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Biomedical subjects

C Xu

Publications and source records attributed to C Xu.

At least 163 records · Page 9Linked to original sources
PubMed1998

A reduction-pyrolysis-catalysis synthesis of diamond

Diamond powder was synthesized through a metallic reduction-pyrolysis-catalysis route with the reaction of carbon tetrachloride and sodium at 700 degreesC, in which the sodium was used as reductant and flux. This temperature is much lower than that of traditional methods. The x-ray powder diffraction patterns showed three strong peaks of diamond. The Raman spectrum showed a sharp peak at 1332 inverse centimeters, which is characteristic of diamond. Although the yield was only 2 percent, this method is a simple means of forming diamond.

Journal Article↗
PubMed1998

Linkage and association analysis of genes encoding cytokines and myelin proteins in multiple sclerosis.

Several genetic factors are likely to play a role in the etiology of multiple sclerosis (MS). We used a candidate gene strategy in a study of polymorphic markers within or close to genes encoding cytokines (interferon-gamma (IFN-gamma), interleukin-2 (IL-2), IL-4, IL-4 receptor (IL-4R), IL-10, transforming growth factor-beta1 and -beta2) and myelin proteins (2',3'-cyclic-nucleotide 3'-phosphohydrolase (CNP:ase), myelin associated glycoprotein, oligodendrocyte myelin glycoprotein, proteolipid protein) in 34 Swedish multiplex MS families and in 147 sporadic MS patients and 95 healthy controls. No evidence for linkage was observed in two-point linkage analysis. However, a slightly positive LOD score of 0.88 (theta = 0.01) for IFN-gamma was found. Affected pedigree member (APM) analysis indicated a possible linkage with TGF-beta2 (p = 0.008) and IL-4R (p = 0.043). None of the cytokine markers were associated with MS in case-control analysis. Our results suggest a possible importance of the TGF-beta2, IL-4R and IFN-gamma genes in MS.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1998

Expression of complement receptors 1 and 2 on follicular dendritic cells is necessary for the generation of a strong antigen-specific IgG response.

Two mechanisms could account for the impaired humoral immune response found in Cr2-/- mice. The absence of complement receptors 1 and 2 (CR1, CR2) on B cells could affect their activation. Alternatively, impaired Ag trapping by follicular dendritic cells (FDC) could affect B cell maturation into Ig-secreting or memory B cells. To compare the roles of CR1 and CR2 on B cells vs FDC in this abnormal response, bone marrow (BM) chimeric mice were generated and immunized with specific T-dependent Ags. The primary and secondary Ab response was measured. Cr2+/+ animals reconstituted with a Cr2-/- BM generated a diminished but detectable humoral immune response compared with controls. When injected with preformed immune complexes (IC), these mice maintained follicular IC localization. Cr2-/- animals reconstituted with a Cr2+/+ BM had an initial rise in the Ab titer, but were unable to maintain it as shown by a pronounced decrease in the IgG titer. This defect persisted during the secondary immune response. Follicular IC trapping was also impaired. Despite the abnormal Ab response, germinal center formation was retained in all of the chimeric animals. These experiments are the first to demonstrate an absolute requirement for CR1 and CR2 expression on FDC in the generation of a normal humoral immune response.

Animals↗
PubMed1998

Specific arrest of cardiogenesis in cultured embryonic stem cells lacking Cripto-1.

The molecular events of cardiac lineage specification and differentiation are largely unknown. Here we describe the involvement of a growth factor with an EGF-like domain, Cripto-1 (Cr-1), in cardiac differentiation. During embryonic development, Cr-1 is expressed in the mouse blastocyst, primitive streak, and later is restricted to the developing heart. To investigate the role of Cr-1, we have generated Cr-1-negative embryonic stem (ES) cell lines by homologous recombination. The resulting double "knockout" ES cells have selectively lost the ability to form beating cardiac myocytes, a process that can be rescued by reintroducing Cr-1 gene back into the Cr(-/-) cells. Furthermore, the lack of functional Cr-1 is correlated with absence of expression of cardiac-specific myosin light and heavy chain genes during differentiation. Differentiation into other cell types including skeletal muscle is not disrupted. These results suggest that Cr-1 is essential for contractile cardiomyocyte formation in vitro.

Animals↗
PubMed1998

Degradation of hammerhead ribozymes by human ribonucleases.

Hammerhead ribozymes were used as substrates to examine endoribonucleolytic activities in cell extracts and cultured human cells. Primer-extension analyses showed that ribozymes directed against tumor necrosis factor-alpha mRNA and human immunodeficiency virus type 1 tat mRNA were cleaved at UA and CA dinucleotides by extracts. Preferred cleavage sites were similar to those observed following digestion with RNase A, and cleavage was blocked by RNasin, an inhibitor of pyrimidine-specific ribonucleases. Removal of UA and CA dinucleotides rendered ribozymes more stable when incubated in cell extracts that were not significantly contaminated by extracellular nucleases. Placement of UA dinucleotides adjacent to a ribozyme in mRNA led to excision of the ribozyme from long transcripts during incubation in extracts. UA dinucleotides also made mRNA more labile than a control RNA when expressed from an endogenous plasmid gene in the human myeloid cell line U937. Similarly, UA and CA dinucleotides caused ribozymes to have a shorter half-life when delivered to U937 cells by lipofectin-mediated transformation. Taken together, these data indicate that one or more members of the pyrimidine-specific ribonuclease family is involved in the intracellular degradation of RNA, and they explain the paucity of UA dinucleotides in eukaryotic mRNA. Judicious manipulation of preferred target sequences of pyrimidine-specific ribonucleases may be useful in designing effective hammerhead ribozymes.

Base Sequence↗
PubMed1998

Modulation of endothelial cell function by normal polyspecific human intravenous immunoglobulins: a possible mechanism of action in vascular diseases.

Intravenous immunoglobulin (IVIg) is increasingly used in the treatment of autoimmune and inflammatory diseases, including vasculitides and Kawasaki disease. However, the outcome of IVIg interaction with endothelial cells of the vascular bed is not clear as yet. We have investigated the effect of IVIg on the in vitro activation of human endothelial cells, as assessed by cell proliferation and reverse transcription-polymerase chain reaction-detected expression of mRNA coding for adhesion molecules (intercellular adhesion molecule-1 and vascular cellular adhesion molecule-1), chemokines (monocyte chemoattractant protein-1, macrophage colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor), and proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6). IVIg inhibited proliferation of endothelial cells in a time-dependent manner. This effect was dependent on both Fc and F(ab')2 fragments of the immunoglobulin molecule and was fully reversible. Tumor necrosis factor-alpha and interleukin-1beta also inhibited thymidine incorporation, but to a lesser degree. IVIg had no effect on basal levels of mRNA coding for the adhesion molecules, chemokines, and proinflammatory cytokines. IVIg fully down-regulated the expression induced by tumor necrosis factor-alpha or interleukin-1beta of mRNA coding for these molecules. Thus, blockade of cellular proliferation and of cytokine-induced expression of adhesion molecules, chemokines, and cytokines may explain the therapeutic effect of IVIg in vascular and inflammatory disorders.

Cell Adhesion Molecules↗
PubMed1998

Antigen mimicry by an anti-idiotypic antibody single chain variable fragment.

For the therapy of cancer patients whose disease is positive for Carcinoembryonic Antigen (CEA), we developed an active specific immunotherapy based on the idiotypic network. The anti-idiotype monoclonal antibody (mAb), 3H1 was generated by immunization of mice with the anti-CEA mAb, 8019. 3H1 mimics CEA both functionally and structurally and acts as a surrogate for CEA. To define the minimum structural requirements for antigen mimicry by 3H1, we constructed plasmid vectors for expression of single chain Fv (scFv) variants of 3H1 in Escherichia coli. Variable heavy (VH) and variable light (VL) chain domains of 3H1 were linked by a 15 amino acid linker (Ln), (Gly4Ser)3 in two constructs, VH-Ln-VL and VL-LnVH. Ln was omitted in two constructs, VH-VL and VL-VH. Each of the scFv constructs has a tag of six His [(His)6 tag] for purification by metal chelate affinity chromatography and detection by enzyme-linked immunoabsorbent assay (ELISA). Comparisons of the binding of 8019 to purified scFv proteins by ELISA and immunoblot experiments showed that only VH-Ln-VL had significant activity. VH-Ln-VL also showed maximum inhibition of binding of 8019 to CEA. Immunization of mice with naked VH-Ln-VL and VH-Ln-VL conjugated to keyhole limpet hemocyanin induced anti-CEA antibodies in mouse sera. Sera from immunized mice inhibited the binding of 8019 to 3H1 as well as CEA. Induction of anti-CEA antibodies in the immunized mice was confirmed by flow cytometric analysis using CEA positive MC-38cea cells. These results demonstrate that for antigen mimicry of 3H1 scFv, the presence of Ln is necessary and the domain order should be VH followed by VL.

Animals↗
PubMed1998

Microscopic evidence against HIV-1 infection of germ cells or attachment to sperm.

For a number of years we have intensively investigated the localization of HIV-1 in male genital tract tissues and secretions using a variety of microscopy techniques including immunocytochemistry, in situ hybridization, in situ PCR and electron microscopy. Our studies have failed to demonstrate an association between HIV-1 and either testicular germ cells or spermatozoa. In this article we present our results in the context of other related studies, and discuss the strengths and weaknesses of the techniques that have been used to address this important research question.

Animals↗
PubMed1998

The case against an association between HIV-1 and sperm: molecular evidence.

In this article we present data from our laboratory, and review the literature available, on the potential association between HIV-1 and sperm. We focus on the use of PCR technology to answer this very important question, and emphasise the importance of using highly purified sperm preparations. We conclude that the likelihood of HIV infection/association with viable mature sperm is low.

DNA, Viral↗
PubMed1998

Protein W, a spore-specific protein in Myxococcus xanthus, formation of a large electron-dense particle in a spore.

The gene for the major spore-specific protein, termed protein W, was cloned, and it was found that protein W is composed of 426 amino acid residues including 31% charged (133 residues) and 39% hydrophobic (166 residues) amino acids. In the protein, a motif consisting of five amino acid residues [(V/L/I)-R-E-R-(V/L/I)] is repeated 28 times, and another motif [M-M-(P/G)-Q-G] five times. Protein W is synthesized during a very late stage of development, forming a single, large electron-dense particle (200-400 nm in diameter) inside a spore. X-ray microanalysis of the particle revealed that it contains a high amount of phosphate in addition to calcium and magnesium. It is proposed that protein W consisting of highly charged repetitive sequences is a polyphosphate storage protein to store energy in spores. The disruption of the gene for protein W resulted in delayed fruiting body formation and a lower spore yield.

Amino Acid Sequence↗
PubMed1998

Simplified percutaneous mitral valvuloplasty with the Inoue balloon.

BACKGROUND: Percutaneous mitral valvuloplasty with the Inoue balloon is conventionally performed with double vascular access: arterial and venous. However, in patients with a good echogenic window it may be performed with venous access only and the procedure monitored by 2D-echocardiography and colour flow mapping. This should result in early ambulation and hospital discharge with reduced arterial complications. AIMS: To compare retrospectively the immediate results of percutaneous mitral valvuloplasty with the Inoue balloon in two groups of patients: Group I: venous access only (no arterial access, n = 102) and Group II: conventional double vascular access (arterial and venous access, n = 275). METHODS AND RESULTS: The baseline characteristics of the two groups were comparable for age, sex, clinical, echocardiographic, radiological and haemodynamic variables. The mitral valve area (Group I: 1.1 +/- 0.3 to 1.85 +/- 0.5 cm2 vs Group II: 1.05 +/- 0.2 to 1.85 +/- 0.5 cm2, P = ns) and transmitral gradient (Group I: 11 +/- 4 to 4.7 +/- 2 mmHg vs Group II: 12 +/- 4 to 4.8 +/- 2 mmHg, P = ns) before and after mitral valvuloplasty were not statistically different. A good immediate result, defined as mitral valve area > 1.5 cm2 and mean mitral gradient < 5 mmHg with mitral regurgitation < or = 2+ at the end of the procedure, was observed in 77% of the cases in the venous-only group and 79% in the double access group (P = ns). The incidence of severe mitral regurgitation (Grade III or IV) was not statistically significant. Procedural duration (71 +/- 24 min vs 109 +/- 26 min, P < 0.01), fluoroscopic time (12.5 +/- 5.5 min vs 18.5 +/- 6 min, P < 0.01) and hospital stay (2.8 +/- 1.5 days vs 4.8 +/- 2.6 days, P < 0.001) were significantly shorter in the venous-only group than in the conventional Inoue series. CONCLUSION: Single venous access balloon mitral valvuloplasty is as equally safe and effective as double vascular access. The additional advantages of single venous access are shorter procedural duration, fluoroscopic time and hospital stay. We recommend that it be performed by an experienced operator (minimum of 100 trans-septal punctures) in patients without major thoracic deformity and a good echogenic window.

Adult↗
PubMed1998

Metalloid resistance mechanisms in prokaryotes.

Resistance to antibiotics and other chemotherapeutic agents is becoming a wide spread health issue. The biochemical mechanisms of resistance vary, but active efflux of the toxic agents is one of the most common. Bacterial resistances to metals provide good model systems for transport-related resistances. One of the best understood metal resistance systems is the product of the ars operon, which provides resistance to arsenicals and antimonials. As a reflection of the ubiquity of arsenic in the environment, ars operons are found in all species of bacteria, carried in chromosomes, plasmids, and transposons. This review focuses on the biochemistry of the proteins of the ars operon of R-factor R773. The system is novel in several respects. First, it is regulated at the transcriptional and allosteric levels, and regulation is effected through cysteine thiol interaction with As(III) or Sb(III). Thus soft metal-thiol chemistry provides a high affinity digital switch to turn the regulated protein on with rapidity. The transport system that provides resistance, on the other hand, uses oxyanions of arsenic or antimony as substrates. This nonmetal chemistry allows for low affinity interactions of the membrane transporter with substrate, conductive with translocation and release of substrate on the outside of the cell membrane. Second, the transporter is uniquely capable of coupling to either electrochemical energy as a secondary carrier protein or the chemical energy of ATP when binding of a catalytic subunit converts it into an anion-translocating ATPase.

Adenosine Triphosphatases↗
PubMed1998

Mechanical analysis of heterogeneous, atherosclerotic human aorta.

An experimental technique was developed to determine the finite strain field in heterogeneous, diseased human aortic cross sections at physiologic pressures in vitro. Also, the distributions within the cross sections of four histologic features (disease-free zones, lipid accumulations, fibrous intimal tissue, and regions of calcification) were quantified using light microscopic morphometry. A model incorporating heterogeneous, plane stress finite elements coupled the experimental and histologic data. Tissue constituent mechanical properties were determined through an optimization strategy, and the distributions of stress and strain energy in the diseased vascular wall were calculated. Results show that the constituents of atherosclerotic lesions exhibit large differences in their bilinear mechanical properties. The distributions of stress and strain energy in the diseased vascular wall are strongly influenced by both lesion structure and composition. These results suggest that accounting for heterogeneities in the mechanical analysis of atherosclerotic arterial tissue is critical to establishing links between lesion morphology and the susceptibility of plaque to mechanical disruption in vivo.

Aged↗
PubMed1998

Fluoroquinolone action against mycobacteria: effects of C-8 substituents on growth, survival, and resistance.

Fluoroquinolones trap gyrase on DNA as bacteriostatic complexes from which lethal DNA breaks are released. Substituents at the C-8 position increase activities of N-1-cyclopropyl fluoroquinolones against several bacterial species. In the present study, a C-8-methoxyl group improved bacteriostatic action against gyrA (gyrase-resistant) strains of Mycobacterium tuberculosis and M. bovis BCG. It also enhanced lethal action against gyrase mutants of M. bovis BCG. When cultures of M. smegmatis, M. bovis BCG, and M. tuberculosis were challenged with a C-8-methoxyl fluoroquinolone, no resistant mutant was recovered under conditions in which more than 1, 000 mutants were obtained with a C-8-H control. A C-8-bromo substituent also increased bacteriostatic and lethal activities against a gyrA mutant of M. bovis BCG. When lethal activity was normalized to bacteriostatic activity, the C-8-methoxyl compound was more bactericidal than its C-8-H control, while the C-8-bromo fluoroquinolone was not. The C-8-methoxyl compound was also found to be more effective than the C-8-bromo fluoroquinolone at reducing selection of resistant mutants when each was compared to a C-8-H control over a broad concentration range. These data indicate that a C-8-methoxyl substituent, which facilitates attack of first-step gyrase mutants, may help make fluoroquinolones effective antituberculosis agents.

Anti-Infective Agents↗
PubMed1998

Killing of Staphylococcus aureus by C-8-methoxy fluoroquinolones.

C-8-methoxy fluoroquinolones were more lethal than C-8-bromine, C-8-ethoxy, and C-8-H derivatives for Staphylococcus aureus, especially when topoisomerase IV was resistant. The methoxy group also increased lethality against wild-type cells when protein synthesis was inhibited. These properties encourage refinement of C-8-methoxy fluoroquinolones to kill staphylococci.

Anti-Bacterial Agents↗
PubMed1998

Human choriocarcinoma JAR cells constitutively express pro-interleukin-1beta that can be released with Fc(gamma) receptor engagement.

Some authors have suggested that fetally derived syncytiotrophoblasts, which form the barrier between mother and the fetus, are an integral part of a complex macrophage-cytokine network involving maternal leukocytes, decidual cells, placental tissues, and even the fetus itself. We report here that syncytiotrophoblast-like JAR cells, a human choriocarcinoma cell line, share another feature common to cells of the monocyte-macrophage lineage, the ability to secrete IL-1beta when stimulated through their Fc(gamma) receptors. We incubated JAR cells with physiologically relevant concentrations of model BSA-rabbit IgG-anti-BSA immune complexes or monomeric rabbit IgG for periods of up to 72 h. Both monomeric IgG and immune complexes induced IL-1beta from JAR cells, although levels produced by immune complexes were approximately twice those induced by monomeric IgG. IL-1beta secretion was not inhibited by cycloheximide, and Western blots of JAR cell lysates using pro-IL-1beta MAb revealed constitutive expression of a 31-kD protein, whose levels declined within 2 h of stimulation by either IgG or immune complexes, but returned to baseline within 18 h.

Animals↗