Isoprostanes, produced in vivo by non-enzymatic
free-radical-induced lipid peroxidation, are markers of oxidative stress. Elevated serum and urine levels of
8-iso-PGF2alpha have been reported in a variety of diseases, many of which are characterized by early perivascular inflammatory infiltrates. It has been suggested that, in addition to being markers of oxidative stress,
isoprostanes may have pathogenic functions. In this study, we investigated the potential role of
8-iso-PGF2alpha in
inflammation, focusing on its effects on adhesion of monocytes to microvascular endothelial cells, an early event in the inflammatory response. In monocyte adhesion assays,
8-iso-PGF2alpha (>10(-8) M) suppressed both basal and
TNF-alpha-induced monocyte adhesion to quiescent or proliferating human dermal (HMEC) and rat renal microvascular endothelial cells. In contrast,
8-iso-PGF2alpha stimulated monocyte adhesion to human umbilical vein endothelial cells (HUVEC) as also reported by others.
8-Iso-PGF2alpha had no effect on the viability (
Trypan Blue exclusion) of U937 monocytes or HMEC.
8-Iso-PGF2alpha also had no effect on HMEC surface expression of
ICAM-1 or
VCAM-1. Exposure of HMEC to
8-iso-PGF2alpha for 1-2 h was sufficient to reduce monocyte adhesion to the cell surface, and this effect was independent of de novo
protein synthesis by HMEC. The effect of
8-iso-PGF2alpha was mimicked by a
thromboxane receptor (TP) agonist (
U46619) and blocked by a TP antagonist (SQ29548), indicating a TP-mediated process. Signal transduction pathway inhibitors (
SB203580,
curcumin, and
PD98059) implicated p38 and JNK, but not ERK, in 8-iso-PGF2alpha-induced suppression of monocyte adhesion. In addition to a direct effect,
conditioned medium (CM) transfer experiments suggest that
8-iso-PGF2alpha induces a secondary mediator, which also suppresses monocyte adhesion but via an alternative mechanism initiated between 3-4 h, which is TP-independent, requires new
protein synthesis, and is primarily dependent on activation of p38. The data show that
8-iso-PGF2alpha can suppress the attachment of monocytes to HMECs via two independent pathways, indicating a potential anti-inflammatory effect of
8-iso-PGF2alpha in the microvasculature.