Inducible nitric oxide synthase mediates cyclooxygenase nitration and eicosanoid production

Abstract

Nitric oxide (NO) modulates the activity of cyclooxygenase (COX) isoforms, thereby varying the biological levels of important cell signaling arachidonate-derived eicosanoids. The complex chemistry of NO and NO-derived species results in interactions with COX that either activates or suppresses its activity. We show that inducible NO synthase (iNOS) and COX-1 co-localize in atherosclerotic lesions from ApoE-null mouse aortae. Tyr nitration in COX-1 occurred in aortic lesions, but was markedly reduced in adjacent non-involved tissue. The absence of 3-NT in lesions from iNOS/ApoE double-null mice confirmed that NO derived from iNOS is essential for 3-NT modification of COX-1. Mass spectrometric studies specifically identified Tyr385 in the active site as a 3-NT modification site in purified COX-1, following peroxynitrite exposure. Our findings indicate that COX-mediated prostaglandin E2 synthesis is increased in cultured iNOS-null versus iNOS-expressing mouse aortic smooth muscle cells. These results indicate that NO derived from iNOS markedly suppresses COX activity in vascular cells. The extent to which iNOS-dependent nitration of Tyr in COX-1 contributes to perturbed eicosanoid biosynthesis in human atherosclerotic lesions awaits future investigations. This research was supported by the NIH, Pfizer Inc., Philip Morris USA Inc. and Philip Morris International.