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Biomedical subjects

W Chen

Publications and source records attributed to W Chen.

At least 523 records · Page 29Linked to original sources
PubMed1999

[Inhibiting effects of the ethanol-soluble extracts from the dried rhizoma of Garcinia oblougififolia on hepatitis B virus in vitro].

Comparing with Ara-Amp, the effects of the ethano-soluble extracts from the dried rhizoma of Garcinia oblougififolia Champ (GOC) on HBeAg and HBsAg expression in 2.2.15 cells, which came from transfected HepG2 cells with coloned HBV DNA, were studied. The results showed that the extracts of GOC had a marked inhibition effects on HBeAg adn HBsAg which expressed by 2.2.15 cells, the effective concentration was range from 195 to 780 micrograms/ml.

Antiviral Agents↗
PubMed1999

[Studies on treacheostomal formation and voice prosthesis after total laryngectomy].

OBJECTIVE: To establish a tracheostomy model with no stricture and "bowl-shaped" collapse. METHODS: Twenty-five cases were reconstructed with Blom-Singer technique after total laryngectomy for tracheoesophageal voice in our department since 1996. Tracheostoma was done with 5 kinds of methods. In 6 cases, anterior cervical U-shaped incision + division of sternal attachments of bilateral sternomastoid muscles + Griffith tracheostoma enlargement (combination method) were used in the primary operation, and the third generation of indwelling prosthesis and tracheostomal valve were installed. RESULTS: In these 25 cases, 23 could speak freely. The successful rate was 92%. In tracheostoma operation, there were 7 cases with their skin sutured directly to tracheal rings, 3 cases with Myers method, 6 cases with Griffith method, 3 cases with [symbol: see text] method. All of them needed cannulation for more than 6 months and had stricture of tracheostoma and "bowl-shaped" collapse of various degrees. But those underwent "combination method" needed no cannulation and no stricture and bowlshaped collapse was found during 6 mouths' follow-up. CONCLUSION: The combination method of tracheostomy makes the installation, postoperative care and replacement of prosthesis and tracheostomal valve easy and the indwelling prosthesis has the best tone quality. The use of tracheostomal valve effectively makes the patient's hand free during speaking.

Follow-Up Studies↗
PubMed1999

[The absorption spectrum of C70].

With the methyl benzene as solution,ultraviolet and visible absorption spectra of the mixture of C60 and C70's methyl benzene saturant solution as specimen, infrared absorption spectrum of the mixture of C60 and C70 was measured. The absorption spectrum of C70 was determined by comparison.

English Abstract↗
PubMed1999

[The polymerization of C60/C70 in air at high temperature].

C60(C70 contained) was sealed in air and heated for 10 minutes at high temperature (850-900 degrees C). It was found from absorption spectrum analysis and SEM observation that the C60(C70) produced polymerization under the action of nitrogen and oxygen.

English Abstract↗
PubMed1999

[Continuous determination of Zn, Cu and Mn in tea by flame atomic absorption spectrophotometry].

This paper reports the determination of trace metals Zn, Cu and Mn in tea by flame atomic absorption spectrophotometry. The method is simple and rapid with good precision and accuracy. The characteristic concentration is 0.009 microg/mL/1% for Zn, 0.031 microg/mL/1% for Cu and 0.017 microg/mL/1% for Mn, respectively. The relative standard deviation is between 0.9% and 5.0%. The recovery rate is between 92.0% and 106.0%.

Camellia sinensis↗
PubMed1998

Characterization of the pathogenic autoreactive T cells in cyclosporine-induced syngeneic graft-versus-host disease.

Administration of the immunosuppressive drug cyclosporine after syngeneic bone marrow transplantation paradoxically elicits a systemic autoimmune syndrome resembling graft-vs-host disease (GVHD). This syndrome, termed syngeneic GVHD, is associated with the development of CD8+ cytolytic T lymphocytes that promiscuously recognize MHC class II molecules in association with a peptide from the invariant chain (CLIP). Clonal analysis reveals a major subset of cells that are pathogenic and require the N-terminal flanking region of CLIP for activation, while there is a minor subset of nonpathogenic T cells that require the C-terminal flanking region. The present studies show that pathogenic T cells produce type 1 cytokines (IL-2; IFN-gamma), while the nonpathogenic clones produce type 2 cytokines (IL-4; IL-10). Moreover, the repertoire of the pathogenic T cells is highly conserved with respect to V beta and V alpha TCR gene expression. The vast majority of clones express V beta8.5 (12/12) and V alpha11 (11/12). Although a limited number was evaluated, the nonpathogenic clones have only a V alpha restriction. Sequence analysis of the pathogenic T cell clones reveals a marked heterogeneity in the complementarity-determining region 3 domain and differential J region gene expression for both TCR alpha- and beta-chains. Evaluation of the specificity of these clones suggests that the functional interaction between the N-terminal flanking region of CLIP (defined by the amino acid sequence -KPVSP-) and the V region of the TCR is critical, allowing effective target cell recognition and tissue destruction in syngeneic GVHD.

Amino Acid Sequence↗
PubMed1998

Biosensor for direct determination of organophosphate nerve agents using recombinant Escherichia coli with surface-expressed organophosphorus hydrolase. 2. Fiber-optic microbial biosensor.

A fiber-optic microbial biosensor suitable for direct measurement of organophosphate nerve agents was developed. The unique features of this novel microbial biosensor were the recombinant Escherichia coli cells expressing the enzyme organophosphorus hydrolase on the cell surface and the optical detection of the products of enzyme-catalyzed organophosphate hydrolysis. The use of cells with the metabolic enzyme expressed on the cell surface as a biological sensing element provides advantages of no resistance to mass transport of the analyte and product across the cell membrane and low cost due to elimination of enzyme purification, over the conventional microbial biosensors based on cells expressing enzyme intracellularly and enzyme-based sensors, respectively. The use of an optical transducer allows the detection of different organophosphates in a mixture, presently not feasible with acetylcholinesterase-based biosensors. E. coli cells expressing organophosphorus hydrolase (OPH) on the cell surface were immobilized in low melting temperature agarose on a nylon membrane and attached to the common end of a bifurcated fiber-optic bundle. OPH-expressing E. coli cells catalyzed the hydrolysis of organophosphorus pesticides to form stoichiometric amounts of chromophoric products that absorb light at specific wavelengths. The backscattered radiation of the specific wavelength incident light was measured using a photomultiplier detector and correlated to the organophosphate concentration. The best sensitivity and response time were obtained using a sensor constructed with 1.5 mg of cells operating in pH 9, 50 mM HEPES buffer with 100 mM NaCl and 0.05 mM CoCl2 at 30 degrees C. At optimized conditions, the biosensor measured paraoxon, parathion, and coumaphos pesticides with high selectivity against triazine and carbamate pesticides in approximately 10 min. The lower detection limits were 3 microM for paraoxon and parathion and 5 microM for coumaphos. When stored in the buffer at 22 degrees C, the biosensor was stable for over a 1-month period and showed no decline in the response for over 75 repeated usages. The new fiber-optic microbial biosensor is an ideal tool for on-line monitoring of the detoxification process for organophosphate pesticides-contaminated wastewaters but may not be suitable for environmental monitoring.

Aryldialkylphosphatase↗
PubMed1998

Oral delivery of group A streptococcal cell walls augments circulating TGF-beta and suppresses streptococcal cell wall arthritis.

Oral administration of autoantigens can influence the outcome of experimental autoimmune diseases, yet little is known about nonself Ag-induced tolerance. In this study, we administered group A streptococcal cell wall (SCW) peptidoglycan-polysaccharide complexes orally and monitored the impact on SCW-induced erosive polyarthritis. Oral administration of low dose SCW (3 microg/day), initiated 7 days before an arthritogenic dose of systemic SCW, virtually eliminated the joint swelling and destruction typically observed during both the acute and chronic phases of the arthritis. High (300 microg), but not intermediate (30 microg), dose regimens also profoundly inhibited the disease. Most previous studies have demonstrated that prior feeding is required for efficacy, yet oral feeding of low dose SCW suppressed the evolution of arthritis even when administration was begun 10-15 days after induction of the arthritis. While the synovial inflammatory cell infiltration and expression of proinflammatory cytokines were markedly suppressed, no local enhancement of the regulatory cytokines IL-4, IL-10, and TGF-beta was detected. Oral administration of low dose SCW, however, up-regulated circulating levels of TGF-beta, concomitant with decreased circulating TNF-alpha and suppression of chronic arthritis. Moreover, IL-10 was increased in tolerized spleen lymphocytes, and unexpectedly, this SCW-specific IL-10 production was TGF-beta dependent. These data support a pivotal role for TGF-beta, although not necessarily in the joint, in the regulation of specific immune tolerance responsible for suppressed synovial inflammation and matrix destruction. The distant induction and up-regulation of regulatory cytokines and/or cells may contribute to the inhibition of the immune response through blunted infiltration of inflammatory cells to the joint.

Acute Disease↗
PubMed1998

UVB irradiation-induced activator protein-1 activation correlates with increased c-fos gene expression in a human keratinocyte cell line.

The effects of UVB irradiation on transcription factor activator protein-1 (AP-1) DNA binding and AP-1 transactivation were studied in a human keratinocyte cell line, HaCaT. UVB-induced AP-1 binding to a consensus AP-1 binding site was observed by gel shift assays with maximum stimulation at 12 h after UVB irradiation. A promoter region of the human collagenase-1 gene containing the same AP-1 binding sequence linked to a luciferase reporter gene was stably transfected into HaCaT cells. UVB irradiation significantly increased luciferase activity in these stably transfected cells, with maximum activity observed at 24 h after UVB irradiation. c-Fos and Jun D were identified by antibody clearing assays as the main components of the bound AP-1 complexes. Inhibition of transcription with actinomycin D and inhibition of protein synthesis with cycloheximide significantly abrogated the effect of UVB on AP-1 DNA binding, indicating that transcription and translation were required for AP-1 activation. Northern and Western analyses revealed a correlation between increased AP-1 activity and accumulation of c-fos mRNA and c-Fos protein after UVB irradiation. UVB irradiation increased c-fos transcription in HaCaT cells stably transfected with a plasmid containing the human c-fos promoter driving a luciferase reporter gene. These results suggest that increased c-fos expression may play an important role in UVB-induced AP-1 activation in HaCaT cells.

Cell Line↗
PubMed1998

Levels of p53 in Epstein-Barr virus-infected cells determine cell fate: apoptosis, cell cycle arrest at the G1/S boundary without apoptosis, cell cycle arrest at the G2/M boundary without apoptosis, or unrestricted proliferation.

The marked increases in p53 and p21/WAF1 levels that occur during Epstein-Barr virus (EBV) infection and the generation of immortal B lymphoblastoid cell lines (LCL) do not lead to growth arrest or apoptosis, although increasing wild-type (wt) p53 levels in EBV-infected cells by transfection or DNA damage induce these effects. We hypothesized that the concentration of p53 relative to that of LMP1 determines whether EBV-infected B cells undergo growth arrest and apoptosis. Cell cycle arrest and apoptosis were evaluated in LCL expressing varying p53 levels achieved by treating the cells with increasing concentrations of cisplatin, and we supplemented this approach with experiments in EBV-infected Burkitt's lymphoma (BL) cells transfected with a temperature-sensitive (ts) mutant human p53 and studies in LCL infected with recombinant adenoviruses expressing wt and ts mutant p53. Small increases in p53 and p21/WAF1 led to cell cycle arrest at the G2/M boundary, but not to apoptosis; moderate increases resulted in growth arrest at the G1/S boundary, also without apoptosis; and large increases also induced apoptosis. These results confirm the hypothesis and reveal unanticipated complexities in cell cycle regulation by p53.

Apoptosis↗
PubMed1998

Engagement of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) induces transforming growth factor beta (TGF-beta) production by murine CD4(+) T cells.

Evidence indicates that cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) may negatively regulate T cell activation, but the basis for the inhibitory effect remains unknown. We report here that cross-linking of CTLA-4 induces transforming growth factor beta (TGF-beta) production by murine CD4(+) T cells. CD4(+) T helper type 1 (Th1), Th2, and Th0 clones all secrete TGF-beta after antibody cross-linking of CTLA-4, indicating that induction of TGF-beta by CTLA-4 signaling represents a ubiquitous feature of murine CD4(+) T cells. Stimulation of the CD3-T cell antigen receptor complex does not independently induce TGF-beta, but is required for optimal CTLA-4-mediated TGF-beta production. The consequences of cross-linking of CTLA-4, together with CD3 and CD28, include inhibition of T cell proliferation and interleukin (IL)-2 secretion, as well as suppression of both interferon gamma (Th1) and IL-4 (Th2). Moreover, addition of anti-TGF-beta partially reverses this T cell suppression. When CTLA-4 was cross-linked in T cell populations from TGF-beta1 gene-deleted (TGF-beta1(-/-)) mice, the T cell responses were only suppressed 38% compared with 95% in wild-type mice. Our data demonstrate that engagement of CTLA-4 leads to CD4(+) T cell production of TGF-beta, which, in part, contributes to the downregulation of T cell activation. CTLA-4, through TGF-beta, may serve as a counterbalance for CD28 costimulation of IL-2 and CD4(+) T cell activation.

Abatacept↗
PubMed1998

Human primary visual cortex and lateral geniculate nucleus activation during visual imagery.

The functional magnetic resonance (fMRI) technique can be robustly used to map functional activation of the visual pathway including the primary visual cortex (V1), the lateral geniculate nucleus (LGN), and other nuclei of humans during visual perception stimulation. One of the major controversies in visual neuroscience is whether lower-order visual areas involve the visual imagery process. This issue was examined using fMRI at high magnetic field. It was demonstrated for the first time that the LGN was activated during visual imagery process in the human brain together with V1 and other activation. There was a tight coupling of the activation between V1 and the LGN during visual imagery.

Adult↗
PubMed1998

Eliciting T cell immunity against poorly immunogenic tumors by immunization with dendritic cell-tumor fusion vaccines.

Dendritic cells (DCs) are the most effective APCs and are being studied as natural adjuvants or Ag delivery vehicles to elicit T cell-mediated antitumor immunity. This study examined whether inoculation of DCs fused with poorly immunogenic tumor cells elicited tumor-reactive T cells for adoptive immunotherapy. DCs derived from bone marrow of C57BL/6 (B6) mice were fused with syngeneic B16 melanoma or RMA-S lymphoma cells by polyethylene glycol. The B16/DC and RMA-S/DC fusion hybrids expressed MHC class I, class II Ags, costimulatory molecules, as well as DC-specific and tumor-derived surface markers. The tumor/DC hybrids were capable of processing and presenting tumor-derived Ags, and immunization of B6 mice with irradiated B16/DC or RMA-S/DC vaccine elicited tumor-specific CTL activities. Vaccination of B6 mice with irradiated B16/DC fusion preparations induced partial host protective immunity against B16 tumor challenge. Reduced tumor incidence and prolonged survival time were observed. Adoptive transfer of T cells derived from B16/DC vaccine-primed lymph nodes into B16 tumor-bearing mice greatly reduced the number of established pulmonary metastases with or without in vivo administration of IL-2. Moreover, adoptive transfer of RMA-S/DC vaccine-primed, cultured lymph node T cells eradicated disseminated FBL-3 tumor. The results demonstrate that tumor/DC fusion products are effective cellular vaccines for eliciting T cell-mediated antitumor immunity.

Adoptive Transfer↗
PubMed1998

Regulation of the Ca2+ gradient across the sarcoplasmic reticulum in perfused rabbit heart. A 19F nuclear magnetic resonance study.

Myocardial contractility depends on Ca2+ release from and uptake into the sarcoplasmic reticulum (SR). The Ca2+ gradient between the SR matrix and the cytosol (SR Ca2+ gradient) is maintained by the SR Ca2+-ATPase using the free energy available from hydrolysis of ATP. The activity of the SR Ca2+-ATPase is not only dependent on the energy state of the cell but is also kinetically regulated by SR proteins such as phospholamban. To evaluate the importance of thermodynamic and kinetic regulation of the SR Ca2+ gradient, we examined the relationship between the energy available from ATP hydrolysis (DeltaGATP) and the energy required for maintenance of the SR Ca2+ gradient (DeltaGCa2+SR) during physiological and pathological manipulations that alter DeltaGATP and the phosphorylation state of phospholamban. We used our previously developed 19F nuclear magnetic resonance method to measure the ionized [Ca2+] in the SR of Langendorff-perfused rabbit hearts. We found that addition of either pyruvate or isoproterenol resulted in an increase in left ventricular developed pressure and an increase in [Ca2+]SR. Pyruvate increased DeltaGATP, and the increase in the SR Ca2+ gradient was matched to the increase in DeltaGATP; DeltaGATP increased from 58.3+/-0.5 to 60.4+/-1.0 kJ/mol (P<0.05), and DeltaGCa2+SR increased from 47.1+/-0.3 to 48.5+/-0.1 kJ/mol (P<0.05). In contrast, the increase in the SR Ca2+ gradient in the presence of isoproterenol occurred despite a decline in DeltaGATP from 58. 3+/-0.5 to 55.8+/-0.6 kJ/mol. Thus, the data indicate that the SR Ca2+ gradient can be increased by an increase in DeltaGATP, and that the positive inotropic effect of pyruvate can be explained by improved energy-linked SR Ca2+ handling, whereas the results with isoproterenol are consistent with removal of the kinetic limitation of phospholamban on the activity of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase, which allows the SR Ca2+ gradient to move closer to its thermodynamic limit. Ischemia decreases DeltaGATP, and this should also have an effect on SR Ca2+ handling. During 30 minutes of ischemia, DeltaGATP decreased by 12 kJ/mol, but the decrease in DeltaGCa2+SR was 16 kJ/mol, greater than would be predicted by the fall in DeltaGATP and consistent with increased SR Ca2+ release and increased SR Ca2+ cycling. Because ischemic preconditioning is reported to decrease SR Ca2+ cycling during a subsequent sustained period of ischemia, we examined whether ischemic preconditioning affects the relationship between the fall in DeltaGATP and the fall in DeltaGCa2+SR during ischemia. We found that preconditioning attenuated the fall in DeltaGCa2+SR during ischemia; the fall in DeltaGCa2+SR was of comparable magnitude to the fall in DeltaGATP, and this was associated with a significant improvement in functional recovery during reperfusion. The data suggest that there is both thermodynamic regulation of the SR Ca2+ gradient by DeltaGATP and kinetic regulation, which can alter the relationship between DeltaGATP and DeltaGCa2+SR.

Adenosine Triphosphate↗