Simplified assessment of acetylcholinesterase inhibition by environmental organophosphorus pesticides

Environmental contaminants, such as pesticides, can inhibit the enzymatic activity of acetylcholinesterase (AChE), an enzyme necessary for neurotransmission. The inhibitory effects of structurally diverse pesticides on AChE may result from either reversible or covalent interactions. Therefore, assessing their potency typically requires different assay design to determine either dissociation constants or rate constants, respectively. To avoid complex kinetic experiments and enable comparison of potencies across structurally diverse pesticides, we optimized an AChE inhibitor detection system using an endpoint Ellman assay in 96-well plates. Given the significant interspecies variability in sensitivity to inhibitors, we investigated AChE inhibition using both electric eel AChE (eeAChE) and human AChE (hAChE). After confirming the repeatability, reproducibility, and solvent compatibility of the detection system using the reversible inhibitor BW284c51, we determined the inhibition potency of selected organophosphorus (OP) pesticides based on IC₅₀ values. We found that chlorpyrifos, fenamiphos and ethoprophos were more potent inhibitors of hAChE than eeAChE. In contrast, phosalone and methamidophos showed similar inhibitory effects on both enzymes. The potencies aligned well with previously reported inhibitory rate constants. In conclusion, since OPs acts as progressive inhibitors of AChE, our optimized assay offers a simplified yet effective method for assessing their inhibitory potency. It also allows for comparative evaluation of various environmental pollutants based solely on IC₅₀ values, eliminating the need for complex kinetic studies.