Cerebrovascular Research Programs: Yuchuan Ding, MD, PhD
Neuroprotection & Mechanism of Ethanol Therapy: New Prospects for an Ancient Drug
Balanced energy metabolism of neural cells and associated mitochondrial functions are critically important for neural survival. Ischemia/reperfusion injury in acute stroke disrupts energy balance by impairing the metabolic state of neural cells and by interrupting mitochondrial activity. In addition, reactive oxygen species (ROS) generated by the mitochondria and in the cytosol trigger cell death cascades. Previous studies have demonstrated that ethanol significantly and consistently decreased whole-brain metabolism, raising the possibility that ethanol could be used to ameliorate metabolic dysfunction in stroke and serve as a clinical neuroprotectant. Our goal is to establish a safe, inexpensive, easy-to-use, and powerful therapeutic strategy by testing the hypothesis that ethanol reduces cerebral ROS generation and cell death in ischemia/reperfusion injury after stroke by slowing down and thus normalizing glycolytic and oxidative metabolism.
Our current studies investigate 1) whether ethanol exerts its neuroprotective effect by suppressing brain energy metabolism, decreasing hyperglycolysis via inhibition of glucose transporter activity, and inhibiting nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) through reduction of NOX complex formation and glycolysis-produced NADPH; and 2) whether ethanol prevents ROS generation and cell death by ameliorating oxidative phosphorylation via inhibition of a key mitochondrial enzyme, cytochrome c oxidase (CcO); and 3) to test the translational potential of ethanol therapy in a more clinically relevant stroke model with a prolonged ischemic period.
Investigation of ethanol therapy on neural metabolism and mitochondrial function in stroke is fundamental for establishing its clinical potential as a new neuroprotective strategy for this devastating disease. This work incorporates a highly innovative approach, validating an ancient, approved drug for a new therapeutic application and proposing new mechanisms for its effect on brain metabolism. Our study will enable preclinical and clinical investigations of ethanol therapy for acute ischemic stroke.
Ischemic Area Infusion and Regional Hypothermia: A Potential Therapy in Stroke
Clinically, there are no effective therapeutic tools for amelioration of cerebral ischemia/reperfusion caused by stroke. It has been emphasized that ischemia/reperfusion injury is initiated by a series of events occurring at the blood-vascular-parenchymal interface, leading to inflammatory injury, disruption of endothelial integrity, and neuron death. Brain cooling is a remarkable neuroprotectant in stroke therapy if applied soon after onset of ischemia. Due to management difficulties, hypothermic induction by surface cooling in current clinical settings is vastly limited.
Results from our recent studies indicate that highly localized intra-arterial "flushing" of the ischemic territory prior to reperfusion significantly reduces brain injury in experimental stroke. The mechanisms of neuroprotection conferred by hypothermia or vascular infusion are thought to be multifunctional. This leads to a new hypothesis that local intra-arterial cold hypertonic solution infusion, concurrent with regional cerebral hypothermia in ischemic areas prior to reperfusion, synergistically minimizes brain injury. This may provide the ultimate neuroprotective "cocktail" that limits inflammation and neurovascular disruption during reperfusion. In our laboratory, we define the therapeutic and systematic optimization of a combined infusion and cooling procedure in our stroke model by evaluating long-term motor deficits, brain infarct volume, as well as cerebral and pulmonary edema. We also elucidate protective mechanisms of the novel model that targets the brains vascular-parenchymal interface by reducing inflammatory mediators, endothelial activation of nuclear factor kappa-B, leukocyte infiltration, matrix metalloproteinase expression, and blood-brain barrier disruption.
Results from these studies will provide fundamental information on the establishment of a novel therapeutic procedure in stroke beyond the levels achieved by current therapy. Intravascular cold infusion into the ischemic region, which combines recanalization of the occluded middle cerebral artery (mechanically or thrombolytically) and administration of neuroprotective drugs, may improve outcome in stroke patients.
Exercise-Induced Endogenous Neuroprotection in Stroke
There is increasing evidence from us and other investigators that exercise produces endogenous protection in the brain after transient ischemia. Our goal is to establish an endogenous neuroprotective concept of exercise preconditioning in stroke and identify the cellular and molecular mechanisms by which exercise induces neuroprotection. We elucidate TNF and HSP signaling pathways that mediate differential endothelial activation and downstream inflammatory, neurovascular integrity and apoptotic events. The proposed strategy of exercised-induced endogenous neuroprotection can be translated to other therapeutic approaches, such as pharmacology. This strategy will allow the development of combined approaches to inhibit and stimulate appropriate targets simultaneously, thus reaching the highest therapeutic potential.
Traumatic Brain Injury (TBI)
Memory storage and learning have been found to be associated with synaptic plasticity. During acute closed head injury and its aftermath, rapid acceleration and deceleration of the head causes diffuse axonal injury in the entire brain, leading to severe synapse loss and damage. Recent work suggests that brain extracellular matrix (ECM) proteins and their regulatory matrix metalloproteinases (MMPs) such as MMP-2 and MMP-9, play a role in synaptic plasticity. Our study assessed the role of MMP-2 and -9 in synaptic damage after TBI and the role of hypoxia inducible factor-1α (HIF-1α), a transcription factor upregulated during hypoxia, in the regulation of MMP-2 and -9 expression post TBI.
TBI causes vasogenic brain edema, where the extracellular space is expanded by fluids from abnormally permeabilized blood vessels. The detrimental effect of AQPs in brain edema has been reported. AQPs, such as AQP4 and 9, can cause either cytotoxic or vasogenic edema in TBI. HIF-1α is a key component of the cellular response to pathophysiologic conditions and can be harmful in cerebral ischemia. Our study determines the role of HIF-1α in regulating expression of AQP-4 and -9 and associated brain edema after close head TBI.