Presented at the Neonatal Society 2008 Spring Meeting.
Hyde MJ1, Griffin JL2, Clarke L3, Kemp PR1 (introduced by N Modi)
1 Section of Molecular Medicine, Sir Alexander Fleming Building, Imperial College London, South Kensington SW7 2AZ, UK
2 Department of Biochemistry, University of Cambridge, Hopkins Building, Tennis Court Road, Cambridge CB2 1QW, UK
3 School of Agriculture, Policy & Development, University of Reading, RG6 6AR, UK
Background: We have previously demonstrated that piglets, delivered by caesarean section close to term, and maintained on total parenteral nutrition (TPN) for 7 days develop fatty liver (1), in agreement to that seen in humans (2). As neonates delivered by caesarean section near-to-term have a different hormonal response to neonates born vaginally (3), we hypothesise that differences in liver metabolism in the neonate may occur due to method of delivery. These differences may alter the hepatic accumulation of lipid irrespective of the nutritional regime.
Method: All experiments were conducted with local ethical approval and under Home Office Licence. Piglets were delivered by caesarean section ≈3 days preterm (PT) or vaginally at term (T). Bilateral jugular vein catheters were surgically inserted 3 hours postpartum and piglets, matched for body weight and sex, received either enteral nutrition (EF: sow formula milk) or TPN (TPN: TPN solution + Intralipid 20%). These nutritional regimes were maintained for ≈7 days after which the pigs were humanely slaughtered to enable tissue sampling. Hepatic lipid was determined gravimetrically following a Folch extraction. Metabolomic analysis was conducted using partial least square-discriminant analysis of NMR spectra of liver tissue extracts, Statistical differences between treatments were assessed by Anova General Linear Model (Minitab v14).
Results: Liver total lipid content was found to be significantly higher (p<0.05) in the groups delivered by caesarean compared with vaginally born piglets on both nutritional regimes (PT-EF 3.4 ± 0.40 vs T-EF 2.13 ± 0.08; PT-TPN 7.6 ± 0.8 vs T-TPN 4.2 ± 0.2 % (w/w) ± SEM). In the PT-TPN piglets the amount of lipid accumulated was in excess of the accepted definition of steatosis (5% (w/w): 4), and in both TPN groups the amount of lipid accumulated was approximately twice that found in their enterally fed comparisons.
Comparison of liver lipid content in samples taken from animals at delivery (PT or T) showed that there is a small increase in lipid content of the liver in the last three days of gestation (PT 2.62 ± 0.07 vs T 3.14 ± 0.22 % (w/w) ± SEM). Therefore, in the subsequent 7 days of enteral feeding, liver lipid increased in animals born by caesarean section but decreased in animals delivered naturally.
Metabolomic analysis showed differentiation of the groups due to different metabolic profiles between caesarean and vaginally born piglets. This separation appeared to be driven by an increase in ketone body production and the concentration of gluconeogenic precursors, irrespective of nutritional regime.
Conclusion: Caesarean delivery, near-to-term, results in different patterns of hepatic metabolism to those seen following vaginal birth. This results in an increase in lipid accumulation in the liver during the first week postpartum and in turn exacerbates the degree of fatty liver disease observed in neonates on TPN. We speculate that this increase in liver lipid is due to a failure to activate normal levels of gluconeogenesis or ketogenesis.
Acknowledgements: The authors wish to thank John Laws, Anne Corson, Kate Perkins and Jennie Litten, for their assistance with animal husbandry. MJH is funded by a BBSRC Studentship.
References
1. Hyde M J, Amusquivar E, Laws J, Corson A M, et al. (2008) Neonatology. 93 pp77-86.
2. Buchman A (2002) JPEN. 26 (5) pp. S43-S48.
3. Clarke L, Heasman L, Frith K, & Symonds M E, (1997) Am J Phys. 272 pp. R1931-R1939.
4. Cairns S R & Peters T (1983) Clin Sci (London). 65 pp. 645-652.