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P Hildebrandt

Publications and source records attributed to P Hildebrandt.

At least 19 recordsLinked to original sources

On the electron transfer mechanism between cytochrome C and metal electrodes. Evidence for dynamic control at short distances.

Cytochrome c was coordinatively bound to self-assembled monolayers of pyridine-terminated alkanethiols on Au and Ag electrodes. The mechanism of heterogeneous electron transfer of the immobilized protein was investigated by cyclic voltammetry and time-resolved surface-enhanced resonance Raman spectroelectrochemistry. The temperature, distance, and overpotential dependencies of the electron transfer rates indicate a change of mechanism from a tunneling controlled reaction at long distances (thicker films) to a solvent/protein friction controlled reaction at smaller distances (thinner films).

Algorithms↗

Intense metabolic control by means of insulin in patients with diabetes mellitus and acute myocardial infarction (DIGAMI 2): effects on mortality and morbidity.

AIMS: Patients with diabetes have an unfavourable prognosis after an acute myocardial infarction. In the first DIGAMI study, an insulin-based glucose management improved survival. In DIGAMI 2, three treatment strategies were compared: group 1, acute insulin-glucose infusion followed by insulin-based long-term glucose control; group 2, insulin-glucose infusion followed by standard glucose control; and group 3, routine metabolic management according to local practice. METHODS AND RESULTS: DIGAMI 2 recruited 1253 patients (mean age 68 years; 67% males) with type 2 diabetes and suspected acute myocardial infarction randomly assigned to groups 1 (n=474), 2 (n=473), and 3 (n=306). The primary endpoint was all-cause mortality between groups 1 and 2, and a difference was hypothesized as the primary objective. The secondary objective was to compare total mortality between groups 2 and 3, whereas morbidity differences served as tertiary objectives. The median study duration was 2.1 (interquartile range 1.03-3.00) years. At randomization, HbA1c was 7.2, 7.3, and 7.3% in groups 1, 2, and 3, respectively, whereas blood glucose was 12.8, 12.5, and 12.9 mmol/L, respectively. Blood glucose was significantly reduced after 24 h in all groups, more in groups 1 and 2 (9.1 and 9.1 mmol/L) receiving insulin-glucose infusion than in group 3 (10.0 mmol/L). Long-term glucose-lowering treatment differed between groups with multidose insulin (> or =3 doses/day) given to 15 and 13% of patients in groups 2 and 3, respectively compared with 42% in group 1 at hospital discharge. By the end of follow-up, HbA1c did not differ significantly among groups 1-3 ( approximately 6.8%). The corresponding values for fasting blood glucose were 8.0, 8.3, and 8.6 mmol/L. Hence, the target fasting blood glucose for patients in group 1 of 5-7 mmol/L was never reached. The study mortality (groups 1-3 combined) was 18.4%. Mortality between groups 1 (23.4%) and 2 (22.6%; primary endpoint) did not differ significantly (HR 1.03; 95% CI 0.79-1.34; P=0.831), nor did mortality between groups 2 (22.6%) and 3 (19.3%; secondary endpoint) (HR 1.23; CI 0.89-1.69; P=0.203). There were no significant differences in morbidity expressed as non-fatal reinfarctions and strokes among the three groups. CONCLUSION: DIGAMI 2 did not support the fact that an acutely introduced, long-term insulin treatment improves survival in type 2 diabetic patients following myocardial infarction when compared with a conventional management at similar levels of glucose control or that insulin-based treatment lowers the number of non-fatal myocardial reinfarctions and strokes. However, an epidemiological analysis confirms that the glucose level is a strong, independent predictor of long-term mortality in this patient category, underlining that glucose control seems to be an important part of their management.

Aged↗

Markers of collagen synthesis is related to blood pressure and vascular hypertrophy: a LIFE substudy.

Cardiac fibrosis and high levels of circulating collagen markers has been associated with left ventricular (LV) hypertrophy. However, the relationship to vascular hypertrophy and blood pressure (BP) load is unclear. In 204 patients with essential hypertension and electrocardiographic LV hypertrophy, we measured sitting BP, serum collagen type I carboxy-terminal telopeptide (ICTP) reflecting degradation, procollagen type I carboxy-terminal propeptide (PICP) reflecting synthesis and LV mass by echocardiography after 2 weeks of placebo treatment and after 1 year of antihypertensive treatment with a losartan- or an atenolol-based regimen. Furthermore, we measured intima-media thickness of the common carotid arteries (IMT), minimal forearm vascular resistance (MFVR) by plethysmography and ambulatory 24-h BP in around half of the patients. At baseline, PICP/ICTP was positively related to IMT (r=0.24, P<0.05), MFVR(men) (r=0.35, P<0.01), 24-h systolic BP (r=0.24, P<0.05) and 24-h diastolic BP (r=0.22, P<0.05), but not to LV mass. After 1 year of treatment with reduction in systolic BP (175+/-15 vs 151+/-17 mmHg, P<0.001) and diastolic BP (99+/-8 vs 88+/-9 mmHg, P<0.001), ICTP was unchanged (3.7+/-1.4 vs 3.8+/-1.4 microg/l, NS) while PICP (121+/-39 vs 102+/-29 microg/l, P<0.001) decreased. The reduction in PICP/ICTP was related to the reduction in sitting diastolic BP (r=0.31, P<0.01) and regression of IMT (r=0.37, P<0.05) in patients receiving atenolol and to reduction in heart rate in patients receiving losartan (r=0.30, P<0.01). In conclusion, collagen markers reflecting net synthesis of type I collagen were positively related to vascular hypertrophy and BP load, suggesting that collagen synthesis in the vascular wall is increased in relation to high haemodynamic load in a reversible manner.

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Impairment of cardiac function in hypertensive patients with Type 2 diabetes: a LIFE study.

AIMS: Type 2 diabetic patients with hypertension have an increased left ventricular (LV) mass and impaired cardiac function compared to hypertensive patients without diabetes. However, it is unknown if the impaired cardiac function can be explained solely by LV hypertrophy, or is independently related to diabetes. The aim of the present study was to compare LV function between diabetic and non-diabetic hypertensive patients with electrocardiographic LV hypertrophy. METHODS: In 937 patients participating in the LIFE echocardiographic substudy, all echocardiograms were centrally evaluated by a core reading centre measuring LV mass, systolic and diastolic LV function. Known diabetes was present in 105 patients. RESULTS: Left ventricular mass was similar in diabetic and non-diabetic patients. Endocardial systolic LV function, estimated by LV ejection fraction, was reduced and indices of midwall systolic LV function were impaired in the diabetic patients. Diastolic LV filling pattern was impaired and arterial stiffness, measured by pulse pressure/stroke index, was increased in diabetic patients. CONCLUSIONS: Systolic and diastolic LV function in hypertensive patients with electrocardiographic LV hypertrophy and diabetes are impaired independent of LV mass, most likely reflecting the adverse effects of diabetes per se.

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Plasma N-terminal pro-brain natriuretic peptide as a major risk marker for cardiovascular disease in patients with type 2 diabetes and microalbuminuria.

AIMS/HYPOTHESIS: We examined whether plasma N-terminal probrain natriuretic peptide (NT-proBNP) predicts cardiovascular outcome in patients with type 2 diabetes. METHODS: A total of 160 microalbuminuric type 2 diabetic patients (mean age 55.1 years [SD 7.2], 119 men) were enrolled in the Steno-2 Study examining the effect of multifactorial treatment, and were divided into two groups according to baseline levels of plasma NT-proBNP below or above the median for the cohort, which was followed for an average of 7.8 years. Cardiovascular outcome was a composite of cardiovascular mortality, myocardial infarction, stroke, revascularisation procedures in the heart or legs, and amputations. RESULTS: In the whole group, plasma NT-proBNP being above the median was associated with an increased risk of cardiovascular disease during follow-up, with an unadjusted hazard ratio of 4.4 (95% CI 2.3-8.4; p<0.0001). A decrease in plasma NT-proBNP of 10 pg/ml during the first 2 years of intervention was associated with a 1% relative reduction in the primary endpoint (p<0.001). Despite polypharmacological treatment targeting cardiovascular disease, the mean plasma NT-proBNP level increased during follow-up. CONCLUSIONS/INTERPRETATION: We conclude that high plasma NT-proBNP is a major risk marker for cardiovascular disease in patients with type 2 diabetes and microalbuminuria.

Albuminuria↗

Plasma N-terminal pro-brain natriuretic peptide as an independent predictor of mortality in diabetic nephropathy.

AIMS/HYPOTHESIS: Raised N-terminal pro-brain natriuretic peptide (NT-proBNP) is independently associated with an increased risk of death in chronic heart failure and acute coronary syndromes in nondiabetic populations. Diabetic nephropathy is characterised by an increased risk of cardiovascular morbidity and mortality. This study investigated the prognostic value of NT-proBNP in a large cohort of type 1 diabetic patients with and without diabetic nephropathy. METHODS: In a prospective observational follow-up study, 198 type 1 diabetic patients with overt diabetic nephropathy (122 men, age [mean+/-SD] 41+/-10 years, duration of diabetes 28+/-8 years, GFR 74+/-33 ml min(-1)) and a matched control group of 188 patients with longstanding type 1 diabetes and persistent normoalbuminuria (114 men, age 43+/-10 years, duration of diabetes 27+/-9 years) were followed for 9.3 (0.0-9.5) years. Plasma NT-proBNP concentration was determined by immunoassay at baseline. RESULTS: In patients with diabetic nephropathy, plasma NT-proBNP concentration was elevated to (median [range]) 110 (5-79640) ng l(-1) vs. 27 (5-455) ng l(-1) in normoalbuminuric patients (p<0.0001). Among patients with nephropathy, 39 (39%) patients with plasma NT-proBNP concentrations above the median and 12 (12%) with values below the median died from any cause (unadjusted hazard ratio 3.86 [95% CI 2.02-7.37], p<0.0001; covariate-adjusted hazard ratio 2.28 [1.04-4.99], p=0.04). This lower mortality rate was attributable to fewer cardiovascular deaths: 31 (31%) and 7 (7%) above and below the median NT-proBNP level respectively (unadjusted hazard ratio 5.25 [2.31-11.92], p<0.0001; covariate-adjusted hazard ratio 3.81 [1.46-9.94], p=0.006). CONCLUSIONS/INTERPRETATION: Elevated circulating NT-proBNP is a new independent predictor of the excess overall and cardiovascular mortality in diabetic nephropathy patients without symptoms of heart failure.

Adult↗

Prevalence of impaired left ventricular systolic function and heart failure in a middle aged and elderly urban population segment of Copenhagen.

OBJECTIVE: To assess the prevalence of impaired left ventricular systolic function and manifest heart failure in a general population aged 50-89 years. DESIGN: In this cross sectional survey, participants filled in a heart failure questionnaire. ECG, blood tests, and echocardiography were performed. SETTING: The study population was recruited from general practitioners situated in the same urban area and examined in a university hospital in Copenhagen, Denmark. PARTICIPANTS: 764 participants (432 women and 332 men, median (SD) age 66 (11) years) participated. The study population was stratified to include a minimum of 150 persons in each age decade. MAIN OUTCOME MEASURES: Prevalence of impaired systolic function and manifest heart failure. RESULTS: The prevalence of systolic dysfunction (left ventricular ejection fraction < or = 40%) was more than twice as high among men (7.6%) as among women (2.6%). In the male population systolic heart failure (left ventricular ejection fraction < or = 40% and symptoms) was found in 1.8% of the 50-59 years age group and approximately doubled for each age decade to reach 13.9% in octogenarians. Among women systolic dysfunction increased from 0.8% to 4.3% in the same age groups. Asymptomatic cases accounted for 44.0% of all cases of systolic dysfunction in the male population and only 9.1% in the female population. CONCLUSIONS: In this age controlled population study impaired left ventricular systolic function and heart failure increased substantially with age and was more than twice as frequent among men as among women. Asymptomatic left ventricular dysfunction occurred more frequently in men than in women and was less prevalent with increasing age.

Age Factors↗

Cloning, functional expression and biochemical characterization of a stereoselective alcohol dehydrogenase from Pseudomonas fluorescens DSM50106.

Sequencing of a genomic library prepared from Pseudomonas fluorescens DSM 50106 identified an orf showing 29% identity to a C alpha-dehydrogenase of Pseudomonas paucimobilis and high homology to several sequences with unknown functions derived from genome projects. The corresponding gene adhF1 encodes a dehydrogenase of 296 amino acids with a calculated molecular mass of 31.997 kDa. The gene was functionally expressed in E. coli using a rhamnose inducible expression system. The resulting recombinant enzyme was active in the pH range 6-10 (best pH 8) and at 5-25 degrees C. This dehydrogenase converts cyclic ketones to the corresponding alcohols utilizing the cofactor NADH. The highest activity was found for cyclohexanone. The enzyme also exhibits high stereoselectivity in the desymmetrization of the prochiral ketone acetophenone, producing optically pure ( R)-alpha-phenyl ethanol (>99%ee) at high conversion (95%).

Alcohol Dehydrogenase↗

Electron transfer dynamics of cytochrome c bound to self-assembled monolayers on silver electrodes.

Cytochrome c (Cyt-c) was electrostatically immobilised on Ag electrodes coated with self-assembled monolayers (SAM) that are formed by omega-carboxyl alkanethiols with different alkyl chain lengths (C(x)). Surface enhanced resonance Raman (SERR) spectroscopy demonstrated that electrostatic binding does not lead to conformational changes of the heme protein under the conditions of the present experiments. Employing time-resolved SERR spectroscopy, the rate constants of the heterogeneous electron transfer (ET) between the adsorbed Cyt-c and the Ag electrode were determined for a driving force of zero electronvolts. For SAMs with long alkyl chains (C(16), C(11)), the rate constants display a normal exponential distance dependence, whereas for shorter chain lengths (C(6), C(3), C(3)), the ET rate constant approaches a constant value (ca. 130 s(-1)). The onset of the non-exponential distance-dependence is paralleled by an increasing kinetic H/D effect, indicating a coupling of the redox reaction with proton transfer (PT) steps. This unusual kinetic behaviour is attributed to the effect of the electric field at the Ag/SAM interface that increasingly raises the energy barrier for the PT processes with decreasing distance of the adsorbed Cyt-c from the electrode. The distance-dependence of the electric field strength is estimated on the basis of a simple electrostatic model that can consistently describe the redox potential shifts of Cyt-c as determined by stationary SERR spectroscopy for the various SAMs. At low electric fields, PT is sufficiently fast so that rate constants, determined as a function of the driving force, yield the reorganisation energy (0.217 electronvolts) of the heterogeneous ET.

Cytochrome c Group↗

Glycosaminoglycans--all round talents in coating technology.

The use of glycosaminoglycans for coating of medical implants had it's beginning in heparin coating of coronary stents and catheters to improve their haemocompatibility. Until now glycosaminoglycans proved as very potent in a variety of medical applications. Glycosaminoglycans not only show anticoagulant properties, also their crystal growth inhibiting effects in urology, inhibition of bacterial adherence and influence on the proliferation behaviour of human cells could be demonstrated. Beside an overview over the development of glycosaminoglycan coatings so far, recent outcomes of a bacteriological and a cell proliferation study with coated surfaces are presented.

Animals↗

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes.

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From Mössbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.

Journal Article↗

Proton-coupled electron transfer of cytochrome c.

Cytochrome c (Cyt-c) was electrostatically bound to self-assembled monolayers (SAM) on an Ag electrode, which are formed by omega-carboxyl alkanethiols of different chain lengths (C(x)). The dynamics of the electron-transfer (ET) reaction of the adsorbed heme protein, initiated by a rapid potential jump to the redox potential, was monitored by time-resolved surface enhanced resonance Raman (SERR) spectroscopy. Under conditions of the present experiments, only the reduced and oxidized forms of the native protein state contribute to the SERR spectra. Thus, the data obtained from the spectra were described by a one-step relaxation process yielding the rate constants of the ET between the adsorbed Cyt-c and the electrode for a driving force of zero electronvolts. For C(16)- and C(11)-SAMs, the respective rate constants of 0.073 and 43 s(-1) correspond to an exponential distance dependence of the ET (beta = 1.28 A(-1)), very similar to that observed for long-range intramolecular ET of redox proteins. Upon further decreasing the chain length, the rate constant only slightly increases to 134 s(-1) at C(6)- and remains essentially unchanged at C(3)- and C(2)-SAMs. The onset of the nonexponential distance dependence is paralleled by a kinetic H/D effect that increases from 1.2 at C(6)- to 4.0 at C(2)-coatings, indicating a coupling of the redox reaction with proton-transfer (PT) steps. These PT processes are attributed to the rearrangement of the hydrogen-bonding network of the protein associated with the transition between the oxidized and reduced state of Cyt-c. Since this unusual kinetic behavior has not been observed for electron-transferring proteins in solution, it is concluded that at the Ag/SAM interface the energy barrier for the PT processes of the adsorbed Cyt-c is raised by the electric field. This effect increases upon reducing the distance to the electrode, until nuclear tunneling becomes the rate-limiting step of the redox process. The electric field dependence of the proton-coupled ET may represent a possible mechanism for controlling biological redox reactions via changes of the transmembrane potential.

Adsorption↗

[Comparison of preventive effect of "new" and "old" antihypertensive agents].

BACKGROUND: Until recently no morbidity-mortality study had examined the effects of newer drugs like angiotensin-converting enzyme inhibitors, calcium-antagonists and alpha-blockers compared to "old" but well-proven thiazide diuretics and beta-blockers in the treatment of essential hypertension. MATERIAL AND METHODS: The prospective and randomized clinical trials CAPPP, STOP-2, NORDIL, INSIGHT and one arm of ALLHAT, with a total of approximately 58,000 middle-aged or elderly hypertensive patients have been assessed. RESULTS: The primary outcome, composite cardiovascular (CV) death, cerebral stroke and myocardial infarction, in one study with heart failure, or composite fatal coronary heart disease and myocardial infarction, was equal in all trials. INTERPRETATION: According to current evidence, prevention of cardiovascular disease in hypertension is the same irrespective of the class of drug.

Adrenergic alpha-Antagonists↗

De novo design and characterization of copper centers in synthetic four-helix-bundle proteins.

The design and chemical synthesis of de novo metalloproteins on cellulose membranes with the structure of an antiparallel four-helix bundle is described. All possible combinations of three different sets of amphiphilic helices were assembled on cyclic peptide templates which were bound by a cleavable linker to the cellulose. In the hydrophobic interior, the four-helix bundle proteins carry a cysteine and several histidines at various positions for copper ligation. This approach was used successfully to synthesize, for the first time, copper proteins based on a four-helix bundle. UV-vis spectra monitored on the solid support showed ligation of copper(II) by about one-third out of the 96 synthesized proteins and tetrahedral complexes of cobalt(II) by most of these proteins. Three of the most stable copper-binding proteins were synthesized in solution and their structural properties analyzed by spectroscopic methods. Circular dichroism, one-dimensional NMR, and size-exclusion chromatography indicate a folding into a compact state containing a high degree of secondary structure with a reasonably ordered hydrophobic core. They displayed UV-vis absorption, resonance Raman, and EPR spectra intermediate between those of type 1 and type 2 copper centers. The present approach provides a sound basis for further optimizing the copper binding and its functional properties by using combinatorial protein chemistry guided by rational principles.

Binding Sites↗

Structural changes of cytochrome c(552) from Thermus thermophilus adsorbed on anionic and hydrophobic surfaces probed by FTIR and 2D-FTIR spectroscopy.

The structural changes of cytochrome c(552) bound to anionic and hydrophobic clay surfaces have been investigated by Fourier transform infrared spectroscopy. Binding to the anionic surface of montmorillonite is controlled by electrostatic interactions since addition of electrolyte (0.5 mol L(-1) KCl) causes desorption of more than 2/3 of the protein molecules. Electrostatic binding occurs through the back side of the protein (i.e., remote from the heme site) and is associated only with subtle changes of the secondary structure. In contrast, adsorption to the hydrophobic surface of talc leads to a decrease in alpha-helical structure by ca. 5% and an increase in beta-sheet structure by ca. 6%. These structural changes are attributed to a hydrophobic region on the front surface of cytochrome c(552) close to the partially exposed heme edge. This part on the protein surface is identified as the interaction domain for talc and most likely also serves for binding to the natural reaction partner, a ba(3)-oxidase. Fourier transform infrared spectra of cytochrome c(552) and the clay-cytochrome c(552) complexes have been measured as a function of time following dissolution and suspension in deuterated buffer, respectively. A two-dimensional correlation analysis was applied to these spectra to investigate the dynamics of the structural changes in the protein. For both complexes, adsorption and subsequent unfolding processes in the binding domains are faster than the time resolution of the spectroscopic experiments. Thus, the processes that could be monitored are refolding of peptide segments and side chain rearrangements following the adsorption-induced perturbation of the protein structure and the solvation of the adsorbed protein. In each case, side chain alterations of solvent-exposed tyrosine, aspartate, and glutamate residues were observed. For the cytochrome c(552)-talc complex, these changes are followed by a slow refolding of the peptide chain in the binding domain and, subsequently, a further H/D exchange of amide group protons.

Adsorption↗

Prevention of surface encrustation of urological implants by coating with inhibitors.

The encrustation of materials used for urological implants is as yet an unresolved problem. The crystallisation-inhibiting effect of the glycosaminoglycan heparin was used to reduce encrustation. Heparin was covalently bound to the surface of slotted-tube stents of tantalum and stainless steel using a spacer molecule. To verify the inhibition of crystallisation processes, reproducible in vitro tests and in vivo tests using the rat as animal model were carried out. The in vitro and in vivo experiments showed that the heparin coating has a significant influence on the encrustation of the surface. After 7 days in vitro and 120 days in vivo, heparin coated stents were free of encrustation, whereas the uncoated reference stents were extensively covered.

Animals↗

The impact of heart failure on prognosis of diabetic and non-diabetic patients with myocardial infarction: a 15-year follow-up study.

BACKGROUND: Information about the occurrence of heart failure in the acute phase of myocardial infarction (MI) in diabetic patients and its impact on prognosis are sparse. AIM: The purpose of the present study was to describe how MI patients with diabetes mellitus (DM) differed from MI patients without DM with respect to the occurrence of heart failure and with respect to the influence of heart failure on mortality during follow-up 30 days extending to 15 years. METHODS: The study is a retrospective long-term follow-up of prospectively recorded data concerning 1954 consecutive cases of MI admitted to one coronary care unit (CCU) between 1979 and 1983. DM was diagnosed in 10% (n=194), with 17% (n=33) on insulin therapy. Patients with DM comprised of a higher proportion of women (DM 36% vs. no DM 26%, P<0.001) compared with non-diabetic patients. Baseline risk factors were more prevalent in the patients with DM. The cumulative incidence of heart failure was higher among patients with than without DM (DM 54% vs. no DM 34%, P<0.001). The incidence of life-threatening arrhythmias were similar in both groups. Only 2% of patients with DM and heart failure survived 10 years of follow-up compared with 15% of the non-diabetic patients with heart failure (P<0.001). In multivariate analysis DM was not independently associated with 30 days mortality. During long-term follow-up DM was an important risk factor for mortality independent on the presence of heart failure. CONCLUSION: DM disposes to the development of heart failure. In acute myocardial infarction diabetic patients with heart failure have a worse prognosis than non-diabetic patients with heart failure.

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