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S Liu

Publications and source records attributed to S Liu.

At least 541 records · Page 30Linked to original sources
PubMed1998

Identification of a novel human glutathione S-transferase using bioinformatics.

In searching the expressed sequence tag (EST) data-base of GenBank with coding sequences of 11 known human glutathione S-transferases in conjunction with bioinformatic analysis, we have identified five ESTs that encode a new human glutathione S-transferase (GST) designated GST A4. The cDNA clone (I.M.A.G.E. Consortium cDNA Clone ID 515157) had an insert length of 1279 bp and contains an open reading frame of 666 bp, which encodes a protein of 222 amino acid residues. The GST A4 protein is identical in length to human GST A1 and A2 and is 54% identical to human GST A1 and A2. Sequence comparison with other human GSTs suggests that it is a new GST belonging to the alpha class GSTs. Northern blot analysis and EST database searches have demonstrated that the GST A4 mRNA is expressed at a high level in brain, placenta, and skeletal muscle and much lower in lung and liver. Analysis of the sequence tagged site (STS) database indicated that the GST A4 gene is located on chromosome 6. This STS represents a previously unidentified transcript further confirming the novelty of the new sequence.

Amino Acid Sequence↗
PubMed1998

Adenosine 5'-tetraphosphate phosphohydrolase activity is an inherent property of soluble exopolyphosphatase from yeast Saccharomyces cerevisiae.

Homogeneous soluble exopolyphosphatase (EC 3.6.1.11) from yeast Saccharomyces cerevisiae, (scPPX1) behaves as an adenosine 5'-tetraphosphate phosphohydrolase (EC 3.6.1.14). The hydrolysis of adenosine 5'-tetraphosphate (p4A) to ATP and orthophosphate absolutely depends on one of the following cations: Co2+>Mn2+>Mg2+>Ni2+. Optimum pH is around 4.75 and the Km for p4A estimated at that pH in 50 mM sodium acetate and at 5 mM CoCl2 is 80+/-10 microM. Adenosine 5'-pentaphosphate (p5A) is degraded under these conditions 18-fold more slowly than p4A. Assuming that the mass of scPPX1 is 45 kDa, the calculated kcat values for p4A and for p5A are 723 and 40 s-1, respectively. Two other nucleoside 5'-tetraphosphates (p4N), guanosine tetraphosphate (p4G) and inosine tetraphosphate (p4I), were hydrolyzed to Pi and either GTP or ITP, respectively, at the same rate as that observed for the hydrolysis of p4A. Ammonium molybdate, sodium o-vanadate and zinc chloride inhibit the hydrolysis of p4A (I50 values are 0.08, 0.3 and 0.4 mM, respectively). This newly recognized 'acidic' adenosine tetraphosphatase activity from yeast is compared with two 'pH 8' adenosine tetraphosphatases described earlier in rabbit and yellow lupin.

Acid Anhydride Hydrolases↗
PubMed1998

Trends and variations in length of hospital stay for childbirth in Canada.

BACKGROUND: Early discharge after childbirth is widely reported. In this study the authors examined trends in maternal length of hospital stay in Canada from fiscal year 1984-85 through fiscal year 1994-95. They also examined variations in length of stay in 1994-95 in most of the Canadian provinces and the territories. METHODS: Epidemiologic analyses of the temporal and geographic variations in maternal length of hospital stay in Canada from 1984-85 to 1994-95 (even years only), based on hospital discharge data collected by the Canadian Institute for Health Information, with a total of 1,456,800 women for the 6 study years. RESULTS: Mean length of hospital stay decreased during the decade, from 5.3 days in 1984-85 to 3.0 days in 1994-95, with similar trends for both cesarean and vaginal delivery. The decrease resulted from both increasing rates of short stay (less than 2 days) and decreasing rates of long stay (more than 4 days). Substantial temporal and interprovincial variations in several medical and obstetric complications were also observed but did not explain the corresponding variations in length of stay. The reduction in length of hospital stay was not restricted to uncomplicated cases: there was an equivalent decrease in cases with complications. In 1994-95 the average length of hospital stay in Alberta was 2.6 days, 0.3 to 1.7 days shorter than in the other provinces and the territories. INTERPRETATION: Length of hospital stay for childbirth has decreased substantially in Canada in recent years, but there remain important interprovincial variations. These trends and variations are not likely due to changes or differences in patient-specific factors.

Canada↗
PubMed1998

Genotoxicity of nitric oxide produced from sodium nitroprusside.

Induction of mutation and micronucleus (MN) formation by nitric oxide (NO) was investigated in mammalian cells using sodium nitroprusside (SNP) as a drug donor of NO. Results showed that the concentration of NO2- in the tested solution rose according to time- and concentration-exposure to SNP. The treatment of SNP (0.5-8 micromol/ml with S9 or 2-8 micromol/ml without S9) induced a concentration-dependent increase in the mutation frequency at the gpt gene locus in g12 cells and caused a 13- (-S9) to 25- (+S9) fold increase above the background level at the highest concentration. A statistically significant increase in the number of micronucleated binucleated cells (MNBN) was also observed in treated groups. MNBN per thousand, MN per thousand and the proportion of the multiple micronuleated cells increased in a concentration-dependent manner in the concentration range of SNP (0.5-4 micromol/ml with S9 or 2-8 micromol/ml without S9). Our results indicate that SNP, an NO releasing drug, is genotoxic in g12 cells.

Cell Line↗
PubMed1998

Axonal regrowth through a collagen guidance channel bridging spinal cord to the avulsed C6 roots: functional recovery in primates with brachial plexus injury.

Intraspinal implantation of a collagen guidance channel (CGC) to promote axon regeneration was investigated in marmosets with brachial plexus injury. After avulsion of the right C5, C6 and C7 spinal roots, a CGC containing (group B) or not (group A) a nerve segment, or a nerve graft (group C), was ventro-laterally implanted into the cord to bridge the ventral horn and the avulsed C6 roots. No spinal cord dysfunction was observed following surgery. Two months later, the postoperative flaccid paralysis of the lesioned arm improved. In five months, a normal electromyogram of the affected biceps muscle was recorded in all repaired animals. Motor evoked potentials were obtained with a mean amplitude of 13.37 +/- 13.66 microV in group A, 13.21 +/- 5.16 microV in group B and 37.14 +/- 35.16 microV in group C. The force of biceps muscle contraction was 27.33 +/- 20.03 g (group A), 24.33 +/- 17.03 g (group B) and 37.38 +/- 21.70 g (group C). Retrograde tracing by horseradish peroxidase showed labelled motoneurons ipsilaterally located in the C5 and C6 ventral horn, nearby the implantation site. The mean labelled neurons was 32.33 +/- 21.13, 219.33 +/- 176.29 and 64.33 +/- 23.54 in group A, B and C respectively. Histological analysis presented numerous myelinated and unmyelinated regenerating axons in the implant of these animals. Statistical analysis did not show significant difference among the three repaired groups. Our results indicate that spinal neurons can regenerate through a CGC to avulsed nerve roots and induce motor recovery in primates.

Animals↗
PubMed1998

Integrin beta cytoplasmic domains differentially bind to cytoskeletal proteins.

Integrin cytoplasmic domains connect these receptors to the cytoskeleton. Furthermore, integrin-cytoskeletal interactions involve ligand binding (occupancy) to the integrin extracellular domain and clustering of the integrin. To construct mimics of the cytoplasmic face of an occupied and clustered integrin, we fused the cytoplasmic domains of integrin beta subunits to an N-terminal sequence containing four heptad repeat sequences. The heptad repeats form coiled coil dimers in which the cytoplasmic domains are parallel dimerized and held in an appropriate vertical stagger. In these mimics we found 1) that both conformation and protein binding properties are altered by insertion of Gly spacers C-terminal to the heptad repeat sequences; 2) that the cytoskeletal proteins talin and filamin are among the polypeptides that bind to the integrin beta1A tail. Filamin, but not talin binding, is enhanced by the insertion of Gly spacers; 3) binding of both cytoskeletal proteins to beta1A is direct and specific, since it occurs with purified talin and filamin and is inhibited in a point mutant (beta1A(Y788A)) or in splice variants (beta1B, beta1C) known to disrupt cytoskeletal associations of beta1 integrins; 4) that the muscle-specific splice variant, beta1D, binds talin more tightly than beta1A and is therefore predicted to form more stable cytoskeletal associations; and 5) that the beta7 cytoplasmic domain binds filamin better than beta1A. The structural specificity of these associations suggests that these mimics offer a useful approach for the analysis of the interactions and structure of the integrin cytoplasmic face.

Amino Acid Sequence↗
PubMed1998

The relationship of galanin immunoreactive nerve fibers to glandular cells in the anterior pituitary in the monkey.

The anterior pituitary is known to be regulated by hypothalamic hormones via the portal system. However, our recent studies have demonstrated the presence of a substantial amount of substance P (SP)-, calcitonin gene-related peptide (CGRP)- and galanin (GAL)- immunoreactive (ir) nerve fibers with numerous varicosities in the anterior pituitaries of the Macaca mulatta monkey. The present study investigated the relationship of the GAL-ir nerve fibers to the glandular cells. The M. mulatta monkeys were used and sections of the anterior pituitary were double immunostained. GAL-ir nerve fibers and/or varicosities were found in proximity to contact directly with corticotropes, somatotropes, lactotropes, gonadotropes and thyrotropes without any exception. These findings indicate that a direct neural factor may be involved in the regulation of adenohypophyseal secretion.

Animals↗
PubMed1998

Rapid analysis of steroidal saponin mixture using electrospray ionization mass spectrometry combined with sequential tandem mass spectrometry.

Using electrospray ionization mass spectrometry (MS) combined with sequential tandem MS(ESI-MSn), two major steroidal saponins extracted from Tribulus terrestris were studied, and considerable useful structural information was obtained. The structure of the proposed known steroidal saponin was verified, and the structure of the unknown saponin was investigated using MSn experiments. Some special fragment ions were also observed, and the corresponding fragmentation mechanisms were investigated which are characteristic for steroidal saponins and can give some information on the linkage position of some sugar groups in saponins. This methodology has been established as a powerful tool for the rapid, comparative analysis of mixtures such as crude plant extracts.

Carbohydrate Sequence↗
PubMed1998

Crystal packing induces a conformational change in profilin-I from Acanthamoeba castellanii.

Profilin-I from Acanthamoeba castellanii is a 13-kDa protein that binds actin and poly-l-proline. The native protein has been crystallized in two different but closely related forms. The second form proved more amenable to three-dimensional structural determination using heavy-atom isomorphous methods to obtain crystallographic phase information. We used the second crystal structure as a test molecule in the molecular replacement procedure to determine the structure of the first crystal form of profilin-I. More residues participate in crystal lattice contacts in the first crystal form than in the second. The two crystal forms differ significantly in the C-terminal helix that interacts with actin and in the loop preceding this helix. Coordinates of some main chain atoms here differ by about 1.0 A, and side chain atoms differ by more than 2.0 A.

Acanthamoeba↗
PubMed1998

Infectivity of African cassava mosaic virus clones to cassava by biolistic inoculation.

Clones of an African cassava mosaic virus isolate originating from Nigeria (ACMV-NOg) were shown to be infectious to cassava by biolistic inoculation. The production of pseudorecombinants between ACMV-NOg and clones of an ACMV isolate originating from Kenya (ACMV-K) indicated that the lack of infectivity of ACMV-K to cassava was due to defect(s) in the DNA B genomic component; this component encodes two proteins involved in cell-to-cell movement. This is the first demonstration of infectivity of a cloned geminivirus to cassava and conclusively proves that ACMV is the causative agent of cassava mosaic disease. The potential uses of infectious ACMV clones and the means by which to introduce them into cassava are discussed.

Cloning, Molecular↗
PubMed1998

A review of nonclinical toxicology studies of becaplermin (rhPDGF-BB).

Becaplermin (recombinant human platelet-derived growth factor-BB [BB homodimer, rhPDGF-BB]) has demonstrated a favorable safety profile in a series of nonclinical studies designed to assess its systemic toxicity, sensitization, local irritation, and genotoxic potential. No significant local or systemic toxicity directly attributable to becaplermin was observed following single and multiple intravenous or subcutaneous administration at doses up to 3 mg/kg in monkeys. Administration of single large intravenous doses (up to 100 mg/kg) and repeated dosing at 1 or 3 mg/kg in mice resulted in rapidly reversible vasodilation and central nervous system depression. In a bone-toxicity study, becaplermin produced histomorphologic changes suggestive of accelerated bone remodeling, which were judged to be potentially reversible. Similar findings have not been observed in humans. Although becaplermin was not considered a dermal or ocular irritant, some skin-sensitizing effects were observed in animals; this finding was not unexpected for a recombinant human-derived protein. Becaplermin was not genotoxic in a variety of in vitro assays and in one in vivo assay.

Animals↗
PubMed1998

The vaccine efficacy of native paramyosin (Sj-97) against Chinese Schistosoma japonicum.

One of the promising anti-schistosome vaccine candidates currently under investigation is paramyosin, a 97-kDa myofibrillar protein located in the muscles and tegument of schistosome worms. Here we describe the results of two vaccination/challenge experiments undertaken in mice using native paramyosin isolated from adult worms of a Chinese strain of Schistosoma japonicum. In both sets of experiments, a relatively low but consistent and significant reduction in worm burden was evident in mice vaccinated subcutaneously with S. japonicum paramyosin and Freund's adjuvant. In contrast, intraperitoneal vaccination of mice with Chinese strain S. japonicum paramyosin without adjuvant did not result in any reduction in worm numbers when compared with a saline control group. These data contrast with the impressive protection figures reported by another group who used a similar intraperitoneal vaccination protocol with native paramyosin extracted from Philippine strain S. japonicum.

Animals↗
PubMed1998

Excitotoxic spinal cord injury: behavioral and morphological characteristics of a central pain model.

Intraspinal injections of the AMPA-metabotropic receptor agonist quisqualic acid (QUIS) were made in an effort to simulate injury induced elevations of excitatory amino acids (EAAs), a well documented neurochemical change following spinal cord injury (SCI). The progressive pathological sequela associated with QUIS injections closely resembles the cascade of events described following ischemic and traumatic SCI and the pathogenesis of cavities in the clinical condition of post-traumatic syringomyelia. Using different injection parameters, i.e. depth and volume, to deliver QUIS into the cord the results have shown that the technique of intraspinal injection can be used to produce graded patterns of neuronal loss in specific regions of the spinal gray matter. Furthermore, neuronal loss in the dorsal horn, sparing the superficial laminae, results in the onset of spontaneous (excessive grooming behavior) and evoked (mechanical allodynia and thermal hyperalgesia) behaviors commonly associated with experimental models of chronic neuropathic pain. Thus, the present results provide a morphological correlate of spontaneous and evoked pain related behaviors following excitotoxic SCI. The behavioral characteristics combined with the similarities between QUIS induced injury and the clinical pathology of SCI support the use of the excitotoxic model in studies related to the central mechanism(s) of altered sensation, including pain, following spinal injury.

Animals↗
PubMed1998

Information and risk perception: a dynamic adjustment process.

It is common in catastrophic food-contamination events that consumers fail to adjust instantaneously to a normal consumption level. One explanation is that consumers only gradually accept new positive information as being trustworthy. The gradual establishment of the trustworthiness of the released information depends on both positive and negative media coverage over time. We examine the individual "trust" effects by extending the prospective reference theory (Viscusi, 1989) to include a dynamic adjustment process of risk perception. Conditions that allow aggregation of changes in risk perceptions across individuals are described. The proposed model describes a general updating process of risk perceptions to media coverage and can be applied to explain the temporal impact of media coverage on consumption of a broad range of goods (food or nonfood). A case study of milk contamination is conducted to demonstrate consumer demand adjustment process to a temporarily unfavorable shock. The results suggest that effects of positive and negative information to adjustment of consumption and risk perception are asymmetric over time.

Animals↗
PubMed1998

Gap-junction-mediated propagation and amplification of cell injury.

Gap junctions are conductive channels that connect the interiors of coupled cells. We determined whether gap junctions propagate transcellular signals during metabolic stress and whether such signaling exacerbates cell injury. Although overexpression of the human proto-oncogene bcl2 in C6 glioma cells normally increased their resistance to injury, the relative resistance of bcl2+ cells to calcium overload, oxidative stress and metabolic inhibition was compromised when they formed gap junctions with more vulnerable cells. The likelihood of death was in direct proportion to the number and density of gap junctions with their less resistant neighbors. Thus, dying glia killed neighboring cells that would otherwise have escaped injury. This process of glial 'fratricide' may provide a basis for the secondary propagation of brain injury in cerebral ischemia.

Animals↗
PubMed1998

EGFR antisense RNA blocks expression of the epidermal growth factor receptor and partially reverse the malignant phenotype of human breast cancer MDA-MB-231 cells.

The effects of human EGFR to the malignant phenotype of human breast cancer cell line MDA-MB-231 were investigated experimentally. A retroviral vector containing a 5'1350bp fragment of the human EGFR cDNA in the antisense orientation was transfected into targeted cells by lipofectamine. The effects on cell proliferation, cell cycle and adherent ability to extracellular matrix (ECM) components were studied after the expression of antisense transcripts to EGFR 5'1350bp fragment in target cells. In vitro studies showed that the growth ability of the transfected cells was partially inhibited in comparison to parental cells and to cells transfected with the plasmid containing the neomycin resistance gene only. It was found that EGF (10 ng/ml) had an argumenation effect on the growth of transfected MDA-AS10 cells but not MDA-MB-231 cells. Flow cytometric analysis showed that the cell cycle of the transfected cells was abnormal with a decrease of cells in G2/M and S phases and an increase of cells in G1 phase, indicating a blockage in phase G1. Immunofluorescence of EGFR expression in transfectants stained with an anti-EGFR antibody was decreased and their growth in soft agarose was also severely impaired. The transfected cells showed less adherence to laminin (LN) and fibronectin (FN). In short, EGFR antisense RNA decreases the expression of EGFR on MDA-MB-231 cells and partially reverses their malignant phenotype as well.

Breast Neoplasms↗
PubMed1998

Characterization of two distinct monoclonal antibodies specific for glial cell line-derived neurotrophic factor.

Here we report the generation and characterization of two distinct monoclonal antibodies, G-90 and B-1531, specific to glial cell line-derived neurotrophic factor (GDNF). ELISA results confirmed that G-90 and B-1531 both recognize GDNF. Western blots showed that G-90 recognized only the GDNF dimer, whereas B-1531 recognized both the monomer and dimer. Peptide competition ELISA (PCE) and BIAcore data suggested that G-90 and B-1531 recognize different epitopes: PCE confirmed that B-1531 binds to NH2-terminal peptides between amino acids 18 and 37, whereas G-90 does not; BIAcore data showed that B-1531 binds to the NH2 terminus of GDNF, whereas G-90 does not. G-90, in a concentration-dependent manner, completely neutralized the GDNF-induced increases of choline acetyltransferase in cultured motoneuron and of dopamine uptake and morphological differentiation in dopaminergic neuron cultures. B-1531 had no neutralizing effects. GDNF-induced Ret autophosphorylation in NGR-38 cells was completely neutralized by G-90, whereas B-1531 had a moderate effect. These data show that G-90 and B-1531 are specific antibodies to GDNF. The data also suggest that the NH2 terminus of GDNF is not critical for activity. Partial inhibition of Ret phosphorylation is insufficient to down-regulate GDNF-induced biological activity.

Animals↗