Vascular endothelial growth factor (VEGF), an endothelial cell mitogen
, is a potent angiogenic factor produced by several cell types. Whethe
r human neutrophils are potential producers of VEGF has not yet been d
escribed. The present work shows that phorbol-12-myristate 13-acetate
(PMA), fMet-Leu-Phe, and tumor necrosis factor-alpha (TNF-alpha) trigg
ered a time-dependent secretion of VEGF by human neutrophils. Cells in
cubated with 50 ng/mL of PMA released significant amounts of VEGF afte
r 15 minutes. Because the extracellular content of VEGF in human neutr
ophils supernatants remained constant over a period of 2 to 24 hours a
nd because PMA is a potent inducer of human neutrophil degranulation,
the PMA-induced secretion of VEGF may be due to a preexisting intracel
lular pool of this molecule. This hypothesis was reinforced by the abs
ence of cycloheximide effect on the PMA-induced secretion of VEGF. The
existence of an intracellular pool of VEGF was confirmed by measuring
the intracellular content of VEGF in resting neutrophils. A dose-depe
ndent inhibition of PMA-induced VEGF secretion was observed when the c
ells were incubated in the presence of pentoxifylline, a methylxanthin
e known to inhibit neutrophil degranulation. To confirm the implicatio
n of neutrophil degranulation in VEGF release, the effects of two indu
cers of physiologic degranulation, fMet-Leu-Phe and TNF-alpha, were de
termined. Both agonists induced a release of VEGF in the absence of cy
tochalasin B, confirming the involvement of neutrophil degranulation a
nd suggesting the intracellular localization of VEGF in the specific g
ranule fraction.; In addition, the kinetics of fMet-Leu-Phe- and TNF-a
lpha-induced secretion of lactoferrin were similar to those of VEGF re
lease induced by these two both agonists. The subcellular fractionatio
n of human neutrophils showed a granule-specific distribution of the i
ntracellular pool of VEGF in resting neutrophils. The finding that hum
an neutrophils contain an intracellular pool of VEGF, secreted in the
extracellular space under PMA-, fMet-Leu-Phe-, and TNF-alpha-induced d
egranulation, suggests a role for human neutrophils as cellular effect
ers of physiologic as well as pathologic angiogenesis. (C) 1997 by The
American Society of Hematology.