Prostacyclin is an important endothelial mediator involved in the interaction of neutrophils (PMN) with the vessel wall. Many studies have shown the beneficial effects of
prostacyclin in
ischemia and reperfusion. However, no previous study has investigated the direct effects of the
prostacyclin analogs
iloprost (ILO) and
alprostadil (
PGE(1)) on the endothelial part of the adhesion process. Human umbilical vein endothelial cells (HUVECs) were grown to confluence, stimulated with 300 U/ml
TNF-alpha and treated with increasing concentrations of ILO and
PGE(1). The cells were washed to remove TNF and the inhibitors and adhesion of fluorescence-green labeled PMN was determined microscopically.
ICAM-1,
VCAM-1 and
E-selectin expression were measured by a cell-surface ELISA. The
chemoattractant activity of the endothelial cell releasate was tested in a Boyden chamber.ILO and
PGE(1) reduced PMN-adhesion in a concentration-dependent manner (ILO: -54 +/- 9 % at 0.5 microM,
PGE1: -46 +/- 10 %
at 10 microM). However, the surface expression of
ICAM-1,
VCAM-1 and
E-selectin remained unaltered. When the supernatant of
iloprost/
PGE(1)-treated cells was transferred onto cells that were activated, but not treated with ILO or
PGE(1), the reduction of PMN adhesion remains sustained. These data indicate that the inhibitory effect of ILO/
PGE(1) treatment is achieved by a reduced
chemoattractant potential. PAF-antagonists were able to block neutrophil adhesion and mimicked the effect of ILO, while exogenous PAF diminished the inhibitory effect of ILO concentration-dependently. This study demonstrates the beneficial effects of ILO and
PGE(1) on inflammatorily activated endothelial cells. These
prostacyclin analogs inhibit PMN-adhesion despite maximal adhesion molecule expression by regulating the balance of - yet to be determined - endothelial-derived mediators.