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Biomedical subjects

J Chen

Publications and source records attributed to J Chen.

At least 343 records · Page 19Linked to original sources
PubMed2001

Comparison of dichloran 18% glycerol (DG18) agar with general purpose mycological media for enumerating food spoilage yeasts.

Dichloran 18% glycerol (DG18) agar was originally developed to enumerate xerophilic foodborne moulds. However, some laboratories are using DG18 agar as a general medium to enumerate foodborne moulds and yeasts. A collaborative study, with the participation of seven laboratories, was undertaken to compare DG18 agar with dichloran rose bengal chloramphenicol (DRBC) agar, tryptone glucose yeast extract chloramphenicol (TGYC) agar, and plate count agar supplemented with chloramphenicol (PCAC) for enumerating 14 species of common food spoilage yeasts. Comparison of the mean values of populations of all yeasts recovered on each medium revealed no significant differences among DRBC agar, PCAC, and TGYC agar, while each of these media supported the development of significantly (P < or = 0.05) higher numbers of colonies than DG18 agar. However, differences were only 0.08 to 0.10 log10 cfu/ml, making the practical significance questionable. The overall coefficient of variation (CV) for within laboratory repeatability was 1.71%, while the CV for reproducibility of counts obtained among laboratories was 6.96%. Compared to DRBC agar, TGYC agar, and PCAC, yeast colonies were smaller on DG18 agar. Growth of Brettanomyces anomalus, Cryptococcus albidus, and Rhodotorula mucilaginosa was particularly retarded or inhibited on DG18 agar. Based on the performance of media in supporting colony development and ease of counting colonies, the use of DG18 agar as a general enumeration medium for foodborne yeasts cannot be recommended.

Agar↗
PubMed2001

Regulation of interleukin (IL)-18 receptor alpha chain expression on CD4(+) T cells during T helper (Th)1/Th2 differentiation. Critical downregulatory role of IL-4.

Interleukin (IL)-18 has been well characterized as a costimulatory factor for the induction of IL-12-mediated interferon (IFN)-gamma production by T helper (Th)1 cells, but also can induce IL-4 production and thus facilitate the differentiation of Th2 cells. To determine the mechanisms by which IL-18 might regulate these diametrically distinct immune responses, we have analyzed the role of cytokines in the regulation of IL-18 receptor alpha chain (IL-18Ralpha) expression. The majority of peripheral CD4(+) T cells constitutively expressed the IL-18Ralpha. Upon antigen stimulation in the presence of IL-12, marked enhancement of IL-18Ralpha expression was observed. IL-12-mediated upregulation of IL-18Ralpha required IFN-gamma. Activated CD4(+) T cells that expressed low levels of IL-18Ralpha could produce IFN-gamma when stimulated with the combination of IL-12 and IL-18, while CD4(+) cells which expressed high levels of IL-18Ralpha could respond to IL-18 alone. In contrast, T cell stimulation in the presence of IL-4 resulted in a downregulation of IL-18Ralpha expression. Both IL-4(-/)- and signal transducer and activator of transcription (Stat)6(-/)- T cells expressed higher levels of IL-18Ralpha after TCR stimulation. Furthermore, activated T cells from Stat6(-/)- mice produced more IFN-gamma in response to IL-18 than wild-type controls. Thus, positive/negative regulation of the IL-18Ralpha by the major inductive cytokines (IL-12 and IL-4) determines the capacity of IL-18 to polarize an immune response.

Animals↗
PubMed2001

T-loop phosphorylation stabilizes the CDK7-cyclin H-MAT1 complex in vivo and regulates its CTD kinase activity.

Cyclin-dependent kinase (CDK)7-cyclin H, the CDK-activating kinase (CAK) and TFIIH-associated kinase in metazoans can be activated in vitro through T-loop phosphorylation or binding to the RING finger protein MAT1. Although the two mechanisms can operate independently, we show that in a physiological setting, MAT1 binding and T-loop phosphorylation cooperate to stabilize the CAK complex of Drosophila. CDK7 forms a stable complex with cyclin H and MAT1 in vivo only when phosphorylated on either one of two residues (Ser164 or Thr170) in its T-loop. Mutation of both phosphorylation sites causes temperature-dependent dissociation of CDK7 complexes and lethality. Furthermore, phosphorylation of Thr170 greatly stimulates the activity of the CDK7- cyclin H-MAT1 complex towards the C-terminal domain of RNA polymerase II without significantly affecting activity towards CDK2. Remarkably, the substrate-specific increase in activity caused by T-loop phosphorylation is due entirely to accelerated enzyme turnover. Thus phosphorylation on Thr170 could provide a mechanism to augment CTD phosphorylation by TFIIH-associated CDK7, and thereby regulate transcription.

Amino Acid Sequence↗
PubMed2001

MAD2B is an inhibitor of the anaphase-promoting complex.

Anaphase-promoting complex (APC), a ubiquitin ligase, controls both sister chromatid separation and mitotic exit. The APC is activated in mitosis and G1 by CDC20 and CDH1, and inhibited by the checkpoint protein MAD2, a specific inhibitor of CDC20. We show here that a MAD2 homolog MAD2B also inhibits APC. In contrast to MAD2, MAD2B inhibits both CDH1-APC and CDC20-APC. This inhibition is targeted to CDH1 and CDC20, but not directly to APC. Unlike MAD2, whose interaction with MAD1 is required for mitotic checkpoint control, MAD2B does not interact with MAD1, suggesting that MAD2B may relay a different cellular signal to APC.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2001

Cloning of a novel retinoid-inducible serine carboxypeptidase from vascular smooth muscle cells.

Retinoids block smooth muscle cell (SMC) proliferation and attenuate neointimal formation after vascular injury, presumably through retinoid receptor-mediated changes in gene expression. To identify target genes in SMC whose encoded proteins could contribute to such favorable biological effects, we performed a subtractive screen for retinoid-inducible genes in cultured SMC. Here, we report on the cloning and initial characterization of a novel retinoid-inducible serine carboxypeptidase (RISC). Expression of RISC is low in cultured SMC but progressively increases over a 5-day time-course treatment with all-trans-retinoic acid. A near full-length rat RISC cDNA was cloned and found to have a 452-amino acid open reading frame containing an amino-terminal signal sequence, followed by several conserved domains comprising the catalytic triad common to members of the serine carboxypeptidase family. In vitro transcription and translation experiments showed that the rat RISC cDNA generates an approximately 51-kDa protein. Confocal immunofluorescence microscopy of COS-7 cells transiently transfected with a RISC-His tag plasmid revealed cytosolic localization of the fusion protein. Western blotting studies using conditioned medium from transfected COS-7 cells suggest that RISC is a secreted protein. Tissue Northern blotting studies demonstrated robust expression of RISC in rat aorta, bladder, and kidney with much lower levels in all other tissues analyzed; high level RISC expression was also observed in human kidney. In situ hybridization verified the localization of RISC to medial SMC of the adult rat aorta. Interestingly, expression in kidney was restricted to proximal convoluted tubules; little or no expression was observed in glomerular cells, distal convoluted and collecting tubules, or medullary cells. Radiation hybrid mapping studies placed the rat RISC locus on chromosome 10q. These studies reveal a novel retinoid-inducible protease whose activity may be involved in vascular wall and kidney homeostasis.

Amino Acid Sequence↗
PubMed2001

[Treatment of spontaneous metastatic lung cancer with tumor antigen-pulsed, interleukin-18 gene-modified dendritic cells].

OBJECTIVE: To investigate the effect of tumor antigen-pulsed, interleukin-18 (IL-18) gene-modified dendritic cells in treatment of spontaneous metastatic lung cancer. METHODS: 3LL Lewis lung cancer cells were injected into the footpads of C57BL/6 mice to establish a spontaneous metastatic lung cancer model. Ninety-six mice with lung cancer were divided into 8 groups, 12 in each. treated differently. One group was treated by subcutaneous vaccination for two times of tumor antigen peptide Mut1-pulsed, IL-18 gene-modified dendritic cells (DC-IL-18/Mut1) that were derived from normal bone marrow. The other groups were treated with other measures. After treatment, the lung weight, number of metastatic nodes on the lung surface, survival time, and NK and CTL activities were examined. RESULTS: Compared with the mice treated with Mut1-pulsed control LacZ gene-modified DC and those treated with untreated DC, the tumor-bearing mice treated with DC-IL-18/Mut1 had the lightest lung weight (215 mg +/- 20 mg Vs 398 mg +/- 23 mg and 987 mg +/- 45 mg, t = 14.7 and 38.4, P < 0.01), the least lung metastatic nodes (0 Vs 7.8 +/- 2.7 and 49, P < 0.01), the longest survival time (chi(2) = 6.78 and 10.49 respectively, P < 0.01), the strongest cytotoxic T cell activity (53.4 +/- 3.1 Vs 41.3 +/- 2.6 and 9.8 +/- 2.1, t = 13.4 and 15, 7 respectively, P < 0.01), and increased proportions of CD4 + Tcells, CD8 + Tcells, and NK cells. CONCLUSION: Tumor antigen-pulsed, IL-18 gene-modified dendritic cells have a significant therapeutic effect on spontaneous netastatic lung cancer through induction of anti-tumor immunological responses.

Animals↗
PubMed2001

[Development and clinical application of posterior STBtrade mark thoracolumbar transpedicular screw-plate fixation system].

OBJECTIVE: To develop a posterior STBTM thoracolumbar transpedicular screw-plate system and to apply it clinically. METHODS: A posterior STBTM thoracolumbar transpedicular screw-plate system was developed with titanium alloy (TC4, Ti64A14V) and was used, from December 1999 to July 2000, to treat 63 cases with thoracolumbar or lumbar injuries or diseases, including thoracolumbar fracture/dislocation (33 cases), lumbar spondylosis and spondylolisthesis (16 cases), lumbar spondylosis and disk protrusion (6 cases), degenerative lumbar instability (4 cases), kyphosis due to ankylosing spondylitis (2 cases), and tuberculosis of spine (2 cases). RESULTS: The 33 cases with thoracolumbar fracture/dislocation showed perfect reduction and fixation after the operation. The height of injured vertebral bodies returned to normal. One month later, all patients with neurological deficits, except the 6 cases with neurological deficits of Frankel grade A, showed improvement by 1 approximately 3 Frankel grades. The radicular symptoms in the 26 patients with lumbar spondylolisthesis, lumbar spondylosis and disk protrusion, and degenerative lumbar instability disappeared after operation. Among those cases, complete reduction was achieved in the 7 cases with grade I spondylolisthesis and 7 out of the 9 cases with grade II spondylolisthesis, and incomplete reduction (grade I) was seen in the remaining 2 cases with grade II spondylolisthesis. Forty cases were followed up for 5 months or over in out-patient department, no complication was found. CONCLUSION: The posterior STBTM thoracolumbar transpedicular screw-plate system has the advantages of biological stability, excellent reduction capacity, easiness of operation, and positive clinical effectiveness.

Adult↗
PubMed2001

Caspase-activated DNase/DNA fragmentation factor 40 mediates apoptotic DNA fragmentation in transient cerebral ischemia and in neuronal cultures.

Nuclear changes, including internucleosomal DNA fragmentation, are characteristic features of neuronal apoptosis resulting from transient cerebral ischemia and related brain insults for which the molecular mechanism has not been elucidated. Recent studies suggest that a caspase-3-mediated mechanism may be involved in the process of nuclear degradation in ischemic neurons. In this study, we cloned from rat brain a homolog cDNA encoding caspase-activated deoxyribonuclease (CAD)/DNA fragmentation factor 40 (DFF40), a 40 kDa nuclear enzyme that is activated by caspase-3 and promotes apoptotic DNA degradation. Subsequently, we investigated the role of CAD/DFF40 in the induction of internucleosomal DNA fragmentation in the hippocampus in a rat model of transient global ischemia and in primary neuronal cultures under ischemia-like conditions. At 8-72 hr after ischemia, CAD/DFF40 mRNA and protein were induced in the degenerating hippocampal CA1 neurons. CAD/DFF40 formed a heterodimeric complex in the nucleus with its natural inhibitor CAD (ICAD) and was activated after ischemia in a delayed manner (>24 hr) by caspase-3, which translocated into the nucleus and cleaved ICAD. Furthermore, an induced CAD/DFF40 activity was detected in nuclear extracts in both in vivo and in vitro models, and the DNA degradation activity of CAD/DFF40 was inhibited by purified ICAD protein. These results strongly suggest that CAD/DFF40 is the endogenous endonuclease that mediates caspase-3-dependent internucleosomal DNA degradation and related nuclear alterations in ischemic neurons.

Animals↗
PubMed2001

Raf-1 promotes cell survival by antagonizing apoptosis signal-regulating kinase 1 through a MEK-ERK independent mechanism.

The Ser/Thr kinase Raf-1 is a protooncogene product that is a central component in many signaling pathways involved in normal cell growth and oncogenic transformation. Upon activation, Raf-1 phosphorylates mitogen-activated protein kinase kinase (MEK), which in turn activates mitogen-activated protein kinase/extracellular signal-regulated kinases (MAPK/ERKs), leading to the propagation of signals. Depending on specific stimuli and cellular environment, the Raf-1--MEK--ERK cascade regulates diverse cellular processes such as proliferation, differentiation, and apoptosis. Here, we describe a MEK--ERK-independent prosurvival function of Raf-1. We found that Raf-1 interacts with the proapoptotic, stress-activated protein kinase ASK1 (apoptosis signal-regulating kinase 1) in vitro and in vivo. Deletion analysis localized the Raf-1 binding site to the N-terminal regulatory fragment of ASK1. This interaction allows Raf-1 to act independently of the MEK--ERK pathway to inhibit apoptosis. Furthermore, catalytically inactive forms of Raf-1 can mimic the wild-type effect, raising the possibility of a kinase-independent function of Raf-1. Thus, Raf-1 may promote cell survival through its protein-protein interactions in addition to its established MEK kinase function.

Animals↗
PubMed2001

Genetic deficiency of inducible nitric oxide synthase reduces atherosclerosis and lowers plasma lipid peroxides in apolipoprotein E-knockout mice.

BACKGROUND: Inducible nitric oxide synthase (iNOS) is expressed by leukocytes and smooth muscle cells in atherosclerotic lesions. To test whether NO produced by iNOS deficiency affects atherosclerosis, we studied apoE/iNOS-double knockout (dKO) and apoE-knockout (KO) control animals fed a "Western-type" diet. METHODS AND RESULTS: After 16 weeks of Western-type diet, the aortic lesion area in apoE/iNOS-dKO males and females was significantly reduced, by 22% and 21%, respectively, compared with apoE-KO males and females. This effect was more pronounced after 24 weeks of Western-type diet, after which lesion formation in male and female dKO mice was reduced by 38% and 40%, respectively. Plasma levels of lipoperoxides in apoE/iNOS-dKO mice (2.0+/-0.23 micromol/L) were significantly lower than in apoE-KO control animals (3.2+/-0.44 micromol/L; P=0.02). To test whether substrate deficiency plays a role in the proatherogenic actions of iNOS, we administered L-arginine to apoE-KO animals for 16 and 24 weeks. L-Arginine treatment did not affect lesion formation in apoE-KO animals fed a Western-type diet. CONCLUSIONS: Genetic deficiency of iNOS decreases diet-induced atherosclerosis and lowers plasma levels of lipoperoxides, a marker for oxidative stress, in apoE-KO animals. Reduction in iNOS-mediated oxidative stress could partly explain protection from lesion formation in dKO animals. L-Arginine supplementation did not change lesion area in apoE-KO mice, indicating that substrate deficiency is not a likely cause for iNOS-mediated injury in this model of atherosclerosis.

Animals↗
PubMed2001

Treatment of stroke in rat with intracarotid administration of marrow stromal cells.

OBJECTIVE: To measure the therapeutic efficacy for the treatment of stroke with intra-arterial administration of bone marrow stromal cells (MSC). BACKGROUND: MSC have characteristics of stem and progenitor cells. The hypothesis that MSC injected into the internal carotid artery after stroke enter into ischemic brain and improve neurologic recovery was tested. METHODS: Twenty-five adult Wistar rats were subjected to transient (2-hour) middle cerebral artery occlusion alone (n = 9), or treated with intracarotid arterial injection of 200 microL phosphate-buffered saline (n = 8) or 2 x 10(6) MSC in 200 microL phosphate-buffered saline (n = 8) 1 day after ischemia. MSC were harvested and isolated from additional adult rats and then cultured and labeled with bromodeoxyuridine. Rats were subjected to neurologic functional tests (adhesive-removal, modified neurologic severity scores) before and at 1, 7, and 14 days after middle cerebral artery occlusion. Immunohistochemistry was used to identify cell-specific proteins of bromodeoxyuridine-reactive MSC. RESULTS: Bromodeoxyuridine-reactive cells ( approximately 21% of 2 x 10(6) injected MSC) distributed throughout the territory of the middle cerebral artery by 14 days after ischemia. Some bromodeoxyuridine-reactive cells expressed proteins characteristic of astrocytes and neurons. Rats with intra-arterial transplantation of MSC exhibited improvement on the adhesive-removal test (p < 0.05) and the modified neurologic severity scores (p < 0.05) at 14 days compared with controls. CONCLUSIONS: MSC injected intra-arterially are localized and directed to the territory of the middle cerebral artery, and these cells foster functional improvement after cerebral ischemia.

Animals↗
PubMed2001

[Curative effect of radical gastrectomy combined with peritoneal lavage with thermal hypoosmotic solution in treatment of gastric cancer].

OBJECTIVE: To evaluate the curative effect and indications of radical gastrectomy combined with peritoneal lavage with thermal hypoosmotic solution, double distilled water (DDW) or DDW plus chlorhexidine acetate, in treatment of gastric cancer. METHODS: Five hundred cases of gastric cancer who underwent radical gastrectomy from January 1986 to December 1995 were divided into three groups: group A with 198 cases who underwent radical gastrectomy and peritoneal lavage for 10 minutes with 400 ml of DDW at 43 degrees C, group B, with 89 cases who underwent radical gastrectomy and peritoneal lavage for ten minutes with 4 000 ml of DDW plus 0.6 g chlorhexidine acetate, and group C, with 213 cases who underwent radical gastrectorny and peritoneal lavage for four minutes with 4 000 ml of normal saline at normal temperature as controls. RESULTS: The group A and group B (called lavage group as a whole) had almost the same curative effects. The one-year survival rates and three-year survival rates were similar among the cases in different stages in no matter what group. The five-year survival rate was 63.8% in the lavage group and 51.2% in the control group, most of the cases with a good effect being at the mid-stage (II and III A stages). CONCLUSION: Peritoneal lavage, helpful in killing the exfoliated cancer cells in peritoneal cavity of patients with gastric cancer at II and III A stages, should be conducted in the treatment of gastric cancer by radical gastrectomy before closing the abdomen.

Adult↗
PubMed2001

The effects of lead on transient outward currents of acutely dissociated rat dorsal root ganglia.

The effects of Pb2+ on transient outward currents (TOCs) were investigated on rat dorsal root ganglia (DRG) neurons at postnatal days of 15 approximately 21, using the conventional whole-cell patch-clamp technique. In media-sized (35 approximately 40 microm) neurons and in the presence of 50 mM TEA, TOCs that preliminarly included an A-current (IA) and a D-current (ID), were clearly present and dominant. Application of Pb2+ lengthened the initial delay of TOCs and increased the onset-peak time in a concentration-dependent manner. The amplitudes of initial outward current peak were reduced with increasing Pb2+ concentrations. The inhibitory effects of Pb2+ on TOCs were reversible with 80 approximately 90% of current reversed in 2 approximately 10 min at 1 approximately 400 microM Pb2+. For the normalized activation curves fitted by a single Boltzmann equation under each condition, there was a shift to more depolarized voltages with increasing concentrations of Pb2+. The V1/2 and the slope factor (k) increased from 12.76+/-1.49 mV and 15.31+/-1.66 mV (n=10) under control condition to 39.91+/-5.44 mV (n=10, P<0.01) and 21.39+/-3.13 mV (n=10, P<0.05) at 400 microM Pb2+, respectively, indicating that Pb2+ decreased the activation of TOCs. For the normalized steady-state inactivation curves, the V1/2 and the k increased from -92.31+/-2.72 and 8.59+/-1.36 mV (n=10) to -55.65+/-3.67 (n=10, P<0.01) and 23.02+/-2.98 mV (n=10, P<0.01) at 400 microM Pb2+, respectively. The curves were shifted to more depolarized voltages by Pb2+, indicating that channels were less likely to be inactivated at higher concentrations of Pb2+ at any given potential. The fast (tf) and slow (ts) decay time-constants were both significantly increased by increasing concentrations of Pb2+ (n=10, P<0.05), indicating that Pb2+ increased the decay time-course of TOCs. These effects were concentration-dependent and partly reversible following washing. Ca2+ modulated the TOCs gating and might share same binding site with Pb2+, for which Ca2+ had very low affinity. In summary, the results demonstrated that Pb2+ was a dose- and voltage-dependent, and reversible blocker of TOCs in rat DRG neurons. After Pb2+ application, normal sensory physiology of DRG neurons was affected, and these neurons might display aberrant firing properties that resulted in abnormal sensations. This variation caused by Pb2+ could underlie the toxical modulation of sensory input to the central nervous system.

Action Potentials↗
PubMed2001

Carbonyl sulfide derived from catalytic oxidation of carbon disulfide over atmospheric particles.

The formation of carbonyl sulfide (COS) by catalytic oxidization of carbon disulfide (CS2) over atmospheric particle catalysts was explored through FT-IR, MS (mass spectrometry), and a fixed-bed stainless steel reactor. Also the crystallizing conditions and specific surfaces (areas) of the catalysts were investigated by means of X-ray diffraction (XRD) and BET. Some oxides such as CaO, Fe2O3, Al2O3, and SiO2 were investigated under the conditions similar to the atmospheric particles as a comparison. The results showed that atmospheric particles and the oxide catalysts exhibited considerable oxidizing activity for CS2 at ambient temperature to form COS. Elemental sulfur as well as COS was one of the main products; even CO2 could be produced by a secondary reaction on some catalysts. Among the catalysts, CaO showed the strongest catalytic activity for oxidizing CS2. The catalytic activities of Fe2O3 and Al2O3 decreased considerably as compared with CaO, and SiO2 had the weakest catalytic activity. Atmospheric particles' catalytic activity is between Fe2O3's and Al2O3's. The atmospheric particles we collected mainly consist of Ca(Al2Si2O8).4H2O, which is also the main component of cement. COS, the main product, is formed by the catalytic oxidizing reaction of CS2 with adsorbed "molecular" oxygen overthe catalysts' surfaces. The concentration of adsorbed oxygen over catalysts' surfaces may be the key factor contributed to the oxidizing activities. This paper first revealed that CS2 could be catalytically oxidized over atmospheric particles to form COS. It induced that this reaction may be another important source of atmospheric COS from CS2.

Air Pollutants↗
PubMed2001

Effects of dissipation on a superconducting single electron transistor.

We measure the effect of dissipation on the minimum zero-bias conductance, G(min)0, of a superconducting single electron transistor (sSET) capacitively coupled to a two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. Depleting the 2DEG with a back gate voltage decreases the dissipation experienced by the sSET in situ. We find that G(min)0 increases as the dissipation is increased or the temperature is reduced; the functional forms of these dependences are compared with the model of Wilhelm et al. in which the leads coupled to the sSET are represented by lossy transmission lines.

Journal Article↗