Metabolism and incorporation into glycerolipids of exogenous 18:3(n-3) and 18:3(n-6) by MDCK cells.

The extent to which exogenous 18:3(n-3) and 18:3(n-6) were desaturated and elongated and the degree to which they and their derivatives altered the unsaturation index of cell glycerolipids were compared using clone 4 MDCK cells grown in lipid- and serum-free medium. Despite differences in the degree of unsaturation of the individual polyunsaturated fatty acids produced from 18:3(n-3) or 18:3(n-6), the unsaturation index of phospholipids increased similarly from 0.7 in control cells grown in serum- and lipid-free medium to ca. 1.6 in those supplemented with fatty acid. The added fatty acids had little effect on cell growth. The conversion of 18:3(n-6) to 20:3(n-6) and 20:4(n-6) was more rapid than that of 18:3(n-3) to 20:4(n-3) and 20:5(n-3). No significant quantities of 20:3(n-3) or 18:4(n-3) were noted. When both 18:3 isomers were supplied simultaneously, marked differences in the amounts of some species of n-3 and n-6 polyunsaturated fatty acids were observed. The presence of 18:3(n-6) and/or its derivatives suppressed levels of 20:4(n-3) and 20:5(n-3), perhaps through inhibition of the delta 6 and delta 5 desaturases responsible for their synthesis from 18:3(n-3). Similarly 18:3(n-3), and/or its longer more unsaturated derivatives, diminished the formation of 20:4(n-6) from 18:3(n-6). No marked effect on the products derived from elongation alone were observed.