Improvement of myocardial ischemic dysfunction with dichloroacetic acid: experimental study by repeated ischemia in dogs

Reperfusion-induced translocation of deltaPKC to cardiac mitochondria prevents pyruvate dehydrogenase reactivation

Cardiac ischemia and reperfusion are associated with loss in the activity of the mitochondrial enzyme pyruvate dehydrogenase (PDH). Pharmacological stimulation of PDH activity improves recovery in contractile function during reperfusion. Signaling mechanisms that control inhibition and reactivation of PDH during reperfusion were therefore investigated. Using an isolated rat heart model, we observed ischemia-induced PDH inhibition with only partial recovery evident on reperfusion. Translocation of the redox-sensitive delta-isoform of protein kinase C (PKC) to the mitochondria occurred during reperfusion. Inhibition of this process resulted in full recovery of PDH activity. Infusion of the deltaPKC activator H2O2 during normoxic perfusion, to mimic one aspect of cardiac reperfusion, resulted in loss in PDH activity that was largely attributable to translocation of deltaPKC to the mitochondria. Evidence indicates that reperfusion-induced translocation of deltaPKC is associated with phosphorylation of the alphaE1 subunit of PDH. A potential mechanism is provided by in vitro data demonstrating that deltaPKC specifically interacts with and phosphorylates pyruvate dehydrogenase kinase (PDK)2. Importantly, this results in activation of PDK2, an enzyme capable of phosphorylating and inhibiting PDH. Thus, translocation of deltaPKC to the mitochondria during reperfusion likely results in activation of PDK2 and phosphorylation-dependent inhibition of PDH.

Brief increase in carbohydrate oxidation after reperfusion reverses myocardial stunning in conscious pigs

BACKGROUND

Previous studies have examined only acute effects of enhanced glucose oxidation on postischemic myocardium. The goal of the present study was to examine prolonged functional recovery subsequent to postischemic, intracoronary pyruvate dehydrogenase kinase inhibition with dichloroacetate (DCA) of stunned myocardium in conscious pigs.

METHODS AND RESULTS

Myocardial stunning was induced in conscious pigs by coronary stenosis, ie, 40% reduction of coronary blood flow for 90 minutes, followed by full reperfusion. After the initial peak, but during early reactive hyperemia (5 minutes of reperfusion), 1 hour of intracoronary infusion at 20% of measured coronary blood flow was begun using 20 mmol/L [2-(13)C]glucose without (n=4) or with (n=5) 20 mmol/L DCA. Coronary stenosis resulted in similar reduction in wall thickening in both untreated (-53+/-3% from 3.27+/-0.22 mm, n=9) and DCA (-51+/-3% from 3.08+/-0.15 mm, n=5) groups. During reperfusion, DCA increased glucose oxidation 10-fold. In the absence of DCA, myocardial stunning was observed; ie, wall thickening was reduced by 48+/-3% at 1 hour of reperfusion and did not fully recover for 48 hours. In contrast, in DCA pigs, myocardial stunning was ameliorated (P<0.05).

CONCLUSIONS

Transient metabolic intervention within a clinically relevant time after ischemia eliminates myocardial stunning in conscious pigs during augmented carbohydrate oxidation and provides sustained benefits in contractile recovery.

Troglitazone improves recovery of left ventricular function after regional ischemia in pigs

BACKGROUND

This study determined whether treatment of normal (nondiabetic) pigs with the insulin-sensitizing agent troglitazone improves recovery of left ventricular (LV) function after acute ischemia and whether such effects are associated with altered myocardial substrate metabolism.

METHODS AND RESULTS

Juvenile pigs (n=6) were treated with troglitazone (75 mg. kg(-1). d(-1) PO) for 8 weeks. Untreated pigs (n=8) served as controls. Under anesthetized, open-chest conditions, pigs underwent 90 minutes of moderate regional LV ischemia and 90 minutes of reperfusion. Regional LV function was assessed with subendocardial sonomicrometry crystals. Fasting plasma insulin and free fatty acid levels were lower in troglitazone-treated pigs than in untreated pigs, whereas blood glucose did not differ between groups. These findings suggest that treatment enhanced systemic insulin sensitivity. Baseline hemodynamics and regional LV function did not differ between groups. After ischemia and reperfusion, systolic function (external work) of the ischemic region recovered to 44+/-6% of baseline in troglitazone-treated pigs versus 18+/-6% of baseline in untreated pigs (P<0.05). Regional diastolic function (maximum rate of wall expansion) recovered to 78+/-7% of baseline in treated pigs versus 52+/-7% of baseline in untreated pigs (P<0.05). Recovery of global LV systolic and diastolic function was also significantly greater in treated pigs. Myocardial glucose uptake did not differ between groups under any condition; however, net myocardial lactate uptake after reperfusion was 7 times greater in troglitazone-treated pigs than in untreated pigs, suggesting that treatment enhanced myocardial carbohydrate oxidation after reperfusion.

CONCLUSIONS

In nondiabetic pigs, chronic troglitazone treatment improves recovery of LV systolic and diastolic function after acute ischemia.

Regulation of pyruvate dehydrogenase activity and glucose metabolism in post-ischaemic myocardium

Pyruvate dehydrogenase (PDH) is regulated both by covalent modification and through modulation of the active enzyme by metabolites. In the isolated heart, post-ischaemic inhibition of PDH, leading to uncoupling of glycolysis and glucose oxidation and a decrease in cardiac efficiency, has been described. In vivo, post-ischaemic reperfusion leads to metabolic abnormalities consistent with PDH inhibition, but the effects of ischaemia/reperfusion on PDH are not well characterized. We therefore investigated PDH regulation following transient ischaemia in vivo. In 33 open-chest dogs, the left anterior descending (LAD) was occluded for 20 min followed by 4 h reperfusion. In 17 dogs, dichloroacetate (DCA) was injected prior to reperfusion, while 16 dogs served as controls. In dogs without DCA, glucose oxidation and lactate uptake were lower in reperfused than in remote tissue, suggesting reduced flux through PDH. However, percent active and total PDH measured in myocardial biopsies were similar in both territories, excluding covalent enzyme modification or loss of functional enzyme. DCA activated PDH activity similarly in both regions and abolished differences in glucose oxidation and lactate uptake. Thus, decreased PDH flux in reperfused myocardium does not result from covalent modification or loss of total enzyme activity, but more likely from metabolite inhibition of the active enzyme. DCA leads to essentially complete activation of PDH, increases overall glucose utilization and abolishes post-ischaemic inhibition of glucose oxidation.