Non-toxic concentrations of peroxynitrite commit U937 cells to mitochondrial permeability transition-dependent...

The present study was aimed at examining the mechanism whereby an otherwise non-toxic concentration of peroxynitrite promotes a rapid necrotic response in U937 cells in which cytosolic phospholipase A(2) is pharmacologically inhibited or genetically depleted. We found that loss of viable cells is appreciable 15min after addition of peroxynitrite, does not further increase at 30min and is mediated by mitochondrial permeability transition (MPT). Both MPT and toxicity were prevented by exogenous arachidonic acid (AA). Various experimental approaches produced results consistent with the notion that the AA-dependent protective mechanism takes place 10-15min after addition of peroxynitrite. The observation that the extent of DNA strand scission induced by peroxynitrite did not vary under conditions of different AA availability suggests that this event is either upstream to mitochondrial dysfunction or irrelevant for cytotoxicity. Collectively, these data indicate that a non-toxic concentration of peroxynitrite commits U937 cells to MTP-dependent necrosis that is however prevented by endogenous AA. Thus, mitochondria are a likely target of the cytoprotective signalling triggered by AA.