Madelyn Blake

Right ventricular failure (RVF) is the leading cause of death in pulmonary arterial hypertension (PAH), but effective therapies for RVF do not exist. Unfortunately, pharmaceuticals for left ventricular failure (LVF) are not particularly efficacious for RVF, establishing an unmet need. Secondary organ impairments differ in RVF and LVF as RVF has more hepatic effects. The liver is the site of ketone synthesis, and there is an induction of ketosis by LVF. Furthermore, ketones exert therapeutic effects through suppression of the NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome and favorable metabolic properties in LVF. However, the relationships between serum ketones and RV function in human PAH are unknown. Moreover, the effects of ketosis on the NLRP3 inflammasome, RV fibrosis, and RV function have not been formally evaluated. Objectives: To examine the relationship between serum ketones and RV function in human and rodent RVF. To determine if a ketogenic diet combats RVF by suppressing macrophage NLRP3 inflammasome activation and fibrosis in rodent RVF. Methods: 50 PAH patients were dichotomized into preserved or impaired RV function based on a cardiac index of 2.2 L/min/m2. Serum levels of ketone bodies acetoacetate (AcAc) and beta-hydroxybutyrate (BOHB) were quantified using ultra performance liquid chromatography and mass spectrometry. The relationships between AcAc and BOHB and hemodynamic and echocardiographic measures of RV function were evaluated. In rodent studies, male Sprague Dawley rats were assigned to three groups: control (saline injection), monocrotaline (MCT) fed a standard chow diet (MCT-SD), and MCT fed a ketogenic diet (MCT-KD) (calorie composition: 0% carbohydrates, 90.5% fat, and 9.5% protein). Immunoblots and confocal microscopy probed macrophage NLRP3 activation in RV extracts and sections. RV fibrosis was determined by Picrosirus Red staining of RV free wall sections. Echocardiography evaluated RV function. Results: Human RVF patients lacked a compensatory ketosis as serum AcAc and BOHB levels were not significantly associated with hemodynamic or echocardiographic measures of RV function. In rodent studies, AcAc and BOHB levels were also not elevated in MCT-mediated RVF, but the ketogenic diet increased AcAc and BOHB levels. Moreover, MCT-KD rats exhibited suppressed NLRP3 activation illustrated by a reduction in NLRP3, ASC (apoptosis-associated speck-like protein containing a CARD), pro-caspase-1, and interleukin-1 beta on immunoblots. Furthermore, the number of ASC-positive macrophage in RV sections were reduced in the MCT-KD group. Finally, RV fibrosis was significantly blunted, and RV function was augmented in the ketogenic diet arm. Conclusions: PAH patients with RVF lack a compensatory ketosis. A ketogenic diet suppresses NLRP3 activation, reduces RV fibrosis, and augments RV function in rodent RVF. Thus, approaches to increase ketone levels may be particularly effective for RVF.