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Biomedical subjects

Yu Chen

Publications and source records attributed to Yu Chen.

At least 253 records · Page 14Linked to original sources
PubMed2003

[The role of superantigen SEB-induced immunotolerance in the immune privileged site].

AIM: To investigate if the immunological tolerance induced by superantigen staphylococcus enterotoxin B (SEB) takes part in the reaction at the immune privileged site. METHODS: Corneal transplantations were carried out using LEW rats as recipient and F344 rats as the donor. The recipient rats were randomly divided into 5 groups, receiving peribulbar SEB injection of a dosage of 30, 60, 90 or 120 microg/kg 7 days before and after operations. The negative control group received saline injection while the positive control group received glucocorticoid(GC), FK506, CsA or interleukin-1 receptor antagon ist (IL-1ra), respectively. The survival time and rejection index of corneal grafts within 30 days postoperation were examined and recorded using anti-rejection index method. The inflammatory cell infiltration of the recipient cornea and changes of local NK cells were examined by PE-conjugated anti-NK1.1 monoclonal antibody. RESULTS: The grafts in the group receiving injection of 120 microg/kg SEB survived 22 days longer than the negative control group. Their survival time is also significantly longer than the groups treated with FK506, CsA, GC or IL-1ra. The graft rejection index was 3.42+/-2.18 in the rats receiving 120 microg SEB/kg,but 6.58+/-3.15 in the negative control group (P<0.01). The edema and new blood vessel indexes were also significantly reduced. The immunostaining showed that the number of NK cells increased following injection of SEB. CONCLUSION: Injection of SEB reduced the rejection to corneal transplants in rats, showing that the immune tolerance induced by superantigen SEB plays a role in the reaction at the immune privileged site.

Animals↗
PubMed2003

[The characters and gene expression of rice seed proteins].

As an important nitrogen source of human being. The composition, structure and synthesis of rice storage protein were concerned by scientists. Now people know a lot about the structure ,expression patterns of rice glutelin genes. On the basis of these knowledge, we may improve the quality of rice grain and use it to produce foreign proteins. In this paper we summarize the knowledge about rice storage proteins that we have got in these years.

English Abstract↗
PubMed2002

Lefty proteins are long-range inhibitors of squint-mediated nodal signaling.

The regulation of signaling pathways by feedback inhibitors has become an emerging theme in the control of pattern formation during development. Nodal and Lefty proteins belong to divergent subfamilies of the TGF-beta family. Nodal signals promote mesendoderm induction in vertebrates, and Lefty proteins antagonize it. In zebrafish, Squint functions as a long-range Nodal signal during mesoderm induction. We report that the range over which Squint induces mesoderm is reduced by Lefty proteins. In contrast, the activity range of the short-range Nodal signal Cyclops is not regulated by Lefty activity. We present three lines of evidence that Lefty proteins diminish the range of Squint signaling by acting not only as antagonists of Squint autoregulation but also as long-range inhibitors of Squint activity. First, Lefty can block Nodal signaling at a distance. Second, Lefty regulates the range of Squint signaling before regulating squint expression. Third, Lefty restricts the range of Squint activity in squint mutant embryos, in which the endogenous gene is not subject to autoregulation. We also find that Lefty restricts the response to both high and low levels of Nodal signaling. These results indicate that Lefty proteins restrict the activity range of Nodal signals by dampening Nodal signaling in surrounding cells.

Animals↗
PubMed2002

Adaptive calibration for object localization in turbid media with interfering diffuse photon density waves.

The amplitude cancellation method that uses dual out-of-phase sources (a phased array system) can sensitively detect and locate small objects in turbid media. The balance of these two sources is crucial to the system's detection sensitivity and accuracy. We describe a convenient method with which to adaptively calibrate the amplitudes of the two sources at each scanning position by use of low-frequency modulation of the intensity of the in-phase and the antiphase sources. We achieve accurate localization ability of the phased array system by accounting for the influence of asymmetrical boundaries and the heterogeneous background absorption. Experimental data on human breast phantoms demonstrate that localization accuracy within several millimeters has been accomplished through this method.

Calibration↗
PubMed2002

Solid-phase synthesis of imidazo[1,2-a]pyridine using sodium benzenesulfinate as a traceless linker.

[formula: see text] The preparation of the first library of imidazo[1,2-a]pyridine derivatives on a solid support is described. A sulfone linker strategy was applied in the synthesis. Key steps involved in the solid-phase synthetic procedure include (i) alpha-haloketone resin formation by sulfinate-->sulfone alkylation, (ii) imidazo[1,2-a]pyridine ring formation by treatment with 2-aminopyridine, (iii) sulfone anion alkylation, and (iv) traceless product release by oxidation-elimination. A library of 12 imidazo[1,2-a]pyridines was synthesized.

Journal Article↗
PubMed2002

Synthesis and optical limiting properties of axially bridged phthalocyanines: [(tBu4PcGa)2O] and [(tBu4PcIn)2O].

Highly soluble [(tBu(4)PcM)(2)O] phthalocyanine dimers (M=Ga(III) (3), In(III) (4)) were prepared by the reaction of [tBu(4)PcMCl] (M=Ga(III) (1), In(III) (2)) with excess of concentrated H(2)SO(4) at -20 degrees C. The Mbond;Obond;M linkages in 3 and 4 are not stable against concentrated H(2)SO(4) at room temperature, 6 n HCl at reflux, or during isolation under column chromatographic conditions (e.g. silica gel/toluene). The stability of 3 in solution is considerably higher than that of 4. The mu-oxo-bridged phthalocyanine dimers 3 and 4 have a more intense photoluminescence emission in the red region than the monomers 1 and 2. The gallium phthalocyanines 1 and 3 have fluorescence lifetimes of a few nanoseconds, while those of the indium phthalocyanines 2 and 4 last for only several hundred picoseconds. Comparison of the fluorescence lifetimes of monomers 1 and 3 with dimers 2 and 4, reveals that the dimers have longer lifetimes of the excited singlet states. The transient absorption spectrum is similar for all of the compounds, and the transient absorption band at about 520 nm, observed by nanosecond laser irradiation, can be assigned to the transition from the lowest triplet excited state to the upper triplet excited states (T-T absorption). The magnitude of the optical limiting exhibited by 1, 2, 3, and 4 in toluene at 532 nm laser pulse irradiation is in the order: 4>3>2>1 [corrected]. The values of the imaginary third-order nonlinear susceptibility Im[chi((3))] of the above compounds at 532 nm in toluene are also reported. These results demonstrate that these compounds are candidates for optical limiting applications.

Journal Article↗
PubMed2002

Intramolecular quenching of tryptophan fluorescence by the peptide bond in cyclic hexapeptides.

Intramolecular quenching of tryptophan fluorescence by protein functional groups was studied in a series of rigid cyclic hexapeptides containing a single tryptophan. The solution structure of the canonical peptide c[D-PpYTFWF] (pY, phosphotyrosine) was determined in aqueous solution by 1D- and 2D-(1)H NMR techniques. The peptide backbone has a single predominant conformation. The tryptophan side chain has three chi(1) rotamers: a major chi(1) = -60 degrees rotamer with a population of 0.67, and two minor rotamers of equal population. The peptides have three fluorescence lifetimes of about 3.8, 1.8, and 0.3 ns with relative amplitudes that agree with the chi(1) rotamer populations determined by NMR. The major 3.8-ns lifetime component is assigned to the chi(1) = -60 degrees rotamer. The multiple fluorescence lifetimes are attributed to differences among rotamers in the rate of excited-state electron transfer to peptide bonds. Electron-transfer rates were calculated for the six preferred side chain rotamers using Marcus theory. A simple model with reasonable assumptions gives excellent agreement between observed and calculated lifetimes for the 3.8- and 1.8-ns lifetimes and assigns the 1.8-ns lifetime component to the chi(1) = 180 degrees rotamer. Substitution of phenylalanine by lysine on either side of tryptophan has no effect on fluorescence quantum yield or lifetime, indicating that intramolecular excited-state proton transfer catalyzed by the epsilon-ammonium does not occur in these peptides.

Algorithms↗
PubMed2002

S-nitrosothiols react preferentially with zinc thiolate clusters of metallothionein III through transnitrosation.

Metallothionein (MT) is a two-domain protein with zinc thiolate clusters that bind and release zinc depending on the redox states of the sulfur ligands. Since S-nitrosylation of cysteine is considered a prototypic cellular redox signaling mechanism, we here investigate the reactions of S-nitrosothiols with different isoforms of MT. MT-III is significantly more reactive than MT-I/II toward S-nitrosothiols, whereas the reactivity of all three isoforms toward reactive oxygen species is comparable. A cellular system, in which all three MTs are similarly effective in protecting rat embryonic cortical neurons in primary culture against hydrogen peroxide but where MT-III has a much more pronounced effect of protecting against S-nitrosothiols, confirms this finding. MT-III is the only isoform with consensus acid-base sequence motifs for S-nitrosylation in both domains. Studies with synthetic and zinc-reconstituted domain peptides demonstrate that S-nitrosothiols indeed release zinc from both the alpha- and the beta-domain of MT-III. S-Nitrosylation occurs via transnitrosation, a mechanism that differs fundamentally from that of previous studies of reactions of MT with NO*. Our data demonstrate that zinc thiolate bonds are targets of S-nitrosothiol signaling and further indicate that MT-III is biologically specific in converting NO signals to zinc signals. This could bear importantly on the physiological action of MT-III, whose biological activity as a neuronal growth inhibitory factor is unique, and for brain diseases that have been related to oxidative or nitrosative stress.

Amino Acid Sequence↗
PubMed2002

Detection limit enhancement of fluorescent heterogeneities in turbid media by dual-interfering excitation.

We report on a quantitative comparison between the single-source and the dual-interfering-source configurations for the detection of fluorescent heterogeneities embedded in a piecewise highly scattering homogeneous fluorescent background. The study is based on simulations with analytical solutions of the frequency-domain fluorescent diffuse photon density waves and practical signal-to-noise ratio considerations. Results show that dual-interfering sources outperform single-source techniques for the detection of heterogeneities in terms of fluorophore concentration and lifetime contrast. To detect the same inhomogeneity, less concentration and lifetime contrast is required with dual-interfering sources.

Coloring Agents↗
PubMed2002

Identification of human uroplakin II promoter and its use in the construction of CG8840, a urothelium-specific adenovirus variant that eliminates established bladder tumors in combination with docetaxel.

Uroplakins (UPs) are a group of integral membrane proteins that are synthesized as the major differentiation products of mammalian urothelium. UPII gene expression is bladder specific and differentiation dependent, but very little is known about its transcription response elements. To identify the promoter elements, a DNA fragment of 2239 bp upstream of the UPII gene was amplified by PCR and linked to a promoterless firefly luciferase reporter gene. Transient transfection experiments showed that the DNA segment located between -1809 and +1 bp resulted in preferential expression in bladder carcinoma cells with negligible expression in nonurothelial cells. This promoter was engineered into adenovirus (Ad) type 5 to drive the expression of the E1A and E1B genes and to create an attenuated replication-competent Ad variant, termed CG8840. Viral replication and the cytopathic effect of CG8840 were evaluated by virus yield and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays in bladder transitional cell carcinoma (TCC) cell lines RT4 and SW780; nonbladder cancer cell lines G361 (melanoma), LNCaP (prostate cancer), PA-1 (ovarian cancer), and U118 (brain cancer); and human primary cells including lung fibroblasts, bladder smooth muscle cells, and mammary epithelial cells. CG8840 replicated in and eliminated bladder TCC efficiently with high specificity (10,000:1) in comparison with nonbladder cells. The antitumor activity of CG8840 was examined in BALB/c nu/nu mice carrying s.c. human TCC xenografts. Intratumoral and i.v. administration of CG8840 in RT4 human bladder cancer xenografts caused significant (P < 0.01) inhibition of tumor growth. Synergistic antitumor efficacy was observed when CG8840 was combined with docetaxel, resulting in significant regression of RT4 bladder cancer xenograft tumors within 6 weeks after i.v. administration of CG8840 (3.33 x 10(9) plaque-forming units/animal on day 1) and docetaxel (20 mg/kg on days 2, 6, and 9). These results demonstrate the utility of the UPII promoter in the generation of urothelium-specific adenoviral vectors and provide a potential foundation for the development of bladder tumor-specific oncolytic viral therapies.

Adenovirus E1B Proteins↗
PubMed2002

Real-coded lattice gas model for ternary amphiphilic fluids.

We have developed an amphiphilic surfactant model in the framework of the real-coded lattice gas (RLG), in order to analyze the dynamics and structure of ternary fluids. Formation of both the oil-in-water and the bicontinuous microemulsion phases, as well as the reduction of surface tension by adsorption of surfactant at interface are successfully reproduced in numerical simulations. Our model is simple in terms of description and implementation, however, complex structures and dynamic behavior of the ternary fluids emerge from the collective dynamics of the RLG and surfactant particles.

Journal Article↗
PubMed2002

In vivo analysis of human multidrug resistance protein 1 (MRP1) activity using transient expression of fluorescently tagged MRP1.

The multidrug resistance protein 1 (MRP1) contributes cellular resistance to a wide array of physiological toxins and chemotherapeutic agents. Its in vivo activity has been studied primarily in cells that have been continuously drug selected, culture conditions that might confound the effects of MRP1 expression with the effects of a cell's detoxification machinery. Transient transfection with a MRP1-green fluorescent protein (EGFP) fusion protein allowed us to measure the activity of MRP1 in cells that had insufficient time to induce other chemoprotective proteins. Furthermore, separate transfections with MRP1-yellow fluorescent protein and a fluorescently tagged P-glycoprotein (MDR1-cyan fluorescent protein) permitted the drug-resistant properties of MRP1-expressing cells to be compared with those of MDR1-expressing cells. Our data showed that the expression of MRP1-EGFP results in significantly decreased cellular accumulation of tetramethylrhodamine ethyl ester (TMRE) and daunorubicin, mildly decreased cellular accumulation of mitoxantrone, and decreased nuclear accumulation of doxorubicin. Additionally, MRP1-EGFP expression protected cells from the microtubule depolymerization caused by vincristine and colchicine, but not by vinblastine.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Role of flow cytometry in the diagnosis of lymphadenopathy in children.

To evaluate the combination of fine-needle aspiration (FNA) and flow cytometric immunophenotyping (FCI) in the diagnosis of lymphadenopathy in children, we reviewed a total of 71 FNA specimens from pediatric patients with persistent lymphadenopathy. Two cases were deemed inadequate. In the remaining 69 cases, 54 (78%) were diagnosed as benign lesions, 9 (13%) as Hodgkin's lymphoma, 4 (6%) as non-Hodgkin's lymphoma or leukemic infiltrate, and 2 as metastatic tumors. Of the 69 cases, 25 cases (38%) were diagnosed based on cytomorphology alone, 30 (43%) by combined cytomorphology and FCI, and 19 (28%) by surgical biopsy. In conclusion, FNA is an easy, safe, and reliable procedure in the diagnosis of lymphadenopathy in children. In difficult cases, FCI can be used to exclude non-Hodgkin's lymphomas.

Adolescent↗
PubMed2002

High frequency of promoter hypermethylation of RASSF1A and p16 and its relationship to aflatoxin B1-DNA adduct levels in human hepatocellular carcinoma.

Epigenetic changes in gene expression due to extensive CpG island methylation is now accepted as the main cause of inactivation of the p16 gene. More recently, it has been suggested that the human ras association domain family (RASSF) 1 gene, cloned from the lung tumor-suppressor locus 3p21.3, also may be inactivated by methylation. It consists of two major alternative transcripts, RASSF1A and RASSF1C. Epigenetic inactivation of isoform A was observed in several carcinomas and tumor cell lines. In this study, promoter hypermethylation of RASSF1A and p16 was investigated in 83 hepatocellular carcinoma (HCC) tissue samples from Taiwan and in two HCC cell lines (Hep3B and HepG2). High frequencies (85% and 47%, respectively) of methylation of the CpG island promoters of RASSF1A and p16 were found in the HCC tissues. The methylation of RASSF1A also was detected in Hep3B cells but not in HepG2 cells; p16 was not methylated in either cell line. Methylation status was determined in 12 normal control liver tissues and 10 adjacent nontumor tissues. No methylation was found in normal liver control tissues for both RASSF1A and p16; methylation was detected in one of 10 and seven of 10 adjacent nontumor tissue sampless for p16 and RASSF1A, respectively, in subjects with positive tumors. These data indicate that aberrant methylation of the CpG island promoters of both genes is a frequent occurrence in hepatocarcinogenesis. The high frequency of RASSF1A methylation in adjacent tissues suggests that this may be an early event. The relationship between methylation status and clinical parameters and tumor markers, including DNA damage resulting from aflatoxin B(1) (AFB(1)), an environmental carcinogen, and p53 status, also was analyzed. A statistically significant association was found between RASSF1A methylation status and the level of AFB(1)-DNA adducts in tumor tissues. No association was found between methylation status and p53 status. These results suggest the hypothesis that exposure to environmental carcinogens may be involved in altered methylation of genes involved in cancer development.

Aflatoxin B1↗
PubMed2002

The myelodysplastic syndromes: analysis of prognostic factors and comparison of prognostic systems in 128 Chinese patients from a single institution.

INTRODUCTION: Although retrospective analysis were frequently undertaken, and many prognostic systems for myelodysplastic syndromes (MDS) have been proposed worldwide, few such studies have been performed and the effectiveness of different scoring systems have not yet been verified in independent patient populations in China. The aim of this single center study was to evaluate the prognostic factors and compare the prognostic scoring systems in Chinese patients with MDS. MATERIALS AND METHODS: One hundred and twenty-eight patients diagnosed as primary MDS in our Institution were studied retrospectively to identify significant prognostic factors and to assess the predictive value of 11 previously described prognostic systems, including French-American-British (FAB) classification, World Health Organization (WHO) classification, Mufti, Sanz, Morra, Aul, Oguma, Toyama, Morel and international prognostic scoring system (IPSS). RESULTS: The median age of the patients was 50 years (range 13-82). The 2- and 5-year survival rate of the patients were 55.22+/-4.90% and 26.09+/-6.36% respectively, with a median survival of 31 months (range 1-127 months). Fifty patients (39.1%) had progressed to acute leukemia (AL) with a median time of 8 months (range 1-43 months). Major independent variables indicated by multivariate analysis were the percentage of bone marrow (BM) blast cells and complex karyotype aberrations for survival (P=0.042 and 0.042, respectively) and only the percentage of BM blast cells for AL transformation (P=0.023). All the systems except Mufti scores successfully discriminated risk groups concerning both survival and AL evolution, especially in the high risk group, ranging from 10 to 20 months and from 4 to 7 months, respectively. The FAB and WHO classification, as well as Sanz, Oguma, Morel and IPSS possessed lower P value (P<0.0001) than that of the rest scoring systems. CONCLUSION: The patients in our study were younger than these of the Western population, whereas the survival and AL transformation ratio were comparable to these previous studies. The BM blast proportion and complex chromosomal defects were highly significant for predicting outcome in MDS patients. Most investigated systems effectively stratified patients into groups with different life expectancies and identified a subset of patients with poor clinical outcome. The FAB, WHO classification, as well as Sanz, Oguma, Morel and IPSS scoring systems were more applicable for predicting survival and leukemia progression.

Adolescent↗
PubMed2002

Analysis on performance and optimization of frequency-domain near-infrared instruments.

Frequency-domain near-infrared techniques have been widely used to detect the optical properties of biological tissues noninvasively. In this paper we propose an analytical model to evaluate the performance of frequency-domain instruments. Based on the diffusion equation and the transfer properties of optoelectronic components, we treat all parts, including the medium, as two-port networks and apply systematic methods to answer questions concerning frequency-domain instruments. Experiments show that this method can reasonably reflect the properties of the instrument within an accuracy of 7%. This kind of method can be used to design suitable instruments for various applications. We also analyze the selection of the instrument parameters to achieve optimal performance at an efficient cost using this analytical model.

Fiber Optic Technology↗
PubMed2002

Magnets on ears helped diabetics.

Magnets were attached on auricular acupuncture points of diabetes patients. This treatment lowered the blood glucose levels and improved eye conditions.

Acupuncture Points↗