Biomedical subjects

K Mann

Publications and source records attributed to K Mann.

At least 235 records · Page 13Linked to original sources

PubMed1996

Single trial analysis of event related potentials: a comparison between schizophrenics and depressives.

The aim of the present paper was to perform a single trial analysis of event-related potentials in order to elucidate the mechanisms behind a reduced P300 amplitude occurring in unmedicated depressives (n = 11) and schizophrenics (n = 18). For this purpose, tools from linear system theory were applied to single trials in an oddball paradigm. This analysis provides estimates of the magnitude of the positive deflection occurring around the latency of P300 following target and nontarget simuli. According to the density functions of these amplitude distributions, we operationally defined "false-negative" (P300 amplitude lower than an individual threshold under target conditions) as well as "false-positive" responses (P300 amplitude higher than the threshold following nontarget stimuli). Our investigations revealed a reduction of the single-trial P300 amplitude in depression and a combination of amplitude reduction along with fewer elicited single-trial P300 waves in schizophrenics.

Adult↗

PubMed1996

Isolation, cloning, sequence analysis and localization of the operon encoding dimethyl sulfoxide/trimethylamine N-oxide reductase from Rhodobacter capsulatus.

The operon encoding the periplasmic enzymes dimethyl sulfoxide reductase (DMSOR) and trimethylamine N-oxide reductase (TMAOR) from the purple, non-sulfur, photosynthetic bacterium Rhodobacter capsulatus was isolated, cloned and sequenced, and its chromosomal location determined. It was shown by analytical and crystallographic data that DMSOR and TMAOR are identical enzymes. Degenerate primers were derived from short peptide sequences generated by automated Edman degradation and a 700 bp fragment was amplified by nested PCR, subsequently cloned and radioactively labeled to screen a prepared lambda DASH library. Positive lambda clones were subcloned into pBluescript and subsequently transformed into Escherichia coli to sequence the DMSOR/ TMAOR operon. The promoter consisted of an A + T-rich region followed by a -35 region, a putative ribosome binding site, and a leader sequence of 13 amino acid residues. The transcription terminator was a G + C-rich dyad sequence capable of forming a hairpin structure, which may act rho-independently. An optimized protein purification of the wild-type enzyme is also described, giving high yields (5 mg protein per liter of culture) and a specific activity of 30 units/mg. The molecular mass was determined by electrospray mass spectrometry to be 85,034 Da; from the deduced amino acid sequence the molecular mass of the apoenzyme was 85,033 Da.

Amino Acid Sequence↗

PubMed1996

Amplitude frequency characteristics of evoked potentials during sleep: an analysis of the brain's transfer properties in depression.

Classical analysis of the spontaneous sleep EEG in depressive disorder commonly reveals alterations of sleep continuity, number of awakenings, slow-wave sleep, and REM sleep compared to healthy controls; however, conventional analysis can not help understand dynamic differences of the sleep EEG during different sleep stages. In order to elicit qualitative alterations of information processing between depressives and healthy controls, we measured late components of auditory and visual evoked potentials (AEPs and VEPs) during different sleep stages of 15 depressive inpatients and in a sex- and age-matched control group from scalp positions Fz, Cz and Pz. According to linear system theory, we then computed the amplitude frequency characteristic (AFC) from averaged AEPs and VEPs in different sleep stages. These AFCs describe the input/output relation of the system under study leading to a characterization of the transfer properties of the brain during sleep in depression. Our investigations showed that information processing appears characteristically altered in depression during non-REM sleep for both auditory and visual stimulation compared to healthy controls. The transfer properties for processing auditory as well as visual information during REM sleep do not appear dynamically impaired in depressive disorder.

Adult↗

PubMed1996

Different susceptibilities of fibulin-1 and fibulin-2 to cleavage by matrix metalloproteinases and other tissue proteases.

Fibulin-1 and fibulin-2 are two novel rod-like proteins which occur either in basement membranes or in interstitial fibrils in close association with fibronectin. They were examined for their sensitivity to proteolysis by matrix metalloproteinases (stromelysin, matrilysin), circulating proteases (thrombin, plasmin, kallikrein), leucocyte elastase and mast cell chymase. Fibulin-1 (95 kDa) was readily cleaved by leucocyte elastase, weakly by matrilysin and not by the other proteases. Cleavage occurred in a domain-connecting link region close to the N-terminus, giving rise to fragments of 70 kDa and 26 kDa. A much more extensive cleavage by all seven proteases was observed for fibulin-2 (195 kDa), giving rise to many fragments in the range 15-150 kDa. Vulnerable sites included two central link regions, the cysteine-free part of the large N-terminal globular domain but also several regions of epidermal-growth-factor(EGF)-like repeats which are a major part of the rod-like domain. The latter domain became much more sensitive to proteolysis in the presence of EDTA, demonstrating that calcium is required for stabilization. Edman degradation demonstrated cleavage of peptide bonds corresponding to the known specificities of these proteases. A similar proteolysis was also observed for fibulin-2 deposited by cultured fibroblasts into a dense fibrillar network. Since fibulin-2 is an abundant component of small and large blood vessels it could be a major target for proteolysis during vascular injuries.

Amino Acid Sequence↗

PubMed1996

Glycosylated threonine but not 4-hydroxyproline dominates the triple helix stabilizing positions in the sequence of a hydrothermal vent worm cuticle collagen.

The cuticle collagen of the vestimentiferan Riftia pachyptila, an organism which is endemic to deep-sea hydrothermal vents, has several unusual properties including an extraordinary length (1.5 microns), a high thermal stability (37 degrees C) in spite of a low 4-hydroxyproline content and an atypically high threonine content (20 mol%). We have now purified the constituent chain of cuticle collagen and show that it contains about 40% carbohydrate, which is mainly galactose, indicating that the chain has a molecular mass of approximately 750 kDa. Several large (30 to 150 kDa) fragments, which all contained carbohydrate, could be produced by cleavage with endoproteinase Lys-C, bacterial collagenase and cyanogen bromide (CNBr). Edman degradation of these and several smaller fragments was used to determine about 3000 sequence positions comprising 60% of the total triple-helical sequence. This demonstrated mainly typical Gly-X-Y triplet repeats with a few imperfections and a longer N-terminal non-triplet sequence. Most of the 4-hydroxyproline was found in triplet position X, where it decreases the stability of the triple helix. About 40% of the Y positions could not be identified, which correlated with a low abundance of threonine in the sequence and the demonstration of threonine in these positions after deglycosylation of several peptides by treatment with hydrofluoric acid. Matrix-assisted laser desorption ionisation mass spectrometry of selected peptides indicated that the blocked threonine residues are occupied by chains of one, two or three hexoses (presumably galactose). These glycosylated threonine residues in Y positions are therefore likely to replace 4-hydroxyproline as the major contributor to triple helix stabilization. Studies with a synthetic (Gly-Pro-Thr)10 oligopeptide demonstrated a low thermal stability of its triple helix which emphasizes a crucial role of glycosylation for stabilization.

Amino Acid Sequence↗

PubMed1996

Structural and functional analysis of the globular domain IVa of the laminin alpha 1 chain and its impact on an adjacent RGD site.

The globular domain IVa (about 250 residues) of the laminin alpha1 chain was obtained in recombinant form from mammalian cell clones. It was prepared either with (alpha1IVa-R) or without (alpha1IVa) an adjacent cell-adhesive RGD site which seems to be masked in laminin-1. The recombinant products could be visualized as globular structures by rotary shadowing, were resistant to trypsin and shared immunological epitopes with laminin-1, indicating folding into a native structure. Sequence analysis of pepsin fragments demonstrated the insertion of the globular domain into an epidermal growth factor-like scaffold which is characteristic of the extracellular laminin domain IV (L4) module. Only little immunological cross-reaction was found, however, with other L4 modules from perlecan and different laminin isoforms. Fragment alpha1IVa-R, but not fragment alpha1IVa, bound to alphaVbeta3 integrin, although to a distinctly lower level than a laminin fragment where the RGD site is fully exposed. The fragments also had no or only little cell attachment activity. This confirmed previous predictions that the globular domain alpha 1IVa masks the RDG site in laminin-1. Domain alpha 1IVa showed, in addition, a weak binding activity for the basement-membrane protein fibulin-1.

Amino Acid Sequence↗

PubMed1996

Relapse prevention by acamprosate. Results from a placebo-controlled study on alcohol dependence.

BACKGROUND: The effectiveness of acamprosate (calcium bisacetylhomotaurinate) as a treatment to maintain abstinence in alcohol-dependent patients was assessed for 1 year. METHODS: After short-term detoxification, 272 patients participated in a randomized, double-blind, placebo-controlled study. Patients received routine counseling and either the study medication or placebo for 48 weeks; they were followed up for another 48 weeks without medication. Statistical analysis was performed according to the intention-to-treat principle. RESULTS: Patients who were receiving acamprosate showed a significantly higher continuous abstinence rate within the first 60 days of treatment compared with patients who were assigned to placebo treatment (67% vs 50%) until completion of the treatment period (43% vs 21%, log rank P = .005), and they had a significantly longer mean abstinence duration of 224 vs 163 days, or 62% vs 45% days abstinent (P < .001); however, there was no difference in psychiatric symptoms. Of the patients who were receiving acamprosate, 41% had dropped out, whereas 60% of the placebo-treated patients dropped out of the study. Few side effects (mainly diarrhea and headache) were recorded. At the end of a further 48 weeks without receiving study medication, 39% and 17% of the acamprosate- and placebo-treated patients, respectively, had remained abstinent (P = .003). CONCLUSION: Acamprosate proved to be a safe and effective aid in treating alcohol-dependent patients and in maintaining the abstinence of patients during 2 years.

Acamprosate↗

PubMed1996

Swelling and fibronectin accumulation in articular cartilage explants after cyclical impact.

The objective of this study was to determine if repeated impact could damage living cartilage and lead to osteoarthritis-like changes in its biology. Canine cartilage explants were subjected to impacts of as much as 50 MPa once every 5 seconds for 30 minutes. On each impact cycle, the loading rate was 100 MPa/sec to the assigned peak stress, which was held for 1 second. After impact testing, the cartilage was kept in defined culture for as long as 10 days. Radiosulfate incorporation in the region that received direct impact varied with load 0-4 hours after impact, but it did not vary with load at 20-24 hours after impact. Even so, most explants were visibly damaged by 20 or 50 MPa, and there was subtle evidence of damage from impacts of 5 or 10 MPa. For example, ion-induced swelling in 0.01 M NaCl was increased, suggesting that the physical integrity of the matrix was reduced relative to controls. Self-diffusion of water, measured by proton magnetic resonance imaging was also increased in the deeper zones of the explant, consistent with changes in structure at the molecular level. Ten days after impact, the water content and the fibronectin content of the loaded region of the explant were both increased. In combination, these osteoarthritis-like changes suggested that the physical strength of normal cartilage limits its ability to withstand cyclical impact.

Animals↗

PubMed1996

A procedure for the large-scale isolation of major bovine seminal plasma proteins.

A method for the stepwise purification of bovine seminal plasma proteins aSFP, PDC-109, TIMP-2, RNAse, and BSP-30K/PDC-109 complex is presented. It is based on the use of nondenaturing, classical chromatographic procedures. The isolation protocol is reproducible, inexpensive, easy to carry out in a common laboratory, and yields large amounts of pure proteins for biochemical and structural studies.

Amino Acid Sequence↗

PubMed1996

Effects of yohimbine on sexual experiences and nocturnal penile tumescence and rigidity in erectile dysfunction.

The therapeutic effect of the alpha 2-antagonist yohimbine in erectile dysfunction was studied in a double-blind placebo-controlled design. Thirty-one male patients underwent extensive clinical, urological, and psychiatric diagnosis and were dichotomically classified into an organic and a nonorganic subgroup. Following a 1-week placebo run-in period, patients were randomly assigned to a placebo or a verum group (yohimbine 15 mg daily) for a treatment period of 7 weeks. The Clinical Global Impression (CGI) scale was used as the primary efficacy parameter. Additionally, nocturnal penile tumescence and rigidity (NPTR) were measured. Global assessment of erectile function applying the CGI scale revealed, beyond a placebo effect in both organic and nonorganic patients, a therapeutic effect in the subgroup of nonorganic patients, with a significantly greater improvement in the yohimbine group compared to the placebo group. No superiority of yohimbine compared to placebo was found in the organic patients. These findings on the subjective level had no correlate in the NPTR recordings. The NPTR parameters were unchanged under yohimbine treatment in both the nonorganic and organic subgroup. No interrelation was found between subjective improvement and NPTR alterations. Polysomnographic control of the NPTR registrations ensured that the duration of REM sleep under treatment was not influenced.

Adult↗

PubMed1996

Posterior retroperitoneoscopy as a new minimally invasive approach for adrenalectomy: results of 30 adrenalectomies in 27 patients.

Posterior retroperitoneoscopic adrenalectomy is a new minimally invasive method. It represents an alternative to conventional open procedures and laparoscopic techniques. Between July 1994 and November 1995 a total of 30 retroperitoneoscopic adrenalectomies were performed on 27 patients. In 24 patients, unilateral tumors were seen (size 1-7 cm): seven Cushing adenomas, five Conn adenomas, seven pheochromocytomas, four hormonally inactive tumors, one cyst. Three patients suffered from Cushing syndrome with bilateral adrenal gland hyperplasias (two inoperable pituitary gland tumors, one bronchial carcinoid with ACTH secretion). The operations were carried out in prone position. After balloon dilatation of the retroperitoneum and creation of a pneumoperitoneum the preparation of the adrenal gland was performed via three trocar sites positioned below the 12th rib. Twenty-five adrenalectomies were completed endoscopically, and five times (among four patients) conversion to the conventional posterior technique was necessary. The average operating time of complete endoscopic adrenalectomies was 124 minutes (45-225 minutes); blood loss was 10 to 120 ml. With minimal need for postoperative analgesia (average dosage 7.9 mg of piritramide), mobilization and adequate food uptake were possible on the day of operation. The posterior retroperitoneoscopic adrenalectomy is a relatively fast, safe method, with the advantages of the posterior open approach and minimally invasive surgery. It therefore represents an important addition to adrenal gland surgery.

Adenoma↗

PubMed1996

Discrimination of sleep stages: a comparison between spectral and nonlinear EEG measures.

During recent years, methods from nonlinear dynamics were introduced into the analysis of EEG signals. Although from a theoretical point of view nonlinear measures quantify properties being independent from conventional spectral measures, it is a crucial question whether in practice nonlinear EEG measures yield additional information, which is not redundant to the information gained by spectral analysis. Therefore, we compared the ability of several spectral and nonlinear measures to discriminate different sleep stages. We evaluated spectral measures (relative delta power, spectral edge, spectral entropy and first spectral moment), and nonlinear measures (correlation dimension D2, largest Lyapunov exponent LI, and approximated Kolmogorof entropy K2), and additionally the stochastic time domain based measure entropy of amplitudes. For 12 healthy subjects these measures were calculated from sleep EEG segments of 2:44 min duration, each segment unambiguously corresponding to one of the sleep stages I, II, SWS and REM. Results were statistically evaluated by multivariate and univariate analyses of variance and by discriminant analyses. Generally, nonlinear measures (D2 and L1) performed better in discriminating sleep stages I and II, whereas spectral measures showed advantages in discriminating stage II and SWS. Combinations of spectral and nonlinear measures yielded a better overall discrimination of sleep stages than spectral measures alone. The best overall discrimination was reached even without inclusion of any of the spectral measures. It can be concluded that nonlinear measures yield additional information, which improves the ability to discriminate sleep stages and which may in general improve the ability to distinguish different psychophysiological states. This confirms the importance and practical reliability of the application of nonlinear methods to EEG analysis.

Adult↗

PubMed1996

Elevated norharman plasma levels in alcoholic patients and controls resulting from tobacco smoking.

Plasma norharman and harman levels were measured by solvent extraction and HPLC with fluorescence detection in alcohol-dependent patients undergoing in-patient abstinence treatment and in control subjects. In both groups, randomly collected samples from smokers contained higher mean norharman levels than those from non-smokers. In three volunteers norharman concentrations rose sharply after smoking of one or two cigarettes and declined to near-basal levels within one hour after one cigarette. When 12 patients kept a smoking-free interval of at least 6 h, they had similarly low plasma norharman concentrations (20 +/- 8 pg/ml) as 18 non-smoking control subjects (17 +/- 8 pg/ml) or as 13 smoking controls who had abstained from smoking (20 +/- 6 pg/ml). Ten of the patients smoked one cigarette and within 5-10 min attained norharman levels of 177 +/- 147 pg/ml plasma. The high prevalence of smokers among chronic alcoholics probably explains the previous finding of elevated norharman plasma levels in these patients.

Adult↗

PubMed1996

Acute, subchronic and discontinuation effects of zopiclone on sleep EEG and nocturnal melatonin secretion.

Zopiclone is a new short half-life cyclopyrrolone hypnotic agent acting at the GABA-benzodiazepine receptor complex. In order to characterize its pharmacological profile, the effects of 7.5 mg zopiclone on nocturnal melatonin secretion were investigated under polysomnographic control in 11 healthy subjects following acute and subchronic administration as well as after abrupt discontinuation of the drug. No effect of zopiclone on the melatonin plasma levels could be observed. Regarding both total melatonin production and the temporal pattern of melatonin secretion during the night, there was no difference between placebo baseline condition, acute and subchronic administration, and discontinuation. In contrast, the sleep EEG data demonstrated the hypnotic efficacy of zopiclone under acute administration and indicated a rebound insomnia after abrupt discontinuation. Moreover, alterations of sleep architecture were found under treatment as well as after discontinuation. Whereas, with regard to sleep EEG parameters, zopiclone appears to be comparable with some short-acting benzodiazepines, a discrepancy between the missing effect of zopiclone on pineal function and the suppressing influence of benzodiazepines known from the literature becomes obvious. The fact that zopiclone does not interfere with nocturnal melatonin secretion at pharmacologically active doses as indicated by alterations in sleep EEG parameters might possibly point to a pharmacodynamic difference between the two drug classes.

Adult↗

PubMed1996

Structural and cell-adhesive properties of three recombinant fragments derived from perlecan domain III.

Domain III of the basement membrane proteoglycan perlecan was produced as three overlapping fragments in stably transfected mammalian cell clones. These recombinant fragments (43-48 kDa) were obtained in purified form and showed complete immunological cross-reactivity with perlecan, indicating their native structure. Rotary shadowing electron microscopy of each fragment demonstrated a small globular structure connected to a short rod. These data were interpreted to indicate that domain III has an elongated shape of 30 nm in length and consists of alternating globular domains (L4 modules) and short connecting segments attributed to tandem arrays of LE (laminin-type of EGF-like) modules which form rod-like segments in laminins. Sequence analyses of pepsin fragments were consistent with the disulfide-bonding patterns known for these modules from studies with laminin fragments, but two additional disulfide loops were also identified. Several cell lines which attached to mouse perlecan and/or human fibronectin failed to adhere to the domain III fragments, despite the fact that one of them contained an RGD (Arg-Gly-Asp) site in the L4 module. Furthermore, no significant binding was observed in solid phase binding assays with alpha 5 beta 1 and alpha v beta 3 integrins underscoring the low activity or accessibility of the RGD site.

Amino Acid Sequence↗

PubMed1996

A cyclophilin-like peptidyl-prolyl cis/trans isomerase from Legionella pneumophila--characterization, molecular cloning and overexpression.

Legionella pneumophila is the causative agent of a severe form of pneumonia in humans (Legionnaires' disease). A major virulence factor, the Mip protein (FK506-binding protein, FKBP25mem), belongs to the enzyme family of peptidyl-prolyl cis/trans isomerases (PPlases). Here we show that L. pneumophila Philadelphia I possesses an additional cytoplasmic PPlase at a level of enzyme activity comparable to that of FKBP25mem. The N-terminal amino acid sequence of the purified protein was obtained by Edman degradation and showed that the protein is a member of the cyclophilin family of PPlases. The Icy gene (Legionella cyclophilin) was cloned and sequenced. It encodes a putative 164-amino-acid protein with a molecular mass of 17968 Da called L. pneumophila cyclophilin 18 (L.p.Cyp18). Amino acid sequence comparison displays considerable similarity to the cytoplasmic and the periplasmic cyclophilins of Escherichia coli with 60.5% and 51.5% identity, respectively. The substrate specificity and inhibition by cyclosporin A revealed a pattern that is typically found for other bacterial cyclophilins. An L. pneumophila Cyp18 derivative with a 19-amino-acid polypeptide extension including a 6-histidine tag and an enterokinase cleavage site exhibits PPlase activity when produced at high levels in E. coli K-12. After removal of the extension by enterokinase, the properties of the recombinant Cyp18 were indistinguishable from those of the authentic enzyme. In order to investigate the influence of Cyp18 on intracellular survival of L. pneumophila an Icy-negative L. pneumophila strain was constructed. Compared with the wild-type strain, the mutant did not exhibit a significant phenotype but was 10-fold less invasive for Acanthamoeba castellanii. Like human cyclophilin, the L. p. Cyp18 exhibits nuclease activity, but this enzymatic activity does not appear to be linked with the native structure of the protein.

Amino Acid Isomerases↗

PubMed1996

Enhanced functional activity in thyroid adenomas in vitro.

The majority of thyroid adenomas have been shown to be of clonal origin. In a portion of them, somatic or germline point mutations leading to altered TSH receptor or Gs alpha-proteins have been found. The constitutive activation of these proteins consecutively stimulate cAMP-levels. Expression of the TSH receptor mutants in mammalian cells leads to increased cAMP-production compared to cells transfected with the wild type receptor. Presently, the role of these mutations in the development and growth of such tumours is still unclear. In our own investigations we made an attempt to evaluate the functional significance of these observations. In nodular tissue derived from patients with functioning autonomous adenoma we found significantly higher basal and TSH stimulated thyroid hormone releasing activity than in the surrounding paranodular tissue and in thyroid tissue derived from patients with euthyroid goiter. These findings indicate a functional relevance of constitutively activated intracellular signal transducing cascade in thyroid adenomas that may lead to hyperthyroidism in the presence or absence of external thyroid stimulators.

Adenoma↗

PubMed1996

The amino acid sequence of the spinach basic cupredoxin plantacyanin.

We describe the amino acid sequence of plantacyanin isolated from spinach leaves. This small basic copper-binding plant cupredoxin contains 91 amino acids (accession no. S70746) and its theoretical average mass of 9788.2 Da was confirmed by electrospray ionization mass spectrometry. When compared to the sequences of other plant cupredoxins, the most similar homologs were cucumber basic blue protein and stellacyanin from Laquer tree with 44-58% identical residues. Other known plant cupredoxins were significantly less similar which may allow to divide the plant cupredoxins into two subgroups, the single-domain cupredoxins (plantacyanin, cucumber basic blue protein and stellacyanin) and the two-domain, hydroxyproline-containing cupredoxins (cucumber peeling cupredoxin, basic blue protein from Arabidopsis thaliana and horseradish umecyanin).

Amino Acid Sequence↗