Leukotriene B4 Regulation in Heart

PROJECT ABSTRACT Patients with type 2 diabetes (T2DM) are at increased risk (~50%) relative to non-diabetic individuals of suffering sudden cardiac death (SCD), most often due to fatal ventricular arrhythmias such as torsades de pointes (TdP). However, the underlying molecular mechanisms are unknown. Therefore, there is the critical

need to identify and validate novel cellular proarrhythmic mechanisms in T2DM. In that regard, we have identified and validated a proarrhythmic lipid mediator, leukotriene B4 (LTB4), that is elevated in diabetes compared to non-diabetic patients suggesting that risk for ventricular arrhythmias may be highest for patients

with high levels of LTB4. LTB4 inhibitors are a class of FDA-approved drugs that have been shown to confer major cardiovascular benefits. Recent evidence showed that LTB4 receptor (LTB4R) knockout or LTB4 inhibitor treatment of myocytes, prevented LTB4-related metabolic defects, supporting the results of a

separate report indicating reduced LTB4 biosynthesis prevented ischemia/reperfusion-induced arrhythmias. Our pilot studies revealed that LTB4 is increased in multiple diabetes mouse models (ob/ob and PANIC- ATTAC), induces a profound prolongation of ventricular action potential duration, triggers cellular

arrhythmogenesis, and severely depresses the repolarizing rapidly activating delayed rectifier K current (IKr) density in guinea pig ventricular myocytes but not in healthy heart cells, consistent with TdP vulnerability. We have further found that guinea pigs challenged with LTB4 displayed prolonged QT interval, and that this can

be prevented with LTB4R inhibition, suggesting that preventing such LTB4-LTB4R effects may be therapeutically beneficial in T2DM ventricular arrhythmias. Our long-term goal is to accelerate the rational development of clinically useful anti-LTB4 agents as treatments for malignant ventricular arrhythmias. The

overall objective for this application is to determine how the LTB4R signaling axis promotes arrhythmia and its usefulness as a preclinical drug target. Our central hypothesis, based on preliminary data described above, is that LTB4 through the LTB4R drives adverse remodeling of ventricular myocyte electrical activity and

propensity for ventricular arrhythmias by promoting impaired IKr biophysics and preventing its functional expression. The rationale for the proposed research is that a science-based determination of the preclinical in vitro proarrhythmic effects of LTB4 and associated mechanisms of LTB4R inhibition is likely to support the

development of new and promising therapeutic strategies in patients with T2DM. Our experimental studies will combine optical (FRET, photo-switchable fluorescent proteins, quantum dot labeling, 3D reconstruction), electrophysiology, genetic and pharmacological tools in guinea pig and human ventricular myocytes. Our

expectation is that, if we understand T2DM ventricular electrical remodeling from a perspective of LTB4 and downstream pathways, we may be better equipped to provide new opportunities for the development of novel therapies for arrhythmia progression and prevention in patients.