Ultrasound-Activated Therapeutic Gas Microbubbles for Treatment of Traumatic Brain Injury - Mild traumatic brain injury (TBI) is a serious health problem, accounting for over 80% of reported cases. Military, law enforcement personnel, veterans, and civilians in combat zones and situations like aggressive crowd control, experience injury via low level blasts repeatedly as part of routine training and field use of heavy weaponry, breaching, and flash-bang stun grenades. This often leads to chronic conditions like PTSD, depression, anxiety, and memory loss. Our work with rodents shows repetitive blasts cause chronic neurodegeneration and gliosis, which affect long-term behavioral outcomes. Despite extensive research in this field, there have been no clinically approved drugs to directly treat TBI. In recent years, noble gases like xenon (Xe) and argon (Ar) have been shown highly promising cytoprotective properties when inhaled to treat different forms of brain injury. Xe is known to be highly effective, while Ar is a hundred times cheaper and more widely available, while still maintaining excellent cytoprotective efficacy. Xe action depends on its interaction with glutamate receptors (NMDA, AMPA) on cell membranes, while Ar is thought to stimulate various endogenous cellular protection signaling pathways, independent of glutamate receptor binding. Importantly, both Xe and Ar can freely diffuse through the blood brain barrier (BBB), overcoming a major hurdle for current TBI candidate drugs. However, current Xe and Ar therapy is systemic making it non-targeted and in the case of xenon, often prohibitively expensive. Here, we propose the utilization of microbubbles (MBs) requiring orders of magnitude lower gas amount for localized delivery of Xe and Ar gas to treat repetitive low-level blast (rLLB) induced injury. The central hypothesis is that XeMB and ArMB will individually and synergistically reduce neurodegeneration, protect the cerebral vasculature, and improve behavioral and cognitive outcomes following rLLB. MBs can be injected via a simple IV line, then visualized and ruptured non-invasively via any portable ultrasound transducer (which can be connected to a phone or tablet) near carotid arteries. The locally released gas freely diffuses through the BBB and reduces secondary injury progression. The PI (Rajarshi Chattaraj) has previously developed noble gas MBs to successfully treat blunt TBI in a porcine model of controlled cortical impact. The Co-I (Bryan Pfister) has years of experience working with blast models of TBI in rodents using an in-house shock-tube setup. Our objective is to show that localized delivery of Xe and Ar can treat rLLB-induced TBI for the first time. This work has the following specific aims: 1) Establish a framework for behavioral and histological outcomes and tolerance towards MBs in male and female mice exposed to rLLB injury. 2) Test that Xe and Ar MBs alone or in combination after TBI will provide short and long- term preservation of neurological function. 3) Show combinatorial effects of Xe+Ar inhalation for the first time and compare efficacy to MB treatment. Cognitive and motor functions, and histological outcomes will be correlated at 1-3 (acute) and 30-33 (chronic) days post injury. This work will validate a novel, BBB-permeabilizing (Xe and Ar) local delivery agent (MBs) without adverse effects for image-guided treatment of repetitive blast TBI.
