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The molecular specificity of inflammatory cell phosphatidylcholine composition and synthesis in human development

Presented at the Neonatal Society 2007 Summer Meeting (programme).

Swain LE1, Allen S1, Harkness P1, Daw M1, Koster G2, Hall M3, Postle AD1

1 School of Medicine, University of Southampton, UK
2 School of Chemistry, University of Southampton, UK
3 Neonatal Unit, Princess Anne Hospital, Southampton, UK

Introduction: In human development, the post-natal adaptation from placental to enteral nutrient supply is the most extreme alteration to lipid nutrition that most will experience during their lifetime. Placental nutrition supplies the polyunsaturated fatty acids (PUFA) arachidonate (20:4n-6) and docosahexaenoate (22:6n-3) preformed from maternal sources to supply the needs of fetal growth and development, while post-natally, infants must synthesise these lipids from the dietary precursors linoleate (18:2n-6) and α-linolenate (18:3n-3). Preterm infants born before the major phase of placental PUFA supply in late pregnancy are at increased risk of PUFA deficiency. Such deficiency in inflammatory and immune cells may compromise host defence mechanisms and contribute to the increased susceptibility to infection in these fragile preterm infants. Consequently, we analysed the composition of phosphatidylcholine (PC) molecular species in plasma, erythrocytes and leukocytes from preterm infants to evaluate the extent of any lipidrelated deficit. Additionally, we examined the effect of intravenous total parenteral nutrition (TPN) on these PC compositions as a further modification of lipid nutrition. Finally, we analysed the plasticity of cord blood leukocyte PC in response to exogenous fatty acid supplementation ex vivo from the incorporation of stable isotope-labelled (methyl-d9)-choline chloride in comparison with adult leukocytes.

Methods: Full ethical approval was granted by Southampton and South West Hampshire Local Research Ethics Committee. Plasma, erythrocyte and peripheral blood mononuclear cells (PBMC) were purified from sequential blood samples (250μl) from preterm infants in our neonatal intensive care unit (12 enteral, 6 TPN). PC compositions of chloroform:methanol extracts were analysed as P184 scans on a Micromass Quattro Ultima triple quadrupole mass spectrometer. Cord blood samples from term deliveries were incubated with (methyl-d9)-choline chloride with and without added 18:2n-6 (30μM) for 3h and processed as above with the addition of a P193 scan to quantify newly synthesised PC species. Blood samples from adult healthy volunteers (n=6) were processed by an identical protocol.

Results: Type of nutrition exerted a significant effect on PC compositions of PBMC as well as of plasma and erythrocytes. In cord blood, all fractions were enriched in PC species containing 20:4 and 22:6. Post-natally, these PUFA-containing PC species declined as that of PC16:0/18:2 and PC18:0/18:2 increased. The pattern of composition and change however, for PBMC, differed significantly from that of either plasma or erythrocytes. Moreover, PC from the preterm infant PBMC was significantly depleted in all 20:4-containing species compared with previous adult cell results. TPN, which is enriched in 18:2n-6, increased the content of PC16:0/18:2 in all fractions, but had no effect on the low abundance of PC18:0/20:4 in PBMC. The pattern of cord blood leukocyte PC synthesis from (methyl-d9)-choline was very different from endogenous compositions, implying extensive acyl remodelling. Moreover, the selectivity of such remodelling differed considerably from that reported previously in adult cells. Finally, incubation ABSTRACT APPEARS TO BE TRUNCATED

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