Metabolic Profiling of Right Ventricular-Pulmonary Vascular Function Reveals Circulating Biomarkers of Pulmonary Hypertension

BACKGROUND Pulmonary hypertension and associated right ventricular (RV) dysfunction are important determinants of morbidity and mortality, which are optimally characterized by invasive hemodynamic measurements. OBJECTIVES This study sought to determine whether metabolite profiling could identify plasma signatures of right ventricular-pulmonary vascular (RV-PV) dysfunction. METHODS We measured plasma concentrations of 105 metabolites using targeted mass spectrometry in 71 individuals (discovery cohort) who underwent comprehensive physiological assessment with right-sided heart catheterization and radionuclide ventriculography at rest and during exercise. Our findings were validated in a second cohort undergoing invasive hemodynamic evaluations (n = 71), as well as in an independent cohort with or without known pulmonary arterial (PA) hypertension (n = 30). RESULTS In the discovery cohort, 21 metabolites were associated with 2 or more hemodynamic indicators of RV-PV function (i.e., resting right atrial pressure, mean PA pressure, pulmonary vascular resistance [PVR], and PVR and PA pressure-flow response [ΔPQ] during exercise). We identified novel associations of RV-PV dysfunction with circulating indoleamine 2,3-dioxygenase (IDO)–dependent tryptophan metabolites (TMs), tricarboxylic acid intermediates, and purine metabolites and confirmed previously described associations with arginine–nitric oxide metabolic pathway constituents. IDO-TM levels were inversely related to RV ejection fraction and were particularly well correlated with exercise PVR and ΔPQ. Multisite sampling demonstrated transpulmonary release of IDO-TMs. IDO-TMs also identified RV-PV dysfunction in a validation cohort with known risk factors for pulmonary hypertension and in patients with established PA hypertension. CONCLUSIONS Metabolic profiling identified reproducible signatures of RV-PV dysfunction, highlighting both new biomarkers and pathways for further functional characterization.