Evaluation of 5- and 6-fluoro derivatives of arachidonic acid and 5,8,14-eicosatrienoic acid as substrates and inhibitors of 5-lipoxygenase.

The 5- and 6-fluoro derivatives of arachidonic acid (5F-ETE and 6F-ETE) were evaluated as substrates of rat basophilic leukaemia cell (RBL-1) 5-lipoxygenase. 5F-ETE was found to be a poor substrate and was converted into a single product, 5-oxoeicosa-6,8,11,14-tetraenoic acid (5-oxo-ETE). 6F-ETE was a good substrate and was mainly converted into 5-hydroperoxy-6-fluoroeicosa-6,8,11,14-tetraenoic acid (5-OOH-6F-ETE) with concomitant formation of a small amount of 5-oxo-6-fluoroeicosa-6,8,11,14-tetraenoic acid (5-oxo-6F-ETE). However the formation of 5,12-dihydroxy-6-fluoroeicosa-6,8,10,14-tetraenoic acids, epimeric at C-12, was not observed. Eicosa-5(Z),8(Z),14(Z)-trienoic acid (ET), previously described as a good substrate of 5-lipoxygenase, is oxidized mainly to 5-hydroperoxyeicosa-6,8,14-trienoic acid (5-OOH-ET), which does not serve as a substrate for the leukotriene A4 (LTA4) synthase activity of 5-lipoxygenase [Navé, Dulery, Gaget & Ducep (1988) Prostaglandins 36, 385-398]. To allow a better estimation of the effect of fluorine substitution on the rate of oxidation of the 5,8-cis,cis-diene moiety by 5-lipoxygenase, the 5- and 6-fluoro derivatives of ET were studied as substrates. Qualitatively, the metabolism of 5F-ET and 6F-ET was found to be similar to that observed for 5F-ETE and 6F-ETE. Quantitatively, 6F-ET proved to be a somewhat better substrate than ET, whereas 5F-ET was poorly metabolized. The relative ability of arachidonic acid, ET and the corresponding 5- and 6-fluoro derivatives to inhibit the 5-lipoxygenase-catalysed oxidation of eicosa-5(Z),8(Z)-dienoic acid (ED) was also investigated. 6F-ETE and 5F-ETE were found to be effective and about equipotent inhibitors of 5-lipoxygenase in the micromolar range. In view of their close structural similarity to arachidonic acid, these two inhibitors are expected to be important tools in the study of the 5-lipoxygenase pathway in vivo.