Beneficial effects of cardiac chymase inhibition during the acute phase of myocardial infarction

Recently, the presence of the chymase-dependent angiotensin (Ang) II-generating system in hamsters, dogs, monkeys, as well as human cardiovascular tissues has been identified. We have reported that the activation of cardiac chymase was more prominent than that of angiotensin converting enzyme (ACE) and that AT1 receptor antagonist treatment rather than ACE inhibitor treatment alone provided significant beneficial effects on cardiac function and survival after MI in hamsters. The aim of the present study was to determine whether this different effects between AT1 receptor antagonist and ACE inhibitor were due to the activation of cardiac chymase after MI in hamsters by using 4-[1-[[bis-(4-methyl-pheny)-methyl]-carbamoyl]-3-(2-ethoxy-benzyl)-4-oxo-azetidine-2-yloxy]-benzoic acid (BCEAB), a novel, orally active and specific chymase inhibitor. The ACE and chymase activities in the infarcted left ventricle were significantly increased 3 days after MI. BCEAB (100 mg/kg/day, p.o.) treatment starting 3 days before MI significantly suppressed the cardiac chymase activity, while it did not affect the plasma and cardiac ACE activities 3 days after MI. A significant improvement in hemodynamics (maximal negative and positive rates of pressure development; left ventricular systolic pressure) was observed for the treatment with BCEAB 3 days after MI. BCEAB (100 mg/kg/day, p.o.) treatment starting 3 days before MI significantly reduced the mortality rate during 14 days of observation following MI (vehicle, 61.1%, n = 18; BCEAB, 27.8%, n = 18; P < 0.05). These findings demonstrated for the first time that cardiac chymase participates directly in the pathophysiologic state after MI in hamsters.     

Gender differences in cardiac function during early remodeling after acute myocardial infarction in mice

There are conflicting data about gender differences in cardiac function after myocardial infarction (MI), including cardiac rupture and mortality. Using a mouse model of MI, we recently found that the cardiac rupture rate during the first week after MI was significantly lower in females than in males, suggesting that females have attenuated structural remodeling. Thus in this study, we attempted to determine whether: a) females have attenuated remodeling and faster healing during the early phase post-MI, and b) females have better cardiac function and outcome during the chronic phase compared to males. MI was induced in 12-week-old male and female C57BL/6J mice. Signs of early remodeling, including cardiac rupture, infarct expansion, inflammatory response, and collagen deposition, were studied during the first 2 weeks post-MI. Left ventricular remodeling and function were followed for 12 weeks post-MI. We found that males had a higher rate of cardiac rupture, occurring mainly at 3 to 5 days of MI and associated with a higher infarct expansion index. Neutrophil infiltration at the infarct border was more pronounced in males than females during the first days of MI, which were also characterized by increased MMP activity. However, the number of infiltrating macrophages was significantly higher in females at day 4. During the chronic phase post-MI, males had significantly poorer LV function, more prominent dilatation and significant myocyte hypertrophy compared to females. In conclusion, males have delayed myocardial healing, resulting in cardiac rupture, and the survivors have poorer cardiac function and pronounced maladaptive remodeling, whereas females show a better outcome during the development of HF.     

Apela improves cardiac and renal function in mice with acute myocardial infarction

Apela was recently identified as a new ligand of the apelin peptide jejunum (APJ) receptor. The purpose of this study was to investigate the role of apela in post‐myocardial infarction (post‐MI) recovery from cardiorenal damage. A murine MI model was established, and apela was then infused subcutaneously for two weeks. Echocardiographs were performed before and after infarction at the indicated times. Renal function was evaluated by serum and urine biochemistry. Immunohistochemistry of heart and kidney tissue was performed by in situ terminal deoxynucleotidyl transferase‐mediated dUPT nick end‐labelling reaction. Compared to the control group (MI/vehicle), the average value of the left ventricular ejection fraction in apela‐treated mice increased by 32% and 39% at 2‐ and 4‐week post‐MI, respectively. The mean levels of serum blood urea nitrogen,creatinine, N‐terminal pro‐brain natriuretic peptide and 24‐hour urine protein were significantly decreased at 4‐week post‐MI in apela‐treated mice relative to that of control animals. At the cellular level, we found that apela treatment significantly reduced myocardial fibrosis and cellular apoptosis in heart and kidney tissue. These data suggest that apela improves cardiac and renal function in mice with acute MI. The peptide may be potential therapeutic agent for heart failure.     

Left ventricular rupture threshold during the healing phase after myocardial infarction in the dog

The mechanical resistance of the infarcted left ventricle to rupture, or rupture threshold, was measured by the balloon technique 1-42 days after left anterior descending coronary artery ligation in 70 dogs: 26 without infarction (18 sham, 8 with ligation) and 44 with infarction. Rupture threshold in noninfarcted hearts was higher than in infarcted hearts (1168 +/- 165 (SD) vs. 754 +/- 223 mmHg (1 mmHg = 133.32 Pa), p less than 0.001) and did not change over 6 weeks. In contrast, rupture threshold in infarcted hearts decreased (p less than or equal to 0.05) after 14 days, the average value for 21-42 days being less than that for 1-14 days: 577 +/- 140 vs. 867 +/- 191 mmHg, p less than 0.001. Passive left ventricular stiffness in infarcted hearts was higher than for noninfarcted hearts throughout the 6 weeks during early filling (11.1 +/- 3.9 vs. 7.1 +/- 1.4 mmHg/mL, p less than 0.001) but decreased (p less than or equal to 0.05) after 14 days during the prerupture phase (11.3 +/- 5.3 vs. 6.2 +/- 3.0 mmHg/mL, p less than 0.005). Between 7 and 42 days, the infarct zone showed marked increase in hydroxyproline (10.0 +/- 2.0 vs. 48.8 +/- 19.7 mg/g dry weight, p less than 0.001), shrinkage (infarct size, 25 +/- 9 vs. 9 +/- 5% of the left ventricle, p less than 0.005), and thinning (infarct to normal wall thickness ratio, 0.83 +/- 0.11 vs. 0.51 +/- 0.09, p less than 0.001) but little further stretching (expansion index or the ratio of lengths of infarcted and noninfarcted segments, 1.14 +/- 0.10 vs. 1.28 +/- 0.17, p less than 0.2). A mild decrease (p less than 0.05) in left atrial pressure and increase (p less than 0.05) in diastolic area and fractional change in area (two-dimensional echocardiography) were detected at 6 weeks. The late decrease in rupture threshold and prerupture stiffness of the infarcted left ventricle and thinning of the scar suggest a late decrease in mechanical strength and resistance of the infarcted left ventricle to distension.     

Transplantation of human villous trophoblasts preserves cardiac function in mice with acute myocardial infarction

Over the past decade, cell therapies have provided promising strategies for the treatment of ischaemic cardiomyopathy. Particularly, the beneficial effects of stem cells, including bone marrow stem cells (BMSCs), endothelial progenitor cells (EPCs), mesenchymal stem cells (MSCs), embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs), have been demonstrated by substantial preclinical and clinical studies. Nevertheless stem cell therapy is not always safe and effective. Hence, there is an urgent need for alternative sources of cells to promote cardiac regeneration. Human villous trophoblasts (HVTs) play key roles in embryonic implantation and placentation. In this study, we show that HVTs can promote tube formation of human umbilical vein endothelial cells (HUVECs) on Matrigel and enhance the resistance of neonatal rat cardiomyocytes (NRCMs) to oxidative stress in vitro. Delivery of HVTs to ischaemic area of heart preserved cardiac function and reduced fibrosis in a mouse model of acute myocardial infarction (AMI). Histological analysis revealed that transplantation of HVTs promoted angiogenesis in AMI mouse hearts. In addition, our data indicate that HVTs exert their therapeutic benefit through paracrine mechanisms. Meanwhile, injection of HVTs to mouse hearts did not elicit severe immune response. Taken together, our study demonstrates HVT may be used as a source for cell therapy or a tool to study cell‐derived soluble factors for AMI treatment.     

Testosterone enhances early cardiac remodeling after myocardial infarction, causing rupture and degrading cardiac function

Cardiac rupture can be fatal after myocardial infarction (MI). Experiments in animals revealed gender differences in rupture rate; however, patient data are controversial. We found a significantly higher rupture rate in testosterone-treated female mice within 1 wk after MI, whereas castration in males significantly reduced rupture. We hypothesized that testosterone may adversely affect remodeling after MI, exaggerating the inflammatory response and increasing cardiac rupture, whereas estrogen may be cardioprotective, attenuating early remodeling and reducing rupture rate. We studied the effect of gender and hormone manipulation on morphological and histological changes during early remodeling after MI in 4-wk-old male and female C57BL/6J mice and how these events could affect cardiac function. Females were randomly divided into 1) sham ovariectomy + placebo (s-ovx + P), 2) s-ovx + testosterone (T), 3) ovx + P, and 4) ovx + T; males were divided into 1) sham castration + P (s-cas + P), 2) s-cas + 17beta-estradiol (E), 3) cas + P, and 4) cas + E. At 6 wk after gonadectomy and hormone manipulation, MI was induced. Mice were randomly killed 1, 2, 4, 7, and 14 days after MI. The left ventricle was weighed and sectioned for evaluation of MI size, infarct expansion index (IEI), and neutrophil infiltration. Transthoracic echocardiography was performed in conscious mice in the 14-day group before organ harvest. Cardiac rupture rate and IEI were significantly higher in testosterone-treated females and noncastrated males than in controls; these effects were accompanied by enhanced neutrophil infiltration and pronounced deterioration of cardiac function and left ventricular dilatation. Ovariectomy in females and estrogen supplementation in males did not confer significant protection from cardiac rupture, IEI, or neutrophil infiltration. We concluded that, in mice, high testosterone levels enhance acute myocardial inflammation, adversely affecting myocardial healing and early remodeling, as indicated by increased cardiac rupture, and possibly causing deterioration of cardiac function after MI, and, conversely, estrogen seems to have no significant protective effect in the acute phase after MI.     

Temporal changes in matrix metalloproteinase expression and inflammatory response associated with cardiac rupture after myocardial infarction in mice

We previously found that male mice with myocardial infarction (MI) had a high rate of cardiac rupture, which generally occurred at 3 to 5 days after MI. Since matrix metalloproteinases (MMPs) play an important role in infarct healing, tissue repair and extracellular matrix (ECM) remodeling post-MI, we studied the temporal relationship of MMP expression and inflammatory response to cardiac rupture after acute MI. Male C57BL/6J mice were subjected to MI (induced by ligating the left anterior descending coronary artery) and killed 1, 2, 4, 7 or 14 days after MI. MMP-2 and MMP-9 activity in the heart were measured by zymography. Collagen content was measured by hydroxyproline assay. We found that after MI, MMP-9 activity increased as early as 1 day and reached a maximum by 2-4 days, associated with a similar increase in neutrophil and macrophage infiltration in the infarct area. MMP-2 started to increase rapidly within 4 days, reaching a maximum by 7 days and remaining high even at 14 days. Intense macrophage infiltration appeared by 4 days after MI and then gradually decreased within 7 to 14 days. Collagen content was unchanged until 4 days after MI, at which point it increased and remained high thereafter. Our data suggest that in mice, overexpression of MMP-2 and MMP-9 (possibly expressed mainly by neutrophils and macrophages) may lead to excessive ECM degradation in the early phase of MI, impairing infarct healing and aggravating early remodeling which in turn causes cardiac rupture.     

Thrombolysis for acute myocardial infarction: drug review

The proof of efficacy of thrombolysis for acute myocardial infarction (AMI) depends on 9 randomized placebo-controlled trials totaling 58,511 patients. The meta-analysis of these trials showed an overall survival advantage of about 2% (11.5% vs 9.6%) in favor of thrombolysis. Iatrogenic deaths from thrombolysis complications occur in about 1% of AMI patients. Timely opening of the infarct-related artery (IRA) allowing myocardial reperfusion has been proposed to explain any survival advantage seen with thrombolysis ("open-artery hypothesis"). Angiographic data does not support the open-artery hypothesis as the mechanism of any benefit of thrombolysis. The "early hazard" (ie, increased mortality in the first 12 hours after thrombolysis) also suggests that the supposed survival benefit is due to something other than early reperfusion. The variable use of aspirin in the meta-analysis trials may have confounded the results and conclusions. In the 4 studies of the meta-analysis in which aspirin was used routinely (n = 21,144), the survival benefit was not statistically significant (P =.14). Lack of blinding in some studies and other methodologic problems may also call the conclusions of the meta-analysis into question. AMI registry reports comparing patients with and without thrombolysis have not borne out a significant survival advantage with thrombolysis. The National Registry of Myocardial Infarction (NRMI) registry data suggest that a significant number of AMI patients may be inappropriately receiving thrombolytics. An independent analysis of the NRMI mortality data adjusted for age and other risk factors would help determine whether thrombolysis for AMI improves survival.     

Sex-related changes in cardiac function following myocardial infarction in mice

Recent awareness of cardiovascular diseases as a number one killer of the middle-aged women has prompted interest in sex differences leading to heart failure (HF). Therefore, we evaluated cardiac function in female and male mice following myocardial infarction (MI) using the Millar pressure-volume (P-V) conductance system in vivo, at time points corresponding to early (2 wk), late compensatory hypertrophy (4 wk), and decompensation (10 wk) to HF. A significant deterioration of the load dependent and independent hemodynamic measurements occurred in both female and male mice during the early phase of hypertrophy. Later, compensatory hypertrophy was marked by a normalization of volumes to control levels in females compared with males. The most notable differences between sexes occurred in the measurements of cardiac contractility during the decompensation to HF. In females, there was a significant improvement in contractility compared with males, which was apparent in the load-independent measurements of preload recruitable stroke work (10 wk post-MI, female=48.7+/-8.0 vs. male=25.2+/-1.8 mmHg, P<0.05) and maximum dP/dt vs. maximum end-diastolic volume (10 wk post-MI, female=359+/-58 vs. male=149+/-28 mmHg.s(-1).microl(-1), P<0.05). Despite these differences, there were no differences in the heart weight to body weight ratio and infarct size between the sexes. These data demonstrate that compensatory hypertrophy is associated with an improvement in contractility and a delayed decompensation to HF in females. However, compensatory hypertrophy in males appears to be undermined by a steady decline in contractility associated with decompensation to HF.     

Elafin-overexpressing mice have improved cardiac function after myocardial infarction

Elevated serine elastase activity after myocardial infarction can contribute to remodeling associated with left ventricular dilatation and dysfunction. We therefore assessed the effects of overexpressing the selective serine elastase inhibitor elafin in transgenic mice in which a myocardial infarction was caused by ligation of the left anterior descending coronary artery (LAD). Elevated serine elastase activity was observed in nontransgenic littermates as early as 6 h after LAD ligation and persisted at 4 and 7 days but not in sham-operated or elafin-overexpressing transgenic mice. Myeloperoxidase activity (index of inflammatory cells) and matrix metalloproteinase 2 were also increased but only at 4 and 7 days and only in nontransgenic mice (P < 0.05 for both comparisons), and this increase correlated with inflammatory cell infiltration. Echocardiographic study at 4 days revealed indexes of diastolic dysfunction in nontransgenic versus elafin-overexpressing mice (P < 0.05). Morphometric and biochemical analyses at 28 days indicated impairment in cardiac performance, with greater scar thinning and infarct expansion in nontransgenic versus elafin transgenic littermates (P < 0.05 for all comparisons). Thus serine elastase inhibition appears to suppress inflammation, cardiac dilatation, and dysfunction after myocardial infarct.     

Features of myocardial remodeling in the most acute phase of experimental myocardial infarction

The features of early postischemic cardiac remodeling have been well studied both in clinical settings and in experiments. However, the data on the course of this process in the first 60 min after occlusion are scarcely available in the literature. In experiments on rats, in which acute myocardial ischemia was reproduced by one-stage ligation of the left coronary artery, echocardiography showed a sharp decline in the left ventricular systolic function during the first minutes of ischemia: after 20 min, the ejection fraction (EF) decreased from 84.5 (79.3?C89.2) to 51.7 (50.2?C54.4)%, p < 0.05; the shortening fraction (SF) decreased from 52.6 (47.8?C59.3) to 26.5 (25.9?C28.1)%, p < 0.05; and the end-systolic dimension (ESD) of the left ventricle of the heart increased from 1.90 (1.70?C2.20) to 3.80 (3.50?C4.10) mm, p < 0.05, whereas no statistically significant disorder of the left ventricular systolic function was observed in sham-operated animals during the observation period (60 min). A gradual relative improvement in the systolic function has been observed in the period from the 20th to the 60th minute of ischemia. After 60 min of ischemia, all the echocardiographic parameters differed significantly (p < 0.05) from those recorded after 10?C20 min of the ischemic period: EF, 62.4 (59.0?C64.3)%; SF, 33.7 (31.1?C35.2)%; ESD, 3.10 (2.80?C3.40) mm, etc. The analysis of the results suggests that the maximum reduction in the left ventricular EF observed in our experiments coincides in time with the arrhythmogenesis peak, i.e., with the maximal risk of sudden cardiac death.     

Inhibition of NOS II prevents cardiac dysfunction in myocardial infarction and congestive heart failure

Strong expression of the inducible form of nitric oxide synthase (NOS II) has been shown in the myocardium of patients with myocardial infarction (MI). We hypothesized that NOS II plays an important role in the development of MI and subsequent heart failure and that inhibition of NOS II may beneficially alter the course of the disease. Long-term administration (2 mo) of the selective NOS II inhibitor S-methylisothiourea (SMT) to rats with MI significantly improved cardiac function. A significant drop in mortality, lung water content, infarct size, and cardiomyocyte hypertrophy was also associated with the use of SMT. Plasma concentration of nitrite and nitrate was also reduced by SMT. Short-term administration of SMT (first 2 wk only) significantly reduced infarct size; however, it did not improve cardiac dysfunction measured 2 mo after MI. These findings demonstrate that induction of NOS II during MI exerts negative effects on cardiac function and structure. Long-term administration of a selective NOS II inhibitor may prove to be beneficial in the treatment of MI and congestive heart failure.     

Identification of drug repurposing candidates based on a miRNA-mediated drug and pathway network for cardiac hypertrophy and acute myocardial infarction

Background

Cardiac hypertrophy and acute myocardial infarction (AMI) are two common heart diseases worldwide. However, research is needed into the exact pathogenesis and effective treatment strategies for these diseases. Recently, microRNAs (miRNAs) have been suggested to regulate the pathological pathways of heart disease, indicating a potential role in novel treatments.

Results

In our study, we constructed a miRNA-gene-drug network and analyzed its topological features. We also identified some significantly dysregulated miRNA-gene-drug triplets (MGDTs) in cardiac hypertrophy and AMI using a computational method. Then, we characterized the activity score profile features for MGDTs in cardiac hypertrophy and AMI. The functional analyses suggested that the genes in the network held special functions. We extracted an insulin-like growth factor 1 receptor-related subnetwork in cardiac hypertrophy and a vascular endothelial growth factor A-related subnetwork in AMI. Finally, we considered insulin-like growth factor 1 receptor and vascular endothelial growth factor A as two candidate drug targets by utilizing the cardiac hypertrophy and AMI pathways.

Conclusion

These results provide novel insights into the mechanisms and treatment of cardiac hypertrophy and AMI.

     

G-CSF prevents cardiac remodeling after myocardial infarction by activating the Jak-Stat pathway in cardiomyocytes

Granulocyte colony-stimulating factor (G-CSF) was reported to induce myocardial regeneration by promoting mobilization of bone marrow stem cells to the injured heart after myocardial infarction, but the precise mechanisms of the beneficial effects of G-CSF are not fully understood. Here we show that G-CSF acts directly on cardiomyocytes and promotes their survival after myocardial infarction. G-CSF receptor was expressed on cardiomyocytes and G-CSF activated the Jak/Stat pathway in cardiomyocytes. The G-CSF treatment did not affect initial infarct size at 3 d but improved cardiac function as early as 1 week after myocardial infarction. Moreover, the beneficial effects of G-CSF on cardiac function were reduced by delayed start of the treatment. G-CSF induced antiapoptotic proteins and inhibited apoptotic death of cardiomyocytes in the infarcted hearts. G-CSF also reduced apoptosis of endothelial cells and increased vascularization in the infarcted hearts, further protecting against ischemic injury. All these effects of G-CSF on infarcted hearts were abolished by overexpression of a dominant-negative mutant Stat3 protein in cardiomyocytes. These results suggest that G-CSF promotes survival of cardiac myocytes and prevents left ventricular remodeling after myocardial infarction through the functional communication between cardiomyocytes and noncardiomyocytes.     

Fatigue and plaque rupture in myocardial infarction

Plaque rupture plays a role in the majority of acute coronary syndromes. Rupture has been associated with stress concentrations, which are affected by tissue properties and anatomy. In this study rupture was not approached as an acute syndrome, but rather as the culmination of a chronic injury or fatigue process. The aim of our study was to investigate the impact of anatomy, tissue properties, and blood pressure on a fatigue mechanism. Incremental crack propagation was dynamically simulated based on evolving stress distributions. Stresses were resolved by a finite element solver, using vessel stiffness properties derived from in vivo data. Plaque fatigue crack growth per pressure pulse was estimated using an adapted Paris-relation. It was demonstrated that cracks begin at the lumen wall at areas of stress concentration, depending on the shape of the lumen, thickness of the fibrous cap and stiffness of the plaque components. Mean or pulse pressure did not affect initiation location. Cracks extended radially and grew at a rate that was highly dependent on both mean and pulse pressure and on lipid stiffness. Rupture rate depended on blood pressure and lipid stiffness. It was concluded that a fatigue mechanism in a pulsatile cardiovascular pressure environment reconciles clinical evidence of acute plaque rupture at seemingly low stress levels, and it could provide a framework for developing strategies to create a biomechanically benign environment which is least conducive to plaque rupture.     

Effects of G-CSF on cardiac remodeling after acute myocardial infarction in swine

We examined whether granulocyte colony-stimulating factor (G-CSF) prevents cardiac dysfunction and remodeling after myocardial infarction (MI) in large animals. MI was produced by ligation of left anterior descending coronary artery in swine. G-CSF (10 microg/kg/day, once a day) was injected subcutaneously from 24h after ligation for 7 days. Echocardiographic examination revealed that the G-CSF treatment induced improvement of cardiac function and attenuation of cardiac remodeling at 4 weeks after MI. In the ischemic region, the number of apoptotic endothelial cells was smaller and the number of vessels was larger in the G-CSF treatment group than in control group. Moreover, vascular endothelial growth factor was more abundantly expressed and Akt was more strongly activated in the ischemic region of the G-CSF treatment group than of control group. These findings suggest that G-CSF prevents cardiac dysfunction and remodeling after MI in large animals.     

Role of coronary artery bypass grafting during the acute and subacute phase of ST-elevation myocardial infarction

Background/Objectives. We aimed to investigate the incidence and clinical outcome of coronary artery bypass grafting (CABG) performed in contemporary patients with ST-elevation myocardial infarction (STEMI) within 30 days after presentation. Methods. All 1071 patients enrolled in the Thrombus Aspiration during Percutaneous coronary intervention in Acute myocardial infarction Study (TAPAS) were included in this analysis. CABG was indicated for both ischaemic and anatomical reasons according to the current treatment guidelines for STEMI. For all surgical as well as non-surgical patients, clinical outcome was assessed at both 30 days and one year. Results. CABG was performed within 30 days of presentation in 59/1071 (5.5%) patients, in 13 (22%) within 24 hours, in eight (14%) between one and three days, and in 38 (64%) between four and 30 days. Compared with non-surgical patients, surgical patients required more initial intra-aortic balloon pump support (33 vs. 5%, p<0.001) and more often had multi-vessel disease (p<0.001). Overall, rethoracotomy was performed in 9/59 (15%) patients. In patients operated within three days, the rethoracotomy rate was markedly higher than after three days (33 vs. 5%, p=0.004). Cardiac mortality at 30 days and one year was 1.7% in the surgical group and 3.2 and 5.3%, respectively, in the non-surgical group. Conclusion. STEMI patients treated with CABG within three days after presentation are at increased risk of rethoracotomy. However, despite this higher incidence of surgical complications and multiple high-risk features at presentation, surgical management during the acute and subacute phase is associated with excellent 30-day and one-year survival. (Neth Heart J 2010;18:348-54.)