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X Shi

Publications and source records attributed to X Shi.

At least 271 records · Page 15Linked to original sources
PubMed1998

[Implementing a relatively rigorous algorithm of dynamic EIT problem on the modified FEM model].

We deduced a relatively rigorous algorithm of dynamic EIT problem-general inverse algorithm, and implemented it on the computer FEM model. Images which can show the changing of the resistivity(i.e. dynamic resistivity images) were gained. Also we modified the ordinary FEM model according to the characteristic of the EIT problem and implemented the general inverse algorithm on the modified model. The ill-posed condition of the forward matrix based on the modified model was fairly improved. It can be seen from the results that the general inverse algorithm with modified FEM model is an algorithm better than the back-projection algorithm in terms of object locating, image definition, and the ability of dealing with complex object and noise.

Algorithms↗
PubMed1998

Laboratory evaluation of the reach tooth & gum care toothbrush and three additional manual toothbrushes for subgingival access.

A new laboratory procedure has been developed to evaluate subgingival access efficacy (SAE) of toothbrush bristles using clinical toothbrushing motions and pressure-sensitive paper placed around simulated tooth shapes and gingival tissues under wet brushing conditions. Subgingival access is determined by measuring the maximum distance of the bristle marks from the brushing stroke on the pressure-sensitive paper under the simulated gingival tissues. Four manual toothbrushes (Reach Tooth & Gum Care, Colgate Total Design, Mentadent and Oral-B Advantage) with differing designs, bristle feathering or outside row dimensions were evaluated. Each toothbrush design was evaluated for 28 assessments on anterior and posterior tooth shapes. On overall assessments for subgingival access, the Reach Tooth & Gum Care toothbrush was significantly (p < 0.05-0.001) superior to the other three commercially available toothbrushes tested.

Analysis of Variance↗
PubMed1997

New generation dopaminergic agents. 1. Discovery of a novel scaffold which embraces the D2 agonist pharmacophore. Structure-activity relationships of a series of 2-(aminomethyl)chromans.

A series of 2-(aminomethyl)chromans (2-AMCs) was synthesized and evaluated for their affinity and selectivity for both the high- and low-affinity agonist states (D2High and D2Low, respectively) of the dopamine (DA) D2 receptor. The 7-hydroxy-2-(aminomethyl)chroman moiety was observed to be the primary D2 agonist pharmacophore. The 2-methylchroman moiety was discovered to be an entirely novel scaffold which could be used to access the D2 agonist pharmacophore. Attaching various simple alkyl and arylalkyl side chains to the 7-hydroxy 2-AMC nucleus had significant effects on selectivity for the D2High receptor vs the 5HT1A and alpha 1 receptors. A novel DA partial agonist, (R)-(-)-2-(benzylamino)methyl)chroman-7-ol [R-(-)-35c], was identified as having the highest affinity and best selectivity for the D2High receptor vs the alpha 1 and 5HT1A receptors. Several regions of the 2-AMC nucleus were modified and recognized as potential sites to modulate the level of intrinsic activity. The global minimum conformer of the 7-hydroxy-2-AMC moiety was identified as fulfilling the McDermed model D2 agonist pharmacophoric criteria and was proposed as the D2 receptor-bound conformation. Structure-activity relationships gained from these studies have aided in the synthesis of D2 partial agonists of varying intrinsic activity levels. These agents should be of therapeutic value in treating disorders resulting from hypo- and hyperdopaminergic activity, without the side effects associated with complete D2 agonism or antagonism.

Animals↗
PubMed1997

The surface region of the bifunctional vaccinia RNA modifying protein VP39 that interfaces with Poly(A) polymerase is remote from the RNA binding cleft used for its mRNA 5' cap methylation function.

VP39 is a single-domain, bifunctional viral protein, which acts at both ends of nascent mRNA. At the 5' end, it acts as a cap-specific 2'-O-methyltransferase. At the 3' end, it acts as a poly(A) polymerase processivity factor, requiring its direct association with poly(A) polymerase. Although crystallographic and biochemical data show the catalytic center and associated binding sites for VP39's methyltransferase function to be juxtaposed around a superficial cleft on the protein surface, surface regions required for VP39's mRNA 3' end modifying functions are not known. Here, we identify a surface region that interfaces directly with poly(A) polymerase, taking three independent approaches: (i) development of a direct in vitro dimerization assay, which is applied to numerous VP39 point mutants; (ii) identification of sites within VP39 that become protected from protease cleavage upon dimerization and further mutagenesis based upon these data; (iii) site-specific photo-cross-linking of VP39 to VP55. We find that the dimerization interface lies on a surface region remote from the methyltransferase cleft and contains a 3-5-residue "hot-spot," which is very sensitive to amino acid substitutions. Various other sites within VP39 consistently became hypersensitive to protease cleavage upon interaction with VP55, indicating the occurrence of extensive conformational changes.

Amino Acid Sequence↗
PubMed1997

Calpain contributes to silica-induced I kappa B-alpha degradation and nuclear factor-kappa B activation.

Both silica and lipopolysaccharide (LPS) induce a rapid degradation of I kappa B alpha, an intracellular inhibitor of the nuclear factor (NF)-kappa B transcription factor. In this report, we demonstrate that MG132, a relatively specific proteasome inhibitor, is capable of suppressing LPS-induced I kappa B alpha degradation and NF-kappa B activation in mouse macrophage line RAW 264.7 cells, but is unable to influence the same induction produced by silica. In contrast, the lysosome inhibitor chloroquine has little effect on I kappa B alpha degradation induced by either silica or LPS. In fact, chloroquine enhances the signal-induced nuclear expression of NF-kappa B p50/p65 heterodimer by inhibiting the resynthesis of I kappa B alpha. With the use of transient transfection of a plasmid that expresses calpastatin, a natural inhibitor for calpain, the silica-induced degradation of I kappa B alpha and NF-kappa B activation was attenuated. In contrast, no inhibition of LPS-induced I kappa B alpha degradation and NF-kappa B activation was observed by the overexpression of calpastatin. This suggests that calpain contributes to silica-induced I kappa B alpha degradation and NF-kappa B activation but not to LPS-induced I kappa B alpha degradation and NF-kappa B activation.

Animals↗
PubMed1997

Synthesis of Cr(IV)-GSH, its identification and its free hydroxyl radical generation: a model compound for Cr(VI) carcinogenicity.

Current models of Cr(VI) carcinogenesis suggest an important role for Cr(IV) as an intermediate, toxic, carcinogenic species, but direct chemical evidence has been lacking. This is because Cr(IV) is a highly reactive oxidation state of Cr and few Cr(IV)-based compounds are known that can be used as a model compound containing a biological ligand. This study reports the isolation of such a stable Cr(IV) complex. The Cr(IV)-GSH complex has been synthesized through the reaction of Cr(VI) with GSH. Its electron paramagnetic resonance (EPR) spectrum exhibits g = 1.9629 and a peak-to-peak line width of 480 G in aqueous medium as well as in the powder form. Magnetic susceptibility measurements showed that the compound has a magnetic moment of 2.53 Bohr magneton per Cr, establishing that the Cr ion has two unpaired electrons, hence its identity as Cr(IV). The Cr(IV)-GSH complex is able to generate hydroxyl (.OH) radical in the presence of molecular oxygen in aqueous medium. Catalase inhibited the .OH radical generation while H2O2 enhanced it, indicating that the .OH radical was generated via a Fenton-like reaction, H2O2 being generated as an intermediate in the reduction of molecular oxygen. Metal ion chelators, deferoxamine and 1,10-phenanthroline, attenuated the generation of Cr(IV)-mediated .OH radical. In the case of deferoxamine, a deferoxamine-derived free radical was generated as shown by EPR measurements. The results imply that Cr(IV) may play an important role in the mechanism of Cr(VI)-induced carcinogenesis and Cr(IV)-GSH can be used as a model compound to study the role of Cr(IV) in this mechanism.

Carcinogens↗
PubMed1997

Monoclonal antibodies specific for beta 7 integrin and mucosal addressin cell adhesion molecule-1 (MAdCAM-1) reduce inflammation in the colon of scid mice reconstituted with CD45RBhigh CD4+ T cells.

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is an adhesion protein expressed on endothelium in mucosal tissues that has been shown to play an important role in the selective homing of lymphocytes to intestinal mucosa and associated lymphoid tissue. To determine whether MAdCAM-1 or its ligand alpha 4 beta 7 would be appropriate targets for therapeutic intervention in gut-associated inflammation, we tested the ability of rat mAbs specific for beta 7 integrin and MAdCAM-1 to inhibit chronic colonic inflammation in scid mice reconstituted with CD4+ T cells enriched for the CD45RBhigh subpopulation. Abs specific for beta 7 and MAdCAM-1 blocked recruitment of lymphocytes to the colitic colon, and more importantly, these Abs significantly reduced the severity of colonic inflammatory disease in this animal model. Therefore, the adhesive interactions mediated by alpha 4 beta 7 and MAdCAM are intimately involved in leukocyte recruitment to gut in chronic inflammatory disease and may be relevant therapeutic targets for patients with inflammatory bowel disease.

Animals↗
PubMed1997

One-electron reduction of chromium(VI) by alpha-lipoic acid and related hydroxyl radical generation, dG hydroxylation and nuclear transcription factor-kappaB activation.

Reaction of chromium(VI) with alpha-lipoic acid (reduced form, also called 1,2-dithiolane-3-pentanoic acid) generated Cr(V) and hydroxyl radical (*OH) as measured by electron spin resonance and ESR spin trapping. 5,5-Dimethyl-1-pyrroline was used as a spin trapping agent. Catalase inhibited the *OH generation and enhanced the Cr(V) formation. Superoxide dismutase had an opposite effect. H2O2 enhanced the *OH generation and decreased the Cr(V) formation in a dose-dependent manner. Metal chelators, EDTA, diethylenetriaminepentaacetic acid, deferoxamine, and 1, 10-phenanthroline inhibited *OH radical generation in the order of EDTA > 1,10-phenanthroline > DTPA > deferoxamine. Oxygen consumption measurements indicated that molecular oxygen was used to generate *OH radical in the mixture of Cr(VI) and alpha-lipoic acid. H2O2 and superoxide radical (O2-) were involved as reactive intermediates. The *OH radical was generated via Cr(V)-mediated Fenton-like reaction (Cr(V) + H2O2 --> Cr(VI) + OH- + *OH). HPLC measurements show that the *OH radical generated by this reaction is capable of generating 8-hydroxyl-2'-deoxyguanosine from 2-deoxyguanosine. Incubation of Cr(VI) with cultured Jurkat cells resulted in an activation of DNA binding activity of the nuclear factor (NF)-kappaB. Addition of alpha-lipoic acid enhanced the NF-kappaB activation, while the *OH radical scavenger, sodium formate, inhibited it, showing that alpha-lipoic acid enhanced Cr(VI)-induced NF-kappaB activation via free radical reactions. The results indicate that while alpha-lipoic acid is considered to be an antioxidant, it may be a cellular one-electron Cr(VI) reductant and could be involved in the mechanism of Cr(VI)-induced carcinogenesis.

Antioxidants↗
PubMed1997

Antisense inhibition of silica-induced tumor necrosis factor in alveolar macrophages.

Tumor necrosis factor-alpha (TNFalpha) has been shown to play an important role in the pathogenesis of silicotic fibrosis. In this study, antisense oligonucleotides targeted to TNFalpha mRNA were used to inhibit silica-induced TNFalpha gene expression in alveolar macrophages. To achieve macrophage-specific oligonucleotide delivery, a molecular conjugate consisting of mannosylated polylysine that exploits endocytosis via the macrophage mannose receptor was used. Complexes were formed between the mannosylated polylysine and oligonucleotides and added to the cells in the presence of silica. Enzyme-linked immunoadsorbent assay showed that the complex consisting of the conjugate and antisense oligomer effectively inhibited TNFalpha production, whereas the oligomer alone had much less effect. Reverse transcriptase-polymerase chain reaction analysis revealed that the reduction in TNFalpha secretion was associated with specific ablation of targeted TNFalpha mRNA. The conjugate alone or conjugate complexed with inverted or sense sequence oligonucleotide had no effect. The promoting effect of the conjugate on antisense activity was shown to be due to enhanced cellular uptake of the oligomer via mannose receptor-mediated endocytosis. Cells lacking mannose receptors showed no susceptibility to the conjugate treatment. These results indicate that effective and selective inhibition of macrophage TNFalpha expression can be achieved using the antisense mannosylated polylysine system.

Animals↗
PubMed1997

Tetrandrine inhibits signal-induced NF-kappa B activation in rat alveolar macrophages.

Tetrandrine is a bisbenzylisoquinoline alkaloid isolated from a natural Chinese herbal medicine. While this alkaloid has been shown to exhibit antifibrotic and anti-inflammatory activities, its mechanism of action is unknown. The present study was designed to investigate the inhibitory effect of tetrandrine on NF-kappa B activation in the alveolar macrophage. Three different provocative stimuli were used to activate NF-kappa B in these cells. The results indicate that tetrandrine can inhibit the activation of NF-kappa B and NF-kappa B-dependent reporter gene expression by LPS, PMA, and silica in a dose-dependent manner. In contrast, at the doses used, tetrandrine did not interfere with Sp-1 DNA binding activity or Sp-1-dependent reporter gene expression in these cells. Western blot analysis suggests that the inhibitory effect of tetrandrine on NF-kappa B activation can be attributed to its ability to suppress signal-induced degradation of I kappa B alpha, a cytoplasmic inhibitor of the NF-kappa B transcription factor.

Alkaloids↗
PubMed1997

Reduction of carcinogenic chromium(VI) on the skin of living rats.

The reduction of chromate (Cr(VI)) on the skin of living rats was investigated using the technique of in vivo electron paramagnetic resonance (EPR) spectroscopy with a surface coil resonator. Topical application of aqueous solution of Cr(VI) on the skin of rats generated the transient species, Cr(V). Partial removal of the stratum corneum increased the rates of formation and decay of Cr(V), as well as Cr(V) signal intensity. The results demonstrate that skin represents one route for chromium to enter into animals and humans. The generation of reactive Cr(V) species in the reduction of Cr(VI) by the skin may play an important role in the mechanism of Cr(VI)-induced skin cancer. These findings indicate the potential for in vivo EPR spectroscopy for studying the metabolism of paramagnetic reactive species in chemical and biochemical reactions occurring in/on the skin of both small and large animals, and possibly humans.

Animals↗
PubMed1997

Aryl radical formation during the metabolism of arylhydrazines by microsomes.

Many arylhydrazines are genotoxins, although the mechanism of their genotoxicity is unknown. Previous studies have shown that arylhydrazines are metabolized to arenediazonium ions, which produce C8-arylguanine adducts in DNA suggesting the intermediacy of an aryl radical. Here we have looked for the formation of aryl radicals from arylhydrazines and microsomes by ESR spin trapping. Only hydroxyl radicals are trapped upon incubation of p-methylphenylhydrazine with rat liver microsomes and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, hydroxyl and aryl radicals were trapped upon incubation of p-(methoxymethyl)phenylhydrazine with rat liver microsomes. Evidence for hydroperoxyl radical formation was also obtained. In contrast, when either of these substrates was incubated with microsomes from C5O cells, aryl and hydroxyl radicals were trapped. The ESR signal intensity of the spin-trapped aryl radicals parallels the extent of C8-arylguanine formation in DNA, and therefore, the aryl radical is likely the intermediate responsible for C8-arylguanine adduct formation. Aryl radicals and C8-arylguanine adducts may be related to the genotoxicity of arylhydrazines and related compounds that are oxidatively metabolized to arenediazonium ions, the precursor to aryl radicals, including arylalkyl nitrosamines, arylazo compounds, and triazenes.

Animals↗
PubMed1997

Cellular delivery of oligonucleotides by synthetic import peptide carrier.

PURPOSE: Inefficient cellular uptake and endosomal entrapment are among the obstacles impeding the therapeutic use of oligonucleotides (ONs). The objectives of this study are to investigate the feasibility of utilizing a synthetic import peptide as a drug carrier for cytoplasmic delivery of ONs and to study its transport mechanisms. METHODS: A molecular conjugate consisting of a signal import peptide (IP) derived from Kaposi fibroblast growth factor (K-FGF) and a polycationic ON linker, polylysine (PL), was synthesized and complexed with 5' fluorescently-labeled ON. Complex formation was verified by spectral shift assay and cellular uptake of the ON complex was studied fluorometrically. Microscopic studies were performed to visualize the intracellular distribution of the ON. RESULTS: Cells treated with the ON:IP-PL complex exhibited a dose-dependent increase in ON uptake over free ON-treated controls. The uptake of the complex was shown to occur via an energy-independent, non-endocytic, process since metabolic and endocytic inhibitors and low temperature did not prevent the uptake. Microscopic studies revealed a non-punctate fluorescence pattern, consistent with the non-endocytic transport process. Intense nuclear fluorescence was observed in cells treated with the complex but not with free ON, suggesting enhanced cytoplasmic delivery and nuclear accumulation of the ON by the conjugate. Efficient complex uptake was shown to require both the ON-binding moiety PL and the IP moiety. The delivery system was found to be non-toxic at the concentrations used. CONCLUSIONS: The peptide carrier was effective in promoting the cellular uptake of ON. The mechanism by which the peptide facilitates ON uptake appears to involve a direct translocation of ON via a non-endocytic process. The peptide carrier has the potential to overcome the problem of ON endosomal entrapment and degradation.

Animals↗
PubMed1997

Fructose transport mechanisms in humans.

BACKGROUND & AIMS: The possible mechanisms of fructose transport are diffusion, a disaccharidase-related transport system, and glucose-facilitated fructose transport. However, these mechanisms in the human small intestine have not been systematically examined. This study was designed to investigate the mechanisms of fructose transport in the human duodenojejunum. METHODS: A triple-lumen tube was fluoroscopically positioned in the duodenojejunum of 7 men. Nine carbohydrate-electrolyte solutions were perfused at the rate of 15 mL/min. Acarbose and lactulose were used to examine the disaccharidase-related transport system and glucose-facilitated fructose transport, respectively. RESULTS: Fructose absorption was greater (P < 0.05) from fructose-glucose (FruGlu) and fructose-glucose-acarbose (FruGluA) solutions than from fructose-mannitol (FruMann) and fructose-mannitol-acarbose (FruMannA) solutions, but there was no difference between FruGlu and FruGluA solutions. A sucrose solution produced greater (P < 0.05) sucrose absorption than a sucrose-acarbose solution. Lactulose absorption (0.016-0.039 mmol.h-1.cm-1) was observed from solutions containing glucose or sucrose. Water absorption was not different among sucrose, FruGlu, and glucose solutions. FruMann solution produced net water secretion. These data suggest that free fructose and glucose transport were not inhibited by acarbose and that the presence of glucose induced lactulose absorption and enhanced fructose absorption. CONCLUSIONS: Fructose is transported transcellularly by facilitated diffusion and paracellularly (based on lactulose transport) via glucose-activated solution drag. In the human small intestine, free fructose and glucose transport does not occur via the disaccharidase system.

Acarbose↗
PubMed1997

UVB irradiation alters cellular responses to cytokines: role in extracellular matrix gene expression.

Solar radiation causes cutaneous photodamage characterized by alterations in the quantity and structure of the extracellular matrix. We determined the direct and cytokine-mediated effects of UV irradiation on mRNA levels for two matrix elements, tropoelastin and fibrillin 1. (i) Comparison of normal versus end-stage photodamaged skin failed to reveal differences in these message levels. (ii) Acutely irradiated skin showed suppression of both tropoelastin and fibrillin mRNAs. (iii) UVB irradiation (50 mJ) of cultured skin fibroblasts suppressed fibrillin mRNA by 50%, consistent with a direct effect of radiation. Addition to the cultured fibroblasts of several cytokines upregulated by UVB showed that IL-1alpha had no effect on fibrillin mRNA in unirradiated cells, but in irradiated cells, this cytokine enhanced the suppression of fibrillin mRNA. There were no changes in the message stability, suggesting altered gene transcription. In contrast, UVB had no effect on tropoelastin mRNA levels in cultured fibroblasts, indicating the absence of a direct effect of radiation. IL-1alpha stimulated tropoelastin mRNA 2.8-fold in unirradiated cells, and this stimulation was entirely blocked by UVB. Overall, our results indicate acute suppression of matrix genes by UVB in vivo. The suppression of fibrillin message was a direct effect of UVB on fibroblasts and was augmented by IL-1alpha. Suppression of tropoelastin message by UVB occurred in vitro only in IL-1alpha-stimulated cells. We conclude that UVB substantially alters the pattern of cellular response to cytokines. The interplay between UVB and cytokines is essential to explain the acute responses of matrix genes to UVB in vivo.

Acute Disease↗
PubMed1997

Cdc73p and Paf1p are found in a novel RNA polymerase II-containing complex distinct from the Srbp-containing holoenzyme.

The products of the yeast CDC73 and PAF1 genes were originally identified as RNA polymerase II-associated proteins. Paf1p is a nuclear protein important for cell growth and transcriptional regulation of a subset of yeast genes. In this study we demonstrate that the product of CDC73 is a nuclear protein that interacts directly with purified RNA polymerase II in vitro. Deletion of CDC73 confers a temperature-sensitive phenotype. Combination of the cdc73 mutation with the more severe paf1 mutation does not result in an enhanced phenotype, indicating that the two proteins may function in the same cellular processes. To determine the relationship between Cdc73p and Paf1p and the recently described holoenzyme form of RNA polymerase II, we created yeast strains containing glutathione S-transferase (GST)-tagged forms of CDC73, PAF1, and TFG2 functionally replacing the chromosomal copies of the genes. Isolation of GST-tagged Cdc73p and Paf1p complexes has revealed a unique form of RNA polymerase II that contains both Cdc73p and Paf1p but lacks the Srbps found in the holoenzyme. The Cdc73p-Paf1p-RNA polymerase II-containing complex also includes Gal11p, and the general initiation factors TFIIB and TFIIF, but lacks TBP, TFIIH, and transcription elongation factor TFIIS as well as the Srbps. The Srbp-containing holoenzyme does not include either Paf1p or Cdc73p, demonstrating that these two forms of RNA polymerase II are distinct. In confirmation of the hypothesis that the two forms coexist in yeast cells, we found that a TFIIF-containing complex isolated via the GST-tagged Tfg2p construct contains both (i) the Srbps and (ii) Cdc73p and Paf1p. The Srbps and Cdc73p-Paf1p therefore appear to define two complexes with partially redundant, essential functions in the yeast cell. Using the technique of differential display, we have identified several genes whose transcripts require Cdc73p and/or Paf1p for normal levels of expression. Our analysis suggests that there are multiple RNA polymerase II-containing complexes involved in the expression of different classes of protein-coding genes.

Amino Acid Sequence↗