Tobacco Smoke Chemicals and Stroke Alter Brain K+ Efflux

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DESCRIPTION (provided by applicant): In terms of cost to society and disability to patients, stroke ranks with Alzheimer's disease as the two most important neurological disorders. Nicotine, a major constituent of tobacco smoke has been shown to have important effects on neuronal injury and brain edema formation in stroke and hampers brain recovery after stroke. It is known that the blood-brain barrier (BBB), which is formed by the cerebral endothelium, plays a critical role in the regulation of water and electrolyte balance within the central nervous system (CNS). Exciting preliminary data in our laboratory suggests that nicotine down regulates the BBB expression and function of a key ion transporter, Na, K,2Cl-cotransporter, which normally mediates brain-to-blood removal of potassium ions during in vitro stroke conditions. With respect to brain ischemia, maintenance of low brain extracellular potassium concentration is necessary for proper neuronal conduction and recovery after stroke. In vitro and in vivo investigations into smoke constituent alteration of BBB properties is critically important and is the focus of this research application. The objective of this application is to systematically test the effects of nicotine and smoke constituents on BBB potassium transport during stroke conditions and determine the physiological role of nAChRs on BBB ion transport. The central hypothesis of our work is that nicotine decreases brain-to-blood potassium transport through nicotinic acetylcholine receptor (nAChR) activation at the blood-brain barrier that impairs ion transport necessary for stroke adaption. We plan to utilize sophisticated, well characterized in vivo models designed to mimic nicotine and tobacco smoke constituent exposure coupled to validated models of stroke. This focused research plan will identify possible therapeutic targets at the blood-brain barrier to prevent brain edema and altered CNS potassium homeostasis during nicotine or smoke constituent exposure coupled to stroke conditions. We hope that new stroke treatments will utilize a combination of agents that modulate multiple processes (both BBB breakdown and ischemic neuronal death) providing the most efficacious treatment of stroke for both smoking and non-smoking patients. This research plan will also identify key biochemical and molecular mechanisms involved in nicotine and other tobacco smoke constituent alteration in BBB function during stroke so that individualized stroke therapies could be designed to improve health outcomes for smokers.