Postischemic Ventricular Dysfunction Research Articles

Targeting mitochondrial reactive oxygen species-mediated oxidative stress attenuates nicotine-induced cardiac remodeling and dysfunction

Long-term nicotine intake is associated with an increased risk of myocardial damage and dysfunction. However, it remains unclear whether targeting mitochondrial reactive oxygen species (ROS) prevents nicotine-induced cardiac remodeling and dysfunction. This study investigated the effects of mitoTEMPO (a mitochondria-targeted antioxidant), and resveratrol (a sirtuin activator) , on nicotine-induced cardiac remodeling and dysfunction. Sprague–Dawley rats were administered 0.6 mg/kg nicotine daily with 0.7 mg/kg mitoTEMPO, 8 mg/kg resveratrol, or vehicle alone for 28 days. At the end of the study, rat hearts were collected to analyze the cardiac structure, mitochondrial ROS level, oxidative stress, and inflammation markers. A subset of rat hearts was perfused ex vivo to determine the cardiac function and myocardial susceptibility to ischemia–reperfusion injury. Nicotine administration significantly augmented mitochondrial ROS level, cardiomyocyte hypertrophy, fibrosis, and inflammation in rat hearts. Nicotine administration also induced left ventricular dysfunction, which was worsened by ischemia–reperfusion in isolated rat hearts. MitoTEMPO and resveratrol both significantly attenuated the adverse cardiac remodeling induced by nicotine, as well as the aggravation of postischemic ventricular dysfunction. Findings from this study show that targeting mitochondrial ROS with mitoTEMPO or resveratrol partially attenuates nicotine-induced cardiac remodeling and dysfunction.

P0519HEXARELIN PROTECTS ISCHEMIA REPERFUSION INDUCED ACUTE KIDNEY INJURY BY TARGETING 14-3-3Σ

Abstract Background and Aims Acute kidney injury (AKI), manifested as a sudden decline in renal function on the order of days or a week, is one of the most common complications and is strongly associated with renal prognosis, medical expenses and length of stay of hospitalized patients. However, incidence of AKI can be reduced by early intervention. Hexarelin is a synthetic analogue of ghrelin with a potent GH releasing activity, which is also found to exhibited a significant protectant activity against postischemic ventricular dysfunction in isolated perfused hearts subjected to low flow ischemia and reperfusion. This study aims to explore the effects of hexarelin on ischemia reperfusion induced acute kidney injury (I/R-AKI) and the underlying mechanism of it. Method Thirty healthy male SPF SD aged at 8 weeks weighing 250-300g rats were divided into 5 groups including normal group, sham operation group, acute kidney injury (AKI) group, acute kidney injury group after hexarelin (HEX + AKI), and acute kidney injury group after saline (Saline + AKI). Bilateral kidney artery clamping was applied for 50 min to induce AKI. The drug-administered group and the saline-controlled group rats were treated with intraperitoneal injections 7 days before modelling and the Hex + AKI group and the saline + AKI group were given Hexarelin (dose 100 μg/kg. d) and equal volume of saline, respectively. To explore the underlying mechanism of HEX on I/R-AKI, gene expression profiling of AKI samples were searched from Pubmed, GEO dataset. Differential expression genes were used to predict canonical signal transduction pathways and signalling networks. Molecular docking was used to predict the combination of hub proteins and HEX. Results 1) Renal function in HEX-pretreated rats was significantly improved compared with control group: HE results showed that renal tubules were less dilated and rebuilt after pretreatment, and the infiltration area was significantly reduced; serum creatinine (P = 0.0005 <0.05), urea nitrogen (P <0.0001) concentration were significantly reduced; RT-qPCR showed that relative expression of Kim-1 (P<0.0001), caspase3 (P = 0.007), Bax (P <0.0001), Bad (P = 0.0168 <0.05) in HEX+AKI group were significantly decreased while the relative expression of Bcl-2 (P <0.05) was significantly increased compared with saline treated rats; 2) Microarray data analysis showed that 63 differential expression genes including SFN, Cyr61, Kim-1 were hub genes in the development of I/R-AKI; 3) Three-dimensional structure of the hub proteins HEX were obtained from the SWISS-MODEL database and the PubChem compound database, and Autodock software was used to calculate the molecular docking between proteins and HEX. Results showed that HEX and the protein that encoded by the gene SFN (SFN, 14-3-3σ) binding stably with a binding energy of -8.51; Conclusion Hexarelin protects ischemia reperfusion induced acute kidney injury by targeting 14-3-3σ.

Limitation of Infarct Size and the Open Artery Hypothesis: A Conversation With Eugene Braunwald, MD.

Eugene Braunwald received an MD from the New York University School of Medicine. He completed an internal medicine residency at Johns Hopkins Hospital and cardiology fellowships at Mount Sinai Hospital, Columbia University, and the National Heart Institute. He served as chief of cardiology and subsequently clinical director of the institute. From 1968 to 1972, he was the founding chair of medicine at the University of California, San Diego. From 1972 to 1996, he served as chair of medicine at the Brigham and Women’s Hospital. In 1975, he was elected to the National Academy of Sciences. He is now the Distinguished Hersey Professor of Medicine at Harvard Medical School and a senior investigator of the TIMI Study Group, which he founded in 1984. Dr Braunwald replies: I became aware of the importance of AMI in 1951 during an elective in cardiology during my senior year at the New York University School of Medicine. At the time, AMI was by far the most common cause of death in adults in the United States. Of the patients who survived to be admitted to hospitals (no one knew how many AMI patients failed to reach hospital emergency departments), about one third died before discharge, either suddenly, presumably from an arrhythmia, or secondary to pump failure. Of the patients who were discharged alive, about one quarter died within a year, most frequently as a consequence of heart failure or recurrent MI. Pathologists had taught that AMI was usually associated with coronary thrombosis. Indeed, during my cardiology elective, Herrick’s classic article describing AMI was required reading. Its title, “Clinical Features of Sudden Obstruction of the Coronary Arteries,” showed how these 2 conditions (coronary occlusion and AMI) were intertwined.1 My direct involvement in the care of several patients who did not survive the acute event left …

Thioredoxin-1 Attenuates Ventricular and Mitochondrial Postischemic Dysfunction in the Stunned Myocardium of Transgenic Mice.

We evaluated the effect of thioredoxin1 (Trx1) system on postischemic ventricular and mitochondrial dysfunction using transgenic mice overexpressing cardiac Trx1 and a dominant negative (DN-Trx1) mutant (C32S/C35S) of Trx1. Langendorff-perfused hearts were subjected to 15 min of ischemia followed by 30 min of reperfusion (R). We measured left ventricular developed pressure (LVDP, mmHg), left ventricular end diastolic pressure (LVEDP, mmHg), and t63 (relaxation index, msec). Mitochondrial respiration, SERCA2a, phospholamban (PLB), and phospholamban phosphorylation (p-PLB) Thr17 expression (Western blot) were also evaluated. At 30 min of reperfusion, Trx1 improved contractile state (LVDP: Trx1: 57.4 ± 4.9 vs. Wt: 27.1 ± 6.3 and DN-Trx1: 29.2 ± 7.1, p < 0.05); decreased myocardial stiffness (LVEDP: Wt: 24.5 ± 4.8 vs. Trx1: 11.8 ± 2.9, p < 0.05); and improved the isovolumic relaxation (t63: Wt: 63.3 ± 3.2 vs. Trx1: 51.4 ± 1.9, p < 0.05). DN-Trx1 mice aggravated the myocardial stiffness and isovolumic relaxation. Only the expression of p-PLB Thr17 increased at 1.5 min R in Wt and DN-Trx1 groups. At 30 min of reperfusion, state 3 mitochondrial O2 consumption was impaired by 13% in Wt and by 33% in DN-Trx1. ADP/O ratios for Wt and DN-Trx1 decrease by 25% and 28%, respectively; whereas the Trx1 does not change after ischemia and reperfusion (I/R). Interestingly, baseline values of complex I activity were increased in Trx1 mice; they were 24% and 47% higher than in Wt and DN-Trx1 mice, respectively (p < 0.01). These results strongly suggest that Trx1 ameliorates the myocardial effects of I/R by improving the free radical-mediated damage in cardiac and mitochondrial function, opening the possibility of new therapeutic strategies in coronary artery disease. Antioxid. Redox Signal. 25, 78-88.

Direct Evidence that Myocardial Insulin Resistance following Myocardial Ischemia Contributes to Post-Ischemic Heart Failure.

A close link between heart failure (HF) and systemic insulin resistance has been well documented, whereas myocardial insulin resistance and its association with HF are inadequately investigated. This study aims to determine the role of myocardial insulin resistance in ischemic HF and its underlying mechanisms. Male Sprague-Dawley rats subjected to myocardial infarction (MI) developed progressive left ventricular dilation with dysfunction and HF at 4 wk post-MI. Of note, myocardial insulin sensitivity was decreased as early as 1 wk after MI, which was accompanied by increased production of myocardial TNF-α. Overexpression of TNF-α in heart mimicked impaired insulin signaling and cardiac dysfunction leading to HF observed after MI. Treatment of rats with a specific TNF-α inhibitor improved myocardial insulin signaling post-MI. Insulin treatment given immediately following MI suppressed myocardial TNF-α production and improved cardiac insulin sensitivity and opposed cardiac dysfunction/remodeling. Moreover, tamoxifen-induced cardiomyocyte-specific insulin receptor knockout mice exhibited aggravated post-ischemic ventricular remodeling and dysfunction compared with controls. In conclusion, MI induces myocardial insulin resistance (without systemic insulin resistance) mediated partly by ischemia-induced myocardial TNF-α overproduction and promotes the development of HF. Our findings underscore the direct and essential role of myocardial insulin signaling in protection against post-ischemic HF.

High cholesterol diet effects on ischemia–reperfusion injury of the heart

Ischemic heart disease is the leading cause of morbi-mortality in developed countries. Both ischemia-reperfusion injury and mechanisms of cardioprotection have been studied for more than 50 years. It is known that the physiopathological mechanism of myocardial ischemia involves several factors that are closely related to its development, of which hypercholesterolemia is one of the main ones. Therefore, the objective of this review was to elucidate the effects of a high-cholesterol diet on normal ventricular function and ischemia-reperfusion injury associated phenomenon such as post-ischemic ventricular dysfunction (stunned myocardium). Although there exist many studies considering several aspects of this physiopathological entity, the majority were carried out on normal animals. Thus, experiments carried out on hypercholesterolemic models are controversial, in particular those evaluating different mechanisms of cardioprotection such as ischemic preconditioning and postconditioning, and cardioprotection granted by drugs such as statins, which apart from exerting a lipid-lowering effect, exert pleiotropic effects providing cardioprotection against ischemia-reperfusion injury. These controversial results concerning the mechanisms of cardioprotection vary according to quality, composition, and time of administration of the high-cholesterol diet, as well as the species used in each experiment. Thus, to compare the results it is necessary to take all of these variables into account, since they can change the obtained results.

Complex I syndrome in myocardial stunning and the effect of adenosine

Isolated rabbit hearts were exposed to ischemia (I; 15 min) and reperfusion (R; 5–30 min) in a model of stunned myocardium. I/R decreased left-ventricle O 2 consumption (46%) and malate–glutamate-supported mitochondrial state 3 respiration (32%). Activity of complex I was 28% lower after I/R. The pattern observed for the decline in complex I activity was also observed for the reduction in mitochondrial nitric oxide synthase (mtNOS) biochemical (28%) and functional (50%) activities, in accordance with the reported physical and functional interactions between complex I and mtNOS. Malate–glutamate-supported state 4 H 2O 2 production was increased by 78% after I/R. Rabbit heart Mn-SOD concentration in the mitochondrial matrix (7.4 ± 0.7 μM) was not modified by I/R. Mitochondrial phospholipid oxidation products were increased by 42%, whereas protein oxidation was only slightly increased. I/R produced a marked (70%) enhancement in tyrosine nitration of the mitochondrial proteins. Adenosine attenuated postischemic ventricular dysfunction and protected the heart from the declines in O 2 consumption and in complex I and mtNOS activities and from the enhancement of mitochondrial phospholipid oxidation. Rabbit myocardial stunning is associated with a condition of dysfunctional mitochondria named “complex I syndrome.” The beneficial effect of adenosine could be attributed to a better regulation of intracellular cardiomyocyte Ca 2+ concentration.

Structural and functional consequences of the Milano mutation (R173C) in human apolipoprotein A-I

Carriers of the apolipoprotein A-I(Milano) (apoA-I(M)) variant, R173C, have reduced levels of plasma HDL but no increase in cardiovascular disease. Despite intensive study, it is not clear whether the removal of the arginine or the introduction of the cysteine is responsible for this altered functionality. We investigated this question using two engineered variations of the apoA-I(M) mutation: R173S apoA-I, similar to apoA-I(M) but incapable of forming a disulfide bond, and R173K apoA-I, a conservative mutation. Characterization of the lipid-free proteins showed that the order of stability was wild type approximately R173K>R173S>R173C. Compared with wild-type apoA-I, apoA-I(M) had a lower affinity for lipids, while R173S apoA-I displayed intermediate affinity. The in vivo effects of the apoA-I variants were measured by injecting apoA-I-expressing adeno-associated virus into apoA-I-null mice. Mice that expressed the R173S variant again showed an intermediate phenotype. Thus, both the loss of the arginine and its replacement by a cysteine contribute to the altered properties of apoA-I(M). The arginine is potentially involved in an intrahelical salt bridge with E169 that is disrupted by the loss of the positively charged arginine and repelled by the cysteine, destabilizing the helix bundle domain in the apoA-I molecule and modifying its lipid binding characteristics.

Rosuvastatin Given During Reperfusion Decreases Infarct Size and Inhibits Matrix Metalloproteinase-2 Activity in Normocholesterolemic and Hypercholesterolemic Rabbits

There is evidence that statin treatment before ischemia protects myocardium from ischemia/reperfusion injury. The objective is to determine whether rosuvastatin administered during reperfusion modifies infarct size and the recovery of postischemic ventricular dysfunction in normocholesterolemic and hypercholesterolemic rabbits. In addition, we also evaluated the role of matrix metalloproteinase type 2 (MMP)-2 activation. Langendorff-perfused rabbit hearts were subjected to 30 minutes of ischemia and 120 minutes of reperfusion. In group 2, we added rosuvastatin after 30 minutes of ischemia and from the beginning of reperfusion. In group 3, an MMP inhibitor (doxycycline) was administered during the first 2 minutes of reperfusion. Finally, we repeated these groups but in hypercholesterolemic rabbits (groups 4, 5, and 6). The infarct size was 16.6% +/- 3.9% in group 1 and 25.6% +/- 2.7% in group 4. Rosuvastatin reduced infarct size to 4.5% +/- 1.1% and 6.1% +/- 1.5% in groups 2 and 5, respectively (P < 0.05). Rosuvastatin significantly decreased MMP-2 activity during reperfusion, and doxycycline induced an inhibition of MMP-2 activity and a reduction of infarct size in normocholesterolemic (4.9% +/- 0.9%) and hypercholesterolemic animals (8.3% +/- 1.6%) (P < 0.05). Rosuvastatin reduces infarct size and attenuates MMP-2 activity. These data and the correlation between MMP-2 and infarct size suggest that MMP-2 plays an important role in the mechanisms of cardioprotection afforded by rosuvastatin.

Effect of preischemic β-adrenoceptor stimulation on postischemic contractile dysfunction

Aims Short periods of preischemic β-adrenoceptor stimulation protect hearts against postischemic left ventricular dysfunction. It was the aim of this study to decide whether this procedure mimics ischemic preconditioning by the generation of preischemic hemodynamic and energetic stress or whether it represents an endogenous phenomenon and to investigate the influence of age and hypertension. Main methods Isolated rat hearts were investigated ex vivo by Langendorff perfusion and exposed to an established ischemia/reperfusion protocol (45 min no-flow ischemia and 90 min reperfusion). Left ventricular developed pressure (LVDP), rate pressure product, and ± d P/d t were analyzed. Key findings Isoprenaline concentration dependently increased LVDP up to 40 ± 15 mm Hg (approximately EC 50 of 9.9 ± 0.5 nM). Isoprenaline given prior to ischemia attenuated the subsequent postischemic ventricular dysfunction (approximately EC 50 of 1.4 ± 0.2 pM). However, concentrations high enough to improve LVDP in normoxic hearts did not improve postischemic recovery albeit a significant reduction of hypercontraction-induced cell damage. The effect on functional recovery was attenuated by atenolol, H89, and wortmannin suggesting that β-adrenoceptor stimulation, protein kinase A, and PI 3-kinase activation are involved. The effect was conserved in hearts from 13 month old rats but lost in age-matched spontaneously hypertensive rats. Significance The study identifies preischemic β-adrenoceptor stimulation as a pharmacological preconditioning protocol that does not simply mimic classical ischemic preconditioning by induction of hemodynamic or energetic stress prior to a prolonged ischemic period. The observed loss of effectiveness in hypertensives may contribute to the reduced ischemic tolerance of hypertensives.

Abstract 2317: Nociceptive Stimulation: A Novel Cardioprotective Strategy

Recent studies show that electro-stimulation from upper extremities or spinal cord elicits cardioprotective effects against I/R injury. In previous studies, we have identified a novel cardioprotective phenomenon that occurs subsequent to remote trauma (abdominal skin incision), termed RPCT. The purpose of this study was to determine whether an abdominal nociceptive stimulation (ANS), either by electrical or by chemical stimulation of remote peripheral sensory nerves along the same area of skin incision can produce cardioprotection similar to that of RPCT against MI. An in vivo mouse I/R model was used. ANS was performed 15 minutes prior to I/R or at the beginning of reperfusion with the needles placed along the line of abdominal incision. Infarct size was used to evaluate the results of I/R injury (45 min coronary occlusion, 24h reperfusion) with or without prior ANS treatments. Histological, immunochemical, cellular and functional studies were performed at appropriate timepoints. The results of demonstrate that both pre and post-conditioning produce an 85% reduction in infarct size (6.3 ± 2.2 vs. 52.6 ± 2.8 in preconditioning, P &lt; 0.01; 10.6 ± 3.1 vs . 60.2 ± 3.8 in post-conditioning, P &lt; 0.01, n = 6). Hematoxylin and Eosin staining showed that there was decreased infiltration after ANS compared to sham. We further show that ANS-preconditioning reduces apoptosis as evidenced by TUNEL staining and DNA fragmentation and reduces post-ischemic ventricular dysfunction. In conclusion, our results support 1) ANS is as protective as early phase of RPCT and 2) ANS elicited pre- and post-conditioning provides cardioprotection against myocardial infarction and dysfunction, at least in part, by reducing cardiomyocyte apoptosis after I/R. These results may suggest a novel therapeutic strategy for cardioprotection against I/R injury and have important implications for surgical patients at risk for myocardial infarction.

Sildenafil reduces L‐NAME‐induced severe hypertension and worsening of myocardial ischaemia–reperfusion damage in the rat

Phosphodiesterase-5 inhibitors are beneficial in pulmonary hypertension and congestive heart failure, the two conditions associated with coronary heart disease and ischaemia. We investigated whether sildenafil counteracts the cardiovascular alterations induced by N -nitro-L-arginine methyl ester (L-NAME) in the rat. Sildenafil was given orally to rats at doses of 0.37, 0.75 or 1.5 mg kg-1day-1 for four weeks, either alone or with L-NAME (35-40 mg kg-1 day-1 in the drinking water). Systolic blood pressure and urinary parameters (6-keto-prostaglandin F1alpha, thromboxane B2, 8-isoprostane-prostaglandin F2 and nitrite/nitrate) were measured in conscious rats. Isolated hearts were subjected to low flow ischaemia-reperfusion, and myocardial levels of guanosine 3', 5'cyclic monophosphate (cGMP) were determined. Endothelial vascular dysfunction was examined in aortic rings. Sildenafil dose-dependently prevented the rise in systolic blood pressure in L-NAME-treated rats. This activity was associated with a normalization of urinary 8-isoprostane-prostaglandin F2alpha and other biochemical parameters. In perfused hearts, the post-ischaemic ventricular dysfunction was worse in preparations from L-NAME-treated rats than in controls. Sildenafil dose-dependently reduced this effect, and creatine kinase and lactate dehydrogenase release were lower too. cGMP levels, which were low in myocardial tissue from L-NAME-treated rats, were restored by sildenafil. In noradrenaline-precontracted aortic rings from L-NAME-treated rats acetylcholine lost its vasorelaxant effect, and sildenafil restored it. In a rat model of chronic nitric oxide deprivation, where hypertension and aggravation of post-ischaemic ventricular dysfunction are associated with loss of vascular endothelium-relaxant function, sildenafil provided significant cardiovascular protection, primarily by maintaining tissue cGMP levels.

Asymmetric dimethylarginine (ADMA) induces vascular endothelium impairment and aggravates post-ischemic ventricular dysfunction in rats

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) inhibitor recognized as an independent risk factor for endothelial dysfunction and coronary heart diseases. This study investigated whether ADMA (10 mg/kg day for 14 days) affected endothelial function and aggravated post-ischemic ventricular dysfunction in the perfused rat heart. Systolic blood pressure and heart rate, plasma levels of ADMA and nitrite/nitrate were measured in vehicle- and ADMA-treated rats. Perfused hearts were submitted to global ischemia–reperfusion and vascular endothelial dysfunction was examined with angiotensin II in coronary vessels and aortic rings. Endothelial NO synthase (eNOS) and angiotensin-converting enzyme (ACE) mRNA expression in aortic and cardiac tissues were measured. ADMA-treated rats had higher systolic blood pressure (1.3-fold, P < 0.01) and slower heart rate (16%, P < 0.05) than controls. Plasma ADMA rose (1.9-fold, P < 0.01) and nitrite/nitrate concentration decreased 59% ( P < 0.001). Ventricular contraction (stiffness) increased significantly, with worsening of post-ischemic ventricular dysfunction. In preparations from ADMA-treated rats the coronary vasculature's response to angiotensin II was almost doubled ( P < 0.01) and the maximal vasorelaxant effect of acetylcholine in aortic rings was significantly lower than in preparations from vehicle-treated rats. In cardiac and aortic tissues eNOS mRNA and ACE mRNA levels were similar in controls and ADMA-treated rats. The increased plasma levels of ADMA presumably cause endothelial dysfunction because of a deficiency in NO production, which also appears involved in the aggravation of myocardial ischemia–reperfusion injury.

Hypercholesterolemia attenuates postischemic ventricular dysfunction in the isolated rabbit heart

The effects of the chronic administration of cholesterol on the stunned myocardium have not been studied. The objective was to determine the effect of a cholesterol enriched diet on postischemic ventricular dysfunction. In group 1 (G1, n = 7) isolated rabbit hearts underwent a follow up of ventricular function during 30 min in aerobic conditions. In group 2 (G2, n = 6) G1 was repeated but the animals were subjected to a 1% cholesterol enriched diet during 4 weeks (hypercholesterolemic animals). In group 3 (G3, n = 8) hearts underwent 15 min of global ischemia followed by 30 min of reperfusion. In Group 4 (G4, n = 11) G3 was repeated, but in hypercholesterolemic animals. Since cholesterol decreased the inotropism in basal situation, and this makes the comparison between groups difficult, we performed a Group 5 (G5, n = 7), in which G4 protocol was repeated but isoproterenol (8 microg/kg/min) was administered 10 min before ischemia, in order to match the preischemic inotropic state with respect to the normocholesterolemic ones. G1 and G2 maintained a stable inotropism during the 30 min of perfusion. The preischemic left ventricular developed pressure (LVDP) in G3 and G4 was 91.4 +/- 4.3 and 70.8 +/- 3.4 mmHg (p < 0.05), respectively, and after 30 min of reperfusion differences were not observed between G3 and G4. Nevertheless, when LVDP is expressed as a percentage, we detected an attenuation of postischemic systolic alterations in hypercholesterolemic animals (67.3 +/- 3.6 in G4 vs. 90.8 +/- 3.1% in G3, p < 0.05). When LVDP in G5 was increased until matching the one of G3, there were no differences after 30 min of reperfusion. Left ventricular end diastolic pressure increased 285 +/- 46%, 61 +/- 25% (p < 0.05 vs. G3 and G5) and 216 +/- 25% in G3, G4 and G5 at 30 min of reperfusion. There were no differences either in the values of tau or infarct size between groups. Thus, in hypercholesterolemic animals, a decrease of the preischemic inotropism exists and there is an attenuation of the stunned myocardium. When contractility of the normo and hypercholesterolemic animals is matched, the beneficial effect disappears.

The aminotetraline derivative (+/-)-(R,S)-5,6-dihydroxy-2-methylamino-1,2,3,4-tetrahydro-naphthalene hydrochloride (CHF-1024) displays cardioprotection in postischemic ventricular dysfunction of the rat heart.

To analyze the protective effects of the aminotetraline derivative (+/-)-(R,S)-5,6-dihydroxy-2-methylamino-1,2,3,4-tetrahydro-naphthalene hydrochloride (CHF-1024), a compound endowed with DA2-dopaminergic/alpha2-adrenergic receptor agonistic activity, in myocardial ischemia/reperfusion damage. A model of isolated and perfused (15 ml/min) electrically driven (300 beats/min) rat heart subjected to global ischemia (1 ml/min for 20 min) and reperfusion (15 ml/min for 30 min) was followed. Cardiac mechanics changes were evaluated together with biochemical markers of cardiac ischemia in perfusate and tissue tumor necrosis factor-alpha (TNF-alpha). CHF-1024, perfused through the heart for 15 min before ischemia at different molar concentrations (1-100 nM), significantly improved left ventricle developed pressure during reperfusion, and normalized left ventricular end-diastolic pressure and coronary perfusion pressure. This anti-ischemic effect of CHF-1024 was associated to a decrease in creatine kinase and lactate dehydrogenase, both released during heart reperfusion. These events were concomitant with maintenance of a higher production of 6-keto-prostaglandin F1alpha The ability of CHF-1024 to improve postischemic ventricular dysfunction was correlated with a dose-dependent inhibition of the release of both norepinephrine (NE), from sympathetic nerve endings, and TNF-alpha from cardiac tissue. The effect of CHF-1024 on NE release was almost completely antagonized by specific antagonists of presynaptic inhibitory receptors domperidone and rauwolscine. The finding that this new aminotetraline derivative possesses anti-ischemic properties and limits NE release from cardiac nerve endings may bear some therapeutic potential in cardiovascular diseases.

HFE mutation and dietary iron content interact to increase ischemia/reperfusion injury of the heart in mice.

Hereditary hemochromatosis is an inherited pathological condition characterized by iron overload in several vital organs including heart. To increase our understanding of the underlying pathogenic mechanisms of hereditary hemochromatosis, we used a HFE gene knockout mouse model that replicates hereditary hemochromatosis. A group of mice with no copies of HFE gene and corresponding wild-type mice were maintained either on low-iron (30 ppm) or high-iron (300 ppm) diet since birth. The results of our study revealed that HFE gene knockout mouse hearts were susceptible to ischemia-reperfusion injury as evidenced by increased postischemic ventricular dysfunction, increased myocardial infarct size and cardiomyocyte apoptosis compared with wild-type control hearts. The degree of injury increased in the hearts of the mice fed high-iron diet. The hearts of the HFE knockout mice showed increased iron deposition, increased content of reactive oxygen species (ROS) as evidenced by the increased formation of malondialdehyde, and reduced antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxidase. The results suggest that increased amount of ROS and reduced antioxidant reserve secondary to iron overloading may be instrumental for the susceptibility of the HFE gene knockout mice to cardiac injury.

Metabolic Modulation

featured in this issue of Circulation presents data showingthat pyruvate, which dose-dependently improved perfor-mance in myocardium from failing human hearts, may be onesuch agent.A number of abnormalities in both energy metabolism andcontractile function have been identified in failing cardiacmuscle. Metabolic changes include decreases in high energyphosphorylation potential, decreases in mitochondrial oxida-tive phosphorylation capacity, and a switch to a more fetalglycolytic metabolism.

Discussion

Discussion

Pathophysiological vs biochemical ischaemia: a key to transition from reversible to irreversible damage

‘Myocardial ischaemia’ is defined as an imbalance between fractional uptake of oxygen and the rate of cellular oxidation in the heart. This condition may have several potential outcomes: (1) when ischaemia is brief, a transient post-ischaemic ventricular dysfunction occurs on reperfusion, a condition named ‘stunned myocardium’; (2) when it is prolonged and severe, irreversible damage occurs, with no recovery in contractile function upon reperfusion; (3) when ischaemia is less severe, but still prolonged, the myocytes may remain viable but exhibit depressed contractile function. Under this condition, named ‘hibernating myocardium’, the reperfusion is able to restore contractility. During these dierent ischaemic conditions, many biochemical changes occur: initially they represent a defensive and protective reaction against ischaemia such as cellular acidosis and increase of inorganic phosphate levels that rapidly abolish the contractile activity. But with the prolongation of ischaemia and restoration of the coronary flow, alterations in ions and overall Ca 2+ homeostasis occur, together with an oxidative stress mediated by oxygen free radicals, not adequately counteracted by the cellular antioxidant defences. The mitochondria are likely to play a central role in these events which leads to membrane damage and irreversible deterioration of contractile function. The issue of reperfusion injury, however, is not unanimously accepted. Many, but not all, cardiologists are of the opinion that some components of reperfusion may be detrimental and able to inflict injury over and above that attributable to ischaemia. This article defines the sequence of events occurring during the transition from angina to

Endocrine, metabolic and cardioprotective effects of hexarelin in obese Zucker rats.

Genetically obese male Zucker rats have an impaired secretion of GH, coupled to hyperinsulinemia, hyperlipidemia and glucose intolerance. The aim of this study was to evaluate whether a chronic treatment with hexarelin, a synthetic enkephalin-derived hexapeptide with a potent GH-releasing activity, might be able to ameliorate the somatotropic function and reverse some metabolic alterations associated with obesity in male obese Zucker rats. Furthermore, as decreased GH secretion and insulin resistance are associated with increased cardiovascular risk, we also tested the capacity of hexarelin to prevent postischemic ventricular dysfunction in hearts of male obese Zucker rats. Obese and lean male rats of the Zucker strain were treated with hexarelin (80 microgram/kg, b.i.d., s.c.) or saline (1 ml/kg, b.i.d., s.c.) for 30 days. An acute hexarelin injection (80 microgram, s.c.) at the 28th day of treatment elicited a rise in plasma GH levels in ! lean but not in obese rats (pretreated or not with hexarelin); lean rats chronically treated with hexarelin showed a greater increase in plasma GH as compared with control counterparts. At the end of the experiment, pituitary GH mRNA levels were significantly reduced in obese rats and hexarelin administration failed to increase pituitary GH mRNA and IGF-I concentrations in plasma and heart. Chronic treatment with hexarelin increased insulinemia and blood glucose levels in obese but not in lean rats, left unaltered the high triglyceride levels but significantly decreased plasma cholesterol concentrations in obese rats. Heart preparations from lean and obese Zucker rats treated with saline, subjected to low flow ischemia and reperfusion, showed at reperfusion: a) a low recovery of postischemic left ventricular developed pressure (LVDP), coupled to a substantial increase in coronary perfusion pressure, and b) a marked increase in creatine kinase released in the perfusates. Hexare! lin administration for 30 days counteracted the heart ischemic damage both in lean and obese Zucker rats. In fact, the recovery of LVDP at reperfusion was significantly higher than in controls and the increase in coronary resistance was minimal. Collectively, these data indicate that a 30-day treatment with hexarelin was unable to improve somatotropic function in male obese Zucker rats but was successful in decreasing plasma cholesterol concentrations. Hexarelin exerted a cardioprotective effect in both lean and obese rats. The heart-protective activity afforded by the peptide was divorced from any stimulation of the GH axis and is probably exerted through activation of specific cardiac receptors.