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Biomedical subjects

Y Xu

Publications and source records attributed to Y Xu.

At least 505 records · Page 28Linked to original sources
PubMed1999

A real time quantitative PCR-based method for the detection and quantification of simian virus 40.

A real time quantitative PCR-based simian virus 40 (SV40) detection and quantification method has been developed. This method takes advantage of the 5' to 3'-exonuclease activity of Taq DNA polymerase and utilizes the PRISM 7700 sequence detection system of PE Applied Biosystems for direct monitoring of PCR product accumulation through a dual-labelled fluorogenic probe. This method provides accurate, precise and reproducible quantification of SV40 DNA over a linear dynamic range of at least 100,000-fold with a minimum detection level of 6.4 copy equivalents/microL of SV40 viral particle in test samples. The sample preparation procedure employed allows for efficient and consistent recovery of SV40 DNA from test samples. High concentrations of protein and cellular DNA presenting in test samples have been demonstrated to have no impact on SV40 quantification. This method offers significant advantages over other PCR methods and cell-based infectivity assays currently available for SV40 detection and quantification. The availability of this method should greatly facilitate the pathogenic investigation of SV40, as well as viral clearance evaluations required for the development of new biological products.

DNA, Viral↗
PubMed1999

Real time quantitative PCR as a method to evaluate simian virus 40 removal during pharmaceutical protein purification.

Continuous cell lines used for pharmaceutical protein manufacturing have the potential to be contaminated by viruses. To ensure the safety of pharmaceutical proteins derived from continuous cell lines, validation of the ability of the manufacturing process to clear potential contaminating viruses is required for product registration. In this paper, a real time quantitative PCR method has been applied to the evaluation of simian virus 40 (SV40) removal during chromatography and filtration procedures. This method takes advantage of the 5'-3' exonuclease activity of Taq DNA polymerase and utilizes the PRISM 7700 sequence detection system of PE Applied Biosystems for automated SV40 DNA quantification through a dual-labeled fluorogenic probe. This method provides accurate and reproducible quantification of SV40 DNA. The SV40 clearance during chromatography and filtration procedures determined by this method is highly comparable with that determined by the cell-based infectivity assay. This method offers significant advantages over cell-based infectivity assays, such as higher sensitivity, greater reliability, higher sample throughput and lower cost. This method can be potentially used to evaluate the clearance of all model viruses during chromatography and filtration procedures. This method can be used to substitute cell-based infectivity assays for process validation of viral removal procedures and the availability of this method should greatly facilitate and reduce the cost of viral clearance evaluations required for new biologic product development.

Antibodies, Monoclonal↗
PubMed1999

Effect of natural dissolved humic material on bioavailability and acute toxicity of fenpropathrin to the grass carp, Ctenopharyngodon idellus.

The effects of aquatic humic acids on the bioconcentration and acute toxicity of fenpropathrin were evaluated using grass carp, Ctenopharyngodon idellus, in laboratory freshwater systems. The results demonstrated that both bioavailability and acute toxicity decreased in the presence of aquatic humic acid 5 and 10 mg/liter. In addition, the extent of influence increased with increasing concentration of aquatic humic acid.

Animals↗
PubMed1999

Characterization of human ovarian carcinomas in a SCID mouse model.

This study characterizes a murine model which is promising for the study of the growth and natural history of ovarian cancer and for testing of new therapies for its treatment. Intact portions of 20 different human ovarian cancer surgical specimens were implanted in over 60 severe combined immunodeficient (SCID) mice using techniques previously developed in our laboratory. Growth of xenografts was evaluated by gross examination and histopathologic analysis. Confirmation of the human origin of the tumor outgrowth was obtained using in situ hybridization analysis. By histological evaluation, all of the patients' tumors showed evidence of invasive growth in at least 1 of the mice implanted with portions of each surgical specimen and these tumors remained morphologically similar to the parent tumors for a long period of time. Furthermore, 65% (13/20) of the xenografts grew rapidly enough (i.e., reached a diameter of 1-2 cm within 2-6 months) to allow passage to subsequent SCID mice. Among the passaged xenografts, 3 eventually developed metastases in a distribution pattern similar to that of naturally occurring ovarian cancer and 2 developed ascites without evidence of further metastatic spread. Upon evaluation of sera from tumor-bearing mice, human antibodies presumably derived from immunoglobulin-secreting cells present in the original tumor specimen were identified. In support of this, human B cells and plasma cells could be seen within the tumor xenograft for more than 6 months following implantation. In summary, transplantation of surgical specimens from ovarian cancer patients into SCID mice results in an attractive model for the study of the natural history of ovarian cancer and may also be useful for analysis or new experimental therapeutic approaches for the treatment of this disease.

Animals↗
PubMed1999

Non-elastic deformation of myocardium in low-flow ischemia and reperfusion: ultrastructure-function relations.

This study tested the hypothesis that regional low-flow ischemia and reperfusion alter myocardial material properties by causing non-elastic deformation. Twenty-two anesthetized, open-chest pigs were studied. Pigs underwent 90 min of regional low-flow ischemia (anterior LV subendocardial blood flow 29+/-7% of baseline) followed by 90 min reperfusion. LV pressure and regional subendocardial segment length were recorded to derive end-diastolic pressure vs segment length (EDP vs EDL) and preload-recruitable stroke work (PRSW) relations. In vivo, non-elastic myocardial deformation was inferred from increases in minimally loaded myocardial dimensions: the EDL at zero EDP (L0) and the EDL at which no regional external work was performed (Lw, the PRSW intercept). In 15 pigs, ultrastructural confirmation of non-elastic deformation was obtained from sarcomere dimensions measured by transmission electron microscopy after in situ perfusion fixation under non-ischemic conditions, after 90 min ischemia, or after 90 min ischemia plus 90 min reperfusion. Ischemia increased L0 and Lw to 1.17+/-0.05 and 1. 13+/-0.04 times baseline, respectively. After reperfusion, L0 and Lw remained increased to 1.09+/-0.03 and 1.15+/-0.02 times baseline (all P<0.05). After reperfusion, PRSW slope was not different from baseline, but regional external work remained depressed (0.38+/-0.03 times baseline) due to the persistent increase in Lw. Neither L0 nor Lw changed in the posterior (non-ischemic) region. In hearts fixed after ischemia or after ischemia plus reperfusion, sarcomere length was significantly greater and transverse distance between thick myofilaments was significantly smaller in the anterior (ischemic) subendocardium than in the posterior (non-ischemic) subendocardium (P<0.01). We conclude that regional low-flow ischemia and reperfusion cause non-elastic deformation of myocardium, manifest in vivo by increased minimally loaded myocardial dimensions (L0 and Lw) and ultrastructurally by increased sarcomere length and decreased transverse interfilament distance. Non-elastic deformation of myocardium may contribute to contractile dysfunction in low-flow ischemia and reperfusion.

Animals↗
PubMed1999

Automated 2D NOESY assignment and structure calculation of Crambin(S22/I25) with the self-correcting distance geometry based NOAH/DIAMOD programs.

The NOAH/DIAMOD program suite was used to automatically assign an experimental 2D NOESY spectrum of the 46 residue protein crambin(S22/I25), using feedback filtering and self-correcting distance geometry (SECODG). Automatically picked NOESY cross peaks were combined with 157 manually assigned peaks to start NOAH/DIAMOD calculations. At each cycle, DIAMOD was used to calculate an ensemble of 40 structures from these NOE distance constraints and random starting structures. The 10 structures with smallest target function values were analyzed by the structure-based filter, NOAH, and a new set of possible assignments was automatically generated based on chemical shifts and distance constraints violations. After 60 iterations and final energy minimization, the 10 structures with smallest target functions converged to 1.48 A for backbone atoms. Despite several missing chemical shifts, 426 of 613 NOE peaks were unambiguously assigned; 59 peaks were ambiguously assigned. The remaining 128 peaks picked automatically by FELIX are probably primarily noise peaks, with a few real peaks that were not assigned by NOAH due to the incomplete proton chemical shifts list.

Amino Acids↗
PubMed1999

Rotational Spectroscopic Investigation of the Weak Interaction between CO and N(2)O.

Pure rotational spectra of the CO-N(2)O complex are reported for the first time. Spectra of five isotopomers, i.e., (12)C(16)O-(14)N(14)NO, (13)C(16)O-(14)N(14)NO, (13)C(18)O-(14)N(14)NO, (13)C(16)O-(15)N(14)NO, and (13)C(16)O-(14)N(15)NO, were measured using a pulsed molecular beam Fourier transform microwave spectrometer. Rotational and quartic centrifugal distortion constants as well as the nuclear quadrupole coupling constants of the terminal and the central (14)N nuclei were determined. Comparisons of the nuclear quadrupole coupling constants with the corresponding values of the N(2)O monomer and with those of other N(2)O-containing complexes indicate significant electronic charge redistribution at the central nitrogen atom upon complex formation. Structural parameters based on the experimental rotational constants were derived. With the isotopic data available, the orientations of the CO and N(2)O subunits in the complex could be determined. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Divergence of a linear and a circular plasmid in disjunct natural isolates of the fungus Neurospora.

It is known from DNA hybridization and other studies that Neurospora plasmids are widely distributed across species of this genus. However few comparisons have been performed of the structure of apparently identical plasmids in widely differing geographical and biological locations. We compare pairs of circular and linear mitochondrial plasmids from distant geographical locations. The circular plasmids (LaBelle and Harbin-1) were from different ecotypes of N. intermedia and the linear plasmids (maranhar and Harbin-3) were from different species (N. crassa and N. intermedia). The structures are highly similar at the sequence level showing that they are closely related. Most of the differences are outside the presumptive genes (coding for polymerases). Furthermore, most of the proposed functional motifs have been retained. Sequence divergence is compatible with a distribution model by vertical descent from a common ancestor, but horizontal transmission cannot be ruled out.

Amino Acid Sequence↗
PubMed1999

Benefit limits in managed behavioral health care: do they matter?

More than half of Americans with insurance coverage for mental health services are enrolled in plans that carve out behavioral health care services with a vendor specializing in the management of these services. However, utilization management has not taken the place of benefit limitations. Do benefit limits matter? This article reports the percentage of enrollees in managed behavioral health care carve-out plans that encounter benefit limits. Estimates are provided on the impact and savings of imposing benefit limits on enrollees in unrestricted plans. Costs to eliminate benefit limits are estimated to be very small. This study finds that benefit limits do matter but only to a very small number of plan enrollees. Furthermore, the results of this study show that for inpatient limits, children are especially vulnerable. These issues have important implications for discussions about the impact of managed care in mental health and for discussions concerning parity legislation.

Adult↗
PubMed1999

Study of the incorporation of selenium into peroxidase isozyme of wheat seedling.

The effects of selenium on the activity of peroxidase (POD) of wheat seedling and its isozyme pattern were studied using a greenhouse hydroponic experiment. The results show that the activity of POD is increased in response to higher Se concentration (approx 5.0 mg/L) in culture medium. The electrophoretic pattern of the POD isozyme was altered by growth of the wheat in a selenium medium. Se could incorporate into some POD isozymes during either seed germination or the seedling growth period. There is a dose-responsive incorporation of selenium in isozyme of POD and selenium content in the isozyme increase along with the increase of selenium concentration in the medium.

Dose-Response Relationship, Drug↗
PubMed1999

Effects of theophylline on plasma levels of interleukin-4, cyclic nucleotides and pulmonary functions in patients with chronic obstructive pulmonary disease.

In order to measure the plasma levels of interleukin-4 (IL-4), cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in patients with chronic obstructive pulmonary disease (COPD) and observe the effects of oral theophylline on them, we divided 28 COPD patients into COPD experimental group and COPD control group. Plasma levels of IL-4, cAMP and cGMP as well as parameters of pulmonary function tests were measured in these 2 groups before and after 2 weeks of treatment with oral theophylline (Protheo, 400 mg, qd) or placebo. Plasma levels of IL-4 and cGMP were significantly elevated in patients with COPD as compared with normal controls (P < 0.05), while cAMP and cAMP/cGMP were significantly lower than those in controls (P < 0.01). Plasma level of IL-4 was inversely correlated with forced expiratory volume at the first second (FEV1) and with maximum expiratory flow rate at 50% of forced vital capacity (V50) (both r = -0.46, P < 0.05) while it was directly correlated with the scores of the clinical manifestations (r = 0.57, P < 0.05) in COPD patients. Two weeks after treatment with theophylline, IL-4 and cGMP in COPD experimental group were decreased significantly while cAMP and cAMP/cGMP increased significantly (P < 0.05). The change of IL-4 was inversely correlated with the changes of FEV1 and V50 (r = -0.53 and -0.54, respectively, P < 0.05). Two weeks after placebo treatment, the COPD control group did not show such changes. We are led to conclude that IL-4 might play a role in the pathogenesis of the airway inflammation and air flow limitation in COPD patients and the mechanisms of theophylline's therapeutic effects of attenuating air-flow limitation may partially depend on its anti-inflammatory effects on the airways which, in turn, is dependent on its inhibitory effects on some inflammatory mediators such as IL-4.

Aged↗
PubMed1999

The effect of astragapolysaccharide on the lymphocyte proliferation and airway inflammation in sensitized mice.

In order to investigate the regulating role of Astragapolysaccharide (APS) in the mice model of asthmatic airway inflammation, the airway eosinophil number, spleen T lymphocyte proliferation, level of IL-2 production and their relationships were studied in sensitized mice and sensitized mice treated with different concentrations of APS. The results showed that the number of eosinophils as well as lymphocytes in the airway of the sensitized animals were significantly increased, and a marked positive correlation between the inflammation cells and spleen T lymphocyte proliferation was found. Moreover, there was a positive correlation between inflammation cells and the level of IL-2 production. The APS of given dosage could significantly reduce the number of eosinophils in the airway of the sensitized animals. At the same time the level of IL-2 secreted by spleen T lymphocytes stimulated with ConA was also significantly decreased and there was a marked positive correlation between them. Our results suggested that APS of given dosage could prevent antigen-induced the number of eosinophils infiltrating into the airway of sensitized mice and inhibit the proliferation and activation of lymphocyte and IL-2 production. Through its immuno-regulating effect, APS can be helpful in the treatment of asthma.

Animals↗
PubMed1999

The evolutionary history of carbamoyltransferases: A complex set of paralogous genes was already present in the last universal common ancestor.

Forty-four sequences of ornithine carbamoyltransferases (OTCases) and 33 sequences of aspartate carbamoyltransferases (ATCases) representing the three domains of life were multiply aligned and a phylogenetic tree was inferred from this multiple alignment. The global topology of the composite rooted tree (each enzyme family being used as an outgroup to root the other one) suggests that present-day genes are derived from paralogous ancestral genes which were already of the same size and argues against a mechanism of fusion of independent modules. A closer observation of the detailed topology shows that this tree could not be used to assess the actual order of organismal descent. Indeed, this tree displays a complex topology for many prokaryotic sequences, with polyphyly for Bacteria in both enzyme trees and for the Archaea in the OTCase tree. Moreover, representatives of the two prokaryotic Domains are found to be interspersed in various combinations in both enzyme trees. This complexity may be explained by assuming the occurrence of two subfamilies in the OTCase tree (OTC alpha and OTC beta) and two other ones in the ATCase tree (ATC I and ATC II). These subfamilies could have arisen from duplication and selective losses of some differentiated copies during the successive speciations. We suggest that Archaea and Eukaryotes share a common ancestor in which the ancestral copies giving the present-day ATC II/OTC beta combinations were present, whereas Bacteria comprise two classes: one containing the ATC II/OTC alpha combination and the other harboring the ATC I/OTC beta combination. Moreover, multiple horizontal gene transfers could have occurred rather recently amongst prokaryotes. Whichever the actual history of carbamoyltransferases, our data suggest that the last common ancestor to all extant life possessed differentiated copies of genes coding for both carbamoyltransferases, indicating it as a rather sophisticated organism.

Amino Acid Sequence↗
PubMed1999

Cytological and biochemical alterations in Carassius auratus hepatocytes from exposure to sediment containing dioxins and related compounds.

Cytological and biochemical alterations of crucial carp (Carassius auratus) hepatocytes were characterized after exposure to sediments from a lake contaminated with dioxins and other industrial chemicals. Carp were exposed in 20 L water containing 25, 50, or 100 g of contaminated sediment for 2 and 4 weeks. Ultrastructural changes in the liver were characterized by severe enlargement of hepatocytes. Alterations in the cell included formation of condensed and irregular cell nucleus, polynuclei, dispersed heterochromatin, enlargement of the nucleolus, and degeneration of the nucleus. Mitochondrial numbers were reduced and cristae were deformed. Myelin figures and lysosomes were increased, and sometimes cell organelles and cell matrix were totally lost after 4 weeks of exposure. The ultrastructural alterations were correlated with exposure time and sediment concentrations. Hepatosometic index was significantly increased in experimental groups at 2 and 4 weeks as compared with the control group. EROD enzyme activities were strongly induced in liver. A trend from rough endoplasmic reticulum (RER) to SER was observed. Our results suggest that the dioxin-like compounds bound by sediment were bioavailable to C. auratus and cause sublethal effects.

Animals↗
PubMed1999

Demonstration of urokinase expression in cancer cells of colon adenocarcinomas by immunohistochemistry and in situ hybridization.

The question whether urokinase is expressed in human colon cancer by the cancer cells themselves or by surrounding stromal elements such as fibroblasts, macrophages, and leukocytes, which transfer the activator to the receptors of the cancer cells, has been a controversial one. In the present study 12 cases of colorectal cancer were investigated by immunohistochemical methods using three monoclonal antibodies of different specificity against urokinase. Cytoplasmic staining of strongly varying intensity was observed in all cases, with the antigen expressed most strongly in the apical and the basal regions of the cancer cells. In some cases, staining was also found in stromal elements surrounding the cancer glands. That the activator was indeed the product of the cancer cells was demonstrated by in situ hybridization using a uPA-cDNA probe, which detected the presence of uPA-mRNA in both the basal and the apical regions of the cancer cells. A monoclonal antibody against the receptor for uPA showed similar localization. These findings indicate that the activator is expressed by the cancer cells and is not recruited by them from stromal elements.

Adenocarcinoma↗
PubMed1999

Physicochemical characterization and purification of cationic lipoplexes.

Cationic lipid-nucleic acid complexes (lipoplexes) consisting of dioleoyltrimethylammoniumpropane (DOTAP) liposomes and plasmid DNA were prepared at various charge ratios (cationic group to nucleotide phosphate), and the excess component was separated from the lipoplex. We measured the stoichiometry of the lipoplex, noted its colloidal properties, and observed its morphology and structure by electron microscopy. The colloidal properties of the lipoplexes were principally determined by the cationic lipid/DNA charge ratio and were independent of the lipid composition. In lipoplexes, the lipid membranes as observed in freeze-fracture electron microscopy were deformed into high-radius-of-curvature features whose characteristics depended on the lipid composition. Lipoplexes prepared at a threefold or greater excess of either DOTAP or DNA could be resolved into complexes with a defined stoichiometry and the excess component by sedimentation to equilibrium on sucrose gradients. The separated, positively charged complex retained high transfection activity and had reduced toxicity. The negatively charged lipoplex showed increased transfection activity compared to the starting mixture. In cryoelectron micrographs the positively charged complex was spherical and contained a condensed but indistinct interior structure. In contrast, the separated negatively charged lipoplexes had a prominent internal 5.9 +/- 0.1-nm periodic feature with material projecting as spikes from the spherical structure into the solution. It is likely that these two lipoplexes represent structures with different lipid and DNA packing.

Animals↗
PubMed1999

Distinctly different interactions of anesthetic and nonimmobilizer with transmembrane channel peptides.

Although it plays no clinical role in general anesthesia, gramicidin A, a transmembrane channel peptide, provides an excellent model for studying the specific interaction between volatile anesthetics and membrane proteins at the molecular level. We show here that a pair of structurally similar volatile anesthetic and nonimmobilizer (nonanesthetic), 1-chloro-1,2,2-trifluorocyclobutane (F3) and 1, 2-dichlorohexafluorocyclobutane (F6), respectively, interacts differently with the transmembrane peptide. With 400 microM gramicidin A in a vesicle suspension of 60 mM phosphatidylcholine-phosphatidylglycerol (PC/PG), the intermolecular cross-relaxation rate constants between (19)F of F3 and (1)H in the chemical shift regions for the indole and backbone amide protons were 0.0106 +/- 0.0007 (n = 12) and 0.0105 +/- 0.0014 (n = 8) s(-1), respectively. No cross-relaxation was measurable between (19)F of F6 and protons in these regions. Sodium transport study showed that with 75 microM gramicidin A in a vesicle suspension of 66 mM PC/PG, F3 increased the (23)Na apparent efflux rate constant from 149.7 +/- 7.2 of control (n = 3) to 191.7 +/- 12.2 s(-1) (n = 3), and the apparent influx rate constant from 182.1 +/- 15.4 to 222.8 +/- 21.7 s(-1) (n = 3). In contrast, F6 had no effects on either influx or efflux rate. It is concluded that the ability of general anesthetics to interact with amphipathic residues near the peptide-lipid-water interface and the inability of nonimmobilizer to do the same may represent some characteristics of anesthetic-protein interaction that are of importance to general anesthesia.

Amino Acid Sequence↗