INDUCIBLE NITRIC-OXIDE - AN AUTOREGULATORY FEEDBACK INHIBITOR OF VASCULAR INFLAMMATION

Inducible nitric oxide (iNO) is produced at sites of vascular inflamma tion by resident and nonresident vascular wall cells, but its role in the inflammatory process is not known. In this study, we show that a n ovel function of iNO is to terminate inflammatory processes. We find t hat iNO produced by murine macrophage-like cells, RAW264.7, can inhibi t cytokine-induced endothelial cell activation in a separated and mixe d endothelial-RAW264.7 coculture system. Both iNO production and endot helial VCAM-1 expression were induced simultaneously with bacterial LP S and murine-specific IFN-gamma, Inhibition of iNO synthase (iNOS) act ivity with N-omega-monomethyl-L-arginine in endothelial-RAW264.7 cocul tures, stimulated with murine-specific IFN-gamma and LPS, decreased iN O production by 86%, augmented VCAM-1 and iNOS expression in endotheli al and RAW264.7 cells, respectively, and increased monocyte adhesion t o the endothelial cell surface. Transient transfection studies using v arious VCAM-1 promoter constructs demonstrated that inhibitory effects of iNO on VCAM-1 gene transcription were mediated, in part, by inhibi tory effects of iNO on kappa B cis-acting elements. Immunofluorescence studies using an Ab to the RelA (p65) subunit of nuclear factor-kappa B revealed that iNO inhibited the activation of nuclear factor-kappa B. These studies indicate that iNO attenuates iNOS expression in macro phages and inhibits monocyte adhesion to endothelial cells, and sugges t that endogenously derived iNO may be an important autoregulatory inh ibitor of vascular inflammation.