Induction Of Acute Myocardial Infarction Research Articles

S-allylcysteine mediates cardioprotection in an acute myocardial infarction rat model via a hydrogen sulfide-mediated pathway

S-allylcysteine (SAC) is an organosulfur-containing compound derived from garlic. Studies have shown that garlic is beneficial in the treatment of cardiovascular diseases. This study aims to elucidate if SAC is responsible for this cardioprotection using acute myocardial infarction (AMI) rat models. In addition, we hypothesized that SAC may mediate cardioprotection via a hydrogen sulfide (H(2)S)-related pathway. Rats were pretreated with saline, SAC (50 mg x kg(-1) x day(-1)), SAC + propagylglycine (PAG; 50 mg + 10 mg x kg(-1) x day(-1)) or PAG (10 mg x kg(-1) x day(-1)) for 7 days before AMI induction and killed 48 h after. Our results showed that SAC significantly lowered mortality (12.5% vs. 33.3%, P < 0.05) and reduced infarct size. SAC + PAG- and PAG-treated rats had larger infarct sizes than controls (60.9 +/- 0.01 and 62.0 +/- 0.03%, respectively, vs. 50.0 +/- 0.03%; P < 0.05). Pretreatment with SAC did not affect BP, but BP was significantly elevated in SAC + PAG and PAG-treated groups (P < 0.05). In addition, plasma H(2)S levels and left ventricular cystathionine-gamma-lyase (CSE) activities were analyzed to investigate the involvement of H(2)S. CSE is the enzyme responsible for H(2)S production in the heart. SAC increased left ventricular CSE activity in AMI rats (2.75 +/- 0.34 vs. 1.23 +/- 0.16 micromol x g protein(-1) x h(-1); P < 0.01). SAC + PAG-treated rats had significantly lower CSE activity compared with the SAC-treated group (1.22 +/- 0.27 vs. 2.75 +/- 0.34 micromol x g protein(-1) x h(-1); P < 0.05). Similarly, SAC-treated rats had higher plasma H(2)S concentration compared with controls and the SAC + PAG-treated group. Protein expression studies revealed that SAC upregulated CSE expression (1.1-fold of control; P < 0.05), whereas SAC + PAG and PAG downregulated its expression (0.88-fold of control in both groups; P < 0.005). In conclusion, our study provides novel evidence that SAC is protective in myocardial infarction via an H(2)S-related pathway.

In Vivo Effects of Myocardial Creatine Depletion on Left Ventricular Function, Morphology, and Energy Metabolism—Consequences in Acute Myocardial Infarction

The failing heart is characterized by disturbed myocardial energy metabolism and creatine (Cr) depletion. The aims of this study were to in vivo evaluate the effects of Cr depletion on: a) left ventricular (LV) function and morphology during rest and stress, b) LV energy metabolism, c) catecholamine in LV and plasma content, and d) incidence of malignant ventricular arrhythmias (MVA) during acute myocardial infarction (MI). Male rats weighing approximately 200 g were used. Two groups were studied: the rats treated with Cr analogue beta-guanidinopropionic acid (BGP) (n = 25) and controls (n = 23). BGP (1 M) was administered by subcutaneously implanted osmotic minipumps over 4 weeks. The rats (BGP n = 9, control n = 12) were than examined with transthoracic echocardiography at basal and at stress conditions induced by transesophageal pacing. In vivo (31)P magnetic resonance spectroscopy (MRS) was used for evaluation of myocardial energy status (BGP n = 7, control n = 12). (31)P MRS, echocardiography and high-performance liquid chromatography analysis of myocardial Cr, total adenine nucleotides and catecholamines in myocardium and plasma were performed on noninfarcted hearts. Myocardial infarction was induced in a subgroup of animals (BGP n = 15, control n = 15) by ligation of the left coronary artery resulting in a large ( approximately 50%) anterolateral MI and acute HF. A computerized electrocardiogram tracing was obtained continuously before induction of MI and up to 60 minutes postinfarction. Qualitative and quantitative variables of ventricular arrhythmias were analyzed using arrhythmia score. Body weight (BW) was lower (P < .01), whereas LV/BW was higher (P < .01) in the BGP group. Total myocardial Cr pool was decreased for at least 50% (P < .01) compared with the controls. There was no difference in total nucleotide pool. Phosphocreatine/adenosine-3-phosphate ratio was lower in the BGP group (P < .01). LV systolic function was disturbed during rest and stress (P < .05). Similarly, LV dimensions were increased in the BGP group (P < .05). Induction of acute MI resulted in markedly increased incidence of MVA and higher mortality in the BGP group (P < .01). Myocardial Cr depletion results in functional and structural LV alterations associated with lower myocardial energy reserve. Intact myocardial Cr metabolism is important for normal LV function during basal and stress conditions. Acute MI in the setting of myocardial Cr depletion leads to excessive mortality from ventricular arrhythmias and progressive heart failure.

Effects of G-CSF on cardiac remodeling and arterial hyperplasia in rats

Although granulocyte colony-stimulating factor (G-CSF) has been shown to prevent cardiac remodeling after acute myocardial infarction, the mechanism and safety of G-CSF treatment acute myocardial infarction remain controversial. The purpose of the present study was to investigate in a rat model the mechanisms underlying the beneficial effect of G-CSF in acute myocardial infarction and to determine whether G-CSF treatment aggravates vascular remodeling of injured artery after acute myocardial infarction. Sprague–Dawley rats received transplanted bone marrow cells from green fluorescent protein (GFP) transgenic rats. Acute myocardial infarction was induced by ligation of the left coronary artery. After 24 h, the right carotid artery was injured with a balloon catheter. G-CSF (100 μg/kg/day) or saline was injected subcutaneously for 5 consecutive days after induction of acute myocardial infarction. G-CSF treatment significantly improved left ventricle function and reduced infarct size in rats with acute myocardial infarction. Expression of mRNA for the angiogenic cytokines was significantly higher in the infarction border area in the G-CSF group than in the control group. The surviving cardiomyocytes in infarction area were more in the G-CSF group. GFP-positive cells were gathered in the infarction border area in both groups; G-CSF did not increase cardiac homing of GFP-positive bone marrow cells in contrast to control group. Most GFP-positive cells were CD68-positive (macrophages). It was difficult to find bone marrow-derived cardiomyocytes in the infarcted area. G-CSF treatment inhibited neointima formation and increased reendothelialization of the injured artery. GFP-positive cells were identified most in the adventitia of the injured artery. A few cells in the neointima and reendothelialization were GFP positive. In conclusion, administration of G-CSF appears to be effective for treatment of left ventricular remodeling after acute myocardial infarction and does not aggravate vascular remodeling. The effect of G-CSF on cardiac and vascular remodeling may occur mainly through a direct action on the heart and arteries.

929. Target Adult Stem Cells to Ischemic Hearts by Regulated Stromal Cell-Derived Factor 1 Gene Transfer

Adult bone marrow-derived stem cells (BMSCs) have emerged as a promising source for regeneration of tissues including those traditionally considered terminally differentiated, for instance, heart and brain. Chronic heart failure afflicts 4.8 million Americans, for those at the end stage of this disease heart transplantation remains the only and last resort. Acute myocardial infarction (AMI) is a leading cause of heart failure. Increasing evidence suggests that the body has a natural response for cardiac repair by up-regulating stromal cell-derived factor 1 (SDF-1), a stem cell active chemokine, which leads to recruitment of circulating BMSCs to ischemic hearts. However, up-regulation of endogenous SDF-1 is transient and inadequate to induce functionally meaningful heart regeneration. Therefore, the current study aimed to enhance stem cell-initiated cardiac repair by targeting circulating BMSCs to ischemic myocardium through targeted and regulated SDF-1 gene expression. To accomplish this goal, we have developed a regulatable system that consists of a MLC-2v promoter for cardiac selective expression as well as an oxygen-sensitive gene switch based on the oxygen-dependent degradation domain of hypoxia inducible factor 1α. It delivers genes of interest in a cardiac-selective and hypoxia-regulated manner in vitro and in vivo. AMI was surgically induced in adult BALB/c mice. DNA plasmid encoding hypoxia-regulated human SDF-1 was administered via intra-myocardial injection. PKH26 labeled BMSCs (6 × 106) were systemically injected immediately after induction of AMI. hSDF-1 expression was evaluated by Western blot analysis and the efficiency of hSDF-1 to attract implanted BMSCs was assessed by immunofluorescent staining and confocal microscopy. 1 week post AMI, hSDF-1 expression was markedly increased in the ischemic mouse heart, while less or no expression was detected in spleen, liver, lung, kidney and skeletal muscle nor in the heart of non-MI group. Confocal microscopy showed that hSDF-1 was highly expressed in the peri-infarct zone, with PKH26-labeled BMSCs enriched nearby. Furthermore, infarct size and cardiac fibrosis were significantly reduced in mice treated with hSDF-1 plus BMSCs compared to BMSCs alone. Taken together, our results indicate that cardiac-selective and hypoxia-inducible SDF-1 gene transfer activated mobilization of BMSCs to ischemic hearts and facilitated post-ischemic repair. This combined approach of regulated gene transfer and adult stem cells may provide a novel, safe and effective strategy for regenerative medicine, leading to efficient and timely repair of injured tissues.

Plasma cardiac troponin T closely correlates with infarct size in a mouse model of acute myocardial infarction

Background: Cardiac troponins replaced creatine kinase and lactate dehydrogenase isoenzymes as criterion standards for the laboratory diagnosis of myocardial damage. However, there are only few publications on correlations of cardiac troponin T (cTnT) with pathologically determined infarct size which are flawed by insufficient sample size. Methods: In 38 anesthetized wildtype mice, the chest and pericardium were opened and the left descending artery was ligated. After sham operation, all mice recovered. Twenty-four hours after surgical induction of acute myocardial infarction heparinized blood samples were collected, the animals sacrificed and hearts harvested. Plasma cTnT was measured by a quantitative rapid assay using the Cardiac Reader (Roche Diagnostics). The hearts were cut into four transverse sections which were stained with 1.5% triphenyltetrazolium chloride for evaluation of necrosis by computerized planimetry. Pearson correlation coefficients were calculated between histological infarct size and cardiac markers. Results: Infarct sizes ranged from 14% to 55% of left ventricle and cTnT concentrations from 3.9 to 14.1 μg/l. cTnT correlated closely with histological infarct size ( r=0.84, p<0.001). Conclusions: This study for the first time demonstrates a close correlation of cTnT release with pathological infarct size in a suitable experimental model with a sufficient sample size.

Long-term treatment with neutral endopeptidase inhibitor improves cardiac function and reduces natriuretic peptides in rats with chronic heart failure.

Increased secretion of atrial and brain natriuretic peptide (ANP and BNP) from hearts is known to exhibit favorable effects in patients and animals with heart failure, and inhibition of neutral endopeptidase (NEP), an enzyme that degrades ANP and BNP, may further increase these peptide levels. However, it is still unknown whether such elevation of the ANP and BNP may offer a therapeutic benefit to the progression of chronic heart failure (CHF). We examined the effects of ONO-9902, a novel NEP inhibitor, on changes in hemodynamic parameters, NEP activity and neurohumoral factors in rats with CHF induced by left coronary artery ligation (CAL). Male Wistar rats (220-240 g) were subjected to induction of acute myocardial infarction by CAL. Rats were orally treated with ONO-9902 (300 mg/kg/day) from the 1st to 6th week after the operation. Hemodynamic and/or biochemical assessments were performed at the 1st and 6th weeks after the operation. A single administration of ONO-9902 inhibited the plasma and kidney NEP activities and thereby further augmented the elevation of plasma ANP concentration in rats with CAL at the 1st week after the operation. In rats with CAL at the 6th week after the operation, the left ventricular end-diastolic pressure (LVEDP) increased and cardiac output index (COI) decreased as compared with those of sham-operated rats. These changes were accompanied by marked increases in the plasma ANP, BNP and endothelin-1 (ET-1). Chronic treatment with ONO-9902 attenuated the increase in LVEDP and the decrease in COI. These changes were associated with a decrease in plasma ANP, BNP and ET-1 concentrations. The results suggest that chronic treatment with NEP inhibitor improves depressed cardiac function in rats with CHF. ONO-9902 may offer a new and possible therapeutic approach in patients with CHF.

Ultrasmall superparamagnetic particles of iron oxide (USPIO) MR imaging of infarcted myocardium in pigs

The purpose of this study is to assess the potential value of ultrasmall superparamagnetic iron oxide (USPIO) for the detection of acute myocardial infarction by magnetic resonance (MR) imaging. Spin-echo magnetic resonance imaging of the heart was performed before, immediately after, and approximately 35 and 90 min after 30 μmol Fe/kg of USPIO administration in seven pigs with surgically induced myocardial infarction. Gradient-echo sequences were used to identify contraction abnormalities at the site of infarction. Myocardial signal intensities were measured using region-of-interest analysis in normal and infarcted myocardium. In addition, liver and lung signal intensities were measured. Pathologic correlation was performed after sacrificing the animals. The infarct area was located with wall-motion analysis. The site of infarction was confirmed at pathologic examination. The signal-intensity ratio between infarcted and normal myocardium was not significantly changed after USPIO administration at equilibrium stages (immediately after injection p = 0.64, at 35 min p = 0.32, at 90 min p = 0.73). The signal intensity of the liver decreased significantly after contrast administration ( p < 0.05). For the lung, the change in signal intensity after USPIO administration was not significant. This pig model is well suited to study wall motion abnormalities after induction of acute myocardial infarction. USPIO-enhanced magnetic resonance imaging does not improve the visualization of acute myocardial infarction at equilibrium stage.

An Experimental Induction of Acute Myocardial Infarction and Arterial Thrombosis in Rabbits

An Experimental Induction of Acute Myocardial Infarction and Arterial Thrombosis in Rabbits

Cardiac vagal reflex modulates intestinal vascular capacitance and ventricular preload in anesthetized dogs with acute myocardial infarction.

The purpose of the present study was to examine the effects of the cardiac vagal reflex on intestinal vascular capacitance and cardiac filling pressure during experimental acute myocardial infarction (AMI). AMI was induced in anesthetized dogs through injection of microspheres into the left main coronary artery. Intestinal blood volume was measured with blood-pool scintigraphy. Portal venous pressure was varied through graded inflation of a portal venous constrictor to determine the intestinal vascular pressure-volume relation. Induction of AMI decreased intestinal blood volume to 88 +/- 3% of the control value (P < .01) and shifted the pressure-volume relation toward the pressure axis. This change was associated with increased left ventricular (LV) end-diastolic pressure (LVEDP) (from 6 +/- 1 to 17 +/- 2 mm Hg, P < .01) and LV segment length (to 112 +/- 4% of the control value, P < .01). During AMI, blockade of the cardiac vagal reflex by intrapericardial application of 2% lidocaine further decreased intestinal blood volume (to 83 +/- 3% of the control value, P < .05, versus AMI without lidocaine), increased LVEDP (to 22 +/- 2 mm Hg, P < .05, versus AMI without lidocaine), and tended to increase LV segment length (to 115 +/- 5%, P < .10). Lidocaine had no effect in dogs with AMI that had been vagotomized. These results suggest that the cardiac vagal reflex modulates the decrease in the intestinal vascular capacitance induced by AMI and modulates ventricular preload through pooling of blood in the intestinal circulation.

Transmural changes in mast cell density in rat heart after infarct induction in vivo.

The cardiac distribution of mast cells was investigated after the induction of acute myocardial infarction in the rat. The left anterior descending coronary artery (LAD) was occluded by ligation in the infarct group, whereas in sham rats only a superficial ligature was placed beside the LAD. Rats of both groups were killed at 4, 7, 14, 21, 35, and 85 days following surgery. Hearts were excised and formalin-fixed. Mast cell densities were monitored in subepicardial and subendocardial layers of the left ventricle (LV) in 6 microns thick toluidine blue-stained cross-sections. In control (non-operated) animals, mast cell densities were comparable in the LV subepicardial and subendocardial layers (1.5-2.0 cells per mm2). Following infarction, the mast cell density at the subepicardial site of the infarction gradually increased, reaching a maximum of 25 cells per mm2 on day 21, while a non-significant increase was observed at the subendocardial site. In the non-infarcted regions, the mast cell density increased transiently to reach a maximum of 7 cells per mm2 on day 35 in the subepicardial layer. Again, changes in mast cell density in the subendocardial layer were non-significant. In the sham group, a gradual increase to 9 cells per mm2 on day 21 and a subsequent decrease to 5 cells per mm2 on day 85 were observed in the subepicardial layers. These findings indicate a massive accumulation of mast cells in the subepicardial layers of the infarcted region and a small but significant effect of the surgical procedure on cardiac mast cell deposition, especially in the outer layers of the left ventricle.

A simple, automatic method for morphometric analysis of the left ventricle in rats with myocardial infarction

Induction of acute myocardial infarction in the rat is an established model for studying effects of therapeutic interventions. Images of sections of the rat left ventricle, stained with nitroblue tetrazolium, were digitized and several parameters estimated by dedicated software on an image analyzer (IBAS 2.0). The method was tested on 7 rats with 48-hr-old myocardial infarction and 4 sham-operated controls. Infarct size can be evaluated by two largely used methods, based on area or on angular extension of the lesion. Results of the two methods are linearly correlated, but area calculations give values half of those obtained from angular extension. Five minutes were needed for a complete evaluation of a section of the left ventricle. Estimates of the parameters showed a relatively low between- and within-operator variability and a good correlation with a classic, but time-consuming, planimetric method. The method simultaneously measures infarct size and left ventricular geometry in the rat. The advantages over previous nonautomatic methods are simplicity, good reproducibility, and speed of execution, which make it particularly useful in the evaluation of drug effects.