Opioid-Induced Cardioprotection Occurs via Glycogen Synthase Kinase β Inhibition During Reperfusion in Intact Rat Hearts

Cardioprotective effect of morphine and a blocker of glycogen synthase kinase 3 beta, SB216763 [3-(2,4-dichlorophenyl)-4(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione], via inhibition of the mitochondrial permeability transition pore

Morphine has been shown to protect the myocardium against ischemia-reperfusion injury through inhibition of glycogen synthase kinase-3beta (GSK-3beta). Given that GSK-3beta is known to modulate the mitochondrial permeability transition pore (mPTP), we investigated the role of mPTP in the cardioprotective effect of morphine and the GSK-3beta inhibitor SB216763 [SB; 3-(2,4-dichlorophenyl)-4(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione] during ischemia-reperfusion. Both morphine (0.3 mg/kg) and SB (0.6 mg/kg) reduced infarct size in a model of regional myocardial ischemia-reperfusion in rats (13 +/- 1 and 14 +/- 3% of the area at risk versus 33 +/- 4% in controls; p < 0.05). Morphine and SB protected the ischemic myocardium against Ca(2+)-induced mPTP opening as demonstrated by the increased capacity of mitochondria to retain Ca(2+) when they were isolated from the ischemic zone 10 min after the onset of reperfusion (59 +/- 8 and 66 +/- 3 versus 29.5 +/- 6 nmol Ca(2+)/mg x protein, respectively; p < 0.05). This was associated with a restoration of mitochondrial oxidative phosphorylation parameters. In isolated adult rat cardiomyocytes subjected to anoxia-reoxygenation, morphine (2 microM), SB (3 microM), and the direct mPTP inhibitor cyclosporine A (3 microM) delayed mPTP opening as assessed by the calcein loading Co(2+)-quenching technique. This was accompanied by an increase in cell survival as measured by nuclear staining with propidium iodide. These in vitro effects of morphine on inhibition of mPTP opening during anoxia-reoxygenation were suppressed by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin (0.1 microM). These data indicate that the infarct-limiting effect of morphine and SB is linked by a cause-effect relationship, which leads to an increased mitochondrial resistance and inhibition of mPTP opening through the PI3-kinase pathway and subsequent inactivation of GSK-3beta.

Mechanisms underlying acute protection from cardiac ischemia-reperfusion injury

Mitochondria play an important role in cell death and cardioprotection. During ischemia, when ATP is progressively depleted, ion pumps cannot function resulting in a rise in calcium (Ca(2+)), which further accelerates ATP depletion. The rise in Ca(2+) during ischemia and reperfusion leads to mitochondrial Ca(2+) accumulation, particularly during reperfusion when oxygen is reintroduced. Reintroduction of oxygen allows generation of ATP; however, damage to the electron transport chain results in increased mitochondrial generation of reactive oxygen species (ROS). Mitochondrial Ca(2+) overload and increased ROS can result in opening of the mitochondrial permeability transition pore, which further compromises cellular energetics. The resultant low ATP and altered ion homeostasis result in rupture of the plasma membrane and cell death. Mitochondria have long been proposed as central players in cell death, since the mitochondria are central to synthesis of both ATP and ROS and since mitochondrial and cytosolic Ca(2+) overload are key components of cell death. Many cardioprotective mechanisms converge on the mitochondria to reduce cell death. Reducing Ca(2+) overload and reducing ROS have both been reported to reduce ischemic injury. Preconditioning activates a number of signaling pathways that reduce Ca(2+) overload and reduce activation of the mitochondrial permeability transition pore. The mitochondrial targets of cardioprotective signals are discussed in detail.

Inhibition of GSK-3beta decreases NF-kappaB-dependent gene expression and impairs the rat liver regeneration

Serine-threonine protein kinase glycogen synthase kinase (GSK)-3 is involved in regulation of many cell functions, but its role in regulating liver regeneration is unknown. Here we investigated the effects of GSK-3beta inhibition on liver regeneration after partial hepatectomy in the rat. The potent and selective GSK-3beta inhibitor SB216763 (0.6 mg/kg intravenously) or vehicle (10% dimethyl sulfoxide) was administered 30 min before 70% partial hepatectomy. Liver regeneration was estimated by the cell proliferation, apoptosis, and the related cell signaling and cycling proteins. In 30 min after hepatectomy in the rat, GSK-3beta was found to be translocated to the nucleus, but GSK-3beta inhibitor SB216763 that could phosphorylate residue Ser9 on GSK-3beta did not attenuated the accumulation. Consequently, the inhibition of GSK-3beta decreased the nuclear factor-kappaB activity, the NF-kappaB-dependent gene expression, and COX2 expression, but enhanced p21(WAF1/Cip1) transcription. Moreover, the injection of SB216763 impaired the proliferation cell nuclear antigen (PCNA) index and increased the apoptosis of liver compared to the vehicle. GSK-3beta plays an important role in rat liver regeneration. We conclude it may partially result from the inhibition of the NF-kappaB pathway and enhancement of p21 (WAF1/Cip1) expression.

The association of opium with coronary artery disease

BACKGROUND

The effects of opium consumption on coronary artery disease are still unknown.

METHODS

A cross-sectional study was conducted on 2405 patients admitted to the Angiographic Ward at Tehran Heart Center from 7 May 2005 to 13 August 2005.

RESULTS

After adjusting for conventional cardiovascular risk factors, opium consumption was a significant risk factor for coronary artery disease (P=0.01 and odds ratio=1.8). Moreover, the amount of opium consumption was associated significantly with the severity of coronary atherosclerosis, as measured by clinical vessel score (r=0.2, P=0.002).

CONCLUSIONS

To our knowledge, this is the first time that the adverse effects of opium consumption on coronary arteries was defined.

Effective pharmacotherapy against oxidative injury: alternative utility of an ATP-sensitive potassium channel opener

Cardiomyocyte viability following ischemia-reperfusion critically depends on mitochondrial function. In this regard, potassium channel openers (KCOs) targeting mitochondria have emerged as powerful cardioprotective agents when applied at the onset of ischemia. However, it is controversial whether openers are still protective when applied at the onset of reoxygenation. Here, H9c2 cardiomyocytes and mitochondria isolated from the rat heart ventricle were subjected to ischemia-reoxygenation or oxidative stress in the absence or presence of 100 microM diazoxide, a potassium channel opener. Ischemia-reoxygenation or oxidative stress significantly reduced cell viability, induced structural damage in association with increased mitochondrial protein release, and impaired oxidative phosphorylation. However, treatment with diazoxide before anoxia or at the onset of reoxygenation, as well as during oxidative stress, prevented cell death and mitochondrial dysfunction and preserved cellular and mitochondrial structural integrity. These protective effects were blocked by 5-hydroxydecanoate. Thus, treatment with potassium channel openers even at the time of reoxygenation may provide a significant protection of the myocardium. The protective mechanism is at least in part endogenous to the mitochondria because protection was also observed in isolated mitochondria.

Delayed cardioprotection afforded by the glycogen synthase kinase 3 inhibitor SB-216763 occurs via a KATP- and MPTP-dependent mechanism at reperfusion

Previous studies in our laboratory suggest that an acute inhibition of glycogen synthase kinase 3 (GSK3) by SB-216763 (SB21) is cardioprotective when administered just before reperfusion. However, it is unknown whether the GSK inhibitor SB21 administered 24 h before ischemia is cardioprotective and whether the mechanism involves ATP-sensitive potassium (K(ATP)) channels and the mitochondrial permeability transition pore (MPTP). Male Sprague-Dawley rats were administered the GSK inhibitor SB21 (0.6 mg/kg) or vehicle 24 h before ischemia. Subsequently, the rats were acutely anesthetized with Inactin and underwent 30 min of ischemia and 2 h of reperfusion followed by infarct size determination. Subsets of rats received either the sarcolemmal K(ATP) channel blocker HMR-1098 (6 mg/kg), the mitochondrial K(ATP) channel blocker 5-hydroxydecanoic acid (5-HD; 10 mg/kg), or the MPTP opener atractyloside (5 mg/kg) either 5 min before SB21 administration or 5 min before reperfusion 24 h later. The infarct size was reduced in SB21 compared with vehicle (44 +/- 2% vs. 61 +/- 2%, respectively; P < 0.01). 5-HD administered either before SB21 treatment or 5 min before reperfusion the following day abrogated SB21-induced protection (54 +/- 4% and 61 +/- 2%, respectively). HMR-1098 did not affect the SB21-induced infarct size reduction when administered before the SB21 treatment (43 +/- 1%); however, HMR-1098 partially abrogated the SB21-induced infarct size reduction when administered just before reperfusion 24 h later (52 +/- 1%). The MPTP opening either before SB21 administration or 5 min before reperfusion abrogated the infarct size reduction produced by SB21 (61 +/- 2% and 62 +/- 2%, respectively). Hence, GSK inhibition reduces infarct size when given 24 h before the administration via the opening K(ATP) channels and MPTP closure.

Evidence that cardioprotection by postconditioning involves preservation of myocardial opioid content and selective opioid receptor activation

Opioids introduced at reperfusion (R) following ischemia (I) reduce infarct size much like postconditioning, suggesting the hypothesis that postconditioning increases cardiac opioids and activates local opioid receptors. Anesthetized male rats subjected to 30 min regional I and 3 h R were postconditioned with three cycles of 10 s R and 10 s reocclusion at onset of R. Naloxone (NL), its peripherally restricted analog naloxone methiodide, delta-opioid receptor (DOR) antagonist naltrindole (NTI), kappa-opioid receptor antagonist norbinaltorphimine (NorBNI), and mu-opioid receptor (MOR) antagonist H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) were administered intravenously 5 min before R. The area at risk (AAR) was comparable among groups, and postconditioning reduced infarct size from 57 +/- 2 to 42 +/- 2% (P < 0.05). None of the antagonists alone altered infarct size. All antagonists abrogated postconditioning protection at higher doses. However, blockade of infarct sparing by postconditioning was lost, since tested doses of NL, NTI, NorBNI, and CTAP were lowered. The efficacy of NorBNI declined first at 3.4 micromol/kg, followed sequentially by NTI (1.1), NL (0.37), and CTAP (0.09), suggesting likely MOR and perhaps DOR participation. Representative small, intermediate, and large enkephalins in the AAR were quantified (fmol/mg protein; mean +/- SE). I/R reduced proenkephalin (58 +/- 9 vs. 33 +/- 4; P < 0.05) and sum total of measured enkephalins, including proenkephalin, peptide B, methionine-enkephalin, and methionine-enkephalin-arginine-phenylalanine (139 +/- 17 vs. 104 +/- 7; P < 0.05) compared with shams. Postconditioning increased total enkephalins (89 +/- 8 vs. 135 +/- 5; P < 0.05) largely by increasing proenkephalin (33 +/- 4 vs. 96 +/- 7; P < 0.05). Thus the infarct-sparing effect of postconditioning appeared to involve endogenously activated MORs and possibly DORs, and preservation of enkephalin precursor synthesis in the AAR.

Interaction of cardiovascular risk factors with myocardial ischemia/reperfusion injury, preconditioning, and postconditioning

Therapeutic strategies to protect the ischemic myocardium have been studied extensively. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate lethal tissue injury, a process termed "reperfusion injury." Ischemia/reperfusion injury may lead to myocardial infarction, cardiac arrhythmias, and contractile dysfunction. Ischemic preconditioning of myocardium is a well described adaptive response in which brief exposure to ischemia/reperfusion before sustained ischemia markedly enhances the ability of the heart to withstand a subsequent ischemic insult. Additionally, the application of brief repetitive episodes of ischemia/reperfusion at the immediate onset of reperfusion, which has been termed "postconditioning," reduces the extent of reperfusion injury. Ischemic pre- and postconditioning share some but not all parts of the proposed signal transduction cascade, including the activation of survival protein kinase pathways. Most experimental studies on cardioprotection have been undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of other disease processes. However, ischemic heart disease in humans is a complex disorder caused by or associated with known cardiovascular risk factors including hypertension, hyperlipidemia, diabetes, insulin resistance, atherosclerosis, and heart failure; additionally, aging is an important modifying condition. In these diseases and aging, the pathological processes are associated with fundamental molecular alterations that can potentially affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Among many other possible mechanisms, for example, in hyperlipidemia and diabetes, the pathological increase in reactive oxygen and nitrogen species and the use of the ATP-sensitive potassium channel inhibitor insulin secretagogue antidiabetic drugs and, in aging, the reduced expression of connexin-43 and signal transducer and activator of transcription 3 may disrupt major cytoprotective signaling pathways thereby significantly interfering with the cardioprotective effect of pre- and postconditioning. The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenous cardioprotection by pre- and postconditioning (i.e., drug applied as trigger or to activate signaling pathways associated with endogenous cardioprotection) and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardioprotection conferred by preconditioning and postconditioning. We emphasize the critical need for more detailed and mechanistic preclinical studies that examine car-dioprotection specifically in relation to complicating disease states. These are now essential to maximize the likelihood of successful development of rational approaches to therapeutic protection for the majority of patients with ischemic heart disease who are aged and/or have modifying comorbid conditions.

Postconditioning: a mechanical maneuver that triggers biological and molecular cardioprotective responses to reperfusion

Infarct size is determined not only by the duration and severity of ischemia, but also by pathological processes initiated at reperfusion (reperfusion injury). Numerous pharmacological strategies have been reported which administer drugs at or just before the onset of reperfusion, with subsequent salubrious effects, notably a reduction in infarct size. However, few if any of these strategies have become standard of care in the catheterization laboratory setting. Postconditioning, defined as repeated brief cycles of reperfusion interrupted by ischemia (or hypoxia) applied at the onset of reperfusion, was recently introduced as a mechanical strategy to attenuate reperfusion injury. Postconditioning intervenes only during the first few minutes of reperfusion. However, it reduces endothelial activation and dysfunction, the inflammatory response to reperfusion, necrosis, and apoptosis both acutely and long-term. Cardioprotection has been demonstrated by multiple independent laboratories and in multiple species. Postconditioning stimulates G-protein coupled receptors by their cognate endogenously released ligands and surprisingly activates survival kinases that may converge on mitochondrial K(ATP) channels and the permeability transition pore. Postconditioning has been shown in two clinical studies to reduce infarct size in patients undergoing percutaneous coronary intervention in the catheterization laboratory, and at least five other studies are in some phase of implementation. This significant reduction in infarct size has implications for reduction in heart failure as a consequence of myocardial infarction, but this link has yet to be demonstrated. The salubrious effects of postconditioning are an indirect validation of the experimental and clinical importance of reperfusion injury in the setting of coronary artery occlusion.

Pharmacologic therapeutics for cardiac reperfusion injury

Cardiovascular disease is the leading cause of morbidity and mortality in industrial societies, with myocardial infarction as the primary assassin. Pharmacologic agents, including the myocardial cell membrane receptor agonists adenosine, bradykinin/angiotensin-converting enzyme inhibitors, opioids and erythropoietin or the mixed cell membrane and intracellular agonists, glucose insulin potassium, and volatile anesthetics, either clinically or experimentally reduce the extent of myocardial injury when administered just prior to reperfusion. Agents that specifically target proteins, transcription factors or ion channels, including PKC agonists/antagonists, PPAR, Phosphodiesterase-5 inhibitors, 3-Hydroxy-3-methyl glutaryl coenzyme A reductase and the ATP-dependent potassium channel are also promising. However, no agent has been specifically approved to reduce reperfusion injury clinically. In this review, we will discuss the advantages and limitations of agents to combat reperfusion injury, their market development status and findings reported in both clinical and preclinical studies. The molecular pathways activated by these agents that preserve myocardium from reperfusion injury, which appear to commonly involve glycogen synthase kinase 3beta and mitochondrial permeability transition pore inhibition, are also described.

Noble gases without anesthetic properties protect myocardium against infarction by activating prosurvival signaling kinases and inhibiting mitochondrial permeability transition in vivo

BACKGROUND

The anesthetic noble gas, xenon, produces cardioprotection. We hypothesized that other noble gases without anesthetic properties [helium (He), neon (Ne), argon (Ar)] also produce cardioprotection, and further hypothesized that this beneficial effect is mediated by activation of prosurvival signaling kinases [including phosphatidylinositol-3-kinase, extracellular signal-regulated kinase, and 70-kDa ribosomal protein s6 kinase] and inhibition of mitochondrial permeability transition pore (mPTP) opening in vivo.

METHODS

Rabbits (n = 98) instrumented for hemodynamic measurement and subjected to a 30-min left anterior descending coronary artery (LAD) occlusion and 3 h reperfusion received 0.9% saline (control), three cycles of 70% He-, Ne-, or Ar-30% O2 administered for 5 min interspersed with 5 min of 70% N2-30% O2 before LAD occlusion, or three cycles of brief (5 min) ischemia interspersed with 5 min reperfusion before prolonged LAD occlusion and reperfusion (ischemic preconditioning). Additional groups of rabbits received selective inhibitors of phosphatidylinositol-3-kinase (wortmannin; 0.6 mg/kg), extracellular signal-regulated kinase (PD 098059; 2 mg/kg), or 70-kDa ribosomal protein s6 kinase (rapamycin; 0.25 mg/kg) or mPTP opener atractyloside (5 mg/kg) in the absence or presence of He pretreatment.

RESULTS

He, Ne, Ar, and ischemic preconditioning significantly (P < 0.05) reduced myocardial infarct size [23% +/- 4%, 20% +/- 3%, 22% +/- 2%, 17% +/- 3% of the left ventricular area at risk (mean +/- sd); triphenyltetrazolium chloride staining] versus control (45% +/- 5%). Wortmannin, PD 098059, rapamycin, and atractyloside alone did not affect infarct size, but these drugs abolished He-induced cardioprotection.

CONCLUSIONS

The results indicate that noble gases without anesthetic properties produce cardioprotection by activating prosurvival signaling kinases and inhibiting mPTP opening in rabbits.

The δ-opioid receptor agonist DADLE at reperfusion protects the heart through activation of pro-survival kinases via EGF receptor transactivation

The specific δ-opioid receptor agonist [d-Ala2-d-Leu5]enkephalin (DADLE) protects against infarction in the heart when given before ischemia. In rabbit, this protection leads to phosphorylation of the pro-survival kinases Akt and extracellular signal-regulated kinase (ERK) and is dependent on transactivation of the epidermal growth factor receptor (EGFR). DADLE reportedly protects rat hearts at reperfusion. We therefore tested whether DADLE at reperfusion could protect isolated rabbit hearts subjected to 30 min of regional ischemia and 120 min of reperfusion and whether this protection is dependent on Akt, ERK, and EGFR. DADLE (40 nM) was infused for 1 h starting 5 min before reperfusion and reduced infarct size from 31.0 ± 2.3% in the control group to 14.6 ± 1.6% ( P = 0.01). This protection was abolished by cotreatment of the metalloproteinase inhibitor (MPI) and the EGFR inhibitor AG1478. In contrast, 20 nM DADLE, although known to be protective before ischemia, failed to protect. Western blotting revealed that DADLE's protection was correlated to increase in phosphorylation of the kinases Akt and ERK1 and -2 in reperfused hearts (2.5 ± 0.5, 1.6 ± 0.2, and 2.3 ± 0.7-fold of baseline levels, P < 0.05 vs. control). The DADLE-dependent increases in Akt and ERK1/2 phosphorylation were abolished by either MPI or AG1478, confirming a signaling through the EGFR pathway. Additionally, DADLE treatment increased phosphorylation of EGFR (1.4 ± 0.2-fold, P = 0.03 vs. control). Thus the δ-opioid agonist DADLE protects rabbit hearts at reperfusion through activation of the pro-survival kinases Akt and ERK and is dependent on the transactivation of the EGFR.

PAR-2 activation at the time of reperfusion salvages myocardium via an ERK1/2 pathway in in vivo rat hearts

Protease-activated receptor-2 (PAR-2) may have proinflammatory effects in some tissues and protective effects in other tissues. The role of PAR-2 in in vivo myocardial ischemia-reperfusion has not yet been determined. This study tested the hypothesis that PAR-2 activation with the PAR-2 agonist peptide SLIGRL (PAR-2 AP) reduces myocardial infarct size when given at reperfusion in vivo, and this cardioprotection involves the ERK1/2 pathway. Anesthetized rats were randomly assigned to the following groups with 30 min of regional ischemia and 3 h reperfusion: 1) control with saline; 2) vehicle (DMSO); 3) PAR-2 AP, 1 mg/kg given intravenously 5 min before reperfusion; 4) scrambled peptide (SP), 1 mg/kg; 5) the ERK1/2 inhibitor PD-98059 (PD), 0.3 mg/kg given 10 min before reperfusion; 6) the phosphatidylinositol 3-kinase inhibitor LY-294002 (LY), 0.3 mg/kg given 10 min before reperfusion; 7) PD + PAR-2 AP, 0.3 mg/kg PD given 5 min before PAR-2 AP; 8) LY + PAR-2 AP, 0.3 mg/kg LY given 5 min before PAR-2 AP; 9) chelerythrine (Chel) alone, 5 mg/kg given 10 min before reperfusion; and 10) Chel + PAR-2 AP, Chel was given 5 min before PAR-2 AP (10 min before reperfusion). Activation of ERK1/2, ERK5, Akt, and the downstream targets of ERK1/2 [P90 RSK and bcl-xl/bcl-2-associated death promoter (BAD)] was determined by Western blot analysis in separate experiments. PAR-2 AP significantly reduced infarct size compared with control (36 +/- 2% vs. 53 +/- 1%, P < 0.05), and SP had no effect on infarct size (53 +/- 3%). PAR-2 AP significantly increased phosphorylation of ERK1/2, p90RSK, and BAD but not Akt or ERK5. Accordingly, the infarct-size sparing effect of PAR-2 AP was abolished by PD (PAR-2 AP, 36 +/- 2% vs. PD + PAR-2 AP, 50 +/- 1%; P < 0.05) and by Chel (Chel + PAR-2 AP, 58 +/- 2%) but not by LY (PAR-2 AP, 36 +/- 2% vs. LY + PAR-2 AP, 38 +/- 3%; P > 0.05). Therefore, PAR-2 activation is cardioprotective in the in vivo rat heart ischemia-reperfusion model, and this protection involves the ERK1/2 pathway and PKC.

The interplay between pro-death and pro-survival signaling pathways in myocardial ischemia/reperfusion injury: apoptosis meets autophagy

INTRODUCTION

Programmed cell death of cardiac myocytes occurs following a bout of ischemia/reperfusion (I/R), which results in reduced function of the heart. Numerous studies, including in vivo, have shown that cell death occurs via necrosis and apoptosis following I/R. Recently, autophagy has emerged as a powerful mediator of programmed cell death, either opposing or enhancing apoptosis, or acting as an alternative form of programmed cell death distinct from apoptosis.

AIM

Here we review the apoptotic and autophagic signaling pathways, their influences on each other, and we discuss the relevance of autophagy in the heart.

Past and present course of cardioprotection against ischemia-reperfusion injury

Despite tremendous advances in cardiovascular research and clinical therapy, ischemic heart disease remains the leading cause of serious morbidity and mortality in western society and is growing in developing countries. For the past 5 decades, many scientists have studied the pathophysiology of myocardial ischemia-reperfusion (I/R) injury leading to infarction. With the exception of reperfusion therapy, attempts to salvage the myocardium during an acute myocardial infarction showed disappointing results in directly decreasing infarct size. Nevertheless, the phenomena of ischemic preconditioning and ischemic postconditioning show a consistent and robust cardioprotective effect in every used experimental animal model. As a result, many studies have focused on the intracellular protective signaling pathways that are involved in preconditioning and postconditioning. More recently, it has been suggested that components of the reperfusion injury salvage kinases pathway, protein kinase B, and the extracellular signal-regulated kinases can induce cardioprotection against I/R injury when they are activated during the postischemic reperfusion period. In addition, inhibition of mitochondrial permeability transition during postischemic reperfusion also shows a strong cardioprotective effect against I/R injury. The present mini-review highlights a short summary of the historical and present course of research into cardioprotection against myocardial I/R injury.

NO mobilizes intracellular Zn2+ via cGMP/PKG signaling pathway and prevents mitochondrial oxidant damage in cardiomyocytes

OBJECTIVE

Our aim was to determine if NO prevents mitochondrial oxidant damage by mobilizing intracellular free zinc (Zn(2+)).

METHODS

Zn(2+) levels were determined by imaging enzymatically isolated adult rat cardiomyocytes loaded with Newport Green DCF. Mitochondrial membrane potential (DeltaPsi(m)) was assessed by imaging cardiomyocytes loaded with tetramethylrhodamine ethyl ester (TMRE).

RESULTS

S-nitroso-N-acetylpenicillamine (SNAP) dramatically increased Zn(2+), which was blocked by both ODQ and NS2028, two specific inhibitors of guanylyl cyclase. The protein kinase G (PKG) inhibitor KT5823 blocked the effect of SNAP while the PKG activator 8-Br-cGMP mimicked the action of SNAP, indicating that the cGMP/PKG pathway is responsible for the effect of SNAP. The increased Zn(2+) was prevented by 5-hydroxydecanoate (5HD) but was mimicked by diazoxide, implying that mitochondrial K(ATP) channel opening may account for this effect. Since chelation of Zn(2+) blocked the preventive effect of SNAP on H(2)O(2)-induced loss of DeltaPsi(m) and exogenous zinc (1 microM ZnCl(2)) prevented dissipation of DeltaPsi(m), Zn(2+) may play a critical role in the protective effect of NO. The MEK (mitogen-activated protein kinase or extracellular signal-regulated kinase) inhibitor PD98059 blocked the preventive effects of SNAP and zinc on DeltaPsi(m), indicating that extracellular signal-regulated kinase (ERK) mediates the protective effect of both these compounds on mitochondrial oxidant damage. A Western blot analysis further showed that ZnCl(2) significantly enhances phosphorylation of ERK, confirming the involvement of ERK in the action of Zn(2+).

CONCLUSIONS

In isolated cardiomyocytes, NO mobilizes endogenous zinc by opening mitochondrial K(ATP) channels through the cGMP/PKG pathway. In these cells, Zn(2+) may be an important mediator of the action of NO on the mitochondrial death pathway.

Chemical genetics: reshaping biology through chemistry

To understand biological processes, biologists typically study how perturbations of protein functions affect the phenotype. Protein activity in living cells can be influenced in many different ways: by manipulation of the genomic information, by injecting inhibitory antibodies, or, more recently, by the use of ribonucleic acid-medicated interference (RNAi). All these methods have proven to be extremely helpful, as they possess a high degree of specificity. However, they are less suitable for experiments requiring precise timing and fast reversibility of the perturbation. The advantage of small molecules is that they specifically interact with their target on a fast time scale and often in a reversible manner. In the last 15 years, this approach, termed "chemical genetics," has received a lot of attention. The term genetics pays tribute to the analogy between chemical genetics and the classic genetic approach, where manipulations at the gene level are used to draw conclusions about the function of the corresponding protein. Chemical genetics has only recently been used as a systematic approach in biology. The term was coined in the 1990's, when combinatorial chemistry was developed as a fast method to synthesize large compound libraries [Mitchison (1994) "Towards a pharmacological genetics," Chem. Biol. 1, 3-6; Schreiber (1998) "Chemical genetics resulting from a passion for synthetic organic chemistry," Bioorg. Med. Chem. 6, 1127-1152].

Preconditioning and postconditioning: united at reperfusion

Despite current optimal treatment, the morbidity and mortality of coronary heart disease (CHD), the leading cause of death worldwide, remains significant, paving the way for the development of novel cardioprotective therapies. Two potential strategies for protecting the heart are ischemic preconditioning (IPC) and ischemic postconditioning (IPost), which describe the cardioprotection obtained from applying transient episodes of myocardial ischemia and reperfusion either before or after the index ischemic event, respectively. Much progress has been made in elucidating the signal transduction pathway, which underlies their protection. Intriguingly, it is the first few minutes of myocardial reperfusion following the index ischemic period, which appear crucial to both IPC- and IPost-induced protection. Emerging evidence suggests that they appear to recruit a similar signaling pathway at time of myocardial reperfusion, comprising cell-surface receptors, a diverse array of protein kinase cascades including the reperfusion injury salvage kinase (RISK) pathway, redox signaling, and the mitochondrial permeability transition pore (mPTP). The common signaling pathway that appears to unite these 2 cardioprotective strategies at the time of reperfusion is the subject of this review. Importantly, this common cardioprotective pathway can be activated at the time of myocardial reperfusion in the clinical setting using pharmacological agents to target the essential signaling components, which should lead to the development of novel treatment strategies for improving the clinical outcomes of patients with CHD.

Reperfusion injury salvage kinase signalling: taking a RISK for cardioprotection

Following an acute myocardial infarction (AMI), early coronary artery reperfusion remains the most effective means of limiting the eventual infarct size. The resultant left ventricular systolic function is a critical determinant of the patient's clinical outcome. Despite current myocardial reperfusion strategies and ancillary antithrombotic and antiplatelet therapies, the morbidity and mortality of an AMI remain significant, with the number of patients developing cardiac failure increasing, necessitating the development of novel strategies for cardioprotection which can be applied at the time of myocardial reperfusion to reduce myocardial infarct size. In this regard, the Reperfusion Injury Salvage Kinase (RISK) Pathway, the term given to a group of pro-survival protein kinases (including Akt and Erk1/2), which confer powerful cardioprotection, when activated specifically at the time of myocardial reperfusion, provides an amenable pharmacological target for cardioprotection. Preclinical studies have demonstrated that an increasing number of agents including insulin, erythropoietin, adipocytokines, adenosine, volatile anesthetics natriuretic peptides and 'statins', when administered specifically at the time of myocardial reperfusion, reduce myocardial infarct size through the activation of the RISK pathway. This recruits various survival pathways that include the inhibition of mitochondrial permeability transition pore opening. Interestingly, the RISK pathway is also recruited by the cardioprotective phenomena of ischemic preconditioning (IPC) and postconditioning (IPost), enabling the use of pharmacological agents which target the RISK pathway, to be used at the time of myocardial reperfusion, as pharmacological mimetics of IPC and IPost. This article reviews the origins and evolution of the RISK pathway, as part of a potential common cardioprotective pathway, which can be activated by an ever-expanding list of agents administered at the time of myocardial reperfusion, as well as by IPC and IPost. Preliminary clinical studies have demonstrated myocardial protection with several of these pharmacological activators of the RISK pathway in AMI patients undergoing PCI. Through the use of appropriately designed clinical trials, guided by the wealth of existing preclinical data, the administration of pharmacological agents which are known to activate the RISK pathway, when applied as adjuvant therapy to current myocardial reperfusion strategies for patients presenting with an AMI, should lead to improved clinical outcomes in this patient group.

Cardiac hypertrophy: mechanisms and therapeutic opportunities

Cardiac hypertrophy and heart failure are major causes of morbidity and mortality in Western societies. Many factors have been implicated in cardiac remodeling, including alterations in gene expression in myocytes, cardiomyocytes apoptosis, cytokines and growth factors that influence cardiac dynamics, and deficits in energy metabolism as well as alterations in cardiac extracellular matrix composition. Many therapeutic means have been shown to prevent or reverse cardiac hypertrophy. New concepts for characterizing the pathophysiology of cardiac hypertrophy have been drawn from various aspects, including medical therapy and gene therapy, or use of stem cells for tissue regeneration. In this review, we focus on various types of cardiac hypertrophy, defining the causes of hypertrophy, describing available animal models of hypertrophy, discussing the mechanisms for development of hypertrophy and its transition to heart failure, and presenting the potential use of novel promising therapeutic strategies derived from new advances in basic scientific research.

Adenosinergic cardioprotection: Multiple receptors, multiple pathways

Adenosine, formed primarily via hydrolysis of 5'-AMP, has been historically dubbed a "retaliatory" metabolite due to enhanced local release and beneficial actions during cellular/metabolic stress. From a cardiovascular perspective, evidence indicates the adenosinergic system is essential in mediation of intrinsic protection (e.g., pre- and postconditioning) and determining myocardial resistance to insult. Modulation of adenosine and its receptors thus remains a promising, though as yet not well-realized, approach to amelioration of injury in ischemic-reperfused myocardium. Adenosine exerts effects through A(1), A(2A), A(2B), and A(3) adenosine receptor subtypes (A(1)AR, A(2A)AR, A(2B)AR, and A(3)AR), which are all expressed in myocardial and vascular cells, and couple to G proteins to trigger a range of responses (generally, but not always, beneficial). Adenosine can also enhance tolerance to injurious stimuli via receptor-independent metabolic effects. Given adenosines contribution to preconditioning, it is no surprise that postreceptor signaling typically mimics that associated with preconditioning. This involves activation/translocation of PKC, PI3 kinase, and MAPKs, with ultimate effects at the level of mitochondrial targets-the mitochondrial K(ATP) channel and/or the mitochondrial permeability transition pore (mPTP). Nonetheless, differences in cytoprotective signaling and actions of the different adenosine receptor subtypes have been recently revealed. Our understanding of adenosinergic cytoprotection continues to evolve, with roles for the A(2) subtypes emerging, together with evidence of essential receptor "cross-talk" in mediation of protection. This review focuses on current research into adenosine-mediated cardioprotection, highlighting recent findings which, together with a wealth of prior knowledge, may ultimately facilitate adenosinergic approaches to clinical cardiac protection.

GSK3β inhibition and KATP channel opening mediate acute opioid-induced cardioprotection at reperfusion

Both glycogen synthase kinase 3beta (GSK3beta) and the ATP-dependant potassium channel (K(ATP)) mediate opioid-induced cardioprotection (OIC). However, whether direct K(ATP) channel openers induce cardioprotection prior to reperfusion and their signaling cascade position with respect to GSK3beta inhibition is unknown. Therefore, we investigated the role of K(ATP) channel opening at reperfusion in OIC, and the interaction between the GSK signaling axis and K(ATP) channels in cardioprotection.Male Sprague-Dawley rats underwent 30 minutes ischemia with 2 hours of reperfusion and infarct size was determined. Rats given the nonselective opioid agonist, morphine (0.3 mg/kg), or the selective delta opioid agonist, BW373U86 (1.0 mg/kg), 5 minutes prior to reperfusion reduced infarct size (40.3+/-1.6*, 39.7+/-1.9* versus 60.0+/-1.1%, respectively, * P<0.001%). This protection was abrogated with prior administration of the putative sarcolemmal K(ATP) antagonist, HMR-1098 (6 mg/kg), or the putative mitochondrial K(ATP) antagonist, 5-HD (10 mg/kg). The putative sK(ATP) channel opener, P-1075 (1microg/kg) or the putative mK(ATP) channel opener, BMS-191095 (1 mg/kg) given 5 minutes prior to reperfusion also reduced infarct size (41.8+/-2.4*, 43.4+/-1.4*) and protection was abrogated by prior administration of the PI3k inhibitor wortmannin (60.0+/-1.7, 64.0+/-2.6%, respectively, * P<0.001). Cardioprotection afforded by the GSK inhibitor SB216763 (0.6 mg/kg) given 5 minutes prior to reperfusion was also partially blocked by either HMR or 5-HD and completely blocked when HMR and 5-HD were given in combination (40.8+/-1.6*, 50.4+/-1.6;; 49.4+/-1.7;, 61.6+/-1.6%, respectively, * or ; P<0.001). These data indicate that both the sK(ATP) and mK(ATP) channel are involved in acute OIC and the GSK signaling axis regulates cardioprotection via K(ATP) channel opening.

Prolonged transient acidosis during early reperfusion contributes to the cardioprotective effects of postconditioning

We have previously reported that the prolonged transient acidosis during early reperfusion mediates the cardioprotective effects in canine hearts. Recently, postconditioning has been shown to be one of the novel strategies to mediate cardioprotection. We tested the contribution of the prolonged transient acidosis to the cardioprotection of postconditioning. Open-chest anesthetized dogs subjected to 90-min occlusion of the left anterior descending coronary artery and 6-h reperfusion were divided into four groups: 1) control group; no intervention after reperfusion ( n = 6); 2) postconditioning (Postcon) group; four cycles of 1-min reperfusion and 1-min reocclusion ( n = 7); 3) Postcon + sodium bicarbonate (NaHCO3) group; four cycles of 1-min reperfusion and 1-min reocclusion with the administration of NaHCO3( n = 8); and 4) NaHCO3group; administration of NaHCO3without postconditioning ( n = 6). Infarct size, the area at risk (AAR), collateral blood flow during ischemia, and pH in coronary venous blood were measured. The phosphorylation of Akt and extracellular signal-regulated kinase (ERK) in ischemic myocardium was assessed by Western blot analysis. Systemic hemodynamic parameters, AAR, and collateral blood flow were not different among the four groups. Postconditioning induced prolonged transient acidosis during the early reperfusion phase. Administration of NaHCO3completely abolished the infarct size-limiting effects of postconditioning. Furthermore, the phosphorylation of Akt and ERK in ischemic myocardium induced by postconditioning was also blunted by the cotreatment of NaHCO3. In conclusion, postconditioning mediates its cardioprotective effects possibly via prolonged transient acidosis during the early reperfusion phase with the activation of Akt and ERK.

Cardiac effects of postconditioning depend critically on the duration of index ischemia

Postconditioning (POC) is known as the phenomenon whereby brief intermittent ischemia applied at the onset of reperfusion following index ischemia limits myocardial infarct size. Whereas there is evidence that the algorithm of the POC stimulus is an important determinant of the protective efficacy, the importance of the duration of index ischemia on the outcome of the effects of POC has received little attention. Pentobarbital sodium-anesthetized Wistar rats were therefore subjected to index ischemia produced by coronary artery occlusions (CAO) of varying duration (15–120 min) followed by reperfusion, without or with postconditioning produced by three cycles of 30-s reperfusion and reocclusion (3POC30). 3POC30 limited infarct size produced by 45-min CAO (CAO45) from 45 ± 3% to 31 ± 5%, and CAO60 from 60 ± 3% to 47 ± 6% (both P ≤ 0.05). In contrast, 3POC30 increased infarct size produced by CAO15 from 3 ± 1% to 19 ± 6% and CAO30 from 36 ± 6 to 48 ± 4% (both P ≤ 0.05). This deleterious effect of 3POC30 was not stimulus sensitive because postconditioning with 3POC5 and 3POC15 after CAO30 also increased infarct size. The cardioprotection by 3POC30 after CAO60 was accompanied by an increased stimulation of Akt phosphorylation at 7 min of reperfusion and a 36% lower superoxide production, measured by dihydroethidium fluorescence, after 2 h of reperfusion. Consistent with these results, cardioprotection by 3POC30 was abolished by phosphatidylinositol-3-OH-kinase inhibition, as well as nitric oxide (NO) synthase inhibition. The deleterious effect of 3POC30 after CAO15 was accompanied by an increased superoxide production with no change in Akt phosphorylation and was not affected by NO synthase inhibition. In conclusion, the effect of cardiac POC depends critically on the duration of the index ischemia and can be either beneficial or detrimental. These paradoxical effects of POC may be related to the divergent effects on Akt phosphorylation and superoxide production.

Preconditioning: The Mitochondrial Connection

Over the past decade there has been considerable progress in elucidating the signaling pathways involved in cardioprotection. Considerable recent data suggest that many of these signaling pathways converge on the mitochondria, where such pathways alter the activity of key mitochondrial proteins, leading to reduced apoptosis and necrosis. Inhibition of the mitochondrial permeability transition pore is emerging as a central mechanism in cardioprotection. This review focuses on mechanisms by which cardioprotection alters mitochondrial proteins and channels that regulate cell death and survival.

Diabetes abolishes morphine-induced cardioprotection via multiple pathways upstream of glycogen synthase kinase-3beta

The cardioprotective effect of opioids or glycogen synthase kinase (GSK) inhibitors given at reperfusion has not been investigated in diabetes models. Therefore, nondiabetic (NDBR) or streptozotocin-induced diabetic (DBR) rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. Groups of NDBR or DBR were administered either vehicle, morphine (0.3 mg/kg), or the GSK inhibitor SB216763 (0.6 mg/kg) 5 min before reperfusion. SB216763 (but not morphine) reduced infarct size in DBRs (44 +/- 1* and 55 +/- 2%, respectively), while both agents reduced infarct size in NDBRs versus untreated NDBRs or DBRs (44 +/- 3*, 42 +/- 3*, 60 +/- 2, and 56 +/- 2%, respectively, *P < 0.001). Morphine-induced phospho- (P-)GSK3beta was reduced 5 min after reperfusion in DBRs compared with NDBRs (0.83 +/- 0.29 and 1.94 +/- 0.12 [P < 0.05] pg/microg tissue, respectively). The GSK3beta mediators, P-Akt, P-extracellular signal-related kinase (ERK)1, and P-signal transducer and activator of transcription (STAT)3, were also significantly reduced in untreated DBR compared with NDBR rats. Morphine-induced elevations of P-Akt, P-ERK1, P-p70s6, P-janus-activated kinase-2, and P-STAT3 in NDBRs were also blunted in DBRs. H9C2 cells raised in 25 mmol/l compared with 5.56 mmol/l glucose media also demonstrated reduced morphine-induced P-GSK3beta, P-Akt, P-STAT3, and P-ERK1 after 15 min. Hence, acute GSK inhibition may provide a novel therapeutic strategy for diabetic patients during an acute myocardial infarction, whereas morphine is less effective due to signaling events that adversely affect GSK3beta.

Beta(2)-Adrenergic activation increases glycogen synthesis in L6 skeletal muscle cells through a signalling pathway independent of cyclic AMP

AIMS/HYPOTHESIS

In skeletal muscle, the storage of glycogen by insulin is regulated by glycogen synthase, which is regulated by glycogen synthase kinase 3 (GSK3). Here we examined whether adrenergic receptor activation, which can increase glucose uptake, regulates glycogen synthesis in L6 skeletal muscle cells.

METHODS

We used L6 cells and measured glycogen synthesis (as incorporation of D: -[U-(14)C]glucose into glycogen) and GSK3 phosphorylation following adrenergic activation.

RESULTS

Insulin (negative logarithm of median effective concentration [pEC(50)] 8.2 +/- 0.3) and the beta-adrenergic agonist isoprenaline (pEC(50) 7.5 +/- 0.3) induced a twofold increase in glycogen synthesis in a concentration-dependent manner. The alpha(1)-adrenergic agonist cirazoline and alpha(2)-adrenergic agonist clonidine had no effect. Both insulin and isoprenaline phosphorylated GSK3. The beta-adrenergic effect on glycogen synthesis is mediated by beta(2)-adrenoceptors and not beta(1)-/beta(3)-adrenoceptors, and was not mimicked by 8-bromo-cyclic AMP or cholera toxin, and also was insensitive to pertussis toxin, indicating no involvement of cyclic AMP or inhibitory G-protein (G(i)) signalling in the beta(2)-adrenergic effect on glycogen synthesis. 12-O-tetra-decanoylphorbol-13-acetate (TPA) increased glycogen synthesis 2.5-fold and phosphorylated GSK3 fourfold. Inhibition of protein kinase C (PKC) isoforms with 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrollo(3,4-c)-carbazole (Gö6976; inhibits conventional and novel PKCs) or 2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide (Gö6983; inhibits conventional, novel and atypical PKCs) inhibited the stimulatory TPA effect, but did not significantly inhibit glycogen synthesis mediated by insulin or isoprenaline. Inhibition of phosphatidylinositol 3-kinase (PI3K) with wortmannin inhibited the effects of insulin and isoprenaline on glycogen synthesis.

CONCLUSIONS/INTERPRETATION

These results demonstrate that in L6 skeletal muscle cells adrenergic stimulation through beta(2)-adrenoceptors, but not involving cyclic AMP or G(i), activates a PI3K pathway that stimulates glycogen synthesis through GSK3.

Phosphoinositide 3-kinase gamma/delta inhibition limits infarct size after myocardial ischemia/reperfusion injury

Although phosphoinositide 3-kinases (PI3Ks) play beneficial pro-cell survival roles during tissue ischemia, some isoforms (gamma and delta) paradoxically contribute to the inflammation that damages these same tissues upon reperfusion. We therefore considered the possibility that selectively inhibiting proinflammatory PI3K isoforms during the reperfusion phase could ultimately limit overall tissue damage seen in ischemia/reperfusion injuries such as myocardial infarction. Panreactive and isoform-restricted PI3K inhibitors were identified by screening a novel chemical family; molecular modeling studies attributed isoform specificity based on rotational freedom of substituent groups. One compound (TG100-115) identified as a selective PI3K gamma/delta inhibitor potently inhibited edema and inflammation in response to multiple mediators known to participate in myocardial infarction, including vascular endothelial growth factor and platelet-activating factor; by contrast, endothelial cell mitogenesis, a repair process important to tissue survival after ischemic damage, was not disrupted. In rigorous animal MI models, TG100-115 provided potent cardioprotection, reducing infarct development and preserving myocardial function. Importantly, this was achieved when dosing well after myocardial reperfusion (up to 3 h after), the same time period when patients are most accessible for therapeutic intervention. In conclusion, by targeting pathologic events occurring relatively late in myocardial damage, we have identified a potential means of addressing an elusive clinical goal: meaningful cardioprotection in the postreperfusion time period.

Inhibition of apoptotic protein p53 lowers the threshold of isoflurane-induced cardioprotection during early reperfusion in rabbits

INTRODUCTION

Exposure to isoflurane before and during early reperfusion protects against myocardial infarction by activating phosphatidylinositol-3-kinase (PI3K)-mediated signaling. The apoptotic protein, p53, is regulated by PI3K, and inhibition of p53 protects against ischemic injury. We tested the hypothesis that p53 inhibition lowers the threshold of isoflurane-induced postconditioning in vivo.

METHODS

Rabbits (n = 73) instrumented for hemodynamic measurement and subjected to a 30-min left anterior descending coronary artery occlusion and 3-h reperfusion received 0.9% saline (control), isoflurane (0.5 or 1.0 minimum alveolar concentration [MAC]) administered for 3 min before and 2 min after reperfusion, the p53 inhibitor pifithrin-alpha (1.5 or 3.0 mg/kg), or 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha. Other rabbits received 3.0 mg/kg pifithrin-alpha or 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha after pretreatment with the selective PI3K inhibitor wortmannin (0.6 mg/kg) or the mitochondrial permeability transition pore opener atractyloside (5 mg/kg).

RESULTS

Isoflurane (1.0 but not 0.5 MAC), pifithrin-alpha (3.0 but not 1.5 mg/kg), and the combination of 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha significantly (P < 0.05) reduced infarct size (21% +/- 4%, 43% +/- 7%, 22% +/- 4%, 45% +/- 4%, and 28% +/- 3% [mean +/- sd], respectively, of left ventricular area at risk; triphenyltetrazolium chloride staining) when compared with control (45% +/- 2%). Atractyloside, but not wortmannin, abolished 3.0 mg/kg pifithrin-alpha-induced cardioprotection, whereas atractyloside and wortmannin blocked reductions in infarct size produced by 0.5 MAC isoflurane plus 1.5 mg/kg pifithrin-alpha.

CONCLUSION

The results indicate that inhibition of the apoptotic protein p53 lowers the threshold of isoflurane-induced cardioprotection during early reperfusion in vivo.

Activation of the Akt/GSK3beta signaling pathway mediates survival of vulnerable hippocampal neurons after transient global cerebral ischemia in rats

Recent studies have revealed that the phosphatidylinositol 3-kinase (PI3-K) pathway is involved in apoptotic cell death after experimental cerebral ischemia. The serine-threonine kinase, Akt, functions in the PI3-K pathway and prevents apoptosis by phosphorylation at Ser473 after a variety of cell death stimuli. After phosphorylation, activated Akt inactivates other apoptogenic factors, including glycogen synthase kinase-3beta (GSK3beta), thereby inhibiting cell death. However, the role of Akt/GSK3beta signaling in the delayed death of hippocampal neurons in the CA1 subregion after transient global cerebral ischemia (tGCI) has not been clarified. Transient global cerebral ischemia for 5 mins was induced by bilateral common carotid artery occlusion combined with hypotension. Western blot analysis showed a significant increase in phospho-Akt (Ser473) and phospho-GSK3beta (Ser9) in the hippocampal CA1 subregion after tGCI. Immunohistochemistry showed that expression of phospho-Akt (Ser473) and phospho-GSK3beta (Ser9) was markedly increased in the vulnerable CA1 subregion, but not in the ischemic-tolerant CA3 subregion. Double staining with phospho-GSK3beta (Ser9) and terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling showed different cellular distributions in the CA1 subregion 3 days after tGCI. Phosphorylation of Akt and GSK3beta was prevented by LY294002, a PI3-K inhibitor, which facilitated subsequent DNA fragmentation 3 days after tGCI. Moreover, transgenic rats that overexpress copper/zinc-superoxide dismutase, which is known to be neuroprotective against delayed hippocampal CA1 injury after tGCI, had enhanced and persistent phosphorylation of both Akt and GSK3beta after tGCI. These findings suggest that activation of the Akt/GSK3beta signaling pathway may mediate survival of vulnerable hippocampal CA1 neurons after tGCI.

Reperfusion injury: does it exist?

It is well established that reperfusion of the heart is the optimal method of salvaging previously ischemic myocardium. However, the idea of reperfusion injury, i.e. injury caused by the process of reperfusion per se, still remains a controversial issue. In this review, we present mounting evidence supporting the concept that reperfusion injury exists, based on work conducted with adenosine and opioid receptor ligands, and the discovery of two new concepts regarding reperfusion injury: 'postconditioning' (POC) and the reperfusion injury salvage kinase (RISK) signaling pathway.

Differential role of PI3K/Akt pathway in the infarct size limitation and antiarrhythmic protection in the rat heart

Endogenous cardiac protection against prolonged ischemic insult can be achieved by repeated brief episodes of ischemia (hypoxia) or by cardiac adaptation to various stresses such as chronic hypoxia. Activation of phosphatidylinositol 3-kinase (PI3K)/Akt is involved in antiapoptotic effects, however, it is not clear whether it is required for overall heart salvage including protection against myocardial infarction and arrhythmias. We focussed on the potential common role of PI3K/Akt in anti-infarct protection, in the experimental settings of long-term adaptation to chronic intermittent hypobaric hypoxia (IHH; 8 h/day, 25-30 exposures, in vivo rats) and acute ischemic preconditioning (IP; Langendorff-perfused hearts). In addition, we explored the role of PI3K/Akt in susceptibility to ischemic ventricular arrhythmias. In normoxic open-chest rats, PI3K/Akt inhibitor LY294002 (LY; 0.3 mg/kg) given 5 min before test occlusion/reperfusion (I/R) did not affect infarct size (IS) normalized to the size of area at risk (AR). In hypoxic rats, LY partially attenuated IS-limiting effect of IHH (IS/AR 59.7 +/- 4.1% vs. 51.8 +/- 4.4% in the non-treated rats; p > 0.05) and increased IS/AR to its value in normoxic rats (64.9 +/- 5.1%). In the isolated hearts, LY (5 muM) applied 15 min prior to I/R completely abolished anti-infarct protection by IP (IS/AR 55.0 +/- 4.9% vs. 15.2 +/- 1.2% in the non-treated hearts and 42.0 +/- 5.5% in the non-preconditioned controls; p < 0.05). In the non-preconditioned hearts, PI3K/Akt inhibition did not modify IS/AR, on the other hand, it markedly suppressed arrhythmias. In the LY-treated isolated hearts, the total number of ventricular premature beats and the incidence of ventricular tachycardia (VT) was reduced from 518 +/- 71 and 100% in the controls to 155 +/- 15 and 12.5%, respectively (p < 0.05). Moreover, bracketing of IP with LY did not reverse antiarrhythmic effect of IP. These results suggest that activation of PI3K/Akt cascade plays a role in the IS-limiting mechanism in the rat heart, however, it is not involved in the mechanisms of antiarrhythmic protection.

Cardioprotective effects of acute and chronic opioid treatment are mediated via different signaling pathways

A 5-day exposure to morphine exerts a profound cardioprotective phenotype in murine hearts. In the present study, we examined mechanisms by which morphine generates this effect, exploring the roles of Gi and Gs proteins, PKA, PKC, and β-adrenergic receptors (β-AR) in acute and chronic opioid preconditioning. Langendorff-perfused hearts from placebo, acute morphine (AM; 10 μmol/l)-, or chronic morphine (CM)-treated mice (75-mg pellet, 5 days) underwent 25-min ischemia and 45-min reperfusion. After reperfusion, placebo-treated hearts exhibited marked contractile and diastolic dysfunction [rate-pressure product (RPP), 40 ± 4% baseline; end-diastolic pressure (EDP), 33 ± 3 mmHg], whereas AM hearts showed significant improvement in recovery of RPP and EDP (60 ± 3% and 23 ± 4 mmHg, respectively; P < 0.05 vs. placebo). Furthermore, CM hearts demonstrated a complete return of diastolic function and significantly greater recovery of contractile function (83 ± 3%, P < 0.05 vs. both placebo and AM). Pretreatment with Gi protein inhibitor pertussis toxin abolished AM protection while partially attenuating CM recovery ( P < 0.05 vs. placebo). Treatment with Gs inhibitor NF-449 did not affect AM preconditioning yet completely abrogated CM preconditioning. Similarly, PKA inhibition significantly attenuated the ischemia-tolerant state afforded by CM, whereas it was ineffective in AM hearts. PKC inhibition with chelerythrine was ineffective in CM hearts while completely abrogating AM preconditioning. Moreover, whereas β1-AR blockade with CGP-20712A failed to alter recovery in CM hearts, the β2-AR antagonist ICI-118,551 significantly attenuated postischemic recovery. These data describe novel findings whereby CM preconditioning is mediated by a PKC-independent pathway involving PKA, β2-AR, and Gs proteins, whereas AM preconditioning is mediated via Gi proteins and PKC.

Rapamycin confers preconditioning-like protection against ischemia-reperfusion injury in isolated mouse heart and cardiomyocytes

Rapamycin (sirolimus) is an antibiotic that inhibits protein synthesis through mammalian target of rapamycin (mTOR) signaling and is used as an immunosuppressant in the treatment of organ rejection in transplant recipients. Recently, the antigrowth properties of rapamycin have been utilized for cardiovascular benefit as stents impregnated with rapamycin effectively reduce coronary restenosis. We report here a novel role of this drug in protection against ischemia/reperfusion (I/R) injury. Adult male ICR mice were treated with rapamycin (0.25 mg/kg, IP) or volume-matched DMSO (solvent for rapamycin). The hearts were subjected to 20 min of global ischemia and 30 min of reperfusion in Langendorff mode. The blocker of mitochondrial KATP channel, 5-hydroxydecanoate (5-HD, 100 microM) was given 10 min before ischemia. Infarct size in the DMSO treated group was 28.2 +/- 1.3% and was reduced to 10.1 +/- 2.8% in the rapamycin-treated mice (64% decrease, P < 0.001). 5-HD blocked the protective effect (infarct area 32.2 +/- 1.8%, P < 0.001 vs. rapamycin). The infarct limiting effect of rapamycin was not associated with improved recovery of ventricular function. We further examined the effect of rapamycin in protection against necrosis and apoptosis in adult cardiomyocytes subjected to simulated ischemia and reoxygenation. Myocytes treated with rapamycin in doses from 25-100 nM demonstrated significantly lower trypan blue-positive necrotic cells and TUNEL-positive apoptotic nuclei, supporting the protective role of drug in the intact heart. These data suggest that rapamycin induces potent preconditioning-like effect against myocardial infarction through opening of mitochondrial KATP channels. We propose that rapamycin may be a novel therapeutic strategy to limit infarction, apoptosis, and remodeling following I/R injury in the heart.

A wave of reactive oxygen species (ROS)-induced ROS release in a sea of excitable mitochondria

Once considered simply as the main source of ATP, mitochondria are now implicated in the control of many additional aspects of cell physiology, such as calcium signaling, and pathology, as in injury incurred on ischemia and subsequent reperfusion (I/R). Mitochondrial respiration is ordinarily accompanied by low-level ROS production, but they can respond to elevated ROS concentrations by increasing their own ROS production, a phenomenon termed ROS-induced ROS release (RIRR). Two modes of RIRR have been described. In the first mode of RIRR, enhanced ROS leads to mitochondrial depolarization via activation of the MPTP, yielding a short-lived burst of ROS originating from the mitochondrial electron transport chain (ETC). The second mode of RIRR is MPTP independent but is regulated by the mitochondrial benzodiazepine receptor (mBzR). Increased ROS in the mitochondrion triggers opening of the inner mitochondrial membrane anion channel (IMAC), resulting in a brief increase in ETC-derived ROS. Both modes of RIRR have been shown to transmit localized mitochondrial perturbations throughout the cardiac cell in the form of oscillations or waves but are kinetically distinct and may involve different ROS that serve as second messengers. In this review, we discuss the mechanisms of these different modes of RIRR.

IB-MECA and Cardioprotection

The adenosine A(3) receptor plays an important role in ischemic preconditioning. Activation of the adenosine A(3) receptor with its agonists induces both early and late pharmacological preconditioning through various mechanisms. As the first potent and selective adenosine A(3) receptor agonist, IB-MECA (N(6)-(3-iodobenzyl)-adenosine-5'-N-methylcarboxamide) has been demonstrated to induce cardioprotection against myocardial ischemia/reperfusion injury when given before onset of ischemia by triggering pharmacological preconditioning. More importantly, IB-MECA can also protect the heart even when administered at the onset of reperfusion after ischemia, indicating a strong likelihood that the drug may be useful for the treatment of patients with acute myocardial infarction. However, since IB-MECA has been reported to have lethal effects at higher concentrations, and may cause systemic hypertension in some species, further studies are needed to find the best treatment strategy to increase its therapeutic potential.

Differential effects of postconditioning on myocardial stunning and infarction: a study in conscious dogs and anesthetized rabbits

Postconditioning, i.e., brief intermittent episodes of myocardial ischemia-reperfusion performed at the onset of reperfusion, reduces infarct size after prolonged ischemia. Our goal was to determine whether postconditioning is protective against myocardial stunning. Accordingly, conscious chronically instrumented dogs (sonomicrometry, coronary balloon occluder) were subjected to a control sequence (10 min coronary artery occlusion, CAO, followed by coronary artery reperfusion, CAR) and a week apart to postconditioning with four cycles of brief CAR and CAO performed at completion of the 10 min CAO. Three postconditioning protocols were investigated, i.e., 15 s CAR/15 s CAO ( n = 5), 30 s CAR/30 s CAO ( n = 7), and 1 min CAR/1 min CAO ( n = 6). Left ventricular wall thickening was abolished during CAO and similarly reduced during subsequent stunning in control and postconditioning sequences (e.g., at 1 h CAR, 33 ± 4 vs. 34 ± 4%, 30 ± 4 vs. 30 ± 4%, and 33 ± 4 vs. 32 ± 4% for 15 s postconditioning, 30 s postconditioning, and 1 min postconditioning vs. corresponding control, respectively). We confirmed this result in anesthetized rabbits by demonstrating that shortening of left ventricular segment length was similarly depressed after 10 min CAO in control and postconditioning sequences (4 cycles of 30 s CAR/30 s CAO). In additional rabbits, the same postconditioning protocol significantly reduced infarct size after 30 min CAO and 3 h CAR (39 ± 7%, n = 6 vs. 56 ± 4%, n = 7 of the area at risk in postconditioning vs. control, respectively). Thus, contrasting to its beneficial effects on myocardial infarction, postconditioning does not protect against myocardial stunning in dogs and rabbits. Conversely, additional episodes of ischemia-reperfusion with postconditioning do not worsen myocardial stunning.

Glycogen synthase kinase-3beta inhibitors protect against the organ injury and dysfunction caused by hemorrhage and resuscitation

Glycogen synthase kinase 3beta (GSK-3beta) is a serine/threonine protein kinase that has recently emerged as a key regulatory switch in the modulation of the inflammatory response. Dysregulation of GSK-3beta has been implicated in the pathogenesis of several diseases including sepsis. Here we investigate the effects of 2 chemically distinct inhibitors of GSK-3beta, TDZD-8 and SB216763, on the circulatory failure and the organ injury and dysfunction associated with hemorrhagic shock. Male Wistar rats were subjected to hemorrhage (sufficient to lower mean arterial blood pressure to 35 mmHg for 90 min) and subsequently resuscitated with shed blood for 4 h. Hemorrhage and resuscitation resulted in an increase in serum levels of (a) creatinine and, hence, renal dysfunction, and (b) alanine aminotransferase and aspartate aminotransferase and, hence, hepatic injury. Treatment of rats with either TDZD-8 (1 mg/kg, i.v.) or SB216763 (0.6 mg/kg, i.v.) 5 min before resuscitation abolished the renal dysfunction and liver injury caused by hemorrhagic shock. In addition, TDZD-8, but not SB216763, attenuated the increase caused by hemorrhage and resuscitation in plasma levels of the proinflammatory cytokine interleukin 6 and also of the anti-inflammatory cytokine interleukin 10. Neither of the GSK-3beta inhibitors however affected the delayed fall in blood pressure caused by hemorrhagic shock. Thus, we propose that inhibition of GSK-3beta may represent a novel therapeutic approach in the therapy of hemorrhagic shock.

Effects of Glycogen Synthase Kinase 3β and Cyclin-Dependent Kinase 5 Inhibitors on Morphine-Induced Analgesia and Tolerance in Rats

Repeated administration of morphine is associated with the development of tolerance, yet the mechanism underlying this phenomenon is still poorly understood. Recent evidence implicating glycogen synthase kinase 3 (GSK3) in opioid receptor signaling pathways has prompted us to investigate its role in morphine tolerance. Administration of 10 mg/kg morphine i.p. to Wistar rats twice daily for 8 days resulted in complete tolerance to its analgesic effects as measured by the tail-flick test. When injections of morphine were preceded by intrathecal (i.t.) administration of either an inhibitor of GSK3 [(3-(2,4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione (SB216763) or 6-bromoindirubin-3'oxime] or an inhibitor of cyclin-dependent kinase (Cdk), roscovitine, development of tolerance to morphine analgesia was completely abolished. In addition, a single i.t. injection of either kinase inhibitor was able to restore in a dose-dependent manner the analgesic effect of morphine in morphine-tolerant rats. None of the inhibitors in doses used in the present study had analgesic effects of their own nor an effect on the analgesic potency of morphine. Repeated i.t. administration of either inhibitor had caused an increase in abundance of GSK-3beta phosphorylated at Ser(9) in the dorsal lumbar part of the spinal cord of rats that were chronically treated with morphine. Furthermore, reversal of morphine tolerance by a single injection of either inhibitor was always associated with increased abundance of phospho-GSK3beta. In conclusion, our data indicate that chronic morphine treatment activates a highly efficient pathway by means of which Cdk5 regulates GSK3beta activity.

Met5-enkephalin-Arg6-Phe7 (MEAP): a cardioprotective hormonal opioid

BACKGROUND

Acute myocardial ischemia is an important cause of morbidity and mortality worldwide. The heart and other organs can be rendered more resistant to the deleterious effects of ischemia through a variety of preconditioning strategies, including treadmill exercise and brief ischemia of skeletal muscle. Some of the beneficial effects of these preconditioning strategies appear to be mediated by as-of-yet unidentified hormonal opioids.

OBJECTIVES

To test the hypothesis that endogenous opioids of the enkephalin class are capable of improving ischemic tolerance and acting in a hormonal manner.

METHODS

In phase one of the investigation, the authors assessed the cardioprotective potential of all four known enkephalins. This was achieved by subjecting isolated buffer-perfused rabbit hearts to a 25-minute period of test ischemia and two hours of reperfusion (protocol 1) after receiving treatment with either saline vehicle (controls) or increasing concentrations of purified enkephalins. On the basis of results from these initial studies, the authors performed additional experiments (protocol 2) to determine whether Met5-enkephalin-Arg6-Phe7 (MEAP) could be absorbed from skeletal muscle and exert a cardioprotective effect. Specifically, MEAP or vehicle (controls) was given intramuscularly 24 hours before the hearts were harvested. A similar assessment of ischemic tolerance as described in protocol 1 was then performed. Postischemic myocardial viability (infarct size) was assessed in all cases by triphenyltetrazolium chloride (TTC) staining. Hemodynamic parameters and infarct sizes for concentration-dependence studies were compared by two-way analysis of variance, and infarct sizes from protocol 2 studies were compared by using Student's t-test (significance set at p < or = 0.05).

RESULTS

Mean infarct size in control hearts (+/- SEM) was 33% (+/- 4%) and 36% (+/- 6%) for protocol 1 and 2, respectively. Of the four enkephalins tested in protocol 1, only MEAP treatment showed a tendency toward cardioprotection. Interestingly, an alternative enkephalin, methionine5-enkephalin-Arg6-Gly7-Leu8, tended to exert an injurious effect. In protocol 2, MEAP treatment 24 hours before ischemia significantly reduced infarct size (14% +/- 4%) compared with controls, suggesting that it can be released from muscle and exert a distant cardioprotective effect.

CONCLUSIONS

When given either directly to the heart or absorbed from a distant tissue, MEAP induces cardioprotection, supporting the hypothesis that it can act as a hormonal modulator of ischemic tolerance.

The JAK/STAT pathway is essential for opioid-induced cardioprotection: JAK2 as a mediator of STAT3, Akt, and GSK-3β

We examined the role for the JAK/STAT signaling pathway in acute opioid-induced cardioprotection (OIC) and whether opioid-induced glycogen synthase kinase-3β (GSK-3β) inhibition is mediated by the JAK/STAT pathway. Rats underwent 30 min of ischemia and either 5 min or 2 h of reperfusion, followed by tissue isolation for molecular analysis or infarct size assessment, respectively. Rats were treated with vehicle, morphine (300 μg/kg), the δ-opioid agonist fentanyl isothiocynate (FIT, 10 μg/kg), or the GSK inhibitor SB-216763 (SB21, 600 μg/kg) 10 min before ischemia. Five minutes before opioid or SB21 treatment, some rats received the putative JAK2 inhibitor AG-490 (3 mg/kg) or the putative JAK3 inhibitor ZM-449829 (3 mg/kg). H9C2 cardiomyoblast cells were also used to investigate FIT-induced signaling (1 μM) in vitro via molecular analysis. Morphine induced the phosphorylation of JAK2, yet not JAK1, in the area at risk. Morphine, FIT, and SB21 also reduced infarct size compared with vehicle (water) when administered before ischemia [43.0 ± 2.8, 39.1 ± 3.1, and 42.1 ± 2.5 (* P < 0.001, respectively) vs. 58.1 ± 1.3%, respectively]. AG-490 abrogated OIC, whereas ZM-449829 had no effect on OIC. Cardioprotection was afforded by SB21 even in the presence of AG-490. Morphine phosphorylated STAT3, Akt, and GSK-3β, and phosphorylation was abrogated by AG-490. FIT stimulation of H9C2 cells also caused a time-dependent phosphorylation of STAT3, Akt, and GSK-3β, and this effect was abrogated by AG-490. STAT3 phosphorylation was also dependent on phosphatidylinositol 3-kinase (PI3K) activation in both tissue and H9C2 cells. These data suggest that OIC occurs via the JAK2 regulation of PI3K pathway-dependent STAT3, Akt, and GSK-3β, with GSK-3β contributing a central role in acute OIC.

Reduction of experimental colitis in the rat by inhibitors of glycogen synthase kinase-3beta

The effects of the inhibitors of glycogen synthase kinase-3beta (GSK-3beta), TDZD-8 and SB 415286, which can substantially reduce the systemic inflammation associated with endotoxic shock in vivo, have now been investigated on the acute colitis provoked by trinitrobenzene sulphonic acid (TNBS) in the rat. Administration of the GSK-3beta inhibitor TDZD-8 (0.1, 0.33 or 1.0 mg kg-1, s.c., b.i.d., for 3 days) caused a dose-dependent reduction in the colonic inflammation induced by intracolonic TNBS assessed after 3 days, both as the area of macroscopic involvement and as a score using 0-10 scale. Likewise, following administration of the GSK-3beta inhibitor SB 415286 (0.1, 0.33 or 1.0 mg kg-1, s.c., b.i.d., for 3 days), the extent and degree of the TNBS-provoked colonic inflammation was reduced. Administration of either TDZD-8 or SB 415286 reduced the fall in body weight following challenge with TNBS at each dose level studied. The increase in myeloperoxidase activity, an index of neutrophil infiltration into the TNBS-induced inflamed colon, was significantly inhibited by both TDZD-8 and SB 415286 at each dose level. The increase in the levels of the proinflammatory cytokine, TNF-alpha, in the inflamed colon was also significantly inhibited by either compound at the highest doses evaluated. The elevated levels of the transcription factor NF-kappaB subunit p65, as determined by Western blot in the nuclear extracts from the TNBS-provoked inflamed colonic tissue, were dose-dependently reduced by TDZD-8 or SB 415286 treatment. These findings demonstrate that two chemically distinct selective inhibitors of the activity of GSK-3beta reduce the inflammation and tissue injury in a rat model of acute colitis. The mechanisms underlying this anti-inflammatory action may be related to downregulation of NF-kappaB activity, involved in the generation of proinflammatory mediators.