Incorporation of n-3 fatty acids into phospholipids of rat liver and white and brown adipose tissues: A time-course study during fish-oil feeding

The aim of this study was to determine the time-course incorporation of dietary n-3 polyunsaturated fatty acids into phospholipids of tissues highly involved in lipid and energy metabolism: the liver and the white (WAT) and brown (BAT) adipose tissues. Rats were fed a diet supplemented with 19% fish oil for up to 4 weeks. Minor changes in the relative proportions of tissue phospholipids were observed in the three tissues. Fish-oil feeding induced rapid and large replacements of n-6 fatty acids by n-3 fatty acids. In liver, the 22:6n-3 level increased progressively and reached a plateau after 3 (phosphatidylethanolamine and phosphatidylserine) or 7 days (phosphatidylcholine and phosphatidylinositol). In contrast, the 20:5n-3 level transiently peaked in all liver phospholipids at days 1–3 before reaching a plateau after day 7. In WAT as in BAT the level of n-3 fatty acids increased progressively and reached in all phospholipids a plateau after day 7. As a general trend, in each phospholipid class the 22:6n-3/20:5n-3 ratio was higher in liver than in the two adipose tissues. This study shows that each dietary n-3 fatty acid is incorporated very rapidly into liver, WAT, and BAT phospholipids but according to time courses and at levels that depend simultaneously on the tissue and phospholipid class considered.