Wouter Oosterlinck

Increased cardiac myocyte PDE5 levels in human and murine pressure overload hypertrophy contribute to adverse LV remodeling.

Background The intracellular second messenger cGMP protects the heart under pathological conditions. We examined expression of phosphodiesterase 5 (PDE5), an enzyme that hydrolyzes cGMP, in human and mouse hearts subjected to sustained left ventricular (LV) pressure overload. We also determined the role of cardiac myocyte-specific PDE5 expression in adverse LV remodeling in mice after transverse aortic constriction (TAC). Methodology/Principal Findings In patients with severe aortic stenosis (AS) undergoing valve replacement, we detected greater myocardial PDE5 expression than in control hearts. We observed robust expression in scattered cardiac myocytes of those AS patients with higher LV filling pressures and BNP serum levels. Following TAC, we detected similar, focal PDE5 expression in cardiac myocytes of C57BL/6NTac mice exhibiting the most pronounced LV remodeling. To examine the effect of cell-specific PDE5 expression, we subjected transgenic mice with cardiac myocyte-specific PDE5 overexpression (PDE5-TG) to TAC. LV hypertrophy and fibrosis were similar as in WT, but PDE5-TG had increased cardiac dimensions, and decreased dP/dtmax and dP/dtmin with prolonged tau (P<0.05 for all). Greater cardiac dysfunction in PDE5-TG was associated with reduced myocardial cGMP and SERCA2 levels, and higher passive force in cardiac myocytes in vitro. Conclusions/Significance Myocardial PDE5 expression is increased in the hearts of humans and mice with chronic pressure overload. Increased cardiac myocyte-specific PDE5 expression is a molecular hallmark in hypertrophic hearts with contractile failure, and represents an important therapeutic target.

Angiotensin-converting enzyme inhibition and food restriction in diabetic mice do not correct the increased sensitivity for ischemia-reperfusion injury

BackgroundThe number of patients with diabetes or the metabolic syndrome reaches epidemic proportions. On top of their diabetic cardiomyopathy, these patients experience frequent and severe cardiac ischemia-reperfusion (IR) insults, which further aggravate their degree of heart failure. Food restriction and angiotensin-converting enzyme inhibition (ACE-I) are standard therapies in these patients but the effects on cardiac IR injury have never been investigated. In this study, we tested the hypothesis that 1° food restriction and 2° ACE-I reduce infarct size and preserve cardiac contractility after IR injury in mouse models of diabetes and the metabolic syndrome.MethodsC57Bl6/J wild type (WT) mice, leptin deficient ob/ob (model for type II diabetes) and double knock-out (LDLR-/-;ob/ob, further called DKO) mice with combined leptin and LDL-receptor deficiency (model for metabolic syndrome) were used. The effects of 12 weeks food restriction or ACE-I on infarct size and load-independent left ventricular contractility after 30 min regional cardiac ischemia were investigated. Differences between groups were analyzed for statistical significance by Student’s t-test or factorial ANOVA followed by a Fisher’s LSD post hoc test.ResultsInfarct size was larger in ob/ob and DKO versus WT. Twelve weeks of ACE-I improved pre-ischemic left ventricular contractility in ob/ob and DKO. Twelve weeks of food restriction, with a weight reduction of 35-40%, or ACE-I did not reduce the effect of IR.ConclusionACE-I and food restriction do not correct the increased sensitivity for cardiac IR-injury in mouse models of type II diabetes and the metabolic syndrome.

Enhanced β-adrenergic cardiac reserve in Trpm4−/− mice with ischaemic heart failure

AIMS Heart failure (HF) is a complex syndrome characterized by critically reduced cardiac contractility and function. We have shown previously that Transient Receptor Potential Melastatin 4 protein (TRPM4) functions as a Ca(2+)-activated non-selective cation channel and constitutes a novel regulator of ventricular contractility. In healthy Trpm4-deficient (Trpm4(-/-)) mice, we observed increased cardiac contractile function after β-adrenergic stimulation. In the current study, cardiac performance was examined in wild-type (WT) and Trpm4(-/-) mice with severe ischaemic HF. METHODS AND RESULTS Myocardial infarction (MI) was induced in WT and Trpm4(-/-) C57Bl6/N mice by ligation of the left anterior descending artery. During the first week after MI, mortality was higher in WT mice. Both groups showed similar infarct-typical ECG patterns during follow-up period. After 10 weeks, reduced ejection fraction and severe dilatation, determined by cardiac MRI, confirmed the development of HF in both genotypes. In vivo pressure-conductance analysis revealed no differences in cardiac contractility in basal conditions. However, during β-adrenergic stimulation, cardiac performance was significantly different between WT and Trpm4(-/-) mice. In contrast to increasing contractility in Trpm4(-/-) mice, WT mice showed a deteriorated cardiac performance. Also 30% of WT animals died during isoprenaline infusion vs. no Trpm4(-/-) mice. Infarct size, determined post mortem, was equal in WT and Trpm4(-/-) hearts. CONCLUSION Deletion of the Trpm4 gene in mice improved survival and significantly enhanced β-adrenergic cardiac reserve after inducing ischaemic HF. This suggests that pharmacological or genetic down-regulation of TRPM4 function might be a novel strategy in the management of HF.

Glucose Tolerance and Left Ventricular Pressure-Volume Relationships in Frequently Used Mouse Strains

We investigated glucose tolerance and left ventricular contractile performance in 4 frequently used mouse strains (Swiss, C57BL/6J, DBA2, and BalbC) at 24 weeks. Glucose tolerance was tested by measuring blood glucose levels in time after intraperitoneal glucose injection (2 mg/g body weight). Left ventricular contractility was assessed by pressure-conductance analysis. Peak glucose levels and glucose area under the curve were higher (all P < .05) in C57BL/6J (418 ± 65 mg/dL and 813 ± 100 mg·h/dL) versus Swiss (237 ± 66 mg/dL and 470 ± 126 mg·h/dL), DBA2 (113 ± 20 mg/dL and 304 ± 49 mg·h/dL, P < .01), and BalbC mice (174 ± 55 mg/dL and 416 ± 70 mg·h/dL). Cardiac output was higher (all P < .05) in Swiss (14038 ± 4530 μL/min) versus C57BL/6J (10405 ± 2683 μL/min), DBA2 (10438 ± 3251 μL/min), and BalbC mice (8466 ± 3013 μL/min). Load-independent left ventricular contractility assessed as recruitable stroke work (PRSW) was comparable in all strains. In conclusion, glucose tolerance and load-dependent left ventricular performance parameters were different between 4 mice background strains, but PRSW was comparable.

Routine thymectomy in congenital cardiac surgery changes adaptive immunity without clinical relevance

The actual importance of the thymus in both children and adults is largely unclear. In congenital cardiac surgery, a partial or total thymectomy is frequently performed to improve access to the heart and great vessels. We performed a literature search to evaluate the effect on the adaptive immune system of the removal of thymus tissue in patients with congenital heart disease. A PubMed search according to Dunnings standard provided 149 articles, of which 13 addressed our search question. Each study has been tabulated with author, cases, controls, follow-up, methods, results and limitations. A first group of articles repeatedly showed the effect on the T-cell compartment, including the impact on subgroups of this compartment. More recent studies, usually with a longer follow-up, confirm that the earlier changes in T-cell population appear to be permanent. Only one author found a normalization of T-cell population five years after thymectomy. In contrast to these clear changes in T-cell population, there is currently no clear clinical relevance. A literature search on thymectomy in congenital cardiac surgery revealed clear changes in T-cell-related immunity; however, there is a lack of clinical relevance. Further investigation of the adaptive immune system is required to explain this discrepancy.

Angiotensin-converting enzyme inhibition and food restriction restore delayed preconditioning in diabetic mice

BackgroundClassical and delayed preconditioning are powerful endogenous protection mechanisms against ischemia-reperfusion damage. However, it is still uncertain whether delayed preconditioning can effectively salvage myocardium in patients with co-morbidities, such as diabetes and the metabolic syndrome. We investigated delayed preconditioning in mice models of type II diabetes and the metabolic syndrome and investigated interventions to optimize the preconditioning potential.MethodsHypoxic preconditioning was induced in C57Bl6-mice (WT), leptin deficient ob/ob (model for type II diabetes) and double knock-out (DKO) mice with combined leptin and LDL-receptor deficiency (model for metabolic syndrome). Twenty-four hours later, 30 min of regional ischemia was followed by 60 min reperfusion. Left ventricular contractility and infarct size were studied. The effect of 12 weeks food restriction or angiotensin-converting enzyme inhibition (ACE-I) on this was investigated. Differences between groups were analyzed for statistical significance by student’s t-test or one-way ANOVA followed by a Fisher’s LSD post hoc test. Factorial ANOVA was used to determine the interaction term between preconditioning and treatments, followed by a Fisher’s LSD post hoc test. Two-way ANOVA was used to determine the relationship between infarct size and contractility (PRSW). A value of p<0.05 was considered significant.ResultsLeft ventricular contractility is reduced in ob/ob compared with WT and even further reduced in DKO. ACE-I improved contractility in ob/ob and DKO mice. After ischemia/reperfusion without preconditioning, infarct size was larger in DKO and ob/ob versus WT. Hypoxic preconditioning induced a strong protection in WT and a partial protection in ob/ob mice. The preconditioning potential was lost in DKO. Twelve weeks of food restriction or ACE-I restored the preconditioning potential in DKO and improved it in ob/ob.ConclusionDelayed preconditioning is restored by food restriction and ACE-I in case of type II diabetes and the metabolic syndrome.

Response of mouse brain perfusion to hypo‐ and hyperventilation measured by arterial spin labeling

We aimed to setup a noninvasive and well‐controlled methodology for evaluation of the cerebrovascular response in mice (C57BL/6J; 12 weeks). Therefore we applied a normo‐, hypo‐, and hyperventilation paradigm combined with arterial spin labeling and monitoring of the expired CO2 (expCO2) (n = 7) or arterial pCO2 (apCO2) (n = 12). Reducing the tidal volume by 25% and the respiratory rate by 20% resulted in hypercapnia (apCO2 from 33 ± 6 mmHg to 64 ± 16 mmHg). Increasing the respiratory rate by 25% and the tidal volume by 20% decreased apCO2 to 22 ± 5 mmHg. Cerebral blood flow (CBF) was 82 ± 21, 163 ± 41 and 64 ± 18 mL/100 g/min during normo, hypo‐, and hyperventilation, respectively (midbrain). The correlation of apCO2 and CBF levels resulted in a cerebrovascular response of 2.7 ± 0.3, 2.1 ± 0.3, 2.1 ± 0.3, and 3.7 ± 0.5 mL/100 g/min/mmHg for midbrain, cortex, hippocampus and thalamus, respectively. As expCO2 levels were correlated with apCO2 (r2 = 0.86; n = 4) and CBF (r2 = 0.67) a cerebrovascular response based on simultaneously recorded CBF and expCO2 levels could be derived (3.3 ± 0.5, 2.5 ± 0.4, 3.0 ± 0.4, and 4.5 ± 0.6 mL/100 g/min/mmHg; order as above). A cross‐over experiment resulted in similar responses. In conclusion, this protocol allows evaluating basal CBF and cerebrovascular response in mice under well‐controlled conditions by simply changing ventilator settings and correlating CBF with apCO2 and/or simultaneously obtained expCO2. Magn Reson Med, 2011.

In vivo evidence for long-term vascular remodeling resulting from chronic cerebral hypoperfusion in mice.

We have characterized both acute and long-term vascular and metabolic effects of unilateral common carotid artery occlusion in mice by in vivo magnetic resonance imaging and positron emission tomography. This common carotid artery occlusion model induces chronic cerebral hypoperfusion and is therefore relevant to both preclinical stroke studies, where it serves as a control condition for a commonly used mouse model of ischemic stroke, and neurodegeneration, as chronic hypoperfusion is causative to cognitive decline. By using perfusion magnetic resonance imaging, we demonstrate that under isoflurane anesthesia, cerebral perfusion levels recover gradually over one month. This recovery is paralleled by an increase in lumen diameter and altered tortuosity of the contralateral internal carotid artery at one year post-ligation as derived from magnetic resonance angiography data. Under urethane/α-chloralose anesthesia, no acute perfusion differences are observed, but the vascular response capacity to hypercapnia is found to be compromised. These hemispheric perfusion alterations are confirmed by water [15O]-H2O positron emission tomography. Glucose metabolism ([18F]-FDG positron emission tomography) or white matter organization (diffusion-weighted magnetic resonance imaging) did not show any significant alterations. In conclusion, permanent unilateral common carotid artery occlusion results in acute and long-term vascular remodeling, which may have immediate consequences for animal models of stroke but also vascular dementia.

Successful repositioning of leadless cardiac pacemaker during open heart surgery

Received 5 September 2016; revision accepted for publication 20 September 2016. A 82-year-old woman with moderately severe valvular (tricuspid and mitral) disease and chronic atrial fibrillation associated with severe bradycardia underwent implantation of a leadless cardiac pacemaker MicraTM(Transcatheter Pacing System (TPS), Model MC1VR01, Medtronic Inc., Minneapolis, MN, USA). The implantation was the fifth scheduled TPS implantation in our centre, all by one single operator (CG). After five redeployments, the TPS was launched at an infero-basal position (pacing threshold of 1.0 V at 0.25 ms, pacing impedance at 510 Ohm and sensing: 11.2 ms) (panel A). Before discharge, the electrical parameters were unchanged. However, 10 days after the implantation, an isolated increase of the pacing threshold (2.50 V at 0.24 ms) was observed that prompted closer follow-up. Three weeks later, the patient was readmitted for pre-syncope and heart failure. ECG showed intermittent ventricular non-capture. Control of the TPS confirmed a high pacing threshold (> 5.00 V at 0.24 ms) with stable pacing impedance and ventricular sensing. Transoesophageal echocardiography showed worsening of the mitral valvular disease and known moderately Successful repositioning of leadless cardiac pacemaker during open heart surgery

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).