Compartmental analyses of 2H5-α-linolenic acid and 13C-U-eicosapentaenoic acid toward synthesis of plasma labeled 22:6-23 in newborn term infants

Background: During early postnatal development, the nervous system accretes docosahexaenoic acid (DHA; 22:6n-3), a highly unsaturated n-3 (omega-3) fatty acid (FA) used in the formation of neural cell membranes. DHA, which is present in human breast milk, may also be biosynthesized from n-3 FAs such as 18:3n-3 [alpha-linolenic acid (ALA)] or 20: 5n-3 [eicosapentaenoic acid (EPA)]. An important concern is to what extent these precursors can supply DHA to the developing infant. Objective: We analyzed measurements of fractional percentages of plasma H-2(5)-ALA and C-13-U-EPA directed toward the synthesis of labeled 22: 6n-3 in 11 newborn infants by using compartmental modeling procedures. Design: One-week-old infants received doses of H-2(5)-ALA and (CU)-C-13-EPA ethyl esters enterally. We drew blood from the infants periodically and analyzed the plasma for endogenous and labeled n-3 FAs. From the time-course concentrations of the labeled FAs, we determined rate constant coefficients, fractional synthetic rates, and plasma turnover rates of n-3 FAs. Results: In infants, approximate to 0.04% of the H-2(5)-ALA dose converted to plasma H-2(5)-EPA. Plasma H-2(5)-EPA and H-2(5)-22: 5n-3 [docosapentaenoic acid (DPA)] efficiently converted to H-2(5)-DPA and (2)H(5)DHA, respectively. The percentage of plasma C-13-U-EPA directed toward the synthesis of C-13-DHA was lower than the percentage of plasma H-2(5)-EPA that originated from H-2(5)-ALA. Conclusions: Endogenously synthesized EPA was efficiently converted to DHA. In comparison, preformed EPA was less efficiently used for DHA biosynthesis, which suggests a differential metabolism of endogenous EPA compared with exogenous EPA. However, on a per mole basis, preformed EPA was 3.6 times more effective toward DHA synthesis than was ALA. Newborns required an intake of approximate to 5 mg preformed DHA . kg(-1).d(-1) to maintain plasma DHA homeostasis. Am J Clin Nutr 2010; 92: 284-93.