Neurotoxicity Assessment of Four Different Pesticides Using In Vitro Enzymatic Inhibition Assays

Pesticides affect different organs and tissues according to their bioavailability, chemical properties and further molecular interactions. In animal models exposed to several classes of pesticides, neurotoxic effects have been described, including the reduction of acetylcholinesterase activity in tissue homogenates. However, in homogenates, the reduction in enzymatic activity may also result from lower enzymatic expression and not only from enzymatic inhibition. Thus, in this work, we aimed to investigate the neurotoxic potential of four distinct pesticides: glyphosate (herbicide), imazalil (fungicide), imidacloprid (neonicotinoid insecticide) and lambda-cyhalothrin (pyrethroid insecticide), by assessing their inhibitory effect on the activity of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and tyrosinase, by using direct in vitro enzymatic inhibition methods. All pesticides dose-dependently inhibited AChE activity, with an inhibition of 11 ± 2% for glyphosate, 48 ± 2% for imidacloprid, 49 ± 3% for imazalil and 50 ± 3% for lambda-cyhalothrin, at 1 mM. Only imazalil inhibited BChE. Imazalil induced dose-dependent inhibition of BChE with identical pattern as that observed for AChE; however, for lower concentrations (up to 500 μM), imazalil showed higher specificity for AChE, and for higher concentrations, the same specificity was found. Imazalil, at 1 mM, inhibited the activity of BChE by 49 ± 1%. None of the pesticides, up to 1 mM, inhibited tyrosinase activity. In conclusion, the herbicide glyphosate shows specificity for AChE but low inhibitory capacity, the insecticides imidacloprid and λ-cyhalothrin present selective AChE inhibition, while the fungicide IMZ is a broad-spectrum cholinesterase inhibitor capable of inhibiting AChE and BChE in an equal manner. Among these pesticides, the insecticides and the fungicide are the ones with higher neurotoxic potential.