Biomedical subjects

Rainer Dietz

Publications and source records attributed to Rainer Dietz.

81 records · Page 5Linked to original sources

PubMed2002

Heart rate variability before the onset of ventricular tachycardia: differences between slow and fast arrhythmias.

BACKGROUND: We tested whether or not heart rate variability (HRV) changes can serve as early signs of ventricular tachycardia (VT) and predict slow and fast VT in patients with an implantable cardioverter defibrillator (ICD). METHODS AND RESULTS: We studied the ICD stored 1000 beat-to-beat intervals before the onset of VT (131 episodes) and during a control time without VT (74 series) in 63 chronic heart failure ICD patients. Standard HRV parameters as well as two nonlinear parameters, namely 'Polvar10' from symbolic dynamics and the finite time growth rates 'Fitgra9' were calculated. Comparing the control and the VT series, no linear HRV parameter showed a significant difference. The nonlinear parameters detected a significant increase in short phases with low variability before the onset of VT (for time series with less than 10% ectopy, P<0.05). Subdividing VT into fast (cycle length 270 ms) events, we found that the onset of slow VT was characterized by a significant increase in heart rate, whereas fast VT was triggered during decreased heart rates, compared to the control series. CONCLUSIONS: Our data may permit the development of automatic ICD algorithms based on nonlinear dynamic HRV parameters to predict VT before it starts. Furthermore, they may facilitate improved prevention strategies.

Adult↗

PubMed2002

Phosphorylation by protein kinase CK2: a signaling switch for the caspase-inhibiting protein ARC.

Caspases play a central role in apoptosis, but their activity is under the control of caspase-inhibiting proteins. A characteristic of caspase-inhibiting proteins is direct caspase binding. It is yet unknown how the localization of caspase-inhibiting proteins is regulated and whether there are upstream signals controlling their function. Here we report that the function of ARC is regulated by protein kinase CK2. ARC at threonine 149 is phosphorylated by CK2. This phosphorylation targets ARC to mitochondria. ARC is able to bind to caspase-8 only when it is localized to mitochondria but not to the cytoplasm. Our results reveal a molecular mechanism by which a caspase-inhibiting protein requires phosphorylation in order to prevent apoptosis.

Animals↗

PubMed2002

Systematic analysis of the regulatory and essential myosin light chain genes: genetic variants and mutations in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) can be caused by mutations in genes encoding for the ventricular myosin essential and regulatory light chains. In contrast to other HCM disease genes, only a few studies describing disease-associated mutations in the myosin light chain genes have been published. Therefore, we aimed to conduct a systematic screening for mutations in the ventricular myosin light chain genes in a group of clinically well-characterised HCM patients. Further, we assessed whether the detected mutations are associated with malignant or benign phenotype in the respective families. We analysed 186 unrelated individuals with HCM for the human ventricular myosin regulatory (MYL2) and essential light chain genes (MYL3) using polymerase chain reaction, single strand conformation polymorphism analysis and automated sequencing. We found eight single nucleotide polymorphisms in exonic and adjacent intronic regions of MYL2 and MYL3. Two MYL2 missense mutations were identified in two Caucasian families while no mutation was found in MYL3. The mutation Glu22Lys was associated with moderate septal hypertrophy, a late onset of clinical manifestation, and benign disease course and prognosis. The mutation Arg58Gln showed also moderate septal hypertrophy, but, in contrast, it was associated with an early onset of clinical manifestation and premature sudden cardiac death. In conclusion, myosin light chain mutations are a very rare cause of HCM responsible for about 1% of cases. Mutations in MYL2 could be associated with both benign and malignant HCM phenotype.

Adolescent↗

PubMed2002

Treatment with darusentan over 21 days improved cGMP generation in patients with chronic heart failure.

In heart failure, the cGMP to natriuretic peptide ratio is decreased and infusion of atrial natriuretic peptide (ANP) induces less cGMP generation. The ratio of the second messenger cGMP to plasma concentrations of ANP or brain natriuretic peptide (BNP) correlates with the effectiveness of natriuretic peptides. It was investigated whether blockade of the ET(A) receptor might improve the cGMP:NP ratio in heart failure. Patients with chronic heart failure (n=142; mean age=57 years) received oral treatment with the ET(A) antagonist darusentan (either 30, 100, 300 mg/day or placebo) on top of standard therapy over a period of 21 days in a randomized, double-blind, placebo-controlled, multicentre study. Plasma concentrations of ANP, BNP and cGMP were determined before randomization and after 21 days of treatment. In parallel with decreased pulmonary and systemic vascular resistance, 3 weeks of oral treatment with the ET(A) receptor antagonist darusentan reduced BNP plasma levels and increased the cGMP:BNP ratio significantly. The improved cGMP:BNP ratio might reflect the ability of chronic ET(A) receptor blockade to facilitate the generation of the second messenger cGMP, which points towards a favourable modulation of the natriuretic peptide effector system, in addition to haemodynamic improvement in heart failure patients.

Atrial Natriuretic Factor↗

PubMed2002

Quantification of valvular aortic stenosis by magnetic resonance imaging.

BACKGROUND: Assessing the aortic valvular orifice is important in judging the severity of aortic stenosis. Magnetic resonance imaging visualizes in-plane valvular motion. We studied the value of magnetic resonance planimetry of the aortic valve orifice. METHODS: We used breath-hold gradient echocardiographic sequences on a clinical magnetic resonance system (1.5 T) and studied 25 patients with symptomatic valvular aortic stenosis. We performed a planimetry of the valvular orifice in systolic images of the valvular plane. The results were compared with echocardiography (continuity equation) and cardiac catheterization (Gorlin formula). RESULTS: Magnetic resonance planimetry was feasible in all patients, and the image quality was invariably adequate. The magnetic resonance imaging results correlated well with the data calculated from catheterization and less robustly with the echocardiographic results. The 3 methods were similar in terms of leading to clinical decisions. CONCLUSIONS: We suggest that magnetic resonance flow planimetry of the aortic valve orifice offers a simple, reliable, fast, and safe method to noninvasively quantify aortic stenosis.

Aged↗

PubMed2002

Regulation of E2F1-dependent gene transcription and apoptosis by the ETS-related transcription factor GABPgamma1.

The E2F family of transcription factors comprises six related members which are involved in the control of the coordinated progression through the G(1)/S-phase transition of cell cycle or in cell fate decision. Their activity is regulated by pocket proteins, including pRb, p107, and p130. Here we show that E2F1 directly interacts with the ETS-related transcription factor GABPgamma1 in vitro and in vivo. The binding domain interacting with GABPgamma1 was mapped to the C-terminal amino acids 310 to 437 of E2F1, which include its transactivation and pRb binding domain. Among the E2F family of transcription factors, the interaction with GABPgamma1 is restricted to E2F1. DNA-binding E2F1 complexes containing GABPgamma1 are characterized by enhanced E2F1-dependent transcriptional activity. Moreover, GABPgamma1 suppresses E2F1-dependent apoptosis by mechanisms other than the inhibition of the transactivation capacity of E2F1. In summary, our results provide evidence for a novel pRb-independent mechanism regulating E2F1-dependent transcription and apoptosis.

Animals↗

PubMed2002

Cardiac and renal effects of growth hormone in volume overload-induced heart failure: role of NO.

Growth hormone (GH) application is a new strategy in the treatment of heart failure. However, clinical and experimental investigations have shown contradictory effects of GH on cardiac performance. We tested the hypothesis that GH could improve cardiac and renal function in volume overload-induced heart failure. The effect of 4 weeks of GH treatment (2 mg/kg daily) was investigated in Wistar rats with aortocaval shunt. GH application did not influence left ventricular contractility and end-diastolic pressure in rats with aortocaval shunt. In contrast, GH treatment normalized impaired diuresis (vehicle 10.8+/-0.6 mL/d, GH 15.8+/-0.7 mL/d; P<0.05) and sodium excretion (vehicle 1.5+/-0.1 mmol/d, GH 2.2+/-0.1 mmol/d; P<0.001) in shunt-operated rats, with a similar increase of fractional sodium excretion. The urinary excretion of cGMP, the second messenger of atrial natriuretic peptide and NO, was higher in animals with shunts than in sham-operated animals and was further increased by GH (vehicle 293+/-38 nmol/d, GH 463+/-57 nmol/d; P<0.01). Although the atrial natriuretic peptide plasma levels were unchanged after GH, the excretion of NO metabolites (nitrate/nitrite) was elevated (vehicle 2020+/-264 nmol/d, GH 2993+/-375 nmol/d; P<0.05) in parallel with increased renal mRNA levels of inducible NO synthase 2. The changes of renal function after GH and the increased excretion of NO metabolites and cGMP were abolished by simultaneous treatment with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester. GH treatment did not influence cardiac function in rats with aortocaval shunts. However, GH improved renal function by increasing diuresis and sodium excretion. The responsible mechanism might be the enhanced activity of the renal NO system.

Angiotensin II↗

PubMed2002

Monocyte-expressed urokinase regulates human vascular smooth muscle cell migration in a coculture model.

Interactions of vascular smooth muscle cells (VSMC) with monocytes recruited to the arterial wall at a site of injury, with resultant modulation of VSMC growth and migration, are central to the development of vascular intimal thickening. Urokinase-type plasminogen activator (uPA) expressed by monocytes is a potent chemotactic factor for VSMC and might serve for the acceleration of vascular remodeling. In this report, we demonstrate that coculture of human VSMC with freshly isolated peripheral blood-derived human monocytes results in significant VSMC migration that increases during the coculture period. Accordingly, VSMC adhesion was inhibited with similar kinetics. VSMC proliferation, however, was not affected and remained at the same basal level during the whole period of coculture. The increase of VSMC migration in coculture was equivalent to the uPA-induced migration of monocultured VSMC and was blocked by addition into coculture of soluble uPAR (suPAR). Analysis of uPA and uPAR expression in cocultured cells demonstrated that monocytes are a major source of uPA, whose expression increases in coculture five-fold, whereas VSMC display an increased expression of cell surface-associated uPAR. These findings indicate that upregulated uPA production by monocytes following vascular injury acts most likely as an endogenous activator of VSMC migration contributing to the remodeling of vessel walls.

Cell Adhesion↗

PubMed2001

Urokinase-dependent human vascular smooth muscle cell adhesion requires selective vitronectin phosphorylation by ectoprotein kinase CK2.

Urokinase (uPA)- and urokinase receptor (uPAR)-dependent cell adhesion to the extracellular matrix protein vitronectin (Vn) is an important event in wound healing, tissue remodeling, immune response, and cancer. We recently demonstrated that in human vascular smooth muscle cells (VSMC) uPA/uPAR are functionally associated with the ectoprotein kinase casein kinase-2 (CK2). We now asked whether CK2 regulates uPA-dependent cell adhesion to Vn, since the latter is a natural CK2 substrate. We found that Vn is indeed selectively phosphorylated by CK2 and that this phosphorylation is uPA-regulated in VSMC. Vn induces release of ecto-CK2 from the cell surface via a process termed as "shedding." CK2-mediated Vn phosphorylation was decisive for the uPA-dependent VSMC adhesion. Specific inhibition of CK2 completely abolished the uPA-induced cell adhesion to Vn. This effect was specific for cell adhesion to Vn and required participation of both uPAR and alpha(v)beta(3) integrins as adhesion receptors. CK2 localization at the cell surface was highly dynamic; Vn induced formation of clusters where CK2 colocalized with uPAR and alpha(v)beta(3) integrins. These results indicate that the uPA-dependent VSMC adhesion is a function of selective Vn phosphorylation by the ectoprotein kinase CK2 and suggest a regulatory role for Vn phosphorylation in the uPA-directed adhesive process.

Casein Kinase II↗