PRODUCTION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR BY MURINE MACROPHAGES - REGULATION BY HYPOXIA, LACTATE, AND THE INDUCIBLE NITRIC-OXIDE SYNTHASE PATHWAY

Murine thioglycolate-induced peritoneal macrophages (MPMs) and the mur ine RAW264.7 macrophage-like cell line (RAW cells) constitutively prod uce vascular endothelial growth factor (VEGF). VEGF production is incr eased under hypoxic conditions or after cell activation with interfero n-gamma (IFN-gamma) and endotoxin (lipopolysaccharide, LPS). In contra st, tumor necrosis factor-alpha is produced only by IFN gamma/LPS-acti vated cells. Lactate (25 mmol/L) does not increase VEGF production by these cells. However, hypoxia, lactate, and IFN gamma/LPS-activated MP Ms express angiogenic activity, whereas normoxic, nonactivated MPMs do not. Lack of angiogenic activity is not due to an antiangiogenic fact or(s) in the medium of these cells. Angiogenic activity produced by hy poxia and lactate-treated MPMs is neutralized by anti-VEGF antibody, w hich also neutralizes most of the angiogenic activity produced by IFN gamma/LPS-activated MPMs. The inducible nitric oxide synthase inhibito rs N-g-nitro-L-arginine-methyl ester (1.5 mmol/L) and aminoguanidine ( 1 mmol/L) block production of angiogenic activity by MPMs and RAW cell s. In RAW cells, N-g-nitro-L-arginine-methyl ester and AG block IFN ga mma/LPS-activated, but not constitutive, VEGF production, whereas in M PMs, neither constitutive nor IFN gamma/LPS-activated VEGF synthesis i s affected. Synthesis of tumor necrosis factor-alpha is also unaffecte d. In contrast to normoxic, nonactivated MPMs, inducible nitric oxide synthase-inhibited, IFN gamma/LPS-activated MPMs produce an. antiangio genic factor(s). We conclude that VEGF is a major contributor to macro phage-derived angiogenic activity, and that activation by hypoxia, lac tate, or IFN gamma/LPS switches macrophage-derived VEGF from a nonangi ogenic to an angiogenic state. This switch may involve a posttranslati onal modification of VEGF, possibly by the process of ADP-ribosylation , ADP-ribosylation by MPM cytosolic extracts or by cholera toxin switc hes rVEGF(165) from an angiogenic to a nonangiogenic state. In IFN gam ma/LPS-activated MPMs, the inducible nitric oxide synthase-dependent p athway also regulates the expression of an antiangiogenic factor(s) th at antagonizes the bioactivity of VEGF and provides an additional regu latory pathway controlling the angiogenic phenotype of macrophages.