Dose reduction in thorax radiography in simulated neonates with additional filtration and digital luminescence radiography

PURPOSE

To determine the minimum acceptable radiation dose for an adequate image quality in thorax a.p. radiographs of neonates using mobile X-ray equipment.

MATERIAL AND METHODS

The influence of additional filtration (1.0 mm Al + 0.1 mm Cu) on image quality and radiation dose was determined for the speed class 400 screen-film system (SFS) and digital luminescence radiography (DLR) by making radiographs of a test phantom. Conventional and digital thorax a.p. radiographs of a rabbit were produced using various tube current-time products. The quality of the rabbit radiographs was judged by eight radiologists applying image quality criteria according to the German guidelines and the recommendations of the European Community.

RESULTS

The added filter resulted in a dose reduction of 39% at 66 kV. DLR gave a further dose reduction of 25% in comparison to the speed class 400 SFS while maintaining adequate image quality, i.e. the radiographs were clinically acceptable with regard to quality criteria.

CONCLUSION

The radiation dose resulting from thorax a.p. radiographs of neonates can be reduced by approximately 50% with the use of additional filtration and DLR.

High resolution crystal structure of pyruvate decarboxylase from Zymomonas mobilis. Implications for substrate activation in pyruvate decarboxylases

The crystal structure of tetrameric pyruvate decarboxylase from Zymomonas mobilis has been determined at 1.9 A resolution and refined to a crystallographic R-factor of 16.2% and Rfree of 19.7%. The subunit consists of three domains, all of the alpha/beta type. Two of the subunits form a tight dimer with an extensive interface area. The thiamin diphosphate binding site is located at the subunit-subunit interface, and the cofactor, bound in the V conformation, interacts with residues from the N-terminal domain of one subunit and the C-terminal domain of the second subunit. The 2-fold symmetry generates the second thiamin diphosphate binding site in the dimer. Two of the dimers form a tightly packed tetramer with pseudo 222 symmetry. The interface area between the dimers is much larger in pyruvate decarboxylase from Z. mobilis than in the yeast enzyme, and structural differences in these parts result in a completely different packing of the subunits in the two enzymes. In contrast to other pyruvate decarboxylases, the enzyme from Z. mobilis is not subject to allosteric activation by the substrate. The tight packing of the dimers in the tetramer prevents large rearrangements in the quaternary structure as seen in the yeast enzyme and locks the enzyme in an activated conformation. The architecture of the cofactor binding site and the active site is similar in the two enzymes. However, the x-ray analysis reveals subtle but significant structural differences in the active site that might be responsible for variations in the biochemical properties in these enzymes.

SAR of novel biarylmethylamine dopamine D4 receptor ligands

SAR for a novel series of dopamine D4 receptor ligands is shown. Very selective, highly potent compounds like 1-(2-pyrimidinyl)-4-(3-(3-thienyl)-benzyl)-piperazine (5f) and 2-(4-(1-fluorenylmethyl)-1-piperazinyl)-pyrimidine (8c) were obtained.

The crystal structure of H-2Dd MHC class I complexed with the HIV-1-derived peptide P18-I10 at 2.4 A resolution: implications for T cell and NK cell recognition

The structure of H-2Dd complexed with the HIV-derived peptide P18-I10 (RGPGRAFVTI) has been determined by X-ray crystallography at 2.4 A resolution. This MHC class I molecule has an unusual binding motif with four anchor residues in the peptide (G2, P3, R/K/H5, and I/L/F9 or 10). The cleft architecture of H-2Dd includes a deep narrow passage accomodating the N-terminal part of the peptide, explaining the obligatory G2P3 anchor motif. Toward the C-terminal half of the peptide, p5R to p8V form a type I' reverse turn; residues p6A to p9T, and in particular p7F, are readily exposed. The structure is discussed in relation to functional data available for T cell and natural killer cell recognition of the H-2Dd molecule.

Nutritional status of children admitted to hospital with different diseases and its relationship to outcome in The Gambia, West Africa

Admission records from two paediatric units in The Gambia were used to explore the relationship between admission weight and different diseases. In total 13579 hospitalized children were analysed. For comparison, 7399 children were recruited from several surveys of well subjects to provide anthropometric values for healthy Gambian children. Compared to the control children, mean admission weights were lower for malaria (weight for age z-score: -1.602), cerebral malaria (-1.547), transfused malarial anaemia (-1.764), pneumonia (-1.725), meningitis (-1.362), gastro-enteritis (-2.497) and malnutrition (-3.786). Children with bronchiolitis did not have a significantly different weight for age than the controls. Outcome of the hospital admission was recorded and related to the weight on admission. In all disease categories the death rate rose with decreasing admission weight with the exception of bronchiolitis. For all diseases taken together, case fatality was 7.2% for children with a weight for age z-score above -2 Standard Deviations (SD), 9.3% between -2 and -3 SD, 15.6% between -3 and -4 SD and 22.7% for children with weight for age SD z-scores less than -4. Malnourished children are more susceptible to several infectious diseases frequently seen in developing countries and nutritional interventions, as well as standard treatment, may improve outcome.

Oligomerization properties of ERp29, an endoplasmic reticulum stress protein

ERp29, a novel and ubiquitously expressed endoplasmic reticulum (ER) stress-inducible protein, was recently isolated and cDNA cloned in our laboratory. Using size exclusion chromatography and chemical cross-linking we have assessed the oligomerization properties of ERp29. Purified ERp29 in solution as well as in rat hepatoma cells self-associates predominantly into homodimers. Labeling of the cells with [35S]methionine with subsequent cross-linking and immunoprecipitation showed that ERp29 interacts with a number of ER proteins, one of which was previously identified as BiP/GRP78. Secondary structure prediction and fold recognition methods indicate that the native conformation of ERp29 resembles the thioredoxin fold, a structural motif characteristic of a number of enzymes with the redox function, including protein disulfide isomerase (with which ERp29 shares limited sequence similarity). Dimerization of the protein is suggested to be advantageous for the protein binding potential of ERp29.

Crystallography and mutagenesis of transketolase: mechanistic implications for enzymatic thiamin catalysis

The ThDP dependent enzyme transketolase is a convenient model system to study enzymatic thiamin catalysis. Crystallographic studies of the enzyme have identified the ThDP binding fold, the V-conformation of ThDP as the relevant conformation in enzymatic catalysis and details of enzyme-substrate interactions. Based on this structural information, the function of various active site residues in substrate binding and catalysis has been probed by site-directed mutagenesis.

Activation of thiamin diphosphate in enzymes

Activation of the coenzyme ThDP was studied by measuring the kinetics of deprotonation at the C2 carbon of thiamin diphosphate in the enzymes pyruvate decarboxylase, transketolase, pyruvate dehydrogenase complex, pyruvate oxidase, in site-specific mutant enzymes and in enzyme complexes containing coenzyme analogues by proton/deuterium exchange detected by 1H-NMR spectroscopy. The respective deprotonation rate constant is above the catalytic constant in all enzymes investigated. The fast deprotonation requires the presence of an activator in pyruvate decarboxylase from yeast, showing the allosteric regulation of this enzyme to be accomplished by an increase in the C2-H dissociation rate of the enzyme-bound thiamin diphosphate. The data of the thiamin diphosphate analogues and of the mutant enzymes show the N1' atom and the 4'-NH2 group to be essential for the activation of the coenzyme and a conserved glutamate involved in the proton abstraction mechanism of the enzyme-bound thiamin diphosphate.

[Evaluation of the effects of bioadhesive substances as addition to oral contrast media: an experimental study]

PURPOSE

To evaluate the additional effect of bioadhesives in combination with iotrolan and barium as oral contrast media in an animal model.

METHOD

The bioadhesives Noveon, CMC, Tylose and Carbopol 934 were added to iotrolan and barium. The solutions were administered to rabbits by a feeding tube. The animals were investigated by computed tomography (CT) and radiography after 0.5, 4, 12, 24 and in part after 48 hours. Mucosal coating and contrast filling of the bowel were evaluated.

RESULTS

Addition of bioadhesives to oral contrast media effected long-term contrast in the small intestine and colon, but no improvement in continuous filling and coating of the gastrointestinal tract was detected. Mucosal coating was seen only in short regions of the caecum and small intestine. In CT the best results for coating were observed with tylose and CMC, in radiography additionally with carbopol and noveon. All contrast medium were well tolerated.

CONCLUSION

The evaluated contrast medium solutions with bioadhesives have shown long-term contrast but no improvement in coating in comparison to conventional oral contrast media.

The crystal structure of phenol hydroxylase in complex with FAD and phenol provides evidence for a concerted conformational change in the enzyme and its cofactor during catalysis

BACKGROUND

The synthesis of phenolic compounds as by-products of industrial reactions poses a serious threat to the environment. Understanding the enzymatic reactions involved in the degradation and detoxification of these compounds is therefore of much interest. Soil-living yeasts use flavin adenine dinucleotide (FAD)-containing enzymes to hydroxylate phenols. This reaction initiates a metabolic sequence permitting utilisation of the aromatic compound as a source of carbon and energy. The phenol hydroxylase from Trichosporon cutaneum hydroxylates phenol to catechol. Phenol is the best substrate, but the enzyme also accepts simple hydroxyl-, amino-, halogen- or methyl-substituted phenols.

RESULTS

The crystal structure of phenol hydroxylase in complex with FAD and phenol has been determined at 2.4 A resolution. The structure was solved by the MIRAS method. The protein model consists of two homodimers. The subunit consists of three domains, the first of which contains a beta sheet that binds FAD with a typical beta alpha beta nucleotide-binding motif and also a fingerprint motif for NADPH binding. The active site is located at the interface between the first and second domains; the second domain also binds the phenolic substrate. The third domain contains a thioredoxin-like fold and is involved in dimer contacts. The subunits within the dimer show substantial differences in structure and in FAD conformation. This conformational flexibility allows the substrate to gain access to the active site and excludes solvent during the hydroxylation reaction.

CONCLUSIONS

Two of the domains of phenol hydroxylase are similar in structure to p-hydroxybenzoate hydroxylase. Thus, phenol hydroxylase is a member of a family of flavin-containing aromatic hydroxylases that share the same overall fold, in spite of large differences in amino acid sequences and chain length. The structure of phenol hydroxylase is consistent with a hydroxyl transfer mechanism via a peroxo-FAD intermediate. We propose that a movement of FAD takes place in concert with a large conformational change of residues 170-210 during catalysis.

Snapshot of a phosphorylated substrate intermediate by kinetic crystallography

The ATP-dependent enzyme dethiobiotin synthetase from Escherichia coli catalyses the formation of dethiobiotin from CO2 and 7, 8-diaminopelargonic acid. The reaction is initiated by the formation of a carbamate and proceeds through a phosphorylated intermediate, a mixed carbamic phosphoric anhydride. Here, we report the crystal structures at 1.9- and 1.6-A resolution, respectively, of the enzyme-MgATP-diaminopelargonic acid and enzyme-MgADP-carbamic-phosphoric acid anhydride complexes, observed by using kinetic crystallography. Reaction initiation by addition of either NaHCO3 or diaminopelargonic acid to crystals already containing cosubstrates resulted in the accumulation of the phosphorylated intermediate at the active site. The phosphoryl transfer step shows inversion of the configuration at the phosphorus atom, consistent with an in-line attack by the carbamate oxygen onto the phosphorus atom of ATP. A key feature in the structure of the complex of the enzyme with the reaction intermediate is two magnesium ions, bridging the phosphates at the cleavage site. These magnesium ions compensate the negative charges at both phosphate groups after phosphoryl transfer and contribute to the stabilization of the reaction intermediate.

A polymerase chain reaction for the diagnosis of Haemophilus influenzae type b disease in children and its evaluation during a vaccine trial

BACKGROUND

Determination of the etiology of pneumonia in young children is difficult because blood culture, the usual method of diagnosis, is positive in only a small proportion of cases. For this reason vaccine trials that include bacterial pneumonia as an endpoint must be large.

OBJECTIVES

To determine whether a diagnostic test based on a polymerase chain reaction could be used as an alternative to conventional blood culture for diagnosis of invasive Haemophilus influenzae type b (Hib) infections in young children investigated during the course of a large vaccine trial.

METHODS

DNA was extracted from blood culture supernatants and probed for the presence of Hib DNA with a PCR assay with primers derived from the cap gene locus of Hib. Results of the PCR assay were compared with those obtained by conventional culture techniques.

RESULTS

Blood cultures were obtained from 1544 children with suspected pneumonia, meningitis or septicemia and from 31 healthy control children who were contacts of cases. Blood culture supernatants were tested for Hib DNA in the PCR test. The sensitivity and specificity of a positive PCR test in blood culture supernatant as against culture of Hib from any normally sterile site were 100 and 99%, respectively. Eleven children had positive Hib PCR tests on blood culture supernatants but were negative by culture. In one of these cases Hib was isolated from a lung aspirate and in two other patients H. influenzae strains other than Hib were obtained from the cerebrospinal fluid. Eight of these 11 children were in the control group. When the results of the PCR assay were used to determine vaccine efficacy, a value of 86% was obtained compared with a figure of 95% obtained when conventional culture techniques were used.

CONCLUSIONS

An Hib PCR assay on blood culture supernatants proved to be sensitive and specific for the diagnosis of Hib disease in children. The distribution of PCR-positive, culture-negative cases between Hib-vaccinated and control groups paralleled that of culture-positive cases, suggesting that most of these children had been infected with Hib. A trial of a highly efficacious vaccine provides a novel way for evaluating new diagnostic tests for which there is no standard diagnostic test of 100% reliability.

Refractory hyperglycemia complicating an evolving connective tissue disease: response to cyclosporine

A 33-year-old woman with longstanding rheumatoid arthritis and Sjögren's syndrome developed type B insulin resistance (diabetes mellitus due to anti-insulin receptor antibodies) simultaneous with the evolution of her rheumatic disease to mixed connective tissue disease. Cyclosporine therapy induced a remission of receptor antibody mediated insulin resistance and controlled clinical manifestations of her systemic lupus erythematosus and dermatomyositis, but had no effect on the sclerodermatous features of her illness.

Peptide design aided by neural networks: biological activity of artificial signal peptidase I cleavage sites

De novo designed signal peptidase I cleavage sites were tested for their biological activity in vivo in an Escherichia coli expression and secretion system. The artificial cleavage site sequences were generated by two different computer-based design techniques, a simple statistical method, and a neural network approach. In previous experiments, a neural network was used for feature extraction from a set of known signal peptidase I cleavage sites and served as the fitness function in an evolutionary design cycle leading to idealized cleavage site sequences. The cleavage sites proposed by the two algorithms were active in vivo as predicted. There seems to be an interdependence between several cleavage site features for the constitution of sequences recognized by signal peptidase. It is concluded that neural networks are useful tools for sequence-oriented peptide design.

Direct association of protein-tyrosine phosphatase PTP-PEST with paxillin

Tyrosine phosphorylation of focal adhesion-associated proteins may be involved in the regulation of the cytoskeleton and in the control of signals for growth and survival. The focal adhesion kinase (FAK) functions in regulating tyrosine phosphorylation of several of these proteins, including paxillin, tensin, and p130(cas). Protein- tyrosine phosphatases, the counterparts of protein-tyrosine kinases, also presumably regulate phosphorylation of these proteins. We have tested the hypothesis that FAK intimately associates with a protein-tyrosine phosphatase. Protein-tyrosine phosphatase activity associated with the recombinant C-terminal domain of FAK in vitro and could be coimmunoprecipitated with both FAK and paxillin from lysates of chicken embryo cells. However, the interaction with FAK appeared to be indirect and mediated via paxillin. The protein-tyrosine phosphatase was subsequently identified as protein-tyrosine phosphatase-PEST, a nonreceptor protein-tyrosine phosphatase. The C-terminal noncatalytic domain of protein-tyrosine phosphatase-PEST directly bound to paxillin in vitro. The association of both a protein-tyrosine kinase and a protein-tyrosine phosphatase with paxillin suggests that paxillin may play a critical role in the regulation of the phosphotyrosine content of proteins in focal adhesions.

Asp477 is a determinant of the enantioselectivity in yeast transketolase

The conserved residue Asp477 in yeast transketolase is located in the substrate channel of the enzyme and forms a hydrogen bond with the C2-hydroxyl group of the acceptor substrate. The significance of this interaction for the recognition of the preferred acceptor substrates, D-alpha-hydroxyaldehydes was investigated by site-directed mutagenesis. In the wild-type enzyme the kcat/KM values are by three to four orders of magnitude lower for 2-deoxyaldoses or substrates with L-configuration at the C2-atom. In the Asp477 Ala mutant, the kcat/KM values for D-alpha-hydroxyaldehydes are decreased by a thousandfold, while the kcat/KM values for substrates with L-configuration or 2-deoxyaldoses are similar to wild-type enzyme. These results indicate that Asp477 is involved in determining the enantioselectivity of transketolase.

Crystal structure of beta-ketoacyl-acyl carrier protein synthase II from E.coli reveals the molecular architecture of condensing enzymes

In the biosynthesis of fatty acids, the beta-ketoacyl-acyl carrier protein (ACP) synthases catalyze chain elongation by the addition of two-carbon units derived from malonyl-ACP to an acyl group bound to either ACP or CoA. The crystal structure of beta-ketoacyl synthase II from Escherichia coli has been determined with the multiple isomorphous replacement method and refined at 2.4 A resolution. The subunit consists of two mixed five-stranded beta-sheets surrounded by alpha-helices. The two sheets are packed against each other in such a way that the fold can be described as consisting of five layers, alpha-beta-alpha-beta-alpha. The enzyme is a homodimer, and the subunits are related by a crystallographic 2-fold axis. The two active sites are located near the dimer interface but are approximately 25 A apart. The proposed nucleophile in the reaction, Cys163, is located at the bottom of a mainly hydrophobic pocket which is also lined with several conserved polar residues. In spite of very low overall sequence homology, the structure of beta-ketoacyl synthase is similar to that of thiolase, an enzyme involved in the beta-oxidation pathway, indicating that both enzymes might have a common ancestor.

Pain, coping and psychological well-being in late life

In the present article, the relationships between pain, coping, functional capacity and psychological well-being are examined in a population of older patients (>/=60 years; n=202) treated for a variety of somatic complaints in a university-affiliated hospital. Results indicate that moderate to extreme pain is common in older patients and often occurs in several body regions simultaneously. Extreme pain in one or more body regions is associated with reduced daily functional capacity, lower values for life satisfaction and self-evaluated competence, and more negative attitudes towards the present and future. Results of a hierarchical cluster analysis reveal interindividual differences in coping approaches among older patients suffering from extreme pain; they also emphasize the importance of cognitive strategies and life-review coping. Relevance for clinical practice with older pain patients is discussed.In the present article, the relationships between pain, coping, functional capacity and psychological well-being are examined in a population of older patients (>/=60 years; n=202) treated for a variety of somatic complaints in a university-affiliated hospital. Results indicate that moderate to extreme pain is common in older patients and often occurs in several body regions simultaneously. Extreme pain in one or more body regions is associated with reduced daily functional capacity, lower values for life satisfaction and self-evaluated competence, and more negative attitudes towards the present and future. Results of a hierarchical cluster analysis reveal interindividual differences in coping approaches among older patients suffering from extreme pain; they also emphasize the importance of cognitive strategies and life-review coping. Relevance for clinical practice with older pain patients is discussed. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.

The clinical spectrum of respiratory syncytial virus disease in The Gambia

BACKGROUND

Respiratory syncytial virus (RSV) is a well-recognized cause of lower respiratory tract infections in early childhood in industrialized countries, but less is known about RSV infection in developing countries.

METHODS

Four outbreaks of RSV infection that occurred between 1993 and 1996 in The Gambia, West Africa, were studied. RSV was sought by immunofluorescent staining of nasopharyngeal aspirate samples among young children who presented with respiratory infections at three hospitals in the Western Region of the country.

RESULTS

Five hundred seventy-four children with RSV infection were identified. The median ages of children seen in 1993 through 1996 were 3, 7, 8 and 5 months, respectively. Sixty-two percent of children <6 months old were boys. Thirteen children (2.4%) had conditions considered to increase the risk of severe RSV infection. On physical examination crepitations were heard in 80% of the children admitted to hospital, whereas wheezes were heard in only 39%. Eighty (16%) children received oxygen because of hypoxemia. Nine of 255 blood cultures (3.5%) were positive: 4 Streptococcus pneumoniae; 2 Haemophilus influenzae type b; 2 Staphylococcus aureus; and 1 Enterobacter agglomerans. Thirteen children died (2.4%). During the 4 study years 90, 25, 75 and 95% of isolates typed were RSV Subgroup A, respectively.

CONCLUSIONS

RSV is a significant cause of lower respiratory tract infection in young children in The Gambia, causing epidemics of bronchiolitis. It poses a significant burden on the health system, especially through the demand for supplementary oxygen. The clinical spectrum of RSV disease in The Gambia is similar to that seen in developed countries; concomitant bacterial infections are uncommon.

Genetic variation in the 3' untranslated region of the neurofibromatosis 1 gene: application to unequal allelic expression

Neurofibromatosis type 1 (NF1) is a common genetic disorder caused by inactivation of neurofibromin, a protein capable of modulating signal transduction by activating Ras-GTPase activity. We have used cDNA cloning and Northern blot analysis to confirm the NF1 gene produces alternatively polyadenylated mRNAs with 3' untranslated regions (3' UTR) that show striking evolutionary conservation. Scanning of the 3'UTRs for genetic variation revealed three common sequence polymorphisms (> 30% heterozygosity), one less informative polymorphism (approximately 5% heterozygosity) and one rare variant (1/144 chromosomes). These differences were used to examine relative levels of expression of normal and mutant NF1 alleles in lymphoblast cell lines and in one case, autopsy tissue, from patients with NF1. Unequal allelic expression (up to 4-fold) was observed in a subset of both sporadic and familial NF1 cases. Where linkage phase could be determined, the allele segregating with the disorder displayed a relative reduction in expression. However, the magnitude of this effect was variable suggesting the operation of additional, non-genetic factors in determining the degree of relative expression of the mutant allele.

CSF, plasma viral load and HIV associated dementia

Plasma viral burden has proven valuable in predicting the future course of systemic HIV related disease and the response to treatment. It is not known whether plasma or cerebrospinal fluid (CSF) viral burden can be used to predict onset of or response to treatment of nervous system disease. We propose a model of viral load mediated neurotoxicity underlying peripheral and central HIV associated neurological disease. The objective of this preliminary study was to assess the relationship of HIV associated neurological disease to quantitative viral load in plasma and CSF. 47 subjects (HIV- = 10, HIV+ = 37) participated in the study. Plasma and CSF samples were collected within a 3 h window. RT-PCR (Roche Amplicor Monitor) was utilized to assess HIV-1 RNA viral load in both plasma and cell free (centrifuged) CSF. Subjects underwent concurrent comprehensive neurological and neuropsychological evaluations. In general, systemic viral load, as measured in plasma, was greater than that found in cell free CSF. Cell free CSF HIV RNA viral load was significantly correlated with neurological dysfunction, whereas plasma viral load was not. The sole subject with an elevated CSF viral load (> 5 Log 10), had HIV associated dementia (HAD) on clinical examination.

A trial of Fansidar plus chloroquine or Fansidar alone for the treatment of uncomplicated malaria in Gambian children

Chloroquine can no longer be recommended as the first-line treatment for uncomplicated malaria in several parts of Africa because of the increasing prevalence of chloroquine resistance. However, chloroquine was a highly effective treatment for malaria not only because of its ability to kill parasites quickly but also because it is an anti-inflammatory drug. Therefore, we have investigated whether Fansidar (pyrimethamine/sulfadoxine) plus chloroquine is a more effective treatment for uncomplicated malaria than Fansidar alone. Four hundred and five Gambian children with uncomplicated Plasmodium falciparum malaria were studied in a randomized controlled trial. Significantly more children treated with Fansidar alone, compared to those treated with Fansidar plus chloroquine (19/203 vs. 2/202; P < 0.001), returned to the clinic with persistent symptoms during the first 3 d after treatment. Three children who had received Fansidar alone had fits, but none of the children treated with Fansidar plus chloroquine did so. At the day 7 follow-up, the parasite failure rate in the Fansidar alone group was 3/198 (1.5%), whilst in the Fansidar plus chloroquine group it was 3/201 (1.5%). At the day 28 follow-up, there was still no significant difference between the parasite failure rate in the Fansidar alone group (15/150; 10.0%) and the Fansidar plus chloroquine group (7/141; 5.0%) and the mean packed cell volume (PCV) in the 2 groups was similar. Thus, a combination of Fansidar plus chloroquine was a more effective symptomatic treatment than Fansidar given alone, but neither the parasite cure rate nor the PCV was enhanced by use of the combination.