Arachidonic and linoleic acid metabolism in mouse intestinal tissue: evidence for novel lipoxygenase activity

Previous studies in our laboratory revealed a high expression of 15-lipoxygenase-1 in human colorectal carcinomas, suggesting the importance of lipoxygenase in colorectal tumor development. In this report, we have investigated the metabolism of arachidonic and linoleic acid by intestinal tissues of Min mice, an animal model for intestinal neoplasia. The polyp and normal tissues from Min mice intestine were homogenized, incubated with arachidonic or linoleic acid, and analyzed by reverse-, straight-, and chiral-phase HPLC. Arachidonic acid was converted to prostaglandins E2 and F2alpha. Little 12- or 15-hydroxyeicosatetraenoic acid was detected. Cyclooxygenase (COX)-2 was detected in polyps and the adjacent normal tissues by Western immunoblotting, but neither COX-1 nor leukocyte-type 12-lipoxygenase, the murine ortholog to human 15-lipoxygenase-1, was detected. These tissue homogenates converted linoleic acid to an equal mixture of 9(S)- and 13(S)-hydroxyoctadecadienoic acid (HODE). Inhibition of lipoxygenase activity with nordihydroguaiaretic acid blocked HODEs formation, but the COX inhibitor indomethacin did not. Degenerative-nested PCR analyses using primers encoded by highly conserved sequences in lipoxygenases detected 5-lipoxygenase, leukocyte-type 12-lipoxygenase, platelet-type 12-lipoxygenase, 8-lipoxygenase, and epidermis-type lipoxygenase-3 in mouse intestinal tissue. All of these PCR products represent known lipoxygenase that are not reported to utilize linoleic acid preferentially as substrate and do not metabolize linoleic acid to an equal mixture of 9(S)- and 13(S)-HODE. This somewhat unique profile of linoleate product formation in Min mice intestinal tissue suggests the presence of an uncharacterized and potentially novel lipoxygenase(s) that may play a role in intestinal epithelial cell differentiation and tumor development.