Abnormal metabolism of arachidonic acid in chronic inflammatory bowel disease: enhanced release of leucotriene B4 from activated neutrophils

Abstract

The metabolism of endogenous arachidonic acid P(AA) was investigated in activated neutrophils from 20 patients with Crohn's disease, 20 with ulcerative colitis, and 25 healthy volunteers. 1-14C-P(AA) was incorporated into intracellular pools of phospholipids prior to activation of the cells with ionophore A23187 and analyses of released arachidonic acid metabolites by thin layer chromatography. Total release of radioactivity expressing the release of arachidonic acid and its metabolites, was equal in the experimental and control groups, which suggests a normal substrate availability. In contrast, there was a marked increase in the relative release of leucotriene B4 (LTB4) and its omega-oxidation products, 20-hydroxy-LTB4 (20-OH-LTB4) and 20-carboxy-LTB4 (20-COOH-LTB4), with LTB4 values exceeding the reference interval in seven of 20 patients with Crohn's disease, median 8.7%, and in six of 20 patients with ulcerative colitis, median 7.7%, as compared with a median of 5.3% in healthy volunteers. Furthermore, a decreased release of unmetabolised arachidonic acid, correlating inversely with the release of LTB4 in all experimental and control groups, and normal values for the production of other metabolites of arachidonic acid--for example, 5-hydroxyeicosatetraenoic acid (5-HETE) and 12-hydroxyheptadecatrienoic acid (HHT), point to an enzymatic abnormality such as increased activity of leucotriene B synthetase. An increased capacity for release of LTB4, the major pro-inflammatory metabolite of arachidonic acid lipoxygenation by polymorphonuclear leucocytes, may contribute to perpetuation of the inflammation and to tissue destruction in chronic inflammatory bowel disease. Our findings agree with previous reports of an increased release of LTB4 by the colonic mucosa in this condition.