium (NGM) with a layer of the bacterium Escherichia coli, on which C. elegans feeds. The worms exist in two natural sexes. C. elegans is one of the most frequently used experimental model organisms in biomedicine. The main advantages of C. elegans as a model organism are its small size, high reproductive capacity, simple cultivation, low maintenance costs, the possibility of long preservation at low temperatures, very short reproductive time and good visibility. C. elegans has been used for analysis of toxicants, investigation of cancer, discovery of antiparasitics and anticancer drugs, and investigation of the functions of the neuromuscular system. The C. elegans model is successful for identifying and characterizing molecular drug targets of all classes of anthelmintics acting on the nervous system. All these characteristics make C. elegans a valuable and prospective model organism in biomedical research. This review article primarily focuses on the utility of C. elegans as a model organism in the evaluation of anthelmintic substances, with particular emphasis on essential oils and natural products, while briefly highlighting its general biomedical applications. The main goal of this paper is to demonstrate our application of this model in some antinematodal research.

Background/Objectives: Drug repurposing is one of the possible sources of new anthelmintics. Afoxolaner is a insecticide/acaricide that acts on the insect GABA receptor and regulates uptake of chloride ions. We examined the interaction of afoxolaner with GABA receptors of nematodes. Methods: We tested the effects of afoxolaner on the motility of the free-living nematode C. elegans and its effect on the contractions/relaxation of the parasitic nematode A. suum. By means of structural bioinformatics, we analyzed the potential binding sites of afoxolaner on the nematode synaptic/exrasynaptic GABA receptor. Results: Afoxolaner inhibited the development of adult C. elegans, significantly reduced the distance traveled, movement speed, and motility score. Afoxolaner significantly inhibited the contractions of the A. suum neuromuscular preparation by increasing the EC₅₀ value of ACh but not changed the E_max. However, afoxolaner neutralized the inhibitory effect of GABA, significantly reduced the EC₅₀ of ACh and increased E_max. In the relaxation study, afoxolaner potentiates GABA-evoked relaxation but inhibited piperazine-induced relaxation. Conclusions: Pharmacological effect of afoxolaner on GABA receptors in nematodes can be defined in two ways: when contractions were induced by ACh, afoxolaner behaves as a partial agonist/antagonist, which would involve binding to an orthosteric site on the receptor. Probably this effect is realized on synaptic GABA receptors between inhibitory interneurons and motoneurons. However, when relaxation is induced by activation of an extrasynaptic GABA receptor, afoxolaner exhibits the characteristics of positive allosteric modulator, it does not cause relaxation by itself, but enhances the effect of GABA and antagonizes the action of piperazine.

The active constituents of essential plant oils (EOAIs), monoterpenoid carvacrol and monoterpene p-cymene, are widely distributed in many aromatic plants and their products. They differ in that carvacrol has a phenolic functional group. The numerous pharmacological effects of these two EOAIs are well known. In different doses/concentrations, they exhibit analgesic, neuroprotective, vasorelaxant, antiinflammatory, antiviral, antibacterial and antiparasitic effects. The acute toxicity of carvacrol and p-cymene in rats and the free-living nematode Caenorhabditis elegans was investigated. Furthermore, the impact of subacute administration of these two ter-penes on general health, CNS integration, i.e. motor coordination and balance of rats, as well as their effects on the movement of adult C. elegans, was also examined. The aim was to compare the effects and describe in more detail the selective toxicity of carvacrol and p-cymene. The calculated LD50 value of carvacrol was 790.15±1.15 mg/kg, while the LD50 value of p-cymene is above 3000 mg/kg. Tested doses of carvacrol and p-cymene administered for 28 days (50, 100, and 200 mg/kg) did not exert any effect on the CNS of rats or cause any clinical disorders. LC50 value of carvacrol for adult C. elegans was 184.13±1.51 micM and for p-cymene 1268±1.65 micM. In subacute testing, carvacrol showed negative effects on C. elegans reproduction, distance traveled, movement speed and rotational index at lower concentrations than p-cymene, indicating higher toxicity. On the other hand, although less toxic to C. elegans, p-cymene exhibited a specific effect on worm motility, with more rolling which should be further investigated, and can be a consequence of cuticle damage or loss of orientation.