Showing papers by "University of Antwerp published in 1997"

Characterization of flavone and flavonol aglycones by collision‐induced dissociation tandem mass spectrometry

Abstract: A mass spectrometric method based on the combined use of fast atom bombardment collisionally-induced dissociation (CID) and tandem mass spectrometry has been used for the structural characterization of free and conjugated flavone and flavonol aglycones. Low-energy CID spectra of the [M + H]+ (or Y+0) ions show simple fragmentation patterns, which allow characterization of the substituents in the A and B rings and, in particular, differentiation between flavones and flavonols. A systematic nomenclature for product ions produced from protonated molecules under CID conditions is proposed. © 1997 John Wiley & Sons, Ltd.

Construction of evolutionary distance trees with TREECON for Windows: accounting for variation in nucleotide substitution rate among sites

Abstract: Motivation: To improve the estimation of evolutionary distances between nucieotide sequences by considering the differences in substitution rates among sites. Results: TREECON for Windows (Van de Peer.Y. and De Wachter.R. Comput. Applic. Biosci., 9, 569-570, 1994) is a software package for the construction and drawing of phylogenetic trees based on distance data computed from nucleic acid and amino acid sequences. For nucleic acids, we here describe the implementation of a recently developed method for estimating evolutionary distances taking into account the substitution rate of individual sites in a sequence alignment. Availability: TREECON for Windows is available on request from the authors. A small fee is asked in order to support the work and to reinvest in new computer hard- and software. More information about the program and substitution rate calibration can be found at URL http://bioc-www.uia.ac.be/uJ yvdp/treeconw. html. Contact: E-mail: yvdp@uia.ua.ac.be

Search for neutral heavy leptons produced in Z decays

Abstract: Weak isosinglet Neutral Heavy Leptons (m) have been searched for using data collected by the DELPHI detector corresponding to 3:3 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived m production giving monojet or acollinear jet topologies, and for long-lived m giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 ! m) of about 1:310−6 at 95% confidence level for m masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the m mass. The results are also interpreted in terms of limits for the single production of excited neutrinos.

Acute phase proteins in schizophrenia, mania and major depression: modulation by psychotropic drugs

Abstract: Recently, an acute phase (AP) protein response has been reported in major depression. In order to examine whether an AP response occurs in other psychiatric disorders, such as schizophrenia and mania, the authors measured plasma AP reactants, such as haptoglobin (Hp), immunoglobulin G (IgG), IgM, fibrinogen (Fb), complement component 3 (C3C), C4, alpha 1-antitrypsin (alpha 1 AT), alpha 1-acid-glycoprotein (alpha 1S) and hemopexin (Hpx), in 27 schizophrenic, 23 manic, 29 major depressed and 21 normal subjects. Schizophrenic patients had significantly higher plasma Hp, Fb, C3C, C4, alpha 1S and Hpx than normal controls. Manic subjects showed significantly higher plasma Hp, Fb, alpha 1S and Hpx than normal volunteers. Depressed subjects had significantly higher plasma Hp, Fb, C3C, C4 and alpha 1S than normal controls. Overall, the above disorders in AP reactants were more pronounced in schizophrenic than in depressed subjects. No significant differences in the above AP reactants could be found between normal volunteers, and schizophrenic, manic or depressed patients who underwent chronic treatment with psychotropic drugs. Plasma Hp, Fb, C3C, C4, alpha 1S, and Hpx were significantly higher in schizophrenic, manic and depressed patients who were non-medicated than in those who were treated with antidepressants, antipsychotics or lithium. The results suggest that not only major depression but also schizophrenia and mania are accompanied by an AP response, and that the latter may be suppressed by (sub)chronic treatment with psychotropic drugs.

Phase transitions in individual sub-micrometre superconductors

Abstract: The properties of a superconductor are expected to change radically when its size becomes comparable to that of the Cooper pairs, the quasiparticles responsible for superconductivity. The effect of such confinement is well understood for the case of thesuppression of superconductivity by magnetic fields (which gives rise to so-called Little–Parks oscillations of the phase boundary)1,2,3,4. But little is known about what happens in small superconductors in the zero-resistance state, which cannot be probed by resistance measurements. Here we apply a new technique of ballistic Hall magnetometry5 to study the magnetization of individual superconducting discs of diameters down to 100 nm. The superconducting state of these discs is found to be qualitatively different from both macroscopic and microscopic6 superconductors, with numerous phase transitions whose character changes rapidly with size and temperature. This exotic behaviour is due to size quantization of the Cooper-pair motion and resulting transitions between discrete states of the superconducting Bose condensate in a magnetic field.

Stochastic seasonality and nonlinear density-dependent factors regulate population size in an African rodent.

Abstract: Ecology has long been troubled by the controversy over how populations are regulated1,2. Some ecologists focus on the role of environmental effects, whereas others argue that density-dependent feedback mechanisms are central3,4,5,6. The relative importance of both processes is still hotly debated, but clear examples of both processes acting in the same population are rare7,8. Key-factor analysis (regression of population changes on possible causal factors) and time-series analysis are often used to investigate the presence of density dependence, but such approaches may be biased and provide no information on actual demographic rates9,10. Here we report on both density-dependent and density-independent effects in a murid rodent pest species, the multimammate rat Mastomys natalensis (Smith, 1834), using statistical capture–recapture models. Both effects occur simultaneously, but we also demonstrate that they do not affect all demographic rates in the same way. We have incorporated the obtained estimates of demographic rates in a population dynamics model and show that the observed dynamics are affected by stabilizing nonlinear density-dependent components coupled with strong deterministic and stochastic seasonal components.

Comparative Physico-mechanical Characterization of New Hybrid Restorative Materials with Conventional Glass-ionomer and Resin Composite Restorative Materials

Abstract: The recently developed hybrid restorative materials contain the essential components of conventional glass ionomers and light-cured resins. The objective of this study was to determine several physical and mechanical properties of eight such materials in comparison with two conventional glass ionomers, one micro-filled, and one ultrafine compact-filled resin composite. The two resin composites and two of the three polyacid-modified resin composites could be polished to a higher gloss than the conventional as well as the resin-modified glass ionomers. After abrasion, surface roughness increased for all materials, but not at the same extent, being the least for the conventional resin composites and one polyacid-modified resin composite, Dyract. In contrast to the later resin composites, of which the surface roughness is principally determined by the presence of protruding filler particles above the resin matrix, roughness of conventional and resin-modified glass ionomers results from both protruding filler particles and intruding porosities. The mean particle size of the hybrid restorative materials fell between the smaller mean particle size of the resin composites and the larger one of the conventional glass ionomers. The micro-hardness and Young's modulus values varied substantially among all eight hybrid restorative materials. For all the resin-modified glass-ionomer restorative materials, the Young's modulus reached a maximum value one month after mixing and remained relatively stable thereafter. The Young's modulus of the conventional and the polyacid-modified resin composites decreased slightly after one month. The conventional glass-ionomer materials undoubtedly set the slowest, since their Young's modulus took six months to reach its maximum. The flexural fatigue limit of the hybrid restorative materials is comparable with that of the micro-filled composite. From this investigation, it can be concluded that the physico-mechanical properties vary widely among the eight hybrid restorative materials, indicating that these materials probably have yet to achieve their optimum properties. Their mechanical strength is inadequate for use in stress-bearing areas, and their appearance keeps them from use where esthetics is a primary concern.

Evolutionary relationships among the eukaryotic crown taxa taking into account site-to-site rate variation in 18S rRNA

Abstract: In this study we constructed a bootstrapped distance tree of 500 small subunit ribosomal RNA sequences from organisms belonging to the so-called crown of eukaryote evolution. Taking into account the substitution rate of the individual nucleotides of the rRNA sequence alignment, our results suggest that (1) animals, true fungi, and choanoflagellates share a common origin: The branch joining these taxa is highly supported by bootstrap analysis (bootstrap support [BS] > 90%), (2) stramenopiles and alveolates are sister groups (BS = 75%), (3) within the alveolates, dinoflagellates and apicomplexans share a common ancestor BS > 95%), while in turn they both share a common origin with the ciliates (BS > 80%), and (4) within the stramenopiles, heterokont algae, hyphochytriomycetes, and oomycetes form a monophyletic grouping well supported by bootstrap analysis (BS > 85%), preceded by the well-supported successive divergence of labyrinthulomycetes and bicosoecids. On the other hand, many evolutionary relationships between crown taxa are still obscure on the basis of 18S rRNA. The branching order between the animal-fungal-choanoflagellates clade and the chlorobionts, the alveolates and stramenopiles, red algae, and several smaller groups of organisms remains largely unresolved. When among-site rate variation is not considered, the inferred tree topologies are inferior to those where the substitution rate spectrum for the 18S rRNA is taken into account. This is primarily indicated by the erroneous branching of fast-evolving sequences. Moreover, when different substitution rates among sites are not considered, the animals no longer appear as a monophyletic grouping in most distance trees.

Classification of all putative permeases and other membrane plurispanners of the major facilitator superfamily encoded by the complete genome of Saccharomyces cerevisiae

Abstract: On the basis of the complete genome sequence of the budding yeast Saccharomyces cerevisiae, a computer-aided analysis was carried out of all members of the major facilitator superfamily (MFS), which typically consists of permeases with 12 transmembrane spans. Analysis of all 5885 predicted open reading frames identified 186 potential MFS proteins. Binary sequence comparison made it possible to cluster 149 of them into 23 families. Putative permease functions could be assigned to 12 families, the largest including sugar, amino acid, and multidrug transport. Phylogenetic clustering of proteins allowed us to predict a possible permease function for a total of 119 proteins. Multiple sequence alignments were made for all families, and evolutionary trees were constructed for families with at least four members. The latter resulted in the identification of 21 subclusters with presumably tightly related permease function. No functional clues were predicted for a total of 41 clustered or unclustered proteins.

Components of biological variation, including seasonality, in blood concentrations of TSH, TT3, FT4, PRL, cortisol and testosterone in healthy volunteers

Abstract: Objective There are few detailed studies of annual or seasonal variations in hormone concentrations in man. This study examines the components of biological variation, including seasonality, in plasma TSH, total T3 (TT3), free T4 (FT4), PRL, cortisol and testosterone in healthy volunteers. Design Monthly blood samplings for the assay of the above hormones were collected during one calendar year. Subjects Thirteen normal men and 13 normal women participated in the present study (mean age 38.7 +/- 13.4 years). Measurements Assays of TSH, TT3 and FT4 were carried out by means of immunoradiometric assays (IRMA), PRL by ELISA, cortisol by a fluorescence immunoassay, and testosterone with RIA. The time series were analysed by means of (bivariate or multivariate) spectral and cosinor analyses. Results Significant annual, four-monthly and biannual rhythms were detected in serum TSH; the lowest TSH values were observed in spring. A significant annual rhythm was detected in TT3, with lower values in spring and summer than in the other seasons. The peak-trough differences in the yearly variation expressed as a percentage of the mean were 29.1% and 8.2% for TSH and TT3, respectively. The yearly variation in plasma cortisol was significantly different between men and women: in men, 5.9% of the variation was explained by an annual rhythm, while in women 14.7% was explained by the fourth and seventh harmonical wave. The peak-trough differences in the yearly variation in plasma cortisol were 17.6% and 31.8% in men and women, respectively. There were no significant seasonal rhythms in PRL, FT4 or testosterone. The intraindividual/interindividual CV values were: TSH 29.3/48.4%, TT3 9.4/ 18.5%, FT4 7.1/9.1%, PRL 39.2/65.0%, cortisol 21.7/ 46.2%, and testosterone 12.6/40.8%. Conclusions The degree of individuality measured in the plasma hormones is such that conventional population-based reference ranges may not correctly identify major alterations in these hormones in individual subjects.

In Vitro and in Vivo Antiplasmodial Activity of Cryptolepine and Related Alkaloids from Cryptolepis sanguinolenta

Abstract: Three different extracts and four alkaloids from the root bark of Cryptolepis sanguinolenta have been assessed in vitro against Plasmodium falciparum D-6 (chloroquine-sensitive strain), K-1, and W-2 (chloroquine-resistant strains). Cryptolepine (1) and its hydrochloride (2), 11-hydroxycryptolepine (3), and neocryptolepine (5) showed a strong antiplasmodial activity against P. falciparum chloroquine-resistant strains. Quindoline (4) was less active. The highest activity was obtained with compound 1. In vivo tests on infected mice showed that crytpolepine (1), when tested as its hydrochloride (2), exhibited a significant chemosuppressive effect against Plasmodium berghei yoelii and Plasmodium berghei berghei, while 1 had the same effect against P. berghei yoelii only. Compounds 3 and 4 did not show activity in this in vivo test system.

RnaViz, a program for the visualisation of RNA secondary structure

Abstract: RnaViz is a user-friendly, portable, windows-type program for producing publication-quality secondary structure drawings of RNA molecules Drawings can be created starting from DCSE alignment files if they incorporate structure information or from mfold ct files The layout of a structure can be changed easily Display of special structural elements such as pseudo-knots or unformatted areas is possible Sequences can be automatically numbered, and several other types of labels can be used to annotate particular bases or areas Although the program does not try to produce an initially non-overlapping drawing, the layout of a properly positioned structure drawing can be applied to a newly created drawing using skeleton files In this way a range of similar structures can be drawn with a minimum of effort Skeletons for several types of RNA molecule are included with the program

Low Efficiency of Ca2+ Entry Through the Na+-Ca2+ Exchanger as Trigger for Ca2+ Release From the Sarcoplasmic Reticulum A Comparison Between L-Type Ca2+ Current and Reverse-Mode Na+-Ca2+ Exchange

Abstract: It has been proposed that Ca2+ entry through the Na+-Ca2+ exchanger can contribute significantly to the trigger for Ca2+ release from the sarcoplasmic reticulum (SR). We have compared the characteristics of Ca2+ release triggered by reverse-mode Na+-Ca2+ exchange and by L-type Ca2+ current (I-CaL) during depolarizing steps in single guinea pig ventricular myocytes (whole-cell voltage clamp, flue 3 and fura-red as [Ca2+](i) indicators, 36+/-1 degrees C, K+-based pipette solution with 20 mmol/L [Na+]). Conditioning pulses to +60 mV ensured comparable Ca2+ loading of the SR. In the presence of I-CaL, [Ca2+](i) transients typically have an early and rapid rising phase reflecting Ca2+ release, which has a bell-shaped voltage dependence with a peak at +10 mV. With Ca2+ entry through Na+-Ca2+ exchange only (20 mu mol/L nisoldipine), Ca2+ release flux from the SR is decreased and directly related to the amplitude of the depolarizing step. Ca2+ release is preceded by a significant delay (81+/-21 ms at +20 mV, 24+/-4 ms at +70 mV) related to Ca2+ entry through the exchanger. Triggered release interrupts Ca2+ entry, as evidenced by reversal of the exchanger current. At potentials positive to +40 mV, Ca2+ influx through Na+-Ca2+ exchange, calculated from the outward exchange current, reaches magnitudes comparable to I-CaL, but Ca2+ release due to reverse-mode Na+-Ca2+ exchange still has a significant delay. We calculated trigger efficiency as the ratio between the maximal rate of Ca2+ release and the Ca2+ influx preceding this release; efficiency of reverse-mode Na+-Ca2+ exchange is approximately four times less than that of I-CaL. With both I-CaL and reverse-mode Na+-Ca2+ exchange present, Ca2+ release is triggered by I-CaL, and a contribution of reverse-mode Na+-Ca2+ exchange to the trigger could not be detected at potentials below +60 mV. These characteristics of reverse; mode Na+-Ca2+ exchange predict that its role as a trigger for Ca2+ release during the action potential is likely to be negligible.

L1-Associated Diseases: Clinical Geneticists Divide, Molecular Geneticists Unite

Abstract: The neuronal cell adhesion molecule L1 (L1CAM) is a transmembrane glycoprotein belonging to the immunoglobulin superfamily and is essential in the development of the nervous system. It is mainly expressed on neurons and Schwann cells, and plays a key role in axon outgrowth and pathfinding through interactions with various extracellular ligands and intracellular second messenger systems. Mutations in L1 are responsible for a wide spectrum of neurologic abnormalities and mental retardation. This spectrum includes X-linked hydrocephalus, MASA syndrome, X-linked complicated spastic paraplegia type 1 and X-linked agenesis of the corpus callosum. These four diseases were initially described as distinct clinical entities with an overlapping clinical spectrum, but can now be lumped into one syndrome caused by mutations in the L1 gene. The main clinical features of this spectrum are Corpus callosum hypoplasia, mental Retardation, Adducted thumbs, Spastic paraplegia and Hydrocephalus, which has led to the acronym CRASH syndrome.

Relevance of nucleic acid amplification techniques for diagnosis of respiratory tract infections in the clinical laboratory.

Abstract: Clinical laboratories are increasingly receiving requests to perform nucleic acid amplification tests for the detection of a wide variety of infectious agents. In this paper, the efficiency of nucleic acid amplification techniques for the diagnosis of respiratory tract infections is reviewed. In general, these techniques should be applied only for the detection of microorganisms for which available diagnostic techniques are markedly insensitive or nonexistent or when turnaround times for existing tests (e.g., viral culture) are much longer than those expected with amplification. This is the case for rhinoviruses, coronaviruses, and hantaviruses causing a pulmonary syndrome, Bordetella pertussis, Chlamydia pneumoniae, Mycoplasma pneumoniae, and Coxiella burnetii. For Legionella spp. and fungi, contamination originating from the environment is a limiting factor in interpretation of results, as is the difficulty in differentiating colonization and infection. Detection of these agents in urine or blood by amplification techniques remains to be evaluated. In the clinical setting, there is no need for molecular diagnostic tests for the diagnosis of Pneumocystis carinii. At present, amplification methods for Mycobacterium tuberculosis cannot replace the classical diagnostic techniques, due to their lack of sensitivity and the absence of specific internal controls for the detection of inhibitors of the reaction. Also, the results of interlaboratory comparisons are unsatisfactory. Furthermore, isolates are needed for susceptibility studies. Additional work remains to be done on sample preparation methods, comparison between different amplification methods, and analysis of results. The techniques can be useful for the rapid identification of M. tuberculosis in particular circumstances, as well as the rapid detection of most rifampin-resistant isolates. The introduction of diagnostic amplification techniques into a clinical laboratory implies a level of proficiency for excluding false-positive and false-negative results.

Solubilization and Separation of a Plant Plasma Membrane NADPH-O2- Synthase from Other NAD(P)H Oxidoreductases

Abstract: Solubilization and ion-exchange chromatography of plasma membrane proteins obtained from bean (Phaseolus vulgaris L.) seedlings resulted in a single NAD(P)H-O2--synthase protein peak. This enzyme showed a high preference toward NADPH as a substrate (reaction rate, 27.4 nmol O2- produced min-1 mg-1 protein), whereas NADH reactions ranged from 0 to maximally 15% of the NADPH reactions. The protein functions as an oxidase and it was clearly resolved from NAD(P)H dehydrogenases identified with commonly used strong oxidants (ferricyanide, cytochrome c, DCIP, and oxaloacetate). The involvement of peroxidases in O2- production is excluded on the basis of potassium-cyanide insensitivity and NADPH specificity. The NADPH oxidase is only moderately stimulated by flavins (1.5-fold with 25 [mu]M flavine adenine dinucleotide and 2.5-fold with 25 [mu]M flavin mononucleotide) and inhibited by 100 [mu]M p-chloromercuribenzenesulfonic acid, 200 [mu]M diphenyleneiodonium, 10 mM quinacrine, 40 mM pyridine, and 20 mM imidazole. The presence of flavins was demonstrated in the O2-synthase fraction, but no b-type cytochromes were detected. The effect of these inhibitors and the detection of flavins and cytochromes in the plant O2- synthase make it possible to compare this enzyme with the NADPH O2- synthase of animal neutrophil cells.

Guanidino compounds in serum and urine of nondialyzed patients with chronic renal insufficiency.

Abstract: Levels of 15 guanidino compounds and urea were determined in serum and urine of nondialyzed patients with chronic renal insufficiency subdivided according to etiology and creatinine clearances. No significantly different guanidino compound levels in serum and urine were found for the interstitial nephritis, glomerulonephritis, nephrangiosclerosis, and diabetic nephropathy subgroups. Subdividing the patients according to creatinine clearance yields the following results: (1) Serum guanidinosuccinic acid (GSA) and methylguanidine levels of patients with end-stage renal failure (creatinine clearance < 10 mL/min) are up to 100 and 35 times higher than control levels, while guanidine, creatinine, and symmetrical dimethylarginine (SDMA) are increased about 10 times. Serum levels of asymmetrical dimethylarginine (ADMA) are only doubled in end-stage renal failure. Serum levels of guanidinoacetic acid (GAA) and homoarginine are significantly decreased. (2) Urinary excretion levels of most guanidino compounds decrease with decreasing creatinine clearance except for GSA and methylguanidine. (3) Greater than 90% of patients with creatinine clearance ranging from subnormal to 40 mL/min have serum SDMA levels higher than the upper-normal limit; up to 80% have increased GSA levels. (4) The clearance rates of some of the guanidino compounds could be calculated: with the exception of arginine, they decrease with decreasing creatinine clearance. This study shows specific abnormal guanidino compound levels in serum and urine of nondialyzed patients with chronic renal insufficiency that can be used as complementary diagnostic parameters. The best correlation between serum guanidino compound levels and the degree of renal insufficiency is found for GSA, SDMA, methylguanidine, and guanidine. Urinary excretion levels of ADMA correlate best with decreasing creatinine clearance. Serum levels of GSA and especially SDMA are candidate indicators for the onset of renal failure.

Integration of hepatitis B vaccination into national immunisation programmes

Abstract: Hepatitis B is a major public health problem even though safe and effective vaccines have been available for over 10 years. Because hepatitis B infection is largely asymptomatic with long term complications occurring after many years it has not received the attention it deserves. Strategies to immunise those at high risk have failed to control the disease. Delegates to the World Health Assembly of the World Health Organisation recommended in May 1992 that all countries should integrate hepatitis B vaccination into their national immunisation programmes by 1997. Some western European countries remain unconvinced that the burden of disease warrants the expense of universal vaccination. However, epidemiological data and economic evaluation show that universal hepatitis B vaccination is cost effective in countries with low endemicity and that it will control hepatitis B, reinforcing the necessity for action.