Daniel P. Griese

Development of heart failure following isoproterenol administration in the rat: role of the renin–angiotensin system

OBJECTIVE High dosages of catecholamines induce cardiomyocyte necrosis and interstitial fibrosis in rats. We investigated whether this initial damage is followed by the development of heart failure and assessed the particular role of the renin-angiotensin system using ramipril. METHODS AND RESULTS Following the administration of 0 mg or 150 mg isoproterenol/kg 6 groups of Wistar rats were followed for 2 or 16 weeks: Sham, isoproterenol, isoproterenol + ramipril. Isoproterenol induced significant increases of echocardiographically measured left ventricular end-diastolic posterior wall thickness and dimension, whereas ramipril treatment significantly attenuated these changes. Left ventricular end-diastolic pressure was markedly increased in isoproterenol-treated rats and normalized following ramipril. Isoproterenol rats were further characterized by hormonal activations including transient elevations of plasma renin activity, aldosterone and cardiac angiotensin converting enzyme activity. Histomorphological characterization of isoproterenol-treated hearts demonstrated cardiomyocyte necrosis and reparative fibrosis. Ramipril treatment only slightly reduced the amount of necrosis as well as the expression of extracellular matrix proteins. CONCLUSIONS In rats, a toxic dosage of isoproterenol caused characteristic myocardial damage that subsequently resulted in mild heart failure. Ramipril administration following isoproterenol was highly effective to attenuate hemodynamic and hormonal alterations as well as the development of left ventricular hypertrophy, but had only little influence on the expression of extracellular matrix proteins. Since angiotensin converting enzyme inhibition had no impact on the initial myocardial injury, the development of heart failure in this model seems to require functional integrity of the renin-angiotensin system.

Evaluation of plasma natriuretic peptides as markers for left ventricular dysfunction

To test the hypothesis that elevated plasma levels of natriuretic peptides may serve to identify patients with left ventricular (LV) dysfunction, we assessed the predictive diagnostic value of natriuretic peptide levels, in addition to clinical and electro-cardiographic risk factors, as noninvasive indicators of cardiac dysfunction. Plasma levels of atrial natriuretic peptide (cANP) (99-126), N-terminal fragment of proANP (nANP) (26-55), nANP(80-96), brain natriuretic peptide (BNP-32), proBNP(22-46), and C-type natriuretic peptide (CNP-22) were measured in 211 subjects before cardiac catheterization. The strongest correlations with parameters of LV function were found for nANP(80-96) (up to r = -0.55, p < 0.0001), whereas there was no significant correlation with proBNP(22-46) or CNP-22. In patients with LV ejection fractions (LVEF) < or = 45% (n = 38) nANP(26-55), nANP(80-96), cANP(99-126), and BNP-32 were significantly increased (p < 0.001). Partition values for elevated versus normal natriuretic peptide levels were obtained from normal controls and used to separate subjects with and without LV dysfunction. Receiver operating characteristic analysis for LVEF < or = 45% indicated a significantly better diagnostic accuracy for high levels of nANP(80-96), nANP(22-56), cANP(99-126), and BNP-32 than for proBNP and CNP-22. Multivariate analysis by logistic regression identified Q waves and bundle branch block in the electrocardiogram as well as elevated plasma levels of cANP, nANP(80-96), and nANP(26-55) as the strongest independent predictors of low ejection fractions. The relative risk of LV dysfunction was raised up to tenfold in subjects with high natriuretic peptide levels (p < 0.001). The addition of nANP(80-96) and nANP(26-55) to the combination of clinical and electrocardiographic risk factors did not further improve the diagnostic sensitivity for the detection of LVEF < or = 45%, but it markedly increased the overall accuracy (59% to 81%, p < 0.001) and specificity (55% to 81%, p < 0.001). Among natriuretic peptides, elevated nANP(80-96) and nANP(26-55) levels have the strongest impact on the detection of LV dysfunction. They add to the diagnostic information contained in clinical and electrocardiographic factors. Plasma levels alone or in combination with clinical factors seem to be of value for a refined identification of abnormal LV function in the individual patient.

Myocardial hypertrophy and enhanced left ventricular contractility in Zucker diabetic fatty rats

Heart failure is known to be a complication of insulin-dependent (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) even in the absence of coronary heart disease or hypertension. The mechanisms leading to diabetic cardiomyopathy are unknown. The aim of the study was to characterize structural and functional alterations in hyperinsulinemic Zucker diabetic fatty (ZDF) rats treated with or without insulin. Diabetic animals showed a twofold increase in cardiomyocyte volume with increased left ventricular ANP but not BNP mRNA levels in spite of a reduced plasma renin activity (PRA) 2 months after onset of diabetes compared to nondiabetic littermates. These changes were associated with an increase in left ventricular performance as assessed by echocardiography. Insulin treatment led to a significant increase in body weight (BW), total heart weight, myocardial protein content, and left ventricular mass (LVM). Perivascular fibrosis and laminin thickness were significantly augmented in diabetic rat myocardium irrespective of insulin treatment, whereas interstitial collagen I and fibronectin were similarly found in diabetic and control myocardium. Initial stages of diabetic cardiomyopathy in hyperinsulinemic rats are characterized by cardiomyocyte hypertrophy and enhanced cardiac contractility. It is suggested that hyperinsulinemia may be involved in cardiac hypertrophy.

Vascular gene delivery of anticoagulants by transplantation of retrovirally-transduced endothelial progenitor cells

OBJECTIVE Recent studies have documented the presence of bone marrow-derived endothelial progenitor cells (EPC) in the circulation of several species. This study was designed to evaluate the use of engineered EPC for vascular gene delivery into angioplasty-induced arterial lesions. METHODS AND RESULTS EPC could easily be isolated from whole bone marrow and peripheral blood of adult rats. Differentiation was induced by culture on fibronectin in the presence of endothelial specific growth factors. Rat EPC shared several phenotypic and functional properties with mature endothelial cells. Recombinant retroviruses were generated encoding for the anticoagulants tissue-type plasminogen activator (tPA) and hirudin. Efficient (>90%) ex vivo gene transfer could be achieved resulting in high levels of transgene production. Engineered EPC were locally infused into freshly balloon-injured carotid arteries. Analysis of day 7 vessels showed 73+/-10% luminal coverage of the lesioned arterial bed with transduced EPC. Sustained secretion of both anticoagulants could be detected in organ cultures of explanted arteries. EPC seeding inhibited dilation of the injured arterial segment and prevented reduction of media thickness. However, rapid repopulation with EPC failed to attenuate neointima formation in this model. CONCLUSIONS Peripheral blood and bone marrow can be used as source for endothelial lineage cells. Cultured EPC can be genetically engineered by retroviral gene transfer and serve as cellular vehicles for vascular gene and drug delivery of anticoagulants. Local transplantation of EPC attenuates reendothelialization of angioplasty-injured arteries but fails to inhibit neointima proliferation.

Differential effects of growth hormone on cardiomyocyte and extracellular matrix protein remodeling following experimental myocardial infarction

OBJECTIVES Growth hormone (GH) causes cardiomyocyte hypertrophy without development of fibrosis in the normal rat heart. The aim of this study was to evaluate the effects of GH on cardiac remodeling following experimental myocardial infarction (MI). METHODS Following ligation of the left coronary artery or sham operation, rats were randomized to receive 2 IU GH/kg/day or vehicle for four weeks (n = 140). Extracellular matrix proteins were assessed in the non-infarcted myocardium of the posterior wall using immunohistochemistry and automatic image analysis. In addition, cardiomyocyte size was measured. RESULTS Compared to sham, vehicle-treated rats with moderate (20-40%) and large (> 40%) infarct size showed left ventricular (LV)-dilatation, reduced fractional shortening as well as increases in LV end-diastolic and right atrial pressures, LV/body weight (BW) ratio and LV posterior wall thickness. Compared to vehicle-treated MI-rats, treatment with GH considerably increased fractional shortening and attenuated LV-dilatation. Vehicle-treated MI-rats displayed progressive increases in cardiomyocyte width and deposition of collagen I, compared to sham rats. Treatment with GH nearly doubled the increase in cardiomyocyte width and reduced collagen I accumulation by 50%. CONCLUSIONS Our study demonstrates that GH, given early after large MI, elicits a unique pattern of structural effects characterized by enhanced cardiomyocyte hypertrophy and reduced adaptive fibrosis. This attenuation of pathological remodeling translates into a significant improvement in systolic and diastolic LV-function.

Norepinephrine upregulates vascular endothelial growth factor in rat cardiac myocytes by a paracrine mechanism

Norepinephrine has growth-promoting effects in cardiac myocytes. The present study in cultured neonatal rat cardiac myocytes tested the hypothesis that norepinephrine also stimulates expression of vascular endothelial growth factor (VEGF), an important angiogenic factor. As assessed by polymerase chain reaction cardiac myocytes and non-myocytes expressed all three isoforms of rat VEGF, with the short isoform (VEGF121) preferentially expressed in non-myocytes. When cardiac myocytes were stimulated with 1 μM norepinephrine for 24h in the presence or absence of the specific α- and β-adrenoceptor antagonists prazosin and propranolol, respectively, VEGF mRNA levels and splice variant pattern did not change, whereas atrial natriuretic peptide mRNA levels increased 3 to 4-fold. CoCl2 increased VEGF mRNA levels in cardiac myocytes five-fold. When cardiac myocytes were cultured with conditioned medium from non-myocytes that had been stimulated with norepinephrine for 24 h VEGF mRNA increased 2-fold. The increase was blocked by antibodies neutralizing TGFβ. These data suggest that norepinephrine stimulates myocardial angiogenesis by a paracrine mechanism that involves cardiac non-myocytes and TGFβ.

Evidence for a Possible Inhibitory Interaction between the HO-1/CO- and Akt/NO-Pathways in Human Endothelial Cells

ObjectiveThe protective properties of heme oxygenase 1 (HO-1) give reason to study this mechanism as a potential therapeutic target for inflammatory and cardiovascular diseases. Recent evidence suggests a possible interaction between the HO-1/CO- and the protein kinase Akt/NO-pathway. This study was designed to examine the effects of continuous HO-1 overexpression in endothelial cells.MethodsOncoretroviral vectors were constructed to achieve constitutive overexpression of HO-1, Akt, and green fluorescence protein in human umbilical vein endothelial cells. [3H]thymidine-incorporation and lipid-peroxidation were measured following exposure to heme and H2O2. Expression of HO-1, Akt and its downstream-target endothelial NO-synthase were quantified by Western blot analysis. NO-synthase-activity was measured using the citrulline-conversion-assay.ResultsHO-1-overexpression reduced proliferative rates and DNA-synthesis of HUVEC, but provided potent protection from oxidative stress induced by heme and H2O2. Phosphorylated-Akt and eNOS was downregulated in HO-1-HUVEC. eNOS-activity was reduced in HO-1-HUVEC. Co-infection with the Akt-retrovirus restored proliferative rates and eNOS-expression and -activity.ConclusionContinuously elevated HO-1-activity protects EC from oxidative stress but inhibits Akt-mediated proliferation and eNOS-expression. This inhibitory feedback mechanism could be a limitation of HO-1 as a target for the treatment of vascular disease.

Dynamic changes in N-terminal pro-brain natriuretic peptide in acute coronary syndromes treated with percutaneous coronary intervention: a marker of ischemic burden, reperfusion and outcome.

Abstract Background: Whereas N-terminal pro-brain natriuretic peptide (NT-proBNP) is approved for risk stratification of patients with acute coronary syndromes (ACS), short-term temporal changes in NT-proBNP concentrations and the optimal time points for sampling are not clear. The purpose of this study was to better define the short-term changes in NT-proBNP in relation to clinical presentation, reperfusion and prognostic value in patients with ACS, as well as to identify the optimum time points for sampling. Methods: We studied daily plasma concentrations of NT-proBNP in 133 unselected patients with myocardial infarction (n=65), stable coronary artery disease (CAD, n=46) and no CAD (n=22) who underwent coronary angiography. Results: Patients with non-ST-elevation myocardial infarction (NSTEMI) presented with markedly higher NT-proBNP than patients with ST-elevation myocardial infarction (STEMI) [1305 (741–3208) ng/L vs. 170 (70–424) ng/L, p<0.001]. Also, time to presentation from onset of pain was much longer in NSTEMI as compared to STEMI (>48 h vs. <6 h, p<0.001). Patients with NSTEMI also presented with higher NT-proBNP as compared with CAD [224 (98–732) ng/L] and no CAD [47 (26–102) ng/L; p<0.001, NSTEMI vs. both]. Following successful percutaneous coronary intervention [thrombolysis in myocardial infarction (TIMI) 3-flow established], NT-proBNP increased markedly within 24 h in patients with STEMI [718 (379–1338) ng/L, p<0.01 vs. 0 h], whereas no change in NT-proBNP was noted in patients with NSTEMI [1190 (1010–2024) ng/L, p=0.88 vs. 0 h]. In both STEMI and NSTEMI, NT-proBNP decreased significantly 96 h after successful reperfusion [STEMI –52%, 372 (189–610) ng/L, p<0.05; NSTEMI –52%, 613 (365–724) ng/L, p<0.05]. Unsuccessful reperfusion (TIMI<3) was associated with unchanged or increased NT-proBNP. NT-proBNP at 96 h and peak NT-proBNP further displayed a strong correlation with cardiac troponin T (r=0.64 and r=0.54, p<0.001), a marker of infarct size, and NT-proBNP at 96 h was a strong predictor of long-term prognosis (hazard ratio 7.29, p=0.025). Conclusions: In patients with NSTEMI, NT-proBNP may be increased as high as concentrations usually associated with acute congestive heart failure despite the absence of clinical signs. In contrast, patients with STEMI and short time to presentation may present with completely normal NT-proBNP, but dramatic short-term increases following reperfusion. NT-proBNP reflects ischemic burden, reperfusion success and prognosis, and the current data support repetitive sampling in patients with ACS. Clin Chem Lab Med 2010;48:875–81.

Eplerenone prevents salt-induced vascular stiffness in Zucker diabetic fatty rats: a preliminary report

BackgroundAldosterone levels are elevated in a rat model of type 2 diabetes mellitus, the Zucker Diabetic fatty rat (ZDF). Moreover blood pressure in ZDF rats is salt-sensitive. The aim of this study was to examine the effect of the aldosterone antagonist eplerenone on structural and mechanical properties of resistance arteries of ZDF-rats on normal and high-salt diet.MethodsAfter the development of diabetes, ZDF animals were fed either a normal salt diet (0.28%) or a high-salt diet (5.5%) starting at an age of 15 weeks. ZDF rats on high-salt diet were randomly assigned to eplerenone (100 mg/kg per day, in food) (ZDF+S+E), hydralazine (25 mg/kg per day) (ZDF+S+H), or no treatment (ZDF+S). Rats on normal salt-diet were assigned to eplerenone (ZDF+E) or no treatment (ZDF). Normoglycemic Zucker lean rats were also divided into two groups receiving normal (ZL) or high-salt diet (ZL+S) serving as controls. Systolic blood pressure was measured by tail cuff method. The experiment was terminated at an age of 25 weeks. Mesenteric resistance arteries were studied on a pressurized myograph. Specifically, vascular hypertrophy (media-to-lumen ratio) and vascular stiffness (strain and stress) were analyzed. After pressurized fixation histological analysis of collagen and elastin content was performed.ResultsBlood pressure was significantly higher in salt-loaded ZDF compared to ZDF. Eplerenone and hydralazine prevented this rise similarily, however, significance niveau was missed. Media-to-lumen ratio of mesenteric resistance arteries was significantly increased in ZDF+S when compared to ZDF and ZL. Both, eplerenone and hydralazine prevented salt-induced vascular hypertrophy. The strain curve of arteries of salt-loaded ZDF rats was significantly lower when compared to ZL and when compared to ZDF+S+E, but was not different compared to ZDF+S+H. Eplerenone, but not hydralazine shifted the strain-stress curve to the right indicating a vascular wall composition with less resistant components. This indicates increased vascular stiffness in salt-loaded ZDF rats, which could be prevented by eplerenone but not by hydralazine. Collagen content was increased in ZL and ZDF rats on high-salt diet. Eplerenone and hydralazine prevented the increase of collagen content. There was no difference in elastin content.ConclusionEplerenone and hydralazine prevented increased media-to-lumen ratio in salt-loaded ZDF-rats, indicating a regression of vascular hypertrophy, which is likely mediated by the blood pressure lowering-effect. Eplerenone has additionally the potential to prevent increased vascular stiffness in salt-loaded ZDF-rats. This suggests an effect of the specific aldosterone antagonist on adverse vascular wall remodelling.

Hyperaldosteronism and altered expression of an SGK1-dependent sodium transporter in ZDF rats leads to salt dependence of blood pressure

This study was designed to test whether altered aldosterone-related sodium handling leads to salt-sensitive blood pressure in diabetes and thus may exaggerate end-organ damage. Zucker diabetic fatty (ZDF) rats, a model of type 2 diabetes, and Zucker lean (ZL) rats, as euglycemic controls, were divided into groups receiving normal (0.28%) (ZDF+N, ZL+N) and high-salt (5.5%) diets (ZDF+S, ZL+S) for 10 weeks. Renal mRNA expression of serum- and glucocorticoid-inducible kinase 1 (SGK1) and sodium transporters (for example, the epithelial sodium channel-α, ENaCα) were measured by quantitative reverse transcriptase-PCR. Vascular hypertrophy (media-to-lumen ratio, M/L) in mesenteric resistance arteries was assessed using a pressurized myograph. Systolic blood pressure (SBP) was significantly higher in ZDF+S vs. ZDF+N (146±2 vs. 133±3 mm Hg; P<0.05), whereas there was no difference between ZL+S and ZL+N (151±3 vs. 147±3 mm Hg). Plasma sodium concentration was higher in ZDF+S vs. ZDF+N, whereas there was no difference between ZL+S and ZL+N. Plasma aldosterone concentration (PAC) was higher in ZDF+N as compared with ZL+N (191±23 vs. 95±35 pg ml−1; P<0.05). PAC decreased to zero in ZL+S, which was not the case in ZDF+S (0±0 vs. 37±2 pg ml−1). Salt loading decreased the mRNA expression of SGK1 in euglycemic controls (ZL+S 0.58±0.2 vs. ZL+N 1.05±0.05; P=0.05), whereas it significantly increased SGK1 expression in diabetic rats (ZDF+S 1.75±0.15 vs. ZDF+N 0.92±0.07; P<0.01). ENaCα mRNA expression paralleled these changes. The M/L of mesenteric resistance arteries was not different between ZDF+N and ZL+N. High salt significantly increased the M/L in ZDF+S vs. ZDF+N, but not in ZL+S vs. ZL+N. Systolic blood pressure in this model of type 2 diabetes mellitus is salt sensitive, leading to marked vascular remodeling. The underlying pathophysiological mechanism may be inappropriately high levels of aldosterone and up-regulation of SGK1-dependent renal sodium transport by ENaCα, leading to net increased sodium retention.