Organophosphorus compounds, including pesticides and nerve agents, irreversibly inhibit acetylcholinesterase, leading to an accumulation of acetylcholine that can cause a cholinergic crisis. Standard treatment of organophosphate poisoning relies on oxime-based reactivators, such as pralidoxime, obidoxime, or asoxime. However, these compounds have several limitations, including poor penetration through the blood-brain barrier and limited efficacy across a broad spectrum of organophosphorus compounds. For this reason, non-oxime reactivators were introduced as potential alternatives. The most promising non-oxime reactivators contain Mannich phenol moiety, imidazole group or combination of both. Some of the non-oxime derivatives demonstrated better efficacy than standard oximes during in vitro evaluation. Nevertheless, these structures have significant drawbacks such as high intrinsic acetylcholinesterase inhibition or high toxicity profile which make them unsuitable for further in vivo tests. In this review, the current progress in the development of non-oxime reactivators is summarized and their bioactivity as well as their limitations are critically discussed.

• Keywords
• Acetylcholinesterase, Butyrylcholinesterase, Nerve agent, Non-oxime, Reactivator,
• MeSH
• Acetylcholinesterase metabolism   MeSH
• Antidotes MeSH
• Cholinesterase Inhibitors * toxicity   MeSH
• Humans MeSH
• Organophosphorus Compounds toxicity   MeSH
• Organophosphate Poisoning * drug therapy   MeSH
• Oximes MeSH
• Cholinesterase Reactivators * pharmacology   chemistry   therapeutic use   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Acetylcholinesterase MeSH
• Antidotes MeSH
• Cholinesterase Inhibitors * MeSH
• Organophosphorus Compounds MeSH
• Oximes MeSH
• Cholinesterase Reactivators * MeSH

Oxime reactivators of acetylcholinesterase are commonly used to treat highly toxic organophosphate poisoning. They are effective nucleophiles that can restore the catalytic activity of acetylcholinesterase; however, their main limitation is the difficulty in crossing the blood-brain barrier (BBB) because of their strongly hydrophilic nature. Various approaches to overcome this limitation and enhance the bioavailability of oxime reactivators in the CNS have been evaluated; these include structural modifications, conjugation with molecules that have transporters in the BBB, bypassing the BBB through intranasal delivery, and inhibition of BBB efflux transporters. A promising approach is the use of nanoparticles (NPs) as the delivery systems. Studies using mesoporous silica nanomaterials, poly (L-lysine)-graft-poly(ethylene oxide) NPs, metallic organic frameworks, poly(lactic-co-glycolic acid) NPs, human serum albumin NPs, liposomes, solid lipid NPs, and cucurbiturils, have shown promising results. Some NPs are considered as nanoreactors for organophosphate detoxification; these combine bioscavengers with encapsulated oximes. This study provides an overview and critical discussion of the strategies used to enhance the bioavailability of oxime reactivators in the central nervous system.

• Keywords
• Acetylcholinesterase, Blood–brain barrier, Delivery system, Nanoparticle, Oxime, Reactivator,
• MeSH
• Acetylcholinesterase * MeSH
• Biological Availability MeSH
• Biological Transport MeSH
• Central Nervous System * MeSH
• Blood-Brain Barrier MeSH
• Humans MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Acetylcholinesterase * MeSH

Certain AChE reactivators, asoxime, obidoxime, K027, K048, and K075, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure the different organs. As a continuation of previously published data, in this study, Wistar rats have sacrificed 24 hrs and 7 days after single im application of 0.1LD50, 0.5LD50 and 1.0LD50 of each reactivator, and examinated tissue samples were obtained for pathohistological and semiquantitative analysis. A severity of tissue alteration, expressed as different tissue damage scores were evaluated. Morphological structure of examinated tissues treated with of 0.1LD50 of all reactivators was comparable with the control group of rats. Moderate injuries were seen in visceral tissues treated with 0.5LD50 of asoxime, obidoxime and K027. Acute damages were enlarged after treatment with 0.5LD50 and 1.0LD50 of all reactivators during the next 7 days. The most prominent changes were seen in rats treated with 1.0LD50 of K048 and K075 (P < 0.001 vs. control and asoxime-treated group). All reactivators given by a single, high, unitary dose regimen, have an adverse effect not only on the main visceral tissue, but on the whole rat as well, but the exact mechanism of cellular injury remains to be confirmed in further investigation.

• MeSH
• Biopsy MeSH
• Chemical Warfare Agents adverse effects   chemistry   toxicity   MeSH
• Histocytochemistry MeSH
• Rats MeSH
• Lethal Dose 50 MeSH
• Molecular Structure MeSH
• Organ Specificity MeSH
• Oximes administration & dosage   adverse effects   chemistry   toxicity   MeSH
• Lung drug effects   metabolism   pathology   MeSH
• Viscera drug effects   pathology   MeSH
• Dose-Response Relationship, Drug MeSH
• Stomach drug effects   pathology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chemical Warfare Agents MeSH
• Oximes MeSH

BACKGROUND: Intoxication by nerve agents could be prevented by using small acetylcholinesterase inhibitors (eg, pyridostigmine) for potentially exposed personnel. However, the serious side effects of currently used drugs led to research of novel potent molecules for prophylaxis of organophosphorus intoxication. METHODS: The molecular design, molecular docking, chemical synthesis, in vitro methods (enzyme inhibition, cytotoxicity, and nicotinic receptors modulation), and in vivo methods (acute toxicity and prophylactic effect) were used to study bispyridinium, bisquinolinium, bisisoquinolinium, and pyridinium-quinolinium/isoquinolinium molecules presented in this study. RESULTS: The studied molecules showed non-competitive inhibitory ability towards human acetylcholinesterase in vitro that was further confirmed by molecular modelling studies. Several compounds were selected for further studies. First, their cytotoxicity, nicotinic receptors modulation, and acute toxicity (lethal dose for 50% of laboratory animals [LD50]; mice and rats) were tested to evaluate their safety with promising results. Furthermore, their blood levels were measured to select the appropriate time for prophylactic administration. Finally, the protective ratio of selected compounds against soman-induced toxicity was determined when selected compounds were found similarly potent or only slightly better to standard pyridostigmine. CONCLUSION: The presented small bisquaternary molecules did not show overall benefit in prophylaxis of soman-induced in vivo toxicity.

• Keywords
• AChE inhibitors, nerve agents, pre-treatment, prophylaxis, soman, toxicity,
• MeSH
• Acetylcholinesterase metabolism   MeSH
• Cell Line MeSH
• Cholinesterase Inhibitors chemistry   pharmacology   MeSH
• HeLa Cells MeSH
• Small Molecule Libraries chemistry   pharmacology   MeSH
• Humans MeSH
• Models, Molecular MeSH
• Molecular Structure MeSH
• Nerve Agents adverse effects   MeSH
• Soman adverse effects   MeSH
• Cell Survival drug effects   MeSH
• Dose-Response Relationship, Drug MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcholinesterase MeSH
• Cholinesterase Inhibitors MeSH
• Small Molecule Libraries MeSH
• Nerve Agents MeSH
• Soman MeSH

Acetylcholinesterase (AChE) reactivators (oximes) are compounds predominantly targeting the active site of the enzyme. Toxic effects of organophosphates nerve agents (OPNAs) are primarily related to their covalent binding to AChE and butyrylcholinesterase (BChE), critical detoxification enzymes in the blood and in the central nervous system (CNS). After exposure to OPNAs, accumulation of acetylcholine (ACh) overstimulates receptors and blocks neuromuscular junction transmission resulting in CNS toxicity. Current efforts at treatments for OPNA exposure are focused on non-quaternary reactivators, monoisonitrosoacetone oximes (MINA), and diacylmonoxime reactivators (DAM). However, so far only quaternary oximes have been approved for use in cases of OPNA intoxication. Five acetylcholinesterase reactivator candidates (K027, K075, K127, K203, K282) are presented here, together with pharmacokinetic data (plasma concentration, human serum albumin binding potency). Pharmacokinetic curves based on intramuscular application of the tested compounds are given, with binding information and an evaluation of structural relationships. Human Serum Albumin (HSA) binding studies have not yet been performed on any acetylcholinesterase reactivators, and correlations between structure, concentration curves and binding are vital for further development. HSA bindings of the tested compounds were 1% (HI-6), 7% (obidoxime), 6% (trimedoxime), and 5%, 10%, 4%, 15%, and 12% for K027, K075, K127, K203, and K282, respectively.

• MeSH
• Acetylcholine metabolism   MeSH
• Acetylcholinesterase metabolism   MeSH
• Adsorption MeSH
• Central Nervous System drug effects   MeSH
• Catalytic Domain MeSH
• Rats MeSH
• Neuromuscular Junction drug effects   metabolism   MeSH
• Organophosphates chemistry   metabolism   MeSH
• Rats, Wistar MeSH
• Cholinesterase Reactivators * blood   metabolism   pharmacokinetics   MeSH
• Serum Albumin metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Acetylcholine MeSH
• Acetylcholinesterase MeSH
• Organophosphates MeSH
• Cholinesterase Reactivators * MeSH
• Serum Albumin MeSH

The blood-brain barrier plays a vital role in the protection of the central nervous system. It is composed of endothelial cells with tight-junctions to limit the penetration of many endogenous and exogenous compounds, particularly hydrophilic xenobiotics. Nerve agents and pesticides are groups of compounds with high penetration potential into the central nervous system. However, oxime type antidotes are known to penetrate blood-brain barrier only in low concentration. The aim of presented study is to describe the pharmacokinetic profile of oxime K027 a novel antidote candidate. The main focus is on penetration of tested substance into the selected brain regions following time-dependent manner. The maximum concentration of the oxime K027 was attaining 15 and 30 min after i.m. application in plasma and brain tissue, respectively. The perfused brain tissue concentration was relatively high (10(-7) M order of magnitude) and depending on the brain region it was constant 15-60 min after application. The highest concentration was found in the frontal cortex 15 min after application while the lowest measured concentration was determined in the basal ganglia. This study showed that oxime K027 is able to achieve high concentration level in perfused brain tissue relatively quickly, but also demonstrated rapid clearance from the central nervous system. These results are probably due to low overall uptake of oxime K027 into the brain.

• MeSH
• Time Factors MeSH
• Central Nervous System drug effects   metabolism   MeSH
• Blood-Brain Barrier drug effects   metabolism   MeSH
• Rats MeSH
• Brain drug effects   metabolism   MeSH
• Oximes metabolism   pharmacokinetics   MeSH
• Rats, Wistar MeSH
• Pyridinium Compounds metabolism   pharmacokinetics   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 1-(4-hydroxyiminomethylpyridinium)-3-(carbamoylpyridinium) propane dibromide MeSH Browser
• Oximes MeSH
• Pyridinium Compounds MeSH