Preconditioning potentiates molecular signaling for myocardial adaptation to ischemia

Fructose-Fed Rat Hearts are Protected Against Ischemia-Reperfusion Injury

High fructose-fed (HFF) rat model is known to develop the insulin-resistant syndrome with a very similar metabolic profile to the human X syndrome. Such metabolic modifications have been associated with a high incidence of cardiovascular disease. The role of free radical attack in diabetes mellitus and its cardiovascular complications have been abundantly documented. The present study examined the susceptibility to myocardial ischemic injury and the involvement of free radical attack and/or protection in the metabolic disorders of high FF rats. Rats were divided into two experimental groups that received diet for 4 weeks: a control group (C, n = 28) receiving a standard diet and a HFF group (FF, n = 28), in which 58% of the total carbohydrate was fructose. The euglycemic clamp technique was performed to assess insulin resistance. For the ischemia-reperfusion procedure, rat hearts were isolated and perfused at constant pressure before they were subjected to a 30-min occlusion of the left coronary artery followed by 120 mins of reperfusion. Hemodynamic parameters were measured throughout the protocol. Infarct-to-risk ratio (I/R) was assessed at the end of the protocol by 2,3,4-triphenyltetrazolium chloride staining and planimetric analysis. Lipid peroxidation, antioxidant enzyme activity, level of vitamin E, and trace element status were measured in blood samples from both groups. Rats of the FF group developed an insulin resistance indicated by the glucose infusion rate, which was decreased by 47%. Infarct size was significantly reduced in rats from the FF group (19.9% ± 6.6%) compared to rats from the control group (34.6% ± 4.9%), and cardiac functional recovery at reperfusion was improved in the FF group. Lipid peroxidation and oxidative stress were higher in the FF group, as indicated by higher malonedialdehyde level, whereas plasma vitamin E/triacylglycerol ratio was also enhanced in this group. This study indicates that fructose feeding affords protection against in vitro ischemia-reperfusion injury, potentially implicating vitamin E.

Selenoproteins and cardiovascular stress

Dietary selenium (Se) is an essential micronutrient that exerts its biological effects through its incorporation into selenoproteins. This family of proteins contains several antioxidant enzymes such as the glutathione peroxidases, redox-regulating enzymes such as thioredoxin reductases, a methionine sulfoxide reductase, and others. In this review, we summarise the current understanding of the roles these selenoproteins play in protecting the cardiovascular system from different types of stress including ischaemia-reperfusion, homocysteine dysregulation, myocardial hypertrophy, doxirubicin toxicity, Keshan disease, and others.

Attenuation of myocardial ischemia-reperfusion injury by trimetazidine derivatives functionalized with antioxidant properties

Trimetazidine (TMZ), an anti-ischemic metabolic drug, is used to treat chest pain (angina pectoris). We hypothesized that derivatives of TMZ with antioxidant functions may improve the cardiac dysfunction caused by ischemia-reperfusion (I/R) above that observed with TMZ alone. Isolated rat hearts perfused with Krebs-Henseleit buffer according to the Langendorff method were subjected to 30 min of global ischemia followed by 45 min of reperfusion. Trimetazidine, TMZ-NH (TMZ modified with a pyrroline moiety), or TMZ-PhiNH (TMZ-NH with a phenyl substitute) were infused (50 microM) for 1 min before the onset of ischemia. Untreated (control) hearts at the end of 45 min of reperfusion showed a significant decrease in the recovery of coronary flow (42%), left ventricular-developed pressure (22%), and rate-pressure product (25%) compared with preischemic baseline values. The I/R hearts also showed markedly increased lactate dehydrogenase and creatine kinase activities in the coronary effluent, significant myocardial infarction (46% of risk area), and activation of Akt, extracellular signal-regulated kinase, and p38 mitogen-activated protein kinase. Pretreatment of hearts with TMZ-NH or TMZ-PhiNH significantly enhanced the recovery of heart function and decreased infarct size. The I/R-induced activation of Akt was further enhanced by TMZ-PhiNH. The present study demonstrated that TMZ-NH and TMZ-PhiNH significantly protected hearts against I/R-mediated cardiac dysfunction and injury. The protective effect of the TMZ derivatives could be due to the combined effects of antioxidant and anti-ischemic activities as well as enhanced pro-survival Akt activity.

TNF-α is required for late ischemic preconditioning but not for remote preconditioning of trauma

BACKGROUND

Ischemic preconditioning (IPC) and remote IPC are cardioprotective phenomena in which ischemia of the myocardium or of a remote tissue, respectively, induces cardioprotection. Despite clinical evidence that surgical trauma can remotely affect myocardial infarction, to date there are no basic science studies addressing the effect of nonischemic trauma at distant sites upon cardiac ischemia/reperfusion (I/R) injury. The objectives of this study were to determine the effects of nonischemic remote surgical trauma upon infarct size after myocardial I/R and to determine the effects of TNF-alpha ablation upon cardioprotective phenomena.

MATERIALS AND METHODS

A minimally traumatic mouse model was used to ascertain the effect of remote nonischemic surgical trauma upon I/R injury. TNF-alpha knockout mice were employed to determine the effect of TNF-alpha ablation.

RESULTS

Carotid artery vascular surgery remotely exacerbates cardiac I/R injury increasing infarct size by 287% (remote cardiac injury or RCI). Nonischemic, nonvascular trauma (abdominal incision) results in remote preconditioning of trauma (RPCT), decreasing infarct size by 81% (early phase) and 40% (late phase) relative to controls. Finally, TNF-alpha is required for late IPC but is not necessary for RCI or for RPCT.

CONCLUSIONS

We show that late IPC is TNF-alpha-dependent and describe two unique TNF-alpha-independent remote effects of nonischemic trauma upon myocardial infarction. Understanding the mechanism of these remote effects will allow the development of novel therapies for the treatment of ischemic heart disease. RPCT and TNF-alpha ablation have an additive protective effect suggesting that combinations of complementary approaches may be a useful strategy for maximizing the clinical efficacy of cardioprotective therapies.

The protective and anti-protective effects of ethanol in a myocardial infarct model

Recent data indicate that acute alcohol exposure can have a preconditioning-like protective effect on the heart. We investigated the effect of ethanol exposure shortly before regional ischemia in an infarct model. Both in the open-chest rabbit and in the isolated rabbit heart, exposure of the heart to ethanol significantly reduced infarct size, but only if the alcohol were washed out or sufficiently metabolized before the onset of ischemia. If ethanol were still present during ischemia, it could not only prevent its own protective effect, but also abolish protection induced by ischemic preconditioning or the mitochondrial K(ATP) channel activator diazoxide. In the in vitro model, we tested for possible mediators of ethanol-induced protection and made comparisons to the signaling cascade of ischemic preconditioning. Neither adenosine receptor blockade with 8-(p-sulfophenyl) theophylline, scavenging of free radicals with N-2-mercaptopropionyl glycine, nor closure of K(ATP) channels with glibenclamide affected ethanol's protective effect. However, either a PKC inhibitor or a protein tyrosine kinase inhibitor could completely block ethanol-induced infarct size reduction. Both the protective and anti-protective effects of ethanol had a threshold of about 5 mM. Thus, ethanol-induced protection is mediated by protein kinase C and at least one protein tyrosine kinase, but, in contrast to ischemic preconditioning, is not triggered by either adenosine receptors, free radicals, or K(ATP) channels. Ethanol can only exert its protective effect if it is removed before the onset of ischemia. If still present during ischemia, ethanol has the opposite effect, and inhibits preconditioning by an as yet unidentified mechanism.

Preconditioning of swine heart with monophosphoryl lipid A improves myocardial preservation

BACKGROUND

Ischemic preconditioning has been proven to be a powerful tool for myocardial protection in the setting of ischemia and reperfusion. A new drug to provide pharmacologic preconditioning, monophosphoryl lipid A (MLA), was administered 24 hours before an acute coronary occlusion in pigs to determine the effect on pharmacologic preconditioning.

METHODS

Two studies were completed. In the first, swine were distributed into five groups: group I, control; group II,. aminoguanidine (AMG) (30 mg/kg), a selective inducible nitric oxide synthase (iNOS) blocker; group III, MLA (10 microg/kg); group IV, MLA (35 microg/kg); and group V, MLA and AMG (35 microg/kg and 30 mg/kg, respectively). Twenty-four hours after administration of the MLA, AMG, or both, regional left anterior descending coronary artery ischemia was induced for 15 minutes followed by one hour of global normothermic cardioplegic arrest and three hour reperfusion. Left ventricular function, tissue injury, and percentage of myocardial infarction were measured. Left ventricular myocardium in the left anterior descending coronary artery region was sampled for iNOS messenger RNA (mRNA) during ischemia and reperfusion. In the second study, pigs were sacrificed 0, 4, 6, 8, and 24 hrs after MLA/AMG administration for iNOS mRNA determination in nonischemic myocardium.

RESULTS

Use of MLA significantly improved postischemic ventricular function, and reduced creatinine kinase release and percentage of infarction. Monophosphoryl lipid A induced expression of iNOS mRNA in nonischemic myocardium within four hours of administration which returned to base line by 24 hours. Normothermic regional ischemia then induced expression of iNOS mRNA, which returned to base line during reperfusion. Aminoguanidine completely abolished both MLA-induced and ischemia-induced iNOS mRNA and blocked the beneficial effects of MLA.

CONCLUSIONS

Use of MLA can provide myocardial preservation through enhanced expression of iNOS mRNA.

A new method of long-term preventive cardioprotection using Lactobacillus

Potential long-term cardioprotection was investigated in an extensive experimental study. Lactobacillus cultivation components (LCC) were administered intravenously in anesthetized rats 1, 7, and 21 days before global ischemia (GI). GI was produced by full stop flow in isolated Langendorff-perfused hearts for 20 min and was followed by reperfusion. Control animals were injected with saline. LCC reduced reperfusion tachyarrhythmia significantly and improved functional recovery of the ischemized rat heart. These beneficial effects were associated with reduction of release of norepinephrine (NE) and prostacyclin at the first minute of reperfusion, activation of myocardial catalase, and overexpression of 70-kDa heat stress protein (HSP-70) at ischemia and reperfusion (P < 0.05). This cardioprotection was documented up to 21 days after a single injection of LCC. Thus Lactobacillus cultivation components are new nontoxic materials that produce marked long-term cardioprotection against ischemia-reperfusion damage. This effect is attributed to an activation of the cellular defense system, manifested by activation of the antioxidant pathway and by expression of protective proteins. NE is involved in this process, and the data also suggest a role for prostacyclin in this model of cardioprotection. The potential of LCC and related compounds working through similar mechanisms in the prevention and therapy of various ischemic heart syndromes should be explored.

Translocation of HSP27 to sarcomere induced by ischemic preconditioning in isolated rat hearts

We investigated the role of the 27-kDa heat shock protein (HSP27) in cardiac protection using Langendorff-perfused rat hearts. After preconditioning (a single episode of 5 min global ischemia followed by 5 min of reperfusion), HSP27 redistributed from the cytosol to the sarcomere and recovery of the contractile function, after 40 min of global ischemia and 50 min of reperfusion, was significantly enhanced. Both SB203580, a p38 MAP kinase inhibitor, and bisindolylmaleimide I, a protein kinase C inhibitor, prevented the effects of preconditioning. Both 2-chloro-N(6)-cyclopentyladenosine (adenosine A1 agonist) and anisomycin (activator of p38 MAP kinase and c-jun N-terminal kinase) mimicked preconditioning. These results suggest that activation of protein kinase C followed by activation of p38 MAP kinase elicits translocation of HSP27 to the sarcomere, a process which may be involved in the cardioprotective mechanism afforded by ischemic preconditioning in rat heart.

S-T segment voltage during sequential coronary occlusions is an unreliable marker of preconditioning

During coronary angioplasty, a stair-step decrease in peak S-T segment elevation from the first to the second coronary occlusion has been assumed to indicate a preconditioning (PC) effect. This association was evaluated with myocardial electrograms in rabbits, which revealed that two sequential 5-min coronary occlusions resulted in a marked decrease in the area under the S-T segment voltage-time curve (P < 0.05) with no change during a third occlusion. Pretreatment with either 5-hydroxydecanoate, a mitochondrial ATP-sensitive potassium (K(ATP)) channel blocker, or anisomycin, an activator of stress-activated protein kinases, had no effect on the stair-step decline in the S-T segment voltage between the first two occlusions. HMR-1883, a potent closer of sarcolemmal K(ATP) channels, abolished changes in S-T segment elevation after brief coronary occlusions but had no effect on the infarct-sparing property of the two preconditioning 5-min occlusions. Interestingly, HMR-1883 blocked myocardial protection from diazoxide, raising doubt that the latter opens only mitochondrial channels. Therefore, myocardial protection and S-T segment changes during ischemia are dissociated. These data suggest that it is the mitochondrial K(ATP) channel that protects the myocardium, and it is the sarcolemmal channel that is responsible for changes in S-T elevation. Therefore, it cannot always be inferred that changes in S-T segment elevation reflect the state of myocardial protection.

Reactive oxygen species function as second messenger during ischemic preconditioning of heart

Ischemic preconditioning has been shown to trigger a signaling pathway by potentiating tyrosine kinase phosphorylation leading to the activation of p38 MAP kinase and MAPKAP kinase 2. Recently, the nuclear transcription factor, NFkappaB, was found to play a role in the signaling process. Since NFkappaB is a target of oxygen free radicals, we hypothesized that reactive oxygen species might play a role in the signaling process. To test this hypothesis, isolated rat hearts were perfused in the absence or presence of either dimethyl thiourea (DMTU), a OH* radical scavenger, or SN 50 peptide, a NFkappaB blocker. Hearts were then subjected to ischemic preconditioning by four repeated episodes of 5 min ischemia each followed by 10 min reperfusion. All hearts were then made globally ischemic for 30 min followed by 2 h of reperfusion. The results of our study demonstrated enhanced tyrosine kinase phosphorylation during ischemic preconditioning which was blocked by DMTU. DMTU also inhibited preconditioning mediated increased phosphorylation of p38 MAP kinase and MAPKAP kinase 2 activity. However, DMTU had no effect on the translocation and activation of protein kinase C (PKC) resulting from preconditioning. Preconditioning reduced myocardial infarct size as expected. This cardioprotective effect of preconditioning was abolished by both DMTU and SN 50. Preconditioning resulted in the nuclear translocation and activation of NFkappaB. Increased NFkappaB binding was blocked by both DMTU and SN 50. The results of this study demonstrate that reactive oxygen species play a crucial role in signal transduction mediated by preconditioning. This signaling process appears to be potentiated by tyrosine kinase phosphorylation resulting in the activation of p38 MAP kinase and MAPKAP kinase 2 leading to the activation of NFkappaB suggesting a role of oxygen free radicals as second messenger. Free radical signaling seems to be independent of PKC although PKC is activated during preconditioning process suggesting the role of two separate signaling pathways in ischemic preconditioning.

Oxygen free radical signaling in ischemic preconditioning

This review will focus on the free radical signaling mechanism of preconditioning. The results from our laboratory as well as studies from other laboratories suggest that reactive oxygen species function as second messenger during myocardial adaptation to ischemia. This review provides evidence for the first time that tyrosine kinase and MAP kinases are the targets for reactive oxygen species generated in the preconditioned myocardium. The finding that p38 MAP kinase might be upstream of NF kappa B further supports our previous reports that MAPKAP kinase 2 could be the most likely link between the preconditioning and adaptation mediated by gene expression. p38 activation appears to be an important step in the translocation and activation of the nuclear transcription factor NF kappa B, which in turn may be involved in the induction of the expression of a variety of stress-inducible genes.

Differential regulation of Bcl-2, AP-1 and NF-kappaB on cardiomyocyte apoptosis during myocardial ischemic stress adaptation

Acute ischemia followed by prolonged reperfusion has been shown to induce cardiomyocyte apoptosis. In this report, we demonstrate that myocardial adaptation to ischemia induced by repeated cyclic episodes of short-term ischemia each followed by another short duration of reperfusion reduced cardiomyocyte apoptosis and DNA fragmentation. This was associated with the induction of the expression of Bcl-2 mRNA and translocation and activation of NF-kappaB. Another transcription factor, AP-1, remained unaffected by repeated ischemia and reperfusion, but exhibited significant upregulation by a single episode of 30 min ischemia followed by 2 h of reperfusion. This activation of AP-1 was inhibited by a scavenger of oxygen free radicals, DMTU. Thirty minutes ischemia and 120 min reperfusion downregulated the induction of the expression of Bcl-2 mRNA, but moderately activated NF-kappaB binding activity. This was associated with an increased number of apoptotic cells and DNA fragmentation in cardiomyocytes which were attenuated by DMTU. The results of this study indicate that Bcl-2, AP-1 and NF-kappaB differentially regulate cardiomyocyte apoptosis mediated by acute ischemia and prolonged reperfusion.

Metabolic and functional effects of carbachol and ischaemic preconditioning in rat isolated heart

1. Metabolic and functional effects of ischaemic preconditioning (IP), pretreatment with carbachol (Ch) and combined interventions were studied in rat isolated working hearts subjected to 20 min global ischaemia (37 degrees C) and 40 min reperfusion. Prior to the ischaemic period, hearts were either perfused according to Langendorff (control group), ischaemically preconditioned by 5 min global ischaemia and 5 min reperfusion (IP group), perfused with 0.1 mumol/L Ch for 5 min and then with Ch-free Krebs'-Henseleit buffer for 5 min (Ch group) or perfused with 0.1 mumol/L Ch for 5 min and then subjected to IP (Ch + IP group). 2. Although Ch exerted slight negative chronotropic and inotropic effects during pre-ischaemic Langendorff perfusion, it did not affect myocardial contents of ATP and phosphocreatine (PCr) prior to sustained ischaemia. At the end of final reperfusion, the IP and Ch groups showed similar recovery of aortic output (67.5 +/- 5.0 and 56.8 +/- 5.4%, respectively), cardiac output (65.4 +/- 5.4 and 63.5 +/- 5.7%, respectively) and stroke volume (73.4 +/- 7.5 and 67.0 +/- 6.7%, respectively) expressed as a percentage of steady state values. These indices were higher than those in the control group (42.8 +/- 4.7, 53.8 +/- 4.3 and 56.1 +/- 5.6%, respectively; P < 0.05). The Ch + IP group exhibited complete recovery of all indices of pump function, including cardiac work, expressed as the cardiac output-mean aortic pressure (CO-MAP) product. 3. There were no differences in ATP recovery between the groups after reperfusion: the ATP content was, on average, 73.1 +/- 3.5% of the initial ATP content. However, all treated groups had enhanced PCr recovery and better preservation of total creatine (sigma Cr = PCr + Cr), an index of cell membrane integrity, than control. Metabolic efficacy of the pre-ischaemic interventions can be ranked as follows: IP < or = Ch < Ch + IP. In all groups, myocardial content of sigma Cr was positively correlated with percentage recovery of the CO-MAP product at the end of reperfusion (r = 0.79, P < 0.05). 4. The results demonstrate that Ch treatment combined with IP provides significantly greater postischaemic myocardial salvage. The similarity of the metabolic and functional effects of Ch treatment and IP strongly suggests muscarinic M2 acetylcholine receptor involvement in acute adaptation of rat heart to ischaemia/reperfusion stress.

Ischemic preconditioning triggers tyrosine kinase signaling: a potential role for MAPKAP kinase 2

Myocardial adaptation to ischemia has been shown to activate protein tyrosine kinase, potentiating activation of phospholipase D, which leads to the stimulation of mitogen-activated protein (MAP) kinases and MAP kinase-activated protein (MAPKAP) kinase 2. The present study sought to further examine the signal transduction pathway for the MAPKAP kinase 2 activation during ischemic adaptation. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase, whereas SB-203580 was used to inhibit p38 MAP kinases. Western blot analysis demonstrated that p38 MAP kinase is phosphorylated during ischemic stress adaptation. Phosphorylation of p38 MAP kinase was blocked by genistein, suggesting that activation of p38 MAP kinase during ischemic adaptation is mediated by a tyrosine kinase signaling pathway. MAPKAP kinase 2 was estimated by following in vitro phosphorylation with recombinant human heat shock protein 27 as specific substrate for MAPKAP kinase 2. Again, both genistein and SB-203580 blocked the activation of MAPKAP kinase 2 during myocardial adaptation to ischemia. Immunofluorescence microscopy with anti-p38-antibody revealed that p38 MAP kinase is primarily localized in perinuclear regions. p38 MAP kinase moves to the nucleus after ischemic stress adaptation. After ischemia and reperfusion, cytoplasmic striations in the myocytes become obvious, indicating translocation of p38 MAP kinase from nucleus to cytoplasm. Corroborating these results, myocardial adaptation to ischemia improved the left ventricular functions and reduced myocardial infarction that were reversed by blocking either tyrosine kinase or p38 MAP kinase. These results demonstrate that myocardial adaptation to ischemia triggers a tyrosine kinase-regulated signaling pathway, leading to the translocation and activation of p38 MAP kinase and implicating a role for MAPKAP kinase 2.

Translocation of HSP27 to cytoskeleton by repetitive hypoxia-reoxygenation in the rat myoblast cell line, H9c2

We investigated the possible changes in the distribution of HSP27 after a brief hypoxia-reoxygenation stress in the rat myoblast cell line, H9c2, as a model of ischemic preconditioning. Cells were exposed to 4 cycles of 5 min. of hypoxia and 5 min. of reoxygenation. In the normoxic condition, HSP27 was exclusively found in the cytosolic fraction. After the hypoxia-reoxygenation cycle, HSP27 redistributed to the cytoskeletal fraction, which was blocked by 10 microM SB 203580, a specific inhibitor of p38 MAP kinase. Cells treated with the repetitive hypoxia-reoxygenation developed resistance against cell death induced by hypoxia for 24 hours. The changes in localization of HSP27 found in the present study may reflect the mechanism of preconditioning in the cardiac myocyte.

Demonstration of an early and a late phase of ischemic preconditioning in mice

It is unknown whether ischemic preconditioning (PC; either early or late) occurs in the mouse. The goal of this study was to answer this question and to develop a reliable and physiologically relevant murine model of both early and late ischemic PC. A total of 201 mice were used. In nonpreconditioned open-chest animals subjected to 30 min of coronary occlusion followed by 24 h of reperfusion, infarct size (tetrazolium staining) averaged 52% of the region at risk. When the 30-min occlusion was performed 10 min after a PC protocol consisting of six cycles of 4-min occlusion and 4-min reperfusion, infarct size was reduced by 75%, indicating an early PC effect. When the 30-min occlusion was performed 24 h after the same PC protocol, infarct size was reduced by 48%, indicating a late PC effect. In mice in which the 30-min occlusion was followed by 4 h of reperfusion, infarct size was similar to that observed after 24 h of reperfusion, indicating that a 4-h reperfusion interval is sufficient to detect the final extent of cell death in this model. Fundamental physiological variables (body temperature, arterial oxygenation, acid-base balance, heart rate, and arterial pressure) were measured and found to be within normal limits. Taken together, these results demonstrate that, in the mouse, a robust infarct-sparing effect occurs during both the early and the late phases of ischemic PC, although the early phase is more powerful. This murine model is physiologically relevant, provides reliable measurements, and should be useful for elucidating the cellular mechanisms of ischemic PC in genetically engineered animals.

Nitric oxide synthase is the mediator of late preconditioning against myocardial infarction in conscious rabbits

BACKGROUND

Despite intense investigation, the effector of the infarct-limiting protection observed during the late phase of ischemic preconditioning (PC) remains unknown. The goal of this study was to test the hypothesis that late PC against myocardial infarction is mediated by the activity of nitric oxide synthase (NOS).

METHODS AND RESULTS

Conscious rabbits underwent a 30-minute coronary occlusion followed by 3 days of reperfusion. In group I (control group, n= 10), infarct size (tetrazolium staining) averaged 56.8+/-5.3% of the risk region, which was decreased to 27.6+/-2.5% (P<0.05) in rabbits preconditioned 24 hours earlier with a sequence of six 4-minute occlusion/4-minute reperfusion cycles (group II, n= 10). When preconditioned rabbits were given the nonselective NOS inhibitor N(omega)-nitro-L-arginine (L-NA, 13 mg/kg i.v. [group III, n=8]) or the selective iNOS inhibitor aminoguanidine (AG, 150 mg/kg SC [group V, n=7]) before the 30-minute occlusion, the protective effect of late PC was completely abrogated; that is, infarct size (59.9+/-4.5% and 65.8+/-3.3%, respectively) was similar to that measured in the control group. Measurements of systolic wall thickening (sonomicrometry) demonstrated that L-NA and AG also abolished the improved recovery of myocardial function effected by late PC in group II. When rabbits were given L-NA or AG without prior PC (group IV [n=8] and group VI [n=6], respectively), infarct size did not differ from that observed in controls (53.8+/-4.3% and 59.8+/-4.3%, respectively), demonstrating that L-NA and AG do not increase the extent of cell death in nonpreconditioned myocardium.

CONCLUSIONS

Taken together, these results indicate that in the conscious rabbit, the infarct-sparing effect of the late phase of ischemic PC is mediated by the activity of NOS and suggest that the specific isoform primarily responsible for this cardioprotective phenomenon is iNOS. Thus, NO appears to be a pivotal component of the pathophysiological cascade of late PC.

An essential role of NFkappaB in tyrosine kinase signaling of p38 MAP kinase regulation of myocardial adaptation to ischemia

We have recently demonstrated that myocardial adaptation to ischemia triggers a tyrosine kinase regulated signaling pathway leading to the translocation and activation of p38 MAP kinase and MAPKAP kinase 2. Since oxidative stress is developed during ischemic adaptation and since free radicals have recently been shown to function as an intracellular signaling agent leading to the activation of nuclear transcription factor, NFkappaB, we examined whether NFkappaB was involved in the ischemic adaptation process. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase while SB 203580 was used to inhibit p38 MAP kinases. Ischemic adaptation was associated with the nuclear translocation and activation of NFkappaB which was significantly blocked by both genistein and SB 203580. The ischemically adapted hearts were more resistant to ischemic reperfusion injury as evidenced by better function recovery and less tissue injury during post-ischemic reperfusion. Ischemic adaptation developed oxidative stress which was reflected by increased malonaldehyde formation. A synthetic peptide containing a cell membrane-permeable motif and nuclear sequence, SN 50, which blocked nuclear translocation of NFkappaB during ischemic adaptation, significantly inhibited the beneficial effects of adaptation on functional recovery and tissue injury. In concert, SN 50 reduced the oxidative stress developed in the adapted myocardium. These results demonstrate that p38 MAP kinase might be upstream of NFkappaB which plays a role in ischemic preconditioning of heart.