Fatty acid metabolism in human preimplantation embryos

BACKGROUND: Little is known of fatty acid metabolism in human embryos. This information would be useful in developing metabolic tests of embryo quality and improving embryo culture media. METHODS: The fatty acid composition of human embryos and their ability to accumulate 13C labelled fatty acids was assessed in relation to the stage of development using gas-chromatography and combustion-isotope-ratio-mass spectrometry. RESULTS: Compared with embryos which did not develop beyond the 4-cell stage, those that did had significantly higher concentrations of the unsaturates, linoleic (12% versus 3%; P=0.02) and oleic (14% versus 7%; P=0.02), and a lower concentration of total saturates (62% versus 77%; P=0.04). There was uptake of both 13C linoleic and palmitic, but the developmental pattern was different for each fatty acid. The net accumulation in pmol/embryo/24h for palmitic was 1 at the 2-cell to <8-cell stage, 4 at the 8-cell-morula stage and negligible at the blastocyst stage. For linoleic, there was little net accumulation at the 2-cell to <8-cell stage, 8 (8-cell-morula stage) and 17 pmol/embryo/24 h (blastocyst stage). CONCLUSION: Preimplantation human embryos actively take up individual fatty acids at different rates at different stages of development. The high unsaturated concentration at the later stages of development may be explained by preferential uptake of linoleic acid.