Shiro Iwanaga

Targeted deletion or pharmacological inhibition of MMP-2 prevents cardiac rupture after myocardial infarction in mice

MMPs are implicated in LV remodeling after acute myocardial infarction (MI). To analyze the role of MMP-2, we generated MI by ligating the left coronary artery of MMP-2-KO and WT mice, the latter of which were administered orally an MMP-2-selective inhibitor or vehicle (TISAM). The survival rate was significantly higher in MMP-2-KO and TISAM-treated mice than in control WT mice. The main cause of mortality in control WT mice was cardiac rupture, which was not observed in MMP-2-KO or TISAM-treated mice. Control WT mice, but not MMP-2-KO or TISAM-treated mice, showed activation of the zymogen of MMP-2, strong gelatinolytic activity, and degradation of ECM components, including laminin and fibronectin, in the infarcted myocardium. Although infarcted cardiomyocytes in control WT mice were rapidly removed by macrophages, the removal was suppressed in MMP-2-KO and TISAM-treated mice. Macrophage migration was induced by the infarcted myocardial tissue from control WT mice and was inhibited by treatment of macrophages with laminin or fibronectin peptides prior to migration assay. These data suggest that inhibition of MMP-2 activity improves the survival rate after acute MI by preventing cardiac rupture and delays post-MI remodeling through a reduction in macrophage infiltration.

Interleukin-6/soluble interleukin-6 receptor complex reduces infarct size via inhibiting myocardial apoptosis.

Apoptosis of cardiomyocytes plays an important role in reperfusion injury following myocardial infarction. Conversely, interleukin-6 (IL-6)—a potent cytokine—inhibits myeloma cell apoptosis by activating GP130 through the IL-6 receptor (IL-6R). We hypothesized that the IL-6/soluble IL-6R complex can inhibit myocardial apoptosis, and limit infarct size in reperfused acute myocardial infarction. Anesthetized rats were randomly divided into five groups: sham, coronary occlusion and reperfusion rats administered IL-6/soluble IL-6R complex, IL-6 alone, soluble IL-6R (sIL-6R) alone, or a control vehicle. Rats were subjected to 30u2009min occlusion of the left coronary artery followed by 3u2009h reperfusion. After reperfusion, the hearts were excised. For detection and quantification of apoptosis, gel electrophoresis of extracted genomic DNA and TUNEL method of paraffin sections were performed. The percentage of the infarct area was measured using tetrazolium chloride staining. The cardiomyocyte apoptosis analysis revealed that apoptosis in the reperfused myocardium was inhibited only in the complex group. Furthermore, the percentage of the infarct area out of the area at risk was remarkably reduced in the complex group (23.8±1.8%), compared with that in the vehicle (37.9±3.7%), the IL-6 (40.7±1.0%), or the sIL-6R (37.5±2.4%) groups (P=0.0002). No significant differences were observed among the vehicle, IL-6, and sIL-6R groups. The IL-6/soluble IL-6 receptor complex inhibits cardiomyocyte apoptosis in reperfused acute myocardial infarction. It possibly reduces irreversible reperfusion injury.

A real-time three-dimensional echocardiographic quantitative analysis of left atrial function in left ventricular diastolic dysfunction.

The evaluation of left ventricular diastolic function provides important information about hemodynamics and has prognostic implications for various cardiac diseases. In particular, left atrial (LA) volume is an increasingly significant prognostic biomarker for diastolic dysfunction. The aim of this study was to assess left ventricular diastolic function by measuring changes in LA volume using real-time 3-dimensional echocardiography. The 106 subjects were divided into 4 groups (normal, impaired relaxation, pseudonormal, and restrictive) on the basis of diastolic function, as assessed by transmitral flow patterns. LA volume was measured during a heart cycle using real-time 3-dimensional echocardiography. LA stroke volume (maximum LA volume - minimum LA volume) and the LA ejection fraction (LA stroke volume/maximum LA volume x 100) were calculated using Doppler imaging to assess their correlation with other parameters used to evaluate left ventricular diastolic function, including transmitral flow pattern and early diastolic mitral annular velocity (E). LA volume indexed to body surface area was dilated in subjects with left ventricular diastolic dysfunction, whereas the LA ejection fraction was lower. The maximum LA volume, minimum LA volume, and LA ejection fraction were significantly different between each group, and each was significantly correlated with the ratio of early diastolic transmitral flow velocity (E) to E (E/E). The LA ejection fraction correlated best with E/E (r = -0.68, p <0.0001). In conclusion, cyclic changes in LA volume could be measured using real-time 3-dimensional echocardiography, and measuring LA function with this method may be a viable alternative for the accurate assessment of left ventricular diastolic function.

Gated single-photon emission tomography imaging protocol to evaluate myocardial stunning after exercise

Abstract. This study was designed to apply ECG-gating to stress myocardial perfusion single-photon emission tomography (SPET) for the evaluation of myocardial stunning after exercise. Technetium-99m sestamibi was selected as the perfusion agent and a rest/exercise 1-day protocol was employed. Fourteen patients without coronary stenosis and 33 patients with coronary stenosis were enrolled in the study. We carried out three data acquisitions with ECG-gating: a 15-min data acquisition starting 30 min after the rest injection (AC1), a 5-min acquisition starting 5 min after the stress injection (AC2) and a 15-min acquisition starting 20 min after the stress injection (AC3). Calculation of left ventricular ejection fraction (LVEF) values was performed by means of automatic determination of the endocardial surface for all gating intervals in the cardiac cycle. Measured global EF values in 14 patients without coronary stenosis were 52.3%±7.6% (AC1), 60.6%±8.9% (AC2) and 55.6%± 5.6% (AC3), and those in 11 patients with severe ischaemia were 53.6%±8.0% (AC1), 45.6%±12.1% (AC2) and 49.7%±10.7%. The magnitude of the depression of post-stress LVEF relative to the rest LVEF correlated with the severity of ischaemia (r=0.594, P=0.002), and segments manifesting post-stress functional depression were associated with ischaemic segments showing reversible perfusion defects. Stress myocardial perfusion SPET with ECG-gating is a feasible method for the evaluation of myocardial stunning as well as exercise-induced ischaemia.

Clinical evaluation of the use-dependent QRS prolongation and the reverse use-dependent QT prolongation of class I and class III antiarrhythmic agents and their value in predicting efficacy.

We measured the QRS duration during a treadmill exercise test and the QT interval using a 24-hour Holter electrocardiogram at various heart rates to identify use-dependent QRS prolongation and reverse use-dependent QT prolongation of class I and III antiarrhythmic drugs. Use-dependent QRS prolongation was detected in 61%, 53%, and 64% of patients receiving disopyramide, mexiletine, and pilsicainide, respectively. Reverse use-dependent QT prolongation was found in 40% and 70% of patients receiving disopyramide and E4031. Drugs suppressed > or = 75% of the total premature ventricular contractions in all patients who had both use-dependent QRS prolongation and reverse use-dependent QT prolongation, in 79% of patients with use-dependent QRS prolongation alone, in 70% with reverse use-dependent QT prolongation alone, and in 11% with neither use-dependent QRS prolongation nor reverse use-dependent QT prolongation. Use-dependent QRS prolongation and reverse use-dependent QT prolongation were identified noninvasively and were useful in evaluating antiarrhythmic efficacy.

Quantitative Analysis of Right Ventricular Function in Patients With Pulmonary Hypertension Using Three-Dimensional Echocardiography and a Two-Dimensional Summation Method Compared to Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is considered the clinical reference standard for measuring the right ventricular (RV) volume and ejection fraction, although real-time 3-dimensional echocardiography (RT3DE) would be a preferred method owing to its convenience and availability for repetitive examinations. However, the feasibility, accuracy, and reproducibility of RT3DE have not been fully examined. The present study sought to validate the correlation of RT3DE with a 2-dimensional summation method compared to MRI for assessing the function of the right ventricle and to evaluate the RV function in patients with pulmonary hypertension (PH). Thirty patients with PH underwent both RT3DE and MRI. The right ventricle was reconstructed with RT3DE using a 2-dimensional summation method to analyze the MRI measurements. The RV end-diastolic volume, RV end-systolic volume, and RV ejection fraction were measured. Fifteen normal subjects underwent the same echocardiographic protocol for comparison. The RV end-diastolic volume index, RV end-systolic volume index, and RV ejection fraction measured using RT3DE correlated well with those measured using MRI (R = 0.96, p <0.001; R = 0.96, p <0.001; p = 0.93, and p <0.001, respectively). All inter- and intraobserver variability values for the RV end-diastolic volume, RV end-systolic volume, and RV ejection fraction were <17%. Both the RV end-diastolic volume index and the RV end-systolic volume index were significantly enlarged in those with PH compared to those in the normal subjects (RVEDVI 123 ± 42 ml/m² vs 74 ± 12 ml/m²; RVESVI 86 ± 33 ml/m² vs 26 ± 5 ml/m² in those with PH and the normal subjects, respectively, p <0.0001). In contrast, the RV ejection fraction was significantly reduced in the patients with PH compared to that in the normal subjects (30 ± 12% vs 65 ± 6%, respectively, p <0.01). Thus, RT3DE with a 2-dimensional summation method might provide comparable and feasible measurements of the RV volume in patients with PH compared to MRI.

Mesenchymal Stem Cells Differentiate into Renin-producing Juxtaglomerular (JG)-like Cells under the Control of Liver X Receptor-α

Renin is a key enzyme for cardiovascular and renal homeostasis and is produced by highly specialized endocrine cells in the kidney, known as juxtaglomerular (JG) cells. The nature and origin of these cells remain as mysteries. Previously, we have shown that the nuclear hormone receptor liver X receptor-α (LXRα) is a major transcriptional regulator of the expression of renin, c-myc, and other genes involved with growth/differentiation. In this study we test the hypothesis that LXRα plays an important role not only in renin expression but also in renin-containing cell differentiation, specifically from the mesenchymal stem cell (MSC), which may be the origin of the JG cell. Indeed, our data demonstrated that LXRα activation by its ligands or cAMP stimulated renin gene expression in both murine and human MSCs. Furthermore, sustained cAMP stimulation of murine MSCs overexpressing LXRα led to their differentiation into JG-like cells expressing renin and α-smooth muscle actin. These MSC-derived JG-like cells contained renin in secretory granules and released active renin in response to cAMP. In conclusion, the activation of LXRα stimulates renin expression and induces MSCs differentiation into renin-secreting, JG-like cells. Our results suggest that the MSC may be the origin of the juxtaglomerular cell and provide insight into novel understanding of pathophysiology of the renin-angiotensin system.

Favorable strategy for the ostial lesion of the left anterior descending coronary artery: Influence on narrowing of circumflex coronary artery

We examined the effectiveness of Palmaz-Schatz (P-S) stent and directional coronary atherectomy (DCA) in ostial lesions of left anterior descending arteries (LAD). The P-S stent was implanted in 11 cases at LAD ostial lesions, and DCA was performed in 13 cases. Percent stenosis and vessel diameter at the target site and the ostium of the circumflex coronary artery (LCX) were measured before and after the procedure. The initial success rate was 100% in both groups. No major complication occurred. LAD ostial lesions were improved from 81.3+/-3.4% to -8.1+/-5.7% by P-S stent and from 82.8+/-2.6% to -2.7+/-3.9% by DCA. LCX ostial vessel diameter was not changed by DCA (from 3.0+/-0.2 mm to 3.1+/-0.3 mm); however, it was significantly decreased by P-S stent (from 2.9+/-0.2 mm to 2.6+/-0.2 mm, P < 0.01). When the angle of LAD and LCX was < or = 80 degrees from the view of RAO 30 degrees and Caudal 30 degrees, the LCX ostium was significantly narrowed by stenting at LAD ostium (P < 0.01). These findings indicate that both the P-S stent and DCA are effective and safe therapies for LAD ostial lesions in cases with LAD-LCX angle > 80 degrees. In cases with LAD-LCX angle < or = 80 degrees, however, DCA is a favored therapy rather than P-S stenting to avoid narrowing of the LCX ostium.

Application of transmission scan-based attenuation compensation to scatter-corrected thallium-201 myocardial single-photon emission tomographic images

Abstract. A practical method for scatter and attenuation compensation was employed in thallium-201 myocardial single-photon emission tomography (SPET or ECT) with the triple-energy-window (TEW) technique and an iterative attenuation correction method by using a measured attenuation map. The map was reconstructed from technetium-99m transmission CT (TCT) data. A dual-headed SPET gamma camera system equipped with parallel-hole collimators was used for ECT/TCT data acquisition and a new type of external source named ”sheet line source” was designed for TCT data acquisition. This sheet line source was composed of a narrow long fluoroplastic tube embedded in a rectangular acrylic board. After injection of 99mTc solution into the tube by an automatic injector, the board was attached in front of the collimator surface of one of the two detectors. After acquiring emission and transmission data separately or simultaneously, we eliminated scattered photons in the transmission and emission data with the TEW method, and reconstructed both images. Then, the effect of attenuation in the scatter-corrected ECT images was compensated with Chang’s iterative method by using measured attenuation maps. Our method was validated by several phantom studies and clinical cardiac studies. The method offered improved homogeneity in distribution of myocardial activity and accurate measurements of myocardial tracer uptake. We conclude that the above correction method is feasible because a new type of 99mTc external source may not produce truncation in TCT images and is cost-effective and easy to prepare in clinical situations.

The EAT/mcl-1 gene, an inhibitor of apoptosis, is up-regulated in the early stage of acute myocardial infarction

EAT/mcl-1 (EAT), a bcl-2-related immediate early gene, is up-regulated at an early stage of differentiation of human embryonal carcinoma cells. Recent studies have revealed that EAT inhibits apoptosis both in vitro and in vivo. In the present study, we demonstrated that the EAT gene was up-regulated in the early stage of rat myocardial infarction. This pattern of up-regulation was apparently different from that of another immediate early gene, c-fos. EAT, an anti-apoptotic molecule, was strongly up-regulated in the non-ischemic region. In contrast, the expression of c-fos was induced in both ischemic and non-ischemic regions, and was higher in the ischemic region. Apoptosis of cardiomyocytes is currently thought to significantly contribute to acute myocardial infarction. We detected cardiomyocyte apoptosis by gel electrophoresis of genomic DNA and in situ nick end labeling in the ischemic region, but not in the non-ischemic region. As an inhibitor of apoptosis, EAT may play a role in the protection of cardiomyocytes in the early stage of acute myocardial infarction.