Cardiac Ischemia Model Research Articles

Local delivery of synthetic prostacycline agonist augments collateral growth and improves cardiac function in a swine chronic cardiac ischemia model

Aims It was reported that administration of angiogenic growth factors can augment collateral growth in ischemic tissues. It is assumed that angiogenic effects of cell transplantation may be mainly mediated by secretion of angiogenic cytokines. We tested feasibility of clinical use of ONO-1301, a synthetic small molecule that stimulates secretion of growth factors from various cell types, to treat patients with chronic myocardial ischemia. Main methods Effects of ONO-1301 on fibroblasts and endothelial cells were evaluated in vitro. We examined the efficacy of local delivery of ONO-1301 in models of rat hindlimb ischemia and swine chronic ischemic myocardium. Key findings ONO-1301 stimulated hepatocyte growth factor secretion from human fibroblasts. ONO-1301 promoted vascular-like tube formation by endothelial cells in vitro. Direct injection of a slow-release form of ONO-1301 (SR-ONO) to rat hindlimb ischemic muscle enhanced perfusion recovery. In a swine cardiac ischemia model, direct injection of SR-ONO into the ischemic myocardium significantly augmented collateral formation (SR-ONO vs. control; 1.7 ± 0.2 vs. 1.0 ± 0.2 Rentrop score), with improved local ventricular wall motion, reduced enlargement of left ventricular diastolic volume (49.5 ± 1.9 mL vs. 59.7 ± 4.2 mL) and increased cardiac index (4.2 ± 0.1 vs. 3.4 ± 0.2 L/min/m 2). Histological analysis revealed that SR-ONO suppressed fibrosis in ischemic tissue (collagen volume fraction; 7.5 ± 1.1% vs. 12.8 ± 2.2%) and enhanced neovascularization (capillary density, 275.6 vs. 159.3/mm 2; arterioles 36.6 vs. 25.5 /mm 2). Significance Local delivery of SR-ONO might be effective for therapeutic angiogenesis and propose that local administration of slow-release of synthetic small molecules represents new strategy for therapeutic angiogenesis.

Dietary fatty acids and protection against experimental cardiac arrhythmias in rats.

Sudden cardiac death accounts for about 50% of total coronary disease mortality in westernized industrial countries. The lack of early symptoms for this disorder makes prevention the preferred strategy. In a rat model of cardiac ischemia, dietary n-6 (sunflower seed oil) and n-3 (fish-oil) polyunsaturated fatty acids were shown to protect against arrhythmia compared with saturated fat, with greatest protection observed with fish oil. The frequency of arrhythmia was similar with monounsaturated fat from olive oil and saturated fat.

A Novel and Orally Active Poly(ADP-Ribose) Polymerase Inhibitor, KR-33889 [2-[Methoxycarbonyl(4-methoxyphenyl) methylsulfanyl]-1H-benzimidazole-4-carboxylic Acid Amide], Attenuates Injury in in Vitro Model of Cell Death and in Vivo Model of Cardiac Ischemia

Blocking of poly(ADP-ribose) polymerase (PARP)-1 has been expected to protect the heart from ischemia-reperfusion injury. We have recently identified a novel and orally active PARP-1 inhibitor, KR-33889 [2-[methoxycarbonyl(4-methoxyphenyl)-methylsulfanyl]-1H-benzimidazole-4-carboxylic acid amide], and its major metabolite, KR-34285 [2-[carboxy(4-methoxyphenyl)methylsulfanyl]-1H-benzimidazole-4-carboxylic acid amide]. KR-33889 potently inhibited PARP-1 activity with an IC(50) value of 0.52 +/- 0.10 microM. In H9c2 myocardial cells, KR-33889 (0.03-30 microM) showed a resistance to hydrogen peroxide (2 mM)-mediated oxidative insult and significantly attenuated activation of intracellular PARP-1. In anesthetized rats subjected to 30 min of coronary occlusion and 3 h of reperfusion, KR-33889 (0.3-3 mg/kg i.v.) dose-dependently reduced myocardial infarct size. KR-34285, a major metabolite of KR-33889, exerted similar patterns to the parent compound with equi- or weaker potency in the same studies described above. In separate experiments for the therapeutic time window study, KR-33889 (3 mg/kg i.v.) given at preischemia, at reperfusion or in both, in rat models also significantly reduced the myocardial infarction compared with their respective vehicle-treated group. Furthermore, the oral administration of KR-33889 (1-10 mg/kg p.o.) at 1 h before occlusion significantly reduced myocardial injury. The ability of KR-33889 to inhibit PARP in the rat model of ischemic heart was confirmed by immunohistochemical detection of poly(ADP-ribose) activation. These results indicate that the novel PARP inhibitor KR-33889 exerts its cardioprotective effect in in vitro and in vivo studies of myocardial ischemia via potent PARP inhibition and also suggest that KR-33889 could be an attractive therapeutic candidate with oral activity for several cardiovascular disorders, including myocardial infarction.

Amniotic mesenchymal cells autotransplanted in a porcine model of cardiac ischemia do not differentiate to cardiogenic phenotypes

Transplantation of stem cells in the acute ischemic myocardium (AMI) may play a role in the recovery of cardiac function. Here, we investigated the ability of amniotic fluid-derived mesenchymal cells (AFC) for phenotypic conversion to vascular cells and cardiomyocytes (CM) when autotransplanted in a porcine model of AMI. Single AFC preparations were taken from 12 fetuses 3 days before normal delivery. AFC were expanded in vitro and stored separately until animals of the original litter weighed 22-25 kg. A new model of AMI, i.e. 45-min circumflex coronary occlusion followed by wall dissection, was used to assess AFC differentiation potential. CMFDA-labeled AFC were autogenically transplanted in the ischemic area 1 week after AMI induction. Thirty days later, pigs were sacrificed and the phenotypic profile of transplanted AFC was assessed and compared to the corresponding pre-injection pattern. AFC showed in vitro to be of mesenchymal type also expressing markers of 'embryonic stem' cells (SSEA4 and Oct-4), as well as endothelial (von Willebrand factor, VE-cadherin) and smooth muscle (SM alpha-actin, SM22) cells. Thirty days after transplantation, in the survived AFC (5+/-1%) 'embryonic stem' cell markers disappeared and mesenchymal cell markers were down regulated with the exception of smooth muscle and endothelial antigens. No evidence for expression of cardiac troponin I was found. In the conditions used in this study, AFC were able to transdifferentiate to cells of vascular cell lineages but not to CM. Thus, porcine AFC may require further ex vivo re-programming to be suitable for therapeutic use in AMI.

Pretreatment with Pinacidil Promotes Arrhythmias in an Isolated Tissue Model of Cardiac Ischemia and Reperfusion

It is not clear whether activation of ATP-sensitive potassium channels (K(ATP)) with pinacidil in advance of ischemia and reperfusion promotes or suppresses arrhythmias. This study determines the effects of pinacidil pretreatment on arrhythmias and the changes in cellular electrophysiological parameters in segments of guinea pig right ventricular free walls exposed to simulated ischemia and reperfusion. Microelectrode recordings were made from endo- and epicardium during endocardial pacing. Preparations were superfused with Tyrode's solution and then exposed for 5 min to either 100 muM pinacidil or its solvent. After a 5-min washout, preparations were exposed to 15 min of ischemic conditions (hypoxia, hypercapnia, hyperkalemia, acidosis, lactate accumulation, and glucose-free) followed by reperfusion with Tyrode's solution. Pinacidil pretreatment increased ischemia-induced abbreviation of endo- and epicardial action potential durations and effective refractory periods. Pinacidil had no effect on endocardial conduction times but greatly prolonged transmural conduction during ischemia and early reperfusion, and it increased the incidence of transmural conduction block. Pinacidil pretreatment caused a significant increase in the incidence of arrhythmias in ischemia and reperfusion. Reperfusion arrhythmias in control preparations had electrophysiological characteristics of activity initiated by afterpotentials; however, arrhythmias with these characteristics were absent in pinacidil-pretreated preparations, and all reperfusion arrhythmias exhibited characteristics of reentry. The increased incidence of re-entrant arrhythmias is likely explained by pinacidil-induced reduction in effective refractory periods in combination with prolonged transmural conduction times. Thus, pinacidil pretreatment enhanced the effects of ischemia and reperfusion on action potential duration, effective refractory period, and transmural conduction, and it promoted re-entrant arrhythmias.

Cytochrome P-450: a new target in the heart and coronary curculation

Cytochrome P-450 enzymes (CYPs) are present in the heart and coronary circulation. The activation of CYP2J2/3 to increase the production of epoxyeicosatrienoic acids (EETs) may be cardioprotective in cardiac ischemia and reperfusion. On the other hand, inhibition of CYP2C9 with cimetidine, or more selectively with sulfaphenazole, is cardioprotective in the perfused rat heart. In a dog model of cardiac ischemia and reperfusion, inhibitors of CYP co-hydroxylases (e.g., CYP4A, CYP4F) reduce infarct size. Inhibition of selected CYPs as an approach to the treatment of myocardial infarction should therefore be further developed. The function of CYPs in the coronary artery and other blood vessels is varied and complex, and only just beginning to be elucidated. In the coronary artery, when nitric oxide (NO) bioavailability is inhibited, the activity of CYPs may be increased, with the production of vasodilatory EETs. Conversely, when CYP2C9 is inactivated in humans with coronary artery disease (CAD), acetylcholine-induced NO-mediated vasodilatation is enhanced. In the presence of CAD/oxidized LDL, the EET vasodilator/system may be inhibited. Drugs that target CYPs and/or EETs are thus expected to be useful in the elucidation of the role of this system, and may also have therapeutic utility. Copyright

Sustained protective effects of 7-monohydroxyethylrutoside in an in vivo model of cardiac ischemia–reperfusion

Earlier studies have shown that 7-monohydroxyethylrutoside (monoHER), an antioxidant flavonoid, protects against doxorubicin-induced cardiotoxicity. In this study, we investigated potential sustained cardioprotective effects of monoHER in a model of ischemia–reperfusion (I/R) in mice. Ischemia was induced for 30 min by ligating the left anterior descending coronary artery. Afterwards, the ligature was removed and reperfusion was allowed for 6 or 24 h or 2 weeks. MonoHER (500 mg/kg) was given intraperitoneally (i.p.) one hour before ischemia. Treatment with monoHER significantly attenuated myocardial neutrophil influx both at 6 and 24 h after reperfusion by 77% and 76%, respectively. Infarct size was also significantly reduced, 24 h and 2 weeks after reperfusion by 58% and 49%, respectively. Whereas ischemia–reperfusion had no influence on basal levels of cardiac contractility (+dp/dt), responses to dobutamine were blunted 24 h and 2 weeks after reperfusion. In mice treated with monoHER, cardiac contractility response was significantly restored. These results indicate that monoHER exerts a sustained cardioprotective effect on ischemia–reperfusion injury and prevents deterioration of cardiac contractility.

Comparison of developmental endothelial locus-1 angiogenic factor with vascular endothelial growth factor in a porcine model of cardiac ischemia

Background This study compared the angiogenic effects of developmental endothelial locus-1 (DEL-1), vascular endothelial growth factor (VEGF), as well as the negative control, β-galactosidase (β-gal), in a porcine model of cardiac ischemia. Methods Twenty pigs underwent left circumflex artery occlusions. After 3 weeks, the animals received myocardial injections of adenovirus expressing β-gal (n=6), DEL-1 (n=7), or VEGF (n=7). At 7 weeks, animals were assessed for both function and coronary flow and compared with baseline measurements. Results Regional wall motion index and global ejection fraction showed deterioration in function in the β-gal group and no change in the VEGF and DEL-1 groups between the treatment and harvest time points. Preload recruitable stroke work suggested functional improvement in the VEGF group (35.8 ± 8.6 vs 56.4 ± 17.8, p = 0.033). The increase in the DEL-1 group was not statistically significant (27.3 ± 9.8 vs, 40.2 ± 19.4, p = 0.067). The β-gal group exhibited minimal change (30.7 ± 14.8 vs 35.9 ± 12.1, p = 0.96). Regional blood flow as assessed by fluorescent microspheres was improved under stress conditions in the VEGF group (1.00 ± 0.15 vs 1.15 ±0.22, p = 0.03). Conclusions Treatment with VEGF led to a modest improvement in regional blood flow and cardiac function in previously ischemic myocardial tissue.

Low-O(2) affinity erythrocytes improve performance of ischemic myocardium.

O(2) transport and O(2) diffusion interact in providing O(2) to tissue, but the extent to which diffusion may be critical in the heart is unclear. If O(2) diffusion limits mitochondrial oxygenation, a change in blood O(2) affinity at constant total O(2) transport should alter cardiac O(2) consumption (VO(2)) and function. To test this hypothesis, we perfused isolated isovolumically working rabbit hearts with erythrocytes at physiological blood-gas values and P(50) (PO(2) required to half-saturate hemoglobin) values at pH of 7.4 of 17 +/- 1 Torr (2,3-bisphosphoglycerate depletion) and 33 +/- 5 Torr (inositol hexaphosphate incorporation). When perfused at 40 and 20% of normal coronary flow, mean VO(2) decreased from the control value by 37 and 46% (P < 0.001), and function, expressed as cardiac work, decreased by 38 and 52%, respectively (P < 0.001). Perfusion at higher P(50) during low-flow ischemia improved VO(2) by 20% (P < 0.001) and function by 36% (P < 0.02). There was also modest improvement at basal flow (P < 0.02 and P < 0.002, respectively). The improvement in VO(2) and function due to the P(50) increase demonstrates the importance of O(2) diffusion in this cardiac ischemia model.

Ischemia elicits a coordinated expression of pro-survival proteins in mouse myocardium.

Cardiomyocytes are post-mitotic, long-lived cells until disruptions to pro-survival factors occur after myocardial ischemia. To gain an understanding of the factors involved with ischemic injury, we examined expression changes in pro-survival and opposing pro-apoptotic signals at early and chronic periods of ischemia using an in vivo murine model. Alterations of pro-survival proteins such as the inhibitor of apoptosis protein on chromosome X (xIAP) and the apoptotic repressor protein (ARC) have not been evaluated in a murine model of cardiac ischemia. Early ischemia (1 day) resulted in a 50% reduction in ARC protein levels relative to sham-operated left ventricles, without significant changes in the expression of xIAP or other pro-survival factors. In contrast, a deficiency of xIAP expression was found in cardiac infarcts starting after 1 week, concomitant with significant evidence of apoptotic cell death and an up-regulation of pro-apoptotic signals including Bax, tumor necrosis factor-a, and caspase-8 activation. Chronic ischemia (after 2 weeks) was associated with elevated levels of other pro-survival factors such as Bcl-xL and the phosphorylated form of Akt, as part of the adaptive remodeling of the myocardium. Altogether, these findings suggest that strategies to increase IAP expression may promote myocyte survival after chronic ischemia.

Cardiomyocyte death induced by myocardial ischemia and reperfusion: measurement with recombinant human annexin-V in a mouse model.

Phosphatidylserine (PS) externalization is regarded as one of the earliest hallmarks of cells undergoing programmed cell death. We studied the use of labeled human recombinant annexin-V, a protein selectively binding to PS, to detect cardiomyocyte death in an in vivo mouse model of cardiac ischemia and reperfusion (I/R). I/R was induced in mouse hearts by ligation and subsequent release of a suture around the left anterior descending coronary artery. Annexin-V (25 mg/kg) fused to a marker molecule was injected intra-arterially 30 minutes before euthanasia. After 15 minutes of ischemia followed by 30 minutes of reperfusion, 1.4+/-1. 2% (mean+/-SD) of the cardiomyocytes in the area at risk were annexin-V positive (n=6). This increased to 11.4+/-1.9% after 15 minutes of ischemia followed by 90 minutes of reperfusion (n=7) and to 20.2+/-3.3% after 30 minutes of ischemia followed by 90 minutes of reperfusion (n=7). In control mice, including those injected with annexin-V at the binding site of PS, no annexin-V-positive cells were observed. DNA gel electrophoresis showed typical laddering starting after 15 minutes of ischemia followed by 30 minutes of reperfusion, suggesting activation of the cell death program. Intervention in the cell death program by pretreatment with a novel Na(+)-H(+) exchange inhibitor substantially decreased annexin-V-positive cardiomyocytes from 20.2% to 2.2% in mice after 30 minutes of ischemia followed by 90 minutes of reperfusion. These data suggest that labeled annexin-V is useful for in situ detection of cell death in an in vivo model of I/R in the heart and for the evaluation of cell death-blocking strategies.

Cardioprotective effects of the aminopeptidase P inhibitor apstatin: studies on ischemia/reperfusion injury in the isolated rat heart.

Aminopeptidase P and angiotensin-converting enzyme (ACE) are responsible for the metabolism of exogenously administered bradykinin in the coronary circulation of the rat. It has been shown that ACE inhibitors decrease cytosolic enzyme release from the ischemic rat heart and reduce reperfusion-induced ventricular arrhythmias by increasing endogenous levels of bradykinin. It was hypothesized that the aminopeptidase P inhibitor apstatin could do the same. In an isolated perfused rat heart preparation subjected to global ischemia and reperfusion, both apstatin and ramiprilat (an ACE inhibitor) significantly decreased creatine kinase (CK) and lactate dehydrogenase (LDH) release. The difference between the postischemia and preischemia levels of released CK was reduced 68% by apstatin and 68% by ramiprilat compared with control. The corresponding reductions in LDH release were 74% for apstatin and 81% for ramiprilat. A combination of the inhibitors was not significantly better than either one alone. Apstatin and ramiprilat also significantly reduced the duration of reperfusion-induced ventricular fibrillation by 69 and 61%, respectively. The antiarrhythmic effect of apstatin was reversed by HOE140, a bradykinin B2-receptor antagonist, suggesting that apstatin is acting by potentiating endogenously formed bradykinin. The results demonstrate that the aminopeptidase P inhibitor apstatin is cardioprotective in this model of cardiac ischemia/ reperfusion injury.

Arrhythmic effects of norepinephrine in a model of cardiac ischemia and reperfusion.

The aim of this study was to assess the direct effects of norepinephrine on mechanisms of arrhythmia induced by conditions of ischemia followed by reperfusion. Isolated canine Purkinje fiber-papillary muscle preparations were studied using standard microelectrode techniques. Tissues were superfused for 40 min with a solution simulating "ischemia" (i.e., hypoxic, acidotic, elevated lactate, and zero substrate) and then "reperfused" for 60 min. Ischemia produced a moderate loss of membrane potential in both tissues. Reperfusion resulted in rapid polarization of the tissues, which was accompanied by oscillatory afterpotentials and aftercontractions in 6 of 12 and 4 of 12 Purkinje fibers, respectively. This was followed by a progressive loss of membrane potential and inexcitability in Purkinje fibers. Recovery was associated with activity resembling depolarization-induced automaticity in 4 of 12 fibers. Addition of norepinephrine (0.5 microM) to the ischemic and reperfusion solutions altered primarily the reperfusion responses. Oscillatory afterpotentials and aftercontractions were larger and occurred in 8 of 8 and 6 of 8 Purkinje fibers, respectively. Norepinephrine also prevented or blunted the progressive depolarization to inexcitability in Purkinje tissues and increased automaticity occurring at low (depolarization-induced automaticity) and more polarized membrane potentials (enhanced normal pacemaker activity). This study demonstrates that norepinephrine exacerbates several potential mechanisms of arrhythmia elicited by reperfusion in canine Purkinje tissues.