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Sudden death could be the first symptom of patients with arrhythmogenic cardiomyopathy (AC), a disease for which clinical indicators predicting adverse progression remain lacking. Recent findings suggest that metabolic dysregulation is present in AC. We performed this study to identify metabolic indicators that predicted major adverse cardiac events (MACEs) in patients with AC and their relatives. Comparing explanted hearts from patients with AC and healthy donors, we identified deregulated metabolic pathways using quantitative proteomics. Right ventricles (RVs) from patients with AC displayed elevated ketone metabolic enzymes, OXCT1 and HMGCS2 , suggesting higher ketone metabolism in AC RVs. Analysis of matched coronary artery and sinus plasma suggested potential ketone body synthesis at early-stage AC, which was validated using patient-derived induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) in vitro. Targeted metabolomics analysis in RVs from end-stage AC revealed a "burned-out" state, with predominant medium-chain fatty acid rather than ketone body utilization. In an independent validation cohort, 65 probands with mostly non-heart failure manifestations of AC had higher plasma β-hydroxybutyrate (β-OHB) than 62 healthy volunteers ( P < 0.001). Probands with AC with MACE had higher β-OHB than those without MACE ( P < 0.001). Among 94 relatives of probands, higher plasma β-OHB distinguished 25 relatives having suspected AC from nonaffected relatives. This study demonstrates that elevated plasma β-OHB predicts MACE in probands and disease progression in patients with AC and their clinically asymptomatic relatives., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Background: Cardiomyocytes derived from animals and induced pluripotent stem cells (iPSCs) are two main cellular models to study cardiovascular diseases, however, neither provides precise modeling of the response of mature human cardiomyocytes to disease or stress conditions. Therefore, there are emerging needs for finding an optimized primary human cardiomyocytes isolation method to provide a bona fide cellular model., Methods and Results: Previous established protocols for the isolation of primary human cardiomyocytes are limited in their application due to relatively low cell yield and the requirement of tissue integrity. Here, we developed a novel, simplified method to isolate human cardiomyocytes robustly with improved viability from tissue slicing. Isolated cardiomyocytes showed intact morphology, retained contractility, ion flux, calcium handling, and responses to neurohormonal stimulation. In addition, we assessed the metabolic status of cardiomyocytes from different health conditions., Conclusion: We present a novel, simplified method for isolation of viable cardiomyocytes from human tissue.

Objective: To investigate the effects of docosahexaenoic acid (DHA) on action potential (AP) and transient outward potassium current (I(to)) on ventricular myocytes of Sprague-Dawley rat., Methods: Calcium-tolerant ventricular myocytes were isolated by enzyme digestion. The changes of AP and I(to) with increasing DHA at concentrations of 0, 10, 20, 40, 60, 80, 100, 120 and 200 micromol/L were recorded by whole-cell patch clamp configuration., Results: (1) Action potential durations (APDs) were not affected by DHA at concentrations from 0 micromol/L to 30 micromol/L, while APDs were gradually prolonged in proportion with increasing DHA concentrations from 30 micromol/L to 200 micromol/L within 5 minutes and remained stable thereafter. APD(25), APD(50) and APD(75) were (7.7 +/- 2.0) ms, (21.2 +/- 3.5) ms, and (100.1 +/- 9.8) ms respectively at 100 micromol/L DHA. APD(25), APD(50), and APD(75) were (15.2 +/- 4.0) ms, (45.7 +/- 6.8) ms, and (215.6 +/- 15.7) ms respectively at 200 micromol/L DHA. (2) I(to) was gradually reduced with the increasing DHA concentrations from 10 micromol/L to 200 micromol/L. I(to) was blocked by DHA in a dose-dependent manner. I(to) current density was (30.1 +/- 7.2) pA/pF at DHA concentration of 60 micromol/L and its half-inhibition concentration was 58.3 micromol/L., Conclusion: APDs are gradually prolonged while I(to) reduced with increasing concentrations of DHA which might contribute to the anti-arrhythmia mechanisms of DHA.

Objective: To investigate the effects of different amlodipine isomers on L-type calcium current (ICa-L) and kinetics of rat ventricular myocytes., Methods: Rat ventricular myocytes were isolated by enzyme digestion. ICa-L, peak currents, I-V curves, steady state activation curves, steady state inactivation curves and recovery curves from inactivation with S-amlodipine, R-amlodipine and R, S-amlodipine at concentrations of 0.1, 0.5, 1, 5, and 10 micromol/L were recorded by whole-cell patch clamp configuration., Results: At the concentrations of 0.1, 0.5, 1, 5, and 10 micromol/L, ICa-L were blocked in a dose-dependent manner by S-amlodipine [(1.5 +/- 0.2)%, (25.4 +/- 5.3)%, (65.2 +/- 7.3)%, (78.4 +/- 8.1)%, and (94.2 +/- 5.0)%] and by R, S-amlodipine [(0.9 +/- 0.1)%, (10.4 +/- 3.2)%, (69.1 +/- 5.3)%, (75.2 +/- 7.0)%, and (81.6 +/- 6.4)%]. I-V curves were significantly shifted upward, steady state activation and inactivation curves were significantly shifted to left by S-amlodipine and R, S-amlodipine (0.1 micromol/L to 10 micromol/L). Recovery time from inactivation was also significantly prolonged by S-amlodipine [(210.1 +/- 19.5) ms, (225.2 +/- 21.3) ms, (241.7 +/- 20.3) ms, (252.3 +/- 24.2) ms, and (282.6 +/- 23.2) ms] and by R, S-amlodipine [(208.7 +/- 17.4) ms, (215.8 +/- 18.3) ms, (225.2 +/- 21.3) ms, (235.8 +/- 22.7) ms, and (252.3 +/- 24.2) ms] in a dose-dependent manner. The observed effects of S-amlodipine were more potent than those of R, S-amlodipine (P < 0.05). However, all these parameters were not affected by R-amlodipine at various concentrations (P > 0.05)., Conclusion: L-type calcium current of rat ventricular myocytes could be blocked by R, S-amlodipine and S-amlodipine in a dose-dependent manner.

Objective: To analysis the effect of amiodarone on funny current (I(f)) and hyperpolarization-activated cation channel (HCN) gene expressions of the neonatal rat ventricular myocytes., Methods: Ventricular myocytes of 1 - 3 days-old rats were isolated and cultured. The cardiomyocytes were treated by amiodarone (0.01, 0.1, 1, 10, 100 micromol/L) for 3 hours or amiodaron (10 micromol/L) for 0, 0.5, 1, 3, 6 hours. The I(f) and HCN 1 - 4 gene expressions were measured through the whole-cell configuration of the patch-clamp technique and real-time quantitative polymerase chain reaction (real-time PCR) using SYBR Green PCR kit., Results: (1) HCN1, HCN2, HCN3 and HCN4 represented (0.23 +/- 0.01)%, (83.58 +/- 0.04)%, (0.79 +/- 0.01)% and (15.44 +/- 0.01)% of total HCN mRNA, respectively. (2) Amiodaron resulted in a dose-dependent I(f) [(3.1 +/- 0.9)%, (9.7 +/- 2.4)%, (36.7 +/- 5.8)%, (80.3 +/- 1.8)% and (85.9 +/- 3.1)%, respectively at -145 mV, IC(50) (1.32 +/- 0.28) micromol/L], HCN2 [(2.1 +/- 0.8)%, (8.9 +/- 3.6)%, (30.1 +/- 4.2)%, (78.3 +/- 3.6)% and (81.1 +/- 1.9)%, respectively] and HCN4 decrease [(0.5 +/- 0.2)%, (2.1 +/- 2.6)%, (8.8 +/- 3.2)%, (60.1 +/- 4.6)% and (59.6 +/- 6.5)%, respectively]. (3) Amiodaron (10 micromol/L) also induced a time-dependent I(f) [(1.1 +/- 0.1)%, (12.6 +/- 2.3)%, (80.6 +/- 2.2)% and (80.1 +/- 2.1)%, respectively], HCN2 [(1.0 +/- 0.1)%, (9.8 +/- 3.9)%, (82.9 +/- 4.6)% and (83.9 +/- 1.7)%, respectively] and HCN4 decrease [(0.1 +/- 0.1)%, (1.9 +/- 1.1)%, (59.4 +/- 7.8)% and (60.9 +/- 3.1)%, respectively]. However, HCN1 and HCN3 expressions were not affected by amiodaron treatment., Conclusion: Current density of I(f) and the expression of HCN2 and HCN4 were decreased by amiodaron which might be the possible antiarrhythmic working mechanisms of amiodaron.

Objective: To investigate the effects of metoprolol on cardiac function and myocyte calcium regulatory protein expressions in rabbits with heart failure., Methods: Rabbit heart failure model was established by aortic insufficiency induced volume overload followed 14 days later by pressure overload induced by abdominal aorta constricting (HF, n = 11), another 8 rabbits with heart failure were treated with metoprolol (ME) for 6 weeks, sham-operated rabbits (n = 11) served as control. Cardiac function was measured by echocardiography at the end of study. Caffeine-induced calcium transients of myocytes loaded by Fluo-3/AM were observed under Laser scanning confocal microscope. Calcium regulatory protein expression was determined by Western blot analysis., Results: Compared to control animals, the ejection fractions [EF, (45.7 +/- 3.0)% vs. (72. 6 +/- 5.0)%, P < 0.01] and the amplitude of caffeine-induced calcium transients [(16.0 +/- 3.5) FI vs. (43.5 +/- 6.2) FI, P < 0.01] were significantly decreased while its time to peak was significantly prolonged [(129.8 +/- 14.5) s vs. (52.2 +/- 7.4) s, P < 0.01] in HF rabbits. The RyR2 (0.106 +/- 0.007 vs. 0.203 +/- 0.021, P < 0.01) and the ratio of SERCA2a and NCX (1.22 +/- 0.23 vs. 1.96 +/- 0.12, P < 0.01) were also significantly reduced in myocytes of HF rabbits. Metoprolol significantly attenuated the decrease of EF [(60.2 +/- 5.1)%], the amplitude of calcium transient [(32.8 +/- 5.4) FI], the RyR2 expression (0.164 +/- 0.016) and the ratio of SERCA2a and NCX (1.68 +/- 0.17, all P < 0.05 vs. HF rabbits) and attenuated the increase of the time to peak of caffeine-induced calcium transients [(91.4 +/- 10.9) s, P < 0.05 vs. HF rabbits]., Conclusion: Metoprolol could improve the cardiac function possibly by preventing the alterations of calcium regulatory proteins and increasing calcium transients in failing heart.