Inhibitory effect of dimethyl sulfoxide on the development of gastrointestinal nematode larvae in the larval development test.

Abstract

Introduction: Dimethyl sulfoxide (DMSO) is an amphipathic solvent for molecules in in vitro tests for detection of anthelmintic resistance of gastrointestinal nematodes (GIN). It has been shown to have a concentration-dependent detrimental effect on Caenorhabditis elegans, a free-living nematode. If GIN are likewise affected, using DMSO in egg-hatch test and larval development test (LDT) may confound their results. Therefore, the DMSO concentration was determined at which it exerted an inhibitory effect on GIN larval development to the third stage.

Material and methods: A standard LDT was performed in 30 replications at DMSO concentrations of 0.0% (control), 0.6%, 1.3%, 2.6%, 5.2%, 10.4%, and 20.8%. The numbers of all developmental stages of Haemonchus contortus, Trichostrongylus spp. and Oesophagostomum spp. (unhatched eggs, larvae of the first, second and third stages (L1-L3) were determined, the proportion of L3 (the percentage of larval development - PD) was calculated and L3 were identified at the species or genus level. A five-parameter logistic curve was fitted to the observed PDs and modelled the DMSO-larval development relationship.

Results: The PD significantly decreased with increasing DMSO concentration and was significantly reduced at the 2.6% concentration. The median inhibitory concentration (IC50) was 3.79%, the concentration for 10% inhibition (IC10) was 1.75% and for 90% inhibition (IC90) was 8.20%. The percentage of L1 and L2 followed an analogical but opposite pattern to that of PD and was complementary to it at each DMSO concentration. The unhatched egg percentage was rarely >1% and showed no pattern.

Conclusion: At ≥2.6% concentration, DMSO significantly inhibited the L3 development of all three GIN species. It had a practically important inhibitory effect (IC10) at as low concentration as 1.75%. At lower concentrations, DMSO did not appear to inhibit larval development. The compound did not seem to exert an in vitro ovicidal effect regardless of the concentration.