CARDIAC TOXICITY OF PHOSPHOLIPID METABOLITES

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DESCRIPTION: (Adapted from the Investigator's Abstract). The goal of this project is to investigate the role of the phospholipid metabolites, leukotoxin (Lx), and leukotoxin-diol (Lx-diol) in the heart. Leukotoxin is an epoxide ring derivative of linoleic acid, a common component of cell membranes, formed by leukocytes in severely burned patients and during normal myocardial ischemia. Plasma levels of Lx have been correlated with late stage multiple organ failure in burn patients. One consequence is vascular collapse and cardiac arrest. Recently, Lx has been shown to cause cardiac arrest in dogs. Recent experiments in a cultured cell model have suggested that for Lx to be cytotoxic, it must first be metabolised to Lx-diol by a soluble epoxide hydrolase (sEH). Their preliminary experiments show that, in rat heart, Lx is without effect; however, Lx-diol suppresses the cardiac action potential, sodium current and transient outward current. This study will test the hypothesis that the mechanism of cardiotoxic effects of Lx is that Lx is metabolized by sEH to Lx-diol, causing its activation. Furthermore, the effects of Lx-diol are mediated by modification of kinetic properties of ion channels through intramembrane interactions with channel proteins. Specifically, the investigators will measure effects of Lx and Lx-diol on the cardiac action potential, sodium, calcium, and potassium channel currents and sodium potassium pump current. Effects on the action potential and membrane currents will be compared between rat, mouse, and guinea pig myocytes, as these species are known to have different intrinsic activities of sEH. Currents identified as being altered by either Lx-diol or Lx will be further characterized as to kinetic and voltage dependent properties to determine the mechanism by which currents are modified. Isolated adult cardiac myocytes will be used as the model system to test this hypothesis. Whole cell patch clamp techniques will be used to measure action potential and ionic currents in the isolated myocytes. Results of current measurements will be used to make predictions on effects in intact cardiac muscle that will be tested with papillary muscle experiments. Results of this study should demonstrate the role of sEH in toxic effects of Lx in which compounds (Lx or Lx-diol) is having a direct effect on the heart and, therefore, may be responsible for the heart failure seen both clinically and in the laboratory animals. Furthermore, this will provide new insights into the mechanisms responsible for this type of heart failure. Finally, they will begin to understand the mechanism of action of these compounds in altering electrophysiological properties of cardiac myocytes. This new evidence will provide a better understanding of these clinically important toxicants and may provide the basis for rationale treatment of these patients.