Calcium-Sensing Receptor (CaSR)-Mediated Anti-inflammatory Effects of L-Amino Acids in Intestinal Epithelial Cells

摘要

Calcium-sensing receptor (CaSR) plays an essential role in sensing nutrients and monitoring ion balance in the human gut. However, no discovery of CaSR-mediated anti-inflammatory effect of L-amino acids (L-AAs) on the gut system has been reported. The aim of this study is to screen and identify the anti-inflammatory activity of various L-AAs in intestinal epithelial cells (IECs) and stepwise illustrate a possible molecular mechanism for anti-inflammation. We used Caco-2 and HT-29 cell lines to evaluate the anti-inflammatory activity of L-AAs and revealed that L-tryptophan (L-Trp) and L-valine (L-Val) have strong anti-inflammatory activity consistent in both cell lines. L-Trp treatment (5 mM) reduced TNF-alpha-induced IL-8 secretion from HT-29 or Caco-2 cells to about 50 or 40%, respectively. L-Trp also significantly inhibited the expression of phosphorylation of JNK or I kappa B alpha to around 50% in HT-29 cells. However, the above inhibitory effects of L-Trp on inflammatory responses in TNF-alpha-induced HT-29 cells were abrogated by NPS-2143. The result of CaSR antagonist NPS-2143 pretreatment study suggests L-Trp exerts anti-inflammatory effects on IECs through CaSR activation. The involvement of beta-arrestin2 was then found to block tumor necrosis factor (TNF)-alpha-induced signaling pathways after CaSR activated by L-Trp. These results validate a novel mechanism underlying CaSR agonistic L-AAs exerting anti-inflammatory effects on human intestinal epithelia.