Biomedical subjects

L Gao

Publications and source records attributed to L Gao.

At least 19 recordsLinked to original sources

PubMed2000

Suppression of ganglioside GD3 expression in a rat F-11 tumor cell line reduces tumor growth, angiogenesis, and vascular endothelial growth factor production.

Ganglioside GD3 is overexpressed in many types of tumors and may be associated with tumor progression and the development of metastatic potential. In our previous study (G. Zeng et al., Biochemistry, 38: 8762-8769, 1999), we established a subclone of the rat dorsal root ganglion-derived F-11 cells in which the expression of ganglioside GD3 was inhibited by stable transfection of the antisense vector against CMP-NeuAc: GM3 alpha2-8 sialyltransferase (GD3-synthase) gene. This cell line exhibits markedly reduced rate of tumor growth in vivo. Here, we further characterized the antisense-transfected cell line, and the results showed that these cells formed small, minimally vascularized tumors exhibiting extensive necrosis. In vivo Matrigel assay revealed reduced vascularization and low hemoglobin content in the antisense xenografts. Significantly fewer new vessels were found on the antisense xenografts and the skin around them than those on/around the xenografts formed by the sense-transfected and untransfected F-11 cells. The hemoglobin content of the antisense xenografts was much lower than that of the xenografts formed by the control cells. The reduced angiogenesis in the antisense xenografts was correlated with a decrease in vascular endothelial growth factor (VEGF) production. The expression of VEGF was suppressed in the antisense xenografts and the conditioned culture media of the antisense-transfected F-11 cells as determined by Western blotting analysis. This was further confirmed by immunohistochemistry of the tumors using antibodies against VEGF and platelet/endothelial cell adhesion molecule (PECAM-1). Therefore, our results demonstrate that reduced tumor growth in nude mice by suppression of GD3-synthase expression in F-11 cells results from minimal angiogenesis of the tumors through down-regulation of the VEGF expression, which indicates an important role for GD3 in tumor angiogenesis.

Animals↗

PubMed2000

Reduced cell migration, tumor growth and experimental metastasis of rat F-11 cells whose expression of GD3-synthase is suppressed.

We previously established a rat F-11 cell line whose expression of ganglioside GD3 was inhibited by stable transfection of the anti-sense vector against the GD3-synthase gene, showing that specific inhibition of GD3-synthase expression in tumor cells greatly reduced their growth rate in nude mice. Here, we report that down-regulation of GD3-synthase expression in anti-sense-transfected F-11 cells correlates with reduced cell migration and invasion in vitro and tumor growth and metastasis in vivo. When cultures were denuded of cells in a 1-mm-wide strip, the anti-sense-transfected F-11 cells migrated very slowly into the denuded area. Differences in migration between anti-sense-transfected cells and control parental cells were easily apparent. In vitro invasion assay of F-11 cells revealed a 3-fold decrease in invasion ability from the GD3-synthase-suppressed cells; colony formation in soft agar was not affected. Injection (i.v.) of control sense-transfected and untransfected F-11 cells resulted in multiple, large metastatic nodules in each of the 12 mice, whereas i.v. injection of anti-sense-transfected F-11 cells formed a single, small metastatic nodule in only 2 of the 8 nude mice. In addition, even if metastasis occurred, the anti-sense-induced metastatic nodules were much smaller than the metastatic nodules formed by control F-11 cells. These results demonstrate that suppression of GD3-synthase expression, which results primarily in a marked decrease in the concentration of ganglioside GD3, greatly reduces cell spreading, invasion and both the incidence and growth rate of experimental metastasis of F-11 cells.

Animals↗

PubMed2000

Adsorption of PBTCA on Alumina Surfaces and Its Influence on the Fractal Characteristics of Sediments.

The adsorption of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on Al(2)O(3) powder has been studied as a function of pH and concentration. The adsorption density of PBTCA is found to decrease with an increase of pH. Zeta potential measurements show that the addition of PBTCA results in a dramatic increase in the absolute zeta potential, as well as a shift of the isoelectric point to the more acidic region. PBTCA considerably enhances the stability of the alumina suspension via an electrostatic mechanism. The surface properties of alumina suspensions are examined by using Auger electron microscopy and FTIR analysis. Chemical interactions take place at the solid/water interface by forming complexes between Al(3+) ions and PBTCA. The dispersing ability of PBTCA is believed to be related to its high adsorption ability and the high number of dissociable protons. The morphology of the sediments is observed with scanning electron microscopy. It is found that the sediment surfaces exhibit fractal characteristics. The fractal dimension values of sediments are correlated with PBTCA concentration in the experimental range. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Anti-Gal antibodies in humans and 1, 3alpha-galactosyltransferase knock-out mice.

BACKGROUND: Due to the absence of alphaGAL epitopes, humans and galactosyltransferase knock-out (GALT/ KO) mice express high levels of anti-Gal antibodies. We describe the properties of mouse anti-GAL antibodies. METHODS: Anti-GAL IgG antibodies were quantified by affinity purification. Antibody affinities and avidities were determined in direct binding and competition assays. Antibody-mediated rejection was investigated using hyperimmunized GALT/KO mice as recipients of GAL+ heart allografts. RESULTS: In young GALT/KO mice the levels of anti-GAL antibodies were low. Immunization of GALT/KO mice resulted in increased anti-GAL antibody expression. In mouse serum 0.6% of IgG was specific for alphaGAL compared to 0.5% in human serum. The avidity of purified mouse and human anti-GAL IgG was 30 and 6 nM, the affinity 15 and 50 microM, respectively. The isotype distribution in mouse and human anti-GAL IgG appeared to be similar to the isotype distribution in normal sera. The affinity of mouse and human anti-GAL IgM was 150 and 750 microM, respectively. Immunized GALT/KO recipients of GAL+ heart transplants rejected their grafts within 2 hr although nonimmunized GALT/KO mice retained their grafts for up to 6 days. Immunohistological examination of the rejected GAL+ hearts revealed massive deposition of IgM and IgG on endothelial cells of the graft with a concomitant deposition of complement. CONCLUSIONS: Our studies demonstrate that anti-GAL antibodies from immunized GALT/KO mice bind alphaGAL with an avidity/affinity similar to human anti-GAL antibodies and are able to induce hyperacute rejection of GAL+ heart allografts.

Animals↗

PubMed2000

Selective elimination of leukemic CD34(+) progenitor cells by cytotoxic T lymphocytes specific for WT1.

Hematologic malignancies such as acute and chronic myeloid leukemia are characterized by the malignant transformation of immature CD34(+) progenitor cells. Transformation is associated with elevated expression of the Wilm's tumor gene encoded transcription factor (WT1). Here we demonstrate that WT1 can serve as a target for cytotoxic T lymphocytes (CTL) with exquisite specificity for leukemic progenitor cells. HLA-A0201- restricted CTL specific for WT1 kill leukemia cell lines and inhibit colony formation by transformed CD34(+) progenitor cells isolated from patients with chronic myeloid leukemia (CML), whereas colony formation by normal CD34(+) progenitor cells is unaffected. Thus, the tissue-specific transcription factor WT1 is an ideal target for CTL-mediated purging of leukemic progenitor cells in vitro and for antigen-specific therapy of leukemia and other WT1-expressing malignancies in vivo.

Adult↗

PubMed2000

Blocking of CD44-hyaluronic acid interaction prolongs rat allograft survival.

BACKGROUND: Lymphocyte activation and infiltration into a transplanted organ is an integral component of the rejection process. Graft infiltration of lymphocytes requires adhesion of leukocytes to the endothelium, diapedesis, and transmigration. One of several proteins involved in this process is CD44, which is known to interact with endothelial hyaluronan (HA). Blockade of cell-matrix and cell-cell interactions have been used extensively for modulation of immune responses and graft rejection. Based on these observations, we evaluated the effects of blocking CD44-HA interactions in a transplantation model. METHODS: We used a low molecular weight hyaluronic acid formulation (LMWHA) for the treatment of rat renal and cardiac allograft recipients. LMWHA was administered intraperitoneally at 0.5-5 mg/kg for 5-10 days after transplantation with or without a subtherapeutic dose of cyclosporine. RESULTS: LMWHA monotherapy prolonged allograft survival significantly, but only for a few days. In combination with low-dose cyclosporine, long-term survival of allografts was observed in some of recipients. CONCLUSION: Further definition of the underlying mechanism of LMWHA therapy may provide a rationale for the development of novel, nontoxic, nonimmunogenic immunotherapies.

Animals↗

PubMed2000

Structure and characterization of the murine p80 coilin gene, Coil.

Cajal bodies (coiled bodies, CBs) are nuclear organelles of unknown function and are characterized by a wide variety of components including various basal transcription and cell cycle proteins, the nucleolar proteins fibrillarin and Nopp140, numerous small nuclear ribonucleoproteins, the survival motor neuron protein complex, and the marker protein, p80 coilin. To gain insight into the role of p80 coilin in CBs, we have cloned the murine gene Coil and have mapped it to the distal portion of chromosome band 11D. The approximately 2.6-kb transcript is detectable in all tissues analyzed, with the highest levels in brain and testis. Sequence analysis shows that, like its human counterpart, the mouse coilin gene is composed of seven exons and spans nearly 30 kb of genomic DNA. The predicted amino acid sequence reveals two conserved N- and C-terminal domains, and comparison with the Xenopus SPH-1 protein reveals that these three genes are indeed orthologous. These results should facilitate gene disruption experiments aimed at creating a genetic model system to study CBs.

Amino Acid Sequence↗

PubMed2000

Uptake of metabolites by gonococci grown with lactate in a medium containing glucose: evidence for a surface location of the sialyltransferase.

Promotion of uptake of essential metabolites is a possible reason for the general stimulation of gonococcal metabolism which is caused by lactate (1 mM) in a defined medium containing glucose (5 mM). However, although uptake of(14)C adenine by gonococci [strain BS4(agar)] held for 4 or 7 min at 37 degrees C in Hanks balanced salt solution was increased for lactate treated gonococci compared with control organisms, uptake of(14)C glucose and(14)C proline under these conditions was unaffected. Hence, there is no evidence that lactate produces general stimulation of metabolite uptake. Unlike the other metabolites, cytidine 5'-monophospho-(14)CN-acetyl neuraminic acid (CMP-(14)CNANA), the substrate for sialylation of gonococcal lipopolysaccharide (LPS), was adsorbed in substantial quantities by gonococci held on ice for 6 min. Also, the increase in uptake of CMP-(14)CNANA at 37 degrees C over that adsorbed at 0 degrees C was much smaller (less than two-fold) than for the other compounds (4-30-fold). The substantial adsorption at 0 degrees C suggested a surface receptor for CMP-(14)CNANA. It is probably the sialyltransferase because a sialyltransferase deficient mutant, JB1, did not absorb CMP-(14)CNANA at 0 degrees C or take it up at 37 degrees C, in contrast to its parent strain, F62, which behaved similarly to strain BS4 (agar). This supports previous evidence for a surface location of the sialyltransferase. There was a small increase in adsorption of CMP-(14)CNANA in lactate treated gonococci indicating a slight increase in the surface enzyme. This could enhance LPS sialylation and hence affect pathogenicity.

Adenine↗

PubMed2000

Evidence for a role of the lumenal M3-M4 loop in skeletal muscle Ca(2+) release channel (ryanodine receptor) activity and conductance.

We tested the hypothesis that part of the lumenal amino acid segment between the two most C-terminal membrane segments of the skeletal muscle ryanodine receptor (RyR1) is important for channel activity and conductance. Eleven mutants were generated and expressed in HEK293 cells focusing on amino acid residue I4897 homologous to the selectivity filter of K(+) channels and six other residues in the M3-M4 lumenal loop. Mutations of amino acids not absolutely conserved in RyRs and IP(3)Rs (D4903A and D4907A) showed cellular Ca(2+) release in response to caffeine, Ca(2+)-dependent [(3)H]ryanodine binding, and single-channel K(+) and Ca(2+) conductances not significantly different from wild-type RyR1. Mutants with an I4897 to A, L, or V or D4917 to A substitution showed a decreased single-channel conductance, loss of high-affinity [(3)H]ryanodine binding and regulation by Ca(2+), and an altered caffeine-induced Ca(2+) release in intact cells. Mutant channels with amino acid residue substitutions that are identical in the RyR and IP(3)R families (D4899A, D4899R, and R4913E) exhibited a decreased K(+) conductance and showed a loss of high-affinity [(3)H]ryanodine binding and loss of single-channel pharmacology but maintained their response to caffeine in a cellular assay. Two mutations (G4894A and D4899N) were able to maintain pharmacological regulation both in intact cells and in vitro but had lower single-channel K(+) and Ca(2+) conductances than the wild-type channel. The results support the hypothesis that amino acid residues in the lumenal loop region between the two most C-terminal membrane segments constitute a part of the ion-conducting pore of RyR1.

Amino Acid Sequence↗

PubMed2000

Neuromuscular paralysis as a pharmacodynamic probe to assess organ function during liver transplantation.

Potential for assessing liver function during liver transplantation surgery by monitoring muscle paralysis from nondepolarizing neuromuscular blockers that are hepatically cleared is critically assessed. Rocuronium is strongly favored as a promising pharmacodynamic probe for predicting allograft liver function because it is predominantly eliminated via the liver and its putative metabolites are not active. Prolongation of recovery from rocuronium paralysis is closely correlated with allograft liver function postoperatively. Vecuronium, pancuronium, and perhaps pipecuronium may also prove to be useful probes, but the two former blockers have active metabolites. Further prospective studies are necessary with more precise measurement of neuromuscular function to confirm the predictive value of this method. Alterations in neuromuscular blocker plasma concentrations that are correlated with changes in liver function and either the dose required or the intensity or duration of paralysis needs to be demonstrated for this technique to be clinically useful.

Androstanols↗

PubMed2000

Hijacking of apoptotic pathwaysby bacterial pathogens.

Increasing evidence indicates that apoptosis of the host cell may constitute a defense mechanism to confine the infection by bacterial pathogens. Certain pathogens have developed elegant mechanisms to modulate the fate of the host cell, which include induction or blockage of apoptosis. These studies will promote our understanding of the pathogenesis of infectious diseases and aid the development of means for therapeutic intervention.

Animals↗

PubMed2000

In a medium containing glucose, lactate carbon is incorporated by gonococci predominantly into fatty acids and glucose carbon incorporation is increased: implications regarding lactate stimulation of metabolism.

The reason for stimulation by lactate of metabolism of gonococci growing in a medium containing glucose, which enhances pathogenicity by increasing growth rate, lipopolysaccharide (LPS) synthesis and protein formation, has been investigated. Tricine dodecylpolyacrylamide gel electrophoresis (SDS-PAGE) and thin layer chromatography (TLC) on homogenates of gonococci grown in this medium with [14C]lactate showed that lactate carbon was preferentially incorporated into lipid and LPS. Nuclear magnetic resonance (NMR) spectroscopy on lipid extracted from gonococci grown in the glucose containing medium with [13C]lactate showed that lactate carbon was incorporated into fatty acid moieties and not into ethanolamine or glycerol moieties. In contrast, NMR on lipid from gonococci grown with [13C]glucose indicated glucose carbon in both moieties. When unlabelled lactate was added, lipid synthesis from [l3C]glucose was stimulated and small amounts of different fatty acids were formed. The NMR data shows that gluconeogenesis from lactate carbon does not occur in the presence of glucose, suggesting that lactate is used solely for rapid production, via pyruvate, of acetyl CoA, the precursor not only for fatty acid synthesis but also for the constituents and products of the citric acid cycle, including ATP. The rapid formation of a high level of acetyl CoA is the probable reason for the stimulation of metabolism and oxygen uptake by lactate. 14C label on LPS was detected in its fatty acids. Most proteins that stained with silver in tricine SDS-PAGE were not significantly labelled by [14C]lactate in the glucose-containing medium. Two of three appreciably labelled proteins were identified by N-terminal sequencing as GroEL and porin 1B, and one of the two less labelled proteins was similar to peroxiredoxin type proteins. There were no signs of specific induction of these proteins by lactate and their labelling was consistent with fatty acids in attached lipid.

Bacterial Proteins↗

PubMed2000

The cell-polarity protein Par6 links Par3 and atypical protein kinase C to Cdc42.

PAR (partitioning-defective) proteins, which were first identified in the nematode Caenorhabditis elegans, are essential for asymmetric cell division and polarized growth, whereas Cdc42 mediates establishment of cell polarity. Here we describe an unexpected link between these two systems. We have identified a family of mammalian Par6 proteins that are similar to the C. elegans PDZ-domain protein PAR-6. Par6 forms a complex with Cdc42-GTP, with a human homologue of the multi-PDZ protein PAR-3 and with the regulatory domains of atypical protein kinase C (PKC) proteins. This assembly is implicated in the formation of normal tight junctions at epithelial cell-cell contacts. Thus, Par6 is a key adaptor that links Cdc42 and atypical PKCs to Par3.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Nitric oxide-dependent vasodilatation of rabbit femoral artery by beta(2)-adrenergic stimulation or cyclic AMP elevation in vivo.

Some studies suggest that beta-adrenoceptor-mediated vasorelaxation is in part mediated through nitric oxide (NO) release. We wished to determine the contribution of the L-arginine / NO system to vasodilatation in response to beta-adrenoceptor stimulation with isoprenaline or cyclic adenosine-3',5'-monophosphate (cyclic AMP) elevation with forskolin and dibutyryl cyclic AMP in vivo, using a rabbit femoral artery constant perfusion model. Baseline femoral artery pressure was similar in rabbits receiving isoprenaline, forskolin or dibutyryl cyclic AMP. Isoprenaline, forskolin and dibutyryl cyclic AMP each decreased femoral artery pressure in a dose-dependent manner. The doses (mol kg(-1)) of isoprenaline, forskolin and dibutyryl cyclic AMP which decreased pressure by 10% from baseline, expressed as a negative logarithm (-log ED(10)) were: 10.0+/-0.2, 9.5+/-0.1 and 4.9+/-0.1 respectively (P<0.0001 for each). Use of beta-adrenoceptor subtype-selective antagonists showed that the vascular response to isoprenaline was purely due to stimulation of the beta(2)-adrenoceptor subtype. Injection of 1 micromol kg(-1) N(G)-nitro-L-arginine methyl ester (L-NAME) did not alter baseline pressure. However, it abolished the pressure response to isoprenaline (P<0.0001), and significantly attenuated the pressure responses to forskolin and dibutyryl cyclic AMP: -log ED(10) values for forskolin and dibutyryl cyclic AMP, in the presence of L-NAME, were 7.9+/-0.1 and 3.5+/-0.3 respectively (P<0.0001 for each, as compared with values in the absence of L-NAME). These results indicate that beta(2)-adrenergic stimulation and cylic AMP elevation activate the L-arginine/NO system in rabbit femoral artery in vivo, and that NO generation contributes importantly to the changes in vascular tone induced by agents which modulate beta-adrenoceptors or cyclic AMP.

Adrenergic beta-2 Receptor Agonists↗

PubMed2000

Post-earthquake quality of life and psychological well-being: longitudinal evaluation in a rural community sample in northern China.

This study aims to observe longitudinal change of quality of life (QOL) and psychological well-being in a community sample affected by an earthquake and to examine the relationship between QOL and disaster exposure, post-disaster support and other related variables. The subjects, from two villages at different distances from the epicenter, were assessed using the brief version of the World Health Organization Quality of Life Assessment (WHOQOL-BREF) and three subscales of a symptoms checklist at 3 months (n=335) and 9 months (n=253) after the earthquake, respectively. Exposure to the earthquake was associated with multidimensional impairment in QOL, including physical, psychological and environmental domains at 3 months, and psychological and environmental domains at 9 months. The victims also suffered significantly more psychological distress in terms of depression, somatization and anxiety. At both assessment points the group that experienced lower initial exposure but then received less post-disaster help reported poorer QOL and psychological well-being. The two victim groups also differed significantly in changing trend along time. The group that received more support showed a general improvement in post-disaster well-being from 3 months to 9 months. The results confirm that post-disaster variables could be as important to post-disaster psychosocial outcomes as variables of pre-disaster vulnerability and disaster per se. A comprehensive and prospective assessment of disaster effects is imperative for the better organization of disaster relief programs and psychosocial interventions.

Adolescent↗

PubMed2000

Down-regulation of GD3 ganglioside and its O-acetylated derivative by stable transfection with antisense vector against GD3-synthase gene expression in hamster melanoma cells: effects on cellular growth, melanogenesis, and dendricity.

The expression of gangliosides in hamster melanoma cells is closely related to cellular growth and degree of differentiation, with slow-growing, highly differentiated melanotic melanoma cells expressing GM3 and fast-growing, undifferentiated amelanotic Ab melanoma cells having a preponderance of GD3 and O-acetyl-GD3. We recently showed that down-regulation of O-acetyl-GD3 expression in hamster melanoma cells by introducing the influenza C virus O-acetylesterase cDNA into the cells resulted in induction of dendricity, with a concomitant increased expression of GD3. To examine the effect of the increased GD3 expression in the plasma membrane on the dendricity of the AbC-1 cells, we first established the cDNA coding for hamster GD3-synthase. We then targeted the sialyltransferase gene expression by the antisense knockdown experiment, and the results showed that inhibition of the expression of gangliosides GD3 and O-acetyl-GD3 induced dendricity in the hamster melanoma AbC-1 cell line. These GD3- and O-acetyl-GD3-depleted cells also demonstrated a decreased rate of cell growth, but their melanogenic potential was not affected. These results rule out the possibility that GD3 may serve as an active molecule for dendrite outgrowth in this cell line and suggest that the enhanced expression of O-acetyl-GD3 ganglioside may stimulate cellular growth and suppress certain differentiated phenotypes such as dendrite formation, but not melanogenesis, in our system.

Animals↗

PubMed2000

Force between two spherical inclusions in a nonlinear host medium

In an attempt to investigate the effect of nonlinear characteristics on particle interactions, a self-consistent mean-field theory in combination with a multiple image method has been employed to compute the interparticle force. Taking the nonlinearity of the host medium into account, the interparticle force exhibits a nonmonotonic behavior as the applied electric field is increased. We show that the interparticle force increases initially at low fields, goes through a maximum at an optimal electric field, then decreases with increasing field, and vanishes at a critical electric field at which the effective dielectric contrast between the host and the inclusions becomes zero. The influence of a larger volume fraction of inclusions on the interparticle force is also investigated.

Journal Article↗

PubMed2000

Genetic erosion in northern marginal population of the common wild rice Oryza rufipogon Griff. and its conservation, revealed by the change of population genetic structure.

In order to monitor genetic erosion within the northern marginal population of common wild rice Oryza rufipogon Griff. from Dongxiang, Jiangxi Province, China, allozyme diversity encoded by 22 loci was analyzed electrophoretically from all the existing subpopulations in 1980, 1985 and 1994. The sample collected from the nine large subpopulations in 1980 showed the highest levels of genetic diversity (A = 1.27, P = 18.20%, Ho = 0.042 and He = 0.049) and a slight deviation from Hardy-Weinberg expectation (F = 0.143), the sample from five moderate ones in 1985 displayed medium levels of genetic diversity (A = 1.14, P = 13.60%, Ho = 0.008 and He = 0.049) and a great deviation from Hardy-Weinberg expectation (F = 0.837), and the sample from two small ones in 1994 demonstrated the lowest levels of genetic diversity (A = 1.09, P = 9.10%, Ho = 0.000 and He = 0.043) and the largest deviation from Hardy-Weinberg expectation (F = 1.000). The results not only documented the genetic erosion stemmed from the extinction of the subpopulations, but also revealed the drastic change of the population genetic structure due to the reduction of the population. Finally, some conservation strategies for the population are proposed.

DNA, Plant↗