Denis Bragin - US grants

SUMMARY Traumatic brain injury (TBI) is a major public health problem in the U.S. which causes 30% of all injury related deaths and 7% long-term functional disabilities in survivors. Currently, 5.3 million Americans are living with permanent functional disabilities resulting from TBI with an estimated lifetime care cost of $4 million per person. New, effective treatments for TBI, especially for the late or recovery phase are urgently needed. Transcranial direct current stimulation (tDCS) has emerged as a promising therapeutic approach, and has recently been investigated as a clinical intervention for TBI. However, due to a lack of controlled animal studies, there are many important questions that need to be addressed to determine the utility of tDCS in TBI, and to refine the intervention to optimize long-term outcomes. These questions include the time windows for intervention and stimulus polarity for application. It is also unknown whether tDCS stimulates endogenous recovery and repair mechanisms that could in future studies be targeted to further enhance the effectiveness of tDCS in TBI survivors. The work in this proposal will address these key unanswered questions, to provide a basis for evaluation and future development of clinical interventions. Our central hypothesis is that tDCS applied in the recovery phase after TBI improves long-term neurologic recovery and is associated with increased migration of endogenous neuronal stem cells (NSC) to peri-infarct regions, and sustained increases in cerebral blood flow (CBF). A mouse controlled cortical impact model of TBI will be used, and repetitive tDCS treatment applied at one and three weeks after TBI. Specific Aim 1 will use a battery of advanced neurobehavioral tests for evaluation stimulus parameters and polarity and intervention time to the effects of tDCS on longitudinal improvement of neurological outcome. Specific Aim 2 will use a genetic labeling approach to assess the effects of tDCS on the migration tracking and long term phenotypic fate mapping of endogenous neural stem cells and their progeny. Specific Aim 3 will use optical imaging techniques to assess effects of tDCS on regional and microvascular cerebral circulation. Together, these studies will provide a valuable basis for improved understanding of the effects of tDCS in recovering brain, and for future refinement clinical applications.

? DESCRIPTION (provided by applicant): Ischemic stroke is a third cause of death in the US with the only FDA-approved therapy, thrombolysis by tissue plasminogen activator (tPA). Due to the high risk of fatal hemorrhages, tPA is not advised later than 3 hrs after stroke onset resultin in only 5% of patients being treated. Thus, there is a need for new interventions for the remaining 95% of patients. We propose a novel approach for stroke treatment applicable at both, early and later time after stroke onset using modulation of the hemodynamic by blood soluble drag reducing polymers (DRPs) which enhance collateral flow. Nanomolar concentrations of intravenous DRPs reduce pressure loss in arteries and arterioles by diminishing flow separations at vessel branch points and, thus, increasing precapillary pressure, which in turn increases the density of functioning capillaries. DRPs are shown to improve hemodynamics and survival in animal models of ischemic myocardium and limb but have not been tested in the brain circulation. Recently, we demonstrated that DRPs increased near-vessel-wall flow velocity in arterioles, restored perfusion in collapsed capillaries, enhanced collateral flow and reduced tissue hypoxia in the ischemic and traumatized rat brain. Since DRPs have systemic physical effects on blood circulation we formulated our central hypothesis: DRPs, through their general action on cerebrovascular circulation, can present a unique and effective therapy for stroke, applicable at both, early and later time, when tPA treatment is prohibited. The objective of this particular application is to test whether DRPs (high MW polyethylene oxide), applied within or beyond the tPA treatment window, can restore cerebral perfusion through collateral flow, reduce hypoxia, facilitate long-term protection from ischemia-induced brain damage and improve functional recovery in a rat model of permanent middle cerebral artery occlusion (pMCAO). The rationale is that demonstration of the efficacy of DRPs in the stroke treatment will provide the basis for the development of a powerful approach that can be used even beyond the tPA treatment window. The ultimate long-term goal is to develop a novel approach for the stroke treatment. To achieve this goal, a rat model of pMCAO with the application of DRPs at 0.5, 3 and 6 hours after stroke onset will be utilized. We will use various optical imaging techniques for in-vivo evaluation of the acute effects of DRPs on cerebral circulation and tissue hypoxia (SA #1), and magnetic resonance imaging, histochemistry and behavioral studies for evaluation of prolonged attenuation of ischemic injury and improving neurological outcome (SA #2). Each aim will independently provide important new information to the field, and then taken together, these mechanistic studies will provide the basis for a novel general approach for the treatment of stroke. The development and use of this approach based on modulation of hemodynamics is innovative and the proposed research is significant since it will provide the proof of the treatment of the ischemic stroke by DRPs, applicable even to the untreatable stage by currently available methods in late or even recovery phases of the ischemic stroke.

Abstract Traumatic brain injury (TBI) is a major health problem, representing a third of all injury-related deaths in the United States and 70% of long-term disabilities in survivors. Decades of TBI research focused almost exclusively on neuroprotective strategies, has failed to develop any therapeutics for clinical treatment. One less explored potential target is the cerebral circulation. In TBI, there is increasing recognition that the peri-contusional areas of TBI suffer microvascular failure and diffusional hypoxia and edema. Our studies on microvascular shunts (MVS) with high intracranial pressure (ICP) corroborate microcirculatory failure. We propose here modulation of hemodynamics with blood soluble drag reducing polymers (DRP) as a novel treatment modality for TBI that specifically targets cerebral microcirculation and that based on physical but not pharmacological principles. Nanomolar amounts of intravenous DRP reduce blood pressure loss in arterioles by diminishing flow separations and microvortices at vessel bifurcations, increase precapillary pressure and the density of functioning capillaries. Increased vascular wall shear rate may reduce transcapillary macrophage migration and inflammation. We showed that 140 µg/kg of intravenous DRP (ED70) increased blood flow velocity in cerebral arterioles, reduced MVS, restored perfusion in capillaries and reduced tissue hypoxia in a rat model of TBI when i.v. injected 30 minutes after the insult. The next logical step, our objective, is to perform a comprehensive study of the dose and time-related efficacy of DRP and to examine the therapeutic mechanisms involved. Central hypothesis: DRP, through their general dose-dependent action on cerebrovascular microcirculation, can present a unique and effective therapy for TBI, applicable at both, early and later time. The rationale is that unlike other TBI therapies tested thus far, the hemorheological effects of DRP are independent of tissue status in terms of tissue or vascular receptor reactivity or sensitivity for its mechanism of action. Our long-term goal is to optimize the application of DRP after TBI for maximal efficacy on long-term recovery and provide for the first time, a therapeutic intervention that may be effective even if delayed hours after injury. Using the lateral fluid percussion injury TBI model in rats, we will address two aims: 1) to study the acute dose-dependent effects of DRP on the time course and relative changes in cerebral microvascular flow, i.e. MVS, tissue oxygenation and metabolism using in-vivo 2-photon laser microscopy and laser speckle imaging after moderate and severe TBI; and 2) to define the optimal dose and therapeutic time window of DRP for clinically relevant long-term outcomes and mechanisms involved using magnetic resonance imaging, behavioral testing and histology, possible anti-inflammatory effects of rheological modulation will be evaluated by ELISA and immunohistochemistry. To comply with NIH requirement, studies will be done on both sexes to evaluate possible female/male differences. The proposed research is significant since it will provide the first non-pharmacologic rheological treatment for TBI targeting impaired cerebral microcirculation and will reveal the blood flow-related pathogenesis and recovery mechanisms in TBI.