Circulating Factors in Single Ventricle Heart Disease Impair Cardiomyocyte Bioenergetics, With Partial Rescue by PDE5 Inhibition.

BACKGROUND: Although operative and perioperative care continues to improve for patients with single ventricle (SV) congenital heart disease, long-term morbidities and mortality remain high. Importantly, phosphodiesterase-5 inhibitor (PDE5i) therapies are increasingly used, but their direct myocardial effects in SV congenital heart disease remain poorly understood. We previously demonstrated that the failing SV myocardium is characterized by increased PDE5 (phosphodiesterase-5) activity and impaired mitochondrial bioenergetics. Here we sought to determine whether systemic circulating factors contribute to pathological metabolic remodeling in SV congenital heart disease, and whether PDE5i therapy mitigates these changes. METHODS: Using an established in vitro model whereby primary cardiomyocytes are treated with patient sera ± PDE5i, we assessed the impact of circulating factors on cardiomyocyte metabolism. Mass spectrometry-based lipidomics and metabolomics assessed phospholipid and metabolite changes. Mitochondrial bioenergetics were evaluated using the Seahorse Bioanalyzer and a stable isotope-based enzyme activity assay. Relative mitochondrial copy number was quantified using reverse transcriptase-quantitative polymerase chain reaction. RESULTS: Our data suggest that circulating factors contribute to fundamental changes in cardiomyocyte bioenergetics, including impaired mitochondrial function associated with decreased cardiolipin and other phospholipid species, impaired carnitine palmitoyltransferase activity, increased reactive oxygen species generation, and altered metabolite milieu. PDE5i treatment partially reversed these abnormalities by restoring phosphatidylglycerol levels, reducing reactive oxygen species, increasing carnitine palmitoyltransferase activity, improving energy production, and normalizing several metabolic intermediates. CONCLUSIONS: Together, these data suggest circulating factors directly impair cardiomyocyte mitochondrial bioenergetics and may drive systemic metabolic dysfunction in SV congenital heart disease. PDE5i therapy partially attenuates these effects, supporting metabolic modulation as a potential therapeutic strategy for SV failure.