Application of neutron radiography to image flow phenomena in porous media

Neutron transmission imaging is a technique ideally suited for imaging various flow phenomena in consolidated porous media because the porous matrix is virtually transparent to thermal neutrons. Hydrogen-containing fluids, however, provide a contrast in the image due to their large thermal neutron cross-sections. This technique has uncovered new phenomena in the study of dissolution and precipitation in porous media. Neutron images of acid-etched porous patterns show that the degree of branching, and the tortuosity of the etched patterns depend on competing effects of acid flow rate, dissolution rate and precipitation rate of the reaction products. The fine structure of etched pathways show that they can propagate against the direction of flow, a phenomenon not previously observed. In a second study, realtime neutron transmission imaging was used to visualize miscible tracer dispersion. It was shown how quantitative information such as the in-situ spatial distributions of the tracer concentrations can be obtained with this technique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37423/1/690380402_ftp.pd

Determination of flow profiles in porous media using shifts in gamma spectra

A new technique was developed to determine the tracer location and fluid velocity in porous media nonintrusively. This technique exploits the competitive effects between the photoelectric interaction and the Compton scattering phenomenon to determine the distance between a radioactive tracer in a porous medium and an externally positioned detector. The photon energy distribution shifts toward lower photon energies as the tracer moves away from the detector. The shift in the energy distribution can be quantified by the ratio of the scattered photon intensity to the full energy photon intensity. A convective-dispersion model was used to determine the spatial distribution of the radioactive tracer. An analog Monte Carlo method was developed to simulate photon transport in porous media. Comparison between experimental data and the model shows that in-situ tracer velocities can be accurately predicted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37416/1/690360604_ftp.pd

Radiation-Induced Hypomethylation Triggers Urokinase Plasminogen Activator Transcription in Meningioma Cells

AbstractOur previous studies have shown the role of radiation-induced urokinase plasminogen activator (uPA) expression in the progression of meningioma. In the present study, we investigated whether modulation of DNA methylation profiles could regulate uPA expression. Initially, radiation treatment was found to induce hypomethylation in meningioma cells with a decrease in DNA (cytosine-5)-methyltransferase 1 (DNMT1) and methyl-CpG binding domain protein (MBD) expression. However, oxidative damage by H2O2 or pretreatment of irradiated cells with N-acetyl cysteine (NAC) did not show any influence on these proteins, thereby indicating a radiation-specific change in the methylation patterns among meningioma cells. Further, we identified that hypomethylation is coupled to an increase in uPA expression in these cells. Azacytidine treatment induced a dose-dependent surge of uPA expression, whereas pre-treatment with sodium butyrate inhibited radiation-induced uPA expression, which complemented our prior results. Methylation-specific polymerase chain reaction on bisulfite-treated genomic DNA revealed a diminished methylation of uPA promoter in irradiated cells. Transfection with small hairpin RNA (shRNA)-expressing plasmids targeting CpG islands of the uPA promoter showed a marked decline in uPA expression with subsequent decrease in invasion and proliferation of meningioma cells. Further, radiation treatment was found to recruit SP1 transcription factor, which was abrogated by shRNA treatment. Analysis on signaling events demonstrated the activation of MAP kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) in radiation-treated cells, while U0126 (MEK/ERK inhibitor) blocked hypomethylation, recruitment of SP1, and uPA expression. In agreement with our in vitro data, low DNMT1 levels and high uPA were found in intracranial tumors treated with radiation compared to untreated tumors. In conclusion, our data suggest that radiation-mediated hypomethylation triggers uPA expression in meningioma cells

Suppression of uPAR Retards Radiation-Induced Invasion and Migration Mediated by Integrin β1/FAK Signaling in Medulloblastoma

Despite effective radiotherapy for the initial stages of cancer, several studies have reported the recurrence of various cancers, including medulloblastoma. Here, we attempt to capitalize on the radiation-induced aggressive behavior of medulloblastoma cells by comparing the extracellular protease activity and the expression pattern of molecules, known to be involved in cell adhesion, migration and invasion, between non-irradiated and irradiated cells.We identified an increase in invasion and migration of irradiated compared to non-irradiated medulloblastoma cells. RT-PCR analysis confirmed increased expression of uPA, uPAR, focal adhesion kinase (FAK), N-Cadherin and integrin subunits (e.g., α3, α5 and β1) in irradiated cells. Furthermore, we noticed a ∼2-fold increase in tyrosine phosphorylation of FAK in irradiated cells. Immunoprecipitation studies confirmed increased interaction of integrin β1 and FAK in irradiated cells. In addition, our results show that overexpression of uPAR in cancer cells can mimic radiation-induced activation of FAK signaling. Moreover, by inhibiting FAK phosphorylation, we were able to reduce the radiation-induced invasiveness of the cancer cells. In this vein, we studied the effect of siRNA-mediated knockdown of uPAR on cell migration and adhesion in irradiated and non-irradiated medulloblastoma cells. Downregulation of uPAR reduced the radiation-induced adhesion, migration and invasion of the irradiated cells, primarily by inhibiting phosphorylation of FAK, Paxillin and Rac-1/Cdc42. As observed from the immunoprecipitation studies, uPAR knockdown reduced interaction among the focal adhesion molecules, such as FAK, Paxillin and p130Cas, which are known to play key roles in cancer metastasis. Pretreatment with uPAR shRNA expressing construct reduced uPAR and phospho FAK expression levels in pre-established medulloblastoma in nude mice.

Upregulation of PTEN in Glioma Cells by Cord Blood Mesenchymal Stem Cells Inhibits Migration via Downregulation of the PI3K/Akt Pathway

PTEN (phosphatase and tensin homologue deleted on chromosome ten) is a tumor suppressor gene implicated in a wide variety of human cancers, including glioblastoma. PTEN is a major negative regulator of the PI3K/Akt signaling pathway. Most human gliomas show high levels of activated Akt, whereas less than half of these tumors carry PTEN mutations or homozygous deletions. The unique ability of mesenchymal stem cells to track down tumor cells makes them as potential therapeutic agents. Based on this capability, new therapeutic approaches have been developed using mesenchymal stem cells to cure glioblastoma. However, molecular mechanisms of interactions between glioma cells and stem cells are still unknown.In order to study the mechanisms by which migration of glioma cells can be inhibited by the upregulation of the PTEN gene, we studied two glioma cell lines (SNB19 and U251) and two glioma xenograft cell lines (4910 and 5310) alone and in co-culture with human umbilical cord blood-derived mesenchymal stem cells (hUCBSC). Co-cultures of glioma cells showed increased expression of PTEN as evaluated by immunofluorescence and immunoblotting assays. Upregulation of PTEN gene is correlated with the downregulation of many genes including Akt, JUN, MAPK14, PDK2, PI3K, PTK2, RAS and RAF1 as revealed by cDNA microarray analysis. These results have been confirmed by reverse-transcription based PCR analysis of PTEN and Akt genes. Upregulation of PTEN resulted in the inhibition of migration capability of glioma cells under in vitro conditions. Also, wound healing capability of glioma cells was significantly inhibited in co-culture with hUCBSC. Under in vivo conditions, intracranial tumor growth was inhibited by hUCBSC in nude mice. Further, hUCBSC upregulated PTEN and decreased the levels of XIAP and Akt, which are responsible for the inhibition of tumor growth in the mouse brain.Our studies indicated that upregulation of PTEN by hUCBSC in glioma cells and in the nude mice tumors downregulated Akt and PI3K signaling pathway molecules. This resulted in the inhibition of migration as well as wound healing property of the glioma cells. Taken together, our results suggest hUCBSC as a therapeutic agent in treating malignant gliomas

Uncertainty analysis of the use of a retailer fidelity card scheme in the assessment of food additive intake

International audienceThe feasibility of using a retailer fidelity card scheme to estimate food additive intake has been investigated in an earlier study. Fidelity card survey information was combined with information provided by the retailer on levels of the food colour Sunset Yellow (E110) in the foods to estimate a daily exposure to the additive in the Swiss population. As with any dietary exposure method the fidelity card scheme is subject to uncertainties and in this paper the impact of uncertainties associated with input variables including amounts of food purchased, levels of E110 in food, proportion of food purchased at retailer, rate of fidelity card usage, proportion of foods consumed outside of home and bodyweights and with systematic uncertainties has been assessed using a qualitative, deterministic and probabilistic approach. An analysis of the sensitivity of the results to each of the probabilistic inputs was also undertaken. The analysis was able to identify the key factors responsible for uncertainty within the model and demonstrate how the application of some simple probabilistic approaches can be used to quantitatively assess uncertainty

Proton-Binding Sites of Acid-Sensing Ion Channel 1

Acid-sensing ion channels (ASICs) are proton-gated cation channels that exist throughout the mammalian central and peripheral nervous systems. ASIC1 is the most abundant of all the ASICs and is likely to modulate synaptic transmission. Identifying the proton-binding sites of ASCI1 is required to elucidate its pH-sensing mechanism. By using the crystal structure of ASIC1, the protonation states of each titratable site of ASIC1 were calculated by solving the Poisson-Boltzmann equation under conditions wherein the protonation states of all these sites are simultaneously in equilibrium. Four acidic-acidic residue pairs—Asp238-Asp350, Glu220-Asp408, Glu239-Asp346, and Glu80-Glu417—were found to be highly protonated. In particular, the Glu80-Glu417 pair in the inner pore was completely protonated and possessed 2 H+, implying its possible importance as a proton-binding site. The pKa of Glu239, which forms a pair with a possible pH-sensing site Asp346, differs among each homo-trimer subunit due to the different H-bond pattern of Thr237 in the different protein conformations of the subunits. His74 possessed a pKa of ≈6–7. Conservation of His74 in the proton-sensitive ASIC3 that lacks a residue corresponding to Asp346 may suggest its possible pH-sensing role in proton-sensitive ASICs