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At least 973 records · Page 54Linked to original sources
PubMed1991

Role of physiological energetics in ecotoxicology.

1. The role of physiological energetic measurements combined with chemical analyses of contaminants in body tissues of mussels in fundamental toxicological studies and pollution monitoring programmes is outlined. 2. Important features of this toxicological approach are briefly reviewed, including aspects of bioaccumulation, sensitivity, quantitative concentration-response relationships, QSARs, mechanistic interpretation, ecological relevance, integration of the consequences of multiple mechanisms of toxicity and effects of contaminant mixtures and application to laboratory and field studies. 3. This review focuses particularly on recent advances in understanding and predicting the effects of complex mixtures of contaminants.

Animals↗
PubMed2006

Temperature dependence of acidity constants, a tool to affect separation selectivity in capillary electrophoresis.

The mathematical models of migration and dispersion in capillary zone electrophoresis of small molecules form a sound basis for separation strategies of complex mixtures. It turned out that the key property is the effective mobility of the sample ions. To tune resolution parameters such as pH, complexation constants and ionic strength are widely used; temperature however is not although mobilities and pK(a) values depend in a more or less degree on temperature. From the temperature dependences of pK(a) values of a number of compounds listed in the literature a general rule can be derived: for carboxylic and inorganic acids dpK(a)/dT values are very small and the pK(a) values change less than +/-0.05 units/10K. Thermodynamically speaking, these compounds exhibit dissociation enthalpies close to zero. Phenols and amines, on the other hand, have systematically larger dpK(a)/dT values of about -0.1 to -0.2 units per 10K (the results of dissociation enthalpies of 20-70 kJ/mole). Based on this classification, a distinction can be made between different situations in capillary electrophoresis: (i) selectivity changes with temperature are largely due to the temperature dependence of the pK(a) of the buffering compound in the background electrolyte, (ii) selectivity changes mainly result from the temperature dependence of the pK(a) of the sample ions, and (iii) temperature effects on the pK(a) values of both, sample and buffer play a role. This work demonstrates such effects on selectivity in capillary electrophoresis highlighting the fact that in some instances temperature can be used to fine-tune separations.

Buffers↗
PubMed2000

New diffusion-edited NMR experiments to expedite the dereplication of known compounds from natural product mixtures.

[reaction: see text] We present two new diffusion-edited NMR experiments, improved DECODES and HETDECODES, that sort the constituents in a mixture by their individual diffusion coefficients. These experiments should allow the partial NMR spectral assignment and cursory structure elucidation of compounds in a complex mixture as an aid in the dereplication of known or nuisance compounds.

Biological Factors↗
PubMed1991

Assembly and analysis of a functional vaccinia virus "amplicon" containing the C-repeat region from the M protein of Streptococcus pyogenes.

Previous studies have shown that when inoculated intranasally into mice, vaccinia virus (VV) recombinants expressing the carboxyl half of the Streptococcus pyogenes M protein [which contains the C-repeat region (CRR)] could elicit a protective immune response against subsequent challenge by both homologous and heterologous serotypes of pathogenic group A streptococci. In the present study, an insertion plasmid was constructed that contained three tandem in-frame repeats of a 310-base-pair DNA sequence encoding the CRR from streptococcal M6 protein under control of a constitutive viral promoter. The plasmid was used to introduce the bacterial sequences into the VV genome by homologous recombination. Surprisingly, the recombinant VV:CRR3X virus that was isolated appeared to represent not an individual recombinant virus but a complex mixture of variants that contained from 1 to greater than 20 tandem copies of the CRR region at the insertion site. This genomic complexity was mirrored at the transcriptional level in that a nested set of coterminal transcripts was detected in VV:CRR3X-infected cells, which increased in size from 1400 to 6600 bases by increments of approximately 300 bases. All transcripts containing two or more CRR inserts appeared functional, as Western (immuno) blot analyses of VV:CRR3X-infected cell extracts revealed a family of CRR-related proteins with apparent molecular masses that increased from 30 kDa upward in increments of 10 kDa. All data are consistent with the hypothesis that variation in the VV:CRR3X recombinants is from random crossover events that occur within the CRR region during viral DNA replication. These results suggest that the genomic diversity generated by the "recombinogenic" properties of vaccinia recombinants containing tandem foreign inserts could be used to facilitate induction of a broadly protective immune response against antigenically diverse pathogenic agents.

Amino Acid Sequence↗
PubMed2004

Phosphopeptide-selective column-switching RP-HPLC with a titania precolumn.

A methodology of phosphopeptide-selective analysis coupled with column-switching HPLC utilizing titania as precolumn media is presented. Phosphopeptides were selectively enriched on titania packing within a protein/peptide mixture without any additional procedure, and analyzed by column-switching high-performance liquid chromatography. First, phospho-compounds were separated from complex mixtures by trapping them under acidic conditions on a titania packing, where non-phosphorylated compounds were effused out of the precolumn. Subsequently, phospho-compounds were desorbed from the titania column under a specific condition and analyzed. The behavior of phospho-compounds on a titania surface, especially adsorption/desorption, was precisely examined and optimized. A phosphoric buffer was successively employed for the elution of phosphopeptides on a titania surface by competition with the free phosphate group. From the successes of a selective concentration/analysis of phosphopeptides with column-switching HPLC with a titania precolumn, a novel phosphopeptide-selective RP-HPLC analysis has been shown to have an application possibility as a tool for phosphoproteomics.

Chromatography, High Pressure Liquid↗
PubMed2000

Screening of ligand binding on melatonin receptor using non-peptide combinatorial libraries.

The screening of combinatorial libraries requires a deconvolution procedure to obtain, in fine, the most active compound of the starting library. The standard screening assays used in regular molecular pharmacology, have been poorly assessed when transposed to combinatorial chemistry-related experiments, particularly those involving large numbers of chemicals in a single assay. One key issue is the effect of the inactive analogs on the identification of the active ligand in mixtures. We chose melatonin receptors to measure the apparent affinity of a single ligand when tested alone or in mixtures of non-peptide low molecular weight compounds. Using ligands with IC50 from the micro- to the picomolar range, mixed with increasingly complex mixtures of 5 to 20 or 25 inactive compounds, we analyzed the displacements from the mt1 and MT2 melatonin receptor subtypes of the radioligand 2-iodomelatonin (KD= 25 pmol/l and 200 pmol/l, respectively) . The behavior of equimolar mixtures in displacement curves led to the conclusion that the observed binding affinity reflects the dilution effect of mixing the active component with inactive compounds but does not reveal noticeable interactions which would interfere with the binding process. From the practical point of view, the concentrations of the active species in the binding assay should be large enough to displace significantly the radioligand, a requirement which may be limited by the solubility of the ligand mixtures. In contrast, previous observations with peptide libraries report that the dilution effect is often compensated by additive or synergic action of structurally related analogs, thus making possible the deconvolution of very large (typically up to 10(7) compounds) peptide libraries.

Binding, Competitive↗
PubMed1998

Synergisms with mixtures of xenoestrogens: a reevaluation using the method of isoboles.

There are concerns about possible combination effects of environmental chemicals with oestrogenic activity and their implications for human health. Such chemicals are present in complex mixtures in our environment. A number of studies searching for possible synergistic interactions between xenoestrogens have appeared in the literature. However, in these studies no account was taken of established concepts and methods for analysing combination effects. In the present review, we highlight conceptual issues which may be useful for a sound analysis of the effects of mixtures of xenoestrogens. We find that much published work suffers from an undue focus on measuring effects of mixtures at only one dose level. Assessments of combination effects are frequently complicated by a lack of information on dose-response relationships. Some studies which purportedly show absence of synergy have in fact overlooked synergisms.

Animals↗
PubMed1991

Statistical issues in risk assessment of reproductive outcomes with chemical mixtures.

Establishing the relationship between a given chemical exposure and human reproductive health risk is complicated by exposures or other concomitant factors that may vary from pregnancy to pregnancy. Moreover, when exposures are to complex mixtures of chemicals, varying with time in number of components, doses of individual components, and constancy of exposure, the picture becomes even more complicated. A pilot study of risk of adverse reproductive outcomes among male wastewater treatment workers and their wives is described here. The wives of 231 workers were interviewed to evaluate retrospectively the outcomes of spontaneous early fetal loss and infertility. In addition, 87 workers participated in a cross-sectional evaluation of sperm/semen parameters. Due to the ever-changing nature of the exposure and the lack of quantification of specific exposures, six dichotomous variables were used for each specific job description to give a surrogate measure of exposure. Hence, no quantitative exposure-response relationships could be modeled. These six variables were independently assigned by two environmental hygienists, and their interrater reliability was assessed. Results are presented and further innovations in statistical methodology are proposed for further applications.

Data Interpretation, Statistical↗
PubMed1999

Affinity NMR.

Because binding ligands are directly detected and identified, the diffusion-based NMR method and NOE pumping approach promise to greatly simplify deconvolution in drug screening. An additional advantage of these techniques is that low-affinity ligands, which might be missed by high-throughput screening, can be detected and could serve as synthetic precursors for higher affinity ligands. The biggest challenge to NMR methodology lies in its sensitivity. Compared with other techniques, such as MS (25), NMR methods for screening mixtures are limited by their relative insensitivity. Because of issues such as solubility, stability, and mass limitation, it is not in general judicious to simply increase the concentration of the mixture. Improvements in hardware and software are necessary to extend the applicability of the affinity NMR method to the screening of larger and more complex mixtures. A boost in sensitivity and screening capacity of NMR technique is possible by the implementation of microcoil (26) and flow probe techniques. An upsurge in the capabilities of mixture analysis could be achieved with a combination of independent and complementary techniques (e.g., HPLC, MS) (27). As a unique, nondestructive, and versatile tool, NMR will continue on its fast track of development in the support of drug discovery.

Drug Evaluation, Preclinical↗
PubMed2001

Novel solution-phase immunoassays for molecular analysis of tumor markers.

at 3 x 10(9) M(-1) and a step-wise binding process with PSA-free MAB. Thus, this solution-phase quantitative ECL immunoassay allowed measurement of the affinity of serum PSAs with their MABs and screening of PSAs based upon their affinity to MABs. Unlike other immunoassays, this immunoassay demonstrated one-step rapid analysis while simultaneously eliminating immobilization, separation and washing steps and detected PSA at a level of 1.7 pg mL(-1), which is 1000-fold more sensitive than current PSA immunoassays. Furthermore, single-molecule (SM) phosphorescence microscopy was developed to detect single serum PSA-free and PSA-complex molecules in solution with no use of antibody showing that PSA-free molecules diffused faster than PSA-complex molecules in solution. This finding is consistent with ECL measurements and implies the possibility of screening individual analytes in a complex mixture using their distinct SM diffusion distance. This is the first report describing the detection of single protein molecules labeled with a metal-complex using phosphorescence microscopy and also the screening of serum tumor markers using ECL and SM phosphorescence solution-phase assays.

Antigen-Antibody Reactions↗
PubMed1983

Micro LC/MS in drug analysis and metabolism studies.

LC/MS has become a routine research tool in some laboratories. Although no single approach to LC/MS presently is without limitations, each approach offers encouraging results and prompts continued improvements. The remaining hurdles appear to be the introduction of total LC effluent into the MS, increased sensitivity, and the ability to analyze higher molecular weight, polar molecules. The micro LC/MS results discussed in this paper offer an opportunity for significantly increased sensitivity by allowing total micro LC effluent introduction into the MS. It remains to be seen whether the development of micro LC column and equipment technology will allow practical micro LC/MS. It may someday provide improved separation of drugs, metabolites, and their conjugates from high levels of endogenous materials in reasonable time periods. Currently, the impressive efficiencies demonstrated for micro LC columns involve mixtures containing low molecular weight solutes that are perhaps more amenable to GC analysis. The analyst routinely involved with problem solving must deal with complex mixtures composed of components with large concentration differences. The future of micro LC, and hence micro LC/MS, will depend upon how well the technique helps solve problems. We believe the future is bright for micro LC/MS. The techniques may require some fine tuning of operating procedures, just as with capillary GC/MS, but certainly the potential for increased efficiency and sensitivity is worth the effort. Currently we are testing a new micro LC/MS DLI probe wherein the exit of the micro column is within 1 cm of the MS ion source [82]. The micro LC column is contained within the DLI probe and should offer the lowest dead volume and the least extracolumn effects yet achieved by LC/MS. Initial testing of this new probe is under way, and experimental results will be reported subsequently. The analytical potential of micro LC/MS is receiving considerable interest. Practical micro LC performance can provide increased capabilities to all types of LC/MS reported to date, and perhaps offer new insight into alternative methods of LC/MS not yet reported. We look forward to learning of these breakthroughs as they become available.

Animals↗
PubMed2002

Forensic analysis of ignitable liquids in fire debris by comprehensive two-dimensional gas chromatography.

The application of comprehensive two-dimensional gas chromatography (GC x GC) for the forensic analysis of ignitable liquids in fire debris is reported. GC x GC is a high resolution, multidimensional gas chromatographic method in which each component of a complex mixture is subjected to two independent chromatographic separations. The high resolving power of GC x GC can separate hundreds of chemical components from a complex fire debris extract. The GC x GC chromatogram is a multicolor plot of two-dimensional retention time and detector signal intensity that is well suited for rapid identification and fingerprinting of ignitable liquids. GC x GC chromatograms were used to identify and classify ignitable liquids, detect minor differences between similar ignitable liquids, track the chemical changes associated with weathering, characterize the chemical composition of fire debris pyrolysates, and detect weathered ignitable liquids against a background of fire debris pyrolysates.

Journal Article↗
PubMed1991

Early haemostatic modifications following cryopreserved graft infusion.

The nature of the graft used for the rescue of patients undergoing autologous bone marrow transplantation is that of a complex mixture of pharmacological agents and cellular debris known to have a number of effects on the haemostatic system. The present study was undertaken to evaluate the occurrence and the degree of haemostatic alterations during and immediately following graft infusion in 24 patients suffering from haematological malignancies. On day 0, before graft infusion, the majority of patients appeared with laboratory signs of enhanced thrombin generation, platelet activation, and endothelial damage, most likely due to the conditioning regimen. However, the graft infusion per se was accompanied in the short term by a further increment of some parameters indicating a thrombotic risk (as thrombin-antithrombin complex, beta-thrombo globulin, platelet factor four, and von Willebrand factor antigen, together with a concomitant prolongation of partial thromboplastin time and a reduction of prothrombin time. In contrast there was no further modification of antithrombin III or protein C levels nor an increase in fibrinopeptide A levels. We hypothesize that complex interactions between agents contained in the graft mixture and host haemostatic system are involved in the pathogenesis of the haemostatic alterations which followed cryopreserved graft infusion; however, in our series, these were not accompanied by clinical signs of thrombotic or haemorrhagic events.

Antithrombin III↗
PubMed1999

Are lipid phase transitions responsible for chilling damage in human platelets?

In previous studies we have proposed that the well-known chilling-induced activation of human blood platelets can be ascribed at least in part to a thermotropic phase transition in membrane lipids. The evidence that this is the case is reviewed and amplified in this review, followed by an examination of the available physical data concerning phase transitions in lipid mixtures that mimic the mixture found in platelet membranes. Assuming complete mixing at all temperatures and equal contributions of the members of the mixture to the phase transition, the lipid mixture found in platelets should give values for Tm ranging from about 1 degrees C to about 16 degrees C, depending on the isomers present in the mixture. (The former value is not in agreement with the observed Tm, but the latter is in excellent agreement.) However, examination of the phase diagram for a binary pair of lipids found in platelet membranes shows that ideal mixing almost certainly does not occur; instead of a linear phase diagram, a convex one was obtained. This shape for the phase diagram, which would displace Tm to an unexpectedly elevated temperature, is in agreement with previously published phase diagrams for mixtures of this type. The prediction, based on thermodynamic properties of lipids found in the platelets, is that Tm will be displaced upward in more complex mixtures of the composition found in platelets, a prediction that requires experimental testing.

Blood Platelets↗
PubMed1985

Peptide-containing fractions in depression.

A mixture of peptides and glycoproteins has been found in benzoic acid-precipitable material from urines of psychomotorically agitated and retarded endogenous depressive patients. This complex mixture of compounds is fractionated on a Sephadex G-25 gel, from which the different peaks are further separated on Biogel P2. The G-25 elution profiles ultraviolet absorbance, 280 nm) from depressive patients deviated from the normal pattern. The increase in hydrolyzable ninhydrin-colorable material of the P2 fractionation step encountered in psychotic depression was several-fold that of the normal population. Neurochemically active peptide-containing fractions were found. As explanation of these findings, it is probable that a genetically determined peptidase insufficiency is present, causing a peptide overflow when the secretion outstrips the breakdown. This model could easily combine more psychodynamic models with the genetic-biological models. The variability of the peptide patterns could possibly reflect the considerable clinical variability of the syndrome. Furthermore, the presence of a group of active compounds with different neuropharmacological activities might reflect the composite nature of the depressive syndrome.

Adult↗
PubMed2005

Optimisation of high performance liquid chromatography separation of neuroprotective peptides. Fractional experimental designs combined with artificial neural networks.

The study of experimental design conjunction with artificial neural networks for optimisation of isocratic ion-pair reverse phase HPLC separation of neuroprotective peptides is reported. Different types of experimental designs (full-factorial, fractional) were studied as suitable input and output data sources for ANN training and examined on mixtures of humanin derivatives. The independent input variables were: composition of mobile phase, including its pH, and column temperature. In case of a simple mixture of two peptides, the retention time of the most retentive component and resolution were used as the dependent variables (outputs). In case of a complex mixture with unknown number of components, number of peaks, sum of resolutions and retention time of ultimate peak were considered as output variables. Fractional factorial experimental design has been proved to produce sufficient input data for ANN approximation and thus further allowed decreasing the number of experiments necessary for optimisation. After the optimal separation conditions were found, fractions with peptides were collected and their analysis using off-line matrix assisted laser desorption/ionisation time of flight mass spectrometry (MALDI-TOF-MS) was performed.

Amino Acid Substitution↗
PubMed2006

Mass spectrometry in toxinology: a 21st-century technology for the study of biopolymers from venoms.

Mass spectrometry, developed in the early days of the 20th century for the structural analysis of ions from organic compounds, has evolved from an analytical technique almost entirely applied to structural studies of small molecules, to a diversified technology that is now increasingly focused on the study of biological macromolecules. Novel instrument developments and appropriate ionization techniques have permitted the application of mass spectrometry to the analysis of biopolymers such as proteins, sugars and nucleic acids and have opened the door to a multiplicity of applications, and not the least being proteomics. Increasingly used as a basic analytical tool in biology laboratories, mass spectrometry has now found another niche of application in the field of venom and toxin studies. The technique is well suited to the analysis of peptide and protein components of venoms, be it for global mass mapping of complex mixtures or structural studies on individual toxins. Further enhanced by hyphenation with separation technologies, mass spectrometry is well adapted to de-convolve the extreme complexity of natural venoms and biological extracts in which toxinologists specialize. This special issue highlights a number of applications of mass spectrometry in this field and presents some of the most recent work illustrating the benefits of various state-of-the-art mass spectrometry technologies for the study of animal venoms and toxins.

Animals↗
PubMed1998

Toxicological evaluation and risk assessment of chemical mixtures.

A major objective of combination toxicology is to establish whether a mixture of chemicals will result in an effect similar to that expected on the basis of additivity. This requires understanding of the basic concepts of the combined toxicological action of the compounds of the mixture: simple similar action (dose addition), simple dissimilar action (effect or response addition), and interaction (synergism, potentiation, antagonism). The number of possible combinations of chemicals is innumerable, and in vivo testing of these mixtures is unattainable from an ethical, economical, or pragmatic perspective. Prediction of the effect of a mixture based on the knowledge of each of the constituents requires detailed information on the composition of the mixture, exposure level, mechanism of action, and receptor of the individual compounds. Often, such information is not or is only partially available and additional studies are needed. Research strategies and methods to assess joint action or interaction of chemicals in mixtures such as whole mixture testing, physiologically based toxicokinetic modeling and isobologram and dose response surface analyses are discussed. Guidance is given for risk assessment of both simple and complex mixtures. We hypothesize that, as a rule, exposure to mixtures of chemicals at (low) non-toxic doses of the individual constituents is of no health concern. To verify the hypothesis is a challenge; to timely detect exceptions to the rule is the real challenge of major practical importance.

Animals↗