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C Xu

Publications and source records attributed to C Xu.

At least 19 recordsLinked to original sources
PubMed2006

Relationship between plasma selenium concentrations and lower genital tract levels of HIV-1 RNA and interleukin type 1beta.

OBJECTIVE: To examine the relationship between selenium nutritional status and intermediates of human immunodeficiency virus (HIV)-1 transmission. DESIGN: Prospective cohort study. SETTING: A study clinic at Muhimbili National Hospital, Dar es Salaam, Tanzania. SUBJECTS: A total of 340 HIV-1-infected pregnant women with gestational ages 12-27 weeks. METHODS: Women's plasma selenium concentrations were determined at enrollment and modeled as tertiles (tertile 1: <114 microg/l (reference); tertile 2: 114-131 microg/l; tertile 3: >131 microg/l). Cervicovaginal lavage specimens were obtained at 36 weeks of gestation to determine HIV-1 RNA and interleukin-1beta (IL-1beta) levels. In subgroup analyses, 123 women with genital tract infections at enrollment were excluded. RESULTS: Plasma selenium concentrations >or=114 microg/l were related to increased risk of lower-genital shedding of HIV-1 RNA. Excluding women with genital tract infections strengthened the associations (relative risk (RR) tertile 2: 1.46, 95% confidence interval (CI)=1.10, 1.92; RR tertile 3: 1.39, 95% CI=1.05, 1.84). There was evidence for an association between plasma selenium concentrations >or=114 microg/l and increased HIV-1 RNA levels among the entire cohort and after excluding women with genital tract infections. There was no association between plasma selenium and IL-1beta concentrations. CONCLUSIONS: High selenium status may lead to increased risk of genital HIV-1 shedding, but data from other studies indicate that the evidence is mixed. Results from ongoing selenium trials are awaited to clarify the impact of selenium on HIV-1-related transmission endpoints. SPONSORSHIP: National Institute of Child Health and Human Development (NICHD R01 32257) and the Fogarty International Center (NIH D43 TW00004).

Adult↗
PubMed2006

Determination of the pion charge form factor at Q2=1.60 and 2.45 (GeV/c)2.

The 1H(e,e'pi+)n cross section was measured at four-momentum transfers of Q2=1.60 and 2.45 GeV2 at an invariant mass of the photon nucleon system of W=2.22 GeV. The charged pion form factor (F(pi)) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F(pi) is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q2 by one sigma, but is still far from its perturbative quantum chromodynamics prediction.

Journal Article↗
PubMed2006

A multivariate model for ordinal trait analysis.

Many economically important characteristics of agricultural crops are measured as ordinal traits. Statistical analysis of the genetic basis of ordinal traits appears to be quite different from regular quantitative traits. The generalized linear model methodology implemented via the Newton-Raphson algorithm offers improved efficiency in the analysis of such data, but does not take full advantage of the extensive theory developed in the linear model arena. Instead, we develop a multivariate model for ordinal trait analysis and implement an EM algorithm for parameter estimation. We also propose a method for calculating the variance-covariance matrix of the estimated parameters. The EM equations turn out to be extremely similar to formulae seen in standard linear model analysis. Computer simulations are performed to validate the EM algorithm. A real data set is analyzed to demonstrate the application of the method. The advantages of the EM algorithm over other methods are addressed. Application of the method to QTL mapping for ordinal traits is demonstrated using a simulated baclcross (BC) population.

Algorithms↗
PubMed2006

Lipid trafficking between the endoplasmic reticulum and the chloroplast.

The photosynthetic (thylakoid) membrane of plants is one of the most extensive biological cell membrane systems found in Nature. It harbours the photosynthetic apparatus, which is essential to life on Earth as carbon dioxide is fixed and atmospheric oxygen released by photosynthesis. Lipid biosynthetic enzymes of different subcellular compartments participate in the biogenesis of the thylakoid membrane system. This process requires the extensive exchange of lipid precursors between the chloroplast and the ER (endoplasmic reticulum). The underlying lipid trafficking phenomena are not yet understood at the mechanistic level, but genetic mutants of the model plant Arabidopsis thaliana with disruptions in lipid trafficking between the ER and the chloroplast have recently become available. Their study has led to the identification of components of the lipid transfer machinery at the inner chloroplast envelope.

Arabidopsis↗
PubMed2006

Increased HO-1 expression and decreased iNOS expression in the hippocampus from adult spontaneously hypertensive rats.

Brain expression of heme oxygenase (HO) and nitric oxide synthase (NOS) in hypertension may participate in the pathogenesis of hypertension-related neuronal disorders, such as vascular dementia. In the present study, expression levels of HO and NOS in spontaneously hypertensive rats (SHR) were investigated using Western immunoblotting assay. Expression level of inducible HO-1 in hippocampus of 4-wk prehypertensive SHR was about twofold of that in age-matched Sprague-Dawley (SD) rats (p < 0.01). In 23-wk SHR with fully developed hypertension, hippocampal HO-1 level was significantly greater than that of age-matched SD rats (p < 0.05), but not different from 4-wk SHR. There was no difference in expression levels of hippocampal HO-2 between SHR and SD rats at different ages. Total enzymatic activity of hippocampal HO was significantly greater in 23-wk SHR than in age-matched SD rats or 4-wk SD/SHR (p < 0.01). Although hippocampal expression of nNOS protein was relatively unchanged, iNOS expression in 23-wk SHR was about fourfold lower than that in age-matched SD rats and 4-wk SD/SHR (p < 0.01). Total enzymatic activity of hippocampal NOS was significantly lower in 23-wk SHR than in age-matched SD rats or 4-wk SD/SHR (p < 0.01). Significantly suppressed Morris water maze performance was found in 23-wk SHR in comparison with age-matched SD rats. Because SHR has been used as a model of vascular dementia and hippocampus is essential for spatial learning and memory, understanding of altered HO/CO and NOS/NO systems in the hippocampus of adult SHR may shed light on the pathogenic development of memory deficits associated with vascular dementia.

Aging↗
PubMed2005

Identification of lumbar spinal neurons controlling simultaneously the prostate and the bulbospongiosus muscles in the rat.

Lumbar spinothalamic neurons in the lamina X of the L3-L4 spinal cord segment have been proposed to constitute the spinal ejaculation generator in male rats. Lumbar spinothalamic cells are immunoreactive for galanin and neurokinin-1 receptors. We previously showed that after injection of pseudorabies virus either in the bulbospongiosus muscle or in the prostate, retrogradely labeled cells in the L3-L4 segment also displayed galanin or neurokinin-1 receptor immunoreactivities, demonstrating a direct link between lumbar spinothalamic cells and two anatomical structures involved in the two phases of ejaculation i.e. the emission and the expulsion phases. In order to provide with a more precise anatomical support for the role of lumbar spinothalamic cells in controlling ejaculation, we injected simultaneously in male adult rats two strains of recombinant pseudorabies virus, expressing either beta-galactosidase (PRV-BaBlu) or green fluorescent protein (PRV-152) in the prostate and in the bulbospongiosus muscle, respectively. After 5 days, we performed multiple immunofluorescence experiments to detect PRV-BaBlu, PRV-152 and galanin or neurokinin-1 receptors in transverse sections of the L1-S1 segment. Double- and triple-labeled cells were counted using confocal laser scanning microscope. Double-labeled neurons with the two strains of pseudorabies virus were mainly found at the L3-L4 segment lateral to the central canal in lamina X and represented about 60% of the total number of pseudorabies virus-labeled neurons. All the double pseudorabies virus-labeled neurons also expressed lumbar spinothalamic and most of them neurokinin-1 receptor, identifying them as lumbar spinothalamic neurons. The convergence of retrograde labeling from prostate and bulbospongiosus muscle on the same lumbar spinothalamic cells strongly reinforce their role in the spinal control and coordination of the emission and expulsion of sperm.

Animals↗
PubMed2005

Beam shifting of an anisotropic negative refractive medium.

We rigorously derive the formulas of the total electric and magnetic fields in a slab of anisotropic negative refractive medium by use of Maxwell's equations. A beam shifting is exhibited from a Gaussian beam for an anisotropic negative refractive slab. Our results indicate that there exist two possible (positive or negative) beam shifting for an anisotropic negative refractive medium due to the special anisotropic properties, which is distinct from the case of an isotropic negative refractive slab. Physical insights are also presented.

Journal Article↗
PubMed2005

Use of CD34+ autologous stem cell transplantation in the treatment of children with refractory systemic lupus erythematosus.

We report on the unique effects and benefits of autologous stem cell transplantation in childhood systemic lupus erythematosus (SLE) and describe this procedure in two young girls with severe and refractory disease. The patients' stem cells were mobilized with granulocyte colony-stimulating factor (G-CSF) and collected by CS-3000 Blood Cell Separator (Baxter Healthcare, Round Lake, Ill., USA), and the CliniMACS CD34+ cell selection device (Miltenyi Biotech, Bergisch Gladbach, Germany) was used to obtain CD34+ cells. A total of 1.7x10(6) and 1.0x10(6)/kg CD34+ cells were obtained, with 2.0x10(5) and 1.0x10(4)/kg of CD3+ cells remaining, respectively. The conditioning regimen consisted of cyclophosphamide (50 mg/kg per day for 4 days) plus antithymocyte globulin (ATG-Fresenius, 5 mg/kg per day for 3 days). Neutrophil counts recovered within 9 days in both cases. Within 15 days, the platelet counts recovered and were sustained over 100x10(9)/l. Cushingoid features disappeared completely 3 months after transplantation because of the removal of corticosteroid medication. One 13-year-old child increased her height by 5 cm in 6 months after stopping steroids. She had not increased her height in her previous 7 years of disease. As of the time of this report, the first patient remains in clinical and laboratory remission for nearly 4 years, while the second suffered a relapse of thrombocytopenia 9 months post-transplantation. One residual effect of their treatment is that their CD4+ cell counts remained in the lower range after one year of transplant. The effect of this conditioning regimen plus CD34+ autologous stem cell transplantation on these two children with refractory SLE was beneficial, but long-term follow-up data and additional experience with this procedure are required. Autologous stem cell transplantation may limit the long-term toxicity of therapy in childhood SLE.

Adolescent↗
PubMed2005

Galanin and neurokinin-1 receptor immunoreactive [corrected] spinal neurons controlling the prostate and the bulbospongiosus muscle identified by transsynaptic labeling in the rat.

Ejaculation requires the coordination of sympathetic, parasympathetic and somatic neural outputs. Timely occurrence of the emission and expulsion of sperm results from an interplay between spinal nuclei innervating the seminal tract and the sexual accessory glands including the prostate on the one hand, and on the other hand perineal striated muscles, particularly the bulbospongiosus muscle. A group of cells essential for ejaculation, located around the central canal and referred to as lumbar spinothalamic neurons have been recently identified. Lumbar spinothalamic neurons are immunoreactive for galanin and neurokinin-1 receptor. In order to investigate the anatomical relationships between lumbar spinothalamic neurons and both the prostate and the bulbospongiosus muscle, pseudorabies virus retrograde tracing technique was used combined with immunohistochemistry. Three to five days after pseudorabies virus injection in the bulbospongiosus muscle or the prostate in male rats, spinal cord sections were processed for double immunofluorescence against pseudorabies virus and galanin or neurokinin-1 receptor. Immunocytochemical experiments against pseudorabies virus and choline acetyltransferase were also performed to discriminate between motoneurons and preganglionic neurons, or interneurons. Spinal sections were examined with confocal laser scanning microscope. Three days after pseudorabies virus injection within the prostate and the bulbospongiosus muscle, sympathetic preganglionic neurons and motoneurons of the dorsomedial nucleus were retrogradely labeled, respectively. Five days after pseudorabies virus injection, transsynaptically labeled choline acetyltransferase-negative neurons were found mainly located in the medial gray surrounding the central canal from L1 to S1. At the L3-L4 level, most of transsynaptically labeled neurons were immunoreactive for galanin and to a lesser extent for neurokinin-1 receptor, strongly suggesting that they could be the lumbar spinothalamic cells. We have thus evidenced connections between these cells and motoneurons of the dorsomedial nucleus and both sympathetic and parasympathetic preganglionic neurons innervating the bulbospongiosus muscle and the prostate, respectively. These anatomical data reinforce the crucial role for lumbar spinothalamic cells in coordinating the spinal control of ejaculation.

Animals↗
PubMed2005

An EM algorithm for mapping quantitative resistance loci.

Many disease resistance traits in plants have a polygenic background and the disease phenotypes are modified by environmental factors. As a consequence, the phenotypic values usually show a quantitative variation. The phenotypes of such disease traits, however, are often measured in discrete but ordered categories. These traits are called ordinal traits. In terms of disease resistance, they are called quantitative resistance traits, as opposed to qualitative resistance traits, and are controlled by the quantitative resistance loci (QRL). Classical quantitative trait locus mapping methods are not optimal for ordinal trait analysis because the assumption of normal distribution is violated. Methods for mapping binary trait loci are not suitable either because there are more than two categories in ordinal traits. We developed a maximum likelihood method to map these QRL. The method is implemented via a multicycle expectation-conditional-maximization (ECM) algorithm under the threshold model, where we can estimate both the QRL effects and the thresholds that link the disease liability and the categorical phenotype. The method is verified in simulated data under various combinations of the parameters. An SAS program is available to implement the multicycle ECM algorithm. The program can be downloaded from our website at www.statgen.ucr.edu.

Algorithms↗
PubMed2004

Evolutionary minority game wtih multiple options.

We propose and study an evolutionary minority game (EMG) in which the agents are allowed to choose among three possible options. Unlike the original EMG where the agents either win or lose one unit of wealth, the present model assigns one unit of wealth to the winners in the least popular option, deducts one unit from the losers in the most popular option, and awards R (-1 R(c), where R(c) (N) is a critical value for optimal performance of the system that drops to zero as the number of agents N increases.

Journal Article↗
PubMed2004

Efficient inhibition of multidrug-resistant human tumors with a recombinant bispecific anti-P-glycoprotein x anti-CD3 diabody.

Overexpressing of P-glycoprotein (Pgp) has been shown to be responsible for cancer resistance to multiple chemotherapeutic agents. Immunotherapy with biological agents, such as bispecific antibodies (BsAbs), may represent a promising approach to overcome the emergence of drug resistance. Here we constructed a recombinant BsAb, a diabody, with specificities to both CD3 on human T-lymphocyte and Pgp on cancer cells. The diabody was produced in Escherichia coli in a soluble functional form and purified by an affinity chromatography with a yield of >4 mg/l culture medium in shaker flask. The diabody binds to both CD3 on T-lymphocytes and Pgp on multidrug-resistant (MDR) tumor cells with affinities that are comparable to its respective parental single chain Fv molecules. In the presence of activated human peripheral blood lymphocytes (PBLs), the diabody mediates effectively the lysis of the Pgp-overexpressing human leukemia K562/A02 and epidermoid carcinoma KBv(200) cells, but is much less potent in mediating the lysis of the parent K562 and KB cells. Further, the diabody localized selectively within the K562/A02 xenografts in mice. When combined with activated PBL, the diabody significantly inhibited the growth of K562/A02 and KBv(200), but had no effect on K562 and KB xenografts. In contrast, treatment with doxorubicin, a standard chemotherapeutic agent, only inhibited the growth of K562 and KB, but had no effect on K562/A02 and KBv(200) xenografts. Taken together, our results suggest that the anti-Pgp x anti-CD3 diabody may have a great potential in the treatment of various MDR cancers.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Additive blockade of beta 2-integrin adhesion of eosinophils by salmeterol and fluticasone propionate.

Migration of human eosinophils is regulated by integrin expression, conformational change, and activation of cytosolic phospholipase A2 (cPLA2). Corticosteroids have been shown to inhibit cPLA2 hydrolysis in human eosinophils. The objective of this study was to determine the mechanisms of fluticasone propionate (FP) alone or in combination with salmeterol (SM) in blocking adhesion mediated by beta 2-integrin in human eosinophils. Human eosinophils were isolated by negative magnetic selection. beta 2-integrin-mediated eosinophil adhesion was measured by residual eosinophil peroxidase activity. Eosinophils were pretreated for 12 h to 24 h with FP and with or without SM for 30 min. Both SM alone and FP alone inhibited eosinophil adhesion in concentration- and time-dependent manner. SM alone modestly (approximately 30%) inhibited interleukin (IL)-5-induced eosinophil adhesion. Blockade of IL-5-induced eosinophil adhesion caused by 10(-7) M FP at 24 h was augmented by 10(-7) M SM from 41.5% to 72.5%. Similar blockade was also observed for eotaxin-induced eosinophil adhesion. Neither SM, FP, nor FP + SM blocked either: 1) upregulation of CD11b surface expression; or 2) phosphorylation of cPLA2. Blockade of beta 2-integrin-mediated eosinophil adhesion by fluticasone propionate is augmented by salmeterol. Decreased adhesion results from augmented blockade of nuclear translocation of cytosolic phospholipase A2 caused by addition of salmeterol to fluticasone.

Adrenergic beta-Agonists↗
PubMed2003

Effects of cross-phase modulation on phase jitter in soliton systems with constant dispersion.

In wavelength-division-multiplexed communication systems phase jitter is driven by amplifier noise and mediated by cross-phase modulation. The variational method is used to derive formulas for the absolute phase variance of an ensemble of solitons and the relative phase variance of ensembles of neighboring solitons. The predictions of these formulas are consistent with the results of numerical simulations.

Journal Article↗
PubMed2003

Biochemical characterization of atherosclerotic plaque constituents using FTIR spectroscopy and histology.

The behavior of vulnerable atherosclerotic plaques is believed to be closely related to plaque composition. There is a need for an effective in vivo technique for examining plaque constituent properties. In this study, Fourier transform infrared spectroscopy using attenuated total reflectance (FTIR-ATR) was used to assess and analyze the biochemical properties of human atherosclerotic plaques. FTIR spectra clearly revealed prominent spectral features corresponding to plaque constituents of interest: the 2930 cm(-1) and 2850 cm(-1) peaks (indicating the presence of lipids), the 1730 cm(-1) peak (lipid esters), the 1550 cm(-1) and 1650 cm(-1) peaks (fibrous tissues), and the 1100-1000 cm(-1) broad phosphate peak (calcification). Spectral data examined on a qualitative basis correlated well with both gross tissue anatomy and histologic features. Gross spatial mappings of tissue sections of both lipidic and calcified plaques were performed. Spectra from various regions of the plaques demonstrated the evolution of lipid peaks, fibrous tissue peaks, and the phosphate calcification band within the plaques. Histologic analysis corroborated the spectral findings in this study.

Arteriosclerosis↗
PubMed2003

Mapping quantitative trait loci underlying triploid endosperm traits.

Endosperm, which is derived from two polar nuclei fusing with one sperm, is a triploid tissue in cereals. Endosperm tissue determines the grain quality of cereals. Improving grain quality is one of the important breeding objectives in cereals. However, current statistical methods for mapping quantitative trait loci (QTL) under diploid genetic control have not been effective for dealing with endosperm traits because of the complexity of their triploid inheritance. In this paper, we derive for the first time the conditional probabilities of F(3) endosperm QTL genotypes given different flanking marker genotypes in F(2) plants. Using these probabilities, we develop a multiple linear regression method implemented via the iteratively reweighted least-squares (IRWLS) algorithm and a maximum likelihood method (ML) implemented via the expectation-maximization (EM) algorithm to map QTL underlying endosperm traits. We use the mean value of endosperm traits of F(3) seeds as the dependent variable and the expectations of genotypic indicators for additive and dominance effect of a putative QTL flanked by a pair of markers as independent variables for IRWLS mapping. However, if an endosperm trait is measured quantitatively using a single endosperm sample, the ML mapping method can be used to separate the two dominance effects. Efficiency of the methods is verified through extensive Monte Carlo simulation studies. Results of simulation show that the proposed methods provide accurate estimates of both the QTL effects and locations with very high statistical power. With these methods, we are now ready to map endosperm traits, as we can for regular quantitative trait under diploid control.

Chromosome Mapping↗