Somatostatin gene delivery to enhance long-term functional recovery from TBI

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The incidence of traumatic brain injury (TBI) is disproportionately high among military personnel. Even mild TBI can have persistent adverse neurobiological effects that can continue to evolve long after the initial injury. Seizures, spasticity, cognitive and affective disorders, sleep problems, and endocrine diseases (diabetes) are prevalent, debilitating, and difficult to treat. Effective long-term rehabilitation will require transformative therapeutic approaches that address the brain processes responsible for the emergence of delayed symptoms. The delayed evolution of these problems post-TBI offers opportunities for prevention and improved long-term outcome. A gene delivery technique we developed produces sustained over-expression of the gene for neuropeptide somatostatin (SST) in discrete brain regions. Intracranial gene delivery using adeno-associated viral (AAV) vectors similar to our SST vector is proving safe and effective in clinical trials for several brain diseases. In the central nervous system SST participates in synaptic inhibition, inflammation, cognition, emotional function, analgesia, and cytoprotection, multiple mechanisms by which it might provide positive benefits against delayed TBI effects. Our SST gene delivery to the hippocampus prevented electrically induced seizures from developing in 70% of rats tested in an established epilepsy model. The next step in translating this approach to clinically useful applications is to test it in more advanced animal models of brain injury. At the same time, determining the safety of this method will be essential for further preclinical development. Efficacy and safety thus comprise 2 specific aims of this Small Project intended to serve as a foundation for translational progress. To test whether efficacy extends to the delayed development of seizures after TBI, we will combine a well-characterized rat model for closed-head TBI with the kindling seizure model in which efficacy was first observed. Anesthetized young adult male rats will be given a controlled brain injury 10 days before receiving intracranial infusion of SST or control gene transfer vectors in hippocampus, and permanently implanted electrodes for electrical stimulation, during a single surgery. A week later a kindling procedure will be initiated composed of timed stimulation twice per day, using intensities sub-threshold for seizure generation. Paired electroencephalograph (EEG) and video recordings obtained during stimulated seizures will be scored blind offline as duplicate measures of severity and duration. Gradually over the following days to weeks mild seizures start and become progressively more severe until reaching a fully kindled state where the stimulation consistently elicits maximally intense seizures in untreated rats. Therapeutic efficacy of hippocampal SST gene delivery will be reflected in reduced seizure severity or duration, delayed progression of seizure severity, or a reduction in the maximal seizure severity that can be consistently evoked. To examine effects of TBI, gene transfer, and kindling on memory performance sensitive to hippocampal injury, a natural tendency of rats to explore alternating arms of a Y-shaped maze on successive trials will be tested repeatedly throughout the study. Cognitive performance will be evaluated on multiple challenge tasks sensitive to learning and memory ability. Natural motor function (activity, rearing, grooming), affective states (anxiety), and circadian physiology (sleep) will be assessed from continuous home cage infrared video. Therapeutic safety will be evaluated from comprehensive behavioral assessments, but also by comprehensive histological analysis of brain pathology as a function of vector treatment. In addition to markers for pathology, we will evaluate the effects of gene transfer in kindled TBI rats on spatial localization patterns of SST receptor proteins. We propose that seizure reduction, and amelioration of progressive cognitive and motor dysfunction post-TBI, will involve multiple efficacy mechanisms that engage several receptor subtypes in specific subregions of the brain. This feasible and innovative Small Project opens new avenues for improving the rehabilitation of Veterans facing decades of debilitating consequences after TBI.