Inhibition of myocardial apoptosis by ischaemic and beta-adrenergic preconditioning is dependent on p38 MAPK

Peroxisome Proliferator-Activated Receptor-Gamma (PPAR-ɣ): Molecular Effects and Its Importance as a Novel Therapeutic Target for Cerebral Ischemic Injury

Cerebral ischemic injury is a leading cause of death and long-term disability throughout the world. Peroxisome proliferator-activated receptor gamma (PPAR-ɣ) is a ligand-activated nuclear transcription factor that is a member of the PPAR family. PPAR-ɣ has been shown in several in vitro and in vivo models to prevent post-ischemic inflammation and neuronal damage by negatively controlling the expression of genes modulated by cerebral ischemic injury, indicating a neuroprotective effect during cerebral ischemic injury. A extensive literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was carried out to understand the nature of the extensive work done on the mechanistic role of Peroxisome proliferator activated receptor gamma and its modulation in Cerebral ischemic injury. PPAR-ɣ can interact with specific DNA response elements to control gene transcription and expression when triggered by its ligand. It regulates lipid metabolism, improves insulin sensitivity, modulates antitumor mechanisms, reduces oxidative stress, and inhibits inflammation. This review article provides insights on the current state of research into the neuroprotective effects of PPAR-ɣ in cerebral ischemic injury, as well as the cellular and molecular mechanisms by which these effects are modulated, such as inhibition of inflammation, reduction of oxidative stress, suppression of pro-apoptotic production, modulation of transcription factors, and restoration of injured tissue through neurogenesis and angiogenesis.

Modification of ischemia/reperfusion induced infarct size by ischemic preconditioning in hypertrophied hearts

This study examined the effects of ischemic preconditioning (IP) on the ischemia/reperfusion (I/R) induced injury in normal and hypertrophied hearts. Cardiac hypertrophy in rabbits was induced by L-thyroxine (0.5 mg/kg/day for 16 days). Hearts with or without IP (3 cycles of 5 min ischemia and 10 min reperfusion) were subjected to I/R (60 min ischemia followed by 60 min reperfusion). IP reduced the I/R-induced infarct size from 68% to 24% and 57% to 33% in the normal and hypertrophied hearts, respectively. Leakage of creatine phosphokinase in the perfusate from the hypertrophied hearts due to I/R was markedly less than that form the normal hearts; IP prevented these changes. Although IP augmented the increase in phosphorylated p38-mitogen-activated protein kinase (p38-MAPK) content due to I/R, this effect was less in the hypertrophied than in the normal heart. These results suggest that reduced cardioprotection by IP of the I/R-induced injury in hypertrophied hearts may be due to reduced activation of p38-MAPK in comparison with normal hearts.

Remote ischemic preconditioning attenuates EGR-1 expression following myocardial ischemia reperfusion injury through activation of the JAK-STAT pathway

BACKGROUND/OBJECTIVES

Remote ischemic preconditioning (RIPC) protects the myocardium from ischemia/reperfusion (I/R) injury however the molecular pathways involved in cardioprotection are yet to be fully delineated. Transcription factor Early growth response-1 (Egr-1) is a key upstream activator in a variety of cardiovascular diseases. In this study, we elucidated the role of RIPC in modulating the regulation of Egr-1.

METHODS

This study subjected rats to transient blockade of the left anterior descending (LAD) coronary artery with or without prior RIPC of the hind-limb muscle and thereafter excised the heart 24h following surgical intervention. In vitro, rat cardiac myoblast H9c2 cells were exposed to ischemic preconditioning by subjecting them to 3cycles of alternating nitrogen-flushed hypoxia and normoxia. These preconditioned media were added to recipient H9c2 cells which were then subjected to 30min of hypoxia followed by 30min of normoxia to simulate myocardial I/R injury. Thereafter, the effects of RIPC on cell viability, apoptosis and inflammatory markers were assessed.

RESULTS

We showed reduced infarct size and suppressed Egr-1 in the heart of rats when RIPC was administered to the hind leg. In vitro, we showed that RIPC improved cell viability, reduced apoptosis and attenuated Egr-1 in recipient cells.

CONCLUSIONS

Selective inhibition of intracellular signaling pathways confirmed that RIPC increased production of intracellular nitric oxide (NO) and reactive oxygen species (ROS) via activation of the JAK-STAT pathway which then inactivated I/R-induced ERK 1/2 signaling pathways, ultimately leading to the suppression of Egr-1.

Saffron (Crocus sativus) pretreatment confers cardioprotection against ischemia-reperfusion injuries in isolated rabbit heart

Restoration of blood flow to the ischemic myocardium is imperative to avoid demise of cardiomyocytes, but is paradoxically associated with irreversible damage to cardiac tissues due to the excessive generation of reactive oxygen species (ROS). We have previously reported that saffron, a natural antioxidant, attenuated ischemia-reperfusion (IR) injuries in vitro; however, its role in a meaningful cardiac recovery remains unknown. Here, we show that saffron supplement (oral administration for 6 weeks) reduced myocardial damage and restored cardiac function in an IR model of rabbit hearts. This was evidenced by improved left ventricle pressure, heart rate and coronary flow, and left ventricle end diastolic pressure (LVEDP) in IR hearts (isolated from rabbits pre-exposed to saffron (S/IR)). Electrophysiological recordings revealed a significant decline in both premature ventricle contraction and ventricle tachycardia/fibrillation in S/IR compared to IR hearts. This was paralleled by increased expression of the contractile proteins α-actinin and Troponin C in the myocardium of S/IR hearts. Histological examination combined to biochemical analysis indicated that hearts pre-exposed to saffron exhibited reduced infarct size, lower lipid peroxidation, with increased glutathione peroxidase activity, and oxidation of nitro blue tetrazolium (by reactive oxygen species). Furthermore, in contrast with IR hearts, saffron pretreatment induced restoration of the phosphorylation level of the survival proteins Akt and 4EBP1 and reduced activity of p38. Collectively, our data demonstrate that the natural antioxidant saffron plays a pivotal role in halting IR-associated cardiac injuries and emerges as a novel preventive tool for ischemic heart disease.

Phosphorylation of p38 MAPK mediates hypoxic preconditioning-induced neuroprotection against cerebral ischemic injury via mitochondria translocation of Bcl-xL in mice

Hypoxic preconditioning (HPC) initiates intracellular signaling pathway to provide protection, but the role of p38 mitogen-activated protein kinase (p38 MAPK) in HPC-induced neuroprotection against cerebral ischemic injuries is a matter of debate. In this study, we found that HPC could reduce 6h middle cerebral artery occlusion (MCAO)-induced infarct volume, edema ratio and cell apoptosis, as well as enhancing the up-regulated p38 MAPK phosphorylation (P-p38 MAPK) levels in the peri-infarct region of mice after 6h MCAO. However, intracerebroventricular injection of p38 MAPK inhibitor SB203580 abolished this HPC-induced neuroprotection. HPC significantly increased the translocation of anti-apoptotic Bcl-2-related protein Bcl-xL from the cytosol to the mitochondria in the peri-infarct region of MCAO mice. Interestingly, the results of reciprocal immunoprecipitation showed that Bcl-xL and P-p38 MAPK were coimmunoprecipitated reciprocally only in the peri-infarct region of HPC and MCAO treated mice, while Bcl-xL and total p38 (T-p38 MAPK), not P-p38 MAPK, could be coimmunoprecipited by each other in the brain of normal control mice. In addition, we found SB203580 significantly decreased P-p38 MAPK levels, and inhibited HPC-induced mitochondria translocation of Bcl-xL in the brain of HPC and MCAO treated mice. Taken together, our findings suggested that P-p38 MAPK mediates HPC-induced neuroprotection against cerebral ischemic injury via mitochondria translocation of Bcl-xL, which might be a key anti-cell apoptotic mechanism of HPC.

Regulation of phosphatase and tensin homolog on chromosome 10 in response to hypoxia

Phosphatase and tensin homolog on chromosome 10 (PTEN) is downregulated during hypertrophic and cancerous cell growth, leading to activation of the prosurvival Akt pathway. However, PTEN regulation in cardiac myocytes upon exposure to hypoxia remains unclear. We explored the role of PTEN in response to hypoxia/ischemia in the myocardium. We validated that PTEN is a transcriptional target of activating transcription factor 2 (ATF-2) and is positively regulated via a p38/ATF-2 signaling pathway. Accordingly, hypoxia-induced upregulation of phosphorylation of ATF-2 and PTEN were reversed by a dominant negative mutant p38. Inhibition of PTEN in cardiomyocytes attenuated hypoxia-induced cell death and apoptosis. Cardiac-specific knockout of PTEN resulted in increased phosphorylation of Akt and forkhead box O 1 (forkhead transcription factors), limited infarct size in animals exposed to ischemia-reperfusion injury, and ameliorated deterioration of left ventricular function and remodeling following permanent coronary artery occlusion. In addition, the activation of Bim, FASL, and caspase was coupled with PTEN activation, all of which were attenuated by PTEN inhibition. In conclusion, cardiomyocyte-specific conditional PTEN deletion limited myocardial infarct size in an in vivo model of ischemia-reperfusion injury and attenuated adverse remodeling in a model of chronic permanent coronary artery ligation.

Role of Mitogen-Activated Protein Kinases in Myocardial Ischemia-Reperfusion Injury during Heart Transplantation

In solid organ transplantation, ischemia/reperfusion (IR) injury during organ procurement, storage and reperfusion is an unavoidable detrimental event for the graft, as it amplifies graft inflammation and rejection. Intracellular mitogen-activated protein kinase (MAPK) signaling pathways regulate inflammation and cell survival during IR injury. The four best-characterized MAPK subfamilies are the c-Jun NH2-terminal kinase (JNK), extracellular signal- regulated kinase-1/2 (ERK1/2), p38 MAPK, and big MAPK-1 (BMK1/ERK5). Here, we review the role of MAPK activation during myocardial IR injury as it occurs during heart transplantation. Most of our current knowledge regarding MAPK activation and cardioprotection comes from studies of preconditioning and postconditioning in nontransplanted hearts. JNK and p38 MAPK activation contributes to myocardial IR injury after prolonged hypothermic storage. p38 MAPK inhibition improves cardiac function after cold storage, rewarming and reperfusion. Small-molecule p38 MAPK inhibitors have been tested clinically in patients with chronic inflammatory diseases, but not in transplanted patients, so far. Organ transplantation offers the opportunity of starting a preconditioning treatment before organ procurement or during cold storage, thus modulating early events in IR injury. Future studies will need to evaluate combined strategies including p38 MAPK and/or JNK inhibition, ERK1/2 activation, pre- or postconditioning protocols, new storage solutions, and gentle reperfusion.

Opposing effects of age and calorie restriction on molecular determinants of myocardial ischemic tolerance

We test the hypothesis that moderate calorie restriction (CR) reverses negative influences of age on molecular determinants of myocardial stress resistance. Postischemic contractile dysfunction, cellular damage, and expression of regulators of autophagy/apoptosis and of prosurvival and prodeath kinases were assessed in myocardium from young adult (YA; 2- to 4-month-old) and middle-aged (MA; 12-month-old) mice, and MA mice subjected to 14 weeks of 40% CR (MA-CR). Ventricular dysfunction after 25%±2%), as was cell death indicated by troponin I (TnI) efflux (1,701±214 ng vs. 785±102 ng in YA). MA hearts exhibited 30% and 65% reductions in postischemic Beclin1 and Parkin, respectively, yet 50% lower proapoptotic Bax and 85% higher antiapoptotic Bcl2, increasing the Bcl2/Bax ratio. Age did not influence Akt or p38-mitogen-activated protein kinase (MAPK) expression; reduced expression of increasingly phosphorylated ribosomal protein S6 kinase (p70S6K), increased expression of dephosphorylated glycogen synthase kinase 3β (GSK3β) and enhanced postischemic p38-MAPK phosphorylation. CR countered the age-related decline in ischemic tolerance, improving contractile recovery (60%±4%) and reducing cell death (123±22 ng of TnI). Protection was not associated with changes in Parkin or Bax, whereas CR partially limited the age-related decline in Beclin1 and further increased Bcl2. CR counteracted age-related changes in p70S6K, increased Akt levels, and reduced p38-MAPK (albeit increasing preischemic phosphorylation), and paradoxically reduced postischemic GSK3β phosphorylation. In summary, moderate age worsens cardiac ischemic tolerance; this is associated with reduced expression of autophagy regulators, dysregulation of p70S6K and GSK3β, and postischemic p38-MAPK activation. CR counters age effects on postischemic dysfunction/cell death; this is associated with reversal of age effects on p70S6K, augmentation of Akt and Bcl2 levels, and preischemic p38-MAPK activation. Age and CR thus impact on distinct determinants of ischemic tolerance, although p70S6K signaling presents a point of convergence.

Role of p38 inhibition in cardiac ischemia/reperfusion injury

The p38 mitogen-activated protein kinases (p38s) are Ser/Thr kinases that are activated as a result of cellular stresses and various pathological conditions, including myocardial ischemia/reperfusion. p38 activation has been shown to accentuate myocardial injury and impair cardiac function. Inhibition of p38 activation and its activity has been proposed to be cardioprotective by slowing the rate of myocardial damage and improving cardiac function. The growing body of evidence on the use of p38 inhibitors as therapeutic means for responding to heart problems is controversial, since both beneficial as well as a lack of protective effects on the heart have been reported. In this review, the outcomes from studies investigating the effect of p38 inhibitors on the heart in a wide range of study models, including in vitro, ex vivo, and in vivo models, are discussed. The correlations of experimental models with practical clinical usefulness, as well as the need for future studies regarding the use of p38 inhibitors, are also addressed.

Comparison of 5 different remifentanil strategies against myocardial ischemia-reperfusion injury

OBJECTIVE

The purpose of this study was to investigate the effects of various remifentanil strategies (preconditioning, postconditioning, or continuous infusion) against myocardial ischemia-reperfusion injury.

DESIGN

An in vitro experimental study using the Langendorff system.

SETTING

A university research laboratory.

PARTICIPANTS

Male Sprague-Dawley rats (each n = 9).

INTERVENTIONS

Five different remifentanil strategies were performed in isolated rat hearts as follows: remifentanil preconditioning (R-Pre), remifentanil postconditioning (R-Post), ischemic targeting remifentanil (R1), reperfusion targeting remifentanil (R2), or both ischemic and reperfusion targeting remifentanil (R3). Infarct size and cardiodynamics were compared.

MEASUREMENT AND MAIN RESULTS

The infarct-risk volume ratio in groups R-Pre (13.7% ± 9.9%), R-Post (13.7% ± 12.3%), and R3 (12.6% ± 6.1%) were decreased significantly compared with the untreated control hearts (32.9% ± 11.1%, p &lt 0.01). There was no significant difference in the left ventricular-developed pressure (LVDP) recovery after reperfusion between the control (43.6% ± 14.5%) and R-Pre (34.8% ± 12.9%, p > 0.05) groups after reperfusion. However, the LVDP recovery in R-Post (21.6% ± 7.7%, p < 0.05), R1 (16.7% ± 19.8%, p < 0.01), R2 (22.2% ± 13.9%, p < 0.05), and R3 (16.2% ± 7.8%, p < 0.01) was decreased significantly compared with control hearts. There was no significant difference in the recovery of dP/dt(max) after reperfusion between the R-Pre (42.0% ± 16.9%) and control groups (39.0% ± 15.4%, p > 0.05), whereas the dP/dt(max) in R3 group (16.9% ± 9.0%) was decreased significantly compared with R-Pre (p < 0.05).

CONCLUSIONS

Preconditioning or postconditioning by remifentanil and the continuous infusion of remifentanil effectively reduce myocardial infarction, whereas reperfusion targeting ischemic targeting or reperfusion targeting remifentanil does not. Remifentanil preconditioning better preserves myocardial function, especially LVDP, than other remifentanil strategies.

Resolvin E1 protects the rat heart against reperfusion injury

The purpose of the present study was to assess whether resolvin E1 (RvE1), an anti-inflammatory mediator derived from eicosapentaenoic acid, would limit myocardial infarct size in the rat. The H9c2 cell line was used to assess whether RvE1 has direct protective effects on cardiomyocytes. In in vivo experiments, Male Sprague-Dawley rats underwent 30 min of ischemia/4 h of reperfusion. Before reperfusion, rats received intravenous RvE1 (0, 0.03, 0.1, or 0.3mg/kg). In in vitro experiments, H9c2 cells were incubated with RvE1 (0, 1, 10, 100, or 1000 nM). Cells were subjected to 18 h of incubation under normoxic conditions, 16 h of hypoxia, or 16 h of hypoxia and 2 h of reoxygenation. In vivo, RvE1 dose dependently reduced infarct size (30.7 +/- 1.7% of the area at risk in the control group and 29.1 +/- 1.6%, 14.7 +/- 1.3%, and 9.0 +/- 0.6% in the 0.03, 0.1, and 0.3 mg/kg groups, respectively, P < 0.001). In vitro, RvE1 increased viability and decreased apoptosis in a dose-dependent fashion in cells exposed to hypoxia or hypoxia/reoxygenation. A maximal effect was achieved at a concentration of 100 nM. RvE1 augmented phosphoinositide 3-kinase activity, attenuated caspase-3 activity, and augmented calcium-dependent nitric oxide synthase activity in cells exposed to hypoxia or hypoxia/reoxygenation. RvE1 increased Akt, ERK1/2, and endothelial nitric oxide synthase phosphorylation and attenuated the levels of activated caspase-3 and phosphorylated p38 levels. AG-1478, an EGF receptor tyrosine kinase inhibitor, blocked the protective effect of RvE1 both in vivo and in vitro and attenuated the RvE1-induced increase in Akt and ERK1/2 phosphorylation. In conclusion, RvE1, an anti-inflammatory mediator derived from eicosapentaenoic acid, has a direct protective effect on cardiomyocytes against ischemia-reperfusion injury and limits infarct size when administered intravenously before reperfusion.

Kinases and phosphatases in ischaemic preconditioning: a re-evaluation

Activation of several protein kinases occurs during myocardial ischaemia and during subsequent reperfusion. In contrast to the intensive investigation into the significance of kinase activation in cardioprotection, relatively little is known about the role of the phosphatases in this regard. The aim of this study was to re-evaluate the putative roles of PP1 and PP2A in ischaemia/reperfusion and in triggering ischaemic preconditioning. Isolated perfused working rat hearts were subjected to sustained global (15 or 20 min) or regional ischaemia (35 min), followed by reperfusion. Hearts were preconditioned using global ischaemia (1 x 5 or 3 x 5 min, alternated with 5 min reperfusion). To inhibit both PP1 and PP2A cantharidin (5 muM) was used. To inhibit PP2A only, okadaic acid (7.5 nM) was used. The drugs were administered during the preconditioning protocol, before onset of sustained ischaemia (pretreatment) or during reperfusion. Endpoints were mechanical recovery during reperfusion, infarct size and activation of PKB/Akt, p38 MAPK and ERK p42/p44, as determined by Western blot. Pretreatment of hearts with okadaic acid or cantharidin caused a significant reduction in mechanical recovery after 15 or 20 min global ischaemia. Administration of the drugs during an ischaemic preconditioning protocol abolished functional recovery during reperfusion and significantly increased infarct size. Administration of the drugs during reperfusion had no deleterious effects and increased functional recovery in 3 x PC hearts. To find an explanation for the differential effects of the inhibitors depending on the time of administration, hearts were freeze-clamped at different time points during the perfusion protocol. Administration of cantharidin before 5 min ischaemia activated all kinases. Subsequent reperfusion for 5 min without the drug maintained activation of the kinases until the onset of sustained ischaemia. Cantharidin given during preconditioning was associated with activation of p38MAPK and PKB/Akt during reperfusion after sustained ischaemia. However, administration of the drug during reperfusion only after sustained ischaemia caused activation of both PKB/Akt and ERK p42/p44. Phosphatase inhibition immediately prior to the onset of sustained ischaemia or during preconditioning abolishes protection during reperfusion, while inhibition of these enzymes during reperfusion either had no effect or enhanced the cardioprotective effects of preconditioning. It is proposed that inhibition of phosphatases during reperfusion may prolong the period of RISK activation and hence protect the heart.

Dexamethasone-induced cardioprotection: a role for the phosphatase MKP-1?

AIMS

Previous studies suggested that p38 MAPK activation during sustained myocardial ischaemia and reperfusion was harmful. We hypothesize that attenuation of p38MAPK activity via dephosphorylation by the dual-specificity phosphatase MKP-1 should be protective against ischaemia/reperfusion injury. Since the glucocorticoid, dexamethasone, induces the expression of MKP-1, the aim of this study was to determine whether upregulation of this phosphatase by dexamethasone protects the heart against ischaemia/reperfusion injury.

MAIN METHODS

Male Wistar rats were treated with dexamethasone (3 mg/kg/day ip) for 10 days, before removal of the hearts for Western blot (ip Dex-P) or perfusion in the working mode (ip Dex+P). Hearts were subjected to 20 min global or 35 min regional ischaemia (36.5 degrees C) and 30 or 120 min reperfusion. In a separate series, dexamethasone (1 microM) was added to the perfusate for 10 min (Pre+Dex) before or after (Rep+Dex) ischaemia.

KEY FINDINGS

Dexamethasone, administered intraperitoneally or added directly to the perfusate, significantly improved post-ischaemic functional recovery and reduced infarct size compared to untreated controls (p<0.05). These were associated with enhanced up-regulation of MKP-1 protein expression (arbitrary units (mean+/-SD): Untreated: 1; ip Dex-P: 2.59+/-0.22; ip Dex+P: 1.51+/-0.22; Pre+Dex: 4.11+/-0.73, Rep+15'Dex: 1.51+/-0.14; untreated vs. all groups, p<0.05) and attenuation of p38 MAPK activation (p<0.05) in all dexamethasone-treated groups, except for Rep+10'Dex. ERK and PKB/Akt activation were unchanged.

SIGNIFICANCE

Dexamethasone-induced cardioprotection was associated with upregulation of the phosphatase MKP-1 and inactivation of pro-apoptotic p38 MAPK.

Kinetics of the translocation and phosphorylation of alphaB-crystallin in mouse heart mitochondria during ex vivo ischemia

alphaB-crystallin (alphaBC) is a small heat shock protein expressed at high levels in the myocardium where it protects from ischemia-reperfusion damage. Ischemia-reperfusion activates p38 MAP kinase, leading to the phosphorylation of alphaBC on serine 59 (P-alphaBC-S59), enhancing its ability to protect myocardial cells from damage. In the heart, ischemia-reperfusion also causes the translocation of alphaBC from the cytosol to other cellular locations, one of which was recently shown to be mitochondria. However, it is not known whether alphaBC translocates to mitochondria during ischemia-reperfusion, nor is it known whether alphaBC phosphorylation takes place before or after translocation. In the present study, analyses of mitochondrial fractions isolated from mouse hearts subjected to various times of ex vivo ischemia-reperfusion showed that alphaBC translocation to mitochondria was maximal after 20 min of ischemia and then declined steadily during reperfusion. Phosphorylation of mitochondrial alphaBC was maximal after 30 min of ischemia, suggesting that at least in part it occurred after alphaBC association with mitochondria. Consistent with this was the finding that translocation of activated p38 to mitochondria was maximal after only 10 min of ischemia. The overexpression of alphaBC-AAE, which mimics alphaBC phosphorylated on serine 59, has been shown to stabilize mitochondrial membrane potential and to inhibit apoptosis. In the present study, infection of neonatal rat cardiac myocytes with adenovirus-encoded alphaBC-AAE decreased peroxide-induced mitochondrial cytochrome c release. These results suggest that during ischemia alphaBC translocates to mitochondria, where it is phosphorylated and contributes to modulating mitochondrial damage upon reperfusion.

Activation of beta-adrenoceptors mimics preconditioning of rat-isolated atria and ventricles against ischaemic contractile dysfunction

The effects of ischaemia and reoxygenation on cardiac contractile function can be abrogated by ischaemic preconditioning (IPC). We tested whether beta-adrenoceptor agonists could mimic IPC and whether IPC was dependent on beta-adrenoceptor activation in rat-isolated cardiac tissues. Paced left atria and right ventricular strips were set-up in Krebs solution and isometric developed tension recorded. Ischaemia was simulated by replacing with hypoxic glucose-free Krebs solution for 30 min. IPC and isoprenaline (10(-7) M) preconditioning for 10 min were examined. Developed tension post-reoxygenation was expressed as a percentage of the pre-ischaemic baseline. Recovery at 15 min was significantly increased by IPC in atria (47 +/- 4.0% vs. 29.3 +/- 1.7%, p < 0.05) and ventricles (39.0 +/- 5.2% vs. 22.4 +/- 2.8%, p < 0.05). At 60 min, isoprenaline-treated atria recovery (75.8 +/- 16.6%) was significantly (p < 0.05) greater than controls (47.9 +/- 2.3%). Propranolol (10(-6) M) abolished both effects. Therefore, both IPC and beta-adrenoceptor agonist-induced improvement of contractile recovery was propranolol-sensitive and beta-adrenoceptor-mediated.

Antiapoptosis and mitochondrial effect of pioglitazone preconditioning in the ischemic/reperfused heart of rat

PURPOSE

Pioglitazone, used clinically in the treatment of type 2 diabetes mellitus, has been implicated as a regulator of cellular inflammatory and ischemic responses. The present study examined whether pioglitazone could inhibit cardiomyocyte apoptosis and reduce mitochondrial ultrastructure injury and membrane potential loss in the ischemic/reperfused heart of the rat. Furthermore, we investigated whether the protective effect of pioglitazone was related to opening of the mitochondrialATP-sensitive potassium channels.

METHODS

Adult male Sprague-Dawley rats were subjected to 30 min of ischemia followed by 4 h of reperfusion. At 24 h before ischemia, rats were randomized to receive 0.9% saline, 5-hydroxydecanoate (5-HD, 10 mg kg(-1), i.v.) plus pioglitazone (3 mg kg(-1), i.v.) or pioglitazone (3 mg kg(-1), i.v.). One group served as sham control. We investigated mitochondrial structure, apoptosis rate and Bcl-2, Bax and Caspase-3 proteins by immunohistochemistry staining. RT-PCR was used to determine the expression of P38MAPKmRNA and JNKmRNA. Western blotting was used to measure the expression of P38MAPK, JNK and NFkappaB P65. A second group of rats were randomly divided into sham-operated, ischemia/reperfusion (I/R), pioglitazone treatment, 5-HD + pioglitazone and 5-HD groups and the size of myocardial infarction was determined. Primary cultured cardiomyocytes of neonatal Sprague-Dawley rats were divided into control, hypoxia reoxygenation, different concentrations of pioglitazone and 5-HD + pioglitazone groups. JC-1 staining flowcytometry was used to examine mitochondrial membrane potential (DeltaPsim).

RESULTS

Pioglitazone decreased mitochondrial ultrastructural damage compared to I/R, and reduced infarct size from 34.93 +/- 5.55% (I/R) to 20.24 +/- 3.93% (P < 0.05). Compared with the I/R group, the apoptosis rate and positive cell index (PCI) of Bax and Caspase-3 proteins in the pioglitazone group were significantly decreased (P < 0.05), while the PCI of Bcl-2 protein was increased (P < 0.05). There was no significant difference between the I/R and 5-HD + pioglitazone groups. Compared with the sham-operated group, the expression of P38MAPK mRNA, JNK mRNA and protein of P38MAPK, JNK and NFkappaB P65 in I/R was increased (P < 0.05). Pioglitazone did inhibit the increase in expressions vs I/R (P < 0.05). The rate of loss DeltaPsim cells in the pioglitazone group was significantly lower than in the hypoxia reoxygenation group, while the addition of 5-HD inhibited the effect of pioglitazone.

CONCLUSION

Pioglitazone inhibited cardiomyocyte apoptosis and reduced mitochondrial ultrastructure injury and membrane potential loss in the ischemic/reperfused heart of rat. These protective effects of pioglitazone may be related to opening mitochondrial(ATP)-sensitive potassium channels.