ARGININE METABOLISM IN KERATINOCYTES AND MACROPHAGES DURING NITRIC-OXIDE BIOSYNTHESIS - MULTIPLE-MODES OF ACTION OF NITRIC-OXIDE SYNTHASE INHIBITORS

Nitric oxide is an important cellular mediator produced in keratinocyt es and macrophages from arginine by the enzyme nitric oxide synthase d uring inflammatory reactions in the skin. We found that gamma-interfer on stimulated nitric oxide production and the expression of inducible nitric oxide synthase in both cell types. However, macrophages produce d more nitric oxide and nitric oxide synthase protein, and at earlier times than keratinocytes. Keratinocytes treated with gamma-interferon took up more arginine than macrophages; however, they were less effici ent in metabolizing this amino acid and exhibited reduced nitric oxide synthase enzyme activity. In both cell types, the nitric oxide syntha se inhibitors, N-G-monomethyl-L-arginine (NMMA), L-N-5-(iminoethyl)orn ithine, L-canavanine, and N-omega-nitro-L-arginine, as well as lysine, ornithine, and homoarginine markedly reduced arginine uptake. In cont rast, N-omega-nitro-L-arginine methyl ester and N-omega-nitro-L-argini ne benzyl ester were poor inhibitors of arginine uptake, while aminogu anidine had no effect on uptake of arginine by the cells. Moreover, NM MA was found to inhibit simultaneously arginine uptake and nitric oxid e synthase enzyme activity in both cell types, whereas aminoguanidine only affected nitric oxide synthase activity. No major differences wer e observed between keratinocytes and macrophages. Taken together, thes e data demonstrate that, although keratinocytes and macrophages both s ynthesize nitric oxide, its production is regulated distinctly in thes e two cell types. Furthermore, in these cells, nitric oxide synthase i nhibitors such as NMMA exhibit at least two sites of action: inhibitio n of nitric oxide synthase and cellular uptake of arginine. (C) 1997 E lsevier Science Inc.