Molecular Interaction and Biological Activity of Fatty Acids and Sterols: An In Silico and In Vitro Approach Against Haemonchus contortus

Background: Haemonchus contortus is a gastrointestinal nematode that affects small ruminants and exhibits widespread resistance to commercial anthelmintics. This has driven interest in natural compounds such as fatty acids and sterols; however, their biological relevance against resistant parasite strains remains insufficiently understood. Methods: The nematicidal potential of four fatty acids (palmitic, linoleic, pentadecanoic, and stearic acids) and two sterols (β-sitosterol and ergosterol), all of them commercially available in Mexico, was evaluated against infective L3 larvae of a benzimidazole-resistant H. contortus strain. In vitro larval mortality and migration inhibition assays were performed, and molecular docking analyses were conducted to explore interactions with the glutamate-gated chloride channel (GluCl) using AutoDock4. Statistical analyses were performed using ANOVA followed by Tukey’s post hoc test (p < 0.05). Results: Molecular docking indicated strong binding affinities of ergosterol and β-sitosterol to GluCl, comparable to that of ivermectin. In vitro assays showed that fatty acids, particularly linoleic acid, produced more pronounced effects on larval motility, suggesting predominantly nematostatic activity. No clear dose–response relationship was observed in migration assays, and in vitro mortality remained limited across treatments. Conclusions: The results highlight a disconnect between in silico binding affinity and in vitro biological activity, particularly in a drug-resistant H. contortus strain. Integrating in vitro bioassays with computational approaches provides valuable mechanistic insight but also underscores the limitations of affinity-based predictions for assessing anthelmintic efficacy.