Dietary Glycine Prevents Peptidoglycan Polysaccharide-Induced Reactive Arthritis in the Rat: Role for Glycine-Gated Chloride Channel

Abstract

Peptidoglycan polysaccharide (PG-PS) is a primary structural component of bacterial cell walls and causes rheumatoid-like arthritis in rats. Recently, glycine has been shown to be a potential immunomodulator; therefore, the purpose of this study was to determine if glycine would be protective in a PG-PS model of arthritis in vivo. In rats injected with PG-PS intra-articularly, ankle swelling increased 21% in 24 to 48 h and recovered in about 2 weeks. Three days prior to reactivation with PG-PS given intravenously (i.v.), rats were divided into two groups and fed a glycine-containing or nitrogen-balanced control diet. After i.v. PG-PS treatment joint swelling increased 2.1 ؎ 0.3 mm in controls but only 1.0 ؎ 0.2 mm in rats fed glycine. Infiltration of inflammatory cells, edema, and synovial hyperplasia in the joint were significantly attenuated by dietary glycine. Tumor necrosis factor alpha (TNF-␣) mRNA was detected in ankle homogenates from rats fed the control diet but not in ankles from rats fed glycine. Moreover, intracellular calcium was increased significantly in splenic macrophages treated with PG-PS; however, glycine blunted the increase about 50%. The inhibitory effect of glycine was reversed by low concentrations of strychnine or chloride-free buffer, and it increased radiolabeled chloride influx nearly fourfold, an effect also inhibited by strychnine. In isolated splenic macrophages, glycine blunted translocation of the p65 subunit of NF-B into the nucleus, superoxide generation, and TNF-␣ production caused by PG-PS. Further, mRNA for the beta subunit of the glycine receptor was detected in splenic macrophages. This work supports the hypothesis that glycine prevents reactive arthritis by blunting cytokine release from macrophages by increasing chloride influx via a glycine-gated chloride channel.

Dietary glycine blunts liver injury after bile duct ligation in rats

“…The glycine receptor exists in a wide variety of cells, beside its typical occurrence at the postsynaptic neuronal membranes of the spinal cord. Besides endothelial cells and renal proximal tubular cells [17,41] , cells involved in inflammatory and immune responses, such as macrophages, monocytes, neutrophils, and T lymphocytes, express a glycine receptor [18,20,[42][43][44] . Glycine acts thru its receptor on inflammatory cells, such as Kupffer cells, to suppress activation of transcription factors and the formation of free radicals and inflammatory cytokines.…”

Dietary Glycine Inhibits Angiogenesis During Wound Healing and Tumor Growth

“…This results in decreased production of oxygen free radicals from inflammatory cells (primarily macrophages) and effectively blunts their function. 3 It is mainly through this mechanism that dietary glycine has been shown to protect against LPS induced endotoxic shock 4 and arthritis, 5 accelerate recovery after alcohol induced liver injury, 6 attenuate CCl4 induced fibrosis, 7 improve survival after liver transplantation 8 and decrease toxicity of certain drugs. 9 Angiogenesis is a complex process through which new blood vessels are formed from the existing vasculature.…”

Amino acids exhibit anti-inflammatory effects in human monocytic leukemia cell line, THP-1 cells

“…Recently it has been reported that some amino acids, such as glycine, histidine, cysteine, glutamine or tryptophan, exhibit anti-inflammatory effects, and that histidine and glutamine are able to suppress NF-jB activation [22][23][24][25][26][27][28][29][30], but there have never been reports about the inhibitory effects of amino acids in human monocytes/macrophages. This is the first report about inhibitory effects in human monocytes/macrophages.…”

“…The cells were incubated with or without alanine, glycine, histidine or cysteine at concentrations of 0.2, 2 and 20 mM for 2 h, prior to stimulation with 2 ng/ml TNF-a (R&D Systems, Minneapolis, MN, USA). We chose these concentrations of amino acids according to previous reports [22,26]. Cell viability was determined using Trypan blue (GIBCO RBL Life technologies, Inc) staining.…”

“…NF-jB is a ubiquitous transcription factor for genes that encode proinflammatory cytokines, chemokines and adhesion molecules that mediate inflammation [12][13][14][15][16][17][18][19][20]. It has been reported that some amino acids exhibit anti-inflammatory effects and that the elemental diet reduces the production of proinflammatory cytokines in Crohn's disease [21][22][23][24][25][26][27][28][29], but there have never been reports about the inhibitory effects of amino acids in human monocytes/macrophages. Therefore, in this study we focused on glycine, histidine and cysteine, amino acids that have been reported to exhibit antiinflammatory effects [21][22][23][24][25][26][27]30], and investigated whether or not these amino acids exhibit inhibitory effects against NF-jB activation in human monocytes/macrophages.…”