Metabolomics for prognostic stratification in pulmonary hypertension patients

Abstract
Pulmonary hypertension (PH) is a condition defined by mPAP>20 mm Hg and characterized by structural and functional changes in the pulmonary vascular bed. Patients are stratified for 1-year risk of disease progression at follow-up based on 6-minute walk distance (6-MWD), WHO functional class (WHO FC) and NT-pro-BNP levels. This stratification results in a prognosis of low, intermediate low/high or high risk for disease worsening in the next year [1].

This observational study includes 46 patients (mean age 65.4 years 66.0% female) referred to a tertiary cardiology clinic with suspected PH. Of these 41 were s diagnosed with PH following right heart catheterization while 6 were not diagnosed with PH but were included as similarly presenting controls. There were 21 Group-1 patients, 4 Group-2, 5 Group-3 and 11 Group-4 patients. Of these patients 16 had a low risk prognosis, 16 intermediate low and 9 intermediate high , no patients in this group had a high risk. Untargeted metabolomics by UHPLC-MS (ultra-high pressure liquid chromatography mass spectrometry) and GC-MS (gas chromatography mass spectrometry) were used to measure a wide range of metabolic features. Multiple linear analyses [2] were applied to determine metabolic features that correlated with progression risk r group and those correlating with key hemodynamic measurements. Pathway enrichment analyses [3,4] identified metabolic pathways associated with prognostic stratification groups and disease hemodynamic markers.

Succinic acid is the most confidently identified metabolite associated with both progression risk grouping and hemodynamic changes. Carnitine derivatives are also confidently identified metabolites associated with disease stratification and both carnitine derivatives, amino acids and other carboxylic acids are also associated with hemodynamic measurements. Pathway analysis for both risk of progression group and hemodynamic markers shows that "Amino Acid Metabolism Pathway Excerpt (Histidine catabolism extension)" from Wikipathways [5] is associated with risk of progression group, mPAP and pulmonary vascular resistance, as are several other metabolic pathways relating to the tricarboxylic cycle. This demonstrates that central components of energy metabolism and oxidative/hypoxic stress are associated with disease severity and prognosis in PH. Several metabolites that are correlated to hemodynamic measurements or to risk of progression group showed the same patterns in an replication cohort (24 Group-1, 11 Group-4 median age 58, 49% female). Therefore, these metabolites are good candidates for future investigations as novel biomarkers to act as markers of disease severity or progression. Since this is a single time point study, it has not been possible to identify metabolic biomarkers for disease progression. A follow-up, longitudinal study is planned that will address this issue and verify the potential markers for disease severity in a larger cohort.