Original articleEpoxyeicosatrienoic acid prevents postischemic electrocardiogram abnormalities in an isolated heart model☆
Introduction
Heart disease and stroke are major causes of illness, disability and death in Western societies [1]. As populations' age and co-morbidities such as obesity and diabetes become more prevalent, increased costs to heath care systems can be anticipated. Ischemic heart disease (IHD), also known as coronary artery disease (CAD) or coronary heart disease (CHD), results from the damage incurred from the reduction in blood flow and oxygen supply to the heart. Resultant alterations in ionic homeostasis in the ischemic myocardium alterresting membrane potential, the action potential duration (APD) and myocyte excitability resulting in EKG abnormalities [2], [3], [4], [5]. Classical electrocardiographic (EKG) abnormalities associated with ischemic injury are prolonged QT interval and ST-segment elevation (STE) [6], [7], where QT prolongation reflects a decreased repolarization following depolarization of the cardiac ventricles, whereas STE provides a measure of ischemic injury. These EKG changes can manifest as serious arrhythmias, thereby impeding cardiac function, with possible fatal outcomes.
Arachidonic acid (AA), an essential polyunsaturated fatty acid found esterified to membrane phospholipids, may be released by phospholipases following stress stimuli such as ischemia [8]. Free AA can then be metabolized by CYP epoxygenase to four regioisomeric eicosanoid metabolites, epoxyeicosatrienoic acids (5,6-, 8,9-, 11,12-, and 14,15-EET) [9], [10]. Conversion to the corresponding dihydroxyeicosatrienoic acids (5,6-, 8,9-, 11,12-, and 14,15-DHET) by soluble epoxide hydrolase (sEH) reduces their biological activity. EETs are important components of many intracellular signaling pathways in both cardiac and extra cardiac tissues. They activate various stress response systems, such as p42/p44 mitogen activated protein kinases (MAPK); enhance membrane ion channel activity, such as K+ channels; and improve postischemic recovery of left ventricular function [11], [12], [13], [14].
Activation of sarcKATP channels can protect the heart against ischemic reperfusion injury by hyperpolarizing the cell, thereby limiting calcium entry, preserving ATP utilization, and maintaining cardiac membrane potential and contractility [12]. Preventing further depolarization of the membrane may avert EKG abnormalities such as QT interval prolongation and STE [12]. Previous studies have shown that EETs are potent activators of vascular and cardiac sarcolemmal ATP-sensitive potassium channels (sarcKATP) [12], [13], [14]. Although the mechanism(s) are unknown, evidence suggests that mouse cardiac sarcKATP channels are activated by EETs directly inhibiting ATP binding, whereas activation of vascular sarcKATP is mediated by a cAMP-Protein Kinase A (PKA) dependent mechanism [14]. There are various reports demonstrating EET-mediated activation of other cardiac ion channels. For example, cell culture models suggest that EETs inhibit cardiac Na+ channels [15], modulate Ca2+ currents [16], [17] and shorten ventricular APD by enhancing Kv4.2 channels in a PKA-dependent manner [18]. Together, these data suggest that EET-mediated action involves modulation of ion channels.
Recently, we reported that transgenic mice with cardiac-specific overexpression of human CYP2J2 or mice with targeted disruption of soluble epoxide hydrolase (sEH null) had increased cardiomyocyte EET biosynthesis, enhanced sarcKATP activity and improved postischemic recovery of left ventricular function [11], [19], [20]. To further examine the cardiac effects of CP-derived eicosanoids towards ischemia–reperfusion induced EKG abnormalities, we evaluated the role of EETs in an ex vivo EKG model. Our initial data shows that elevated levels of EETs attenuate changes in measures of electrocardiogram parameters (QT interval and STE). Moreover, the data suggest that this cardioprotection is mediated by CYP epoxygenase metabolites of AA and involves activation of the PKA and sarcKATP channels and PKA channels.
Section snippets
Animals
Commercially available C57Bl/6 mice were purchased from Charles River Laboratories (Charles River Laboratories, Inc.). Mice with cardiac myocyte-specific over expression of human CYP2J2 (CYP2J2 Tr) [11] were obtained from Dr. Darryl Zeldin (NIEHS, RTP, NC, USA). All studies used mice aged 3–4 months, weighing 25–35 g. Experiments were conducted in strict guidelines provided by the University of Alberta Health Sciences Laboratory Animal Services (HSLAS).
Ex vivo cardiac function and electrocardiogram recording
Hearts were perfused in the Langendorff
Characterization
EKG parameters obtained from the ex vivo model were first characterized by recording changes in C57BL/6 hearts perfused with halofantrine (+/−). Isolated hearts were first perfused for 10 min to obtain stable baseline readings, and then subsequently perfused with different concentrations of halofantrine (+/−) (0, 50 or 100 μM, Fig. 1, Fig. 2). Prolongation of QTc intervals were observed following increasing concentrations of halofantrine (Fig. 2A). These data indicated that our ex vivo model
Discussion
While evidence has begun to identify the significance of cardiac cytochrome P450s to heart function and protection, effects are dependent on the metabolites produced [11], [19], [30], [31], [32], [33], [34]. CYP epoxygenases (EETs) have well established cardioprotective effects within the cardiovascular system [11], [35], whereas metabolites from CYP hydroxylases (20-HETE) can be detrimental. CYP epoxygenase-derived eicosanoids can affect cardiomyocyte function [15], [16], [36] and improve
Acknowledgments
JMS is the recipient of a New Investigator Award from the Heart and Stroke Foundation of Canada and a Health Scholar Award from the Alberta Heritage Foundation for Medical Research.
References (51)
- et al.
Time course and rate dependence of Q–T interval changes during noncomplicated acute transmural myocardial infarction in human beings
Am. J. Cardiol.
(1981) - et al.
Prolongation of the QTc interval is seen uniformly during early transmural ischemia
J. Am. Coll. Cardiol.
(2007) QT interval and mortality from coronary artery disease
Prog. Cardiovasc. Dis.
(2000)- et al.
Prolonged QT interval at onset of acute myocardial infarction in predicting early phase ventricular tachycardia
Am. Heart J.
(1981) - et al.
Epoxyeicosatrienoic acids (EETs): metabolism and biochemical function
Prog. Lipid Res.
(2004) - et al.
Molecular cloning, expression and characterization of an endogenous human cytochrome P450 arachidonic acid epoxygenase isoform
Arch. Biochem. Biophys.
(1995) - et al.
Role of epoxyeicosatrienoic acids in protecting the myocardium following ischemia/reperfusion injury
Prostaglandins Other Lipid Mediat.
(2007) Cardiotoxicity of antimalarial drugs
Lancet Infect. Dis.
(2007)- et al.
A-kinase anchoring proteins take shape
Curr. Opin. Cell Biol.
(2007) Cyclic AMP-dependent modulation of cardiac L-type Ca2+ and transient outward K+ channel activities by epoxyeicosatrienoic acids
Prostaglandins Other Lipid Mediat.
(2007)
Cytochrome P450 omega-hydroxylase inhibition reduces infarct size during reperfusion via the sarcolemmal KATP channel
J. Mol. Cell. Cardiol.
Molecular cloning and expression of CYP2J2, a human cytochrome P450 arachidonic acid epoxygenase highly expressed in heart
J. Biol. Chem.
Molecular cloning, expression, and functional significance of a cytochrome P450 highly expressed in rat heart myocytes
J. Biol. Chem.
Mechanisms by which epoxyeicosatrienoic acids (EETs) elicit cardioprotection in rat hearts
J. Mol. Cell. Cardiol.
Acute ischaemia: a dynamic influence on QT dispersion
Lancet
K(ATP) opener-induced delayed cardioprotection: involvement of sarcolemmal and mitochondrial K(ATP) channels, free radicals and MEK1/2
J. Mol. Cell. Cardiol.
Physiological and pathophysiological roles of ATP-sensitive K+ channels
Prog. Biophys. Mol. Biol.
Diet and lifestyle recommendations revision 2006: a scientific statement from the American Heart Association Nutrition Committee
Circulation
Mechanism and time course of S–T and T–Q segment changes during acute regional myocardial ischemia in the pig heart determined by extracellular and intracellular recordings
Circ. Res.
Electrophysiology and electrocardiology of acute myocardial ischemia
Can. J. Cardiol.
P-450 metabolites of arachidonic acid in the control of cardiovascular function
Physiol. Rev.
Enhanced postischemic functional recovery in CYP2J2 transgenic hearts involves mitochondrial ATP-sensitive K+ channels and p42/p44 MAPK pathway
Circ. Res.
Activation of ATP-sensitive K(+) channels by epoxyeicosatrienoic acids in rat cardiac ventricular myocytes
J. Physiol.
Stereospecific activation of cardiac ATP-sensitive K(+) channels by epoxyeicosatrienoic acids: a structural determinant study
Mol. Pharmacol.
Cardiac and vascular KATP channels in rats are activated by endogenous epoxyeicosatrienoic acids through different mechanisms
J. Physiol.
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Funding: This work was supported by Canadian Institutes of Health Research Grant (JMS MOP79465), USPHS NIH (JRF GM31278) and the Robert A. Welch Foundation (JRF).