MODULATION IN DELTA-9, DELTA-6, AND DELTA-5 FATTY-ACID DESATURASE ACTIVITY IN THE HUMAN INTESTINAL CACO-2 CELL-LINE

We report the influence of media lipids, growth in lipid-poor medium, and cell differentiation on Delta 9, Delta 6, and Delta 5 desaturase a ctivity in the human CaCo-2 enterocyte cell line. We also describe the level of incorporation of palmitic (16:0), linoleic (18:2n-6), and ei cosapentaenoic (EPA) acids (20:5n-3) and their higher homologues into cytosolic and membrane lipids during long-term (10 days) medium supple mentation in fully differentiated 16- to 18-day-old cultures. CaCo-2 m onolayers reached confluency by day 6 with subsequent development of m icrovilli and maximal expression of microvillus membrane sucrose, alka line phosphatase, and gamma-glutamyltransaminase occurring between day s 16 and 23 after plating. There was evidence of the presence and modu lation of Delta 9, Delta 6, and Delta 5 desaturase activity (Delta 9 > Delta 6 > Delta 5). Delta 6 Desaturase activity decreased approximate ly 2-fold between days 6 and 24 of culture and when the fetal bovine s erum concentration was increased from 0.5% to 25%; in contrast, when c ells were starved for 72 h, activity increased 5.4-fold. When the medi a was supplemented with either linoleic acid and/or EPA, both Delta 6 and Delta 5 desaturase activities were inhibited, the greatest reducti on of Delta 5 desaturase activity occurring with EPA. Incorporation of media fatty acids plus their desaturase and elongase products was hig hly dependent on medium composition with the homologues of Delta 9 > D elta 6 > Delta 5. Supplementation of cellular media with 100 mu M EPA for 10 days decreased membrane phosphatidylethanolamine arachidonic ac id level from 13.2 to 8.9%. From these results we conclude that entero cyte membrane fatty acid composition and desaturase enzyme activity ar e regulated by both dietary fat intake and cell maturation. The clinic al relevance of these observations on lipid dietary modification for t he management of chronic inflammatory bowel disease is still uncertain but these observations suggest that the beneficial effects of EPA sup plements on human ulcerative colitis may be due to a reduction in ente rocyte arachidonic acid content by down-regulation of Delta 6 and Delt a 5 desaturase activity.