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

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.

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.

Total artificial nutrition is associated with major changes in the fecal flora

BACKGROUND

Animal studies have demonstrated dramatic changes in the intestinal flora during total enteral (TEN) or parenteral (TPN) nutrition.

AIM OF THE STUDY

To assess the impact of TEN and TPN on human intestinal microflora.

METHODS

Eight patients on fiber-free TEN, five patients on TPN, and ten controls were studied. Fecal bacteria were identified and numbered (logCFU/g feces), and fecal short-chain fatty acids (SCFAs) were measured in stool samples, by gas-liquid chromatography.

RESULTS

In TEN patients, compared to controls (P < 0.01), aerobes were increased (8.46 +/- 0.24) while anaerobes were decreased (5.79 +/- 0.84). In TPN patients, both aerobes and anaerobes were decreased compared to controls (5.64 +/- 0.27 and 5.31 +/- 1.09 respectively, P < 0.01). Total SCFAs were lower in TPN patients than in TEN patients (48.3 +/- 16.6 vs 118.6 +/- 24.1 mmol/kg, P < 0.05).

CONCLUSIONS

Both TPN and TEN induce modifications in the intestinal microflora. During TPN, a homogeneous decrease occurs in both aerobic and anaerobic bacteria. TEN decreases only anaerobic bacteria, while aerobic bacteria are increased. This imbalance may play a role in the pathophysiology of TEN-induced diarrhea.

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 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 the excretory/secretory products of six nematode species, parasites of the digestive tract, on the proliferation of HT29-D4 and HGT-1 cell lines

The excretory/secretory (ES) products of the nematode parasite Trichostrongylus colubriformis have been found to increase the in vitro proliferation of the epithelial cell line HT29-D4. To assess the specificity of this effect, ES products from other trichostrongyle species were tested on colonic (HT29-D4) and gastric (HGT-1) tumour cell lines. Adult worms of six different nematode species, parasites of the stomach or the small intestine of ruminants, were incubated in vitro in Dulbecco's Modified Eagle's Medium for 24 h. The conditioned media were then added at different concentrations to the culture medium of the two cell lines. A stimulation of the HT29-D4 cell growth occurred with the ES products of two parasite species of the small intestine, at the concentrations of 0.1 microgram protein/ml (Trichostrongylus vitrinus) and 1.0-5.0 micrograms/ml (Cooperia curticei). Inversely, a decrease in cell number was observed with the ES products of another intestinal species, Nematodirus battus at concentrations of 1.0-5.0 micrograms/ml. With the ES products of the abomasal nematodes, a proliferation of HT29-D4 cells was obtained at 0.25-5.0 micrograms/ml with ES products of Teladorsagia circumcincta but no significant effect was observed for Haemonchus contortus. On the tumoral gastric cell line HGT-1, the ES products from the 6 nematode species gave a similar stimulative effect. These in vitro results suggest that nematode parasite species secrete or excrete component(s) which could affect the epithelial regeneration of the host digestive tract.

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.

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.

New model to study cholesterol uptake in the human intestine in vitro

A new model to study cholesterol uptake in the human intestine in vitro is described. Human small intestine organ cultures were incubated with mixed micelles containing bile acid, phospholipid, and cholesterol or its nonabsorbable analogue, sitosterol; trace amounts of labeled cholesterol or sitosterol were added to the micelles. After incubation, the lipids were extracted from the cells and cholesterol and sitosterol uptake was evaluated. Specific cholesterol uptake was determined as a difference between cholesterol and sitosterol uptake. Cholesterol, but not sitosterol, uptake was time- and dose-dependent. Rapid and slow phases of cholesterol uptake were observed. Cholesterol uptake was also temperature-dependent. Removal of epithelial cells from human intestine explants reduced cholesterol, but not sitosterol, uptake. Inhibition of acyl CoA:cholesterol acyltransferase by Sandoz compound 58-035 and treatment with monensin reduced cholesterol uptake, but not sitosterol uptake, in a dose-dependent manner. In contrast, treatment of cultures with an inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, lovastatin, stimulated cholesterol, but not sitosterol, uptake in a dose-dependent manner; mevalonic acid reversed the effect of lovastatin. The presented model allows large-scale in vitro studies of different stages of cholesterol absorption in the human intestine.

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.

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.

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.

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 to cholera toxin of 2 epithelial intestinal cell lines. Effect of 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.

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.

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.

Establishment and characterization of an epithelial intestinal cell line from rat fetus

An epithelial intestinal cell line has been established from explants of fetal rat small intestine. After the 9th passage (approx. 25 population doublings) epithelial-like cells acquired the properties of a permanent cell line. The epithelial nature of this cell line, and of clone IRD 98 subsequently isolated, is supported by morphological and ultrastructural criteria, and also by the presence of enzymes characteristic of enterocytes, such as aminopeptidase, alkaline phosphatase, gamma-glutamyl transferase, lactase and maltase. The occurrence of the triglyceride pathway enzyme monoacylglycerol acyltransferase and of apoproteins (Apo A1 and Apo E) can also be demonstrated. Taken together, the results presented here provide evidence that clone IRD 98 is an epithelial cell line, most likely originating from the relatively differentiated cell layer of fetal rat small intestine.

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.