Trans-right ventricle and transpulmonary metabolite gradients in human pulmonary arterial hypertension

Figure 1. Catheter positions during cardiac catheterisation used in this study. Selected metabolites in the trans-RV and transpulmonary gradients and the direction of their change are shown. The changes in octadecanedioate suggest disruption of peroxisomal β-oxidation and a compensatory shift to ω-oxidation of fatty acids in the hypertensive RV of PAH patients. Accumulation of stearoylcarnitine in PAH RV indicates incomplete mitochondrial fatty acid oxidation. Accumulation of both octadecanedioate and stearoylcarnitine contribute to lipotoxicity in PAH. A more complete overview of the trans-RV metabolic changes and their likely effects in PAH is presented in figure 6. AAO, ascending aorta; Con, control; GPE, glycerophosphoethanolamine; GPC, glycerophosphocholine; PA, pulmonary artery (right or left); PAH, pulmonary arterial hypertension; PC, phosphatidylcholine; RV, right ventricle; SVC, superior vena cava; Trans-PC, transpulmonary circulation.

Figure 2. Several metabolites have differential trans-RV (PA vs SVC) gradients in paediatric PAH (vs non-PAH control). Statistical test: Wald χ2 test (linear mixed effects models). Data filtration: Metabolites with a missing value in at least one of the three catheterisation sites were removed from the gradient analysis. Outliers were removed using a recursive removal procedure for the outliers identified using Grubb’s test as described in the statistics section of the online supplement. (A) Step-up (FC=2.31) in PAH and step-down (FC=0.70) in controls for 1-palmitoyl-GPE (16:0) levels (FDR-adjusted p value=0.0133); raw data (normalised ion counts) for 1-palmitoyl-GPE (16:0) levels in all three catheterisation sites; correlation of 1-palmitoyl-GPE (16:0) levels with haemodynamics (TAPSE). (B) Step-up (FC=1.48) in PAH and step-down (FC=0.78) in controls for 1-oleoyl-GPE (18:1) levels (FDR-adjusted p value=0.0767); raw data (normalised ion counts) for 1-oleoyl-GPE (18:1) levels in all three catheterisation sites; correlation of 1-oleoyl-GPE (18:1) levels with haemodynamics (TAPSE). (C) No change (FC=1.09) in PAH and step-down (FC=0.77) in controls for octadecanedioate levels (FDR-adjusted p…

Figure 3. Several lipids have differential trans-RV (PA vs SVC) and transpulmonary (AAO vs PA) gradients in paediatric PAH (vs non-PAH control). Volcano plots (A and B) show pairs of lipids with statistically significant fold change differences. Interestingly, all such lipids had a step-up in PAH and a step-down in controls trans-RV (A), while the fold change direction was reversed (PAH down, non-PAH controls up) for the lipids with significantly different gradients transpulmonary (B). Statistical test: Wald χ2 test (linear mixed effects models). Data filtration: see legend for figure 1. AAO, ascending aorta; CE, cholesterol ester; DAG, diacylglycerol; FA, fatty acid; FFA, free FA; FDR, false discovery rate; FC, fold change; PAH, pulmonary arterial hypertension; PC, phosphatidylcholine; RV, right ventricle; SVC, superior vena cava; TAG, triacylglycerol; Trans-PC, transpulmonary circulation.

Figure 4. Several metabolites have differential transpulmonary (AAO vs PA) gradients in paediatric PAH (vs non-PAH control). Statistical test: Wald χ2 test (linear mixed effects models). Data filtration: see legend for figure 1. (A) Step-up (FC=1.53) in PAH and step-down (FC=0.71) in controls for N6-acetyllysine levels (FDR-adjusted p value=0.0476); raw data (normalised ion counts) for N6-acetyllysine levels in all three catheterisation sites; correlation of N6-acetyllysine levels with haemodynamics (dTPG). (B) Step-down (FC=0.83) in PAH and step-up (FC=1.22) in controls for 2-palmitoyl-GPC (16:0) levels (FDR-adjusted p value=0.0184); raw data (normalised ion counts) for 2-palmitoyl-GPC (16:0) levels in all three catheterisation sites; correlation of 2-palmitoyl-GPC (16:0) levels with haemodynamics (PVR/SVR). (C) Step-down (FC=0.72) in PAH and no change (FC=1.05) in controls for N-acetylcarnosine levels (FDR-adjusted p value=0.0683); raw data (normalised ion counts) for N-acetylcarnosine levels in all three catheterisation sites; correlation of N-acetylcarnosine levels with haemodynamics (PAWP). (D) Step-down (FC=0.42) in PAH and step-up (FC=1.22) in controls for azelate (nonanedioate)…

Figure 5. Several metabolites have differential levels in paediatric PAH (vs non-PAH control) in SVC and PA. Mean±SEM statistical test: Mann-Whitney U test with FDR correction for multiple testing. Significance levels: *p<0.15, **p<0.05 for FDR-adjusted p values. (A) Plasma levels of heptanoate (7:0) in SVC (significant upregulation), PA and AAO. (B) Plasma levels of caproate (6:0) in SVC (significant upregulation), PA and AAO. (C) Plasma levels of glycocholenate sulfate in SVC (significant upregulation), PA and AAO. (D) Plasma levels of 1-stearoyl-GPI (18:0) in SVC, PA (significant upregulation) and AAO. (E) Plasma levels of N6-acetyllysine in SVC, PA (significant downregulation) and AAO. AAO, ascending aorta; Con, control; FC, fold change; GPI, glycosylphosphatidylinositol; mPAP, mean pulmonary arterial pressure; mAAO, mean ascending aorta pressure; PA, pulmonary artery; PAH, pulmonary arterial hypertension; PVRi, pulmonary vascular resistance index; RVAW, right ventricular anterior wall diameter; RVEDD, right ventricular end-diastolic diameter; SVC, superior vena cava; WU, Wood units.

Figure 6. Disruption of β-oxidation in the right ventricle in human PAH indicates major disturbance of lipid and energy metabolism (model). Our results in this article are shown in blue font. Conversion of carboxylic acids to dicarboxylic acids is facilitated by ω-oxidation, which results in conversion of the methyl group (CH3) at the ω-end into a carboxyl group (COOH). The produced dicarboxylic acids (eg, octadecanedioate) are further metabolised by β-oxidation. Unlike β-oxidation, ω-oxidation does not require acyl-CoAs and provides an alternative for disrupted β-oxidation. The accumulation of octadecanedioate (a dicarboxylic acid) in PAH that we demonstrated as trans-RV blood plasma gradient, strongly suggests disruption of peroxisomal β-oxidation in the hypertensive RV, because very long chain and long chain dicarboxylyl-CoAs (such as the end-product of octadecanedioate ω-oxidation) can only be metabolised by peroxisomal β-oxidation. The accumulation of stearoylcarnitine and other acylcarnitines suggests incomplete mitochondrial fatty acid oxidation (FAO), probably resulting from FAO flux outpacing TCA flux. The lipotoxic effects of the molecules with detected accumulation in the PAH RV…