Organophosphorus nerve agent poisoning: managing the poisoned patient

Safety and Efficacy of New Oximes to Reverse Low Dose Diethyl-Paraoxon-Induced Ventilatory Effects in Rats

Background: Oximes are used in addition to atropine to treat organophosphate poisoning. However, the efficiency of oximes is still a matter of debate. In vitro experiments suggested than new oximes are more potent than the commercial oximes. However, the antidotal activity of new oximes has not been assessed in vivo. Methods: The aim of this work was to assess the safety and efficiency of new oximes compared to pralidoxime in a rat model of diethyl paraoxon-induced non-lethal respiratory toxicity. Results: Safety study of oximes showed no adverse effects on ventilation in rats. KO-33, KO-48, KO-74 oximes did not exhibit significant antidotal effect in vivo. In contrast, KO-27 and BI-6 showed evidence of antidotal activity by normalization of respiratory frequency and respiratory times. KO-27 became inefficient only during the last 30 min of the study. In contrast, pralidoxime demonstrated to be inefficient at 30 min post injection. Inversely, the antidotal activity of BI-6 occurred lately, within the last 90 min post injection. Conclusion: This study showed respiratory safety of new oximes. Regarding, the efficiency, KO-27 revealed to be a rapid acting antidote toward diethylparaoxon-induced respiratory toxicity, meanwhile BI-6 was a late-acting antidote. Simultaneous administration of these two oximes might result in a complete and prolonged antidotal efficiency.

A national toxicology program systematic review of the evidence for long-term effects after acute exposure to sarin nerve agent

Sarin is a highly toxic nerve agent that was developed for chemical warfare during World War II and is used in present conflicts. Immediate effects of acute sarin exposure are established; however, whether effects persist after initial signs have subsided is debated. The National Toxicology Program (NTP) conducted a systematic review to evaluate the evidence for long-term neurological effects following acute (<24 hour) exposure to sarin. The literature search and screening process identified 32 data sets within the 34 human studies and 47 data sets within the 51 animal studies (from 6837 potentially relevant references) that met the objective and the inclusion criteria. Four main health effect categories of neurological response were identified as having sufficient data to reach hazard conclusions: (1) cholinesterase levels; (2) visual and ocular effects; (3) effects on learning, memory, and intelligence; and (4) morphology and histopathology in nervous system tissues. NTP concluded that acute sarin exposure is known to be a neurological hazard to humans in the period following exposure up to 7 days and suspected to be a hazard week to years after exposure, given a lower level of evidence in later time periods. Effects included reduced cholinesterase, visual and ocular effects, impaired learning and memory, and altered nervous system morphology. Further mechanistic, targeted animal studies, translational research, and rapid research responses after human exposures may reduce uncertainties on long-term consequences of sarin.

Targeting organophosphorus compounds poisoning by novel quinuclidine-3 oximes: development of butyrylcholinesterase-based bioscavengers

A library of 14 mono-oxime quinuclidinium-based compounds with alkyl or benzyl substituent were synthesized and characterized in vitro as potential antidotes for organophosphorus compounds (OP) poisoning treatment. We evaluated their potency for reversible inhibition and reactivation of OP inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and evaluated interactions by molecular docking studies. The reactivation was notable for both AChE and BChE inhibited by VX, cyclosarin, sarin and paraoxon, if quinuclidinium compounds contained the benzyl group attached to the quinuclidinium moiety. Out of all 14, oxime Q8 [4-bromobenzyl-3-(hydroxyimino)quinuclidinium bromide] was singled out as having the highest determined overall reactivation rate of approximately 20,000 M^-1 min^-1 for cyclosarin-inhibited BChE. Furthermore, this oxime in combination with BChE exhibited a capability to act as a bioscavenger of cyclosarin, degrading within 2 h up to 100-fold excess of cyclosarin concentration over the enzyme. Molecular modeling revealed that the position of the cyclohexyl moiety conjugated with the active site serine of BChE directs the favorable positioning of the quinuclidinium ring and the bromophenyl moiety of Q8, which makes phosphonylated-serine easily accessible for the nucleophilic displacement by the oxime group of Q8. This result presents a novel scaffold for the development of new BChE-based bioscavengers. Furthermore, a cytotoxic effect was not observed for Q8, which also makes it promising for further in vivo reactivation studies.

In vitro evaluation of two different types of obidoxime-loaded nanoparticles for cytotoxicity and blood-brain barrier transport

Nerve agents (NA) are chemical warfare munitions and their exposure causes a progressive inhibition of acetylcholinesterase (AChE). This inhibition causes NA-induced brain damage in central nervous system (CNS). Oximes reactivate AChE in both the peripheral nervous system and the CNS. Transport of the oxime across the blood-brain barrier (BBB) in the existed therapeutic concentrations at the brain parenchyma determines the effectiveness of antidote therapy on respiratory depression and NA-induced brain damage. However, oximes could not cross the BBB in therapeutic concentrations. The aim of this study was to load AChE reactivator obidoxime chloride to PLGA and PEG-b-PLGA nanoparticles and to improve the BBB transport of the molecule. Brain microvascular endothelial cells were used as the BBB model. 79.3 ± 4.2% of obidoxime was released from PLGA nanoparticles and 88.2 ± 4.4% of obidoxime was released from PEG-b-PLGA nanoparticles within 24 h. It was found that PEG-b-PLGA nanoparticles were ideal drug carrier because of its low tissue toxicity, few side effects, and controllable drug release profile. Transport efficiency of obidoxime across the BBB is a major challenge in the prevention of the CNS, the effectiveness of NA poisoning and new strategies like using obidoxime-loaded PEG-b-PLGA nanoparticles could overcome this challenge for the management of NA-induced brain damage.

A case report of cholinesterase inhibitor poisoning: cholinesterase activities and analytical methods for diagnosis and clinical decision making

Suicidal ingestion of organophosphorus (OP) or carbamate (CM) compounds challenges health care systems worldwide, particularly in Southeast Asia. The diagnosis and treatment of OP or CM poisoning is traditionally based on the clinical appearance of the typical cholinergic toxidrome, e.g. miosis, salivation and bradycardia. Yet, clinical signs might be inconclusive or even misleading. A current case report highlights the importance of enzymatic assays to provide rapid information and support clinicians in diagnosis and rational clinical decision making. Furthermore, the differentiation between OP and CM poisoning seems important, as an oxime therapy will most probably not provide benefit in CM poisoning, but—as every pharmaceutical product—it might result in adverse effects. The early identification of the causing agent and the amount taken up in the body are helpful in planning of the therapeutic regimen including experimental strategies, e.g. the use of human blood products to facilitate scavenging of the toxic agent. Furthermore, the analysis of biotransformation products and antidote levels provides additional insights into the pathophysiology of OP or CM poisoning. In conclusion, cholinesterase activities and modern analytical methods help to provide a more effective treatment and a thorough understanding of individual cases of OP or CM poisoning.