Synergistic Cytotoxicity of Permethrin and N,N-Diethyl-Meta-Toluamide on Sinonasal Epithelial Cells

Background: N,N-Diethyl-Meta-Toluamide (DEET) and permethrin are pesticides commonly used in combination due to their synergistic insecticidal and repellent properties. This study investigates whether simultaneous exposure to these compounds elicits synergistic cytotoxicity in sinonasal epithelial cells (SNECs). Material and Methods: Ethmoid sinus mucosal specimens were procured from eight patients during endoscopic sinus surgery. SNECs were expanded on culture plates and exposed to various concentrations of DEET and permethrin (0-5μm), individually and concurrently, for up to 156 hours. Experiments were replicated in triplicates and cell viability was recorded every 2 hours using IncuCyte real-time cell imaging system. Synergy score was calculated on the basis of Loewe additivity synergy finder model. Results: DEET and permethrin exhibited synergistic cytotoxicity across all eight tissues, albeit with variations in onset and magnitude. Peak synergy was observed at 144h for tissue 1 (SLoewe 4.2, 95% CI 1.8-7.3; [permethrin concentration, DEET concentration] [2.5μM, 1.25μM]), 48h for tissue 2 (19.9, 16.5-23.6; [1.25, 0.625]), 144h for tissue 3 (15.2, 3.9-30.4; [0.625, 1.25]), 144h for tissue 4 (6.4, -3.6 to 18.0; [0.625, 0.625]), 48h for tissue 5 (10.1, 8.9-12.5; [0.625, 1.25]), 96h for tissue 6 (24.7, 12.2-36.3; [0.625, 0.625]), 48h for tissue 7 (47.7, 29.6-62.2; [0.625, 1.25]), and 96h for 8 (47.4, 26.8-67.0; [0.625, 0.625]). Conclusion: The concurrent exposure of DEET and permethrin can lead to synergistic cytotoxicity in sinonasal epithelia. Further research is warranted in preclinical animal models to explore whether this synergy accelerates the pathogenesis of chronic rhinosinusitis.