抑制組蛋白去乙醯酶可作為心肌電生理與結構異常疾病之新穎療法

Background: Atrial fibrillation (AF) is a common cardiac arrhythmia associated with high mortality and morbidity. Current treatments of AF have limited efficacy and considerable side effects. Pulmonary veins (PVs) with distinctive electrical and Ca2+ handling abnormalities are the most important ectopic foci for AF and play a major role in the pathophysiology of AF. Modulating PV calcium homeostasis controls PV electrical activity, which may reduce the risk of AF. Heart failure (HF) is a leading contributor of human morbidity and mortality. HF is one of the most prominent risk factors for AF, and HF and AF frequently coexist. HF affects cardiac metabolism and inflammation. Histone deacetylase (HDACs), important epigenetic regulatory enzymes, influence cell death, inflammation, fibrosis and contractility, play critical roles in the pathophysiology of cardiovascular diseases and contribute to calcium homeostasis and AF genesis. Therefore, HDAC inhibition may prove a novel therapeutic strategy for AF through upstream therapy and modifications of AF electrical and structural remodeling. However, the effects of HDAC inhibitors on cardiac electrophysiological and structural remodeling remain unclear.
Objectives: First, we investigated whether HDAC inhibition can regulate PV electrical activity through calcium modulation. Second, we evaluated whether HDAC inhibition can regulate HF by modifying cardiac inflammation, cardiac fibroblast growth factor (FGF) receptor and peroxisome-proliferator-activated receptor (PPAR) isoforms.
Materials and Methods: In study I, Whole-cell patch-clamp, confocal microscopic with fluorescence, and Western blot were used to evaluate electrophysiological characteristics and Ca2+ dynamics in individual isolated rabbit PV cardiomyocytes with and without MPT0E014 (a pan HDAC inhibitor), MS-275 (HDAC1 and 3 inhibitor), and MC-1568 (HDAC4 and 6 inhibitor) for 5~8 h. Atrial electrical activity and induced-AF (rapid atrial pacing and acetylcholine infusion) were measured in rabbits with and without MPT0E014 (10 mg/kg treated for 5 hours) in vivo. In study II, echocardiography, electrocardiography, ELISA, and Western blot were performed in rats with isoproterenol-induced HF with and without orally administered MPT0E014 (50 mg/kg for 7 consecutive days).
Results: Study I showed that MPT0E014 (1 µM)-treated PV cardiomyocytes (n=12) had slower beating rates (2.1±0.2 vs. 2.8±0.1 Hz, p<0.05) than control PV cardiomyocytes. Control and MPT0E014-treated PV cardiomyocytes without spontaneous activities had similar 20%, 50%, and 90% AP durations. However, control (n=11) and MPT0E014 (1 µM)-treated (n=12) SAN cardiomyocytes had similar beating rates (3.2±0.2 vs. 2.9±0.3 Hz). MS-275-treated PV cardiomyocytes (n=12, 2.3±0.2 Hz), but not MC-1568-treated PV cardiomyocytes (n=14, 3.1±0.3 Hz) had slower beating rates than control PV cardiomocytes. MPT0E014-treated PV cardiomyocytes (n=14) had a lower frequency (2.4±0.6 vs. 0.3±0.1 spark/mm/s, p<0.05) of Ca2+ sparks than control PV (n=17) cardiomyocytes. As compared to control, MPT0E014-treated PV cardiomyocytes had reduced Ca2+ transient amplitudes, sodium-calcium exchanger (NCX) currents than control PV cardiomyocytes. Moreover, MPT0E014-treated PV cardiomyocyte have lower expressions of the ryanodine receptor (RyR) and NCX proteins than control PV cardiomyocytes. Moreover, MPT0E014-treated rabbits had less AF and shorter AF duration than control rabbits. Study II showed the left ventricles (LVs) of HF rats expressed significantly higher HDAC1, HDAC2, HDAC3, HDAC4 and HDAC6 than the healthy LVs did. HF rats treated with MPT0E014 exhibited improved cardiac fraction shortening with reduced LV end diastolic and systolic diameter than HF without MPT0E014. The MPT0E014-treated HF LVs exhibited a smaller increase in the expression of interleukin (IL)-6, p22, SMAD2/3, extracellular signal-regulated kinase (ERK) 1/2, PPAR isoforms, and circulatory tumor growth factor (TGF)-β1 than the untreated HF LVs did. Moreover, MPT0E014-treated HF LVs expressed less fibroblast growth factor receptor (FGFR) than untreated HF LVs did. Additionally, MPT0E014-treated HF rats had less QT interval prolongation than HF without MPT0E014.
Conclusions: HDAC inhibition reduced PV arrhythmogenesis and AF inducibility with modulation on calcium homeostasis with decreased RyR and NCX protein expressions. Therefore, HDAC inhibition can improve cardiac function and attenuate the effects of HF on FGF receptors, cardiac metabolism and inflammation, which might contribute to the beneficial effects of HDAC inhibition in AF through multiple target modifications.