Peroxynitrite stimulates the activity of cytosolic phospholipase A2 in U937 cells: the extent of arachidonic acid formation regulates the balance between cell survival or death.

Peroxynitrite stimulates in U937 cells release of arachidonic acid (AA) sensitive to various phospholipase A2 (PLA2) inhibitors, including arachidonyl trifluoromethyl ketone (AACOCF3), which specifically inhibits cytosolic PLA2 (cPLA2). This response linearly increases using non toxic concentrations of the oxidant, and reaches a plateau at levels at which toxicity becomes apparent. Three separate lines of evidence are consistent with the notion that AA generated by cPLA2 promotes survival in cells exposed to peroxynitrite. Firstly, toxicity was suppressed by nanomolar levels of exogenous AA, or by AA generated by the direct PLA2 activator melittin. Secondly AACOCF3, or other PLA2 inhibitors, promoted cell death after exposure to otherwise non toxic concentrations of peroxynitrite; exogenous AA abolished the enhancing effects mediated by the PLA2 inhibitors. Finally, U937 cells transfected with cPLA2 antisense oligonucleotides were killed by concentrations of peroxynitrite that were non-toxic for cells transfected with nonsense oligonucleotides. This lethal response was insensitive to AACOCF3 and prevented by exogenous AA.