Metabolomic Signatures Associated With Pulmonary Arterial Hypertension Outcomes

Abstract

Background: Pulmonary arterial hypertension (PAH) is a complex disease characterized by progressive right ventricular (RV) failure leading to significant morbidity and mortality. Investigating metabolic features and pathways associated with RV dilation, mortality, and measures of disease severity can provide insight into molecular mechanisms, identify subphenotypes, and suggest potential therapeutic targets.

Methods: We collected data from a prospective cohort of PAH participants and performed untargeted metabolomic profiling on 1045 metabolites from circulating blood. Analyses were intended to identify metabolomic differences across a range of common metrics in PAH (eg, dilated versus nondilated RV). Partial least squares discriminant analysis was first applied to assess the distinguishability of relevant outcomes. Significantly altered metabolites were then identified using linear regression, and Cox regression models (as appropriate for the specific outcome) with adjustments for age, sex, body mass index, and PAH cause. Models exploring RV maladaptation were further adjusted for pulmonary vascular resistance. Pathway enrichment analysis was performed to identify significantly dysregulated processes.

Results: A total of 117 participants with PAH were included. Partial least squares discriminant analysis showed cluster differentiation between participants with dilated versus nondilated RVs, survivors versus nonsurvivors, and across a range of NT-proBNP (N-terminal pro-B-type natriuretic peptide) levels, REVEAL 2.0 composite scores, and 6-minute-walk distances. Polyamine and histidine pathways were associated with differences in RV dilation, mortality, NT-proBNP, REVEAL score, and 6-minute walk distance. Acylcarnitine pathways were associated with NT-proBNP, REVEAL score, and 6-minute walk distance. Sphingomyelin pathways were associated with RV dilation and NT-proBNP after adjustment for pulmonary vascular resistance.

Conclusions: Distinct plasma metabolomic profiles are associated with RV dilation, mortality, and measures of disease severity in PAH. Polyamine, histidine, and sphingomyelin metabolic pathways represent promising candidates for identifying patients at high risk for poor outcomes and investigation into their roles as markers or mediators of disease progression and RV adaptation.

Keywords: histidine; metabolomics; mortality; pulmonary arterial hypertension; right-sided heart failure; sphingomyelins; systems biology.

Figure 1:. Overview of metabolomic analysis and Partial Least Squares Discriminant Analysis (PLS-DA) of global metabolomic profiles in participants with pulmonary arterial hypertension across a range of metrics of severity.

Panel A: diagram of the 4 main components in metabolomic analyses; Panel B: PLS-DA plot for right ventricular dilation; Panel C: PLS-DA plot for categories of NT-proBNP; Panel D: PLS-DA plot for categories of REVEAL 2.0 scores; Panel E: PLS-DA plot for categories of 6MWD; Panel F: PLS-DA plot for all-cause mortality.

Figure 2:. Heatmap of z-scores of the thirty-two significantly altered metabolites in pulmonary arterial hypertension participants with dilated relative to non-dilated right ventricles.

Note the metabolites in the polyamine and histidine metabolism pathways are significantly associated with right ventricular dilation.

Figure 3:. Heatmap of z-scores of the 45 significant metabolites in a Cox proportional hazards model for mortality in pulmonary arterial hypertension participants.

Note the metabolites in the polyamine and histidine metabolism pathways are significantly associated with mortality.

Figure 4:. Summary heatmap of the 49 pathways associated with at least one metric of severity. The superpathway in which each pathway is nested is provided for reference.

Polyamine and histidine pathways were highly enriched across clinical measures.

Figure 5:. Heatmap of z-scores of the 25 significantly altered metabolites in pulmonary arterial hypertension participants with right ventricular dilation relative to no dilation, but with otherwise similar pulmonary vascular resistance.

Note the predominance of metabolites mapping ot sphingomyelin metabolic pathways.

Figure 6:. Summary heatmap of the 44 pathways associated with a metric suggesting right ventricular vulnerability in individuals with otherwise similar pulmonary vascular resistance. The superpathway in which each pathway is nested is provided for reference.

After adjustment for PVR, sphingomyelin and dihydrosphingomyelin pathways became strongly associated with RV dilation and NT-proBNP levels.

Figure 7:. Leveraging metabolomic information to predict 3-year mortality in participants with pulmonary arterial hypertension in Servetus.

In-sample ROC curves for mortality were used to compare mortality prediction based on (i) REVEAL 2.0 score, (ii) the 11 overlapping metabolites selected by univariate Cox, and (iii) a combination of both approaches.