The potential role of bioscavenger in the medical management of nerve-agent poisoned casualties.

The provision of effective Medical Countermeasures (MedCM) for all agents and routes of exposure is a strategic goal of defence research and development. In the case of military autoinjector-based therapies for nerve agent poisoning, current treatment effectiveness is limited by the oxime reactivator being effective against only certain agents, by rapid clearance times of the drugs and because the doses may not be optimal for treatment of severe poisoning. Prolonged poisoning by nerve agents entering the body through the skin is also challenging. Since casualty handling timelines have reduced significantly in recent years, it may be sufficient for first aid therapy to provide protection for only a few hours until further medical treatment is available. Therefore, the traditional evaluation of first aid therapy in animal models of survival at 24 h may not be appropriate. At various echelons of medical care, further therapeutic interventions are possible. The current basis for the medical management of nerve-agent poisoned casualties is derived mainly from clinical experience with pesticide poisoning. Adjunct therapy with a bioscavenger (such as human butyrylcholinesterase (huBChE)), could have utility as a delayed intervention by reducing the toxic load. It has previously been demonstrated that huBChE is an effective post-exposure therapy against percutaneous VX poisoning. It is recommended that the scope of animal models of nerve agent MedCM are extended to cover evaluation of both first aid MedCM over significantly reduced timescales, and subsequent supportive therapeutic and medical management strategies over longer timescales. In addition to bioscavengers, these strategies could include repeated combined and individual therapy drugs to alleviate symptoms, other classes of drugs or ventilatory support. Crown Copyright © [2016] Published by Elsevier Ireland Ltd. This is an open access article under the Open Government Licence (OGL) (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/).

Pharmacokinetic profile and quantitation of protection against soman poisoning by the antinicotinic compound MB327 in the guinea-pig.

Current organophosphorus nerve agent medical countermeasures do not directly address the nicotinic effects of poisoning. A series of antinicotinic bispyridinium compounds has been synthesized in our laboratory and screened in vitro. Their actions can include open-channel block at the nicotinic receptor which may contribute to their efficacy. The current lead compound from these studies, MB327 1,1'-(propane-1,3-diyl)bis(4-tert-butylpyridinium) as either the diiodide (I2) or dimethanesulfonate (DMS) has been examined in vivo for efficacy against nerve agent poisoning. MB327 I2 (0-113mgkg(-1)) or the oxime HI-6 DMS (0-100mgkg(- 1)), in combination with atropine and avizafone (each at 3mgkg(-1)) was administered to guinea-pigs 1min following soman poisoning. Treatment increased the LD50 of soman in a dose-dependent manner. The increase was statistically significant (p<0.01) at the 33.9mgkg(-1) (MB327) or 30mgkg(-1) (HI-6) dose with a comparable degree of protection obtained for both compounds. Following administration of 10mgkg(-1) (i.m.), MB327 DMS reached plasma Cmax of 22µM at 12min with an elimination t1/2 of 22min. In an adverse effect study, in the absence of nerve agent poisoning, a dose of 100mgkg(-1) or higher of MB327 DMS was lethal to the guinea-pigs. A lower dose of MB327 DMS (30mgkg(-1)) caused flaccid paralysis accompanied by respiratory impairment. Respiration normalised by 30min, although the animals remained incapacitated to 4h. MB327 or related compounds may be of utility in treatment of nerve agent poisoning as a component of therapy with atropine, anticonvulsant and oxime, or alternatively as an infusion under medical supervision.

Toxicity and medical countermeasure studies on the organophosphorus nerve agents VM and VX.

To support the effort to eliminate the Syrian Arab Republic chemical weapons stockpile safely, there was a requirement to provide scientific advice based on experimentally derived information on both toxicity and medical countermeasures (MedCM) in the event of exposure to VM, VX or VM-VX mixtures. Complementary in vitro and in vivo studies were undertaken to inform that advice. The penetration rate of neat VM was not significantly different from that of neat VX, through either guinea pig or pig skin in vitro. The presence of VX did not affect the penetration rate of VM in mixtures of various proportions. A lethal dose of VM was approximately twice that of VX in guinea pigs poisoned via the percutaneous route. There was no interaction in mixed agent solutions which altered the in vivo toxicity of the agents. Percutaneous poisoning by VM responded to treatment with standard MedCM, although complete protection was not achieved.

Human plasma-derived BuChE as a stoichiometric bioscavenger for treatment of nerve agent poisoning.

Potent organophosphorous (OP) agents, such as VX, are hazardous by absorption through the skin and are resistant to conventional pharmacological antidotal treatments. The residence time of a stoichiometric bioscavenger, human butyrylcholinesterase (huBuChE), in the plasma more closely matches that of VX than do the residence times of conventional therapy drugs (oxime, anti-muscarinic, anticonvulsant). Intramuscular (i.m.) huBuChE afforded almost complete protection when administered prior to the onset of observable cholinergic signs of VX poisoning, but once signs of poisoning became evident the efficacy of i.m. huBuChE decreased. A combination of nerve agent therapy drugs (oxime, anti-muscarinic, anticonvulsant) with huBuChE (i.m.) protected 100% (8/8) of guinea-pigs from a lethal dose of VX (0.74 mg/kg) to 48 h, even when administered on signs of poisoning. Survival was presumed to be due to immediate alleviation of the cholinergic crisis by the conventional pharmacological treatment drugs, in conjunction with bioscavenger that prevented further absorbed agent reaching the AChE targets. Evidence to support this proposed mechanism of action was obtained from PKPD experiments in which multiple blood samples and microdialysate samples were collected from individual conscious ambulatory animals. Plasma concentrations of intramuscularly-administered atropine, diazepam and HI-6 reached a peak within 15 min and were eliminated rapidly within 4h. Plasma concentrations of huBuChE administered by the i.m. route took approximately 24h to reach a peak, but were well-maintained over the subsequent 7days. Thus, the pharmacological therapy rapidly treated the initial signs of poisoning, whilst the bioscavenger provided prolonged protection by neutralising further nerve agent entering the bloodstream and preventing it from reaching the target organs.

Efficacy and physiological effects of human butyrylcholinesterase as a post-exposure therapy against percutaneous poisoning by VX in the guinea-pig.

The physiological effects of human plasma-derived butyrylcholinesterase (huBuChE) administration and its modulation of the effects of percutaneous VX challenge are poorly understood. Percutaneously administered nerve agents are more slowly absorbed than inhaled agents; consequently, signs of poisoning occur later, with a longer duration. Telemetry was used to monitor heart rate, EEG, temperature and activity in guinea-pigs. Treatment with huBuChE at 30 or 120 min following percutaneous VX challenge ( approximately 2.5 x LD(50)) provided 100% protection from lethality. When huBuChE administration was delayed until the onset of observable signs of poisoning only 1 out of 6 animals survived to the end of the experiment at 7 days. This study adds to the body of evidence demonstrating the efficacy of huBuChE in animals by describing the successful therapeutic use of a protein bioscavenger as a post-exposure treatment against dermal exposure to VX up to 2h post-exposure. This study simultaneously used telemetric methods to show that the efficacy of huBuChE is linked to the prevention of detrimental physiological changes observed in control VX-treated animals. Post-exposure therapy is a promising additional indication for the concept of use of this material, and one that has particular relevance in a civilian exposure scenario.

A novel approach to assessing percutaneous VX poisoning in the conscious guinea-pig.

Nerve agents like VX (S-2-diisopropylaminoethyl-O-ethyl-methylphosphonothiolate) are potent irreversible acetylcholinesterase (AChE) inhibitors. Following percutaneous nerve agent exposure there is a slower rate of absorption, later onset and longer duration of signs of poisoning. Relatively little is known about the physiological effects of percutaneously applied nerve agent in unanaesthetised laboratory animals. Heart rate (ECG), brain electrical activity (EEG), body temperature, locomotor activity and clinical signs were monitored following percutaneous application of VX to conscious guinea-pigs.A fall in heart rate (bradycardia) preceded incapacitation following the highest VX dose, and occurred in the absence of incapacitation at the lower doses. Following the highest dose of VX (0.592 mg kg(-1)) three out of four animals died within 24 h. The lower two doses of VX (0.296 and 0.148 mg kg(-1)), produced extended periods of bradycardia in the absence of observable signs of poisoning. Bradycardia preceded, or occurred in the absence of, a temperature decrease; seizure-like EEG changes were not observed at any of the VX doses tested. Acetylcholinesterase activity was significantly inhibited in the blood and most brain areas at 48 h. There were significant dose-related decreases in body weight at 24 and 48 h following VX. This preliminary study suggests that decreased heart rate may be an early sign of the toxic effects of VX, whereas temperature and observable clinical signs are not good early indicators of percutaneous VX poisoning in this animal model. Future studies will use this model to assess the benefit of administering medical countermeasures in response to a defined decrease in heart rate.