Cardioprotective Effect Of Ischemic Preconditioning Research Articles

Ovariectomy Reinstates the Infarct Size-Limiting Effect of Postconditioning in Female Rabbits

Gender seems to interfere with the cardioprotective effect of ischemic preconditioning (PreC) and postconditioning (PostC); PreC-conferred protection is weaker or lost in female animals after ovariectomy (Ov), while the role of PostC is still in dispute. We sought to investigate the effect of PostC in female rabbits, its interaction with Ov, and the potential implicated intracellular pathways. Intact or Ov adult female rabbits (n = 46) were subjected to 30 min ischemia and reperfusion with PostC (PostC or OvPostC), which consisted of six cycles of 30-s ischemia/30-s reperfusion at the end of ischemia, or without PostC (Fem or OvFem). Infarct size (I) and area at risk (R) were determined by TTC staining and fluorescent particles, respectively, after 3-h reperfusion in 30 out of 46 animals. Plasma levels of estradiol and nitrite/nitrate (NO x ) were evaluated. ERKs, p38-MAPK, and Akt assessment was performed in excised hearts 1-min after starting the final reperfusion period in the remaining 16 animals. Infarct size was significantly reduced only in OvPostC group (I/R ratio, 25.3 ± 2.7, vs 48.1 ± 2.0, 43.6 ± 4.2 and 55.1 ± 5.6 % in Fem, OvFem, and PostC groups, p < 0.05). In ovariectomized rabbits, plasma estradiol and NO x levels were lower than in the normal ones. Akt phosphorylation in ischemic regions was significantly higher in OvPostC group, whereas ERK1/2 and p38-MAPK activation was observed in all ovariectomized animals irrespective of PostC. PostC is not effective in female rabbits, but the protection is reinstated after Ov potentially via the RISK pathway.

Journal-related Activities and Other Special Activities at the 2012 American Society of Anesthesiologists Annual Meeting

Journal-related Activities and Other Special Activities at the 2012 American Society of Anesthesiologists Annual Meeting

Preconditioning protects the heart in a prolonged uremic condition

Metabolic diseases such as hyperlipidemia and diabetes attenuate the cardioprotective effect of ischemic preconditioning. In the present study, we examined whether another metabolic disease, prolonged uremia, affects ischemia/reperfusion injury and cardioprotection by ischemic preconditioning. Uremia was induced by partial nephrectomy in male Wistar rats. The development of uremia was verified 29 wk after surgery. Transthoracic echocardiography was performed to monitor cardiac function. At week 30, hearts of nephrectomized and sham-operated rats were isolated and subjected to a 30-min coronary occlusion followed by 120 min reperfusion with or without preceding preconditioning induced by three intermittent cycles of brief ischemia and reperfusion. In nephrectomized rats, plasma uric acid, carbamide, and creatinine as well as urine protein levels were increased as compared with sham-operated controls. Systolic anterior and septal wall thicknesses were increased in nephrectomized rats, suggesting the development of a minimal cardiac hypertrophy. Ejection fraction was decreased and isovolumic relaxation time was shortened in nephrectomized rats demonstrating a mild systolic and diastolic dysfunction. Infarct size was not affected significantly by nephrectomy itself. Ischemic preconditioning significantly decreased infarct size from 24.8 ± 5.2% to 6.6 ± 1.3% in the sham-operated group and also in the uremic group from 35.4 ± 9.5% to 11.9 ± 3.1% of the area at risk. Plasma ANG II and nitrotyrosine were significantly increased in the uremic rats. We conclude that although prolonged experimental uremia leads to severe metabolic changes and the development of a mild myocardial dysfunction, the cardioprotective effect of ischemic preconditioning is still preserved.

Role of δ2 Opioid Receptor in Cardioprotection Against Hypoxia–Reoxygenation Injury

Several lines of in vivo evidence demonstrated that activation of δ-opioid receptors (ORs) with agonists mimics the cardioprotective effect of ischemic preconditioning. However, the subtypes of ORs involved and the molecular and cellular mechanisms are not entirely clear. To investigate the significance of the contribution by δ ORs to cardiomyocyte survival, we used an in vitro model of hypoxia/reoxygenation (H/R) in primary cultures of neonatal rat cardiomyocytes to study the role of different δ ORs in cardiomyocyte apoptosis and the relevant downstream signaling pathway. The results showed that apoptosis in neonatal cardiomyocytes induced by H/R was reversed by δ2 OR agonist, deltorphin E but not by δ1 OR agonist DPDPE; the deltorphin E-induced cytoprotection was totally abrogated by the MEK inhibitor PD98059 and overexpression of dominant interfering form of MEK1; in contrast, overexpression of constitutive active form of MEK1 exerted a similar protective effect as deltorphin E. These results suggest that δ2 OR, but not δ1 OR, plays a key role in preventing cardiomyocytes from apoptosis during H/R injury, which is mainly mediated by the MEK/ERK1/2 pathway.

Застосування геніпіну інгібітора роз’єднувальних білків пригнічує захисний ефект ішемічного прекондиціювання

The functional significance of uncoupling proteins UCP2 and UCP3 in the cell and the organism remains unknown. There have been reports about their involvement in cellular protection mechanisms underlying the phenomenon of ischemic preconditioning. The purpose of this study was to elucidate the role of uncoupling proteins UCP2 and UCP3 in the formation of cardioprotective effect of ischemic preconditioning. In experiments on isolated rat hearts we show here an increase in the level of UCP2 and UCP3 gene expression in the heart tissue under the influence of ischemic preconditioning with three episodes of 5 min stopping the flow perfusion. Similar effects were induced by a prolonged ischemia-reperfusion of myocardium. The blockade of the UCP2 activity by genipin (Wako Inc., USA, 10(-5) mol/L, isolated heart perfusion for 15 minutes) abolished the protective effect of adaptation to ischemia. It was concluded that uncoupling proteins take part in the cardioprotective effect ofischemic preconditioning.

Involvement of adenosine and standardization of aqueous extract of garlic (Allium sativum Linn.) on cardioprotective and cardiodepressant properties in ischemic preconditioning and myocardial ischemia-reperfusion induced cardiac injury

The present study investigated the effect of garlic (Allium sativum Linn.) aqueous extracts on ischemic pre-conditioning and ischemiareperfusion induced cardiac injury, as well as adenosine involvement in ischemic pre-conditioning and garlic extract induced cardioprotection. A model of ischemiareperfusion injury was established using Langendorff apparatus. Aqueous extract of garlic dose was standardized (0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.07%, 0.05%, 0.03%, 0.01%), and the 0.05% dose was found to be the most effective. Higher doses (more than 0.05%) were highly toxic, causing arrhythmia and cardiodepression, whereas the lower doses were ineffective. Garlic exaggerated the cardioprotective effect of ischemic preconditioning. The cardioprotective effect of ischemic preconditioning and garlic cardioprotection was significantly attenuated by theophylline (1,000 μmol/L) and 8SPT (10 mg/kg, i.p.) and expressed by increased myocardial infarct size, increased LDH level, and reduced nitrite and adenosine levels. These findings suggest that adenosine is involved in the pharmacological and molecular mechanism of garlic induced cardioprotection and mediated by the modulation of nitric oxide

Abstract P270: Resin-Assisted Capture Reveals Unique Targets of Oxidation in Ischemic Preconditioning

Proper maintenance of cellular thiol redox status is critical in the regulation of many processes that dictate normal myocardial function. Cell death signaling, in particular, is especially susceptible to alterations in thiol redox state. Myocardial ischemic preconditioning (IPC) is a redox sensitive process that is thought to provide protection from ischemia-reperfusion (IR) injury, in part, via reversible oxidative signaling. Protein S -nitrosylation (SNO) is a reversible, thiol-based modification that we and others have shown to provide cardioprotection by modulating the activity of target proteins and by shielding cysteine residues from irreversible oxidation. Additional thiol-based modifications are also thought to play an important role in cardioprotection, and these include disulfide bridges and glutathiolation. Therefore, it is of interest to identify these redox sensitive targets that are unique to IPC. Langendorff perfused mouse hearts were subjected to various perfusion protocols (control, IPC, IR, IPC-IR) and homogenized. Specific sites of oxidation were identified using oxidation-resin assisted capture (Ox-RAC) with mass spectrometry. Consistent with a role for oxidative signaling in cardioprotection, Ox-RAC analysis identified 56 proteins that were oxidized with IPC, but not IR or IPC-IR. These proteins are likely to be reversibly oxidized, as evidenced by the fact that they are oxidized with IPC, but are no longer oxidized following reperfusion (IPC-IR). These proteins may represent important targets in cardioprotective signaling and include F-actin-capping protein β, Egl nine homolog 1, and numerous members of the heat shock family (HSP60, HSP70, HSP90β). Heat shock proteins are important in the cellular stress response and have been shown to play an important role in cardioprotection. Pathway analysis also revealed that more than 30% (19 of 56) of the proteins uniquely oxidized following IPC were involved with cell death pathways. These proteins include Aminoacyl tRNA synthase complex-interacting multifunctional protein 1, Charged multivesicular body protein 5, and Lamin-A/C. These results indicate that the cardioprotective effects of IPC may occur, in part, through the reversible oxidation of key protein targets.

Abstract P283: Parkin Mediates Mitophagy in Cardioprotection

Autophagy-dependent mitochondrial turnover in response to cellular stress is necessary for maintaining cellular homeostasis. However, the mechanisms that govern the selective targeting of damaged mitochondria are poorly understood. Parkin, an E3 ubiquitin ligase, has been shown to be essential for the selective clearance of damaged mitochondria. Parkin is expressed in the heart, yet its function has not been investigated in the context of cardioprotection. We previously reported that autophagy is required for cardioprotection by ischemic preconditioning (IPC). In the present study, we used simulated ischemia in vitro and IPC in hearts (in vivo and ex vivo) to investigate the role of Parkin in mediating cardioprotection. In HL-1 cells, simulated ischemia induced Parkin translocation to mitochondria and mitochondrial elimination. Mitochondrial loss was blunted in Atg5-deficient cells, revealing the requirement for autophagy in mitochondrial elimination. Consistent with previous reports implicating p62/SQSTM1 in mitophagy, we found that downregulation of p62 attenuated mitophagy and exacerbated cell death in HL-1 cardiomyocytes subjected to simulated ischemia. While wild type mice showed p62 translocation to mitochondria after IPC, Parkin knockout mice exhibited attenuated translocation of p62 to mitochondria. Importantly, ablation of Parkin in mice abolished the cardioprotective effects of IPC. These results reveal for the first time the crucial role of Parkin and mitophagy in cardioprotection.

Possible involvement of caveolin in attenuation of cardioprotective effect of ischemic preconditioning in diabetic rat heart

BackgroundNitric oxide (NO) has been noted to produce ischemic preconditioning (IPC)-mediated cardioprotection. Caveolin is a negative regulator of NO, which inhibits endothelial nitric oxide synthase (eNOS) by making caveolin-eNOS complex. The expression of caveolin is increased during diabetes mellitus (DM). The present study was designed to investigate the involvement of caveolin in attenuation of the cardioprotective effect of IPC during DM in rat.MethodsExperimental DM was induced by single dose of streptozotocin (50 mg/Kg, i.p,) and animals were used for experiments four weeks later. Isolated heart was mounted on Langendorff's apparatus, and was subjected to 30 min of global ischemia and 120 min of reperfusion. IPC was given by four cycles of 5 min of ischemia and 5 min of reperfusion with Kreb's-Henseleit solution (K-H). Extent of injury was measured in terms of infarct size by triphenyltetrazolium chloride (TTC) staining, and release of lactate dehydrogenase (LDH) and creatin kinase-MB (CK-MB) in coronary effluent. The cardiac release of NO was noted by measuring the level of nitrite in coronary effluent.ResultsIPC- induced cardioprotection and release of NO was significantly decreased in diabetic rat heart. Pre-treatment of diabetic rat with daidzein (DDZ) a caveolin inhibitor (0.2 mg/Kg/s.c), for one week, significantly increased the release of NO and restored the attenuated cardioprotective effect of IPC. Also perfusion of sodium nitrite (10 μM/L), a precursor of NO, significantly restored the lost effect of IPC, similar to daidzein in diabetic rat. Administration of 5-hydroxy deaconate (5-HD), a mito KATP channel blocker, significantly abolished the observed IPC-induced cardioprotection in normal rat or daidzein and sodium nitrite perfused diabetic rat heart alone or in combination.ConclusionsThus, it is suggested that attenuation of the cardioprotection in diabetic heart may be due to decrease the IPC mediated release of NO in the diabetic myocardium, which may be due to up -regulation of caveolin and subsequently decreased activity of eNOS.

Propofol post-conditioning protects against cardiomyocyte apoptosis in hypoxia/reoxygenation injury by suppressing nuclear factor-kappa B translocation via extracellular signal-regulated kinase mitogen-activated protein kinase pathway

Perioperative myocardial ischaemia leads to an exceedingly high mortality. Previous studies have indicated that propofol pre-conditioning could mimic the cardioprotective effects of ischaemic pre-conditioning. The purpose of this study was to determine whether propofol post-conditioning is cardioprotective and to explore the possible molecular mechanism of propofol post-conditioning. Primary cultured neonatal rat cardiomyocytes were exposed to 12 h of hypoxia followed by 4 h of reoxygenation (H/R) and post-conditioned by different concentrations of propofol at the onset of reperfusion with and without a specific inhibitor of extracellular signal-regulated kinases (ERKs). Cell apoptosis and the generation of intracellular reactive oxygen species were measured using FACScalibur flow cytometric analysis. ERK1/2 phosphorylation and nuclear factor-kappa B (NF-κB) translocation were determined by western blot and immunofluorescence, respectively. Propofol post-conditioning enhanced cell viability (86.6 ± 6.5 versus 64.1 ± 3.4%) and reduced apoptosis (3.6 ± 0.4 versus 12.5 ± 2.1%) to protect cardiomyocytes against H/R injury. Meanwhile, propofol post-conditioning stimulated expression of phosphor-ERKs. H/R markedly induced p65 NF-κB nuclear translocation in cardiomyocytes, whereas propofol post-conditioning significantly suppressed H/R-primed NF-κB translocation. Moreover, addition of the mitogen-activated protein kinase kinase 1 inhibitor U0126 into cardiomyocytes 30 min before H/R eliminated the cardioprotection of propofol post-conditioning. Propofol exerts cardioprotection when administered at the early phase of reperfusion. The effect is mediated through decrease in cardiomyocyte apoptosis and NF-κB nucleus translocation potentially via ERK signalling pathways.

Gα(i2)-mediated protection from ischaemic injury is modulated by endogenous RGS proteins in the mouse heart.

Regulator of G protein signalling (RGS) proteins act as molecular 'off switches' that terminate G protein signalling by catalyzing the hydrolysis of Gα-bound GTP to GDP. Many different Gα(i)-coupled receptors have been implicated in the cardioprotective effects of ischaemic preconditioning. However, the role of RGS proteins in modulating cardioprotection has not been previously investigated. We used mice that were homozygous (GS/GS) or heterozygous (GS/+) for a mutation in Gα(i2) rendering it RGS-insensitive (G184S) to determine whether interactions between endogenous RGS proteins and Gα(i2) modulate Gα(i)-mediated protection from ischaemic injury. Langendorff-perfused mouse hearts were subjected to 30 min global ischaemia and 2 h reperfusion. Infarcts in GS/GS (14.5% of area at risk) and GS/+ (22.6% of AAR) hearts were significantly smaller than those of +/+ hearts (37.2% of AAR) and recovery of contractile function was significantly enhanced in GS/GS and GS/+ hearts compared with +/+ hearts. The cardioprotective phenotype was not reversed by wortmannin or U0126 but was reversed by 5-hydroxydecanoic acid and HMR 1098, indicating that RGS-insensitive Gα(i2) protects the heart through a mechanism that requires functional ATP-dependent potassium channels but does not require acute activation of extracellular-regulated kinase or Akt signalling pathways. This is the first study to demonstrate that Gα(i2)-mediated cardioprotection is suppressed by RGS proteins. These data suggest that RGS proteins may provide novel therapeutic targets to protect the heart from ischaemic injury.

Ischemic Preconditioning Effect of Prodromal Angina Is Attenuated in Acute Myocardial Infarction Patients With Hypertensive Left Ventricular Hypertrophy

Several animal experiments on acute myocardial infarction (AMI) have shown that the cardioprotective effects of ischemic preconditioning are more significant in hypertensive subjects. However, because there are no clinical data on the impact of hypertension on ischemic preconditioning in patients with AMI, whether clinical ischemic preconditioning of prodromal angina was beneficial in AMI patients with hypertension was investigated in the present study. 125 patients with a first anterior AMI who had undergone successful reperfusion therapy were divided into 2 groups, with or without hypertension, and into 2 further subgroups based on the presence or absence of prodromal angina. Dual-isotope (thallium-201(TL)/Tc-99m pyrophosphate) single-photon emission computed tomography (SPECT) was performed within 1 week of reperfusion therapy. Left ventricular (LV) function and LV mass index (LVMI) were measured by left ventriculography and echocardiography, respectively. In patients without hypertension, prodromal angina resulted in significantly less myocardial damage on TL-SPECT, better LV ejection fraction and a greater myocardial blush grade compared to patients without prodromal angina. However, these cardioprotective effects of prodromal angina were significantly diminished in hypertensive patients. Importantly, the myocardial salvage effects of prodromal angina showed a significant negative correlation with LVMI, which was significantly greater in hypertensive patients. The cardioprotective effects of prodromal angina were attenuated in patients with hypertension. Hypertensive LV hypertrophy may crucially limit the effects of ischemic preconditioning in AMI.

Cytochrome P450 2J3/epoxyeicosatrienoic acids mediate the cardioprotection induced by ischaemic post‐conditioning, but not preconditioning, in the rat

1. Cytochrome P450 (CYP) epoxygenases and their arachidonic acid metabolites play a protective role against ischaemia-reperfusion injury. In the present study, we investigated whether endogenous CYP2J3/epoxyeicosatrienoic acid (EET) mediates the cardioprotective effects of ischaemic preconditioning (IPC) and ischaemic post-conditioning (IPost). 2. Male Wistar rats were subjected to two cycles of IPC, consisting of 5 min ischaemia and 5 min reperfusion, followed by 45 min occlusion and 2 h reperfusion; IPost consisted of three cycles of 30 s reperfusion and 30 s re-occlusion at the onset of reperfusion. The selective CYP epoxygenase inhibitor N-methylsulphonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH; 3 mg/kg) was administered 10 min before ischaemia or during ischaemia 10 min before reperfusion started. Cardiac function was measured continuously with a angiocatheter connected to a fluid-filled pressure transducer and myocardial infarct size was assessed by triphenyl tetrazolium chloride staining at the end of the experiment. 3. Subjecting rats to IPC and IPost similarly improved cardiac function and reduced myocardial infarct size. Interestingly, IPost, but not IPC, significantly increased CYP2J3 mRNA (1.75 ± 0.22 vs 1.0; P < 0.05) and protein (1.62 ± 0.22 vs 1.0; P < 0.05), as well as 11,12-EET synthesis compared to I/R (6.2 ± 0.2 vs 2.9 ± 0.2 ng/mg wet weight, respectively; P < 0.01). Administration of MS-PPOH before ischaemia significantly decreased 11,12-EET synthesis in both IPC and IPost compared with I/R rats (2.1 ± 0.2, 3.2 ± 0.3 and 2.9 ± 0.2 ng/mg wet weight, respectively; P < 0.01), but decreased the cardioprotective effects, as evidenced by cardiac function and myocardial infarct size, of IPost only. 4. These data indicate that endogenous activation of CYP2J3/EET may be an essential trigger leading to the protective effects of IPost, but not IPC, in the rat heart.

Role of endogenous oxytocin in cardiac ischemic preconditioning

BackgroundThe aim of the present study is to assess the role of endogenous oxytocin (OT) in cardioprotective effects of ischemic preconditioning (IPC) in anesthetized rat. Materials and methodsAnimals were divided into five groups: 1) ischemia–reperfusion (IR); (n=6), hearts were subjected to 25min regional ischemia and 60min reperfusion, 2) OT; (n=6), oxytocin was administered (0.03μg/kg i.p) 10min prior to ischemia, 3) IPC; (n=7), IPC was induced via a 5min regional ischemia followed by 5min of reperfusion before IR, 4) IPC+ATO (Atosiban); (n=6), atosiban (1.5μg/kg i.p) was used as OT receptor selective antagonist in the beginning of IPC and 5) IR+ATO; (n=6), atosiban was injected 10min prior to ischemia–reperfusion. ResultsIn our experiment, Infarct size was decreased significantly in OT and IPC groups compared to IR (23±1.5% and 19±0.6% vs. 45±2.9% in IR group, P<0.05). Administration of atosiban in IPC+ATO group increased infarct size to 39±0.9% in comparison with OT and IPC groups (P<0.05). The use of OT and IPC prior to ischemia significantly declined ventricular arrhythmias severity in compared to IR group (1.2±0.4 and 1±0.5 respectively, vs. 4±0.4 in IR group, P<0.05). Blockade of OT receptor by atosiban abolished the cardiopreconditioning effects of IPC. ConclusionThis study shows that, in part, the cardioprotective effects of IPC can be induced by endogenous OT.

Editorial [Hot topic: Crucial Role of Redox Signaling in the Regulation of Heart Health (Guest Editor: Dipak K. Das)

Editorial [Hot topic: Crucial Role of Redox Signaling in the Regulation of Heart Health (Guest Editor: Dipak K. Das)

Modulation of the cardioprotective effect of ischemic preconditioning in hyperlipidaemic rat heart

Ischemic preconditioning (IPC) produces cardioprotection by phosphorylation of glycogen synthaes kinase-3β (GSK-3β) that inhibits the opening of mitochondrial permeability transition pore (MPTP), and this cardioprotective action of IPC is attenuated by hyperlipidaemia. The present study investigated the role of GSK-3β in attenuation of cardioprotective effect of IPC, by hyperlipidaemia in the rat heart. Hyperlipidaemia was produced in rat by feeding high fat diet for six weeks. Isolated perfused rat heart was subjected to 30 min of ischemia followed by 120 min of reperfusion. Myocardial infarct size was estimated by triphenyltetrazolium chloride (TTC) staining and l actate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) was analyzed from coronary effluent. IPC significantly decreased the myocardial infarct size and the release of LDH and CK-MB from normal rat heart. IPC induced myocardial protection was attenuated in hyperlipidaemic rat heart. However, cardioprotective effect of pharmacological preconditioning with GSK-3β inhibitors i.e. Lithium Chloride (LiCl) (20 mM), Indirubin – 3 Monooxime (1 μM) and 3-(2, 4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)-1H-pyrrole-2, 5-dione (SB216763) (3 μM), was not attenuated. This differential attenuation by hyperlipidaemia, of IPC and pharmacological preconditioning induced cardioprotection is a new finding in our study. GSK-3β inhibition is reported to increase the threshold of opening for MPTP during reperfusion. Administration of atractyloside (20 μM), an opener of MPTP, significantly attenuated the cardioprotective effect of IPC in normal heart, and pharmacological preconditioning in the hyperlipidaemic rat heart. Thus, the attenuation of cardioprotective effect of IPC in hyperlipidaemic heart may be due to inhibition of protective signaling pathways upstream of GSK-3β and inhibition of opening of MPTP.

Involvement of GSK-3β in attenuation of the cardioprotective effect of ischemic preconditioning in diabetic rat heart

Ischemic preconditioning (IPC) produces cardioprotection by phosphorylation of glycogen synthase kinase-3β (GSK-3β) that inhibits the opening of mitochondrial permeability transition pore (MPTP). The activity of glycogen GSK-3β is elevated during diabetes mellitus (DM). This study investigated the role of GSK-3β in attenuation of cardioprotective effect of IPC in diabetic rat. DM was induced by single administration of streptozotocin (STZ, 50 mg/kg, i.p.). Isolated perfused heart was subjected to 30 min of ischemia followed by 120 min of reperfusion. Myocardial infarct size was estimated by triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) was analyzed in coronary effluent. IPC significantly decreased myocardial infarct size and release of LDH and CK-MB from normal rat heart. The cardioprotective effect of IPC was significantly attenuated in diabetic rat. Four episodes of preconditioning by either of GSK-3β inhibitors, lithium chloride (LiCl, 20 mM), indirubin-3 monooxime (1 μM), and SB216763 (3 μM) significantly reduced the LDH and CK-MB release and decreased infarct size in diabetic rat heart. Perfusion of atractyloside, an opener of MPTP, significantly attenuated, the cardioprotective effect of IPC in normal rat heart, and of GSK-3β inhibitor induced preconditioning in the DM rat heart. Our results suggest that preconditioning with GSK-3β inhibitors in diabetic rat heart may provide a more consistent cardioprotection, as compared to IPC. Also, the mechanism of diabetes mellitus-induced attenuation of cardioprotective effect of IPC involves activation of GSK-3β, due to impaired protective upstream signaling pathways and opening of MPTP during reperfusion.

Landiolol does not enhance the effect of ischemic preconditioning in isolated rat hearts

To determine the effect of landiolol on ischemic preconditioned rat hearts. Isolated perfused rat hearts were divided into 8 groups. In the control group, there was no treatment before the 30-min global ischemia. In the landiolol infused groups, landiolol (100, 300, and 500 microM) was infused without ischemic preconditioning (IPC). In other groups, hearts were pretreated with 2 episodes of 5-min global ischemia and reperfusion before the 30-min ischemia. During the preconditioning, landiolol (0, 100, 300, and 500 microM) was infused. Recoveries of coronary flow (CF) and myocardial oxygen consumption (MVO(2)) at the 120th min after global ischemia to 86 +/- 18 and 112 +/- 19% of the baseline in the IPC group was, respectively, significantly greater than that to 65 +/- 10 and 72 +/- 10% in the control group. Landiolol 300 microM also increased the CF and MVO(2) significantly (97 +/- 19 and 98 +/- 39%) compared to the control. IPC + landiolol 500 microM reduced the increase in LV end-diastolic pressure significantly compared to the control. IPC, landiolol (100, 300, and 500 microM), and IPC + landiolol (100, 300, and 500 microM) all decreased infarct sizes significantly to 23.5 +/- 15.2, 29.8 +/- 12.1, 30.2 +/- 13.3, 22.8 +/- 14.8, 21.6 +/- 7.8, 34.2 +/- 14.7 and 25.5 +/- 11.3% of the total left ventricular mass, respectively, compared to the control (53.3 +/- 12.5%), but there were no significant differences among these groups. IPC and landiolol have cardioprotective effects on ischemia-reperfusion injury in isolated rat hearts, but pretreatment with landiolol does not enhance the cardioprotective effect of IPC.

Innate immunity mediates myocardial preconditioning through Toll-like receptor 2 and TIRAP-dependent signaling pathways

Recent studies have implicated Toll-like receptor 2 (TLR2) and TLR4 signaling in delimiting liver and brain injury following ischemia-reperfusion (I/R). To determine whether TLR2 and TLR4 conferred cytoprotection in the heart, we subjected hearts of wild-type (WT) mice and mice deficient in TLR2 (TLR2D), TLR4 (TLR4D), and TIR domain-containing adapter protein (TIRAP-D) to ischemic preconditioning (IPC). Langendorff-perfused hearts were subjected to 30 min ischemia and 60 min reperfusion with or without IPC. IPC resulted in a significant increase (P < 0.05) in the percent recovery of left ventricular developed pressure (%LVDP) in WT mouse hearts (54.4 +/- 2.7% of baseline), whereas there was no significant increase in %LVDP (P > 0.05) in TIRAP-D mouse hearts (43.8 +/- 1.9%) after I/R injury. IPC also resulted in a significant (P < 0.05) decrease in I/R-induced creatine kinase release and Evans blue dye uptake in WT but not TIRAP-D hearts. Interestingly, IPC resulted in a significant (P < 0.05) increase in %LVDP in TLR4-deficient hearts (52.7 +/- 3%) but not in TLR2D hearts (39.3 +/- 1.5%). Pretreatment with a specific TLR2 ligand (Pam3CSK) protected WT hearts against I/R-induced left ventricular dysfunction. The loss of IPC-induced cardioprotection in TIRAP-D mouse hearts was accompanied by a decreased translocation of protein kinase C-epsilon and decreased phosphorylation of GSK-3beta. Taken together, these data suggest that the cardioprotective effect of IPC is mediated, at least in part, through a TLR2-TIRAP-dependent pathway, suggesting that the modulation of this pathway represents a viable target for reducing I/R injury.

Adenosine-A1 Receptors Activation Restores the Suppressed Cardioprotective Effects of Ischemic Preconditioning in Hyperhomocysteinemic Rat Hearts

We have previously shown that the cardioprotective effect of ischemic preconditioning (IPC) is suppressed in hyperhomocysteinemic rat hearts. The present study investigated the effect of 2-chloro-N-cyclopentyladenosine (CCPA), a selective adenosine-A1 receptor agonist, in hyperhomocysteinemia-induced attenuation of the cardioprotective effect of IPC. Rats were administered L-methionine (1.7 g/kg/day po) for 8 weeks to produce hyperhomocysteinemia. Isolated Langendorff perfused normal and hyperhomocysteinemic rat hearts were subjected to 30-minute global ischemia, followed by a 120-minute reperfusion. Myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride staining. Coronary effluent was analyzed for lactate dehydrogenase and CK-MB release to assess the extent of cardiac injury. The oxidative stress in the heart was assessed by measuring thiobarbituric acid reactive substance and reduced form of glutathione. Ischemia and reperfusion (I/R) produced myocardial injury by increasing myocardial infarct size, elevating lactate dehydrogenase and CK-MB release in coronary effluent, decreasing coronary flow rate, and inducing oxidative stress in normal and hyperhomocysteinemic rat hearts. The hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with high oxidative stress. The IPC afforded cardioprotection against I/R-induced myocardial injury in normal rat hearts. However, IPC-mediated myocardial protection against I/R injury was abolished in hyperhomocysteinemic rat hearts. Administration of CCPA did not alter the cardioprotective effect of IPC in normal rat hearts, but its administration markedly restored the cardioprotective effect of IPC in hyperhomocysteinemic rat hearts. It may be concluded that the activation of adenosine-A1 receptors using CCPA markedly restored the suppressed cardioprotective and infarct size-limiting effects of IPC in hyperhomocysteinemic rat hearts. Thus, the reduced availability of extracellular adenosine and impaired activation of adenosine-A1 receptors may be responsible for abolishing the cardioprotective potential of IPC against I/R-induced myocardial injury in hyperhomocysteinemic rat hearts.