Clinical trials using vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) showed minimal success in stimulating collateral growth in patients with coronary artery disease (CAD). We recently reported that transient, repetitive ischemia (RI) or VEGF delivery, which induce coronary collateral growth (CCG) in healthy animals, failed to elicit CCG in a rat model of CAD and insulin resistance (Zucker obese fatty rat). Our preliminary data demonstrate that CCG is likewise impaired in the JCR rat model of the metabolic syndrome. These results indicate that stimuli, which normally elicit CCG, appear to be ineffective in at risk patients and animal models of cardiovascular disease. A common denominator of risk factors for CAD including obesity, diabetes and hypertension is oxidative stress. Ang II potently elicits oxidative stress, activates several redox-sensitive signaling pathways, including p38, Akt and Src, and has been reported to both inhibit and promote angiogenesis. We have recently shown that p38 inhibition abrogated CCG. Our preliminary data show similar results with Akt and Src inhibition, and demonstrate that extent and duration of activation of these kinases are critically important to CCG, are vastly different between healthy and JCR animals, and are differentially regulated by Ang II between the two phenotypes. Thus, we hypothesize that the reason for the disparate effects of Ang II on angiogenesis is AT1R-dependent regulation of myocardial oxidative stress and redox-sensitive signaling, which are critically dependent on the background of normal vs. elevated (JCR) oxidative stress. The following specific aims will be addressed: 1. Determine myocardial oxidative stress and redox-sensitive signaling profiles for normal vs. metabolic syndrome during RI- induced CCG. ROS amounts generated by RI and myocardial redox state during CCG will be determined quantitatively by using X-band electroparamagnetic resonance (EPR). Temporal regulation of ROS-dependent signaling (p38, Akt, Src) activation during CCG, as well as requirement for their activation will also be determined;2. Determine the effect of Ang II on CCG, myocardial oxidative stress and activation of redox-dependent signaling in vivo, in normal vs. metabolic syndrome animals. We will compare the effect of Ang II infusion or AT1R blockade in normal (WKY) vs. JCR;and 3. Establish treatment paradigms to achieve maximal restoration of CCG in the metabolic syndrome. Based on profiles obtained in Aims 1 and 2, we will use temporally-specific therapies to regulate ROS production and redox-sensitive signaling in conjunction with AT1R blockade to promote CCG. These in vivo studies will provide insight into the complex mechanistic basis of impaired CCG in the animal model analogous to the human metabolic syndrome. As such they have a potential to provide important information regarding therapeutic angiogenesis, especially as it relates to the use of AT1R blockers in the management of patients at risk for or with established CAD.
Metabolic syndrome (type II diabetes, obesity and hypertension) patients are at high risk fatal myocardial infarction, in part because they fail to grow collateral vessels in response to transient ischemia (angina pectoris). The first goal of this proposal is to understand the molecular basis of impaired coronary collateral growth in an animal model, which mimics the pathology of the human metabolic syndrome. Since most patients suffering from the metabolic syndrome are on angiotensin type 1 receptor (AT1R) blockers for clinical management of hypertension, heart and/or renal failure, the second goal of this proposal is to understand the interaction between AT1R signaling and the metabolic syndrome phenotype, on a molecular level (signal transduction and oxidative stress) as it relates to coronary collateral growth. The final goal of this proposal is to construct specific therapies aimed at restoration of coronary collateral growth, relevant to the clinical management of metabolic syndrome patients on AT1R blockers.
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