bluuebunny/crossref_metadata_2025 huggingface dataset:
Gastric enteric neurones that respond to luminal injury
Authors: Schicho R. , Holzer P. , Lippe I. TH.
Published: April 2004

Challenge of the rat gastric mucosa with HCl stimulates intrinsic neurones in the myenteric plexus of the stomach as demonstrated by immunohistochemical detection of c‐Fos. In multiple labelling experiments of whole‐mounts and sections of the gastric corpus we determined the chemical code of the stimulated neurones and investigated further whether neural pathways involving capsaicin‐sensitive afferents, cholinergic neurones or the vagal system contribute to the stimulation of these neurones. Intragastric (IG) administration of 0.5 m HCl caused c‐Fos expression in 12% of myenteric neurones, whereas IG saline failed to induce c‐Fos. All stimulated neurones stained for nitric oxide synthase (NOS), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY), but not for choline acetyltransferase (ChAT). Fibres coexpressing NOS/VIP/NPY were found predominantly in the external muscle layer and the muscularis mucosae of the stomach wall. Pretreatment with capsaicin or hexamethonium, combination of both pretreatments or vagotomy reduced HCl‐induced c‐Fos expression by 54%, 66%, 63% and 68%, respectively. The data indicate that mucosal acid challenge of the stomach stimulates inhibitory motor neurones in the myenteric plexus and that capsaicin‐sensitive afferents as well as cholinergic neurones participate in the neuronal stimulation probably via a vago–vagal reflex.
Role of peripheral CRF signalling pathways in stress‐related alterations of gut motility and mucosal function
Authors: Taché Y. , Perdue M. H.
Published: April 2004

Central corticotrophin releasing‐factor (CRF) signalling pathways are involved in the endocrine, behavioural and visceral responses to stress. Recent studies indicate that peripheral CRF‐related mechanisms also contribute to stress‐induced changes in gut motility and intestinal mucosal function. Peripheral injection of CRF or urocortin inhibits gastric emptying and motility through interaction with CRF2 receptors and stimulates colonic transit, motility, Fos expression in myenteric neurones and defecation through activation of CRF1 receptors. With regard to intestinal epithelial cell function, intraperitoneal CRF increases ion secretion and mucosal permeability to macromolecules. The motility and mucosal changes induced by peripheral CRF mimic those induced by acute stress. In addition, CRF receptor antagonists given peripherally prevent acute restraint and water avoidance stress‐induced delayed gastric emptying, stimulation of colonic motor function and mucosal permeability. Similarly, early trauma enhanced intestinal mucosal dysfunction to an acute stressor in adult rats and the response is prevented by peripheral injection of CRF antagonist. Chronic psychological stress results in reduced host defence and initiates intestinal inflammation through mast cell‐dependent mechanisms. These findings provide convergent evidence that activation of peripheral CRF receptors and mast cells are important mechanisms involved in stress‐related alterations of gut physiology.
New insights into human enteric neuropathies
Authors: De Giorgio R. , Guerrini S. , Barbara G. , Cremon C. , Stanghellini V. , Corinaldesi R.
Published: April 2004

The functioning of enteric neuronal circuitries has been elucidated in the recent past. Evidence is now gathering to explain how dysfunction of the enteric nervous system (ENS) may lead to human gastrointestinal motor disorders. These conditions include achalasia, congenital hypertrophic pyloric stenosis, chronic intestinal pseudo‐obstruction, Hirschsprung's disease, chronic idiopathic constipation, and probably irritable bowel syndrome. Degenerative, inflammatory and genetic mechanisms exert a critical role in ENS dysfunction underlying gut dysmotility. The study of the ENS abnormalities in gut dysmotility provides a framework to better understand the mechanisms involved in degeneration and neuronal loss and fosters the development of targeted therapeutic options.
Pathophysiology of vascular dysfunction in a rat model of chronic joint inflammation
Authors: Egan Colin G. , Lockhart John C. , Ferrell William R.
Published: April 2004

The impact of chronic joint inflammation on articular vascular function in rats was investigated to address whether joint swelling and the associated vascular dysfunction are dependent upon a common prostanoid mechanism. Urinary nitrate/nitrite (NOx) and PGE2 excretion, knee joint diameter and body weight were measured following induction of adjuvant‐induced arthritis (AIA). Ten days postinduction of AIA, joint vascular reactivity was assessed by measuring the perfusion response using a laser Doppler imager (LDI) to topical application of acetylcholine (ACh) and sodium nitroprusside (SNP). Four groups were compared: a non‐inflamed control group and three AIA groups treated i.p. with vehicle, indomethacin or SC‐236 (at equimolar doses). The selective cyclooxygenase‐2 (COX‐2) inhibitor (SC‐236) was used to differentiate between COX‐1 and ‐2‐derived prostaglandins. Urinary NOx and PGE2 levels increased substantially during the early phase of AIA but decreased thereafter. Toxicity to indomethacin but not SC‐236 was observed, as indicated by a marked decrease in body weight. Joint swelling was similarly attenuated by indomethacin and SC‐236 (P= 0.0001 cf. vehicle‐treated AIA; n= 5–6 per group), indicating that this is due to COX‐2 and not COX‐1 inhibition. The AIA‐induced changes in urinary NOx and PGE2 were corrected by both COX inhibitors. While vascular reactivity to ACh and SNP was significantly attenuated by AIA (P < 0.002; n= 5–10 per group), the perfusion responses to these vasodilating agents were similar in all three AIA groups, demonstrating that the vascular dysfunction was not corrected by inhibition of either COX‐1 or COX‐2 enzymes. Furthermore, the attenuation of both ACh and SNP‐induced responses in AIA suggest that vascular dysfunction was not exclusively endothelial in nature. In conclusion, the joint swelling and vascular dysfunction associated with AIA appear to be mediated, at least in part, by independent mechanisms. While COX‐1/COX‐2 inhibition reduced joint swelling, vascular dysfunction in AIA is independent of constitutive or inducible prostanoid mechanisms, and appears not to be solely endothelial‐derived, but to involve other components such as the vascular smooth muscle.
Glycine transporter type 1 blockade changes NMDA receptor‐mediated responses and LTP in hippocampal CA1 pyramidal cells by altering extracellular glycine levels
Authors: Martina Marzia , Gorfinkel Yelena , Halman Samantha , Lowe John A. , Periyalwar Pranav , Schmidt Christopher J. , Bergeron Richard
Published: April 2004

Long‐term potentiation (LTP) in the hippocampal CA1 region requires the activation of NMDA receptors (NMDARs). NMDAR activation in turn requires membrane depolarization as well as the binding of glutamate and its coagonist glycine. Previous pharmacological studies suggest that the glycine transporter type 1 (GlyT1) maintains subsaturating concentrations of glycine at synaptic NMDARs. Antagonists of GlyT1 increase levels of glycine in the synaptic cleft and, like direct glycine site agonists, can augment NMDAR currents and NMDAR‐mediated functions such as LTP. In addition, stimulation of the glycine site initiates signalling through the NMDAR complex, priming the receptors for clathrin‐dependent endocytosis. We have used a new potent GlyT1 antagonist, CP‐802,079, with whole‐cell patch‐clamp recordings in acute rat hippocampal slices to determine the effect of GlyT1 blockade on LTP. Reverse microdialysis experiments in the hippocampus of awake, freely moving rats, showed that this drug elevated only the extracellular concentration of glycine. We found that CP‐802,079, sarcosine and glycine significantly increased the amplitude of the NMDAR currents and LTP. In contrast, application of higher concentrations of CP‐802,079 and glycine slightly reduced NMDAR currents and did not increase LTP. Overall, these data suggest that the level of glycine present in the synaptic cleft tightly regulates the NMDAR activity. This level is kept below the ‘set point’ of the NMDAR internalization priming mechanism by the presence of GlyT1‐dependent uptake.
Detection of the Intrinsic Size of Sagittarius A* Through Closure Amplitude Imaging
Authors: Bower Geoffrey C. , Falcke Heino , Herrnstein Robeson M. , Zhao Jun-Hui , Goss W. M. , Backer Donald C.
Published: April 2004

We have detected the intrinsic size of Sagittarius A*, the Galactic center radio source associated with a supermassive black hole, showing that the short-wavelength radio emission arises from very near the event horizon of the black hole. Radio observations with the Very Long Baseline Array show that the source has a size of 24 ± 2 Schwarzschild radii at 7-millimeter wavelength. In one of eight 7-millimeter epochs, we also detected an increase in the intrinsic size of

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. These observations place a lower limit to the mass density of Sagittarius A* of 1.4 × 10
4
solar masses per cubic astronomical unit.
MARKOV QUANTUM FIELDS ON A MANIFOLD
Authors: DIMOCK J.
Published: April 2004

We study scalar quantum field theory on a compact manifold. The free theory is defined in terms of functional integrals. For positive mass it is shown to have the Markov property in the sense of Nelson. This property is used to establish a reflection positivity result when the manifold has a reflection symmetry. In dimension d=2 we use the Markov property to establish a sewing operation for manifolds with boundary circles. Also in d=2 the Markov property is proved for interacting fields.
STRUCTURAL WEB SEARCH ENGINE
Authors: RAKHSHAN ARASH , HOLDER LAWRENCE B. , COOK DIANE J.
Published: April 2004

We present a new approach in web search engines. The web creates new challenges for information retrieval. The vast improvement in information access is not the only advantage resulting from the keyword search. Additionally, much potential exists for analyzing interests and relationships within the structure of the web. The creation of a hyperlink by the author of a web page explicitly represents a relationship between the source and destination pages which demonstrates the hyperlink structure between web pages. Our web search engine searches not only for the keywords in the web pages, but also for the hyperlink structure between them. Comparing the results of structural web search versus keyword-based search indicates an improved ability to access desired information. We also discuss steps toward mining the queries input to the structural web search engine.
A STUDY OF HEURISTIC APPROACHES FOR BREAKING SHORT CRYPTOGRAMS
Authors: MORELLI RALPH , WALDE RALPH , SERVOS WILLIAM
Published: April 2004

In this study, we compare the use of genetic algorithms (GAs) and other forms of heuristic search in the cryptanalysis of short cryptograms. This paper expands on the work presented at FLAIRS-2003, which established the feasibility of a word-based genetic algorithm (GA) for analyzing short cryptograms.1 In this study the following search heuristics are compared both theoretically and experimentally: hill-climbing, simulated annealing, word-based and frequency-based genetic algorithms. Although the results reported apply to substitution ciphers in general, we focus in particular on short substitution cryptograms, such as the kind found in newspapers and puzzle books. Short cryptograms present a more challenging form of the problem. The word-based approach uses a relatively small dictionary of frequent words. The frequency-based approaches use frequency data for 2-, 3- and 4-letter sequences. The study shows that all of the optimization algorithms are successful at breaking short cryptograms, but perhaps more significantly, the most important factor in their success appears to be the choice of fitness measure employed.
MDL-BASED CONTEXT-FREE GRAPH GRAMMAR INDUCTION AND APPLICATIONS
Authors: JONYER ISTVAN , HOLDER LAWRENCE B. , COOK DIANE J.
Published: April 2004

We present an algorithm for the inference of context-free graph grammars from examples. The algorithm builds on an earlier system for frequent substructure discovery, and is biased toward grammars that minimize description length. Grammar features include recursion, variables and relationships. We present an illustrative example, demonstrate the algorithm's ability to learn in the presence of noise, and show real-world examples.
ORTHOGRAPHIC CASE RESTORATION USING SUPERVISED LEARNING WITHOUT MANUAL ANNOTATION
Authors: NIU CHENG , LI WEI , DING JIHONG , SRIHARI ROHINI K.
Published: April 2004

One challenge in text processing is the treatment of case insensitive documents such as speech recognition results. The traditional approach is to re-train a language model excluding case-related features. This paper presents an alternative two-step approach whereby a preprocessing module (Step 1) is designed to restore case-sensitive form which is subsequently processed by the original system (Step 2). Step 1 is mainly implemented as a Hidden Markov Model trained on a large raw corpus of case sensitive documents. It is demonstrated that this approach (i) outperforms the feature exclusion approach for named entity tagging, (ii) leads to limited degradation for parsing, relationship extraction and case insensitive question answering, (iii) reduces system complexity, and (iv) has wide applicability: the restored text can be used in both statistical model and rule-based systems.
A MEREOLOGICAL THEORY OF FRAMES OF REFERENCE
Authors: BITTNER THOMAS
Published: April 2004

In this paper a mereological theory of frames of reference is presented. It shows that mereology extended by the notion of granularity and approximation is sufficient to provide a theory for location based features of frames of reference. More complex theories, taking also into account orientation and metric properties can be built as extensions of the presented theory. In order to take the hierarchical organization of frames of reference into account we introduce the notion of stratified approximation to facilitate transformations between different levels of granularity. This paper shows that the ontological grounding of the theory of frames of reference into mereology allows us to give a clear semantics to the notion 'degree of parthood' which is central to the notion of approximation. It also shows how epistemic aspects which affect the use of frames of reference help us to understand the feature of epistemic vagueness and the way it affects the notions of approximation and of degree of parthood.
PREDICTING INHABITANT ACTION USING ACTION AND TASK MODELS WITH APPLICATION TO SMART HOMES
Authors: RAO SIRA PANDURANGA , COOK DIANE J.
Published: April 2004

An intelligent home is likely in the near future. An important ingredient in an intelligent environment such as a home is prediction – of the next low-level action, the next location, and the next high-level task that an inhabitant is likely to perform. In this paper we model inhabitant actions as states in a simple Markov model. We introduce an enhancement to this basic approach, the Task-based Markov model (TMM) method. TMM discovers high-level inhabitant tasks using the supplied unlabeled data. We investigate clustering of actions to identify tasks, and integrate clusters into a hidden Markov model that predicts the next inhabitant action. We validate our approach and observe that for simulated data we achieve good accuracy using both the simple Markov model and the TMM, whereas on real data we see that simple Markov models outperform the TMM. We also perform an analysis of the performance of the HMM in the framework of the TMM when diverse patterns are introduced into the data.
Phorbol esters affect skeletal muscle glucose transport in a fiber type-specific manner
Authors: Wright David C. , Geiger Paige C. , Rheinheimer Mark J. , Han Dong Ho , Holloszy John O.
Published: April 2004

Recent evidence has shown that activation of lipid-sensitive protein kinase C (PKC) isoforms leads to skeletal muscle insulin resistance. However, earlier studies demonstrated that phorbol esters increase glucose transport in skeletal muscle. The purpose of the present study was to try to resolve this discrepancy. Treatment with the phorbol ester 12-deoxyphorbol-13-phenylacetate 20-acetate (dPPA) led to an ∼3.5-fold increase in glucose transport in isolated fast-twitch epitrochlearis and flexor digitorum brevis muscles. Phorbol ester treatment was additive to a maximally effective concentration of insulin in fast-twitch skeletal muscles. Treatment with dPPA did not affect insulin signaling in the epitrochlearis. In contrast, phorbol esters had no effect on basal glucose transport and inhibited maximally insulin-stimulated glucose transport ∼50% in isolated slow-twitch soleus muscle. Furthermore, dPPA treatment inhibited the insulin-stimulated tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and the threonine and serine phosphorylation of PKB by ∼50% in the soleus. dPPA treatment also caused serine phosphorylation of IRS-1 in the slow-twitch soleus muscle. In conclusion, our results show that phorbol esters stimulate glucose transport in fast-twitch skeletal muscles and inhibit insulin signaling in slow-twitch soleus muscle of rats. These findings suggest that mechanisms other than PKC activation mediate lipotoxicity-induced whole body insulin resistance.
SDF-1/CXCL12 regulates cAMP production and ion transport in intestinal epithelial cells via CXCR4
Authors: Dwinell Michael B. , Ogawa Hiroyuki , Barrett Kim E. , Kagnoff Martin F.
Published: April 2004

Human colonic epithelial cells express CXCR4, the sole cognate receptor for the chemokine stromal cell-derived factor (SDF)-1/CXC chemokine ligand (CXCL) 12. The aim of this study was to define the mechanism and functional consequences of signaling intestinal epithelial cells through the CXCR4 chemokine receptor. CXCR4, but not SDF-1/CXCL12, was constitutively expressed by T84, HT-29, HT-29/-18C1, and Caco-2 human colon epithelial cell lines. Studies using T84 cells showed that CXCR4 was G protein-coupled in intestinal epithelial cells. Moreover, stimulation of T84 cells with SDF-1/CXCL12 inhibited cAMP production in response to the adenylyl cyclase activator forskolin, and this inhibition was abrogated by either anti-CXCR4 antibody or receptor desensitization. Studies with pertussis toxin suggested that SDF-1/CXCL12 activated negative regulation of cAMP production through Giα subunits coupled to CXCR4. Consistent with the inhibition of forskolin-stimulated cAMP production, SDF-1/CXCL12 also inhibited forskolin-induced ion transport in voltage-clamped polarized T84 cells. Taken together, these data indicate that epithelial CXCR4 can transduce functional signals in human intestinal epithelial cells that modulate important cAMP-mediated cellular functions.
Chronic allergy to dietary ovalbumin induces lymphocyte migration to rat small intestinal mucosa that is inhibited by MAdCAM-1
Authors: Ogawa Toshiko , Miura Soichiro , Tsuzuki Yoshikazu , Ogino Takashi , Teramoto Ken , Inamura Toshiaki , Watanabe Chikako , Hokari Ryota , Nagata Hiroshi , Ishii Hiromasa
Published: April 2004

Few models have described a chronic food allergy with morphological changes in the intestinal mucosa. Here we established an ovalbumin (OVA)-induced, cell-mediated, allergic rat model and examined lymphocyte migration in the gut. Brown Norway rats were intraperitoneally sensitized to OVA and then given 10 mg OVA/day by gastric intubation for 6 wk. Lymphocyte subsets and adhesion molecules were examined immunohistochemically, and the migration of T lymphocytes to microvessels of Peyer's patches and villus mucosa was observed by using an intravital microscope. Serum OVA-specific IgG and IgE levels were increased in animals repeatedly exposed to OVA. Significant villus atrophy and increased crypt depth was accompanied by increased infiltration of T lymphocytes in the small intestinal mucosa of the group given OVA. Expression of rat mast cell protease II and of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was also increased in these groups. The administration of anti-MAdCAM-1 antibody significantly attenuated the OVA-induced changes in the mucosal architecture and in CD4 T lymphocyte infiltration. Intravital observation demonstrated that in rats with a chronic allergy, T lymphocytes significantly accumulated in villus microvessels as well as in Peyer's patches via a MAdCAM-1-dependent process. Our model of chronic food allergy revealed that lymphocyte migration was increased with MAdCAM-1 upregulation.
IGF-I increases IGFBP-5 and collagen α1(I) mRNAs by the MAPK pathway in rat intestinal smooth muscle cells
Authors: Xin Xiping , Hou Yong Tai , Li Lina , Schmiedlin-Ren Phyllissa , Christman Gregory M. , Cheng Hsin-Lin , Bitar Khalil N. , Zimmermann Ellen M.
Published: April 2004

IGF-I is a potent fibrogenic growth factor that stimulates proliferation of intestinal smooth muscle cells and increases synthesis of collagen and IGF-I-binding proteins by the cells. These processes contribute to intestinal fibrosis that develops in patients with Crohn's disease and in Lewis-strain rats with experimental Crohn's disease. The aim of this study was to determine which early docking proteins are associated with IGF-I receptor signal transduction and which transduction pathway is involved in IGF-I-mediated gene regulation in intestinal smooth muscle cells. Primary cultures of smooth muscle cells isolated from the muscularis externa of the distal colon of Lewis rats were treated with IGF-I (100 ng/ml). Immunoprecipitation studies demonstrated that IGF-I stimulation resulted in tyrosine phosphorylation of IRS-1, IRS-2, and Shc. Coimmunoprecipitation demonstrated a close association between the IGF-I receptor and these three early docking proteins. Concurrent treatment with the MAPK inhibitor PD98059 (10 μM) resulted in an inhibition of the IGF-I-mediated increase in IGFBP-5 and collagen α1(I) mRNAs, while concurrent treatment with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin (100 nM) had no effect. In additional experiments, cells were transiently transfected with adenoviral vectors dominantly expressing inactive mutant Akt or constitutively expressing wild-type Akt. In both cases, the IGF-I-mediated increase in collagen I protein did not differ from that observed in control cultures that had been transfected with an adenoviral vector carrying the LacZ reporter gene. These results suggest that the MAPK pathway is key to IGF-I-mediated gene regulation in intestinal smooth muscle cells, whereas data do not suggest a role for the Akt-dependent pathway in our system.
NOS2 deficiency increases intestinal metabolism both in nonstimulated and endotoxemic mice
Authors: Vissers Yvonne L. J. , Hallemeesch Marcella M. , Soeters Peter B. , Lamers Wouter H. , Deutz Nicolaas E. P.
Published: April 2004

Animal studies have suggested that nitric oxide (NO) synthases (NOS) play a role in the regulation of protein metabolism in endotoxemia. We therefore investigated the role of inducible NOS (NOS2) on intestinal protein and neuronal NOS (NOS1) and endothelial NOS (NOS3) on amino acid metabolism. Three groups of mice were studied: 1) wild-type (WT), 2) NOS2 knockout (NOS2-KO), and 3) NOS2-KO + Nω-nitro-l-arginine methyl ester (NOS2-KO + l-NAME), both in nonstimulated and LPS-treated conditions. By infusion of the stable isotopes l-[phenyl-2H5]Phe, l-[phenyl-2H2]Tyr, l-[guanidino-15N2]Arg, and l-[ureido-13C; 2H2]citrulline (Cit), intestinal protein, amino acid, and Arg/NO metabolism were studied on the whole body level and across intestine. In nonstimulated situations, NOS2 deficiency increased whole body protein turnover and intestinal Gln uptake and Cit production. In NOS2-KO + l-NAME, the above-mentioned changes were reversed. After LPS in WT, whole body NO and Cit production increased. In contrast to this, LPS decreased net intestinal Gln uptake, whole body NO, and Cit production in NOS2-KO mice. Treatment of NOS2-KO + l-NAME with LPS was lethal in eight of eleven mice (73%). The surviving mice in this group showed a major drop in intestinal protein breakdown and synthesis to almost zero. Thus both in baseline conditions and during endotoxemia, the absence of NOS2 upregulated NOS1 and/or NOS3, which increased intestinal metabolism. The drop in intestinal protein metabolism in the endotoxemic NOS2-KO + l-NAME group might play a role in mortality in that group.
Dietary cholesterol stimulates CYP7A1 in rats because farnesoid X receptor is not activated
Authors: Xu Guorong , Pan Lu-xing , Li Hai , Shang Quan , Honda Akira , Shefer Sarah , Bollineni Jaya , Matsuzaki Yasushi , Tint G. Stephen , Salen Gerald
Published: April 2004

Cholesterol feeding upregulates CYP7A1 in rats but downregulates CYP7A1 in rabbits. To clarify the mechanism responsible for the upregulation of CYP7A1 in cholesterol-fed rats, the effects of dietary cholesterol (Ch) and cholic acid (CA) on the activation of the nuclear receptors, liver X-receptor (LXR-α) and farsenoid X-receptor (FXR), which positively and negatively regulate CYP7A1, were investigated in rats. Studies were carried out in four groups ( n = 12/group) of male Sprague-Dawley rats fed regular chow (control), 2% Ch, 2% Ch + 1% CA, and 1% CA alone for 1 wk. Changes in mRNA expression of short heterodimer partner (SHP) and bile salt export pump (BSEP), target genes for FXR, were determined to indicate FXR activation, whereas the expression of ABCA1 and lipoprotein lipase (LPL), target genes for LXR-α, reflected activation. CYP7A1 mRNA and activity increased twofold and 70%, respectively, in rats fed Ch alone when the bile acid pool size was stable but decreased 43 and 49%, respectively, after CA was added to the Ch diet, which expanded the bile acid pool 3.4-fold. SHP and BSEP mRNA levels did not change after feeding Ch but increased 88 and 37% in rats fed Ch + CA. This indicated that FXR was activated by the expanded bile acid pool. When Ch or Ch + CA were fed, hepatic concentrations of oxysterols, ligands for LXR-α increased to activate LXR-α, as evidenced by increased mRNA levels of ABCA1 and LPL. Feeding CA alone enlarged the bile acid pool threefold and increased the expression of both SHP and BSEP. These results suggest that LXR-α was activated in rats fed both Ch or Ch + CA, whereas CYP7A1 mRNA and activity were induced only in Ch-fed rats where the bile acid pool was not enlarged such that FXR was not activated. In rats fed Ch + CA, the bile acid pool expanded, which activated FXR to offset the stimulatory effects of LXR-α on CYP7A1.
Tumor necrosis factor-α inhibits peroxisome proliferator-activated receptor γ activity at a posttranslational level in hepatic stellate cells
Authors: Sung Chin K. , She Hongyun , Xiong Shigang , Tsukamoto Hidekazu
Published: April 2004

Diminished activity of peroxisome proliferator-activated receptor γ (PPARγ) is implicated in activation of hepatic stellate cells (HSC), a critical event in the development of liver fibrosis. In the present study, we investigated PPARγ regulation by TNF-α in an HSC line designated as BSC. In BSC, TNF-α decreased both basal and ligand (GW1929)-induced PPARγ mRNA levels without changing its protein expression. Nuclear extracts from BSC treated with TNF-α showed decreased binding of PPARγ to PPAR-responsive element (PPRE) as determined by electrophoretic mobility shift assay. In BSC transiently transfected with a PPARγ1 expression vector and a PPRE-luciferase reporter gene, TNF-α decreased both basal and GW1929-induced transactivation of the PPRE promoter. TNF-α increased activation of ERK1/2 and JNK, previously implicated in phosphorylation of Ser82 of PPARγ1 and resultant negative regulation of PPARγ transactivity. In fact, TNF-α failed to inhibit transactivity of a Ser82Ala PPARγ1 mutant in BSC. TNF-α-mediated inhibition of PPARγ transactivity was not blocked with a Ser32Ala/Ser36Ala mutant of inhibitory NF-κBα (IκBα). These results suggest that TNF-α inhibits PPARγ transactivity in cultured HSC, at least in part, by diminished PPARγ-PPRE (DNA) binding and ERK1/2-mediated phosphorylation of Ser82 of PPARγ1, but not via the NF-κB pathway.
Hydrogen peroxide contributes to motor dysfunction in ulcerative colitis
Authors: Cao Weibiao , Vrees Matthew D. , Kirber Michael T. , Fiocchi Claudio , Pricolo Victor E.
Published: April 2004

Ulcerative colitis (UC) affects colonic motor function, but the mechanism responsible for this motor dysfunction is not well understood. We have shown that neurokinin A (NKA) may be an endogenous neurotransmitter mediating contraction of human sigmoid colonic circular muscle (HSCCM). To elucidate factors responsible for UC motor dysfunction, we examined the role of hydrogen peroxide (H2O2) in the decrease of NKA-induced response of HSCCM. As previously demonstrated, NKA-induced contraction or Ca2+increase of normal muscle cells is mediated by release of Ca2+from intracellular stores, because it was not affected by incubation in Ca2+-free medium (CFM) containing 200 μM BAPTA. In UC, however, CFM reduced both cell contraction and NKA-induced Ca2+increase, suggesting reduced Ca2+release from intracellular stores. In normal Ca2+medium, NKA and KCl caused normal Ca2+signal in UC cells but reduced cell shortening. The decreased Ca2+signal and contraction in response to NKA or thapsigargin were partly recovered in the presence of H2O2scavenger catalase, suggesting involvement of H2O2in UC-induced dysmotility. H2O2levels were higher in UC than in normal HSCCM, and enzymatically isolated UC muscle cells contained much higher levels of H2O2than normal cells, which were significantly reduced by catalase. H2O2treatment of normal cells in CFM reproduced the reduction of NKA-induced Ca2+release observed in UC cells. In addition, H2O2caused a measurable, direct release of Ca2+from intracellular stores. We conclude that H2O2may contribute to reduction of NKA-induced Ca2+release from intracellular Ca2+stores in UC and contribute to the observed colonic motor dysfunction.
Adaptative increase of ornithine production and decrease of ammonia metabolism in rat colonocytes after hyperproteic diet ingestion
Authors: Mouillé Béatrice , Robert Véronique , Blachier François
Published: April 2004

Chronic high-protein consumption leads to increased concentrations of NH4+/NH3in the colon lumen. We asked whether this increase has consequences on colonic epithelial cell metabolism. Rats were fed isocaloric diets containing 20 (P20) or 58% (P58) casein as the protein source for 7 days. NH4+/NH3concentration in the colonic lumen and in the colonic vein blood as well as ammonia metabolism by isolated surface colonic epithelial cells was determined. After 2 days of consumption of the P58 diet, marked increases of luminal and colonic vein blood NH4+/NH3concentrations were recorded when compared with the values obtained in the P20 group. Colonocytes recovered from the P58 group were characterized at that time and thereafter by an increased capacity for l-ornithine and urea production through arginase ( P < 0.05). l-Ornithine was mostly used in the presence of NH4Cl for the synthesis of the metabolic end product l-citrulline. After 7 days of the P58 diet consumption, however, the ammonia metabolism into l-citrulline was found lower ( P < 0.01) when compared with the values measured in the colonocytes recovered from the P20 group despite any decrease in the related enzymatic activities (i.e., carbamoyl-phosphate synthetase I and ornithine carbamoyl transferase). This decrease was found to coincide with a return of blood NH4+/NH3concentration in colonic portal blood to values close to the one recorded in the P20 group. In response to increased NH4+/NH3concentration in the colon, the increased capacity of the colonocytes to synthesize l-ornithine is likely to correspond to an elevated l-ornithine requirement for the elimination of excessive blood ammonia in the liver urea cycle. Moreover, in the presence of NH4Cl, colonocytes diminished their synthesis capacity of l-citrulline from l-ornithine, allowing a lower cellular utilization of this latter amino acid. These results are discussed in relationship with an adaptative process that would be related to both interorgan metabolism and to the role of the colonic epithelium as a first line of defense toward luminal NH4+/NH3concentrations.
Calcineurin mediates pancreatic growth in protease inhibitor-treated mice
Authors: Tashiro Mitsuo , Samuelson Linda C. , Liddle Rodger A. , Williams John A.
Published: April 2004

CCK acts on pancreatic acinar cells to increase intracellular Ca2+leading to secretion of digestive enzymes and, in the long term, pancreatic growth. Calcineurin (CN) is a serine/threonine-specific protein phosphatase activated by Ca2+and calmodulin that recently has been shown to participate in the growth regulation of cardiac and skeletal myocytes. We therefore tested the effect of two different CN inhibitors, cyclosporine A (CsA) and FK506, on mouse pancreatic growth induced by oral administration of the synthetic protease inhibitor camostat, a known stimulator of endogenous CCK release. Mice were fed a powdered diet with or without 0.1% camostat. Pancreatic wet weight, protein, and DNA were increased in response to camostat in a time-dependent manner over 10 days in ICR mice but not in CCK-deficient mice. Both CsA (15 mg/kg) and FK506 (3 mg/kg) given twice daily blocked the increase in pancreatic wet weight and protein and DNA content induced by camostat. The increase in plasma CCK induced by camostat was not blocked by CsA or FK506. Camostat feeding also increased the relative amount of CN protein, whereas levels of MAPKs, ERKs, and p38 were not altered. In summary, 1) CCK released by chronic camostat feeding induces pancreatic growth in mice; 2) this growth is blocked by treatment with both CsA and FK506, indicating a role for CN; 3) CCK stimulation also increases CN protein. In conclusion, activation and possibly upregulation of CN may participate in regulation of pancreatic growth by CCK in mice.
Dual role of MEK/ERK signaling in senescence and transformation of intestinal epithelial cells
Authors: Boucher Marie-Josée , Jean Dominique , Vézina Anne , Rivard Nathalie
Published: April 2004

The mitogen-activated protein kinase cascade operates downstream of Ras to convey cell-surface signals to the nucleus via nuclear translocation of ERK1 and ERK2. We and others have recently demonstrated that activation of ERK1/2 by growth factors is required for proliferation of intestinal epithelial crypt cells. However, it remained to be established whether ERK1/2 activation alone was sufficient to trigger intestinal epithelial cell (IEC) proliferation. To this aim, retrovirus encoding the hemagglutinin-tagged MAPK/ERK kinase (MEK)1 wild type (wtMEK), the upstream activator of ERK1/2, or a constitutively active mutant of MEK1 (MEK1-S218D/S222D; caMEK) were used to infect nonimmortalized human normal intestinal epithelial crypt cell cultures [human intestinal epithelial cells (HIEC)] and rodent immortalized intestinal crypt cells (IEC-6). Stable expression of caMEK but not wtMEK in HIEC led to the irreversible arrest of cellular proliferation (premature senescence). Concomitant with the onset of cell-cycle arrest was the induction of the cyclin-dependent kinase inhibitors p21Cip, p53, and p16INK4A. By contrast, overexpression of caMEK in IEC-6 cells induced growth factor relaxation for DNA synthesis, promoted morphological transformation and growth in soft agar, and did not affect expression of p21Cip, p53, and p16INK4A. We provided evidences that ERK1b, an alternatively spliced isoform of ERK1, is activated and may contribute to the deregulation of contact inhibition cell growth and transformation of these cells. Constitutive activation of MEK in IECs can produce either premature senescence or forced mitogenesis depending on the integrity of a senescence program controlled by the cell cycle inhibitors p53, p16INK4A, and p21CIP.
Role of liver-enriched transcription factors and nuclear receptors in regulating the human, mouse, and rat NTCP gene
Authors: Jung Diana , Hagenbuch Bruno , Fried Michael , Meier Peter J. , Kullak-Ublick Gerd A.
Published: April 2004

Hepatic uptake of bile acids is mediated by the Na+-taurocholate cotransporting polypeptide (NTCP; SLC10A1) of the basolateral hepatocyte membrane. Several cis-acting elements in the rat Ntcp gene promoter have been characterized. However, little is known about the mechanisms that control the expression of the human or mouse NTCP/Ntcp. We, therefore, compared the transcriptional regulation of the human and mouse NTCP/Ntcp gene with that of the rat. By computer alignment, a sequence in the 5′-regulatory region that is conserved between species was identified near the transcription start site. Huh7 cells were transfected with luciferase constructs containing the conserved region from each species. The hepatocyte nuclear factors (HNF)1α and -4α and the retinoid X receptor/retinoic acid receptor dimer (RXRα/RARα) bound and transactivated the rat but not the human or mouse NTCP/Ntcp promoters. In contrast, activation by the CCAAT/enhancer binding protein-β was specific for human and mouse NTCP/Ntcp. The only consensus motif present in all three species was HNF3β. HNF3β formed a specific DNA-protein complex in electrophoretic mobility shift assays and inhibited NTCP/Ntcp promoter activity in cotransfection assays. Finally, a minor repressive effect of bile acids was only found for rat Ntcp. The transcriptional repressor small heterodimer partner (SHP) did not affect NTCP/Ntcp promoter activity. We conclude that 1) the transcriptional regulation of the conserved NTCP/Ntcp 5′-regulatory region differs considerably among human, mouse, and rat; and 2) the conserved NTCP/Ntcp regulatory region is not directly regulated by SHP. Bile acids may regulate NTCP/Ntcp indirectly by modulating the capacity of nuclear factors to activate gene expression.
Distribution and function of the cannabinoid-1 receptor in the modulation of ion transport in the guinea pig ileum: relationship to capsaicin-sensitive nerves
Authors: MacNaughton Wallace K. , Van Sickle Marja D. , Keenan Catherine M. , Cushing Kelly , Mackie Ken , Sharkey Keith A.
Published: April 2004

We investigated the distribution and function of cannabinoid (CB)1receptors in the submucosal plexus of the guinea pig ileum. CB1receptors were found on both types of submucosal secretomotor neurons, colocalizing with VIP and neuropeptide Y (NPY), the noncholinergic and cholinergic secretomotor neurons, respectively. CB1receptors colocalized with transient receptor potential vanilloid-1 receptors on paravascular nerves and fibers in the submucosal plexus. In the submucosal ganglia, these nerves were preferentially localized at the periphery of the ganglia. In denervated ileal segments, CB1receptor immunoreactivity in submucosal neurons was not modified, but paravascular and intraganglionic fiber staining was absent. Short-circuit current ( Isc) was measured as an indicator of net electrogenic ion transport in Ussing chambers. In the ion-transport studies, Iscresponses to capsaicin, which activates extrinsic primary afferents, and to electrical field stimulation (EFS) were reduced by pretreatment with the muscarinic antagonist atropine, abolished by tetrodotoxin, but were unaffected by VIP receptor desensitization, hexamethonium, α-amino-3-hydroxy-5-methlisoxazole-4-proprionic acid, or N-methyl-d-aspartate glutamate receptor antagonists. The responses to capsaicin and EFS were reduced by 47 ± 12 and 30 ± 14%, respectively, by the CB1receptor agonist WIN 55,212–2. This inhibitory effect was blocked by the CB1receptor antagonist, SR 141716A. Iscresponses to forskolin or carbachol, which act directly on the epithelium, were not affected by WIN 55,212–2. The inhibitory effect of WIN 55,212–2 on EFS-evoked secretion was not observed in extrinsically denervated segments of ileum. Taken together, these data show cannabinoids act at CB1receptors on extrinsic primary afferent nerves, inhibiting the release of transmitters that act on cholinergic secretomotor pathways.
Gastrointestinal Satiety Signals III. Glucagon-like peptide 1, oxyntomodulin, peptide YY, and pancreatic polypeptide
Authors: Stanley Sarah , Wynne Katie , Bloom Steve
Published: April 2004

Many peptides are synthesized and released from the gastrointestinal tract and pancreas, including pancreatic polypeptide (PP) and the products of the gastrointestinal L cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY). Whereas their roles in regulation of gastrointestinal function have been known for some time, it is now evident that they also influence eating behavior. This review considers the anorectic peptides PYY, PP, GLP-1, and oxyntomodulin, which decrease appetite and promote satiety in both animal models and humans.
Vasoconstrictor effects of insulin in skeletal muscle arterioles are mediated by ERK1/2 activation in endothelium
Authors: Eringa Etto C. , Stehouwer Coen D. A. , van Nieuw Amerongen Geerten P. , Ouwehand Lenneke , Westerhof Nico , Sipkema Pieter
Published: April 2004

Insulin exerts both NO-dependent vasodilator and endothelin-dependent vasoconstrictor effects on skeletal muscle arterioles. The intracellular enzymes 1-phosphatidylinositol 3-kinase (PI3-kinase) and Akt have been shown to mediate the vasodilator effects of insulin, but the signaling molecules involved in the vasoconstrictor effects of insulin in these arterioles are unknown. Our objective was to identify intracellular mediators of acute vasoconstrictor effects of insulin on skeletal muscle arterioles. Rat cremaster first-order arterioles ( n = 40) were isolated, and vasoreactivity to insulin was studied using a pressure myograph. Insulin induced dose-dependent vasoconstriction of skeletal muscle arterioles (up to −22 ± 3% of basal diameter; P < 0.05) during PI3-kinase inhibition with wortmannin (50 nmol/l). Insulin-induced vasoconstriction was abolished by inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) with PD-98059 (40 μmol/l). In addition, inhibition of ERK1/2 without PI3-kinase inhibition uncovered insulin-mediated vasodilatation in skeletal muscle arterioles (up to 37 ± 10% of baseline diameter; P < 0.05). Effects of insulin on ERK1/2 activation in arterioles were then investigated by Western blot analysis. Insulin induced a transient 2.4-fold increase in ERK1/2 phosphorylation (maximal at ∼15 min) in skeletal muscle arterioles ( P < 0.05). Removal of the arteriolar endothelium abolished insulin-induced vasoconstriction, which suggests that activation of ERK1/2 in endothelial cells is involved in acute insulin-mediated vasoconstriction. To investigate this, acute effects of insulin on ERK1/2 phosphorylation were studied in human microvascular endothelial cells. In support of the findings in skeletal muscle arterioles, insulin induced a 1.9-fold increase in ERK1/2 phosphorylation (maximal at ∼15 min) in microvascular endothelial cells ( P < 0.05). We conclude that acute vasoconstrictor effects of insulin in skeletal muscle arterioles are mediated by activation of ERK1/2 in endothelium. This ERK1/2-mediated vasoconstrictor effect antagonizes insulin-induced, PI3-kinase-dependent vasodilatation in skeletal muscle arterioles. These findings provide a novel mechanism by which insulin may determine blood flow and glucose disposal in skeletal muscle.
Ozone-induced production of nitric oxide and TNF-α and tissue injury are dependent on NF-κB p50
Authors: Fakhrzadeh Ladan , Laskin Jeffrey D. , Laskin Debra L.
Published: April 2004

Ozone-induced lung injury is associated with increased production of reactive nitrogen intermediates and TNF-α, which have been implicated in the pathogenic process. Generation of these mediators is regulated in part by transcription factors, e.g., NF-κB and CCAAT/enhancer-binding protein (C/EBP). The present studies used NF-κB p50 knockout mice to assess the role of this transcription factor protein in ozone-induced inflammatory mediator production and toxicity. Treatment of wild-type (WT) mice with ozone (0.8 ppm, 3 h) resulted in a rapid increase in NF-κB binding activity in alveolar macrophages that peaked after 6–12 h. This response was attenuated in NF-κB p50−/−mice. In WT mice, but not NF-κB p50−/−mice, C/EBP was also markedly increased in macrophages following ozone inhalation. Ozone also induced changes in the mobility of C/EBP in gel shift assays, suggesting alterations in the transcription factor complex that may be important in controlling inflammatory gene expression. Whereas macrophages from WT mice produced increased quantities of nitric oxide and TNF-α following ozone inhalation, this was not observed in cells from NF-κB p50−/−mice. Ozone-induced decreases in expression of the anti-inflammatory cytokine IL-10 were also prevented in NF-κB p50−/−mice. In WT mice, ozone inhalation caused an increase in bronchoalveolar lavage protein, a marker of tissue damage. This was not evident in NF-κB p50−/−mice. There was also no evidence of peroxynitrite-mediated lung injury in these mice. These findings demonstrate that NF-κB and possibly C/EBP signaling are important in ozone-induced production of reactive nitrogen intermediates and TNF-α and in tissue injury.
Dissociation of hypothalamic noradrenergic activity and sympathoadrenal responses to recurrent hypoglycemia
Authors: de Vries Martin G. , Lawson Marcus A. , Beverly J. Lee
Published: April 2004

This study evaluated whether attenuation of sympathoadrenal responses to recurrent hypoglycemia is mediated by diminished noradrenergic activity in the hypothalamus. Male Sprague-Dawley rats received either once daily insulin (1.0 units/kg) injections or an equal administration of saline for 3 days. Both groups received an administration of insulin on the fourth day, during which blood glucose and plasma catecholamines were determined, and extracellular norepinephrine (NE) in the ventromedial hypothalamus (VMH) or paraventricular hypothalamic nucleus (PVN) was monitored with microdialysis. The peak response of plasma epinephrine to insulin-induced hypoglycemia (nadir ∼3.2 mmol/l) was significantly reduced during the fourth hypoglycemic episode (774 ± 134 pg/ml) compared with the first episode (2,561 ± 410 pg/ml, P < 0.001). Baseline levels of extracellular NE were elevated ∼25% ( P = 0.07) in the VMH and ∼46% ( P = 0.03) in the PVN after multiple hypoglycemic episodes. There was no difference in noradrenergic activity during the first or fourth hypoglycemic episode in either brain area. The reduced sympathoadrenal output after recurrent hypoglycemia is likely postsynaptic from hypothalamic NE release or is mediated via a collateral pathway.