These findings demonstrate that stimulating glucose oxidation via targeting either PDH or MCD decreases the infarct size, validating the concept that optimizing myocardial metabolism is a novel therapy for ischaemic heart disease.

1 This study examined effects of adenosine and selective adenosine A, and A2 receptor agonists on glucose metabolism in rat isolated working hearts perfused under aerobic conditions and during reperfusion after 35 min of global no-flow ischaemia.2 Hearts were perfused with a modified Krebs-Henseleit buffer containing 1.25 mM Ca2+, 11 mM glucose, 1.2 mM palmitate and insulin (100 Mu ml-'), and paced at 280 beats min-'. Rates of glycolysis and glucose oxidation were measured from the quantitative production of 3H20 and "'CO2, respectively, from [5-3H/U-"'C]-glucose.3 Under aerobic conditions, adenosine (100 Mm) and the adenosine A, receptor agonist, N6-cyclohexyladenosine (CHA, 0.05 gM), inhibited glycolysis but had no effect on either glucose oxidation or mechanical function (as assessed by heart rate systolic pressure product). The improved coupling of glycolysis to glucose oxidation reduced the calculated rate of proton production from glucose metabolism. The adenosine Al receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX 0.3 MM) did not alter glycolysis or glucose oxidation per se but completely antagonized the adenosine-and CHAinduced inhibition of glycolysis and proton production.4 During aerobic reperfusion following ischaemia, CHA (0.05 gM) again inhibited glycolysis and proton production from glucose metabolism and had no effect on glucose oxidation. CHA also significantly enhanced the recovery of mechanical function. In contrast, the selective adenosine A2, receptor agonist, CGS-21680 (1.0 yM), exerted no metabolic or mechanical effects. Similar profiles of action were seen if these agonists were present during ischaemia and throughout reperfusion or when they were present only during reperfusion. 5 DPCPX (0.3 uM), added at reperfusion, antagonized the CHA-induced improvement in mechanical function. It also significantly depressed the recovery of mechanical function per se during reperfusion.Both the metabolic and mechanical effects of adenosine (100 gM) were antagonized by the nonselective Al/A2 antagonist, 8-sulphophenyltheophylline (100 yM).6 These data demonstrate that inhibition of glycolysis and improved recovery of mechanical function during reperfusion of rat isolated hearts are mediated by an adenosine Al receptor mechanism. Improved coupling of glycolysis and glucose oxidation during reperfusion may contribute to the enhanced recovery of mechanical function by decreasing proton production from glucose metabolism and the potential for intracellular Ca2+ accumulation, which if not corrected leads to mechanical dysfunction of the postischaemic myocardium.

Pressure overload-induced heart failure and I/R shift the preference of substrate oxidation from glucose and lactate to fatty acid due to a selective reduction in carbohydrate oxidation. Normalizing the balance between metabolic substrate utilization may alleviate pressure-overload-induced heart failure and ischaemia.

BackgroundIntralipid® administration at reperfusion elicits protection against myocardial ischemia-reperfusion injury. However, the underlying mechanisms are not fully understood.MethodsSprague-Dawley rat hearts were exposed to 15 min of ischemia and 30 min of reperfusion in the absence or presence of Intralipid® 1% administered at the onset of reperfusion. In separate experiments, the reactive oxygen species (ROS) scavenger N-(2-mercaptopropionyl)-glycine was added either alone or with Intralipid®. Left ventricular work and activation of Akt, STAT3, and ERK1/2 were used to evaluate cardioprotection. ROS production was assessed by measuring the loss of aconitase activity and the release of hydrogen peroxide using Amplex Red. Electron transport chain complex activities and proton leak were measured by high-resolution respirometry in permeabilized cardiac fibers. Titration experiments using the fatty acid intermediates of Intralipid® palmitoyl-, oleoyl- and linoleoylcarnitine served to determine concentration-dependent inhibition of complex IV activity and mitochondrial ROS release.ResultsIntralipid® enhanced postischemic recovery and activated Akt and Erk1/2, effects that were abolished by the ROS scavenger N-(2-mercaptopropionyl)glycine. Palmitoylcarnitine and linoleoylcarnitine, but not oleoylcarnitine concentration-dependently inhibited complex IV. Only palmitoylcarnitine reached high tissue concentrations during early reperfusion and generated significant ROS by complex IV inhibition. Palmitoylcarnitine (1 µM), administered at reperfusion, also fully mimicked Intralipid®-mediated protection in an N-(2-mercaptopropionyl)-glycine -dependent manner.ConclusionsOur data describe a new mechanism of postconditioning cardioprotection by the clinically available fat emulsion, Intralipid®. Protection is elicited by the fatty acid intermediate palmitoylcarnitine, and involves inhibition of complex IV, an increase in ROS production and activation of the RISK pathway.

In this study isolated perfused working rat hearts were used to investigate the role of palmitate-regulated protein kinase B (PKB) phosphorylation on glucose metabolism. Rat hearts were perfused aerobically in working mode with 11 mM glucose and either 100 microU/ml insulin or 100 microU/ml insulin and 1.2 mM palmitate. PKB activity and phosphorylation state were reduced in the presence of 1.2 mM palmitate, which correlates with a decrease in glycolysis (47%), glucose oxidation (84%), and glucose uptake (43%). In contrast to skeletal muscle, neither p38 nor ERK underwent changes in their phosphorylation states in response to insulin or insulin and palmitate. Moreover, pharmacological restoration of glucose oxidation rates in hearts perfused with 1.2 mM palmitate demonstrated no increase in PKB phosphorylation state. In cultured mouse cardiac muscle HL-1 cells, insulin markedly increased PKB phosphorylation, which was blunted by pre- and cotreatment with 1.2 mM palmitate. However, neither palmitate nor C(2)-ceramide treatment of insulin-stimulated cells was able to accelerate PKB dephosphorylation beyond that observed following the removal of insulin alone. Taken together, these experiments show the control of PKB phosphorylation by palmitate is independent of ceramide and suggest that this signaling event may be an important regulator of myocardial glucose uptake and oxidation.