Effect of Different Oximes on Rat and Human Cholinesterases Inhibited by Methamidophos: A Comparative In Vitro and In Silico Study

Abstract

Methamidophos is one of the most toxic organophosphorus (OP) compounds. It acts via phosphorylation of a serine residue in the active site of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), leading to enzyme inactivation. Different oximes have been developed to reverse this inhibition. Thus, our work aimed to test the protective or reactivation capability of pralidoxime and obidoxime, as well as two new oximes synthesised in our laboratory, on human and rat cholinesterases inhibited by methamidophos. In addition, we performed molecular docking studies in non-aged methamidophos-inhibited AChE to understand the mechanisms involved. Our results suggested that pralidoxime protected and reactivated methamidophos-inhibited rat brain AChE. Regarding human erythrocyte AChE, all oximes tested protected and reactivated the enzyme, with the best reactivation index observed at the concentration of 50 lM. Concerning BChE, butane-2,3-dionethiosemicarbazone oxime (oxime 1) was able to protect and reactivate the methamidophos-inhibited BChE by 45% at 50 lM, whereas 2(3-(phenylhydrazono) butan-2-one oxime (oxime 2) reactivated 28% of BChE activity at 100 lM. The two classical oximes failed to reactivate BChE. The molecular docking study demonstrated that pralidoxime appears to be better positioned in the active site to attack the O-P moiety of the inhibited enzyme, being near the oxyanion hole, whereas our new oximes were stably positioned in the active site in a manner similar to that of obidoxime. In conclusion, our work demonstrated that the newly synthesised oximes were able to reactivate not only human erythrocyte AChE but also human plasma BChE, which could represent an advantage in the treatment of OP compounds poisoning. Acetylcholinesterase (EC 3.1.1.7, AChE) is an enzyme that catalyses the hydrolysis of acetylcholine to choline and acetate. The biological function of this enzyme is to terminate acetylcholine activity in the terminal nervous junction with its effector organs or post-synaptic sites [1]. The mechanism of action of organophosphorus (OP) compounds with anticholin-esterase activity involves the phosphorylation of the serine hydroxyl group in the active site of AChE, leading to an inactive enzyme (AChE-OP) [2]. The inactivation of AChE results in the accumulation of acetylcholine at cholinergic receptor sites, causing a cholinergic crisis that can lead to death [3]. Methamidophos is a potent AChE inhibitor used to control plague of insects on a variety of crops [4] and may present anticholinesterase activity against human cholinesterases [5,6]. In Brazil in particular, methamidophos is commonly used on many crops, including cotton, soybeans and wheat, resulting in food [7] and occupational exposure [8]. A recent study demonstrated that over 90% of small farmers use methamido-phos and nearly 60% of them exhibit typical OP intoxication symptoms [9]. Mechanistically, methamidophos may inhibit AChE by covalently binding a serine residue (Ser203) in the active site, and this moiety could form two dif...

Pre‐clinical evidence of safety and protective effect of isatin and oxime derivatives against malathion‐induced toxicity

“…In vitro studies revealed that PHBO is an oxime with antioxidant and AChE reactivator potential in human blood. 11,28,46,47 However, in the present study, PHBO did not reactivate the AChE inhibited by malathion in A salina. Therefore, it is possible to assume that PHBO protected A salina from the death induced by malathion due to its antioxidant effect; nevertheless, further research is needed to validate this hypothesis.…”

Toxic effects of methamidophos on paraoxonase 1 activity and on rat kidney and liver and ameliorating effects of alpha‐tocopherol

“…Besides being one of the metabolic products of acephate, MT is a systemic insecticide and acaricide. It is still used in developing countries, on some crops such as wheat, soybeans, potatoes, citrus fruits, cotton, and maize (Maroni et al, ; Araoud et al, ; Lugokenski et al, ; Uriostegui‐Acosta et al, ). World Health Organization (WHO) classified the technical product as Class 1B “Highly Hazardous,” and an Acceptable Daily Intake (ADI) of 0.004 mg/kg body weight was established by the Joint Meeting on Pesticide Residues (Maroni et al, ).…”

The Evaluation of Prophylactic Efficacy of Newly Developed Reversible Inhibitors of Acetylcholinesterase in Soman‐Poisoned Mice – A Comparison with Commonly Used Pyridostigmine

“…The limitations of post‐exposure treatment of acute poisonings with highly toxic organophosphorus compounds, especially soman, are well recognized . In situations allowing the administration of prophylactic agents, better therapeutic effects can be achieved by pre‐treatment with reversible AChE inhibitors .…”

“…soman, are well recognized [3][4][5][6][19][20][21][22]. In situations allowing the administration of prophylactic agents, better therapeutic effects can be achieved by pre-treatment with reversible AChE inhibitors [12,23].…”