Accumulation of Branched-Chain Amino Acids in Cerebral Interstitial Fluid Following Cardiopulmonary Bypass in Neonatal Swine

B. Smood¹, D. I. Aronowitz², C. Shoffler³, D. Abbasian³, M. Noji³, J. Axsom³, R. Degani⁴, K. L. Fiock⁵, M. Hefti⁵, C. Petucci³, Z. Arany³, M. Yudkoff⁶, D. Licht⁷, T. Kilbaugh⁴, J. Gaynor², C. D. Mavroudis^2
1Division of Cardiovascular Surgery, Department of Surgery, Hospital of The University of Pennsylvania, Philadelphia, Pennsylvania, United States., Philadelphia, Pennsylvania ²Division of Cardiothoracic Surgery, Department of Surgery, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States., Philadelphia, Pennsylvania ³Department of Medicine, Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States., Philadelphia, Pennsylvania ⁴Resuscitation Science Center and Department of Anesthesiology and Critical Care Medicine, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania, United States., Philadelphia, Pennsylvania ⁵Department of Pathology, University of Iowa Health Care, Iowa City, Iowa, United States., Iowa City, Iowa ⁶Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States., Philadelphia, Pennsylvania ⁷The Zickler Family Prenatal Pediatrics Institute, Children’s National Hospital, Washington D.C., USA., Washington D.C., District of Columbia

Purpose: Neonatal brain injury following cardiopulmonary bypass (CPB) has been associated with glutamate excitotoxicity [1]. Glutamate homeostasis is tightly linked to branched-chain amino acid (BCAA) metabolism, particularly leucine, and impaired BCAA metabolism can also cause neurologic injury [2,3]. This investigation assessed altered BCAA and mitochondrial metabolism in neonatal piglets following CPB.

Methods: Perioperative BCAA metabolism was assessed in fifteen piglets using an established neonatal swine model of continuous CPB (flow rate >100 mL/kg/minute at 34 °C) [4]. Cerebral interstitial fluid (CIF) was serially collected by microdialysis from the right frontal cortex at 6hr intervals for up to 24hrs post-CPB. Plasma was collected at similar timepoints. Cortical brain tissue was collected upon study completion at 12hrs, 18hrs, and 24hrs post-CPB (n=5 per cohort). Additionally, three piglets were survived for 4hrs following a similar sham procedure without cannulation or CPB. Liquid chromatography-mass spectrometry was used to quantify changes in all BCAAs (leucine, isoleucine, and valine) and 12 acylcarnitines associated with BCAA metabolism in plasma, CIF, and cortical brain tissue samples. Multiple comparisons tests were performed using one-way analysis of variance with Bonferroni adjustments to compare metabolomic profiles in plasma, CIF, and cortical brain tissue at various timepoints.

Results: BCAAs increased in CIF post-CPB (valine [FC 2.2, P=0.075]; isoleucine [FC 1.9, P=0.141]; leucine [FC 2.1, P=0.034]), and were significantly elevated at 24hrs post-CPB (P < 0.001; see Figure). Plasma BCAAs also increased post-CPB (valine [FC 1.6, P=0.001]; isoleucine [FC 1.4, P=0.039]; leucine [FC 1.8, P< 0.001]), but at 24hrs post-CPB, plasma leucine concentrations had returned to baseline (P=1.000; see Figure) and only valine remained elevated in plasma (P=0.041). At 24hrs post-CPB, leucine concentrations within the CIF also increased significantly relative to plasma concentrations (P < 0.001). In cortical brain tissue, there was no significant difference in leucine (P=0.831) or valine (P=0.898) following CPB, and isoleucine tended to decrease (P=0.050). Elevated concentrations of leucine within the CIF following CPB were accompanied by a significant decrease in glutamate (P=0.032).

Conclusion: Following continuous, mild hypothermic CPB, leucine and other BCAAs significantly increase in CIF. This is consistent with reports of impaired BCAA metabolism associated with neurotoxicity in the neonatal period [2,3]. Further studies are warranted to determine if BCAA accumulation contributes to neurologic injury and adverse neurodevelopmental outcomes after neonatal cardiac surgery.

Identify the source of the funding for this research project: This investigation was supported by the Institute for Translational Medicine and Therapeutics of the Perelman School of Medicine at the University of Pennsylvania, and the National Center for Advancing Translational Sciences of the National Institutes of Health under award number TL1TR001880. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This study was also supported by the Thoracic Surgery Foundation Nina Starr Braunwald Research Fellowship Award, as well as the Daniel M. Tabas and Thomas L. Spray Endowed Chairs in Pediatric Cardiothoracic Surgery, the William J. Greeley Endowed Chair in Translational Science and Innovation, and the Jonathan Chen Institutional Development Fund at Children's Hospital of Philadelphia.