AN INHIBITOR OF MACROPHAGE ARGININE TRANSPORT AND NITRIC-OXIDE PRODUCTION (CNI-1493) PREVENTS ACUTE-INFLAMMATION AND ENDOTOXIN LETHALITY

Background: Nitric oxide (NO), a small effector molecule produced enzy matically from L-arginine by nitric oxide synthase (NOS), is a mediato r not only of important homeostatic mechanisms (e.g., blood vessel ton e and tissue perfusion), but also of key aspects of local and systemic inflammatory responses. Previous efforts to develop inhibitors of NOS to protect against NO-mediated tissue damage in endotoxin shock have been unsuccessful, largely because such competitive NOS antagonists in terfere with critical vasoregulatory NO production in blood vessels an d decrease survival in endotoxemic animals. Accordingly we sought to d evelop a pharmaceutical approach to selectively inhibit NO production in macrophages while sparing NO responses in blood vessels. Materials and Methods: The processes of cytokine-inducible L-arginine transport and NO production were studied in the murine macrophage-like cell line (RAW 264.7). A series of multivalent guanylhydrazones were synthesize d to inhibit cytokine-inducible L-arginine transport. One such compoun d (CNI-1493) was studied further in animal models of endothelial-deriv ed relaxing factor (EDRF) activity, carrageenan inflammation, and leth al lipopolysaccharide (LPS) challenge.Results: Upon activation with cy tokines, macrophages increase transport of L-arginine to support the p roduction of NO by NOS. Since endothelial cells do not require this ad ditional arginine transport to produce NO, we reasoned that a competit ive inhibitor of cytokine-inducible L-arginine transport would not inh ibit EDRF activity in blood vessels, and thus might be effectively emp loyed against endotoxic shock. CNI-1493, a tetravalent guanylhydrazone , proved to be a selective inhibitor of cytokine-inducible arginine tr ansport and NO production, but did not inhibit EDRF activity. In mice, CNI-1493 prevented the development of carrageenan-induced footpad inf lammation, and conferred protection against lethal LPS challenge. Conc lusions: A selective inhibitor of cytokine-inducible L-arginine transp ort that does not inhibit vascular EDRF responses is effective against endotoxin lethality and significantly reduces inflammatory responses.