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Production of angiogenic activity by human monocytes requires an L-arginine/nitric oxide-synthase-dependent effector
S J Leibovich1, P J Polverini, T W Fong
1Department of Basic Sciences, Northwestern University Dental School, Chicago, IL 60611.
Abstract:
Human monocytes (M phi) require stimulation with substances such as bacterial endotoxin [LPS (lipopolysaccharide)] to produce angiogenic activity. In this study, we report that stimulation of M phi with LPS (5 micrograms/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 M phi 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 M phi-derived angiogenic activity. LPS-induced production of the cytokines 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 presence of L-arginine. These results suggest that the LPS-stimulation-dependent generation of angiogenic activity by M phi requires an L-arginine-dependent NO-synthase effector mechanism that may be independent of the generation of TNF-alpha and IL-8.
Insights
Human monocytes require L-arginine for producing angiogenic activity after lipopolysaccharide (LPS) stimulation. This process involves nitric oxide synthase (NO synthase) and is independent of TNF-alpha and IL-8 production.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Human monocytes (M phi) necessitate stimulation, like with bacterial lipopolysaccharide (LPS), to generate angiogenic activity.
- Angiogenesis, the formation of new blood vessels, is a critical process in development and disease.
Purpose of the Study:
- To investigate the role of L-arginine and nitric oxide synthase (NO synthase) in LPS-induced angiogenic activity production by human monocytes.
- To determine if this pathway is linked to the production of cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 8 (IL-8).
Main Methods:
- Monocytes were stimulated with LPS in the presence or absence of L-arginine.
- Angiogenic activity was assessed in vivo (rat corneas) and in vitro (human umbilical vein endothelial cell chemotaxis).
- The effects of NO synthase inhibitors (L-NMMA, L-NAME) and D-arginine were evaluated. Cytokine production (TNF-alpha, IL-8) was also measured.
Main Results:
- Absence of L-arginine significantly reduced LPS-stimulated monocyte production of angiogenic activity.
- NO synthase inhibitors (L-NMMA, L-NAME) blocked angiogenic activity generation in LPS-stimulated monocytes, indicating NO synthase involvement.
- LPS-induced production of TNF-alpha and IL-8 was not significantly affected by L-arginine absence or NO synthase inhibition.
Conclusions:
- LPS-induced angiogenic activity generation by monocytes requires an L-arginine-dependent NO synthase pathway.
- This NO synthase-mediated mechanism appears to be independent of TNF-alpha and IL-8 production.