Different roles for nitrogen monoxide and peroxynitrite in lipid peroxidation induced by activated neutrophils

We studied the roles of nitrogen monoxide (NO.) and peroxynitrite produced by the polymorphonuclear leukocytes (PMNs) isolated from an inflammatory ex udate. PMNs were incubated either in a medium with a submicromolar concentr ation of iron or in a diethylenetriaminepenta-acetic acid (DTPA)-containing medium, and stimulated with phorbol 12-myristate 13-acetate (PMA) to gener ate free radicals. In both conditions superoxide anion (O-2(.-)), NO. and p eroxynitrite were produced. In the presence of arachidonic acid, malondiald ehyde (MDA) was generated. This MDA was generated in one of two way; the pe roxynitrite iron-independent mechanism (40%) and the Fenton reaction, cause d by free iron (60%). We also observed that the addition of L-arginine was followed by a 42% reduction in MDA, which can be explained by the antioxida nt effect of NO.. These results indicate that lipid peroxidation can occur in the absence of iron, through a peroxynitrite-mediated mechanism, and tha t NO. may act as an antioxidant when it is produced in large amounts. (C) 2 000 Elsevier Science Inc.