The short and long-term effects of DHA in preterm infants: free fatty acids, lipid mediators and neurodevelopmental outcomes

Abstract

Infants born preterm (< 37 weeks’ completed gestation) are at an increased risk of short and long-term health complications. This may be in part because they miss out on the in utero accretion of nutrients, including lipids. Lipids, in particular the omega-3 and omega-6 long chain polyunsaturated fatty acids (LCPUFA) are thought to play an important role in neurodevelopment and immune function. These LCPUFA exhibit their biological action when released from the cell membrane into the free fatty acid (FFA) pool, where they are oxidised to downstream lipid mediators, collectively known as oxylipins. Measuring these compounds may therefore give us an insight to the functional lipid status in these infants. Although there are a number of existing methods for measuring FFA and oxylipins in human blood samples, these all have some limitations, most notably the need for relatively large sample volumes and laborious, multi-step extraction processes or potential loss of compounds due to oxidation/degradation. Therefore, a new method is required to measure these compounds. Very few studies have assessed the endogenous concentration of FFA and oxylipins in infants born preterm at birth. It is important to measure the level of FFA and oxylipins in infants born preterm to determine the status at birth, whether levels change after birth or following nutrient supplementation, and to understand whether the endogenous level of these compounds are related to adverse clinical outcomes in this infant population. Infants born preterm miss out on the peak period of in utero docosahexaenoic acid (DHA), an omega-3 LCPUFA, accretion into the brain at a time of rapid brain development, during the last trimester of pregnancy. This may contribute to the higher incidence of neurodevelopmental deficits observed in this population. It is unclear whether supplementing infants born preterm with DHA in the early postnatal period may promote brain development and improve neurodevelopmental outcomes in early childhood. The aims of this PhD project were 1) To develop and validate a method for measuring FFA and oxylipins from dried blood spot (DBS), 2) To estimate the volume of blood in a small disc (3 mm or 6 mm) obtained from a DBS, 3) To measure the levels of FFA and oxylipins in infants born preterm and assess the effect of DHA supplementation on these levels and 4) To determine whether DHA supplementation in infants born preterm during early postnatal period improves attention at 18 months’ corrected age. A method for quantitation of 6 individual omega-3 and omega-6 FFA and 21 oxylipins from DBS were developed and validated by liquid chromatography tandem mass spectrometry (LC–MS/MS) using stable isotope dilution analysis. The volume of blood in 3 mm and 6 mm discs obtained from DBS was estimated using four different methods. Concentrations of FFA and oxylipins were measured in ~ 70 infants born preterm (< 29 weeks’ gestation) who received either a high-dose of DHA (60 mg/kg/day) or no DHA (soy oil) from within a few days of birth until 36 week’s postmenstrual age (PMA). DHA supplementation in infants born preterm resulted in an increased concentration of free DHA and the DHA oxylipin, 4-hydroxydocosahexaenoic acid (4-HDHA) in the DHA group compared to the control group at 36 weeks’ PMA. Attention was assessed at 18 months’ corrected age in the same population of preterm infants using a specialised attention assessment. There was no evidence of a difference in any measures of attention between the DHA and control groups. In conclusion, we successfully developed methods for assessment of FFA and oxylipins in DBS using LC-MS/MS technology. DHA supplementation in infants born preterm resulted in changes in the FFA and oxylipin profile. However, there was no effect of supplemental DHA on attention outcomes in these children at 18 months’ corrected age. These results need confirmation in larger studies.