Cholinesterase Reactivators: The Fate and Effects in the Organism Poisoned with Organophosphates/Nerve Agents

Abstract

Understanding the mechanism of action of organophosphates (OP)/nerve agents -irreversible acetylcholinesterase (AChE, EC 3.1.1.7) inhibition at the cholinergic synapses followed by metabolic dysbalance of the organism -two therapeutic principles for antidotal treatment are derived. The main drugs are anticholinergics that antagonize the effects of accumulated acetylcholine at the cholinergic synapses and cholinesterase reactivators (oximes) reactivating inhibited AChE. Anticonvulsants such as diazepam are also used to treat convulsions. Though there are experimental data on a good therapeutic effects of reactivators, some attempts to underestimate the role of reactivators as effective antidotes against OP poisoning have been made. Some arguments on the necessity of their administration following OP poisoning are discussed. Their distribution patterns and some metabolic and pharmacological effects are described with the aim to resolve the question on their effective use, possible repeated administration in the treatment of OP poisonig, their peripheral and central effects including questions on their penetration through the blood brain barrier as well as a possibility to achieve their effective concentration for AChE reactivation in the brain. Reactivation of cholinesterases in the peripheral and central nervous system is described and it is underlined its importance for the survival or death of the organism poisoned with OP. Metabolization and some other effects of oximes (not connected with AChE reactivation) are discussed (e.g. forming of the phosphonylated oxime, parasympatholytic action, hepatotoxicity, behavioral changes etc.). An universality of oximes able to reactivate AChE inhibited by all OP is questioned and therefore, needs of development of new oximes is underlined.

The effect of chlorpyrifos upon ATPase activity of sarcoplasmic reticulum and biomechanics of skeletal muscle contraction

“…The toxicity of organophosphate insecticides is explained by irreversible inhibition of acetylcholine esterase leading to acetylcholine accumulation and excessive activation of cholinergic receptors [9,10].…”

Biomonitoring of Organophosphorus Agent Exposure by Reactivation of Cholinesterase Enzyme Based on Carbon Nanotube-Enhanced Flow-Injection Amperometric Detection

“…The reactivation of inhibited ChE is dependent on both the amount of reactivator and phosphorylated enzyme 37. The “aged enzyme” undergoes dealkylation, where, after a molecular rearrangement of the alkylphosphate group attached to the serine residue, it is resistant to reactivation 38.…”

Reactivation Potency of the Acetylcholinesterase Reactivator Obidoxime Is Limited

“…As resulted, obidoxime was able to reactivate AChE inhibited by all tested nerve agents and pesticides. As it is known, the sufficient reactivation potency causing survival of the intoxicated organism should be over 10% 17 . From this point of view, cyclosarin-, soman -and methylchlorpyrifos-inhibited AChE was not sufficiently reactivated.…”