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Biomedical subjects

C Xu

Publications and source records attributed to C Xu.

At least 199 records · Page 11Linked to original sources
PubMed1998

[Antitumor activity of howiinol (GHM-10) on L1210 cells in vitro].

Howiinol(GHM-10) is a new compound isolated from Goniothalamus howii. Previous studies showed that GHM-10 significantly inhibited the growth of cancer cells both in vitro and in vivo. In the present study, the characteristics of the inhibitory effect of GHM-10 on L1210 cells was investigated. The results showed that the IC50 of L1210 cells treated with GHM-10 for 1 h, 24 h, and 7 d was 6.85, 3.32 and 1.59 micrograms.ml-1, respectively. This outcome is in compliance with the hypothesis that GHM-10 is a cell cycle non-specific cytotoxic drug. When L1210 cells were treated with 1-2 micrograms.ml-1 of GHM-10 for 24 h, the growth rate and mitotic index were decreased and the morphology of cell nuclei changed, but the cell viability remained at the level of 96% or more, indicating that GHM-10 mainly inhibited cell proliferation. The cell cycle kinetics of L1210 cells were studied by using a flow cytometer. The results showed that the transition of cells from G1 phase to S phase was blocked to certain extent by the treatment of GHM-10 4 micrograms.ml-1 for 12 h. The fluidity of cell membrane was also increased when the L1210 cells were exposed to 2-3 micrograms.ml-1 of GHM-10 for 24 h.

Animals↗
PubMed1998

[FTIR-PAS of rare earth coordinated compounds of Schiff base derived from vanillin and p-toluidine].

The Fourier transform infrared photoacoustic spectra (FTIR-PAS) of Schiff base derived from vanillin (3-methoxy-4-hydroxybenzaldehyde) and p-toluidine and its rare earth coordinated compounds in the 3800-200cm(-1) were measured and inverstigated. The coordinated compounds have two classes: [LnL2Cl x 3H2O]Cl2(Ln:La,Ce,Pr,Nd,Sm,Eu,Gd,Dy;L:Schiff base ligand) and [LnL2Cl2 x 2H2O] Cl x H2O(Ln:Ho,Er,Tm,Yb,Lu). In the coordinated compounds there is intermolecular hydrogen bond derived from phenolic hydroxy group. The bands at 400 and 300cm(-1) are respectively assigned to bonds M-O (water) and M-N.

Benzaldehydes↗
PubMed1998

Infectious disease surveillance in China.

A national system of infectious disease surveillance was established in 1959 in China. Now it consists of three subunits, namely, national disease reporting system (NDRS), nationwide disease surveillance points (DSPs), and surveillance network for specific infectious diseases. There are 35 notifiable infectious diseases, which are divided into Classes A, B, and C. The functions of the surveillance include explaining the natural history of infectious diseases, describing the distribution of case occurrence, triggering disease-control effort, monitoring epidemic of infectious diseases during natural disasters, predicting and controlling epidemics and providing the base of policy adjustment.

China↗
PubMed1997

DNA topoisomerase targets of the fluoroquinolones: a strategy for avoiding bacterial resistance.

Fluoroquinolones are antibacterial agents that attack DNA gyrase and topoisomerase IV on chromosomal DNA. The existence of two fluoroquinolone targets and stepwise accumulation of resistance suggested that new quinolones could be found that would require cells to obtain two topoisomerase mutations to display resistance. For wild-type cells to become resistant, the two mutations must be acquired concomitantly. That is expected to occur infrequently. To identify such compounds, fluoroquinolones were tested for the ability to kill a moderately resistant gyrase mutant. Compounds containing a C8-methoxyl group were particularly lethal, and incubation of wild-type cultures on agar containing C8-methoxyl fluoroquinolones produced no resistant mutant, whereas thousands arose during comparable treatment with control compounds lacking the C8 substituent. When the test strain contained a preexisting topoisomerase IV mutation, which by itself conferred no resistance, equally high numbers of resistant mutants were obtained for C8-methoxyl and control compounds. Thus C8-methoxyl fluoroquinolones required two mutations for expression of resistance. Although highly lethal, C8-methoxyl fluoroquinolones were not more effective than C8-H controls at blocking bacterial growth. Consequently, quinolone action involves two events, which we envision as formation of drug-enzyme-DNA complexes followed by release of lethal double-strand DNA breaks. Release of DNA breaks, which must occur less frequently than complex formation, is probably the process stimulated by the C8-methoxyl group. Understanding this stimulation should provide insight into intracellular quinolone action and contribute to development of fluoroquinolones that prevent selection of resistant bacteria.

Anti-Infective Agents↗
PubMed1997

Cadmium-induced apoptosis in the urogenital organs of the male rat and its suppression by chelation.

Cadmium-induced apoptosis is shown to occur, in vivo, in several organs of the male Wistar rat urogenital system, 48 h after cadmium administration i.p. at a dose of 0.03 mmol/kg. Characteristic DNA fragmentation (as measured by an enzyme-linked immunosorbent-assay, ELISA) and histopathologically observed changes characteristic of apoptosis are found in the kidney, prostate, seminal vesicles, testes, and epididymis. TUNEL assay also demonstrates the apoptosis. Such changes are absent from bladder and vas deferens tissue. Timely administration of an appropriate chelating agent capable of reaching intracellular cadmium binding sites can suppress the processes leading to apoptosis. Administration of monoisomyl meso-2,3-dimercaptosuccinate (Mi-ADMS, 0.5 mmol/kg i.p.) to cadmium-treated rats is effective in greatly reducing typical histopathologic signs of apoptosis and the associated chromatin DNA fragmentation as revealed by ELISA when the antagonist is administered 1 h after cadmium. Administration of the chelating agent at law times results in greater degradation of DNA into oligonucleotides and more prominent histopathological evidence of apoptotic changes in the affected organs of the rat urogenital system. There is also a progressive increase in apoptotic changes indicated by TUNEL assay, as the antagonist is administered at progressively greater intervals after cadmium.

Animals↗
PubMed1997

Dimerization is essential for DNA binding and repression by the ArsR metalloregulatory protein of Escherichia coli.

Arsenical resistance (ars) operons produce resistance to trivalent and pentavalent salts of the metalloids arsenic and antimony in cells of Escherichia coli. The first gene in the operon, arsR, was previously shown to encode a homodimeric trans-acting metalloregulatory repressor protein. Dimerization of ArsR was investigated using the yeast two-hybrid system in which the ArsR protein was fused to the Saccharomyces cerevisiae GAL4 DNA-binding domain and GAL4 activation domain to produce chimeric proteins. Transcriptional activation of lacZ reporter indicated that dimerization of the ArsR is stable in yeast. The results indicated that residues 1-8 and 90-117 are not required for ArsR dimerization. The genes for a series of truncated ArsR proteins containing six histidine tags were constructed and the proteins purified. The mass of each recombinant protein, as determined by size exclusion chromatography, was consistent with the results from two-hybrid analysis. The results of beta-galactosidase assays in vivo and gel mobility shift assays in vitro showed that dimers retained the ability to bind to the ars promoter and to respond to inducer, whereas monomeric ArsRs did neither. These results suggest that a core sequence of about 80 residues has all of the information necessary for dimerization, repression, and metal recognition.

Amino Acid Sequence↗
PubMed1997

Pharmacology and regulation of the neuronal dopamine transporter.

The dopamine transporter, a member of the family of Na+,Cl(-)-dependent transporters, mediates uptake of dopamine into dopaminergic neurons by an electrogenic, Na(+)- and Cl(-)-transport-coupled mechanism. Dopamine and blockers of uptake such as cocaine probably bind to both shared and separate domains on the transporter, which can be influenced dramatically by the presence of cations. Regulation of the dopamine transporter occurs both by chronic occupancy with blocker and by acute effects of D2 dopamine receptors or second messengers such as diacylglycerol (protein kinase C) and arachidonic acid. The dopamine transporter is involved in the uptake of toxins generating Parkinson's disease; it is also an important target for psychostimulant drugs, ligands for in vivo imaging and medications used for neurologic diseases involving changes in the dopamine system.

Binding, Competitive↗
PubMed1997

Hyper-Rayleigh and hyper-Raman scattering background of liquid water in two-photon excited fluorescence detection.

The detection of two-photon excited fluorescence is practically free from background caused by linear scattering because two-photon excited fluorescence occurs at a much shorter wavelength region than the excitation light. This property can be used to achieve ultrasensitive fluorescence detection. However, similar to linear scattering in the detection of one-photon excited fluorescence, the question arises whether background caused by non-linear scattering may limit the detection sensitivity of two-photon excited fluorescence. In this work, quantitative comparisons between two-photon induced scattering of liquid water and two-photon excited dye fluorescence in a standard epifluorescence geometry show that the relative scattering background is typically reduced by orders of magnitude in two-photon excitation as compared to single-photon excitation with confocal detection. Hyper-Rayleigh and hyper-Raman (3400 cm-1) cross sections of liquid water have been measured to be 8 x 10(-62) and 7 x 10(-63) cm4.s/photon, respectively, at 840 nm incident wavelength, with absolute values calibrated with respect to the known two-photon fluorescence excitation cross section of fluorescein.

Fluorescence↗
PubMed1997

Selenite suppression of cadmium-induced testicular apoptosis.

The characteristic apoptotic ladder-like patterns of rat testicular DNA on agarose gel electrophoresis which results from treatment with CdCl2 are suppressed by the administration of Na2SeO3. The examination of testicular tissue using an ELISA programmed cell death detection procedure confirmed this selenite suppression of cadmium-induced apoptosis. The administration of the Na2SeO3 at either 0.5, 1, 2 h prior to or 0.5, 1, 2 h after the administration of the CdCl2 appear to be almost equally effective at suppressing the apoptotic response. These results are in accord with previous studies on the Na2SeO3 suppression of cadmium induced necrotic changes in tissues and suggest that Na2SeO3 interferes with both necrosis and apoptosis.

Animals↗
PubMed1997

In vitro induction of proinflammatory cytokine secretion by juvenile rheumatoid arthritis synovial fluid immune complexes.

OBJECTIVE: To characterize juvenile rheumatoid arthritis synovial fluid (SF) immune complexes and to examine their interaction with leukocytes. METHODS: SF immunoglobulin-containing fractions were prepared by sequential chromatography on protein A and Sephacryl 300. Fractions were subdivided according to molecular weight, characterized for immunoglobulin and complement content, and incubated with either promonocytic U937 cells or normal human peripheral blood mononuclear cells (PBMC). RESULTS: High molecular weight SF immunoglobulin-containing fractions stimulated the release of interleukin-1beta (IL-1beta) from U937 cells. These same complexes stimulated tumor necrosis factor alpha (TNFalpha), IL-1beta, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor (GM-CSF) from PBMC. Lower molecular weight material was less efficient in inducing any of the cytokines. TNFalpha and IL-1beta were the earliest of the messenger RNAs examined to be induced by the high molecular weight complexes. However, the secretion of IL-6, IL-8, and GM-CSF stimulated by the complexes was not completely dependent upon the secretion of IL-1beta. Addition of IL-1 receptor antagonist to the cell cultures reduced GM-CSF and IL-6 production by 40% and IL-8 production by 25% in PBMC. CONCLUSION: SF immunoglobulin fractions contain immune complexes that vary in size, composition, and phlogistic potential. High molecular weight complexes are capable of inducing a spectrum of proinflammatory cytokines, all of which have been implicated in the pathogenesis of rheumatic disease.

Adolescent↗
PubMed1997

Binding domains for blockers and substrates on the dopamine transporter in rat striatal membranes studied by protection against N-ethylmaleimide-induced reduction of [3H]WIN 35,428 binding.

Binding sites for 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)[3H]tropane ([3H]WIN 35,428) on rat striatal membranes were alkylated with N-ethylmaleimide (NEM), and the protective potency was measured of the blockers cocaine, N[1-(2-benzo[b]thiophenyl) cyclohexyl]piperidine (BTCP), benztropine, WIN 35,428; and nomifensine, and of the substrates dopamine, norepinephrine, S(+)-amphetamine, tyramine, and metaraminol. In general, the protective potency was lower (at least 3 times) than the potency in inhibiting [3H]WIN 35,428 binding with the compounds present under the same experimental conditions used for the NEM-induced alkylation. However, the disparity was substantially greater for all substrates tested (10- to 93-fold) than for the blockers (2- to 6-fold), especially cocaine and BTCP (3-fold). [3H]WIN 35,428 binding was best described by a l-site model under the present conditions. The results are discussed in terms of models involving blocker-induced conformational changes and overlapping nonidentical binding domains for blockers and substrates.

Amphetamine↗
PubMed1997

Stress response of lysosomal cysteine proteinases in rat C6 glioma cells.

Acid proteinases of C6 rat glioma cells were analyzed by means of gelatine polyacrylamide electrophoresis with respect to their responses to stress (heat shock and butanol). Proteinase activities on gelatine gels were characterized by their molecular masses. pH-optima, isoelectric points and reactions to inhibitors. Four bands of 25, 35 and 65/85 kDa most probably represent active and proforms as well as precursor complexes of lysosomal cysteine proteinases with pH optima between 4.0 and 5.0. The 25-kDa band seems to contain cathepsin L and B, the 35-kDa band proforms of cathepsin L and B and the 65/85-kDa bands possibly precursor complexes of cathepsin L and B. After 30-min heat shocks of different temperatures (40-50 degrees C), the 35-kDa activity increased, whereas the 65/85-kDa activity decreased after exposure to 42 and 44 degrees C, which also caused a strong increase in the level of the inducible heat shock protein of 68 kDa (HSP 68). The alterations of the proteinase activities and the increases of the HSP 68 levels occur at heat shock treatments that cause cell death in about 25-40% of the population as determined by Trypan blue staining. HSP 68 induction and proteinase activity changes were also observed 12 hr after a 1-hr treatment with different butanol concentrations (0.14-0.16 M). Kinetics of the response to a 30-min heat shock (44 degrees C) revealed a maximal decrease of the 35-kDa and a maximal increase of the 65/85-kDa activities after 12 hr recovery. When cells were exposed to repeated heat shocks (44 degrees C) at 12-hr intervals, the HSP 68 level further increased, whereas the 35-kDa and 65/85-kDa proteinase activities did not change. This result indicates a role of HSP 68 (or other HSPs) in the processing or stability of the putative cathepsin precursors (65/85-kDa complexes).

Animals↗
PubMed1997

Factors associated with increased levels of human immunodeficiency virus type 1 DNA in semen.

Human immunodeficiency virus type 1 (HIV-1)-infected cells have been isolated from semen and may be a major source of transmissible virus. Quantitative polymerase chain reaction (PCR) assay was used to determine HIV proviral DNA load in cellular fractions of semen from 74 antiviral therapy-naive HIV-1-seropositive men and 53 paired blood samples. HIV-1 DNA was detected in 65% of semen (range: <10-5000 copies/mL) and 100% of blood samples (range: 20-2500 copies/mL). HIV-1 DNA copy numbers in semen correlated significantly with those in blood, but for most cases, the concentration of blood HIV-1 DNA was higher (mean blood-to-semen ratio = 2.9). Factors associated with elevated HIV-1 provirus levels in semen included reduced peripheral CD4 cell count and asymptomatic genital tract inflammation (>10(6) white blood cells/mL of semen). These data provide evidence that genital tract inflammation and reduced peripheral CD4 cell count may be associated with enhanced sexual transmission of HIV-1 because of increased numbers of HIV-1-infected cells in semen.

CD4 Lymphocyte Count↗
PubMed1997

T lymphocytes and macrophages, but not motile spermatozoa, are a significant source of human immunodeficiency virus in semen.

The cellular fraction of semen contains spermatozoa, immature germ cells, leukocytes, and epithelial cells. Recent evidence implicates seminal cells as a major source of sexually transmitted human immunodeficiency virus (HIV) in semen, but the identity and infectious potential of infected cells remains poorly understood. HIV provirus was found in 75% of viable semen cell samples by polymerase chain reaction and in 88% of paired blood cell samples from HIV-seropositive men. When semen cell subpopulations were isolated by an immunomagnetic bead technique, T cells were found to be most commonly HIV-infected (75% of samples), followed by macrophages (38% of samples). Viral DNA was never detected in motile spermatozoa or immature germ cell populations. Semen leukocytes proliferated in response to mitogenic and antigenic challenge and produced p24 following stimulation with irradiated allogeneic cells. These data provide evidence that both T cells and macrophages, but not germ cells, are cellular vectors of HIV transmission in semen.

Cell Division↗
PubMed1997

Multiphoton-excited visible emission by serotonin solutions.

Nonlinear excitation of the neurotransmitter serotonin (5HT) in aqueous solution is shown to generate a blue-green-emitting photoproduct in addition to UV fluorescence characteristic of native 5HT. The visible emission rate in diffusional steady-state measurements scales as the sixth power of excitation intensity, demonstrating that absorption of six near-IR photons is required to generate emission of one visible photon. Transient measurements reveal that this process is composed of two sequential nonlinear steps, the first excited by four photons and the second by two photons. These results, in combination with measurements of multiphoton-excited serotonin UV fluorescence, support a model in which 5HT is photochemically transformed as a consequence of four-photon absorption (Etot approximately 6 eV) to a photoproduct that then emits in the visible region via two-photon excitation. A minimum bound of approximately 10(-51) cm4 s photon-1 is observed for the two-photon emission action cross section at 830 nm. Photoionization, rather than reaction with a dissolved oxygen species, appears to be the primary mechanism for generation of the blue-green-emitting photoproduct. The peak intensities required to generate significant blue-green emission (approximately 5 x 10(11) W cm-2 from 80 MHz 150 fs titanium: sapphire laser pulses) are approximately five-fold higher than are typically used in two-photon laser scanning microscopy but are still substantially lower than the estimated intensity needed to induce dielectric breakdown of water.

Diffusion↗
PubMed1997

Identification of Candida species by randomly amplified polymorphic DNA fingerprinting of colony lysates.

We have characterized a method that produces simple yet diagnostic fingerprints that are unique to isolates of Candida species. DNA from individual colonies can be amplified from crude single-colony lysates. Randomly amplified polymorphic DNA (RAPD) fingerprints generated from a single primer correctly identified the species of most (>98%) of the isolates identified with CHROMagar Candida plates as non-Candida albicans Candida species. RAPD fingerprints were much more informative than the plates, since they distinguished between all tested species and required less time. Most (91%) of these identifications agreed with those assigned by API 20C tests. In almost every incident of species identity mismatch, electrophoretic karyotyping showed that the RAPD fingerprint was correct. This underscores the improved objectivity and reliability of this method over those of conventional diagnostic tools. The identities of approximately 30% of C. albicans isolates identified in clinical laboratories by positive germ tube tests are not verified by either testing on CHROMagar Candida plates or RAPD fingerprinting. Data suggest that clinical isolates conventionally identified as C. albicans in clinical settings are heterogeneous, consisting of both misidentified and atypical yeasts. RAPD fingerprints obtained from primary culture plate colonies allows for rapid, highly accurate determinations of Candida species, hence permitting earlier selection of appropriate antifungal agents in the clinical setting.

Candida↗
PubMed1997

The physical and chemical properties of ultrathin oxide films.

Thin oxide films (from one to tens of monolayers) of SiO2, MgO, NiO, Al2O3, FexOy, and TiO2 supported on refractory metal substrates have been prepared by depositing the oxide metal precursor in a background of oxygen (ca 1 x 10(-5) Torr). The thinness of these oxide samples facilitates investigation by an array of surface techniques, many of which are precluded when applied to the corresponding bulk oxide. Layered and mixed binary oxides have been prepared by sequential synthesis of dissimilar oxide layers or co-deposition of two different oxides. Recent work has shown that the underlying oxide substrate can markedly influence the electronic and chemical properties of the overlayer oxide. The structural, electronic, and chemical properties of these ultrathin oxide films have been probed using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (ELS), ion-scattering spectroscopy (ISS), high-resolution electron energy loss spectroscopy (HREELS), infrared reflectance absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS).

Journal Article↗