Leuktriene synthesis by human gastrointestinal tissues

Abstract

The prostaglandin and leukotriene synthesizing capacity of human gastrointestinal tissues obtained at surgery was investigated using radioimmunoassays for prostaglandin E 2, leukotriene B 4 and sulfidopeptide leukotrienes. The leukotriene inimunoassay data were validated by high-pressure liquid chromatography (HPLC). During incubation at 37°C, fragments of human gastric, jejuno-ileal and colonie mucosa released considerably larger amounts of prostaglandin E 2 than of leukotriene B 4 and sulfidopeptide leukotrienes. Gastrointestinal smooth muscle tissues released even larger amounts of prostaglandin E 2, but smaller amounts of leukotrienes than the corresponding mucosal tissues. Adenocarcinoma tissue released larger amounts of leukotriene B 4, sulfidopeptide leukotrienes and prostaglandin E 2 than normal colonie mucosa. Ionophore A23187 (5 μg/ml) did not stimulate release of prostaglandin E 2 from any of the tissues investigated, but enhanced release of leukotriene B 4 and sulfidopeptide leukotrienes. HPLC analysis demonstrated that immunoreactive leukotriene B 4 co-chromatographed almost exclusively with standard leukotriene B 4, while immunoreactive sulfidopeptide leukotrienes consisted of a mixture of leukotrienes C 4, D 4 and E 4. Leukotriene synthesis by human gastrointestinal tissues was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the dual enzyme inhibitor BW755C (3-amino-1-(trifluoromethylphenyl)-2-pyrazoline hydrochloride). Synthesis of prostaglandin E 2 was inhibited by the cyclooxygenase inhibitor indomethacin as well as by BW755C. Incubation of gastrointestinal tissues in the presence of glutathione decreased the amounts of leukotrienes D 4 and E 4, while release of leukotriene C 4 was simultaneously increased. On the other hand, incubation of tritiated leukotriene C 4 with incubation media from human gastric or colonic mucosa resulted in conversion of the substrate to [ 3H]leukotriene D 4 and [ 3H]Ieukotriene E 4. The results indicate the capacity of human gastrointestinal tissues to synthesize the 5-lipoxygenase-derived products of arachidonate metabolism, leukotriene B 4 and sulfidopeptide leukotrienes, in addition to larger amounts of prostaglandin E 2. Furthermore, considerable activities of the sulfidopeptide leukotriene-metabolizing enzymes γ-glutamyl transpeptidase and dipeptidase were detected in human gastrointestinal tissues. These enzymes might play an important role in biological inactivation and/or change of biological profile of sulfidopeptide leukotrienes generated in the human gastrointestinal tract.