Ionophore-dependent generation of eicosanoids in human dispersed lung cells: Modulation by 6,9-deepoxy-6,9-(phenylimino)- Δ6,8 prostaglandin I 1 (U-60,257)

Abstract

6,9-Deepoxy-6-9-(phenylimino)- Δ 6,8-prostaglandin I 1, a prostacyclin analogue reported to inhibit sulphidopeptide leukotriene formation in animals, was evaluated for its pharmacological activity against eicosanoid and histamine release from human dispersed lung cells (HDLC). In the absence of drug, challenge of HDLC with A23187 (2.5 μM) increased immunoreactive eicosanoid generation by factors of 7.6 for prostaglandin (PG) D 2, 9.1 for TXB 2, 3.2 for PGF 2α, 2.0 for 5-HETE, 6.3 for LTC 4, in association with a twofold increase in histamine release. When exogenous [ 14C]-arachidonic acid was added to HDLC simultaneously with A23187 challenge, radiolabelled eicosanoids were recovered in the supernatant, but on separating the products by radio-thin layer chromatography the proportions of individual eicosanoids were not significantly different from unchallenged cells. With endogenous arachidonate, U-60,257 was a potent inhibitor of i-LTC 4 generation at l μM, but between 3 and 300 μM there was a concentration-related reversal of this inhibition. The effects of U-60,257 on the metabolism of exogenous [ 14C]-arachidonic acid were also studied. Under these circumstances the drug was a potent inhibitor of both 5-HETE and 5,12-diHETE formation, without significantly affecting the formation of other mono-HETES. In agreement with previous endogenous substrate experiments there was a concentration-dependent inhibition of TxB 2 formation from exogenous arachidonic acid. These findings highlight the complex pharmacological actions of U-60,257 which appear dependent on the source of arachidonic acid substrate.