We recently established a large animal model that recapitulates key clinical features of heart failure with preserved ejection fraction (HFpEF) and tested the effects of the pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). SAHA reversed and prevented the development of cardiopulmonary impairment. This study evaluated the effects of SAHA at the level of cardiomyocyte and contractile protein function to understand how it modulates cardiac function. Both isolated adult feline ventricular cardiomyocytes (AFVM) and left ventricle (LV) trabeculae isolated from non-failing donors were treated with SAHA or vehicle before recording functional data. Skinned myocytes were isolated from AFVM and human trabeculae to assess myofilament function. SAHA-treated AFVM had increased contractility and improved relaxation kinetics but no difference in peak calcium transients, with increased calcium sensitivity and decreased passive stiffness of myofilaments. Mass spectrometry analysis revealed increased acetylation of the myosin regulatory light chain with SAHA treatment. SAHA-treated human trabeculae had decreased diastolic tension and increased developed force. Myofilaments isolated from human trabeculae had increased calcium sensitivity and decreased passive stiffness. These findings suggest that SAHA has an important role in the direct control of cardiac function at the level of the cardiomyocyte and myofilament by increasing myofilament calcium sensitivity and reducing diastolic tension.

Heart failure with preserved ejection fraction (HFpEF) is a highly prevalent and intractable form of cardiac decompensation commonly associated with diastolic dysfunction. Here, we show that diastolic dysfunction in patients with HFpEF is associated with a cardiac deficit in nicotinamide adenine dinucleotide (NAD(+)). Elevating NAD(+) by oral supplementation of its precursor, nicotinamide, improved diastolic dysfunction induced by aging (in 2-year-old C57BL/6J mice), hypertension (in Dahl salt-sensitive rats), or cardiometabolic syndrome (in ZSF1 obese rats). This effect was mediated partly through alleviated systemic comorbidities and enhanced myocardial bioenergetics. Simultaneously, nicotinamide directly improved cardiomyocyte passive stiffness and calcium-dependent active relaxation through increased deacetylation of titin and the sarcoplasmic reticulum calcium adenosine triphosphatase 2a, respectively. In a long-term human cohort study, high dietary intake of naturally occurring NAD(+) precursors was associated with lower blood pressure and reduced risk of cardiac mortality. Collectively, these results suggest NAD(+) precursors, and especially nicotinamide, as potential therapeutic agents to treat diastolic dysfunction and HFpEF in humans.

Introduction: Heart failure (HF) is a global issue and approximately 50% of patients are classified as having HF with preserved Ejection Fraction (HFpEF), with no FDA approved therapies available. We previously characterized a large animal model that recapitulates key features of HFpEF and tested the effects of suberanilohydroxamic acid (SAHA, pan-HDAC inhibitor), which reversed and prevented the development of cardiopulmonary dysfunction. Parallel studies in cardiac tissue from humans and large mammals were designed to evaluate the effects of SAHA at the cellular level. Hypothesis: SAHA treatment will improve cardiomyocyte function. Methods: Adult feline ventricular cardiomyocytes (AFVM) were isolated from male domestic short hair cats and treated with 2.5μM SAHA or vehicle (DMSO) for 90 minutes, then incubated with a calcium (Ca 2+ ) indicator (Fluo-4AM) and electrically stimulated (0.5Hz) to record Ca 2+ transients and contractions. Human left ventricle (LV) trabeculae isolated from non-failing donor hearts were treated with 10μM SAHA or vehicle for 120 minutes while being electrically stimulated (1Hz) to record developed force and relaxation parameters. Skinned myocytes were isolated from treated AFVM and human trabeculae to assess myofilament Ca 2+ sensitivity and passive stiffness. Mass spectrometry (MS) was performed on AFVM skinned myocytes to identify novel acetylation sites. Results: There was no difference in AFVM peak Ca 2+ transients with SAHA treatment, but calcium removal was increased (tau, time to 30% baseline). There was a significant increase in contractility (fractional shortening) and relaxation kinetics (time to 50% baseline, return velocity). Trabeculae treated with SAHA had decreased diastolic tension and an increase in developed force. Skinned myocytes were isolated from treated AFVMs and trabeculae and both had a significant improvement in myofilament Ca 2+ sensitivity and significant decrease in passive stiffness with SAHA. MS of AFVM skinned myocytes revealed increased acetylation of the myosin regulatory light chain, driven by lysine 115. Conclusions: These findings suggest that SAHA may have an important role in regulating cardiac function via the cardiomyocyte and myofilament in feline and human myocardium.