Production of angiogenic activity by human monocytes requires an L-arginine/nitric oxide-synthase-dependent effector mechanism

Abstract

Human monocytes (Mφ) require stimulation with substances such as bacterial endotoxin [LPS (lipopolysaccharide)] to produce angiogenic activity. In this study, we report that stimulation of Mφ with LPS (5 μg/ml) in the absence of L-arginine greatly reduced their production of angiogenic activity, as assessed in vivo in rat corneas and in vitro by chemotaxis of human umbilical vein endothelial cells (HU-VECs). D-Arginine did not substitute for L-arginine in the production of angiogenic activity. The nitric oxide synthase (NO synthase, EC 1.14.13.39) inhibitors NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) both inhibited the production of angiogenic activity by LPS-stimulated Mφ in the presence of L-arginine, suggesting the involvement of this enzyme in the pathway that generates angiogenic activity. Neither of these substances directly inhibited the Mφ-derived angiogenic activity. LPS-induced production of the cytokines tumor necrosis factor α (TNF-α) and interleukin 8 (IL-8) was not significantly reduced when Mφ 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 Mφ in the presence of L-arginine. These results suggest that the LPS-stimulation-dependent generation of angiogenic activity by Mφ requires an L-arginine-dependent NO-synthase effector mechanism that may be independent of the generation of TNF-α and IL-8.