Plasma Citrulline Utility and Arginine Synthesis in a Neonatal Short Bowel Syndrome piglet model

  • Author / Creator
    Lansing, Marihan
  • Premature infants are at increased risk of short bowel syndrome (SBS), which leads to dependence on parenteral nutrition (PN). While lifesaving, PN support has multiple complications, such as increased risk of sepsis and liver disease. Autonomy from PN is dependent on adaptation of the remnant intestine. Because citrulline (Cit) is synthesized but not utilized in the intestine, measurement in blood has been proposed as a biomarker of intestinal adaptation. However, the neonatal intestine lacks the enzyme arginase and has more arginosuccinase synthase than later in life, thus the neonatal intestine preferably exports arginine (Arg) rather than Cit. Arg is a semi essential amino acid with critical metabolic roles in nitric oxide production and ammonia detoxification. Previous studies have shown that the intestine is responsible for 60% of Arg synthesis. Thus, our aim was to evaluate the utility of Cit as a biomarker of intestinal adaptation and assess the effect of intestinal resection on Arg synthesis in the neonate. We used a validated neonatal SBS piglet model, with 75% intestinal resection. In particular, given ileal resection, this model mimics the most common anatomical form of neonatal intestinal failure and has dependency on PN. 80-100% PN was provided to meet piglet nutrient requirements and 20 or 40% enteral nutrition was provided as necessary for a trophic effect to enhance adaptation. In all piglets, intestinal length was measured, plasma or serum amino acids profiles were determined at initiation and termination of the trial and measured using liquid chromatography–mass spectrometry. For assessment of Arg synthesis intragastric stable isotope labelled proline (Pro) and Arg tracers were infused and the plasma isotope enrichments were measured using API 4000 triple quadrupole mass spectrometry; hence, flux and synthesis were calculated. At termination, jejunal tissue samples were taken to histologically assess microscopic adaptive changes, such as villus height and crypt depth. In Chapter 3, we determined that plasma Cit levels discriminate between large differences in gut length, hence are able to identify SBS versus the non-resected sham, but do not differentiate adaptation within the anatomical subtypes of SBS studied, with and without ileum, that varied in their adaptive response. Therefore, citrulline does not appear to be a useful as a sensitive biomarker of intestinal adaptation in the neonate. In Chapter 4, we concluded that SBS piglets without an ileum did not have differences in whole body Arg synthesis from Pro, compared to the non-resected sham. This was despite the sham having 3x longer intestinal length. When correcting the synthesis of Arg from Pro for intestinal length it appears that SBS piglets may be able to upregulate synthesis of Arg in the intestine. This was supported by an increase in the expression of the enzyme arginosuccinase synthase in the SBS versus sham piglets. This research is the first study of Arg synthesis in a neonatal model of SBS, while undergoing PN and partial EN. Preterm neonates are uniquely at risk of SBS and prolonged PN, as it may take months to years for enteral autonomy. This occurs at a time when the enzyme expression within the intestine is geared to participate significantly in whole body Arg metabolism. Hence, we find that assumptions made about the utility of plasma Cit at other ages do not apply to the neonate; and that the intestine may adapt to support whole body Arg synthesis in the SBS neonate. These findings require further confirmation, both in other neonatal experimental models and in neonatal humans. Furthermore, the potential benefits of supplementation of dietary precursors for Arg synthesis in the intestine (both by enteral and parenteral routes) warrant further investigation.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
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  • License
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