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Biomedical subjects

H Lorenz

Publications and source records attributed to H Lorenz.

At least 19 recordsLinked to original sources
PubMed2002

Mutant prion protein acquires resistance to protease in mouse neuroblastoma cells.

Conversion of the cellular isoform of the prion protein (PrP(C)) into the pathogenic isoform (PrP(Sc)) is thought to be the causative event in prion diseases. Biochemically, PrP(Sc) differs from PrP(C) in its partial resistance to proteinase K (PK). The amino acid sequence AGAAAAGA, comprising residues 112-119 of the murine PrP(C), has been shown to be amyloidogenic and evolutionarily conserved. To assess the effect of mutations at and around this hydrophobic sequence on protease resistance, the sequence was replaced either by alanines or by glycines and, in a third mutant, a large part surrounding this region was removed. The PrP mutant carrying substitutions of glycines for alanines showed PK resistance and aberrant proteolytic processing. Tetracycline-induced expression of this mutant indicated that resistance to protease is acquired concurrent with the synthesis of the protein. These findings indicate that mutations in the central hydrophobic region lead to immediate alterations in PrP structure and processing.

Animals↗
PubMed2001

Coupling of simulated moving bed chromatography and fractional crystallisation for efficient enantioseparation.

An optimised coupling of liquid chromatography and fractional crystallisation is suggested for efficient enantioseparation. As a first stage, a chromatographic separation, preferably simulated moving bed (SMB) chromatography, is applied to achieve an enantiomeric enrichment sufficient for a subsequent crystallisation. First results of the experimental and modelling work for the model system (+)-/(-)-mandelic acid in an aqueous solution are described. Chromatographic investigations involve the estimation of adsorption isotherms on a suitable chiral stationary phase and the simulation and optimisation of a corresponding SMB process. From the ternary phase diagram measured for the (+)-/(-)-enantiomer/ solvent system, the conditions required to crystallise a pure enantiomer from an asymmetric mixture can be derived. The productivity gains achievable from the combined process compared to the application of chromatography alone are discussed.

Chromatography, Liquid↗
PubMed2001

Chondrocyte expressed protein-68 (CEP-68), a novel human marker gene for cultured chondrocytes.

In the search for new marker genes suitable to distinguish chondrocytes from osteoblasts and mesenchymal stem cells in culture, we have identified and characterized a novel gene called chondrocyte expressed protein-68 (CEP-68), harbouring an N-terminal leader peptide and an epidermal growth factor-like calcium-binding domain. CEP-68 defines a new family of proteins and complements collagen type II as a new marker for stem-cell-based chondrogenic tissue engineering.

Amino Acid Sequence↗
PubMed2001

Two distinct reproductive strategies are correlated with an ovarian phenotype in co-existing parthenogenetic strains of a parasitic wasp.

The question whether different organisms are able to compete for the same resource is of fundamental importance to evolutionary biology. Sympatric co-existence of similar species on a single resource has long been claimed to be unstable. However, indirect evidence suggests that parasitic wasps exhibit evolutionarily stable mixtures of life-history strategies. Here we describe genetically distinct strains of a parthenogenetic wasp Venturia canescens, with different ovarian phenotypes that affect egg numbers in oviducts. Wasp females with large egg load search for caterpillars and deposit eggs immediately after host encounter, whereas females with fewer eggs delay parasitism. Since the outcome of interlarval competition within super-parasitized caterpillars depends on the age distribution of competing larvae, the two egg deposition strategies may co-exist under conditions that favor super-parasitism.

Journal Article↗
PubMed2001

Fusion proteins for combined analysis of autoantibodies to the 65-kDa isoform of glutamic acid decarboxylase and islet antigen-2 in insulin-dependent diabetes mellitus.

BACKGROUND: Prediction, risk assessment, and diagnosis of autoimmune diseases often rely on detection of autoantibodies directed to multiple target antigens, such as the 65-kDa isoform of glutamic acid decarboxylase (GAD65-abs) and the tyrosine phosphatase-like protein islet antigen-2 (IA2-abs), the two major subspecificities of islet cell antibodies (ICAs) associated with insulin-dependent diabetes mellitus. We hypothesized that a combination of autoantigens in a fusion protein unifying the important immunodominant epitopes could provide an efficient target for cost-effective, one-step screening of sera. METHODS: Chimeric proteins composed of GAD65 and IA2 residues were constructed, analyzed for their immune reactivity with monoclonal antibodies and sera, and used in a diagnostic assay with (35)S-labeled protein as antigen. RESULTS: Length and order of GAD65 and IA2 sequences were critical for conservation of the conformational epitopes in the fusion protein. Among four chimera tested, only IA2((606-979))/GAD65((1-585)) retained wild-type-like folding of GAD65 and IA2 domains and yielded a stable protein after baculovirus expression. Reactivity of GAD65 antibody- and IA2 antibody-positive sera from patients newly diagnosed with insulin-dependent diabetes mellitus, from ICA-positive prediabetics, and from ICA-positive first-degree relatives demonstrated conservation of the relevant autoreactive epitopes. The assay based on the in vitro translated fusion antigen had a sensitivity and specificity identical to those for detection of GAD65- and IA2-abs based on the two separate GAD65 and IA2 proteins. CONCLUSIONS: Autoantigens such as GAD65 and IA2 can be combined successfully in a fusion protein of similar immune reactivity. This allows simultaneous detection of GAD65- and IA2-abs in a one-step screening assay and cost-effective identification of positive individuals at risk of diabetes or at onset of disease.

Animals↗
PubMed2000

Etiopathogenesis of systemic lupus erythematosus.

Systemic lupus erythematosus is an autoimmune disease of unknown etiology. Research efforts of the last few years have mainly focused on basic molecular and cellular pathogenetic processes of the disease. Consequently, this paper reviews the etiopathogenetic hallmarks, such as impaired amount and presentation of nuclear antigens, production of antinuclear antibodies by T-cell-dependent B cell stimulation and organ damage by anti-dsDNA antibodies or immune complexes that are discussed at the present time. In summary, the hypothesis of a dysregulation of apoptotic cell clearance is strongly supported and broadly discussed.

Animals↗
PubMed1999

Induction of necrosis but not apoptosis after anoxia and reoxygenation in isolated adult cardiomyocytes of rat.

OBJECTIVES: Apoptosis is one feature of myocardial damage after ischemia-reperfusion, but the causes for its induction are unclear. The present study was undertaken to investigate whether apoptosis in cardiomyocytes is directly initiated by their sub-lethal injury that results from ischemia-reperfusion. METHODS: Ischemia was simulated on isolated ventricular cardiomyocytes of adult rats by anoxia in a glucose free medium, pH 6.4. Induction of apoptosis was detected by (1) DNA laddering of genomic DNA, (2) TUNEL positive cells (terminal deoxynucleotidyl transferase-mediated-UTP nick end labelling) and (3) annexinV-fluorescein isothiocyanate (annexinV-FITC) binding to cells under exclusion of propidium iodide. Necrotic cells were identified by (1) staining with both annexinV-FITC and propidium iodide, (2) unspecific DNA degradation and (3) enzyme release. RESULTS: Simulated ischemia caused a > 75% loss of high-energy phosphates within 2 h, which was reversible upon reoxygenation at pH 7.4. Even after 18 h of simulated ischemia, creatine phosphate contents recovered to 55.2 +/- 7.3% of control within 1 h. Apoptosis could be induced by UV irradiation (80 J/m2), H2O2 and the NO-donor N2-acetyl-S-nitroso-D,L-penicillinaminamide. In contrast to this, simulated ischemia and reoxygenation could not induce apoptosis in the cells, but with prolonged ischemia more cells became necrotic. After 18 hours of simulated ischemia and 4 h of reoxygenation 41.2 +/- 10.2% myocytes were necrotic (vs. 6.3 +/- 4.4% of control) and only 1.7 +/- 0.5% (vs. 8.7 +/- 4.6% of control) were apoptotic. The percentage of necrotic cells correlated with an increase in lactate dehydrogenase release from 9.9 +/- 0.6% (of total activity) of normoxic controls to 37.9 +/- 5.1% after 18 h of simulated ischemia and 12 h of reoxygenation. CONCLUSIONS: Simulated ischemia-reoxygenation causes necrosis of isolated cardiomyocytes but is not sufficient for induction of apoptosis.

Analysis of Variance↗
PubMed1999

Construction and characterization of murine neuroblastoma cell clones allowing inducible and high expression of the prion protein.

A tetracycline-inducible expression system has been established for the prion protein (PrP) in murine neuroblastoma cells (N2a). For this purpose, N2a cells were first stably transfected with either the tetracycline-controlled transactivator or the reverse transactivator. After selection of N2a clones which carried one of these transactivators, the murine PrP gene (Prnp) was introduced under the control of the transactivator-responsive promoter in a second round of stable transfection. Stably double-transfected N2a clones carrying the reverse type but not the normal transactivator were found to be fully inducible, giving a low background of Prnp expression before induction and high expression after induction. Stably double-transfected N2a cells were at least as productive as N2a cells over-expressing Prnp permanently under the control of a strong viral promoter. Furthermore, the selected N2a clones allowed the Prnp expression level to be quantitatively controlled by varying the level of the effector substance, the tetracycline-derivative doxycycline. The clones were fully controllable, as over-expression could be switched on and off as desired. These N2a clones may become an important tool for elucidation of the cellular function of PrP and may pave the way for the tetracycline-inducible expression of many genes in this neuroblastoma cell line.

Animals↗
PubMed1998

PCR detection of Coxiella burnetii from different clinical specimens, especially bovine milk, on the basis of DNA preparation with a silica matrix.

For PCR detection of Coxiella burnetii in various clinical specimens we developed a sample preparation method in which silica binding of DNA was used. This method was found to be fast, easily performed with large numbers of samples, and equally sensitive for all of the specimens tested (livers, spleens, placentas, heart valves, milk, blood). The DNA preparation method described here can also be used as an initial step in any PCR-based examination of specimens. The procedure was tested with more than 600 milk samples, which were taken from 21 cows that were seropositive for C. burnetii and reportedly had fertility problems (and therefore were suspected of shedding the agent through milk intermittently or continuously). Of the 21 cows tested, 6 were shedding C. burnetii through milk. Altogether, C. burnetii DNA was detected in 6% of the samples. There was no correlation between the shedding pattern and the serological results.

Animals↗
PubMed1998

Effects of felodipine ER, a dihydropyridine calcium antagonist, on blood pressure and serum lipids.

In an open trial, the antihypertensive efficacy of felodipine and its effects on lipid metabolism were investigated in 117 Nordic patients with mild to moderate essential hypertension and hyperlipidaemia. In the intent-to-treat analysis (n = 106) a significant (p < 0.01) drop in the mean systolic and diastolic blood pressure values was observed between baseline and 24 weeks' treatment from 157/100 mmHg to 145/92 (supine) and from 155/103 to 145/96 mmHg (erect). No relevant differences were seen in the pulse rate. Median total cholesterol and triglycerides remained unchanged, whereas HDL-cholesterol increased significantly from 1.30 mmol/l to 1.33 mmol/l (p < 0.02); LDL- and VLDL-cholesterol, apolipoprotein A1 and apolipoprotein B remained unchanged during the 24-week treatment period. In the per protocol analysis (n = 76), blood pressure values changed significantly from 158/100 mmHg to 144/91 mmHg (supine) and from 157/104 mmHg to 143/95 mmHg (erect) (p < 0.01 for both). HDL-cholesterol increased significantly (p = 0.03), whereas LDL- and VLDL-cholesterol, total cholesterol and triglycerides, as well as the apolipoproteins, remained unchanged during the trial. Felodipine thus proved to possess positive effects on lipid parameters in hypertensive patients.

Adult↗
PubMed1998

Efficacy of ramipril in therapy-resistant hypertension.

In an open, 48-week study the antihypertensive efficacy of ramipril when administered as add-on therapy to existing triple antihypertensive treatment (diuretics, beta-blockers, vasodilators) was investigated in 56 patients (24 females, 32 males) with therapy-resistant hypertension. The main variable (sitting diastolic blood pressure) decreased from 112 mmHg at baseline to 91 mmHg at week 8 (p < 0.01) and remained stable thereafter until the end of the trial. The systolic blood pressure in the sitting position decreased from 175 mmHg at baseline to 146 mmHg at week 8 (p < 0.01) and also remained stable thereafter until the end of the trial. Ramipril doses between week 8 and the end of the trial were not changed in 82% of patients. 45% of patients were treated with 5 mg ramipril/day, 33% with 10 mg/day and 22% with 20 mg/day at the end of the study. Addition of ramipril allowed a reduction in the doses of concurrrent therapy, especially in relation to beta-blockers (p < 0.02) and vasodilators (p < 0.01). The safety was good--no serious adverse events were observed. Ramipril is, therefore, a suitable drug for the patients with therapy-resistant hypertension allowing reduction of the doses of concomitant medication.

Adult↗
PubMed1996

Gas-potentiometric method with solid electrolyte oxygen sensors for the investigation of combustion.

Gas-potentiometric analysis using oxide-ion-conducting solid electrolytes as stabilized zirconia is a worthwhile method for the investigation of combustion processes. In the case of gas and oil flames specific parameters like the flame contour, the degree of burn-out and mixing can be determined and information about flame turbulence and reaction density can be gained from the temporal resolution of the sensor signal. Measurements carried out with solid electrolyte oxygen sensors in a fluidized bed show that combustion processes of solid fuels are also analyzable. This analysis results in fuel specific burn-out curves finally leading to burn-out times and to parameters of a macrokinetics of the combustion process as well as to ideas about the burn-out mechanism. From the resulting constants of the effective reaction rate a reactivity relative to bituminous coal coke can be given for any solid fuel.

Journal Article↗
PubMed1994

Role of 21-deoxyaldosterone in human hypertension.

21-Deoxyaldosterone has been postulated to be a precursor of aldosterone in an alternative biosynthesis pathway and Kelly's-M1 is considered to be its metabolite. In healthy volunteers, the excretion rate of 21-deoxyaldosterone and of Kelly's-M1 are significantly lower than the aldosterone metabolites, aldosterone-18-glucuronide and tetrahydro-aldosterone and than the aldosterone precursor 18-OH-corticosterone. Essential hypertension patients (with low and normal renin) excrete comparable values of 21-deoxyaldosterone and Kelly's-M1 as normotensives. In 66% of aldosterone-producing adenoma cases (APA) and in 60% of idiopathic hyperaldosteronism (IHA) patients, significantly raised values of 21-deoxyaldosterone and Kelly's-M1 were found. The patients with the high excretion rates of both steroids showed only moderately increased values of the aldosterone metabolites, aldosterone-18-glucuronide and tetrahydro-aldosterone, as well as of the aldosterone precursor 18-OH-corticosterone. In contrast, the latter mentioned steroids were excreted in higher amounts in those patients with normal excretion of 21-deoxyaldosterone and Kelly's-M1. Hence, it is suggested that aldosterone is produced alternatively either via 18-OH-corticosterone alone or additionally via 21-deoxyaldosterone. Furthermore, in three cases of "incidentally" discovered adrenal adenomas, 21-deoxyaldosterone and Kelly's-M1 were the only elevated steroids. After adrenalectomy, excretion of 21-deoxyaldosterone and of Kelly's-M1 and blood pressure returned to normal, which proves that these steroids play a role in blood pressure regulation. In essential hypertension, ACTH infusion induced a significant increase of 21-deoxyaldosterone and Kelly's-M1. However, the increase after angiotensin II was 3- to 6-fold higher than after ACTH. IHA patients proved to be more responsive to angiotensin II; and, in contrast, APA cases proved to be more sensitive to ACTH. The data suggest that beside the main route of aldosterone biosynthesis via 11-deoxycorticosterone, corticosterone and 18-OH-corticosterone an alternative pathway exists via 21-deoxyaldosterone in healthy and in hypertensive patients. There are similarities between the regulation of 21-deoxyaldosterone and the regulation of aldosterone. The determination of 21-deoxyaldosterone and its possible metabolite Kelly's-M1 might be appropriate in the diagnosis of mineralocorticoid-induced forms of hypertension, especially when an adrenal adenoma is discovered.

Adenoma↗
PubMed1994

Absence of the left pulmonary artery in a young man with haemoptysis.

We report the case of a white male aged 21 yrs, who was admitted for acute onset of haemoptysis. His past medical history was normal and he had not previously been hospitalized. He was very active in track and field sports and was trained in scuba-diving. Physical examination revealed a grade 2/6 holosystolic heart murmur. Laboratory parameters, blood gases and pulmonary function tests were within the normal range. Fibreoptic bronchoscopy revealed normal geometry of the bronchi, with blood clots in the left lower lobe. An X-ray of the chest showed that the heart was shifted to the left side. In the perfusion scan, defects of the tracer on the left lung were detected. By ergospirometry, no significantly pathological response to exercise using a bicycle ergometer could be observed. By means of pulmonary artery catheterization, cardioangiography and selective angiography of the aorta the absence of the left pulmonary artery could be established, without any further malformations of the cardiopulmonary system. Because of the spontaneous cessation of haemoptysis, no surgical intervention was necessary.

Adult↗