Role of the arginine-nitric oxide pathway in the regulation of vascular smooth muscle cell proliferation

The objective of this study was to elucidate the mechanisms by which nitric oxide (NO) inhibits rat aortic smooth muscle cell (RASMC) proliferation. T wo products of the arginine-NO pathway interfere with cell growth by distin ct mechanisms. N-G-hydroxyarginine and NO appear to interfere with cell pro liferation by inhibiting arginase and ornithine decarboxylase (ODC), respec tively. S-nitroso-N-acetylpenicillamine, (Z)-1-[N-(2-aminoethyl)-N-(2-amino ethyl)-amino]-diazen-1-ium-1,2-diolate, and a nitroaspirin derivative (NCX 4016), each of which is a NO donor agent, inhibited RASMC growth at concent rations of 1-3 muM by cGMP-independent mechanisms. The cytostatic action of the NO donor agents as well as alpha -difluoromethylornithine (DFMO), a kn own ODC inhibitor, was prevented by addition of putrescine but not ornithin e. These observations suggested that NO, like DEMO, may directly inhibit OD C. Experiments with purified, recombinant mammalian ODC revealed that NO in hibits ODC possibly by S-nitrosylation of the active site cysteine in ODC. DFMO, as well as the NO donor agents, interfered with cellular polyamine (p utrescine, spermidine, spermine) production. Conversely, increasing the exp ression and catalytic activity of arginase I in RAS[WC either by transfecti on of cells with the arginase I gene or by induction of arginase I mRNA wit h IL-4 resulted in increased urea and polyamine production as well as cell proliferation. Finally, coculture of rat aortic endothelial cells, which ha d been pretreated with lipopolysaccharide plus a cytokine mixture to induce NO synthase and promote NO production, caused NO-dependent inhibition of t arget RASMC proliferation. This study confirms the inhibitory role of the a rginine-NO pathway in vascular smooth muscle proliferation and indicates th at one mechanism of action of NO is cGMP-independent and attributed to its capacity to inhibit ODC.