RESUMEN

Values are presented for thermal conductivity, specific heat, spectral and total hemispherical emissivity of ThO2 (a potential nuclear fuel material) in a temperature range representative of a nuclear accident - 2000 K to 3050 K. For the first time direct measurements of thermal conductivity have been carried out on ThO2 at such high temperatures, clearly showing the property does not decrease above 2000 K. This could be understood in terms of an electronic contribution (arising from defect induced donor/acceptor states) compensating the degradation of lattice thermal conductivity. The increase in total hemispherical emissivity and visible/near-infrared spectral emissivity is consistent with the formation of donor/acceptor states in the band gap of ThO2. The electronic population of these defect states increases with temperature and hence more incoming photons (in the visible and near-infrared wavelength range) can be absorbed. A solid state physics model is used to interpret the experimental results. Specific heat and thermal expansion coefficient increase at high temperatures due to the formation of defects, in particular oxygen Frenkel pairs. Prior to melting a gradual increase to a maximum value is predicted in both properties. These maxima mark the onset of saturation of oxygen interstitial sites.

RESUMEN

The OECD QSAR Toolbox is a software application intended to be used by governments, the chemical industry and other stakeholders in filling gaps in (eco)toxicity data needed for assessing the hazards of chemicals. The development and release of the Toolbox is a cornerstone in the computerization of hazard assessment, providing an 'all inclusive' tool for the application of category approaches, such as read-across and trend analysis, in a single software application, free of charge. The Toolbox incorporates theoretical knowledge, experimental data and computational tools from various sources into a logical workflow. The main steps of this workflow are substance identification, identification of relevant structural characteristics and potential toxic mechanisms of interaction (i.e. profiling), identification of other chemicals that have the same structural characteristics and/or mechanism (i.e. building a category), data collection for the chemicals in the category and use of the existing experimental data to fill the data gap(s). The description of the Toolbox workflow and its main functionalities is the scope of the present article.

RESUMEN

Animals and humans are exposed to a wide array of xenobiotics and have developed complex enzymatic mechanisms to detoxify these chemicals. Detoxification pathways involve a number of biotransformations, such as oxidation, reduction, hydrolysis and conjugation reactions. The intermediate substances created during the detoxification process can be extremely toxic compared with the original toxins, hence metabolism should be accounted for when hazard effects of chemicals are assessed. Alternatively, metabolic transformations could detoxify chemicals that are toxic as parents. The aim of the present paper is to describe specificity of eukaryotic metabolism and its simulation and incorporation in models for predicting skin sensitization, mutagenicity, chromosomal aberration, micronuclei formation and estrogen receptor binding affinity implemented in the TIMES software platform. The current progress in model refinement, data used to parameterize models, logic of simulating metabolism, applicability domain and interpretation of predictions are discussed. Examples illustrating the model predictions are also provided.

Asunto(s)

Simulación por Computador , Mamíferos/metabolismo , Modelos Biológicos , Medición de Riesgo , Xenobióticos/metabolismo , Xenobióticos/toxicidad , Animales , Biotransformación , Humanos , Redes y Vías Metabólicas , Modelos Estadísticos , Relación Estructura-Actividad Cuantitativa

RESUMEN

Computer simulation of xenobiotic metabolism and degradation is usually performed proceeding from a set of expert-developed rules modelling the actual enzyme-driven chemical reactions. With the accumulation of extensive metabolic pathway data, the analysis required to derive such chemical reaction patterns has become more objective, but also more convoluted and demanding. Herein we report on our computer-based approach for the analysis of metabolic maps, leading to the construction of reaction rules statistically suitable for simulation purposes. It is based on the set of so-called bare transformations which encompass all unique reaction patterns as obtained by a heuristically enhanced maximum common subgraph algorithm. The bare transformations guarantee that no existing metabolite is missed in simulation at the expense of an enormous amount of false positive predictions. They are rendered more selective by correlating the generated true and false positives to the locations of typical chemical functional groups in the potential reactants. The approach and its results are illustrated for a metabolic map collection of 15 cycloalkanes.

Asunto(s)

Cicloparafinas/metabolismo , Contaminantes Ambientales/metabolismo , Contaminantes Ambientales/toxicidad , Modelos Biológicos , Animales , Bacterias/metabolismo , Biotransformación , Simulación por Computador , Cicloparafinas/toxicidad , Humanos , Redes y Vías Metabólicas , Modelos Estadísticos , Relación Estructura-Actividad Cuantitativa

RESUMEN

Family focal segmental glomerulosclerosis (FSGS) is characterized by sclerosis and hyalinosis of particular loops of glomeruli and is one of the causes of the nephrotic syndrome. Certain mutations in the structure of TRPC6 channels are the genetic impetus for FSGS development resulting in podocytes functional abnormalities and various nephropathies. We have recently demonstrated that non-steroid anti-inflammatory drugs (NSAID) ibuprofen and diclofenac decrease the activity of endogenous TRPC like cal cium channels in the podocytes of the freshly isolated rat glomeruli. It has also been shown that TRPC6 chan nels are expressed in the podocytes. In the current study we have functionally reconstituted TRPC6 channels in mammalian cells to investigate the effects of diclofenac on the activity of wild type TRPC6 channel and TRPC6P112Q channel containing a mutation in the N-terminus that was described in FSGS patients. Intracellular calcium level measurements in transfected cells revealed a more intensive carbachol induced increase of calcium concentration in HEK 293 cells expressing TRPC6P112Q versus the cells expressing wild-type TRPC6. We also performed patch-clamp experiments to study TRPC6 channels reconstituted in Chinese hamster ovary (CHO) cell line and found that application of diclofenac (500 µM) acutely reduced single channel activity. Preincubation with diclofenac (100 µM) also decreased the whole cell current in CHO cells overexpressing TRPC6P112Q. Therefore, our previously published data on the effects of NSAID on TRPC-like channels in the isolated rat glomeruli, along with this current investigation on the cultured overexpressed mammalian cells, allows hypothesizing that TRPC6 channels may be a target for NSAID that can be impor tant in the treatment of FSGS.

RESUMEN

Information regarding the metabolism of xenobiotic chemicals plays a central role in regulatory risk assessments. In regulatory programmes where metabolism studies are required, the studies of metabolic pathways are often incomplete and the identification of activated metabolites and important degradation products are limited by analytical methods. Because so many more new chemicals are being produced than can be assessed for potential hazards, setting assessment priorities among the thousands of untested chemicals requires methods for predictive hazard identification which can be derived directly from chemical structure and their likely metabolites. In a series of papers we are sharing our experience in the computerized management of metabolic data and the development of simulators of metabolism for predicting the environmental fate and (eco)toxicity of chemicals. The first paper of the series presents a knowledge-based formalism for the computer simulation of non-intermediary metabolism for untested chemicals, with an emphasis on qualitative and quantitative aspects of modelling metabolism.

Asunto(s)

Biotransformación , Simulación por Computador , Xenobióticos/metabolismo , Xenobióticos/toxicidad , Redes y Vías Metabólicas , Modelos Teóricos , Medición de Riesgo/métodos

RESUMEN

The unprecedented pollution of the environment by xenobiotic compounds has provoked the need to understand the biodegradation potential of chemicals. Mechanistic understanding of microbial degradation is a premise for adequate modelling of the environmental fate of chemicals. The aim of the present paper is to describe abiotic and biotic models implemented in CATALOGIC software. A brief overview of the specificities of abiotic and microbial degradation is provided followed by detailed descriptions of models built in our laboratory during the last decade. These are principally new models based on unique mathematical formalism already described in the first paper of this series, which accounts more adequately than currently available approaches the multipathway metabolic logic in prokaryotes. Based on simulated pathways of degradation, the models are able to predict quantities of transformation products, biological oxygen demand (BOD), carbon dioxide (CO(2)) production, and primary and ultimate half-lives. Interpretation of the applicability domain of models is also discussed.

Asunto(s)

Biotransformación , Simulación por Computador , Contaminantes Ambientales/metabolismo , Contaminantes Ambientales/toxicidad , Xenobióticos/metabolismo , Xenobióticos/toxicidad , Análisis de la Demanda Biológica de Oxígeno , Dióxido de Carbono/metabolismo , Contaminantes Ambientales/química , Redes y Vías Metabólicas , Medición de Riesgo/métodos , Programas Informáticos , Xenobióticos/química

RESUMEN

We have recently shown that epithelial sodium channels (ENaC) are regulated by the actin-binding protein cortactin via the Arp2/3 protein complex. However, it has been also demonstrated that GTPase, dynamin, which is known to regulate clathrin-mediated endocytosis, can as well initiate signaling cascades regulated by cortactin. This study was designed to investigate the involvement of dynamin into cortactin-mediated regulation of ENaC. Initially, a recently described inhibitor of dynamin, dynasore, was used. However, use of this inhibitor seemed to be inappropriate due to discovered side effects. F. i., treatment of mpkCCD(c14) cells monolayers with dynasore (in concentrations of 10 and 100 microM) resulted in a decrease in ENaC-mediated transepithelial currents. Besides, the same concentrations of dynasore caused reduced currents in CHO cells transfected with ENaC subunits. Therefore, the data demonstrated that dynasore down regulates both native and overexpressed channel's activity and is not suitable for studies of a role of dynamin in the clathrin-mediated endocytosis of ENaC. This effect is most likely caused either by dynasore's toxic effect upon the cells or by enhanced endocytosis of ENaC-activating proteins. In the following experiments designed to study the role of dynamin different plasmids encoding mutant forms of dynamin and cortactin were used. Dominant negative dynamin K44A transfected into CHO cells together with ENaC subunits significantly increased amiloride-sensitive current density compared to cells transfected with ENaC subunits only (control); additional transfection of cortactin in this system resulted in current density restitution back to the control level. Moreover, ENaC overexpression with the SH3 domain of cortactin, which is responsible for dynamin binding, caused a decrease if ENaC current. Thus, we have shown in this study that cortactin can mediate ENaC activity not only via the Arp2/3 complex, but apart from that dynamin and related processes also might be involved into ENaC regulation by cortactin.

Asunto(s)

Cortactina/metabolismo , Dinaminas/metabolismo , Células Epiteliales/metabolismo , Canales Epiteliales de Sodio/metabolismo , Transporte Iónico/fisiología , Riñón/metabolismo , Bloqueadores de los Canales de Sodio/farmacología , Complejo 2-3 Proteico Relacionado con la Actina/metabolismo , Amilorida/farmacología , Animales , Células CHO , Cortactina/química , Cortactina/genética , Cricetinae , Cricetulus , Dinaminas/genética , Células Epiteliales/citología , Bloqueadores del Canal de Sodio Epitelial , Canales Epiteliales de Sodio/genética , Expresión Génica , Riñón/citología , Potenciales de la Membrana/fisiología , Ratones , Microscopía Electrónica , Técnicas de Placa-Clamp , Plásmidos , Transfección , Dominios Homologos src

RESUMEN

The distribution of the glyprolines Pro-Gly-Pro and Thr-Lys-Pro-Arg-Pro-Gly-Pro (Selanc) was analyzed and compared in tissues of rat organs after different ways of their administration using the peptides uniformly labeled with tritium. Comparative data on changes in concentrations of the peptides in the rat organs after their intraperitoneal, intranasal, intragastric, and intravenous administration are given. The intranasal administration of both peptides was shown to be optimal for the delivery of glyproline molecules in the CNS. A high affinity of the studied glyprolines for gastric tissues was found for all the ways of their administration. We suggest that a high efficiency of action of glyprolines on homeostasis of the gastric mucous tunic was partially provided by accumulation of these peptides (to high concentrations) in gastric tissues.

Asunto(s)

Oligopéptidos/farmacocinética , Prolina/análogos & derivados , Animales , Vías de Administración de Medicamentos , Mucosa Gástrica/metabolismo , Oligopéptidos/administración & dosificación , Prolina/administración & dosificación , Prolina/farmacocinética , Ratas , Distribución Tisular

RESUMEN

Antiulcer properties of a synthetic anxiolytic Selank and in vivo formed metabolites of this compound were studied on 3 experimental models of ulceration. The test peptides decreased the area of experimental gastric ulcers.

Asunto(s)

Antiulcerosos/farmacología , Mucosa Gástrica/efectos de los fármacos , Oligopéptidos/farmacología , Úlcera Gástrica/prevención & control , Ácido Acético , Animales , Antiulcerosos/metabolismo , Antiulcerosos/uso terapéutico , Etanol , Mucosa Gástrica/patología , Homeostasis , Masculino , Oligopéptidos/metabolismo , Oligopéptidos/uso terapéutico , Ratas , Ratas Wistar , Úlcera Gástrica/etiología , Úlcera Gástrica/patología , Estrés Psicológico/complicaciones

RESUMEN

Biodegradation plays a key role in the environmental risk assessment of organic chemicals. The need to assess biodegradability of a chemical for regulatory purposes supports the development of a model for predicting the extent of biodegradation at different time frames, in particular the extent of ultimate biodegradation within a '10 day window' criterion as well as estimating biodegradation half-lives. Conceptually this implies expressing the rate of catabolic transformations as a function of time. An attempt to correlate the kinetics of biodegradation with molecular structure of chemicals is presented. A simplified biodegradation kinetic model was formulated by combining the probabilistic approach of the original formulation of the CATABOL model with the assumption of first order kinetics of catabolic transformations. Nonlinear regression analysis was used to fit the model parameters to OECD 301F biodegradation kinetic data for a set of 208 chemicals. The new model allows the prediction of biodegradation multi-pathways, primary and ultimate half-lives and simulation of related kinetic biodegradation parameters such as biological oxygen demand (BOD), carbon dioxide production, and the nature and amount of metabolites as a function of time. The model may also be used for evaluating the OECD ready biodegradability potential of a chemical within the '10-day window' criterion.

Asunto(s)

Bacterias/metabolismo , Biodegradación Ambiental , Modelos Biológicos , Modelos Químicos , Dióxido de Carbono/metabolismo , Simulación por Computador , Semivida , Cinética , Oxígeno/metabolismo , Análisis de Regresión , Relación Estructura-Actividad

RESUMEN

A multi-dimensional formulation of the COmmon REactivity PAttern (COREPA) modeling approach has been used to investigate chemical binding to the human estrogen receptor (hER). A training set of 645 chemicals included 497 steroid and environmental chemicals (database of the Chemical Evaluation and Research Institute, Japan - CERI) and 148 chemicals to further explore hER-structure interactions (selected J. Katzenellenbogen references). Upgrades of modeling approaches were introduced for multivariate COREPA analysis, optimal conformational generation and description of the local hydrophobicity of chemicals. Analysis of reactivity patterns based on the distance between nucleophilic sites resulted in identification of distinct interaction types: a steroid-like A-B type described by frontier orbital energies and distance between nucleophilic sites with specific charge requirements; an A-C type where local hydrophobic effects are combined with electronic interactions to modulate binding; and mixed A-B-C (AD) type. Chemicals were grouped by type, then COREPA models were developed for within specific relative binding affinity ranges of >10%, 10 > RBA > or = 0.1%, and 0.1 > RBA > 0.0%. The derived models for each interaction type and affinity range combined specific prefiltering requirements (interatomic distances) and a COREPA classification node using no more than 2 discriminating parameters. The interaction types are becoming less distinct in the lowest activity range for each chemicals of each type; here, the modeling was performed within chemical classes (phenols, phthalates, etc.). The ultimate model was organized as a battery of local models associated to interaction type and mechanism.

Asunto(s)

Disruptores Endocrinos/química , Receptores de Estrógenos/química , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Ligandos , Modelos Químicos , Estructura Molecular , Análisis Multivariante , Relación Estructura-Actividad Cuantitativa , Medición de Riesgo

RESUMEN

The tissue metabolic simulator (TIMES) modeling approach is a hybrid expert system that couples a metabolic simulator together with structure toxicity rules, underpinned by structural alerts, to predict interaction of chemicals or their metabolites with target macromolecules. Some of the structural alerts representing the reactivity pattern-causing effect could interact directly with the target whereas others necessitated a combination with two- or three-dimensional quantitative structure-activity relationship models describing the firing of the alerts from the rest of the molecules. Recently, TIMES has been used to model bacterial mutagenicity [Mekenyan, O., Dimitrov, S., Serafimova, R., Thompson, E., Kotov, S., Dimitrova, N., and Walker, J. (2004) Identification of the structural requirements for mutagenicity by incorporating molecular flexibility and metabolic activation of chemicals I: TA100 model. Chem. Res. Toxicol. 17 (6), 753-766]. The original model was derived for a single tester strain, Salmonella typhimurium (TA100), using the Ames test by the National Toxicology Program (NTP). The model correctly identified 82% of the primary acting mutagens, 94% of the nonmutagens, and 77% of the metabolically activated chemicals in a training set. The identified high correlation between activities across different strains changed the initial strategic direction to look at the other strains in the next modeling developments. In this respect, the focus of the present work was to build a general mutagenicity model predicting mutagenicity with respect to any of the Ames tester strains. The use of all reactivity alerts in the model was justified by their interaction mechanisms with DNA, found in the literature. The alerts identified for the current model were analyzed by comparison with other established alerts derived from human experts. In the new model, the original NTP training set with 1341 structures was expanded by 1626 proprietary chemicals provided by BASF AG. Eventually, the training set consisted of 435 chemicals, which are mutagenic as parents, 397 chemicals that are mutagenic after S9 metabolic activation, and 2012 nonmutagenic chemicals. The general mutagenicity model was found to have 82% sensitivity, 89% specificity, and 88% concordance for training set chemicals. The model applicability domain was introduced accounting for similarity (structural, mechanistic, etc.) between predicted chemicals and training set chemicals for which the model performs correctly.

Asunto(s)

Modelos Biológicos , Mutágenos/química , Mutágenos/farmacología , Preparaciones Farmacéuticas/metabolismo , Simulación por Computador , ADN/genética , Bases de Datos Genéticas , Estructura Molecular , Mutágenos/metabolismo

RESUMEN

Biologically active peptides evenly labeled with tritium were used for studying the in vitro and in vivo biodegradation of the peptides. Tritium-labeled peptides with a specific radioactivity of 50-150 Ci/mmol were obtained by high temperature solid phase catalytic isotope exchange (HSCIE) with spillover tritium. The distribution of the isotope label among all amino acid residues of these peptides allows the simultaneous determination of practically all possible products of their enzymatic hydrolysis. The developed analytical method includes extraction of tritium-labeled peptides from organism tissues and chromatographic isolation of individual labeled peptides from the mixture of degradation products. The concentrations of a peptide under study and the products of its biodegradation were calculated from the results of liquid scintillation counting. This approach was used for studying the pathways of biodegradation of the heptapeptide TKPRPGP (Selank) and the tripeptide PGP in blood plasma. The pharmacokinetics of Selank, an anxiolytic peptide, was also studied in brain tissues using the intranasal in vivo administration of this peptide. The concentrations of labeled peptides were determined, and the pentapeptide TKPRP, tripeptide TKP, and dipeptides RP and GP were shown to be the major products of Selank biodegradation. The study of the biodegradation of the heptapeptide MEHFPGP (Semax) in the presence of nerve cells showed that the major products of its biodegradation are the pentapeptide HFPGP and tripeptide PGP. The enkephalinase activity of blood plasma was studied with the use of evenly tritium-labeled [Leu]enkephalin. A high inhibitory effect of Semax on blood plasma enkephalinases was shown to arise from its action on aminopeptidases. The method, based on the use of evenly tritium-labeled peptides, allows the determination of peptide concentrations and the activity of enzymes involved in their degradation on a tg scale of biological samples both in vitro and in vivo.

Asunto(s)

Oligopéptidos/farmacocinética , Tritio , Hormona Adrenocorticotrópica/análogos & derivados , Hormona Adrenocorticotrópica/farmacocinética , Aminopeptidasas/sangre , Aminopeptidasas/metabolismo , Animales , Encéfalo/metabolismo , Cromatografía Líquida de Alta Presión , Encefalina Leucina/metabolismo , Encefalinas/sangre , Encefalinas/metabolismo , Hidrólisis , Técnicas In Vitro , Marcaje Isotópico , Neprilisina/antagonistas & inhibidores , Neprilisina/metabolismo , Oligopéptidos/química , Fragmentos de Péptidos/farmacocinética , Ratas , Ratas Sprague-Dawley

RESUMEN

The role of metabolism in prioritising chemicals according to their potential adverse health effects is extremely important given the fact that innocuous parents can be transformed into toxic metabolites. Our recent efforts in simulating metabolic activation of chemicals are reviewed in this work. The application of metabolic simulators to predict biodegradation (microbial degradation pathways), bioaccumulation (fish liver metabolism), skin sensitisation (skin metabolism), mutagenicity (rat liver S-9 metabolism) are discussed. The ability of OASIS approach to predict metabolism (toxicokinetics) and toxicity (toxicodynamics) of chemicals resulting from their metabolic activation in a single modelling platform is an important advantage of the method. It allows prioritisation of chemicals due to predicted toxicity of their metabolites.

Asunto(s)

Biotransformación , Modelos Estadísticos , Relación Estructura-Actividad Cuantitativa , Animales , Biodegradación Ambiental , Humanos , Pruebas de Mutagenicidad , Ratas , Piel/efectos de los fármacos

RESUMEN

This paper presents the framework of a QSAR-based decision support system which provides a rapid screening of potential hazards, classification of chemicals with respect to risk management thresholds, and estimation of missing data for the early stages of risk assessment. At the simplest level, the framework is designed to rank hundreds of chemicals according to their profile of persistence, bioaccumulation potential and toxicity often called the persistent organic pollutant (POP) profile or the PBT (persistent bioaccumulative toxicant) profile. The only input data are the chemical structure. The POPs framework enables decision makers to introduce the risk management thresholds used in the classification of chemicals under various authorities. Finally, the POPs framework advances hazard identification by integrating a metabolic simulator that generates metabolic map for each parent chemical. Both the parent chemicals and plausible metabolites are systematically evaluated for metabolic activation and POPs profile.

Asunto(s)

Técnicas de Apoyo para la Decisión , Contaminantes Ambientales/clasificación , Relación Estructura-Actividad Cuantitativa , Medición de Riesgo , Programas Informáticos , Animales , Biodegradación Ambiental , Biotransformación , Simulación por Computador , Contaminantes Ambientales/metabolismo , Contaminantes Ambientales/toxicidad , Peces , Modelos Moleculares , Conformación Molecular

RESUMEN

The influence of a new heptapeptide Selank on microcirculation in anesthetized white rats was investigated. Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) is a new synthetic anxiolytic which exerts obvious antiulcerogenic action and promotes healing of experimental ulcers. Action of the peptide on gastric blood flow in the stomach by using the method ofhydrogenic clearance and Selank action on mesenteric lymphatic contractility by microscopical observation in situ, were studied. Selank fail to influence basal gastric blood flow but it can normalize blood flow reduced by indomethacin. The study of dose-depended of Selank effect on lymphatic vessels contractility showed that its low concentration (10(-12)--10(-14) M) enhanced amplitude and increase frequency of lymphatic vessel contractions which indicates an enhancement of lymphatic flow. The high doses of peptide (10(-6)--10(-10) M) also augmented the contraction amplitude but decreased its frequency. The maintenance of adequate blood flow and lymphatic vessel contractility can be one of the mechanisms of the Selank antiulcerogenic properties.

Asunto(s)

Ansiolíticos/farmacología , Vasos Linfáticos/efectos de los fármacos , Oligopéptidos/farmacología , Circulación Esplácnica/efectos de los fármacos , Estómago/irrigación sanguínea , Vasoconstricción/efectos de los fármacos , Animales , Vasos Linfáticos/fisiología , Microcirculación/efectos de los fármacos , Ratas , Estómago/efectos de los fármacos

Asunto(s)

Ansiolíticos/farmacología , Mucosa Gástrica/patología , Oligopéptidos/farmacología , Úlcera Gástrica/patología , Úlcera Gástrica/psicología , Estrés Psicológico , Ácido Acético , Secuencia de Aminoácidos , Animales , Etanol , Mucosa Gástrica/efectos de los fármacos , Ratas , Restricción Física , Úlcera Gástrica/inducido químicamente , Relación Estructura-Actividad

RESUMEN

Taftsin, an endogenous peptide immunostimulator, exhibits also high antiulcer activity. In a dose of 0.6 micromol/kg Taftsin decreases the area of ulcerative lesions in albino rats on various models of ulceration.

Asunto(s)

Úlcera Gástrica/tratamiento farmacológico , Tuftsina/uso terapéutico , Ácido Acético , Adyuvantes Inmunológicos/uso terapéutico , Animales , Etanol , Masculino , Ratas , Restricción Física , Úlcera Gástrica/inducido químicamente , Estrés Fisiológico/fisiopatología

Asunto(s)

Síndromes del Arco Aórtico , Humanos