Neuroprotectant Activity of Novel Water-Soluble Synthetic Neurosteroids on Organophosphate Intoxication and Status Epilepticus-Induced Long-Term Neurological Dysfunction, Neurodegeneration, and Neuroinflammation

Protective Activity of Novel Hydrophilic Synthetic Neurosteroids on Organophosphate Status Epilepticus-induced Chronic Epileptic Seizures, Non-Convulsive Discharges, High-Frequency Oscillations, and Electrographic Ictal Biomarkers

Nerve agents and organophosphates (OP) are neurotoxic chemicals that induce acute seizures, status epilepticus (SE), and mortality. Long-term neurologic and neurodegenerative effects manifest months to years after OP exposure. Current benzodiazepine anticonvulsants are ineffective in preventing such long-term neurobehavioral and neuropathological changes. New and effective anticonvulsants are needed for OP intoxication, especially for mitigating the long-term sequelae after acute exposure. We developed neurosteroids as novel anticonvulsants and neuroprotectants in OP exposure models. In this study, we evaluated the long-term efficacy of novel synthetic neurosteroids in preventing the development of chronic epilepsy and hyperexcitable ictal events in a rat OP model of SE. Rats were exposed to the OP nerve agent surrogate diisopropylfluorophosphate (DFP), and the experimental groups were treated with the synthetic neurosteroid valaxanolone (VX) or lysaxanolone (LX) 40 minutes post-exposure in conjunction with midazolam. Video-electroencephalography was monitored for two months to assess spontaneous recurrent seizures (SRS), epileptiform discharges, interictal spikes, and high-frequency oscillations (HFOs). Within 60 days of DFP exposure, rats developed chronic epilepsy characterized by frequent SRS, epileptiform discharges, and HFOs. LX treatment was associated with a dose-dependent reduction of epilepsy occurrence and overall seizure burden with a significant decrease in SRS and epileptiform discharges. It also significantly reduced the occurrence of epileptic biomarkers of HFOs and interictal spikes, indicating potential disease-modifying activity. Similarly, the neurosteroid analog VX also significantly attenuated SRS, discharges, HFOs, and ictal events. These results demonstrate the long-term protective effects of synthetic neurosteroids in the OP-exposed post-SE model, indicating their disease-modifying potential to prevent epilepsy and ictal abnormalities. SIGNIFICANCE STATEMENT: The effects of nerve agents and organophosphate (OP) exposure are persistent, and survivors suffer from a number of devastating, chronic neurological dysfunctions. Currently, there is no specific therapy for preventing this disastrous impact of OP exposure. We propose synthetic neurosteroids that activate tonic inhibition provide viable options for preventing the long-term neurological effects of OP intoxication. The results from this study reveal the disease-modifying potential of two novel synthetic neurosteroids in preventing epileptogenesis and chronic epileptic seizures after OP-induced SE.

Progress and Challenges in Developing Medical Countermeasures for Chemical, Biological, Radiological, and Nuclear Threat Agents

This Commentary delves into the current progress and challenges on ongoing research on medical countermeasures (MCs) for chemical, biologic, radiologic, and nuclear (CBRN) threats. CBRN agents pose a serious risk to human health and safety, with the potential for mass casualties in both military and civilian settings. Chemical threats are toxic compounds that could be used in a terrorist attack, an accidental release, or chemical warfare. They include nerve agents, organophosphates, pulmonary agents, metabolic/cellular agents, vesicants, ocular toxicants, and opioid agents. Developing effective MCs is crucial for mitigating the acute and chronic effects of exposure to CBRN agents. The papers in this special issue of JPET highlights the latest advancements in MC research, showcasing insightful outcomes on experimental models, mechanisms, and translational research on MCs for CBRN threats. They portray several notable contributions, including the development of neurosteroid and combination anticonvulsant therapies for nerve agent poisoning, the exploration of chronic impacts and diagnostic tracers for OP neurotoxicity, the establishment of innovative pediatric OP models, the identification of novel molecules for ocular, pulmonary and vesicant injuries, and the repurposing of existing drugs for the treatment of botulism, cyanide, and OP poisoning. These crucial outcomes underscore the breadth of current research covering a variety of chemical threats. Overall, this collection of articles highlights the importance of ongoing research and development in the field of MCs, emphasizing the potential of these countermeasures to effectively treat and mitigate the effects of toxicant exposures and thereby enhance our preparedness for mass casualty incidents. SIGNIFICANCE STATEMENT: CBRN agents pose a significant threat to public health. Effective MCs exist for certain chemical threats, but there is a need for new and improved MCs for many others. The research presented in this special issue of JPET highlights the latest advancements in MCs for CBRN threats. This research has the potential to lead to the development of new and repurposed MCs that are more effective, broad-spectrum, and easier to administer to mitigate acute and long-term consequences of chemical exposures.