title: Ammonia promotes endothelial cell survival via the heme oxygenase-1-mediated release of carbon monoxide.
abstract: Although endothelial cells produce substantial quantities of ammonia during cell metabolism, the physiologic role of this gas in these cells is not known. In this study, we investigated if ammonia regulates the expression of heme oxygenase-1 (HO-1), and if this enzyme influences the biological actions of ammonia on endothelial cells. Exogenously administered ammonia, given as ammonium chloride or ammonium hydroxide, or endogenously generated ammonia stimulated HO-1 protein expression in cultured human and murine endothelial cells. Dietary supplementation of ammonia also induced HO-1 protein expression in murine arteries. The increase in HO-1 protein by ammonia in endothelial cells was first detected 4h after ammonia exposure and was associated with the induction of HO-1 mRNA, enhanced production of reactive oxygen species (ROS), and increased expression and activity of NF-E2-related factor-2 (Nrf2). Ammonia also activated the HO-1 promoter and this was blocked by mutating the antioxidant responsive element or by overexpressing dominant-negative Nrf2. The induction of HO-1 expression by ammonia was dependent on ROS formation and prevented by N-acetylcysteine or rotenone. Finally, prior treatment of endothelial cells with ammonia inhibited tumor necrosis factor-α-stimulated cell death. However, silencing HO-1 expression abrogated the protective action of ammonia and this was reversed by the administration of carbon monoxide but not bilirubin or iron. In conclusion, this study demonstrates that ammonia stimulates the expression of HO-1 in endothelial cells via the ROS-Nrf2 pathway, and that the induction of HO-1 contributes to the cytoprotective action of ammonia by generating carbon monoxide. Moreover, it identifies ammonia as a potentially important signaling gas in the vasculature that promotes endothelial cell survival.
authors.affiliation: Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri-Columbia, M409 Medical Sciences Building, One Hospital Drive, Columbia, MO 65212, USA.
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Liu
authors.affiliation: Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri-Columbia, M409 Medical Sciences Building, One Hospital Drive, Columbia, MO 65212, USA.
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Peyton
authors.affiliation: Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri-Columbia, M409 Medical Sciences Building, One Hospital Drive, Columbia, MO 65212, USA. Electronic address: durantew@health.missouri.edu.
authors.forename: William
authors.initials: W
authors.lastname: Durante
mesh_terms: D000111:Acetylcysteine / Q000008:administration & dosage; D000641:Ammonia / Q000008:administration & dosage / Q000378:metabolism*; D000643:Ammonium Chloride / Q000008:administration & dosage; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D002248:Carbon Monoxide / Q000008:administration & dosage; D002470:Cell Survival / Q000187:drug effects; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D051547:Heme Oxygenase-1 / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D012402:Rotenone / Q000008:administration & dosage; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
chemical_list: D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; D000643:Ammonium Chloride; D012402:Rotenone; D000641:Ammonia; D002248:Carbon Monoxide; D051547:Heme Oxygenase-1; D000111:Acetylcysteine
keywords: Ammonia; Carbon monoxide; Cytoprotection; Endothelial cells; Heme oxygenase-1