title: Effect of arginase inhibition on pulmonary L-arginine metabolism in murine Pseudomonas pneumonia.
abstract: BACKGROUND
  Infection of the lung with Pseudomonas aeruginosa results in upregulation of nitric oxide synthases (NOS) and arginase expression, and both enzymes compete for L-arginine as substrate. Nitric oxide (NO) production may be regulated by arginase as it controls L-arginine availability for NOS. We here studied the effect of systemic arginase inhibition on pulmonary L-arginine metabolism in Pseudomonas pneumonia in the mouse.
  
  
  METHODS
  Mice (C57BL/6, 8-10 weeks old, female) underwent direct tracheal instillation of Pseudomonas (PAO-1)-coated agar beads and were treated by repeated intra-peritoneal injections of the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) or PBS until lungs were harvested on day 3 of the infection. L-arginine metabolites were quantified using liquid chromatography-tandem mass spectrometry, NO metabolites nitrate and nitrite by Griess reagent and cytokines by ELISA.
  
  
  RESULTS
  NO metabolite concentrations (48.5±2.9 vs. 10.9±2.3 µM, p<0.0001), as well as L-ornithine (29.6±1.7 vs 2.3±0.4 µM, p<0.0001), the product of arginase activity, were increased in Pseudomonas infected lungs compared to naïve controls. Concentrations of the NOS inhibitor asymmetric dimethylarginine (ADMA) were also increased (0.44±0.02 vs. 0.16±0.01 µM, p<0.0001). Arginase inhibition in the infected animals resulted in a significant decrease in L-ornithine (14.6±1.6 µM, p<0.0001) but increase in L-arginine concentration (p<0.001), L-arginine/ADMA ratio (p<0.001), L-arginine availability for NOS (p<0.001), and NO metabolite concentrations (67.3±5.7 µM, p<0.05). Arginase inhibitor treatment also resulted in an increase in NO metabolite levels in animals following intratracheal injection of LPS (p = 0.015). Arginase inhibition was not associated with an increase in inflammatory markers (IFN-γ, IL-1β, IL-6, MIP-2, KC or TNF-α) in lung. Concentrations of the L-ornithine-dependent polyamines putrescine, spermidine and spermine were increased in Pseudomonas infected lungs (p<0.001, respectively) but were unaffected by ABH treatment.
  
  
  CONCLUSIONS
  Systemic arginase inhibition with ABH during Pseudomonas pneumonia in mice results in an increase in pulmonary NO formation but no pro-inflammatory effect.
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada; Division of Respiratory Medicine, Department of Pediatrics, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada; Department of Pediatric Pulmonology and Immunology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Mehl
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
authors.forename: Peyman
authors.initials: P
authors.lastname: Ghorbani
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada; Pulmonary and Critical Care Medicine Division, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Douda
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
authors.forename: Hailu
authors.initials: H
authors.lastname: Huang
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
authors.forename: Nades
authors.initials: N
authors.lastname: Palaniyar
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada; Division of Respiratory Medicine, Department of Pediatrics, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
authors.forename: Felix
authors.initials: F
authors.lastname: Ratjen
authors.affiliation: Program in Physiology and Experimental Medicine, SickKids Research Institute, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada; Division of Respiratory Medicine, Department of Pediatrics, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Grasemann
mesh_terms: D000818:Animals; D001119:Arginase / Q000037:antagonists & inhibitors*; D001120:Arginine / Q000378:metabolism*; D005260:Female; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018410:Pneumonia, Bacterial / Q000378:metabolism* / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification*
chemical_list: D001120:Arginine; D001119:Arginase