The metaboliam of linoleic acid in healthy subjects after intake if single dose of ¹³C-linoleic acid

OBJECTIVE: To investigate the in vivo oxidation of (13)C18:2n-6 and its conversion 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 olive oil. In three subjects, breath was also sampled and CO(2) production measured every hour during the first 12 h. Subjects consumed their habitual diets. Plasma (13)C-enrichments were measured by GC-C-IRMS and fatty acid compositions 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 was 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 48-336 h. Time to peak TTRs 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 after 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 of 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 (13)CO(2) in breath, it might be necessary to study other accessible lipid fractions as well to study the overall conversion of linoleic acid.