title: Glycine transporter GLYT1 is essential for glycine-mediated protection of human intestinal epithelial cells against oxidative damage.
abstract: Glycine protects mammalian intestine against oxidative damage caused by ischaemia-reperfusion (IR) injury and prevents or reverses experimentally-induced colitis. However the mechanism of protection remains largely unknown. The objectives of the current study were to demonstrate directly glycine-mediated protection of human intestinal epithelial cells and to determine the requirement for glycine uptake by the specific transporter GLYT1. Exogenous glycine protected human intestinal Caco-2 and HCT-8 cells against the oxidative agent tert-butylhydroperoxide and reduced the intracellular concentration of reactive oxygen species, when applied prior to but not concomitant with the oxidative challenge. Glycine given prior to oxidative challenge preserved intracellular glutathione concentration but had no effect on the rate of glycine uptake. Protection was dependent on GLYT1 activity, being blocked by a specific GLYT1 inhibitor, supporting a requirement for intracellular glycine accumulation. Maintained intracellular glutathione content is indicated as a mechanism through which the protective effect may in part be mediated. However expression of the genes encoding GLYT1 and the glutathione synthesising enzymes glutamate-cysteine ligase, both catalytic and modifier subunits, and glutathione synthetase was not altered by glycine or tert-butylhydroperoxide, suggesting transcriptional regulation is not involved. This work has demonstrated a novel role of GLYT1 in intestine and shown that intestinal epithelial cells respond directly to oxidative challenge without reliance on extra-epithelial tissues or functions such as neurone, blood-flow or immune responses for antioxidant defence. The protective actions of glycine and maintenance of epithelial antioxidant defences suggest it may be beneficial in treatment of inflammatory bowel disease.
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Faculty of Medical Sciences, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Alison
authors.initials: A
authors.lastname: Howard
authors.forename: Imran
authors.initials: I
authors.lastname: Tahir
authors.forename: Sajid
authors.initials: S
authors.lastname: Javed
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Waring
authors.forename: Dianne
authors.initials: D
authors.lastname: Ford
authors.forename: Barry H
authors.initials: BH
authors.lastname: Hirst
mesh_terms: D018938:Caco-2 Cells; D002460:Cell Line; D005978:Glutathione / Q000378:metabolism; D005998:Glycine / Q000494:pharmacology*; D050487:Glycine Plasma Membrane Transport Proteins / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D020122:tert-Butylhydroperoxide / Q000009:adverse effects / Q000494:pharmacology
chemical_list: D050487:Glycine Plasma Membrane Transport Proteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C493268:SLC6A9 protein, human; D020122:tert-Butylhydroperoxide; D005978:Glutathione; D005998:Glycine