TETRAHYDROBIOPTERIN-DEPENDENT FORMATION OF NITRITE AND NITRATE IN MURINE FIBROBLASTS

The present study demonstrates that murine dermal fibroblasts produce nitrite (NO2−) and nitrate (NO3−) upon treatment with interferon γ (IFN-γ). This formation is dependent on L-arginine and can be inhibited by the L-arginine analogue NG-monomethyl-L-arginine. The effect ofIFN-γ is drastically increased by cotreatment with tumor necrosis factor a (TNF-α), interleukin 1 (IL-1), or lipopolysaccharide (LPS). The tested cytokines also induce formation of tetrahydrobiopterin in murine fibroblasts. Inhibition of guanosine triphosphate-cyclohydrolase I, the key enzyme of tetrahydrobiopterin de novo synthesis with 2,4-diamino-6-hydroxy-pyrimidine, leads to decreased formation of NO2− and NO3−. This effect can be reversed by addition of sepiapterin, which provides tetrahydrobiopterin via a salvage pathway. Methotrexate, which inhibits the salvage pathway, blocks the restoration of NO2−and NO3−production by sepiapterin. The cytotoxic effect of combinations ofIFN-a with TNF-γ, IW, or LPS is attenuated by inhibition of tetrahydrobiopterin synthesis. These results show that intracellular concentrations of tetrahydrobiopterin control the amount of NO2−and NO3−produced in situ and suggest that the role of cytokine-induced tetrahydrobiopterin synthesis is to provide cells with the active cofactor for production of nitrogen oxides. © 1990, Rockefeller University Press., All rights reserved.