Oxidative biotransformation of organophosphotioate pesticides and acetylcholinesterase enzymatic inhibition

Abstract

Pesticides have lethal properties, capable of controlling or eliminating a living organism; they block the organisms' vital metabolic processes. They cause serious problems for human health, as they are highly toxic. The most used pesticides that are considered toxic are known as organophosphothioates (OP/P=S) in their commercialized form and organophosphates (OP/P=O) in their active form. These compounds have been the subject of studies on their metabolism and toxicology. According to research, these pesticides' toxicity is increased when oxidative metabolic desulfurization reactions occur, with the P=S bond being transformed into a P=O bond. This toxicity is due to the ability of OP/P=O species to inhibit the human acetylcholinesterase enzyme (HssAChE). To study the oxidative biotransformation of OP/P=S pesticides and the inhibition of the HssAChE enzyme by OP/P=S and OP/P=O using the molecular docking technique and QM/MM calculations. The theoretical results showed that parathion is the compound with the greatest capacity to transform its P=S bonds into P=O bonds, thus forming the active paraoxon metabolite in the oxidative biotransformation process. In the HssAChE inhibition by OP/P=S and OP/P=O, our results showed that of all the compounds investigated, those with the highest inhibitory activities are parathion, paraoxon, malathion, diazoxon, chlorpyrifos and omethoate. This study was essential due to the lack of information in the literature about the oxidative biotransformation process of OP/P=S pesticides and the ability of these compounds to inhibit HssAChE. With this study, it was possible to observe that, in the oxidative biotransformation, chlorpyrifos and parathion have greater capacities to transform into their active metabolites and in the inhibition of the HssAChE enzyme, it was possible to observe that not all OF/P=O are the ones with the highest abilities to inhibit the HssAChE enzyme.