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Biomedical subjects

L Tang

Publications and source records attributed to L Tang.

At least 91 records · Page 5Linked to original sources
PubMed2000

[Effects of IFN-alpha combined with IL-6 on cell growth and related genes expression and apoptosis of bone marrow cells from CGL patients].

OBJECTIVE: To investigate the effects of interferon-alpha (IFN-alpha) and IFN-alpha combined with interleukin-6 (IL-6) on cell growth and bcr/abl, bcl-2 and c-myc genes expression in the bone marrow mononuclear cells (MNC) from chronic granulocytic leukemia (CGL) patients. METHODS: MNCs were cultured in liquid medium at the presence of IFN-alpha (200 U/ml) or IFN-alpha (200 U/ml) plus IL-6 (100 ng/ml). The viable cells were counted and the expression levels of beta-actin, bcr/abl, bcl-2 and c-myc genes were quantitatively detected by reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: The cell growth was markedly inhibited by IFN-alpha, but the extent of the inhibition was slightly decreased when IFN-alpha combined with IL-6. The expression levels of bcr/abl and bcl-2 gene were reduced by IFN-alpha or IFN-alpha plus IL-6. The expression of c-myc gene was inhibited by IFN-alpha but promoted by IL-6. CONCLUSIONS: Both IFN-alpha and IFN-alpha plus IL-6 can inhibit the expression of anti-apoptosis genes, and modulate the expression of c-myc. It is the possible mechanism of IFN-alpha therapy for CGL in chronic phase.

Adolescent↗
PubMed2000

[Three-dimensional finite element stress analysis of supporting bone of mandibular posterior fixed bridge. Part III. Comparative analysis with stress of the cortical bone beneath different pontics of fixed bridge].

OBJECTIVE: To analysis stress of the cortical bone beneath different pontics of mandibular posterior fixed bridge by using three-dimentional finite element method. METHODS: According to the measured data, the characters of all components of fixed bridge and the supporting tissues, and the principals of finite element, the three-dimentional finite element model was developed on the basis of an adult mandible. The model consisted of 1363 nodes and 1134 elements after the fixed bridge was placed. Three different pontics were designed. Young's mudulus and Poisson's ratio were obtained from the literature for each type of tissue or materials in the model. The surfaces of pontic next to the mucosa beneath the pontic consisted of nine elements and the contact area were respectively reduced 1/3. It was assumed all materials in the model were homogeneous, isotropic and linearly elastic. One vertical load of 20 kg and one horizontal load of 20 kg were applied respectively on the occlusal surface of the abutments and the pontics of three different fixed bridge. Three-dimentional finite element stress analysis was used to calculate the epsilon max and the epsilon min of the cortical bone beneath pontics of fixed bridge. RESULTS: Under the vertical loading, the cortical bone beneath the pontics appeared compressive stresses, the stress values of the cortical bone beneath the pontics were respectively -0.211(-)-0.119 (epsilon max, kg/mm2), -0.355(-)-0.201 (epsilon min), -0.224(-)-0.125 (epsilon max), -0.375(-)-0.215 (epsilon min), -0.239(-)-0.133 (epsilon max), -0.395(-)-0.228 (epsilon min). Under the horizontal loading, the cortical bone beneath the pontics exhibited tensile stresses and compressive stresses. The stress values of the cortical bone beneath the pontics were respectively -0.004-0.283 (epsilon max, kg/mm2), -0.249(-)-0.009 (epsilon min), -0.0042-0.301 (epsilon max), -0.264(-)-0.0095 (epsilon min), -0.0045-0.322 (epsilon max), -0.281(-)-0.0101 (epsilon min). The stress in the cortical bone beneath the pontics increased when the area of contact was reduced, the stress values changed in 5%-7%, but the rules of stress distribution of three different pontics were similar. CONCLUSION: Stress values in the cortical bone beneath three pontics are small, and the change of stress in the cortical bone beneath the different pontics of mandibular posterior fixed bridge is small too.

Dental Abutments↗
PubMed2000

[Uptake of drug-containing nanoparticles in dog catotid and femoral arteries].

OBJECTIVE: To study the uptake of drug-containing nanoparticles in artery for local therapy of restenosis. METHODS: Polylactic polyglycolic acid copolymer (PLGA) nanoparticles containing an antiproliferative agent 2-amino-chromone were formulated with an oil-in-water sonication emulsion/solvent evaporation technique. Arterial uptake of nanoparticles was assessed both in vitro and in vivo models of dog and rat carotid and femoral arteries. Epoxide, cyanoacrylate, fibrinogen, fibronectin, didodecyldimethylammonium bromide (DMAB), L-alpha-phosphatidylethanolaine, and lipofectin were selected to modify the surface of nanoparticles to enhance arterial uptake of nanoparticles. RESULTS: The nanoparticle size ranged from 100 nm to 200 nm, the drug loading in nanoparticles was about 15%, the nanoparticle morphology was observed by scanning electron microscopy and showed spherical shape with smooth surface. Arterial uptake of nanoparticles was enhanced greatly by surface modified nanoparticle with positively charged active agent DMAB. Once nanoparticles located in artery, a high drug level could be maintained at local site for 2 days in vivo model. CONCLUSION: The primary results of animal experiments suggested that nanoparticle could be used as drug carrier of local drug delivery for treating cardiovascular diseases.

Animals↗
PubMed1999

The crystal structure of a T cell receptor in complex with peptide and MHC class II.

The crystal structure of a complex involving the D10 T cell receptor (TCR), 16-residue foreign peptide antigen, and the I-Ak self major histocompatibility complex (MHC) class II molecule is reported at 3.2 angstrom resolution. The D10 TCR is oriented in an orthogonal mode relative to its peptide-MHC (pMHC) ligand, necessitated by the amino-terminal extension of peptide residues projecting from the MHC class II antigen-binding groove as part of a mini beta sheet. Consequently, the disposition of D10 complementarity-determining region loops is altered relative to that of most pMHCI-specific TCRs; the latter TCRs assume a diagonal orientation, although with substantial variability. Peptide recognition, which involves P-1 to P8 residues, is dominated by the Valpha domain, which also binds to the class II MHC beta1 helix. That docking is limited to one segment of MHC-bound peptide offers an explanation for epitope recognition and altered peptide ligand effects, suggests a structural basis for alloreactivity, and illustrates how bacterial superantigens can span the TCR-pMHCII surface.

Animals↗
PubMed1999

Crystal structure of the nuclear matrix targeting signal of the transcription factor acute myelogenous leukemia-1/polyoma enhancer-binding protein 2alphaB/core binding factor alpha2.

Transcription factors of the acute myelogenous leukemia (AML)/polyoma enhancer-binding protein (PEBP2alpha)/core-binding factor alpha (CBFA) class are key transactivators of tissue-specific genes of the hematopoietic and bone lineages. AML-1/PEBP2alphaB/CBFA2 proteins participating in transcription are associated with the nuclear matrix. This association is solely dependent on a highly conserved C-terminal protein segment, designated the nuclear matrix targeting signal (NMTS). The NMTS of AML-1 is physically distinct from the nuclear localization signal, operates autonomously, and supports transactivation. Our data indicate that the related AML-3 and AML-2 proteins are also targeted to the nuclear matrix in situ by analogous C-terminal domains. Here we report the first crystal structure of an NMTS in an AML-1 segment fused to glutathione S-transferase. The model of the NMTS consists of two loops connected by a flexible U-shaped peptide chain.

Amino Acid Sequence↗
PubMed1999

Structural consequences of the B5 histidine --> tyrosine mutation in human insulin characterized by X-ray crystallography and conformational analysis.

The addition of phenols to hexameric insulin solutions produces a particularly stable hexamer, resulting from a rearrangement in which residues B1-B8 change from an extended conformation (T-state) to form an alpha-helix (R-state). The R-state is, in part, stabilized by nonpolar interactions between the phenolic molecule and residue B5 His at the dimer-dimer interface. The B5 His --> Tyr mutant human insulin was constructed to see if the tyrosine side chain would mimic the effect of phenol binding in the hexamer and induce the R-state. In partial support of this hypothesis, the molecule crystallized as a half-helical hexamer (T(3)R(3)) in conditions that conventionally promote the fully nonhelical (T6) form. As expected, in the presence of phenol or resorcinol, the B5 Tyr hexamers adopt the fully helical (R6) conformation. Molecular modeling calculations were performed to investigate the conformational preference of the T-state B5 Tyr side chain in the T(3)R(3) form, this side chain being associated with structural perturbations of the A7-A10 loop in an adjacent hexamer. For an isolated dimer, several different orientations of the side chain were found, which were close in energy and readily interconvertible. In the crystal environment only one of these conformations remains low in energy; this conformation corresponds to that observed in the crystal structure. This suggests that packing constraints around residue B5 Tyr result in the observed structural rearrangements. Thus, rather than promoting the R-state in a manner analogous to phenol, the mutation appears to destabilize the T-state. These studies highlight the role of B5 His in determining hexamer conformation and in mediating crystal packing interactions, properties that are likely be important in vivo.

Amino Acid Substitution↗
PubMed1999

Direct evidence that the rifamycin polyketide synthase assembles polyketide chains processively.

The assembly of the polyketide backbone of rifamycin B on the type I rifamycin polyketide synthase (PKS), encoded by the rifA-rifE genes, is terminated by the product of the rifF gene, an amide synthase that releases the completed undecaketide as its macrocyclic lactam. Inactivation of rifF gives a rifamycin B nonproducing mutant that still accumulates a series of linear polyketides ranging from the tetra- to a decaketide, also detected in the wild type, demonstrating that the PKS operates in a processive manner. Disruptions of the rifD module 8 and rifE module 9 and module 10 genes also result in accumulation of such linear polyketides as a consequence of premature termination of polyketide assembly. Whereas the tetraketide carries an unmodified aromatic chromophore, the penta- through decaketides have undergone oxidative cyclization to the naphthoquinone, suggesting that this modification occurs during, not after, PKS assembly. The structure of one of the accumulated compounds together with (18)O experiments suggests that this oxidative cyclization produces an 8-hydroxy-7, 8-dihydronaphthoquinone structure that, after the stage of proansamycin X, is dehydrogenated to an 8-hydroxynaphthoquinone.

Actinomycetales↗
PubMed1999

Anti-inflammatory properties of triblock siloxane copolymer-blended materials.

Implantable biomaterials often trigger a variety of adverse responses. Because polydimethyl siloxane surfaces have good hemo- and bio-compatibility, it is generally believed that surface biocompatibility may be improved by modifying biomaterial surfaces with silicone-like properties. For this, we developed a series of polycaprolactone-polydimethylsiloxane-polycaprolactone (PDMS-PCL) copolymers. By mixing the substrate material--polyvinyl chloride--with low concentrations (1.2 and 2.4%) of the PDMS-PCL copolymer, we generated materials with silicone-like surface properties as reflected by increased surface silicon content and surface contact angles. We assessed the biocompatibility of these surfaces in vitro and found that the addition of PDMS-PCL significantly reduced the percentages of surface-'denatured' fibrinogen, a critical element of genesis of many adverse responses to implanted biomaterials. Indeed, using an animal implantation model, we find that PDMS-PCL-blended materials triggered significantly weaker inflammatory responses than did polyvinyl chloride, the substrate control. The results from these experiments suggest that the use of PDMS-PCL additives (2.4%) in polymer blends is a useful means of camouflaging the substrate surface properties and improving the biocompatibility of biomaterials.

Adsorption↗
PubMed1999

Genetic engineering of stent grafts with a highly efficient pseudotyped retroviral vector.

PURPOSE: The purpose of this study was first to compare the gene transfer efficiency of amphotrophic murine leukemia viral vector (ampho-MuLV) with the efficiency of MuLV pseudotyped with the vesicular stomatitis virus G glycoprotein (VSVG-MuLV) in tissue of vascular origin. The second purpose of this study was to determine cell retention after the implantation of genetically engineered stent grafts. METHODS: Gene transfer efficiency was ascertained with the b-galactosidase assay. The target tissues included endothelial cells (ECs), smooth muscle cells (SMCs), and human saphenous veins (HSVs). Polyurethane stent grafts were suffused with lac Z-transduced ECs and SMCs that were harvested from porcine jugular vein. The grafts were implanted into the iliac artery of each pig whose jugular vein had been harvested. Cell retention was analyzed at 1 and 4 weeks with X-Gal staining. RESULTS: VSVG-MuLV transduction efficiency exceeded that of ampho-MuLV in human ECs (VSVG-MuLV, n = 24, 89% +/- 6%; ampho-MuLV, n = 18, 14% +/- 6%; P <. 001), human SMCs (VSVG-MuLV, n = 5, 92% +/- 3%; ampho-MuLV, n = 4, 17% +/- 2%; P <.001), pig ECs (VSVG-MuLV, n = 4, 81% +/- 2%; ampho-MuLV, n = 4, 13% +/- 3%; P <.001), and pig SMCs (VSVG-MuLV, n = 5, 89% +/- 3%; ampho-MuLV, n = 4, 16% +/- 1%; P <.001). As much as a 10-fold higher transduction efficiency was observed with VSVG-MuLV in HSVs. After the stent graft implantation, the engineered cells were retained and proliferated on the stent membrane, with ingrowth into the underlying intima. CONCLUSION: VSVG-MuLV significantly increased the gene transfer efficiency in vascular SMCs and ECs and in organ-cultured HSVs. The cells were retained and proliferated on stent grafts for the short term in the pig.

Animals↗
PubMed1999

Elucidating the mechanism of chain termination switching in the picromycin/methymycin polyketide synthase.

BACKGROUND: A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates. RESULTS: The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones. CONCLUSIONS: These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.

Amino Acid Sequence↗
PubMed1999

High efficiency in vitro gene transfer into vascular tissues using a pseudotyped retroviral vector without pseudotransduction.

Murine leukemia virus (MuLV)-derived retroviral vectors have had limited application in vascular gene therapy because of low transduction efficiency of vascular tissues, both in vitro and in vivo. In this study, we compared the gene transfer efficiency of two retroviral vectors: amphotropic MuLV and a MuLV vector pseudotyped with the vesicular stomatitis virus G glycoprotein (VSV-G) envelope. Target vascular tissues included human endothelial cells (EC), smooth muscle cells (SMC) and saphenous veins (SV). Transduction efficiency of human EC and SMC was significantly higher for VSV-G pseudotyped MuLV vector (90%) than for Amphotropic MuLV (20%). Luminal surface en face analysis of transduced cultured SV showed a six- to 10-fold greater transduction efficiency with VSV-G pseudotyped MuLV. The tissue plasminogen activator (tPA) gene was transduced into EC using each vector. Four days following transduction, a 12-fold higher tPA antigen concentration and a 38-fold higher tPA enzymatic activity was measured from cells transduced with the VSV-G pseudotyped vectors as compared with the amphotropic MuLV. There was no detectable pseudotransduction (protein transfer) associated with the VSV-G MuLV vector. Both AZT inhibition of reverse transcriptase and cell division arrest by gamma irradiation inhibited transduction, indicating that viral transduction correlated with RNA reverse transcription and cell proliferation. MuLV pseudotyped with the VSV-G envelope glycoprotein is an effective retroviral vector for vascular gene therapy.

Cell Division↗
PubMed1999

Induction of apoptosis and differentiation by fludarabine in human leukemia cells (U937): interactions with the macrocyclic lactone bryostatin 1.

We have examined interactions between the purine nucleoside analog fludarabine (9-beta-arabinofuranosyl-2-fluoroadenine) and the macrocyclic lactone bryostatin 1 in the human monocytic leukemic cell line U937. Fludarabine exerted dose-dependent effects on U937 cell viability and growth which were associated with both induction of apoptosis, as well as cellular maturation. Incubation of cells with bryostatin 1 (10 nM; 24 h) after, but not before a 6-h exposure to 10 microM fludarabine resulted in a modest but significant increase in apoptosis, and was associated with greater than a 1 log reduction in clonogenicity. Subsequent exposure to bryostatin 1 also increased the percentage of fludarabine-treated cells displaying differentiation-related features (eg plastic adherence, CD11b positivity) compared to cells exposed to fludarabine alone. Bryostatin 1 did not increase the retention of the active fludarabine metabolite, F-ara-ATP, nor did it increase 3H-F-ara-A incorporation into DNA. Despite its capacity to trigger cellular maturation, fludarabine exposure (either with or without bryostatin 1) failed to induce the cyclin-dependent kinase inhibitors (CDKls) p21WAF1/CIP1 and p27KIP1. Nevertheless, dysregulation of p21 (resulting from stable transfection of cells with a p2lWAF1/CIP1 antisense construct) reduced fludarabine-mediated differentiation, while inducing a corresponding increase in apoptosis. Enforced expression of Bcl-2 partially protected cells from fludarabine-related apoptosis, an effect that was overcome, in part, by subsequent exposure of cells to bryostatin 1. Interestingly, Bcl-2-overexpressing cells were as or in some cases, more susceptible to differentiation induction by fludarabine (+/- bryostatin 1) than their empty vector-containing counterparts. Collectively, these results indicate that the antiproliferative effects of fludarabine toward U937 leukemic cells involve both induction of apoptosis and cellular maturation, and that each of these processes may be enhanced by bryostatin 1.

Antineoplastic Agents↗
PubMed1999

Drug release from film-coated chlorpheniramine maleate nonpareil beads: water influx and development of a new drug release model.

The purpose of this work was to investigate drug release from film-coated chlorpheniramine maleate (CPM) nonpareils (sugar spheres) and the effect of water influx on the drug release mechanism. The methods used in the study involved the layering of CPM onto nonpareil cores using a fluid-bed apparatus. These CPM cores were then coated with an aqueous ethylcellulose dispersion, which was blended with a solution of hydroxylpropylmethylcellulose (HPMC) at different concentrations. The net water influx was determined by measuring water uptake during dissolution. The film surface area was calculated from bead diameters measured with an optical microscope. Drug release profiles were measured using USP dissolution method I (basket). The results showed that significant water influx occurred, which produced an internal liquid phase ranging from 0 to 1.8 x 10(3) mm3/g of sample. As a result of the water uptake, an increase in bead size was observed. The bead surface area varied over the range of 40-80 x 10(3) mm2/g sample because of a combined effect of the water uptake and the release of the bead contents. A bead geometry parameter was proposed as the ratio of the bead surface area to the volume of the internal liquid phase. This bead geometry parameter was measured as a function of time and fit to an equation using a computer curve-fitting technique. This equation was substituted into an existing drug release model to give a more appropriate mathematical model describing drug release from this system. The conclusion drawn from these results is that the influx of water during drug dissolution creates a progressive increase in the liquid phase within the nonpareil bead; this causes a corresponding increase in the bead surface area which influences the drug release rate.

Algorithms↗
PubMed1999

Expression of cell cycle regulators in human cutaneous malignant melanoma.

We postulate that genes involved in the control of cell proliferation are important determinants of melanoma growth and/or transformation. Using Western blot analysis, we compared the expression of nine key cell cycle regulators in metastatic melanomas with that in benign acquired naevi. Among the cyclin-dependent kinases (CDKs) examined, CDK2 was consistently and significantly overexpressed (three- to eight-fold) in metastatic melanomas compared with naevi. CDK1 and CDK4 exhibited no significant difference in expression between benign naevi and metastatic melanomas. CDK6 expression was variable, with four out of 10 metastatic melanomas showing higher expression than naevi. All the cyclins examined, especially cyclins A and D, were expressed more in metastatic melanomas than in naevi. Cyclin E was not detected in benign naevi, but was easily detectable in most of the metastatic melanomas. In addition, there was significantly greater expression of CDC25A, a tyrosine phosphatase that activates CDK kinases, in the metastatic melanomas. Over-expression of CDK2, CDK6, CDC25A and cyclin A was confirmed in melanoma cell lines. These cell cycle regulators may play an important role in melanoma growth and/or transformation.

Blotting, Western↗
PubMed1999

Crystallization and preliminary X-ray analysis of human muscle creatine kinase.

Creatine kinase is a key enzyme in the energy homeostasis of cells and tissues with high and fluctuating energy demands. Human muscle MM creatine kinase is a dimeric protein with a molecular weight of approximately 43 kDa for each subunit. It has been crystallized by the hanging-drop vapor-diffusion method using 2-methyl-2, 4-pentanediol as precipitant. The crystals belong to the enantiomorphous space group P6222 or P6422 with cell parameters of a = b = 89.11 and c = 403.97 A. The asymmetric unit of the crystal contains two subunits. A data set at 3.3 A resolution has been collected using synchrotron radiation.

Creatine Kinase↗
PubMed1999

Structure of agkistrodotoxin in an orthorhombic crystal form with six molecules per asymmetric unit.

The structure of agkistrodotoxin crystallized under basic conditions has been determined at 2.8 A resolution by the molecular-replacement technique and refined to a crystallographic R factor of 0.194 and a free R factor of 0.260 with good stereochemistry. The molecular packing in the crystal differs from other PLA(2)s. The six molecules in the asymmetric unit form three dimers linked by Ca(2+) ions in a near-perfect six-ligand octahedral coordinating system. Extensive intermolecular hydrophobic interactions occur at the interfacial recognition site of each neurotoxin molecule, which provides an insight into phospholipase A(2)-membrane interactions. This hydrophobic interaction-induced molecular association along the interfacial recognition site suggests a self-protection mechanism of agkistrodotoxin.

Agkistrodon↗
PubMed1999

Proton nuclear magnetic resonance measurement of p-boronophenylalanine (BPA): a therapeutic agent for boron neutron capture therapy.

Noninvasive in vivo quantitation of boron is necessary for obtaining pharmacokinetic data on candidate boronated delivery agents developed for boron neutron capture therapy (BNCT). Such data, in turn, would facilitate the optimization of the temporal sequence of boronated drug infusion and neutron irradiation. Current approaches to obtaining such pharmacokinetic data include: positron emission tomography employing F-18 labeled boronated delivery agents (e.g., p-boronophenylalanine), ex vivo neutron activation analysis of blood (and very occasionally tissue) samples, and nuclear magnetic resonance (NMR) techniques. In general, NMR approaches have been hindered by very poor signal to noise achieved due to the large quadrupole moments of B-10 and B-11 and (in the case of B-10) very low gyromagnetic ratio, combined with low physiological concentrations of these isotopes under clinical conditions. This preliminary study examines the feasibility of proton NMR spectroscopy for such applications. We have utilized proton NMR spectroscopy to investigate the detectability of p-boronophenylalanine fructose (BPA-f) at typical physiological concentrations encountered in BNCT. BPA-f is one of the two boron delivery agents currently undergoing clinical phase-I/II trials in the U.S., Japan, and Europe. This study includes high-resolution 1H spectroscopic characterization of BPA-f to identify useful spectral features for purposes of detection and quantification. The study examines potential interferences, demonstrates a linear NMR signal response with concentration, and presents BPA NMR spectra in ex vivo blood samples and in vivo brain tissues.

Boron Compounds↗