1 Peroxynitrite (ONOO 7 ) the highly reactive coupling product of nitric oxide and superoxide, has been implicated in the pathogenesis of an increasing number of (in¯ammatory) diseases. At present, however, selective peroxynitrite antagonizing agents with therapeutic potential are not available. Therefore, the NADPH-oxidase inhibitor apocynin (4-hydroxy-3-methoxy-acetophenone) was tested for its ability to inhibit peroxynitrite formation in vitro 2 The murine macrophage cell-line J774A.1, stimulated with IFNg/LPS, was used as a model. Conversion of 123-dihydrorhodamine (123-DHR) to its oxidation product 123-rhodamine was used to measure peroxynitrite production. 3 Stimulated peroxynitrite formation could be completely inhibited by apocynin, by the superoxide scavenger TEMPO as well as by the nitric oxide synthase inhibitor aminoguanidine. Apocynin and aminoguanidine speci®cally inhibited superoxide and nitric oxide formation respectively as con®rmed by measuring lucigenin enhanced chemiluminescence and nitrite accumulation. 4 It is concluded that J774A.1 macrophages produce signi®cant amounts of peroxynitrite, which is associated with nitric oxide production and NADPH-oxidase dependent superoxide formation. The NADPH-oxidase inhibitor apocynin proved to be a potent inhibitor of both superoxide and peroxynitrite formation by macrophages, which may be of future therapeutic signi®cance in a wide range of in¯ammatory disorders.

Administration of peroxynitrite directly into the airways of BALB/c mice, induces airway inflammation, but not airway hyperresponsiveness. It is suggested that antioxidants in the epithelial lining fluid and/or the epithelium itself form an efficient barrier, which prevents peroxynitrite from reaching putative targets in the airway interstitium.

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