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Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 685 records · Page 38Linked to original sources
PubMed1998

Preparation, Characterization, and Catalytic Properties of Polymer-Stabilized Ruthenium Colloids.

Poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium colloids were prepared by NaBH4 reduction at room temperature and characterized by transmission electron microscopy and x-ray photoelectron spectra. The average diameters of the colloids were 1.3-1.8 nm with final sigma = 0.4-0.7 nm with respect to the preparation conditions. The PVP-stabilized ruthenium colloids were used as catalysts in the hydrogenations of cyclooctene and n-heptene and the selective hydrogenation of citronellal to citronellol. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

A selenium-containing abzyme, the activity of which surpassed the level of native glutathione peroxidase.

Using two different glutathione derivatives as hapten, we have prepared two abzymes, which display glutathione peroxidase (GPX) activity. Their GPX activities are 0.2 and 1.6 times that of natural GPX from rabbit liver, respectively. Selenium content analysis indicates that the activity difference between the two abzymes is possibly attributed to the conformation difference of the abzymes.

Animals↗
PubMed1998

Specific suppression of human CD4+ Th cell responses to pig MHC antigens by CD8+CD28- regulatory T cells.

Evidence that T cells can down-regulate the immune response by producing or consuming certain cytokines or by lysing APCs or Th cells has been provided in various systems. However, the generation and characterization of suppressor T cell lines have met with limited success. Here we show that xenospecific suppressor T cells can be generated by in vitro stimulation of human T cells with pig APCs. Similar to allospecific suppressors, these xenospecific suppressor T cells carry the CD8+CD28- phenotype and react to MHC class I Ags expressed by the APCs used for priming. TCR spectratyping of T suppressor cells showed oligoclonal usage of TCR-Vbeta families, indicating that xenostimulation of CD8+CD28- T cells results in Ag-driven selection of a limited Vbeta repertoire. Xenospecific T suppressor cells prevent the up-regulation of CD154 molecules on the membrane of Th cells, inhibiting their ability to react against the immunizing MHC class II xenoantigens. The mechanism of this suppression, therefore, appears to be blockade of CD154/CD40 interaction required for efficient costimulation of activated T cells.

Animals↗
PubMed1998

[Association between the debrisoquine hydroxylase gene polymorphism and the genetic susceptibility of Parkinson's disease].

OBJECTIVE: To clarify the relation of the debrisoquine hydroxylase gene polymorphism with the genetic susceptibility of Parkinson's disease. METHODS: The debrisoquine hydroxylase gene polymorphisms were analyzed with the polymerase chain reaction-restriction fragment length polymorphism methods in 100 cases of Parkinson's disease and 100 age-,sex-matched normal controls. RESULTS: It was found that the frequencies of A and B mutation of debrisoquine hydroxylase gene in group of patients were higher than those in the controls, and the risk of suffering Parkinson's disease increased 2 times. In group of the patients, the frequencies of C188-->T, G4268-->C and C2938-->T were also higher than those in the controls. Especially in those with C2938-->T mutation, the risk of suffering the disease increased 2.58 times. CONCLUSION: The result suggested that the defect of the detoxifying enzymes might be a factor contributing to the genetic susceptibility of Parkinson's disease.

Adult↗
PubMed1998

Rh50 glycoprotein gene and rhnull disease: a silent splice donor is trans to a Gly279-->Glu missense mutation in the conserved transmembrane segment.

Rhnull disease includes the amorph and regulator types that are thought to result from homozygous mutations at the RH30 and RH50 loci, respectively. Here we report an unusual regulator Rhnull where two G-->A nucleotide (nt) transitions occurred in trans, targeting different regions of the two copies of Rh50 gene. The nt 836 G-->A mutation was a missense change located in exon 6; it converted Gly into Glu at position 279, a central amino acid of the transmembrane segment 9 (TM9). While cDNA analysis showed expression of the 836A(Glu279) allele only, genomic studies showed the presence of both 836A(Glu279) and 836G(Gly279) alleles. A detailed analysis of gene organization led to the identification in the Rh50(836G) allele of a defective donor splice site, caused by a G-->A mutation in the invariant GT element of intron 1. This is the first known example of such mutations that has apparently abolished the functional splicing of a pre-mRNA encoding a multipass integral membrane protein. With a silent phenotypic copy in trans, the negatively charged Glu279 residue may disrupt TM9 and impair the interaction of the missense protein with Rh30 polypeptides. To evaluate the significance of the mutation, we took a comparative genomic approach and identified Rh50 homologues in different species. We found that Gly279 is a conserved residue and its adjacent amino acid sequence is identical from Caenorhabditis elegans to human. These findings provide new insight into the diversity of Rhnull disease and suggest that the C-terminal region of Rh50 may also participate in protein-protein interactions involving Rh complex formation.

Amino Acid Sequence↗
PubMed1998

Synthesis, physicochemical properties, and evaluation of N-substituted-2-alkyl-3-hydroxy-4(1H)-pyridinones.

The synthesis of a range of 3-hydroxy-4(1H)-pyridinones with potential for the chelation of iron(III) is described. The pKa values of respective ligands and the stability constants of their iron(III) complexes are presented. The distribution coefficient values of a range of 48 hydroxypyridinones and their corresponding iron(III) complexes between 1-octanol and MOPS buffer (pH 7.4) are reported. The range of log Dcomplex values covers 7 orders of magnitude. The results suggest the existence of a biphasic relationship between the distribution coefficient values of the chelator and the corresponding iron(III) complexes. For ligands with a log Dligand = -1, a linear relationship exists with a value of the slope 2.53, whereas with ligands with a log Dligand < -1, a linear relationship exists with a slope of 0.49. The reduced slope for the more hydrophilic molecules of the series offers some advantage for this type of hydroxypyridinone as the distribution coefficients for such complexes do not change so rapidly with increasing ligand hydrophilicity. The ability of selected 3-hydroxypyridinones to facilitate the excretion of iron in bile was investigated in non-iron-overloaded, bile duct-cannulated rats and in a [59Fe]ferritin-loaded rat model. Both systems compare the ability of chelators to remove iron from the liver, the prime target organ in thalassemia. The N-(hydroxyalkyl)-3-hydroxypyridin-4-ones are demonstrated to be orally active under the in vivo conditions adopted. Thus both 1-(hydroxyalkyl)- and 1-(carboxyalkyl)pyridinones are able to remove iron from the liver. Although 1-(carboxyalkyl)hydroxypyridinones are active, they do not demonstrate any clear advantage over Deferiprone (1,2-dimethyl-3-hydroxypyridin-4-one). Indeed 1-(hydroxyalkyl)hydroxypyridinones which are known to be rapidly converted to 1-(carboxyalkyl)hydroxypyridinones are also marginally superior to Deferiprone. In contrast, 2-ethyl-1-(2'-hydroxyethyl)-3-hydroxypyridin-4-one, which is not metabolized to the corresponding (carboxyalkyl)hydroxypyridinone, was found to be superior to Deferiprone and therefore deserves further consideration as an orally active iron chelator with potential for the treatment of iron overload associated with transfusion-dependent thalassemia.

Animals↗
PubMed1998

Gelatinase B-deficient mice are resistant to experimental bullous pemphigoid.

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease characterized by deposition of autoantibodies at the basement membrane zone. In an experimental BP model in mice, the subepidermal blistering is mediated by antibodies directed against the hemidesmosomal protein BP180 (collagen XVII, BPAG2), and depends on complement activation and neutrophil infiltration. Gelatinase B is present in BP blister fluid and can cleave BP180. In this study we investigated the role of gelatinase B in the immunopathogenesis of experimental BP using mice containing targeted disruption of the gelatinase B (MMP-9, 92 kD gelatinase) gene. Gelatinase B-deficient mice were resistant to the blistering effect of intracutaneous anti-mBP180 antibodies, although these mice showed deposition of autoantibodies at the basement membrane zone and neutrophil recruitment to the skin comparable to that observed in the control mice. Interleukin 8 given intradermally concomitantly with pathogenic anti-mBP180 elicited a significant neutrophil recruitment into the skin in gelatinase B-deficient mice, but blistering did not occur. However, gelatinase B-deficient mice reconstituted with neutrophils from normal mice developed blistering in response to anti-mBP180 antibodies. These results implicate neutrophil-derived gelatinase B in the pathogenesis of experimental BP and might lead to novel therapeutic strategies for BP.

Animals↗
PubMed1998

CD8+ T-lymphocyte activation in HIV-1 disease reflects an aspect of pathogenesis distinct from viral burden and immunodeficiency.

The CD8+ T-cell response is central to control and eventual elimination of persistent viral infections. Although it might be expected that CD8+ T-cell activation would be associated with a better clinical outcome during viral infections, in long-term HIV-1 infection, high levels of CD8+ T-cell activation are instead associated with faster disease progression. In this study, cell surface expression of CD38, a flow cytometric marker of T-cell activation of CD8+ T cells, had predictive value for HIV-1 disease progression that was in part independent of the predictive value of plasma viral burden and CD4+ T-cell number. Measurements of CD38 antigen expression on CD8+ T cells in HIV-1-infected patients may be of value for assessing prognosis and the impact of therapeutic interventions. The pathogenetic reason why CD8+ T-cell activation is associated with poor outcome in HIV-1 disease remains unknown. Possibly CD8+ T-cell activation contributes to immunologic exhaustion, hyporesponsiveness of T cells to their cognate antigens, or perturbations in the T-cell receptor repertoire.

ADP-ribosyl Cyclase↗
PubMed1998

Benzo[a]pyrene enhances the formation of 8-hydroxy-2'-deoxyguanosine by ultraviolet A radiation in calf thymus DNA and human epidermoid carcinoma cells.

The objective of this study is to investigate if benzo[a]pyrene (BaP) and ultraviolet (UV) radiation synergistically induce oxidative DNA damage. Calf thymus DNA was incubated with BaP and irradiated with UVB (280-320 nm) and UVA (335-400 nm). BaP substantially enhanced the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) by UVA, but only moderately increased the level of 8-OHdG by UVB. Formation of 8-OHdG proportionally correlated with both UV dose and BaP concentration. Human epidermoid carcinoma cells were incubated with 10 microg of BaP/mL for 24 h and then exposed to 10 kJ/m2 UVB and 25 kJ/m2 UVA. UVB plus BaP did not affect the level of 8-OHdG in cultured cells, whereas UVA plus BaP substantially increased 8-OHdG by over 4-fold compared to BaP and UVA controls. To confirm what reactive oxygen species (ROS) are involved in BaP plus UVA-induced oxidative DNA damage, less or more specific ROS quenchers were added to DNA solution. The results showed that only superoxide dismutase and genistein significantly quenched BaP plus UVA-induced 8-OHdG, whereas catalase, sodium azide, and mannitol exhibited no effect. Our studies suggest that BaP enhances the formation of 8-OHdG in purified DNA and cultured cells by UVA, but not by UVB, and that superoxide anion plays an important role in the synergistic induction of oxidative DNA damage.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1998

99mTc-HL91: "hot spot" detection of ischemic myocardium in vivo by gamma camera imaging.

BACKGROUND: 99mTc-HL91 is a new hypoxia imaging agent that demonstrates increased uptake and retention in globally hypoxic myocardium in vitro. The purpose of this study was to determine whether 99mTc-HL91 could detect regional ischemia in vivo by gamma camera imaging. METHODS AND RESULTS: Eight open-chest dogs with left circumflex (LCx) stenoses were studied. Injection of 5 mCi of 99mTc-HL91 and microspheres was followed by imaging over 4 hours. Heart slices were imaged, then stained with triphenyltetrazolium chloride (TTC), and tissues were well-counted. TTC staining demonstrated no injury. Mean LCx blood flow was 0.32+/-0.04 mL x min(-1) x g(-1), and mean left anterior descending coronary artery (LAD) flow was 0.96+/-0.02 mL x min(-1) x g(-1) (ratio, 0.33). "Hot spots" were detected in 8 of 8 experiments in vivo within 60 minutes and improved over 4 hours. Region of interest analysis of LCx/LAD activity ratios demonstrated significant increases within 30 minutes (final ratio, 3.0; P<0.05). LCx and LAD washout curves demonstrated significant differences within 15 minutes. Washout curves were biexponential over 1 hour, followed by linear retention from 1 to 4 hours. Four-hour fractional retention was 0.12 for LAD and 0.44 for LCx (P<0.01). Myocardial flow versus tracer uptake demonstrated 2 phases: phase 1 (flow, 0.05 to 0.7 mL x min(-1) x g(-1)) had an inverse linear correlation (r= -0.80); phase 2, (flow, >0.7 mL x min(-1) x g(-1)) had no correlation. Ischemic heart/liver ratios remained near 1.0 for 4 hours. CONCLUSIONS: 99mTc-HL91 positively identifies regional myocardial ischemia in a canine model using 99mTc imaging. Quantitative techniques allowed identification of ischemic myocardium within 15 minutes of tracer administration.

Animals↗
PubMed1998

Synaptic reorganization following kainic acid-induced seizures during development.

Prolonged seizures in the adult brain causes neuronal loss in the hippocampus and aberrant growth (sprouting) of granule cell axons (mossy fibers) in the supragranular zone of the fascia dentata and stratum infrapyramidale of CA3. There is considerable evidence that these changes in neuronal growth following seizures are age related, with younger animals having fewer reactive changes following prolonged seizures than older animals. However, there is little information available regarding the age at which seizures in the developing brain result in alterations in axonal growth and synapse formation. In this study, we evaluated the effects of kainic acid (KA)-induced seizures during development on synaptic reorganization using the expression of growth-associated protein-43 (GAP-43), a marker for synaptogenesis and Timm stain which detects the presence of zinc in granule cell axons. Age specific doses of KA were used to induce seizures of similar intensity at various ages (postnatal days (P) 12, 21, 25, 35, 45, 60) in Sprague-Dawley rats. Up to the age of P25, there were no differences in either Timm or GAP-43 staining between animals with KA seizures and controls. In P25 and older KA-treated rats, Timm staining was found in the supragranular layer of the dentate gyrus. This staining increased with age at the time of KA injection. Seizures in adult (P60), but not younger rats also resulted in increased staining in the suprapyramidal layer of the CA3 subfields. Changes in GAP-43 were delayed compared to the Timm staining with no differences between KA-treated animals and controls until P35 when a band of GAP-43 immunostaining appeared in the supragranular inner molecular layer, progressively increasing in intensity and thickness with time. This study demonstrates that seizure-induced reactive synaptogenesis is age-related. Since both Timm and GAP-43 reflect different aspects of reactive synaptogenesis, used in combination these methods provide useful information about the structural changes following seizures during development.

Aging↗
PubMed1998

Biochemical characterization of selenium-containing catalytic antibody as a cytosolic glutathione peroxidase mimic.

A selenium-containing catalytic antibody (Se-4A4), prepared by converting reactive serine residues of a monoclonal antibody (4A4) raised against a GSH derivative into selenocysteines, acts as a mimic of cytosolic glutathione peroxidase (cGPX). To clarify the mechanism of action of this catalytic antibody, detailed studies on kinetic behaviour and biological activity were carried out. A rate of acceleration (kcat/Km/kuncat) 10(7)-fold that of the uncatalytic reaction is observed. Under similar conditions, the turnover number (kcat) of Se-4A4 is 42% of that of the natural rabbit liver cGPX. The Se-4A4 reaction involves a Ping Pong mechanism, which is the same as that of the natural cGPX. The selenocysteine residue is located in the binding site of the antibody and is shown to be crucial for this activity. Of the thiol compounds tested, only GSH is able to serve as substrate for Se-4A4. It was demonstrated, using the free-radical-damage system (hypoxanthine/xanthine oxidase) of cardiac mitochondria, that Se-4A4 can protect mitochondria from free-radical damage at least 10(4)-fold more effectively than the natural cGPX.

Antibodies, Catalytic↗
PubMed1998

Seizures in rats treated with kainic acid induce Fos-like immunoreactivity in locus coeruleus.

Kainic acid-triggered seizures (KATS) induce Fos-like immunoreactivity (FLI) in limbic structures, which send efferents to the locus coeruleus (LC). Following KATS, brain stem sections were stained for Fos immunocytochemistry and double immunostained for Fos and dopamine beta-hydroxylase (DBH). KA-treated animals showed significantly greater numbers of FLI neurons in the LC than control animals (p < 0.05). Co-localization of DBH/Fos was observed in 89.7% of the LC neurons in KA-treated animals and in 1.4% of LC neurons in control animals. Thus, KATS heavily induce Fos in DBH-containing neurons in the LC, which are known to project to the hippocampus. However, the role of activation of the LC noradrenergic neurons during KATS is not well understood at this present time.

Animals↗
PubMed1998

The spacing between binding sites controls the mode of cooperative DNA-protein interactions: implications for evolution of regulatory circuitry.

The CI repressors of lambdoid phages bind cooperatively to adjacent binding sites. Although these binding sites are found at complex operators containing three binding sites, cooperative binding occurs only between dimers bound at two of the sites, a mode of binding termed pairwise cooperativity. At the level of regulation, pairwise cooperativity allows the proper operation of the genetic switch. At the mechanistic level, it has been proposed to result from steric distortion of the complex, such that a protein dimer bound to a central site cannot contact both flanking dimers because it "leans" towards one of the two sites. We have tested this model using the CI repressor of phage HK022. Previous work suggested that reducing the spacing between adjacent operators might allow cooperative interaction among three dimers, a mode of cooperativity we term extended. Using a set of synthetic templates, we have shown that reducing the spacing allows extended cooperativity among three binding sites. Accordingly, the mode of cooperativity changes qualitatively in response to changes in the inter-site spacing. That is, the change in spacing has major functional consequences for the properties of the complex. We suggest that such changes can play important roles in the evolution of gene regulatory circuitry and of other processes involving nucleoprotein complexes.

Bacteriophage lambda↗
PubMed1998

Hepatocyte growth factor/scatter factor stimulates chemotaxis and growth of malignant mesothelioma cells through c-met receptor.

Hepatocyte growth factor (HGF) and its receptor c-met are present in several human tissues but their expression in mesothelial cells has not been examined. In this study, we have investigated the expression of HGF and c-met in normal human mesothelial cells and 11 human malignant mesothelioma cell lines. Using RT-PCR and Western blotting we found that HGF is produced by 3/11 mesothelioma cell lines whereas c-met is expressed in 11/11 mesothelioma cell lines. In addition, c-met expression was also found in 6/6 cell samples obtained from pleural fluids of patients with mesothelioma. In contrast, neither normal cultured mesothelial cells nor mesothelial cells obtained directly from patients without mesothelioma expressed HGF nor c-met. We have also analysed the biological function of HGF and c-met in mesothelioma cell lines. Recombinant human (rh) HGF stimulated both directional (chemotactic) and random (chemokinetic) motility in all mesothelioma cell lines tested. Furthermore, mesothelioma serum free conditioned medium containing HGF stimulated mesothelioma cell migration. This effect could be blocked in the presence of neutralizing anti-HGF monoclonal antibodies (MAbs) in the assay. Addition of HGF to mesothelioma cells cultured on collagen type IV was associated with induction of bipolar shape and protrusion of prominent pseudopodia. We have also found that rhHGF was mitogenic for mesothelioma cells. Our findings suggest that expression of HGF/c-met is involved not only in mesothelioma progression but also in its growth and migration and that c-met expression found in mesothelioma cells taken directly from patients may be of diagnostic importance.

Cell Division↗
PubMed1998

Clinical relevance of chromosome abnormalities in non-small cell lung cancer.

The relationship between clonal chromosome alterations and various clinical parameters was evaluated in 70 patients with non-small cell lung cancer (NSCLC) for whom detailed karyotypic assessment was possible. Included in the analysis are karyotypes of 63 previously published cases and seven new NSCLCs. Clinical features investigated were diagnosis, tumor stage and grade, gender, smoking history measured in pack years, and survival. Certain chromosome abnormalities were significantly associated with histologic subtype, tumor grade, stage, and prognosis. Rearrangements involving chromosome arms 2p and 3q were more common in squamous cell carcinoma (SCC) than in adenocarcinoma (ADC). Loss of 3p was observed more often in SCC. Gain of 7p was more frequent in ADC. Rearrangement of 17p was associated with a lower tumor grade. Rearrangement of Xp and loss of chromosome 12 or 22 were each associated with higher tumor stage. Rearrangement of 3p or 6q was correlated with a better survival outlook. In contrast, loss of chromosomes 4 or 22 portended a poor prognosis. Finally, an increased number of marker chromosomes was observed in patients having a higher number of pack years. These data indicate that chromosome abnormalities can have clinical and pathologic significance in NSCLC.

Adult↗