Intestinal barrier function in response to abundant or depleted mucosal glutathione in Salmonella-infected rats

ABSTRACT: BACKGROUND: Glutathione, the main antioxidant of intestinal epithelial cells, is suggested to play an important role in gut barrier function and prevention of inflammation-related oxidative damage as induced by acute bacterial infection. Most studies on intestinal glutathione focus on oxidative stress reduction without considering functional disease outcome. Our aim was to determine whether depletion or maintenance of intestinal glutathione changes susceptibility of rats to Salmonella infection and associated inflammation. Rats were fed a control diet or the same diet supplemented with buthionine sulfoximine (BSO; glutathione depletion) or cystine (glutathione maintenance). Inert chromium ethylenediamine-tetraacetic acid (CrEDTA) was added to the diets to quantify intestinal permeability. At day 4 after oral gavage with Salmonella enteritidis (or saline for non-infected controls), Salmonella translocation was determined by culturing extra-intestinal organs. Liver and ileal mucosa were collected for analyses of glutathione, inflammation markers and oxidative damage. Faeces was collected to quantify diarrhoea. RESULTS: Glutathione depletion aggravated ileal inflammation after infection as indicated by increased levels of mucosal myeloperoxidase and interleukin-1beta. Remarkably, intestinal permeability and Salmonella translocation were not increased. Cystine supplementation maintained glutathione in the intestinal mucosa but inflammation and oxidative damage were not diminished. Nevertheless, cystine reduced intestinal permeability and Salmonella translocation. CONCLUSIONS: Despite increased infection-induced mucosal inflammation upon glutathione depletion, this tripeptide does not play a role in intestinal permeability, bacterial translocation and diarrhoea. On the other hand, cystine enhances gut barrier function by a mechanism unlikely to be related to glutathione

Cholesterol, bile acid and triglyceride metabolism intertwined

Hyperlipidemie wordt gekarakteriseerd door verhoogd plasma cholesterol en/of triglyceriden en sterk geassocieerd met het risico op cardiovasculaire aandoeningen. Dit proefschrift beschrijft onderzoek naar de regulatie van plasma cholesterol en triglyceriden concentraties en de achterliggende mechanismen. In hoofdstuk 3 is onderzoek gedaan naar het mechanisme van triglyceride verlaging na plant sterolen/stanolen inname. Resultaten van deze studie hebben aangetoond dat de lever onder invloed van plant sterolen/stanolen minder triglyceriden uitscheidt naar het plasma. Statines zijn één van de meest gebruikte medicijnen ter wereld en vreemd genoeg is er nooit uitvoerig onderzoek gedaan of deze cholesterol synthese remmers ook daadwerkelijk de cholesterol synthese remmen. Deze kwestie is in hoofdstuk 4 uitvoerig onderzocht in statine behandelde muizen en dit resulteerde in een paradoxale waarneming. Behandeling met statines verhoogt de cholesterol synthese. De verhoogde cholesterol synthese resulteerde in een verhoogde uitscheiding van cholesterol naar de feces. In hoofdstuk 5 werd het achterliggende mechanisme van transintestinale cholesterol excretie (TICE), een cholesterol excretie route waarin cholesterol vanuit het bloed direct wordt uitgescheiden in de darmen, deels opgehelderd. In de darm spelen hydrofiele galzouten, de nucleaire receptor FXR en cholesterol transporter ABCG5/G8 een belangrijke rol in de regulatie van TICE. Hoofdstuk 6 beschrijft het experiment waarin onderscheid is gemaakt tussen de hepatobiliaire en de TICE route met betrekking tot de fecale uitscheiding van overtollig cholesterol. Resultaten van deze proef hebben aangetoond dat de uitscheiding van overtollig cholesterol zowel via de hepatobiliaire route als de TICE route verloopt. Echter, de bijdrage van de hepatobiliaire route is het grootst

Bile salts in control of lipid metabolism

Purpose of review The view on bile salts has evolved over the years from being regarded as simple detergents that aid intestinal absorption of fat-soluble nutrients to being important hormone-like integrators of metabolism. This review provides an update on the rapidly developing field of interactions between bile salts and lipid metabolism, with a particular emphasis on the underlying mechanisms. Recent findings The nuclear receptor farnesoid X receptor (FXR) plays major roles in bile salt-mediated signaling pathways. The recent identification of novel FXR targets and factors involved in FXR signaling highlights the interactions of bile acids with lipid metabolism. Exciting data have been reported on the use of intestine-specific FXR agonists as well as antagonists. In addition, encouraging results for treatment of hepatic steatosis obtained with obeticholic acid in the FLINT trial underline the therapeutic potential of bile salt signaling and metabolism for the treatment of lipid disorders. Summary Modulation of FXR activity appears to be a potent target, not only for improving bile salt homeostasis, but also to improve lipid metabolism. Depending on the metabolic context both, FXR agonists as well as antagonists, could prove to be of therapeutic benefit

Retrograde cholesterol transport in the human Caco-2/TC7 cell line: A model to study trans-intestinal cholesterol excretion in atherogenic and diabetic dyslipidemia

The dyslipidemia associated with type 2 diabetes is a major risk factor for the development of atherosclerosis. Trans-intestinal cholesterol excretion (TICE) has recently been shown to contribute, together with the classical hepatobiliary route, to fecal cholesterol excretion and cholesterol homeostasis. The aim of this study was to develop an in vitro cell model to investigate enterocyte-related processes of TICE. Differentiated Caco-2/TC7 cells were grown on transwells and incubated basolaterally (blood side) with human plasma and apically (luminal side) with lipid micelles. Radioactive and fluorescent cholesterol tracers were used to investigate cholesterol uptake at the basolateral membrane, intracellular distribution and apical excretion. Our results show that cholesterol is taken up at the basolateral membrane, accumulates intracellularly as lipid droplets and undergoes a cholesterol acceptor-facilitated and progressive excretion through the apical membrane of enterocytes. The overall process is abolished at 4 A degrees C, suggesting a biologically active phenomenon. Moreover, this trans-enterocytic retrograde cholesterol transport displays some TICE features like modulation by PCSK9 and an ABCB1 inhibitor. Finally, we highlight the involvement of microtubules in the transport of plasma cholesterol from basolateral to apical pole of enterocytes. The human Caco-2/TC7 cell line appears a good in vitro model to investigate the enterocytic molecular mechanisms of TICE, which may help to identify intestinal molecular targets to enhance reverse cholesterol transport and fight against dyslipidemia