Sodium-hydrogen exchange inhibition and beta-blockade additively decrease infarct size.

BACKGROUND: Perioperative myocardial infarction adversely affects survival after cardiac operations. In animal studies Na+/H+ exchange inhibitors protect hearts against ischemia-reperfusion injury, but human trials have failed to consistently show beneficial effects. The aim of this study was to investigate whether the combination of the Na+/H+ exchange inhibitor cariporide and the beta-blocker metoprolol additively protects hearts from severe ischemia-reperfusion injury. METHODS: Isolated Langendorff-perfused rat hearts were randomly assigned to a vehicle-treated control group, or groups with 10-minute preischemia infusions of cariporide (10 micromol/L), metoprolol (10 micromol/L), or both cariporide and metoprolol. The hearts were then subjected to 20 minutes of global ischemia followed by 60 minutes of reperfusion. At the end of reperfusion, the hearts were randomly assigned to undergo either infarct size measurements or left ventricular mitochondrial function analyses. RESULTS: The combination of cariporide and metoprolol limited infarct size significantly compared with control group or cariporide alone (5% +/- 1% versus 58% +/- 9% or 38.4% +/- 4% of risk zone; p < 0.05). Cariporide alone did not reduce infarct size significantly as compared with the control group. As compared with the control group, cariporide and metoprolol decreased mitochondrial calcium content (6.4 +/- 1.2 versus 10.2 +/- 1.1 nmol/mg protein; p < 0.05), and increased respiratory control ratio (9.5 +/- 0.6 versus 5.3 +/- 0.7; p < 0.05). However, hearts treated with cariporide or metoprolol alone did not show significant improvement in mitochondrial calcium content (7.8 +/- 1.2 and 7.8 +/- 1.5 nmol/mg protein) or respiratory control ratio (5.0 +/- 0.7 and 7.3 +/- 0.7). CONCLUSIONS: The combination of cariporide and metoprolol additively limits infarct size after severe ischemia-reperfusion injury in an isolated rat heart model. Infarct size reduction occurs in association with protection from increased mitochondrial calcium content after reperfusion.

Induction of the permeability transition and cytochrome c release by 15-deoxy-Delta12,14-prostaglandin J2 in mitochondria.

The electrophilic lipid 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) is known to allow adaptation to oxidative stress in cells at low concentrations and apoptosis at high levels. The mechanisms leading to adaptation involve the covalent modification of regulatory proteins, such as Keap1, and augmentation of antioxidant defences in the cell. The targets leading to apoptosis are less well defined, but mitochondria have been indirectly implicated in the mechanisms of cell death mediated by electrophilic lipids. To determine the potential of electrophilic cyclopentenones to induce pro-apoptotic effects in the mitochondrion, we used isolated liver mitochondria and demonstrated that 15d-PGJ2 promotes Ca2+-induced mitochondrial swelling and cytochrome c release. The mechanisms involved are consistent with direct modification of protein thiols in the mitochondrion, rather than secondary formation of reactive oxygen species or lipid peroxidation. Using proteomic analysis in combination with biotinylated 15d-PGJ2, we were able to identify 17 potential targets of the electrophile-responsive proteome in isolated liver mitochondria. Taken together, these results suggest that electrophilic lipid oxidation products can target a sub-proteome in mitochondria, and this in turn results in the transduction of the electrophilic stimulus to the cell through cytochrome c release.

Mitochondrial dysfunction in cardiac ischemia-reperfusion injury: ROS from complex I, without inhibition.

A key pathologic event in cardiac ischemia reperfusion (I-R) injury is mitochondrial energetic dysfunction, and several studies have attributed this to complex I (CxI) inhibition. In isolated perfused rat hearts, following I-R, we found that CxI-linked respiration was inhibited, but isolated CxI enzymatic activity was not. Using the mitochondrial thiol probe iodobutyl-triphenylphosphonium in conjunction with proteomic tools, thiol modifications were identified in several subunits of the matrix-facing 1alpha sub-complex of CxI. These thiol modifications were accompanied by enhanced ROS generation from CxI, but not complex III. Implications for the pathology of cardiac I-R injury are discussed.

Multiple treatment approach to limit cardiac ischemia-reperfusion injury.

BACKGROUND: This study evaluates a multiple treatment approach (ie, pharmacologic preconditioning [diazoxide], sodium-proton exchange inhibition [cariporide], and controlled reperfusion) to improve the outcome from severe cardiac ischemia-reperfusion injury that occurs during a cardiac operation. METHODS: Five groups of 10 pigs (group 1: control, group 2: diazoxide, group 3: cariporide, group 4: controlled reperfusion, and group 5: combination of diazoxide and cariporide-controlled reperfusion) underwent 75 minutes of left anterior descending occlusion, 1 hour of cardioplegic arrest, and 2 hours of reperfusion. Prior to occlusion, each group received an infusion of vehicle alone (ie, dimethylsulfoxide for the control and the controlled reperfusion groups) or vehicle with drug (ie, diazoxide or cariporide, or both for all other groups). Infarct size (primary outcome) was measured and was normalized to the region at risk. Regional function (secondary outcome) was measured using preload recruitable work area. RESULTS: Infarct size as a function of area at risk was decreased by cariporide-controlled reperfusion, and combination treatment compared with the control group (14 +/- 6%, 15 +/- 8%, and 9 +/- 4% vs 24 +/- 9%; p < 0.02), and variation in infarct size was decreased by combination treatment compared with the controlled reperfusion group alone (p < 0.02). Recovery of systolic function during reperfusion significantly improved in the left anterior descending region in the cariporide and combination groups compared with the control, controlled reperfusion, or diazoxide groups (group-time effect, p < 0.05). CONCLUSIONS: Combined use of controlled reperfusion, cariporide, and diazoxide decreases myocyte necrosis and loss of systolic function compared with an untreated control group. Combination treatment has the potential to improve the results of cardiac surgery, however further improvements are needed before clinical application.