¹Istituto di Farmacologia e Farmacognosia, Università degli Studi di Urbino 'Carlo Bo', Via S Chiara, 27-61029 Urbino (PU), Italy

Correspondence: O Cantoni, Istituto di Farmacologia e Farmacognosia, Università degli Studi di Urbino 'Carlo Bo', Via S Chiara, 27-61029 Urbino (PU), Italy. Tel: +39 0722 303523; Fax: +39 0722 303521; E-mail: cantoni@uniurb.it

Received 3 July 2003; Revised 17 December 2003; Accepted 26 January 2004; Published online 21 May 2004.

Abstract

We have studied the relationships existing between delayed formation of H₂O₂ and activation of cytosolic phospholipase A₂ (cPLA₂), events respectively promoting toxicity or survival in U937 cells exposed to peroxynitrite. The outcome of an array of different approaches using phospholipase A₂ inhibitors, or cPLA₂ antisense oligonucleotides, as well as specific respiratory chain inhibitors and respiration-deficient cells led to the demonstration that H₂O₂ does not mediate toxicity by producing direct molecular damage. Rather, the effects of H₂O₂ were found to be upstream to the arachidonic acid (AA)-mediated cytoprotective signalling and in fact causally linked to inhibition of cPLA₂. Thus, it appears that U937 cells exposed to nontoxic concentrations of peroxynitrite are nevertheless committed to death, which however is normally prevented by the activation of parallel pathways resulting in cPLA₂-dependent release of AA. A rapid necrotic response, however, takes place when high concentrations of peroxynitrite promote formation of H₂O₂ at levels impairing the cPLA₂ cytoprotective signalling.