Authors :
Presenting Author: Sirisha Parameswaran, DVM – Iowa State University
Nyzil Massey, DVM, PhD – Iowa State University
Suraj Sundara Vasanthi, DVM – Iowa State University
Christina Meyer, MS – Iowa State University
Nikhil S Rao, DVM, PhD – Iowa State University
Sridhar S. Kannurpatti, PhD – New Jersey Medical School
Thimmasettappa Thippeswamy, DVM, PhD – Iowa State University
Rationale:
Acute exposure to organophosphate nerve agents (OPNAs) like VX irreversibly inhibits acetylcholinesterase (AChE), leading to a cholinergic crisis and potentially triggering status epilepticus (SE). While the short-term effects of VX have been studied, its long-term neurological consequences remain poorly understood. Previously, iNOS upregulation has been implicated in epileptogenesis in soman-exposed rats, and 1400W (a selective iNOS inhibitor) has been shown to reduce gliosis, nitrooxidative stress, and proinflammatory cytokines (PMID: 37438764). In this study, we evaluated the long-term neuroprotective effects of 1400W as a potential disease-modifying strategy in a rat model of acute VX exposure.
Methods:
Sprague Dawley rats (7–8-week, mixed sex) were exposed to VX (12µg/kg, s.c.), co-administered with atropine sulphate (2mg/kg, i.m.) and HI-6 (125mg/kg, i.m.) to counteract peripheral cholinergic effects. Seizures were monitored 1-hour post-exposure for assessing SE severity followed by midazolam (3 mg/kg, i.m.) administration. Animals with comparable SE were randomly distributed into three groups: VX+Vehicle, VX+1400W (20mg/kg, i.m., for two weeks) along with a control group (no VX or 1400W). Neurobehavioral testing and MRI were conducted between weeks 5-10. From weeks 10-18, animals were monitored for continuous video-EEG via the implanted telemetry device. The brain, serum, and CSF were collected after euthanasia. Brain tissues were processed for histological assessment (neuroinflammation and neurodegeneration), blood and CSF samples for cytokines and inflammatory markers. Data analyses were carried out with appropriate statistical tests.
Results:
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VX exposure caused SE severity (< 12 minutes) and 21.8% mortality.
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No significant deficits were observed in cognitive, motor or fear extinction behavior at 5-7 weeks post-exposure.
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Functional MRI revealed a significant reduction in resting-state functional connectivity in the thalamus and amygdala in VX exposed animals.
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video-EEG monitoring (weeks 10–18) identified frequent non-convulsive and convulsive seizures in VX-exposed rats, which was significantly attenuated by 1400W.
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VX exposure induced a significant upregulation in reactive oxygen species in the serum.
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Immunohistochemistry revealed increased astrocytes in VX-exposed groups, which was mitigated by 1400W treatment.
Conclusions:
VX exposure caused mild symptoms with 21.8% mortality and induced significant neuropathological changes and reduced the thalamic and amygdalar connectivity and seizures frequency that were partially mitigated by 1400W. Despite these changes, no behavioural deficits were observed, perhaps due to the initial mild symptoms. Biochemical and histological analyses revealed increased oxidative stress and gliosis in VX-exposed animals, which were also attenuated by 1400W. These findings highlight that VX induces latent neurotoxicity in long-term, and 1400W can mitigate VX-induced brain pathology.
Funding:
NIH/NINDS (U01 NS117284-01, CounterACT program)