Comparative physiology and efficacy of atropine and scopolamine in sarin nerve agent poisoning

Review of Possible Therapies in Treatment of Novichoks Poisoning and HAZMAT/CBRNE Approaches: State of the Art

Novichoks-organophosphorus compounds belong to the nerve agents group, constituting the fourth generation of chemical warfare agents. The tremendous toxicity of Novichoks is assumed to be several times greater than that of VX, whereas no published experimental research supports this. They were surreptitiously created during the Cold War by the Soviet Union. Novichok’s toxic action mechanism consists of the inhibition of acetylcholinesterase activity. The review includes data on treating poisoning caused by OPs which could be used as guidelines for the therapy in case of Novichok exposure and HAZMAT/CBRNE approaches. Novichoks pose a severe threat due to their toxicity; however, there is insufficient information about the identity of A-series nerve agents. Filling in the missing data gaps will accelerate progress in improving protection against Novichoks and developing optimal therapy for treating poisoning casualties. Furthermore, introducing solutions to protect medical personnel in contact with a hazardous substance increases the chances of saving casualties of HAZMAT/CBRNE incidents.

A complete, evidence-based review on novichok poisoning based on epidemiological aspects and clinical management

Background: The whole world has learned about the existence of a highly toxic neuro-paralytic substance called Novichok. A wide range of neuro-paralytic toxins were used during the wars of decades ago, which also had harmful and irreversible effects. Fortunately, the establishment of conventions prohibiting the use of these weapons prevented the adverse clinical consequences of these compounds. What we did in the present study was to evaluate the clinical features of Novichok, how to manage exposure to it, and to evaluate the prognostic aspects associated with this poisoning agent. Methods: The manuscript especial databases including Medline, Web of knowledge, Google scholar, and Scopus were deeply searched by the two blinded investigators for all eligible studies based on the considered keywords. Initially 98 articles were initially collected by database searching that considering eligibility criteria, 83 articles were finally eligible for the final assessment. There is a lack of clinical trials and case-cohort studies on general population about treatment and side effects when it comes to human nerve agents and most of the data in our search is based on animal studies. Results: In evaluating various clinical, auto physiological and prognostic aspects of exposure to these substances, special attention was necessary to the following points. First, Novichok agents are considered more potent than other toxic agents. Pathophysiologically, these agents irreversibly bind acetylcholinesterase and produce a rapid cholinergic toxidrome which is responsible for the clinical manifestations as well as the potential dangerous and life threatening side effects caused by these agents. Uniquely, these agents are thought to also target every neuron in the central and peripheral nervous system. As a managerial and therapeutic approach, early and timely treatment of its related complication along with prevents massive exposure and decontamination in addition to rapid resuscitation can prohibit debilitating neuropathy and death due to facing it. Conclusion: The present review highlights the importance of recognizing the potential acute toxic effects of Novichok agents, diagnostic and therapeutic approaches (life-saving antidotal therapy) to complications and ultimately the application of guidelines to improve the prognosis of exposure to these agents for both victims and medical community.

Neurotoxicity evoked by organophosphates and available countermeasures

Organophosphorus compounds (OP) are a constant problem, both in the military and in the civilian field, not only in the form of acute poisoning but also for their long-lasting consequences. No antidote has been found that satisfactorily protects against the toxic effects of organophosphates. Likewise, there is no universal cure to avert damage after poisoning. The key mechanism of organophosphate toxicity is the inhibition of acetylcholinesterase. The overstimulation of nicotinic or muscarinic receptors by accumulated acetylcholine on a synaptic cleft leads to activation of the glutamatergic system and the development of seizures. Further consequences include generation of reactive oxygen species (ROS), neuroinflammation, and the formation of various other neuropathologists. In this review, we present neuroprotection strategies which can slow down the secondary nerve cell damage and alleviate neurological and neuropsychiatric disturbance. In our opinion, there is no unequivocal approach to ensure neuroprotection, however, sooner the neurotoxicity pathway is targeted, the better the results which can be expected. It seems crucial to target the key propagation pathways, i.e., to block cholinergic and, foremostly, glutamatergic cascades. Currently, the privileged approach oriented to stimulating GABA_AR by benzodiazepines is of limited efficacy, so that antagonizing the hyperactivity of the glutamatergic system could provide an even more efficacious approach for terminating OP-induced seizures and protecting the brain from permanent damage. Encouraging results have been reported for tezampanel, an antagonist of GluK1 kainate and AMPA receptors, especially in combination with caramiphen, an anticholinergic and anti-glutamatergic agent. On the other hand, targeting ROS by antioxidants cannot or already developed neuroinflammation does not seem to be very productive as other processes are also involved.

Determination of Scopolamine Distribution in Plasma and Brain by LC-MS/MS in Rats

Scopolamine, as a tropane alkaloid found in plants such as belladonna and datura, is used clinically as a transdermal patch and is highly neurotoxic. This study aimed to develop a simple, sensitive, and selective LC-MS/MS method for the determination of the content and distribution of scopolamine in rat plasma and brain after drug administration. In our study, sample pretreatment consisted of protein precipitation with acetonitrile followed by nitrogen blow concentration. Gradient elution of scopolamine and internal standard was performed on a ZORBAX Eclipse Plus C18 (2.1 $\ast$ 100 mm, 3.5 μm) column with water containing 0.1% formic acid (v/v) and acetonitrile as a mobile phase. Those samples were quantified in ESI positive ion mode using an API 4000 triple quadrupole mass spectrometer. The results showed that scopolamine was linear in the calibration range of 2–2500 ng/mL, and the selectivity, accuracy, precision, matrix effect, stability, and recovery of the method were within acceptable limits. The method has been validated and has been successfully used for toxicokinetic studies of scopolamine. After intraperitoneal injection, the time to peak toxic concentrations of scopolamine in rats was 0.5 h. The concentrations of scopolamine in the hippocampus and cortex were much higher than those in the striatum, indicating that the likely targets of its neurotoxic damage were the hippocampus and cortex. Overall, this study provides the basis for the neurotoxicity of scopolamine and provides a reference for its toxicokinetic studies.

The pharmacological treatment of acute vestibular syndrome

Acute vestibular syndrome (AVS) represents a clinical picture that involves urgent management due to the important procession of symptoms accompanying the event, which can be positively or negatively influenced by therapeutic choices and intervention timing. This forces a differential diagnosis and therapeutic choices to be made in conditions that are not always favorable and often not in the specialist field. In this work, we will examine in detail the pharmacological therapeutic possibilities, correlating them to the differential and, as far as possible, to the etiological diagnosis. In particular, the pharmacological possibilities for the two main conditions we can face will be investigated, namely, vestibular neuritis and posterior circulation stroke.

Safety evaluation of antibacterial and analgesic autoinjector devices for rapid administration during emergency situations: a crossover study in rabbits

Objective:

The objective of the present study was to evaluate the safety and tolerability of autoinjector devices (AIDs) in rabbits by intramuscular (i.m.) administration, using haematological and biochemical markers.

Introduction:

Emergency and mass casualty situations require immediate drug delivery for which AIDs are preferred. The tolerability of amikacin as antibacterial and buprenorphine as analgesic AID has been studied in rats by intraperitoneal administration. In the present study, it was evaluated in rabbits by i.m. administration.

Methods:

Water-filled glass cartridges (2.3–2.4 mL) were converted to amikacin (106 mg/mL) and buprenorphine (0.128 mg/mL) cartridges. Dual dose AID was used for i.m. administration (1.2 mL). The study was done as a crossover design on 12 rabbits. Initially, three rabbits each were given manually or AID, 57 mg/kg amikacin, and three rabbits each by manual or by AID, 0.07 mg/kg buprenorphine for 7 days. After 1 month, the injections were changed in the rabbits. In the place of manual injection, AID and in the place of amikacin, buprenorphine injection was given. This ensured that all rabbits received 14 injections, 7 manual and 7 AID consisting of 7 amikacin and 7 buprenorphine. 24 h before and 24 h after last drug administrations, blood was withdrawn from ear vein for haematological and biochemical estimations.

Results:

The rabbits were healthy, active and no sign of any injection-related changes were observed after administration of amikacin and buprenorphine by manually or by AID. The haematological and biochemical parameters showed similar changes in manual and AID administration of amikacin and buprenorphine.

Conclusion:

The present study of amikacin and buprenorphine by AID shows the safety of the device and is recommended for further experimentation. These AIDs are intended for self-administration during emergency and mass causality situation and are suitable for adults and children, as well as farm and pet animals.

Drug-Drug Interactions in Vestibular Diseases, Clinical Problems, and Medico-Legal Implications

Peripheral vestibular disease can be treated with several approaches (e.g., maneuvers, surgery, or medical approach). Comorbidity is common in elderly patients, so polytherapy is used, but it can generate the development of drug-drug interactions (DDIs) that play a role in both adverse drug reactions and reduced adherence. For this reason, they need a complex kind of approach, considering all their individual characteristics. Physicians must be able to prescribe and deprescribe drugs based on a solid knowledge of pharmacokinetics, pharmacodynamics, and clinical indications. Moreover, full information is required to reach a real therapeutic alliance, to improve the safety of care and reduce possible malpractice claims related to drug-drug interactions. In this review, using PubMed, Embase, and Cochrane library, we searched articles published until 30 August 2021, and described both pharmacokinetic and pharmacodynamic DDIs in patients with vestibular disorders, focusing the interest on their clinical implications and on risk management strategies.

Many Drugs of Abuse May Be Acutely Transformed to Dopamine, Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.

A delayed treatment model for the evaluation of scopolamine for VX nerve agent intoxication

Most research on medical countermeasures for nerve agent exposure assumes a military scenario, in which (autoinjector) treatment is envisaged to be available immediately. In a civilian setting however, treatment is delayed until arrival of first-aid responders. This may significantly affect treatment efficacy and the requirements for secondary intensive care. The aim of the current study was to develop a guinea pig model to evaluate the efficacy of delayed treatment following nerve agent exposure. We identified a trigger-to-treat based on a progressive stage of the toxidrome following VX exposure, which was associated with the subsiding of clonic movements. This paradigm resulted in treatment consistently being administered between 15 and 25 min post-exposure. Using the model, we investigated the potential for the anticholinergic scopolamine to act as a delayed treatment either as a standalone treatment, or as an adjunct to delayed treatment with Standard of Care (SOC), containing atropine, 2-PAM, and midazolam. The study provides a framework for a small animal model for evaluating the efficacy of treatment administered at a specific stage of the toxidrome, when immediate treatment is absent. As an adjunct, scopolamine treatment did not result in improved survival, but did show a beneficial effect on recovery, in terms of general posture. As a standalone treatment, scopolamine showed a significant, dose-responsive, beneficial effect on survival and recovery. These promising results warrant additional studies to investigate which observed physiological improvements are relevant for the recovery process and residual injury.

3-Quinuclidinyl benzilate (agent BZ) toxicokinetics in rats

3-Quinuclidinyl benzilate (BZ) ranks among incapacitating military warfare agents. It acts as a competitive inhibitor on muscarinic receptors leading to non-lethal mental impairment. The present study aimed to investigate toxicokinetics of BZ in rats. Moreover, BZ can be exploited to produce a pharmacological model of Alzheimer's disease; thus, this paper focuses mainly on the BZ distribution to the brain. Wistar rats were administered i.p. with BZ (2 and 10 mg/kg). The BZ concentration was determined using LC-MS/MS in plasma, urine, bile, brain, kidney and liver. The sample preparation was based on a solid phase extraction (liquids) or protein precipitation (organ homogenates). The plasma concentration peaked at 3 min (204.5 ± 55.4 and 2185.5 ± 465.4 ng/ml). The maximal concentration in the brain was reached several minutes later. Plasma elimination half-life was 67.9 ± 3.4 in the 2 mg/kg group and 96.6 ± 27.9 in the 10 mg/kg group. BZ concentrations remained steady in the brain, with slow elimination (t_1/2 506.9 ± 359.5 min). Agent BZ is excreted mainly via the urine. Steady BZ concentration in the brain could explain the previously published duration of the significant impairment in passive avoidance tasks in rats after an injection of BZ.

Efficacy of atropine and scopolamine on airway contractions following exposure to the nerve agent VX

Nerve agents are highly toxic organophosphorus compounds that inhibit acetylcholinesterase resulting in rapid accumulation of the neurotransmitter acetylcholine (ACh) causing a cholinergic syndrome including respiratory failure. In the present study, respiratory responses and antimuscarinic treatment efficacy was evaluated ex vivo using rat precision-cut lung slices (PCLS) exposed to the nerve agent VX. The respiratory effects were evaluated either by adding exogenous ACh directly to the culture medium or by applying electric-field stimulation (EFS) to the PCLS to achieve a release of endogenous ACh from neurons in the lung tissue. The airway contraction induced by both methods was enhanced by VX and resulted in lingering airway recovery, in particular when airways were exposed to a high VX-dose. Both contractions induced by EFS and exogenously added ACh were significantly reduced by administration of the antimuscarinic drugs atropine or scopolamine. Two additions of atropine or scopolamine after maximal ACh-induced airway response was demonstrated effective to reverse the contraction. By adding consecutive doubled doses of antimuscarinics, high efficiency to reduce the cholinergic airway response was observed. However, the airways were not completely recovered by atropine or scopolamine, indicating that non-muscarinic mechanisms were involved in the smooth muscle contractions. In conclusion, it was demonstrated that antimuscarinic treatment reversed airway contraction induced by VX but supplemental pharmacological interventions are needed to fully recover the airways. Further studies should therefore clarify the mechanisms of physiological responses in lung tissue following nerve agent exposures to improve the medical management of poisoned individuals.

Repeated low-dose exposures to sarin disrupted the homeostasis of phospholipid and sphingolipid metabolism in guinea pig hippocampus

Repeated low-level exposure to sarin results to hippocampus dysfunction. Metabonomics involves a holistic analysis of a set of metabolites in an organism in the search for a relationship between these metabolites and physiological or pathological changes. The objective of the present study was to evaluate the effects of repeated exposure to low-level sarin on the metabonomics in hippocampus of a guinea pig model. Guinea pigs were divided randomly into control and sarin treated groups (n = 14). Guinea pigs in the control group received saline; while the sarin-treated group received 0.4×LD₅₀ (16.8 μg/kg) sarin. Daily injections (a total of 14 days) were administered sc between the shoulder blades in a volume of 1.0 ml/kg body weight. At the end of the final injection, 6 animals in each group were chosen for Morris water maze test. The rest guinea pigs (n = 8 for each group) were sacrificed by decapitation, and hippocampus were dissected for analysis. Compared with the control-group, the escape latency in sarin-group was significantly (p < 0.05) longer while the crossing times were significantly decreased in the Morris water task (p < 0.05). Sarin inhibited activities of acetylcholinesterase (AChE) and neuropathy target esterase (NTE) in hippocampus. The AChE activity of hippocampus from sarin-treated groups is equivalent to 59.9 ± 6.4 %, and the NTE activity of hippocampus from sarin-groups is equivalent to 78.1 ± 8.3 % of that from control-group. Metabolites were identified and validated. A total of 14 variables were selected as potential biomarkers. Phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylinositol (PI), Lysophosphatidylethanolamine (LysoPE or LPE)] and sphingolipids (SPs) [sphinganine (SA), phytosphingosine (PSO) and sphinganine-1-phosphate (SA1P)] were clearly modified. In conclusion, repeated low-dose exposures to sarin disrupted the homeostasis of phospholipid and sphingolipid metabolism in guinea pig hippocampus and may lead to a neuronal-specific function disorders. Identified metabolites such as SA1P need to be studied more deeply on their biological function that against sarin lesions. In future research, we should pay more attention to characterize the physiological roles of lipid metabolism enzymes as well as their involvement in pathologies induced by repeated low-level sarin exposure.

A novel biosensor for the detection of organophosphorus (OP)-based pesticides using organophosphorus acid anhydrolase (OPAA)-FL variant

Indiscriminate use of organophosphorus (OP)-based insecticides is a great concern to human health because of bioaccumulation-induced health hazards. Potentially fatal consequences and limited treatment methods of OP poisoning necessitate the need for the development of reliable, selective, cost-effective, and sensitive methods of OP detection. To tackle this issue, the development of effective devices and methods is required to sensitively detect as well as degrade OPs. Enzymatic sensor systems have gained popularity due to high catalytic activity, enhanced detection limits, and high sensitivity with the environmentally benign operation. Organophosphorus acid anhydrolase (OPAA) from Alteromonas sp. JD6.5 is capable of hydrolyzing the P-F, P-O, P-S, and P-CN bonds, in OPs, including nerve agents of the G/V-series. Several mutants of OPAA are reported which have greater activity against various OPs. In this study, recombinant expression of the OPAA-FL variant in Escherichia coli was performed, purified, and subsequently tested for activity against ethyl paraoxon. OPAA-FL variant showed its optimum activity at pH 8.5 and 50 °C. Colorimetric and fluorometric assays were used for estimation of ethyl paraoxon based on p-nitrophenol and fluorescein isothiocyanate (FITC) fluorescence intensity, respectively. Colorimetric and fluorometric assay estimation indicates that ethyl paraoxon can be estimated in the linear range of 0.01 to 1 mM and 0.1 to 0.5 mM, with LOD values 0.04 mM and 0.056 mM, respectively. Furthermore, the OPAA-FL variant was immobilized into alginate microspheres for colorimetric detection of ethyl paraoxon and displayed a linear range of 0.025 to 1 mM with a LOD value of 0.06 mM. KEY POINTS: • Biosensing of paraoxon with purified and encapsulated OPAA-FL variant. • Colorimetric and fluorometric biosensing assay developed using OPAA-FL variant for paraoxon. • First report on alginate encapsulation of OPAA-FL variant for biosensing of paraoxon. Graphical abstract.