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Biomedical subjects

B Xing

Publications and source records attributed to B Xing.

18 recordsLinked to original sources
PubMed2001

Localization of an integrin binding site to the C terminus of talin.

Talin, consisting of a 47-kDa N-terminal head domain (residues 1-433) and a 190-kDa C-terminal rod domain (residues 434-2541), links integrins to the actin cytoskeleton. We previously reported that the binding stoichiometry of integrin alpha(IIb)beta(3):talin is approximately 2:1. More recently, an integrin binding site has been localized to the talin head domain. In the present study, we identified another integrin binding site at the C-terminal region of the talin rod domain. In a solid phase binding assay, RGD affinity-purified alpha(IIb)beta(3) bound in a dose-dependent manner to microtiter wells coated with the isolated 190-kDa proteolytic fragment of the talin rod domain. Additionally, alpha(IIb)beta(3) also bound to the talin rod domain captured by 8d4, an anti-talin monoclonal antibody. Polyclonal antibodies raised against a recombinant protein fragment corresponding to the entire talin rod domain (anti-talin-R) inhibited alpha(IIb)beta(3) binding to intact talin by approximately 50% but completely blocked alpha(IIb)beta(3) binding to the talin rod domain. To localize the integrin binding site, we examined alpha(IIb)beta(3) binding to recombinant polypeptide fragments corresponding to partial sequences of the talin rod domain. Whereas alpha(IIb)beta(3) bound effectively to talin-(1075-2541) and talin-(1984-2541), it failed to bind to talin-(434-1076) and talin-(434-1975). Furthermore, the binding of alpha(IIb)beta(3) to talin-(1984-2541) was inhibited by anti-talin-R. These results indicate that an integrin binding site is located within residues 1984-2541 of the talin rod domain. Thus, talin contains two integrin binding sites, one in the homologous FERM (band four-point-one, ezrin, radixin, moesin) domain and another near its C terminus. Because talin exists as an anti-parallel homodimer in focal adhesions, the two integrin binding sites in the adjacent talin molecules would be in close proximity with each other.

Actins↗
PubMed2001

New structural information on a humic acid from two-dimensional 1H-13C correlation solid-state nuclear magnetic resonance.

New information on the chemical structure of a peat humic acid has been obtained using a series of two-dimensional 1H-13C heteronuclear correlation solid-state NMR (HETCOR) experiments with different contact times and with spectral editing by dipolar dephasing and 13C transverse relaxation filtering. Carbon-bonded methyl groups (C-CH3) are found to be near both aliphatic and O-alkyl but not aromatic groups. The spectra prove that most OCH3 groups are connected directly with the aromatic rings, as is typical in lignin. As a result, about one-third of the aromatic C-O groups is not phenolic C-OH but C-OCH3. Both protonated and unprotonated anomeric O-C-O carbons are identified in the one- and two-dimensional spectra. COO groups are found predominantly in OCHn-COO environments, but some are also bonded to aromatic rings and aliphatic groups. All models of humic acids in the literature lack at least some of the features observed here. Compositional heterogeneity was studied by introducing 1H spin diffusion into the HETCOR experiment. Comparison with data for a synthetic polymer, polycarbonate, indicates that the separation between O-alkyl and aromatic groups in the humic acid is less than 1.5 nm. However, transverse 13C relaxation filtering under 1H decoupling reveals heterogeneity on a nanometer scale, with the slow-relaxing component being rich in lignin-like aromatic-C-O-CH3 moieties and poor in COO groups.

Carbon Isotopes↗
PubMed2001

Sorption of naphthalene and phenanthrene by soil humic acids.

Humic acids are a major fraction of soil organic matter (SOM), and sorption of hydrophobic organic chemicals by humic acids influences their behavior and fate in soil. A clear understanding of the sorption of organic chemicals by humic acids will help to determine their sorptive mechanisms in SOM and soil. In this paper, we determined the sorption of two hydrophobic organic compounds, naphthalene and phenanthrene by six pedogenetically related humic acids. These humic acids were extracted from different depths of a single soil profile and characterized by solid-state CP/MAS 13C nuclear magnetic resonance (NMR). Aromaticity of the humic acids increased with soil depth. Similarly, atomic ratios of C/H and C/O also increased with depth (from organic to mineral horizons). All isotherms were nonlinear. Freundlich exponents (N) ranged from 0.87 to 0.95 for naphthalene and from 0.86 to 0.92 for phenanthrene. The N values of phenanthrene were consistently lower than naphthalene for a given humic acid. For both compounds, N values decreased with increasing aromaticity of the humic acids, such an inverse relationship was never reported before. These results support the dual-mode sorption model where partitioning occurs in both expanded (flexible) and condensed (rigid) domains while nonlinear sorption only in condensed domains of SOM. Sorption in the condensed domains may be a cause for slow desorption, and reduced availability and toxicity with aging.

Adsorption↗
PubMed2001

In vitro binding of an orally active platinum antitumor drug, JM216 to metallothionein.

The in vitro binding of an orally active anticancer drug JM216 to metallothionein is firstly investigated in this paper. It is revealed that a redox reaction following a substitution reaction from JM216 with rabbit liver Zn7MT-II is presented. The reaction feature, the metal binding stoichiometry and the oxidation states of platinum and sulfur in the products are studied by UV-visible, chromatography and X-ray photoelectron spectroscopy methods. Parts of MT are oxidized to precipitate products with intra and intermolecular CyS-SCy disulfides linkages. Pt(IV) is reduced to its Pt(II) counterpart. And the reduced Pt(II) replace the metal ions in native MTs. Meanwhile it can also cause the dimerization of MT. Increasing the reaction ratio of JM216 to MT leads to a concomitant increase in the apparent yield of the precipitate and dimeric products and the elevation of the binding stoichiometry of Pt to the protein. Based on the experimental data, the reaction mechanism between JM216 and Zn7MT-II in vitro are discussed.

Administration, Oral↗
PubMed2000

Ground discarded tires remove naphthalene, toluene, and mercury from water.

Ground discarded tires adsorb naphthalene, toluene, and mercury ions (Hg2+) from aqueous solutions. Their sorption properties and kinetics were determined by batch equilibration techniques at 20 degrees C. The isotherms were linear for naphthalene and toluene and their sorption coefficients were about 1340 and 255 (ml/g), respectively. Sorption of the organic compounds by the ground rubber particles was relatively fast (within 30 min). However, the mercury isotherms were non-linear, and its sorption was slow as compared to the sorption of the organics. The rubber particles had a strong affinity for Hg2+. These results show that ground discarded tires are effective in removing organic compounds and Hg2+ from wastewater and other contaminated environments. In addition it would be a useful, environmentally friendly use of discarded tires (one tire per year per capita is discarded in the United States).

Adsorption↗
PubMed2000

Sorption and desorption of the diketonitrile metabolite of isoxaflutole in soils.

Isoxaflutole is a new pre-emergence corn herbicide that undergoes rapid conversion to a diketonitrile derivative (DKN) in soils. Sorption-desorption studies were conducted in five different soils varying in physical and chemical properties. A batch equilibration technique was used with total initial aqueous solution concentrations of DKN at 0.25, 0.75, 2.0, 8.0, 25, 75, 150, and 250 mg l(-1). After the sorption process, two subsequent desorptions were conducted with an equilibration period of 7 days. A high correlation existed between the desorption coefficient, K(Fd) and the organic matter content of soils (r(2)=0.844 for the first desorption and r(2)=0.861 for the second desorption), while the clay content did not greatly influence the desorption of DKN. Although the sorption of DKN was generally reversible, a sorption-desorption hysteresis was apparent in all soils. The site energy distribution curves emphasized the fact that DKN binds tightly to soils with higher organic matter content and greater proportion of DKN was retained by those soils

Journal Article↗
PubMed2000

Retention of organic and inorganic chemicals by the drainage/supply piping material.

A critical issue facing the turfgrass industry is the environmental fate and transport of organic and inorganic chemicals used on golf courses. The fate and distribution of those chemicals are strongly influenced by sorptive interactions with soil and sediment. In this study, the drainage and water supply piping material (used for construction of a prototype encapsulated golf green) was utilized to determine its potential sorption of three organic chemicals [2,4-dichloro-phenoxyacetic acid] (2,4-D), naphthalene and toluene and nitrate. Crushed piping material (small-to-large particle sizes) was evaluated. Isotherms were constructed using a batch equilibration technique. The results showed that the drainage/supply piping material at small particle sizes (<2.5 mm) has higher sorptive ability compared to soil (1.7 for 2,4-D and 13.4 for naphthalene). The K(F) value was 44, 253 and 70 for 2,4-D, naphthalene and toluene, respectively. K(oc) values were much higher than those of peat and soil at lower equilibrium concentrations. However, sorption decreased dramatically with increasing particle size (approaching zero at particle size 10 mm), due to reduction of surface areas and sorption sites. Sorption of NO(3)-N by the piping material was negligible. We concluded that sorption by intact drainage/supply piping material would not affect the recycling efficiency of pesticides and nutrients in the constructed encapsulated green. Conversely, drainage/supply piping material particles smaller than 2.5 mm in diameter can effectively be utilized as a filtering material.

Journal Article↗
PubMed2000

Kinetic studies of the reactions of some metal reconstituted metallothioneins with the electrophilic disulfide 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB).

Rabbit liver Pt7MT, Zn7MT, Bi7MT were reconstituted and the kinetic studies of the reactions with electrophilic disulphide 5, 5'-dithiobis-(2-nitrobenzoic acid) (DTNB) were investigated to explore the possible mechanism of metals release from metallothioneins. It is revealed that the Pt7MT, Zn7MT react with DTNB biphasically, yielding a four-term rate law: Rate = k1f [MT] + k2f [DTNB][MT] + k1s [MT] + k2s [DTNB][MT]. Zn7MT reacts with disulphide DTNB more rapidly and has significantly greater observed rate constants ks, kf than Pt7MT. The kinetic data for Bi7MT indicate that the reaction is monophasic and the rate law is proved to be: Rate = k1 [MT] + k2 [DTNB][MT]. The observed pseudo-first order rate constants for above MTs are insensitive to pH value. Based on the available experimental data, the different kinetic behaviors of MTs reactions with electrophilic disulphide DTNB and a possible mechanism to release the coordinated metal ions are discussed.

Animals↗
PubMed2000

Binding properties of an orally active platinum anti-tumor drug JM216 with metallothionein in vivo.

The abilities of the orally active platinum anti-tumor drug JM216 [trans-bis-acetato-cis-dichloroammine (cyclohexylamine) platinum (IV)] to induce the biosynthesis of metallothionein (MT) were investigated in rabbits given oral administrations or injections s.c. It is revealed that oral administration of JM216 can induce the MT synthesis in the liver but not in the kidney. The hepatic MT contained 7.11 +/- 0.11 Zn and only little Pt or Cu. Injections of JM216 to rabbits can greatly elevate the MT levels in the liver, but increase the renal MT levels only slightly. The MT content as well as Pt concentration in the liver was much higher than that in the kidney. The metal stoichiometry in the purified renal MT was determined to be 4.41 +/- 0.04 Zn, 0.36 +/- 0.11 Pt and 2.50 +/- 0.18 Cu per mole protein. The hepatic MT was still characterized as Zn7MT. Both the treatment with oral administration and injections s.c. cannot lead to the increase of Pt content in the kidney. The oxidation state of platinum in the MT from the kidney was determined to be +2 by X-ray photoelectron spectroscopy. As compared with zinc compounds, JM216 was a very poor stimulator for MT biosynthesis in vivo. Pre-injections with Zn(NO3)2 significantly enhanced the MT levels as well as the Pt concentration compared with that resulting from injections with JM216 alone. Based on the experimental data, the role of MT in relation to its involvement in the metabolism and the mechanism of detoxification of Pt(IV) complexes are discussed.

Animals↗
PubMed1999

[Experimental study of interleukin-4 gene therapy for glioma].

OBJECTIVE: To study IL-4 gene therapy for glioma. METHODS: Using recombinant retrovirus vector, mIL-4 was transfected into psi 2 packaging cells and rat C6 glioma cells, respectively by lipofectamine. The IL-4 secretting cell clones psi 2 IL-4 and C6IL-4 were studied in vitro and in vivo. RESULTS: Apart from a decrease in cloning efficiency, no difference was observed between the transfected and the wild type glioma cells in proliferation and cell cycle in vitro. Tumorigenicity of subcutaneously and intracranially inoculated C6IL-4 was reduced. Tumor growth could be suppressed by perineoplastic inoculation of psi 2 IL-4 cells. CONCLUSION: IL-4 gene-modified C6 glioma has decreased tumorigenicity. Local production of IL-4 by psi 2 IL-4 cells can lead to regression of established glioma.

Animals↗
PubMed1998

Binding properties and stoichiometries of a palladium(II) complex to metallothioneins in vivo and in vitro.

This paper will be the first to discuss the in vivo and in vitro properties of a Pd(II) complex, K2PdCl4, interacting with metallothioneins (MTs). In vivo experiments revealed that intraperitoneal injections of K2PdCl4 into rabbits led to the simultaneous synthesis of Pd-MT in the kidney and Zn7MT in the liver. The renal Pd-MT complex contains 3.6 +/- 0.3 Pd, 2.1 +/- 0.2 Zn, and 1.0 +/- 0.1 Cu per mole protein. It was found that pre-treatment with Zn(NO3)2 before K2PdCl4 injections significantly enhanced renal Pd-MT level. The same pre-treatment also increases hepatic Zn-MT levels. These results strongly suggest that Pd(II) ions can be bound in vivo by MT existing in the rabbit kidneys to form Pd-MT. Gel-filtration chromatographic studies after the incubation of either native Cd5Zn2MT2 or Zn7MT2 with K2PdCl4 in vitro demonstrate that Pd(II) ions promote the non-oxidative oligomerization of native MTs. Increasing the level of Pd(II) relative to MT led to a concomitant increase in the apparent yield of MT oligomers. At relatively low Pd-MT ratio, Pd(II) is found predominantly in the oligomers while the monomeric products are chiefly composed of the reactants, Cd5Zn2MT2 or Zn7MT2. Based on our experimental data, the mechanisms of the reactions between Pd(II) and MTs in vivo and in vitro are discussed.

Animals↗
PubMed1998

[A new rat brain-glioma model].

OBJECTIVE: To build a new rat brain glioma model with LacZ as a reporter gene. METHODS: Plasmid BAG was transfected into C6 glioma cell. The cell cycle, cell proliferation, malignant infiltrative ability of wild and transfected glioma cell were observed. Rat glioma model was built using stereotaxic implantation. RESULTS: There was no difference between transfected and wild glioma cell in cell growth characteristics and tumorigenesis. CONCLUSIONS: It was easy to observe the infiltrative area on cellular level from the rat glioma model made by transfected tumor cell. The method is satisfactory for radiation and chemotherapeutic trials of glioma.

Animals↗
PubMed1997

[Gastric carcinoma in the young people].

We studied the characteristics of the incidence, and prognosis of the gastric carcinoma in young people. The clinicopathological findings and follow-up data of the gastric carcinoma patients treated from 1976 to 1991 were compared in 624 olderly patients. The male to female ratio was 1:1.2 in young patients and it increased with age up to a peak: in the 50-59 year-old group (2.8:1). An increase of poorly differentiated tumors was found significantly in the young people (88.2%) compared with the olderly (P < 0.01). A slight preponderance of diseases in stage III and IV was found in the young people (72.5%, P > 0.1). There was no significant difference of resectability and postoperative actuarial survival between the two groups. Most young patients were diagnosed in the late stage. Early detection of the carcinoma in the young patients plays a significant role in improving their treatment results.

Adenocarcinoma↗
PubMed1996

[The effect of long-term tamoxifen therapy on the occurrence of contralateral primary breast cancer].

From January 1 1985 to December 31 1990, 874 cases of female primary breast cancer were treated in the Department of Surgery at Beijing Institute for Cancer Research. Of these, 21 patients suffered from contralateral primary breast cancer after surgery. These patients were divided into two groups, 523 patients received adjuvant tamoxifen therapy (20mg daily) for 2 to 5 years as the treated group. There were 351 patients without tamoxifen therapy as the control group. The medium follow-up of the treated and the control group was 7.8 years and 7.0 years, respectively. The incidence of contralateral primary breast cancer in the treated group was 1.5% (8/523), and that in the control group was 3.7% (13/351, P < 0.05). This result suggests that tamoxifen is useful to reduce the risk of contralateral primary breast cancer.

Adult↗
PubMedDate not supplied

Influence of cytokines on the expression of fas ligand and CD44 splice variants in colon carcinoma cells.

The expression of Fas ligand (FasL) by malignant cells might be a mechanism for tumor immune escape. We investigated FasL expression by LS 174T colon carcinoma cells. Furthermore, the effects of in vitro stimulation with rIL-2, rIFN-gamma and rTNF-alpha were investigated with regard to a possible regulation of the FasL expression by cytokines. FasL expression was detected by flow cytometry and RT-PCR. We observed a spontaneous expression of FasL by LS 174T cells. Incubation with high-dose rTNF-alpha induced an upregulation of FasL of 23%. rIL-2 and rIFN-gamma did not significantly affect FasL expression. To control whether our cytokine stimulation experiments were suitable to prove an upregulation of membrane proteins by tumor cells, we investigated the expression of ICAM-1, N-CAM, CD44s, CD44v6 and CD44v10. These adhesion molecules were spontaneously expressed by LS 174T cells. Only ICAM-1 and CD44v10 were significantly upregulated by rIFN-gamma and rTNF-alpha, respectively. These results could indicate that cytokines, released by tumor-infiltrating leukocytes, may induce the FasL-dependent apoptotic signal by which tumors downregulate an immunological host response.

Adenocarcinoma↗