Biomedical subjects

Xiang Zhang

Publications and source records attributed to Xiang Zhang.

At least 55 records · Page 3Linked to original sources

PubMed2005

Data pre-processing in liquid chromatography-mass spectrometry-based proteomics.

MOTIVATION: In a liquid chromatography-mass spectrometry (LC-MS)-based expressional proteomics, multiple samples from different groups are analyzed in parallel. It is necessary to develop a data mining system to perform peak quantification, peak alignment and data quality assurance. RESULTS: We have developed an algorithm for spectrum deconvolution. A two-step alignment algorithm is proposed for recognizing peaks generated by the same peptide but detected in different samples. The quality of LC-MS data is evaluated using statistical tests and alignment quality tests. AVAILABILITY: Xalign software is available upon request from the author.

Algorithms↗

PubMed2005

Preparation of [5,6]- and [6,6]-oxahomofullerene derivatives and their interconversion by Lewis acid assisted reactions of fullerene mixed peroxides.

[60]Fullerene mixed peroxides C60(O)(OOtBu)4 exhibit chemo- and regioselective reactions under mild conditions. The epoxy moiety is opened by ferric chloride to form vicinal hydroxy chloride C60Cl(OH)(OOtBu)4. BF3 is also effective in opening the epoxy moiety. The O-O bond of the fullerene mixed peroxide is cleaved by aluminum chloride to form both [5,6]- and [6,6]-fullerene hemiketals (oxohomo[60]fullerenes). A Hock-type rearrangement is proposed for the formation of the hemiketals, in which a fullerene C-C bond is cleaved. Lewis acids and/or visible light can initiate isomerization of the hemiketal isomers. Single-crystal X-ray analysis and theoretical calculations confirmed the results.

Journal Article↗

PubMed2005

Investigation of radical cation in electrophilic fluorination by ESI-MS.

Reaction solutions of selectfluor (1) with triphenylethylene (4a) and tetraphenylethylene (4b) were monitored by ESI-MS and ESI-MS/MS. Detection and characterization of the key radical cationic intermediates 5a.+ and 5b.+) fully supports the SET mechanism in electrophilic fluorination as depicted above. [reaction: see text]

Journal Article↗

PubMed2005

Semiclassical model of stimulated Raman scattering in photonic crystals.

We study the stimulated Raman scattering (SRS) of light from an atomic system embedded in a photonic crystal and coherently pumped by a laser field. In our study, the electromagnetic field is treated classically and the atomic system is described quantum mechanically. Considering a decomposition of the pump and Stokes fields into the Bloch modes of the photonic crystals and using a multiscale analysis, we derive the Maxwell-Bloch equations for SRS in photonic crystals. These equations contain effective parameters that characterize the SRS gain, the nonlinear atomic response to the electromagnetic field, and the group velocity and that can be calculated in terms of the Bloch modes of the unperturbed photonic crystal. We show that if the pump laser frequency is tuned near a photonic band edge and the atomic system is carefully chosen such that the Stokes mode matches another photonic band edge, low-threshold, enhanced Raman amplification is possible. Possible physical realizations of SRS in photonic crystals are also discussed.

Journal Article↗

PubMed2005

[Research on relationship of survivin gene expression with malignant proliferation and apoptosis of brain glioma].

OBJECTIVE: To investigate the expression level of inhibitor of apoptosis protein survivin gene in human brain glioma and its role in malignant proliferation and antiapoptosis of brain glioma. METHODS: Eighty-three cases of brain glioma specimen was chosen, protein expression of survivin and proliferating cell nuclear antigen (PCNA) was investigated by immunohistochemistry streptavidin-biotin complex (SABC) method, the immunoreactivity score (IRS) of survivin and the proliferative index (PI) were counted. Apoptotic cells were screened by TdT-mediated dUTP-biotin nick-end labeling (TUNEL) method, and the apoptotic index (AI) of brain glioma was calculated. RESULTS: The survivin IRS, PI and AI of brain glioma were 3.8 +/- 3.9, (28.4 +/- 19.5)% and (1.0 +/- 0.8)% respectively, and all of them were elevated with the increase of pathological grade of brain glioma (P < 0.01 for all). PI in survivin positive group was significantly higher than that in survivin negative group (P < 0.01), and PI was positively correlated with survivin IRS (r = 0.740, P < 0.01). There was no significant difference between AI in survivin positive group and that in survivin negative group (P > 0.05), however, AI was negatively correlated with survivin IRS (r = -0.307, P < 0.01). CONCLUSIONS: Survivin is overexpressed in brain glioma, and which may play important roles in malignant proliferation and antiapoptosis of brain glioma.

Adolescent↗

PubMed2005

[Neuroendoscope-assisted endonasal-transsphenoidal surgery for pituitary neoplasms].

OBJECTIVE: To evaluate the effect of curative effect of endonasal transsphenoidal approach for removal of pituitary neoplasms (PNs) assisted by neuroendoscopy. METHODS: Seventy-eight consecutive PNs patients with sellar mass causing compression of optic nerve and optic chiasm shown by MRI or CT underwent tumor removal via the endonasal transsphenoidal approach with the help of neuroendoscope. RESULTS: Total removal of tumor in 71 cases (91.0%) and subtotal removal in 5 cases (6.4%) were achieved. Partial removal was carried out in the remaining 2 cases (2.6%) with fibrous tumor. There was no postoperative death. Follow-up with a median of 3 months in 67 patients revealed that preoperative diminished acuity caused by optic nerve compression was recovered in 64 cases (95.5%), and improved in 3 cases (4.5%). Among the 62 patients with preoperative visual field defects, postoperative recovery was achieved in 60 cases (96.8%), and improvement in 2 cases (3.2%). CONCLUSION: Endonasal transsphenoidal approach assisted by neuroendoscopy is an effective minimally invasive method for removing the PNs. Changing the angle of the endoscope intraoperatively helps removing the tumor safely and completely.

Adult↗

PubMed2005

Sub-diffraction-limited optical imaging with a silver superlens.

Recent theory has predicted a superlens that is capable of producing sub-diffraction-limited images. This superlens would allow the recovery of evanescent waves in an image via the excitation of surface plasmons. Using silver as a natural optical superlens, we demonstrated sub-diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength. By proper design of the working wavelength and the thickness of silver that allows access to a broad spectrum of subwavelength features, we also showed that arbitrary nanostructures can be imaged with good fidelity. The optical superlens promises exciting avenues to nanoscale optical imaging and ultrasmall optoelectronic devices.

Journal Article↗

PubMed2005

Theoretical studies on the mechanism of acid-promoted hydrolysis of N-formylaziridine in comparison with formamide.

[reaction: see text] We present an ab initio study of the acid-promoted hydrolysis reaction mechanism of N-formylaziridine in comparison with formamide. Since the rate of amide hydrolysis reactions depends on the formation of the tetrahedral intermediate, we focused our attention mainly on the reactant complex, the tetrahedral intermediate, and the transition state connecting these two stationary points. Geometries were optimized using the density functional theory, and the energetics were refined using ab initio theory including electron correlation. Solvent effects were investigated by using polarizable continuum method calculations. The proton-transfer reaction between the O-protonated and N-protonated amides was investigated. In acidic media, despite that the N-protonated species is more stable than the O-protonated one, it is predicted that both N-protonated and O-protonated pathways compete in the hydrolysis reaction of N-formylaziridine.

Journal Article↗

PubMed2005

Altered expression patterns of metabotropic glutamate receptors in diffuse brain injury.

The metabotropic glutamate receptors (mGluRs), as one of the newly found glutamate receptors, play an important role in the physiological processes of the central nervous system. The authors examined the changes of expression patterns of mGluRs after diffuse brain injuries (DBI) in rats. DBI was produced by Marmarou's methods. The mRNA expression of mGluRs was detected by hybridization in situ at different time points after brain injuries. Compared with normal control and sham-operated control, the animals with DBI showed a significantly increased expression of group I and group III mGluRs (except mGluR6, P<0.05). The increased peak of group I appeared at 24 h after injuries and group III at 6 h after injuries. While, group II mGluRs decreased after DBI (P<0.05) and the lowest point occurred at 48 h after DBI. The difference of time sequence of the expression alterations between group I and group III mGluRs may reflect a self-protection first mechanism of the damaged neurons. It may provide new insight for the development of new pharmaceuticals in the treatment of DBI.

Animals↗

PubMed2005

Cartilage biomarkers in ankylosing spondylitis: relationship to clinical variables and treatment response.

OBJECTIVE: Ankylosing spondylitis (AS) is a progressive disease in which chronic inflammation can lead to extensive new bone formation throughout the spine. At present, few measures of the activity or extent of the disease are available. In this study, we sought to determine whether markers of cartilage synthesis and degradation could provide such quantitative measures. METHODS: Serum samples from 23 patients receiving infliximab treatment for AS were obtained at baseline and at weeks 2, 6, 14, and 22. Patients were stratified with respect to joint involvement and baseline levels of inflammatory markers, and responders were defined according to the Assessments in Ankylosing Spondylitis 20% criteria. Serial measurements of interferon-gamma, tumor necrosis factor alpha, transforming growth factor beta (TGFbeta), interleukin-10 (IL-10), and IL-1 were done at each time point. The following biomarkers were measured by enzyme-linked immunosorbent assay: the proteoglycan aggrecan 846 epitope, a marker of cartilage turnover; C-propeptide of type II collagen (CPII), a biosynthesis marker; and the Col2-3/4(long mono) (C2C) and Col2-3/4(short) (C1-2C) neoepitopes, reflecting collagen cleavage of type II collagen and type I/type II collagen, respectively. RESULTS: At baseline, patients with AS demonstrated significant elevations in serum levels of CPII, the 846 epitope, and the CPII-to-C2C (CPII:C2C) ratio (but not C2C or C1-2C) compared with normal controls. Of the biomarkers examined, only CPII:C2C showed a correlation with the C-reactive protein (CRP) level. Among the biomarker-cytokine relationships, TGFbeta demonstrated a trend toward a positive correlation with the 846 epitope. CONCLUSION: In AS, elevated serum levels of CPII and the 846 epitope may be related to biosynthetic turnover of hyaline cartilage and the intervertebral discs but may also reflect progressive bone formation as a result of endochondral ossification. The correlation of the CPII:C2C ratio with CRP suggests that the CPII:C2C ratio might prove to be a useful marker of disease activity in AS.

Adult↗

PubMed2005

Innate immunity and arthritis: neutrophil Rac and toll-like receptor 4 expression define outcomes in infection-triggered arthritis.

OBJECTIVE: The role of innate immunity in Chlamydia-induced arthritis has not been defined. The purpose of this study was to examine the role of neutrophils in experimental arthritis in mice with targeted elimination of the small GTPases Rac1 and Rac2, as well as the role of Toll-like receptors (TLRs) in this model. METHODS: Arthritis was induced by intraarticular inoculation of synoviocyte-packaged Chlamydia trachomatis. The degree of arthritis was assessed according to joint swelling and pathology scores. The persistence of Chlamydia in joints was assessed by immunoassay. The expression of TLR-2 and TLR-4 in neutrophils was detected by semiquantitative reverse transcription-polymerase chain reaction. RESULTS: In the acute phase, wild-type mice developed more severe arthritis than did Rac-deficient mice, with abundant infiltration of neutrophils into the joint. In the chronic phase, the Rac-deficient mice developed more severe arthritis and demonstrated defective clearance of the pathogen from the joint. In vitro stimulation of neutrophils with Chlamydia up-regulated the expression of TLR-4, but not TLR-2, in wild-type mice. However, neutrophils from Rac-deficient mice did not show this up-regulation of TLR-4. Sustained TLR-4 expression in neutrophils was found to be dependent on the expression of Rac. Mice genetically deficient in TLR-4 demonstrated more severe arthritis than did the controls. Thus, Rac expression plays a profound role in infection-triggered arthritis and demonstrates a bimodal influence on the disease process, exacerbating acute joint inflammation but controlling chronic arthritis. Rac deficiency was associated with diminished TLR-4 expression, impaired host clearance of the pathogen, and more severe chronic arthritis. CONCLUSION: In infection-triggered arthritis, innate immunity plays a critical role. Effective host clearance of an arthritogenic pathogen depends on intact expression of Rac and appropriate expression of TLR-4 by neutrophils.

Animals↗

PubMed2005

Identification of natural compounds with antiviral activities against SARS-associated coronavirus.

More than 200 Chinese medicinal herb extracts were screened for antiviral activities against Severe Acute Respiratory Syndrome-associated coronavirus (SARS-CoV) using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay for virus-induced cytopathic effect (CPE). Four of these extracts showed moderate to potent antiviral activities against SARS-CoV with 50% effective concentration (EC50) ranging from 2.4 +/- 0.2 to 88.2 +/- 7.7 microg/ml. Out of the four, Lycoris radiata was most potent. To identify the active component, L. radiata extract was subjected to further fractionation, purification, and CPE/MTS assays. This process led to the identification of a single substance lycorine as an anti-SARS-CoV component with an EC50 value of 15.7 +/- 1.2 nM. This compound has a CC50 value of 14980.0 +/- 912.0 nM in cytotoxicity assay and a selective index (SI) greater than 900. The results suggested that four herbal extracts and the compound lycorine are candidates for the development of new anti-SARS-CoV drugs in the treatment of SARS.

Amaryllidaceae Alkaloids↗

PubMed2005

An automated method for the analysis of stable isotope labeling data in proteomics.

An algorithm is presented for the generation of a reliable peptide component peak table from liquid chromatography-mass spectrometry (LC-MS) and subsequent quantitative analysis of stable isotope coded peptide samples. The method uses chemical noise filtering, charge state fitting, and deisotoping toward improved analysis of complex peptide samples. Overlapping peptide signals in mass spectra were deconvoluted by correlation with modeled peptide isotopic peak profiles. Isotopic peak profiles for peptides were generated in silico from a protein database producing reference model distributions. Doublets of heavy and light labeled peak clusters were identified and compared to provide differential quantification of pairs of stable isotope coded peptides. Algorithms were evaluated using peptides from digests of a single protein and a seven-protein mixture that had been differentially coded with stable isotope labeling agents and mixed in known ratios. The experimental results correlated well with known mixing ratios.

Algorithms↗

PubMed2005

Mass spectrometric studies of the gas phase retro-Michael type fragmentation reactions of 2-hydroxybenzyl-N-pyrimidinylamine derivatives.

The gas-phase fragmentation reactions of 2-hydroxybenzyl-N-pyrimidinylamine derivatives (Compounds 1 to 6), the O-N-type acid-catalyzed Smiles rearrangement products of 2-pyrimidinyloxy-N-arylbenzylamine derivatives, have been examined via positive ion matrix-assisted laser desorption/ionization (MALDI) infrared multiphoton dissociation (IRMPD) mass spectrometry in FT-ICR MS and via negative ion electrospray ionization (ESI) in-source collision-induced dissociation (CID) mass spectrometry, respectively. The major fragmentation pathway of protonated 1 to 6 gives the F ions under IRMPD; theoretical results show that the retro-Michael reaction channel is more favorable in both thermodynamics and kinetics. This explanation is supported by H/D exchange experiments and the MS/MS experiment of acetylated 1. Deprotonated 1 to 6 give rise to the solitary E ions (aromatic nitrogen anions) in the negative ion in-source CID; theoretical calculations show that a retro-Michael mechanism is more reasonable than a gas-phase intramolecular nucleophilic displacement (SN2) mechanism to explain this reaction process.

Amines↗

PubMed2005

The effect of cyclin D expression on cell proliferation in human gliomas.

The expression of three cyclin D subtypes was defined immunohistochemically with cyclin D1, D2 and D3 monoclonal antibodies in 52 human glioma biopsies and eight control samples of normal brain tissue. PCNA labeling indices (LI) were used to evaluate proliferation in the glioma biopsies. LI of cyclin D1, D2 and D3 were compared with histological grade and the proliferating cell nuclear antigen (PCNA) LI. Cyclin D1 expression only was observed in normal brain tissue, but marked overexpression of cyclin D1 and cyclin D3 was observed in glioma. Cyclin D1 LI increased with malignancy, in parallel with an increase in PCNA LI. Lower expression of cyclin D2 was found in a small fraction of the gliomas, but its LI did not vary significantly with grade. Cyclin D3 was mainly expressed by malignant gliomas and was rarely observed in low-grade glioma. Cyclin D2 and D3 expression correlated with PCNA LI, but not as strongly as for cyclin D1. Expression of cyclin D1 is closely related to both the oncogenesis and progression of glioma, while cyclin D3 is associated with transformation to a malignant phenotype. Cyclin D2 is weakly expressed and shows no marked relationship with any aspect of tumorigenesis. The exact contribution of cyclin D subtypes to cell cycle progression in neoplastic and reactive cells remains to be defined.

Brain Neoplasms↗

PubMed2005

Facial nerve function after excision of large acoustic neuromas via the suboccipital retrosigmoid approach.

We review our results for facial nerve preservation in 105 patients with large acoustic neuromas (diameter 4.0 cm or larger) undergoing excision via the suboccipital retrosigmoid approach. Microneurosurgical techniques and facial nerve monitoring were used. Complete tumor removal was achieved in 91 cases (86.7%) and subtotal removal in 14 (13.3%). There were two postoperative deaths (1.9%). The facial nerve was preserved anatomically in 83 (79.1%) patients. Using the House-Brackmann grading system, facial nerve function was assessed immediately after surgery, at the time of discharge and 1 year after surgery. Excellent function (Grades I and II) was present in 41.0%, 41.8%, and 56.7% of patients at each time interval, respectively, with acceptable function (Grade I-IV) in 78.5% (68/87 cases) at follow-up assessment at one year. The suboccipital retrosigmoid approach resulted in good anatomical and functional preservation of the facial nerve during excision of large acoustic neuromas, with minimal other morbidity and low mortality. We recommend this approach for excision of large acoustic neuromas.

Adult↗

PubMed2005

Surface plasmon interference nanolithography.

A new nanophotolithography technique based on the interference of surface plasmon waves is proposed and demonstrated by using computer simulations. The wavelengths of the surface plasmon waves at metal and dielectric interfaces can reach the nanometer scale while their frequencies remain in the optical range. As a result, the resolution of this surface plasmon interference nanolithography (SPIN) can go far beyond the free-space diffraction limit of the light. Simulation results show that one-dimensional and two-dimensional periodical structures of 40-100 nm features can be patterned using interfering surface plasmons launched by 1D gratings. Detailed characteristics of SPIN such as field distribution and contrast are also investigated.

Computer Simulation↗

PubMed2005

Focusing surface plasmons with a plasmonic lens.

We report the focusing of surface plasmon polaritons by circular and elliptical structures milled into optically thick metallic films or plasmonic lenses. Both theoretical and experimental data for the electromagnetic nearfield is presented. The nearfield is mapped experimentally using nearfield scanning optical microscopy and plasmonic lithography. We find that the intensity at the focal points of the plasmonic lenses increases with size.

Journal Article↗