Primitive cells capable of generating small resistance arterioles and capillary structures in the injured myocardium have been identified repeatedly. However, these cells do not form large conductive coronary arteries that would have important implications in the management of the ischemic heart. In the current study, we determined whether the human heart possesses a class of progenitor cells that regulates the growth of endothelial cells (ECs) and smooth muscle cells (SMCs) and vasculogenesis. The expression of vascular endothelial growth-factor receptor 2 (KDR) was used, together with the stem cell antigen c-kit, to isolate and expand a resident coronary vascular progenitor cell (VPC) from human myocardial samples. Structurally, vascular niches composed of c-kit-KDR-positive VPCs were identified within the walls of coronary vessels. The VPCs were connected by gap junctions to ECs, SMCs, and fibroblasts that operate as supporting cells. In vitro, VPCs were self-renewing and clonogenic and differentiated predominantly into ECs and SMCs and partly into cardiomyocytes. To establish the functional import of VPCs, a critical stenosis was created in immunosuppressed dogs, and tagged human VPCs were injected in proximity to the constricted artery. One month later, there was an increase in coronary blood flow (CBF) distal to the stenotic artery, resulting in functional improvement of the ischemic myocardium. Regenerated large, intermediate, and small human coronary arteries and capillaries were found. In conclusion, the human heart contains a pool of VPCs that can be implemented clinically to form functionally competent coronary vessels and improve CBF in patients with ischemic cardiomyopathy.

Rationale Vascular endothelial growth factor (VEGF)-B selectively binds VEGF receptor (VEGFR)-1, a receptor that does not mediate angiogenesis, and is emerging as a major cytoprotective factor. Objective To test the hypothesis that VEGF-B exerts non–angiogenesis-related cardioprotective effects in nonischemic dilated cardiomyopathy. Methods and Results AAV-9–carried VEGF-B167 cDNA (1012 genome copies) was injected into the myocardium of chronically instrumented dogs developing tachypacing-induced dilated cardiomyopathy. After 4 weeks of pacing, green fluorescent protein–transduced dogs (AAV-control, n=8) were in overt congestive heart failure, whereas the VEGF-B–transduced (AAV-VEGF-B, n=8) were still in a well-compensated state, with physiological arterial PO2. Left ventricular (LV) end-diastolic pressure in AAV-VEGF-B and AAV-control was, respectively, 15.0±1.5 versus 26.7±1.8 mm Hg and LV regional fractional shortening was 9.4±1.6% versus 3.0±0.6% (all P<0.05). VEGF-B prevented LV wall thinning but did not induce cardiac hypertrophy and did not affect the density of α-smooth muscle actin–positive microvessels, whereas it normalized TUNEL-positive cardiomyocytes and caspase-9 and -3 activation. Consistently, activated Akt, a major negative regulator of apoptosis, was superphysiological in AAV-VEGF-B, whereas the proapoptotic intracellular mediators glycogen synthase kinase (GSK)-3β and FoxO3a (Akt targets) were activated in AAV-control, but not in AAV-VEGF-B. Cardiac VEGFR-1 expression was reduced 4-fold in all paced dogs, suggesting that exogenous VEGF-B167 exerted a compensatory receptor stimulation. The cytoprotective effects of VEGF-B167 were further elucidated in cultured rat neonatal cardiomyocytes exposed to 10−8 mol/L angiotensin II: VEGF-B167 prevented oxidative stress, loss of mitochondrial membrane potential, and, consequently, apoptosis. Conclusions We determined a novel, angiogenesis-unrelated cardioprotective effect of VEGF-B167 in nonischemic dilated cardiomyopathy, which limits apoptotic cell loss and delays the progression toward failure.

We have investigated the effects of hyperglycemia on cardiomyocyte physiology and ventricular function. Our results indicate that defective Ca handling is a critical component of the progressive deterioration of cardiac performance of the diabetic heart.

Severe heart failure (HF) is characterized by profound alterations in cardiac metabolic phenotype, with down-regulation of the free fatty acid (FFA) oxidative pathway and marked increase in glucose oxidation. We tested whether fenofibrate, a pharmacological agonist of peroxisome proliferator-activated receptor-␣, the nuclear receptor that activates the expression of enzymes involved in FFA oxidation, can prevent metabolic alterations and modify the progression of HF. We administered 6.5 mg/kg/day p.o. fenofibrate to eight chronically instrumented dogs over the entire period of highfrequency left ventricular pacing (HF ϩ Feno). Eight additional HF dogs were not treated, and eight normal dogs were used as a control. Feno (14.1 Ϯ 1.6 mm Hg) compared with HF (18.7 Ϯ 1.3 mm Hg), but it increased up to 25 Ϯ 2 mm Hg, indicating end-stage failure, in both groups after 29 Ϯ 2 days of pacing. FFA oxidation was reduced by 40%, and glucose oxidation was increased by 150% in HF compared with control, changes that were prevented by fenofibrate. Consistently, the activity of myocardial medium chain acyl-CoA dehydrogenase, a marker enzyme of the FFA ␤-oxidation pathway, was reduced in HF versus control (1.46 Ϯ 0.25 versus 2.42 Ϯ 0.24 mol/min/gram wet weight (gww); p Ͻ 0.05) but not in HF ϩ Feno (1.85 Ϯ 0.18 mol/min/gww; N.S. versus control). Thus, preventing changes in myocardial substrate metabolism in the failing heart causes a modest improvement of cardiac function during the progression of the disease, with no effects on the onset of decompensation.The cardiac metabolic phenotype undergoes profound alterations during heart failure (HF), including defective energy production, lower mechanical efficiency, and a partial shift in energy substrate use . Oxidation of free fatty acids (FFA), which constitutes the preferential energy source for the normal heart, decreases in overt heart failure, whereas glucose oxidation markedly increases. The mechanisms underlying this phenomenon are numerous and complex. There is reduced myocardial expression and activity of key enzymes of the FFA oxidative pathway in different models of human as well as experimental heart failure (Sack et al., 1996;Martin et al., 2000;Rosenblatt et al., 2001;Osorio et al., 2002). The expression of these enzymes is under the control of the peroxisome proliferator-activated receptor (PPAR)-␣ and retinoid X receptor-␣ nuclear receptors that were also found down-regulated in the failing heart (Osorio et al., 2002;Karbowska et al., 2003). Whether such alterations in substrate metabolism play a role in the pathophysiological progression of heart failure remains an open question, with obvious implications for new therapeutic strategies based on metabolic modulators . It has

Recchia FA. Reverse changes in cardiac substrate oxidation in dogs recovering from heart failure. Am J Physiol Heart Circ Physiol 295: H2098 -H2105, 2008. First published September 26, 2008 doi:10.1152/ajpheart.00471.2008.-When recovering from heart failure (HF), the myocardium displays a marked plasticity and can regain normal gene expression and function; however, recovery of substrate oxidation capacity has not been explored. We tested whether cardiac functional recovery is matched by normalization of energy substrate utilization during post-HF recovery. HF was induced in dogs by pacing the left ventricle (LV) at 210 -240 beats/min for 4 wk. Tachycardia was discontinued, and the heart was allowed to recover. An additional group was studied in HF, and healthy dogs served as controls (n ϭ 8/group). Cardiac free fatty acids (FFAs) and glucose oxidation were measured with [ 3 H]oleate and [ 14 C]glucose. At 10 days of recovery, hemodynamic parameters returned to control values; however, the contractile response to dobutamine remained depressed, LV end-diastolic volume was 28% higher than control, and the heart mass-to-body mass ratio was increased (9.8 Ϯ 0.4 vs. 7.5 Ϯ 0.2 g/kg, P Ͻ 0.05). HF increased glucose oxidation (76.8 Ϯ 19.7 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 ) and decreased FFA oxidation (20.7 Ϯ 6.4 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 ), compared with normal dogs (24.5 Ϯ 6.3 and 51.7 Ϯ 9.6 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 , respectively), and reversed to normal values at 10 days of recovery (25.4 Ϯ 6.0 and 46.6 Ϯ 6.7 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 , respectively). However, similar to HF, the recovered dogs failed to increase glucose and fatty acid uptake in response to pacing stress. The activity of myocardial citrate synthase and aconitase was significantly decreased during recovery compared with that in control dogs (58 and 27% lower, respectively, P Ͻ 0.05), indicating a persistent reduction in mitochondrial oxidative capacity. In conclusion, cardiac energy substrate utilization is normalized in the early stage of post-HF recovery at baseline, but not under stress conditions. dilated cardiomyopathy; fatty acids; glucose; tachypacing THE CAPACITY OF THE FAILING heart to recover and restore, at least in part, a normal structure and function has been well demonstrated, both in animal models (12,13,26,28) and in patients (3,25). In pacing-induced heart failure (HF), an established model of dilated cardiomyopathy, hemodynamic and neurohormonal alterations, as well as myocyte function, return to control level within the first 2 wk of recovery after discontinuation of cardiac stimulation (28). Moreover, a number of studies have been performed in end-stage HF patients sustained with mechanical left ventricular (LV) assist devices while awaiting cardiac transplantation. The availability of ventricular tissue samples collected during the procedures of assist device implantation and removal has stimulated a strong interest in the molecular and cellular alterations occurring before and after mechanical unloading. Mechanical assistance favors reverse remodeling at...