Effects of Dietary n-3 Fatty Acids on the Phospholipid Molecular Species of Monkey Brain

Abstract

We examined the changes in the molecular species of brain ethanolamine glycerophospholipids of monkeys fed diets containing widely ranging amounts of n-3 fatty acids. Two groups of rhesus monkeys were fed pre- and postnatally either a control diet (soy oil; containing 8% of fatty acids as 18:3n-3) or a deficient diet (safflower oil; containing <0.3% 18:3n-3). The brains of these animals were analyzed at 22 months of age. A third group of monkeys was fed the safflower oil diet to 22 months of age and then switched to a fish oil diet (28% long-chain n-3 fatty acids) for 1–2 years before autopsy. The molecular species of the diacyl, alkylacyl, and alkenylacyl ethanolamine glycerophospholipids from frontal cortex were separated by HPLC. A total of 24 molecular species were identified. Fatty acids in the sn-2 position differed markedly among the diet groups, but the sn-1 position always contained only 16:0, 18:0, or 18:1. In the diacyl subclass of the control brain, the n-3 molecular species represented 41% of total and the n-6 species 45%, whereas in the deficient brain the n-3 molecular species decreased to 9% and n-6 molecular species increased to 77%. The fatty acid 22:5n-6 did not replace 22:6n-3 in a symmetrical fashion in the molecular species of the deficient brain. In the brains of the fish oil-fed monkeys, the n-3 molecular species amounted to 61% and n-6 molecular species were reduced to 25%. The species 18:1–22:6, 16:0–22:6, and 18:0–22:6 generally changed proportionally in response to diet. However, 18:1–20:4, 16:0–20: 4, and 18:0–20:4 responded differently. The fish oil diet led to an increase in the proportion of 18:1–20:4 in the alkenylacyl subclass, whereas 16:0–20:4 and 18:0–20:4 decreased. Thus, total species containing sn-1 18:1 increased at the expense of sn-1 16:0 in the fish oil animals. Regardless of diet, each subclass of ethanolamine glycerophospholipid showed a strikingly different ratio of sn-1 16:0 to 18:0 to 18:1 for a given sn-2 fatty acid. In conclusion, the different diets had profound qualitative and quantitative effects on the molecular species of brain phospholipids, and these changes have implications for possible functional changes.