Generation of 8-epiprostaglandin F-2 alpha by human monocytes - Discriminate production by reactive oxygen species and prostaglandin endoperoxide synthase-2

F-2-isoprostanes are free radical-catalyzed products of arachidonic acid. One of these compounds, 8-epiprostaglandin F-2 alpha (8-epi-PGF(2 alpha)), is a mitogen and vasoconstrictor. We have shown that 8-epi-PGF(2 alpha), unlike other F-2-isoprostanes, is a minor product of the prostaglandin endoperoxide synthase-1 (PG G/H S-1) expressed in human platelets (Pratico, D., Lawson, J. A., and FitzGerald, G. A. (1995) J. Biol. Chem. 270, 9800-9808). Human monocytes express PG G/H S-1 constitutively and exhibit regulated expression of PG G/H S-2. Induction of PO G/H S-2 by concanavalin A, the phorbol ester, phorbol 12-myristate 13-acetate, and bacterial lipopolysaccharide was confirmed with a specific antibody in monocytes pretreated with aspirin to inhibit PC: G/H S-1. Induction of PO G/H S-2 by all three stimuli coincided with increased formation of prostaglandin E(2) (PGE(2)), thromboxane B-2 (TxB(2)), and 8-epi-PGF(2 alpha), but not of other F-2-isoprostanes. Confirmation of PG G/H S-2 as the source of 8-epi-PGF(2 alpha) formation was obtained by down-regulating the enzyme with dexamethasone; preventing protein synthesis with cycloheximide; and preventing synthesis of PGE(2), TxB(2), and 8-epi-PGF(2 alpha) with the specific PG G/H S-2 inhibitor, L 745,337. Monocytes also exhibit the facility to generate 8-epi-PGF(2 alpha) in a free radical-dependent manner. Thus, stimulation with opsonized zymosan or coincubation with low density lipoprotein was unassociated with product formation. However, coincubation of low density lipoprotein with zymosan-stimulated human monocytes resulted in marked formation of 8-epi-PGF(2 alpha), but not of PGE(2) or TxB(2). Production of 8-epi-PGF(2 alpha) coincided with that of thiobarbituric acid-reactive substances and lipid hydroperoxides, but was unaccompanied by PG G/H S-2 induction. Pretreatment of monocytes with the antioxidant, butylated hydroxytoluene or with superoxide dismutase, but not with L 745,337, suppressed formation of 8-epi-PGF(2 alpha), thiobarbituric acid-reactive substances, and lipid hydroperoxides. In conclusion, human monocytes may form bioactive 8-epi-PGF(2 alpha) either via free radical- or enzyme-catalyzed pathways. 8-Epi-PGF(2 alpha) is a more abundant product of monocyte PG G/H S-2 than of platelet PG G/H S-1. Formation by inducible PG G/H S-2 must be considered as a source of this compound in vivo.