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

Abstract

The effects of reactive oxygen species (superoxide anion radical—O2−, hydrogen peroxide—H2O2 and hydroxyl radical—OH; 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-1-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 50μM. 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 O2−, both activated and inhibited the COX-1 and -2 activities, depending on ONOO− concentration. At a low concentration of ONOO− (5μM) 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 200μM; COX-2, >50μM). These results suggest that H2O2, NO and ONOO− can have different modulatory effects on the COX-1 and -2 activities.