Compartmental modeling to quantify α-linolenic acid conversion after longer term intake of multiple tracer boluses

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 C-12- and C-13-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 C-13 data of the participants. A similar tracee model was solved using the averaged C-13 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. - Goyens, P. L. L., M. E. Spilker, P. L. Zock, M. B. Katan, and R. P. Mensink. Compartmental modeling to quantify alpha-linolenic acid conversion after longer term intake of multiple tracer boluses.