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Biomedical subjects

J Xu

Publications and source records attributed to J Xu.

At least 19 recordsLinked to original sources
PubMed1992

Proficiency of the Tradescantia-micronucleus image analysis system for scoring micronucleus frequencies and data analysis.

The Tradescantia-micronucleus (Trad-MCN) bioassay is an efficient short-term test for genotoxicity of pollutants. In order to increase the efficiency and to standardize the micronucleus (MCN) scoring process, an automated scoring system was developed using the principle of image analysis in computer science. This assemblage is called the Tradescantia-micronucleus image analysis (Trad-MCNIA) system. The MCN frequencies scored by this system were compared with those scored by human observation for its proficiency. A set of low MCN frequency (around 5 MCN/100 tetrads) slides prepared from a control group, a set of medium MCN frequency (around 20 MCN/100 tetrads) slides prepared from sodium azide treated plant cuttings and a set of high MCN frequency (around 50 MCN/100 tetrads) slides prepared from X-ray treated materials were used for this study. In the low MCN frequency slides, the Trad-MCNIA system scored about the same value as human observation. In the medium and high frequency slides, MCN frequencies scored by the system were lower than those scored by human observers. This discrepancy was corrected by increasing the power of the objective of the microscope in the system. The MCN frequencies scored by the system attained 90% congruity with those scored by human observers after the correction. The scoring speed of the system was about 3.5 times as fast as that by human observers, and the data could be statistically analyzed immediately after the data scores were recorded. Further improvements can be made by upgrading the video camera and the computer speed.

Azides↗
PubMed1992

Expression and immunochemical analysis of rat and human fibroblast growth factor receptor (flg) isoforms.

Potentially 96 splice variants among four genes that code for the human heparin-binding fibroblast growth factor receptor family complicate study of structure, metabolism, and function of single isoforms in mammalian cells. As an alternative, we expressed structural subdomains and isoforms of the flg receptor gene in bacteria and baculoviral-infected insect cells. We developed and characterized a panel of 16 isoform and domain-specific polyclonal and monoclonal antibodies. The panel of antibodies was used to distinguish mature glycosylated ligand-binding and kinase-active and -inactive recombinant isoforms in baculoviral insect cells and transfected mammalian cells and natural isoforms in rat prostate and human liver cells. The results revealed a cell type-specific expression of the flg gene and isoforms that result from combinations of splice variations. Reactive epitopes of monoclonal antibodies against both the three (alpha) and two (beta) immunoglobulin-like disulfide loop extracellular domain isoforms were mapped by cross-reactivity with synthetic polypeptide sequences and deletion mutants expressed in bacteria. The native alpha and beta receptor isoforms differed in display of shared epitopes and suggested that the NH2-terminal Loop I and COOH-terminal Loops II and III of the alpha isoform are interactive. Although the common Loops II and III appear qualitatively sufficient for ligand binding, the results suggest that tertiary relationships among loops in the three and two loop isoforms are distinct and, therefore, the two isoforms may have distinct activities. Spatial models for arrangement of immunoglobulin-like loops in the extracellular domain of the two isoforms are presented.

Amino Acid Sequence↗
PubMed1992

Assessment of the in vivo aneuploidy/micronucleus assay in mouse bone marrow cells with 16 chemicals.

Assessment of the in vivo aneuploidy/micronucleus Assay in bone marrow cells with 16 chemicals is described. This assay is based on the detection of kinetochores (KC) in micronuclei (MN) by antikinetochore-specific (CREST) antibodies. Among sixteen chemicals tested, six were known clastogens, three were known aneuploidy-inducers, and the other seven were suspected spindle poisons. These chemicals were tested for their ability to induce micronuclei with kinetochore(s) in bone marrow cells of CD-1 mice. The majority of MN formed in bone marrow cells treated with aneuploidy-inducing agents contained kinetochore(s) which are considered to be formed from whole chromosomes or centric fragments, while in clastogen treated bone marrow cells, majority of them contained no kinetochore(s) which are considered to be formed from acentric chromosomal fragments. Classification of chemicals into either aneuploidy inducing agents or clastogens is based on the relative frequency of MN with and without KC, respectively. These results suggest that the in vivo aneuploidy/micronucleus assay has a great potential to identify aneuploidy-inducing agents.

Aneuploidy↗
PubMed1992

Absence of hepatitis B virus precore mutants in patients with chronic hepatitis B responding to interferon-alpha.

Precore defective HBV mutants may gradually prevail because of immune selection and explain spontaneous seroconversion from HBeAg to anti-HBe in HBV carriers. We have analyzed whether the presence of precore HBV mutants is a determinant of responsiveness to interferon-alpha therapy. Fifteen carriers (nine responders and six nonresponders) who were treated with interferon-alpha were examined. Serum samples were collected before and after therapy. After extraction of DNA, the precore region was amplified by the polymerase chain reaction, and the product was identified by gel electrophoresis and ethidium bromide staining and then Southern blotting and molecular hybridization. The amplified products in all patients were asymmetrically amplified by a modified polymerase chain reaction, and the precore region was directly sequenced. All patients were HBV DNA positive initially. Circulating HBeAg-negative mutants were not identified before treatment in either responders or nonresponders. All nine responders were negative for HBV DNA in serum by dot blot during or after treatment, but seven remained positive by polymerase chain amplification and Southern-blot hybridization. All of the nonresponders remained positive for HBV DNA by dot blot. A silent mutation involving the substitution of an A for G at position 1888 was found in seven carriers; however, no HBeAg-negative mutants were detected in the follow-up of either responders or nonresponders to interferon-alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Transcriptional inhibition by carcinogenic chromate: relationship to DNA damage.

Hexavalent chromium compounds are carcinogenic to humans, are potent inducers of tumors in experimental animals, and can neoplastically transform cells in culture. In this study, the effects of sodium chromate on the expression of the 78-kDa glucose-regulated protein (GRP78) gene and on general transcription were investigated with respect to the DNA damage induced by this agent. DNA single-strand breaks, DNA-protein cross-links, and chromium-DNA adducts were present in CHO cells immediately after 2 h of treatment with sodium chromate. Subsequently, these types of damage were repaired at different rates. Single-strand breaks were essentially repaired after 8 h. By 24 h posttreatment, no cross-links remained in cells exposed to 30 or 150 microM chromate, although cells treated with the 300-microM concentration still contained cross-links at that time. DNA-chromium adducts remained unrepaired for at least 32 h. The moderate constitutive level of GRP78 mRNA was not affected by chromate. Chromate did, however, suppress induction of this gene by tunicamycin in a concentration-and time-dependent manner. Thirty micromolar sodium chromate (96% survival), which caused the least DNA damage, had no effect on GRP78 induction, general RNA synthesis, or mRNA synthesis. Induction of GRP78 was suppressed immediately and 12 h after treatment with 150 microM chromate (54% survival), although there was a partial recovery of induction at 24 h after treatment, which correlated with the repair of DNA-protein cross-links. In contrast, both total cytoplasmic RNA and mRNA synthesis were suppressed by approximately 60-75% for at least 32 h by 150 microM chromate. At the 300-microM concentration (8% survival), where DNA-protein cross-links persisted beyond 24 h, GRP78 induction was totally suppressed for at least 24 h, while total RNA and mRNA synthesis were suppressed by 80-90% for at least 32 h. Overall, the effects of chromate on GRP78 induction correlated most closely with the presence of DNA-protein cross-links, but suppression of total RNA and mRNA synthesis correlated with the presence of DNA-chromium adducts. These results indicate that chromate exerts differential effects on the induction of the GRP78 gene and on general transcription.

Animals↗
PubMed1992

DNA damage induced by carcinogenic lead chromate particles in cultured mammalian cells.

Particulate lead chromate is a highly water-insoluble cytotoxic and carcinogenic agent, but its mechanism of action remains obscure. We investigated its effects on DNA damage in CHO cells after a 24-h exposure using alkaline or neutral filter elution and cytogenetic studies. Concentrations (0.08, 0.4 and 0.8 micrograms/cm2), which reduced the colony-forming efficiency of CHO cells to 94, 50 and 10%, respectively, produced dose-dependent DNA single-strand breaks and DNA-protein crosslinks, but no DNA double-strand breaks or DNA-DNA crosslinks were observed. The single-strand breaks were absent from cells given a 24-h recovery period after removal of the treatment medium, even though most of the particles remained adhered to cells and to the culture dish. In contrast, both the DNA-protein crosslinks and chromosomal aberrations persisted even after the 24-h recovery period. These results suggest that the mechanism of the particle-induced early DNA single-strand breaks may be different from DNA-protein crosslinks and the lesions leading to chromosomal aberrations, or alternatively, that the repair of single-strand breaks is more efficient than the repair of DNA-protein crosslinks in the unavoidable continuing presence of carcinogen. These results also suggest that the chromosome damage may be related to the persistent DNA-protein crosslinks, and further confirm the genotoxic activity of carcinogenic lead chromate particles.

Animals↗
PubMed1992

Protective effect of methylprednisolone on vascular injury in rat spinal cord injury.

High-dose methylprednisolone (MP) given to patients within 8 h of traumatic spinal cord improved neural function at 6 and 12 months, suggesting a probable secondary injury process that may be amenable to therapeutic intervention. Vascular injury plays an important role in the secondary injury process of CNS trauma. We have examined the effect of MP on vascular changes, including tissue edema, vascular permeability, and polymorphonuclear (PMN) cell infiltration in a rat model of spinal cord impact injury. MP significantly reduced extravasation of fluorescein isothiocyanate dextran (FITC-D), a macromolecular tracer, by 64.3% and 50.7% with trauma forces of 20 and 40 g-cm, respectively, when MP was administered IV immediately after trauma at a bolus of 165 mg/kg, with a subsequent continuous MP infusion at 31.5 mg/kg/h for 23 h. MP reduced the water content in the 40 g-cm traumatic cord lesion to 73.0% compared to the traumatic control (74.3%, p < 0.001) at the same schedule of large dose 24-h infusion. The same doses of MP showed a trend to decrease the extent of neutrophil infiltration as determined by myeloperoxidase (MPO) activity, but the change was not significant. MP had little effect in decreasing FITC-D extravasation and cord edema when given at a lower dose (bolus of 30 mg/kg with continued infusion of 1.3 mg/kg/h for 23 h). MP did not reduce extravasation of FITC-D and edema when administered IV as one bolus injection at high (165 mg/kg) or low (30 mg/kg) doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Identification of the glycoprotein H gene of murine cytomegalovirus.

Partial sequencing of the HindIII C fragment of murine cytomegalovirus (MCMV) revealed an open reading frame of 2172 nucleotides in length encoding a 724 amino acid protein with a predicted Mr of 80.4K. Analysis of the predicted amino acid sequence revealed homology with glycoprotein H (gH) from a number of other herpesviruses. MCMV gH showed strongest amino acid identity with human (H) CMV and human herpesvirus 6 gH, and less identity with the gH protein sequences of Epstein-Barr virus, varicella-zoster virus and herpes simplex virus type 1. The greatest identity between MCMV and HCMV gH occurs in the C-terminal region. The MCMV gH is characterized by having a 14 amino acid signal sequence, a 23 amino acid transmembrane region, a seven amino acid positively charged cytoplasmic anchor sequence and eight putative N-linked glycosylation sites. Comparison of MCMV gH with that of HCMV indicates that there are 12 conserved cysteine residues and three conserved potential N-linked glycosylation sites.

Amino Acid Sequence↗
PubMed1992

Widespread differentiation stage-specific expression of the gene encoding phosphoprotein p19 (metablastin) in mammalian cells.

p19 is a highly conserved 19 kD cytosolic protein that undergoes phosphorylation in response to diverse extracellular factors in mammalian cells. Its expression is abundant in brain and testis and is developmentally regulated. To gain insights regarding its function, we analyzed the expression of p19 mRNA in a variety of cell types during induction of differentiation. Murine erythroleukemia cells showed a moderate increase followed by a marked decrease in the abundance of p19 mRNA during induction of differentiation. In murine C2 myoblasts and primary fetal rat osteoblasts, p19 mRNA was abundant in replicating cells and decreased to undetectable levels during differentiation. In resting human peripheral blood lymphocytes, p19 mRNA was virtually undetectable but was strongly induced during blast transformation of both B and T cells. In rat liver, p19 mRNA was abundant on embryonic day 17 and decreased during early postnatal development. Upon fractionation of adult rat liver cells by centrifugal elutriation, p19 mRNA was not detected in hepatocytes while a low level was observed in a fraction enriched in non-parenchymal epithelial cells. CCl4-induced liver regeneration resulted in induction of p19 mRNA in hepatocytes. Primary cultures of embryonic and neonatal rat brain were analyzed by indirect immunofluorescence using co-staining with stage-specific markers. p19 expression was restricted to immature neurons and oligodendrocyte precursors. In contrast to the other cell types examined, the neuronal and glial precursors that express p19 were shown, using BrdU labeling, to be postmitotic both in primary culture and in vivo. The data demonstrate widespread, stage-specific expression of p19 and suggest that the protein exerts a general, lineage-independent function during induction of differentiation of mammalian cells. In view of the available evidence on the stimulation of serine phosphorylation of p19 by several growth factors, our working hypothesis is that phosphorylation of p19 may be involved in the mechanism by which growth factors control cell differentiation.

Animals↗
PubMed1992

Receptor-linked hydrolysis of phosphoinositides and production of prostacyclin in cerebral endothelial cells.

The receptor agonist-mediated hydrolysis of phosphoinositides and production of prostacyclin were studied in murine cerebral endothelial cells (MCEC). Of 11 neurotransmitters and neuromodulators examined, carbachol, noradrenaline (NE), bradykinin, and thrombin significantly increased 3H-inositol phosphate accumulation in the presence of LiCl (20 mM). The maximal stimulation of [3H]inositol monophosphate ([3H]IP1) reached approximately 11, 11, seven, and four times the basal levels for carbachol, NE, bradykinin, and thrombin, respectively. The EC50 values of IP1 accumulation for carbachol and NE were 34 and 0.16 microM, respectively. The muscarinic antagonists, atropine and pirenzepine, blocked the carbachol-induced IP1 accumulation with Ki values of 0.3 and 30 nM, respectively. The adrenergic antagonist, prazosin, blocked NE-induced IP1 accumulation with a Ki of 0.1 nM. The calcium ionophore A23187, histamine, glutamate, vasopressin, serotonin, platelet activating factor, and substance P did not stimulate IP1 accumulation. A23187, bradykinin, and thrombin stimulated prostacyclin release to approximately four, four, and two times the basal levels, respectively, whereas carbachol and NE had little effect upon prostacyclin release. These results suggest that the activation of phospholipase C and of phospholipase A2 in MCEC are regulated separately.

Animals↗
PubMed1992

Stimulation of fetal rat lung cell proliferation in vitro by mechanical stretch.

On the basis of in vivo animal studies and on experiments of nature, it has been suggested that fetal breathing movements are essential for normal lung growth in utero. To study this hypothesis in vitro, we examined the effect of mechanical stretch on proliferation of fetal rat lung cells maintained in organotypic culture to provide a three-dimensional matrix. Initial studies demonstrated that stretch-mediated effects on cell division and DNA synthesis in such cultures were influenced by cell inoculation density, fetal calf serum concentration, and by the amplitude, frequency, periodicity, and duration of the applied stretch. After a 48-h exposure to an intermittent stretch pattern (5% elongation, 60 stretches/min for 15 min of each hour), cell number increased 10% (P less than 0.05), cell doubling time was reduced from 71 to 55 h (P less than 0.05), [3H]thymidine incorporation into DNA increased 61% (P less than 0.01), and the [3H]thymidine-labeling index increased 2.8-fold (P less than 0.001) compared with nonstretched controls. This effect did not appear to be mediated by prostaglandins or leukotrienes because the prostaglandin synthase inhibitors ibuprofen (2.5-50 microM) or BW 755C (5 microM), leukotriene biosynthesis inhibitors BW 755C (5 microM) or MK-886 (0.3 microM), and leukotriene D4 receptor antagonist MK-571 (0.3 microM) did not block stretch-mediated effects. We conclude that mechanical forces act directly to stimulate fetal rat lung cell growth and that these results are compatible with a significant role for fetal breathing in normal fetal lung growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Computerized plotting of low skin impedance points.

The distribution of low skin impedance points (LSIP) was studied on 68 subjects with a computer system designed for the measurement of skin impedance. The results demonstrated that LSIPs were basically distributed along the 14 channels, the overwhelming majority located right on or within 5 mm bilaterally to their courses. LSIPs were found in the area between every two channels only in a few cases. Moreover, there was no marked natural fluctuation of skin impedance in the human body and the distribution of LSIPs was considerably stable, which could be plotted on any day in the experiment. It is clear that such particular distribution of LSIPs along channels was really a biological phenomenon, not an experimental error. However, the distribution of low skin impedance was not an uninterrupted solid line but a series of LSIPs basically along the channel course. The method used in this work was accurate, reliable and repeatable which has upgraded the measurement of LSIPs to a new level. Under certain conditions, skin impedance can be used as an objective index in channel research.

Adult↗
PubMed1992

[Photoocclusion analysis for the reduction of occlusal table dimension of the pontics].

50 cases of mandibular dentitions with normal morphology and occlusion are analyzed by using photoocclusion. The occlusal surfaces of the molars are divided into four regions buccolingually. That are the buccal inclines and lingual inclines of the buccal and lingual cusps of the molars. The relationship of sigma epsilon value among these four regions is 3:5:2:0 respectively. This indicates that it is effective to get force reduction by adjusting the buccal incline of the pontic in fixed bridge restoration.

Biomechanical Phenomena↗
PubMed1992

[Research on sterilization of pathogens by high electrostatic voltage method].

An experimental research has been carried out on the sterilization of four kinds of pathogens by high electrostatic method along with an inquiry into the influence of voltage waveform and the treated time on sterilization. It is concluded that pathogens can be killed efficiently by corona discharge field.

Candida albicans↗
PubMed1992

[Studies of distribution of subtypes of transferrin, group-specific component, alpha 1-antitrypsin in gastric cancer patients from Shanghai area].

The genetic polymorphism of transferrin (Tf) and alpha 1-Antitrypsin (alpha 1-AT) in 202 gastric cancer patients and 202 controls in Shanghai Hans were analyzed by isoelectric focusing. In transferrin, the phenotype frequency of C1C1 and gene frequencies of c1 and c2 were 0.3713, 0.5718 and 0.4109 respectively in gastric cancer patients, and 0.5149, 0.6782 and 0.2970 separately in controls. The frequencies of the c1c1 phenotype and the C1 gene increased significantly (p < 0.01) among the controls, while the frequency of the C2 gene greatly increased (p < 0.01) among the patients. The frequencies of the C2C2 in gastric cancer patients and controls were 0.2228 and 0.1436 respectively, showing a significant difference between them (p < 0.05). The genetic polymorphisms of group-specific component (Gc) in 200 gastric cancer patients and 200 controls in Shanghai Hans were studied with isoelectric focusing followed by immunofixation. The Gc1F1F phenotype frequency and 1Fgene frequency were 0.22 and 0.4375 in gastric cancer patients, and 0.14 and 0.3600 in controls, respectively. The frequencies of the Gc1F1F phenotype and the 1F gene were significantly increased (p < 0.05) among the patients. In alpha 1-Antitrypsin, there was no significant difference in phenotype frequencies and gene frequencies between the patients and controls. The data reported here indicate that the gastric cancer is associated positively with TfC2 and Gc1F, and negatively with TfC1. These facts support the notion that cancerogenesis is a multi-step process controlled by multifactorial inheritance.

Adult↗
PubMed1992

Utilization of the protoplast fusion technique to explore directional altering lincomycin producing microorganism.

Interspecific protoplast fusion between Streptomyces lincolnensis var. lincolnensis (LM gamma, CTC gamma, producing lincomycin) protoplast and Streptomyces aureofaciens (LM gamma, CTC gamma, producing chlorotetracycline) protpolast which had been treated with UV radiation 40 min for inactivation was performed with PEG 6000, the fusants were obtained by directly selecting from the regeneration plates containing CTC 50 micrograms/ml, the fusion frequency was about 9.05 x 10(-5). From many fusants, only 4 stable recombinants were obtained. These species produced antibiotics which are different from lincomycin and chlorotetracycline. Preliminary identification of the antibiotic synthesized by one of the recombinants suggests that its basic structure might be similar to that of lincomycin. The fermentation product of recombinant No. 2 showed new chromatographic spot which is similar to that of clindamycin. Though the products remain to be identified further, this strategy seems to be worthy of exploring for screening new antibiotics.

Anti-Bacterial Agents↗
PubMed1992

[The immunologic studies on experimental heterogeneous penetrating keratoplasty].

Using the experimental model of chicken-rabbit penetrating corneal grafting, micro-whole-blood 3H-TdR incorporation and ELISA the authors dynamically observed the functional state of cellular and humoral immunities for 10 weeks after operation. The results showed, (1) In both the homogroup and the hetero-group, the transformational degree of lymphocytes in peripheral blood increased, most obviously in the 3rd or 4th week postoperatively. (2) In the hetero-group, specific anti-corneal antibody appeared obviously in the serum during 2-8 weeks postoperatively. Combined with morphologic observation, it has proved that: (1) The immune rejection is mainly cellular mediated immunoresponse, meanwhile, the humoral immunoresponse also participates in it, and the humoral immunoresponse participates in the heterokeratoplasty more obviously. (2) Applying the micro-whole-blood 3H-TdR incorporation is capable of determining the immunologic state of the body after corneal transplantation. (3) Attention should be focused on the 3-4 week period postoperatively when immunosuppressive-agent is administered.

Animals↗