Abstract
To estimate in vivo alpha-linolenic acid (ALA; C18:3n-3) conversion, 29 healthy subjects consumed for 28 days a diet providing 7% of energy from linoleic acid (C18:2n-6) and 0.4% from ALA. On day 19, subjects received a single bolus of 30 mg of uniformly labeled [(13)C]ALA and for the next 8 days 10 mg twice daily. Fasting plasma phospholipid concentrations of (12)C- and (13)C-labeled ALA, eicosapentaenoic acid (EPA; C20:5n-3), docosapentaenoic acid (DPA; C22:5n-3), and docosahexaenoic acid (DHA; C22:6n-3) were determined on days 19, 21, 23, 26, 27, and 28. To estimate hepatic conversion of n-3 fatty acids, a tracer model was developed based on the averaged (13)C data of the participants. A similar tracee model was solved using the averaged (12)C values, the kinetic parameters derived from the tracer model, and mean ALA consumption. ALA incorporation into plasma phospholipids was estimated by solving both models simultaneously. It was found that nearly 7% of dietary ALA was incorporated into plasma phospholipids. From this pool, 99.8% was converted into EPA and 1% was converted into DPA and subsequently into DHA. The limited incorporation of dietary ALA into the hepatic phospholipid pool contributes to the low hepatic conversion of ALA into EPA. A low conversion of ALA-derived EPA into DPA might be an additional obstacle for DHA synthesis.
Highlights
To estimate in vivo ␣-linolenic acid (ALA; C18: 3n-3) conversion, 29 healthy subjects consumed for 28 days a diet providing 7% of energy from linoleic acid (C18:2n-6) and 0.4% from ALA
2) was set up that incorporated the kinetic parameters derived from the tracer system, the averaged values of the tracee measurements of the 29 subjects, and their mean daily dietary ALA intake
Of this ALA pool, 99.98% was converted to eicosapentaenoic acid (EPA), which corresponded to 6.95% (78.4 mg) of ALA intake
Summary
Thirty healthy volunteers (15 men and 15 women) participated in the study. One male subject was excluded before analysis of the results because of gastrointestinal complaints and related weight loss during the study. The study protocol was approved by the Medical Ethics Committee of Maastricht University, and written informed consent was obtained from each participant This tracer study was part of a dietary intervention trial that studied the effects of polyunsaturated fatty acids on cardiovascular risk markers. Isotopic 13C enrichments of the FAMEs of ALA, EPA, docosapentaenoic acid (DPA), and DHA were determined on a gas chromatograph-combustion-isotope ratio mass spectrometer (MAT 252; Finnigan, Bremen, Germany) with a BPX-70 column (50 m ϫ 0.33 mm, 0.25 m film thickness; SGE, Austin, TX) and helium as the carrier gas (injector inlet pressure of 124 kPa). Where CTOTAL(t) is the total concentration (12C ϩ 13C) in mmol/l of a given fatty acid as determined by gas chromatography-flame ionization detection at time point (t) Model input parameters such as daily ALA consumption and the 12C and 13C n-3 fatty acid concentrations in the plasma phospholipid pool followed a normal distribution. The analysis resulted in maximum a posteriori Bayesian estimates of the parameters
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