Effects of reactive oxygen and nitrogen species on cyclooxygenase-1 and-2 activities

The effects of reactive oxygen species (superoxide anion radical-O-2(.-), hydrogen peroxide-H2O2 and hydroxyl radical-(OH)-O-.; the reaction products of xanthine plus xanthine oxidase system) and reactive nitrogen species [nitric oxide-NO.; from 1-hydroxyl-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-l-triazene-NOC7 and peroxynitrite-ONOO-] on the activities of purified cyclooxygenase (COX)-1 and -2 were studied. Xanthine plus xanthine oxidase suppressed the COX-1 and -2 activities in a xanthine oxidase concentration-dependent fashion. This effect was reversed by addition of catalase to the reactive oxygen species-generating system but not by superoxide dismutase or mannitol, indicating that H2O2 is the responsible metabolite. NOC7 activated the COX-1 activity but inhibited the COX-2 activity at concentrations ranging from 1 to 50 muM. Experiments utilizing a NO. antidote, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide revealed that the observed effects of NOC7 are caused by NO.. ONOO-, a product of NO. and O-2(.-), both activated and inhibited the COX-1 and -2 activities, depending on ONOOconcentration. At a low concentration of ONOO- (5 muM) there was enhancement of the COX-1 and -2 activities, but with higher concentrations there was suppression of these two enzyme activities (COX- 1, at 200 muM; COX-2, > 50 muM). These results suggest that H>O2, NO. and ONOO- can have different modulatory effects on the COX-1 and -2 activities. (C) 2004 Elsevier Ltd. All rights reserved.