Neurosteroid Therapy for Gulf War Illness
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Background: Gulf War Illness (GWI) is a chronic multi-symptom illness affecting the brain and other systems. Almost 40% of 700,000 troops deployed to the Persian Gulf War are diagnosed with GWI. Cognitive and mood impairments are among the primary neurological symptoms in GWI Veterans. Epidemiological and animal investigations suggest that GWI in a significant fraction of Veterans is linked to a combination of chemical exposures encountered by Service personnel during the Gulf War. The chemicals included pyridostigmine bromide (PB), N,Ndiethyl-m-toluamide (DEET), and permethrin (PM). While PB pills were consumed daily for variable periods of time as a prophylactic agent against possible nerve gas agent attacks during the war, exposures to DEET (a mosquito repellant) and PM (an insecticide) have occurred because of their extensive use on the skin and/or uniforms with the intension of offsetting infectious diseases transmitted by insects and ticks in the desert region. However, there is currently no effective therapy for GWI Veterans, who continue to suffer still to date with debilitating illness. Objectives and Hypothesis: This project is designed to test the delayed (10 and 15 months after GWI) therapeutic efficacy of neurosteroid therapy in the rat model of chronic GWI using magnetic resonance imaging (MRI) and behavioral techniques. The proposed delayed therapy (15 months = human 35 years) falls beyond 25 years that many GWI Veterans have had GWI. Since GWI is purportedly caused by exposure to low-level sarin and other chemicals, tonic inhibition-promoting neurosteroids are proposed as effective treatment because they have been shown to be highly efficacious against acute and chronic neurotoxicity caused by nerve agent exposure. This is a logical plan as per the GWI pathophysiology and neurosteroidâ€™s promise as experimental treatment. Our team is poised to lead this project as we have preclinical expertise and experience in GWI models. The central hypothesis is that neurosteroids (Food and Drug Administration [FDA]-approved ganaxolone) that enhance extrasynaptic tonic inhibition and neurogenesis effectively control GWI chemical agent-induced neuronal damage and thereby completely mitigate neurological morbidity. Ganaxolone (GX) and related neurosteroids promote tonic inhibition, mediated by extrasynaptic receptors that play a critical role in controlling anxiety, memory, and hyperexcitability disorders. Cholinergic hyperactivation cause a huge decrease in synaptic GABA-ARs, but do not affect extrasynaptic deltaGABA-ARs (targets for neurosteroids). Neurosteroids also enhance neurogenesis, which is essential for recovery from brain injury. These concepts, as validated earlier in the CounterACT program, suggest the viability of tonic inhibition therapy for GWI. Broad-spectrum profile, safety, and ready availability make ganaxolone a practical drug for GWI.Specific Aims: We will test this hypothesis by addressing three specific aims using young rats (test drug will be given for 2 months at 10 and 15 months after GWI; equivalent to estimated 25 and 35 human years).Aim 1 (Years 1 and 2): To determine the efficacy of ganaxolone against GWI agent-induced brain damage using MRI. Experiments in this section will address two key questions (collaboration with Dr. Sridhar for MRI):(1A) Does GWI chemical exposure cause progressive neuronal abnormalities in GWI model?(1B) Does ganaxolone therapy rescue GWI agent-induced neuronal damage after late/delayed therapy?Aim 2 (Year 1 and 2): To determine the efficacy of GW against GWI agent-induced peripheral, central behavioral and memory deficits. Studies in this section will address two key questions (with Dr. Shetty):(2A) Does GWI chemical exposure cause progressive memory and neurological abnormalities in GWI model?(2B) Does GX therapy control GWI agent-induced peripheral, neurological, and memory deficits?Aim 3 (Year 1 and 2): To determine the efficacy of GX against GWI agent-induced neuropathological changes. Experiments in this section will address two key questions (in collaboration with Dr. Shetty):(3A) Does GWI chemical exposure cause neuronal injury, neuron loss, and neuroinflammation in GWI model?(3B) Does GX therapy prevent GWI-induced neurodegeneration, low neurogenesis, and neuroinflammation?Research Strategy: We will employ standard multidisciplinary strategies to assess test drug therapy using a well-validated rat model of chronic GWI developed by the Shetty lab. Rats will be randomly assigned to sham control or GWI groups (N=20) receiving GWI-related chemicals PB, PM, and DEET. The test drug ganaxolone (10 mg/kg, sc) will be given for 8 weeks as delayed therapy (10 month later) or late therapy (15 months later). Aside from behavior, brain pathology will be measured by MRI scanning at 5, 10, 15, 18, and 20 months post-GWI at the Texas A&M Institute for Preclinical Studies (TIPS) core facility. The drug efficacy is determined as per five primary outcomes: (i) MRI profile, (ii) memory and behavioral protection, (iii) neuroprotection in reducing neuron loss, (iv) reduction in neuroinflammation, and (v) extent of neurogenesis in the brain. MRI is a versatile tool for checking delayed brain pathology (15-20 months).Overall Impact: This innovative project will identify unexplored treatment for GWI, centering on neurosteroids in the brain. Our goal is to identify effective intervention of GWI, focusing on tonic inhibition by synthetic (FDA approvable) neurosteroid ganaxolone. It will allow us to begin validation of MRI as a noninvasive predictive biomarker of behavior and memory decline after GWI. These studies are rapidly translatable to clinical trials with immediate benefit to Veterans with GWI. Thus, the overall impact of this project is enormous for GWI Veterans.