Biomedical subjects

X Wang

Publications and source records attributed to X Wang.

At least 469 records · Page 26Linked to original sources

PubMed2001

Synthesis of paucidisperse poly(gamma-benzyl-alpha,L-glutamate) oligomers and star polymers with rigid arms.

The synthesis of highly uniform gamma-benzyl-alpha,L-glutamate (BLG) oligomers via a convergent solution phase approach is reported. BLG oligomers were produced with designed lengths of 4, 8, 12, and 16 as a first step to production of BLG-4-mer and BLG-8-mer rod stars. The star oligomers were purified by size-exclusion chromatography and reversed phase HPLC, and characterized by MALDI-TOF mass spectrometry and reversed phase HPLC. These star-shaped BLG oligomers could be used as initiators for growing larger stars.

Chromatography, Gel↗

PubMed2001

Determination of total N-nitroso compounds and their precursors in frankfurters, fresh meat, dried salted fish, sauces, tobacco, and tobacco smoke particulates.

Total N-nitroso compounds (NOC) and NOC precursors (NOCP) were determined in extracts of food and tobacco products. Following Walters' method, NOC were decomposed to NO with refluxing HBr/HCl/HOAc/EtOAc and NO was measured by chemiluminescence. NOC were determined after sulfamic acid treatment to destroy nitrite, and NOCP were determined after treatment with 110 mM nitrite and then sulfamic acid. Analysis without HBr gave results < or =20% of those with HBr. This NOC method was efficient for nitrosamines but not nitrosoureas. The standard nitrosation for determining NOCP gave high yields for readily nitrosated amines, including 1-deoxy-1-fructosylvaline, but not for simple amines, dipeptides, and alkylureas. Mean NOC and NOCP results were (respectively, in micromol/kg of product) 5.5 and 2700 for frankfurters, 0.5 and 660 for fresh meat, 5.8 and 5800 for salted, dried fish, and 660 and 2900 for chewing tobacco (all for aqueous extracts) and 220 and 20000 nmol/cigarette for MeCN extracts of cigarette smoke filter pads.

Animals↗

PubMed2001

Physiological levels of melatonin enhance gap junction communication in primary cultures of mouse hepatocytes.

Gap junction communication is known to be involved in controlling cell proliferation and differentiation, and seems to play a crucial role in suppression of tumor promotion. Melatonin, a hormone secreted by the pineal gland, has putative oncostatic properties. Intercellular communication through gap junctions was assessed by microinjecting Lucifer yellow fluorescent dye into primary hepatocytes and visualizing the spread of the dye to adjacent neighboring cells using phase contrast/fluorescent microscopy. Treatment of primary hepatocyte cultures with a physiological range of melatonin concentrations for 24 h prior to microinjection resulted in significant enhancement in intercellular communication at 0.2 and 0.4 nmol/L but not at lower (0.1 nmol/L) or higher (0.8 or 1.0 nmol/L) concentrations. A time-dependent study showed that the changes in intercellular communication began 10 h after melatonin treatment and reached a maximum at 12 h of treatment. This nonlinear, functional gap junction response to melatonin occurred in the physiological concentration range detected in blood of mammals during nightly releases of the hormone by the pineal gland. These melatonin levels may affect the ability of gap junction communication to exert cell growth control in vivo. The uneven decline between individuals in nocturnal release of melatonin that occurs with age could identify potentially sensitive subpopulations susceptible to developing pathologies involving alterations in biological processes dependent on gap junction communication.

Analysis of Variance↗

PubMed2001

Human CMV-IGIV (CytoGam) neutralizes human cytomegalovirus (HCMV) infectivity and prevents intracellular signal transduction after HCMV exposure.

Pretreatment of human cytomegalovirus (HCMV) with human hyperimmune globulin (CytoGam) in human embryonic lung (HEL) fibroblast culture showed successful inhibition of infectivity, and decreased extracellular viral titers and extracellular viral DNA. CytoGam prevented HCMV from inducing intracellular activation of NF-kappaB, Sp-1, and P13-K signaling pathways and the production of immediate-early (IE), early (E), and late (L) viral proteins. CytoGam neutralization of HCMV in this cell culture model prevented the earliest known signal transduction events (NF-kappaB, Sp-1, P13-K activation) after viral specific glycoproteins bind to their cognate cell membrane receptors, suggesting that this agent contains highly effective neutralizing antibodies against HCMV.

Antiviral Agents↗

PubMed2001

Herpesvirus connection in the expression of autoimmune vitiligo in Smyth line chickens.

The Smyth line (SL) chicken is an animal model for human vitiligo, a common acquired depigmentary disorder affecting about 1-2% of people worldwide. The vitiligo-like depigmentation in SL chickens typically develops when the birds are between 6 and 14 weeks of age and may affect 70-95% of hatch mates. The development of SL vitiligo is considered to depend on two interacting components, namely an inherent melanocyte defect and an autoimmune reaction to melanocytes. Recently, a role for an environmental factor in the expression of vitiligo was suggested by the observation that only 10% of SL chicks imported from the University of Massachusetts (UM) and reared in isolation at biosecurity level 2 (BSL 2) at the University of Arkansas (UA) exhibited vitiligo. Following further assessment of environmental differences between UA and UM SL chickens, three environmental factors that may have influenced the expression of SL vitiligo were identified. Included were housing condition, status of Mycoplasma synoviae infection, and turkey herpesvirus (HVT) vaccination status. Studies were subsequently conducted at UA and UM to assess the role of these environmental factors in the expression of SL vitiligo. M. synoviae infection was not found necessary for vitiligo expression in SL chickens. However, HVT emerged as a strong candidate for an important environmental factor in SL vitiligo. The connection between HVT and SL vitiligo was confirmed for both BSL 2 and conventional housing. Therefore, the observations reported here suggest a strong causative link between HVT infection and SL vitiligo.

Age Factors↗

PubMed2001

Structural basis for recognition of AU-rich element RNA by the HuD protein.

Hu proteins bind to adenosine-uridine (AU)-rich elements (AREs) in the 3' untranslated regions of many short-lived mRNAs, thereby stabilizing them. Here we report the crystal structures of the first two RNA recognition motif (RRM) domains of the HuD protein in complex with an 11-nucleotide fragment of a class I ARE (the c-fos ARE; to 1.8 A), and with an 11-nucleotide fragment of a class II ARE (the tumor necrosis factor alpha ARE; to 2.3 A). These structures reveal a consensus RNA recognition sequence that suggests a preference for pyrimidine-rich sequences and a requirement for a central uracil residue in the clustered AUUUA repeats found in class II AREs. Comparison to structures of other RRM domain-nucleic acid complexes reveals two base recognition pockets in all the structures that interact with bases using residues in conserved ribonucleoprotein motifs and at the C-terminal ends of RRM domains. Different conformations of nucleic acid can be bound by RRM domains by using different combinations of base recognition pockets and multiple RRM domains.

AT Rich Sequence↗

PubMed2001

Metaplastic carcinoma of the breast: p53 analysis identified the same point mutation in the three histologic components.

A rare case of metaplastic carcinoma of the breast with both squamous metaplasia and cartilaginous metaplasia was reported. Histologically, the neoplasm revealed complex features, which were consisting of invasive ductal carcinoma, squamous carcinomatous component and chondrosarcomatoid component. Gradual transition of each component was recognized microscopically. p53 mutation analysis disclosed the same point mutation in three histologically different components, but not in the normal epithelium. Based on the morphologic findings, immunohistochemical findings and the p53 mutation analysis, we concluded that these three components in the tumor originated from the same duct progenitor cells.

Base Sequence↗

PubMed2001

Temporal and rate representations of time-varying signals in the auditory cortex of awake primates.

Because auditory cortical neurons have limited stimulus-synchronized responses, cortical representations of more rapidly occurring but still perceivable stimuli remain unclear. Here we show that there are two largely distinct populations of neurons in the auditory cortex of awake primates: one with stimulus-synchronized discharges that, with a temporal code, explicitly represented slowly occurring sound sequences and the other with non-stimulus-synchronized discharges that, with a rate code, implicitly represented rapidly occurring events. Furthermore, neurons of both populations displayed selectivity in their discharge rates to temporal features within a short time-window. Our results suggest that the combination of temporal and rate codes in the auditory cortex provides a possible neural basis for the wide perceptual range of temporal information.

Acoustic Stimulation↗

PubMed2001

Preoperative high-dose chemotherapy with peripheral blood stem cell support as a primary management of locally advanced breast cancer.

Locally advanced breast cancer (LABC) has a poor prognosis with a high risk of local recurrence and distant metastasis. Preoperative combined chemotherapy with or without granulocyte colony-stimulating factor (G-CSF) support does not improve the long-term survival rate. In our report, two patients with LABC received preoperative high-dose chemotherapy with peripheral blood stem cell support (HDC/PBSCs). Prior to high-dose chemotherapy with peripheral blood stem cell support, they both received induction chemotherapy of cyclophosphamide, epirubicin and 5-fluorouracil (FEC) for two cycles which resulted in a partial response. PBSC mobilization and collection were carried out following the second cycle of induction chemotherapy followed by G-CSF. High-dose cyclophosphamide (2500 mg/m2), carboplatin (600 mg/m2) and etoposide (600 mg/m2) were administered with PBSC support. A radical mastectomy was performed followed by adjuvant chemotherapy with FEC regimen for four cycles, followed by local irradiation, and endocrine therapy with tamoxifen. Both patients achieved a remarkable response in the primary lesion after HDC/PBSCs and tolerated the whole treatment well. Preoperative HDC/PBSCs as a new strategy in the treatment of LABC seems practical but it needs to be studied more deeply.

Adult↗

PubMed2001

C/EBPalpha and G-CSF receptor signals cooperate to induce the myeloperoxidase and neutrophil elastase genes.

To assess cooperation between G-CSF signals and C/EBPalpha, we characterized Ba/F3 pro-B cell lines expressing C/EBPalphaWT-ER and the G-CSF receptor (GCSFR). In these lines, GCSFR signals can be evaluated independent of their effect on C/EBPalpha levels. G-CSF alone did not induce the MPO, NE, LF, or PU.1 RNAs, and C/EBPalphaWT-ER alone stimulated low-level MPO and high-level PU.1 expression. Simultaneous activation of the GCSFR and C/EBPalphaWT-ER markedly increased MPO and NE induction at 24 h, and LF mRNA was detected at 48 h. G-CSF did not increase endogenous GCSFR, endogenous C/EBPalpha or exogenous C/EBPalphaWT-ER levels, and C/EBPalphaWT-ER did not induce endogenous or exogenous GCSFR. Several GCSFR mutants were also co-expressed with C/EBPalphaYWT-ER. Mutation of all four cytoplasmic tyrosines prevented NE induction but enhanced MPO induction. Mutation of Y704 was required for increased MPO induction. Consistent with this finding, removing IL-3 without G-CSF addition enabled MPO, but not NE, induction by C/EBPalphaWT-ER. GCSFR signals or related signals from other receptors may cooperate with C/EBPalpha to direct differentiation of normal myeloid stem cells.

Animals↗

PubMed2001

Speciation of aluminium(III) in natural waters using differential pulse voltammetry with a pyrocatechol violet-modified electrode.

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different AlIII forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm(-3) NaOAc-HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20 mol dm(-3) NH3.H2O-NH4Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester AlIII from AlIII-natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll's 8-hydroxyquinoline extraction-ion exchange method.

Aluminum↗

PubMed2001

Identification of the ligand-binding domain of human vascular-endothelial-growth-factor receptor Flt-1.

The vascular-endothelial-growth-factor (VEGF) receptor Flt-1 has been shown to be involved in vasculogenesis and angiogenesis. The receptor is characterized by seven immunoglobulin-like loops within the extracellular domain and the first three N-terminal immunoglobulin-like loops are involved in high-affinity binding of VEGF. The minimal extracellular domains of Flt-1 to achieve VEGF binding were screened using the yeast two-hybrid system. The result showed that the binding capacity of loop2-3 was close to that of loop1-3. The two truncated mutants consisting of loop2-3 and loop1-3 were expressed in the methylotrophic yeast Pichia pastoris at high levels (0.3 g[corrected]/litre). The corresponding proteins, named soluble (s)Flt-1(2-3) and sFlt-1(1-3), were purified. An in vitro biological activity assay showed that the binding capacity of sFlt-1(2-3) to human VEGF(165) and the inhibiting effect of it on human umbilical-vein endothelial cell proliferation stimulated by human VEGF(165) were close to those of sFlt-1(1-3). Animal tests showed that sFlt-1(2-3) could significantly inhibit the formation of regenerated blood vessels stimulated by hVEGF(165).

Angiogenesis Inhibitors↗

PubMed2001

Interplay between insulin and nutrients in the regulation of translation factors.

Protein synthesis in mammalian cells is regulated through alterations in the states of phosphorylation of eukaryotic initiation factors and elongation factors (eIFs and eEFs respectively) and of other regulatory proteins. This modulates their activities or their abilities to interact with one another. Insulin activates several of these proteins including the following: the guanine-nucleotide exchange factor eIF2B; the eIF4F complex, which (through eIF4E) interacts with the cap of the mRNA; p70 S6 kinase; and elongation factor eEF2, which mediates the translocation step of elongation. Control of the last three of these is linked to mTOR (mammalian target of rapamycin). In Chinese hamster ovary cells, regulation of all these proteins by insulin is modulated by the presence of amino acids and/or glucose in the medium. For example, p70 S6 kinase activity declines in the absence of amino acids and cannot be stimulated by insulin under this condition. The readdition of amino acids, especially leucine, restores activity and sensitivity to insulin. With eIF2B and eEF2, both amino acids and glucose must be provided for insulin to regulate their activities. In contrast, insulin-stimulation of the formation of eIF4F complexes requires glucose but not amino acids. Glucose metabolism is required for this permissive effect. Our recent studies have also identified the mechanism by which mTOR signalling regulates the phosphorylation of eEF2. eEF2 kinase is phosphorylated by p70 S6 kinase at Ser-366; this results in the inactivation of eEF2 kinase, especially at low (micromolar) Ca concentrations.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Effects of the flavonoid baicalin and its metabolite baicalein on androgen receptor expression, cell cycle progression and apoptosis of prostate cancer cell lines.

Recent studies on the Chinese herbal medicine PC SPES showed biological activities against prostate cancer in vitro, in vivo and in patients with advanced stages of the disease. In investigating its mode of action, we have isolated a few of the active compounds. Among them, baicalin was the most abundant (about 6%) in the ethanol extract of PC SPES, as determined by HPLC. Baicalin is known to be converted in vivo to baicalein by the cleavage of the glycoside moiety. Therefore, it is useful to compare their activities in vitro. The effects of baicalin and baicalein were studied in androgen-positive and -negative human prostate cancer lines LNCaP and JCA-1, respectively. Inhibition of cell growth by 50% (ED(50)) in LNCaP cells was seen at concentrations of 60.8 +/- 3.2 and 29.8 +/- 2.2 microM baicalin and baicalein, respectively. More potent growth inhibitory effects were observed in androgen-negative JCA-1 cells, for which the ED(50) values for baicalin and baicalein were 46.8 +/- 0.7 and 17.7 +/- 3.4, respectively. Thus, it appears that cell growth inhibition by these flavonoids is independent of androgen receptor status. Both agents (1) caused an apparent accumulation of cells in G(1) at the ED(50) concentration, (2) induced apoptosis at higher concentrations, and (3) decreased expression of the androgen receptor in LNCaP cells.

Antineoplastic Agents, Phytogenic↗

PubMed2001

Patterns of DNA sequence variation in chromosomally recognized taxa of Anopheles gambiae: evidence from rDNA and single-copy loci.

Patterns of DNA sequence variation in the ribosomal DNA (rDNA) second internal transcribed spacer (ITS2) and five unlinked single-copy nuclear loci were examined for evidence of reproductive isolation among four chromosomally recognized taxa of Anopheles gambiae from West Africa: Savanna, Bamako, Mopti and Forest, as well as sibling species An. arabiensis and An. merus. Included among the single-copy loci were three sequence-tagged random amplified polymorphic DNA (RAPD) loci, two of which (R15 and R37) had been reported as discriminating between Mopti and other chromosomal forms. Each of the five single-copy sequences were highly polymorphic in most samples. However, the R15 and R37 loci had no diagnostic value, and therefore are not recommended as tools in recognition of field-collected An. gambiae chromosomal forms. Although pairwise comparisons between species generally revealed significant levels of differentiation at all five loci, variation was not partitioned by chromosomal form within An. gambiae at any single-copy locus examined. The few exceptions to these trends appear related to a location either inside or nearby chromosomal inversions. At the tryptophan oxygenase locus inside inversion 2Rb, variation was structured only by inversion orientation and not by taxonomic designation even between An. gambiae and An. arabiensis, providing the first molecular evidence that the 2Rb inversion was transferred between species by introgressive hybridization. By contrast, the rDNA showed fixed differences between species and a difference diagnostic for Mopti, consistent with effective, if not complete, reproductive isolation. The apparent disagreement between the data from this locus and multiple single-copy loci within An. gambiae may be explained by the much lower effective population size of rDNA, owing to concerted evolution, which confers increased sensitivity at much shorter divergence times. Taken together with the accompanying reports by della Torre et al. (2001), Favia et al. (2001) and Gentile et al. (2001), our data suggest that neutral molecular markers may not have the sensitivity required to detect isolation between these recently established taxa.

Animals↗

PubMed2001

Molecular epidemiology of preterm delivery: methodology and challenges.

Preterm delivery (PTD) appears to be a complex trait determined by both genetic and environmental factors. Few studies have examined genetic influence on PTD. The overall goal of our study is to examine major candidate genes of PTD and to test gene-environment interactions. Our study includes 500 preterm trios, including 500 preterm babies and their parents and 500 maternal age-matched term controls. We will perform the transmission/disequilibrium test (TDT) on candidate genes thought to be important in each of the four biological pathways of PTD: (1) decidual chorioamionotic inflammation: interleukin 1 (IL-1), IL-6, and tumour necrosis factor (TNF); (2) maternal and fetal stress: corticotropin-releasing hormone (CRH); (3) uteroplacental vascular lesions: methylenetereahydrofolate reductase (MTHFR); and (4) susceptibility to environmental toxins: GSTM1, GSTT1, CYP1A1, CYP2D6, CYP2E1, NAT2, NQO1, ALDH2, and EPHX. We will also perform standard case-control analyses on the 500 preterm cases and 500 term controls to examine gene-environment interactions. The major environmental, nutritional and social factors as well as clinical variables known or suspected to be associated with PTD will be used to test for gene-environment interactions. This study integrates epidemiological and clinical data as well as genetic markers along major pathogenic pathways of PTD. The findings from this study should improve our understanding of genetic influences on PTD and gene-environment interactions.

Adult↗

PubMed2001

Gastrodianin-like mannose-binding proteins: a novel class of plant proteins with antifungal properties.

The orchid Gastrodia elata depends on the fungus Armillaria mellea to complete its life cycle. In the interaction, fungal hyphae penetrate older, nutritive corms but not newly formed corms. From these corms, a protein fraction with in vitro activity against plant-pathogenic fungi has previously been purified. Here, the sequence of gastrodianin, the main constituent of the antifungal fraction, is reported. Four isoforms that encoded two different mature proteins were identified at the cDNA level. Another isoform was detected in sequenced peptides. Because the antifungal activity of gastrodianins produced in and purified from Escherichia coli and Nicotiana tabacum was comparable to that of gastrodianin purified from the orchid, gastrodianins are the active component of the antifungal fractions. Gastrodianin accumulation is probably an important part of the mechanism by which the orchid controls Armillaria penetration. Gastrodianin was found to be homologous to monomeric mannose-binding proteins of other orchids, of which at least one (Epipactis helleborine mannose-binding protein) also displayed in vitro antifungal activity. This establishes the gastrodianin-like proteins (GLIPs) as a novel class of antifungal proteins.

Amino Acid Sequence↗

PubMed2001

Regulation of plant water loss by manipulating the expression of phospholipase Dalpha.

Phospholipase D (PLD) has been implicated in various processes, including signal transduction, membrane trafficking, and membrane degradation. Multiple forms of PLD with distinct biochemical properties have been described in the cell. In Arabidopsis, PLDalpha and PLDgamma, but not PLDbeta, were detected in guard cells, and antisense suppression resulted in a specific loss of PLDalpha. The abrogation of PLDalpha rendered plants less sensitive to abscisic acid and impaired stomatal closure induced by water deficits. PLDalpha-depleted plants exhibited accelerated transpirational water loss and a decreased ability to tolerate drought stress. Overexpression of PLDalpha enhanced the leaf's sensitivity to abscisic acid. These findings provide molecular and physiological evidence that PLDalpha plays a crucial role in regulating stomatal movement and plant-water status.

Abscisic Acid↗