Why Variant Colloid Transport Behaviors Emerge among Identical Individuals in Porous Media When Colloid-Surface Repulsion Exists.

We herein demonstrate the cause of well-observed variant transport behaviors for apparently identical colloids in porous media under conditions of colloid-collector repulsion (unfavorable attachment conditions). We demonstrate that variant colloid transport behavior under unfavorable conditions can be explained by inherently variable colloid residence times prior to arrest on grains (collectors). We demonstrate that the residence time distributions derived from particle trajectory simulations incorporating representative nanoscale heterogeneity provide quantitative prediction of colloid transport under unfavorable conditions. We quantitatively predict hyper-exponential retention profiles in glass beads from representative nanoscale heterogeneity determined for glass, and we qualitatively predict nonmonotonic retention profiles in quartz sand from an estimated representative nanoscale heterogeneity for quartz. We also demonstrate that the transition from hyper-exponential to nonmonotonic profiles among glass beads versus quartz sand under otherwise equivalent conditions is primarily driven by greater grain angularity and consequent greater length and number of grain to grain contacts in quartz sand relative to glass beads. That continuum-scale transport behaviors emerge from upscaling of simulated pore-scale colloid residence times corroborates the utility of representative nanoscale heterogeneity for quantitative prediction of colloid transport under unfavorable conditions.

Neuroblastoma cells injected into experimental mature teratoma reveal a tropism for embryonic loose mesenchyme.

Embryonic neural tumors are responsible for a disproportionate number of cancer deaths in children. Although dramatic improvements in survival for pediatric malignancy has been achieved in previous years advancements seem to be slowing down. For the development of new enhanced therapy and an increased understanding of the disease, pre-clinical models better capturing the neoplastic niche are essential. Tumors of early childhood present in this respect a particular challenge. Here, we explore how components of the embryonic process in stem­cell induced mature teratoma can function as an experimental in vivo microenvironment instigating the growth of injected childhood neuroblastoma (NB) cell lines. Three human NB cell lines, IMR-32, Kelly and SK-N-BE(2), were injected into mature pluripotent stem cell­induced teratoma (PSCT) and compared to xenografts of the same cell lines. Proliferative NB cells from all lines were readily detected in both models with a typical histology of a poorly differentiated NB tumor with a variable amount of fibrovascular stroma. Uniquely in the PSCT microenvironment, NB cells were found integrated in a non­random fashion. Neuroblastoma cells were never observed in areas with well-differentiated somatic tissue i.e. bone, muscle, gut or areas of other easily identifiable tissue types. Instead, the three cell lines all showed initial growth exclusively occurring in the embryonic loose mesenchymal stroma, resulting in a histology recapitulating NB native presentation in vivo. Whether this reflects the 'open' nature of loose mesenchyme more easily giving space to new cells compared to other more dense tissues, the rigidity of matrix providing physical cues modulating NB characteristics, or if embryonic loose mesenchyme may supply developmental cues that attracted or promoted the integration of NB, remains to be tested. We tentatively hypothesize that mature PSCT provide an embryonic niche well suited for in vivo studies on NB.

Crystal growth of aragonite and calcite in presence of citric acid, DTPA, EDTA and pyromellitic acid.

The influence of four calcium complexing substances, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), on the crystal growth rate of the calcium carbonate polymorphs aragonite and calcite has been studied. Using a seeded constant supersaturation method supersaturation was maintained at 4 by keeping a constant pH of 8.5 through addition of sodium carbonate and calcium chloride solutions. The unique composition of each solution was calculated using chemical speciation. The growth rate was interpreted in terms of an overall growth rate. For both calcite and aragonite, the crystal growth rate is significantly reduced in the presence of the calcium complexing substances. The growth retarding effect depends on both the concentration and the polymorph. The relative crystal growth rate was correlated to the total complexing agent concentration using a Langmuir adsorption approach. Aragonite appeared fully covered for lower total concentrations than calcite. Furthermore, CIT very efficiently blocked aragonite growth contrary to what was observed for calcite. This is thought to be related to certain distinct features of the dominant aragonite crystal faces compared to the dominant calcite faces.

Nucleation of calcium carbonate in presence of citric acid, DTPA, EDTA and pyromellitic acid.

The influence of four calcium complexing additives, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), and their concentration on the induction time of calcium carbonate nucleation has been studied. The experiments were performed by rapidly mixing a sodium carbonate solution and a calcium chloride solution of various concentrations. The induction time was obtained by recording the white light absorption of the solution. Chemical speciation was used to estimate the initial thermodynamic driving force of each experiment. The induction time was found to increase with additive concentration. The effect varies from one additive to another. CIT causes the greatest increase in induction time and PMA the least. Using classical nucleation theory the experimental data were evaluated in terms of the interfacial energy. In pure water a value of 37.8 mJ m(-2) was obtained, showing good agreement with other works. CIT, DTPA and EDTA caused a notable increase of the interfacial energy at a concentration of 0.5 mmol l(-1). PMA does not appear to have any effect at all on the interfacial energy. Different mechanisms for the influence of the additives on the measured induction time and on the estimated interfacial energy are discussed.

Heat transfer in vial lyophilization.

Heat transfer in vial lyophilization has been studied experimentally and theoretically as a first step in developing a theoretical model for vial lyophilization. Heat transfer was studied by cooling and heating sealed vials containing water in a pilot scale freeze-dryer. The factors studied were bottom curvature of the vial, chamber pressure, fill volume, position on the shelf and the state of the water. A theoretical dynamic and two-dimensional axisymmetric model that comprised both the vial and its content was developed. It was constructed using physical models for thermal conductivity of gases at low pressure, thermal conduction and radiation. The coefficients in the model were based on physical constants and geometrical data and not assessed from experiments. The resulting differential equations were solved numerically. The theoretical model could well describe both heat transfer and heat accumulation in the vial. The dynamics of the corner vials could also be well modeled by adding heat transfer to the side of the vial. The effect of the curvature of the vial bottom, the heat accumulation in the glass vial and the heat transfer to the sidewalls of vials in the corner of the shelf all contributed to a significant radial influence on the heat transfer.

Somatic and germline mutagenesis assayed by the unstable zeste-white test in Drosophila melanogaster.

This investigation is an attempt to compare mutation rates in germinal and somatic cells by the use of the unstable zeste-white assay in Drosophila melanogaster. In this system it is possible to use the same genetic end point to measure both somatic mutations (aberrantly pigmented spots in the eyes of adult flies) and germinal mutations (males with aberrantly pigmented eyes). We used two mutagens, formaldehyde and methylmethane sulphonate (MMS), to induce mutations and two different routes of mutagen administration, larval feeding and adult feeding, and scored mutations in somatic as well as germinal cells. Both types of tissues were susceptible to MMS mutagenesis, showing elevated frequencies of both germline mutations and eye spots. Formaldehyde, however, gave no increase in the germinal mutation rate but caused somatic mutations. These were found after larval exposure, but also among the offspring of exposed males, as formation of delayed somatic mutations. The results show that somatic cells are much more sensitive in monitoring induced mutations than germinal cells in this system. We also found that spontaneous mutation rate among germinal cells is 200 times higher than that in somatic cells, which presumably is due to the involvement of a mobile element.

Uptake and incorporation in pteridines of externally supplied GTP in normal and pigment-deficient eyes of Drosophila melanogaster.

Some aspects of the synthesis of drosopterins in the eyes of Drosophila melanogaster have been studied in flies with different levels of white gene expression. The activity of GTP cyclohydrolase was found to differ between wild-type and yellow-eyed mutants in vivo but not in vitro. To elucidate the uptake of substrate, we measured the removal of labeled GTP from the incubation medium by excised pupal eyes and followed the subsequent fate of this label. It was found that GTP was dephosphorylated to guanosine extracellularly before label was taken up by the eye tissue. The uptake was much lower in yellow and white eyes than in wild-type eyes, and in the latter, a considerable part of the label was present in pteridine compounds. The strain differences in the uptake of label seem to be due to different rates of intracellular utilization of guanine derivatives in pteridine synthesis. We suggest that this is caused by a hampered transport of precursor (possibly GTP) in white and zeste eyes through the membrane of red pigment granules.

Binding of antithrombin to immobilized heparin under varying flow conditions.

Rheologic factors are likely to influence the balance between thrombotic and antithrombotic forces at the level of the vascular wall. In this study, the effects of flow-velocity/wall shear stress on the interaction of antithrombin (AT) with surface-immobilized heparin were investigated. The binding of AT to low-affinity and high-affinity heparin could be discriminated by measurements at physiological of elevated ionic strength. Under low shear stress conditions, substantial binding of AT to both high- and low-affinity heparin was observed, in relative quantities largely reflecting the proportion of these polysaccharide populations on the surface. With increasing shear stress, the binding to high-affinity sites was relatively constant, while total low-affinity binding decreased. Furthermore, under the highest shear stress (greater than 1,000 N/m2), the binding of AT to low-affinity heparin completely disappeared while binding to the high-affinity fraction persisted. These results were related to values obtained in a mathematical model, describing the theoretical maximum transport of AT from the liquid phase to the surface under the conditions used in the experimental system.

Influence of high and low wall shear rates on the inhibition of factor Xa and thrombin at surfaces coated with immobilized heparin.

The thromboresistant function of a surface with end-point attached heparin is based upon interaction among the immobilized heparin, antithrombin, and at least factor Xa or thrombin. Heparinized arteriovenous shunts were implanted in dogs. By compressing a segment of the shunt, high and low wall shear rate regions were obtained in each shunt. After removal, the tubings were tested for their factor Xa and thrombin inhibitory capacity. It was found that on a molar basis, the factor Xa and thrombin inhibitory capacity were similar in low wall shear rate segments. In high wall shear rate segments, the thrombin inhibitory capacity was decreased, thus indicating that the AT-mediated inhibition of the serine protease is dependent on the wall shear rate.

Induction of mutations by tritiated water and 3H-thymidine in Drosophila melanogaster assayed by the somatic zeste-white eye mutation system.

In order to study the mutagenic effect of exposure to tritium, Drosophila melanogaster larvae were treated with tritiated water (3H2O) or tritiated thymidine (3H-TdR) during development. Dose rates ranged from 0.0058 to 0.058 rad/h per nucleus for 3H-TdR and from 0.049 to 0.122 rad/h for 3H2O. Induction of mutations was measured by the appearance of somatic mutations in the eyes of an unstable strain of Drosophila melanogaster. Both substances caused a significant increase in mutation frequency. With the assumption that each mutation observed in this assay is caused by one DNA break, the effectiveness of tritium to create DNA breaks is estimated to be 0.20 breaks per decay for 3H-TdR and 0.27 breaks per decay for 3H2O.

Mutagenic effects of some water-soluble metal compounds in a somatic eye-color test system in Drosophila melanogaster.

Nickel, cadmium, lead, arsenic, manganese and chromium salts as well as MeHgOH were screened for mutagenicity, using a sensitive somatic eye-color test system in Drosophila melanogaster. The test is based on the insertion of a mobile element which causes instability in the white locus that is somatically enhanced by mutagens. This white locus expression is combined with a mutation, zeste, in another gene, to produce a light yellow eye color. Larval feeding with mutagens causes somatic mutations in the eye imaginal disc cells that develop into easily detectable red spots in the yellow eyes of adult males. Survival tests showed large differences in the toxicity of different metals, but only hexavalent chromium increased the frequency of somatic mutations above the control level. When combined treatments were carried out with MMS and various metals, sodium arsenite caused a reduction of the MMS-induced mutation frequency while methylmercury increased the frequency of somatic spots.

Biological effects of high-frequency electromagnetic fields on Salmonella typhimurium and Drosophila melanogaster.

Salmonella typhimurium and Drosophila melanogaster were exposed to continuous wave (CW) 2.45-GHz electromagnetic radiation, pulsed 3.10-GHz electromagnetic radiation, CW 27.12-MHz magnetic fields, or CW 27.12-MHz electric fields (only Drosophila). The temperatures of the treated sample and the nonexposed control sample were kept constant. The temperature difference between exposed and control samples was less than +/- 0.3 degrees C. Ames' assays were made on bacteria that had been exposed to microwaves (SAR 60-130 W/kg) or RF fields (SAR up to 20 W/kg) when growing exponentially in nutrient broth. Survival and number of induced revertants to histidine prototrophy were determined by common plating techniques on rich and minimal agar plates. The Drosophila test consisted of a sensitive somatic system where the mutagenicity was measured by means of mutations in a gene-controlling eye pigmentation. In none of these test systems did microwave or radiofrequency fields induce an elevated mutation frequency. However, a significantly higher concentration of cells was found in the bacterial cultures exposed to the 27-MHz magnetic field or 2.45-GHz CW and 3.10-GHz pulsed microwave radiation.

Comparative studies of the induction of somatic eye-color mutations in an unstable strain of Drosophila melanogaster by MMS and X-rays at different developmental stages.

An unstable white locus in Drosophila melanogaster originally described by Rasmuson and Green (1974) and further by Rasmuson et al. (1978, 1980) contains an IS element. This constellation interacts with the zeste mutation and forms a mutationally unstable system that is sensitive to a variety of mutagens. Mutational shifts between zeste and wild-type eye color as well as deletions and transpositions of the white locus are frequently occurring in the unstable X-chromosome in germ line and in somatic tissue. Germinal mutations from zeste to wild-type eye color are associated with an insertion of a piece of DNA, proximal to the wsp site, and the shifts from red to zeste are caused by an excision of the same piece (Rasmuson, in preparation). Mutations to pigmentless phenotype are interpreted as deletions of the white locus, while they always are irreversible and show non-complementation with wsp. The somatic system can be used as a screening test for potential mutagens, described by Rasmuson et al. (1984). This survey is an attempt to correlate the size of the mutated area of the eyes with the age of the larvae at mutagen treatment. X-Rays and MMS were used to give an indication of the mechanism of the instability, according to the different kinds of DNA damage induced. The results show that the mean size of red spots decreased with increasing age of larvae at treatment, while the mutation frequencies were increased because of the multiplication of the cells in the eye anlage susceptible to the mutagens. This is contradictory to the hypothesis maintained by Fahmy and Fahmy (1980) that the somatic shifts are not mutagenic but epigenetic events, due to altered regulation of the gene expression. Red spots induced with MMS are smaller in size than X-ray-induced red spots, indicating a delay in the establishment of mutations from chemically-induced lesions compared to irradiation damage. White spots on the other hand were equally large in size, irrespective of inducing agent and about twice the size of the chemically-induced red spots, implying a faster and more direct action for fixation of deletions than for the production of MMS induced shifts in eye color from zeste to red.

Effects of DNA-repair-deficient mutants on somatic and germ line mutagenesis in the UZ system in Drosophila melanogaster.

To analyze the underlying mechanisms of the UZ system in Drosophila melanogaster, i.e., the unstable white locus with an IS element included originally described by Rasmuson and Green (1974), the repair deficient mutants mei-9b and mei-4lD5 and the meiotic mutant mei-2l8 were introduced into X-chromosomes containing the UZ system. These strains were submitted to larval feeding of MMS to analyze differences occurring in mutation rate and survival. The mei-9b and mei-4l strains were markedly sensitive to MMS treatment, while mei-2l8 did not affect survival. Only the mutant mei-4l, which is lacking in post-replication repair, affected the somatic mutation rate of the UZ system, decreasing it by 50%. The spontaneous germ line mutation rate of UZ, on the other hand, was increased by introducing mei-4l or mei-9b, possibly as a result of the high frequency of unrepaired spontaneous chromosome breaks that occur in these mutants.

Genetic instability in Drosophila melanogaster: evidence for regulation, excision and transposition at the white locus.

An unstable long tandem duplication which includes the white locus twice, marked with wsp in the left and w17g in the right locus, when kept in males has been found to produce red-eyed sons which have lost the long duplication and with it the wsp and w17g mutants. Such exceptions were produced also when w17g had been exchanged for wa. Stocks originating from these exceptions are unstable, producing: 1) zeste males, also unstable, 2) w- deletions, stable, 3) transpositions of the white locus to sites in other chromosomes. The instability is interpreted as the effect of an IS element, within or adjacent to the white locus, which is supposed to retain a duplication of the proximal zeste interacting part of this locus. According to the orientation of the IS element the duplicated part can be active or inactive, giving a zeste or red eye phenotype. The frequency of exceptional offspring after X-ray treatment of the red and zeste unstable stocks have been compared to stable stocks with corresponding genotypes.

A negative test for mutagenic action of microwave radiation in Drosophila melanogaster.

Microwave radiation (2450 MHz CW) was tested for mutagenicity in Drosophila melanogaster. Embryos in water were exposed to the electromagnetic field with a mean specific absorption rate of 100 W/kg. A sensitive somatic test system was used, in which mutagenicity was measured as the frequency of somatic mutations for eye pigmentation. With the test system used, microwaves did not show any mutagenic activity.

The use of a mutationally unstable X-chromosome in Drosophila melanogaster for mutagenicity testing.

Somatic eye-colour mutations in an unstable genetic system, caused by a transposable element in the white locus of the X-chromosome in Drosophila melanogaster, is suggested as an assay system for mutagenicity testing. The system is evaluated by comparison with a corresponding system in a stable X-chromosome. Its sensitivity is confirmed with X-ray and EMS treatment, and it is found to be confined to the specific segment of the X-chromosome where the transposable element is localized.