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Biomedical subjects

X Yan

Publications and source records attributed to X Yan.

At least 73 records · Page 4Linked to original sources
PubMed2000

Identification of urocortin mRNA antisense transcripts in rat tissue.

Urocortin (UCN) has 45% sequence homology with corticotropin releasing factor (CRF) and binds to CRF receptors. We used reverse-transcriptase-polymerase chain reaction to demonstrate the presence of UCN RNA in various brain regions and in peripheral tissues. Ribonuclease protection assay (RPA) using sense and antisense riboprobes demonstrated the presence of a naturally occurring antisense UCN RNA transcript in a number of tissues. Northern blot indicated that the antisense transcript was the same size as sense UCN. RPA, using probes that covered bases 1 to 560 of 579 bp sequence of rat UCN, indicated that the antisense sequence was complementary to sense UCN but did not contain an open reading frame. Sense and antisense UCN RNA were co-expressed in all tissues that contained levels of either transcript detectable by RPA. Sense RNA expression was greater than antisense in the midbrain, the two transcripts were expressed equally in the hypothalamus and antisense was expressed at higher levels than sense in the liver, heart, and skeletal muscle. Antisense RNA expression was stress responsive, suggesting that it may play a role in regulating transcription or translation of UCN mRNA.

Animals↗
PubMed2000

Carbachol blocks beta-amyloid fragment 31-35-induced apoptosis in cultured cortical neurons.

We reported previously that many neurodegenerative changes characteristic of apoptosis could be induced by a short fragment of beta-amyloid protein, A(beta31-35), in cultured newborn mice cortical neurons, and that these changes were accompanied with alterations in expression of some genes. This study was designed to examine whether the apoptotic processes and related gene modulations in this model could be affected by coadministration of carbachol by electrophoretic analysis for DNA ladder formation and by RT-PCR assays for genomic modulation. The results showed that (1) simultaneous incubation with carbachol dose- and time-dependently blocked the specific DNA ladder formation induced by exposure to A(beta31-35) and (2) the A(beta31-35)-induced downregulation of bcl-2 and upregulations of bax, p53, and c-fos genes were reversed or ameliorated by the coadministration of carbachol. It is proposed that A(beta31-35)-induced apoptosis can be prevented by carbachol through mechanisms that modulate the expression of related genes.

Amyloid beta-Peptides↗
PubMed2000

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric analysis of the recombinant human macrophage colony stimulating factor beta and derivatives.

The potential of electrospray ionization (ESI) Fourier transform ion cyclotron mass spectrometry (FTICR-MS) to assist in the structural characterization of monomeric and dimeric derivatives of the macrophage colony stimulating factor beta (rhM-CSF beta) was assessed. Mass spectrometric analysis of the 49 kDa protein required the use of sustained off-resonance irradiation (SORI) in-trap cleanup to reduce adduction. High resolution mass spectra were acquired for a fully reduced and a fully S-cyanylated monomeric derivative (approximately 25 kDa). Mass accuracy for monomeric derivatives was better than 5 ppm, after applying a new calibration method (i.e., DeCAL) which eliminates space charge effects upon high accuracy mass measurements. This high mass accuracy allowed the direct determination of the exact number of incorporated cyanyl groups. Collisionally induced dissociation using SORI yielded b- and y-fragment ions within the N- and C-terminal regions for the monomeric derivatives, but obtaining information on other regions required proteolytic digestion, or potentially the use of alternative dissociation methods.

Amino Acid Sequence↗
PubMed2000

Cernuosides A and B, two sucrase inhibitors from Pulsatilla cernua.

Two oleanane-type oligoglycosides, cernuosides A (1) and B (2), were isolated from the roots of Pulsatilla cernua (Ranunculaceae). Structure elucidation was accomplished by 1D and 2D NMR (DQF-COSY, TOCSY, HMQC, HMBC, and ROESY) methods, FABMS, and hydrolysis. Both compounds showed moderate activity against sucrase.

Animals↗
PubMed2000

Selecting and expressing protective single-chain Fv fragment to stabilize L-asparaginase against inactivation by trypsin.

Four non-inhibitory specific single-chain Fv (sc Fv) fragments directed against L-asparaginase (ASNase) of Escherichia coli were selected from a synthetic phage-display scFv library. The scFv46 fragment could enhance the resistance of ASNase to trypsin proteolysis, with 70% of the initial ASNase activity present after the ASNase-scFv46 complex had been treated with trypsin for 30 min at 37 degrees C, whereas little residual activity was detected without the scFv46 fragment. The scFv46 gene was cloned to an expression vector pET-21a and expressed at high levels (about 45% of total cell protein) in E. coli BL21 (DE3) as inclusion bodies. The refolded and purified scFv46 fragment was proved to protect ASNase, and the protective effect was further confirmed by SDS/PAGE. It was found that under optimum conditions of molar ratio of scFv to ASNase, incubation time and temperature, the residual activity of the ASNase-scFv46 complex could reach about 78% after treatment with trypsin for 30 min at 37 degrees C. The results demonstrated that scFv fragments prepared by phage-antibody library technology could be used to protect target proteins.

Asparaginase↗
PubMed2000

Formation of low time-bandwidth product, single-sided exponential optical pulses in free-electron laser oscillators

The detailed shape of picosecond optical pulses from a free-electron laser (FEL) oscillator has been studied for various cavity detunings. For large values of the cavity detuning the optical pulse develops an exponential leading edge, with a time constant proportional to the applied cavity detuning and the quality factor of the resonator. This behavior has been observed at two separate FELs that have completely different resonator layouts and electron beam characteristics, and using different methods of optical pulse length measurement. The optical pulses have a full width at half maximum time-bandwidth product Deltat(FWHM)Deltaf(FWHM) of 0.2-0.3. The results presented here can be used to predict the optical pulse length and corresponding minimum spectral width that can be generated in a FEL pumped by short electron bunches. This is important for the design of new infrared free-electron laser user facilities, which need to make a balanced choice between short pulses for high temporal resolution and narrow bandwidth for linear and nonlinear spectroscopy.

Journal Article↗
PubMed2000

Measured capacitance of a condenser microphone as a function of diaphragm displacement

This paper shows that the capacitance of a polarized condenser microphone measured with a sinusoidal electrical signal is quantitatively related to the displacement of the microphone diaphragm. In fact, the capacitance measured with an ac signal is the "input capacitance" of the microphone when it acts as a transmitter. The expressions for the diaphragm displacement and the input capacitance are derived with damping taken into account. The input capacitance differs from the static capacitance with bias by an additional term which varies with the polarization voltage and frequency. Therefore, in general, it is impossible to measure the static capacitance with bias using a low frequency ac signal without the diaphragm being blocked. In order to measure the true static capacitance with bias, a static method based on the dc voltage distribution is presented. The experimental results for the input capacitance and the static capacitance with bias, obtained with the abovementioned ac and dc methods, respectively, give a high level of confidence in the theory. The experimental results reported by some others also support the theory.

Journal Article↗
PubMed2000

A method for measuring the diaphragm tension of condenser microphones using electric admittance

This paper presents a method to measure the diaphragm tension of a condenser microphone where the fundamental frequency of the diaphragm is found from the input conductance of the microphone as a function of frequency. In this contact-free, purely electrical approach only the diaphragm and the backplate of the microphone are used as the main system for exciting and detecting the diaphragm vibration.

Journal Article↗
PubMed2000

A new diterpene glycoside from Rabdosia rubescens.

A new ent-kaurene beta-D-glucoside was isolated from Rabdosia rubescens, together with the known compounds oridonin, ponicidin, and pedalitin. The structure of new compound was determined, on the basis of spectral data and X-ray crystallographic analysis, to be ent-7 beta,20-epoxy-kaur-16-ene-1 beta,6 alpha,7 alpha,14 alpha,15 alpha-pentanol 1-O-beta-D-glucopyranoside.

Crystallography, X-Ray↗
PubMed2000

PEC films prepared from Chitosan-Alginate coacervates.

Chitosan-alginate polyelectrolyte complex (PEC) have been prepared in situ in beads and microspheres. This study examines the preparation of suitable chitosan-alginate coacervates for casting into homogeneous PEC films for potential applications in packaging, controlled release systems and wound dressings. Coacervation between chitosan and alginate was rapid, but the rate may be controlled with the addition of water miscible organic solvents. Compared with ethanol and PEG200, acetone was the more promising solvent moderator. Suspensions of fine, uniformly dispersed coacervates were produced by a dropwise addition of 0.25% w/v chitosan solution (solvent: 1: 1 v/v of 2% acetic acid and acetone) into 0.25% w/v sodium alginate solution in water under rapid agitation. The PEC films were transparent and flexible. They exhibited high permeability to water vapor, but resisted complete dissolution in 0.1 M HCI, distilled water and pH 7.4 phosphate buffer solution. Microscopic heterogeneity in the films could be reduced by immersion in aqueous media, but this was accompanied by modifications in the thickness, permeability and mechanical property of the films.

Alginates↗
PubMed2000

[Relationship between the expression of cell cycle regulators and microsatellite instability in colorectal carcinomas].

OBJECTIVE: To explore the relationship between the expression of cell cycle regulators and microsatellite instability (MSI) in colorectal carcinomas(CRC). METHODS: The expression of cell cycle regulators cyclin D1, P16, P21WAF1/CIP1, P53, Rb and PCNA were detected by immunohistochemical staining, and MSI at six microsatellite loci (D18S34, D17S799, D5S409, TCF-2, Rb and P53) were examined by PCR-SSLP in 56 cases of colorectal carcinomas. RESULTS: The overall positive rate of MSI of CRC was 44.6% (25/56). MSI was positive at 1 locus in 7 cases, at 2 and more than 2 loci in 18 cases. In CRC with MSI, the positive rate of cyclin D1 and P53 protein was significantly lower, while that of P21 protein was significantly higher than those without MSI (P < 0.05). The positive rate of P16 in CRC with MSI was higher than those without MSI. The expression of Rb proteins was similar in frequency in CRC with or without MSI. CONCLUSION: Overexpression of P21 may play an important role in MSI genesis in CRC. It may also be related to decreased expression of cyclin D1 and P53 and overexpression of P16.

Cell Cycle↗
PubMed2000

[The prevention of primary liver cancer by selenium in high risk populations].

OBJECTIVE: To study the preventive effects of selenium on primary liver cancer. METHODS: After screening of blood samples in 18,000 males from 20 to 65 years-old in Qidong, Jiangsu province (a high risk area for liver cancer), 2,065 cases of HBsAg positive, AFP negative and normal liver function (normal ALT values) were found. The subjects were randomly divided into two groups, based on their residence areas; 1,112 subjects (experimental group) received one tablet of sodium selenite (0.5 mg Se) every day and 953 subjects (control group) received one placebo tablet every day. RESULTS: During three years of intervention and follow up, the blood selenium concentration and glutathione peroxidase activity of the subjects in the experimental group were increased and had significant difference as compared with those of the control group (P < 0.01). At the same time, the prevalence rate of micronucleus cells in peripheral blood lymphocytes in the experimental group was significantly lower than that of the control group (P < 0.01), and the incidence of new liver cancer in the experimental group (3 057.55/10(6), 34 cases out of 1,112 subjects) was significantly lower than the control group (5 981.11/10(6); 57 cases out of 953 subjects) (P < 0.01). CONCLUSION: The results confirms that selenium supplementation in general populations lived in high risk is effective in the prevention of liver cancer and the using of selenium tablets is simple and feasible.

Adult↗
PubMed2000

[Effects of deoxynivalenol on proliferation and tumor necrosis factor-alpha secretion of human peripheral blood mononuclear cells in vitro].

Deoxynivalenol (DON) is one of the most common contaminating mycotoxins in food at high risk areas of esophageal carcinoma in China. The effects of DON on proliferation and tumor necrosis factor-alpha (TNF-alpha) secretion of human peripheral blood mononuclear (HPBM) cells in vitro were determined with flow cytometric (FCM) analysis, cell counting, MTT bioassay and ELISA method respectively. FCM analysis revealed that after HPBM were prestimulated with PHA for 48 h, the proliferation indexes(PI) of the cells treated with low concentration of DON (50-500 ng/ml) for 6 h were all dramatically lower than that of normal control (19.80%-26.01% vs 37.84%), while the PI of cells treated with high concentration of DON(1000-2000 ng/ml) for 24 h were higher than that of normal control (35.74%-34.37% vs 22.85%). Cell number counting and MTT bioassay results showed that at the presence of PHA, DON inhibited the proliferation of HPBM. Double antibody sandwich enzyme linked immunosorbent assay (ELISA) showed that the secretion of TNF-alpha in cells treated with DON(500-1000 ng/ml) was significantly lower than that in the control (P < 0.01). The results suggested that DON could either inhibit or stimulate cell proliferation depending on active time, concentration and PHA stimulation. In general, DON mainly inhibited the proliferation of HPBM and decrease TNF-alpha secretion in vitro. Thus, DON might have some negative impacts on human immunological system.

Cell Division↗
PubMed2000

[Alteration of free radical generation in pulmonary tissue after quick decompression].

The purpose of this experiment was to evaluate decompression-induced pulmonary injury by means of measurement of ascorbate free radical (Vc-.) alteration in pulmonary tissue of the rats which experienced rapid decompression. 29 male S-D rats were divided into 4 groups: A was executed at 45 min post-decompression; B was control for A; C was executed at 90 min; D was ontrol for C. Group A and group C were to compress up to 0.5 MPa(air) and stay for 60 min, then were decompressed smoothly to normbaric in 1 min. The 0.05 M N-tert-butyl-alpha-phenylnitrone (PBN) was given at 20 min after completion of decompression (groups A and B) or at 65 min (groups C and D). At 25 min after PBN injection the animals were killed by cutting arteria coeliaca, and 0.75 g pulmonary tissues were taken. These tissues were homogenized for electron paramagnetic resonance (EPR) assay. The results demonstrated that the ascorbate free radical (Vc-.) signals were obtained at all samples. The intensity of signals measured in group C rose markedly (P < 0.05) and that in group A was close to control's. So it can be concluded that rapid decompression would increase the generation of free radical in lung.

Animals↗