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Biomedical subjects

Gang Chen

Publications and source records attributed to Gang Chen.

At least 271 records · Page 15Linked to original sources
PubMed2003

[Studies on stability of chlorogenic acid in extract of Flos lonicerae].

OBJECTIVE: To investigate the stability of chlorogenic acid in extract of flos lonicerae in different conditions. METHOD: The stability of chlorogenic acid in extract of flos lonicerae in phosptat buffe with different pH values, methanol, ethanol and different base solutions(Ca(OH)2 and NaOH) was investigated by the classical isothermal method. RESULT: The experiments showed the chlorogenic acid in extract of flos lonicerae was more stable in acidic water than in basic water. It was stable in these organic solutions and base solution[Ca(OH)2]. CONCLUSION: In different conditions, the stability of chlorogenic acid in extract of flos lonicerae was different. It provided a reference to the extraction and analysis of chlorogenic acid and production of chlorogenic acid preparation.

Calcium Hydroxide↗
PubMed2003

[Maize starch biosynthesis and its genetic manipulation].

Starch is the most important source of calories and a vital storage component in plants. The characterization and production of starch variants from mutation and with transgenic technology has improved our understanding of the synthesis of starch granule. In starch biosynthesis in plants, four enzymes, including ADP-glucose pyrophosphorylase, starch synthase, starch branching enzyme and starch debranching enzyme, are widely accepted from an enormous amount of research aimed primarily at enzyme characterization. As many genes encoding the enzymes and their multiple isoforms in starch biosynthesis pathway have been isolated, genetic manipulation of the starch biosynthesis pathway shows to be a practical way by which starch quantity is increased and starch with novel properties can be created.

English Abstract↗
PubMed2002

GM-CSF increases airway smooth muscle cell connective tissue expression by inducing TGF-beta receptors.

Fibrosis around the smooth muscle of asthmatic airway walls leads to irreversible airway obstruction. Bronchial epithelial cells release granulocyte/macrophage colony-stimulating factor (GM-CSF) in asthmatics and are in close proximity to airway smooth muscle cells (ASMC). The findings in this study demonstrate that GM-CSF induces confluent, prolonged, serum-deprived cultures of ASMC to increase expression of collagen I and fibronectin. GM-CSF also induced ASMC to increase the expression of transforming growth factor (TGF)-beta receptors type I, II, and III (TbetaR-I, TbetaR-II, TbetaR-III), but had no detectable effect on the release of TGF-beta1 by the same ASMC. The presence of GM-CSF also induced the association of TGF-beta1 with TbetaR-III, which enhances binding of TGF-beta1 to TbetaR-II. The induction of TbetaRs was parallel to the increased induction of phosphorylated Smad2 (pSmad2) and connective tissue growth factor (CTGF), indicative of TGF-beta-mediated connective tissue synthesis. Dexamethasone decreased GM-CSF-induced TbetaR-I, TbetaR-II, TbetaR-III, pSmad2, CTGF, collagen I, and fibronectin. In conclusion, GM-CSF increases the responsiveness of ASMC to TGF-beta1-mediated connective tissue expression by induction of TbetaRs, which is inhibited by corticosteroids.

Animals↗
PubMed2002

Inhibitory mode of 1,5-diarylpyrazole derivatives against cyclooxygenase-2 and cyclooxygenase-1: molecular docking and 3D QSAR analyses.

The Lamarckian genetic algorithm of AutoDock 3.0 has been employed to dock 40 1,5-diarylpyrazole class compounds into the active sites of cyclooxygenase-2 (COX-2) and cyclooxygenase-1 (COX-1). The binding models were demonstrated in the aspects of inhibitor's conformation, subsite interaction, and hydrogen bonding. The data of geometrical parameters and RMSD values compared with the known inhibitor, SC-558 (43), show that these inhibitors interact respectively with COX-2 and COX-1 in a very similar way. The r(2) values of 0.648 for COX-2 and 0.752 for COX-1 indicate that the calculated binding free energies correlate well with the inhibitory activities. The structural and energetic differences in inhibitory potencies of 1,5-diarylpyrazoles were reasonably explored, and the COX-2/COX-1 selectivity was demonstrated by the three-dimensional (3D) interaction models of inhibitors complexing with these two enzymes. Using the binding conformations of 1,5-diarylpyrazoles, consistent and highly predictive 3D quantitative structure-activity relationship (QSAR) models were developed by performing comparative molecular field analyses (CoMFA) and comparative molecular similarity analyses (CoMSIA). The q(2) values are 0.635 and 0.641 for CoMFA and CoMSIA models, respectively. The predictive ability of these models was validated by SC-558 (43) and a set of 10 other compounds that were not included in the training set. Mapping these models back to the topology of the active site of COX-2 leads to a better understanding of vital diarylpyrazole compounds and COX-2 interactions. Structure-based investigations and the final 3D QSAR results provided possible guidelines and accurate activity predictions for novel inhibitor design.

Algorithms↗
PubMed2002

In vitro wounding of airway smooth muscle cell monolayers increases expression of TGF-beta receptors.

During an exacerbation of asthma, there is bronchial epithelial cell injury and influx of inflammatory cells. In these instances, the release of proteases and various cytokines could lead to injury of the airway smooth muscle cells (ASMCs). Airway remodeling is a characteristic finding in asthma but the role of ASMC injury in remodeling is unknown. Previously, we demonstrated that mechanical wounding of confluent monolayers of bovine ASMCs resulted in the release of biologically active transforming growth factor-beta1 (TGF-beta1), which in turn, induced collagen I expression. In the present study, we demonstrate that after mechanical wounding, ASMCs had an increased expression of the signal transducing TGF-beta receptors TbetaR-I and TbetaR-II as detected by flow cytometry and Western analysis. Corticosteroids are standard therapy in asthma and the presence of dexamethasone decreased wound-induced release of TGF-beta1 and the expression of collagen I, fibronectin, and TbetaR-II. These results suggest that ASMC injury may play an important role in airway fibrosis mediated by TGF-beta1, which can be prevented by the use of corticosteroids.

Activin Receptors, Type I↗
PubMed2002

Most antiviral CD8 T cells during chronic viral infection do not express high levels of perforin and are not directly cytotoxic.

Despite the frequency of HIV-specific CD8 T cells, most HIV-infected patients do not control viral replication without antiviral drugs. Although CD8 T cells are important in containing acute HIV and simian immunodeficiency virus (SIV) infection, CD8 T-cell functions are compromised in chronic infection. To investigate whether functional deficits are specific to HIV, the phenotypic and functional properties of HIV, Epstein-Barr virus (EBV), and cytomegalovirus (CMV)-specific CD8 T cells, labeled with HLA A2.1 or B8 tetramers, were compared in 35 HIV-infected and 9 healthy donors. Cytotoxic T lymphocytes express the cytolytic molecules perforin and granzymes, and are thought to be CD45RA(+)CD27(-). Although most HIV- specific cells are antigen experienced and express granzyme A (median, 85%), few express high levels of perforin (median, 10%) or CD45RA (median, 14%) or have down-modulated CD27 (median, 12%). Perforin expression by HIV-specific cells is not significantly different from that of EBV- or CMV-specific cells in the same donors or in healthy donors. EBV- and CMV-specific cells, like HIV-specific cells, are often not cytotoxic when tested directly ex vivo. HIV-specific T-cell expression of other phenotypic markers is similar to that of EBV- and CMV-specific CD8 T cells in healthy donors. However, CMV-specific cells (and, to a lesser extent, EBV-specific cells) in HIV-infected donors are more likely to be CD27(-), CD45RA(+), and GzmA(+). These results suggest that the chance to eradicate an infection by T-cell-mediated lysis may be undermined once an infection becomes chronic. Impaired antiviral cytotoxicity during chronic infection is not specific to HIV but likely represents the immune response to chronic antigenic exposure.

CD8-Positive T-Lymphocytes↗
PubMed2002

Determination of the rate constants and activation energy of acetaminophen hydrolysis by capillary electrophoresis.

A method based on capillary electrophoresis with electrochemical detection (CE-ED) was developed for the simultaneous determination of p-aminophenol and acetaminophen in the hydrolysates of acetaminophen. Effects of several important factors such as the acidity and concentration of running buffer, separation voltage, injection time, and working potential were investigated to acquire the optimum conditions. The detection electrode was a 300 microm carbon disc electrode at a working potential of +0.80 V (versus SCE). The two analytes can be well separated within 6 min in a 50 cm length fused silica capillary at a separation voltage of 18 kV in a 25 mM phosphate buffer (pH 6.5). The rate constants of acetaminophen hydrolysis in 0.5 M HCl at different temperatures were determined by monitoring the concentration changes of acetaminophen. At 70, 80, 90 and 100 degrees C, the measured rate constants of acetaminophen hydrolysis were 5.027 x 10(-3), 8.522 x 10(-3), 18.60 x 10(-3) and 32.76 x 10(-3) min(-1), respectively. The activation energy for acetaminophen hydrolysis was calculated to be 68.13 kJ mol(-1), which is in good agreement with the value in the literature.

Acetaminophen↗
PubMed2002

New WHO histologic classification predicts prognosis of thymic epithelial tumors: a clinicopathologic study of 200 thymoma cases from China.

BACKGROUND: In 1999, a World Health Organization (WHO) committee published histologic criteria for distinct thymoma entities (labeled as Type A, AB, B1, B2, B3 thymomas) and for the heterogeneous group of thymic carcinomas, collectively called Type C thymomas. Whether WHO-defined histologic thymoma subtypes are of independent prognostic relevance has yet to be proved. METHODS: Two hundred thymomas from the Shanghai Chest Hospital with a mean follow-up time of 15 years (range, 1-246 months) were studied for the relevance of WHO histologic subtype and other factors (stage, therapy, and myasthenia gravis [MG]) for survival. RESULTS: In order of frequency, 68 patients (34.0%) had Type AB, 39 (19.5%) had Type B2, 36 (18.0%) had Type C, 27 (13.5%) had Type B3, 17 (8.5%) had Type B1, and 8 (4.0%) had Type A thymoma. Five cases (2.5%) were rare thymomas not mentioned in the WHO classification. Survival data showed significant differences among the histologic subtypes (log rank test: P < 0.001). Among patients with Type A and AB thymomas, none died of tumor; of the Type B1 thymoma patients, only one (5.9%) died at 22 months. Type B2, B3, and C thymomas had a significantly worse prognosis with 5-year survival rates of 75.0%, 70.0%, and 48.0%, respectively. Ninety-six patients (48.0%) were in Masaoka Stage I, 26 (13.0%) were in Stage II, 65 (32.5%) were in Stage III, and 13 (6.5%) were in Stage IV. Stage was highly significant in predicting survival (log rank, test P < 0.001). The association between histologic subtype and invasive behavior (stage) was statistically significant (P < 0.001). However, histology was an independent predictive factor of survival in Stage I and II thymomas: Type B2, B3, and C thymomas had a worse prognosis than Type A, AB, and B1 thymomas (log rank test: P < 0.003). Thirty patients (15.0%) presented with MG. MG was significantly more frequent in Type B2 and B3 than in Type A, AB, and B1 thymomas (P < 0.01). On multivariate analysis, MG had no adverse effect on survival (P = 0.17). Radiation or chemotherapy improved patients' survival at 5 and 10 years in Type B2, B3, and C thymomas (log rank test: P < 0.003). CONCLUSIONS: Tumor stage is the most important determinant of survival in thymoma patients, but the WHO histologic subtype is an independent prognostic factor in Stage I and II thymomas, among which WHO Type A, AB, and B1 thymomas form a low-risk group. Patients with high-risk thymomas might profit from novel adjuvant radiochemotherapy regimens.

Adolescent↗
PubMed2002

Determination of hesperidin and synephrine in Pericarpium Citri Reticulatae by capillary electrophoresis with electrochemical detection.

A method based on capillary electrophoresis with electrochemical detection (CE-ED) has been developed for the determination of hesperidin (HP) and synephrine (SP) in the Chinese traditional herbal drug, Pericarpium Citri Reticulatae, the dried rind of the ripe fruits of Citrus reticulata Blanco (mandarin orange). The effects of some important factors such as the acidity and concentration of running buffer, separation voltage, and detection potential were investigated to determine the optimum conditions. The working electrode was a 300 microm diameter carbon disc electrode positioned opposite the outlet of the capillary. Both analytes could be well separated within 5 min in a 40 cm long capillary at a separation voltage of 12 kV in 50 mmol L(-1) borate buffer (pH 9.0). Excellent linearity was observed for the dependence of peak current on analyte concentration in the range from 2.5 x 10(-6) to 1.0 x 10(-3) mol L(-1) for SP and from 5.0 x 10(-6) to 1.0 x 10(-3) mol L(-1) for HP. The detection limits (S/N=3) for SP and HP were 4.96 x 10(-7) mol L(-1) and 6.54 x 10(-7) mol L(-1), respectively. This method has been successfully applied for the analysis of real samples, with satisfactory results.

Drugs, Chinese Herbal↗
PubMed2002

Determination of purine and pyrimidine bases in DNA by micellar electrokinetic capillary chromatography with electrochemical detection.

A method based on micellar electrokinetic capillary chromatography with electrochemical detection was developed for the determination of cytosine, 5-methylcytosine (5-MC), thymine, adenine, and guanine in the hydrolysates of DNA. The working electrode was fabricated in a novel self-positioning carbon disc electrode system that can align the capillary outlet with the working electrode without a three-dimensional micromanipulator. The five analytes could be well separated within 10 min in a 40 cm length capillary at a separation voltage of 9 kV in a 40 mmol/l borate buffer (pH 10.0) containing 100 mmol/l sodium dodecyl sulfate. Good linearity was observed between peak current and concentration of bases over three orders of magnitude with the detection limits (SIN=3) ranging from 1.28 x 10(-6) to 5.02 x 10(-6) mol/l. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 5% for both migration time and peak current (n=7). It has been successfully applied to determine bases including 5-MC in the hydrolysates of fish sperm DNA, calf thymus DNA, and DNA isolated from spleen cells of female mice.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Biexciton quantum coherence in a single quantum dot.

Nondegenerate (two-wavelength) two-photon absorption using coherent optical fields is used to show that there are two different quantum mechanical pathways leading to formation of the biexciton in a single quantum dot. Of specific importance to quantum information applications is the resulting coherent dynamics between the ground state and the biexciton from the pathway involving only optically induced exciton/biexciton quantum coherence. The data provide a direct measure of the biexciton decoherence rate which is equivalent to the decoherence of the Bell state in this system, as well as other critical optical parameters.

Journal Article↗
PubMed2002

Genotoxic activity of extractable organic matter from urban airborne particles in Shanghai, China.

The aim of this research is to investigate the impact of air pollution on the population in Shanghai. The genotoxicity of extractable organic matter (EOM) from the air particles was investigated by the means of the Salmonella plate incorporation assay, rat hepatocyte unscheduled DNA repair assay, and mice micronuclei test. The airborne particles were collected in 13 locations during the summer of 1992 and winter of 1993. The crude extracts were fractionated by acid-base partitioning into acid, base and neutral fractions. The neutral fractions were further fractionated by resin-silica gel column chromatography into three subfractions. The induction of revertants with the crude extracts was higher in winter samples than in summer samples. Both indirect-acting and direct-acting mutagenicity were observed. The mutagenicity was detected with TA98, but was not detected with TA100. The mutagenic activity was the greatest in the acid, aromatic and polar fractions from summer samples. The fractions from the winter samples did not show clear differences. There was no substantial location-related variance in the mutagenic potencies of EOM, but substantial location- or time-related variances in the mutagenic potencies of the airborne particles per cubic meter air were found. While rat hepatocyte unscheduled DNA synthesis (UDS) assay revealed genotoxicity for all the samples, there was no big variance in the genotoxicity of the fractions. The mouse micronuclei test showed results similar to the UDS assay. The difference of locality did not have statistical significance.

Air Pollutants↗
PubMed2002

Electronic structure of glassy chalcogenides As4Se4 and As2Se3: a joint theoretical and experimental study.

We present an interpretation of the x-ray absorption spectra of arsenic chalcogenide glasses, As4Se4 and As2Se3, from a first-principles calculation. Our calculation identifies the atomistic origins of the observed photoemission data. The importance of structural "building blocks" present in a particular glass to the electron states is emphasized. The effects of disorder on the electronic spectra are clearly demonstrated by a significant change in the electronic density of states, originating in the breakdown of long-range order coherence in the bonding states of the building blocks. We discuss the relation between observed in situ light-induced changes and the electronic structure.

Journal Article↗
PubMed2002

Increase in the beta chain of hepatocyte growth factor (HGF beta) precedes c-met expression after bleomycin-induced lung injury in the rat.

After lung injury the regeneration of the alveolar epithelium is highly dependent on the proliferation of type II alveolar epithelial cells (AECs). Hepatocyte growth factor (HGF), a potent epithelial cell mitogen, is present as a single chain in normal tissue, but after injury HGF is converted to an active form composed of an alpha and a beta chain. In this study it was demonstrated that there was an increase in the beta chain of HGF 4 days after bleomycin administration, coinciding with the time of maximal type II AEC proliferation. Bronchoalveolar lavage fluid (BALF) obtained 4 days after bleomycin administration was maximally mitogenic to L2 cells, a nontransformed rat alveolar epithelial cell line. Type II cells isolated from normal rats do not express the HGF receptor, c-met. However, 4 days after bleomycin injury, using Western blot analysis, an increase in c-met was detected in AEC protein extracts. HGF induced c-met expression by L2 cells and neutralizing antibodies to HGF inhibited the mitogenic activity in the BALF. These findings suggest that HGF may regulate its own receptor on AECs and is an important mitogen for AECs 4 days after bleomycin administration.

Animals↗
PubMed2002

Pharmacokinetic-pharmacodynamic modelling of magnesium plasma concentration and blood pressure in preeclamptic women.

OBJECTIVE: To describe the relationship between plasma magnesium (Mg(2+)) concentration and blood pressure response in pregnant women with preeclampsia. METHODS: Fifty-one preeclamptic women were studied after receiving two consecutive magnesium sulfate infusions (120 mg/kg for 1 hour and 24 mg/kg for 5 hours). Mg(2+) concentration and systolic/diastolic blood pressure were measured at 0, 0.5, 1, 2, 4, 6, 7, 9, 11, 13 and 15 hours after the beginning of the first infusion. A population pharmacokinetic-pharmacodynamic model was fitted to the data with the computer program NONMEM. RESULTS: Pharmacokinetics were described by a two-compartment model. Population parameter estimates were 5.0 L/h for body clearance (CL), 24L for central volume (V(c), 25L for peripheral volume ((V)(p)) and 5.6 L/h for intercompartment clearance (Q). The interindividual variability in CL, V(c), V(p) and Q was 39, 26, 38, and 59%, respectively. The mean population estimates for systolic (diastolic) blood pressure were 36.8 (27.8) mm Hg for the maximum decrease (E(max)), 0.75 (0.88) mmol/L for the Mg2+ concentration (above baseline) eliciting half-maximum effect (EC(50)) and 0.76 (0.5) h(-1) for the equilibrium rate (k(eo)) of the effect compartment model. CONCLUSION: Mg(2+ )concentrations within the range (2-4 mmol/L) proposed for treatment of preeclampsia produce greater than half-maximal lowering of systolic and diastolic blood pressure.

Bayes Theorem↗
PubMed2002

[Effect of the endoexpander pressure of continuous and constant pressure expansion on the drug permeability].

OBJECTIVE: To investigate the effect of the endoexpander pressure of continuous and constant pressure expansion on the drug permeability. METHODS: The expanders were divided into two groups, the normal expansion and the continuous and constant pressure expansion (4.6 kPa). Each expander was filled with 0.2% Metronidazole, then the expanders were immersed wholly in normal saline and sealed totally. At several intervals over 72 hours, the surrounding saline was sampled and the drug concentration of the sample was measured respectively. RESULTS: Both groups were permeable to the Metronidazole and the concentration outside the expander would reach the effective concentration in 48 hours. The drug concentration of the continuous and constant pressure expansion was higher than that of the normal one and there was significant difference between the two groups (P < 0.01). CONCLUSION: The endoexpander pressure in continuous and constant pressure expansion can enhance the drug permeability. In view of this, in the course of continuous and constant pressure expansion, 0.2% Metronidazole can be used to prevent and control the infection.

Humans↗
PubMed2002

Approval summary: letrozole in the treatment of postmenopausal women with advanced breast cancer.

Letrozole (Femara; Novartis Pharmaceuticals Corp., East Hanover, NJ) is a nonsteroidal inhibitor of aromatase enzyme complex. It inhibits the peripheral conversion of circulating androgens to estrogens. In postmenopausal women, letrozole decreases plasma concentrations of estradiol, estrone, and estrone sulfate by 75-95% from baseline with maximal suppression achieved within 2-3 days of treatment initiation. Suppression is dose related, with doses of >or=0.5 mg giving estrone and estrone sulfate values that were often below assay detection limits. At clinically used dosage, letrozole does not impair adrenal synthesis of glucocorticoids or aldosterone. In 1998, letrozole was approved by the United States Food and Drug Administration (FDA) for the treatment of advanced breast cancer in postmenopausal women, with hormone receptor positive or unknown breast cancer, who had failed one prior antiestrogen treatment (i.e., for "second-line" treatment). Approval was based on two randomized trials comparing tumor RRs of patients receiving 0.5 mg of letrozole, 2.5 mg of letrozole, and either megestrol acetate (MA) or aminoglutethimide. In the megestrol trial, 2.5 mg/day letrozole was superior to 0.5 mg of letrozole and MA (RRs 24, 13, and 16%, respectively), whereas in the aminoglutethimide trial, there was no significant difference in 2.5 mg of letrozole and 0.5 mg of letrozole RRs (20 and 17%). There was a trend toward RR superiority of 2.5 mg of letrozole over aminoglutethimide (P = 0.06). Letrozole (2.5 mg) was the dose chosen for comparison with tamoxifen in the first-line setting. In July 2000, a marketing application for first-line letrozole treatment of postmenopausal women with hormone receptor positive or hormone receptor unknown locally advanced or metastatic breast cancer was submitted to the FDA. A single double-blind, double dummy, randomized, and multicenter trial compared 2.5 mg of letrozole to 20 mg of tamoxifen (456 patients/arm). Letrozole was superior to tamoxifen with regard to time to progression (TTP) and objective response rate (RR). The median TTP for letrozole treatment was 9.9 months [95% confidence interval (CI) 9.1-12.2] versus 6.2 months (95% CI 5.8-8.5) for tamoxifen, P = 0.0001, hazard ratio 0.713, (95% CI 0.61-0.84). RR was 32% for letrozole versus 21% for tamoxifen (odds ratio 1.74, 95% CI 1.29-2.34, P = 0.0003). Preliminary survival data (survival data are still blinded) indicate that letrozole is unlikely to be worse than tamoxifen. Both treatments were similarly tolerated. On the basis of these results, the United States FDA approved letrozole tablets, 2.5 mg/day, for first-line treatment of postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer. The manufacturer made a commitment to provide updated information on survival.

Antineoplastic Agents↗