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Biomedical subjects

P Lu

Publications and source records attributed to P Lu.

At least 109 records · Page 6Linked to original sources
PubMed1997

Heme-coordinating analogs of lauric acid as inhibitors of fatty acid omega-hydroxylation.

A series of omega-substituted fatty acids with potential heme-coordinating groups was synthesized as inhibitors of lauric acid omega-hydroxylation. The compounds were evaluated using liver microsomes from clofibrate (CF)-induced rats and an engineered expressed CYP4A1-derived fusion protein called f4A1. omega-Imidazolyl-decanoic acid (compound 11) and omega-aminolauric acid (compound 7) were potent Type II ligands and potent inhibitors of lauric acid omega-hydroxylation in both CF-microsomes and f4A1. Replacing their terminal amino or imidazolyl groups with other potential iron-binding groups such as omega-methylsulfinyl-, omega-cyano-, omega-azido-, or omega-formamido all greatly reduced their potency as inhibitors of omega-hydroxylation and their affinity for cytochrome P450 as measured by Ks values. In CF-microsomes, inhibition of (omega-1)-hydroxylation of lauric acid by a homologous series of omega-imidazolyl-alkanoic acids varied only 2-fold but in the same incubations inhibition of omega-hydroxylation increased 22-fold upon going from C-8 to C-12. A similar dependence of binding affinity and inhibitory potency on chain length was also seen in the f4A1 system. In contrast, chain length had little effect on activity among n-alkylamines or N-alkylimidazoles lacking a carboxyl or other polar functional group, suggesting that 7, 11, and related bifunctional compounds interact with CYP4A1 in CF-microsomes and with f4A1 in a specific bidentate fashion. Imidazoles containing phenyl, benzyl, or phenylethyl substituents at N-1 interact less strongly than related N-alkyl-imidazoles of similar carbon number and hydrophobicity, suggesting that the steric bulk and/or rigidity of the phenyl ring is not well accommodated in the active site.

Animals↗
PubMed1997

The function of costimulatory molecules and the development of IL-4-producing T cells.

The development of IL-4-producing effector T cells during a type 2 immune response requires signaling through B7 ligands, but probably not CD40 ligands. Here, William Gause and colleagues review the still controversial role of CD28 and CTLA-4 on T cells, and B7-1 and B7-2 on antigen-presenting cells, and provide a model to incorporate recent findings.

Abatacept↗
PubMed1997

Regulation of self-tolerance by CD80/CD86 interactions.

Antigen presentation by CD80/CD86-positive 'professional APCs' induces T-cell activation, whereas antigen presentation in the absence of sufficient CD80/CD86 costimulation may induce a form of tolerance. Blocking CD80/CD86 constimulation inhibits autoimmune disease progression in a variety of animal models, but whether these effects result from restoration of self-tolerance or temporary disease blockade is still unclear. The individual roles of CD80 and CD86 in autoimmune diseases are complicated by multiple factors in vivo. Data from B7 gene knockout mice further clarify the importance of CD80/CD86 in the regulation of T-cell activation and tolerance.

Animals↗
PubMed1997

Lac repressor-operator complex.

For many years the lac operon of Escherichia coli has been the paradigm for gene regulation. Recently, the structures of the lac repressor core bound to isopropyl-beta-D-1-thiogalactoside (IPTG), the intact apo lac repressor, the intact lac repressor complexes with IPTG and a 21-base-pair symmetric operator, and the refined headpiece of the repressor have been determined. These structures have provided a framework for understanding a wealth of biochemical and genetic information. An analysis of these structures, as well as a description of their function and a comparison to homologous proteins, is now possible.

Allosteric Regulation↗
PubMed1997

Lac repressor genetic map in real space.

Here, we present a graphic display of the phenotypes of more than 4000 single amino acid substitution mutations on the three-dimensional structure of the lac repressor tetramer bound to DNA. The genetic data and the X-ray diffraction studies contribute to define an allosteric mechanism and yield a visual demonstration of the importance of core or buried residues in protein structure.

Allosteric Site↗
PubMed1997

A New Mechanism for the Regulation of Stomatal Aperture Size in Intact Leaves (Accumulation of Mesophyll-Derived Sucrose in the Guard-Cell Wall of Vicia faba).

At various times after pulse-labeling broad bean (Vicia faba L.) leaflets with 14CO2, whole-leaf pieces and rinsed epidermal peels were harvested and subsequently processed for histochemical analysis. Cells dissected from whole leaf retained apoplastic contents, whereas those from rinsed peels contained only symplastic contents. Sucrose (Suc)-specific radioactivity peaked (111 GBq mol-1) in palisade cells at 20 min. In contrast, the 14C content and Sucspecific radioactivity were very low in guard cells for 20 min, implying little CO2 incorporation; both then peaked at 40 min. The guard-cell apoplast had a high maximum Suc-specific radioactivity (204 GBq mol-1) and a high Suc influx rate (0.05 pmol stoma-1 min-1). These and other comparisons implied the presence of (a) multiple Suc pools in mesophyll cells, (b) a localized mesophyll-apoplast region that exchanges with phloem and stomata, and (c) mesophyll-derived Suc in guard-cell walls sufficient to diminish stomatal opening by approximately 3 [mu]m. Factors expected to enhance Suc accumulation in guard-cell walls are (a) high transpiration rate, which closes stomata, and (b) high apoplastic Suc concentration, which is elevated when mesophyll Suc efflux exceeds translocation. Therefore, multiple physiological factors are integrated in the attenuation of stomatal aperture size by this previously unrecognized mechanism.

Journal Article↗
PubMed1997

[Preparation and clinical application of blocking glue for cancerous serosa].

The blocking glue of cancerous serosa (F-TH glue) is unharmful to human body. It has characteristics of shorter solidification time to become membrane, good elasticity and close adherence to tissue, mainly used for covering cancerous serosa in operation to prevent dropping of cancer cells. In this group, F-TH glue was used in 200 cases of gastrointestinal cancer, in which 75 had positive results of imprinting slice of cancerous serosa, and all became negative. It was confirmed that the glue adhered to cancerous serosa firmly and formed intact protective membrane. No rhagades and dropping of glue were seem by naked eye magnifying glass and electron microscope. The membrane of glue forbid cancer cells not penetrated. It was an excellent glue to block the cancerous serosa.

Cyanoacrylates↗
PubMed1997

[The study on three-dimensional laser scanning of dental model and computer aided set-up].

A new laser scanning and measurement method was introduced for dental model three-dimensional form. A laser diode was used as scanning light source, two CCDs (they were fixed specially) received the diffused light reflected from the dental model. The dental model rotating-moved back and forth, and horizontal moved from one side to another along horizontal axis simultaneously. Whole dental model can be scanned in 3 minutes, general precision was up to 0.03 mm. The computer can display distinctly three-dimensional images of dental model in different directions and give three-dimensional coordinate data, distance, angle, and remove teeth and make set-up after scanning. With advantages of high precision, fast speed and excellent object, the new method can be of an important applied value in orthodontic clinic.

Computer Simulation↗
PubMed1997

[Theoretical investigation of dynamic process in capillary column gas chromatographic system--effect of radial diffusion on elution profile].

Based on a mass balance equation, in this paper, the kinetic model of chromatography including influence of the radial diffusion on the mass transfer process is set up. Based on the hypothesis of Giddings, this model has been simplified. In this way, the expressions of the first moment, the second and the third central moment for this model are derived by Laplace transform in detail. The results show the radial diffusion affects not only the column efficiency, the peak spreading and the peak symmetry, but also the retention time.

English Abstract↗
PubMed1997

[Peak shape distribution rule of high performance liquid chromatography in the end of column under linear and nonideal conditions].

The central moments of chromatographic elution curve are important parameters for describing the column efficiency and chromatographic peak shape. According to the equation of chromatographic dynamics, we can get the second central moment and the third central moment of elution curve of HPLC under linear nonideal conditions. In our work, we investigated the relationships between second central moment, third central moment, coefficient of skewness of components distribution in the end of column and chromatographic column parameters, operation conditions, such as diameter of packing particle, desorption constant, diffusion coefficient in mobile phase, linear velocity of mobile phase, effect of extra column and so on. By means of computer, we discovered that there are no significant differences the second central moment, third central moment and coefficient of skewness for different components with different distribution coefficients. In the column end, therefore, different components have similar peak shape if there exist no obvious extra column effects. The column extra effect which stems from joint line and/or dead volume of detector is an important factor, causing column efficiency lower and peak shape tailing.

English Abstract↗
PubMed1996

Fluorescence emission of ethidium bromide intercalated in defined DNA duplexes: evaluation of hydrodynamics components.

The arrangement and stacking of noncovalently contiguous double-helical sections are increasingly invoked in single-stranded DNA and RNA tertiary structure. These tertiary structures of nucleic acids are defined by their double stranded regions, and their orientation in the molecular frame constitutes an important component of the nucleic acid structure. A direct view of these tertiary structures can be obtained by fluorescence polarization anisotropy of bound ethidium bromide (EB). The orientation of the dye in the molecular frame of the nucleic acid yields the orientation of the helix. The complete anisotropy function for EB intercalated in genome-derived DNA duplexes was derived by Allison and Schurr (1979) and accounts for base-pair twisting and DNA bending. Single-stranded ribozymes, ribosomal and transfer RNAs, and model DNA junctions contain double-stranded regions shorter than 35 bp in length, for which bending is not significant. We developed and experimentally verified an expression of the anisotropy function for short DNA duplexes which is theoretically compatible with the existing theory, originally developed for long nucleic acids (Schurr et al., 1992). Simulations showed that for DNA duplexes shorter than 35 bp, our expression of the anisotropy function is equivalent to Schurr's and is consistent with experiments carried out on eight DNA duplexes. Modeling the eight duplexes as cylinders, we calculate a duplex diameter of 1.91 +/- 0.15 nm when EB makes a 90 degrees angle with the DNA helix axis and undergoes anisotropic wobbling and 1.97 +/- 0.15 nm when EB makes a 70.5 degrees angle and undergoes isotropic wobbling, respectively. We used this treatment to establish the conformation of five DNA oligonucleotides made of single and tethered hairpins, some designed to exhibit coaxial stacking. Analysis of the fluorescence anisotropy decays shows that the tethered hairpins take an extended rather than parallel conformation. It also shows that the DNA oligonucleotides made of two tethered hairpins exhibit freedom compatible with two independent hairpins. When the linker between hairpins is shortened, the two hairpins are not independent anymore as probed by fluorescence anisotropy, suggesting coaxial stacking of the two helices.

Base Sequence↗
PubMed1996

Secondary structure content of the HDV ribozyme in 95% formamide.

The Hepatitis Delta Virus (HDV) ribozyme self-cleaving activity in 20 M formamide solutions is unique. Does this catalytic activity result from the conservation of its tertiary structure in 20 M formamide? We followed the ribozyme structure in formamide solutions by monitoring the amount of bound Ethidium Bromide (EB). We were able to measure the quantity of dye bound using time-resolved fluorescence spectroscopy, as an estimate of the ribozyme double helical content. This method, calibrated by using oligonucleotides with defined tertiary structure and denaturing solvents, parallels NMR and UV measurements as a function of temperature. Measurements with the HDV ribozyme lead to three conclusions: (a) both the precursor and product RNAs are structured to 24 M (95% w/w) formamide or 4 M H2O solutions which is equivalent to 4 M H2O; (b) the HDV ribozyme is the only RNA sequence investigated in this study that retains so much structure in formamide; and (c) DNA analogs of formamide resistant HDV ribozyme sequences lose their structure at less than 15 M formamide. Thus, the structural integrity of the HDV ribozyme is an intrinsic property of the RNA molecule and its sequence.

Base Sequence↗
PubMed1996

Secondary structure of the r(CUUCGG) tetraloop.

The oligonucleotide r(GGACUUCGGUCC) has been observed to adopt a hairpin conformation by solution NMR and a double helical conformation by X-ray diffraction. In order to understand this apparent conflict, we used time-resolved fluorescence depolarization and 19fluorine NMR to follow the secondary structure of this dodecamer as the solution composition was changed stepwise from the NMR experimental conditions to those used for crystallization. Calculation of the dodecamer concentration in the crystal (180 mM strands) and the cation concentration needed for neutrality (>2 M) prompted investigation of a tethered species, in which two dodecamers are connected by a string of 4 nt, geometrically equivalent to approximately 100 mM strands, in 2.5 M NaCl. The RNA tetraloop and its DNA analog maintain a single-strand hairpin conformation in solution, even under the conditions used to grow the crystal. Under high salt conditions, the tethered RNA and DNA analogs of this sequence yield secondary components which could be the double helical conformation. Crystal contacts in addition to solvent changes and high RNA concentrations are needed to obtain the double helix as the predominant species.

Chemical Phenomena↗
PubMed1996

Immunosuppression by YAC-1 lymphoma: role of shed gangliosides.

Shedding of gangliosides from tumor cells may regulate immune responses in cancer. A major mechanism of T-cell immunosuppression by gangliosides in vitro entails blocking of the interaction of interleukin-2 (IL-2) with its receptor; however, its involvement in immune suppression by gangliosides shed by tumor cells is not known. A model system was developed for assessing inhibition of IL-2-stimulated T-cell proliferation by components shed from murine YAC-1 lymphoma. Gangliosides shed by YAC-1 into the culture medium were present mainly in micellar form. YAC-1 supernatant suppressed both DNA synthesis and cellular growth in HT-2, while DNA synthesis in lymphokine-independent cell lines was unaffected. The immunosuppressive activity of YAC-1 supernatant was evident early in the IL-2 signaling pathway, and it had no permanent effect on proliferative capacity of the cells. Inhibition of DNA synthesis was reversed by high levels of IL-2, and YAC-1 supernatants blocked binding of [125I]IL-2 to high-affinity IL-2 receptors. Taken together, these data suggest that one mechanism by which ganglioside micelles shed from YAC-1 exert their immunosuppressive effects on T-cells involves blocking the IL-2/IL-2 receptor system.

Animals↗
PubMed1996

CD40-mediated stimulation contributes to lymphocyte proliferation, antibody production, eosinophilia, and mastocytosis during an in vivo type 2 response, but is not required for T cell IL-4 production.

CD40/CD40 ligand interactions are required for the development of T cell-dependent Ab responses in vivo. The role of these cell surface molecules in contributing to T cell cytokine production and the development of effector populations other than B cells and T cells is, however, less well defined. We have examined the in vivo effects of blocking CD40/CD40 ligand interactions on the type 2 mucosal immune response that follows oral inoculation of mice with the nematode parasite, Heligmosomoides polygyrus. Administration of anti-gp39 (CD40L) mAb (MR1) blocked H. polygyrus-induced elevations in serum IgG1 levels and inhibited elevations in blood eosinophils and mucosal mast cells at day 14 after inoculation. Anti-gp39 mAb markedly inhibited B cell blastogenesis 8 days after H. polygyrus inoculation but did not inhibit elevations in B cell class II MHC expression. Maximal elevations in B7-2 expression required signaling through both CD40 and the IL-4R. Elevations in T cell cytokine gene expression and elevations in the number of IL-4-secreting cells were unaffected by treatment with anti-gp39 mAb, although IL-4 production was inhibited by anti-IL-4R mAb. These results suggest that CD40/CD40L interactions are not required to activate T cells to produce cytokines but are required for the activation and proliferation of other effector cells associated with the type 2 response.

Animals↗
PubMed1996

Crystal structure of the lactose operon repressor and its complexes with DNA and inducer.

The lac operon of Escherichia coli is the paradigm for gene regulation. Its key component is the lac repressor, a product of the lacI gene. The three-dimensional structures of the intact lac repressor, the lac repressor bound to the gratuitous inducer isopropyl-beta-D-1-thiogalactoside (IPTG) and the lac repressor complexed with a 21-base pair symmetric operator DNA have been determined. These three structures show the conformation of the molecule in both the induced and repressed states and provide a framework for understanding a wealth of biochemical and genetic information. The DNA sequence of the lac operon has three lac repressor recognition sites in a stretch of 500 base pairs. The crystallographic structure of the complex with DNA suggests that the tetrameric repressor functions synergistically with catabolite gene activator protein (CAP) and participates in the quaternary formation of repression loops in which one tetrameric repressor interacts simultaneously with two sites on the genomic DNA.

Allosteric Regulation↗
PubMed1996

Safety of adenovirus-mediated transfer of the human cystic fibrosis transmembrane conductance regulator cDNA to the lungs of nonhuman primates.

To define the toxicity of cystic fibrosis transmembrane conductance regulator gene (CFTR) gene therapy with a replication-deficient recombinant adenovirus (Av1Cf2) in a nonhuman primate model, 10(10) plaque forming units (pfu) were instilled directly through a bronchoscope into the right lung of 5 macaques, and a lower dose of 4 x 10(6) pfu was administered to the right lung of 1 macaque. One sham-treated control received phosphate-buffered saline (PBS). The macaques were evaluated sequentially by clinical examination, vital signs, weight, hematology, blood chemistry, chest radiography, pulse oximetry, and bronchoalveolar lavage (BAL) at baseline and 3-28 days post-treatment. After the period of observation, macaques were sacrificed for autopsy and histological examination. The macaques tolerated the experimental therapy clinically with no changes in body temperature, oxygen saturation, heart rate, body weight, or blood pressure. However, 1 macaque with visible evidence of aspiration at the time of initial bronchoscopy developed tachypnea with right lower lobe (RLL) pneumonia on chest radiograph and by histology. There were no changes in Hgb, Wbc, BUN, plasma electrolytes, bilirubin, or hepatic transaminases. In the macaques that received 10(10) pfu, there was a progressive increase in the number of CD8+ lymphocytes in BAL that was maximal at 28 days. Histological examination of the treated lungs of the high-dose macaques at 3 days showed marked peribronchial and perivascular cuffing by inflammatory cells and alveolar accumulation of neutrophils and macrophages. The alveolitis appeared to be resolving at 28 days, although the perivascular and peribronchial aggregates of mononuclear cells were still present. In the high-dose macaques, BAL interleukin-8 (IL-8) was increased at all time points (256-388 pg/ml versus 1-84 pg/ml at baseline and in control), whereas IL-1 beta was increased only at days 21 and 28 (341-852 pg/ml versus 30-92 pg/ml at baseline and in control). There were no increases in BAL cell counts, IL-1 beta or IL-8, and histological changes were mild in the macaque that received 4 x 10(6) pfu. Evaluation for Av1Cf2-derived human CFTR expression using RS-PCR demonstrated expression at 3, 10, and 21, but not 28 days in macaques treated with 10(10) pfu of Av1Cf2. In situ hybridization analysis demonstrated human CFTR mRNA in the alveolar regions of the lobes that received the vector at 10 and 21 days. There was no evidence of expression after treatment with 4 x 10(6) pfu. This study showed that high-dose adenoviral vector administration to the lung achieved CFTR gene transfer and expression but was associated with increased concentrations of cytokines in BAL and alveolar inflammation. A low dose, equivalent to the maximum clinical dose currently proposed for phase I trials in human subjects, was not associated with cellular or cytokine evidence of inflammation, and histological abnormalities were mild.

Adenoviridae↗