γ-Glutamyl cysteine and γ-glutamyl valine inhibit TNF-α signaling in intestinal epithelial cells and reduce inflammation in a mouse model of colitis via allosteric activation of the calcium-sensing receptor

Background: The extracellular calcium-sensing receptor (CaSR) is distributed throughout the gastrointestinal tract, and its activation has been shown to promote intestinal homeostasis, suggesting that CaSR may be a promising target for novel therapies to prevent chronic intestinal inflammation such as inflammatory bowel disease (IBD). The gamma-glutamyl dipeptides gamma-glutamyl cysteine (gamma-EC) and gamma-glutamyl valine (gamma-EV) are dietary flavor enhancing compounds, and have been shown to activate CaSR via allosteric ligand binding. The aim of this study was to examine the anti-inflammatory effects of gamma-EC and gamma-EV in vitro in intestinal epithelial cells and in a mouse model of intestinal inflammation. Results: In vitro, treatment of Caco-2 cells with gamma-EC and gamma-EV resulted in the CaSR-mediated reduction of TNF-alpha-stimulated pro-inflammatory cytokines and chemokines including IL-8, IL-6, and IL-1 beta, and inhibited phosphorylation of JNK and I kappa B alpha, while increasing expression of IL-10. In vivo, using a mouse model of dextran sodium sulfate (DSS)-induced colitis, gamma-EC and gamma-EV treatment ameliorated DSS-induced clinical signs, weight loss, colon shortening and histological damage. Moreover, gamma-EC and gamma-EV reduced the expression of TNF-alpha, IL-6, IL-1 beta, and IL-17, and increased the expression of IL-10 in the colon, in a CaSR-dependent manner. The CaSR-mediated anti-inflammatory effects of gamma-EC were abrogated in beta-arrestin2 knock-down Caco-2 cells, and involvement of beta-arrestin2 was found to inhibit TNF-alpha-dependent signaling via cross-talk with the TNF-a receptor (TNFR). Conclusions: Thus CaSR activation by gamma-EC and gamma-EV can aid in maintaining intestinal homeostasis and reducing inflammation in chronic inflammatory conditions such as IBD. (C) 2015 Elsevier B.V. All rights reserved.