Toll-like receptor 9 modifies intestinal serotonergic system.

Introduction: Toll-like receptor 9 (TLR9) is expressed in intestinal epithelial cells, which recognize microbiota developing different responses 1. Several studies have shown that TLR9 seems to be involved in Inflammatory Bowel Diseases (IBD) due to an inappropriate defensive response against microorganisms 2. Moreover, intestinal serotonergic system is also altered in IBD, where extracellular serotonin (5–HT) levels are increased 3. 5-HT bioavailability is mainly regulated by the serotonin transporter (SERT), expressed in enterocytes 4. Aims & Methods: The aim of the present study was to analyse whether TLR9 activation affects SERT expression and activity, and expression of other elements from the serotonergic system (TPH1, TPH2 and 5-HT receptors). Human enterocyte-like Caco-2 cells, and ileum and colon from TLR9-/- mice and Dextran Sulphate Sodium (DSS) mouse colitis model were used as experimental models. mRNA expression was determined by RT-qPCR, and protein expression by western blot..

Oxidative stress balance between pro- and anti-inflammatory factors in human intestinal epithelial cells

Background: Oxidative stress plays a key role in the development of intestinal inflammatory diseases. Several pro-inflammatory mediators may generate oxidation products that exacerbate the inflammatory damage. Gastrointestinal molecules, like serotonin (5- HT), adenosine and melatonin, which are involved in intestinal physiology, have also been described as intestinal pro-inflammatory factors; whereas IL-10, a known anti-inflammatory cytokine, has also been implicated in intestinal pathophysiology. Aim: The aim of this study was to analyze the contribution of pro-inflammatory and anti-inflammatory molecules to oxidative stress balance, as well as to assess their effect on cellular antioxidant enzymes activity, in intestinal epithelial cells. Methods: Caco-2 cells were treated with the different molecules, and the oxidative stress was determined by measuring lipid peroxidation (MDA+4HDA) and protein carbonyl levels. The activity of the anti-oxidant enzymes (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) was also analyzed in treated cells. Results: Pro-inflammatory factors (5-HT, adenosine, melatonin and TNFa) increased oxidative damage in both lipids and proteins. Theses molecules, except melatonin, also inhibited the activity of antioxidant enzymes. With regard to IL-10, this cytokine was not shown to alter cellular oxidative damage, but was able to reduce the oxidative damage g by pro-inflamatory factors, and to restore their effects on anti-oxidant enxymes activities. Unexpectedly, IL-10, together with melatonin, was found to increase the antioxidant activity above the control. Conclusions: The anti-oxidant effect of IL-10 emphasizes the role of this cytokine as a potential therapy for the treatment of intestinal inflammation induced by pro-inflammatory molecules