title: Arginase II inhibition prevents nitrate tolerance.
abstract: OBJECTIVE
  Nitrate tolerance, the loss of vascular responsiveness with continued use of nitrates, remains incompletely understood and is a limitation of these therapeutic agents. Vascular superoxide, generated by uncoupled endothelial NOS (eNOS), may play a role. As arginase competes with eNOS for L-arginine and may exacerbate the production of reactive oxygen species (ROS), we hypothesized that arginase inhibition might reduce nitrate tolerance.
  
  
  METHODS
  Vasodilator responses were measured in aorta from C57Bl/6 and arginase II knockout (argII -/-) mice using myography. Uncoupling of eNOS, determined as eNOS monomer : dimer ratio, was assessed using low-temperature SDS-PAGE and ROS levels were measured using L-012 and lucigenin-enhanced chemiluminescence.
  
  
  RESULTS
  Repeated application of glyceryl trinitrate (GTN) on aorta isolated from C57Bl/6 mice produced a 32-fold rightward shift of the concentration-response curve. However this rightward shift (or resultant tolerance) was not observed in the presence of the arginase inhibitor (s)-(2-boronethyl)-L-cysteine HCl (BEC; 100 µM) nor in aorta isolated from argII -/- mice. Similar findings were obtained after inducing nitrate tolerance in vivo. Repeated administration of GTN in human umbilical vein endothelial cells induced uncoupling of eNOS from its dimeric state and increased ROS levels, which were reduced with arginase inhibition and exogenous L-arginine. Aortae from GTN tolerant C57Bl/6 mice exhibited increased arginase activity and ROS production, whereas vessels from argII -/- mice did not.
  
  
  CONCLUSIONS
  Arginase II removal prevents nitrate tolerance. This may be due to decreased uncoupling of eNOS and consequent ROS production.
authors.affiliation: Baker IDI Heart and Diabetes Institute, Melbourne, Australia.
authors.forename: S M L
authors.initials: SM
authors.lastname: Khong
authors.forename: K L
authors.initials: KL
authors.lastname: Andrews
authors.forename: N N
authors.initials: NN
authors.lastname: Huynh
authors.forename: K
authors.initials: K
authors.lastname: Venardos
authors.forename: A
authors.initials: A
authors.lastname: Aprico
authors.forename: D L
authors.initials: DL
authors.lastname: Michell
authors.forename: M
authors.initials: M
authors.lastname: Zarei
authors.forename: K T
authors.initials: KT
authors.lastname: Moe
authors.forename: G J
authors.initials: GJ
authors.lastname: Dusting
authors.forename: D M
authors.initials: DM
authors.lastname: Kaye
authors.forename: J P F
authors.initials: JP
authors.lastname: Chin-Dusting
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D001119:Arginase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D001120:Arginine / Q000378:metabolism; D001897:Boronic Acids / Q000494:pharmacology; D004361:Drug Tolerance / Q000502:physiology; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D005996:Nitroglycerin / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: C425062:(2-boronoethyl)-cysteine; D001897:Boronic Acids; D017382:Reactive Oxygen Species; D014665:Vasodilator Agents; D001120:Arginine; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; C481673:Arg2 protein, mouse; D001119:Arginase; D005996:Nitroglycerin