Ischemic preconditioning prevents in vivo hyperoxygenation in postischemic myocardium with preservation of mitochondrial oxygen consumption

Mitochondrial redox regulation and myocardial ischemia-reperfusion injury

Mitochondrial reactive oxygen species (ROS) have emerged as an important mechanism of disease and redox signaling in the cellular system. Under basal or pathological conditions, electron leakage for ROS production is primarily mediated by complexes I and III of the electron transport chain (ETC) and by the proton motive force (PMF), consisting of a membrane potential (ΔΨ) and a proton gradient (ΔpH). Several factors control redox status in mitochondria, including ROS, the PMF, oxidative posttranslational modifications (OPTM) of the ETC subunits, SOD2, and cytochrome c heme lyase (HCCS). In the mitochondrial PMF, increased ΔpH-supported backpressure due to diminishing electron transport and chemiosmosis promotes a more reductive mitochondrial physiological setting. OPTM by protein cysteine sulfonation in complex I and complex III has been shown to affect enzymatic catalysis, the proton gradient, redox status, and enzyme-mediated ROS production. Pathological conditions associated with oxidative or nitrosative stress, such as myocardial ischemia and reperfusion (I/R), increase mitochondrial ROS production and redox dysfunction via oxidative injury to complexes I and III, intensely enhancing protein cysteine sulfonation and impairing heme integrity. The physiological conditions of reductive stress induced by gains in SOD2 function normalize I/R-mediated ROS overproduction and redox dysfunction. Further insight into the cellular mechanisms by which HCCS, biogenesis of c-type cytochrome, and OPTM regulate PMF and ROS production in mitochondria will enrich our understanding of redox signal transduction and identify new therapeutic targets for cardiovascular diseases in which oxidative stress perturbs normal redox signaling.

Role of microRNA-145 in protection against myocardial ischemia/reperfusion injury in mice by regulating expression of GZMK with the treatment of sevoflurane

This study aims to investigate the role of microRNA-145 (miR-145) in protection against myocardial ischemia/reperfusion (I/R) injury in mice by regulating expression of granzyme K (GZMK) with the treatment of sevoflurane. The mice model of myocardial I/R injury was established by left coronary artery ligation. The expression of miR-145 and GZMK in myocardial tissues of mice was detected by Reverse transcription quantitative polymerase chain reaction and western blot analysis. The changes of the cardiac function and hemodynamics, pathological changes of myocardial tissues, the ultrastructure of cardiomyocytes, myocardial infarction area, and cardiomyocyte apoptosis were observed. The expression of the apoptosis-related protein cleaved-caspase-3, Bax, and Bcl-2 was detected by western blot analysis. The levels of malondialdehyde, myeloperoxidase, superoxide dismutase in myocardial tissues were detected by spectrophotometric colorimetry. The levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α in the serum of mice were detected by the enzyme-linked immunosorbent assay. The level of oxidative stress and the expression of inflammatory factors increased in mice with myocardial I/R injury. Sevoflurane postconditioning could reduce myocardial I/R injury in mice. Sevoflurane postconditioning may protect myocardial I/R injury through miR-145-regulation of GZMK in mice. Inhibition of miR-145 expression could reduce the protective effect of sevoflurane posttreatment on myocardial I/R injury in mice. Low expression of GZMK could attenuate the inhibitory effect of miR-145 on myocardial I/R injury after sevoflurane treatment in mice. Our study suggests that sevoflurane postconditioning may protect against myocardial I/R injury by upregulating miR-145 expression and downregulating GZMK expression.

KRT1 gene silencing ameliorates myocardial ischemia-reperfusion injury via the activation of the Notch signaling pathway in mouse models

Myocardial ischemia and reperfusion injury (MIRI) includes major drawbacks, such as excessive formation of free radicals and also overload of calcium, which lead to cell death, tissue scarring, and remodeling. The current study aims to explore whether KRT1 silencing may ameliorate MIRI via the Notch signaling pathway in mouse models. Myocardial tissues were used for the determination of the positive rate of KRT1 protein expression, apoptosis of myocardial cells, creatine kinase (CK) and lactate dehydrogenase (LDH) expression, expression of related biomarkers as well as myocardial infarction area. The transfected myocardial cells were treated with KRT1-siRNA, Jagged1, and DAPT (inhibitor of Notch-1 signaling pathway). The expression of KRT1, NICD, Hes1, Bcl-2, and Bax protein was detected. The MTT assay was applied for cell proliferation and flow cytometry was used for cell apoptosis. Mice with MIRI had a higher positive rate of KRT1 protein expression, apoptosis of myocardial cells, CK and LDH expression, myocardial infarction area, increased expression of MDA, NO, SDH, IL-1, IL-6, TNF-α, CRP, KRT1, Bax protein, CK, and LDH, and decreased expression of SOD, NICD, Hes1, and Bcl-2. The downregulation of KRT1 led to decreased expression of KRT1 and Bax protein, increased expression of NICD, Hes1, and Bcl-2, decreased cell apoptosis, and improved cell proliferation. The inhibition of the Notch signaling pathway leads to reduced expression of Bax, increased expression of NICD, Hes1, and Bcl 2, and also decreased cell apoptosis and increased cell proliferation. Our data conclude that KRT1 silencing is able to make MIRI better by activating the Notch signaling pathway in mice.

Mitochondrial complex I in the post-ischemic heart: reperfusion-mediated oxidative injury and protein cysteine sulfonation

A serious consequence of ischemia-reperfusion injury (I/R) is oxidative damage leading to mitochondrial dysfunction. Such I/R-induced mitochondrial dysfunction is observed as impaired state 3 respiration and overproduction of O₂^-. The cascading ROS can propagate cysteine oxidation on mitochondrial complex I and add insult to injury. Herein we employed LC-MS/MS to identify protein sulfonation of complex I in mitochondria from the infarct region of rat hearts subjected to 30-min of coronary ligation and 24-h of reperfusion in vivo as well as the mitochondria of sham controls. Mitochondrial preparations from the I/R regions had enhanced sulfonation levels on the cysteine ligands of iron‑sulfur clusters, including N3 (C₄₂₅), N1b (C₉₂), N4 (C₂₂₆), N2 (C₁₅₈/C₁₈₈), and N1a (C₁₃₄/C₁₃₉). The 4Fe-4S centers of N3, N1b, N4, and N2 are key redox-active components of complex I, thus sulfonation of metal-binding sites impaired the main electron transfer pathway. The binuclear N1a has a very low redox potential and an antioxidative function. Increased C₁₃₄/C₁₃₉ sulfonation by I/R impaired the N1a cluster, potentially contributing to overall O₂^- generation by the FMN moiety of complex I. MS analysis also revealed I/R-mediated increased sulfonation at the core subunits of 51 kDa (C₁₂₅, C₁₈₇, C₂₀₆, C₂₃₈, C₂₅₅, C₂₈₆), 75 kDa (C₃₆₇, C₅₅₄, C₅₆₄, C₇₂₇), 49 kDa (C₁₄₆, C₃₂₆, C₃₄₇), and PSST (C₁₈₈). These results were consistent with the consensus indicating that 51 kDa and 75 kDa are two of major subunits hosting regulatory thiols, and their enhanced sulfonation by I/R predisposed the myocardium to further oxidant stress with impaired ubiquinone reduction. MS analysis further showed I/R-mediated enhanced sulfonation at the supernumerary subunits of 42 kDa (C₆₇, C₁₁₂, C₁₈₃, C₂₅₃), 15 kDa (C₄₃), and 13 kDa (C₇₉). The 42 kDa protein is metazoan-specific, which was reported to stabilize mammalian complex I. C₄₃ of the 15 kDa subunit forms an intramolecular disulfide bond with C₅₆, which was reported to stabilize complex I structure. C₇₉ of the 13 kDa subunit is involved in Zn²⁺-binding, which was reported functionally important for complex I assembly. C₇₉ sulfonation by I/R was found to impair Zn²⁺-binding. No significant enhancement of protein sulfonation was observed in mitochondrial complex I from the rat heart subjected to 30-min ischemia alone in vivo despite a decreased state 3 respiration, suggesting that the physiologic conditions of hyperoxygenation during reperfusion mediated an increase in complex I sulfonation and oxidative injury. In conclusion, sulfonation of specific cysteines of complex I mediates I/R-induced mitochondrial dysfunction via impaired ETC activity, increasing ^•O₂^- production, and mediating redox dysfunction of complex I.

Inactivated Lactobacillus promotes protection against myocardial ischemia-reperfusion injury through NF-κB pathway

Although restoration of blood flow to an ischemic organ is essential to prevent irreversible cellular injury, reperfusion may augment tissue injury in excess of that produced by ischemia alone. So this experiment was designed to study the protective effects and mechanism of inactivated Lactobacillus (Lac) on myocardial ischemia–reperfusion (I–R) injury (MIRI). MIRI rat models were established by ligation of left anterior descending coronary artery for ~30 min and then, reperfusion for 120 min and divided into control group, model group, and Lac (10⁶, 10⁷, and 10⁸ cfu/kg) groups. At the end of the test, the creatine kinase (CK) activity, lactate dehydrogenase (LDH) activity, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were assayed by corresponding kits. The heart was obtained from rats and the myocardial infarction area was determined by TTC staining and myocardial endothelial cell apoptosis rate was determined by Tunel kit. Besides, A20, IκB, nuclear factor (NF)-κB, and nitric oxide (NO) synthase (NOS) were also assayed by Western blot. When compared with model group, Lac obviously reduces MIRI in the rat by reducing myocardial infarction area and the apoptosis rate of endothelial cells; reduce the serum CK, LDH, and MDA content; increase the serum SOD activity; and suppress NF-κB signaling and NOS expression in the myocardial tissues. Lac pretreatment can inhibit lipid peroxidation and effectively improve MIRI caused by oxygen free radical through inhibiting NF-κB signaling.

Measurement of Reactive Oxygen Species, Reactive Nitrogen Species, and Redox-Dependent Signaling in the Cardiovascular System: A Scientific Statement From the American Heart Association

Reactive oxygen species and reactive nitrogen species are biological molecules that play important roles in cardiovascular physiology and contribute to disease initiation, progression, and severity. Because of their ephemeral nature and rapid reactivity, these species are difficult to measure directly with high accuracy and precision. In this statement, we review current methods for measuring these species and the secondary products they generate and suggest approaches for measuring redox status, oxidative stress, and the production of individual reactive oxygen and nitrogen species. We discuss the strengths and limitations of different methods and the relative specificity and suitability of these methods for measuring the concentrations of reactive oxygen and reactive nitrogen species in cells, tissues, and biological fluids. We provide specific guidelines, through expert opinion, for choosing reliable and reproducible assays for different experimental and clinical situations. These guidelines are intended to help investigators and clinical researchers avoid experimental error and ensure high-quality measurements of these important biological species.

Resveratrol attenuated hydrogen peroxide-induced myocardial apoptosis by autophagic flux

Background

Resveratrol is a Sirt-1-specific activator, which also exerts cardioprotective effects that regulate redox signalling during oxidative stress and autophagy during cardiovascular disease (CVD).

Objective

This study investigated the protective effects of resveratrol against hydrogen peroxide-induced damage in cardiomyocytes.

Design

In this article, hydrogen peroxide-induced autophagy and apoptosis in H9c2 cardiomyoblasts were studied at an increasing concentration from 0 to 100 µM.

Results

Resveratrol pretreatment with concentrations of 10, 20, and 50 µM inhibits autophagic apoptosis by increasing p-Akt and Bcl-2 protein levels in H9c2 cells. Interestingly, resveratrol treatment activates the Beclin-1, LC3, p62, and the lysosome-associated protein LAMP2a within 24 h of administration.

Conclusions

These results suggest that resveratrol-regulated autophagy may play a role in degrading damaged organelles in H9c2 cells rather than causing apoptosis, and this may be a possible mechanism by which resveratrol protects the heart during CVD.

Functional electron paramagnetic resonance imaging of ischemic rat heart: Monitoring of tissue oxygenation and pH

PURPOSE

Electron paramagnetic resonance (EPR) imaging in the spectral-spatial domain with application of soluble paramagnetic probes provides an opportunity for spatially resolved functional measurements of living objects. The purpose of this study was to develop EPR methods for visualization of oxygenation and acidosis of ischemic myocardium.

METHODS

EPR oxygen measurements were performed using isotopically substituted (2) H,(15) N-dicarboxyproxyl. The radical has an EPR line width of 320 mG and oxygen-induced line broadening of 0.53 mG/mm Hg, providing oxygen sensitivity down to 5 μM. pH measurements were performed using previously developed pH-sensitive imidazoline nitroxide. The radical has an EPR spectrum with pH-dependable hyperfine splitting, pK = 6.6, providing pH sensitivity of approximately 0.05 U in the physiological range.

RESULTS

EPR imaging of isolated and perfused rat hearts was performed in the two-dimensional + spectral domain. The spatial resolution of the measurements was about 1.4 mm. Marked tissue hypoxia was observed in the ischemic area of the heart after occlusion of the left anterior descending coronary artery. Tissue oxygenation was partly restored upon reperfusion. EPR mapping of myocardial pH indicated acidosis of the ischemic area down to pH 6.7-6.8.

CONCLUSION

This study demonstrates the capability of low-field EPR and the nitroxide spin probes for mapping of myocardial oxygenation and pH. The developed approaches might be used for noninvasive investigation of microenvironment on living objects. Magn Reson Med 76:350-358, 2016. © 2015 Wiley Periodicals, Inc.

Ischemic preconditioning accelerates muscle deoxygenation dynamics and enhances exercise endurance during the work-to-work test

Ischemic preconditioning (IPC) improves maximal exercise performance. However, the potential mechanism(s) underlying the beneficial effects of IPC remain unknown. The dynamics of pulmonary oxygen uptake (VO2) and muscle deoxygenation during exercise is frequently used for assessing O2 supply and extraction. Thus, this study examined the effects of IPC on systemic and local O2 dynamics during the incremental step transitions from low- to moderate- and from moderate- to severe-intensity exercise. Fifteen healthy, male subjects were instructed to perform the work-to-work cycling exercise test, which was preceded by the control (no occlusion) or IPC (3 × 5 min, bilateral leg occlusion at >300 mmHg) treatments. The work-to-work test was performed by gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 min, moderate intensity at 90% of the gas exchange threshold (GET) for 4 min, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the exercise test, the breath-by-breath pulmonary VO2 and near-infrared spectroscopy-derived muscle deoxygenation were continuously recorded. Exercise endurance during severe-intensity exercise was significantly enhanced by IPC. There were no significant differences in pulmonary VO2 dynamics between treatments. In contrast, muscle deoxygenation dynamics in the step transition from low- to moderate-intensity was significantly faster in IPC than in CON (27.2 ± 2.9 vs. 19.8 ± 0.9 sec, P < 0.05). The present findings showed that IPC accelerated muscle deoxygenation dynamics in moderate-intensity exercise and enhanced severe-intensity exercise endurance during work-to-work test. The IPC-induced effects may result from mitochondrial activation in skeletal muscle, as indicated by the accelerated O2 extraction.

Endurance exercise accelerates myocardial tissue oxygenation recovery and reduces ischemia reperfusion injury in mice

Exercise training offers cardioprotection against ischemia and reperfusion (I/R) injury. However, few essential signals have been identified to underscore the protection from injury. In the present study, we hypothesized that exercise-induced acceleration of myocardial tissue oxygenation recovery contributes to this protection. C57BL/6 mice (4 weeks old) were trained on treadmills for 45 min/day at a treading rate of 15 m/min for 8 weeks. At the end of 8-week exercise training, mice underwent 30-min left anterior descending coronary artery occlusion followed by 60-min or 24-h reperfusion. Electron paramagnetic resonance oximetry was performed to measure myocardial tissue oxygenation. Western immunoblotting analyses, gene transfection, and myography were examined. The oximetry study demonstrated that exercise markedly shortened myocardial tissue oxygenation recovery time following reperfusion. Exercise training up-regulated Kir6.1 protein expression (a subunit of ATP-sensitive K(+)channel on vascular smooth muscle cells, VSMC sarc-K(ATP)) and protected the heart from I/R injury. In vivo gene transfer of dominant negative Kir6.1AAA prolonged the recovery time and enlarged infarct size. In addition, transfection of Kir6.1AAA increased the stiffness and reduced the relaxation capacity in the vasculature. Together, our study demonstrated that exercise training up-regulated Kir6.1, improved tissue oxygenation recovery, and protected the heart against I/R injury. This exercise-induced cardioprotective mechanism may provide a potential therapeutic intervention targeting VSMC sarc-K(ATP) channels and reperfusion recovery.

Effects of losartan and vanillic Acid co-administration on ischemia-reperfusion-induced oxidative stress in isolated rat heart

Background:

Experimental studies have demonstrated that angiotensin II (ANG-II)-induced oxidative stress contributes to the pathogenesis of I/R injury.

Objectives:

This study was aimed to investigate the protective effects of co-administration of losartan, as a selective ANG-II type 1 receptor (AT1R) blocker, and vanillic acid (VA), as an antioxidant, in I/R-induced oxidative stress in isolated rat heart.

Materials and Methods:

Adult male Wistar rats were randomly divided to sham, control, and five treatment groups (n = 10). Two doses of VA (5 and 10 mg/kg), one dose of losartan (20 mg/kg) alone, and one dose of losartan in combination with either doses of VA were administered orally for 10 days. The hearts were isolated and exposed to 30 minutes ischemia and 60 minutes reperfusion, using Langendorff apparatus. I/R-induced myocardial injury was assessed by estimating the release of lactate dehydrogenase (LDH), creatine phosphokinase (CPK) and myocardial creatine kinase (CK-MB) in coronary effluent at 5, 15, and 60 minutes of reperfusion. The oxidative stress in the hearts was assessed by estimating malondialdehyde (MDA). The effects of treatments on endogenous antioxidant enzymes were assessed by measuring superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT).

Results:

There was a more significant decrease in the levels of LDH, CPK, CK-MB, and MDA as well as increase in the levels of SOD, CAT and GPx in groups that had received combined treatment in comparison to VA or losartan alone.

Conclusions:

It may be concluded that combination of losartan with higher dose of VA decreases ischemic markers and lipid peroxidation and augments endogenous antioxidant and hence, protects myocardium against I/R-induced oxidative stress injuries.

Ischemic preconditioning results in an ATP-dependent inhibition of cytochrome C oxidase

PURPOSE

This study addresses the effect of short myocardial ischemia on inhibitory effect of ATP for mitochondrial cytochrome c oxidase (CytOx) activity in myocardium and subsequent hemodynamic alterations. The activity of CytOx is inhibited by ATP (primary substrate control). This additional mechanism was proposed to be switched off at higher mitochondrial membrane potential values in case of stress. The ATP-dependent allosteric enzyme inhibition (second respiratory control) is suggested to reduce the formation of reactive oxygen species and thus is pivotal for cytoprotection. This report addresses the possible involvement of this mechanism in case of myocardial preconditioning.

METHODS

Rat hearts were perfused in a Langendorff system (n = 5 each group). The first two groups underwent short recurrent ischemic periods (three times 5 min) and subsequent high or low reperfusion for 40 min. Besides four control groups, hearts were exposed to an ischemia of 15 min and high flow reperfused for 30 min, in addition. Hemodynamic data were evaluated in parallel. Mitochondria were separated for the polarographic respiration measurements in the presence of ADP or ATP, respectively. Phosphorylation patterns of the CytOx subunits were studied by immunoblotting with P-Ser, P-Thr, and P-Tyr antibodies.

RESULTS

Short recurrent episodes of ischemia result in an ATP-dependent inhibition of CytOx. Electrophoretic analysis and blotting techniques reveal different phosphorylation patterns of the enzyme. Frequent short-lasting ischemic impacts and subsequent increased coronary flow seem to be essential for this effect.

CONCLUSION

The procedure of preconditioning is likely to be dependent on the mechanism of ATP-dependent inhibition of CytOx activity.

Delayed preconditioning prevents ischemia/reperfusion-induced endothelial injury in rats: role of ROS and eNOS

Ischemic preconditioning (IPC) strongly protects against ischemia/reperfusion (I/R) injury; however, the molecular mechanism involved in delayed preconditioning-induced endothelial protection in peripheral arteries is unknown. Therefore, we examined using functional, morphologic and molecular biologic studies whether delayed IPC decreases formation of reactive oxygen species and upregulates endothelial nitric oxide synthase (eNOS) that in turn contributes to vascular endothelial protection. Adult male Sprague-Dawley rats were subjected to 30-min ischemia induced by mesenteric artery occlusion followed by 60-min reperfusion 24 h after sham surgery or preconditioning (three cycles of 5-min ischemia/5-min reperfusion). Delayed preconditioning prevented the I/R-induced impairment of endothelium-dependent relaxations to acetylcholine (maximal relaxation: sham 91.4±2.2%; I/R 54.0±4.0%; IPC 80.2±6.3%). This protective effect was abolished by NOS inhibitor N(G)-nitro-L-arginine methyl ester and not changed by ascorbic acid. Electron microscopy showed marked endothelial damage after I/R and the ultrastructural changes were prevented by delayed preconditioning. Following I/R, the impairment of eNOS phosphorylation and expression was observed in mesenteric vessels. Furthermore, phosphatidylinositol 3-kinase (PI3K) and Akt phosphorylation were reduced, although total PI3K and Akt remained unchanged. IPC restored I/R-induced impairment of eNOS expression and activity. This was possibly the result of the recovery of PI3K/Akt phosphorylation. Furthermore, I/R increased serum level of malondialdehyde, intravascular superoxide and nitrotyrosine generation, which were abrogated by IPC. These results suggest that delayed preconditioning prevented I/R-induced endothelial injury in peripheral resistance vasculature, both in terms of functional and structural changes. Endothelial protection afforded by delayed IPC is associated with inhibition of oxidative stress and upregulation of PI3K/Akt/eNOS pathway.

Hyperoxia and transforming growth factor β1 signaling in the post-ischemic mouse heart

AIMS

Following ischemic injury, myocardial healing and remodeling occur with characteristic myofibroblast trans-differentiation and scar formation. The current study tests the hypothesis that hyperoxia and nitric oxide (NO) regulate TGF-β1 signaling in the post-ischemic myocardium.

MAIN METHODS

C57BL/6 wild-type (WT), endothelial and inducible nitric oxide synthase knockout (eNOS(-/-) and iNOS(-/-)) mice were subjected to 30-min left anterior descending coronary artery occlusion followed by reperfusion. Myocardial tissue oxygenation was monitored with electron paramagnetic resonance oximetry. Protein expressions of TGF-β1, receptor-activated small mothers against decapentaplegic homolog (Smad), p21 and α-smooth muscle actin (α-SMA) were measured with enzyme-linked immunosorbent assay (ELISA), Western immunoblotting, and immunohistochemical staining.

KEY FINDINGS

There was a hyperoxic state in the post-ischemic myocardial tissue. Protein expressions of total and active TGF-β1, p-Smad2/3 over t-Smad2/3 ratio, p21, and α-SMA were significantly increased in WT mice compared to Sham control. Knockout of eNOS or iNOS further increased protein expression of these signals. The expression of α-SMA was more abundant in the infarct of eNOS(-/-) and iNOS(-/-) mice than WT mice. A protein band indicating nitration of TGF-β type-II receptor (TGFβRII) was observed from WT heart. Carbogen (95% O2 plus 5% CO2) treatment increased the ratio of p-Smad2/t-Smad2, which was inhibited by 10006329 EUK (EUK134) and sodium nitroprusside (SNP). In conclusion, hyperoxia up-regulated and NO/ONOO(-) inhibited cardiac TGF-β1 signaling and myofibroblast trans-differentiation.

SIGNIFICANCE

These findings may provide new insights in myocardial infarct healing and repair.

Tyrosine nitration of voltage-dependent anion channels in cardiac ischemia-reperfusion: reduction by peroxynitrite scavenging

Excess superoxide (O(2)(-)) and nitric oxide (NO) forms peroxynitrite (ONOO(-)) during cardiac ischemia reperfusion (IR) injury, which in turn induces protein tyrosine nitration (tyr-N). Mitochondria are both a source of and target for ONOO(-). Our aim was to identify specific mitochondrial proteins that display enhanced tyr-N after cardiac IR injury, and to explore whether inhibiting O(2)(-)/ONOO(-) during IR decreases mitochondrial protein tyr-N and consequently improves cardiac function. We show here that IR increased tyr-N of 35 and 15kDa mitochondrial proteins using Western blot analysis with 3-nitrotyrosine antibody. Immunoprecipitation (IP) followed by LC-MS/MS identified 13 protein candidates for tyr-N. IP and Western blot identified and confirmed that the 35kDa tyr-N protein is the voltage-dependent anion channel (VDAC). Tyr-N of native cardiac VDAC with IR was verified on recombinant (r) VDAC with exogenous ONOO(-). We also found that ONOO(-) directly enhanced rVDAC channel activity, and rVDAC tyr-N induced by ONOO(-) formed oligomers. Resveratrol (RES), a scavenger of O(2)(-)/ONOO(-), reduced the tyr-N levels of both native and recombinant VDAC, while L-NAME, which inhibits NO generation, only reduced tyr-N levels of native VDAC. O(2)(-) and ONOO(-) levels were reduced in perfused hearts during IR by RES and L-NAME and this was accompanied by improved cardiac function. These results identify tyr-N of VDAC and show that reducing ONOO(-) during cardiac IR injury can attenuate tyr-N of VDAC and improve cardiac function.

Electron paramagnetic resonance monitoring of ischemia-induced myocardial oxygen depletion and acidosis in isolated rat hearts using soluble paramagnetic probes

A new low-field electron paramagnetic resonance approach for noninvasive measurements of myocardial oxygen tension and tissue acidity was developed. The approach was applied to monitor myocardial pO(2) and pH in a model of global no-flow ischemia (30 min) and reperfusion in isolated perfused rat hearts. The myocardial oxygen measurements were performed using deuterated Finland trityl radical probe. A rapid decrease in myocardial pO(2) from 160 mmHg to about 2 ± 1 mmHg was observed within the first minute of ischemia followed by incomplete restoration of pO(2) to 50 mmHg during 30 min of reperfusion. The lower oxygen concentration after ischemia was attributed to the 50% reduction in coronary flow after ischemia as a consequence of myocardial ischemia and reperfusion damage. Myocardial pH measurements using a specially designed imidazoline pH-sensitive nitroxide showed severe myocardial acidification to pH 6.25 during 30 min of ischemia. Preconditioning of the hearts with two 5-min periods of ischemia significantly reduced the acidification of myocardial tissue during sustained ischemia. Noninvasive electron paramagnetic resonance monitoring of myocardial oxygenation and pH may provide important insights into the mechanisms of ischemia and reperfusion injury and a background for development of new therapeutic approaches.

The cellular and molecular origin of reactive oxygen species generation during myocardial ischemia and reperfusion

Myocardial ischemia-reperfusion injury is an important cause of impaired heart function in the early postoperative period subsequent to cardiac surgery. Reactive oxygen species (ROS) generation increases during both ischemia and reperfusion and it plays a central role in the pathophysiology of intraoperative myocardial injury. Unfortunately, the cellular source of these ROS during ischemia and reperfusion is often poorly defined. Similarly, individual ROS members tend to be grouped together as free radicals with a uniform reactivity towards biomolecules and with deleterious effects collectively ascribed under the vague umbrella of oxidative stress. This review aims to clarify the identity, origin, and progression of ROS during myocardial ischemia and reperfusion. Additionally, this review aims to describe the biochemical reactions and cellular processes that are initiated by specific ROS that work in concert to ultimately yield the clinical manifestations of myocardial ischemia-reperfusion. Lastly, this review provides an overview of several key cardioprotective strategies that target myocardial ischemia-reperfusion injury from the perspective of ROS generation. This overview is illustrated with example clinical studies that have attempted to translate these strategies to reduce the severity of ischemia-reperfusion injury during coronary artery bypass grafting surgery.

Mechanisms of the beneficial actions of ischemic preconditioning on subcellular remodeling in ischemic-reperfused heart

Cardiac function is compromised by oxidative stress which occurs upon exposing the heart to ischemia reperfusion (I/R) for a prolonged period. The reactive oxygen species (ROS) that are generated during I/R incur extensive damage to the myocardium and result in subcellular organelle remodeling. The cardiac nucleus, glycocalyx, myofilaments, sarcoplasmic reticulum, sarcolemma, and mitochondria are affected by ROS during I/R injury. On the other hand, brief periods of ischemia followed by reperfusion, or ischemic preconditioning (IPC), have been shown to be cardioprotective against oxidative stress by attenuating the cellular damage and alterations of subcellular organelles caused by subsequent I/R injury. Endogenous defense mechanisms, such as antioxidant enzymes and heat shock proteins, are activated by IPC and thus prevent damage caused by oxidative stress. Although these cardioprotective effects of IPC against I/R injury are considered to be a consequence of changes in the redox state of cardiomyocytes, IPC is considered to promote the production of NO which may protect subcellular organelles from the deleterious actions of oxidative stress. The article is intended to focus on the I/R-induced oxidative damage to subcellular organelles and to highlight the cardioprotective effects of IPC. In addition, the actions of various endogenous cardioprotective interventions are discussed to illustrate that changes in the redox state due to IPC are cardioprotective against I/R injury to the heart.

Cardiac proteomic responses to ischemia-reperfusion injury and ischemic preconditioning

Cardiac ischemia and ischemia-reperfusion (I/R) injury are major contributors to morbidity and mortality worldwide. Pathological mechanisms of I/R and the physiological mechanisms of ischemic preconditioning (IPC), which is an effective cardiac protective response, have been widely investigated in the last decade to search for means to prevent or treat this disease. Proteomics is a powerful analytical tool that has provided important information to identify target proteins and understand the underlying mechanisms of I/R and IPC. Here, we review the application of proteomics to I/R injury and IPC to discover target proteins. We analyze the functional meaning of the accumulated data on hundreds of proteins using various bioinformatics applications. In addition, we review exercise-induced proteomic alterations in the heart to understand the potential cardioprotective role of exercise against I/R injury. Further developments in the proteomic field that target specialized proteins will yield new insights for optimizing therapeutic targets and developing a wide range of therapeutic agents against ischemic heart disease.

Endothelial NOS activity and myocardial oxygen metabolism define the salvageable ischemic time window for ischemic postconditioning

Ischemic postconditioning (IPOC) could be ineffective or even detrimental if the index ischemic duration is either too short or too long. The present study is to demonstrate that oxygen supply and metabolism defines a salvageable ischemic time window of IPOC in mice. C57BL/6 mice underwent coronary artery occlusion followed by reperfusion (I/R), with or without IPOC by three cycles of 10 s/10 s R/I. In vivo myocardial tissue oxygenation was monitored with electron paramagnetic resonance oximetry. Regional blood flow (RBF) was measured with a laser Doppler monitor. At the end of 60 min reperfusion, tissue from the risk area was collected, and mitochondrial enzyme activities were assayed. Tissue oximetry demonstrated that I/R induced a reperfusion hyperoxygenation state in the 30- and 45-min but not 15- and 60-min ischemia groups. IPOC attenuated the hyperoxygenation with 45 but not 30 min ischemia. RBF, eNOS phosphorylation, and mitochondrial enzyme activities were suppressed after I/R with different ischemic time, and IPOC afforded protection with 30 and 45 but not 60 min ischemia. Infarct size measurement indicated that IPOC reduced infarction with 30 and 45 min but not 60 min ischemia. Clearly, IPOC protected mouse heart with a defined ischemic time window between 30 and 45 min. This salvageable time window was accompanied by the improvement of RBF due to increased phosphorylated eNOS and the preservation of mitochondrial oxygen consumption due to conserved mitochondrial enzyme activities. Interestingly, this salvageable ischemic time window was mirrored by tissue hyperoxygenation status in the postischemic heart.

Late phase ischemic preconditioning preserves mitochondrial oxygen metabolism and attenuates post-ischemic myocardial tissue hyperoxygenation

AIMS

Late phase ischemic preconditioning (LPC) protects the heart against ischemia-reperfusion (I/R) injury. However, its effect on myocardial tissue oxygenation and related mechanism(s) is unknown. The aim of the current study is to determine whether LPC attenuates post-ischemic myocardial tissue hyperoxygenation through preserving mitochondrial oxygen metabolism.

MAIN METHODS

C57BL/6 mice were subjected to 30 min coronary ligation followed by 60 min or 24 h reperfusion with or without LPC (3 cycles of 5 min I/5 min R): Sham, LPC, I/R, and LPC+I/R group. Myocardial tissue Po(2) and redox status were measured with electron paramagnetic resonance (EPR) spectroscopy.

KEY FINDINGS

Upon reperfusion, tissue Po(2) rose significantly above the pre-ischemic level in the I/R mice (23.1 ± 2.2 vs. 12.6 ± 1.3 mmHg, p<0.01). This hyperoxygenation was attenuated by LPC in the LPC+I/R mice (11.9 ± 2.0 mmHg, p<0.01). Activities of NADH dehydrogenase (NADH-DH), succinate-cytochrome c reductase (SCR) and cytochrome c oxidase (CcO) were preserved or increased in the LPC group, significantly reduced in the I/R group, and conserved in the LPC+I/R group. Manganese superoxide dismutase (Mn-SOD) protein expression was increased by LPC in the LPC and LPC+I/R mice compared to that in the Sham control (1.24 ± 0.01 and 1.23 ± 0.01, p<0.05). Tissue redox status was shifted to the oxidizing state with I/R (0.0268 ± 0.0016/min) and was corrected by LPC in the LPC+I/R mice (0.0379 ± 0.0023/min). Finally, LPC reduced the infarct size in the LPC+I/R mice (10.5 ± 0.4% vs. 33.3 ± 0.6%, p<0.05).

SIGNIFICANCE

Thus, LPC preserved mitochondrial oxygen metabolism, attenuated post-ischemic myocardial tissue hyperoxygenation, and reduced I/R injury.

Ischemic preconditioning decreases mitochondrial proton leak and reactive oxygen species production in the postischemic heart

BACKGROUND

Proton leak (H(+) leak) dissipates mitochondrial membrane potential (mΔΨ) through the re-entry of protons into the mitochondrial matrix independent of ATP synthase. Changes in H(+) leak may affect reactive oxygen species (ROS) production. We measured H(+) leak and ROS production during ischemia-reperfusion and ischemic preconditioning (IPC) and examined how changing mitochondrial respiration affected mΔΨ and ROS production.

MATERIALS AND METHODS

Isolated rat hearts (n = 6/group) were subjected to either control-IR or IPC. Rate pressure product (RPP) was measured. Mitochondria were isolated at end reperfusion. Respiration was measured by polarography and titrated with increasing concentrations of malonate (0.5-2 mM). mΔΨ was measured using a tetraphenylphosphonium electrode. H(+) leak is the respiratory rate required to maintain membrane potential at -150 mV in the presence of oligomycin-A. Mitochondrial complex III ROS production was measured by fluorometry using Amplex-red.

RESULTS

IPC improved recovery of RPP at end reperfusion (63% ± 4% versus 21% ± 2% in control-IR, P < 0.05). Ischemia-reperfusion caused increased H(+) leak (94 ± 12 versus 31 ± 1 nmol O/mg protein/min in non-ischemic control, P < 0.05). IPC attenuates these increases (55 ± 9 nmol O/mg protein/min, P < 0.05 versus control-IR). IPC reduced mitochondrial ROS production compared with control-IR (31 ± 2 versus 40 ± 3 nmol/mg protein/min, P < 0.05). As mitochondrial respiration decreased, mΔΨ and mitochondrial ROS production also decreased. ROS production remained lower in IPC than in control-IR for all mΔΨ and respiration rates.

CONCLUSIONS

Increasing H(+) leak is not associated with decreased ROS production. IPC decreases both the magnitude of H(+) leak and ROS production after ischemia-reperfusion.

eNOS is required for acute in vivo ischemic preconditioning of the heart: effects of ischemic duration and sex

Ischemic preconditioning (IPC) is a powerful phenomenon that provides potent cardioprotection in mammalian hearts; however, the role of endothelial nitric oxide (NO) synthase (eNOS)-mediated NO in this process remains highly controversial. Questions also remain regarding this pathway as a function of sex and ischemic duration. Therefore, we performed extensive experiments in wild-type (WT) and eNOS knockout (eNOS(-/-)) mice to evaluate whether the infarct-limiting effect of IPC depends on eNOS, ischemic periods, and sex. Classical IPC was induced by three cycles of 5 min of regional coronary ischemia separated by 5 min of reperfusion and was followed by 30 or 60 min of sustained ischemia and 24 h of reperfusion. The control ischemia-reperfusion protocol had 30 or 60 min of ischemia followed by 24 h of reperfusion. Protection was evaluated by measuring the myocardial infarct size as a percentage of the area at risk. The major findings were that regardless of sex, WT mice exhibited robust IPC with significantly smaller myocardial infarction, whereas eNOS(-/-) mice did not. IPC-induced cardiac protection was absent in eNOS(-/-) mice of both Jackson and Harvard origin. In general, female WT mice had smaller infarctions compared with male WT mice. Although prolonged ischemia caused significantly larger infarctions in WT mice of both sexes, they were consistently protected by IPC. Importantly, prolonged myocardial ischemia was associated with increased mortality in eNOS(-/-) mice, and the survival rate was higher in female eNOS(-/-) mice compared with male eNOS(-/-) mice. In conclusion, IPC protects WT mice against in vivo myocardial ischemia-reperfusion injury regardless of sex and ischemic duration, but the deletion of eNOS abolishes the cardioprotective effect of classical IPC.

Periodic acceleration (pGz) prior to whole body ischemia reperfusion injury provides early cardioprotective preconditioning

AIMS

Periodic acceleration (pGz) is a method that applies repetitive sinusoidal head-to-foot motion to the horizontally positioned body. pGz adds pulses to the circulation as a function of frequency, thereby increasing shear stress to the endothelium. Pulsatile shear stress increases release of cardioprotective endothelial-derived nitric oxide prostaglandin E-2 and prostacyclin into the circulation. We investigated whether pGz may be effective as an early preconditioning strategy when applied one hour prior to whole body ischemia reperfusion injury induced by ventricular fibrillation (VF).

MAIN METHODS

Twenty anesthetized and paralyzed male swine were randomized to one hour of pGz and conventional mechanical ventilation [PC] or solely conventional mechanical ventilation [Control] prior to VF and resuscitation. After eight minutes of unsupported VF, cardiopulmonary resuscitation was carried out followed by defibrillation. Hemodynamics, electrocardiogram, echocardiogram, regional blood flows, and markers of global myocardial injury were measured. Protein expression of endothelial-derived nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), serine/threonine kinase Akt total (t-Akt), and phosphorylated (p-Akt) were determined by immunoblotting.

KEY FINDINGS

All animals had spontaneous return of circulation after cardiopulmonary resuscitation (CPR) and defibrillation. Preconditioned animals had less hemodynamically significant arrhythmias, less myocardial stunning, and greater regional blood flows to the brain, heart, kidneys, and ileum than Controls. Troponin I and creatine phosphokinase values in PC were 65% of the values present in Controls. In addition, preconditioned animals had higher protein expression of cardiac eNOS, p-eNOS, t-Akt, and p-Akt than Controls.

SIGNIFICANCE

pGz preconditioning confers early cardioprotection in a model of whole body ischemia reperfusion injury.

Electron paramagnetic resonance oximetry and redoximetry

Reactive oxygen/nitrogen species (ROS/RNS) have been increasingly recognized as important mediators and play a number of critical roles in cell injury, metabolism, disease pathology, diagnosis, and clinical treatment. Electron paramagnetic resonance (EPR) spectroscopy enables the spectral information at certain spatial position, and, from the observed line-width and signal intensity, the localized tissue oxygenation, and tissue redox status can be determined. We applied in vivo EPR oximetry and redoximetry technique and implemented its physiological/pathophysiological applications, along with the use of biocompatible lithium pthalocyanine (liPc) and nitroxide redox sensitive probes, on in vivo tissue oxygenation and redox profile of the ischemic and reperfused heart in living animals. We have observed that the hypoxia during myocardial ischemia limited mitochondrial respiration and caused a shift of tissue redox status to a more reduced state. ROS/RNS generated at the beginning of reperfusion not only caused a shift of redox status to a more oxidized state which may contribute to the postischemic myocardial injury, but also a marked suppression of in vivo tissue O(2) consumption in the postischemic heart through modulation of mitochondrial respiration based on alterations in enzyme activity and mRNA expression of NADH dehydrogenase (NADH-DH) and cytochrome c oxidase (CcO). In addition, ischemic preconditioning was found to be able to markedly attenuate postischemic myocardial hyperoxygenation with less ROS/RNS generation and preservation of mitochondrial O(2) metabolism, due to conserved NADH-DH and CcO activities. These studies have demonstrated that EPR oximetry and redoximetry techniques have advanced to a stage that enables in-depth insight in the process of ischemia reperfusion injury.

Opening of the mitoKATP channel and decoupling of mitochondrial complex II and III contribute to the suppression of myocardial reperfusion hyperoxygenation

Diazoxide, a mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel opener, protects the heart from ischemia-reperfusion injury. Diazoxide also inhibits mitochondrial complex II-dependent respiration in addition to its preconditioning effect. However, there are no prior studies of the role of diazoxide on post-ischemic myocardial oxygenation. In the current study, we determined the effect of diazoxide on the suppression of post-ischemic myocardial tissue hyperoxygenation in vivo, superoxide (O(2)(-*)) generation in isolated mitochondria, and impairment of the interaction between complex II and complex III in purified mitochondrial proteins. It was observed that diazoxide totally suppressed the post-ischemic myocardial hyperoxygenation. With succinate but not glutamate/malate as the substrate, diazoxide significantly increased ubisemiquinone-dependent O(2)(-*) generation, which was not blocked by 5-HD and glibenclamide. Using a model system, the super complex of succinate-cytochrome c reductase (SCR) hosting complex II and complex III, we also observed that diazoxide impaired complex II and its interaction with complex III with no effect on complex III. UV-visible spectral analysis revealed that diazoxide decreased succinate-mediated ferricytochrome b reduction in SCR. In conclusion, our results demonstrated that diazoxide suppressed the in vivo post-ischemic myocardial hyperoxygenation through opening the mitoK(ATP) channel and ubisemiquinone-dependent O(2)(-*) generation via inhibiting mitochondrial complex II-dependent respiration.

Proteomic analysis of protein tyrosine nitration after ischemia reperfusion injury: mitochondria as the major target

Endothelial nitric oxide synthase-derived NO and its derivative, peroxynitrite (ONOO(-)), suppresses oxygen consumption by nitration of mitochondrial proteins after reperfusion. However, very few nitrated proteins are identified to date. In this paper, ischemia/reperfusion (I/R) injury was induced in mouse heart by ligation and release of the left anterior descending coronary artery. Western blotting showed that tyrosine nitration was higher in I/R hearts. Nitrated proteins were identified by capillary-liquid chromatography-nanospray tandem mass spectrometry. A total of 23 proteins were identified as being nitrated after I/R and 10 of them were from mitochondria. The nitrated mitochondrial proteins included 4 subunits from the oxidative phosphorylation system (the 24 and the 30 kDa subunits of complex I, the Rieske ISP of complex III, and the alpha subunit of ATP synthase), five enzymes in the matrix, and voltage-dependent anion channel. In purified complex I treated with ONOO(-), 3-NT was identified locating at the residue of Y247 of the 30 kDa subunit and the residues of Y47, Y53 of the 49 kDa subunit. In conclusion, I/R induced protein nitration and mitochondrial proteins were the major targets. Selective nitration of proteins from the oxidative phosphorylation system at the beginning of reperfusion may contribute to the suppression of oxygen consumption.

Protein tyrosine nitration of the flavin subunit is associated with oxidative modification of mitochondrial complex II in the post-ischemic myocardium

Increased O(2)* and NO production is a key mechanism of mitochondrial dysfunction in myocardial ischemia/reperfusion injury. A crucial segment of the mitochondrial electron transport chain is succinate ubiquinone reductase (SQR or Complex II). In SQR, oxidative impairment and deglutathionylation of the 70-kDa flavin protein occurs in the post-ischemic heart ( Chen, Y. R., Chen, C. L., Pfeiffer, D. R., and Zweier, J. L. (2007) J. Biol. Chem. 282, 32640-32654 ). To gain insights into the oxidative modification of the 70-kDa protein in the post-ischemic myocardium, we used the identified S-glutathionylated peptide ((77)AAFGLSEAGFNTACVTK(93)) of the 70-kDa protein as a chimeric epitope incorporating a "promiscuous" T cell epitope to generate a high titer polyclonal antibody, AbGSC90. Purified AbGSC90 showed a high binding affinity to isolated SQR. Antibodies of AbGSC90 moderately inhibited the electron transfer and superoxide generation activities of SQR. To test for protein nitration, rats were subjected to 30 min of coronary ligation followed by 24 h of reperfusion. Tissue homogenates were immunoprecipitated with AbGSC90 and probed with antibodies against 3-nitrotyrosine. Enhancement of protein tyrosine nitration was detected in the post-ischemic myocardium. Isolated SQR was subjected to in vitro protein nitration with peroxynitrite, leading to site-specific nitration at the 70-kDa polypeptide and impairment of SQR electron transfer activity. Protein nitration of SQR further impaired its protein-protein interaction with Complex III. Liquid chromatography/tandem mass spectrometry analysis indicated that Tyr-56 and Tyr-142 were involved in protein tyrosine nitration. When the isolated SQR was subjected to in vitro S-glutathionylation, oxidative modification and impairment mediated by peroxynitrite were significantly decreased, thus confirming the protective effect of S-glutathionylation from the oxidative damage of nitration.

Formation of hydrogen peroxide and reduction of peroxynitrite via dismutation of superoxide at reperfusion enhances myocardial blood flow and oxygen consumption in postischemic mouse heart

Reactive oxygen/nitrogen species suppress myocardial oxygen consumption. In this study, we determined that endogenous hydrogen peroxide through dismutation of superoxide enhances postischemic myocardial blood perfusion and oxygen consumption. Electron paramagnetic resonance oximetry was applied to monitor in vivo tissue Po2 in mouse heart subjected to regional ischemia reperfusion. Heart rate, arterial blood pressure, blood flow, infarction, and activities of mitochondrial NADH dehydrogenase and cytochrome c oxidase were measured in six groups of wild-type (WT) and endothelial nitricoxide synthase knock-out (eNOS(-/-)) mice treated with phosphate-buffered saline (PBS), superoxide dismutase mimetic (SOD(m)) M40403 [a manganese(II)-bis(cyclohexylpyridine)-substituted macrocyclic superoxide dismutase mimetic, C21H35Cl2MnN5], 10006329 EUK 134 [EUK134, manganese 3-methoxy N,N(1)-bis(salicyclidene)ethylenediamine chloride], and SOD(m) plus glibenclamide to study the protective effect of hydrogen peroxide via dismutation of superoxide on the activation of sarcolemmal potassium channels. In the PBS group, there was an overshoot of tissue Po2 after reperfusion. Treatment with SOD(m), EUK134, and SOD(m) + glibenclamide protected mitochondrial enzyme activities, reduced infarct size, and suppressed the postischemic hyperoxygenation. In particular, in the SOD(m)-treated group, there was a transient peak of tissue Po2 at 9 min after reperfusion, which was dependent on endogenous hydrogen peroxide but not nitric oxide formation as it appeared in both WT and eNOS(-/-) mice. Blood flow and rate pressure product were higher in the SOD(m) group than in other groups, which contributed to the transient oxygen peak. Thus, SOD mimetics protected mouse heart from superoxide-induced reperfusion injury. With treatment of different SOD mimetics, it is concluded that endogenous hydrogen peroxide via dismutation of superoxide at reperfusion enhances postischemic myocardial blood perfusion and mitochondrial oxygen consumption, possibly through activation of sarcolemmal ATP-sensitive potassium channels.