PRODUCTION OF ANGIOGENIC ACTIVITY BY HUMAN MONOCYTES REQUIRES AN L-ARGININE NITRIC-OXIDE SYNTHASE-DEPENDENT EFFECTOR MECHANISM

Human monocytes (M phi) require stimulation with substances such as ba cterial endotoxin [LPS (lipopolysaccharide)] to produce angiogenic act ivity. In this study, we report that stimulation of M phi with LPS (5 mu g/ml) in the absence of L-arginine greatly reduced their production of angiogenic activity, as assessed in vivo in rat corneas and in vit ro by chemotaxis of human umbilical vein endothelial cells (HU-VECs). D-Arginine did not substitute for L-arginine in the production of angi ogenic activity. The nitric oxide synthase (NO synthase, EC 1.14.13.39 ) inhibitors N-G-monomethyl-L-arginine (L-NMMA) and N-G-nitro-L-argini ne methyl ester (L-NAME) both inhibited the production of angiogenic a ctivity by LPS-stimulated M phi in the presence of L-arginine, suggest ing the involvement of this enzyme in the pathway that generates angio genic activity. Neither of these substances directly inhibited the M p hi-derived angiogenic activity. LPS-induced production of the cytokine s tumor necrosis factor alpha (TNF-alpha) and interleukin 8 (IL-8) was not significantly reduced when M phi were incubated in the absence of L-arginine. Similarly, L-NMMA and L-NAME did not significantly reduce the LPS-induced production of these cytokines by M phi in the presenc e of L-arginine. These results suggest that the LPS-stimulation-depend ent generation of angiogenic activity by M phi requires an L-arginine- dependent NO-synthase effector mechanism that may be independent of th e generation of TNF-alpha and IL-8.