Regional lung metabolic profile in a piglet model of cardiopulmonary bypass with circulatory arrest

Abstract

Introduction: Acute lung injury is common following cardiopulmonary bypass and deep hypothermic circulatory arrest for congenital heart surgery with the most severe injury in the dorsocaudal lung. Metabolomics offers promise in deducing mechanisms of disease states, providing risk stratification, and understanding therapeutic responses in regards to CPB/DHCA related organ injury.

Objectives: Using an infant porcine model, we sought to determine the individual and additive effects of CPB/DHCA and lung region on the metabolic fingerprint, metabolic pathways, and individual metabolites in lung tissue.

Methods: Twenty-seven infant piglets were divided into two groups: mechanical ventilation + CPB/DHCA (n = 20) and mechanical ventilation only (n = 7). Lung tissue was obtained from dorsocaudal and ventral regions. Targeted analysis of 235 metabolites was performed using HPLC/MS-MS. Data was analyzed using Principal Component Analysis (PCA), Partial Least Square Discriminant Analysis (PLS-DA), ANOVA, and pathway analysis.

Results: Profound metabolic differences were found in dorsocaudal compared to ventral lung zones by PCA and PLS-DA (R2 = 0.7; Q2 = 0.59; p < 0.0005). While overshadowed by the regional differences, some differences by exposure to CPB/DHCA were seen as well. Seventy-four metabolites differed among groups and pathway analysis revealed 20 differential metabolic pathways.

Conclusion: Our results demonstrate significant metabolic disturbances between dorsocaudal and ventral lung regions during supine mechanical ventilation with or without CPB/DHCA. CPB/DHCA also leads to metabolic differences and may have additive effects to the regional disturbances. Most pathways driving this pathology are involved in energy metabolism and the metabolism of amino acids, carbohydrates, and reduction-oxidation pathways.

Keywords: Acute lung injury; Cardiopulmonary bypass; Congenital heart disease surgery; Kynurenine metabolism; Metabolomics; Pathway analysis.

Fig. 1

Principal component analysis score plot and 2-dimensional partial least squares discriminant analysis score plot. A Principal Component Analysis Score Plot. Principal components 1 and 2 are shown. B 2-Dimensional Partial Least Squares Discriminant Analysis Score Plot. Components 1 and 2 are shown. Circles reflect samples for each group as described in the legend. Shaded regions represent 95% confidence intervals for each group. D-CPB/DHCA Dorsocaudal region cardiopulmonary bypass and deep hypothermic circulatory arrest (CPB/DHCA), D-MV Dorsocaudal region mechanical ventilation (MV), V-CPB/DHCA Ventral region CPB/DHCA, V-MV Ventral region MV

Fig. 2

Variable importance in projection scores and heat map. Metabolites with a Variable Importance in Projection (VIP) score greater than 1.5 contributing to variation in metabolic fingerprints between groups are shown. The heat map on the right demonstrates relative intensities of each metabolite in each group. DB Dorsocaudal region cardiopulmonary bypass and deep hypothermic circulatory arrest (CPB/DHCA), DM Dorsocaudal region mechanical ventilation (MV), UDP Uridine diphosphate, VB Ventral region, VM Ventral region MV

Fig. 3

Select box-plots for significant metabolites on ANOVA, Fisher FDR Post-Hoc testing. Y-axis represents transformed and scaled relative peak intensities. Yellow diamond represents the mean. A. Glyceric acid peak intensity was significantly higher in the both dorsocaudal cardiopulmonary bypass/deep hypothermic circulatory arrest (CPB/DHCA) and dorsocaudal mechanical ventilation (MV) compared to the ventral region CPB/DHCA and MV groups B. Acetoacetatic acid peak intensity was significantly higher in the CPB/DHCA groups compared to MV groups C. Citric acid peak intensity is significantly higher in both the ventral regions compared to dorsocaudal regions and also with CPB/DCHA compared to MV. It also shows an additive effect in that the relative peak intensity is significantly elevated in the ventral region CPB/DHCA group compared to all the other groups. DB Dorsocaudal CPB/DHCA, DM Dorsocaudal MV, VB Ventral CPB/DHCA, VM Ventral MV

Fig. 4

Pathway analysis. The x-axis reflects the impact factor calculated from Topographic Analysis; the y-axis reflects the negative logarithm of the p-value calculated from the Metabolite Set Enrichment Analysis. Each circle reflects a pathway. Node size reflects the impact value and node color reflects the p-value with lower p-values displayed as red and higher p-values displayed as more yellow-white. Select pathways are labeled. A. Pathways contributing to regional differences. B. Pathways contributing to cardiopulmonary bypass/deep hypothermic circulatory arrest differences (CPB/DHCA). AM Aspartate metabolism, APM Arginine and proline metabolism, BM Betaine metabolism, CAC Citric acid cycle, GluM Glutamate metabolism, Gly Glycolysis, GM Glutathione metabolism, GN Gluconeogenesis, GSM Glycine and serine metabolism, HD Homocysteine degradation, KBM Ketone body metabolism, MM Methionine metabolism, NNM Nicotinate and nicotinamide metabolism, PM Pyruvate metabolism, PTM Phenylalanine and tyrosine metabolism, SSB Spermine and spermidine biosynthesis, UC Urea cycle, WE Warburg effect