title: L-2-oxothiazolidine-4-carboxylic acid attenuates oxidative stress and inflammation in retinal pigment epithelium.
abstract: OBJECTIVE
  Oxidant- and inflammation-induced damage to retinal pigment epithelial (RPE) cells is central to the pathogenesis of age-related macular degeneration (AMD). Thus, developing novel strategies to protect these cells is important. We reported previously on the robust antioxidant and therefore cell-protective effects of the cysteine pro-drug L-2-oxothiazolidine-4-carboxylic acid (OTC) in cultured human RPE cells. New reports citing a novel anti-inflammatory role for OTC in addition to the known glutathione-stimulating and antioxidant properties emerged recently; however, this role has not been evaluated in RPE cells or in intact retina. Given the crucial causative roles of oxidative stress and inflammation in AMD pathogenesis, knowing whether OTC might exhibit a similar benefit in this cell and tissue type has high clinical relevance; thus, we evaluated OTC in the present study.
  
  
  METHODS
  ARPE-19 and primary RPE cells isolated from wild-type, Gpr109a(-/-) , or Slc5a8(-/-) mouse eyes were exposed to TNF-α in the presence or absence of OTC, followed by analysis of IL-6 and Ccl2 expression with real-time quantitative polymerase chain reaction or enzyme-linked immunosorbent assay. Cellular and molecular markers of inflammation and oxidative stress (i.e., IL-1β, TGF-β, ABCG1, ABCA1, reduced glutathione, and dihydroethidium) were evaluated in Ccl2(-/-)/Cx3cr1(-/-) double knockout mice on rd8 background (DKO rd8) treated with OTC (10 mg/ml) in drinking water for a period of 5 months.
  
  
  RESULTS
  OTC treatment significantly inhibited the expression and secretion of IL-6 and Ccl2 in TNF-α-stimulated ARPE-19 cells. Studies conducted using DKO rd8 animals treated with OTC in drinking water confirmed these findings. Cellular and molecular markers of inflammation were significantly suppressed in the retinas of the OTC-treated DKO rd8 animals. Subsequent in vitro and in vivo studies of the possible mechanism(s) to explain these actions revealed that although OTC is an agonist of the anti-inflammatory G-protein coupled receptor GPR109A and a transportable substrate of the sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8), these properties may play a role but do not explain entirely the anti-inflammatory effects this compound elicits in cultured RPE cells and the intact mouse retina.
  
  
  CONCLUSIONS
  This study represents, to our knowledge, the first report of the suppressive effects of OTC on inflammation in cultured RPE cells and on inflammation and oxidative stress in the retina in vivo.
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, GA.
authors.forename: Wanwisa
authors.initials: W
authors.lastname: Promsote
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, GA.
authors.forename: Rajalakshmi
authors.initials: R
authors.lastname: Veeranan-Karmegam
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, GA.
authors.forename: Sudha
authors.initials: S
authors.lastname: Ananth
authors.affiliation: Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, MD.
authors.forename: Defen
authors.initials: D
authors.lastname: Shen
authors.affiliation: Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, MD.
authors.forename: Chi-Chao
authors.initials: CC
authors.lastname: Chan
authors.affiliation: Department of Pharmacology and Toxicology, Georgia Regents University, Augusta, GA.
authors.forename: Nevin A
authors.initials: NA
authors.lastname: Lambert
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, GA ; James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, GA.
authors.forename: Vadivel
authors.initials: V
authors.lastname: Ganapathy
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, GA ; Department of Ophthalmology, and the Georgia Regents University, Augusta, GA ; James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, GA.
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Martin
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000378:metabolism; D002460:Cell Line; D018932:Chemokine CCL2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007249:Inflammation / Q000473:pathology*; D053583:Interleukin-1beta / Q000378:metabolism; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D027501:Monocarboxylic Acid Transporters; D018384:Oxidative Stress / Q000187:drug effects*; D011761:Pyrrolidonecarboxylic Acid / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D053778:Thiazolidines / Q000494:pharmacology*; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D018528:ATP-Binding Cassette Transporters; D000893:Anti-Inflammatory Agents; D000975:Antioxidants; D027682:Cation Transport Proteins; D018932:Chemokine CCL2; C473652:Hcar2 protein, mouse; D053583:Interleukin-1beta; D015850:Interleukin-6; D027501:Monocarboxylic Acid Transporters; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D011978:Receptors, Nicotinic; C507459:Slc5a8 protein, mouse; D053778:Thiazolidines; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D011761:Pyrrolidonecarboxylic Acid; C029536:2-oxothiazolidine-4-carboxylic acid