The metabolism of linoleic acid in healthy subjects after intake of a single dose of C-13-linoleic acid

Objective: To investigate the iii viva oxidation of (13)C18:2n-6 and its co nversion into longer-chain polyunsaturates (LCPs) in healthy subjects, Design: Blood samples were collected from six subjects before (fasted) and 7, 11 (non-fasted), 24, 48, 72. 168 and 336 h (fasted) after ingestion of a single bolus of 45 mg uniformly labeled (13)C18:2n-6 dissolved in 8 g oliv e oil. In three subjects, breath was also sampled and CO2 production measur ed every hour during the first 12 h. Subjects consumed their habitual diets . Plasma C-13-enrichments were measured by GC-C-IRMS and fatty acid composi tions by GC;FID. Setting: Maastricht University Department of Human Biology. Subjects: Three men and three women, recruited by local advertisement. Results: The tracer/tracee ratio (TTR) of C18:2n-6 In plasma total lipids w as already increased 5 h after tracer intake. The mean peak amount (+/- s.e .m) of (13)C18:2n-6 (3.4 +/- 0.8 mg; 7.6% of dose) was found after about 17 h, (13)C18:3n-6 (0,018 +/- 0.008 mg; 0.04% of dose) after 7-48 h, and (13) C20:3n-6 (0.028 +/- 0.011 mg; 0.06% of dose) after 18-336 h. Time to peak T TRs of C20:4n-6 varied between subjects and were on average 0.022 +/- 0.006 mg (0.05% of dose). The proportion of (13)C18:2n-6 recovered in breath aft er 12 h ranged between 16.8 and 25.1%. Conclusions: These findings suggest that a single bolus of 45 mg U-(13)C18: 2n-6 can be used to study the oxidation of (13)C18:2n-6. However, because o f the low TTRs for C20:4n-6, a higher dose is recommended for studying the conversion of (13)C18:2n-6 into LCPs. In addition, since only about 35% of the tracer was found in plasma total lipids and as (CO2)-C-13 in breath, it might be necessary to study other accessible lipid fractions as well to st udy the overall conversion of linoleic acid.