Relation of early mononuclear and polymorphonuclear cell infiltration to late scar thickness after experimentally induced myocardial infarction in the rat

Ultrasonic Cavitation-Enabled Treatment for Therapy of Hypertrophic Cardiomyopathy: Proof of Principle

Ultrasound myocardial cavitation-enabled treatment was applied to the SS-16^BN rat model of hypertrophic cardiomyopathy for proof of the principle underlying myocardial reduction therapy. A focused ultrasound transducer was targeted using 10-MHz imaging (10 S, GE Vivid 7) to the left ventricular wall of anesthetized rats in a warmed water bath. Pulse bursts of 4-MPa peak rarefactional pressure amplitude were intermittently triggered 1:8 heartbeats during a 10-min infusion of a microbubble suspension. Methylprednisolone was given to reduce initial inflammation, and Losartan was given to reduce fibrosis in the healing tissue. At 28 d post therapy, myocardial cavitation-enabled treatment significantly reduced the targeted wall thickness by 16.2% (p <0.01) relative to shams, with myocardial strain rate and endocardial displacement reduced by 34% and 29%, respectively, which are sufficient for therapeutic treatment. Premature electrocardiogram complexes and plasma troponin measurements were found to identify optimal and suboptimal treatment cohorts and would aid in achieving the desired impact. With clinical translation, myocardial cavitation-enabled treatment should fill the need for a new non-invasive hypertrophic cardiomyopathy therapy option.

Multiple ultrasound cavitation-enabled treatments for myocardial reduction

Background

Ultrasound myocardial cavitation enabled treatment (MCET) is an image-guided method for tissue reduction. In this study, a strategy of fractionated (multiple) treatments was tested for efficacy.

Methods

Dahl SS rats were anesthetized and prepared for treatment with a focused ultrasound transducer in a warm water bath. Aiming at the anterior left ventricular wall was facilitated by imaging with a 10 MHz phased array (10S, GE Vivid 7, GE Vingmed Ultrasound, Horten, Norway). MCET was accomplished at 1.5 MHz by pulse bursts of 4 MPa peak rarefactional pressure amplitude, which were intermittently triggered 1:8 from the ECG during infusion of a microbubble suspension for cavitation nucleation. Test groups were sham, a 200 s treatment, three 200 s treatments a week apart, and a 600 s treatment. Treatment outcome was observed by plasma troponin after 4 h, echocardiographic monitoring and histology at 6 wk.

Results

The impacts of the fractionated treatments summed to approximately the same as the long treatment; e. g. the troponin result was 10.5 ± 3.2 for 200 s, 22.7 ± 5.4 (p < 0.001) for the summed fractionated treatments and 29.9 ± 6.4 for 600 s (p = 0.06 relative to the summed fractionated). While wall thickness was not reduced for the fractionated treatment, tissue strain was reduced by 35% in the target area relative sham (p < 0.001).

Conclusion

The ability to fractionate treatment may be advantageous for optimizing patient outcome relative to all-or nothing therapy by surgical myectomy or alcohol ablation.

Maturation of Lesions Induced by Myocardial Cavitation-Enabled Therapy

Myocardial contrast echocardiography at enhanced therapeutic parameters may be a novel means of tissue reduction therapy, as for hypertrophic cardiomyopathy. Dahl/SS rats were anesthetized and treated with high-amplitude pulsed ultrasound guided by 10-MHz ultrasound images. Contrast microbubbles were infused via the tail vein during intermittent pulse-burst exposure at 4 MPa. A sham group, a low-impact group (group A, 5 cycle pulses with Gaussian modulation and 1:4 trigger for 5 min) and a high-impact group (group B, 10 cycle pulses with 4-ms square modulation and 1:8 trigger for 10 min) were tested. The higher exposure used in group B yielded more substantial injury than the lower exposure in group A. Treated rats in both groups A and B had significant increases in wall thickness measured by echocardiography the next day, which returned to normal by the end of 6 wk. Six weeks after ultrasound exposure, heart tissue samples exhibited tissue fibrosis in Masson's trichrome stained histology. Maturation of lesions involved fibrosis replacement, preserving structural tissue integrity. This study indicates that myocardial injury noted previously progresses into permanent loss of myocardial tissue that may be sufficient for possible hypertrophic cardiomyopathy therapy. More research is needed to define the treatment parameters required for symptomatic relief for hypertrophic cardiomyopathy.

Monocyte and macrophage subsets along the continuum to heart failure: Misguided heroes or targetable villains?

The important contribution of monocytes and macrophages to cardiovascular disease and heart failure pathophysiology has attracted significant attention in the past several years. Moreover, subsets of these cells have been shown to partake in the initiation and exacerbation of several cardiovascular pathologies including atherosclerosis, myocardial infarction, pressure overload, cardiac ischemia and fibrosis. This review focuses on the role of monocytes and macrophages along the continuum to heart failure and the contribution of different cell subsets in promoting or inhibiting cardiac injury or repair. It outlines a primary role for the monocyte/macrophage system as an important regulator of cardiac inflammation and extracellular matrix remodelling in early and late stage heart disease with particular focus on phenotypic plasticity and the inflammatory and fibrotic functions of these cells. It also summarizes evidence from pre-clinical and clinical studies evaluating monocyte type regulation and its functional significance for development of cardiovascular disease and heart failure. Finally, current and prospective therapeutic approaches based on monocyte and macrophage manipulation for the treatment of cardiovascular disease and heart failure are discussed. Based on these data, future work in this fertile research area may aid in identifying potential diagnostic biomarkers and novel therapies for chronic heart failure.

Mesenchymal-stem-cell-based experimental and clinical trials: current status and open questions

INTRODUCTION

Mesenchymal stem cells (MSCs) possess remarkable self-renewal ability and are able to differentiate into various cell lineages. MSCs can also enhance tissue repair and angiogenesis through a paracrine mechanism. It has been recognized that these cells hold great promise for tissue regeneration and treatment of immune-related diseases.

AREAS COVERED

This review aims at discussing the mechanisms of MSC-mediated immunomodulation and tissue repair and the related clinical trials, with special emphasis on factors that influence the efficiency of MSC-based therapy, including the source of MSCs, cell passage, cell dose, timing and route of administration.

EXPERT OPINION

MSCs may facilitate tissue repair through cell replacement and/or improving the microenvironment by releasing growth factors. Some of these factors also mediate the immunomodulatory effects of MSCs. It is important to establish global guidelines, protocols and standards for production and clinical trials of MSCs, so that MSCs can become a therapeutic agent with a reliable efficacy and good safety.

Monocytes in heart failure: relationship to a deteriorating immune overreaction or a desperate attempt for tissue repair?

Monocytes play an important role in immune defence, inflammation, and tissue remodelling. Nevertheless, the role of monocytes in cardiovascular disease is obscure. Indeed, monocytes infiltrate dysfunctional tissue and augment tissue damage and are actively involved in tissue regeneration and healing. In support of the latter, recent studies have provided data on the functional and structural plasticity of monocytes. Monocytes are also actively involved in processes associated with tissue regeneration such as angiogenesis and vasculogenesis, either by producing pro-angiogenic factors or even by evolving to structural components of the vascular wall. This review article provides an overview on whether monocytes represent deteriorating immune overreaction in heart failure (HF), or a desperate attempt for tissue repair or physiological compensation in the failing heart. Perhaps, it is time to reconsider our attitude towards monocytes and consider more 'monocyte activation' rather than 'monocyte suppression' as a potential therapeutic target in HF.

Inhibition of tumor necrosis factor receptor-1-mediated pathways has beneficial effects in a murine model of postischemic remodeling

The aim of the present study was to investigate the importance of tumor necrosis factor (TNF)-alpha receptor-1 (TNFR1)-mediated pathways in a murine model of myocardial infarction and remodeling. One hundred and ninety-four wild-type (WT) and TNFR1 gene-deleted (TNFR1KO) mice underwent left coronary artery ligation to induce myocardial infarction. On days 1, 3, 7, and 42, mice underwent transesophageal echocardiography. Hearts were weighed, and the left ventricle (LV) was assayed for matrix metalloproteinase (MMP)-2 and -9 activity and for tissue inhibitor of MMP (TIMP)-1 and -2 expression. Deletion of the TNFR1 gene substantially improved survival because no deaths were observed in TNFR1KO mice versus 56.4% and 18.2% in WT males and females, respectively (P < 0.002). At 42 days, LV remodeling, assessed by LV function (fractional area change of 31.9 +/- 7.9%, 32.2 +/- 7.7%, and 21.6 +/- 7.1% in TNFR1KO males, TNFR1KO females, and WT females, respectively, P < 0.04), and hypertrophy (heart weight-to-body weight ratios of 5.435 +/- 0.986, 5.485 +/- 0.677, and 6.726 +/- 0.704 mg/g, P < 0.04) were ameliorated in TNFR1KO mice. MMP-9 activity was highest at 3 days postinfarction and was highest in WT males (1.9 +/- 0.4 4, 3.6 +/- 0.24, 1.15 +/- 0.28, and 1.3 +/- 1.2 ng/100 microg protein, respectively, in TNFR1KO males, WT males, TNFR1KO females, and WT females, respectively, P < 0.002), whereas at 3 days TIMP-1 mRNA fold upregulation compared with type- and sex-matched controls was lowest in WT males (138.32 +/- 13.05, 46.74 +/- 5.43, 186.09 +/- 28.07, and 101.76 +/- 22.48, respectively, P < 0.002). MMP-2 and TIMP-2 increased similarly in all infarcted groups. These findings suggest that the benefits of TNFR1 ablation might be attributable at least in part to the attenuation of cytokine-mediated imbalances in MMP-TIMP activity.

Gene expression and in situ localization of diacylglycerol kinase isozymes in normal and infarcted rat hearts: effects of captopril treatment

Diacylglycerol (DG) kinase (DGK) terminates signaling from DG, which serves as an activator of protein kinase C (PKC), by converting DG to phosphatidic acid. DGK is thus regarded as an attenuator of the PKC activity. In rats, five DGK isozymes have been cloned, but little is known about their role in the heart. In this study, the spatiotemporal expression of DGK isozymes was investigated in rat hearts under a normal condition and after myocardial infarction (MI) by in situ hybridization histochemistry and immunohistochemistry. In normal left ventricular myocardium, DGKalpha, DGKepsilon, and DGKzeta mRNAs were expressed evenly throughout the myocardium, although the DGKalpha expression was very low. In infarcted hearts, the expression of DGKzeta was enhanced in the peripheral zone of the necrotic area and at the border zone 3 and 7 days after MI, and to a lesser extent in the middle layer of the granulation tissue 21 days after MI. The enhanced DGKzeta expression in the infarcted and border areas could be attributed to granulocytes and macrophages. In contrast, the expression of DGKepsilon in the infarcted and border areas was lower than that in the viable left ventricle (LV) throughout the postoperation period. Furthermore, DGKepsilon expression in the viable myocardium 21 days after MI decreased significantly compared with left ventricular myocardium in the sham-operated rats and was completely restored by treatment with captopril. Our results demonstrate that three DGK isozymes are expressed in the heart and that each isozyme might have different functional characteristics in the healing and LV remodeling after MI.

Ventricular remodeling after acute myocardial infarction: effect of low-intensity laser irradiation

BACKGROUND AND OBJECTIVE

Low-intensity laser irradiation is claimed to enhance wound healing. Healing after myocardial infarction results in ventricular enlargement and wall thinning. If laser treatment accelerated cardiac healing, we speculated that ventricular remodeling would be attenuated.

STUDY DESIGN/MATERIALS AND METHODS

In vitro, fibroblasts were irradiated for 1 minute twice a day for 4 days (5 mW; wavelength, 780 nm). One day after infarction, rats were randomly assigned to 5 or 10 mW transdermal irradiation twice a day for 4 days or to sham. One week after infarction, we measured the remodeling parameters; cavity volume, infarct thickness, and vascular structure, and the healing parameters; collagen content and inflammation.

RESULTS

Laser-treated fibroblasts occupied more area than controls. Hearts receiving the 10 mW treatment had smaller volumes than sham hearts. Laser treatment reduced infarct thinning and preserved arterial lumen area; however, collagen was not increased and inflammation was inhibited.

CONCLUSIONS

Low-intensity irradiation attenuated infarct-associated remodeling. In contrast to expectations from in vitro study, these effects were not a result of enhanced healing.

Reperfusion injury after focal myocardial ischaemia: polymorphonuclear leukocyte activation and its clinical implications

The only way to rescue ischaemic tissue is to re-instate the oxygen supply to the tissue. However reperfusion of the ischaemic area not only oxygenates the tissue but also initiates a cascade of processes, which may in some cases result in temporary dysfunction of the myocardium. In order to devise protective measures, it is essential to understand the mechanisms and the triggers of this reperfusion phenomenon. In this review we will mainly focus on the inflammatory response caused by reperfusion. We will cover the different steps of polymorphonuclear leukocyte activation and will briefly discuss the molecular biology of the receptors involved. The currently used pharmacological medications in acute cardiology will be reviewed and in particular their actions on polymorphonuclear leukocyte activation, adhesion and degranulation. This review is a compilation of the current knowledge in the field and the therapeutic progress in the prevention of reperfusion injury made today.

Myocardial neutrophil infiltration, lipid peroxidation, and antioxidant activity after coronary artery thrombosis and thrombolysis

Neutrophil accumulation and free radical release are implicated in the genesis of reperfusion injury. However, little is known about the changes in myocardial lipid peroxidation and antioxidant activity in relation to coronary artery thrombosis and thrombolysis. To investigate this issue, 18 dogs with electrically induced occlusive thrombus in the left anterior descending (LAD) coronary artery were given tissue-type plasminogen activator (TPA). Sustained reflow (lasting > 120 min) occurred in 4 dogs, reocclusion after initial thrombolysis (transient reflow, duration of reflow 5 to 25 min) occurred in 7 dogs, and no reperfusion was evident in 7 dogs. Myocardial neutrophil infiltration was determined by measuring myeloperoxidase (MPO) activity, lipid peroxidation by malondialdehyde (MDA) levels and antioxidant activity by superoxide dismutase (SOD) activity in the myocardial regions supplied by the nonischemic left circumflex (Cx) and the ischemic LAD coronary arteries. In dogs with ischemia alone (no reperfusion), MPO activity and MDA levels in the LAD-supplied myocardium were modestly higher and SOD activity modestly lower than in the corresponding Cx-supplied myocardium. In dogs with sustained reperfusion there was a marked increase in MPO and MDA and a marked reduction in SOD activity in the reperfused myocardium. The MPO and MDA values in the myocardium of dogs with transient reperfusion, although much higher than the corresponding normal myocardial values, were less marked than in the myocardium of dogs with sustained reperfusion, and the SOD activity was preserved in the transiently reperfused regions. Myocardial shortening fraction in the LAD region was worse in dogs with sustained reperfusion than in those with sustained ischemia or transient reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation of proteins in rat heart and lungs by polymorphonuclear leukocyte oxidants

The ability of the polymorphonuclear leukocyte (PMN) oxidants, hypochlorous acid (HOC1) and hydrogen peroxide (H2O2), to oxidize proteins in rat heart and lung tissues was investigated. Cardiac myocytes, heart tissue slices, isolated perfused hearts, and lung tissue slices, were treated with HOC1 and H2O2 and the extent of methionine and cysteine oxidation was determined in the cellular proteins. Cardiac tissues were found to be highly susceptible to oxidation by physiological concentrations of HOC1. For example, in isolated hearts perfused for 60 min with 100 microM HOC1, approximately 18% of the methionine and 28% of the cysteine residues were oxidized. Lung tissues, unlike those of the heart, were resistant to physiological concentrations of HOC1, showing no oxidation of proteins. HOC1 was much more effective than H2O2 in oxidizing proteins, suggesting that HOC1 may be the most reactive oxidant produced by activated PMN. These studies show that PMN oxidants, in particular HOC1, can cause significant oxidation of proteins in target tissues, and may therefore constitute a primary cause of tissue injury at sites of inflammation. In addition, these studies show that different tissues may have varying susceptibilities to PMN oxidants.

Superoxide dismutase does not cause scar thinning after myocardial infarction

Previous studies demonstrated that treatment with superoxide dismutase, a scavenger of superoxide anions, limits the extent of myocardial injury in a canine preparation of regional myocardial ischemia and reperfusion. Little is known, however, about the effects of superoxide dismutase on the healing of a myocardial infarct. Therefore, this study was performed to determine whether treatment with superoxide dismutase during myocardial ischemia impairs formation of scar tissue after infarction. Dogs received 2 hour infusions of superoxide dismutase or albumin (controls) by way of the left atrium beginning 15 minutes before and ending 15 minutes after a 90 minute occlusion of the left circumflex coronary artery. Six weeks later the animals were killed. Two-dimensional echocardiography was performed before surgery and before induced death. Wall thickening in the central ischemic zone was decreased at 6 weeks compared with baseline studies (p less than 0.05), but the decrease was similar for both groups. The hydroxyproline concentrations (microgram/mg dry weight) of the scar tissue in the superoxide dismutase and control groups, respectively, were 35.3 +/- 3.8 and 28.7 +/- 5.0 (p less than 0.05). The ratios of the scar thickness to normal wall thickness were superoxide dismutase 0.91 +/- 0.03 and control 0.89 +/- 0.03 (p greater than 0.05). Thus, superoxide dismutase had no adverse effect on wall thickening or scar formation assessed 6 weeks after myocardial infarction, and may be useful to limit oxygen radical-mediated damage during reperfusion of the ischemic myocardium.