Biomedical subjects

Y Sun

Publications and source records attributed to Y Sun.

At least 469 records · Page 26Linked to original sources

PubMed1999

[The 1. 54 microm laser and upconversion luminescence of YELPP noncrystalline induced by 969 nm LD laser].

In this paper, the absorption of Er3+, Yb3+ penta-phosphate noncrystalline (YELPP) was measured and the basic spectral parameters were calculated. Adopting the longitudinal-pump method with a domestic diode laser (LD), we achieved CW 1.5 microm chipped laser in China for the first time. The power of 1.5 microm laser was quite stable. The target of 1.5 microm laser reached the international level of early 1990s' in this field. In addition, the up-conversion luminescence was measured under the condition that 1.5 microm laser was either oscillating or not. The relationship between 1.5 microm chipped laser and up-conversion luminescence was analyzed initially.

English Abstract↗

PubMed1999

[Microwave acid-digestion ICP-MS method for the determination of sixteen elements in marine products].

Microwave acid-digestion samples and ICP-MS method were established for the determination of Na, Mg, Al, P, Cr, Mn, Fe, Ni, Cu, Zn, As, Sr, Mo, Cd, Pb and Hg in marine product. According standard sample GBW08571 mussel, we cheek the method accuracy and precision. The accuracy average values are 96.7%. These results are very suitable for the reference values. The RSDs of all elements are less than 5%. We use several internal standard correction method to correct the matrix interference. The method is simple, rapid, accurate and reliable.

Animals↗

PubMed1999

[Study on the Co(DC)2-NaDC mixed micelle system].

Eight coordinated complex samples of CoCl2-NaDC were obtained,using various concentration and initial molar ratio of CoCl2 and NaDC. They exhibited distinct appearances and characters. Their different structures and components were investigated by FTIR spectroscopy, X-ray diffraction analysis and ICP analysis. We can give the following conclusions: (1) when the concentration of NaDC is smaller than C.M.C, Co2+ ions react with mono-molecular NaDC and the component of the pink wadding-like resultant is Co(DC)2 x 3H2O. (2) When the concentration of NaDC is larger than C.M.C, and the concentration of CoCl2 is higher (0.5 mol/L), Co2+ ions destroy NaDC micelles, and the component of the pink wadding-like resultant is also Co(DC)2 x 3H2O. (3) When the concentration of NaDC is larger than C.M.C, and the concentration of CoCl2 is lower (0.1 mol/L or more lower), Co(DC)2 and NaDC may form mixed micelles, and some of NaDC micelles connect with each other through the Co2+ bridges to produce complicate Co(DC)2-NaDC complex with gel character and macromolecular network structure. In human body,the concentration of metal ions is usually lower and the concentration of NaDC is larger than C.M.C, So the third kind is suggested as an ideal model of the interaction between Co2+ ions and NaDC in vivo.

Bile Acids and Salts↗

PubMed1999

[Femtosecond time-resolved fluorescence spectra of LDS751].

The femtosecond time-resolved fluorescence depletion method has been introduced. In this method two beams of femtosecond laser was used. One excited the sample molecular to emit fluorescence. Then after specified time delay the second laser beam was introduced to deplete the fluorescence through the stimulate emission process. This method has been applied to LDS751 molecules in solution and its time-resolved fluorescence spectrum has been obtained.

Fluorescent Dyes↗

PubMed1999

[Direct upconversion sensitization luminescence of Tm(0.1) Yb (10.9) oxyfluoride vitroceramincs].

This paper studied the direct upconversion sensitization luminescence of Tm (0.1) Yb (10.9) oxyfluoride vitroceramics pumped by 966 nm diode laser for the first time. We found that there are both strong 477 nm three-photon upconversion fluorescence of 1G4 --> 3H6 transition and 799.5 nm two-photon upconversion fluorescence of 3H4 --> 3H6 transition as well as weak upconversion fluorescence of 1D2 --> 3H6, 1Dz --> 3F4,1G4 --> 3F4 and 3F3 --> 3H6 transitions at 361 nm, 449.5 nm, 647.0 nm and (679.5, 698.5 nm), respectively.

English Abstract↗

PubMed1998

A critical role for DNA end-joining proteins in both lymphogenesis and neurogenesis.

XRCC4 was identified via a complementation cloning method that employed an ionizing radiation (IR)-sensitive hamster cell line. By gene-targeted mutation, we show that XRCC4 deficiency in primary murine cells causes growth defects, premature senescence, IR sensitivity, and inability to support V(D)J recombination. In mice, XRCC4 deficiency causes late embryonic lethality accompanied by defective lymphogenesis and defective neurogenesis manifested by extensive apoptotic death of newly generated postmitotic neuronal cells. We find similar neuronal developmental defects in embryos that lack DNA ligase IV, an XRCC4-associated protein. Our findings demonstrate that differentiating lymphocytes and neurons strictly require the XRCC4 and DNA ligase IV end-joining proteins and point to the general stage of neuronal development in which these proteins are necessary.

Animals↗

PubMed1998

Transcriptional suppression of matrix metalloproteinase-2 gene expression in human astroglioma cells by TNF-alpha and IFN-gamma.

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that function in the turnover of extracellular matrix components during development. In addition, MMPs also contribute to pathological conditions associated with inflammation, angiogenesis, and tumor invasion. A 72-kDa type IV collagenase, also referred to as gelatinase A or MMP-2, has been proposed to potentiate the invasion and metastasis of malignant tumors. In particular, MMP-2 activity has been shown to constitute an important component of human astroglioma invasion. We investigated the influence of various cytokines, both proinflammatory and immunosuppressive, on MMP-2 gene expression in two human astroglioma cell lines (U251-MG and CRT). Our results indicate that the cell lines constitutively express high levels of MMP-2 mRNA, protein, and bioactivity as assessed by ribonuclease protection assay, immunoblotting, and zymography assays, respectively. The proinflammatory cytokines TNF-alpha and IFN-gamma individually can inhibit constitutive MMP-2 expression, and function in an additive manner for near-complete inhibition of MMP-2 expression. Inhibition of MMP-2 mRNA levels by TNF-alpha and IFN-gamma is not due to destabilization of the MMP-2 message; rather, inhibition is mediated at the transcriptional level. Furthermore, TNF-alpha/IFN-gamma inhibition of MMP-2 expression results in decreased invasiveness of the human astroglioma cells through an extracellular matrix. These results raise the possibility that TNF-alpha and IFN-gamma may have beneficial effects in attenuating astroglioma invasive properties.

Astrocytes↗

PubMed1998

Effects of D2 dopamine receptor agonist and antagonist on brain activity in the rat assessed by functional magnetic resonance imaging.

The effects of D2 dopamine receptor agonist, bromocriptine (BROMO), and antagonist, haloperidol (HPD), on brain activity were investigated in rats by functional magnetic resonance imaging. T2*-weighted signal intensity was increased in the hypothalamus at 120 min after acute administration of BROMO, and in the ventral posterior and dorsomedial nuclei of the thalamus from 30 to 120 min. In contrast, the signal intensity was decreased in the caudate-putamen at 30 min after acute administration of HPD, in the hypothalamus from 30 to 60 min, and in the perirhinal cortex at 30 min. After chronic (2 weeks) HPD treatment, acute administration of HPD decreased signal intensity in the caudate-putamen at 60 min, in the hypothalamus at 30 min, the perirhinal cortex from 2 to 120 min, the dorsomedial and ventral posterior nuclei of the thalamus from 2 to 120 min, and the medial nucleus of the amygdala from 60 to 120 min. These results suggest that (1) the D2 receptor agonist increased the activity of the thalamic nuclei and the hypothalamus, while the D2 receptor antagonist suppressed brain activity in the regions where D2 receptors were present, (2) the suppression of brain activity in the thalamic nuclei and the perirhinal cortex by acute HPD administration was enhanced by chronic HPD treatment, and (3) the effects of antipsychotic drugs on the thalamus, amygdala, and perirhinal cortex may be related to their therapeutic efficacy, since clinical improvement in schizophrenic patients appears several days after the start of HPD treatment.

Amygdala↗

PubMed1998

Pb(II)-translocating P-type ATPases.

The cad operon of Staphylococcus aureus plasmid pI258, which confers cadmium resistance, encodes a transcriptional regulator, CadC, and CadA, an ATP-coupled Cd(II) pump that is a member of the superfamily of cation-translocating P-type ATPases. The Escherichia coli homologue of CadA, termed ZntA, is a Zn(II)/Cd(II) pump. The results described in this paper support the hypothesis that ZntA and CadA are Pb(II) pumps. First, CadC is a metal-responsive repressor that responds to soft metals in the order Pb>Cd>Zn. Second, both CadA and ZntA confer resistance to Pb(II). Third, transport of 65Zn(II) in everted membrane vesicles of E. coli catalyzed by either of these two P-type ATPase superfamily members is inhibited by Pb(II).

Adenosine Triphosphatases↗

PubMed1998

Regulation of the proinflammatory effects of Fas ligand (CD95L).

Fas ligand (CD95L) inhibits T cell function in immune-privileged organs such as the eye and testis, yet in most tissues CD95L expression induces potent inflammatory responses. With a stably transfected colon carcinoma cell line, CT26-CD95L, the molecular basis for these divergent responses was defined. When injected subcutaneously, rejection of CT26-CD95L was caused by neutrophils activated by CD95L. CT26-CD95L survived in the intraocular space because of the presence of transforming growth factor-beta (TGF-beta), which inhibited neutrophil activation. Providing TGF-beta to subcutaneous sites protected against tumor rejection. Thus, these cytokines together generate a microenvironment that promotes immunologic tolerance, which may aid in the amelioration of allograft rejection.

Animals↗

PubMed1998

Structure of a glutamate-receptor ligand-binding core in complex with kainate.

Ionotropic glutamate receptors (iGluRs) mediate excitatory synaptic transmission in vertebrates and invertebrates through ligand-induced opening of transmembrane ion channels. iGluRs are segregated into three subtypes according to their sensitivity to the agonists AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid), kainate (a structural analogue of glutamate) or NMDA (N-methyl-D-aspartate). iGluRs are important in the development and function of the nervous system, are essential in memory and learning, and are either implicated in or have causal roles in dysfunctions ranging from Alzheimer's, Parkinson's and Huntington's diseases, schizophrenia, epilepsy and Rasmussen's encephalitis to stroke. Development of iGluR agonists and antagonists has been hampered by a lack of high-resolution structural information. Here we describe the crystal structure of an iGluR ligand-binding region in a complex with the neurotoxin (agonist) kainate. The bilobed structure shows the determinants of receptor-agonist interactions and how ligand-binding specificity and affinity are altered by remote residues and the redox state of the conserved disulphide bond. The structure indicates mechanisms for allosteric effector action and for ligand-induced channel gating. The information provided by this structure will be essential in designing new ligands.

Allosteric Site↗

PubMed1998

Differential expression of tissue inhibitors of metalloproteinases in the failing human heart.

BACKGROUND: Extracellular matrix turnover is regulated by matrix metalloproteinases (MMPs) and a family of tissue inhibitors of metalloproteinases (TIMPs). Together, these proteins may contribute to myocardial remodeling in congestive heart failure. We hypothesized that the expression of MMPs and TIMPs might be differentially regulated in the failing human heart. METHODS AND RESULTS: Northern blot analyses were performed with probes to TIMP-1 to -4 and GAPDH with poly A+ mRNA from ventricular tissues of patients with ischemic cardiomyopathy (ICM, n=16) or idiopathic dilated cardiomyopathy (DCM, n=15) and nonfailing control hearts (n=15). TIMP-1 to -4 and MMP-9 proteins were quantified by ELISA and/or Western blot, and the total gelatinolytic activity was studied by gelatin zymography. The results showed that cardiac expression of TIMP-1 and -3 transcripts and proteins was significantly reduced in ICM and DCM. No significant difference was observed in TIMP-2 and -4 transcripts. However, TIMP-4 protein was significantly reduced in ICM myocardium. MMP-9 protein content and total gelatinolytic activity were upregulated in the same samples. CONCLUSIONS: These studies demonstrated a selective downregulation of TIMPs along with upregulation of MMP-9 and gelatinolytic activity in the failing hearts, alterations that favor matrix degradation and turnover. These findings might be of pathophysiological significance and might suggest new therapeutic targets for limiting the ventricular remodeling and dilatation process characteristic of the failing human heart.

Adult↗

PubMed1998

Isolation and characterization of the human prosaposin promoter.

Prosaposin is a multifunctional protein that encodes four glycoproteins, named saposins A, B, C and D. They participate in the catabolism of glycosphingolipids in lysosomes. When secreted, intact prosaposin may function as a neuritogenic factor. Human and mouse prosaposin displayed similar temporal and spatial regulation of expression. To gain insight into the transcriptional regulation of this locus, the 5' region was characterized from the human prosaposin gene. The putative human promoter was shown to be TATA-less, i.e. it belonged to the TATA-less housekeeping gene family. The transcription initiation sites were localized to -23, -27, -31 and -83bp 5' to ATG, compared to -87 and -94bp in the mouse. In SK-N-SH neuroblastoma cells, positive regulatory elements were detected -343 to -813bp upstream of ATG. A negative regulatory region existed between -813 and -2500bp using SK-N-SH, H441 and NS20Y cells. EMSA and DNA-footprint analysis showed that Sp1 and Sp3 are involved in human prosaposin gene regulation. Compared to the mouse promoter, the human promoter is missing a Sp1 cluster within a 310-bp upstream segment, and has AP-1, Oct-1 and two RORalpha sites that are protected from DNaseI by selected nuclear extracts.

Animals↗

PubMed1998

Up-regulation of tissue inhibitor of metalloproteinases-3 gene expression by TGF-beta in articular chondrocytes is mediated by serine/threonine and tyrosine kinases.

The balance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) regulates extracellular matrix turn-over in normal animal development, cancer cell metastasis, atherosclerotic plaque rupture and erosion of arthritic cartilage. Transforming growth factor beta (TGF-beta), an inducer of matrix synthesis, potently enhances mRNA and protein of a recently characterized MMP inhibitor, TIMP-3, in bovine articular chondrocytes. We examined the implication of protein kinases in the TGF-beta-mediated induction of TIMP-3 expression by utilizing activators and inhibitors of these enzymes. Protein kinase A activators, dibutyryl cyclic AMP, or forskolin had little or no effect, respectively, while phorbol 12-myristate 13-acetate (PMA), a PKC activator, increased TIMP-3 gene expression. H7, a serine/threonine protein kinase inhibitor, markedly reduced the response of TIMP-3 gene to TGF-beta. Furthermore, two protein tyrosine kinase inhibitors, genistein and herbimycin A, inhibited TGF-beta induction of TIMP-3. H7 and genistein also suppressed TGF-beta-induced TIMP-3 protein expression. These results suggest that TGF-beta signaling for TIMP-3 gene induction involves H7-sensitive serine/threonine kinase as well as herbimycin A- and genistein-sensitive protein tyrosine kinases.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1998

Expression of grass carp growth hormone by baculovirus in silkworm larvae.

A total of five recombinant Bombyx mori nuclear polyhedrosis viruses (BMNPV) carrying the grass carp (Ctenopharyngodon idellus) growth hormone (GH) cDNA were constructed in this study. Two of them were able to express the hormone up to a level of 12 microgram/ml medium when cultured B. mori cells were infected for 4 days. Inoculation of the viruses into silkworm (B. mori) host significantly increased the level of GH achievable. The amount of hormone produced per larva was estimated to be around 1 mg. The recombinant grass carp GH had immunological and biological activities similar to the native hormone. The N-terminal sequence of the recombinant hormone was the same as the native one, indicating that the fish signal peptide was correctly processed by the insect cells. Silkworm powder prepared from larvae infected with the recombinant virus was used as food supplement for fish. Compared with the control, this dietary supplement was effective in increasing the growth rate of juvenile carp.

Animals↗

PubMed1998

Synthesis and Photophysical Properties of ZnS Colloidal Particles Doped with Silver.

The synthesis and photophysical characterization of ZnS:Ag colloid are reported. The presence of mercaptoacetic acid has an important effect not only on the formation of doped and undoped ZnS but also on the photophysical properties. ZnS colloid doped with silver shows a strong green emission upon ultraviolet excitation, the intensity of which was enhanced significantly compared with that of the undoped colloid. The green emission was ascribed to a transition from a donor level such as anion vacancy to the levels of the Ag impurities. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

A helical coat protein recognition domain of the bacteriophage P22 scaffolding protein.

The scaffolding protein of bacteriophage P22 directs the assembly of an icosahedral procapsid, a metastable shell that is the precursor for DNA packaging. The full-length protein has been shown previously to exist in a monomer-dimer-tetramer equilibrium of elongated and predominantly alpha-helical molecules. Two deletion-mutant fragments of the scaffolding protein, comprising amino acid residues 141 to 303 and 141 to 292, respectively, have been constructed, overexpressed in Escherichia coli, and purified. Removal of residues 1 to 140 yields a protein that is assembly-active both in vitro and in vivo, while the removal of the C-terminal 11 residues (293 to 303) leads to complete loss of scaffolding activity. Sedimentation analysis reveals that both scaffolding fragments exist in a monomer-dimer equilibrium governed by apparent dissociation constants Kd(141-303)=640 microM and Kd(141-292)=880 microM. Tetramer formation is not observed for either fragment; thus, the tetramerization domain of the scaffolding subunit resides in the N-terminal portion of the polypeptide chain. Examination of both fragments by circular dichroism, Raman and NMR spectroscopies indicates a highly alpha-helical fold in each case. Nonetheless, pronounced differences are observed between spectral signatures of the two fragments. Notably, Raman spectra of fragments 141-292 and 141-303 indicate that elimination of residues 293 to 303 results in unfolding of an alpha-helical coat protein "recognition" domain encompassing about 20 to 30 residues. The thermostability of fragment 141-303, monitored over a wide concentration range by circular dichroism and Raman spectroscopy, indicates a broad denaturation transition for the monomeric (low concentration) form, while more cooperative unfolding is observed for the dimeric (high concentration) form. A lesser increase in cooperativity upon dimerization is obtained for fragment 141-292. Additionally, the C-terminal recognition domain constitutes the most stable and cooperative unit in the 141-303 fragment. Measurement of hydrogen-isotope exchange kinetics in scaffolding fragments by time-resolved Raman spectroscopy shows that the C terminus is the only protected segment of the polypeptide chain. On the basis of the measured hydrodynamic and spectroscopic properties, a domain structure is proposed for the scaffolding subunit. The roles of these domains in P22 procapsid assembly are discussed.

Bacteriophage P22↗

PubMed1998

Origin and characteristics of ultraviolet-B radiation-induced suppressor T lymphocytes.

Cutaneous exposure to low dose (2 kJ/m2) ultraviolet B radiation impairs the induction of contact hypersensitivity (CHS) responses to haptens applied to UV-irradiated skin and induces hapten-specific suppressor T lymphocytes (Ts). Cells collected from the draining lymph nodes of UV-irradiated, FITC-sensitized mice have impaired Ag-presenting activity and induce Ts cells upon injection into syngeneic recipients. This study investigates whether Ts cells originate in the UV-irradiated donor mice or are induced in lymph node cell recipients and the mechanism of suppression. Using congenic mice, we determined that the Ts cells in recipient animals were derived from T cells in the draining lymph nodes of the UV-irradiated donors. Cell lines and clones established from unirradiated and UV-irradiated, FITC-sensitized mice were CD4+, CD8-, TCR-alpha/beta+, MHC restricted, and hapten specific. The T cells proliferated in response to APC sensitized in vivo, but not to APC coupled in vitro with FITC. Cell lines from unirradiated mice were Th1 like, producing large amounts of IFN-gamma, but little IL-4 or IL-10, whereas cloned Ts cells from UV-irradiated mice produced IL-10, but no IL-4 or IFN-gamma. Ts cells blocked APC functions and IL-12 production in vitro. Injection of 5 x 10(4) cloned Ts cells into untreated recipients suppressed the induction of CHS. These results suggest that UV radiation can induce a distinct T regulatory type 1-like Ts population that may block the activation of Th1 cell-mediated immune responses.

Animals↗