Combination of allergic factors can worsen diarrheic irritable bowel syndrome: role of barrier defects and mast cells.

OBJECTIVES: Recent evidence suggests a role for increased colonic permeability and mucosal mast cell (MC) mediators on symptoms related to the irritable bowel syndrome (IBS). Whether allergic factors (AFs) are involved in the pathophysiology of IBS is unclear. We addressed the question of the possible influence of an allergic background on IBS symptoms. METHODS: We assessed paracellular permeability, mucosal MCs counts, and spontaneous release of tryptase of colonic biopsy specimens in 34 IBS patients and 15 healthy subjects. The severity of IBS was assessed through self-reported questionnaires. All individuals were tested for the presence of AF, including self-perception of adverse reaction to food, personal and familial history of atopic disease, elevated total or specific immunoglobulin E against food/inhalant antigens, blood eosinophilia, and skin tests. RESULTS: IBS patients had significant enhanced colonic permeability, higher number of MCs, and spontaneous release of tryptase than healthy subjects. The severity of IBS was significantly correlated with colonic permeability (r=0.48, P=0.004), MCs counts (r=0.36, P=0.03), and tryptase (r=0.48, P=0.01). In 13 IBS patients (38.2%) having at least three AFs, symptoms scores, colonic permeability, MCs counts, and tryptase release by colonic biopsies were significantly higher than in those with less than three AFs. IBS patients with at least three AFs were more prone to diarrhea or alternating symptoms. None AF was found to be predictive of IBS severity. CONCLUSIONS: In IBS patients, the presence of an allergic background correlates with a more severe disease and diarrhea predominance, possibly by enhancing mucosal MC activation and paracellular permeability.

Impaired intestinal barrier integrity in the colon of patients with irritable bowel syndrome: involvement of soluble mediators.

BACKGROUND: Growing evidence suggests that patients with irritable bowel syndrome (IBS) have increased intestinal permeability. In addition, mucosal soluble mediators are involved in the pathophysiology of pain in IBS. We aimed to investigate (1) paracellular permeability in colonic biopsies of patients with IBS; and (2) the ability of soluble factors from colonic biopsies to reproduce these alterations in vitro. METHODS: Paracellular permeability in colonic biopsies of healthy subjects and patients with IBS was measured by mounting the biopsies in Ussing chambers. Cleared supernatant (SUP) of the culture from colonic biopsies was collected and applied to Caco-2 cells for 48 h. Paracellular permeability and transepithelial resistance (TER) were evaluated. mRNA expression of the tight junction proteins, zonula occludens (ZO)-1 and occludin, was assessed in colonic biopsies. Abdominal pain was assessed using a validated questionnaire. RESULTS: Permeability of colonic biopsies was significantly higher in patients with IBS compared to healthy subjects. These changes were associated with significantly lower expression of ZO-1 mRNA in biopsies of IBS as compared to healthy subjects. Compared to healthy subjects, SUP of IBS markedly reduced TER and significantly increased permeability in Caco-2 cells. SUP of IBS patients induced a significant decrease of ZO-1 mRNA in Caco-2 as compared to healthy subjects. SUP-induced increased paracellular permeability correlated with the severity of abdominal pain. CONCLUSIONS: Our study shows that colonic soluble mediators are able to reproduce functional (permeability) and molecular (ZO-1 mRNA expression) alterations observed in IBS patients. These findings might pave the way both to identify novel biomarkers as well as new therapeutic targets in IBS.

Purification and biological properties of an epithelial intestinal cell growth inhibitor from a human small intestine.

Endogenous mitotic inhibitors act as control-mechanisms in intestinal epithelium proliferation. The presence of an inhibitor of cultured intestinal epithelial cell from a villous extract of rat jejunum has been reported in one of our papers. The object of the study now reported was to find the presence of a growth inhibitor in the villous extract from man's small intestine and to purify and characterize this factor when found. Our results reveal that: (1) Such an inhibitor was found in a supernatant preparation obtained from human intestinal epithelial cells. The inhibition of the proliferation of epithelial cells (IRD-98) it induced was seem to be dose-dependent and non-cytotoxic. (2) After chromatography on hydroxylapatite, on DEAE and then on ACA 54 (gel permeation), a low-molecular-weight protein (15 kDa) called purified intestinal inhibitor (PII) was isolated (purification factor of approx. 50,000 with respect to the supernatant fraction). This fraction proved to inhibit the IRD-98 cells in a reversible manner. When cells are incubated with this protein, cells prove to be arrested in phase G1 of the cell cycle as is revealed by the flow cytometry studies. The results obtained support the hypothesis that regulation of cell proliferation is mediated by endogenous inhibitors at the epithelial level.

Regulation of cholesterol synthesis and binding of lipoproteins in cultured rat intestinal epithelial cells.

The regulation of cholesterol synthesis has been studied using a rat epithelial intestinal cell line (IRD 98) as a cellular model. As observed in other cell types, mevinolin increases the levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) and concomitantly reduces the incorporation of [14C]acetate into cholesterol. Free cholesterol is able to suppress reductase activity. In contrast, when cells are shifted from standard culture medium to lipoprotein-deficient medium, an increase in hydroxymethylglutaryl-CoA reductase specific activity (2-5-fold) is observed. The possible regulatory roles of the different classes of human lipoproteins were thus compared. The effects of a long-term exposure to LDL and HDL vary according to cell density. In actively growing cells, VLDL and LDL cause a decrease in the level of hydroxymethylglutaryl-CoA reductase, whereas HDL do not have a significant effect. In contrast, in subconfluent preresting cells, HDL provoke large decreases in hydroxymethylglutaryl-CoA reductase activity as compared to VLDL and LDL. While LDL binding is constant, the maximal binding capacity of HDL in subconfluent cells is seven times that of actively growing cells. Altogether, these results suggest an important role for HDL in the regulation of intestinal cholesterol synthesis.

Regulation of cholesterol uptake in the rat intestinal cell line.

A new model to study cholesterol absorption in the rat intestinal cells is described. Rat intestine epithelial cells IRD98 were incubated with mixed micelles containing bile acid, phospholipid, cholesterol or its nonabsorbable analogue, sitosterol, and trace amounts of [3H]cholesterol or [14C]sitosterol. Cholesterol and sitosterol uptake was then determined following lipid extraction; specific cholesterol uptake was determined as the difference between cholesterol and sitosterol uptake. Cholesterol, but not sitosterol, uptake was time- and dose-dependent and saturable. Loading of cells with non-lipoprotein cholesterol reduced cholesterol, but not sitosterol, uptake in a dose-dependent manner. In contrast, treatment of cells with an inhibitor of cholesterol synthesis, lovastatin, stimulated cholesterol, but not sitosterol, uptake in a dose-dependent manner. Treatment of cells with palmitic, caproic and oleic acids up-regulated specific cholesterol uptake, while linoleic and stearic acids had an opposite effect. None of the fatty acids affected sitosterol uptake.

Cholesterol uptake in the human intestine. Hypo- and hyperresponsiveness.

Cholesterol uptake was studied at the small intestine biopsies taken from patients without intestinal malfunction. Three distinct groups of patients were described: those with low (146 +/- 19) nmol/mm2 per 2 h), medium (455 +/- 18 nmol/mm2 per 2 h) and high (833 +/- 24 nmol/mm2 per 2 h) rates of cholesterol uptake. Positive correlation between cholesterol uptake and intestinal cholesterol synthesis was observed in the last two groups.

Hydrolysis of an aliphatic monoester in emulsion by swine pancreas lipase: influence of interfacial bile salts molecules upon reaction rate.

The accumulation of four bile salts at the interface between water and n-hexyl laurate is studied. Gibb's interfacial excesses of these salts are calculated, starting from interfacial tension measurements. At the same time, emulsions of the ester are treated by lipase and reactions rates are plotted against the bile salt concentrations present in the water phase of the emulsions. Inhibition by conjugated bile salts appear before the critical micellar concentration is approached. There is no defined relationship between this inhibition and the fraction of interfacial area covered by detergent molecules. In accordance with recent publication, the discussion suggests that the energy level of interfaces is important for lipase action and that, when interfacial tension becomes too small, lipase does not attach to interfaces and appears as inactive.

Effects of the excretory/secretory products of Trichostrongylus colubriformis on the growth of different cell lines.

The effects of the excretory/secretory (ES) products of the parasitic nematode Trichostrongylus colubriformis were examined on the proliferation of seven cell lines derived from a digestive or non-digestive origin. The excretory/secretory products of T. colubriformis were incorporated in the culture medium of the different cell lines and cell proliferation was measured by means of the 5-bromo-2'-deoxy-uridine (Brdu) assay. An increase in cell numbers was found with the three epithelial intestinal cells (RIC, IEC-6, IRD-98) and with epithelial kidney cells (MDCK). In contrast, an inhibition in the proliferation of epithelial ovarian cells (CHO) and fibroblasts (3T3) was observed with the addition of the excretory/secretory products and no effect was detected on the cell growth of hepatocytes (HepG2). These data are discussed with respect to the tissue specificity of the existing mitogenic effect of the worms on the intestinal crypt cells during parasitism.

Effects of eicosapentaenoic acid, gamma-linolenic acid and prostaglandin E1 on three human colon carcinoma cell lines.

Several studies have demonstrated that certain essential fatty acids present a specific cytotoxicity for tumor cells. However, no investigation of this type has been performed on human colon cancer cells to date. This study investigated the effect of gamma-linolenic acid (GLA), eicosapentaenoic acid (EPA) and prostaglandin (PG) E1 on the proliferation and metabolism of three human colon cancer cell lines: HT 29, HRT 18, and CACO 2. GLA, EPA and PGE1 all inhibited the proliferation of the three cell lines, but with a decreasing gradient of sensitivity: HRT 18 > HT 29 > CACO 2, and with different IC50 values. PGE1 was markedly less effective than the other two. GLA and EPA increased lipid peroxidation and membrane fluidity in a dose-dependent manner. The presence of indomethacin did not modify the effects of GLA and EPA. In addition, PGE1 had little effect on membrane fluidity and lipid peroxidation. The antitumoral effect thus does not appear to be mediated by PGE1. Addition of vitamin E decreased the effects of GLA and EPA, which supports the hypothesis of direct action by these fatty acids. In conclusion, while EPA and GLA have an antitumoral effect in vitro, their effect on primary cultures of normal human colon cells must be investigated to determine whether this effect is specific to tumoral cells, as has been observed for other cell types.

Lipid metabolism by the intestinal mucosa in malnourished subjects following enteral nutrition supplemented with omega3 fatty acids.

UNLABELLED: Chronic malnutrition results in severe metabolic imbalance in man as the body modifies its modes of regulation of different nutrients, and in particular lipids. This study of the modifications in lipid metabolism induced by 15 days of enteral renutrition include: 12 malnourished patients (global nutritional deficit (GND) <20%) were given a cyclical enteral diet for 15 days under two conditions: ternary diet (Sondalis) or a similar diet whose lipid concentration was enriched by 5.3 g omega3 fatty acid per day. On Day 0 and Day 15, the serum lipid values were assayed and duodenal biopsies were taken to measure HMG-CoA reductase and (14)C acetate incorporation in the various classes of lipids. After 15 days of refeeding, the GND had been corrected by an average of 27% and HMG-CoA reductase activity had increased by 37% (60.2 +/- 7.46 vs 82.88 +/- 14.8 pmol/min/mg protein; p < 0.05). In 7 12 patients, the serum cholesterol values had increased (p < 0.01). No difference was observed in synthesis of FA, DG or cholesterol. Synthesis of phosphatidylcholines (PC) and phosphatidylglycerols (PG) was reduced by 12% and 23% respectively. Triglyceride synthesis (TG) increased by 20% (p < 0.05). The only difference between the two diets was in TG synthesis in organ-specific culture, which was increased only by the standard diet. IN CONCLUSION: (i) refeeding is accompanied by an increase in intestinal HMG-CoA reductase activity, a decrease in PC and PG synthesis, and an increase in TG synthesis; (ii) a diet enriched in omega3 FA increases TG synthesis less than the standard diet.

Effect of selenium on the growth of three human colon cancer cell lines.

The effects of selenium were investigated on three human colon cancer cell lines: Caco 2, HRT 18, and HT 29. At low concentrations (10-100 nM), selenium stimulated cell growth in serum-free medium. Thus, selenium is an essential trace element for cell proliferation. At higher concentrations, selenium inhibited cell growth. The rate of 75Se uptake was the same in all of the cell lines studied, but the quantity incorporated differed. GSH-Px activity was dependent on the selenium content of the medium. DNA and protein synthesis paralleled the growth curve. Comparison with the curve of viability revealed that selenium inhibited cell growth in two ways: by inhibiting DNA synthesis, without affecting cell viability, and, at higher doses, by cytotoxicity.

[Response of the IRD intestinal epithelial cell line to Clostridium difficile toxins A and B in rats. Effect of Saccharomyces boulardii]. / Réponse aux toxines A et B de Clostridium difficile d'une lignée de cellules épithéliales intestinales de rat: IRD 98. Effet de Saccharomyces boulardii.

In vivo, Clostridium difficile acts by releasing 2 toxins: toxin A, an enterotoxin, and toxin B, a cytotoxin. This study was performed to determine: a) whether the rat epithelial intestinal cell line IRD 98 responds to Clostridium difficile toxin A and B; b) whether the yeast Saccharomyces boulardii has an effect on this model. Evaluation of 3H-thymidine incorporation into IRD 98 cells exposed to toxin B revealed that DNA synthesis was inhibited for low concentrations (10 ng/ml). For higher concentrations, DNA synthesis was not modified. Evaluation of 14C-leucine incorporation into IRD 98 cells exposed to toxin B revealed that this toxin affected protein synthesis. Whereas cholera toxin stimulates adenylate cyclase in IRD 98 cells, cAMP levels in cells exposed to various quantities of toxin A was similar to that in control cells. As opposed to cholera toxin, which does not affect the cytoskeletal structure of IRD 98 cells, 7 micrograms/ml of toxin A and even smaller amounts of toxin B (1 ng/ml) were found to cause structural alterations by immunofluorescence studies. Prior exposition of cells to Saccharomyces boulardii reduced or prevented the rounding of cells in the presence of these toxins. IRD 98 cells can thus be considered a good model for in vitro investigation of the effects of Clostridium difficile toxins A and B, and findings suggest that Saccharomyces boulardii has a protective effect against the action of these toxins.

[Response to cholera toxin of 2 epithelial intestinal cell lines. Effect of Saccharomyces boulardii]. / Réponse à la toxine cholérique de deux lignées de cellules épithéliales intestinales. Effet de Saccharomyces boulardii.

Cholera toxin acts in vivo by activating intestinal adenylate cyclase. This study was designed to determine (1) whether normal rat epithelial intestinal cell lines (IRD 98 and IEC 17) respond to cholera toxin (CT) by an increased concentration of cyclic AMP and (2) whether the yeast Saccharomyces boulardii, which reduced CT-induced secretion of water and electrolytes using the isolated jejunal loop technique, has an effect on these models. The cAMP concentration evaluated in cells exposed to Saccharomyces boulardii and to cholera toxin (1 microgram/ml for 90 min) was compared to the concentration of cAMP obtained in control cells without yeast. Prior exposure of IRD 98 and IEC 17 cells to Saccharomyces boulardii, reduced CT-induced cAMP by 50 p. 100. This effect disappeared after destruction of the yeast by heating. Results show that the IRD 98 and IEC 17 cells are good models for in vitro investigation of the effects of cholera toxin. Our results suggests that Saccharomyces boulardii prevents the water and electrolyte secretion induced by cholera toxin.

Inhibition of intestinal cell proliferation by villous cell extract.

In order to verify the hypothesis that intestinal cell proliferation is controlled by a mitotic inhibitor, extracts of villous epithelial cells from different species were analysed to study their effect on the proliferation of various intestinal cells. Villous extracts from rat and rabbit strongly and reversibly inhibited cell division and DNA synthesis in a rat intestinal epithelial cell line and a primary culture of rabbit intestinal epithelial cells. This non-cytotoxic, tissue specific but not species specific factor is present in both villous cells and crypt cells, with the highest concentrations occurring in the superficial epithelial cells. Assay of a partial purification of this factor showed that it has a molecular weight of approximately 190,000 daltons.

Effect of enprostil and cimetidine on ethanol-induced damage to intestinal epithelial cell lines IRD 98 and IEC 17.

In addition to their inhibitory action on gastric acid secretion, prostaglandins may exert part of their protective effect on the gastrointestinal mucosa by specifically maintaining the cellular integrity of the intestinal epithelium. This in vitro study investigated the cytoprotective effect conferred on intestinal epithelial cell lines IRD 98 and IEC 17 against ethanol injury by the synthetic prostaglandin enprostil and compared effects with those of the histamine H2-receptor blocker cimetidine. Exposure to 3% ethanol (652 mM) reduced cell viability and increased the cAMP and membrane fluidity of both cell lines. Our results demonstrate that: (i) enprostil exerts a significant cytoprotective effect against damage by ethanol; (ii) cimetidine has no cytoprotective effect; (iii) IRD 98 cells are more sensitive to enprostil than IEC 17 cells.

Characterization of delta-opioid receptors and effect of enkephalins on IRD 98 rat epithelial intestinal cell line.

Using 3H-Tyr-D-Ala-Gly-Phe-D-Leu-OH (3H-DADLE) as a radioligand, delta-opioid binding sites on the IRD 98 rat epithelial cell line were identified. These sites were found to be reversible, saturable, specific and displayed high affinity for DADLE. Scatchard analysis revealed a dissociation constant (Kd) of 4.9+/-0.5 nmol/l, a maximum binding capacity (Bmax) of 1.7 pmol/mg protein, and 5x10(5) binding sites per cell. The presence of opioid receptors suggests the possibility that enkephalins directly control ion transport in enterocytes. In order to verify this hypothesis, investigations were designed to determine whether these receptors are functional and whether enkephalins can inhibit the stimulation of adenosine 3',5' cyclic monophosphate (cAMP) synthesis induced by cholera toxin. The increase in cAMP synthesis induced by cholera toxin was inhibited in a dose-dependent manner by H-Tyr-D-Ser-Gly-Phe-Leu-Thr-OH (DSLET), a delta-agonist. The enkephalinase inhibitor thiorphan potentiated this effect on IRD 98 cells, which contain enkephalinase. The action of DSLET was increased by 40% in the presence of this inhibitor. This effect was reversed by naltrindole, a potent delta-antagonist. Enkephalins can regulate intestinal secretion by acting directly on enterocytes: they thus have an antidiarrheal role, especially in the presence of an enkephalinase inhibitor.

Effects of ethanol on an intestinal epithelial cell line.

The effect of exposure of an intestinal epithelial cell line to various concentrations of ethanol [217 mM (1%) to 652 mM (3%)] during 24, 48, and 72 hr was investigated in vitro using a rat intestinal epithelial cell line (IRD 98). Incubation of these cells in the presence of ethanol significantly decreased cell growth. This inhibition was accompanied by a strong increase in cellular protein. Stimulation of specific disaccharidases, gamma-glutamyl transferase, and aminopeptidase activities by ethanol was dose- and time-dependent. Ethanol induces a change in the relative proportions of the different lipid classes synthesized; triglycerides, fatty acids, and cholesterol esters were preferentially synthethysed. Our findings show that cell lines are good models for investigation of the effects of ethanol, and that alcohol considerably modifies the functions of intestinal epithelial cells.

Effects of an inhibitor isolated from human small intestine on organ culture of intestinal mucosa.

Endogenous mitotic inhibitors have been implicated as controlling mechanisms of intestinal epithelium proliferation. We previously reported the purification of an inhibitor of intestinal epithelial cells in culture isolated from a villous extract of human jejunum. This article describes the biologic effects of this inhibitor on organ cultures of rabbit intestinal mucosa. Our results reveal that (1) this factor is not cytotoxic; (2) it inhibits intestinal epithelial cell proliferation in a dose-dependent and reversible manner; (3) it does not appear to be species-specific; (4) it is specific to the digestive tract, and more particularly to the small intestine.

Mevinolin, an inhibitor of cholesterol biosynthesis, drastically depresses Ca2+ channel activity and uncouples excitation from contraction in cardiac cells in culture.

Mevinolin (MK803), a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) (Ki, 30 X 10(-9) M), depressed de novo synthesis of cholesterol in 11-day chicken embryonic cardiac cells cultured in lipoprotein-deficient serum (LPDS). Cardiac cells exposed to different concentrations of mevinolin for 1-3 days presented different electrophysiological and mechanical properties: The resting membrane potential, the rate of increase, and the shape of the action potential and contractile properties were changed at concentrations as low as 0.1 microM mevinolin. At a concentration of 1 microM mevinolin, the cardiac cells became quiescent and electrical stimulation induced action potentials of short duration without contraction. Isoproterenol and Bay K8644 were unable to restore excitability and contraction. Although the number of receptors for the tritiated Ca2+ channel blocker nitrendipine was the same in control and in mevinolin-treated cells, voltage-clamp data on isolated cardiac cells and 45Ca2+ flux experiments on monolayers showed that most of the slow Ca2+ channel activity was lost in mevinolin-treated cells. These results suggest that the disappearance of Ca2+ channel activity is most probably at the origin of the loss of cardiac contractility.

Stimulation of HT29-D4 cell growth by excretory/secretory products of the parasite nematode Trichostrongylus colubriformis.

The presence of the nematode parasite Trichostrongylus colubriformis in the small intestine is associated with an increase in epithelial renewal. To assess the possible role of excretory/secretory products from the worm on cell proliferation, adult Trichostrongylus colubriformis were incubated in vitro in Dulbecco's Modified Eagle's Medium for 24 h and the conditioned medium was added to the culture medium of the transformed epithelial cell line HT29-D4. A stimulation of the HT29-D4 cell growth was ascertained at concentrations of 0.25-1.0 micrograms protein/ml using counts of cell numbers, the MTT method and incorporation of tritiated thymidine. An increased incorporation of tritiated thymidine was also observed with the excretory/secretory products from T. colubriformis fourth stage larvae at 1.0 microgram/ml. Dialysis of the medium conditioned by the worms indicated that the molecular weight of the factor is greater than 8000 Daltons in size. Heat treatment, acid hydrolysis and precipitation by trichloracetic acid of the conditioned medium resulted in the disappearance of the proliferative effect while treatment with trypsin partially depleted the stimulative activity. These results suggest that T. colubriformis produce some protein factor which could increase the epithelial regeneration in the host small intestine.