PubMed Health⌕ Search

Biomedical subjects

Yi Xie

Publications and source records attributed to Yi Xie.

At least 37 records · Page 2Linked to original sources
PubMed2006

Heterostructures with ZnSe sheaths coating on carbon submicrotubes: preparation, characterization, and formation mechanism.

We designed a feasible one-step process to synthesize heterostructures with inorganic functional materials coating on carbon submicrotubes under a mild condition. The heterostructures of carbon submicrotubes with ZnSe sheaths were successfully synthesized through the polymerization-carbonization-coating process with glucose as both the carbon source and the reductive reagent and ammonia providing an alkaline environment and acting as a soft template. The compositions of the as-obtained product were confirmed by Raman spectroscopy and XRD measurement; the morphology and microstructure were studied by SEM, TEM, and HRTEM. Room-temperature photoluminescence (PL) measurement indicates the as-prepared tubular heterostructures have a sharp and well-resolved NBE emission centered at 436 nm besides the DL emission at 589 nm, which is possibly caused by the interface associated with the combination of carbon submicrotube and ZnSe nanocrystal. One of the advantages in this process is that glucose and ammonia play manifold roles in the formation of the submicroscaled tubular heterostructures. This suggests a new path for convenient synthesis of novel tubular heterostructures with inorganic functional materials attached on carbon tubes. Furthermore, this kind of tubular heterostructure may be an ideal system applied in the fabrication of submicroscaled optoelectronics devices, and investigations on its physical properties could extend the understanding of the structure-property relationships in solids, which are in progress.

Journal Article↗
PubMed2006

Identification and characterization of Escherichia coli RS218-derived islands in the pathogenesis of E. coli meningitis.

BACKGROUND: Escherichia coli K1 is the most common gram-negative bacterium causing neonatal meningitis, but the mechanisms by which E. coli K1 causes meningitis are not clear. METHODS: We identified 22 E. coli RS218-derived genomic islands (RDIs), using a comparative genome analysis of meningitis-causing E. coli K1 strain RS218 (O18:K1:H7) and laboratory K-12 strain MG1655. Series of RDI deletion mutants were constructed and examined for phenotypes relevant to E. coli K1 meningitis. RESULTS: We identified 9 RDI deletion mutants (RDI 1, 4, 7, 12, 13, 16, 20, 21, and 22) that exhibited defects in meningitis development. RDI 16 and 21 mutants had profound defects in the induction of a high level of bacteremia in neonatal rats, and RDI 4 mutants exhibited a moderate defect in the induction of bacteremia. RDI 1 and 22 mutants showed defects in the ability to invade human brain microvascular endothelial cells (HBMECs), and RDI 12 mutants were defective in the ability to bind to HBMECs. RDI 13 and 20 mutants were defective in the ability to both bind to and invade HBMECs. RDI 7 mutants were defective in the induction of bacteremia and in the ability to both bind to and invade HBMECs. CONCLUSIONS: These results provide a framework for the future discovery and analysis of bacteremia and meningitis caused by E. coli K1 strain RS218.

Animals↗
PubMed2006

DNA repair gene XRCC3 polymorphisms and cancer risk: a meta-analysis of 48 case-control studies.

The X-ray repair cross-complementing group 3 (XRCC3) is a highly suspected candidate gene for cancer susceptibility. However, association studies on the XRCC3 polymorphisms (4541A>G, Thr(241)Met, 17893A>G) in cancer have shown conflicting results. Therefore, we performed a meta-analysis to better assess the purported associations. Forty eight eligible case-control studies including 24,975 cancer patients and 34, 209 controls were selected for our meta-analysis. Overall, individuals carrying the XRCC3 Met/Met genotype showed a small cancer risk under a recessive genetic model. The subgroup and meta-regression analysis demonstrated different scenarios concerning the XRCC3 Met/Met genotype's role in cancer susceptibility for different subgroups. Specially, there was a significantly increased risk of breast cancer (OR, 1.14; P=0.0004; 95% CI, 1.06-1.23; P=0.37 for heterogeneity), elevated but not significant risk of cancer for head and neck, bladder, surprisingly, a significantly decreased risk of non-melanoma skin cancer (OR, 0.76; P=0.007; 95% CI, 0.62-0.93; P=0.61 for heterogeneity). A significantly elevated risk of cancer was observed in population-based case-control studies but not in nested or hospital based studies. Similarly, we found a significantly increased risk of cancer for A4541G and a decreased risk for A17893G under dominant genetic models. Our meta-analysis results support that the XRCC3 might represent a low-penetrance susceptible gene especially for cancer of breast, bladder, head and neck, and non-melanoma skin cancer. A single larger study should be required to further evaluate gene-gene and gene-environment interactions on XRCC3 polymorphisms and tissue-specific cancer risk in an ethnicity specific population.

Amino Acid Substitution↗
PubMed2006

CTLA4 polymorphisms and ophthalmopathy in Graves' disease patients: association study and meta-analysis.

Studies in the past have clearly established that cytotoxic T-lymphocyte antigen-4 (CTLA4) is a susceptible gene for Graves' disease (GD). However, association studies between the CTLA4 exon-1 +49A/G polymorphism and the risk of developing Graves' ophthalmopathy (GO) in GD patients have revealed conflicting results. In this study, associations of two CTLA4 polymorphisms (+49A/G and CT60) with GD risk and GO susceptibility in GD patients were investigated in a Chinese population. In addition, a meta-analysis was performed to better assess the purported association between the +49A/G polymorphism and GO susceptibility in GD patients. Our results demonstrated that both the +49A/G and CT60 polymorphisms were associated with GD susceptibility in the Chinese population. No significant association with GO susceptibility in GD patients was confirmed regardless of which polymorphism was tested individually. Similarly, the meta-analysis results provided minimal evidence about the role of the +49A/G polymorphism and GO risk in GD patients. Interestingly, haplotypic analysis demonstrated different scenarios concerning the role of CTLA4 in GO susceptibility in the Chinese GD patients. We found that the +49A-CT60G haplotype was marginally statistically associated with the increased risk of GO in GD patients (OR = 1.63, 95%CI 1.00-2.64, p = 0.05). In conclusion, our results suggested that CTLA4 might be involved in the susceptibility to GD in the Chinese population. Although neither +49A/G nor CT60 polymorphism was associated with the risk of GO in GD patients, the haplotypic analysis provided some evidence about its role in GO susceptibility in the Chinese GD patients. We suggest that more association studies recruiting haplotypic analysis should be performed to investigate the role of CTLA4 gene in GO susceptibility in patients from different nations.

Adult↗
PubMed2006

Layer-by-layer films of hemoglobin or myoglobin assembled with zeolite particles: electrochemistry and electrocatalysis.

Positively charged hemoglobin (Hb) or myoglobin (Mb) at pH 5.0 in solutions and negatively charged zeolite particles in dispersions were alternately adsorbed onto solid surfaces forming [zeolite/protein](n) layer-by-layer films, which was confirmed by quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The protein films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV peaks at about -0.35 V vs. SCE at pH 7.0, characteristic of the heme Fe(III)/Fe(II) redox couples. Hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)) in solution were catalytically reduced at [zeolite/protein](7) film modified electrodes, and could be quantitatively determined by CV and amperometry. The shape and position of infrared amide I and II bands of Hb or Mb in [zeolite/protein](7) films suggest that the proteins retain their near-native structure in the films. The penetration experiments of Fe(CN)(6)(3-) as the electroactive probe into these films and scanning electron microscopy (SEM) results indicate that the films possess a great amount of pores or channels. The porous structure of ]zeolite/protein](n) films is beneficial to counterion transport, which is crucial for protein electrochemistry in films controlled by the charge-hopping mechanism, and is also helpful for the diffusion of catalysis substrates into the films. The proteins with negatively charged net surface charges at pH 9.0 were also successfully assembled with like-charged zeolite particles into layer-by-layer films, although the adsorption amount was less than that assembled at pH 5.0. The possible reasons for this were discussed, and the driving forces were explored.

Adsorption↗
PubMed2006

Biomolecule-assisted synthesis and electrochemical hydrogen storage of Bi2S3 flowerlike patterns with well-aligned nanorods.

Bi2S3 flowerlike patterns with well-aligned nanorods were synthesized using a facile solution-phase biomolecule-assisted approach in the presence of L-cysteine (an ordinary and cheap amino acid), which turned out to serve as both the S source and the directing molecule in the formation of bismuth sulfide nanostructures. Emphatically, no nauseous scent (H2S) appeared in our experiments, which could not be avoided in other previous reports. The morphology, structure, and phase composition of the as-prepared Bi2S3 products were characterized using various techniques (scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, selected area electron diffraction, and high-resolution transmission electron microscopy). The formation mechanism for the bismuth sulfide flowerlike assemblies with well-arranged nanorods was also discussed. In addition, other Bi2S3 homogeneous nanostructures (e.g., networklike nanoflakes, nanorod-based bundles, and nanoflakes) were obtained through varying the experimental parameters. Interestingly, we have found that these synthesized bismuth sulfide nanostructures using the biomoleucle-assisted approach could electrochemically charge and discharge with the capacity of 142 (mA h)/g (corresponding to 0.51 wt % hydrogen in single-walled carbon nanotubes) under normal atmosphere at room temperature. A novel two-plateau phenomenon was observed in the synthesized Bi2S3 nanostructures, suggesting that there were two independent steps in the charging process. It has been demonstrated that the bismuth sulfide's morphology and the constant charge-discharge current density had a noticeable influence on their capacity of electrochemical hydrogen storage. These differences in hydrogen storage capacity are likely due to the size and density of space/pores as well as the morphology of different Bi2S3 nanostructures. The novel Bi2S3 nanomaterials may find potential applications in hydrogen storage, high-energy batteries, luminescence, optoelectronic and catalytic fields, as well as in the studies of structure-property relationships. This facile, environmentally benign, and solution-phase biomolecule-assisted method can be potentially extended to the preparation of other metal chalcogenides including FeS, CuS, NiS, PbS, MnS, and CoS nanostructures.

Bismuth↗
PubMed2006

Large-scale fabrication of TiO2 hierarchical hollow spheres.

In this Communication, we report the fabrication of well-crystallized rutile-phase TiO2 hollow spheres using potassium titanium oxalate as the precursor. The spheres exhibited unique three-dimensional hierarchical architectures and demonstrated a significantly improved photocatalytic performance. The synthetic strategy used in this process represents a general approach and therefore may contribute to the formation mechanisms of hollow nanostructures.

Journal Article↗
PubMed2006

Cloning, characterization and subcellular localization of a gene encoding a human Ubiquitin-conjugating enzyme (E2) homologous to the Arabidopsis thaliana UBC-16 gene product.

Ubiquitin charging and activation of class III E2 enzymes has been directly linked to their nuclear import. It has not been published whether other classes E2s also abide by this mechanism. During the large-scale sequencing analysis of a human fetal brain cDNA library, we isolated a cDNA clone that is 2252 base pair in length, encoding a putative 162 amino acid protein, which shares high homology to Arabidopsis thaliana ubiquitin-conjugating enzyme 16 (Accession number NP_565110, 51% identity and 71% similarity) at protein level. Bioinformatics analysis revealed that the gene is composed of 7 exons, located on human chromosome 8q13-8q21.1, and that the predicted protein of the gene is a class I E2, for only composed of a conserved approximately 150-amino acid catalytic core, ubiquitin-conjugating enzyme E2 domain (UBC domain). In the C-terminal of the UBC domain sequence, there are two nuclear localization signals (NLSs). RT-PCR showed that this gene is ubiquitously expressed in 16 kinds of normal human tissues, but expression level is very low, unless in human heart, brain, liver, and pancreas. The subcellular localizations of the new human Ubiquitin conjugating enzyme E2 and its mutation were also examined, which showed that the nuclear localization of hUBC16 depended on two conditions: It has NLS, and at the same time, has enzyme active site, too, at least in HEK293 cells.

Amino Acid Sequence↗
PubMed2006

Analysis of common gene expression patterns in four human tumor cell lines exposed to camptothecin using cDNA microarray: identification of topoisomerase-mediated DNA damage response pathways.

Camptothecin (CPT) is a potent inhibitor of DNA topoisomerase I with a wide spectrum of anti-tumor activity. Relatively little information is available regarding the relation of known topoisomerase-mediated DNA damage with other intracellular pathways. To gain an insight into the intracellular molecular mechanisms of Topoisomerase I inhibitor camptothecin-mediated DNA damage leading to cell death, we used a high-density cDNA microarray to assess sensitive early gene expression profiles in SGC7901 (gastric cancer), Hela (cervical adenocarcinoma), K562 (chronic myelogenous leukemia) and HL60 (promyelocytic leukemia) tumor cells stimulated with camptothecin for 1 h at the concentrations of GI50 (50 % growth inhibition after 24 h of treatment). Analysis of the differentially expressed genes obtained 29 response genes common to all four cell lines. Moreover, these cell lines also shared the direction of regulation. Most of these common response genes were functionally related to cell proliferation or apoptosis, and some of them were involved in ATM (ataxia-telangiectasia mutated) and ATR (ATM-and Rad3 related) checkpoint pathways, JNK (c-Jun N-terminal kinase) pathway, the survival phosphatidylinositol (PI) 3 kinase-Akt-dependent pathway, mitochondrial cell death pathway, endoplasmic reticulum (ER)-related cell death pathway, and to ubiquitin/proteasome dependent protein degradation pathway. The data provides evidence for a linkage between topoisomerase-mediated DNA damage and intracellular signaling events, which may facilitate our understanding of the camptothecin mediated molecular mechanisms of action.

Antineoplastic Agents, Phytogenic↗
PubMed2006

The role of Thr5 in human neuron growth inhibitory factor.

GIF, a member of the metallothionein (MT) family (assigned as MT3), is a neuron growth inhibitory factor that inhibits neuron outgrowth in Alzheimer's disease. The conserved Thr5 is one of the main differences between GIF and other members in the MT family. However, natural sheep GIF has an unusual Ala5, casting doubt on the role of common Thr5. We constructed a series of human GIF mutants at site 5, and characterized their biochemical properties by UV spectroscopy, circular dichroism spectroscopy, EDTA reaction, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) reaction, and pH titration. Their inhibitory activity toward neuron survival and neurite extension was also examined. Interestingly, the T5A mutant exhibited distinct metal thiolate activity in the EDTA and DTNB reactions, and also lost its bioactivity. Meanwhile, the T5S mutant had similar biochemical properties and biological activity as wild-type human GIF, indicating the hydroxyl group on the Thr5 was critical to the bioactivity of human GIF. We suggest the hydroxyl group in human GIF may help stabilize the biologically active conformation. On the other hand, lack of the hydroxyl group in sheep GIF may be partially compensated by its abnormal structure.

Animals↗
PubMed2006

Chromosomal aberrations induced by (12)C6+ ions and 60Co gamma-rays in mouse immature oocytes.

The ovaries of Kun-Ming strain mice (3 weeks) were irradiated with different doses of (12)C6+ ion or (60)Co gamma-ray. Chromosomal aberrations were analyzed in metaphase II oocytes at 7 weeks after irradiation. The relative biological effectiveness (RBE) of (12)C6+ ion was calculated with respect to 60Co gamma-ray for the induction of chromosomal aberrations. The (12)C6+ ion and 60Co gamma-ray dose-response relationships for chromosomal aberrations were plotted by linear quadratic models. The data showed that there was a dose-related increase in frequency of chromosomal aberrations in all the treated groups compared to controls. The RBE values for (12)C6+ ions relative to 60Co gamma-rays were 2.49, 2.29, 1.57, 1.42 or 1.32 for the doses of 0.5, 1.0, 2.0, 4.0 or 6.0 Gy, respectively. Moreover, a different distribution of the various types of aberrations has been found for (12)C6+ ion and 60Co gamma-ray irradiations. The dose-response relationships for (12)C6+ ion and 60Co gamma-ray exhibited positive correlations. The results from the present study may be helpful for assessing genetic damage following exposure of immature oocytes to ionizing radiation.

Animals↗
PubMed2006

Biomolecule-assisted synthesis and electrochemical hydrogen storage of porous spongelike Ni3S2 nanostructures grown directly on nickel foils.

Nanothread-based porous spongelike Ni3S2 nanostructures were synthesized directly on Ni foil by using a simple biomolecule-assisted method. By varying the experimental parameters, other novel Ni3S2 nanostructures could also be fabricated on the nickel substrate. The electrochemical hydrogen-storage behavior of these novel porous Ni3S2 nanostructures was investigated as an example of the potential properties of such porous materials. The thread-based porous spongelike Ni3S2 could electrochemically charge and discharge with the high capacity of 380 mAh g(-1) (corresponding to 1.4 wt % hydrogen in single-walled nanotubes (SWNT)). A novel two-charging-plateaux phenomenon was observed in the synthesized porous spongelike Ni3S2 nanostructures, suggesting two independent steps in the charging process. We have demonstrated that the morphology of the synthesized Ni3S2 nanostructures had a noticeable influence on their electrochemical hydrogen-storage capacity. This is probably due to the size and density of the pores as well as the microcosmic morphology of different nickel sulfide nanostructures. These novel porous Ni3S2 nanostructures should find wide applications in hydrogen storage, high-energy batteries, luminescence, and catalytic fields. This facile, environmentally benign, and solution-phase biomolecule-assisted method can be potentially extended to the preparation of other metal sulfide nanostructures on metal substrates, such as Cu, Fe, Sn, and Pb foils.

Cysteine↗
PubMed2006

Responses of brain and non-brain endothelial cells to meningitis-causing Escherichia coli K1.

Bacterial interaction with specific host tissue may contribute to its propensity to cause an infection in a particular site. In this study, we examined whether meningitis-causing Escherichia coli K1 interaction with human brain microvascular endothelial cells, which constitute the blood-brain barrier, differed from its interaction with non-brain endothelial cells derived from skin and umbilical cord. We showed that E. coli K1 association was significantly greater with human brain microvascular endothelial cells than with non-brain endothelial cells. In addition, human brain microvascular endothelial cells maintained their morphology and intercellular junctional resistance in response to E. coli K1. In contrast, non-brain endothelial cells exhibited decreased transendothelial electrical resistance and detachment from the matrix upon exposure to E. coli K1. These different responses of brain and non-brain endothelial cells to E. coli K1 may form the basis of E. coli K1's propensity to cause meningitis.

Adhesins, Escherichia coli↗
PubMed2006

An ancient balanced polymorphism in a regulatory region of human major histocompatibility complex is retained in Chinese minorities but lost worldwide.

The coding regions of many of the major histocompatibility complex (MHC) (human leukocyte antigen [HLA] in humans) molecules are believed to be subject to balancing selection. But it is less certain whether the regulatory regions of such coding sequences are also subject to the same type of selection. Here, we studied the polymorphism of the regulatory regions of the HLA-DPA1 and HLA-DPB1 genes among ethnic minorities in southwestern China. Phylogenetic analysis revealed two deep clades >10 million years old. There is almost complete linkage disequilibrium between the regulatory and coding regions of HLA-DPA1, which hints at coadaptive balancing selection on the entire region. Thus, the molecular mechanism of balancing selection in MHC may involve expression modulation in addition to coding-region polymorphisms. Although the frequency of clade II is >30% in some ethnic minorities, it decreases to <5% among southern Han Chinese and vanishes among Europeans. As suspected, some ancient balanced polymorphisms, lost in major populations, still exist in isolated ethnicities. These isolated populations may thus contribute disproportionately to the total diversity of modern humans.

Amino Acid Sequence↗
PubMed2006

Loss of primary cilia results in deregulated and unabated apical calcium entry in ARPKD collecting duct cells.

Recent genetic analysis has identified a pivotal role of primary cilia in the pathogenesis of polycystic kidney disease (PKD). However, little is known regarding how cilia loss/dysfunction contributes to cyst development. In epithelial cells, changes in apical fluid flow induce cilia-mediated Ca2+ entry via polycystin-2 (PC2), a cation channel. The Oak Ridge Polycystic Kidney (orpk) mouse contains a mutated Tg737 gene that disrupts expression of polaris, a protein required for ciliogenesis. These studies examine the effect of cilia malformation on Ca2+ entry in orpk cilia(-) collecting duct principal cells, and in orpk cells in which wild-type Tg737 was reintroduced, orpk cilia(+). [Ca2+]i was monitored in confluent cell monolayers using fluorescence microscopy. Intrinsic apical Ca2+ entry was measured by Mn2+ quenching and Ca2+ depletion/readdition under flow conditions below the threshold for stimulation. We found that unstimulated apical Ca2+ entry was markedly increased in cilia(-) cells and was sensitive to Gd3+, an inhibitor of PC2. Electrophysiological measurements demonstrate increased abundance of an apical channel, consistent with PC2, in cilia(-) cells. Immunofluorescence studies revealed that PC2, normally expressed on and at the base of cilia in orpk cilia(+) cells, was observed throughout the apical membrane in cilia(-) cells. Furthermore, cilia(-) cells displayed elevated subapical Ca2+ levels measured with the near-membrane Ca2+ indicator FFP-18. We propose that cilia exert a tonic regulatory influence on apical Ca2+ entry, and absence of cilia results in loss of spatial organization of PC2, causing unregulated Ca2+ entry and elevations in subapical [Ca2+], a factor which may contribute to cyst formation.

Animals↗
PubMed2006

Co-evolutionary analysis of insulin/insulin like growth factor 1 signal pathway in vertebrate species.

Insulin/insulin like growth factor 1 signaling pathway plays an essential role on the regulation of variant, interrelated and fundamental processes, such as metabolism, growth, reproduction and aging. This pathway is highly conserved during evolution. We analyzed eight vertebrate species' insulin/insulin like growth factor 1 pathway and examined the co-evolutionary relationship between different protein components by quantifying similarity of phylogenetic trees. The collected species include Takifugu rubripes, Danio rerio, Xenopus laevis, Gallus gallus, Mus musculus, Rattous norvegicus, Pan troglodytes and Homo sapiens. Results show that interacting proteins in this pathway share highly co-evolutionary relationship while contrarily the proteins without interaction have low co-evolutionary relationship. We also predict some receptor and ligand partners enjoy highly binding potential in corresponding species' pathway.

Animals↗