Oxidative Stress Na Channel Gating and Arrhythmias

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DESCRIPTION (provided by applicant): Sudden cardiac death due to ventricular fibrillation (VF) in the setting of myocardial infarction remains a major public health problem. While the seminal mechanistic features of ischemic VF remain obscure, growing evidence implicates an interaction between cardiac sodium (Na) channels and the acutely ischemic myocardium. While a mechanism whereby ischemia might alter Na channel function has not been clearly identified, our preliminary studies form the basis for our hypothesis that oxidative stress plays a causative role. In particular, we have found that highly reactive gamma-ketoaldehydes (isoketals, IsoKs) that are produced as products of the isoprostane pathway of free radical mediated lipid peroxidation induce slow recovery from inactivation of hH1 Na channels expressed in HEK cells and that these effects are mimicked by oxidation of these cells with t-butylperoxide. Preliminary data demonstrates that levels of F2-isoprostanes are increased in the border zone of the canine infarcted heart. Therefore, studies are proposed to determine to what extent IsoKs are overproduced in tissues from the epicardial border zone in canine infarcted hearts. We will also determine whether IsoKs directly adduct the Na channel and detemine, which adducted lysyl residues, mediate the effect of IsoKs, utilizing mutagenesis approaches. We will also explore novel pharmacologic agents to mitigate these effects first in HEK cells expressing hill Na channel. These include (a) lipophilic analogs of pyridoxamine and 2-hydroxybenzylamine, which intercept IsoKs from adducting to proteins, and (b) vitamin E succinate, a novel potent and rapid acting form of vitamin E. Agents found to effectively prevent the changes in Na channel gating induced by IsoKs and oxidation in the cells will then be tested in the canine model of myocardial infarction to assess their ability to prevent or mitigate Na channel remodeling in vivo. These studies should improve our understanding of the mechanisms linking oxidant injury and arrhythmias and have the potential to identify novel antiarrhythmic therapeutic strategies.