Effects of the ω‐6:ω‐3 Fatty Acid Ratio of Fat Emulsions on the Fatty Acid Composition in Cell Membranes and the Anti‐Inflammatory Action

Background: This study investigated the effects of parenterally administered fish oil (FO) on the fatty acid composition in rats to determine the optimal ω‐6:ω‐3 polyunsaturated fatty acid (PUFA) ratio of fat emulsions to achieve an anti‐inflammatory effect. Methods: Male Sprague‐Dawley rats were infused a parenteral nutrition (PN) solution containing fat emulsions with different ω‐6:ω‐3 PUFA ratios. The fatty acid content of phospholipids in the membranes of splenocytes was analyzed by gas chromatography (experiment 1). In addition, the amounts of leukotriene (LT) B₄ and LTB₅ released from peritoneal polymorphonuclear leukocytes (PMNs) were measured by high‐performance liquid chromatography (experiment 2). Results: In experiment 1, after infusion of the fat emulsion containing FO, the ω‐3 PUFA content in cell membranes rose to 70% of the peak value on day 1 and nearly reached a plateau on day 3. The highest ratio of eicosapentaenoic acid (EPA) to arachidonic acid (AA) was achieved by administrating a PN solution with the smallest ω‐6:ω‐3 PUFA ratio. In experiment 2, a larger amount of LTB₅ was released from Ca‐ionophore‐stimulated PMNs taken from rats given a larger quantity of FO. The ratio of LTB₅:LTB₄ released from PMNs correlated positively with the EPA:AA ratio in the membranous phospholipid and in serum. Conclusions: The ω‐3 PUFAs were readily incorporated into the cell membrane within 3 days of infusion with the fat emulsion. The EPA:AA ratio in membranous phospholipid in PMNs was positively correlated with the LTB₅:LTB₄ production ratio and was a good indicator of anti‐inflammatory effects.