bluuebunny/crossref_metadata_2025 huggingface dataset:
BIFURCATIONS OF TRAVELING WAVE AND BREATHER SOLUTIONS OF A GENERAL CLASS OF NONLINEAR WAVE EQUATIONS
Authors: LI JIBIN , CHEN GUANRONG
Published: October 2005

Bifurcations of a general class of traveling wave solutions are analyzed. In particular, the existence of solitary wave, kink and anti-kink wave solutions, and uncountably infinite periodic wave solutions and breather solutions of a general class of traveling wave equations is proved. Also, the existence of breaking wave solution is discussed in detail. Under different parametric conditions, several sufficient conditions for the existence of these solutions are derived. Sufficient simulation results are provided to visualize the theoretical results.
A COMPARISON OF POLYNOMIAL AND WAVELET EXPANSIONS FOR THE IDENTIFICATION OF CHAOTIC COUPLED MAP LATTICES
Authors: GUO L. Z. , BILLINGS S. A.
Published: October 2005

A comparison between polynomial and wavelet expansions for the identification of coupled map lattice (CML) models for deterministic spatiotemporal dynamical systems is presented in this paper. The pattern dynamics generated by smooth and nonsmooth nonlinear maps in a well-known two-dimensional CML structure are analyzed. By using an orthogonal feedforward regression algorithm (OFR), polynomial and wavelet models are identified for the CML's in chaotic regimes. The quantitative dynamical invariants such as the largest Lyapunov exponents and correlation dimensions are estimated and used to evaluate the performance of the identified models.
IMAGE PROCESSING AND SELF-ORGANIZING CNN
Authors: ITOH MAKOTO , CHUA LEON O.
Published: October 2005

CNN templates for image processing and pattern formation are derived from neural field equations, advection equations and reaction–diffusion equations by discretizing spatial integrals and derivatives. Many useful CNN templates are derived by this approach. Furthermore, self-organization is investigated from the viewpoint of divergence of vector fields.
A FAST AND SIMPLE IMPLEMENTATION OF CHUA'S OSCILLATOR WITH CUBIC-LIKE NONLINEARITY
Authors: O'DONOGHUE KEITH , KENNEDY MICHAEL PETER , FORBES PEADAR , QU MIN , JONES STEPHANIE
Published: October 2005

The nonlinearity in Chua's oscillator is commonly implemented as a three-segment piecewise-linear resistor. The piecewise-linear nature of the element means that the implementation requires a significant amount of circuitry and the speed of operation is limited. The qualitative behavior of Chua's oscillator has also been captured using a smooth cubic nonlinearity; the implementation of the latter also requires a significant amount of circuitry and suffers from limited speed of operation.

This work describes a novel implementation of Chua's oscillator using just four transistors and a battery to produce a cubic-like nonlinearity. The circuit is simple, robust, and capable of operating at frequencies over one thousand times greater than the original Chua's oscillator.
CONSTRUCTIVE ACTION OF ADDITIVE NOISE IN OPTIMAL DETECTION
Authors: CHAPEAU-BLONDEAU FRANÇOIS , ROUSSEAU DAVID
Published: October 2005

The optimal detection of a signal of known form hidden in additive white noise is examined in the framework of stochastic resonance and noise-aided information processing. Conditions are exhibited where the performance in the optimal detection increases when the level of the additive (non-Gaussian bimodal) noise is raised. On the additive signal–noise mixture, when a threshold quantization is performed prior to the optimal detection, another form of improvement by noise can be obtained, with subthreshold signals and Gaussian noise. Optimization of the quantization threshold shows that even in symmetric detection settings, the optimal threshold can be away from the center of symmetry and in subthreshold configuration of the signals. These properties concerning non-Gaussian noise and nonlinear preprocessing in optimal detection, are meaningful to the current exploration of the various modalities and potentialities of stochastic resonance.
THE ORIGIN OF A CONTINUOUS TWO-DIMENSIONAL "CHAOTIC" DYNAMICS
Authors: ALVAREZ-RAMIREZ JOSE , DELGADO-FERNANDEZ JOAQUIN , ESPINOSA-PAREDES GILBERTO
Published: October 2005

Ten years ago, Dixon et al. [1993] studied the behavior of a continuous-time system displaying erratic, apparently chaotic, dynamics. This is a paradoxical case since the system is two-dimensional, which is seemingly a violation of the Poincare–Bendixon theorem. Using numerical studies, Dixon et al. explained such a behavior from the presence of an attracting singularity, which induces arbitrarily large sensitivity to initial conditions. The aim of this letter is to use singularity regularization techniques to study the dynamics around the system singularity. The results obtained in this way explain the paradoxical situation of having continuous "chaotic" dynamics in a two-dimensional system.
ISOCHRONOUS SECTIONS VIA NORMALIZERS
Authors: SABATINI M.
Published: October 2005

We present some sufficient conditions for the existence of isochronous sections of planar differential systems. We consider isochronous sections at a critical point, a cycle, the boundary of a central or attraction region.
ON A BICOMPLEX DISTANCE ESTIMATION FOR THE TETRABROT
Authors: MARTINEAU ÉTIENNE , ROCHON DOMINIC
Published: October 2005

In this article, we present some distance estimation formulas that can be used to ray traced slices of the bicomplex Mandelbrot set and the bicomplex filled-Julia sets in dimension three. We also present a simple method to explore and infinitely approach these 3D fractals. Because of its rich fractal structure and symmetry, we emphasize our work on the generalized Mandelbrot set for bicomplex numbers in dimension three: the Tetrabrot.
CLINICAL EXPERIENCE WITH A PNEUMATIC VEST — UNLOADING THE SPINE IN THE UPRIGHT POSTURE
Authors: Loguidice Vito , Mahoney C. B. , Haldeman J. , Andersson Gunnar B. J.
Published: October 2005

This is a prospective multi-center cohort study to evaluate the acceptability and effectiveness of a new device the OrthoTrac™ which aims at unloading the spine in an upright posture. Three hundred and thirteen patients (313) were enrolled and 201 completed an eight-week trial. Outcomes were determined using a Visual Analog Scale and SF-36. Both scales improved significantly over the eight-week period.

We conclude that this novel treatment benefit patients with back pain. Subgroups need to be identified and randomized controlled trials performed on these groups.
THE DOVETAIL CONFIGURATION: A BIOMECHANICAL ANALYSIS OF A V-SHAPED OSTEOTOMY DOCKING SITE
Authors: Lai Derek W. T. , Yip Daniel K. H. , Li Song-Jian , Lu William , Wong J. W. K.
Published: October 2005

Large allograft bones are commonly used in limb salvage procedures for the reconstruction of bone defects after resection of a bone tumor. A V-shaped osteotomy may perform better than the traditional transverse osteotomy as it increases the stability of the docking site and increases the contact area between an allograft and the host cortex. The aim of this study is to investigate the biomechanical properties of a V-shaped docking site of different angles.

orcine femurs with 45°, 60° or 90° V-shaped osteotomy were first tested with 1000 N compression, followed by 2 and 5 Nm torque. The torsional stiffness of the 45° specimen group at 5 Nm torque was significantly higher (P<0.05) than the 90° group. Therefore, our results show that 45° V-shaped osteotomy is found to be the most stable docking angle.
MOLECULAR MARKERS IN OSTEOSARCOMA – A cDNA MICROARRAY AND RT-PCR ANALYSIS
Authors: Hameed Meera R. , Lin Tao-Zhen , Coffman Frederick , Cohen Marion C. , Fernandes Helen , Benevenia Joseph , Patterson Francis , Aisner Seena C. , Cohen Stanley
Published: October 2005

Osteosarcomas account for about 20% of all primary bone neoplasms, and affect predominantly adolescents. Important prognostic factors include the presence or absence of metastases at the time of presentation and tumor response to neoadjuvant chemotherapy. Biological markers predicting metastases and chemoresistance are not well characterized. cDNA microarray analysis enables one to examine the expression of thousands of genes in tumor samples. We performed cDNA microarray analysis of histologically low and high grade areas in osteosarcomas to identify gene expression patterns which may depict aggressive behavior. Microarray analysis with 1.2 K cancer array revealed many differentially expressed genes (both upregulated and downregulated), in histologically high grade tumor samples as compared with a low grade sample. Selected up and down regulated markers in the high grade sarcomas were tested in a group of high grade osteosarcomnas (OS) with varying responses to chemotherapy. Of the multiple markers analyzed, ezrin, a member of the ERM family of membrane-cytoskeleton linkers showed an expression pattern statistically significant between tumors with good response to chemotherapy compared with tumors with poor response (p = 0.036). We discuss our findings, with current review of literature.
EXPERTS' EARNING FORECASTS: BIAS, HERDING AND GOSSAMER INFORMATION
Authors: GUEDJ OLIVIER , BOUCHAUD JEAN-PHILIPPE
Published: October 2005

We study the statistics of earning forecasts of US, EU, UK and JP stocks during the period 1987–2004. We confirm, on this large data set, that financial analysts are on average over-optimistic and show a pronounced herding behavior. These effects are time dependent, and were particularly strong in the early 1990s and during the Internet bubble. We furthermore find that their forecast ability is, in relative terms, quite poor and comparable in quality, a year ahead, to the simplest "no change" forecast. As a result of herding, analysts agree with each other five to ten times more than with the actual result. We have shown that significant differences exist between US stocks and EU stocks, that may partly be explained as a company size effect. Interestingly, herding effects appear to be stronger in the US than in the Eurozone. Finally, we study the correlation of errors across stocks and show that significant sectorization occurs, some sectors being easier to predict than others. These results add to the list of arguments suggesting that the tenets of Efficient Market Theory are untenable.
A CONSTRAINED LEAST SQUARE METHOD FOR ESTIMATING A SMOOTH, NONNEGATIVE FORWARD RATE SEQUENCE
Authors: KONNO HIROSHI , ITO SUMITO
Published: October 2005

We will develop an efficient method for estimating a smooth nonnegative forward rate sequence using the market price of riskless bonds. This method is an improvement of the classical Carleton–Cooper's method based on standard least square method, which often generates a non-smooth forward rate sequence and hence is not used in practice. The method to be proposed in this paper is intended to resolve this difficulty. We will impose a smoothness condition while maintaining the fitting error within an acceptable level. The resulting optimization problem is shown to be convex in the region of interest. Therefore, we can calculate a globally optimal solution very fast by standard nonlinear programming algorithms. We will demonstrate that this method generates a smooth forward rate sequence at the expense of a very small increase of fitting error.
PRICING PRECIPITATION BASED DERIVATIVES
Authors: CARMONA RENÉ , DIKO PAVEL
Published: October 2005

We consider the problem of pricing a derivative contract written on precipitation at a specific location during a given period of time. We propose a jump Markov process model for the stochastic dynamics of the underlying precipitation. Our model is based on pulse Poisson process models widely used in hydrology. We develop maximum likelihood parameter estimation procedures to fit our model to rainfall data. In order to price derivatives, we assume the existence of a traded asset whose price dynamics are influenced by the precipitation at the location in question, and we rely on the utility indifference approach. Two utility functions are considered: exponential and power utility. We derive explicit solutions for the exponential and bounds for the power utility.

Finally, we apply our model fitting and pricing techniques to a sample rainfall contract in Norway.
A GENERAL EQUILIBRIUM MODEL OF THE TERM STRUCTURE OF INTEREST RATES UNDER REGIME-SWITCHING RISK
Authors: WU SHU , ZENG YONG
Published: October 2005

This paper develops a general equilibrium model of the term structure of interest rates in the presence of the systematic risk of regime shifts. The model elucidates the economic nature of the regime-shift risk premium and introduces a new source of time-variation in bond returns. A closed-form solution for the term structure of interest rates is obtained under an affine model using log-linear approximation. The model is estimated by Efficient Method of Moments. The regime-switching risk is found to be statistically significant and mostly affect the long-end of the yield curve.
ENERGY BARRIERS, DEMONS, AND MINIMUM ENERGY OPERATION OF ELECTRONIC DEVICES
Authors: CAVIN RALPH K. , ZHIRNOV VICTOR V. , HUTCHBY JAMES A. , BOURIANOFF GEORGE I.
Published: October 2005

The presence of thermal noise dictates that an energy barrier is needed to preserve a binary state. Therefore, all electronic devices contain at least one energy barrier to control electron flow. The barrier properties determine the operating characteristics of electronic devices. Furthermore, changes in the barrier shape require changes in charge density. Operation of all charge transport devices includes charging/discharging capacitances to change barrier height. We analyze energy dissipation for several schemes of charging capacitors. A basic assumption of Reversible Computing is that the computing system is completely isolated from the thermal bath. An isolated system is a mathematical abstraction never perfectly realized in practice. Errors due to thermal excitations are equivalent to information erasure, and thus computation dissipates energy. Another source of energy dissipation is due to the need of measurement and control. To analyze this side of the problem, the Maxwell's Demon is a useful abstraction. We hold that apparent "energy savings" in models of adiabatic circuits result from neglecting the total energy needed by other parts of the system to implement the circuit.
Sub-continental-scale geochemical mapping: sampling, quality control and data analysis issues
Authors: Reimann Clemens
Published: October 2005

During 1996/97,
c.
1500 samples of agricultural soils from ten northern European countries (western Belarus, Estonia, Finland, northern Germany, Latvia, Lithuania, Norway, Poland, northwestern Russia and Sweden) were collected from the A
p
and B/C-horizons at 750 sites. The sample sites were evenly spread over a 1 800 000 km
2
area, giving an average sample density of one site per 2500 km
2
. The <2 mm fractions (Poland: <1 mm) of all samples were analysed for up to 62 chemical elements following ammonium acetate, aqua regia and HF extractions, and for total element concentrations by X-ray fluorescence spectrometry. Electrical conductivity, pH (water extraction) and loss on ignition (1030°C) were also determined. Each method was applied to all the samples in one laboratory only.

The analytical results were evaluated and mapped using exploratory data analysis techniques. Even at this low sample density, regional-scale geochemical patterns emerge for all elements. These patterns show the influence of factors such as geology, agriculture, pollution, topography, marine aerosols and climate, and their relative importance for the observed element concentrations in the soils. Low-density geochemical mapping of agricultural soils is a viable tool to study the geochemical processes that determine the element distribution in soils at a sub-continental scale.
GSUE: urban geochemical mapping in Great Britain
Authors: Fordyce F.M. , Brown S.E. , Ander E.L. , Rawlins B.G. , O'Donnell K.E. , Lister T.R. , Breward N. , Johnson C.C.
Published: October 2005

The British Geological Survey is responsible for the national strategic geochemical survey of Great Britain. As part of this programme, the Geochemical Surveys of Urban Environments (GSUE) project was initiated in 1992 and to date, 21 cities have been mapped. Urban sampling is based upon the collection of top (0.05 to 0.20 m) and deeper (0.35 to 0.50 m) soil samples on a 500 m grid across the built environment (one sample per 0.25 km
2
). Samples are analysed for
c.
46 total element concentrations by X-ray fluorescence spectrometry, pH and loss on ignition as an indicator of organic matter content. The data provide an overview of the urban geochemical signature and because they are collected as part of a national baseline programme, can be readily compared with soils in the rural hinterland to assess the extent of urban contamination. The data are of direct relevance to current UK land use planning, urban regeneration and contaminated land legislative regimes. An overview of the project and applications of the data to human health risk assessment, water quality protection and contaminant source identification are presented.
LXRS AND FXR: The Yin and Yang of Cholesterol and Fat Metabolism
Authors: Kalaany Nada Y. , Mangelsdorf David J.
Published: October 2005

▪ Abstract  Liver X receptors (LXRs) and farnesoid X receptor (FXR) are nuclear receptors that function as intracellular sensors for sterols and bile acids, respectively. In response to their ligands, these receptors induce transcriptional responses that maintain a balanced, finely tuned regulation of cholesterol and bile acid metabolism. LXRs also permit the efficient storage of carbohydrate- and fat-derived energy, whereas FXR activation results in an overall decrease in triglyceride levels and modulation of glucose metabolism. The elegant, dual interplay between these two receptor systems suggests that they coevolved to constitute a highly sensitive and efficient system for the maintenance of total body fat and cholesterol homeostasis. Emerging evidence suggests that the tissue-specific action of these receptors is also crucial for the proper function of the cardiovascular, immune, reproductive, endocrine pancreas, renal, and central nervous systems. Together, LXRs and FXR represent potential therapeutic targets for the treatment and prevention of numerous metabolic and lipid-related diseases.
Dual mechanism of the potentiation by glucose of insulin secretion induced by arginine and tolbutamide in mouse islets
Authors: Ishiyama Nobuyoshi , Ravier Magalie A. , Henquin Jean-Claude
Published: October 2005

Glucose induces insulin secretion (IS) and also potentiates the insulin-releasing action of secretagogues such as arginine and sulfonylureas. This potentiating effect is known to be impaired in type 2 diabetic patients, but its cellular mechanisms are unclear. IS and cytosolic Ca2+concentration ([Ca2+]i) were measured in mouse islets during perifusion with 3–15 mmol/l glucose (G3–G15, respectively) and pulse or stepwise stimulation with 1–10 mmol/l arginine or 5–250 μmol/l tolbutamide. In G3, arginine induced small increases in [Ca2+]ibut no IS. G7 alone only slightly increased [Ca2+]iand IS but markedly potentiated arginine effects on [Ca2+]i, which resulted in significant IS (already at 1 mmol/l). For each arginine concentration, both responses further increased at G10 and G15, but the relative change was distinctly larger for IS than [Ca2+]i. At all glucose concentrations, tolbutamide dose dependently increased [Ca2+]iand IS with thresholds of 25 μmol/l for [Ca2+]iand 100 μmol/l for IS at G3 and of 5 μmol/l for both at G7 and above. Between G7 and G15, the effect of tolbutamide on [Ca2+]iincreased only slightly, whereas that on IS was strongly potentiated. The linear relationship between IS and [Ca2+]iat increasing arginine or tolbutamide concentrations became steeper as the glucose concentration was raised. Thus glucose augmented more the effect of each agent on IS than that on [Ca2+]i. In conclusion, glucose potentiation of arginine- or tolbutamide-induced IS involves increases in both the rise of [Ca2+]iand the action of Ca2+on exocytosis. This dual mechanism must be borne in mind to interpret the alterations of the potentiating action of glucose in type 2 diabetic patients.
Whole body leucine flux in HIV-infected patients treated with or without protease inhibitors
Authors: Prod’homme Magali , Rochon Cécile , Balage Michèle , Laurichesse Henri , Tauveron Igor , Champredon Claude , Thieblot Philippe , Beytout Jean , Grizard Jean
Published: October 2005

The present study was carried out to assess the effects of protease inhibitor (PI) therapy on basal whole body protein metabolism and its response to acute amino acid-glucose infusion in 14 human immunodeficiency virus (HIV)-infected patients. Patients treated with PIs (PI+, 7 patients) or without PIs (PI−, 7 patients) were studied after an overnight fast during a 180-min basal period followed by a 140-min period of amino acid-glucose infusion. Protein metabolism was investigated by a primed constant infusion of l-[1-13C]leucine. Dual-energy X-ray absorptiometry for determination of fat-free mass (FFM) and body fat mass measured body composition. In the postabsorptive state, whole body leucine balance was 2.5 times ( P < 0.05) less negative in the PI+ than in the PI− group. In HIV-infected patients treated with PIs, the oxidative leucine disposal during an acute amino acid-glucose infusion was lower (0.58 ± 0.09 vs. 0.81 ± 0.07 μmol·kg FFM−1·min−1 using plasma [13C]leucine enrichment, P = 0.06; or 0.70 ± 0.10 vs. 0.99 ± 0.08 μmol·kg FFM−1·min−1 using plasma [13C]ketoisocaproic acid enrichment, P = 0.04 in PI+ and PI− groups, respectively) than in patients treated without PIs. Consequently, whole body nonoxidative leucine disposal (an index of protein synthesis) and leucine balance (0.50 ± 0.10 vs. 0.18 ± 0.06 μmol·kg FFM·−1·min−1 in PI+ and PI− groups respectively, P < 0.05) were significantly improved during amino acid-glucose infusion in patients treated with PIs. However, whereas the response of whole body protein anabolism to an amino acid-glucose infusion was increased in HIV-infected patients treated with PIs, any improvement in lean body mass was detected.
Glucose inhibits GABA release by pancreatic β-cells through an increase in GABA shunt activity
Authors: Wang Chen , Kerckhofs Karen , Van de Casteele Mark , Smolders Ilse , Pipeleers Daniel , Ling Zhidong
Published: October 2005

GABA is the major inhibitory neurotransmitter in the nervous system. It is also released by the insulin-producing β-cells, providing them with a potential paracrine regulator. Because glucose was found to inhibit GABA release, we investigated whether extracellular GABA can serve as a marker for glucose-induced mitochondrial activity and thus for the functional state of β-cells. GABA release by rat and human β-cells was shown to reflect net GABA production, varying with the functional state of the cells. Net GABA production is the result of GABA formation through glutamate decarboxylase (GAD) and GABA catabolism involving a GABA-transferase (GABA-T)-mediated shunt to the TCA cycle. GABA-T exhibits Kmvalues for GABA (1.25 mM) and for α-ketoglutarate (α-KG; 0.49 mM) that are, respectively, similar to and lower than those in brain. The GABA-T inhibitor γ-vinyl GABA was used to assess the relative contribution of GABA formation and catabolism to net production and release. The nutrient status of the β-cells was found to regulate both processes. Glutamine dose-dependently increased GAD-mediated formation of GABA, whereas glucose metabolism shunts part of this GABA to mitochondrial catabolism, involving α-KG-induced activation of GABA-T. In absence of extracellular glutamine, glucose also contributed to GABA formation through aminotransferase generation of glutamate from α-KG; this stimulatory effect increased GABA release only when GABA-T activity was suppressed. We conclude that GABA release from β-cells is regulated by glutamine and glucose. Glucose inhibits glutamine-driven GABA formation and release through increasing GABA-T shunt activity by its cellular metabolism. Our data indicate that GABA release by β-cells can be used to monitor their metabolic responsiveness to glucose irrespective of their insulin-secretory activity.
Insulin secretion in the conscious mouse is biphasic and pulsatile
Authors: Nunemaker Craig S. , Wasserman David H. , McGuinness Owen P. , Sweet Ian R. , Teague Jeanette C. , Satin Leslie S.
Published: October 2005

Islets in most species respond to increased glucose with biphasic insulin secretion, marked by a sharp first-phase peak and a slowly rising second phase. Mouse islets in vitro, however, lack a robust second phase. To date, this observation has not been extended in vivo. We thus compared insulin secretion from conscious mice with isolated mouse islets in vitro. The arterial plasma insulin response to a hyperglycemic clamp was measured in conscious mice 1 wk after surgical implantation of carotid artery and jugular vein catheters. Mice were transfused using clamps with blood from a donor mouse to maintain blood volume, allowing frequent arterial sampling. When plasma glucose in vivo was raised from ∼5 to ∼13 mM, insulin rose to a first-phase peak of 403 ± 73% above basal secretion ( n = 5), followed by a rising second phase of mean 289 ± 41%. In contrast, perifused mouse islets (∼75 islets/trial) responded with a similar first phase of 508 ± 94% ( n = 4) but a smaller and virtually flat second phase of 169 ± 9% ( n = 4, P < 0.05). Furthermore, the slope of the second-phase response differed significantly from zero in mice (2.63 ± 0.39%/min, P < 0.01), in contrast to perifused islets (0.18 ± 0.14%/min, P > 0.30). Mice also displayed pulsatile patterns in insulin concentration (period: 4.2 ± 0.4 min, n = 8). Conscious mice thus responded to increased glucose with biphasic and pulsatile insulin secretion, as in other species. The robust second phase observed in vivo suggests that the processes needed to generate second-phase insulin secretion may be abrogated by islet isolation.
Low-intensity contraction activates the α1-isoform of 5′-AMP-activated protein kinase in rat skeletal muscle
Authors: Toyoda Taro , Tanaka Satsuki , Ebihara Ken , Masuzaki Hiroaki , Hosoda Kiminori , Sato Kenji , Fushiki Tohru , Nakao Kazuwa , Hayashi Tatsuya
Published: October 2005

Skeletal muscle expresses two catalytic subunits, α1 and α2, of the 5′-AMP-activated protein kinase (AMPK), which has been implicated in contraction-stimulated glucose transport and fatty acid oxidation. Muscle contraction activates the α2-containing AMPK complex (AMPKα2), but this activation may occur with or without activation of the α1-containing AMPK complex (AMPKα1), suggesting that AMPKα2 is the major isoform responsible for contraction-induced metabolic events in skeletal muscle. We report for the first time that AMPKα1, but not AMPKα2, can be activated in contracting skeletal muscle. Rat epitrochlearis muscles were isolated and incubated in Krebs-Ringer bicarbonate buffer containing pyruvate. In muscles stimulated to contract at a frequency of 1 and 2 Hz during the last 2 min of incubation, AMPKα1 activity increased twofold and AMPKα2 activity remained unchanged. Muscle stimulation did not change the muscle AMP concentration or the AMP-to-ATP ratio. AMPK activation was associated with increased phosphorylation of Thr172of the α-subunit, the primary activation site. Muscle stimulation increased the phosphorylation of acetyl-CoA carboxylase (ACC), a downstream target of AMPK, and the rate of 3- O-methyl-d-glucose transport. In contrast, increasing the frequency (≥5 Hz) or duration (≥5 min) of contraction activated AMPKα1 and AMPKα2 and increased AMP concentration and the AMP/ATP ratio. These results suggest that 1) AMPKα1 is the predominant isoform activated by AMP-independent phosphorylation in low-intensity contracting muscle, 2) AMPKα2 is activated by an AMP-dependent mechanism in high-intensity contracting muscle, and 3) activation of each isoform enhances glucose transport and ACC phosphorylation in skeletal muscle.
Bile salt exposure increases proliferation through p38 and ERK MAPK pathways in a non-neoplastic Barrett’s cell line
Authors: Jaiswal Kshama , Lopez-Guzman Christie , Souza Rhonda F. , Spechler Stuart J. , Sarosi George A.
Published: October 2005

Bile reflux has been implicated in the neoplastic progression of Barrett’s esophagus (BE). Bile salts increase proliferation in a Barrett’s-associated adenocarcinoma cell line (SEG-1 cells) by activating ERK and p38 MAPK pathways. However, it is not clear that these findings in cancer cells are applicable to non-neoplastic cells of benign BE. We examined the effect of bile salts on three human cell lines: normal esophageal squamous (NES) cells, non-neoplastic Barrett’s cells (BAR cells), and SEG-1 cells. We hypothesized that bile salt exposure activates proproliferative and antiapoptotic pathways to promote increased growth in BE. NES, BAR, and SEG-1 cells were exposed to glycochenodeoxycholic acid (GCDA) at a neutral pH for 5 min. Proliferation was measured by Coulter counter cell counts and a 5-bromo-2′-deoxyuridine (BrdU) incorporation assay. GCDA-induced MAPK activation was examined by Western blot analysis for phosphorylated ERK and p38. Apoptosis was measured by TdT-mediated dUTP nick-end labeling and annexin V staining after GCDA and UV-B exposure. Statistical significance was determined by ANOVA. NES cells exposed to 5 min of GCDA did not increase cell number. In BAR cells, GCDA exposure increased cell number by 31%, increased phosphorylated p38 and ERK levels by two- to three-fold, increased BrdU incorporation by 30%, and decreased UV-induced apoptosis by 15–20%. In conclusion, in a non-neoplastic Barrett’s cell line, GCDA exposure induces proliferation by activation of both ERK and p38 MAPK pathways. These findings suggest a potential mechanism whereby bile reflux may facilitate the neoplastic progression of BE.
The CDX2 transcription factor regulates furin expression during intestinal epithelial cell differentiation
Authors: Gendron Fernand-Pierre , Mongrain Sébastien , Laprise Patrick , McMahon Stéphanie , Dubois Claire M. , Blais Mylène , Asselin Claude , Rivard Nathalie
Published: October 2005

CDX2, a member of the caudal family of transcription factors, is involved in enterocyte lineage specification. CDX2 activates many intestine-specific genes, such as sucrase-isomaltase and lactase-phlorizin hydrolase (LPH), and adhesion proteins, namely, LI-cadherin and claudin-2. In this study, we show that the proprotein convertase furin, involved in proteolytic maturation of proprotein substrates including LPH and cell surface proteins, is a CDX2 target. Indeed, expression of the rat furin homolog was induced 1.5-fold, as determined by microarray experiments that compared control with CDX2-expressing intestinal epithelial cells (IEC-6). As determined by transient transfection assays in Caco-2/15 cells, the furin P1 promoter 1.3-kb fragment between SacI and NheI was essential for CDX2 transcriptional activation. Electrophoretic mobility shift/supershift assays followed by site-specific mutagenesis and chromatin immunoprecipitation identified the CDX DNA-binding site (CBS)2 sequence from nt −1827 to −1821 as the major CBS involved in furin P1 promoter activation. Increased furin mRNA and protein expression correlated with both CDX2 expression and intestinal epithelial cell differentiation. In addition, furin mRNAs were detected predominantly in differentiated epithelial cells of the villus, as determined by in situ hybridization. Treatment of Caco-2/15 cells with a furin inhibitor led to inhibition of LPH activity. Morphological differentiation of enterocyte-like features in Caco-2/15 such as epithelial cell polarity and brush-border formation were strongly attenuated by furin inhibition. These results suggest that CDX2 regulates furin expression in intestinal epithelial cells. Furin may be important in modulating the maturation and/or activation of key factors involved in enterocyte differentiation.
Roles of ZO-1, occludin, and actin in oxidant-induced barrier disruption
Authors: Musch Mark W. , Walsh-Reitz Margaret Mary , Chang Eugene B.
Published: October 2005

Oxidants such as monochloramine (NH2Cl) decrease epithelial barrier function by disrupting perijunctional actin and possibly affecting the distribution of tight junctional proteins. These effects can, in theory, disturb cell polarization and affect critical membrane proteins by compromising molecular fence function of the tight junctions. To examine these possibilities, we investigated the actions of NH2Cl on the distribution, function, and integrity of barrier-associated membrane, cytoskeletal, and adaptor proteins in human colonic Caco-2 epithelial monolayers. NH2Cl causes a time-dependent decrease in both detergent-insoluble and -soluble zonula occludens (ZO)-1 abundance, more rapidly in the former. Decreases in occludin levels in the detergent-insoluble fraction were observed soon after the fall of ZO-1 levels. The actin depolymerizer cytochalasin D resulted in a decreased transepithelial resistance (TER) more quickly than NH2Cl but caused a more modest and slower reduction in ZO-1 levels and in occludin redistribution. No changes in the cellular distribution of claudin-1, claudin-5, or ZO-2 were observed after NH2Cl. However, in subsequent studies, the immunofluorescent cellular staining pattern of all these proteins was altered by NH2Cl. The actin-stabilizing agent phalloidin did not prevent NH2Cl-induced decreases in TER or increases of apical to basolateral flux of the paracellular permeability marker mannitol. However, it partially blocked changes in ZO-1 and occludin distribution. Tight junctional fence function was also compromised by NH2Cl, observed as a redistribution of the α-subunit of basolateral Na+-K+-ATPase to the apical membrane, an effect not found with the apical membrane protein Na+/H+exchanger isoform 3. In conclusion, oxidants not only disrupt perijunctional actin but also cause redistribution of tight junctional proteins, resulting in compromised intestinal epithelial barrier and fence function. These effects are likely to contribute to the development of malabsorption and dysfunction associated with mucosal inflammation of the digestive tract.
Cyclical upregulated iNOS and long-term downregulated nNOS are the bases for relapse and quiescent phases in a rat model of IBD
Authors: Porras M. , Martín M. T. , Torres R. , Vergara P.
Published: October 2005

We previously reported that indomethacin induces a chronic intestinal inflammation in the rat where the cyclical characteristic phases of Crohn's disease are manifested with a few days' interval and lasting for several months: active phase (high inflammation, hypomotility, bacterial traslocation) and reactive phase (low inflammation, hypermotility, no bacterial traslocation). In this study, we investigated the possible role of both constitutive and inducible isoforms of nitric oxide (NO) synthase (NOS) and cyclooxygenase (COX) in the cyclicity of active and reactive phases in rats with chronic intestinal inflammation. Rats selected at either active or reactive phases and from 2 to 60 days after indomethacin treatment were used. mRNA expression of both constitutive and inducible NOS and COX isoforms in each phase was evaluated by RT-PCR and cellular enzyme localization by immunohistochemistry. The effects of different COX and NOS inhibitors on the intestinal motor activity were tested. mRNA expression of COX-1 was not modified by inflammation, whereas mRNA expression of neuronal NOS was reduced in all indomethacin-treated rats. In contrast, NOS and COX inducible forms showed a cyclical oscillation. mRNA expression and protein of both iNOS and COX-2 increased only during active phases. The intestinal hypomotility associated with active phases was turned into hypermotility after the administration of selective iNOS inhibitors. Sustained downregulation of constitutive NOS caused hypermotility, possibly as a defense mechanism. However, this reaction was masked during the active phases due to the inhibitory effects of NO resulting from the increased levels of the inducible NOS isoform.
Secretion of soluble leptin receptors by exocrine and endocrine cells of the gastric mucosa
Authors: Cammisotto Philippe G. , Gingras Diane , Renaud Christian , Levy Emile , Bendayan Moïse
Published: October 2005

Leptin is a hormone secreted by the gastric mucosa into the lumen of the stomach. It is present in its intact form in the intestine where it regulates nutrient absorption and intestinal mucosa integrity. We have identified the binding protein that protects leptin from the harsh conditions of the gastric juice. Immunoprecipitations and Western blot analyses demonstrated that leptin is present in the gastric mucosa and the gastric juice, bound to a protein corresponding to the extracellular domain of the leptin receptor. In the absence of this soluble receptor, leptin is rapidly degraded. Immunocytochemistry on rat gastric mucosa identified the cells and intracellular compartments involved in secretion of this complex. Leptin receptor extracellular domain and leptin are present along the rough endoplasmic reticulum-Golgi-granules secretory pathways and form a complex in the secretory granules of Chief and specific endocrine cells. The long-form membrane leptin receptor OB-Rb, the protease activator furin, and proprotein convertase 7 were found in Chief cell granules but not in those of endocrine cells. The shedding of the receptor occurs in the immature granules. It is concluded that in the immature secretory granules of Chief cells, furin activates proprotein convertase 7 that, in turn, cleaves the extracellular portion of membrane-bound leptin receptors. Leptin bound to its soluble receptor forms a complex that is resistant to the gastric juice. Endocrine cells, on the other hand, generate a soluble leptin receptor by mechanisms different from those of the exocrine cells.
Cardiomyocyte function associated with hyperactivity and/or hypertension in genetic models of LV hypertrophy
Authors: Palmer Bradley M. , Chen Zengyi , Lachapelle Richard R. , Hendley Edith D. , LeWinter Martin M.
Published: October 2005

We examined cardiomyocyte intracellular calcium ([Ca2+]i) dynamics and sarcomere shortening dynamics in genetic rat models of left ventricular (LV) hypertrophy associated with or without hypertension (HT) and with or without hyperactive (HA) behavior. Previous selective breeding of the spontaneously hypertensive rat (SHR) strain, which is HA and HT, with the Wistar-Kyoto (WKY) rat strain, which is not hyperactive (NA) and not hypertensive (NT), has led to two unique strains: the WKHA strain, selected for HA and NT, and the WKHT strain, selected for NA and HT. Cardiomyocytes were isolated from young adult males and females of each strain, paced at 2, 3, and 4 Hz in 1.2 mM external Ca2+ concentration at 37°C, and cardiomyocyte [Ca2+]i and sarcomere dynamics were recorded simultaneously. Under these conditions, LV cardiomyocyte systolic and diastolic [Ca2+]i dynamics and diastolic sarcomere dynamics in the WKHT were significantly enhanced compared with WKY controls, suggesting an underlying LV hypertrophic response that successfully compensated for HT in the absence of HA. LV cardiomyocyte [Ca2+]i dynamics in the WKHA and SHR were strikingly similar to each other and only slightly reduced compared with WKY. LV cardiomyocyte systolic and diastolic sarcomere dynamics, on the other hand, were significantly reduced in the SHR compare with WKHA and more so in male than in female SHR. We conclude from these data that HT alone is an insufficient descriptor of the cause of LV hypertrophy and diminished LV cardiomyocyte function in the SHR rat. These data further suggest that HA (augmented by male sex) in the SHR may interact with the HT state to initiate impaired cardiomyocyte function and thereby inhibit or undermine an otherwise compensatory response that may occur with HT in the absence of HA.
Contribution of p16INK4aand p21CIP1pathways to induction of premature senescence of human endothelial cells: permissive role of p53
Authors: Chen Jun , Huang Xuan , Halicka Dorota , Brodsky Sergey , Avram Ari , Eskander Jonathan , Bloomgarden Noah A. , Darzynkiewicz Zbigniew , Goligorsky Michael S.
Published: October 2005

We have previously found that nonenzymatically glycated collagen I (GC), mimicking diabetic microenvironment, can induce senescent phenotype in early passage human umbilical vein endothelial cells (HUVECs). In the present study, we explored the functional involvement of cell cycle checkpoint pathways in initiating GC-induced premature endothelial cell senescence. When compared with native collagen, early passage HUVECs showed increased p53, p21CIP1(p21), and p16INK4a(p16) mRNA expression after exposure to GC. Twenty-four hours after transfection of p16, p21, and p53-enhanced green fluorescent protein (EGFP) recombinant plasmids, HUVECs entered G1-phase cell cycle arrest. By days 3 and 5, HUVECs transfected with p16-EGFP showed an increased proportion of senescent cells, and this increase was more prominent in the GFP-positive cell population, which exhibited 68% of senescent cells. Transfection of p21 also induced senescence but only by day 5. Cotransfection of p16 and p21 showed no additive effect. Transfection of p21 or p53 induced apoptosis in HUVECs. Next, we suppressed endogenous p53, p21, p16, or retinoblastoma (Rb) gene expression through small interference RNA strategy and investigated their influence in p16- and p21-initiated endothelial cell senescence. Analysis indicated that suppression of p53 expression can abolish senescence induced by p16 overexpression. Paradoxically, this effect was not observed when p21 was suppressed. On the other hand, suppression of Rb eliminated senescence initiated by either p16 or p21 overexpression. In summary, the p53/p21 pathway is mainly responsible for GC-induced apoptosis, but the coordinated activation of the p53/p21 and p16 pathway is responsible for GC-induced endothelial cell senescence through a Rb-dependent mechanism.
Mesenchymal stem cell adhesion to cardiac microvascular endothelium: activators and mechanisms
Authors: Segers Vincent F. M. , Van Riet Ivan , Andries Luc J. , Lemmens Katrien , Demolder Marc J. , De Becker Ann J. M. L. , Kockx Mark M. , De Keulenaer Gilles W.
Published: October 2005

Circulating stem cells home within the myocardium, probably as the first step of a tissue regeneration process. This step requires adhesion to cardiac microvascular endothelium (CMVE). In this study, we studied mechanisms of adhesion between CMVE and mesenchymal stem cells (MSCs). Adhesion was studied in vitro and in vivo. Isolated 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate-labeled rat MSCs were allowed to adhere to cultured CMVE in static and dynamic conditions. Either CMVE or MSCs were pretreated with cytokines [IL-1β, IL-3, IL-6, stem cell factor, stromal cell-derived factor-1, or TNF-α, 10 ng/ml]. Control or TNF-α-treated MSCs were injected intracavitarily in rat hearts in vivo. In baseline in vitro conditions, the number of MSCs that adhered to CMVE was highly dependent on the flow rate of the superfusing medium but remained significant at venous and capillary shear stress amplitudes. Activation of both CMVE and MSCs with TNF-α or IL-1β before adhesion concentration dependently increased adhesion of MSCs at each studied level of shear stress. Consistently, in vivo, activation of MSCs with TNF-α before injection significantly enhanced cardiac homing of MSCs. TNF-α-induced adhesion could be completely blocked by pretreating either CMVE or MSCs with anti-VCAM-1 monoclonal antibodies but not by anti-ICAM-1 antibodies. Adhesion of circulating MSCs in the heart appears to be an endothelium-dependent process and is sensitive to modulation by activators of both MSCs and endothelium. Inflammation and the expression of VCAM-1 but not ICAM-1 on both cell types have a regulatory effect on MSC homing in the heart.
Effect of thrombolysis on myocardial injury: recombinant tissue plasminogen activator vs. alfimeprase
Authors: Hong Ting-Ting , Huang Jinbao , Lucchesi Benedict R.
Published: October 2005

Plasmin-dependent thrombolytic agents are potentially prothrombotic and proinflammatory. Alfimeprase, a zinc-containing metalloproteinase, degrades fibrin directly and achieves thrombolysis independent of plasmin formation. This study examines the hypothesis that thrombolysis in the absence of plasmin generation results in improved myocardial salvage on reperfusion. The thrombolytic effects of recombinant tissue plasminogen activator [rt-PA; 0.022 mg/kg, 1/10 of which was administered as a loading dose; the rest (9/10) was infused over 60 min by intracoronary (ic) administration] or alfimeprase (0.5 mg/kg over 1 min ic) were evaluated in a canine model of arterial thrombosis involving electrolytic injury of the left circumflex (LCX) coronary artery. Both agents induced thrombolysis, with onset of reperfusion being more rapid after alfimeprase compared with rt-PA (1.5 ± 0.6 vs. 10.1 ± 2.1 min). In the absence of adjunctive therapy, time to reocclusion after alfimeprase was 3.2 ± 0.5 min compared with 77.5 ± 31.9 min with rt-PA. The glycoprotein IIb/IIIa platelet receptor antagonist CRL-42796 prolonged reperfusion time after thrombolysis with alfimeprase or rt-PA. The effect of each lytic agent on myocardial infarct size was examined in a separate group of dogs subjected to 60 min of LCX coronary artery ligation and 4 h of reperfusion. Myocardial infarct size, expressed as percentage of the risk region, was larger (32.16 ± 3.95%) after rt-PA compared with alfimeprase (19.85 ± 3.61%) or that of the saline control group (18.46 ± 3.34%). rt-PA in contrast to alfimeprase, a direct-acting fibrinolytic agent, is associated with an increase in myocyte reperfusion injury.
Sustained preconditioning induced by cardiac transgenesis with the tetracycline transactivator
Authors: Turnbull Lynne , Zhou Hui-Zhong , Swigart Philip M. , Turcato Sally , Karliner Joel S. , Conklin Bruce R. , Simpson Paul C. , Baker Anthony J.
Published: October 2005

Preconditioning protocols that protect the heart from ischemic injury may aid in the development of new therapies. However, the temporal window of cardioprotection is limited to a few days after the preconditioning stimulus. Here we report a sustained cardioprotected phenotype in mice expressing a tetracycline transactivator (tTA) transcription factor under the control of the α-myosin heavy chain (αMHC) promoter. αMHC-tTA mice were originally designed for tetracycline-regulated gene expression in the heart (Tet system). However, we found that after 45 min of global ischemia at 37°C, left ventricular developed pressure (LVDP) of Langendorff-perfused αMHC-tTA mouse hearts rapidly recovered in 5 min to 60% of initial levels, whereas LVDP of wild-type (WT) littermates recovered to only 10% of the initial level. Improved postischemic recovery of function for αMHC-tTA hearts was associated with a 50% decrease of infarct size and a significantly smaller release of lactate dehydrogenase to the coronary effluent. Improved postischemic recovery was not attributable to differences in coronary flow that was similar for WT- and αMHC-tTA hearts during recovery. Moreover, improved postischemic recovery of αMHC-tTA hearts was not abolished by inhibitors of classical cardioprotective effectors (mitochondrial ATP-sensitive K+ channels, PKC, or adenosine receptors), suggesting a novel mechanism. Finally, the tetracycline analog doxycycline, which inhibits binding of tTA to DNA, did not abolish improved recovery for αMHC-tTA hearts. The sustained cardioprotected phenotype of αMHC-tTA hearts may have implications for developing new therapies to minimize cardiac ischemic injury. Furthermore, investigations of cardioprotection using the Tet system may be aberrantly influenced by sustained preconditioning induced by cardiac transgenesis with tTA.