Cardioprotection of Interleukin-2 Is Mediated via κ-Opioid Receptors

Pathophysiological Effects of Various Interleukins on Primary Cell Types in Common Heart Disease

Myocardial infarction (MI), heart failure, cardiomyopathy, myocarditis, and myocardial ischemia-reperfusion injury (I/R) are the most common heart diseases, yet there is currently no effective therapy due to their complex pathogenesis. Cardiomyocytes (CMs), fibroblasts (FBs), endothelial cells (ECs), and immune cells are the primary cell types involved in heart disorders, and, thus, targeting a specific cell type for the treatment of heart disease may be more effective. The same interleukin may have various effects on different kinds of cell types in heart disease, yet the exact role of interleukins and their pathophysiological pathways on primary cell types remain largely unexplored. This review will focus on the pathophysiological effects of various interleukins including the IL-1 family (IL-1, IL-18, IL-33, IL-37), IL-2, IL-4, the IL-6 family (IL-6 and IL-11), IL-8, IL-10, IL-17 on primary cell types in common heart disease, which may contribute to the more precise and effective treatment of heart disease.

The Role of microRNAs in Heart Failure: A Systematic Review

MicroRNAs are highly investigated for their role in the pathogenesis of cardiovascular diseases. Nevertheless, evidence for clinical implementation is still lacking. In our systematic review, we evaluated the potential of microRNAs as pathophysiological and diagnostic biomarkers of heart failure. We identified 72 differentially expressed microRNA molecules among groups of heart failure patients and control groups by searching the PubMed database. We did not identify a substantial overlap of differentially expressed microRNAs among different studies; only five microRNAs (miR-1228, miR-122, miR-423-5p, miR-142-3p, and exosomal miR-92b-5p) were differentially expressed in more than one included study. Gene set enrichment analysis, based on the gene targets of microRNAs presented in the included studies, showed that gene targets of differentially expressed microRNAs were enriched in the MAPK, TGFβ, PI3K-Akt, and IL-2 signaling pathways, as well as apoptosis pathway, p53 activity regulation, and angiogenesis pathway. Results of our systematic review show that there is currently insufficient support for the use of any of the presented microRNAs as pathophysiological or prognostic biomarkers in the clinical setting.

Role of cytokines and inflammation in heart function during health and disease

By virtue of their actions on NF-κB, an inflammatory nuclear transcription factor, various cytokines have been documented to play important regulatory roles in determining cardiac function under both physiological and pathophysiological conditions. Several cytokines including TNF-α, TGF-β, and different interleukins such as IL-1 IL-4, IL-6, IL-8, and IL-18 are involved in the development of various inflammatory cardiac pathologies, namely ischemic heart disease, myocardial infarction, heart failure, and cardiomyopathies. In ischemia-related pathologies, most of the cytokines are released into the circulation and serve as biological markers of inflammation. Furthermore, there is an evidence of their direct role in the pathogenesis of ischemic injury, suggesting cytokines as potential targets for the development of some anti-ischemic therapies. On the other hand, certain cytokines such as IL-2, IL-4, IL-6, IL-8, and IL-10 are involved in the post-ischemic tissue repair and thus are considered to exert beneficial effects on cardiac function. Conflicting reports regarding the role of some cytokines in inducing cardiac dysfunction in heart failure and different types of cardiomyopathies seem to be due to differences in the nature, duration, and degree of heart disease as well as the concentrations of some cytokines in the circulation. In spite of extensive research work in this field of investigation, no satisfactory anti-cytokine therapy for improving cardiac function in any type of heart disease is available in the literature.

The contribution of interleukin-2 to effective wound healing

Ineffective skin wound healing is a significant source of morbidity and mortality. Roughly 6.5 million Americans experience chronically open wounds and the cost of treating these wounds numbers in the billions of dollars annually. In contrast, robust wound healing can lead to the development of either hypertrophic scarring or keloidosis, both of which can cause discomfort and can be cosmetically undesirable. Appropriate wound healing requires the interplay of a variety of factors, including the skin, the local microenvironment, the immune system, and the external environment. When these interactions are perturbed, wounds can be a nidus for infection, which can cause them to remain open an extended period of time, or can scar excessively. Interleukin-2, a cytokine that directs T-cell expansion and phenotypic development, appears to play an important role in wound healing. The best-studied role for Interleukin-2 is in influencing T-cell development. However, other cell types, including fibroblasts, the skin cells responsible for closing wounds, express the Interleukin-2 receptor, and therefore may respond to Interleukin-2. Studies have shown that treatment with Interleukin-2 can improve the strength of healed skin, which implicates Interleukin-2 in the wound healing process. Furthermore, diseases that involve impaired wound healing, such as diabetes and systemic lupus erythematosus, have been linked to deficiencies in Interleukin-2 or defects Interleukin-2-receptor signaling. The focus of this review is to summarize the current understanding of the role of Interleukin-2 in wound healing, to highlight diseases in which Interleukin-2 and its receptor may contribute to impaired wound healing, and to assess Interleukin-2-modulating approaches as potential therapies to improve wound healing.

Upregulation of the kappa opioidergic system in left ventricular rat myocardium in response to volume overload: Adaptive changes of the cardiac kappa opioid system in heart failure

Opioids have long been known for their analgesic effects and are therefore widely used in anesthesia and intensive care medicine. However, in the last decade research has focused on the opioidergic influence on cardiovascular function. This project thus aimed to detect the precise cellular localization of kappa opioid receptors (KOR) in left ventricular cardiomyocytes and to investigate putative changes in KOR and its endogenous ligand precursor peptide prodynorphin (PDYN) in response to heart failure. After IRB approval, heart failure was induced using a modified infrarenal aortocaval fistula (ACF) in male Wistar rats. All rats of the control and ACF group were characterized by their morphometrics and hemodynamics. In addition, the existence and localization as well as adaptive changes of KOR and PDYN were investigated using radioligand binding, double immunofluorescence confocal analysis, RT-PCR and Western blot. Similar to the brain and spinal cord, [(3)H]U-69593 KOR selective binding sites were detected the left ventricle (LV). KOR colocalized with Cav1.2 of the outer plasma membrane and invaginated T-tubules and intracellular with the ryanodine receptor of the sarcoplasmatic reticulum. Interestingly, KOR could also be detected in mitochondria of rat LV cardiomyocytes. As a consequence of heart failure, KOR and PDYN were up-regulated on the mRNA and protein level in the LV. These findings suggest that the cardiac kappa opioidergic system might modulate rat cardiomyocyte function during heart failure.

Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart

Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

Protective effects of the delta opioid peptide [D-Ala2, D-Leu5]enkephalin in an ex vivo model of ischemia/reperfusion in brain slices

INTRODUCTION

The delta opioid peptide [D-Ala2, D-Leu5]enkephalin (DADLE) plays a key role in neuronal protection against both hypoxic and ischemic conditions. However, the cellular mechanisms of action of DADLE under these conditions remain unclear.

METHODS

Ischemia was simulated with perfusing the brain slices with glucose-free artificial cerebrospinal fluid. Apoptosis was examined using an in situ cell death detection kit and expressed as the percentage of positively labeled neurons relative to total number of neurons. PCR was performed by adding cDNA, 5 pm dNTP, 1 μL Taqase, and primers. PCR products were separated with electrophoresis, stained with ethidium bromide, and visualized under ultraviolet light.

AIMS

To investigate the potential effects of DADLE in an ex vivo model of cerebral ischemia/reperfusion.

RESULTS

DADLE attenuated lactic dehydrogenase release and neuronal apoptosis in a concentration-dependent manner. The protective effects of DADLE were attenuated by representative selective delta2, but not delta1 opioid antagonists. Treatment with PD98059, a selective inhibitor of ERK kinase (MEK), also blocked the protective effect of DADLE as well as ERK phosphorylation induced by DADLE.

CONCLUSIONS

Endogenous opioid peptides could promote cell survival via delta2 opioid receptors, possibly through the downstream MEK-ERK pathway.

Morphine postconditioning attenuates ICAM-1 expression on endothelial cells

The purpose of this study is to determine 1) whether morphine post condition (MPostC) can attenuate the intercellular adhesion molecules-1 (ICAM-1) expression after reoxygenation injury and 2) the subtype(s) of the opioid receptors (ORs) that are involved with MPostC. Human umbilical vein endothelial cells (HUVECs) were subjected to 6 hr anoxia followed by 12 hr reoxygenation. Three morphine concentrations (0.3, 3, 30 µM) were used to evaluate the protective effect of MPostC. We also investigated blockading the OR subtypes' effects on MPostC by using three antagonists (a µ-OR antagonist naloxone, a κ-OR antagonist nor-binaltorphimine, and a δ-OR antagonist naltrindole) and the inhibitor of protein kinase C (PKC) chelerythrine. As results, the ICAM-1 expression was significantly reduced in the MPostC (3, 30 µM) groups compared to the control group at 1, 6, 9, and 12 hours reoxygenation time. As a consequence, neutrophil adhesion was also decreased after MPostC. These effects were abolished by co administering chelerythrine, nor-binaltorphimine or naltrindole, but not with naloxone. In conclusion, it is assumed that MPostC could attenuate the expression of ICAM-1 on endothelial cells during reoxygenation via the κ and δ-OR (opioid receptor)-specific pathway, and this also involves a PKC-dependent pathway.

Sevoflurane postconditioning reduces myocardial reperfusion injury in rat isolated hearts via activation of PI3K/Akt signaling and modulation of Bcl-2 family proteins

Sevoflurane postconditioning reduces myocardial infarct size. The objective of this study was to examine the role of the phosphatidylinositol-3-kinase (PI3K)/Akt pathway in anesthetic postconditioning and to determine whether PI3K/Akt signaling modulates the expression of pro- and antiapoptotic proteins in sevoflurane postconditioning. Isolated and perfused rat hearts were prepared first, and then randomly assigned to the following groups: Sham-operation (Sham), ischemia/reperfusion (Con), sevoflurane postconditioning (SPC), Sham plus 100 nmol/L wortmannin (Sham+Wort), Con+Wort, SPC+Wort, and Con+dimethylsulphoxide (DMSO). Sevoflurane postconditioning was induced by administration of sevoflurane (2.5%, v/v) for 10 min from the onset of reperfusion. Left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), maximum increase in rate of LVDP (+dP/dt), maximum decrease in rate of LVDP (-dP/dt), heart rate (HR), and coronary flow (CF) were measured at baseline, R30 min (30 min of reperfusion), R60 min, R90 min, and R120 min. Creatine kinase (CK) and lactate dehydrogenase (LDH) were measured after 5 min and 10 min reperfusion. Infarct size was determined by triphenyltetrazolium chloride staining at the end of reperfusion. Total Akt and phosphorylated Akt (phospho-Akt), Bax, Bcl-2, Bad, and phospho-Bad were determined by Western blot analysis. Analysis of variance (ANOVA) and Student-Newman-Keuls' test were used to investigate the significance of differences between groups. The LVDP, + or - dP/dt, and CF were higher and LVEDP was lower in the SPC group than in the Con group at all points of reperfusion (P<0.05). The SPC group had significantly reduced CK and LDH release and decreased infarct size compared with the Con group [(22.9 + or - 8)% vs. (42.4 + or - 9.4)%, respectively; P<0.05]. The SPC group also had increased the expression of phospho-Akt, Bcl-2, and phospho-Bad, and decreased the expression of Bax. Wortmannin abolished the cardioprotection of sevoflurane postconditioning. Sevoflurane postconditioning may protect the isolated rat heart. Activation of PI3K and modulation of the expression of pro- and antiapoptotic proteins may play an important role in sevoflurane-induced myocardial protection.

Delayed uncoupling is related to cardioprotection induced by κ-agonist U-50,488H in rat heart

OBJECTIVES

To determine whether the kappa-opioid receptor agonist U50,488H affects electrical uncoupling during prolonged ischemia and, if so, whether the changes are associated with its cardioprotective action.

DESIGN

The isolated rat heart was perfused in a Langendorff apparatus. Formazan content, lactate dehydrogenase (LDH) and hemodynamic parameters were measured to confirm the cardioprotective effect of U50,488H. The effects of U50,488H on electrical coupling during prolonged ischemia were also measured.

RESULTS

U50,488H concentration-dependently increased formazan content and reduced LDH release, and the ameliorating effect of 10(-5) mol/L U50,488H was abolished by 5 x 10(-6) mol/L nor-binaltorphimine (nor-BNI), a selective kappa-opioid receptor antagonist, or 10(-4) mol/L 5-hydroxydecanoate (5-HD), a selective mitochondrial ATP-sensitive K(+) (K(ATP)) channel blocker. The onset of electrical uncoupling during prolonged ischemia was delayed by U50,488H, and the delay was not only abolished, but also advanced by nor-BNI or 5-HD relative to the control group.

CONCLUSIONS

These results demonstrate that delayed uncoupling during prolonged ischemia is associated with the cardioprotection of U50,488H, and these effects of U50,488H are mediated by mitochondrial K(ATP) channels.

Postconditioning of sevoflurane and propofol is associated with mitochondrial permeability transition pore

BACKGROUND

Sevoflurane and propofol are effective cardioprotective anaesthetic agents, though the cardioprotection of propofol has not been shown in humans. Their roles and underlying mechanisms in anesthetic postconditioning are unclear. Mitochondrial permeability transition pore (MPTP) opening is a major cause of ischemia-reperfusion injury. Here we investigated sevoflurane- and propofol-induced postconditioning and their relationship with MPTP.

METHODS

Isolated perfused rat hearts were exposed to 40 min of ischemia followed by 1 h of reperfusion. During the first 15 min of reperfusion, hearts were treated with either control buffer (CTRL group) or buffer containing 20 micromol/L atractyloside (ATR group), 3% (v/v) sevoflurane (SPC group), 50 micromol/L propofol (PPC group), or the combination of atractyloside with respective anesthetics (SPC+ATR and PPC+ATR groups). Infarct size was determined by dividing the total necrotic area of the left ventricle by the total left ventricular slice area (percent necrotic area).

RESULTS

Hearts treated with sevoflurane or propofol showed significantly better recovery of coronary flow, end-diastolic pressures, left ventricular developed pressure and derivatives compared with controls. Sevoflurane resulted in more protective alteration of hemodynamics at most time point of reperfusion than propofol. These improvements were paralleled with the reduction of lactate dehydrogenase release and the decrease of infarct size (SPC vs CTRL: (17.48+/-2.70)% vs (48.47+/-6.03)%, P<0.05; PPC vs CTRL: (35.60+/-2.10)% vs (48.47+/-6.03)%, P<0.05). SPC group had less infarct size than PPC group (SPC vs PPC: (17.48+/-2.70)% vs (35.60+/-2.10)%, P<0.05). Atractyloside coadministration attenuated or completely blocked the cardioprotective effect of postconditioning of sevoflurane and propofol.

CONCLUSION

Postconditioning of sevoflurane and propofol has cardioprotective effect against ischemia-reperfusion injury of heart, which is associated with inhibition of MPTP opening. Compared to propofol, sevoflurane provides superior protection of functional recovery and infarct size.

Lidocaine abolishes the myocardial protective effect of sevoflurane post-conditioning

BACKGROUND

Post-ischemic administration of volatile anesthetics activates ischemia-reperfusion injury salvage process and decreases myocardial damage. However, the mechanisms underlying anesthetic post-conditioning and effects of lidocaine on it remain unclear. Here we report the cardioprotection of sevoflurane-induced post-conditioning and the effects of lidocaine on it.

METHODS

Isolated perfused rat hearts were exposed to 40 min of ischemia followed by 1 h of reperfusion. Volatile anesthetic post-conditioning was induced by 15 min of 3 vol% sevourane (1.5 minimum alveolar concentration) administered at the onset of reperfusion. In some experiments, lidocaine was coadministered with sevoflurane in different concentrations (2, 10 and 20 microg/ml). Infarct size was determined by dividing the total necrotic area of the left ventricle by the total left ventricular slice area (percent necrotic area).

RESULTS

Sevoflurane-induced post-conditioning signicantly improved post-ischemia functional recovery and decreased infarct size (47.3+/-5.6% in unprotected hearts vs. 18.6+/-3.1% in anesthetic post-conditioning, P<0.05). Sevourane-mediated cardioprotection was abolished by 20 microg/ml lidocaine.

CONCLUSIONS

Sevourane-induced post-conditioning effectively protected myocardium against reperfusion damage and its cytoprotection was reversed by 20 microg/ml lidocaine.

Interleukin-2 confers cardioprotection by inhibiting mitochondrial permeability transition pore

In the present study, we determined whether interleukin-2 (IL-2) confers cardioprotection by inhibiting mitochondria permeability transition pore (MPTP) opening. In isolated rat hearts subject to 30 min ischemia and 120 min reperfusion (IR), IL-2 (50 U/ml) decreased the infarct size and LDH release, effects blocked by a selective kappa-opioid receptor antagonist, Nor-BNI (5 microM) or an opener of MPTP, atractyloside (Atr, 20 microM). In isolated ventricular myocytes subjected to anoxia and reoxygenation (AR), which reduced both the amplitude of the electrically induced [Ca2+]i transient and diastolic [Ca2+]i, IL-2 attenuated the AR-induced alterations and their effects were abolished by Atr. In addition, IL-2 attenuated the reduction in calcein fluorescence in myocytes subject to AR and reduced calcium-induced swelling in mitochondria of rat hearts subjected to IR, which were similar to effect of inhibitor of MPTP. The observations indicated that IL-2 confers cardioprotection by inhibiting the MPTP opening.

The K(Ca) channel as a trigger for the cardioprotection induced by kappa-opioid receptor stimulation -- its relationship with protein kinase C

We first determined whether the cardioprotection resulting from kappa opioid receptor (kappa-OR) stimulation was blocked by the K(Ca) channel inhibitor, paxilline (Pax), administered before or during ischaemic insults in vitro. In isolated rat hearts, 30 min of ischaemia and 120 min of reperfusion induced infarction and increased lactate dehydrogenase (LDH) release. In isolated ventricular myocytes subjected to 5 min of metabolic inhibition and anoxia followed by 10 min of reperfusion, the percentage of live cells and the amplitude of the electrically induced intracellular Ca(2+) ([Ca(2+)](i)) transient decreased, while diastolic [Ca(2+)](i) increased. Pretreatment with 10 microM U50,488H, a kappa-OR agonist, attenuated the undesirable effects of ischaemic insults in both preparations. The beneficial effects of kappa-OR stimulation, that were abolished by 5 microM nor-BNI, a kappa-OR antagonist, were also abolished by 1 microM Pax administered before ischaemic insults or 20 microM atractyloside, an opener of the mitochondrial permeability transition pore. Activation of protein kinase C (PKC) with 0.1 microM phorbol 12-myristate 13-acetate decreased the infarct size and LDH release in isolated rat hearts subjected to ischaemia/reperfusion, and these effects were abolished by blockade of PKC with its inhibitors, 10 microM GF109203X or 5 microM chelerythrine, and more importantly by 1 microM Pax. On the other hand, the cardioprotective effects of opening the K(Ca) channel with 10 microM NS1619 were not altered by either PKC inhibitor. In conclusion, the high-conductance K(Ca) channel triggers cardioprotection induced by kappa-OR stimulation that involves inhibition of MPTP opening. The K(Ca) channel is located downstream of PKC.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

DELAYED UNCOUPLING CONTRIBUTES TO THE PROTECTIVE EFFECT OF HEPTANOL AGAINST ISCHAEMIA IN THE RAT ISOLATED HEART

1. It is known that infusion of the gap junction uncoupler heptanol, before ischaemia or during reperfusion, limits myocardial infarct size. However, whether this cardiac effect is linked to the effect of heptanol on communication across gap junctions has not been elucidated. The aims of the present study were to examine the effect of heptanol on infarct size, arrhythmias and myocardial tissue resistance and to assess whether changes in electrical coupling correlate with cardiac protection. 2. Rat isolated, perfused hearts were subjected to a 24 min infusion of heptanol (0.05, 0.1, 0.5 or 1.0 mmol/L) followed by 20 min regional ischaemia and 60 min reperfusion, or by 70 min global no-flow ischaemia. The effective refractory period, action potential and conduction velocity were measured in papillary muscles from the right ventricle. Heptanol markedly decreased arrhythmia scores during ischaemia and reperfusion, as well as reducing infarct size to a degree similar to that induced by ischaemic preconditioning. In the prolonged ischaemia model, heptanol delayed the onset of uncoupling, increased time to plateau and decreased the maximal rate of uncoupling during ischaemia. Ischaemic preconditioning had similar effects on these parameters. In papillary muscle, heptanol reduced the conduction velocity of the action potential in a dose-dependent manner, but had no significant effect on resting potential, action potential amplitude, action potential duration, maximal upstroke of depolarization or effective refractory period. 3. These results demonstrate that treatment with the gap junction uncoupler heptanol confers cardioprotection against ischaemia and this effect is related to delayed electrical uncoupling during prolonged ischaemia.

Remifentanil mimics cardioprotective effect of ischemic preconditioning via protein kinase C activation in open chest of rats

AIM

To examine whether the protective effect of remifentanil preconditioning (RPC) on postischemic hearts is mediated by protein kinase (PKC) activation in comparison with ischemic preconditioning (IPC).

METHODS

Male Sprague-Dawley rats were anesthetized and their chests were opened. The experiment was performed with chelerythrine (CHE, 2 mg/kg), GF109203X (0.05 mg/kg) protein kinase C (PKC) inhibitors administered before RPC (remifentanil 6 microg x kg(-1) x min(-1) x 3 cycle) or IPC, respectively. Infarct size (IS), as a percentage of the area at risk (AAR), was determined by triphenyltetrazolium staining.

RESULTS

In groups subjected to IPC and RPC the IS/AAR were significantly reduced (IS/AAR from 52.7%+/-5.5% to 12.9%+/-3.4%, P<0.01 vs CON and 16.2%+/-6.4%, P<0.01 vs CON), respectively. CHE and GF, both PKC inhibitors, administered 5 min before RPC or IPC completely abolished the cardioprotective effect of RPC (IS/AAR: CHE+RPC 51.2%+/-5.0%, GF+RPC 53.6%+/-6.1%, P>0.05 vs CON) or IPC (CHE+IPC 53.7%+/-4.3%, GF+IPC 54.1%+/-6.2%, P>0.05 vs CON). The difference was not significant in any of the hemodynamic parameters between control and treatment groups during ischemia and reperfusion.

CONCLUSION

Remifentanil confers myocardial protection against ischemic injury through a mechanism that is similar to IPC and involves PKC activation.

Opioid-induced preconditioning: recent advances and future perspectives

Opioids, named by Acheson for compounds with morphine-like actions despite chemically distinct structures, have received much research interest, particularly for their central nervous system (CNS) actions involved in pain management, resulting in thousands of scientific papers focusing on their effects on the CNS and other organ systems. A more recent area which may have great clinical importance concerns the role of opioids, either endogenous or exogenous compounds, in limiting the pathogenesis of ischemia-reperfusion injury in heart and brain. The role of endogenous opioids in hibernation provides tantalizing evidence for the protective potential of opioids against ischemia or hypoxia. Mammalian hibernation, a distinct energy-conserving state, is associated with depletion of energy stores, intracellular acidosis and hypoxia, similar to those which occur during ischemia. However, despite the potentially detrimental cellular state induced with hibernation, the myocardium remains resilient for many months. What accounts for the hypoxia-tolerant state is of great interest. During hibernation, circulating levels of opioid peptides are increased dramatically, and indeed, are considered a "trigger" of hibernation. Furthermore, administration of opioid antagonists can effectively reverse hibernation in mammals. Therefore, it is not surprising that activation of opioid receptors has been demonstrated to preserve cellular status following a hypoxic insult, such as ischemia-reperfusion in many model systems including the intestine [Zhang, Y., Wu, Y.X., Hao, Y.B., Dun, Y. Yang, S.P., 2001. Role of endogenous opioid peptides in protection of ischemic preconditioning in rat small intestine. Life Sci. 68, 1013-1019], skeletal muscle [Addison, P.D., Neligan, P.C., Ashrafpour, H., Khan, A., Zhong, A., Moses, M., Forrest, C.R., Pang, C.Y., 2003. Noninvasive remote ischemic preconditioning for global protection of skeletal muscle against infarction. Am. J. Physiol. Heart Circ. Physiol. 285, H1435-H1443], the CNS [Borlongan, C.V., Wang, Y., Su, T.P., 2005. Delta opioid peptide (d-ala 2, d-leu 5) enkephalin: linking hiberation and neuroprotection. Front Biosci. 9, 3392-3398] and the myocardium [Romano, M.A., Seymour, E.M., Berry, J.A., McNish, R.A., Bolling, S.F., 2004. Relative contribution of endogenous opioids to myocardial ischemic tolerance. J Surg Res. 118, 32-37; Peart, J.N., Gross, G.J., 2004a. Exogenous activation of delta- and kappa-opioid receptors affords cardioprotection in isolated murine heart. Basic Res Cardiol. 99(1), 29-37]. For the purpose of this review, we will focus primarily on the protective effects of opioids against post-reperfusion myocardial stunning and infarction.

Calcium-activated potassium channel triggers cardioprotection of ischemic preconditioning

We tested the hypothesis that the high-conductance calciumactivated potassium (K(Ca)) channel is involved in the cardioprotection of preconditioning with ischemic insults. In the isolated perfused rat heart subjected to ischemia/reperfusion, effects of ischemic preconditioning (IPC) on infarct size and lactate dehydrogenase (LDH) release were abolished by 1 microM paxilline (Pax), an inhibitor of the K(Ca) channel, administered 30 min before, but not during, ischemia. In isolated ventricular myocytes subjected to metabolic inhibition and anoxia (MI/A), preconditioning with MI/A increased their viability, and the effect was abolished by administering Pax before MI/A. Like IPC, 10 microM NS1619 (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-trifluoromethyl-2Hbenzimidazol-2-one; NS), an opener of K(Ca) channels, reduced infarct size and LDH release, effects attenuated by Pax. The harmful and protective effects of blockade and activation of the K(Ca) channel were accompanied by impaired and improved left ventricular contractile functions, respectively. In addition, the effect of NS was not altered by 100 microM 5-hydroxydecanoate, an inhibitor of the K(ATP) channel. Neither was the effect of 100 microM diazoxide, an activator of the K(ATP) channel, altered by Pax. Furthermore, opening of the mitochondrial permeability transition pore (mPTP) with 20 microM atractyloside abolished the beneficial effects of IPC or NS in the isolated rat heart and myocyte. Inhibition of mPTP opening with 0.2 microM cyclosporin A decreased the infarct size and LDH release and improved the contractile function, effects not attenuated by Pax. In conclusion, the study provides evidence that the K(Ca) channel triggers cardioprotection of IPC, which involves mPTP.