Biosynthesis of lipoxygenase and cyclo-oxygenase products from [14C]-arachidonic acid by human colonic mucosa

Abstract

The human colon synthetises several prostanoids which may have a role in inflammatory bowel diseases. As lipoxygenase products of arachidonate metabolism have been implicated in inflammatory processes, we have now investigated the formation of both lipoxygenase and cyclo-oxygenase metabolites from [14C]-arachidonic acid ([14C]-AA) by human colonic tissue. Homogenates of human colonic mucosa were incubated with [14C]-AA and after extraction into diethyl ether, separated by thin layer chromatography using two solvent systems that allowed resolution of cyclo-oxygenase and lipoxygenase products. The predominant cyclo-oxygenase products, as identified by their chromatographic mobility, were PGE2>PGF(2α)>PGD2>TXB2>6-keto-PGF(1α). The formation of these products was inhibited both by indomethacin (1-10 μM) and the dual pathway inhibitor, BW755C (1-30 μM). The predominant lipoxygenase products formed, which had the chromatographic mobility of 11-, 12-, 15-HETE (which ran together) were inhibited by BW755C (19 μM) but not by indomethacin (3μM). Further resolution of this TLC band, performed using normal phase HPLC, indicated that both 12-HETE and 15-HETE were major lipoxygenase products formed by human colonic homogenate. The present findings indicate that human colonic tissue can convert [14C]-AA into lipoxygenase as well as cyclo-oxygenase products and support the suggestion that lipoxygenase products may have a role in inflammatory bowel disease.