Abstract 3886: Prevention of Dilated Cardiomyopathy with Nitroxides
Tempol (TPL), a nitroxyl radical, has been shown to decrease infarct size after myocardial ischemia-reperfusion ex vivo, although the exact mechanism remains controversial. Investigators have reported that TPL both functions as a free radical scavenger and increases HIF-1a signaling. To understand the mechanism better, we compared the effect of TPL to its reduced form, hydroxy-Tempol (TPLH), in an in vivo model of ischemic cardiomyopathy . We hypothesized that increased HIF1a signaling is responsible for the beneficial effects of TPL. Male Lewis rats underwent LAD ligation and received a single 100 mg/kg i.v. dose of TPL, TPLH, or PBS immediately after infarction. Four hours post-infarct, we measured serum Troponin I and myocardial HIF1a, VEGF, and apoptosis in the infarct. Twenty-eight days post-infarct, we assessed cardiac function with echo and cardiac MRI. Left ventricle (LV) scar was examined with Trichrome. We evaluated the effects of TPL and TPLH on (a) survival in hypoxic human aortic endothelial cells (HAEC), and (b) HIF1a function in HAEC transiently transfected with a HIF1a reporter plasmid. Four hours after infarction, TPL and TPLH reduced serum Troponin I levels (PBS 58.6±17.5, TPL 37.9±15, TPLH 27.34±8.9, p<0.03); increased HIF1a (2.35±0.73 and 3.31±0.75 fold over PBS, p<0.03) and VEGF levels (1.54±0.48 and 1.93±0.21 fold over PBS, p<0.02); and decreased apoptosis as measured by TUNEL staining. After 28 days, TPL and TPLH increased fractional shortening (PBS 0.25±0.004, TPL 0.45±0.06 and TPLH 0.42±0.06, p<0.01), increased ejection fraction (PBS 34±1.4%, TPL 55±9.4% and TPLH 56±8.7%, p<0.02), and decreased LV scar (PBS 11±1.8%, TPL 3.7±1.15%, and TPLH 2.89±1.87%, p<0.003). After 48 hours of hypoxia, cell survival increased (PBS 41.4±13%, 0.1mM TPL 72.7±0.027% and 10mM TPLH 66.1±0.1, p<0.03), and there was a dose dependent increase in HIF1a with TPL and TPLH. This study suggests that TPL may provide a new treatment strategy for the prevention of ischemic cardiomyopathy after myocardial infarction. By comparing TPL and TPLH, we have shown that is it not TPL’s role as a free radical scavenger, but increased HIF1a signaling in the early post-infarct period that results in the beneficial effects.