Presented at the Neonatal Society 2013 Summer Meeting.
Oliver HL, Goss VM, Rhodes-Kitson J, Townsend JP, Brandsma J, Gunda R, Clark HW, Goss KCW, Postle AD
Faculty of Medicine, University of Southampton, UK
NIHR Respiratory BRU, Southampton, UK
Background: A previous study using an infusion of methyl-D9 choline (a stable isotope label) given to ventilated preterm neonates has successfully investigated phosphatidylcholine (PC) kinetics in endotracheal aspirates and plasma. We have now analysed metabolites and PC found in the urine of these individuals to investigate for the first time postnatal renal-specific handling of lipids in the preterm neonate. We hypothesise that time-dependent changes in the lipid and metabolite profile demonstrate the transition between pre- and postnatal function and renal maturation over the first 10 days of life.
Methods: Labelled methyl-D9 choline infusions were administered to consented preterm neonates within 48 hours of birth. Infants who remained ventilated were given a second methyl-D9 choline infusion 120 hours after recruitment. Lipid extracts and aqueous phase aliquots from urine samples at specific time points after infusion were analysed using electrospray ionisation tandem mass spectrometry (ESI MS/MS) and ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) respectively.
Results: There is a mixture of mono-, di- and polyunsaturated PC species present in the urine. Compared to other species, there is more endogenous and newly synthesised urinary PC16:0/18:1, but there is a lack of polyunsaturated species in the urine. Maximal label enrichment of urinary phosphatidylcholine (PC) species occurs at 24 hours after each methyl-D9 choline infusion but rates of enrichment decrease slowly and remain more constant than previously demonstrated in plasma. Endogenous urinary PC concentrations decrease over time and newly synthesised lysospecies were not detectable in analysed samples. There is rapid fractional label incorporation into the choline and betaine pools, as previously seen in plasma, with significant increases in incorporation after the second infusion of labelled choline at 120 hours (P=0.001). Concentrations of urinary choline and betaine also decrease over time.
Conclusion: This study is the first demonstration of the profiling of choline metabolites and PC kinetics in the urine of preterm neonates. It demonstrates that the powerful methyl-D9 choline labelling technique can be used to model tissue-specific PC kinetics throughout the body. We have demonstrated time-dependent alterations to the profile of PC and choline metabolites in the urine, suggesting rapid changes in postnatal renal PC metabolism. This is independent of plasma metabolism, which probably reflects PC synthesis and secretion by the kidney as it matures and adapts to postnatal function.
Corresponding author: email@example.com
Goss KCW. PhD Thesis, University of Southampton, 2012