Maintenance of lower proportions of (n − 6) eicosanoid precursors in phospholipids of human plasma in response to added dietary (n − 3) fatty acids

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Abstract

Competition between the (n − 3) and (n − 6) types of highly unsaturated fatty acids can diminish the abundance of (n − 6) eicosanoid precursors in a tissue, which in turn can diminish the intensity of tissue responses that are mediated by (n − 6) eicosanoids. The mixture of 20- and 22-carbon highly unsaturated fatty acids maintained in the phospholipids of human plasma is related to the dietary intake of 18:2 (n − 6) and 18:3 (n −3) by empirical hyperbolic equations in a manner very similar to the relationship reported for laboratory rats (Lands, W.E.M., Morris, A. and Libelt, B. (1990) Lipids 25, 505–516). Analytical results from volunteers ingesting self-selected diets showed an inter-individual variance for the proportion of (n − 6) eicosanoid precursors in the fatty acids of plasma phospholipids of about 5%, but the variance among multiple samples taken from the same individual throughout the day was less (about 3%), closer to the experimental variance of the analytical procedure (about 1%). The reproducibility of the results makes it likely that analysis of fatty-acid composition of plasma lipids from individuals will prove useful in estimating the diet-related tendency for severe thrombotic, arthritic of other disorders that are mediated by (n − 6) eicosanoids. Additional constants and terms were included in the equations to account for the effects of 20- and 22-carbon highly unsaturated (n − 3) fatty acids in the diet. A lower constant for the 20- and 22-carbon (n − 3) fatty acids compared to that for the 18-carbon (n − 3) fatty acid in decreasing the ability of dietary 18:2 (n − 6) to maintain 20:4 (n − 6) in tissue lipids confirmed the greater competitive effectiveness of the more highly unsaturated n − 3 fatty acids in the elongation/ desaturation process. Also, a lower constant for direct incorporation of 20-carbon fatty acids of the n − 6 vs. the n − 3 type indicated a greater competitive effectiveness of 20:4 (n − 6) relative to 20:5 (n − 3) in reesterification after release from tissue lipids. The equations may be used in reverse to estimate the dietary intakes of the (n − 3) and (n − 6) fatty acids by using the composition of the fatty acids that had been maintained in plasma lipids.

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