[Detecting a peak in fraction beta by capillary electrophoresis: interference due to iomeprol]. / Détection d'un pic en fraction bêta par électrophorèse capillaire : interférence due à l'ioméprol.

Capillary zone electrophoresis for analysis of serum proteins, is a technic more and more used in laboratory medicine. We report the case of an interference of iomeprol, radioopaque agent, in a context of acute renal failure and aregenerative anemia in a 53 year-old patient.

Enteral delivery of proteins stimulates protein synthesis in human duodenal mucosa in the fed state through a mammalian target of rapamycin-independent pathway.

BACKGROUND: Glutamine modulates duodenal protein metabolism in fasted healthy humans, but its effects in a fed state remain unknown. OBJECTIVE: We aimed to assess the effects of either glutamine or an isonitrogenous protein mixture on duodenal protein metabolism in humans in the fed state. DESIGN: Twenty-four healthy volunteers were randomly included in 2 groups. Each volunteer was studied on 2 occasions in a random order and received, during 5 h, either an enteral infusion of maltodextrins alone (0.25 g · kg⁻¹ · h⁻¹; both groups) that mimicked a carbohydrate fed state or maltodextrins with glutamine (group 1) or an isonitrogenous (22.4 mg N · kg⁻¹ · h⁻¹) protein powder (group 2). Simultaneously, a continuous intravenous infusion of ¹³C-leucine and ²H5-phenylalanine (both 9 µmol · kg⁻¹ · h⁻¹) was performed. Endoscopic duodenal biopsies were taken. Leucine and phenylalanine enrichments were assessed by using gas chromatography-mass spectrometry in duodenal proteins and the intracellular free amino acids pool to calculate the mucosal fractional synthesis rate (FSR). Proteasome proteolytic activities and phosphokinase expression were assessed by using specific fluorogenic substrates and macroarrays, respectively. RESULTS: The FSR and proteasome activity were not different after the glutamine supply compared with after maltodextrins alone. In contrast, the FSR increased (1.7-fold increase; P < 0.05) after protein-powder delivery without modification of total proteasome activity. The protein powder increased insulinemia, PI3 kinase, and erk phosphorylation but did not affect the mammalian target of rapamycin (mTOR) pathway and mitogen-activated protein kinase signal-integrating kinase 1 phosphorylation. A trend for an increase of eukaryotic translation initiation factor 4E phosphorylation was observed (P = 0.07). CONCLUSION: In the carbohydrate fed state, enteral proteins but not glutamine increased duodenal protein synthesis through an mTOR independent pathway in humans.

Effects of essential amino acids or glutamine deprivation on intestinal permeability and protein synthesis in HCT-8 cells: involvement of GCN2 and mTOR pathways.

GCN2 and mTOR pathways are involved in the regulation of protein metabolism in response to amino acid availability in different tissues. However, regulation at intestinal level is poorly documented. The aim of the study was to evaluate the effects of a deprivation of essential amino acids (EAA) or glutamine (Gln) on these pathways in intestinal epithelial cells. Intestinal epithelial cell, HCT-8, were incubated during 6 h with 1/DMEM culture medium containing EAA, non EAA and Gln, 2/with saline as positive control of nutritional deprivation, 3/DMEM without EAA, 4/DMEM without Gln or 5/DMEM without Gln and supplemented with a glutamine synthase inhibitor (MSO, 4 mM). Intestinal permeability was evaluated by the measure of transepithelial electric resistance (TEER). Using [L-(2)H(3)]-leucine incorporation, fractional synthesis rate (FSR) was calculated from the assessed enrichment in proteins and free amino acid pool by GCMS. Expression of eiF2α (phosphorylated or not), used as marker of GCN2 pathway, and of 4E-BP1 (phosphorylated or not), used as a marker of mTOR pathway, was evaluated by immunoblot. Results were compared by ANOVA. Six-hours EAA deprivation did not significantly affect TEER and FSR but decreased p-4E-BP1 and increased p-eiF2α. In contrast, Gln deprivation decreased FSR and p-4E-BP1. MSO induced a marked decrease of TEER and FSR and an increase of p-eiF2α, whereas mTOR pathway remained activated. These results suggest that both mTOR and GCN2 pathways can mediate the limiting effects of Gln deprivation on protein synthesis according to its severity.

Glutamine induces nuclear degradation of the NF-κB p65 subunit in Caco-2/TC7 cells.

In the intestine, NF-κB is the main transcription factor involved in the anti-inflammatory effect of glutamine and we previously demonstrated that glutamine via its conversion to glutamate diminished the p65 protein content in Caco-2/TC7 cell nuclei without affecting the stimulating effect of IL-1ß on NF-κB [21]. However, the molecular mechanism by which glutamine acts is not established. We therefore tried to identify such a mechanism. Our results demonstrate that glutamine decreased the intracellular NF-κB through the nuclear ubiquitin-proteasome pathway requiring therefore the nuclear translocation of the factor. Indeed, time-course study revealed that glutamine induced an increase in the nuclear p65 content within the first 15 min of culture, the p65 nuclear and cytosolic content decreasing gradually thereafter to reach 50 % of the control value after 60 min. This translocation was initiated by the phosphorylation of IκBα by the IKKß subunit inducing its degradation and the p65 translocation. In parallel, glutamine activated the IKKα subunit which in turn phosphorylates p65 at Ser 536 which was responsible for p65 degradation by the nuclear proteasome. We also demonstrate that p38 MAPK lies between glutamine and the NF-κB pathway. In conclusion, this study identified for the first time the signaling pathway by which glutamine may protect against inflammatory conditions.

Effects of an enteral glucose supply on protein synthesis, proteolytic pathways, and proteome in human duodenal mucosa.

BACKGROUND: Previous studies have shown that the glucose supply reduces postoperative insulin resistance and improves patient outcomes. However, the effects of luminal glucose on intestinal mucosal proteins remain unknown. OBJECTIVE: We aimed to assess the effects of an enteral glucose supply on protein synthesis, proteolytic pathways, and proteome in human duodenal mucosa. DESIGN: Twenty healthy volunteers received a 5-h enteral infusion of either saline or glucose (0.12 g · kg(-1) · h(-1)). Simultaneously, a continuous intravenous infusion of l-[1-(13)C]leucine (12 µmol · kg(-1) · h(-1)) was maintained until endoscopy. The duodenal mucosal protein fractional synthesis rate (FSR) was calculated from leucine enrichments assessed in protein and free amino acid pools by gas chromatography-mass spectrometry. Cathepsin D, calpains, and chymotrypsin-like proteasome mucosal activities were evaluated by using specific fluorogenic substrates. A 2-dimensional PAGE-based comparative proteomics analysis was also performed on additional duodenal mucosal biopsy samples to identify differentially expressed proteins. RESULTS: Duodenal mucosal protein FSR and protease activities were not affected by glucose infusion relative to saline. Nevertheless, the comparative proteomics analysis indicated that 10 protein spots were significantly differentially expressed (ie, at least ±1.5-fold modulated; Student's t test, P < 0.05) in response to the glucose infusion relative to saline. Of the 8 proteins identified by mass spectrometry, α-enolase, cytoplasmic aconitate hydratase, and glutathione S-transferase ω-1 were upregulated, whereas epoxide hydrolase 2 was downregulated. CONCLUSION: Enteral glucose supply affected neither duodenal mucosal protein FSR nor activities of mucosal proteases but altered the duodenal mucosal proteome by modulating the expression of several enzymes involved mainly in carbohydrate and xenobiotic metabolism. This trial is registered at clinicaltrials.gov as NCT00213551.

Influence of leucine on protein metabolism, phosphokinase expression, and cell proliferation in human duodenum1,3.

BACKGROUND: Although leucine increases protein anabolism through the mammalian target of rapamycin (mTOR) pathway in human muscles, its effects on intestinal mucosal proteins remain unknown. OBJECTIVE: We aimed to assess the effects of leucine on duodenal protein metabolism in healthy humans and to elucidate the signaling pathways involved. DESIGN: Eleven healthy volunteers received for 5 h, on 2 occasions and in random order, an enteral supply of maltodextrins (0.25 g . kg(-1) . h(-1)) or maltodextrins and leucine (0.035 g . kg(-1) . h(-1)) simultaneously with a continuous intravenous infusion of [(2)H(5)]phenylalanine (9 µmol . kg(-1) .h(-1)). Endoscopic duodenal biopsy samples were collected and frozen until analyzed. Phenylalanine enrichment was assessed by gas chromatography-mass spectrometry in duodenal protein and in free intracellular amino acid pools used as precursor to calculate the mucosal fractional synthesis rate (FSR). Proteasome proteolytic activities and phosphokinase expression were assessed by using specific fluorogenic substrates or macroarrays, respectively. RESULTS: Leucine supplementation slightly reduced FSR (mean ± SEM: 81.3 ± 6.3%/d) compared with maltodextrins alone (91.7 ± 8.5%/d; P = 0.0537). In addition, total proteasome activity decreased significantly with leucine (236 ± 21 compared with 400 ± 58 relative fluorescence units/µg protein; P < 0.05), with no modification of chymotrypsin-like, trypsin-like, caspase-like, or peptidase activities. Leucine did not affect the mTOR pathway but did increase the phosphorylation states of PI3K, Akt, AMPK, p38 MAPK, JNK, GSK-3α/ß, STAT3, and STAT5 and increased cyclin D1 mRNA concentrations, which suggested that leucine may enhance cell proliferation. CONCLUSION: Enteral leucine supplementation decreased proteasome activity in duodenal mucosa and enhanced cell proliferation through the PI3K/Akt/GSK-3α/ß-catenin pathway. This trial was registered at clinicaltrials.gov as NCT01254110.

Immunoassay for human serum hemojuvelin.

BACKGROUND: Hemojuvelin, a critical regulator of iron homeostasis, is involved in the regulation of hepcidin expression and iron homeostasis. It is expressed both as a membrane-bound form and as a soluble one. Serum hemojuvelin can be produced by secretion following furin cleavage or by proteolytic cleavage of the membrane-bound form by matriptase 2 (TMPRSS6). These forms contribute to down-regulation of hepcidin expression upon iron deficiency or hypoxia. This study describes the development and validation of the first enzyme-linked immunosorbent assay for hemojuvelin in human serum. DESIGN AND METHODS: This assay is based on the use of a recombinant human repulsive guidance molecule-c peptide and a polyclonal antibody against hemojuvelin able to recognize the recombinant peptide and the native soluble hemojuvelin by immunoprecipitation. RESULTS: The enzyme-linked immunosorbent assay was validated and appeared to be a robust method with intra- and inter-coefficients of variance ranging from 2.6% to 15%. The assay was able to quantify hemojuvelin levels in a control population within a range from 0.88 to 1.14 mg/L. Patients with iron-refractory iron-deficiency anemia with a mutation in the TMPRSS6 gene were found to have lower levels of circulating hemojuvelin than those in healthy patients. The enzyme-linked immunosorbent assay also showed that soluble hemojuvelin levels were significantly higher in patients with anemia of chronic disease than in control individuals. CONCLUSIONS: This enzyme-linked immunosorbent assay has a good specificity and sensitivity for the quantification of soluble hemojuvelin in human serum and could be a valuable aid to understanding the physiological role of this protein.

Amino acid regulation of mammalian gene expression in the intestine.

Some amino acids exert a wide range of regulatory effects on gene expression via the activation of different signalling pathways and transcription factors, and a number of cis elements were shown to respond to changes in amino acid concentration. Particular attention has been paid to the effects of glutamine and arginine, which modulate a number of cell functions through the activation of various pathways in different tissues. In the intestine, appropriate concentrations of both arginine and/or glutamine contribute to facilitate cell proliferation, to limit the inflammatory response and apoptosis, and to modulate intermediary metabolism through specific transcription factors. Particularly, besides its role as a major fuel for enterocytes, the regulatory effects of glutamine have been extensively studied and the molecular mechanisms involved appear diversified and complex. Indeed, in addition to a major role of NF-kappaB in its anti-inflammatory action and a stimulatory role of AP-1 in its growth-promoting action and cell survival, the involvement of some other transcription factors, such as PPAR-gamma or HSF-1, was shown to maintain intestinal cell integrity. The signalling pathways leading to the activation of transcription factors imply several kinases, particularly MAP kinases in the effect of glutamine and p70 S6 kinase for those of arginine, but in most cases the precise pathways from the entrance of the aminoacid into the cell to the activation of gene transcription has remained elusive.

Is heparin plasma suitable for the determination of B-type natriuretic peptide on the Beckman-Coulter Access 2?

BACKGROUND: The use of heparin as an alternative to EDTA in the production of plasma samples is of particular interest for B-type natriuretic peptide (BNP) measurements. Lithium heparin is now widely used for the determination of biochemical parameters, including cardiac markers. The goal of this study was to determine the feasibility of measuring BNP using heparin plasma instead of EDTA plasma with the Access 2 system (Beckman-Coulter). METHODS: BNP was determined in heparin plasma and EDTA plasma from 24 patients within 1 h of blood collection. Additional measurements were performed with heparin plasma, every hour for the first 4 h, and then 8 h after the collection of blood that was stored at room temperature. RESULTS: At H(0), the observed BNP concentrations in heparin plasma were much higher (mean values 65% higher) than those in EDTA plasma. Using predetermined thresholds, this difference would lead to 30% discordance between samples in heparin and EDTA. BNP stability decreased over time in heparin plasma: immunoreactivity decreased approximately by 30% during the first 2 h and by 60% after 8 h. CONCLUSIONS: Heparin plasma does not seem to be a suitable alternative to EDTA plasma for measurement of BNP using the Access 2 system, even if measurements are performed immediately after blood sampling.

A diet containing whey protein, glutamine, and TGFbeta modulates gut protein metabolism during chemotherapy-induced mucositis in rats.

BACKGROUND: Mucositis, a common side effect of chemotherapy, is characterized by compromised digestive function, barrier integrity and immune competence. AIMS: Our aim was to evaluate the impact of a specifically designed diet Clinutren Protect (CP), which contains whey proteins, TGFbeta-rich casein, and free glutamine, on mucositis in rats. METHODS: Mucositis was induced by three consecutive injections (day 0, day 1, day 2) of methotrexate (2.5 mg/kg). Rats had free access to CP or placebo diets from days -7 to 9. In the placebo diet, whey proteins and TGFbeta-rich casein were replaced by TGFbeta-free casein and glutamine by alanine. Intestinal parameters were assessed at day 3 and 9. Values, expressed as mean +/- SEM, were compared using two-way ANOVA. RESULTS: At day 3, villus height was markedly decreased in the placebo (296 +/- 11 microm) and CP groups (360 +/- 10 microm) compared with controls (464 +/- 27 microm), but more markedly in the placebo as compared to CP group. The intestinal damage score was also reduced in the CP compared with the placebo group. Glutathione content increased in the CP compared with the placebo group (2.2 +/- 0.2 vs. 1.7 +/- 0.2 micromol/g tissue). Gut protein metabolism was more affected in the placebo than in the CP group. The fractional synthesis rate was decreased in the placebo group (93.8 +/- 4.9%/day) compared with controls (121.5 +/- 12.1, P < 0.05), but not in the CP group (106.0 +/- 13.1). In addition, at day 9, rats exhibited improved body weight and food intake recovery in the CP compared to the placebo group. CONCLUSIONS: Clinutren Protect feeding reduces intestinal injury in the acute phase of methotrexate-induced mucositis in rats and improves recovery.

Control of mammalian gene expression by amino acids, especially glutamine.

Molecular data rapidly accumulating on the regulation of gene expression by amino acids in mammalian cells highlight the large variety of mechanisms that are involved. Transcription factors, such as the basic-leucine zipper factors, activating transcription factors and CCAAT/enhancer-binding protein, as well as specific regulatory sequences, such as amino acid response element and nutrient-sensing response element, have been shown to mediate the inhibitory effect of some amino acids. Moreover, amino acids exert a wide range of effects via the activation of different signalling pathways and various transcription factors, and a number of cis elements distinct from amino acid response element/nutrient-sensing response element sequences were shown to respond to changes in amino acid concentration. Particular attention has been paid to the effects of glutamine, the most abundant amino acid, which at appropriate concentrations enhances a great number of cell functions via the activation of various transcription factors. The glutamine-responsive genes and the transcription factors involved correspond tightly to the specific effects of the amino acid in the inflammatory response, cell proliferation, differentiation and survival, and metabolic functions. Indeed, in addition to the major role played by nuclear factor-kappaB in the anti-inflammatory action of glutamine, the stimulatory role of activating protein-1 and the inhibitory role of C/EBP homology binding protein in growth-promotion, and the role of c-myc in cell survival, many other transcription factors are also involved in the action of glutamine to regulate apoptosis and intermediary metabolism in different cell types and tissues. The signalling pathways leading to the activation of transcription factors suggest that several kinases are involved, particularly mitogen-activated protein kinases. In most cases, however, the precise pathways from the entrance of the amino acid into the cell to the activation of gene transcription remain elusive.

Methotrexate induces intestinal mucositis and alters gut protein metabolism independently of reduced food intake.

One of the main secondary toxic side effects of antimitotic agents used to treat cancer patients is intestinal mucositis. This one is characterized by compromised digestive and absorptive functions, barrier integrity, and immune competence. At the same time, food intake is decreased, which may induce intestinal damages per se. The aim of the study was to characterize which alterations are specific to methotrexate, independently of the anorexic effect of the drug. Male Sprague-Dawley rats received subcutaneously saline solution as control group or 2.5 mg/kg of methotrexate during 3 days (D0-D2). Methotrexate-treated rats were compared with ad libitum and pair-fed controls. Histological examinations and specific markers of the immune and nonimmune gut barrier function were assessed at D4 or D7. Compared with ad libitum and pair-fed controls, methotrexate induced at D4 villus atrophy associated with epithelial necrosis. Mucosal protein synthesis rate and mucin contents of methotrexate treated rats were reduced. At the same time, cathepsin D proteolytic activity was increased compared with ad libitum and pair-fed controls, whereas calpain activity was increased when compared with the only pair-fed controls. These intestinal lesions were associated with various metabolic disturbances such as increased TNF-alpha level and inflammation score in the jejunum but also disturbances of amino acid concentrations in the duodenum and plasma. At D7, these alterations were partially or completely normalized. In addition to the consequences of a low food intake, methotrexate further impairs different biological processes leading to a dramatic loss of gut homeostasis. Targeted nutritional management of chemotherapy receiving patients should be set up to prevent or limit such alterations.

Combined enteral infusion of glutamine, carbohydrates, and antioxidants modulates gut protein metabolism in humans.

BACKGROUND: Available data suggest that nutrients can affect intestinal protein metabolism, which contributes to the regulation of gut barrier function. OBJECTIVE: We aimed to assess whether an oral nutritional supplement (ONS) containing glutamine (as the dipeptide Ala-Gln), carbohydrates, and antioxidants would modulate duodenal protein metabolism in healthy humans. DESIGN: Thirty healthy control subjects were included and, over a period of 5 h, received by nasogastric tube either saline or ONS providing 11.7 kcal/kg as 0.877 g Ala-Gln/kg, 3.9 g carbohydrates/kg, and antioxidants (29.25 mg vitamin C/kg, 9.75 mg vitamin E/kg, 195 microg beta-carotene/kg, 5.85 mg Se/kg, and 390 microg Zn/kg) or glutamine (0.585 g/kg, 2.34 kcal/kg). Simultaneously, a continuous intravenous infusion of l-[1-(13)C]-leucine was done until endoscopy. Leucine enrichment was assessed by using gas chromatography-mass spectrometric analysis, and mucosal fractional synthesis rate was calculated by using intracellular amino acid enrichment as precursor. Mucosal proteolytic pathways were also evaluated. RESULTS: ONS infusion resulted in a doubling increase (P < 0.01) of duodenal fractional synthesis rate and a significant (P < 0.05) decrease in cathepsin D-mediated proteolysis compared with saline, whereas proteasome and Ca(2+)-dependent activities were unaffected. ONS infusion significantly (P < 0.01) decreased duodenal glutathione but not glutathione disulfide concentrations or the ratio of glutathione to glutathione disulfide. Insulinemia increased after ONS infusion, whereas plasma essential amino acids decreased. Infusion of glutamine alone did not reproduce ONS effects. CONCLUSIONS: ONS infusion improves duodenal protein balance in healthy humans. Further investigations are needed to study the origin of these effects and to evaluate ONS supply in stressed persons.

Glutamine and interleukin-1beta interact at the level of Sp1 and nuclear factor-kappaB to regulate argininosuccinate synthetase gene expression.

We previously demonstrated that the expression of the argininosuccinate synthetase (ASS) gene, a key step in nitric oxide production, is stimulated either by interleukin-1beta[Brasse-Lagnel et al. (2005) Biochimie 87, 403-9] or by glutamine in Caco-2 cells [Brasse-Lagnel et al. (2003) J. Biol. Chem. 278, 52504-10], through the activation of transcription factors nuclear factor-kappaB and Sp1, respectively. In these cells, the fact that glutamine stimulated the expression of a gene induced by pro-inflammatory factors appeared paradoxical as the amino acid is known to exert anti-inflammatory properties in intestinal cells. We therefore investigated the effect of simultaneous addition of both glutamine and interleukin-1beta on ASS gene expression in Caco-2 cells. In the presence of both compounds for 4 h, the increases in ASS activity, protein amount and mRNA level were almost totally inhibited, implying a reciprocal inhibition between the amino acid and the cytokine. The inhibition was exerted at the level of the transcription factors Sp1 and nuclear-kappaB: (a) interleukin-1beta inhibited the glutamine-stimulated DNA-binding of Sp1, which might be related to a decrease of its glutamine-induced O-glycosylation, and (b) glutamine induced per se a decrease in the amount of nuclear p65 protein without affecting the stimulating effect of interleukin-1beta on nuclear factor-kappaB, which might be related to the metabolism of glutamine into glutamate. The present results constitute the first demonstration of a reciprocal inhibition between the effects of an amino acid and a cytokine on gene expression, and provide a molecular basis for the protective role of glutamine against inflammation in the intestine.

Lack of effect of acute enteral arginine infusion on whole-body and intestinal protein metabolism in humans.

Arginine is a conditionally essential amino acid and exerts anabolic effects. We studied the effects of enteral arginine on whole-body and duodenal protein metabolism. Eight healthy fasted volunteers received randomly a 5-hr enteral infusion of either arginine (Arg; 20 g) or an isonitrogenous amino acid mixture (AA) and an IV infusion of [13C]leucine. Duodenal biopsies were performed. Whole-body protein turnover and duodenal protein synthesis (FSR) were calculated from GC/MS-assessed enrichment. The mRNA levels for major components of proteolytic pathways, ubiquitin, cathepsin D, and m-calpain, were evaluated by RT-PCR. Results were compared using paired Wilcoxon test. Endogenous, oxidative, and nonoxidative leucine fluxes were not different after Arg and AA infusions, respectively. Duodenal mucosal protein FSR (71% +/- 26% vs 81% +/- 30%/day) and mRNA levels of ubiquitin, cathepsin D, and m-calpain were also similar after Arg and AA infusions. We conclude that in healthy subjects, arginine infusion exerts no effect on whole-body and duodenal protein metabolism. Whether arginine might specifically affect these parameters in catabolic or inflammatory situations remains to be determined.

Biphasic effect of IL-1beta on the activity of argininosuccinate synthetase in Caco-2 cells. Involvement of nitric oxide production.

The expression of the argininosuccinate synthetase gene (ASS), the limiting enzyme of arginine synthesis, was previously shown to be rapidly induced by a short-term (4 h) exposure to IL-1beta in Caco-2 cells [Biochimie, 2005, 403-409]. The present report shows that, by contrast, a long-term (24 h) exposure to IL-1beta inhibited the ASS activity despite an increase in both specific mRNA level and protein amount, demonstrating a post-translational effect. Concerning the mechanism involved, we demonstrate that the inhibiting effect is linked to the production of nitric oxide (NO) induced by IL-1beta. Indeed, the inhibiting effect of IL-1beta was totally blocked in the presence of l-NMMA, an inhibitor of the inducible nitric oxide synthase, or by culturing the cells in an arginine-deprived medium. Moreover, a decrease in the ASS activity was induced by culturing the cells in the presence of SNAP, a NO donor. Conversely, blocking the action of NO by antioxidant agents, the stimulatory effect of IL-1beta on ASS activity was restored, as measured at 24 h. Finally, such an inhibiting effect of NO on ASS activity may be related, at least in part, to S-nitrosylation of the protein. The physiological relevance of the antagonistic effects of IL-1beta and NO on ASS is discussed.

IL-1beta stimulates argininosuccinate synthetase gene expression through NF-kappaB in Caco-2 cells.

Argininosuccinate synthetase (ASS) is limiting the arginine synthesis and can be stimulated by immunostimulants. We previously identified a putative NF-kappaB element in the human ASS gene promoter but its functionality was unknown (Husson et al., Eur. J. Biochem. 270 (2003) 1887). In the present study, using Caco-2 cells, a human enterocyte line, we demonstrate that IL-1beta rapidly induces the expression of the ASS gene at a transcriptional level through NF-kappaB activation. Using gel shift assay and double-strand oligonucleotide sequence of the identified putative NF-kappaB binding site of the ASS promoter, we provide evidence that NF-kappaB may functionally interact with this element.

Osmotic stress, a proinflammatory signal in Caco-2 cells.

Hyper- (450 mOsm/l) and hypoosmotic exposure (150 mOsm/l) of Caco-2 cells, a human intestinal epithelial cell line, induced a twofold- and a fivefold increase in the production of IL-8, a constitutively expressed cytokine, respectively. This was observed both in the presence or in the absence of added proinflammatory cytokines and the stimulatory effect of osmotic stress was additive to that induced by the cytokines. Thus, IL-8 production appeared minimal around isoosmolarity, i.e. 300 mOsm/l. Concerning the signalling pathway involved, specific inhibition of p38- or p42/44 MAP kinases decreased the IL-8 production by about 30% independently of the osmotic condition used. Inhibition of c-jun-NH2-terminal kinase (JNK) by using both dicoumarol and SP600125 totally inhibited the stimulatory effect of hypoosmolarity. Moreover, hypoosmolarity induced an about threefold increase in JNK activity demonstrating that JNK was specifically involved in the effect of hypoosmolarity on IL-8 production. This is not the case for hyperosmolarity. Such an effect of osmotic stress was not restricted to IL-8, but was also observed on the production of IL-6, a non-constitutively expressed cytokine. Again, IL-6 production appeared minimal in isoosmotic condition. Taken together, these results demonstrate that osmotic stress is a proinflammatory signal in Caco-2 cells and suggest that an osmosensor might specifically exist in intestinal epithelial cells.