Search PubMed⌕ Search

Biomedical subjects

Y Guo

Publications and source records attributed to Y Guo.

At least 253 records · Page 14Linked to original sources
PubMed1999

Formulation strategies for the stabilization of tetanus toxoid in poly(lactide-co-glycolide) microspheres.

The development of a single-dose tetanus vaccine based on Poly(Lactic acid) (PLA) or Poly(Lactide-co-Glycolide) (PLGA) microspheres has been complicated due to the instability of tetanus toxoid (TT) inside these systems. Herein we report an attempt to re-design PLGA microspheres by co-encapsulating TT in the dry solid state together with potential protein stabilizers, such as trehalose, bovine serum albumin, alginate, heparin, dextran or poloxamer 188 and by using an appropriate microencapsulation technique. These newly developed PLGA microspheres were able to release in vitro antigenically active TT for at least 5 weeks, the amount released being highly dependent on the stabilizing excipient used. More specifically, results showed that dextran and heparin provided a particularly stabilizing environment for TT inside the microspheres during the polymer degradation process. The efficacy of this strategy was demonstrated by the high, long lasting titers of neutralizing antibodies achieved after in vivo administration of dextran-containing microspheres with a small amount of alum-adsorbed TT, as compared to the commercial adsorbable tetanus vaccine. These findings suggest that future developments in the area of vaccinology depend on ability to combine a detailed knowledge of the microencapsulation technology with a rational choice of stabilizing excipient or combination of excipients.

Animals↗
PubMed1999

Genetic characterization of the pathogenic influenza A/Goose/Guangdong/1/96 (H5N1) virus: similarity of its hemagglutinin gene to those of H5N1 viruses from the 1997 outbreaks in Hong Kong.

Analysis of the sequences of all eight RNA segments of the influenza A/G oose/Guangdong/1/96 (H5N1) virus, isolated from a sick goose during an outbreak in Guangdong province, China, in 1996, revealed that the hemagglutinin (HA) gene of the virus was genetically similar to those of the H5N1 viruses isolated in Hong Kong in 1997. However, the remaining genes showed greater similarity to other avian influenza viruses. Notably, the neuraminidase gene did no have the 19-amino-acid deletion in the stalk region seen in the H5N1 Hong Kong viruses and the NS gene belonged to allele B, while that of the H5N1 Hong Kong viruses belonged to allele A. These data suggest that the H5N1 viruses isolated from the Hong Kong outbreaks derived their HA genes from a virus similar to the A/Goose/Guangdong/1/96 virus or shared a progenitor with this goose pathogen.

Animals↗
PubMed1999

Two mechanisms for tumor evasion of preexisting cytotoxic T-cell responses: lessons from recurrent tumors.

Tumors evade host immunity at both the induction and effector phases Most studies have focused on tumor evasion at the induction phase, and, due in part to poor antitumor CTL responses to most tumors, the mechanism for evasion of CTL effector function is less clear. Here we have taken advantage of the strong CTL responses to a costimulator B7-1-transfected tumor to study the mechanism for tumor evasion of preexisting host immunity. We have investigated six independent recurrent tumors isolated from mice that were challenged with and had rejected B7-1-transfected J558 (J558-B7) tumors. Because the mice had developed strong antitumor CTL responses, these recurrent tumors must have evaded preexisting antitumor CTLs. Indeed, whereas the parental J558-B7 cell line is efficiently lysed by the ex vivo tumor-infiltrating lymphocytes, all of the recurrent tumors are resistant to such lysis. Interestingly, the recurrent tumors can be divided into two groups. The group 1 tumors have vastly reduced levels of cell surface MHC class I with a concurrent reduction in the expression of multiple genes devoted to MHC class I antigen presentation. In contrast, the group 2 tumors have lost the expression of costimulatory molecule B7-1 while retaining cell surface MHC class I and expression of all antigen presentation genes studied. These results demonstrate that tumors can evade preexisting CTLs either by avoiding presentation of the tumor antigen or, surprisingly, by down-regulation of costimulatory molecules. The paradoxical requirements of both antigen and costimulatory molecules at the effector phase raised an interesting question on the nature of antitumor immunity.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

A fork junction DNA-protein switch that controls promoter melting by the bacterial enhancer-dependent sigma factor.

Results of binding assays using DNA fork junction probes indicate that sigma 54 contains multiple determinants that regulate melting to allow RNA polymerase to remain in closed promoter complexes in order to respond to enhancers. Gel mobility shift studies indicate that the -12 promoter element and parts of sigma 54 act together to form a molecular switch that controls melting. The DNA sequences and the sigma 54 N-terminus help direct polymerase to the location within the -12 promoter element where melting will initiate. However, the fork junction that would lead to melting does not form, due to the action of an inhibitory DNA element. Such unregulated melting is inhibited further by the lack of availability of the single-strand binding elements, which are needed to spread opening from the junction to the transcription start site. Thus, in the absence of looping enhancer protein, proper regulation is maintained as the sigma 54 polymerase remains bound in an inactive state. These complex protein-DNA interactions allow the controls over protein recruitment and DNA melting to be separated, enhancing the diversity of accessible mechanisms of transcription regulation.

Base Pairing↗
PubMed1999

[Discovery of men infected by avian influenza A (H9N2) virus].

OBJECTIVE: To understand whether the avian influenza A(H9N2) virus can infect men or not. METHODS: Seroepidemiological surveys for avian (H9N2) virus in human, chickens and pigs were conducted. The specimens for viral isolation were taken from throat of patients with influenza like disease, as well as from chickens, then the specimens were inoculated into embryonated chicken eggs. Afterward, the idsolates were identified with HI and NI tests. Meanwhile, the patients who would be studied individually were found to carry H9N2 virus. RESULTS: Approximately 19% of human had antibody to H9N2 virus with HI titers > or = 20, 5 strains of influenza A (H9N2) virus were isolated from the patients. CONCLUSION: Avian influenza A(H9N2) virus can infect men.

Antibodies, Viral↗
PubMed1999

Regulators of G-protein signaling (RGS) 1 and 16 are induced in response to bacterial lipopolysaccharide and stimulate c-fos promoter expression.

Regulators of G-protein signaling (RGS) are negative regulators of G-protein-coupled receptor (GPCR) signaling. Sepsis is a pathophysiological condition that is induced primarily in response to bacterial infection and is associated with decreased responsiveness to a number of vasoactive GPCR agonists. Using a degenerate RT-PCR screen, we report that RGS1 and RGS16 were amplified from the heart and aorta of septic animals. By Northern blot analysis, RGS1 and RGS16 were upregulated, with their respective levels increasing 6- and 50-fold in septic hearts. Using a yeast-based bioassay, both RGS1 and RGS16 were found to be equipotent in their ability to attenuate GPCR signaling. These results suggest that both RGS1 and RGS16 contribute to the sepsis-mediated decrease in GPCR signaling. Elevated levels of some RGSs may also lead to an increase in Gbetagamma-activated signaling pathways in the absence of GPCR agonists. Using a c-fos luciferase reporter gene that is responsive to Gbetagamma-activated signaling pathways, we observed a respective 8- and 7-fold increase in the basal luciferase in serum-deprived transfected mammalian cells overexpressing RGS1 or RGS16. This suggests that RGSs play a role in promoting the sepsis-mediated increases in the activation of intracellular signal transduction pathways.

Amino Acid Sequence↗
PubMed1999

Restoration of transforming growth factor beta signaling pathway in human prostate cancer cells suppresses tumorigenicity via induction of caspase-1-mediated apoptosis.

Previous studies (Y. Guo and N. Kyprianou, Cell Growth Diff., 9: 185-193, 1998) have demonstrated that overexpression of transforming growth factor (TGF) beta type II receptor (TbetaRII) gene in human prostate cancer cells LNCaP, which are refractory to TGF-beta1 and lack TbetaRII receptor expression, can restore TGF-beta1 sensitivity and suppress in vitro tumorigenic growth by inhibiting cell proliferation. In the present study, we investigated the effect of TbetaRII receptor overexpression in LNCaP cells on apoptosis induction and tumorigenicity. The ability of LNCaP cells that overexpress TbetaRII to undergo apoptosis in response to TGF-beta1 was examined by DNA fragmentation and terminal transferase-mediated dUTP-biotin end labeling analysis. To explore the potential apoptotic nature of TGF-beta1-mediated antitumor effect against human prostate cancer cells, the expression of apoptotic proteins bcl-2 and bax was examined by Western blot analyses. The significance of caspase 1 in TGF-beta1-mediated apoptosis was also determined by examining the expression and activation of caspase 1 by reverse transcription-PCR and Western blot analyses, respectively. Comparative analysis of tumorigenicity of the parental LNCaP and TbetaRII-overexpressing clones in severely combined immunodeficient mice revealed a significant suppression of tumor growth in TbetaRII transfectant clones compared with parental LNCaP cells and neomycin-control clones (P < 0.05). A significantly higher incidence of endogenous apoptosis was observed in TbetaRII clone-61-derived tumor compared with the parental LNCaP tumors. This induction of apoptosis in the LNCaP tumors with restored TGF-beta1 signaling was associated with decreased bcl-2 expression, increased bax, and caspase-1 immunoreactivty. Moreover, an increased expression of the cyclin-dependent kinase inhibitor p27Kip1 was detected in TbetaRII-overexpressing tumors compared with the parental tumors. LNCaP TbetaRII transfectant cells exhibited a marked induction of apoptosis, paralleled with a decreased bcl-2 expression in response to TGF-beta1 treatment in vitro. This TGF-beta1-mediated apoptosis induction in TbetaRII transfectant cells was significantly protected by the caspase-1 inhibitor (zVAD-fmk) in a dose-dependent manner. Furthermore, a significant temporal induction of caspase-1 mRNA and protein expression was detected in TbetaRII cells in response to TGF-beta1 treatment. Our findings suggest that restoration of TGF-beta1 signaling suppresses tumorigenicity of human prostate cancer cells by inducing apoptosis, potentially via a caspase-1-mediated pathway.

Animals↗
PubMed1999

Cytotoxic T lymphocytes to an unmutated tumor rejection antigen P1A: normal development but restrained effector function in vivo.

Unmutated tumor antigens are chosen as primary candidates for tumor vaccine because of their expression on multiple lineages of tumors. A critical issue is whether unmutated tumor antigens are expressed in normal cells, and if so, whether such expression imposes special restrictions on cytotoxic T lymphocyte (CTL) responses. In this study, we use a transgenic approach to study the development and effector function of T cells specific for P1A, a prototypical unmutated tumor antigen. We report here that although P1A is expressed at low levels in normal tissues, including lymphoid tissues, the P1A-specific transgenic T cells develop normally and remain highly responsive to the P1A antigen. The fact that transgenic expression of P1A antigen in the thymus induces T cell clonal deletion demonstrates that normal hematopoietic cells can process and present the P1A antigen and that P1A-specific T cells are susceptible to clonal deletion. By inference, P1A-specific T cells must have escaped clonal deletion due to low expression of P1A in the thymus. Interestingly, despite the fact that an overwhelming majority of T cells in the T cell receptor for antigen (TCR)-transgenic mice are specific for P1A, these mice are no more resistant to a P1A-expressing plasmocytoma than nontransgenic littermates. Moreover, when the same TCR-transgenic mice were challenged simultaneously with B7-1(+) and B7-1(-) tumors, only B7-1(+) tumors were rejected. Therefore, even though P1A can be a tumor rejection antigen, the effector function of P1A-specific CTL is restrained in vivo. These results have important implications for the strategy of tumor immunotherapy.

Animals↗
PubMed1999

Identification of an endogenous dominant-negative short isoform of caspase-9 that can regulate apoptosis.

Alternatively spliced isoforms of certain apoptosis regulators, such as Bcl-x, Ced-4, and Ich-1, have been shown to play opposing roles in regulating apoptosis. Here, we describe the identification of an endogenous alternatively spliced isoform of caspase-9, named caspase-9b, which lacks the central large subunit caspase domain. Caspase-9b is detectable in many cell lines by PCR and at the mRNA and protein levels. Caspase-9b can interact with the caspase recruitment domain of Apaf-1, and like the active site mutant of caspase-9, it can inhibit multiple forms of apoptosis, including those triggered by oligomerization of death receptors. It can also block activation of caspase-9 and -3 by Apaf-1 in an in vitro cytochrome c-dependent caspase activation assay. These results suggest that caspase-9b functions as an endogenous apoptosis inhibitory molecule by interfering with the formation of a functional Apaf-1-caspase-9 complex.

Alternative Splicing↗
PubMed1999

Extracellular reduced glutathione increases neuronal vulnerability to combined chemical hypoxia and glucose deprivation.

In addition to its intracellular antioxidant role, reduced glutathione (GSH) is released by CNS cells and may mediate or modulate excitatory neurotransmission. Although extracellular GSH levels rise in the ischemic cortex, its effect on the viability of energy-compromised neurons has not been defined. In this study, we tested the hypothesis that exogenous GSH would increase the vulnerability of cultured cortical neurons to azide-induced chemical hypoxia combined with glucose deprivation. Thirty minutes azide exposure in a glucose-free buffer was tolerated by most neurons, with release of less than 10% of neuronal LDH over the subsequent 21-25 h. Concomitant treatment with 10-100 microM GSH increased cell death in a concentration-dependent fashion, to 71.6+/-5.1% of neurons at 100 microM; GSH alone was nontoxic. Injury was blocked by the selective N-methyl-d-aspartate (NMDA) antagonist MK-801 but not by the AMPA/kainate antagonist NBQX. The sulfhydryl reducing agent mercaptoethanol (10-100 microM) mimicked the action of GSH; however, the zinc chelator ethylenediaminetetraacetic acid (EDTA) was ineffective. Two GSH analogues that lack a sulfhydryl group, S-hexylglutathione (SHG) and oxidized glutathione (GSSG), were inactive per se but attenuated the effect of both GSH and mercaptoethanol. These results suggest that micromolar concentrations of GSH enhance neuronal loss due to energy depletion by altering the extracellular redox state, resulting in increased NMDA receptor activation.

Animals↗
PubMed1999

Serum bound forms of PSP94 (prostate secretory protein of 94 amino acids) in prostate cancer patients.

PSP94 (prostate secretory protein of 94 amino acids) was regarded as a possible prostate cancer marker, however, it has been controversial. All prior studies were designed to test the free form in serum using antibodies to PSP94. Results presented here demonstrate that PSP94 exists in prostate cancer patients in two forms, free and bound, and that the majority is present as serum bound complexes. This result was demonstrated by using both native and SDS-PAGE analyses of serum proteins from prostate cancer patients. Chromatographic separation of serum total proteins by a molecular sieve column generated two peaks (peak I and II), which were reactive with rabbit antiserum to human PSP94 in Western blot experiments. Peak I was eluted before the IgG fraction at a molecular weight larger than 150 kDa, and peak II appeared after serum albumin ( approximately 67 kDa) was eluted. By using a biotinylated PSP94 as an indicator of the free form of PSP94, we demonstrate that peak I contains serum PSP94-bound complexes and peak II is likely the free form of serum PSP94. Since the molecular weight of serum PSP94-bound complexes is close to IgG during molecular sieve separation, serum PSP94 complexes were further purified through two rounds of protein A column separation, followed by DEAE-ion exchange column chromatography. In vitro dissociation tests of the purified PSP94-bound complexes showed that the binding of serum PSP94-complexes is probably via disulfide bonds and is chemically stable. The results presented here indicate that serum PSP94-bound complexes must be considered in evaluating the clinical utility of PSP94 as a prostate cancer marker.

Antibodies↗
PubMed1999

Modulation of tolerance by mutant heat shock transcription factors.

It ought to be possible to recruit normal cellular defenses to mitigate ischemia/reperfusion damage and to reduce toxicity of chemotherapeutic drugs. Stress-preconditioned cells acquire a tolerant state characterized by increased resistance to such insults. This state is widely believed to be mediated, partially, by heat shock proteins (Hsps). Indirect evidence suggests that stress-induced Hsp expression is controlled by heat shock transcription factor 1 (Hsf1), which factor may therefore represent a preferred target for therapeutic modulation of tolerance. In support, positively acting (Hsf1(+)) and negatively acting (Hsf1(-)) mutants of Hsf1 were identified. Inhibition of endogenous Hsf1 activity by Hsf1(-) prevents stress-induced Hsp synthesis and development of tolerance. Hsf1(+) drastically enhances expression of major Hsps in the absence of stress and induces tolerance against heat, simulated ischemia and toxicity by cyclophosphamide. Where compared, tolerance induced was slightly better than that produced by heat preconditioning. Thus, development of the tolerant state is dependent on increased levels of the cohort of Hsps induced by stress preconditioning, and Hsf1 can induce accumulation of a typical set of Hsps, which proteins are alone capable of providing tolerance at a similar level as heat preconditioning. These findings make Hsf1 a preferred target for pharmacological intervention to deliberately induce tolerance.

Cell Division↗
PubMed1999

The androgen receptor: genetic considerations in the development and treatment of prostate cancer.

The action of androgens in the development and growth of prostate carcinomas is well documented. The androgen receptor (AR) facilitates androgen-induced regulation of genes involved in cellular proliferation and differentiation. Since the early 1940s androgen ablation has been the cornerstone of treatment for metastatic prostate cancer. Although initially highly effective, hormonal therapy is not curative, and resistant disease will ultimately prevail. Mutations that alter AR conformation, function, and regulation may provide a selective growth advantage for subpopulations of cells within the tumor that are then able to proliferate in an androgen-deprived environment. Clinically, these mutations are important because they may lead to the growth of androgen-independent tumors and progression to a refractory state. Further characterization of AR mutations will lead to a more thorough understanding of their role in the development of prostate carcinomas. This information, in addition to discovering which genes are regulated by the AR, can aid in the future development of more effective pharmacotherapy for prostate cancer.

Androgen Antagonists↗
PubMed1999

Preconcentration and voltammetry of mercury on a functionalized sol-gel thin film modified glassy carbon electrode.

A functionalized sol-gel thin film modified glassy carbon electrode has been prepared for the determination of mercury. The tetrasulfide in the sol-gel matrix has a high affinity for mercury species. The chemically integrated functional groups in the sol-gel precursor ensure a high chemical and mechanical stability of the modified electrodes, and therefore a stable and reproducible analytical performance. By medium exchange anodic stripping voltammetry, this modified electrode allows reliable, low cost and interference-free determination of mercury.

Calibration↗
PubMed1999

Inhibitory effect of resveratrol on interleukin 6 release by stimulated peritoneal macrophages of mice.

In the present investigation, interleukin 6 (IL-6) activity in the supernatant of cultured mouse peritoneal macrophages was monitored using a sensitive bioassay involving the IL-6-dependent murine hybridoma B9 cell line. The effects of resveratrol on Il-6 release by mouse peritoneal macrophages stimulated with calcium ionophore A23187 and fMLP were explored. Resveratrol, at a concentration range from 5 x 10(-6) to 4 x 10(-5) mol.l-1, was found to dose-dependently inhibit IL-6 release by cultured macrophages induced by A23187 and fMLP, and showed no direct cytotoxic effect, but induced proliferation of cultured mouse thymus cells. Resveratrol, at a concentration range from 10(-8) to 10(-5) mol.l-1, was shown to dose-dependently inhibit calcium ion influx into the cells with the stimulation of fMLP (10(-6) mol.l-1). These results suggest that the blocking of calcium ion influx into cells by reveratrol is one of the possible mechanisms of the IL-6 biosynthesis inhibitory action of resveratrol.

Animals↗
PubMed1999

Transmission Electron Microscopy Characterization and Application of Sol-Gel Membranes.

: Using standard square mesh grids as supports, we have prepared sol-gel membranes from a functionalized silane precursor, bis[3-(triethoxysilyl)propyl]tetrasulfide in various organic solvents. These mesh-supported membranes allow direct characterization of their microstructure and morphology by transmission electron microscopy (TEM). Homogeneous membranes without prominent microstructural features (or featureless) at nanometer scale were obtained from dimethyl formamide (DMF), isopropanol, and butanol solutions. However, highly porous membranes were produced from DMF and ethylene glycol binary system. Heterogeneous membranes filled with nanoparticles were formed from dimethyl sulfoxide solution. The featureless sol-gel membranes with tunable performances provide a useful alternative as supporting films for TEM applications.

Journal Article↗
PubMed1999

A novel system based on a poloxamer/PLGA blend as a tetanus toxoid delivery vehicle.

PURPOSE: Previous work on the encapsulation of proteins and antigens in poly(lactic-co-glycolic acid) (PLGA) microspheres has led to the conclusion that microencapsulated antigens are frequently inactivated due to their interaction with the polymer. To improve the compatibility of the antigen with the polymer, we have devised a novel microencapsulated system consisting of a blend of PLGA 50:50 and poloxamer 188 (Pluronic F68) and applied it to the delivery of tetanus antigen. METHODS: Tetanus toxoid was encapsulated in microspheres containing different amounts of poloxamer using an anhydrous procedure based on an oil-in-oil solvent extraction process. The compatibility of the polymers was studied by Fourier transform infrared (FT-IR) spectroscopy. Microspheres were assayed in vitro and in vivo for their ability to deliver active antigen for extended periods of time. RESULTS: Analysis by FT-IR spectroscopy evidenced the miscibility of both polymers by a hydrogen bonding mechanism. In vitro release studies revealed that microspheres containing poloxamer released antigenically active TT, in a pulsatile manner, for up to 50 days. In addition, it was observed that the intensity and duration of the pulses were dependent on both poloxamer content and TT loading in the microspheres. The in vivo evaluation of this new system showed that the neutralizing antibodies elicited by the TT encapsulated in poloxamer-PLGA microspheres were considerably higher and more prolonged than those obtained after administration of the aluminum phosphate-adsorbed toxoid. CONCLUSIONS: These results indicate the importance of devising new microencapsulation approaches specially adapted for preserving the activity of protein antigens incorporated within PLGA microspheres.

Animals↗