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At least 253 records · Page 14Linked to original sources
PubMed1988

Gas chromatographic analysis of histidine: effect on other amino acids present.

Earlier proposals aimed at increasing the detector responses of histidine in gas chromatographic analysis have been compared and contrasted with regard to their effect on the other amino acids present. Twenty-one amino acids have been measured in the form of their N,O,(S)-trifluoroacetyl (TFA) isobutyl esters. Detector responses of the amino acid N,O,(S)-TFA isobutyl esters of dichloromethane solutions alone and mixed with acetic anhydride were recorded and compared with those of other TFA esters. Reproducibility data for chosen representative amino acid N,O,(S)-TFA isobutyl esters are presented.

Amino Acids↗
PubMed1991

Automated phenylthiocarbamyl amino acid analysis of carboxypeptidase/aminopeptidase digests and acid hydrolysates.

A fully automated exopeptidase digestion procedure for the partial determination of N- and C-terminal peptide/protein sequence is described. The digestion of various substrates with aminopeptidase M, carboxypeptidase A, P or Y was accomplished with the Varian 9090 autosampler's robotic automix routines. The released free amino acids, in addition to free amino acids from acid hydrolysates, were derivatized with phenylisothiocyanate in an automated fashion and subsequently chromatographed on a C18 column for separation and quantitation. The advantages of automating this precolumn phenylisothiocyanate derivatization are the virtual elimination of sample manipulation errors and very reproducible data due to the precise control of the reaction conditions both of which, facilitate the interpretation of the exopeptidase reaction kinetic data.

Amino Acids↗
PubMed2002

Comparison of solid-phase extraction methods for the determination of azaspiracids in shellfish by liquid chromatography-electrospray mass spectrometry.

Azaspiracids have been identified as the cause of a new toxic syndrome called azaspiracid poisoning (AZP) that has led to incidents of human intoxications throughout Europe following the consumption of mussels. Although five AZP toxins have been structurally elucidated to-date, azaspiracid (AZA1), 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3) are the predominant toxins. Separation of the three main AZP toxins was achieved using reversed-phase liquid chromatography (LC) and coupled to an electrospray ionisation source of an ion-trap mass spectrometer. Five reversed-phase (C18) and three diol solid-phase extraction (SPE) cartridges were compared for their efficacy in the cleanup of shellfish matrix. The comparison was based on the optimum recoveries of AZA1, AZA2 and AZA3 from extracts of mussel tissues. LC-electrospray MS3 analysis was used to quantify the AZP toxins in wash and eluate fractions in the SPE studies. Good recovery and reproducibility data were obtained for one diol SPE cartridge and two C18 SPE cartridge types.

Chromatography, Liquid↗
PubMed2002

Liquid chromatography with electrospray ion-trap mass spectrometry for the determination of yessotoxins in shellfish.

Yessotoxins are a group of large polyether toxins, produced by marine dinoflagellates, which cause widespread contamination of filter-feeding shellfish. A new, sensitive liquid chromatography-mass spectrometry (LC-MS) method has been developed for the determination of yessotoxin (YTX) and 45-hydroxy-yessotoxin (45-OHYTX), a major metabolite in shellfish. The LC system was coupled, via an electrospray ionisation (ESI) source, to an ion-trap MS in negative mode. The molecular related ion species at m/z 1141 [M-2Na+H]- was used as the parent ion for multiple MS experiments. MS-MS and MS3 gave major fragment ions at m/z 1061 [1141-SO3H]- and m/z 945 [1061-C9H12O]-. Predominant ions, that are due to the fragmentation of the backbone structure of YTXs, were observed at the MS4 stage. Reversed-phase LC using a C16 amide column was preferable to C18 phases for the separation of YTX and 45-OHYTX. Optimum calibration and reproducibility data were obtained for YTX using LC-MS-MS; r 2=0.9960, RSD < or = 6.3% at 0.25 microg YTX/g (n=5). The detection limit (S/N=3) was 30 pg YTX on-column which corresponded to 3 ng/g shellfish tissue.

Animals↗
PubMed2003

Effects of peak anomalies with the hydrophilic or hydrophobic properties of reservoirs during serial injection on a capillary electrophoresis microchip.

Several anomalies, e.g., in peak shape, migration time, and baseline drift, all due to pressure-driven backflow, were previously reported to occur during serial injection on capillary electrophoresis (CE) chips. Since these anomalies were worse for polydimethylsiloxane (PDMS) microchips than for glass microchips, reproducible data on PDMS microchips were difficult to obtain. In this paper, we found that these problems were affected by the hydrophilic or hydrophobic properties of the reservoirs on the microchip and demonstrated that these anomalies were reduced by converting the hydrophobic properties of the reservoirs on the PDMS microchip into hydrophilic ones. Thus, compared with hydrophobic reservoirs, hydrophilic reservoirs were suitable for the formation of a stable plug. Several chip designs were suggested to reduce these pressure-driven backflows.

Dimethylpolysiloxanes↗
PubMed2001

A C3 convertase assay for nephritic factor functional activity.

C3 nephritic factor (C3NeF) is an autoantibody against the C3 convertase which stabilizes this otherwise inherently labile neoenzyme and induces a continuous activation of the alternative pathway with C3 depletion. NeF is found in patients with membranoproliferative glomerulonephritis and/or partial lipodystrpohy. NeF activity is usually detected in plasma by hemolytic tests. In order to obtain reproducible data for the functional activity of purified C3NeF IgG a solid phase assay was developed. C3 convertase was generated on immobilized C3b by incubation with factors B and D in the presence of Ni(2+). Convertase sites were left to decay in the presence of normal IgG or NeF IgG. Residual convertase activity was measured by adding 125I-C3 and capturing nascent 125I-C3b on the plate surface via covalently coupled NH2-Glu-Tyr dipeptide. In the presence of factor H during C3 convertase decay, a dose dependent stabilizing activity was shown for NeF IgG including NeF IgG purified from urine. A second format of the assay was developed in which C3 convertase was assembled on C3b(2)-IgG complexes in the presence of Mg(2+). Since these complexes are more efficient as convertase precursors the signal was five-fold higher than with C3b. Convertase decay, on the other hand, was not influenced by the nature of the precursor and in both systems the stabilizing activity of NeF IgG was similar.

Adult↗
PubMed1997

Analyzing cytotoxic T lymphocyte activity: a simple and reliable flow cytometry-based assay.

A flow cytometry-based assay for analyzing cytotoxic T lymphocyte (CTL) activity is presented. This new approach is characterized by easy handling, the generation of highly reproducible data sets and is not dependent on the use of radioactivity. Before exposure to primed CTL effector cells the target cells were labeled with the green fluorescent dye DiO18(3) which is incorporated stably into the cell membrane. After a 4-h incubation period, samples were counterstained with the red fluorescent nuclear dye propidium iodide in order to permit discrimination between live and dead cells within both cell populations. The assay has been used to quantitate CTL effector activity against allogeneic lymphoblasts. Results derived from this novel flow cytometry assay show an excellent correlation (r = 0.988) with data obtained using the standard 51chromium release assay. An additional advantage of the assay is that freshly prepared splenocytes may be used as target cells because culturing and activation of target cells is no longer required. The results demonstrate that the fluorescent dyes DiO18(3) and propidium iodide in combination with flow cytometry permit accurate analysis of cytotoxic T cell activity.

Animals↗
PubMed1987

Understanding laboratory test results. Conditions for appropriate use of laboratory tests.

The appropriate use of laboratory tests requires that valid, reliable, and reproducible data be obtained and that the clinician know both how to interpret the information provided by diagnostic tests and how to apply it to individual clinical situations. Appropriate interpretation and clinical use of diagnostic tests requires that clinicians understand the principles of laboratory testing, the information provided and not provided by laboratory tests, and how to evaluate the clinical efficacy of laboratory tests. As laboratory testing moves from regional and hospital laboratories into office laboratories, clinicians need to become more knowledgeable regarding the technical and quality control factors that affect diagnostic test accuracy. This will require the establishment of stronger, more effective links between clinicians and laboratory pathologists.

Clinical Laboratory Techniques↗
PubMed1998

Modeling the physiological responses of anuran R3 ganglion cells.

Teeters and Arbib (Bio Cybernet 1991;64:197-207) presented a model of the anuran retina which qualitatively accounts for some of the characteristic response properties used to distinguish ganglion cell type in anurans. Teeters et al. (Vis Res 1993;33:2361-2379) tested the model's ability to reproduce data of Ewert and Hock (Exp Brain Res 1972;16:41-59) relating toad R2, R3 and R4 ganglion cell responses to moving worm, antiworm and square-shaped stimuli of various edge lengths for stimulus shape and size dependency. In this paper we provide an exhaustive analysis of the performance of the modeled R3 cells with respect to most of the known qualitative and quantitative physiological properties of natural R3 ganglion cells. We also introduce several relevant predictions of the model relating different responses of R3 cells under the effect of changes in different model components. In some cases the predictions have been tested in neurophysiological experiments.

Animals↗
PubMed1998

The thin electrolyte layer approach to corrosion testing of dental materials--characterization of the technique.

An innovative technique for corrosion testing of metallic dental materials is introduced. The thin electrolyte layer technique (TET) simulates the physical characteristics of the oral environment by employing a still, thin layer of an electrolyte, in contrast to bulk electrolyte techniques (BET) which utilize relatively large quantities of fluid. Limiting current density tests on a platinum electrode revealed a lower surface oxygen content for TET. Borate buffer (pH 6.8) was employed as an electrolyte. The effect of lower oxygen content in TET on passivation and polarization characteristics of 316L SS in 0.9% saline was investigated. The results revealed differences in the polarization resistance and open circuit potential development with time, as well as in anodic and cathodic polarization behavior. Lower O2 concentration in TET was attributed to different electrolyte convection characteristics under both testing conditions. Additionally, use of the TET resulted in better data reproducibility. Overall, this investigation led to a deeper understanding of the electrochemical processes inherent in thin electrolytes such as those found in the oral environment.

Alloys↗
PubMed2001

Crosslinking of the complementary strands of DNA by UV light: dependence on the oligonucleotide composition of the UV irradiated DNA.

UV light crosslinks the complementary strands of DNA. The interstrand crosslinks may contribute to the biological and pathological effects that UV irradiation is known to bring about. Here alkaline agarose gel electrophoresis was used to assess the crosslinked fraction of 31 selected restriction fragments of six viral and plasmid DNA molecules exposed to UVC light irradiation. As many as 17 independent experiments were performed with the particular DNA fragments to get sufficiently precise data suitable for quantitative analyses. The data were used to determine how the crosslinked fraction depended on the dinucleotide, trinucleotide and tetranucleotide contents of the irradiated DNA fragments. This analysis demonstrated that DNA conformation and/or flexibility, rather than the local double helix thermostability, governed the phenomenon of crosslinking. For example, (GA).(TC) suppressed the crosslink formation in DNA more than any dinucleotide composed of only G and C. In addition, (CTAG).(CTAG) promoted crosslinking much more than any other tetranucleotide, including e.g. (TATA).(TATA), whereas the closely related (CATG).(CATG) belonged among the tetranucleotides that most suppressed the UV light induced crosslinks between the complementary strands of DNA. The present data reproduced crosslinking of the analyzed 31 restriction fragments with a correlation coefficient exceeding 0.90. This result will be useful to predict crosslinking along the whole human genome.

Base Sequence↗
PubMed1979

Determination of erythrocyte amino acids by gas chromatography.

Erythrocyte amino acid levels were determined, by gas chromatography, in a group of 34 normal human adults. No significant sex or age correlations were noted. A method for the quantitative gas chromatographic analysis of free amino acids in erythrocytes is described. Following hemolysis and deproteinization the amino acids were isolated on a cation-exchange resin. Glutathione was removed from the amino acid mixture by adsorption on an anion-exchange resin. Following conversion to their N-acetyl-n-propyl esters, 19 amino acids were separated and quantitated by gas chromatography on a single column in 18 min. Typical reproducibility data indicate that a coefficient of variation of 2-5% is attainable.

Adult↗
PubMed1990

Determination of tryptophan and its metabolites in human plasma and serum by high-performance liquid chromatography with automated sample clean-up system.

An automated high-performance liquid chromatographic method that incorporates direct injection of biological samples followed by chromatographic sample clean-up in a precolumn is described for the determination of tryptophan and its metabolites in human plasma and serum. The system gave reproducible data with a coefficient of variation of less than 3% with a sample size of 100 microliters of human plasma. The major tryptophan metabolites found in 100 microliters of human plasma were kynurenine, indolelactic acid, indoleacetic acid, indolepropionic acid, serotonin and 5-hydroxyindoleacetic acid. The level of tryptophan and kynurenine in individuals was constant in comparison with other metabolites. Analysis of samples from normal controls, diabetics, gravida and their foetuses showed a tendency for tryptophan metabolites to be low in maternal plasma.

Autoanalysis↗
PubMed1999

Continuous intrapartum pH, pO2, pCO2, and SpO2 monitoring.

The goal of intrapartum surveillance and its further development is better patient care for both the fetus and the gravida. A normal FHR pattern is usually associated with the delivery of a normal well-oxygenated infant; however, a nonreassuring FHR is not always associated with the delivery of a compromised infant. This situation has led to an increase in unnecessary obstetric interventions in the form of a rising cesarean section rate. Fetal scalp sampling was developed in an attempt to improve the predictive value of electronic FHR monitoring, but because this technique is not widely used, management decisions are frequently made using FHR patterns alone. Much research has been performed in the search for a continuous biochemical measurement of fetal status, including continuous pH, pO2, or pCO2 and various combinations of these methodologies. None of these measurements are used in current clinical practice, mainly owing to technical problems and difficulties associated with the continuous direct measurement of these parameters in fetal blood throughout labor. The promising new field of fetal pulse oximetry has the potential to provide reliable, meaningful, and reproducible data as shown in early cross-sectional studies and more recent longitudinal studies. By identifying developing hypoxia, this technology may reduce the uncertainty associated with electronic FHR monitoring. Fetal pulse oximetry may also provide critical information relating to the detection and management of the hypoxic fetus. Any new method of intrapartum fetal monitoring requires careful evaluation to assess its potential value before its introduction into clinical practice. The use of fetal SpO2 monitoring in the presence of a nonreassuring FHR pattern is being examined in a multicenter randomized controlled trial. This study will address the question of whether supplementary monitoring of fetal SpO2 levels can lead to a reduction in the cesarean section rate for fetal distress. The available data on fetal noninvasive pulse oximetry have been obtained from a combination of well-designed cohort studies (level II-2 evidence) or from earlier multiple time series (level II-3 evidence). The results from the US Multicenter Trial (level I evidence) should provide a significant addition to current evidence. A continuous fetal noninvasive monitor measuring fetal oxygenation directly could lead to an improvement in the sensitivity and specificity of fetal surveillance. This improvement could ultimately result in a reduction in unnecessary interventions by differentiating hypoxic fetuses from nonhypoxic fetuses and, more importantly, may lead to earlier intervention for fetuses in danger of serious compromise.

Acid-Base Equilibrium↗
PubMed2002

A practical method of measuring electron isodose curves using a linear detector array for validation of treatment planning system data.

A practical method of measuring electron isodose curves for validation of treatment planning system data using a linear detector array in a water phantom is described. The detector array was used to measure both the profile and depth dose data required. A depth-dependent correction was required, determined from a comparison with diode-measured depth dose. Application of this correction enabled accurate reconstruction of isodose curves. Isodose curves were also measured with diodes, to verify the array measurements. The two were found to be in good agreement. The advantage of the array-based method is a substantial saving in linear accelerator time when compared with point-by-point detector measurements. Although the data reproduced here are specific to the linear detector array of one manufacturer, the overall measurement technique is generally applicable.

Algorithms↗
PubMed1995

Herpes simplex virus vaccines as immunotherapeutic agents.

As persistent viruses can escape immune surveillance, chronic or recurrent disease can be a major problem. Only after nearly 60 years of work have recent reproducible data, using herpes simplex virus infection as a model for persistent viral disease, established that vaccine immunotherapy is effective in the treatment of such viral infections.

Animals↗
PubMed2003

Bile duct disorders.

Drug-induced bile duct injury related prolonged or chronic cholestasis is recognized as a common side effect of treatment with several drugs. The severity and duration of the clinical symptoms suggest that this increase in number of reports is not only related to clinician and pathologists being increasingly aware of the condition, but also may represent a true increase in incidence likely related to a time-related growing experience with newer drugs. This clinical presentation encompasses a wide variety of features that may be the source of diagnostic difficulties, especially in the cases where cholestasis occurs days or weeks after the completion of therapy. Even more puzzling is the initial picture of hepatocholangitis, which may be silent and ensuing bile duct paucity with chronic anicteric cholestasis may be another source of diagnostic difficulties in the long-term. These diagnostic difficulties suggest that some of the cases of the so-called "idiopathic adulthood ductopenia" may originate from overlooked drug induced vanishing bile duct syndrome. The pathogenesis of the syndrome remains largely unknown and the determinants of prognosis and outcome. From reproducible data obtained in different studies investigating HLA-dependent predisposition, one may assume that genetics plays a major role even if other unknown additive factors are also likely involved. Severity of initial hepatocholangitis is likely to represent another important determinant of severity and prognosis, however to be assessed in larger longitudinal studies. Therapy of large bile duct injury mimics that of primary sclerosing cholangitis. Treatment of small bile duct injury remains disappointing. Corticosteroids are invariably ineffective. Ursodeoxycholic acid as been shown to induce improvement of clinical and biochemical cholestasis in some selected cases, its efficacy being however unpredictable. Preliminary data about the natural history of the vanishing bile duct syndrome suggest that therapy might be more effective when initiated early.

Animals↗
PubMed2000

Estimation of the total range of 1J(CC) couplings in heterocyclic compounds: pyridines and their N-oxides, the experimental and DFT studies.

A very large set of one-bond spin-spin carbon carbon coupling constants, 1J(CC), has been measured for 32 variously mono- and disubstituted pyridine N-oxides and for 14 substituted pyridines. The N-oxides studied were 2-, 3- and 4-monosubstituted isomers, and a series of disubstituted compounds. A variety of substituents has been employed (CH3, COCH3, C5H4NO, CN, F, Br, Cl, OH, OCH3, NH2, N(CH3)2 and NO2), which allowed us to study substituent effects thoroughly. Good linear relationships between 1J(C3C4) in 3- and/or 4-substituted pyridine N-oxides and 1J(CipsoCortho) in benzenes and between 1J(C2C3) in 2- and/or 3-substituted pyridine N-oxides and 1J(CipsoCortho) in benzenes have been found. An analogous linear relationship has been observed between 1J(C3C4) in 3- and/or 4-substituted pyridines and 1J(CipsoCortho) in benzenes. It has been also concluded that, by analogy to 1J(CC) couplings in substituted benzenes, those in pyridines and their N-oxides are the substituent electronegativity dependent. The estimated total range covered by 1J(CC), couplings in substituted compounds varies, in the case of 1J(C2C3) couplings for example, from 25 Hz in 2-lithiopyridine N-oxide to ca. 100 Hz in 2,3-difluoropyridine N-oxide and from 18 Hz in 2-lithiopyridine to 92 Hz in 2,3-difluoropyridine. The DFT calculations have been carried out for the parent compounds and for a set of their 2-lithio, and variously substituted fluoro derivatives. The DFT data reproduced very well the experimental coupling values and revealed that the Fermi contact contribution is the dominating factor which governs the magnitude of the CC coupling across one bond.

Cyclic N-Oxides↗