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

Abstract

Objective: To investigate the in vivo oxidation of ¹³C18:2n-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 ¹³C18:2n-6 dissolved in 8 g olive oil. In three subjects, breath was also sampled and CO₂ production measured every hour during the first 12 h. Subjects consumed their habitual diets. Plasma ¹³C-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 ¹³C18:2n-6 (3.4±0.8 mg; 7.6% of dose) was found after about 17 h, ¹³C18:3n-6 (0.018±0.008 mg; 0.04% of dose) after 7–48 h, and ¹³C20:3n-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 ¹³C18:2n-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-¹³C18:2n-6 can be used to study the oxidation of ¹³C18:2n-6. However, because of the low TTRs for C20:4n-6, a higher dose is recommended for studying the conversion of ¹³C18:2n-6 into LCPs. In addition, since only about 35% of the tracer was found in plasma total lipids and as ¹³CO₂ in breath, it might be necessary to study other accessible lipid fractions as well to study the overall conversion of linoleic acid.

European Journal of Clinical Nutrition (2001) 55, 321–326