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Two scalar fields characterizing respectively pseudo-Hölder exponents and local energy transfers are used to capture the topology and the dynamics of the velocity fields in areas of lesser regularity. The present analysis is conducted using velocity fields from two direct numerical simulations of the Navier-Stokes equations in a triply periodic domain. A typical irregular structure is obtained by averaging over the 213 most irregular events. Such structure is similar to a Burgers vortex, with nonaxisymmetric corrections. A possible explanation for such asymmetry is provided by a detailed time-resolved analysis of birth and death of the irregular structures, which shows that they are connected to vortex interactions, possibly vortex reconnection.
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It is still not known whether solutions to the Navier-Stokes equation can develop singularities from regular initial conditions. In particular, a classical and unsolved problem is to prove that the velocity field is Hölder continuous with some exponent h<1 (i.e., not necessarily differentiable) at small scales. Different methods have already been proposed to explore the regularity properties of the velocity field and the estimate of its Hölder exponent h. A first method is to detect potential singularities via extrema of an "inertial" dissipation D*=lim_{ââ0}D_{â}^{I} that is independent of viscosity [Duchon and Robert, Nonlinearity 13, 249 (2000)0951-771510.1088/0951-7715/13/1/312]. Another possibility is to use the concept of multifractal analysis that provides fractal dimensions of the subspace of exponents h. However, the multifractal analysis is a global statistical method that only provides global information about local Hölder exponents, via their probability of occurrence. In order to explore the local regularity properties of a velocity field, we have developed a local statistical analysis that estimates locally the Hölder continuity. We have compared outcomes of our analysis with results using the inertial energy dissipation D_{â}^{I}. We observe that the dissipation term indeed gets bigger for velocity fields that are less regular according to our estimates. The exact spatial distribution of the local Hölder exponents however shows nontrivial behavior and does not exactly match the distribution of the inertial dissipation.
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On the basis of (i) particle image velocimetry data of a turbulent boundary layer with large field of view and good spatial resolution and (ii) a mathematical relation between the energy spectrum and specifically modeled flow structures, we show that the scalings of the streamwise energy spectrum E_{11}(k_{x}) in a wave-number range directly affected by the wall are determined by wall-attached eddies but are not given by the Townsend-Perry attached eddy model's prediction of these spectra, at least at the Reynolds numbers Re_{τ} considered here which are between 10^{3} and 10^{4}. Instead, we find E_{11}(k_{x})â¼k_{x}^{-1-p} where p varies smoothly with distance to the wall from negative values in the buffer layer to positive values in the inertial layer. The exponent p characterizes the turbulence levels inside wall-attached streaky structures conditional on the length of these structures. A particular consequence is that the skin friction velocity is not sufficient to scale E_{11}(k_{x}) for wave numbers directly affected by the wall.
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Pseudomonas aeruginosa is a key opportunistic pathogen causing disease in cystic fibrosis (CF) and other lung diseases such as chronic obstructive pulmonary disease (COPD). However, the pulmonary host defense mechanisms regulating anti-P. aeruginosa immunity remain incompletely understood. Here we demonstrate, by studying an airway P. aeruginosa infection model, in vivo bioluminescence imaging, neutrophil effector responses and human airway samples, that the chemokine receptor CXCR1 regulates pulmonary host defense against P. aeruginosa. Mechanistically, CXCR1 regulates anti-Pseudomonas neutrophil responses through modulation of reactive oxygen species and interference with Toll-like receptor 5 expression. These studies define CXCR1 as a novel, noncanonical chemokine receptor that regulates pulmonary anti-Pseudomonas host defense with broad implications for CF, COPD and other infectious lung diseases.
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Fibrosis Quística/inmunología , Neutrófilos/inmunología , Infecciones por Pseudomonas/inmunología , Pseudomonas aeruginosa/inmunología , Enfermedad Pulmonar Obstructiva Crónica/inmunología , Receptores de Interleucina-8A/metabolismo , Mucosa Respiratoria/inmunología , Animales , Células Cultivadas , Modelos Animales de Enfermedad , Femenino , Interacciones Huésped-Patógeno , Humanos , Inmunidad Innata , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Especies Reactivas de Oxígeno/metabolismo , Receptores de Interleucina-8A/inmunología , Mucosa Respiratoria/microbiología , Receptor Toll-Like 5/genética , Receptor Toll-Like 5/metabolismo , Adulto JovenRESUMEN
PURPOSE: The aim of this study was to determine the psychological effects and difficulties that radiation therapists (RTs) experience while treating paediatric patients. This study is intended to provide some information to assist RTs in their occupation and to complement the literature on this topic. METHODS: A survey was conducted to capture data on the emotional effects and opinions of RTs at The Ottawa Hospital Regional Cancer Centre (TOHRCC) treating children with cancer. A questionnaire was created specifically for this study standardized to TOHRCC conditions and methods and inspired from the limited literature around this issue. The study converged on the reactions of RTs while children received radiation treatment at TOHRCC and the impact on their emotional state around this component of their practice. The questionnaire was distributed electronically via e-mail to all RTs within the Radiation Therapy Department at TOHRCC. RESULTS: This study involved 62 of 104 RTs employed at TOHRCC who completed the survey of 20 questions and submitted their responses. Due to the sample size, statistical correlations and links between variables were limited. The questionnaire was analysed based on the answers given by the RTs on the provided Likert scale for each question. The questionnaire showed that gender and age played no major role in the RTs' ability to cope mentally. Half of the RTs had children themselves; and of these, 66% indicated that having children made it somehow more difficult to cope emotionally with paediatric patients. Seventy-five percent of all RTs indicated that the emotional state of parents or care givers of the affected children played a key role in the anxiety they felt during a child's treatment. Eighty-one percent of RTs stated that treating children caused higher anxiety levels than treating adults. Finally, our survey suggests that time constraints play a large part in the RTs' stress level during treatments. CONCLUSION: Overall, treating children did not cause much more distress than treating adults. Results from this survey were used to create a new tool describing the cognitive stages in children to help RTs treat paediatric patients in the future.
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Transmission electron microscopy (TEM), atomic force microscopy (AFM), and EDX methods were used to study morphology and chemical composition of SiGe/Si(001) islands grown at 700 degrees C and covered at 550 degrees C and 700 degrees C by Si layers of different thickness. The samples were grown in ultra high vacuum chemical vapor deposition process (UHVCVD) controlled with in situ reflection of high-energy electron diffraction (RHEED). The islands transformed from initial pyramid and dome shapes to lens shape for 1.4 nm and 3.7 nm cap layer thickness at 550 degrees C and 700 degrees C, respectively. An increase of lateral to vertical ratio was observed during the transformation. For the higher depositing temperature the ratio was bigger and was increasing continuously with cap layer thickness. Also, with increasing Si cap layer thickness, the Ge concentration was decreasing, which was more observable for higher capping temperature.
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We report direct numerical simulations of dynamo generation for flow generated using a Taylor-Green forcing. We find that the bifurcation is subcritical and show its bifurcation diagram. We connect the associated hysteretic behavior with hydrodynamics changes induced by the action of the Lorentz force. We show the geometry of the dynamo magnetic field and discuss how the dynamo transition can be induced when an external field is applied to the flow.
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We use direct and stochastic numerical simulations of the magnetohydrodynamic equations to explore the influence of turbulence on the dynamo threshold. In the spirit of the Kraichnan-Kazantsev model, we model the turbulence by a noise, with given amplitude, injection scale, and correlation time. The addition of a stochastic noise to the mean velocity significantly alters the dynamo threshold and increases it for any noise at large scale. For small-scale noise, the result depends on its correlation time and on the magnetic Prandtl number.
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Previous studies of the structure of core nanocrystals of ferritin (Ft) in the brains of patients with Alzheimer's disease (AD) have shown differences in the mineral compound in comparison with physiological Ft. Both Ft cores have a polyphasic composition but whereas the major phase in physiological Ft is hexagonal ferric iron oxide (ferrihydrite), the major phases in brain AD Ft are two cubic mixed ferric-ferrous iron oxides (magnetite and wüstite). One of these (wüstite) is similar to what is detected in hemosiderin (Hm) cores in primary hemochromatosis (Quintana, C., Cowley, J.M, Marhic, C., 2004. Electron nanodiffraction and high resolution electron microscopy studies of the structure and composition of physiological and pathological ferritin. J. Struct. Biol. 147, 166-178). We have studied, herein, the distribution of iron, Ft, and Hm in sections of AD hippocampus using analytical microscopy. Iron present in Ft cores was directly mapped in a nanoSIMS microscope and the iron distribution has been correlated with the constituent elements N, P, and S. Ft and Hm cores were visualized at an ultrastructural level in an analytical transmission electron microscope. In senile plaques, Ft was observed in the coronal region associated with a non-beta-amyloid component and in the periphery of plaques, together with Hm, in sulfur-rich dense bodies of dystrophic neurites. Hm was also found in lysosomes and siderosomes of glial cells. Ft was observed in the cytoplasm and nucleus of oligodendrocytes. Ft was particularly abundant in myelinated axons in association with oligodendrocyte processes. These findings provide new arguments to support the hypothesis of a dysfunction of Ft (with eventual degradation to Hm) in AD resulting in an increase of toxic brain ferrous ions that may contribute to the production of free radicals that induce both cellular oxidative stress and aged-related myelin breakdown associated with cognitive decline and AD (Bartzokis, G., 2004. Age-related myelin breakdown: a developmental model of cognitive decline and Alzheimer's disease. Neurobiol. Aging 25, 5-18).
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Enfermedad de Alzheimer/patología , Ferritinas/análisis , Hemosiderina/análisis , Hipocampo/química , Hierro/análisis , Anciano , Anciano de 80 o más Años , Enfermedad de Alzheimer/metabolismo , Axones/química , Axones/ultraestructura , Femenino , Hipocampo/ultraestructura , Humanos , Inmunohistoquímica , Masculino , Microscopía Electrónica de Transmisión , Persona de Mediana Edad , Vaina de Mielina/química , Vaina de Mielina/ultraestructura , Espectrometría de Masa de Ion Secundario/métodosRESUMEN
The effects of a lethal gamma irradiation were investigated on cerebral NO-ergic system by using a voltammetric method in freely moving rats. It is reported that the cortical NO concentration increases right from the end of the radiation exposure (15 Gy) and reaches a maximal magnitude (+120%) 24 h later. A dose-effect relationship from 2 to 15 Gy for gamma-ray exposure has also been observed. The effects, obtained with either an NO synthase inhibitor nonselective for the different NO synthase isoforms or an NO synthase inhibitor selective for the constitutive isoform, suggest that the radiation-induced increase in NO is likely to be dependent on the inducible NO synthase isoform. Moreover, experiments performed under ex vivo conditions showed that the cortical mRNA level for Ca(++)-independent NO synthase, the brain NOS activity, and urinary nitrites/nitrates increased significantly 24 h after gamma-ray exposure. These results demonstrate that a supralethal whole-body irradiation alters the NO-ergic pathways. The increase in NO obtained under such conditions might constitute a good index of central nervous system radiosensitivity during the acute phase of the radiation syndrome.
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Química Encefálica/efectos de la radiación , Óxido Nítrico/análisis , Animales , Relación Dosis-Respuesta en la Radiación , Inhibidores Enzimáticos/farmacología , Rayos gamma , Masculino , Óxido Nítrico Sintasa/análisis , Óxido Nítrico Sintasa/antagonistas & inhibidores , Óxido Nítrico Sintasa/genética , ARN Mensajero/análisis , Ratas , Ratas Sprague-Dawley , Irradiación Corporal TotalRESUMEN
Numerical simulations are made for forced turbulence at a sequence of increasing values of Reynolds number Re keeping fixed a strongly stable, volume-mean density stratification. At smaller values of Re, the turbulent velocity is mainly horizontal, and the momentum balance is approximately cyclostrophic and hydrostatic. This is a regime dominated by so-called pancake vortices, with only a weak excitation of internal gravity waves and large values of the local Richardson number Ri everywhere. At higher values of Re there are successive transitions to (a) overturning motions with local reversals in the density stratification and small or negative values of Ri; (b) growth of a horizontally uniform vertical shear flow component; and (c) growth of a large-scale vertical flow component. Throughout these transitions, pancake vortices continue to dominate the large-scale part of the turbulence, and the gravity wave component remains weak except at small scales.
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The continuous displacement field within elastically relaxed GaInAs islands was calculated from digitized HREM images of [110] cross sections of In0.35Ga0.65As layers grown on GaAs by molecular beam epitaxy. Experimental maps of the deformations parallel to the interface (epsilonx) and along the growth direction (epsilonz) were drawn and compared with the ones calculated via the finite element method. It was found that epsilonx exp was systematically higher than epsilonx calc and the significant maximum observed for epsilonz exp within the island could not be found for epsilonz calc. These discrepancies were attributed to a variation of the chemical composition in the island. The maps showing the indium concentration gradient drawn from HREM and FE calculations were compared to quantitative profiles for indium concentration obtained by nanometric X-ray microanalysis in TEM. The measured gradient within the island backs our assumption.
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Aleaciones/química , Arseniatos/análisis , Microanálisis por Sonda Electrónica/métodos , Galio/análisis , Indio/análisis , Nanotecnología/métodos , Cristalización , Procesamiento de Imagen Asistido por Computador , Microscopía Electrónica/instrumentación , Microscopía Electrónica/métodosRESUMEN
Clustered damage induced by ionizing radiation--two or more oxidized bases, abasic sites, or strand breaks within a few DNA helical turns--have been postulated to be major lethal and/or mutagenic sites. Although they have recently been shown to be induced in genomic DNAs by ionizing photons and particles, little is known of the factors that affect their yields or the relative levels of the classes of clusters. Toward this aim we have investigated the effect of DNA milieu, specifically, a nonradioquenching (phosphate) or radioquenching (Tris) solution, upon the generation of clustered lesions in a well-defined molecule, T7 bacteriophage DNA. Irradiation of DNA in Tris reduces the yields of all clustered damages to 1-3% of the levels formed in phosphate. Further, although the percentage of the total clusters in oxidized purine clusters is largely unchanged, and the level of abasic clusters decreases, the frequencies of double-strand breaks and oxidized pyrimidine clusters increase in the radioquenching solution. The ratio of the level of oxidized pyrimidine clusters to double-strand breaks in a DNA in radioquenching solution is similar to that obtained in DNA in human cells, also a radioquenching environment.
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Daño del ADN/efectos de la radiación , ADN Viral/efectos de la radiación , Rayos gamma , Bacteriófago T7/genética , Bacteriófago T7/efectos de la radiación , ADN Viral/genética , Humanos , Fosfatos , TrometaminaRESUMEN
Thermal stability of Escherichia coli Fpg protein was studied using far-UV circular dichroism and intrinsic fluorescence. Experimental data indicate that Fpg irreversibly aggregates under heating above 35 degrees C. Heat aggregation is preceded by tertiary conformational changes of Fpg. However, the secondary structure of the fraction that does not aggregate remains unchanged up to approximately 60 degrees C. The kinetics of heat aggregation occurs with an activation enthalpy of approximately 21 kcal/mol. The fraction of monomers forming aggregates decreases with increasing urea concentration, with essentially no aggregation observed above approximately 3 M urea, suggesting that heat aggregation results from hydrophobic association of partially unfolded proteins. With increasing urea concentration, Fpg unfolds in a two-state reversible transition, with a stability of approximately 3.6 kcal/mol at 25 degrees C. An excellent correlation is observed between the unfolded fraction and loss of activity of Fpg. A simple kinetic scheme that describes both the rates and the extent of aggregation at each temperature is presented.
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Proteínas de Escherichia coli , Escherichia coli/enzimología , N-Glicosil Hidrolasas/química , Dicroismo Circular , ADN-Formamidopirimidina Glicosilasa , Estabilidad de Enzimas , Calor , Cinética , Desnaturalización Proteica , Pliegue de Proteína , Espectrometría de Fluorescencia , Temperatura , Urea/químicaRESUMEN
The formamidopyrimidine N-DNA glycosylase (Fpg protein) of Escherichia coli is a DNA repair enzyme that is specific for the removal of purine-derived lesions from DNA damaged by free radicals and other oxidative processes. We investigated the effect of single mutations on the specificity of this enzyme for three purine-derived lesions in DNA damaged by free radicals. These damaging agents generate a multiplicity of base products in DNA, with the yields depending on the damaging agent. Wild type Fpg protein (wt-Fpg) removes 8-hydroxyguanine (8-OH-Gua), 4,6-diamino-5-formamidopyrimidine (FapyAde), and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) from damaged DNA with similar specificities. We generated five mutant forms of this enzyme with mutations involving Lys-57-->Gly (FpgK57G), Lys-57-->Arg (FpgK57R), Lys-155-->Ala (FpgK155A), Pro-2-->Gly (FpgP2G), and Pro-2-->Glu (FpgP2E), and purified them to homogeneity. FpgK57G and FpgK57R were functional for removal of FapyAde and FapyGua with a reduced activity when compared with wt-Fpg. The removal of 8-OH-Gua was different in that the specificity of FpgK57G was significantly lower for its removal from irradiated DNA, whereas wt-Fpg, FpgK57G, and FpgK57R excised 8-OH-Gua from H2O2/Fe(III)-EDTA/ascorbic acid-treated DNA with almost the same specificity. FpgK155A and FpgP2G had very low activity and FpgP2E exhibited no activity at all. Michaelis-Menten kinetics of excision was measured and kinetic constants were obtained. The results indicate an important role of Lys-57 residue in the activity of Fpg protein for 8-OH-Gua, but a lesser significant role for formamidopyrimidines. Mutations involving Lys-155 and Pro-2 had a dramatic effect with Pro-2-->Glu leading to complete loss of activity, indicating a significant role of these residues. The results show that point mutations significantly change the specificity of Fpg protein and suggest that point mutations are also expected to change specificities of other DNA repair enzymes.
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Proteínas de Escherichia coli , Escherichia coli/química , Guanina/análogos & derivados , Mutagénesis Sitio-Dirigida , N-Glicosil Hidrolasas/química , N-Glicosil Hidrolasas/genética , N-Glicosil Hidrolasas/metabolismo , Ácido Ascórbico/farmacología , ADN/metabolismo , Daño del ADN , Reparación del ADN , ADN-Formamidopirimidina Glicosilasa , Ácido Edético/farmacología , Compuestos Férricos/farmacología , Rayos gamma , Guanina/metabolismo , Peróxido de Hidrógeno/farmacología , Lisina , Prolina , Relación Estructura-ActividadRESUMEN
When present in DNA, 3,N(4)-ethenocytosine (epsilon C) residues are potentially mutagenic and carcinogenic in vivo. The enzymatic activity responsible for the repair of the epsilon C residues in human cells is the hTDG protein, the human thymine-DNA-glycosylase that removes thymine in a T/G base pair [Proc. Natl. Acad. Sci., U.S.A., 95 (1998) 8508]. One of the distinctive properties of the hTDG protein is that it remains tightly bound to the AP-site resulting from its glycosylase activity. In this paper we report that the human AP endonuclease, the HAP1 (Ape1, APEX Ref-1) protein, stimulates the processing of epsilon C residues by the hTDG protein in vitro, in a dose-dependent manner. This property of HAP1 protein is specific since E.coli Fpg, Nfo and Nth proteins, all endowed with an AP nicking activity, do not show similar features. The results suggest that the HAP1 protein displaces the hTDG protein bound to the AP-site and therefore increases the turnover of the hTDG protein. However, using a variety of techniques including gel retardation assay, surface plasmon resonance and two-hybrid system, it was not possible to detect evidence for a complex including the substrate, the hTDG and HAP1 proteins.
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Liasas de Carbono-Oxígeno/metabolismo , Citosina/análogos & derivados , Citosina/metabolismo , Reparación del ADN/fisiología , Endodesoxirribonucleasas/metabolismo , Proteínas de Escherichia coli , Sitios de Unión/efectos de los fármacos , Sitios de Unión/fisiología , Liasas de Carbono-Oxígeno/química , Liasas de Carbono-Oxígeno/farmacología , Citosina/química , ADN Ligasas/química , ADN Ligasas/metabolismo , Reparación del ADN/efectos de los fármacos , ADN-(Sitio Apurínico o Apirimidínico) Liasa , ADN-Formamidopirimidina Glicosilasa , Desoxirribonucleasa (Dímero de Pirimidina) , Desoxirribonucleasa IV (Fago T4-Inducido) , Relación Dosis-Respuesta a Droga , Endodesoxirribonucleasas/química , Endodesoxirribonucleasas/farmacología , Activación Enzimática/efectos de los fármacos , Humanos , Magnesio/farmacología , N-Glicosil Hidrolasas/metabolismo , N-Glicosil Hidrolasas/farmacología , Oligonucleótidos/química , Oligonucleótidos/genética , Oligonucleótidos/metabolismo , Unión Proteica/fisiología , Resonancia por Plasmón de Superficie , Técnicas del Sistema de Dos HíbridosRESUMEN
We use high resolution numerical simulations over several hundred of turnover times to study the influence of small scale dissipation onto vortex statistics in 2D decaying turbulence. A scaling regime is detected when the scaling laws are expressed in units of mean vorticity and integral scale, like predicted in Carnevale et al., Phys. Rev. Lett. 66, 2735 (1991), and it is observed that viscous effects spoil this scaling regime. The exponent controlling the decay of the number of vortices shows some trends toward xi=1, in agreement with a recent theory based on the Kirchhoff model [C. Sire and P. H. Chavanis, Phys. Rev. E 61, 6644 (2000)]. In terms of scaled variables, the vortices have a similar profile with a functional form related to the Fermi-Dirac distribution.
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A new allergen from horse dander, Equ c 5 has been purified. Its biochemical and biophysical properties have been characterized and compared with those of Equ c 1, Equ c 2 and Equ c 4. Their molecular masses, determined by mass spectrometry, were 22 kDa for Equ c 1, 16 kDa for Equ c 2, 18.7 kDa for Equ c 4 and 16.7 kDa for Equ c 5. Their pI values were between 3.8 and 5.25. Equ c 2 and Equ c 5 are not glycosylated, while Equ c 4 contains a tri-antennary tri-sialylated N-linked glycan. Linkages of terminal N-acetylneuraminic acid to galactose were: alpha-(2-->6) in Equ c 4, and both alpha-(2-->3) and alpha-(2-->6) in Equ c 1. Oligosaccharide portions of Equ c 1 or Equ c 4 were barely involved in IgE-immunoreactivity. Partial N-terminal sequence of Equ c 4 shares a significant sequence homology with the rat submandibular gland protein A. No matching was found for two internal peptides of Equ c 5. Surfactant properties of horse allergens as well as other proteins were investigated. In contrast to Equ c 2 and Equ c 3, solutions of Equ c 1, Equ c 4 and Equ c 5 significantly lowered the surface tension. Relationship between a property such as this, involving oriented hydrophobic patches of a molecule and allergenicity, is addressed.
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Alérgenos/química , Alérgenos/metabolismo , Glicoproteínas/química , Glicoproteínas/metabolismo , Tensoactivos/química , Secuencia de Aminoácidos , Animales , Western Blotting , Relación Dosis-Respuesta a Droga , Electroforesis en Gel de Poliacrilamida , Ensayo de Inmunoadsorción Enzimática , Glicosilación , Caballos , Humanos , Concentración de Iones de Hidrógeno , Inmunoglobulina E/metabolismo , Focalización Isoeléctrica , Cinética , Espectrometría de Masas , Datos de Secuencia Molecular , Monosacáridos/química , Oligosacáridos/química , Unión Proteica , Ratas , Análisis de Secuencia de Proteína , Homología de Secuencia de Aminoácido , Factores de TiempoRESUMEN
One of the most important concerns in the decontamination of aflatoxin-containing feed commodities is the safety of the products for food-producing animals and for human consumption of products derived from these animals. A new method, based on the use of florisil and C18 solid phase extraction columns, was developed for the preparation of extracts from decontaminated peanut meal, which allowed testing with in vitro genotoxicity assays without interference of the residual aflatoxin B1. Recovery of degradation products in the extracts was evaluated by the use of radiolabelled [14C]-aflatoxin B1 (AFB1) added to naturally-contaminated peanut meal (3.5 mg AFB1/kg). The meal was treated by a small-scale version of an industrial decontamination process based on ammoniation. Following decontamination, more than 90% of the label could not be extracted from the meal. AFB1 accounted for about 10% of the radiolabel present in the extractable fraction, indicating a total AFB1 reduction of more than 99%. Decontamination of the meal by a number of other small- and industrial-scale ammonia-based processes resulted in similar efficiencies. Application of the extraction procedure resulted in AFB1-rich and AFB1-poor fractions, the latter containing half of the extractable decontamination products but less than 1% of the residual AFB1. Testing in the Salmonella/microsome mutagenicity assay (TA 100, with S9-mix) of the original crude extracts and AFB1-rich fractions prepared from non-treated and decontaminated meal, showed the positive results expected from the AFB1 contents as determined by HPLC analysis. Analysis and testing of the AFB1-poor fractions showed that the various decontamination processes not only resulted in a successful degradation of AFB1 but also did not produce other potent mutagenic compounds. Slight positive results obtained with these extracts were similar for the untreated and treated meals and may be due to unknown compounds originally present in the meal. Results obtained with an unscheduled DNA synthesis (UDS) and Comet assay with rat hepatocytes supported this conclusion. Positive results obtained with the micronucleus assay, using immortalized mouse hepatocytes (GKB), did not clearly reflect the mycotoxin levels and require further examination. It is concluded that the newly developed extraction procedure yields highly reproducible fractions and hence is very suitable for examining the possible formation of less potent degradation products of aflatoxins in short-term genotoxicity tests.