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PubMed2002

Antioxidant activity of coffee model systems.

Coffee model systems prepared from combinations of chlorogenic acid (CGA), N(alpha)-acetyl-1-arginine (A), sucrose (S), and cellulose (C) were roasted at 240 degrees C for 4 min prior to analysis by UV-visible spectrophotometry, capillary zone electrophoresis (CZE), and the ABTS radical cation decolorization assay. The A/CGA/S/C and A/S/C systems were also fractionated by gel filtration chromatography. Antioxidant activity of the systems showed a positive, nonlinear relationship with the amount of CGA remaining after roasting. Sucrose degradation was a major source of color in the heated systems. There was no relationship between antioxidant activity and color generation.

Antioxidants↗
PubMedDate not supplied

Formation of heterocyclic amines using model systems.

Initially, modeling was used to identify the mutagenic heterocyclic amines and their precursors. Major precursors have been shown to be single amino acids or amino acids together with creatine or creatinine. There is also evidence that Maillard reactions are involved since heating sugar and amino acids together with creatine or creatinine has been shown to produce several of the mutagenic heterocyclic amines, especially the aminoimidazoazaarenes (AIA compounds), e.g., IQ, MeIQ, MeIQx, DiMeIQx and PhIP. Due to a low yield in the model systems, the mechanisms behind the formation of the mutagenic heterocyclic amines are still unclear and need further substantiation. The fact that some AIA compounds are also produced in the absence of sugar casts some doubts on an obligatory participation of the Maillard reaction; alternative routes might exist. Further work using isotopically labeled precursors needs to be done and so far such work has only been performed for PhiP. The formation of mutagenic heterocyclic amines is dependent on time, temperature, pH, concentration of the precursors, type of amino acid, and the presence of certain divalent ions. Water may have an impact both as a temperature regulator and as a solvent medium for the reactants.

Amines↗
PubMedDate not supplied

[The interaction of soil micromycetes with "hot" particles in a model system].

A model system which permits observing for a long time and fixing interaction of fungi with a radiation source has been created on the basis of an isolated "hot" particle, deficient mineral medium (saccharose content 60 mg/l) and suspension of fungal conidia. Five species (six strains) of micromycetes isolated from radionuclide-contaminated soils and fifteen "hot" particles have been tested. It has been found out for the first time that Cladosporium cladosporioides and Penicillium roseo-purpureum are able actively overgrow "hot" particles whose radioactivity did not exceed 3.1-1.0(-7) Ci by gamma-spectrum and to destroy them 50-150 days later. Certain changes in morphology of fungi-destructors of "hot" particles are revealed. A problem on ecological significance of the found phenomenon is discussed.

Accidents↗
PubMed2004

Effects of species diversity on establishment and coexistence: a phylloplane fungal community model system.

A model system was devised, evaluating the influence that species diversity (species richness) has on fungal establishment and coexistence. Seven members of the fungal phylloplane community of Vaccinium macrocarpon (American cranberry) were selected to assess how species diversity affected development and coexistence of another community member, Pestalotia vaccinii. Pestalotia was engaged in competitive interactions on 1% Malt Extract Agar (MEA) petri dishes with each of the seven individual saprotrophs (two-way interaction), in random combinations with three of the seven saprotrophs (four-way interaction), and in random combinations with five of the seven saprotrophs (six-way interaction). The saprotrophic fungi used in this study were Aspergillus sp., Alternaria alternata, Cladosporium cladosporoides, Curvularia lunata, Epicoccum purpuracens, Penicillium sp., and Pithomyces chartarum. We hypothesized that species diversity would have a significant impact on the establishment and coexistence of Pestalotia vaccinii in culture. In an effort to minimize density-dependent effects, the number of viable spores employed in the three types of interactions was kept constant. Target spore concentrations of 50 viable spores of P. vaccinii and 50 saprotroph spores were used, regardless of the number of species involved in the interaction. This proved to be a very important factor in the experiment. As our results show, species diversity had little or no effect on the establishment and coexistence of Pestalotia vaccinii; however, spore density played an extremely important role in the establishment and development of fungal propagules in our model.

Ascomycota↗
PubMed2000

Origin of carbohydrate degradation products in L-Alanine/D-[(13)C]glucose model systems.

Maillard model systems consisting of labeled D-[(13)C]glucoses and L-[(13)C]alanines have been utilized to identify the origin of carbon atoms in glycolaldehyde, pyruvaldehyde, 1-hydroxy-2-propanone (acetol), 2,3-butanedione, 3-hydroxy-2-butanone, 2,3-pentanedione, and compounds containing C(5) and C(6) intact glucose carbon chains. The origin of carbon atoms in glycolaldehyde and pyruvaldehyde was inferred from the analysis of label incorporation pattern of methyl and dimethylpyrazines. The origin of carbon atoms in the remaining compounds was determined by direct analysis. The data indicated that glycolaldehyde incorporated intact C5-C6 and C1-C2 carbon chains of glucose. Acetol and pyruvaldehyde incorporated intact C1-C2-C3 and C4-C5-C6 carbon chains of glucose. On the other hand, 2, 3-butanedione and 3-hydroxy-2-butanone incorporated intact C3-C4-C5-C6 carbon chain of glucose. In addition, analysis of compounds containing intact glucose C(5) carbon chains have indicated that glucose in the presence of L-alanine can lose either C-1 atom to produce a pentitol moiety responsible for the formation of furanmethanol or it can lose the C-6 atom to produce a pentose moiety responsible for the formation of furfural. Plausible mechanisms, consistent with the observed label incorporation, were proposed for the formation of sugar degradation products.

Alanine↗
PubMed1985

Quantitative aspects of cytochemical methods for acetylcholinesterase studied with a cytochemical model system.

A model system of polyacrylamide films containing the Triton extract of rat brain homogenate was applied to investigate quantitatively some aspects of three methods for the cytochemical demonstration of acetylcholinesterase activity (Lewis 1961; Karnovsky and Roots 1964; Tsuji 1974). Biochemical determinations showed that about 90% of the acetylcholinesterase activity originally present in the Triton extract were still detectable in the films. The relationship of the formation of cuprous thiocholine iodide in the case of the methods of Lewis (1961) or Tsuji (1974) and of cupric ferrocyanide at the reaction of Karnovsky and Roots (1964) to either enzyme concentration or incubation time were tested in detail. The results showed that for the method of Tsuji and, with some restrictions, also for the method of Karnovsky and Roots a linearity exists in these two respects. In the case of the Lewis technique, an approximate linearity between the amount of reaction product and incubation time could only be found from 90 min onward, but no linearity was detected in relation to the enzyme concentration. At low enzyme concentrations, too little white precipitate was formed in comparison to higher ones. Therefore it is suggested that this technique, as compared to the methods of Tsuji and Karnovsky and Roots, probably is less suitable as a quantitative cytochemical method.

Acetylcholinesterase↗
PubMed1975

Combined staining of protein-bound sulphydryl groups and DNA in polyacrylamide model systems.

A model system of polyacrylamide films containing protein and DNA has been used to examine the feasibility of combining the dihydroxydinaphthyldisulphide (DDD)-diazonium salt procedure for localizing protein-bound sulphydryl groups with the Feulgen technique for DNA to make possible the direct measurement of both these parameters simultaneously. Optimun conditions for the sulphydryl group reaction require reduction of the protein-containing films in 10% aqueous ammonium sulphide for 3 hr at 50 degree C followed by treatment with a DDD solution at 50 degree C for 4 hr. The final coloured product was developed in a solution of the diazonium salt, Fast Red TR, for 15 min. The azo compound thus produced was completely resistant to hydrochloric acid hydrolysis in the manner of the Feulgen reaction. Calculation of protein-bound sulphydryl groups and DNA from measurements made on doubly-stained films showed excellent agreement between the measured and the expected values.

Acrylamides↗
PubMed1999

Individual causal models and population system models in epidemiology.

A group of individuals behaves as a population system when patterns of connections among individuals influence population health outcomes. Epidemiology usually treats populations as collections of independent individuals rather than as systems of interacting individuals. An appropriate theoretical structure, which includes the determinants of connections among individuals, is needed to develop a "population system epidemiology." Infection transmission models and sufficient-component cause models provide contrasting templates for the needed theoretical structure. Sufficient-component cause models focus on joint effects of multiple exposures in individuals. They handle time and interactions between individuals in the definition of variables and assume that populations are the sum of their individuals. Transmission models, in contrast, model interactions among individuals over time. Their nonlinear structure means that population risks are not simply the sum of individual risks. The theoretical base for "population system epidemiology" should integrate both approaches. It should model joint effects of multiple exposures in individuals as time related processes while incorporating the determinants and effects of interactions among individuals. Recent advances in G-estimation and discrete individual transmission model formulation provide opportunities for such integration.

Causality↗
PubMed1992

Accuracy and precision of the corneal analysis system and the topographic modeling system.

Two computer-assisted topographic analysis systems were evaluated with calibrated spherical surfaces and normal human corneas. The Topographic Modeling System-1 (TMS-1) was found to be statistically more accurate in determining the power of calibrated spheres near the apex and at 1 mm from the apex than the Corneal Analysis System (CAS). The CAS, however, was statistically more accurate at 3 mm from the apex with each calibrated sphere. The small differences in accuracy between the two instruments, however, are unlikely to be of clinical significance. The topographic patterns on color-coded maps from 22 normal corneas of 11 subjects were similar with the two instruments. Simulated keratometry values with the CAS more accurately identified the keratometer-determined major cylinder axis compared with the TMS-1. Conversely, the TMS-1 was more accurate than the CAS at determining the level of corneal astigmatism.

Astigmatism↗
PubMed2001

Model Systems: transgenic mouse models for measles pathogenesis.

Studies of the diseases caused by measles virus (MV) in humans have been restricted owing to the lack of suitable animal models. The discovery of cellular receptors for MV entry has facilitated the development of transgenic mice that are susceptible to MV infection, and that mimic certain aspects of the central nervous system diseases and immunosuppression that can occur in infected humans. Moreover, such mouse models have allowed a clearer understanding of the contributions of the innate and adaptive immune response following infection, and will no doubt be important tools in the future for the development of new antiviral and vaccine reagents.

Acute Disease↗
PubMed2001

Neuropeptides are ubiquitous chemical mediators: Using the stomatogastric nervous system as a model system.

The stomatogastric nervous system (STNS) controls the movements of the foregut and the oesophagus of decapod crustaceans and is a good example for demonstrating that peptides are ubiquitously distributed chemical mediators in the nervous system. The stomatogastric ganglion (STG), one of the four ganglia of the STNS, contains the most intensively investigated neuronal circuits. The other ganglia, including the two commissural ganglia (CoGs) and the oesophageal ganglion (OG), are thought to be modulatory control centres. Peptides reach the STNS either as neurohormones or are released as transmitters. Peptide neurohormones can be released either from neurohaemal organs or from local neurohaemal release zones located on the surface of nerves and connectives. There were thought to be no peptidergic neurones with cell bodies in the STG itself. However, some have recently been described in adults of four species, in addition to a transient expression of peptides during development in two species. None of these peptidergic neurones has been investigated physiologically, in contrast to peptidergic neurones that project to the STG and have cell bodies in either the CoGs or the OG. It has been shown that neurones containing the same peptide elicit different motor patterns, that the peptide transmitter and the classical transmitter are not necessarily co-released and that the effect of a peptidergic neurone depends on its firing frequency and on which other modulatory neurones are co-active. The activity of modulatory projection neurones can be elicited by sensory neurones, and their activity can depend on the firing frequency of the sensory neurone. In addition to being found within the neuropile of ganglia, peptides are present in neuropile patches located within the nerves of the STNS, suggesting that these nerves can integrate as well as transfer information. Furthermore, sensory neurones and muscles exhibit peptide-like immunoreactivity and are modulated by peptides. Bath-applied peptides elicit peptide-specific motor patterns within the STG by targeting subsets of neurones. This divergence is contrasted by a convergence at the level of currents: five different peptides modulate a single current. Peptides not only induce motor patterns but can also switch the alliance of neurones from one network to another or are able to fuse different networks. In general, peptides are the most abundant group of modulators within the STNS; they are ubiquitously present, indicating that they play multiple roles in the plasticity of neural networks.

Animals↗
PubMed2001

[Synthesis and characterization of model system in biological related function--model compounds for investigation of metal-metal interaction and nucleobase-aromatics interaction].

Several kinds of compounds available as model systems to investigation on metal-metal interaction in metalloproteins and on interaction of aromatics with nucleobases in arene intercalation to DNA were synthesized and characterized by spectrometry. Double and triple layered porphyrinophanes linked with 1,1'- or 1,3-disubstituted ferrocene moieties and their iron and cobalt complexes were prepared. Stabilities of their oxygenation complexes depended on bridging mode, lengths of alkyl linkers, distance between metals, and feature of hydrophobic cavity. Ferrocenophane derivatives in which nucleobase and aromatic hydrocarbon (naphthalene or anthracene) moieties substituted to their cyclopentadienyl rings in a stacking mode between the two chromophores were synthesized, as a model system of intercalation of aromatic condensed-ring hydrocarbons to DNA. Characterization of the ferrocenophanes by spectrometry and molecular modeling suggested that these chromophores interacted due to NH-pi hydrogen bonding and pi-pi charge transfer. A number of porphyrin derivatives covalently connected with a nucleobase or a nucleobase pair in a face-to-face mode between the porphyrin and nucleobase moiety were synthesized. The spectroscopic behavior of the derivatives indicate a greater affinity of the guanine-cytosine pair for porphyrin in comparison with the adenine-thymine pair. These results are compatible with the already reported spectroscopic and kinetic properties of mixing system of DNA and porphyrin derivatives. Moreover, the fluorescence spectra of the nucleobase-porphyrin derivatives gave a piece of evidence to cause DNA cleavage by photosensitizer via "type I" mechanism, in which direct action of singlet or triplet state of photosensitizer excited by laser irradiation brings about damage of cell or DNA.

DNA Damage↗
PubMed1984

The preferred solution conformation of warfarin at the active site of cytochrome P-450 based on the CD spectra in octanol/water model system.

An octanol/water model system and circular dichroism (CD) spectroscopy have been used to study the solution conformation of warfarin in aqueous and lipid environments. Upon partitioning of (S)-warfarin from buffer pH 7.4 into octanol, the position of the absorption band due to the alpha, beta-unsaturated carbonyl chromophore shifts from 210 nm in the aqueous phase to 220 nm in the octanol phase. The shift is coupled to an increase in the molecular ellipticity of the band, suggesting the formation of a dissymmetric chromophore. Comparison of CD spectra of conformationally fixed analogues of warfarin to that of warfarin in solution suggests that the compound shifts from the open side chain keto form in the aqueous phase at pH 7.4 to the cyclic hemiketal form after partitioning into the lipid octanol phase. On the basis of these results, the hemiketal form is proposed as the preferred solution conformation of warfarin in the lipid environment of the active site of cytochrome P-450 and the relationship between solution conformation and stereoselectivity of warfarin metabolism by beta-naphthoflavone inducible cytochrome P-450 is discussed.

4-Hydroxycoumarins↗
PubMed1988

Effects of relative humidity on lipid autoxidation in a model system.

A new model system was developed for the study of autoxidation of thin films of neat lipid and the effect of relative humidity on the oxidation reaction. In the model system, the surface-to-volume ratio of lipid was large and measureable, and the relative humidity (RH) and oxygen partial pressure were controlled. Methyl linoleate, oxidized at six different RH as a thin film in an atmosphere of pure oxygen, exhibited a maximum rate of oxidation at 32% RH and minimum rates at 0% and 100% RH. The rates of oxygen uptake, determined manometrically, were linear and reproducible at all six RH. The maximum rate at 32% RH was attributed to solvation and stabilization of the propagation transition state by water. Increasing the RH beyond 32% resulted in solvation of the peroxy radical, sterically hindering the radical from entering the propagation transition state.

Humidity↗
PubMed1983

Chronic graft-versus-host disease (GVHD) as a model for scleroderma. I. Description of model systems.

A model murine system of chronic graft-versus-host disease (GVHD) was explored to determine its suitability for studying scleroderma-like syndromes. The basic protocol was to inject lymphoid cell suspensions into irradiated semiallogeneic or allogeneic recipients which had been irradiated. Serial body weights, skin biopsies, and anti-nuclear antibodies were followed. Changes seen in the skin included increased collagen deposition, a mononuclear infiltrate deep in the dermis, loss of dermal fat, and "dropout" of skin appendages such as hair follicles. Body weight loss was a sensitive index of GVHD. Anti-nuclear antibodies occurred at times, but did not correlate with the tissue changes in the skin of mice undergoing GVHD. This chronic GVHD syndrome was produced across major and minor histocompatibility barriers. The most consistent findings were seen in BALB/c recipients of B10.D2 cells. These strains are nonreactive in unprimed mixed-leukocyte cultures. This combination represents primarily a GVH reaction against minor antigens where the HVG reaction is suppressed by irradiation. Some data suggest that the cutaneous changes may be reversible with time.

Animals↗
PubMed1995

Flow-cytometric identification and follow-up of mice exposed to x-irradiation: evaluation of a model system.

An experimental model system is presented that allows the identification and follow-up of mice exposed to ionizing radiation using flow-cytometric measurements of peripheral blood cells. In an experiment, properties of peripheral blood cells were analysed with flow cytometry for a rapid identification of individuals exposed to radiation. Individuals were then followed longitudinally in an attempt to identify those developing neoplasias. Male CBA mice, 25 days old, were subjected to fractionated x-irradiation (4 x 1.31 Gy) to induce haematopoietic malignancies. By repeated blood sampling followed by flow cytometry, frequencies of micronucleated erythrocytes and of proliferating nucleated cells were determined. Neoplasias were diagnosed by histopathology. Five days after the end of radiation exposure, increased frequencies of proliferating cells, polychromatic erythrocytes and micronucleated normochromatic erythrocytes clearly distinguished the exposed group from the control group. Increased cell proliferation in peripheral blood cells could be used to identify animals with manifest tumours, although these animals were at a late stage of tumour development. Animals with thymic lymphoma (not generalized) could not be identified with the flow-cytometric parameters used. We consider that this model system has a potential use when a small number of risk individuals need to be identified and monitored within a large population.

Animals↗
PubMed1994

Colonization of urinary catheters by Escherichia coli and Providencia stuartii in a laboratory model system.

A laboratory model system was developed to investigate the progressive colonization of urinary catheters by Escherichia coli Providencia stuartii, prominent organisms in the polymicrobial bacteriuria of the long-term catheterized urinary tract. We hypothesized that colonization of the catheter and artificial urine by E. coli is influenced by the presence of P. stuartii. E. coli or P. stuartii in pure culture both rapidly colonized the artificial urine and catheters, and both persisted throughout all experiments. In systems containing both organisms, P. stuartii occurred in significantly higher numbers in the artificial urine and on the catheters than E. coli (p < 0.05). To obtain similar numbers of E. coli and P. stuartii in the artificial urine, citrate was eliminated; however, P. stuartii still dominated on the catheter surfaces. The presence of P. stuartii appeared to facilitate growth of E. coli in the artificial urine, yet reduce numbers of E. coli on the catheter. In a separate experiment using different strains of E. coli and P. stuartii, the latter was dominant in the artificial urine and on the catheter surfaces. However, this strain of P. stuartii (which was urease positive) did not facilitate growth of E. coli. The interaction between these strains may have been considerably affected by urea hydrolysis, which resulted in an increase in pH (6.5 to > 8.5) and considerable precipitate formation in the model system. The paradox of P. stuartii enhancing colonization by E. coli in the artificial urine, yet inhibiting its colonization on the catheter surface, illustrates the complexity of polymicrobial interactions in colonization of the catheterized urinary tract.

Bacteriuria↗