Use of the gadolinium-based collagen-targeting contrast agent, EP-3533, enabled in vivo molecular MR imaging of fibrosis in a mouse model of healed postinfarction myocardial scarring.

Objective The purpose of this study was to establish a reliable, chronic model of abdominal aortic aneurysm (AAA). Materials and methods 120 eight-week old C56BL/6 male mice were equally divided into three groups: 1) BAPN Group: 0.2% 3-aminopropionitrile fumarate salt (BAPN) drinking water was provided to mice two days before surgery until the end of study. Sham aneurysm induction surgery was performed using 5 μl of heat de-activated elastase. 2) Elastase Group: Mice were given regular drinking water without BAPN. During aneurysm induction surgery, 5 μl of active form elastase (10.3mg protein/ml, 5.9units/mg protein) was applied on top of adventitia of infrarenal abdominal aorta for 5 minutes. 3) BAPN+Elastase Group: Mice were given both BAPN drinking water and active form of elastase application as above. On post-operative days 7, 14, 21, 28 and 100, aortic samples were collected for histology, cytokine array and gelatin zymography after aortic diameter measurement. Results Compared with Elastase group, BAPN+Elastase group had higher AAA formation rate (93% vs 65%, P < .01) with more advanced-staged AAAs (25/42 vs 1/40 for Stage II & III, P < .001). Aneurysms from the BAPN+Elastase Group demonstrated persistent long-term growth (221.5 ± 36.6%, 285.8 ± 78.6%, 801 ± 160% on day 21, 28 and 100 respectively, P ˂ .001), with considerable thrombus formation (54%) and rupture (31%) at the advanced stages of AAA development. Cytokine levels (pro-MMP9, IL-1β, IL-6, CCL-5, TREM-1, MCP-1 and TIMP-1) in BAPN+Elastase Group were higher than Elastase Group on day 7. After day 7, cytokine levels returned to baseline with the exception of elevated MMP2 activity. By histology, CD3⁺T cells in the BAPN+Elastase Group were elevated on days 28 and 100. Conclusions A combination of oral BAPN administration and peri-aortic elastase application induced a chronic, advanced staged AAA with characteristics of persistent aneurysm growth, thrombus formation, and spontaneous rupture. Future studies should utilize this model, especially for examining tissue remodeling during the late stages of aneurysm development.

BackgroundChanges in energy substrate metabolism are first responders to hemodynamic stress in the heart. We have previously shown that hexose‐6‐phosphate levels regulate mammalian target of rapamycin (mTOR) activation in response to insulin. We now tested the hypothesis that inotropic stimulation and increased afterload also regulate mTOR activation via glucose 6‐phosphate (G6P) accumulation.Methods and ResultsWe subjected the working rat heart ex vivo to a high workload in the presence of different energy‐providing substrates including glucose, glucose analogues, and noncarbohydrate substrates. We observed an association between G6P accumulation, mTOR activation, endoplasmic reticulum (ER) stress, and impaired contractile function, all of which were prevented by pretreating animals with rapamycin (mTOR inhibition) or metformin (AMPK activation). The histone deacetylase inhibitor 4‐phenylbutyrate, which relieves ER stress, also improved contractile function. In contrast, adding the glucose analogue 2‐deoxy‐d‐glucose, which is phosphorylated but not further metabolized, to the perfusate resulted in mTOR activation and contractile dysfunction. Next we tested our hypothesis in vivo by transverse aortic constriction in mice. Using a micro‐PET system, we observed enhanced glucose tracer analog uptake and contractile dysfunction preceding dilatation of the left ventricle. In contrast, in hearts overexpressing SERCA2a, ER stress was reduced and contractile function was preserved with hypertrophy. Finally, we examined failing human hearts and found that mechanical unloading decreased G6P levels and ER stress markers.ConclusionsWe propose that glucose metabolic changes precede and regulate functional (and possibly also structural) remodeling of the heart. We implicate a critical role for G6P in load‐induced mTOR activation and ER stress.

Background Sustained pressure overload leads to changes in cardiac metabolism, function, and structure. Both time course and causal relationships between these changes are not fully understood. Therefore, we studied spontaneously hypertensive rats (SHR) during early hypertension development and compared them to control Wistar Kyoto rats. Methods and Results We serially evaluated myocardial glucose uptake rates (Ki) with dynamic 2‐[ 18 F] fluoro‐2‐deoxy‐D‐glucose positron emission tomography, and ejection fraction and left ventricular mass to body weight ratios with cardiac magnetic resonance imaging in vivo, determined glucose uptake and oxidation rates in isolated perfused hearts, and analyzed metabolites, mammalian target of rapamycin activity and endoplasmic reticulum stress in dissected hearts. When compared with Wistar Kyoto rats, SHR demonstrated increased glucose uptake rates (Ki) in vivo, and reduced ejection fraction as early as 2 months of age when hypertension was established. Isolated perfused SHR hearts showed increased glucose uptake and oxidation rates starting at 1 month. Cardiac metabolite analysis at 2 months of age revealed elevated pyruvate, fatty acyl‐ and branched chain amino acid‐derived carnitines, oxidative stress, and inflammation. Mammalian target of rapamycin activity increased in SHR beginning at 2 months. Left ventricular mass to body weight ratios and endoplasmic reticulum stress were elevated in 5 month‐old SHR. Conclusions Thus, in a genetic hypertension model, chronic cardiac pressure overload promptly leads to increased myocardial glucose uptake and oxidation, and to metabolite abnormalities. These coincide with, or precede, cardiac dysfunction while left ventricular hypertrophy develops only later. Myocardial metabolic changes may thus serve as early diagnostic markers for hypertension‐induced left ventricular hypertrophy.

A black blood gradient echo sequence for multiphase cardiac MRI of the mouse heart was implemented on a 4.7-T scanner and compared to a conventional bright blood sequence. Black blood was achieved using the double inversion recovery technique. Ten mice were imaged using both the bright and the black blood sequences, and 2 of the mice were additionally imaged using bright and black blood sequences modified to perform myocardial tagging. Manual planimetry of the images was performed by two independent observers to detect the endocardial and epicardial borders and subsequently to compute chamber volumes and myocardial mass. Weight of the excised left ventricle was used as a gold standard for myocardial mass. Bland-Altman analysis demonstrated reduced interobserver variability for the measurement of cardiac volumes using the black blood sequence compared to the bright blood sequence (95% confidence interval was ؊0.89 -0.73 L for black blood versus ؊1.86 -1.28 L for bright blood). Also, Bland-Altman analysis showed that the black blood sequence provides improved accuracy for the measurement of myocardial mass compared to the bright blood sequence (average difference between MRI versus weight was 0.9 g for black blood and ؊11.2 g for bright blood, P < 0.01).