Inorganic nitrite attenuates NADPH oxidase-derived superoxide generation in activated macrophages via a nitric oxide-dependent mechanism.
Oxidative stress contributes to the pathogenesis of many disorders, including diabetes and cardiovascular disease. Immune cells are major sources of superoxide (O2(∙-)) as part of the innate host defense system, but exaggerated and sustained O2(∙-) generation may lead to progressive inflammation and organ injuries. Previous studies have proven organ-protective effects of inorganic nitrite, a precursor of nitric oxide (NO), in conditions manifested by oxidative stress and inflammation. However, the mechanisms are still not clear. This study aimed at investigating the potential role of nitrite in modulating NADPH oxidase (NOX) activity in immune cells. Mice peritoneal macrophages or human monocytes were activated by lipopolysaccharide (LPS), with or without coincubation with nitrite. O2(∙-) and peroxynitrite (ONOO(-)) formation were detected by lucigenin-based chemiluminescence and fluorescence techniques, respectively. The intracellular NO production was measured by DAF-FM DA fluorescence. NOX isoforms and inducible NO synthase (iNOS) expression were detected by qPCR. LPS increased both O2(∙-) and ONOO(-) production in macrophages, which was significantly reduced by nitrite (10µmol/L). Mechanistically, the effects of nitrite are (1) linked to increased NO generation, (2) similar to that observed with the NO donor DETA-NONOate, and (3) can be abolished by the NO scavenger carboxy-PTIO or by the xanthine oxidase (XO) inhibitor febuxostat. Nox2 expression was increased in activated macrophages, but was not influenced by nitrite. However, nitrite attenuated LPS-induced upregulation of iNOS expression. Similar to that observed in mice macrophages, nitrite also reduced O2(∙-) generation in LPS-activated human monocytes. In conclusion, XO-mediated reduction of nitrite attenuates NOX activity in activated macrophages, which may modulate the inflammatory response.
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Ting
T
Yang
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Maria
M
Peleli
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Christa
C
Zollbrecht
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; Department of Clinical Science, Faculty of Medicine, Marche Polytechnic University, Ancona, Italy.
Alessia
A
Giulietti
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Niccolo
N
Terrando
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Jon O
JO
Lundberg
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Eddie
E
Weitzberg
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden. Electronic address: mattias.carlstrom@ki.se.
Mattias
M
Carlström
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000494:pharmacology*; D018384:Oxidative Stress; D030421:Peroxynitrous Acid / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013481:Superoxides / Q000378:metabolism*
D009573:Nitrites; D012333:RNA, Messenger; D013481:Superoxides; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D019255:NADPH Oxidases
Lipopolysaccharide; Macrophage; NADPH oxidase; Nitrate; Nitric oxide; Nitrite; Oxidative stress; Reactive oxygen species; iNOS