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

Tissue sterol composition in Atlantic salmon (Salmo salar L.) depends on the dietary cholesterol content and on the dietary phytosterol:cholesterol ratio, but not on the dietary phytosterol content

The aim of the study was to investigate how the dietary sterol composition, including cholesterol, phytosterol:cholesterol ratio and phytosterols, affect the absorption, biliary excretion, retention, tissue storage and distribution of cholesterol and individual phytosterols in Atlantic salmon (Salmo salar L.). A feeding trial was conducted at two different temperatures (6 and 12°C), using nine different diets with varying contents of phytosterols, cholesterol and phytosterol:cholesterol ratio. Cholesterol retention values were clearly dependent on dietary cholesterol, and showed that fish fed cholesterol levels <1000 mg/kg feed produced considerable quantities of cholesterol de novo. Despite this production, cholesterol content increased with increasing dietary cholesterol in liver, plasma, bile, muscle, adipose tissue and whole fish at 12°C, and in plasma, bile and whole fish at 6°C. The tissue sterol composition generally depended on the dietary cholesterol content and on the dietary phytosterol:cholesterol ratio, but not on the dietary phytosterol content in itself. Campesterol and brassicasterol appeared to be the phytosterols with the highest intestinal absorption in Atlantic salmon. There was a high biliary excretion of campesterol, but not of brassicasterol, which accumulated in tissues and particularly in adipose tissue, with 2-fold-higher retention at 12°C compared with 6°C. Campesterol had the second highest retention of the phytosterols in the fish, but with no difference between the two temperatures. Other phytosterols had very low retention. Although brassicasterol retention decreased with increasing dietary phytosterols, campesterol retention decreased with increasing dietary cholesterol, indicating differences in the uptake mechanisms for these two sterols.

The effects of atorvastatin on gluten-induced intestinal T cell responses in coeliac disease

Various experimental models suggest that the cholesterol-lowering drugs statins may also modulate immune responses. Cellular level studies on human disorders are needed, however, to provide a rational basis for clinical testing of statins as immune therapy. Coeliac disease, a chronic small intestinal inflammation driven by HLA-DQ2 restricted mucosal T cells that are specific for ingested wheat gluten peptides, is in many ways ideal for this purpose. In addition, there is a need for alternative treatment to the gluten-free diet in this disorder. Here we have assessed the effects of atorvastatin on gluten-reactive T cells, dendritic cells and the coeliac mucosa by in vitro culture of biopsies. Atorvastatin inhibited gluten-induced proliferation and specific cytokine production of human intestinal gluten-reactive T cell clones and lines. Dendritic cells exposed to atorvastatin displayed a reduced expression of the costimulatory molecule CD83 upon maturation with lipopolysaccharide. Incubation of intestinal biopsy specimens with atorvastatin in vitro, however, did not influence gluten-induced cytokine release. In conclusion, atorvastatin has specific effects on isolated gluten-reactive T cells and dendritic cells, but does not shut down the gluten-induced production of proinflammatory cytokines in intestinal biopsies.

Ionophores have limited effects on jejunal glucose absorption and energy metabolism in mice

Two experiments, Trial 1 (in vitro) and Trial 2 (in vivo), were conducted to examine the effects of ionophores, monensin, laidlomycin, and laidlomycin propionate on whole-animal O2 consumption, organ weights, jejunal glucose absorption, and O2 utilization, as well as growth, feed and water consumption, and feed efficiency. In Trial 1, 30 male Swiss-Webster mice, 8 wk old, were used to measure the in vitro effects of each of the ionophores at concentrations of 1.62 or 16.2 mM. Six combinations of three ionophores at two concentrations resulted in a total of eight treatments. All eight treatments were exposed to jejunal rings from a single mouse for a total of 30 observations per treatment. Jejunal rings were exposed to each ionophore treatment for 15 min. Laidlomycin propionate (16.2 mM) decreased (P < 0.02) glucose absorption, as estimated by H3-3-O-methyl glucose uptake compared with all other treatments, whereas laidlomycin propionate (1.62 mM) increased (P = 0.032) jejunal DM content compared with 16.2 mM laidlomycin propionate. In Trial 2, 40 5-wk-old mice were allotted into four treatments--control and 16.2 mM each of monensin, laidlomycin, and laidlomycin propionate--for a total of 10 observations per treatment. Ionophores were administered via the drinking water for 14 d. No ionophore treatment had any effect on whole-mouse O2 consumption. Monensin increased (P = 0.004) stomach size and decreased (P = 0.049) the efficiency of BW gain compared with controls. Laidlomycin propionate decreased (P = 0.032) the percentage of whole jejunum oxygen consumption due to oubain-sensitive respiration compared with control. The efficiency of intestinal glucose absorption was not changed due to treatment in either trial. Under the conditions of these studies, monensin, laidlomycin, and laidlomycin propionate had minimal and inconsistent effects on jejunal function and energy utilization in mice. This investigation suggests that changes in the energetic requirements of animals treated with ionophores are not an issue in animal production.

Influence of glutamine on cytokine production by human gut in vitro

BACKGROUND

glutamine modulates cytokine production by immune cells in vitro and protects the gut from experimental enterocolitis, but data on the effect of glutamine on cytokine production in human gut are lacking.

AIM

to assess the effect of glutamine pre-treatment in vivo and in vitro on cytokine production by intestinal mucosa.

METHODS

nine fasted volunteers received either enteral glutamine or saline over 6 h in a cross-over design. Duodenal biopsies were cultured for 24 h with or without glutamine. Cytokine content of culture media was analysed by ELISA, and the expression of cytokine mRNA in biopsies was assessed by semi-quantitative RT-PCR.

RESULTS

glutamine given in vivo and in vitro significantly decreased IL-6 [1.4 (0.8-8.5) vs 8.9 (1.0-43.9)] and IL-8 production [5.8 (0-51.4) vs. 53.0 (2.5-114.6), pg/mg wet tissue], median (range), both P< or =0.01, in comparison to no glutamine experiments. Glutamine did not influence IL-4 production. IL-1beta, IL-10 and TNF-alpha were not detectable in culture media. The expression of any cytokine mRNA was not influenced by glutamine.

CONCLUSIONS

glutamine reduces pro-inflammatory cytokine production by human intestinal mucosa, probably by a post-transcriptional pathway. Glutamine could be useful to modulate inflammatory conditions with imbalanced cytokine production.

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.