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Biomedical subjects

X Chen

Publications and source records attributed to X Chen.

At least 541 records · Page 30Linked to original sources
PubMed2000

The relevance of cell proliferation, vascular endothelial growth factor, and basic fibroblast growth factor production to angiogenesis and tumorigenicity in human glioma cell lines.

Tumor growth is partially dependent on angiogenesis, a process that relies on angiogenic factors. Tumorigenicity of cancer cells is thought to be associated with the production of various angiogenic factors that stimulate or inhibit the rate of endothelial cell migration and proliferation. However, the relative importance of specific individual factors originally studied in cancer cell lines has yet to be determined in vivo. In this study, we examined seven human glioma cell lines for dynamic changes of two major angiogenic factors, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), and for doubling time and tumorigenicity in nude mice. Various correlation studies demonstrated that in these glioma cell lines, VEGF expression correlated well with RBC density in tumor sections (r2 = 0.804) and with average tumor weight (r2 = 0.987). In contrast, bFGF expression in the observed glioma cell lines did not correlate with tumorigenicity (r2 = 0.001) or with VEGF expression (r2 = 0.255). Furthermore, there was no correlation between doubling time and tumorigenicity in these cell lines (r2 = 0.160). Taken together, these results suggest that VEGF plays a major role in glioma formation and that down-regulation of VEGF, rather than bFGF, would be a more effective choice for glioma gene therapy.

Animals↗
PubMed2000

Cone properties of retinal margin cells in the monkey (Macaca mulatta).

PURPOSE: To characterize a cell population in the monkey retinal margin that was labeled with a cone-specific antibody and to determine the presence of additional markers. METHODS: Retinal whole-mount preparations from infant and adult rhesus monkeys (Macaca mulatta) were immunolabeled by incubation overnight with the primary antibodies 7G6, a cone-specific antibody; SV2, a synaptic-vesicle antibody; and opsin antibodies that recognize either the short or long/middle wavelength-sensitive opsins. RESULTS: The retinal margin cells labeled by 7G6 lay within 1 mm of the ora serrata and differed from 7G6-labeled cones in the central retina. The margin cells possessed a soma, a fiber process, and a terminal enlargement that lay in the plane of the retina; no outer segment was discernible. A total of 5400 and 7252 margin cones cells were found in each of two monkeys. The terminal enlargement and soma of the labeled margin cells also showed SV2 immunoreactivity. Surprisingly, opsin immunoreactivity extended throughout the margin cell, which is consistent with the absence of a discernible outer segment. CONCLUSIONS: Cells with immunoreactive cone properties were found in the margin of the monkey retina. The absence of an outer segment and the presence of somatic opsin and SV2 are reminiscent of features observed in the central cones of fetal monkey retinas. These results suggest that a subpopulation of cones in the retinal margin might fail to mature completely and thus retain juvenile characteristics into adulthood.

Aging↗
PubMed2000

Effects of vitamin E and selenium supplementation on esophageal adenocarcinogenesis in a surgical model with rats.

Two well-known antioxidative nutrients, vitamin E and selenium, were used in this study to investigate possible inhibitory action against the formation of esophageal adenocarcinoma (EAC) in rats. In this model, carcinogenesis is believed to be driven by oxidative stress. Male Sprague-Dawley rats (8 weeks old) were divided into four groups and received esophagoduodenal anastomosis (EDA) surgery plus iron supplementation (12 mg/kg/week). Vitamin E and selenium were supplemented in the diet in the forms of alpha-tocopheryl acetate (750 IU/kg) and sodium selenate (1.7 mg Se/kg), which were 10 times the regular amounts in the basic AIN93M diet. At 40 weeks after surgery, all the EDA groups had lower body weights than the non-operated control group. Iron nutrition (hemoglobin, total serum iron and transferrin saturation) was normal as a result of iron supplementation after EDA. Vitamin E supplementation maintained the normal plasma level of alpha-tocopherol in EDA rats, but not those of gamma-tocopherol and retinol. Selenium supplementation increased the serum and liver selenium contents of the EDA rats. Histopathological analysis showed that selenium supplementation increased the incidence of EAC and the tumor volume. The selenium level in the tumor is higher than that in the duodenum of the same animal. Vitamin E supplementation, however, inhibited carcinogenesis, especially in the selenium-supplemented group. We believe that vitamin E exerts its effect through its antioxidative properties, and a high dose of inorganic selenium may promote carcinogenesis by enhancing oxidative stress.

Absorption↗
PubMed2000

Mechanism of protein import across the chloroplast envelope.

The development and maintenance of chloroplasts relies on the contribution of protein subunits from both plastid and nuclear genomes. Most chloroplast proteins are encoded by nuclear genes and are post-translationally imported into the organelle across the double membrane of the chloroplast envelope. Protein import into the chloroplast consists of two essential elements: the specific recognition of the targeting signals (transit sequences) of cytoplasmic preproteins by receptors at the outer envelope membrane and the subsequent translocation of preproteins simultaneously across the double membrane of the envelope. These processes are mediated via the co-ordinate action of protein translocon complexes in the outer (Toc apparatus) and inner (Tic apparatus) envelope membranes.

Amino Acid Sequence↗
PubMed2000

[Molecular cytogenetic characterization of a new wheat line YW443 with resistance to barley yellow dwarf virus].

A new wheat line YW443 with BYDV resistance and good traits was developed from the combination of PP9-1/Shan7859¿Fengkang 8. The wheat line YW443 was identified by BYDV resistance analysis, genomic in situ hybridization (GISH), RFLP and RAPD analysis. The results indicated as follows: (1) YW443 was resistant to GPV and GAV strains of BYDV; (2) YW443 is a homozygous wheat-Thinopyrum intermedium translocation line with a pair of BYDV resistance genes; (3) The 7StL segment of Th. intermedium carring BYDV resistance gene was transferred onto the distal end of the wheat chromosome 7D long arm, the line YW443 was 7DS.7DL-7StL translocation; (4) A RAPD marker OPR19(-900) could detect the DNA of Th. intermedium 7StL in L1 and L1 derivatives including translocation lines YW443, YW642 etc. The markers may be used as a selecting marker for the BYDV resistance breeding program.

In Situ Hybridization↗
PubMed2000

Chalcone, acyl hydrazide, and related amides kill cultured Trypanosoma brucei brucei.

BACKGROUND: Protozoan parasites of the genus Trypanosoma cause disease in a wide range of mammalian hosts. Trypanosoma brucei brucei, transmitted by tsetse fly to cattle, causes a disease (Nagana) of great economic importance in parts of Africa. T. b. brucei also serves as a model for related Trypanosoma species, which cause human sleeping sickness. MATERIALS AND METHODS: Chalcone and acyl hydrazide derivatives are known to retard the growth of Plasmodium falciparum in vitro and inhibit the malarial cysteine proteinase, falcipain. We tested the effects of these compounds on the growth of bloodstream forms of T. b. brucei in cell culture and in a murine trypanosomiasis model, and investigated their ability to inhibit trypanopain-Tb, the major cysteine proteinase of T. b. brucei. RESULTS: Several related chalcones, acyl hydrazides, and amides killed cultured bloodstream forms of T. b. brucei, with the most effective compound reducing parasite numbers by 50% relative to control populations at a concentration of 240 nM. The most effective inhibitors protected mice from an otherwise lethal T. b. brucei infection in an in vivo model of acute parasite infection. Many of the compounds also inhibited trypanopain-Tb, with the most effective inhibitor having a Ki value of 27 nM. Ki values for trypanopain-Tb inhibition were up to 50- to 100-fold lower than for inhibition of mammalian cathepsin L, suggesting the possibility of selective inhibition of the parasite enzyme. CONCLUSIONS: Chalcones, acyl hydrazides, and amides show promise as antitrypanosomal chemotherapeutic agents, with trypanopain-Tb possibly being one of their in vivo targets.

Amides↗
PubMed2000

Catecholamines and angiotensinogen gene expression in kidney proximal tubular cells.

To investigate the molecular mechanism(s) of action of catecholamines on the expression of the angiotensinogen (ANG) gene in kidney proximal tubular cells, we used opossum kidney (OK) cells with a fusion gene containing the 5'-flanking regulatory sequence of the rat ANG gene fused with a human growth hormone (hGH) gene as a reporter, pOGH (rANG N-1498/+18), permanently integrated into their genomes. The level of expression of the ANG-GH fusion gene was quantified by the amount of immunoreactive-hGH (IR-hGH) secreted into the medium. The addition of norepinephrine (NE), isoproterenol (a beta1/beta2-adrenergic receptor (AR) agonist) and iodoclonidine (an alpha2-AR agonist) stimulated the expression of the ANG-GH fusion gene in a dose-dependent manner, whereas the addition of epinephrine and phenylephrine (alpha1-AR agonist) had no effect. The stimulatory effect of NE was blocked by the presence of propranolol (beta-AR blocker), atenolol (beta1-AR blocker), yohimbine (alpha2-AR blocker), Rp-cAMP (an inhibitor of cAMP-dependent protein kinase AI & AII) and staurosporine (an inhibitor of protein kinase C), but was not blocked by ICI 118, 551 (beta2-AR blocker) and prazosin (alpha1-AR blocker). The addition of a combination of isoproterenol and iodoclonidine or a combination of 8-Bromo-cAMP (8-Br-cAMP) and phorbol 12-myristate (PMA) synergistically stimulated the expression of the ANG-GH fusion gene as compared to the addition of isoproterenol, iodoclonidine, 8-Br-cAMP or PMA alone. Furthermore, the addition of NE, 8-Br-cAMP or PMA stimulated the expression of pOGH (rANG N-806/-779/-53/+18), a fusion gene containing the putative cAMP responsive element (CRE, ANG N-806/-779) upstream of the ANG promoter (ANG N-53/+18) in OK cells, but had no effect on the expression of fusion genes containing the mutant of the CRE. Gel mobility shift assays revealed that the ANG-CRE binds with the DNA-binding domain (bZIP254-327) of the cAMP-responsive binding protein (CREB). The binding of the labeled ANG-CRE to CREB (bZIP254-327) was displaced by unlabeled ANG-CRE and the CRE of the somatostatin gene but not by the mutants of the ANG-CRE. Finally, NE stimulated the phosphorylation of CREB in OK cells. These studies demonstrate that the molecular mechanism(s) of NE action on the expression of the ANG gene in OK cells may be mediated via both the PKA and PKC signalling pathways and via the phosphorylation of CREB. The phosphorylated CREB then interacts with the CRE in the 5'-flanking region of the ANG gene and subsequently stimulates the gene expression.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2000

Impaired expression of the CD3-zeta chain in peripheral blood T cells of patients with chronic myeloid leukaemia results in an increased susceptibility to apoptosis.

In patients with myeloid malignancies, cell-mediated immunity is often suppressed, being most profound in those with advanced disease. Such immune dysfunction, as demonstrated in many patients with chronic lymphocytic leukaemia (CLL) and myelodysplastic syndrome (MDS), may, at least in part, be due to altered expression of the CD3-zeta chain, which is an important component of the T-cell receptor (TCR). We speculated that impaired expression of the TCR-zeta chain would be evident in peripheral blood T cells of patients with chronic myeloid leukaemia (CML) and that such an abnormality would result in an increased ex vivo susceptibility to apoptosis. In this study, we demonstrated that, compared with normal controls, zeta chain expression was significantly downregulated in all of the T-cell subsets (P < 0.009) in more than 90% of CML patients. In addition, there was a significantly lower expression of the CD3-epsilon chain (P < 0.001) in patients than in controls. In those patients with abnormal zeta chain expression, the proportion of lymphocytes with spontaneous DNA fragmentation, as determined by terminal deoxynucleotide transferase-mediated dUTP-biotin nick-end labelling (TUNEL) assays, was also significantly higher (P < 0.002) than controls. From all of the patients tested, it was possible to upregulate partially zeta chain expression and hence to reduce the susceptibility to apoptosis by cross-linking the T cells with interleukin (IL)-2, interferon (IFN)-alpha or immobilized CD3. In addition, such cross-linked T cells showed a significantly higher capacity to proliferate than the native CML T cells.

Adult↗
PubMed2000

[Identification of the barley chromosome in wheat by GISH and RFLP].

The barley chromosome in wheat was identified by genomic in situ hybridization (GISH) in which biotin labelled total genomic DNA of barley Betzes was used as probe and the unlabelled total DNA of common wheat Chinese Spring (CS) as blocking DNA. A series of wheat materials were tested as follows: two disomic alien substitution and monosomic alien addition lines, 2n = 43; two monosomic alien substitution lines, 2n = 42; seven disomic alien substitution lines, 2n = 42. RFLP probe psr131 on the short arm of the homologous group 2 was used to analyze the barley chromosome in wheat. The result indicated that there was a same band in barley Betzes and substitution line A5. The chromosome 2A of A5 was substituted by the chromosome 2H of barley. These materials will be useful in transferring the valuable genes in the chromosome 2H to wheat.

Chromosomes↗
PubMed2000

[Study on COL7A1 gene mutation in a epidermolysis bullosa pruriginosa family].

OBJECTIVE: To identify gene mutation of a epidermolysis bullosa pruriginosa family. METHODS: Polymerase chain reaction (PCR), DNA sequencing, multiplex PCR using allele-specific oligonucleotide primers. RESULTS: A G6100A transition of COL7A1 was found in patients, resulting in G2034R substitution in type VII collagen. The mutation was not found in control normal individuals. CONCLUSION: The mutation of G2034R is the underlying cause of epidermolysis bullosa pruriginosa in this family, not common polymorphism.

Collagen↗
PubMed2000

[Clinical analysis of 25 cases of malignant transformation of endometriosis of the ovary].

OBJECTIVE: To study clinicopathologic characteristics, treatment and prognostic factors of malignant transformation of endometriosis of the ovary. METHODS: From 1981 to 1999, a total of 25 patients with malignant transformation of endometriosis of the ovary were retrospectively analyzed. RESULTS: The main symptoms were pelvic masses, abdominal pain, abdominal distension and abnormal vaginal bleeding or discharge. Histological type: of the 25 cases, 14 were endometrioid carcinomas, 2 were clear-cell carcinomas, 2 were adenoacanthoma, 1 was serous papillary adenocarcinomas, 6 were mixed epithelium tumor of ovary. The exact area of histologic transition from benign to malignant epithelium was observed in 25 patients. Stage: stage I 14, stage II 7, stage III 3, stage IV 1. The actual 5-year survival rate was 77.7%. CONCLUSIONS: The exact incidence and prevalence of malignant transformation in endomertriosis is unknown. Radical tumor resection combined with chemotherapy is the main therapeutic approach for malignant transformation of endometriosis of the ovary.

Adult↗
PubMed2000

Flow injection analysis of fluoride: optimization of experimental conditions and non-linear calibration using artificial neural networks.

This paper deals with the application of artificial neural networks (ANNs) to two common problems in spectroscopy: optimization of experimental conditions and non-linear calibration of the result, with particular reference to the determination of fluoride by flow injection analysis (FIA). The FIA system was based on the formation of a blue ternary complex between zirconium(IV), p-methyldibromoarsenazo and F- with the maximum absorption wavelength at 635 nm. First, optimization in terms of sensitivity and sampling rate was carried out by using jointly a central composite design and ANNs, and a neural network with a 3-7-1 structure was confirmed to be able to provide the maximum performance. Second, the relationship between the concentration of fluoride and its absorbance was modeled by ANNs. In this process, cross-validation and leave-k-out were used. The results showed that good prediction was attained in the 1-4-1 neural net. The trained networks proved to be very powerful in both applications. The proposed method was successfully applied to the determination of free fluoride in tea and toothpaste with recoveries between 96 and 101%.

Calibration↗
PubMed2000

[Studies of multidrug resistance gene expression and apoptosis in stomach carcinoma].

OBJECTIVE: To investigate the influence of multidrug resistance gene (MDR) expression and apoptosis on stomach cancer. METHODS: A total of 80 cases of paraffin embedded stomach cancer tissues was stained immunohistochemically for P-gp, GST-pi and TOPO II using monoclonal antibodies and apoptosis (in terms of apoptotic index, AI) in tissues was musured by the TUNEL method. The results were correlated with tumor type, clinical stage and prognosis. RESULTS: Normal stomach tissue expression of P-gp was associated with better survival, but higher level of P-gp expression in tumor tissues was associated with poor prognosis. The expression of GST-pi didnot show a relationship with cell differentiation of stomach cancer and clinical stage of the disease, but positive correlation did exist between intensity of expression and survival time. Although the expression of TOPO II was associated with tumor cell differentiation, it did not affect prognosis. Apoptosis was demonstrated in 73% of the cases and was related to clinical stage of stomach carcinoma. CONCLUSION: While P-gp expression in tumor cells is indicative of poor prognosis, its expression in normal tissue has the opposite effect. Positive correlation exits between GST-pi expression intensity in tumor cells and survival. MDR and apoptosis are related to the biologic behavior of the tumor.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

The regulatory action of the modified Yu Ping Feng Tang on cellular immunity in mice under amputation-induced stress.

To approach the action of modified Yu Ping Feng Tang ([symbol: see text] Jade-Screen Decoction) on cellular immunity, an experiment was conducted in mice under amputation-induced stress. On the 3rd day after amputation, acute atrophy was found in the thymus, the reactivities of T- and B-lymphocytes to Con-A and LPS were decreased, the IL-2 content and its activity reduced and the activity of NK cells lowered. The high, moderate and low concentrations of the modified Yu Ping Feng (YPF) Decoction all have antagonistic action on the above manifestations of immune inhibition.

Adjuvants, Immunologic↗
PubMed2000

[Molecular cloning and sequencing of 5' non-coding region of TTV-like mini virus].

OBJECTIVE: To investigate the TTV- like mini virus (TLMV) infection in Chinese patients with non A-G hepatitis and to analyse sequence of 5' non-coding region (5'NCR)of TLMV. METHODS: TLMV DNA was detected by nested - PCR from 53 serum samples of non A-G hepatitis patients without TTV infection. PCR products were cloned and sequenced. RESULTS: TLMV DNA were positive in 37 of 53 patients (69.8%). The sequence of 5' NCR of 8 TLMV isolates was compared with that reported by Takahashi (GenBank Accession No. ab 026930-026931) and showed nucleotide identity between 64% - 83%. CONCLUSIONS: The results of this study indicated that TLMV infection is common in TTV negative patients with non A-G hepatitis. The 5' NCR sequence of TLMV showed a great degree of diversity. The pathogenicity of TLMV and its relationship to non A-G hepatitis need to be confirmed and further study is required.

Adolescent↗
PubMed2000

[Further study on the genetic characteristics of a strain of A/PR/8/34/].

OBJECTIVE: Through the test and analysis of nucleotide sequences of seven different RNA segments of the virion to exclude the possibility that A/Guangdong/6/91 (H1N1) strain might be derived from laboratory contamination and to determine how many RNA segments are there with nucleotide sequence difference between A/Guangdong/6/91 (H1N1) and A/PR/8/34 (H1N1) viruses, as well as to determine is A/Guangdong/6/91 virus a reassortant? METHODS: Virion RNA was transcribed into cDNA by reverse transcriptase, cDNA was amplified by PCR, the products of PCR were purified. Afterward, RNA sequence test was performed by the dideoxynucleotide chain termination method using synthetic oligodeoxynucleotide primers. RESULTS: There are no nucleotide sequence differences in RNA segments 6 and 7 between A/Guangdong/6/91 (H1N1) and PR8 strains, while there are 20,5, 11, 7 and 6 differences in nucleotide sequences of RNA segments 1, 2, 3, 5 and 8 between these two strains, respectively. These differences induce 10, 2, 1, 0 and 4 differences in amino acid sequences on PB2, PB1, PA,NP and NS protein molecules between A/Guangdong/6/91 (H1N1) and PR8 strains, respectively. CONCLUSIONS: The possibility of laboratory contamination of A/Guangdong/6/91 (H1N1) virus can be ruled out completely. A/Guangdong/6/91 (H1N1) virus is a PR8 like strain, but not a reassortant.

China↗