Biomedical subjects

B He

Publications and source records attributed to B He.

At least 145 records · Page 8Linked to original sources

PubMed1998

Fabrication of nanocolumns for liquid chromatography.

This paper shows that in situ micromachining can be used to simultaneously position and define (i) support particles, (ii) convective transport channels, (iii) an inlet distribution network of channels, and (iv) outlet channels in multiple chromatography columns on a single quartz wafer to the level of a few tenths of a micrometer. Stationary phases were bonded to 5 x 5 x 10 microns collocated monolith support structures separated by rectangular channels 1.5 microns wide and 10 microns deep with a low degree of deviation of channel width between the top and bottom of channels. High aspect ratio microfabrication can only be achieved with deep reactive ion etching. The volume of a 150 microns x 4.5 cm column was 18 nL. Column efficiency was evaluated in the capillary electrochromatography (CEC) mode using rhodamine 123 and a hydrocarbon stationary phase. Plate heights in these columns were typically 0.6 micron in the nonretained and 1.3 microns in the retained modes of operation. Columns were designed to have identical mobile-phase velocity in all channels in an effort to minimize outgassing during operation. When the total lateral cross-sectional area of channels at all points along the separation axis is identical, linear velocity of the mobile phase in a CEC column should be the same. Columns were operated at atmospheric pressure.

Chromatography, Liquid↗

PubMed1998

Microfabricated liquid chromatography columns based on collocated monolith support structures.

There is great interest today in massively parallel analytical strategies as a way to accelerate the rate of discovery in biological research; among them being 'biochips' and 'laboratories-on-a-chip'. The concept in the 'chip' approach is that minaturization will allow large numbers of operations to be performed in parallel in a small space, as in electronics. Proceeding with the semiconductor analogy, this paper demonstrates that in situ micromachining can be used to simultaneously fabricate millions of micrometer size, particle like structures in multiple liquid chromatography columns on a single wafer. Reduction of this widely used bioanalytical tool to the nanoliter volume, parallel processing, chip format is a significant step toward laboratories-on-a-chip.

Chemistry Techniques, Analytical↗

PubMed1998

Calculation of concentrations of equilibrium components in an in vitro activity test of vancomycin antibiotics and the possible mode of action.

The vancomycin group of antibiotics is considered to act by binding the bacterial cell wall mucopeptide precursor terminating in -L-Lys-D-Ala-D-Ala. The dimerization of these antibiotics is also believed to play a role in the action. In this paper, we analyzed the equilibria in the in vitro antibacterial activity test of the vancomycin antibiotics both with and without the cell wall precursor analogue di-acetyl-L-Lys-D-Ala-D-Ala (DALAA). Based on the equilibria and concentration balance, we obtained 10 equations (seven quadratic equations and three linear equations) containing 10 equilibrium concentrations which relate to the antibiotic, cell wall precursor and DALAA. A computer program was written to solve these equations from known dimerization constant and the binding constants (both monomer and dimer) with DALAA of the antibiotic. The concentrations in the test for vancomycin and eremomycin were obtained. The antibiotic activity of these antibiotics may be quantitatively correlated with their dimerization constants and the binding constants through the calculation. By analyzing the calculated results, we concluded that the cell wall-bound dimer may be the major contributor to the antibiotic activity in the case of eremomycin, while the cell wall-bound monomer is possibly the determinant for the activity of vancomycin.

Anti-Bacterial Agents↗

PubMed1998

The gamma134.5 protein of herpes simplex virus 1 has the structural and functional attributes of a protein phosphatase 1 regulatory subunit and is present in a high molecular weight complex with the enzyme in infected cells.

The carboxyl-terminal domain of the gamma134.5 protein of the herpes simplex virus 1 binds to protein phosphatase 1alpha (PP1) and is required to prevent the shut-off of protein synthesis resulting from phosphorylation of the alpha subunit of eIF-2 by the double-stranded RNA-activated protein kinase. The corresponding domain of the conserved GADD34 protein homologous to gamma134.5 functionally substitutes for gamma134.5. This report shows that gamma134.5 and PP1 form a complex in the infected cells, that fractions containing this complex specifically dephosphorylate eIF-2alpha, and that both gamma134.5 and GADD34 proteins contain the amino acid sequence motif common to subunits of PP1 that is required for binding to the PP1 catalytic subunit. An oligopeptide containing this motif competes with gamma134.5 for binding to PP1. Substitution of Val193 and Phe195 in the PP1-binding motif abolished activity. These results suggest that the carboxyl-terminal domain of gamma134.5 protein has the structural and functional attributes of a subunit of PP1 specific for eIF-2alpha, that it has evolved to preclude shut-off of protein synthesis, and that GADD34 may have a similar function.

Amino Acid Sequence↗

PubMed1998

Characterization of an unusual, sequence-specific termination signal for T7 RNA polymerase.

We have characterized an unusual type of termination signal for T7 RNA polymerase that requires a conserved 7-base pair sequence in the DNA (ATCTGTT in the non-template strand). Each of the nucleotides within this sequence is critical for function, as any substitutions abolish termination. The primary site of termination occurs 7 nucleotides downstream from this sequence but is context-independent (that is, the sequence around the site of termination, and in particular the nucleotide at the site of termination, need not be conserved). Termination requires the presence of the conserved sequence and its complement in duplex DNA and is abolished or diminished if the signal is placed downstream of regions in which the non-template strand is missing or mismatched. Under the latter conditions, much of the RNA product remains associated with the template. The latter results suggest that proper resolution of the transcription bubble at its trailing edge and/or displacement of the RNA product are required for termination at this class of signal.

Base Sequence↗

PubMed1998

Pausing and termination by bacteriophage T7 RNA polymerase.

Two types of sites are known to cause pausing and/or termination by bacteriophage T7 RNA polymerase (RNAP). Termination at class I sites (typified by the signal found in the late region of T7 DNA, TPhi) involves the formation of a stable stem-loop structure in the nascent RNA ahead of the point of termination, and results in termination near runs of U. Class II sites, typified by a signal first identified in the cloned human preproparathyroid hormone (PTH) gene, generate no evident structure in the RNA but contain a conserved sequence ahead of the point of termination, and also contain runs of U. Termination at class I and class II sites may involve non-equivalent mechanisms, as mutants of T7 RNA polymerase have been identified that fail to recognize class II sites yet continue to recognize class I sites. In this work, we have analyzed pausing and termination at several class II sites, and variants of them. We conclude that the 7 bp sequence ATCTGTT (5' to 3' in the non-template strand) causes transcribing T7 or T3 RNA polymerase to pause. Termination 6 to 8 bp past this sequence is favored by the presence of runs of U, perhaps because they destabilize an RNA:DNA hybrid. The effects of T7 lysozyme on pausing and termination are consistent with the idea that termination involves a reversion of the polymerase from the elongation to the initiation conformation, and that lysozyme inhibits the return to the elongation conformation. A kinetic model of pausing and termination is presented that provides a consistent interpretation of our results.

Bacteriophage T7↗

PubMed1998

Linkage and association analysis of genes encoding cytokines and myelin proteins in multiple sclerosis.

Several genetic factors are likely to play a role in the etiology of multiple sclerosis (MS). We used a candidate gene strategy in a study of polymorphic markers within or close to genes encoding cytokines (interferon-gamma (IFN-gamma), interleukin-2 (IL-2), IL-4, IL-4 receptor (IL-4R), IL-10, transforming growth factor-beta1 and -beta2) and myelin proteins (2',3'-cyclic-nucleotide 3'-phosphohydrolase (CNP:ase), myelin associated glycoprotein, oligodendrocyte myelin glycoprotein, proteolipid protein) in 34 Swedish multiplex MS families and in 147 sporadic MS patients and 95 healthy controls. No evidence for linkage was observed in two-point linkage analysis. However, a slightly positive LOD score of 0.88 (theta = 0.01) for IFN-gamma was found. Affected pedigree member (APM) analysis indicated a possible linkage with TGF-beta2 (p = 0.008) and IL-4R (p = 0.043). None of the cytokine markers were associated with MS in case-control analysis. Our results suggest a possible importance of the TGF-beta2, IL-4R and IFN-gamma genes in MS.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1998

Promoter specificity determinants of T7 RNA polymerase.

The high specificity of T7 RNA polymerase (RNAP) for its promoter sequence is mediated, in part, by a specificity loop (residues 742-773) that projects into the DNA binding cleft (1). Previous work demonstrated a role for the amino acid residue at position 748 (N748) in this loop in discrimination of the base pairs (bp) at positions -10 and -11 (2). A comparison of the sequences of other phage RNAPs and their promoters suggested additional contacts that might be important in promoter recognition. We have found that changing the amino acid residue at position 758 in T7 RNAP results in an enzyme with altered specificity for the bp at position -8. The identification of two amino acid:base pair contacts (i.e., N748 with the bp at -10 and -11, and Q758 with the bp at -8) provides information concerning the disposition of the specificity loop relative to the upstream region of the promoter. The results suggest that substantial rearrangements of the loop (and/or the DNA) are likely to be required to allow these amino acids to interact with their cognate base pairs during promoter recognition.

Amino Acid Sequence↗

PubMed1998

Neuropeptide Y antibody attenuates 2-deoxy-D-glucose induced feeding in rats.

2-deoxy-D-glucose (2-DG) has been shown to induce increased feeding responses in animals. Recent studies suggest the possible involvement of neuropeptide Y (NPY) in 2-DG-induced feeding. The present study examined the effect of immunoneutralization of endogenous NPY on 2-DG-induced feeding. NPY antibody injected into the paraventricular nucleus of the rats significantly attenuated 2-DG-induced feeding, suggesting that hypothalamic NPY may mediate, at least partly, the effect of 2-DG on food intake.

Animals↗

PubMed1998

Differential requirements for CD28 and CD40 ligand in the induction of experimental autoimmune myasthenia gravis.

The interactions of CD28-B7 and CD40-CD40 ligand (CD40L) pathways in T cell costimulation and autoimmune disease are incompletely understood. We sought to address this issue by investigation of the genesis of acetylcholine receptor (AChR)-induced antibody-mediated experimental autoimmune myasthenia gravis (EAMG) in CD28- and CD40L-deficient mice (CD28-/-, CD40L-/-). Compared to wild-type mice, the CD28-/- mice became less susceptible, and CD40L-/- mice were completely resistant to EAMG induction. Analysis of T helper functions, reflected by cytokine responses, revealed a switch to a Th1 profile in CD28-/- mice. Consistently, levels of serum AChR-specific antibodies of the IgG1 isotype were decreased in CD28-/- mice. In the CD40L-/- mice, both Th1 and Th2 cytokine responses were diminished, and T cell-dependent AChR-reactive B cell responses were more severely impaired than in the CD28-/- mice. Thus, CD28 and CD40L are differentially required for induction of EAMG.

Amino Acid Sequence↗

PubMed1998

Treatment of intracranial gliomas in immunocompetent mice using herpes simplex viruses that express murine interleukins.

This report describes a test of the hypothesis that the oncolytic effect of genetically engineered, replication competent herpes simplex viruses (HSV) depends both on cell destruction by the virus and an immune response to the tumor cells induced in an immunocompetent animal system. The oncolytic vector was a HSV recombinant virus in which both copies of the gamma 1 34.5 gene were replaced with the murine genes encoding the cytokine interleukin-4 (IL-4) or interleukin-10 (IL-10). The hypothesis predicted that if an immune response plays a role in survival following intratumoral treatment of tumor-bearing animals with HSV, expression of IL-4 should prolong survival whereas expression of IL-10 should reduce it. The results are that (1) these cytokines can be expressed by HSV in productively infected cells both in vitro and in vivo; (2) HSV-expressing IL-4 or IL-10 genes were able to infect and destroy glioma cells in vitro; (3) intracerebral inoculation of HSV expressing either IL-4 or IL-10 into syngeneic murine glioma GL-261 cells implanted in the brains of immunocompetent C57BL/6 mice produced dramatically opposite physiologic responses. The IL-4 HSV significantly prolonged survival of tumor bearers, whereas tumor-bearing mice that received the IL-10 HSV had a median survival that was identical to that of saline treated controls; (4) immunohistochemical analyses of mouse brains at 3 and 7 days after virus inoculation showed marked accumulation of inflammatory cells composed primarily of macrophages/microglia, with various proportions of CD8+ and CD4+ T cells, but few B lymphocytes. We conclude that the cytokines expressed from genes encoded in the viral genome influence HSV therapy of tumors and this is probably due to the host immune response. Thus, cytokine expression may be an important adjunct to tumor therapy utilizing genetically engineered HSV.

Animals↗

PubMed1998

IL-15 mRNA expression is up-regulated in blood and cerebrospinal fluid mononuclear cells in multiple sclerosis (MS).

IL-15, produced by monocytes and epithelial cells, is a novel cytokine with actions similar to IL-2. IL-15 induces T cell proliferation, B cell maturation and natural killer (NK) cell cytotoxicity, and is a chemoattractant for T cells. We investigated the expression of IL-15 mRNA in blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) in MS, an inflammatory disease of the central nervous system where cytokines are involved. MS patients had higher numbers of IL-15 mRNA-expressing blood MNC than patients with aseptic meningo-encephalitis (AM) and healthy controls. In CSF, MS patients had even higher numbers of IL-15 mRNA-expressing cells than in blood. This discrepancy between IL-15 mRNA expression between blood and CSF MNC was not seen in AM patients. Patients examined during the secondary chronic-progressive phase of MS had higher numbers of IL-15 mRNA-expressing blood MNC compared with patients examined during the relapsing-remitting phase. Levels of IL-15 mRNA-positive blood MNC were similar in patients with AM, myasthenia gravis, non-inflammatory neurological diseases and healthy controls. Taken together these data indicate that IL-15 mRNA expression is up-regulated in MS, further suggesting a role for proinflammatory cytokines in the pathogenesis of MS.

Adult↗

PubMed1998

Experimental autoimmune myasthenia gravis induction in B cell-deficient mice.

Experimental autoimmune myasthenia gravis (EAMG) is an animal model for human myasthenia gravis (MG). Autoantibody-induced functional loss of nicotinic acetylcholine receptor (AChR) at the postsynaptic membrane is an important pathogenic feature of both MG and EAMG. To evaluate the extent at which the humoral immune response against AChR operates in the pathogenesis of EAMG, we immunized B cell knockout (muMT) and wild-type C57BL/6 mice with AChR and complete Freund's adjuvant. The ability of AChR-primed lymph node cells to proliferate and secrete IFN-gamma in response to AChR and its dominant peptide alpha146-162 were intact in muMT mice as in wild-type mice. Similar amounts of mRNA for IFN-gamma, IL-4 and IL-10 in AChR-reactive lymph node cells were detected in muMT and wild-type mice. However, muMT mice had no detectable anti-AChR antibodies and remained completely free from clinical EAMG. We conclude that B cells are critically required for the genesis of clinical EAMG, but not for AChR-specific T cell priming.

Animals↗

PubMed1998

Discussion about surface boundary conditions of radon concentration and surface exhalation rate calculations in indoor concrete slab.

In this paper, the rationality of boundary conditions that assume radon concentration at the surface of a concrete slab to be zero, or radon concentration at an infinite point in air to be zero, are discussed in the calculations of radon concentration and surface exhalation rate from a concrete slab. Expressions to calculate radon concentration and surface exhalation rate in indoor concrete slab are given for both boundary conditions.

Air Pollutants, Radioactive↗

PubMed1998

On the algorithm for computing body surface Laplacians in an inhomogeneous volume conductor of arbitrary shape.

In this short communication, a corrected version of algorithm for calculating the body surface Laplacian (BSL) in an inhomogeneous volume conductor of arbitrary shape is described. The present computer simulation results show that the corrected algorithm can give an accurate numerical solution. This algorithm was then applied to examine the effect of the lung inhomogeneity on the BSL's in a realistically shaped torso model. The simulation results show that the low-conductivity lungs have little effect on both topology and magnitudes of body surface Laplacian maps (BSLM's) for a single dipole source.

Algorithms↗

PubMed1998

A computer simulation study of cortical imaging from scalp potentials.

In this paper, computer simulation studies were conducted to test the feasibility of imaging brain electrical activity from the scalp electroencephalograms. The inhomogeneous three-concentric-sphere head model was used to represent the head volume conductor. Closed spherical dipole layers, consisting of several thousand uniformly distributed dipoles, were used to reconstruct the cortical potential maps corresponding to neuronal sources located inside the brain. Simulation results indicate that the present procedure can image both cortical and deep sources, and for the cortical sources, a spatial resolution as high as 1.2 cm can be achieved.

Brain↗

PubMed1998

Body surface Laplacian mapping in patients with left or right ventricular bundle branch block.

Body surface Laplacian maps (BSLMs) have been previously reported to provide enhanced capability in localizing and resolving multiple spatially separate myocardial events. However, only a few studies have been reported on the clinical applications of BSLM. To test the clinical utility of BSLMs, BSLMs and body surface potential maps (BSPMs) during ventricular depolarization for complete right or left ventricular bundle branch block (CRBBB or CLBBB) were studied in ten patients in each group. As a control group, ten healthy subjects were also studied using the same procedure. One hundred and twenty-eight electrodes were placed uniformly over the entire chest and back of the subjects. BSLMs were computed from recorded potentials, using a numerical algorithm. The BSLMs showed multiple and more localized positive and negative activities compared with the BSPMs. In healthy subjects, the BSLMs showed multiple areas of positive activity overlying the RV, LV, and the RV outflow, and negative activity corresponding to RV free-wall breakthrough and LV anterolateral breakthrough sites, whereas the BSPMs could not separate RV and LV activities. In the patients with CRBBB, the BSLMs showed more localized areas of activity corresponding to the LV apex breakthrough and LV lateral breakthrough, and separated LV lateral and posterior activation. In the patients with CLBBB, the BSLMs showed multiple RV activation, and propagating activation of LV from lateral to posterior. The BSLMs appear to provide enhanced capability in detecting multiple ventricular electrical events associated with normal and abnormal conduction and a more detailed activation sequence of both ventricles in healthy subjects and in the patients with CRBBB and CLBBB. BSLM may provide an important alternative to other imaging modalities in localizing cardiac electrical activity noninvasively.

Action Potentials↗

PubMed1998

The myelin basic protein gene in multiple sclerosis: identification of discrete alleles of a 1.3 kb tetranucleotide repeat sequence.

Myelin basic protein (MBP) is a potential autoantigen in multiple sclerosis (MS) and its gene therefore is an attractive candidate to confer genetic susceptibility to this disease. Linkage and association with certain alleles of a 1.2 kb tetranucleotide repeat region 5' to the MBP gene with MS have been reported in Finnish patients, and an association has been reported from Denmark. However, these findings have not been confirmed in subsequent analyses in other populations. A limitation of previous studies has been the low resolution of the typing procedure. We have investigated the same polymorphism in thirty-four Swedish nuclear families with 2 or 3 MS patients. and in 149 unrelated Swedish MS patients and 95 healthy controls using a fluorescence-based semi-automated technique which allowed the identification of discrete tetrarepeat numbers. Neither parametric two-point linkage analysis nor a nonparametric affected pedigree members analysis showed any sign of linkage. In addition, the distribution of alleles was similar in patients and controls. We conclude that the MBP gene does not influence susceptibility to MS in Swedish patients.

Alleles↗