A value-added application of eugenol as acaricidal agent: The mechanism of action and the safety evaluation

INTRODUCTION: Eugenol is a major component of essential oils of several plants, it exhibits significant antiparasitic and acaricidal activities, yet its molecular targets remain unknown. OBJECTIVES: We aimed to systematically investigate the mechanism of action and the potential targets of eugenol against P. cuniculi, and evaluate the safety for laying the theoretical foundation for clinical application as an acaricide. METHODS: Using RNA-Seq analysis, surface plasmon resonance analysis and RNA interference assay, the mode of action of eugenol against Psoroptes cuniculi was investigated. The effect on the mitochondrial membrane potential and complex I of PC12 cells and C6/36 cells was assayed to investigate the species specificity of eugenol in insects and mammals. Finally, a safety evaluation of eugenol in vivo was performed. RESULTS: Eugenol inhibited complex I activity of the mitochondrial respiratory chain in the oxidative phosphorylation pathway by binding to NADH dehydrogenase chain 2 and resulted in the death of mites. The inhibition rates were 37.89% for 50 μg/mL and 60.26% for 100 μg/mL, respectively. Further experiments indicated that the difference in the complex I sequence between insects and mammals led to the different affinity of eugenol to specific peptide, resulting in species specificity. Eugenol exhibited significant inhibitory effects against the mitochondrial membrane potential and complex I in Aedes albopictus C6/36 cells but was not active in rat PC12 cells. Insect cells were particularly sensitive to eugenol. In contrast to the known inhibitor rotenone, eugenol had better safety and did not result in Parkinson’s disease or other diseases in rats. CONCLUSION: This is the first report on acaricidal eugenol targeting complex I of the mitochondrial respiratory chain. This work lays the foundation for the development of eugenol as an environmentally alternative acaricidal agent.