title: 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.
abstract: 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 γ-glutamyl dipeptides γ-glutamyl cysteine (γ-EC) and γ-glutamyl valine (γ-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 γ-EC and γ-EV in vitro in intestinal epithelial cells and in a mouse model of intestinal inflammation.
  
  
  RESULTS
  In vitro, treatment of Caco-2 cells with γ-EC and γ-EV resulted in the CaSR-mediated reduction of TNF-α-stimulated pro-inflammatory cytokines and chemokines including IL-8, IL-6, and IL-1β, and inhibited phosphorylation of JNK and IκBα, while increasing expression of IL-10. In vivo, using a mouse model of dextran sodium sulfate (DSS)-induced colitis, γ-EC and γ-EV treatment ameliorated DSS-induced clinical signs, weight loss, colon shortening and histological damage. Moreover, γ-EC and γ-EV reduced the expression of TNF-α, IL-6, INF-γ, IL-1β, 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 γ-EC were abrogated in β-arrestin2 knock-down Caco-2 cells, and involvement of β-arrestin2 was found to inhibit TNF-α-dependent signaling via cross-talk with the TNF-α receptor (TNFR).
  
  
  CONCLUSIONS
  Thus CaSR activation by γ-EC and γ-EV can aid in maintaining intestinal homeostasis and reducing inflammation in chronic inflammatory conditions such as IBD.
authors.affiliation: Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Hua
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Kovacs-Nolan
authors.affiliation: Ajinomoto Co. Ltd., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, Kanagawa 210-8681, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kodera
authors.affiliation: Ajinomoto Co. Ltd., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, Kanagawa 210-8681, Japan.
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Eto
authors.affiliation: Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada. Electronic address: ymine@uoguelph.ca.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Mine
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D018938:Caco-2 Cells; D003092:Colitis / Q000139:chemically induced / Q000378:metabolism / Q000517:prevention & control*; D016207:Cytokines / Q000378:metabolism; D016264:Dextran Sulfate; D004151:Dipeptides / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D007422:Intestines / Q000166:cytology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008807:Mice, Inbred BALB C; D010766:Phosphorylation / Q000187:drug effects; D034622:RNA Interference; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000494:pharmacology*; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D016207:Cytokines; D004151:Dipeptides; D018836:Inflammation Mediators; D044169:Receptors, Calcium-Sensing; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D000071557:beta-Arrestins; C482621:gamma-glutamylvaline; D016264:Dextran Sulfate; D048031:JNK Mitogen-Activated Protein Kinases; C017341:gamma-glutamylcysteine
keywords: Calcium-sensing receptor (CaSR); Dextran sodium sulfate (DSS) colitis; Inflammatory bowel disease (IBD); Intestinal epithelium; Tumor necrosis factor (TNF); γ-Glutamyl dipeptides