A Safer Alternative Bio-Repellent: Targeting Mosquito Odorant-Binding Proteins with Catnip-Derived Nepetalactones from Nepeta cataria Leaves

The reliance on synthetic repellents such as N,N-diethyl-meta-toluamide (DEET) has raised health and environmental concerns, prompting the search for safer, plant-based alternatives. Catnip (<i>Nepeta cataria</i> L.), a rich source of iridoid monoterpenes, particularly nepetalactones, known for strong insect-repellent activity. However, their efficient extraction and molecular mechanisms in insect inhibition remains challenging. This study examined the chemical composition, protein-ligand interactions, and safety profiles of nepetalactones in comparison with DEET, with particular focus on mosquito odorant-binding proteins (OBPs) from <i>Anopheles gambiae</i> (<i>Agam</i>OBP), <i>Culex quinquefasciatus</i> (<i>Cqui</i>OBP), and <i>Aedes aegypti</i> (<i>Aaeg</i>OBP). GC-MS/MS analysis identified nepetalactone isomers as the predominant constituents in catnip extracts obtained via steam distillation and olive oil extraction from dried leaves. Molecular docking results indicated that <i>cis,cis</i>-, <i>cis,trans</i>-, and nepetalactone isomers exhibited higher binding affinities toward the target OBPs than DEET. Furthermore, molecular dynamics simulations confirmed that all nepetalactone-OBP complexes exhibited stable conformations characterized by low average RMSD values and persistent hydrogen bond formation. Notably, <i>cis,trans</i>-NL-<i>Aaeg</i>OBP, NL-<i>Aaeg</i>OBP, and <i>cis,cis</i>-NL-<i>Agam</i>OBP complexes displayed lower binding free energies (Δ<i>G_MM-PBSA</i>) compared to DEET. These findings suggest that nepetalactones stabilize OBP-ligand interactions while inducing subtle conformational flexibility, potentially disrupting mosquito odorant recognition in a manner distinct from DEET. ADMET predictions indicated that nepetalactones exhibit favorable absorption, distribution, and safety profiles with reduced predicted toxicity compared to DEET. Collectively, these results establish nepetalactones as promising candidates for the development of effective, safe, and sustainable plant-based repellents.