Galantamine counteracts development of learning impairment in guinea pigs exposed to the organophosphorus poison soman: Clinical significance
Highlights
► The organophosphorus (OP) poison soman affects cognition in guinea pigs. ► Guinea pigs show learning deficit in the Morris water maze 3 months after soman exposure. ► Galantamine, a drug for Alzheimer's disease, prevents soman-induced cognitive impairment. ► Galantamine emerges as an effective medical countermeasure against OP toxicity.
Introduction
Organophosphorus (OP) compounds, including pesticides and the nerve agents soman, sarin and VX, are among the most toxic man-made chemicals. Although different OPs interact with specific targets in the peripheral and central nervous systems (Albuquerque et al., 1985), their acute toxicity is characterized by overstimulation followed by desensitization of cholinergic muscarinic and nicotinic receptors that results in part from the irreversible inhibition of acetylcholinesterase (AChE) – the enzyme that hydrolyzes acetylcholine (Newmark, 2007).
Some of the nerve agents have been used with catastrophic results in wars and terrorist attacks (Coupland and Leins, 2005, Romano and King, 2001). The 1995 terrorist attack with sarin in the Tokyo subway is the largest documented exposure of a civilian population to a nerve gas. Approximately 95% of the victims who were admitted to hospitals and diagnosed as moderately or severely intoxicated were treated intravenously with atropine to block the muscarinic receptors and pralidoxime to reactivate OP-inhibited AChE; diazepam was used as needed to control the convulsions (Okumura et al., 1996). Extended follow-up studies of six months to ten years reported an increased incidence of post-traumatic stress disorder (Ohtani et al., 2004) and chronic memory decline (Hood, 2001, Nishiwaki et al., 2001) among victims of the sarin attack, suggesting that the approved treatments of OP poisoning did not effectively prevent the delayed development of neurological disorders.
Studies from multiple laboratories have successfully identified neurobehavioral deficits in rats, guinea pigs, and non-human primates following a single exposure to nerve agents. For instance, following low-level inhalation exposure to sarin, rats showed significant impairment in spatial discrimination in the Y-Maze (Kassa et al., 2002). In that study the levels of sarin were sufficiently low to trigger no or only mild signs of cholinergic hyperstimulation. Other studies reported that rats and mice that developed severe signs of acute toxicity, including convulsions, following a single subcutaneous (sc) exposure to 1–1.2xLD50 soman presented acute and delayed cognitive impairments in the Morris water maze (MWM) (Filliat et al., 1999, Filliat et al., 2007, Raveh et al., 2002). Of particular interest is a report that in asymptomatic, soman-challenged mice cognitive deficits could be detected at three months, but not one month following the challenge (Filliat et al., 2007).
Reports that the intensity and duration of convulsions in rodents exposed to soman correlate with the magnitude of neuropathology scores and behavioral deficits (McDonough and Shih, 1997, Raveh et al., 2002) suggested that early management of soman-induced convulsions would be sufficient to reduce the neuropathology and the accompanying cognitive impairments. However, neurodegeneration and the resulting cognitive deficits observed in soman-intoxicated rodents can be significantly reduced by therapeutic interventions that, although unable to control the seizures, effectively decrease glutamate excitotoxicity (Filliat et al., 1999). Identifying an antidote capable of counteracting the delayed neurotoxic effects of an exposure to nerve agents is crucial for management of a population exposed to these agents either during military operations or in the event of a terrorist attack.
It is well accepted that guinea pigs are the best non-primate model for predicting the effectiveness of antidotal therapies for OP poisoning in humans (Maxwell et al., 1987). We have demonstrated that galantamine, a drug approved for treatment of Alzheimer's disease (Corey-Bloom, 2003), effectively counteracts the lethality and the acute toxicity of OPs in guinea pigs (Albuquerque et al., 2006). Functional analyses of synaptic transmission and plasticity, histological evaluation of neuronal viability, and magnetic resonance imaging (MRI) analysis of the structural integrity of the brains of nerve agent-challenged guinea pigs subjected to different treatments provided additional evidence that galantamine is an effective and safe antidote against the acute toxicity induced by OPs (Alexandrova et al., 2010, Alkondon et al., 2009, Gullapalli et al., 2010).
The present study was designed to test the hypothesis that a single exposure of guinea pigs to soman triggers cognitive deficits that can be prevented by galantamine. To test this hypothesis, guinea pigs were tested in the MWM at four days or three months after their challenge with 1xLD50 soman and/or treatment with galantamine. Earlier studies have reported that AChE activity is quickly inhibited in guinea pigs injected with 1xLD50 soman (Lintern et al., 1998, Shih et al., 2005). Recovery of the enzyme activity is very slow, and seven days following the soman challenge AChE activity remains significantly inhibited in some brain regions of guinea pigs (Lintern et al., 1998). Thus, studying the guinea pigs four days and three months after the initial soman challenge is essential to delineate the contribution of AChE inhibition to behavioral deficits induced by the nerve agent. The MWM, which was originally developed to assess spatial learning in rats (Morris et al., 1986), has proven to be a valuable task to assess spatial behavior, learning, and memory processes in guinea pigs (Byrnes et al., 2004, de Groot et al., 2001, Dringenberg et al., 2001, Filliat et al., 2002, Lewejohann et al., 2010). The results presented here strongly support the hypothesis and demonstrate that galantamine is a highly effective medical countermeasure to prevent the delayed learning impairment that develops as a result of an acute exposure to soman.
Section snippets
Animal care and treatments
Female Hartley guinea pigs [Crl(HA)Br; Charles River Laboratories, Wilmington, MA] were housed in groups of four in stainless steel cages (60 × 60 × 25 cm) in a climate controlled animal-care facility (21 ± 0.5 °C; 12-h light/dark cycle). Animals were 30–33 days old on arrival, and were acclimated for at least 48 h before any treatment. Food and water were available ad libitum. All investigators complied with the regulations and standards of the Animal Welfare Act and adhered to the principles of the
Acute signs of intoxication presented by guinea pigs challenged with 1xLD50 soman
The modified Racine scale described in Aracava et al. (2009) was used to define qualitatively the severity of the acute signs of intoxication presented by guinea pigs that were challenged with 1xLD50 soman (26.5 μg/kg, sc). Animals in stage 0–1, 2–3, and 4–5 (see Table 1) were considered mildly, moderately, and severely intoxicated, respectively. In animals that reached stages 0–3, signs of acute intoxication were not life-threatening and subsided within a few hours after the soman challenge. In
Discussion
The present study demonstrates that guinea pigs considered mildly to moderately intoxicated when challenged with 1xLD50 soman present learning impairment in the MWM task three months after the challenge, despite the fact that neurodegeneration is detectable as early as 48 h following the challenge. Evidence is also provided that pre-treatment with a clinically relevant dose of galantamine effectively counteracts the soman-induced neurodegeneration and cognitive deficits. Mechanisms that
Conflict of interest statement
The authors declare that there are no conflicts of interest.
The use of galantamine as an antidote against OP poisoning is protected under the International Patent Application PCT/US05/33789 filed on September 23, 2005.
The opinions or assertions contained herein are the private views of the authors and are not to be construed as reflecting the view of the National Institutes of Neurological Disorders and Stroke, the Department of the Army, the Department of Defense, or the federal government.
Acknowledgments
This work was funded by the National Institutes of Health CounterACT Program through the National Institute of Neurological Disorders and Stroke [Grant UO1NS059344].The authors would like to thank Dr. Yasco Aracava for her help with treating and caring for the animals. The authors are also indebted to Ms. Mabel Zelle for her technical assistance. Finally, the authors are deeply indebted to Dr. Anil Jaiswal, Professor in the Department of Pharmacology and Experimental Therapeutics of the
References (59)
- et al.
The synthetic cannabinoid WIN 55212-2 differentially modulates thigmotaxis but not spatial learning in adolescent and adult animals
Neurosci Lett
(2011) - et al.
Multiple actions of anticholinesterase agents on chemosensitive synapses: molecular basis for prophylaxis and treatment of organophosphate poisoning
Fundam Appl Toxicol
(1985) - et al.
Spatial acquisition in the Morris water maze and hippocampal long-term potentiation in the adult guinea pig following brain growth spurt–prenatal ethanol exposure
Neurotoxicol Teratol
(2004) - et al.
Thalamic and hippocampal mechanisms in spatial navigation: a dissociation between brain mechanisms for learning how versus learning where to navigate
Behav Brain Res
(2006) - et al.
Effects of medial and lateral caudate-putamen lesions on place- and cue-guided behaviors in the water maze: relation to thigmotaxis
Behav Brain Res
(1999) - et al.
Spatial learning in the guinea pig: cued versus non-cued learning, sex differences, and comparison with rats
Behav Brain Res
(2001) - et al.
Long-term behavioral consequences of soman poisoning in mice
Neurotoxicology
(2007) - et al.
Magnetic resonance imaging reveals that galantamine prevents structural brain damage induced by an acute exposure of guinea pigs to soman
Neurotoxicology
(2010) - et al.
Glutamate receptor pathology is present in the hippocampus following repeated sub-lethal soman exposure in the absence of spatial memory deficits
Neurotoxicology
(2008) - et al.
Spatial orientation strategies in Morris-type virtual water task for humans
Behav Brain Res
(2005)
Binding of some organophosphorus compounds at adenosine receptors in guinea pig brain membranes
Neurosci Lett
An acute exposure to a sub-lethal dose of soman triggers anxiety-related behavior in guinea pigs: interactions with acute restraint
Neurotoxicology
The effect of carboxylesterase inhibition on interspecies differences in soman toxicity
Toxicol Lett
Parallel information processing in the water maze: evidence for independent memory systems involving dorsal striatum and hippocampus
Behav Neural Biol
Neuropharmacological mechanisms of nerve agent-induced seizure and neuropathology
Neurosci Biobehav Rev
Report on 640 victims of the Tokyo subway sarin attack
Ann Emerg Med
Caramiphen and scopolamine prevent soman-induced brain damage and cognitive dysfunction
Neurotoxicology
Fluoro-Jade B: a high affinity fluorescent marker for the localization of neuronal degeneration
Brain Res
In vivo cholinesterase inhibitory specificity of organophosphorus nerve agents
Chem Biol Interact
Putative M2 muscarinic receptors of rat heart have high affinity for organophosphorus anticholinesterases
Toxicol Appl Pharmacol
Thigmotaxis as an index of anxiety in mice. Influence of dopaminergic transmissions
Behav Brain Res
A long-acting cholinesterase inhibitor reverses spatial memory deficits in mice
Pharmacol Biochem Behav
Thigmotaxis as a test for anxiolytic activity in rats
Pharmacol Biochem Behav
Cognitive evaluation of disease-modifying efficacy of galantamine and memantine in the APP23 model
Eur. Neuropsychopharmacol
Nicotinic modulation in an animal model of a form of associative learning impaired in Alzheimer's disease
Behav Brain Res
Effective countermeasure against poisoning by organophosphorus insecticides and nerve agents
Proc Natl Acad Sci USA
Mammalian nicotinic acetylcholine receptors: from structure to function
Physiol Rev
Pretreatment of guinea pigs with galantamine prevents immediate and delayed effects of soman on inhibitory synaptic transmission in the hippocampus
J Pharmacol Exp Ther
A single in vivo application of cholinesterase inhibitors has neuron type-specific effects on nicotinic receptor activity in guinea pig hippocampus
J Pharmacol Exp Ther
Cited by (17)
Letrozole delays acquisition of water maze task in female BALB/c mice: Possible involvement of anxiety
2024, Hormones and BehaviorAcetylcholinesterase inhibitors (nerve agents) as weapons of mass destruction: History, mechanisms of action, and medical countermeasures
2020, NeuropharmacologyCitation Excerpt :This could be done by enzymes that hydrolyze nerve agents (catalytic bioscavengers), or specific proteins including antibodies that bind to the agents preventing them from binding to AChE (stoichiometric bioscavengers). Such bioscavengers are currently under intense investigation (Lenz et al., 2007; Nachon et al., 2013; Worek et al., 2016a; Goldsmith and Ashani, 2018; Lushchekina et al., 2018; Pope and Brimijoin, 2018; Zhang et al., 2019). The standard antidotal treatment for acute nerve agent exposure consists of atropine and an oxime.
Prophylactic and therapeutic measures in nerve agents poisonings
2020, Handbook of Toxicology of Chemical Warfare AgentsIn vitro pharmacological characterization of the bispyridinium non-oxime compound MB327 and its 2- and 3-regioisomers
2018, Toxicology LettersCitation Excerpt :They play important functional roles in cholinergic neurotransmission in both the peripheral (PNS) and central nervous system (CNS) and are implicated in different CNS disorders, e.g. Alzheimer’s and Parkinson’s disease, schizophrenia, depression, tobacco addiction, and PNS disorders, e.g. congenital myasthenic syndrome, myasthenia gravis (Gotti and Clementi, 2004; Melzer et al., 2016). Consequently, drugs that modulate nAChR functions are becoming increasingly important (Hogg and Bertrand, 2004; Gündisch, 2005; D’Hoedt and Bertrand, 2009; Hurst et al., 2013), especially for the treatment of intoxications, e.g. by organophosphorus compounds (OPCs) (Mamczarz et al., 2011). Conventional nAChR antagonists are not appropriate, because of their low therapeutic index between sufficient antagonism and muscle paralysis (Sheridan et al., 2005).
Plant-Derived Alkaloids: A Promising Window for Neuroprotective Drug Discovery
2018, Discovery and Development of Neuroprotective Agents from Natural Products: Natural Product Drug Discovery