Effects of Insulin Replacements, Inhibitors of Angiotensin, and PKCβ's Actions to Normalize Cardiac Gene Expression and Fuel Metabolism in Diabetic Rats

Abstract

High-density oligonucleotide arrays were used to compare gene expression of rat hearts from control, untreated diabetic, and diabetic groups treated with islet cell transplantation (ICT), protein kinase C (PKC)␤ inhibitor ruboxistaurin, or ACE inhibitor captopril. Among the 376 genes that were differentially expressed between untreated diabetic and control hearts included key metabolic enzymes that account for the decreased glucose and increased free fatty acid utilization in the diabetic heart. ICT or insulin replacements reversed these gene changes with normalization of hyperglycemia, dyslipidemia, and cardiac PKC activation in diabetic rats. Surprisingly, both ruboxistaurin and ACE inhibitors improved the metabolic gene profile (confirmed by real-time RT-PCR and protein analysis) and ameliorated PKC activity in diabetic hearts without altering circulating metabolites. Functional assessments using Langendorff preparations and 13 C nuclear magnetic resonance spectroscopy showed a 36% decrease in glucose utilization and an impairment in diastolic function in diabetic rat hearts, which were normalized by all three treatments. In cardiomyocytes, PKC inhibition attenuated fatty acid-induced increases in the metabolic genes PDK4 and UCP3 and also prevented fatty acid-mediated inhibition of basal and insulin-stimulated glucose oxidation. Thus, PKC␤ or ACE inhibitors may ameliorate cardiac metabolism and function in diabetes partly by normalization of fuel metabolic gene expression directly in the myocardium. Diabetes 56:1410-1420, 2007 C ardiac failure in diabetic patients can be induced by vascular insufficiency and contractile dysfunction resulting from abnormal levels of metabolites (1,2). For the latter, elevations of plasma glucose and free fatty acids (FFAs) in diabetes may decrease the efficiency of energy production by suppressing glucose utilization and enhancing FFA metabolism (3,4). Because enhancements of angiotensin and protein kinase C (PKC) actions may cause myocardial dysfunction (5,6), we have studied the effects of ACE and PKC inhibitors on the gene expression profile, glucose metabolism, and functions of the myocardium in diabetes.Cardiovascular protective actions of ACE inhibitors in diabetic patients (5) have been ascribed secondarily to hemodynamic effects or to their additional anti-ischemic and metabolic effects (7,8). High glucose levels can induce functional abnormalities in isolated ventricular myocytes, which are prevented by angiotensin II type 1 receptor blockade (9), suggesting that local angiotensin II may be involved in mediating high glucose-induced effects.Multiple isoforms of the PKC family, a family of 12 serine-threonine kinases, can affect cardiac functions and partially mediate angiotensin II actions. We have previously reported (6) that the ␤-isoform is preferentially activated in the diabetic rat heart. Transgenic mice overexpressing the ␤2 isoform of PKC specifically in the myocardium develop cardiac hypertrophy, fibrosis, impairment of left ventricular performance, and prog...

Inhibition of Protein Kinase C–β by Ruboxistaurin Preserves Cardiac Function and Reduces Extracellular Matrix Production in Diabetic Cardiomyopathy

“…32 Ruboxistaurin treatment was associated with reduced body weight, higher plasma glucose, reduced heart rate, and lower blood pressure when compared with vehicle-treated diabetic animals. These findings are similar to that reported by Arikawa et al 33 who demonstrated similar nonsignificant reductions in body weight and higher glucose levels in ruboxistaurin-treated diabetic animals. However, in clinical trials of patients with diabetic nephropathy and diabetic retinopathy no change in body mass index, glycemic control, heart rate, or blood pressure were reported.…”

“…18 Although the present study demonstrated that diabetes and PKC-␤ inhibition had a range of effects on cardiac function, structure, growth factors, and lusitropic intermediates, the role of PKC-␤ in diabetes-associated alterations in cardiac fuel metabolism, the subject of a recent in-depth study, were not explored in this report. 33 To compare the effects of PKC-ß inhibition with current first-line treatment for heart failure, we also examined the effects of angiotensin-converting enzyme inhibition. Both ruboxistaurin and perindopril reduced the abnormal structure and diastolic dysfunction in diabetic rats to a similar extent.…”

Agonist-Induced Hypertrophy and Diastolic Dysfunction Are Associated With Selective Reduction in Glucose Oxidation

“…Importantly, AT1R blockade using irbesartan prevents the Ang II-induced alterations in cardiac metabolism, while preventing pathological hypertrophy and diastolic dysfunction. Our results are consistent with findings in diabetic hearts where angiotensin-converting enzyme inhibition reduces the expression of PDK4 33 and in cardiacspecific overexpression of PDK4, which results in reduced glucose oxidation. showing diastolic dysfunction as illustrated by reduced E/A ratio (E) and decreased E'/A' ratio (F) in response to treatment with PE.…”

Chronic Hyperinsulinemia Causes Selective Insulin Resistance and Down-regulates Uncoupling Protein 3 (UCP3) through the Activation of Sterol Regulatory Element-binding Protein (SREBP)-1 Transcription Factor in the Mouse Heart

“…Although this has been confirmed in many occasions for rodent models of type 1 diabetes (22)(23)(24)(25)(26), evidence is lacking to infer the same with type 2 diabetes (20). Moreover, Schrauwen et al (27) reported that UCP3 protein levels in vastus lateralis muscle of patients with type 2 diabetes were half the levels found in nondiabetic subjects.…”