The Effect of Dietary Menhaden Fish Oil on α-Tocopherol Status in Rodents is Both Concentration and Tissue Dependent

Abstract

This study was designed to measure the dose and time dependent effect of menhaden fish oil (MFO) on immune cell α-tocopherol in the rat. The level of dietary fat and α-tocopherol (equalized in amount and chemical form) were constant across all experimental groups with increasing percentages of lard replaced with MFO. As the proportion of fish oil in the diet increased, plasma α-tocopherol decreased. Splenocyte α-tocopherol increased significantly with time with rats fed 4.5% MFO for 2 week having significantly higher α-tocopherol than rats on all other diets ( P < 0.05). Plasma arachidonic acid (AA) decreased and docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) increased as the percentage fish oil in the diet increased. Splenocyte fatty acid composition was significantly altered by diet, with inclusion of as little as 4.5% MFO sufficient to decrease AA from 25% to 12% of total fatty acids ( P < 0.001) and increase EPA from 1% to 4% of the total fatty acids ( P < 0.001). Additional MFO significantly increased splenocyte EPA and DHA to approximately 7% and 5% of the total fatty acids, respectively, without any further decline in splenocyte AA. Changes in splenocyte fatty acid composition occurred rapidly with approximately 85% of the total change occurring within the first week of dietary treatment. The rapid and dose dependent enrichment of immune cells with (n-3) fatty acids may compromise the antioxidant status of these cells. However, at the lowest level of dietary fish oil tested (4.5%), immune cells appeared to compensate for the higher (n-3) polyunsaturated fatty acid content with a significant accumulation of α-tocopherol. That changes in fatty acid composition preceded changes in vitamin E status of the immune cell suggests that the former affects the latter.