Linoleate, α-linolenate, and docosahexaenoate recycling into saturated and monounsaturated fatty acids is a major pathway in pregnant or lactating adults and fetal or infant rhesus monkeys

Carbon recycling and desaturation and elongation of linoleate, α-linolenate and docosahexaenoate in ten fetuses and two nursing infants of chow-fed rhesus monkey mothers were studied in vivo using uniformly labeled tracer molecules and high precision mass spectrometry. Doses of [U-¹³C]-18:2n-6, [U-¹³C]-18:3n-3 or [U-¹³C]-22:6n-3 free fatty acids were infused intravenously to the adults, and milk, maternal plasma, fetal plasma and tissues, and infant plasma were analyzed for enrichment in fatty acids of length C₁₄ to C₂₂. Conversion of tracer fatty acids to palmitic, stearic, oleic, and long chain polyunsaturated fatty acids was observed in fetal liver, brain, and retina ca. 5 days after dosing, and in milk and infant plasma 1 and 7 days after dosing. Animals dosed with [U-¹³C]-22:6n-3 accumulated more label in the fetal organs compared to the animals dosed with [U-¹³C]-18:3n-3 or [U-¹³C]-18:2n-6. The greatest fractions of doses were found in the fetal brains at levels of 0.21%, 0.24%, and 1.7% for the [U-¹³C]-18:2n-6, [U-¹³C]-18:3n-3, and [U-¹³C]-22:6n-3-dosed mothers, respectively. Label was found in saturated and monounsaturated fatty acids in liver, brain and retina (0.05-1.5 ppm dose/mg lipid) for all doses. jlr These results demonstrate that 1) recycling of carbon from 18:2n-6, 18:3n-3, and 22: 6n-3 into saturates and monounsaturates is a major metabolic pathway in chow-fed primates in the perinatal period; 2) less than 2% of the n-3 doses are found in brain fatty acids of developing fetuses from chow-fed mothers; and 3) [¹³C]-22:6n-3 accumulates in retina and brain at an order of magnitude higher level when provided as preformed [¹³C]-22:6 n-3 compared to [¹³C]-18:3n-3.