Induction of human neutrophil apoptosis by nitric oxide donors: Evidence for a caspase-dependent, cyclic-GMP-independent, mechanism

This study investigated the regulatory effects of the major inflammatory me diator, nitric oxide (NO), on human neutrophil apoptosis in vitro. Go-cultu re of human neutrophils with the NO donors GEA 3162 (1,2,3,4-oxatriazolium, 5-amino-3-(3,4 dichlorophenyl)-chloride) (10-100 mu M) and 3-morpholino-syd noni mine (SIN-1) (0.3-3 mM) caused a dramatic and concentration- dependent induction of apoptosis. However, N-formyl-methionyl-leucyl-phenylalanine ( FMLP)-induced neutrophil activation (actin reorganization and chemotaxis) w as inhibited by CEA 3162 treatment. The pro-apoptotic effects of the NO don ors were (i) unaffected by the soluble guanylate cyclase inhibitor LY-83583 (6-anilino-5,8-quinolinedione; 100 mu M), (ii) antagonized by superoxide d ismutase (6 mu g/mL), (iii) mimicked by exogenous peroxynitrite (at concent rations >100 mu M), and (iv) inhibited by the caspase inhibitor Z-Val-Ala-D L-Asp fluoromethylketone (100 mu M). The pro-apoptotic effect of the NO don ors was nor: mimicked by the cell-permeable cyclic nucleotide analogue, N-6 ,2-O-dibutyrylguanosine-3 ',5'-cyclic monophosphate (dibutyryl-cGMP) at con centrations less than or equal to 0.2 mM. Indeed, at high concentrations (g reater than or equal to 2 mM), dibutyryl-cGMP caused an inhibition of apopt osis. These results suggest that NO mediated apoptosis, although caspase-de pendent, is mediated by a cGMP-independent mechanism and involves the concu rrent generation of oxygen free radicals and, potentially, peroxynitrite. O ur data reveal a unique role for NO in inflammatory responses with differen tial effects upon neutrophil activation and survival, with important implic ations for the successful resolution of inflammation. (C) 1999 Elsevier Sci ence Inc.