Journal Name:
Lipids
Article Title:
Alpha-Linolenic Acid Increases Brain but not Heart and Liver Docosahexaenoic Acid Levels
Date Written:
2005
Volume:
40
Number:
0
Page:
40
Author(s):
Barceló-Coblijn, G.; Collison, L.W.; Jolly, C.A.; Murphy, E.J.
Article:
Alpha linolenic acid (ALA) can be elongated and desaturated to EPA (20:5n-3), 22:5n-3 (docosapentaenoic acid), and DHA (22:6n-3). A number of studies in mammals demonstrate the effective conversion of 18:3n-3 into 20:5n-3 and 22:5n-3. More controversial is the effectiveness of the conversion and accumulation of 22:6n-3 from dietary 18:3n-3 Because a number of variables can modulate the efficiency of 18:3n-3 conversion to 22:6n-3, including the amount of 18:3n-3 ingested, the n-3 to n-6 ratio in the diet, and the dietary background of the animals prior to the study, it is important to compare, in a single study, the effects flax oil and fish oil diets on tissue n-3 accretion. To address this, the effect of flax oil (rich in 18:3n-3) and fish oil (rich in 20:5n-3 and 22:6n-3) were assessed on the liver, heart, and brain phospholipid mass and phospholipid acyl chain mass using standard lipid analytical techniques. Rats wwre fed the ALA, fish oil or safflower oil (rich in 18:2n-6) for 8 wk. In the heart and liver phospholipids, DHA 22:6n-3 levels increased only in the fish oil group, although rats fed ALA accumulated EPA 20:5n-3 and DPA 22:5n-3. However, in the brain, the ALA and fish oil diets increased the phospholipid DHA 22:6n-3 mass. In all tissues, these diets decreased the arachadonic acid AA mass, although the effect was more marked in the fish oil than in the ALA group. Although these data do not provide direct evidence for ALA 18:3n-3 elongation and desaturation by the brain, they demonstrate that 18:3n-3-enriched diets reduced tissue AA 20:4n-6 levels and increased cellular n-3 levels in a tissue-dependent manner. Based on the lack of increased DHA 22:6n-3 but increased 18:3n-3 in the liver and heart, the ALA diet appears to increase circulating 18:3n-3, thereby presenting tissue with this EFA for further elongation and desaturation. These results indicate that 18:3n-3 is elongated, desaturated, and accumulated and that these processes were highly tissue dependent. The apparent elongation and desaturation of 18:3n-3 to 22:6n-3 in the brain compared with the limited conversion in the heart and liver may reflect a distinct need by the brain for 22:6n-3. The accumulation of n-3 PUFA, together with the decrease in n-6 PUFA, might account for the beneficial health effects associated with 18:3n-3-enriched diets.
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