Pioglitazone increases PGC1-α signaling within chronically ischemic myocardium.

The peroxisome proliferator-activated receptor (PPAR)-γ drug pioglitazone (PIO) has been shown to protect tissue against oxidant stress. In a swine model of chronic myocardial ischemia, we tested whether PIO increases PGC1-α signaling and the expression of mitochondrial antioxidant peptides. Eighteen pigs underwent a thoracotomy with placement of a fixed constrictor around the LAD artery. At 8 weeks, diet was supplemented with either PIO (3 mg/kg) or placebo for 4 weeks. Regional myocardial function and blood flow were determined at the time of the terminal study. PGC1-α expression was quantified from nuclear membranes by gels and respiration, oxidant stress markers and proteomics by iTRAQ were determined from isolated mitochondria. In the chronically ischemic LAD region, wall thickening from the PIO and control groups was 42 ± 6 and 45 ± 5 %, respectively (NS) with no intergroup differences in basal blood flow (0.72 ± 0.04 versus 0.74 ± 0.04 ml/min g, respectively; NS). In the PIO group, the expression of nuclear bound PGC1-α was higher (11.3 ± 2.6 versus 4.4 ± 1.4 AU; P < 0.05) and the content of mitochondrial antioxidant peptides including superoxide dismutase 2, aldose reductase, glutathione S-transferase and thioredoxin reductase were greater than controls. Although isolated mitochondria from the PIO group showed lower state 3 respiration (102 ± 13 versus 161 ± 22 nmol/min mg; P < 0.05), no differences in oxidant stress were noted by protein carbonyl (1.7 ± 0.7 versus 1.1 ± 0.1 nmol/mg). Chronic pioglitazone does not reduce regional myocardial blood flow or function in a swine model of chronic myocardial ischemia, but may have an important role in increasing expression of antioxidant proteins through PGC1-α signaling.

The Recovery of Hibernating Hearts Lies on a Spectrum: from Bears in Nature to Patients with Coronary Artery Disease.

Clinicians often use the term "hibernating myocardium" in reference to patients with ischemic heart disease and decreased function within viable myocardial regions. Because the term is a descriptor of nature's process of torpor, we provide a comparison of the adaptations observed in both conditions. In nature, hearts from hibernating animals undergo a shift in substrate preference in favor of fatty acids, while preserving glucose uptake and glycogen. Expression of electron transport chain proteins in mitochondria is decreased while antioxidant proteins including uncoupling protein-2 are increased. Similarly, hibernating hearts from patients have a comparable metabolic signature, with increased glucose uptake and glycogen accumulation and decreased oxygen consumption. In contrast to nature however, patients with hibernating hearts are at increased risk for arrhythmias, and contractility does not fully recover following revascularization. Clearly, additional interventions need to be advanced in patients with coronary artery disease and hibernating myocardium to prevent refractory heart failure.

Continued depression of maximal oxygen consumption and mitochondrial proteomic expression despite successful coronary artery bypass grafting in a swine model of hibernation.

OBJECTIVE: Clinical studies indicate incomplete functional recovery of hibernating myocardium after coronary artery bypass grafting. We hypothesized that persistent contractile abnormalities after coronary artery bypass grafting are associated with decreased mitochondrial proteins involving electron transport chain that might limit maximal oxygen consumption. METHODS: Seven pigs with hibernating myocardium underwent off-pump revascularization with left internal thoracic artery to mid left anterior descending artery. At 4 weeks, left internal thoracic artery anastomosis was patent by multidetector computed tomography. Regional function (transthoracic echocardiography) and blood flow (microspheres) were assessed at rest and during high-dose dobutamine (40 µg/[kg · min]). Expression of electron transport chain proteins was analyzed with isobaric tags for relative and absolute quantification. RESULTS: After revascularization, multidetector computed tomography confirmed severe left anterior descending stenosis and patent left internal thoracic artery graft. Regional function and blood flow normalized at rest; however, function in left anterior descending distribution remained depressed relative to remote regions, and myocardial blood flow in that region did not increase normally when challenged with high-work state. Concomitant with reduced maximal blood flow response in left anterior descending region was more than 40% reduction in electron transport chain proteins essential to adenosine triphosphate production. CONCLUSIONS: Despite successful revascularization of hibernating myocardium, regional function and blood flow remained depressed during catecholamine stress. Electron transport chain proteins known to be downregulated during adaptive process within hibernating myocardium did not normalize after revascularization. These data demonstrate a potential bioenergetic cause of persistent dysfunction and heart failure within successfully revascularized hibernating myocardium.

Measurement of myocardial free radical production during exercise using EPR spectroscopy.

Exercise is associated with an increase in oxygen flux through the mitochondrial electron transport chain that has recently been demonstrated to increase the production of reactive oxygen species (ROS) in skeletal muscle. This study examined whether exercise also causes free radical production in the heart. We measured ROS production in seven chronically instrumented dogs during rest and treadmill exercise (6.4 km/h at 10 degrees grade; and heart rate, 204 +/- 3 beats/min) using electron paramagnetic resonance spectroscopy in conjunction with the spin trap alpha-phenyl-tert-butylnitrone (PBN) (0.14 mol/l) in blood collected from the aorta and coronary sinus (CS). To improve signal detection, the free radical adducts were deoxygenated over a nitrogen stream for 15 min and extracted with toluene. The hyperfine splitting constants of the radicals were alpha(N) = 13.7 G and alpha(H) = 1.0 G, consistent with an alkoxyl or carbon-centered radical. Resting aortic and CS PBN adduct concentrations were 6.7 and 6.3 x 10(8) arbitrary units (P = not significant). Both aortic and CS adduct concentrations increased during exercise, but there was no significant difference between the aortic and CS concentrations. Thus, in contrast to skeletal muscle, submaximal treadmill exercise did not result in detectable free radical production by the heart.