Effects of CoA-independent transacylase inhibitors on the production of lipid inflammatory mediators

The enzyme CoA-independent transacylase (CoA-IT) has been proposed to mediate the movement of arachidonate between specific phospholipid subclasses, and we have shown that two inhibitors of CoA-IT (SK and F 98625 and SK and F 45905) block this movement. In this report, we use these inhibitors to further characterize the role of CoA-IT in the production of lipid mediators. SK and F 98625 (diethyl 7-(3,4,5-triphenyl-2-oxo-2,3- dihydro-imidazol-1-yl)heptane-phosphonate) and SK and F 45905 (2[2-[3-(4- chloro-3-trifluoromethylphenyl)ureido]-4-trifluoromethyl phenoxy]-4,5- dichlorobenzenesulfonic acid) inhibited CoA-IT activity (IC₅₀ values of 9 μM and 6 μM, respectively). Neither compound had any effect on cyclooxygenase, 14-kDa PLA₂ or acetyltransferase activities at concentrations below 20 μM. However, SK and F 45905 inhibited 85-kDa PLA₂ activity (IC₅₀ = 3 μM), and both compounds inhibited 5-lipoxygenase activity (IC₅₀ values of 2-4 μM). In ionophore-stimulated neutrophils, SK and F 98625 and SK and F 45905 blocked the liberation of arachidonic acid from phospholipids, which suggests that the movement of arachidonate into specific phospholipid pools is a prerequisite for release. Both compounds also inhibited the production of platelet-activating factor in ionophore- stimulated neutrophils and antigen-stimulated mast cells. This inhibition of platelet-activating factor and arachidonic acid release was not mimicked by an inhibitor of 5-lipoxygenase, zileuton, which indicates that the primary mode of action of SK and F 98625 and SK and F 45905 is via inhibition of CoA- IT. SK and F 98625 and SK and F 45905 were able to decrease prostaglandin production in several inflammatory cells and to block signs of inflammation in ears of phorbol ester-challenged mice. Taken together, these results show that blockade of CoA-IT, which leads to inhibition of arachidonate remodeling between phospholipids, results in the attenuation of platelet-activating factor production, arachidonic acid release and the formation of eicosanoid products.