DELTA-8 DESATURATION IN-VIVO OF DEUTERATED EICOSATRIENOIC ACID BY MOUSE-LIVER

In vitro evidence has been reported for an alternate pathway that invo lves Delta 8 desaturation of n-6 and n-3 polyunsaturated fatty acids ( PU FA). The present study was designed to allow detection of Delta 8 d esaturation in vivo and to provide an estimation of the relative contr ibution of Delta 8 desaturation to the in vivo synthesis of n-3 fatty acids. Male adult ICR mice were fed a semisynthetic fat-free diet for eight days, and then the diets were supplemented for three days with d euterated 11,14,17-eicosatrienoic acid (20:3-d(8)) labeled at the 3,3, 4,4,8,8,9,9 carbon positions. Analysis of liver total lipid by gas chr omatography/mass spectroscopy indicates that the total deuterated fatt y acids contained 22.3% 20:3n-3-d(8) and 28.9% of metabolites formed b y elongation and Delta 5 desaturation of 20:3n-3-d(8). Deuterated meta bolites resulting from retroconversion to 18:3-d(6) and subsequent met abolism by classical pathways represented 35.3% of the total deuterate d fatty acids. The retroconversion product (18:4n-3-d6) of 20:4n-3-d6 and/or -d(8) was 9.0% of the total. A minor percentage (4.4%) of the p roducts identified (20:4n-3-d(6), 20:5n-3-d(6), 22:5n-3-d(6), 22:6n-3- d(5) and 24:6n-3-d(5)) were formed by Delta 8 desaturation. This study provides the first clear evidence of Delta 8 desaturation in vivo in the mouse liver. Whether Delta 8 desaturation would have a greater imp ortance in vivo when the Delta 6 desaturase pathway is disrupted remai ns to be determined.