Extracorporeal membrane oxygenation (ECMO) supports infants and children with severe cardiopulmonary compromise. Nutritional support for these children includes provision of medium- and long-chain fatty acids (FAs). However, ECMO induces a stress response, which could limit the capacity for FA oxidation. Metabolic impairment could induce new or exacerbate existing myocardial dysfunction. Using a clinically relevant piglet model, we tested the hypothesis that ECMO maintains the myocardial capacity for FA oxidation and preserves myocardial energy state. Provision of 13-Carbon labeled medium-chain FA (octanoate), long-chain free FAs (LCFAs), and lactate into systemic circulation showed that ECMO promoted relative increases in myocardial LCFA oxidation while inhibiting lactate oxidation. Loading of these labeled substrates at high dose into the left coronary artery demonstrated metabolic flexibility as the heart preferentially oxidized octanoate. ECMO preserved this octanoate metabolic response, but also promoted LCFA oxidation and inhibited lactate utilization. Rapid upregulation of pyruvate dehydrogenase kinase-4 (PDK4) protein appeared to participate in this metabolic shift during ECMO. ECMO also increased relative flux from lactate to alanine further supporting the role for pyruvate dehydrogenase inhibition by PDK4. High dose substrate loading during ECMO also elevated the myocardial energy state indexed by phosphocreatine to ATP ratio. ECMO promotes LCFA oxidation in immature hearts, while maintaining myocardial energy state. These data support the appropriateness of FA provision during ECMO support for the immature heart.

Cardiopulmonary bypass (CPB) is required during most cardiac surgeries. CBP drives systemic inflammation and multi-organ dysfunction that is especially severe in neonatal patients. Limited understanding of molecular mechanisms underlying CPB-associated inflammation presents a significant barrier to improve clinical outcomes. To better understand these clinical issues, we performed the first mRNA-sequencing on total circulating leukocytes from neonatal patients undergoing CPB. Our data identified myeloid cells, particularly monocytes, as the major cell type driving transcriptional responses to CPB. Furthermore, interleukin-8 (IL8) and tumor necrosis factor-α (TNFα) were inflammatory cytokines robustly upregulated in leukocytes from both patients and piglets exposed to CPB. To delineate the molecular mechanism, we exposed THP-1 human monocytic cells to CPB-like conditions including artificial surfaces, high shear stress, and cooling/rewarming. Shear stress was found to drive cytokine upregulation via calciumdependent signaling pathways. We also observed that a subpopulation of THP-1 cells died via TNFα-mediated necroptosis, which we hypothesize contributes to post-CPB inflammation. Together, our study identifies a shear-stress modulated molecular mechanism that drives systemic inflammation in pediatric CPB patients. These are also the first data to demonstrate that shear-stress causes necroptosis. Finally, we observe that calcium and TNFα signaling are novel targets to ameliorate post-CPB inflammation.

Extracorporeal membrane oxygenation (ECMO) provides essential mechanical circulatory support necessary for survival in infants and children with acute cardiac decompensation. However, ECMO also causes metabolic disturbances, which contribute to total body wasting and protein loss. Cardiac stunning can also occur, which prevents ECMO weaning, and contributes to high mortality. The heart may specifically undergo metabolic impairments, which influence functional recovery. We tested the hypothesis that ECMO alters oxidative metabolism and protein synthesis. We focused on the amino acid leucine and integration with myocardial protein synthesis. We used a translational immature swine model in which we assessed in heart 1) the fractional contribution of leucine (FcLeucine) and pyruvate to mitochondrial acetyl-CoA formation by nuclear magnetic resonance and 2) global protein fractional synthesis (FSR) by gas chromatography-mass spectrometry. Immature mixed breed Yorkshire male piglets (n = 22) were divided into four groups based on loading status (8 h of normal circulation or ECMO) and intracoronary infusion [(13)C(6),(15)N]-L-leucine (3.7 mM) alone or with [2-(13)C]-pyruvate (7.4 mM). ECMO decreased pulse pressure and correspondingly lowered myocardial oxygen consumption (∼40%, n = 5), indicating decreased overall mitochondrial oxidative metabolism. However, FcLeucine was maintained and myocardial protein FSR was marginally increased. Pyruvate addition decreased tissue leucine enrichment, FcLeucine, and Fc for endogenous substrates as well as protein FSR. The heart under ECMO shows reduced oxidative metabolism of substrates, including amino acids, while maintaining 1) metabolic flexibility indicated by ability to respond to pyruvate and 2) a normal or increased capacity for global protein synthesis.

The protooncogene C-Myc (Myc) regulates cardiac hypertrophy. Myc promotes compensated cardiac function, suggesting that the operative mechanisms differ from those leading to heart failure. Myc regulation of substrate metabolism is a reasonable target, as Myc alters metabolism in other tissues. We hypothesize that Myc-induced shifts in substrate utilization signal and promote compensated hypertrophy. We used cardiac specific Myc-inducible C57/BL6 male mice between 4–6 months old that develop hypertrophy with tamoxifen (tam) injections. Isolated working hearts and 13Carbon (13C)-NMR were used to measure function and fractional contributions (Fc) to the citric acid cycle by using perfusate containing 13C-labeled free fatty acids, acetoacetate, lactate, unlabeled glucose and insulin. Studies were performed at pre-hypertrophy (3-days tam, 3dMyc), established hypertrophy (7-days tam, 7dMyc) or vehicle control (Cont). Non-transgenic siblings (NTG) received 7-days tam or vehicle to assess drug effect. Hypertrophy was assessed by echocardiograms and heart weights. Western blots were performed on key metabolic enzymes. Hypertrophy occurred in 7dMyc only. Cardiac function did not differ between groups. Tam alone did not affect substrate contributions in NTG. Substrate utilization was not significantly altered in 3dMyc versus Cont. The free fatty acid FC was significantly greater in 7dMyc versus Cont with decreased unlabeled Fc, which is predominately exogenous glucose. Free fatty acid flux to the citric acid cycle increased while lactate flux was diminished in 7dMyc compared to Cont. Total protein levels of a panel of key metabolic enzymes were unchanged; however total protein O-GlcNAcylation was increased in 7dMyc. Substrate utilization changes for the citric acid cycle did not precede hypertrophy; therefore they are not the primary signal for cardiac growth in this model. Free fatty acid utilization and oxidation increase at established hypertrophy. Understanding the mechanisms whereby this change maintained compensated function could provide useful information for developing metabolic therapies to treat heart failure. The molecular signaling for this metabolic change may occur through O-GlcNAcylation.

Anesthetics used in infants and children are implicated in the development of neurocognitive disorders. Although propofol induces neuroapoptosis in developing brain, the underlying mechanisms require elucidation and may have an energetic basis. We studied substrate utilization in immature swine anesthetized with either propofol or isoflurane for 4 hours. Piglets were infused with 13-Carbon-labeled glucose and leucine in the common carotid artery to assess citric acid cycle (CAC) metabolism in the parietal cortex. The anesthetics produced similar systemic hemodynamics and cerebral oxygen saturation by near-infrared spectroscopy. Compared with isoflurane, propofol depleted ATP and glycogen stores. Propofol decreased pools of the CAC intermediates, citrate, and a-ketoglutarate, while markedly increasing succinate along with decreasing mitochondrial complex II activity. Propofol also inhibited acetyl-CoA entry into the CAC through pyruvate dehydrogenase, while promoting glycolytic flux with marked lactate accumulation. Although oxygen supply appeared similar between the anesthetic groups, propofol yielded a metabolic phenotype that resembled a hypoxic state. Propofol impairs substrate flux through the CAC in the immature cerebral cortex. These impairments occurred without systemic metabolic perturbations that typically accompany propofol infusion syndrome. These metabolic abnormalities may have a role in the neurotoxity observed with propofol in the vulnerable immature brain.