Inhibitors of CoA-independent transacylase block the movement of arachidonate into 1-ether-linked phospholipids of human neutrophils.

The enzyme CoA-independent transacylase (CoA-IT) has been proposed to mediate the movement of arachidonate between phospholipid subclasses and influence the formation of arachidonic acid metabolites and platelet-activating factor. To substantiate the critical role of CoA-IT, we have developed two structurally diverse inhibitors of CoA-IT activity, SK&F 98625 [diethyl 7-(3,4,5-triphenyl-2-oxo-2,3-dihydro-imidazole-1-yl)heptane phosphonate] and SK&F 45905 [2-[2-(3-4-chloro-3-(trifluoromethyl)phenyl)-ureido]-4- (trifluoromethyl)phenoxy]-4,5-dichlorobenzenesulfonic acid]. These compounds were tested for their capacity to block microsomal CoA-IT activity using two assay systems, the transacylation of 1-alkyl-2-lyso-sn-glycero-3-phosphocholine (GPC) and the transfer of [14C]arachidonate from 1-acyl-2-[14C]arachidonoyl-GPC to lyso-PE. Both SK&F 98625 and SK&F 45905 inhibited CoA-IT activity (IC50s 6-19 microM) in these two assays. In contrast, SK&F 98625 or SK&F 45905 had little or no effect on other lipid-modifying activities, including CoA-dependent acyltransferase or acetyltransferase. Kinetic analysis revealed that both SK&F 98625 and SK&F 45905 interact directly with the enzyme and prevented the acylation of lysophospholipids in a competitive manner. In intact human neutrophils, both SK&F 98625 and SK&F 45905 completely blocked the movement of [3H]arachidonate from 1-acyl-linked phospholipids into 1-alkyl-2-arachidonoyl-GPC and 1-alk-1'-enyl-2-arachidonoyl-GPE. In contrast, these compounds did not inhibit the incorporation of free arachidonic acid into cellular lipids indicating that they did not alter CoA-dependent acyl transferase activities in the intact cell.(ABSTRACT TRUNCATED AT 250 WORDS)

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&F 98625 and SK&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&F 98625 (diethyl 7-(3,4,5-triphenyl-2-oxo-2,3-dihydro-imidazol-1-yl)heptane- phosphonate) and SK&F 45905 [2(-)[3-(4-chloro-3-trifluoromethylphenyl)ureido]-4-trifluoromethyl phenoxy]-4,5-dichlorobenzenesulfonic acid) inhibited CoA-IT activity (IC50 values of 9 microM and 6 microM, respectively). Neither compound had any effect on cyclooxygenase, 14-kDa PLA2 or acetyltransferase activities at concentrations below 20 microM. However, SK&F 45905 inhibited 85-kDa PLA2 activity (IC50 = 3 microM), and both compounds inhibited 5-lipoxygenase activity (IC50 values of 2-4 microM). In ionophore-stimulated neurotrophils, SK&F 98625 and SK&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&F 98625 and SK&F 45905 is via inhibition of CoA-IT. SK&F 98625 and SK&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 remodelling between phospholipids, results in the attenuation of platelet-activating factor production, arachidonic acid release and the formation of eicosanoid products.