Effect of dietary arachidonic acid on metabolism of deuterated linoleic acid by adult male subjects

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Abstract
The influence of dietary supplementation with 20:4n−6 on uptake and turnover of deuterium-labeled linoleic acid (18:2n−6[d2]) in human plasma lipids and the synthesis of desaturated and elongated n−6 fatty acids from 18:2n−6[d2] were investigated in six adult male subjects. The subjects were fed either a high-arachidonic acid (HIAA) diet containing 1.7 g/d or a low-AA (LOAA) diet containing 0.21 g/d of AA for 50 d. Each subject was then dosed with about 3.5 g of 18:2n−6[d2] as the triglyceride (TG) at 8:00 a.m., 12:00, and 5:00 p.m. The total 18:2n−6[d2] fed to each subject was about 10.4 g and is approximately equal to one-half of the daily intake of 18:2n−6 in a typical U.S. male diet. Nine blood samples were drawn over a 96-h period. Methyl esters of plasma total lipid (TL), TG, phospholipid, and cholesterol ester were analyzed by gas chromatography-mass spectroscopy. Dietary 20:4n−6 supplementation did not affect uptake of 18:2n−6[d2] in plasma lipid classes over the 4-d study period nor the estimated half-life of 24–36 h for 18:2n−6[d2]. The percentages of major deuterium-labeled desaturation and elongation products in plasma TL, as a percentage of total deuterated fatty acids, were 1.35 and 1.34% 18:3n−6[d2]; 0.53 and 0.50% 20:2n−6[d2]; 1.80 and 0.92% 20:3n−6[d2] and 3.13 and 1.51% 20:4n−6[d2] for the LOAA and HIAA diet groups, respectively. Trace amounts (d2] and 20:4n−6[d2] were 48% lower (P<0.05) in samples from the HIAA diet group than in samples from the LOAA diet group. For a normal adult male consuming a typical U.S. diet, the estiamted accumulation in plasma TL of 20:4n−6 synthesized from 20 g/d (68 mmole) of 18:2n−6 is 677 mg/d (2.13 mmole). Dietary supplementation with 1.5 g/d of 20:4n−6 reduced accumulation of 20:4n−6 synthesized from 20 g/d of 18:2n−6 to about 326 mg/d (1.03 mmole).

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