In vivo investigation of the placental transfer of 13C-labeled fatty acids in humans

Placental fatty acid transfer in humans in vivo was studied using stable isotopes. Four pregnant women undergoing cesarean section received 4 h before delivery an oral dose of [C-13]pahnitic acid (PA), [C-13]oleic acid (OA), [C-13]linoleic acid (LA), and [C-13]docosahexaenoic acid (DHA). Maternal blood samples were collected at -4 h (basal), -3 h, -2 h, -1 h, 0 h, and +1 h relative to time of cesarean section. At the time of birth, venous cord blood and placental tissue were collected. Fatty acid composition was determined by gas-liquid chromatography and isotopic enrichment by gas chromatography-combustion-isotope ratio mass spectrometry. C-13-enrichment of fatty acids in the nonesterified fatty acids (NEFA) of cord plasma tended to be higher than in NEFA of placenta, with statistically significant differences for the nonesterified OA and DHA ([C-13]PA, 0.024 +/- 0.011 vs. 0.001 +/- 0.001; [C-13]OA, 0.042 +/- 0.008 vs. 0.005 +/- 0.003; [C-13]LA, 0.038 +/- 0.010 vs. 0.008 +/- 0.002; [C-13]DHA, 0.059 +/- 0.009 vs. 0.010 +/- 0.003). The ratio of tracer fatty acid concentrations of placenta to maternal plasma was significantly higher for [13C]DHA than for the other fatty acids ([C-13]PA, 7.1 +/- 1%; [C-13]OA, 3.8 +/- 0.4%; [C-13]LA, 9.2 +/- 1.3%; [C-13]DHA, 25.9 +/- 3.4%). These results suggest that only a part of the placental NEFA participated in fatty acid transfer, and that the placenta showed a preferential accretion of DHA relative to the other fatty acids.