PepT1-Mediated Tripeptide KPV Uptake Reduces Intestinal Inflammation

Background & Aims: KPV is a tripeptide (Lys-Pro-Val), which possesses anti-inflammatory properties; however, its mechanisms of action still remain unknown. PepT1 is a di/tripeptide transporter normally expressed in the small intestine and induced in colon during inflammatory bowel disease (IBD). The aim of this study was to 1) investigate whether the KPV anti-inflammatory effect is PepT1-mediated in intestinal epithelian and immune cells, and 2) examine the anti-inflammatory effects in two models of mice colitis. Methods: Human intestinal epithelial cells Caco2-BBE, HT29-Cl.19A, and human T cells (Jurkat) were stimulated with pro-inflammatory cytokines in the present or absence of KPV. KPV anti-inflammatory effect was assessed using a NF-κB luciferase gene reporter, Western blot, real-time RT-PCR and ELISA. Uptake experiments were performed using cold KPV as a competitor for PepT1 radiolabelled substrate or using [³H]KPV to determine kinetic characteristics of KPV uptake. Anti-inflammatory effect of KPV was also investigated in DSS- and TNBS-induced colitis in mice. KPV was added to drinking water and inflammation was assessed at the histologic level and by proinflammatory cytokine mRNA expression. Results: Nanomolar concentrations of KPV inhibit the activation of NF-κB and MAP kinase inflammatory signaling pathways, and reduce pro-inflammatory cytokine secretion. We found that KPV acts via PepT1 expressed in immune and intestinal epithelial cells. Furthermore, oral administration of KPV reduces the incidence of DSS- and TNBS-induced colitis indicated by a decrease in pro-inflammatory cytokine expression. Conclusions: This study indicates tht KPV is transported into cells by PepT1 and might be a new therapeutic agent for IBD.

Abbreviations used in this paper: cAMP_i, intracellular cyclic adenosine monophosphate, DSS, dextran sodium sulfate, ELISA, enzyme-linked immunosorbent assay, Gly-Leu, glycine-leucine, Gly-Sar, glycine-sarcosine, IEC, intestinal epithelial cell, IL, interleukin, KPV, Lys-Pro-Val, MAPK, mitogen-activated protein kinase, MCR, melanocortin receptor, MPO, myeloperoxidase, α−MSH, α-melanocyte–stimulating hormone, NF-κB, nuclear factor-κB, PepT1, H⁺-coupled oligopeptide transporter 1, RT-PCR, reverse-transcription polymerase chain reaction, TNF-α, tumor necrosis factor-α