Nitrite generation in interleukin-4-treated human macrophage cultures does not involve the nitric oxide synthase pathway.
The search continues for high-output nitric oxide biosynthesis in human macrophages analogous to murine phagocytes. Recently, generation of nitrite in culture supernatants of human macrophages exposed to interferon-gamma and interleukin-4 (IFN-gamma/IL-4) was reported. The present study reproduces these findings and shows that L-arginine is not consumed and L-citrulline is not produced during this process. Furthermore, the biosynthesis of the obligatory cofactor tetrahydrobiopterin is not coinduced. These biochemical data provide support against a nitric oxide synthase contribution to nitrite accumulation. Nitrite was generated from nitrate salts even in cell-free media. Nitric oxide synthase activity but not nitrate reduction depended on molecular oxygen. Nitrite accumulation in experiments with IFN-gamma/IL-4 in human monocytes appears to be an in vitro artifact produced by nitrate-reducing activities contained in cytokine preparations.
Schneemann
M
M
Department of Medicine, University of Zurich Medical School, University of Zurich Children's Hospital, Switzerland.
Schoedon
G
G
Linscheid
P
P
Walter
R
R
Blau
N
N
Schaffner
A
A
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000378:metabolism; D001708:Biopterins / Q000031:analogs & derivatives / Q000096:biosynthesis; D002478:Cells, Cultured; D003470:Culture Media; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D015847:Interleukin-4 / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D019798:Neopterin; D009566:Nitrates / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology
D000596:Amino Acids; D003470:Culture Media; D009566:Nitrates; D009573:Nitrites; D011994:Recombinant Proteins; D015847:Interleukin-4; D001708:Biopterins; D019798:Neopterin; D007371:Interferon-gamma; D001120:Arginine; D019001:Nitric Oxide Synthase; C003402:sapropterin