Sabine Voll

Factor XIII Deficiency Causes Cardiac Rupture, Impairs Wound Healing, and Aggravates Cardiac Remodeling in Mice With Myocardial Infarction

Background— Identification of key molecular players in myocardial healing could lead to improved therapies, reduction of scar formation, and heart failure after myocardial infarction (MI). We hypothesized that clotting factor XIII (FXIII), a transglutaminase involved in wound healing, may play an important role in MI given prior clinical and mouse model data. Methods and Results— To determine whether a truly causative relationship existed between FXIII activity and myocardial healing, we prospectively studied myocardial repair in FXIII-deficient mice. All FXIII−/− and FXIII−/+ (FXIII activity <5% and 70%) mice died within 5 days after MI from left ventricular rupture. In contradistinction, FXIII−/− mice that received 5 days of intravenous FXIII replacement therapy had normal survival rates; however, cardiac MRI demonstrated worse left ventricular remodeling in these reconstituted FXIII−/− mice. Using a FXIII-sensitive molecular imaging agent, we found significantly greater FXIII activity in wild-type mice and FXIII−/− mice receiving supplemental FXIII than in FXIII−/− mice (P<0.05). In FXIII−/− but not in reconstituted FXIII−/− mice, histology revealed diminished neutrophil migration into the MI. Reverse transcriptase–polymerase chain reaction studies suggested that the impaired inflammatory response in FXIII−/− mice was independent of intercellular adhesion molecule and lipopolysaccharide-induced CXC chemokine, both important for cell migration. After MI, expression of matrix metalloproteinase-9 was 650% higher and collagen-1 was 53% lower in FXIII−/− mice, establishing an imbalance in extracellular matrix turnover and providing a possible mechanism for the observed cardiac rupture in the FXIII−/− mice. Conclusions— These data suggest that FXIII has an important role in murine myocardial healing after infarction.

Serial Magnetic Resonance Imaging of Microvascular Remodeling in the Infarcted Rat Heart

BackgroundAlterations in the coronary circulation are important determinants of myocardial function. Few data are available, however, about microvascular changes in reactive hypertrophy. With MRI, serial determination of myocardial microcirculation after myocardial infarction (MI) is feasible. Methods and ResultsWe quantitatively determined myocardial perfusion and relative intracapillary blood volume using an MRI technique. Infarct size, myocardial mass, and left ventricular volumes were determined with cine MRI. Rats were investigated at 8, 12, and 16 weeks after MI (mean MI size 24.1±2.0%) or sham operation. Vasodilation was induced by adenosine. In the infarcted group, maximum perfusion decreased significantly from 8 to 16 weeks (5.6±0.3 versus 3.5±0.2 mL · g−1 · min−1, P <0.01) compared with sham animals (5.5±0.3 versus 5.0±0.2 mL · g−1 · min−1, P =0.17). Myocardial mass increased significantly (559.1±20.8 mg at 8 weeks versus 690.9±42.7 mg at 16 weeks, P <0.05) compared with sham-operated animals (516.3±41.7 versus 549.2±32.3 mg). Basal relative intracapillary blood volume increased significantly to 15.7±0.5 vol% at 8 weeks after MI and remained elevated (16.8±0.6 vol%) at 16 weeks compared with 12.1±0.3 vol% (P <0.01) in sham-operated rats. ConclusionsOur results indicate that significant microvascular changes occur during cardiac remodeling. Hypoperfusion in the hypertrophied myocardium is related to an increase in vascular capacity, suggesting a compensatory vasodilatory response at the capillary level. These microvascular changes may therefore contribute to the development of heart failure.

Perfusion-corrected mapping of cardiac regional blood volume in rats in vivo.

Measurement of regional blood volume (RBV) in the myocardium in vivo is important for the assessment of tissue viability and function. The method in this work is based on the acquisition of a T1 map before and after intravascular contrast agent application. It is known that this method is influenced by perfusion that causes an overestimation of RBV values. In order to solve this problem, the new method is proposed which acquires T1 maps with slice selective inversion pulses. Due to blood flow nonexcited spins enter the detection slice, which leads to an acceleration of the relaxation time. A model that divides tissue into two compartments is adapted to slice selective inversion in order to derive a simple expression for perfusion‐corrected RBV. The aim of the study is to demonstrate the feasibility and accuracy of this technique for quantification of RBV in rat myocardium in vivo. RBV maps were obtained for five rats, and the reproducibility was determined by repeating the experiment several times. A mean RBV value of 12.8 ± 0.7% (v/v) over all animals was obtained in the myocardium. The results were compared with RBV maps obtained with perfusion‐sensitive RBV imaging in the same five rats and with first‐pass RBV studies. In order to demonstrate the strength of the new method the vasodilator adenosine was administered and alterations in microcirculation were imaged. Magn Reson Med 42:500–506, 1999.

Myocardial perfusion imaging using a non-contrast agent MR imaging technique

Introduction: A MR imaging (MRI) method has been developed to determine quantitatively myocardial perfusion (P) in the rat heart in vivo. This method has the potential to non-invasively measure cardiac perfusion without the use of a contrast agent by exploiting the endogenous contrast from flowing blood itself. Method and Results: Principle of the technique is the arterial spin labeling of endogenous water protons within the short axis imaging slice. Arterial spin labeling techniques are based on a model that uses inflow effects to relate intrinsic changes in longitudinal relaxation (T1) to tissue perfusion. Perfusion is determined from the difference between a slice selective and a global inversion recovery experiment. Perfusion was determined at rest and during hyperemia induced by intravenous adenosine (3 mg/(kgmin)). The MR perfusion values were compared with perfusion data obtained in the same animal using the colored microspheres (MS) technique as the gold standard. The MR perfusion (mean ± SEM) was 3.3 ± 0.2 ml/min/g at rest and 4.6 ± 0.6 ml/min/g during adenosine. Perfusion values obtained by colored MS were 3.4 ± 0.2 and 4.7 ± 0.8 ml/min/g at rest and during vasodilation, respectively. Adenosine decreased mean arterial pressure (MAP) from 120 to 65 mmHg which implies a reduction of coronary resistance (CR) to about 50% of baseline. Conclusion: Our study shows that quantitative mapping of perfusion may be performed non-invasively by MRI. The MR perfusion data are in excellent correlation with data obtained by the well-established colored MS technique. Determination of perfusion reserve confirms that coronary perfusion is highly dependent on blood pressure due to changes in CR.

Impact of Thoracic Surgery on Cardiac Morphology and Function in Small Animal Models of Heart Disease: A Cardiac MRI Study in Rats

Background Surgical procedures in small animal models of heart disease might evoke alterations in cardiac morphology and function. The aim of this study was to reveal and quantify such potential artificial early or long term effects in vivo, which might account for a significant bias in basic cardiovascular research, and, therefore, could potentially question the meaning of respective studies. Methods Female Wistar rats (n = 6 per group) were matched for weight and assorted for sham left coronary artery ligation or control. Cardiac morphology and function was then investigated in vivo by cine magnetic resonance imaging at 7 Tesla 1 and 8 weeks after the surgical procedure. The time course of metabolic and inflammatory blood parameters was determined in addition. Results Compared to healthy controls, rats after sham surgery showed a lower body weight both 1 week (267.5±10.6 vs. 317.0±11.3 g, n<0.05) and 8 weeks (317.0±21.1 vs. 358.7±22.4 g, n<0.05) after the intervention. Left and right ventricular morphology and function were not different in absolute measures in both groups 1 week after surgery. However, there was a confined difference in several cardiac parameters normalized to the body weight (bw), such as myocardial mass (2.19±0.30/0.83±0.13 vs. 1.85±0.22/0.70±0.07 mg left/right per g bw, p<0.05), or enddiastolic ventricular volume (1.31±0.36/1.21±0.31 vs. 1.14±0.20/1.07±0.17 µl left/right per g bw, p<0.05). Vice versa, after 8 weeks, cardiac masses, volumes, and output showed a trend for lower values in sham operated rats compared to controls in absolute measures (782.2±57.2/260.2±33.2 vs. 805.9±84.8/310.4±48.5 mg, p<0.05 for left/right ventricular mass), but not normalized to body weight. Matching these findings, blood testing revealed only minor inflammatory but prolonged metabolic changes after surgery not related to cardiac disease. Conclusion Cardio-thoracic surgical procedures in experimental myocardial infarction cause distinct alterations upon the global integrity of the organism, which in the long term also induce circumscribed repercussions on cardiac morphology and function. This impact has to be considered when analyzing data from respective animal studies and transferring these findings to conditions in patients.

Eya4 Induces Hypertrophy via Regulation of p27kip1

Background—E193, a heterozygous truncating mutation in the human transcription cofactor Eyes absent 4 (Eya4), causes hearing impairment followed by dilative cardiomyopathy. Methods and Results—In this study, we first show Eya4 and E193 alter the expression of p27kip1 in vitro, suggesting Eya4 is a negative regulator of p27. Next, we generated transgenic mice with cardiac-specific overexpression of Eya4 or E193. Luciferase and chromatin immunoprecipitation assays confirmed Eya4 and E193 bind and regulate p27 expression in a contradictory manner. Activity and phosphorylation status of the downstream molecules casein kinase-2&agr; and histone deacetylase 2 were significantly elevated in Eya4- but significantly reduced in E193-overexpressing animals compared with wild-type littermates. Magnetic resonance imaging and hemodynamic analysis indicate Eya4-overexpression results in an age-dependent development of hypertrophy already under baseline conditions with no obvious functional effects, whereas E193 animals develop onset of dilative cardiomyopathy as seen in human E193 patients. Both cardiac phenotypes were aggravated on pressure overload. Finally, we identified a new heterozygous truncating Eya4 mutation, E215, which leads to similar clinical features of disease and a stable myocardial expression of the mutant protein as seen with E193. Conclusions—Our results implicate Eya4/Six1 regulates normal cardiac function via p27/casein kinase-2&agr;/histone deacetylase 2 and indicate that mutations within this transcriptional complex and signaling cascade lead to the development of cardiomyopathy.