Long-term saturated fat feeding induced changes in rat myocardial phospholipid fatty acids are reversed by cross-over to polyunsaturated diets: Differences between n-3 and n-6 lipid supplements

Abstract

The reversal of long-term saturated fat feeding induced changes in cardiac phospholipids by cross-over to different polyunsaturated lipid diets was investigated. Rats were maintained on standard pellets supplemented (12% w/w) with sheep fat (SF) for 9 months and then crossed-over to either n-6 enriched sunflower seed oil (SSO) or n-3 polyunsaturated tuna fish oil (TFO) supplemented diets and fed for a further 9 months. A third group of rats was fed the SF diet continuously. Although there were no differences in body weights at the time of cross-over, at sacrifice the TFO supplemented rats were found to be heavier (p<0.05) than the SSO diet fed group. The cross-over to different polyunsaturated diets significantly altered the fatty acid composition of cardiac phospholipids. However, the nature and extent of these changes varied considerably between the n-3 and n-6 lipid supplements. For example, in total phospholipids, linoleic acid proportion was increased in the SSO group whilst a considerable reduction was apparent following the TFO diet. In contrast, only the n-3 diet altered the proportion of arachidonic acid (20:4, n-6) in cardiac membranes. Nevertheless, the extent of displacement of 20:4 by n-3 acids showed some class specificity, with phosphatidylethanolamine (PE) displaying the greatest reduction. The incorporation of n-3 unsaturated eicosapentaenoic (20:5) acid into cardiac phospholipids was relatively small (<1%) compared to docosahexaenoic acid (DHA; 22:6, n-3) which amounted to 16% in phosphatidylcholine, 25% in diphosphatidylglycerol and up to 40% in PE following n-3 supplementation, demonstrating a specificity between different phospholipid classes for the incorporation and/or conversion of dietary fatty acids. The observations of the present study clearly indicate that dietary intervention with polyunsaturated lipid supplements in mature animals results in considerable changes in membrane lipid composition depending on the type of unsaturation.