Western diet given to healthy rats mimics the human phenotype of diabetic cardiomyopathy.

Diabetes mellitus (DM) is a major problem worldwide. Within this patient group, cardiovascular diseases are the biggest cause of morbidity and mortality. Diabetic cardiomyopathy (DCM) is defined as diabetes-associated structural and functional changes in the myocardium, not directly attributable to other confounding factors such as coronary artery disease or hypertension. Pathophysiology of DCM remains unclear due to a lack of adequate animal models reflecting the current pandemic of diabetes, associated with a high increased sugar intake and the 'Western' lifestyle. The aim of this study was to develop an animal model mimicking this 'Western' lifestyle causing a human-like phenotype of DCM. Twenty-four Sprague-Dawley rats were randomly assigned into a normal or a 'Western' diet group for 18 weeks. Glucose and insulin levels were measured with an OGTT. Heart function was assessed by echocardiography and hemodynamic measurements in vivo. Cardiac fibrosis and inflammation were investigated in vitro. 'Western' diet given to healthy rats for 18 weeks induced hyperglycemia together with increased AGEs levels, insulin levels and hypertriglyceridemia. Heart function was altered with increased end-diastolic pressure, left ventricle hypertrophy. Changes in vivo were associated with increased collagen deposition and increased PAI-1 levels in the heart. High-sugar diet or 'Western' diet causes T2DM and the hallmarks of DCM in rats, reflecting the phenotype of the disease seen in patients. Using this new model of T2DM with DCM might open new insight in understanding the pathophysiology of DCM and on a long term, test targeted therapies for T2DM with DCM patients.

Serial assessment of left ventricular morphology and function in a rodent model of ischemic cardiomyopathy.

Left ventricular remodelling (LVr) occurs post myocardial infarction (MI), predisposing people to heart failure (HF). LV mechanics and morphology are important in this process. We hence sort to characterize LV mechanics and geometry in a post-MI rodent model. Thirty-two male Sprague-Dawley rats (150-200 g) sustained MI (n = 24) or sham (Sham; n = 8) surgery. In another six sham rats invasive blood pressure measurements were performed. Ultrasound imaging was done at baseline, and 1, 3, 7, 14, 30 and 60 days following surgery, and LV mechanics and morphology assessed. LV volumes increased with time (p < 0.01), at a greater rate in the MI group than the Sham group (p < 0.01). Strain was impaired in MI rats at day 1 (13.50 ± 6.64 vs. 25.71 ± 4.94%, p < 0.01) and remained impaired at day 60 (14.07 ± 5.37 vs. 22.98 ± 5.87%, p < 0.01). Strain rate was lower at day 1 (4.11 ± 1.29 vs. 8.10 ± 2.18%/s, p < 0.01), remained lower throughout follow-up (p < 0.01), and decreased at a greater rate in MI rats (p < 0.01). Mean systolic (204 ± 43 vs. 322 ± 75 1/m, p < 0.01) and diastolic (167 ± 21 vs. 192 ± 11 1/m, p < 0.01) curvature was lower in the MI rats at day 1 post surgery and throughout follow-up (p < 0.01). Maximum principal curvature decreased throughout time (p < 0.01), while minimum principal curvature did not (p = 0.86). Wall stress increased significantly after infarction in MI rats (p < 0.01). ST-elevation myocardial infarction (STEMI) changed LV shape and contractile function. The assessment of these indices may prove useful in understanding LVr and the development of HF.

Pyridoxamine improves survival and limits cardiac dysfunction after MI.

Advanced glycation end products (AGEs) play a key role in the progression of heart failure. Whether treatments limiting AGEs formation would prevent adverse left ventricular remodeling after myocardial infarction (MI) remain unknown. We investigated whether pyridoxamine (PM) could limit adverse cardiac outcome in MI. Rats were divided into MI, MI + PM and Sham. Echocardiography and hemodynamic parameters were used to assess cardiac function 8 weeks post-surgery. Total interstitial collagen, collagen I and collagen III were quantified using Sirius Red and polarized light microscopy. PM improved survival following LAD occlusion. Pre-treatment with PM significantly decreased the plasma AGEs levels. MI rats treated with PM displayed reduced left ventricular end-diastolic pressure and tau compared to untreated MI rats. Deformation parameters were also improved with PM. The preserved diastolic function was related to the reduced collagen content, in particular in the highly cross-linked collagen type I, mainly in the peri-infarct region, although not via TGF-ß1 pathway. Our data indicate that PM treatment prevents the increase in AGEs levels and reduces collagen levels in a rat model of MI, resulting in an improved cardiac phenotype. As such, therapies targeting formation of AGEs might be beneficial in the prevention and/or treatment of maladaptive remodeling following MI.

Cross-linking versus RAGE: How do high molecular weight advanced glycation products induce cardiac dysfunction?

BACKGROUND: Several clinical and experimental studies have demonstrated that advanced glycation end products (AGEs) are associated with adverse cardiac outcome. Growing evidence shows that high molecular weight AGEs (HMW-AGEs) might be as important as the characterized low molecular weight AGEs. To date, the role of HMW-AGEs in the pathogenesis of cardiac remodeling remains unknown. In this study, we investigated whether HMW-AGEs are involved in cardiac dysfunction. METHODS: Healthy rats were daily ip injected with 20mg/kg BSA-derived HMW-AGEs or, as a control, unmodified BSA, during 6 weeks. Cardiac function was assessed with echocardiography. Plasma levels of glucose, AGEs and soluble RAGE (sRAGE) were measured. AGEs, RAGE and lysyl oxidase (LOX) expression were determined by western blot. RESULTS: After 6 weeks, animals displayed a sustained increase in circulating total AGEs without hyperglycemia. HMW-AGEs injections induced cardiac dysfunction characterized by wall hypertrophy, increased heart sphericity, reduced strain and strain rate with preserved ejection fraction. Plasma sRAGE levels were significantly higher compared to control and correlated significantly with decreased strain. RAGE expression, TNF-α and IL-6 remained unchanged. Finally, HMW-AGEs induced prominent cardiac fibrosis associated with an increased LOX expression. CONCLUSION: Our data demonstrate that rather than via a specific activation of RAGE, the deleterious effects of HMW-AGEs are likely mediated via an increased collagen cross-linking responsible for the observed cardiac stiffness. Additionally, we show that in the setting of elevated HMW-AGEs, increased sRAGE levels are markers of altered cardiac function.

Exercise improves cardiac function and attenuates insulin resistance in Dahl salt-sensitive rats.

BACKGROUND: The development of heart failure (HF) secondary to hypertension is a complex process related to a series of physiological and molecular factors including glucose dysregulation. The overall objective of this study was to investigate whether exercise training could improve cardiac function and insulin resistance in a rat model of hypertensive HF. METHODS: Seven week old Dahl salt-sensitive rats received either 8% NaCl (n = 30) or 0.3% NaCl (n = 18) diet. After a 5-week diet, animals were randomly assigned to exercise training (treadmill running at 18 m/min, 5% inclination for 60 min, 5 days/week) or kept sedentary for 6 additional weeks. 2D echocardiography was used to calculate left ventricular (LV) dimensions, volumes and global functional parameters. LV global deformation parameters were measured with speckle tracking echocardiography. Insulin resistance was assessed using 1h oral glucose tolerance testing. RESULTS: High salt diet led to cardiac hypertrophy and HF, characterized by increased wall thicknesses and LV volumes as well as reduced deformation parameters. In addition, high salt diet was associated with the development of insulin resistance. Exercise training improved cardiac function, reduced the extent of interstitial fibrosis and reduced insulin levels 60 min post-glucose administration. CONCLUSIONS: Even if not fully reversed, exercise training in HF animals improved cardiac function and insulin resistance. Adjusted modalities of exercise training might offer new insights not only as a preventive strategy, but also as a treatment for HF patients.

2-D strain assessment in the mouse through spatial compounding of myocardial velocity data: in vivo feasibility.

Ultrasound assessment of myocardial strain can provide valuable information on regional cardiac function. However, Doppler-based methods often used in practice for strain estimation suffer from angle dependency. In this study, a partial solution to that fundamental limitation is presented. We have previously reported using simulated data sets that spatial compounding of axial velocities obtained at three steering angles can theoretically outperform 2-D speckle tracking for 2-D strain estimation in the mouse heart. In this study, the feasibility of the method was analyzed in vivo using spatial compounding of Doppler velocities on six mice with myocardial infarction and five controls, and results were compared with those of tagged microscopic magnetic resonance imaging (µMRI). Circumferential estimates quantified by means of both ultrasound and µMRI could detect regional dysfunction. Between echocardiography and µMRI, a good regression coefficient was obtained for circumferential strain estimates (r = 0.69), whereas radial strain estimates correlated only moderately (r = 0.37). A second echocardiography was performed after µMRI to test the reproducibility of the compounding method. This yielded a higher correlation coefficient for the circumferential component than for the radial component (r = 0.74 circumferentially, r = 0.49 radially).

Comparison of a new methodology for the assessment of 3D myocardial strain from volumetric ultrasound with 2D speckle tracking.

An alternative approach to extract 3D myocardial strain based on elastic registration of the ultrasound images (3DSE) was developed by our lab. The aim of the present study was to test its clinical performance by comparing strain values obtained by 3DSE with the ones obtained with 2D speckle tracking (2DST). Standard 2D B-mode and volumetric datasets were acquired in 12 patients with coronary heart disease (CHD) and in 12 control subjects. Longitudinal (ε(LL)), circumferential (ε(CC)) and radial (ε(RR)) strain values were obtained from 2D datasets using commercially available 2DST software and from volumetric datasets using the 3DSE approach. 3DSE provided lower strain values than 2DST. With both approaches global ε(LL) and ε(CC) were significantly lower in patients with CHD than in controls. Global ε(LL) and ε(CC) correlated well between both methods (R = 0.83, R = 0.86, respectively), while segmental correlations were moderate [R = 0.63 (ε(LL)), R = 0.41 (ε(CC))]. The highest differences in ε(LL) values obtained by the two methods and the highest number of erroneous ε(LL) with 3DSE were observed in the basal LV segments. This study shows that in real-life datasets our 3DSE method provides global and regional ε(LL) and ε(CC) values that are comparable with the ones obtained from 2DST, even though they are not interchangeable with each other. As only a single acquisition is required, 3D methods may offer advantages over the current 2D techniques. However, the accuracy of the 3DSE can still be improved by solving the problems that appear with deformation estimation in the basal segments.

Non-invasive characterization of the area-at-risk using magnetic resonance imaging in chronic ischaemia.

AIMS: we investigated the performance of quantitative stress perfusion magnetic resonance imaging (MRI) as a basis for identifying and characterizing the area-at-risk subtending a chronic coronary artery (CA) stenosis. METHODS AND RESULTS: pigs underwent a percutaneous copper-coated stent implantation in the circumflex CA (n = 11) or a sham operation (n = 5). After 6 weeks, angiography and MRI were performed including cine (rest, low- and high-dose dobutamine stress), dual-bolus first-pass perfusion (rest and adenosine stress), and contrast-enhanced imaging to quantify myocardial infarction (MI). Myocardial blood flow (MBF) was quantified based on Fermi-model deconvolution and compared with microsphere measurements. On the basis of Evan's blue staining, MBF thresholds to define the area-at-risk were determined by receiver-operating characteristic (ROC) analysis. CA stenosis was 94 ± 7% and infarct size (IS) 7.3 ± 3.1% of left ventricular mass. Segmental thresholds of hyperaemic MBF yielded the best performance for detecting area-at-risk. There was a good correlation between MRI and microsphere perfusion (r(2) = 0.84, P < .0001). The area-at-risk presented a mixed substrate of non-infarcted (non-MI), <50% infarcted (MI+), and >50% infarcted (MI++) segments. MBF was reduced in at-risk vs. remote segments at rest (non-MI, 0.50 ± 0.21; MI+, 0.47 ± 0.14; MI++, 0.42 ± 0.14; remote, 0.84 ± 0.25 mL/min/g) and during stress (non-MI, 0.69 ± 0.09; MI+, 0.66 ± 0.14; MI++, 0.51 ± 0.11; remote, 1.70 ± 0.36 mL/min/g). Segmental wall thickening showed different responses to stress (remote, progressive increase during incremental stress; non-MI, increase at low-dose and discontinued at high-dose; MI+, initial increase and decrease at high-dose; MI++, progressive decrease). CONCLUSION: quantitative hyperaemic perfusion MRI accurately defines segments in the area-at-risk in chronic ischaemia, which present with different functional response to stress related to segmental IS.