Efficacy of selenium- and tellurium-based organocompounds against ruminant gastrointestinal nematodes in vitro

Gastrointestinal nematode (GIN) infections significantly impact the health of ruminants. The indiscriminate use of anthelmintics contributes to the selection of drug-resistant parasites. Compounds containing selenium (Se) and tellurium (Te) have emerged as promising alternatives. This study aimed to evaluate the anthelmintic activity of diphenyl diselenide (PhSe)2, phenylselenenyl chloride (4-Cl-PhSe)2, and ammonium trichloro (dioxoethylene-O,O') tellurate (AS-101) on eggs and larvae (L3) of GIN. The compounds were tested using egg-hatch and larval-migration inhibition tests. Additionally, the possible in vitro cytotoxic effects were evaluated using the AlamarBlue assay. (PhSe)2 exhibited the highest ovicidal effect, with a 50% inhibitory concentration (IC50) of 1.801 mmol L-1 for GIN isolated from sheep and 1.845 mmol L-1 for GIN from cattle. AS-101 showed the highest larvicidal activity, with IC50 values of 0.976 mmol L-1 for GIN of sheep and 1.035 mmol L-1 for GIN of cattle. Combinations of (PhSe)2 with ivermectin (IVM) showed a mild synergistic effect, with an additive interaction of 13.33%. Among the tested compounds, (PhSe)2 showed the lowest cytotoxicity in LLC-MK2 cells. Taken together, these data highlight the therapeutic potential of the novel molecules.