Comparison of C 18 −, C 20 − and C 22 −unsaturated fatty acids in reducing fatty acid synthesis in isolated rat hepatocytes

Abstract

C 18 −, C 20 − and C 22 −unsaturated acids were tested for inhibition of fatty acid synthesis in hepatocytes isolated from essential fatty acid-deficient rats. Fatty acid synthesis was measured by incorporation of radioactivity from [1- 14C]-acetate or 3H 2O into fatty acids. C 20 −polyunsaturated fatty acids included arachidonic acid (20 : 4 ( n−6)) and 4 other fatty acids formed from linoleic acid (18 : 2 ( n−6)) or linolenic acid (18 : 3 ( n−3)). These were (11,14)-icosadienoic acid (20 : 2 ( n−6)), (8,11,14)-icosatrienoic acid (20 : 3 ( n−6)), (11,14,17)-icosatrienoic acid (20 : 3 ( n−3)) and (5,8,11,14,17)-icosapentaenoic acid (20 : 5 ( n−3)). All of these have essential fatty acid activity. The fatty acid (5,8,11)-icosatrienoic acid (20 : 3 ( n−9)) was also tested. This fatty acid is formed from oleic acid (18 : 1 ( n−9)) and is not an essential fatty acid or a prostaglandin precursor. C 20 −unsaturated fatty acids and (22 : 6 ( n−3)) were as effective as stearic acid in inhibiting fatty acid synthesis and were more inhibitory than their precursor C 18-unsaturated fatty acids. These results are evidence that C 20 −unsaturated fatty acids of the linoleic and linolenic acid series can act in short-term inhibition as well as in adaptive inhibition of fatty acid synthesis (Bloch, K. and Vance, D. (1977) Annu. Rev. Biochem. 46, 263–298). The effectiveness of (5,8,11)-icosatrienoic acid indicates that short-term inhibition by C 20 −unsaturated fatty acids is not limited to those fatty acids which have essential fatty acid activity.