Introduction: Valine, leucine, and isoleucine are essential branched chain amino acids (BCAA), and recent epidemiological studies report elevated BCAAs predict worse outcomes in several cardiovascular diseases with metabolic origins such as diabetes, heart failure, and hypertension. However, the role of BCAA metabolism in pulmonary arterial hypertension pathophysiology is relatively unexplored.

Hypothesis: BCAAs are elevated in human PAH and reduction of BCAAs via small molecule activation of BCAA catabolism and dietary interventions combats PAH severity in preclinical PAH.

Methods: Literature search of human PAH metabolomics studies was conducted. For rodent studies, male Sprague Dawley rats were divided into three groups: control (saline injection), monocrotaline (MCT) vehicle (MCT-V), or MCT-BT2, a small molecule inducer of BCAA catabolism. BT2 was administered at 20mg/kg/day. A low BCAA dietary intervention was implemented, with male Sprague Dawley rats divided into two groups: MCT-standard chow diet and MCT-low BCAA diet. To assess exercise capacity, rodents underwent a maximal exercise testing protocol before echocardiographic and hemodynamic assessments of PAH. Proteomic analysis of lung mitochondrial extracts was performed to define the molecular effects of BT2.

Results: Of 11 studies evaluating human PAH metabolomics, 7 studies reported elevated BCAAs or BCAA metabolites in PAH. BT2 treatment improved exercise performance, reduced PA pressures, and augmented RV function. Moreover, the MCT-BT2 group possessed a distinct lung proteomic signature with changes in inflammatory and metabolic pathways. Finally, the low BCAA diet intervention modestly combatted PAH severity.

Conclusions: BCAA metabolism is disrupted in human PAH and interventions that reduce circulating BCAAs display therapeutic potential in rodent PAH.