Increase In Myocardial Infarct Size Research Articles

Cardiac ischemia/reperfusion stress reduces inner mitochondrial membrane protein (mitofilin) levels during early reperfusion

Mitochondrial inner membrane protein (Mitofilin or Mic60) is a mitochondria-shaping protein that plays a key role in maintaining mitochondrial cristae structure and remodeling. We recently showed that Mitofilin knockdown in H9c2 myoblasts induces mitochondrial structural damage resulting in mitochondrial dysfunction that is responsible for cell death via apoptosis. Here, we investigated the role of Mitofilin regulation in ischemia/reperfusion (I/R) injury and studied the relationship between Mitofilin and Cyclophilin (CypD), a key regulator of mitochondrial permeability transition pore (mPTP) opening. C57Bl6 male mice hearts were subjected to different ischemia times (15, 30, or 45 min) followed by a 2 h reperfusion period, or 45 min ischemia followed by 0, 15, 30, 60, or 120 min reperfusion to determine the impact of ischemia or reperfusion times on Mitofilin levels and its interaction with CypD. We found that the increase in myocardial infarct size and the reduction of mitochondrial calcium retention capacity were concomitant with Mitofilin reduction as a function of ischemic duration. We also found that 15 min reperfusion after 45 min ischemia was sufficient to cause a reduction of Mitofilin levels compared to sham, while 45 min ischemia alone was not enough to cause a significant decrease of Mitofilin. We revealed that the c-terminus coiled-coiled domain of Mitofilin is important for its interaction with CypD and the deletion of this identified sequence resulted in a loss of Mitofilin-CypD link, dissipation of mitochondrial membrane potential and increase in cell death. A decrease of the levels of Mitofilin was also associated with mitochondrial structural integrity damage, increased reactive oxygen species (ROS) production, and calpain activity. Our results indicate that Mitofilin physically binds to CypD in the inner mitochondrial membrane and the disruption of this interaction may play a critical role in the increase of mitochondrial dysfunction and initiation of myocytes’ death after I/R injury.

Diabetes aggravates myocardial ischaemia reperfusion injury via activating Nox2-related programmed cell death in an AMPK-dependent manner.

Cardiovascular diseases such as myocardial ischaemia have a high fatality rate in patients with diabetes. This study was designed to expose the crosstalk between oxidative stress and AMPK, a vital molecule that controls biological energy metabolism, in myocardial ischaemia reperfusion injury (I/RI) in diabetic rats. Diabetes was stimulated in rats using streptozotocin injection. Rats were separated on random into control, control + I/R, Diabetes, Diabetes + I/R, Diabetes + I/R + N‐acetylcysteine and Diabetes + I/R + Vas2870 groups. Myocardial infarct size was determined, and the predominant Nox family isoforms were analysed. In vitro, the H9C2 cells were administered excess glucose and exposed to hypoxia/reoxygenation to mimic diabetes and I/R. The AMPK siRNA or AICAR was used to inhibit or activate AMPK expression in H9C2 cells, respectively. Then, myocardial oxidative stress and programmed cell death were measured. Diabetes or high glucose levels were found to aggravate myocardial I/RI or hypoxia/reoxygenation in H9C2 cells, as demonstrated by an increase in myocardial infarct size or lactate dehydrogenase levels, oxidative stress generation and induction of programmed cell death. In diabetic rat hearts, cardiac Nox1, Nox2 and Nox4 were all heightened. The suppression of Nox2 expression using Vas2870 or Nox2‐siRNA treatment in vivo or in vitro, respectively, protected diabetic rats from myocardial I/RI. AMPK gene knockout increased Nox2 protein expression while AMPK agonist decreased Nox2 expression. Therefore, diabetes aggravates myocardial I/RI by generating of Nox2‐associated oxidative stress in an AMPK‐dependent manner, which led to the induction of programmed cell death such as apoptosis, pyroptosis and ferroptosis.

Role of fibrates in attenuated cardioprotective effect of ischemic preconditioning in hyperlipidemic rat heart

The present study has been designed to investigate the beneficial role of Fenofibrate in attenuated the cardioprotective effect of ischemic preconditioning (IPC) in hyperlipidemic (Hpl) rat heart. Experimental Hpl was produced by feeding high fat diet to rats for a period of 28 days. Isolated langendorff's perfused normal and Hpl rat hearts were subjected to global ischemia for 30 min followed by reperfusion for 120 min. The myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride staining. Coronary effluent was analyzed for lactate dehydrogenase (LDH) and creatine kinase-MB release to assess the extent of cardiac injury. Moreover, the oxidative stress in heart was assessed by measuring thiobarbituric acid reactive substance, superoxide anion generation and reduced form of glutathione. Moreover, I/R produced myocardial injury, which was assessed in terms of increase in myocardial infarct size, LDH and CK-MB release in coronary effluent and decrease in coronary flow rate. Four episodes of IPC (5 min each) afforded cardioprotection against I/R-induced myocardial injury in normal rat heart. On the other hand, IPC mediated myocardial protection against I/R-injury was abolished in Hpl rat heart. However, Treatment with Fenofibrate (100 mg/kg/day, i.p.) as agonists of PPAR-α have not affected the cardioprotective effect of IPC in normal rat heart, but its treatment markedly restored the cardioprotective potentials of IPC in Hpl rat heart. It is noted that the high degree of oxidative stress produced in Hpl rat heart during reperfusion and consequent down regulation of PPAR-α may be responsible to abolish the cardioprotectivepotentials of IPC.

Resolvin D1 Attenuates Myocardial Infarction in a Rodent Model with the Participation of the HMGB1 Pathway.

Myocardial infarction (MI) is associated with high morbidity and mortality worldwide. This study aimed to explore the roles of resolvin D1 (RvD1), a metabolite of omega-3 polyunsaturated fatty acids, in protection against MI and investigate its influences on high mobility group box 1 protein (HMGB1) and related molecular mechanisms. Three-month-old male Sprague-Dawley rats were divided into five groups: sham, MI, MI+0.02μg RvD1, MI+0.1μg RvD1, and MI+0.3μg RvD1. Vehicle control or different doses of RvD1 were injected into the left ventricle (LV) cavity 5min before MI induction. During MI induction, myocardial ischemia lasted for 45min followed by 180min of reperfusion. After the reperfusion, blood and LV samples were collected for biochemical examination. The MI group produced a significant increase in myocardial infarct size, serum cardiac biomarkers (LDH and CK-MB), proinflammatory cytokines (TNF-α and IL-6), and MDA levels, and a significant decrease in SOD level compared with the sham group. Moreover, a significant upregulation of gene and protein expressions of HMGB1 and its related TLR4 and NF-κB were observed in the MI group when compared with the sham group. Pretreatment of RvD1 ameliorated the biochemical changes caused by MI. Our results suggested that RvD1 pretreatment exhibited protective effects against MI through downregulation of HMGB1 and its related TLR4 and NF-κB expressions.

Ebselen protects rat hearts against myocardial ischemia-reperfusion injury.

Ebselen is an organoselenium compound that has demonstrated potent antioxidant and anti-inflammatory effects in previous studies. The present study was conducted to evaluate the effect of ebselen on myocardial ischemia-reperfusion (I/R) injury in a rat model and to elucidate the related mechanisms. Myocardial infarct size was assessed using triphenyltetrazolium chloride staining. Myocardial injury was evaluated according to the histopathological and ultrastructural alterations of rat hearts and the serum activity levels of cardiac enzymes, including creatine kinase (CK), CK-MB isoenzyme and lactate dehydrogenase (LDH). Cardiomyocyte apoptosis was detected using the terminal dUTP nick end-labelling (TUNEL) assay. In addition, the expression of apoptosis-associated proteins was measured using western blot analysis. In heart tissue specimens the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx), and levels of malondialdehyde (MDA) and protein carbonyl (PC) were also detected. The results indicated that ebselen reduced I/R-induced increase in myocardial infarct size and prevented the I/R-induced decreases in ejection fraction and fractional shortening. Further of note, ebselen improved I/R-induced rat heart injury. This was indicated by attenuation of histological and ultrastructural changes; reduction of serum CK, CK-MB and LDH activity levels; and decreased cell apoptosis on TUNEL staining, which was verified by decreased expression of cleaved (C)-Caspase-8, C-Caspase-3, B-cell lymphoma 2 (Bcl-2)-associated X protein and C-PARP, and increased expression of Bcl-2. Additionally, SOD and GPx activity levels were significantly higher, while MDA and PC levels were significantly lower in the ebselen + I/R group compared with in the I/R group. In conclusion, the present results suggested that ebselen serves an important role in protecting against myocardial I/R injury. The underlying mechanism may involve suppression of cardiomyocyte apoptosis and promotion of antioxidant activity.

Neonatal Lipopolysaccharide Exposure Gender-Dependently Increases Heart Susceptibility to Ischemia/Reperfusion Injury in Male Rats.

Background: Adverse stress exposure during the early neonatal period has been shown to cause aberrant development, resulting in an increased risk of adult disease. We tested the hypothesis that neonatal exposure to lipopolysaccharide (LPS) does not alter heart function at rest condition but causes heart dysfunction under stress stimulation later in life. Methods: Saline control or LPS were administered to neonatal rats via intraperitoneal injection. Experiments were conducted in 6 week-old male and female rats. Isolated hearts were perfused in a Langendorff preparation. Results: Neonatal LPS exposure exhibited no effects on the body weight of the developing rats, but induced decreases in the left ventricle (LV) to the body weight ratio in male rats. Neonatal LPS exposure showed no effects on the baseline heart function determined by in vivo and ex vivo experiments, but caused decreases in the post-ischemic recovery of the LV function in male but not female rats. Neonatal LPS-mediated LV dysfunction was associated with an increase in myocardial infarct size and the LDH release in the male rats. Conclusion: The present study provides novel evidence that neonatal immune challenges could induce gender-dependent long-term effects on cardiac development and heart function, which reinforces the notion that adverse stress exposure during the early neonatal period can aggravate heart functions and the development of a heart ischemia-sensitive phenotype later in life.

Studies of Ischemic Preconditioning Mechanisms in Langendorff Rat Heart Model the Impact of Phosphocreatin Kinase and ATP Sensitive Potasium Channels Pharmachological Openers and Blockers on Cardioprotection

Abstract Ischemic preconditioning (IPC) induced by administration of brief episodes of ischemia-reperfusion represents a protective mechanism of the heart against prolonged episodes of ischemia. Although the mechanism of ischemic preconditioning has been extensively studied, however, until now it is insufficient elucidated. Using a Langendorff rat heart model with 45 minutes ischemia followed by 120 minute reperfusion we aimed to evaluate the role of Phosphocreatin Kinase-C (PCK) in ischemic rat myocardium and demonstration of its involvment in the path of pharmachological preconditioning (PP) by using PKC activators 1,2-dioctanoyl-sn-glycerol (DOG) and inhibitors chelerythrine (CHE) and evaluation of the role of K ATP channels in pharmachological preconditioning (PP) mechanism by administration of a K ATP channel opener (Cromakalim) (CRK) or by blocking the opening of K ATP channels with glibenclamide(GLB). The activators of PCK(DOG) and of K ATP channel (CRK) limited the infarct size when perfused before lethal ischemia, mimicking the ischemic preconditioning in rat heart When activator of PCK DOG + GLB, a K ATP channel inhibitor were coperfused before the lethal ischemia, there was an increase in myocardial infarct size, expressed as a percentage of the area at risk, versus control, the cardioprotective effect of DOG being abolished by GLB. The same results were obtained when CHE the inhibitor of PCK was coperfused with CRK the activator of K ATP channel. The effect of CHE and GLB perfused at the beginning of IPC resulted in loss of protection accompanied by a significant increase in infarct size area. The finding that treatment with a DOG PKC activator and CRK activator of K ATP channel gives a similar degree of protection against infarction as that seen after ischemic preconditioning and that this protection can be blocked by CHE a PCK pharmachological inhibitor provides support for the hypothesis that PKC plays a pivotal role in ischemic preconditioning. Our data may have a significance in pharmachological preconditioning (PP) with decrease in infarct size as an end point.

Role of atrial natriuretic peptide in ischemic preconditioning–induced cardioprotection in the diabetic rat heart

BackgroundIt has been noted that nitric oxide (NO) is involved in the ischemic preconditioning (IPC)–mediated cardioprotection. Diabetes is a downregulator of atrial natriuretic peptide (ANP), resulting in low expression of endothelial nitric oxide synthase (eNOS) by which NO level get reduced. The purpose of the present study was to investigate the role of ANP in attenuated cardioprotective effect of IPC in the diabetic rat heart. MethodsThe heart was isolated from the diabetic rat and mounted on Langendorff's apparatus, subjected to 30-min ischemia and 120-min reperfusion. IPC was mediated by four cycles of 5-min ischemia and 5-min reperfusion. The infarct size was estimated using triphenyltetrazolium chloride stain, and coronary effluent was analyzed for lactate dehydrogenase and creatinine kinase-MB release to assess the degree of myocardial injury. The cardiac release of NO was estimated indirectly by measuring the release of nitrite in coronary effluent. ResultsIPC-mediated cardioprotection was significantly attenuated in the diabetic rat as compared with the normal rat. Perfusion of ANP (0.1 μM/L) in the diabetic rat heart significantly restored the attenuated cardioprotective effect of IPC and also increased the release of NO. However, this observed cardioprotection was significantly attenuated by perfusion of N-nitro L-arginine methyl ester, an eNOS inhibitor (100 μM/L) noted in terms of increase in myocardial infarct size, release of lactate dehydrogenase and creatinine kinase-MB, and also decreases in release of NO. ConclusionsThus, it is suggested that ANP restores the attenuated cardioprotective effect in the diabetic heart which may be due to increase in the expression of eNOS and subsequent increase in the activity of NO.

Abrogated cardioprotective effect of ischemic preconditioning in ovariectomized rat heart.

Ischemic heart disease is the leading cause of death in postmenopausal women. The expression of caveolin, a membrane protein and a negative regulator of nitric oxide (NO), increases after menopause. The present study was designed to determine the effect of daidzein (DDZ), a phytoestrogen in attenuated cardioprotective effect of ischemic preconditioning (IPC) in ovariectomized rat heart. Heart was isolated from ovariectomized rat and mounted on Langendorff's apparatus, subjected to 30 min ischemia and 120 min reperfusion. IPC was mediated by four cycles of 5 min ischemia and 5 min reperfusion. The infarct size was estimated using triphenyltetrazolium chloride stain, and coronary effluent was analyzed for lactate dehydrogenase and creatine kinase MB (CK-MB) release to assess the degree of myocardial injury. The release of NO was estimated indirectly by measuring the release of nitrite in coronary effluent. IPC-induced cardioprotection was significantly attenuated in ovariectomized rats as compared to normal rats, which was restored by treatment of DDZ, a caveolin inhibitor (0.2 mg/kg subcutaneously) for 1 week. However, this observed cardioprotection was significantly attenuated by perfusion of l-nitroarginine methyl ester, an endothelial nitric oxide synthase (eNOS) inhibitor (100 µM/L) and glibenclamide, an adenosine triphosphate-sensitive potassium ion channel blocker (10 µM/L) alone or in combination, noted in terms of increase in myocardial infarct size, release of LDH and CK-MB, and also decrease in the release of NO. Thus, it is suggested that DDZ restores the attenuated cardioprotective effect in ovariectomized rat heart, which may be due to downregulation of caveolin and subsequent increase in the activity of eNOS.

A comparative study on the cardioprotective potential of atorvastatin and simvastatin in hyperhomocysteinemic rat hearts

The present study has been deliberated in order to compare the cardioprotective potential of 3-hydroxymethyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors, Atorvastatin and Simvastatin in hyperhomocysteinemic rat hearts. l-methionine (1.7g/kg/day orally) was administered to rats for 4 weeks to produce experimental hyperhomocysteinemia (Hhcy). Isolated Langendorff-perfused normal and hyperhomocysteinemic rat hearts were subjected to global ischemia for 30min followed by reperfusion for 120min. The extent of myocardial damage was assessed in terms of myocardial infarct size using triphenyltetrazolium chloride (TTC) staining, and release of creatine kinase (CK) and lactate dehydrogenase (LDH) in the coronary effluent; whereas the oxidative stress in the heart was assessed by measuring lipid peroxidation, superoxide anion generation and reduced glutathione. Ischemia-reperfusion (I/R) was noted to produce myocardial injury in normal and hyperhomocysteinemic rat hearts, assessed in terms of increase in myocardial infarct size, LDH and CK in coronary effluent and oxidative stress. Treatment with Atorvatstain (50µM) and Simvastatin (10µM) afforded cardioprotection against I/R-induced myocardial injury in normal and hyperhomocysteinemic rat hearts as assessed in terms of reductions in myocardial infarct size, LDH and CK levels in coronary effluent and oxidative stress. It may be concluded that reductions in the high degree of oxidative stress may be responsible for the observed cardioprotective potential of Atorva-and Simvastatin, and both statins can be used interchangeably to afford cardioprotection against I/R-induced myocardial injury in normal and hyperhomocysteinemic rat hearts.

0191 : The increase in myocardial infarct size induced by intermittent hypoxia and HIF-1 activation, is attenuated by endoplasmic reticulum stress inhibition

Obstructive sleep apnea (OSA) is a highly prevalent disease characterized by repetitive upper airway collapse during sleep leading to chronic intermittent hypoxia (IH). It has been shown in patients that OSA contributes to myocardial infarct expansion. The lack of knowledge about the mechanisms involved in OSA-associated cardiovascular complications had limited the development of specific treatment whereas the gold standard treatment is little tolerated. In the context of cardiomyocytes death or life, this study purposes to investigate the role of endoplasmic reticulum (ER) stress and hypoxia inducible factor-1 (HIF-1) in myocardial susceptibility to ischemia-reperfusion (I/R) induced by chronic IH. C57Bl6J, HIF-1α +/– and their control mice were exposed to 14 days of IH (21–5% FiO2, 60s cycle, 8h/day). Then, mice were submitted to an in vivo ischemia-reperfusion to assess infarct size (IS, in % relative to area at risk) or hearts were removed to assess ER stress markers and HIF-1 activity using Western-blot and ELISA. In additional groups, TUDCA (an ER stress inhibitor, 75mg. kg-1) was administered daily during N or IH exposition to assess the role of ER stress in IH-susceptibility to I/R. Whereas chronic IH induced an increase in infarct size (33.7±9.4 vs 61.0±5.6% in N and IH groups, respectively, p<0.05), IH failed to increase infarct size in HIF1α +/- mice (42.4±2.7 vs 24.7±3.4% in HIF1α +/- -N and HIF1α +/- -IH, respectively). An increase in HIF-1 activity and ER stress markers was also observed in IH-mice. By the way, TUDCA totally abolished the IH-increased in infarct size (49.9±3.0 vs 61.0±5.6% in IH-TUDCA, respectively) as well as the IH-increased in HIF-1 activity (1.3±0.04 vs 0.14±0.02 fold increase in IH and IH/TUDCA, p<0.0001 vs non treated mice). These results suggest that the “ER stress-HIF-1“axe should be considered in apneic patients as a potential therapeutic target to limit myocardial ischemic damages.

Endothelial Cx40 limits myocardial ischaemia/reperfusion injury in mice

Gap junctions are indispensable for the function of heart and blood vessels by providing electrical coupling and direct cell-to-cell transfer of small signalling molecules. Gap junction channels between neighbouring cells are composed of 12 connexins (Cx). Changes in Cx43 expression, localization, and channel properties in cardiomyocytes contribute to infarction and reperfusion injury of the heart. It is increasingly recognized that deleterious consequences of ischaemia/reperfusion (IR) are modulated by the inflammatory response and endothelial function. The role of the endothelial connexins, i.e. Cx40 and Cx37, in cardiac IR injury is, however, not known. Following 30 min ischaemia and 24 h reperfusion, we found a significant increase in myocardial infarct size in mice with endothelial-specific deletion of Cx40 (Cx40del), but not in Cx37-deficient mice. The cardioprotective effect of endothelial Cx40 was associated with a decrease in neutrophil infiltration. Moreover, beneficial effects of endothelial Cx40 were not observed in isolated Langendorff-perfused hearts, suggesting direct involvement of endothelial-leucocyte interactions in the cardiac injury. Single-dose administration of methotrexate, a CD73 activator, reduced infarct size and neutrophil infiltration into the infarcted myocardium in Cx40del but not in control mice. Similar to Cx40del mice, CD73-deficient mice showed increased sensitivity to cardiac IR injury, which could not be conversed by methotrexate. Endothelial Cx40, but not Cx37, is implicated in resistance of the heart to IR injury by activation of the CD73 pathway. Thus, the Cx40-CD73 axis may represent an interesting target for controlling reperfusion damage associated with revascularization in coronary disease.

Possible involvement of PKC-δ in the abrogated cardioprotective potential of ischemic preconditioning in hyperhomocysteinemic rat hearts

The present study has been designed to investigate the possible role of protein kinase C-delta (PKC-δ) in hyperhomocysteinemia-induced attenuation of cardioprotective potential of ischemic preconditioning (IPC). Rats were administered l-methionine (1.7 g/kg/day, p.o.) for 4 weeks to produce hyperhomocysteinemia. Isolated Langendorff perfused normal and hyperhomocysteinemic rat hearts were subjected to global ischemia for 30 min followed by reperfusion for 120 min. Myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride (TTC) staining. Coronary effluent was analyzed for lactate dehydrogenase (LDH) and creatine kinase (CK) release to assess the degree of cardiac injury. Moreover, the oxidative stress in heart was assessed by measuring lipid peroxidation and superoxide anion generation. The ischemia-reperfusion (I/R) was noted to produce myocardial injury as assessed in terms of increase in myocardial infarct size, LDH and CK in coronary effluent and oxidative stress in normal and hyperhomocysteinemic rat hearts. In addition, the hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with high degree of oxidative stress as compared with normal rat hearts subjected to I/R. Four episodes of IPC (5 min each) afforded cardioprotection against I/R-induced myocardial injury in normal rat hearts as assessed in terms of reduction in myocardial infarct size, LDH, CK and oxidative stress. On the other hand, IPC mediated myocardial protection against I/R-injury was abolished in hyperhomocysteinemic rat hearts. Treatment with rottlerin (10 μM), a selective inhibitor of PKC-δ did not affect the cardioprotective effects of IPC in normal rat hearts; but its treatment significantly restored the cardioprotective potentials of IPC in hyperhomocysteinemic rat hearts. The high degree of oxidative stress produced in hyperhomocysteinemic rat hearts during reperfusion may activate PKC-δ, which may be implicated in the observed paradoxically abrogated cardioprotective potentials of IPC in hyperhomocysteinemic rat hearts.

Possible Role of JAK-2 in Attenuated Cardioprotective Effect of Ischemic Preconditioning in Hyperhomocysteinemic Rat Hearts

The present study investigated the possible role of Janus kinase-2 (JAK-2) in hyperhomocysteinemia-induced attenuation of the cardioprotective effects of ischemic preconditioning (IPC). Rats were administered L-methionine (1.7 g/kg/day, p.o.) for 4 weeks to produce hyperhomocysteinemia. Isolated Langendorff's perfused normal and hyperhomocysteinemic rat hearts were subjected to global ischemia for 30 min, followed by reperfusion for 120 min. Myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride staining. Coronary effluent was analyzed for lactate dehydrogenase (LDH) and creatine kinase (CK) release to assess the extent of cardiac injury. The oxidative stress in the heart was assessed by measuring thiobarbituric acid-reactive substances (TBARS), superoxide anion generation and the reduced form of glutathione. Ischemia-reperfusion (I/R) induced oxidative stress by increasing TBARS, superoxide anion generation and decreasing reduced form of glutathione in normal and hyperhomocystenemic rat hearts. Moreover, I/R produced myocardial injury, which was assessed in terms of the increase in myocardial infarct size, LDH and CK release in coronary effluent, and decrease in coronary flow rate in normal and hyperhomocysteinemic rat hearts. The hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with a high degree of oxidative stress as compared with normal rat hearts subjected to I/R. Four episodes of IPC (5 min each) afforded cardioprotection against I/R-induced myocardial injury in normal rat hearts as assessed in terms of improvement in coronary flow rate and reduction in myocardial infarct size, levels of LDH, CK, and oxidative stress. On the other hand, IPC-mediated myocardial protection against I/R-injury was abolished in hyperhomocysteinemic rat hearts. Tyrphostin AG490 (5 microM), a selective inhibitor of JAK-2, did not affect the cardioprotective effects of IPC in normal rat hearts, but its administration markedly restored the cardioprotective potential of IPC in hyperhomocysteinemic rat hearts. Administration of diazoxide (30 microM), an ATP-sensitive potassium (K(ATP)) channel opener, also restored the cardioprotective effects of IPC in hyperhomocysteinemic rat hearts. In conclusion, it is suggested that the high degree of oxidative stress produced in hyperhomocysteinemic rat hearts during reperfusion and consequent activation of JAK-2 and closure of K(ATP) channels may be responsible for abolishing the cardioprotective potential of IPC against I/R-induced myocardial injury.

Modulation of cardioprotective effect of ischemic pre- and postconditioning in the hyperhomocysteinemic rat heart

The present study was designed to investigate the effect of hyperhomocysteinemia (Hhcy) on cardioprotective potentials of ischemic preconditioning (IPC) and postconditioning (IPost). Rats were administered L-methionine (1.7 g/kg/day orally) for 4 weeks to produce Hhcy. Isolated Langendorff-perfused normal and hyperhomocysteinemic rat hearts were subjected to global ischemia for 30 min followed by reperfusion for 120 min. Myocardial infarct size was assessed macroscopically by volume method using triphenyltetrazolium chloride staining. Coronary effluent was analyzed for the release of lactate dehydrogenase (LDH) and creatine kinase (CK) to assess the degree of cardiac injury. Moreover, oxidative stress in the heart was assessed by measuring lipid peroxidation, superoxide anion generation and reduced glutathione. Ischemia-reperfusion (I/R) was noted to produce myocardial injury, as assessed in terms of increase in myocardial infarct size, LDH and CK in coronary effluent and oxidative stress in normal and hyperhomocysteinemic rat hearts. In addition, the hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with a high degree of oxidative stress in comparison with normal rat hearts subjected to I/R. Four episodes of IPC (5 min each) and six episodes of IPost (10 s each) afforded cardioprotection against I/R-induced myocardial injury in normal rat hearts, as assessed in terms of reduction in myocardial infarct size, LDH, CK and oxidative stress. However, surprisingly, IPC- and IPost-mediated myocardial protection against I/R injury was abolished in the hyperhomocysteinemic rat heart. It may be concluded that Hhcy may make the heart susceptible to oxidative stress induced by I/R, and that the high degree of oxidative stress produced in the hyperhomocysteinemic rat heart in response to reperfusion may be responsible for abolishing the cardioprotective potential of IPC and IPost against I/R injury.

Critical role of angiopoietins/Tie-2 in hyperglycemic exacerbation of myocardial infarction and impaired angiogenesis

Angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) are the two ligands of the Tie-2 receptor, a receptor tyrosine kinase that is expressed on the endothelium. A balanced angiopoietin/Tie-2 system is critical for the maintenance of vascular integrity. We investigated the potential role of a disrupted angiopoietin/Tie-2 system on hyperglycemic exacerbation of myocardial infarction and impaired angiogenesis. Using streptozotocin (STZ) mice subjected to myocardial ischemia, we examined the effects of shifting the Ang-2-to-Ang-1 ratio on myocardial infarction size, apoptosis, bone marrow (BM) cell-endothelial progenitor cell (EPC) differentiation, and angiogenesis. In control mice, myocardial ischemia increased expression of both Ang-2 and Tie-2. In STZ mice, Ang-2 expression was elevated, whereas Tie-2 expression was reduced, and neither was significantly altered by ischemia. Myocardial infarct size and apoptosis were increased in STZ compared with control mice. Using in vivo administration of an adenovirus containing Ang-1 or Ang-2, we found that shifting the Ang-2-to-Ang-1 ratio to favor Ang-1 reduced myocardial apoptosis and infarct size in STZ mice, while shifting the Ang-2-to-Ang-1 ratio to favor Ang-2 resulted in a significant increase in myocardial infarct size and apoptosis in control mice. Myocardial ischemia-stimulated BM cell-EPC differentiation was inhibited and myocardial angiogenesis was reduced in STZ mice. Systemic administration of Ad-Ang-1 restored BM cell-EPC differentiation and increased myocardial VEGF expression and angiogenesis in STZ mice. Our data demonstrate that disturbed angiopoietin/Tie-2 signaling contributes to the hyperglycemic exacerbation of myocardial infarction and impaired angiogenesis. Restoration of the Ang-2-to-Ang-1 ratio may be a novel therapeutic strategy for the treatment of diabetic myocardial ischemic diseases.

Thioredoxin redox signaling in the ischemic heart: an insight with transgenic mice overexpressing Trx1

This study examined if thioredoxin, the major redox-regulator in the mammalian system, plays any role in the redox signaling of ischemic myocardium. Isolated working rat hearts were made globally ischemic for 30 min followed by 2 h of reperfusion. Another group of hearts was rendered tolerant to ischemia by four cyclic episodes of 5 min ischemia each followed by another 10 min of reperfusion. Reperfusion of ischemic myocardium resulted in the downregulation of thioredoxin 1 (Trx1) expression, which was upregulated in the adapted myocardium. The increased expression of Trx1 was completely blocked with cis-diammine-dichloroplatinum (CDDP), an inhibitor of Trx1. CDDP also abolished cardioprotection afforded by ischemic adaptation as evidenced by a reduction of post-ischemic ventricular recovery, increase in myocardial infarct size and cardiomyocyte apoptosis. The decreased amount of reactive oxygen species in the adapted heart was increased significantly, when Trx1 was blocked with CDDP. The cardioprotective role of Trx1 was further confirmed with transgenic mouse hearts overexpressing Trx1. The Trx1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size as compared to the corresponding wild-type mouse hearts. Taken together, the results of this study implicate a crucial role of Trx1 in redox signaling of the ischemic myocardium.

C-reactive-protein-associated increase in myocardial infarct size after ischemia/reperfusion.

C-Reactive protein (CRP), a marker for acute inflammation, is associated with increased risk of cardiovascular events. The mechanism underlying this association is uncertain. An acute inflammatory response was induced in rabbits by subcutaneous injection of croton oil (CO) 1 to 3 days before 30 min of regional myocardial ischemia/180 min of reperfusion. CO treatment increased plasma CRP from below the limit of detection to 2.5 +/- 0.5 mg/dl and was associated with an increase in infarct size expressed as percentage of risk region [32 +/- 6% vehicle controls (n = 7) to 47 +/- 9% CO-treated rabbits (n = 7; P < 0.05]. After 10 min of ischemia and 180 min reperfusion, no infarct was found in controls; however, an infarct of 7 +/- 1% was found in CO-treated rabbits (P < 0.05; CRP, 2.3 +/- 0.4 mg/dl). The CRP-related increase in infarct size was not observed in croton oil-treated, C6-deficient rabbits (n = 5/group), indicating the involvement of complement. In these rabbits, infarct size was 22 +/- 2% (P < 0.05) despite having plasma CRP of 4.3 +/- 0.4 mg/dl. The CRP-associated increase in infarct size was ameliorated by pretreatment with heparin (n = 7; infarct size 33 +/- 3%; CRP, 2.3 +/- 0.3 mg/dl; P < 0.05) or N-acetylheparin (n = 7; infarct size 23 +/- 4%; CRP, 3.1 +/- 0.5 mg/dl; P < 0.05). These observations may explain why increased serum CRP is associated with an augmented risk for cardiovascular events.

Comparison of acute myocardial infarct size in patients ≥65 years versus

It is well established that cardiac death and complications associated with acute myocardial infarction (AMI) occur more often in elderly patients.1–4 Although the exact mechanism for this increased morbidity and mortality is not known, one potential explanation is that an age-associated increase in myocardial infarct size could play a role. Certainly, larger infarcts are associated with greater complications such as a greater risk of developing left ventricular dysfunction and congestive heart failure.

Coronary steal-induced increase in myocardial infarct size after pharmacologic coronary vasodilation

This study was performed to determine if maximal coronary arterial vasodilation of nonischemlc areas would produce an increase in myocardial infarct size through a “steal” of collateral flow from an ischemic region. Myocardial infarction was produced by a 2 hour occlusion and reperfusion of the distal left anterior descending coronary artery in anesthetized dogs. Five minutes after occlusion, 7 dogs were given saline solution, and in 12 dogs the coronary vasodilator chromonar (8 mg/kg, intravenously) was administered. Chromonar produced a significant Increase (p < 0.05) in blood flow to nonischemic regions and a concomitant decrease in flow to ischemic areas. Associated with these changes in flow was an elevation in total release and peak plasma creatine kinase compared with values in saline-treated control dogs. Myocardial infarct size determined with nitroblue tetrazolium staining was significantly increased (p < 0.05). These data demonstrate that maximal coronary vasodilation of nonischemic areas can result in an extension of myocardial infarction by a steal of collateral flow away from the ischemic region.