Nitrosation by stimulated macrophages. Inhibitors, enhancers and substrates

Abstract

Macrophages and their immortalized cell lines can be activated to form nitrite and nitrate via oxidation of arginine and this is accompanied by the formation of N-nitroso compounds. The mechanism of nitrosamine formation has been investigated through the use of compounds which are known either to inhibit or enhance acid-catalyzed nitrosation. The range of nitrogen acceptors has been expanded to include ureas as well as amines of varying pK_a and structure. The results are consistent with a mechanism in which NO is oxidized to N₂O₃ and N₂O₄, which are capable of nitrosating amines, but not ureas or amides, at neutral pH. This is in agreement with a recent observation that macrophage cell-free extracts can oxidize arginine to NO. The effect of ascorbic acid on intact activated macrophages is complex since nitrite formation is enhanced over a very wide range of ascorbate concentrations (5–500 μM) while nitrosation is inhibited at ascorbate concentrations >50 μM.