Histological assessment of cardiac amyloidosis in patients undergoing transcatheter aortic valve replacement.

AIMS: Studies have reported a strongly varying co-prevalence of aortic stenosis (AS) and cardiac amyloidosis (CA). We sought to histologically determine the co-prevalence of AS and CA in patients undergoing transcatheter aortic valve replacement (TAVR). Consequently, we aimed to derive an algorithm to identify cases in which to suspect the co-prevalence of AS and CA. METHODS AND RESULTS: In this prospective, monocentric study, endomyocardial biopsies of 162 patients undergoing TAVR between January 2017 and March 2021 at the University Medical Centre Göttingen were analysed by one pathologist blinded to clinical data using haematoxylin-eosin staining, Elastica van Gieson staining, and Congo red staining of endomyocardial biopsies. CA was identified in only eight patients (4.9%). CA patients had significantly higher N-terminal pro-brain natriuretic peptide (NT-proBNP) levels (4356.20 vs. 1938.00 ng/L, P = 0.034), a lower voltage-to-mass ratio (0.73 vs. 1.46 × 10-2 mVm2/g, P = 0.022), and lower transaortic gradients (Pmean 17.5 vs. 38.0 mmHg, P = 0.004) than AS patients. Concomitant CA was associated with a higher prevalence of post-procedural acute kidney injury (50.0% vs. 13.1%, P = 0.018) and sudden cardiac death [SCD; P (log-rank test) = 0.017]. Following propensity score matching, 184 proteins were analysed to identify serum biomarkers of concomitant CA. CA patients expressed lower levels of chymotrypsin (P = 0.018) and carboxypeptidase 1 (P = 0.027). We propose an algorithm using commonly documented parameters-stroke volume index, ejection fraction, NT-proBNP levels, posterior wall thickness, and QRS voltage-to-mass ratio-to screen for CA in AS patients, reaching a sensitivity of 66.6% with a specificity of 98.1%. CONCLUSIONS: The co-prevalence of AS and CA was lower than expected, at 4.9%. Despite excellent 1 year mortality, AS + CA patients died significantly more often from SCD. We propose a multimodal algorithm to facilitate more effective screening for CA containing parameters commonly documented during clinical routine. Proteomic biomarkers may yield additional information in the future.

Bioactive adrenomedullin and interleukin-6 in COVID-19: potential biomarkers of acute kidney injury and critical illness.

BACKGROUND: The aim of this study was to investigate whether bioactive adrenomedullin (bio-ADM) and interleukin-6 (IL-6) are related to acute kidney injury (AKI) and severe illness in COVID-19 patients. METHODS: 153 patients with COVID-19 admitted to the emergency department (ED) were included. Blood samples were collected from each patient at admission. Bio-ADM and IL-6, as well as DPP3 and routinely measured markers were evaluated regarding the endpoints AKI (22/128 hospitalized patients) and a composite endpoint of admission to intensive care unit and/or in-hospital death (n = 26/153 patients). RESULTS: Bio-ADM and IL-6 were significantly elevated in COVID-19 patients with AKI compared to COVID-19 patients without AKI (each p < 0.001). According to ROC analyses IL-6 and bio-ADM had the largest AUC (0.84 and 0.81) regarding the detection of AKI. Furthermore, bio-ADM and IL-6 were significantly elevated in COVID-19 patients reaching the composite endpoint (each p < 0.001). Regarding the composite endpoint ROC analysis showed an AUC of 0.89 for IL-6 and 0.83 for bio-ADM in COVID-19 patients. In the multivariable logistic model bio-ADM and IL-6 presented as independent significant predictors regarding both endpoints AKI and the composite endpoint in COVID-19 patients (as well as creatinine regarding the composite endpoint; each p < 0.05), opposite to leukocytes, C-reactive protein (CRP) and dipeptidyl peptidase 3 (DPP3; each p = n.s.). CONCLUSION: Elevated levels of bio-ADM and IL-6 are associated with AKI and critical illness in patients with COVID-19. Therefore, both biomarkers may be potential tools in risk stratification in COVID-19 patients at presentation in the ED.

Dipeptidyl-peptidase 3 and IL-6: potential biomarkers for diagnostics in COVID-19 and association with pulmonary infiltrates.

Coronavirus SARS-CoV-2 spread worldwide, causing a respiratory disease known as COVID-19. The aim of the present study was to examine whether Dipeptidyl-peptidase 3 (DPP3) and the inflammatory biomarkers IL-6, CRP, and leucocytes are associated with COVID-19 and able to predict the severity of pulmonary infiltrates in COVID-19 patients versus non-COVID-19 patients. 114 COVID-19 patients and 35 patients with respiratory infections other than SARS-CoV-2 were included in our prospective observational study. Blood samples were collected at presentation to the emergency department. 102 COVID-19 patients and 28 non-COVID-19 patients received CT imaging (19 outpatients did not receive CT imaging). If CT imaging was available, artificial intelligence software (CT Pneumonia Analysis) was used to quantify pulmonary infiltrates. According to the median of infiltrate (14.45%), patients who obtained quantitative CT analysis were divided into two groups (> median: 55 COVID-19 and nine non-COVID-19, ≤ median: 47 COVID-19 and 19 non-COVID-19). DPP3 was significantly elevated in COVID-19 patients (median 20.85 ng/ml, 95% CI 18.34-24.40 ng/ml), as opposed to those without SARS-CoV-2 (median 13.80 ng/ml, 95% CI 11.30-17.65 ng/ml; p < 0.001, AUC = 0.72), opposite to IL-6, CRP (each p = n.s.) and leucocytes (p < 0.05, but lower levels in COVID-19 patients). Regarding binary logistic regression analysis, higher DPP3 concentrations (OR = 1.12, p < 0.001) and lower leucocytes counts (OR = 0.76, p < 0.001) were identified as significant and independent predictors of SARS-CoV-2 infection, as opposed to IL-6 and CRP (each p = n.s.). IL-6 was significantly increased in patients with infiltrate above the median compared to infiltrate below the median both in COVID-19 (p < 0.001, AUC = 0.78) and in non-COVID-19 (p < 0.05, AUC = 0.81). CRP, DPP3, and leucocytes were increased in COVID-19 patients with infiltrate above median (each p < 0.05, AUC: CRP 0.82, DPP3 0.70, leucocytes 0.67) compared to infiltrate below median, opposite to non-COVID-19 (each p = n.s.). Regarding multiple linear regression analysis in COVID-19, CRP, IL-6, and leucocytes (each p < 0.05) were associated with the degree of pulmonary infiltrates, as opposed to DPP3 (p = n.s.). DPP3 showed the potential to be a COVID-19-specific biomarker. IL-6 might serve as a prognostic marker to assess the extent of pulmonary infiltrates in respiratory patients.

Urinary N-Terminal Pro-Brain Natriuretic Peptide Predicts Acute Kidney Injury and Severe Disease in COVID-19.

INTRODUCTION: The ongoing COVID-19 pandemic is placing an extraordinary burden on our health care system with its limited resources. Accurate triage of patients is necessary to ensure medical care for those most severely affected. In this regard, biomarkers could contribute to risk evaluation. The aim of this prospective observational clinical study was to assess the relationship between urinary N-terminal pro-brain natriuretic peptide (NT-proBNP) and acute kidney injury (AKI) as well as severe disease in patients with COVID-19. METHODS: 125 patients treated with an acute respiratory infection in the emergency department of the University Hospital Regensburg were analyzed. These patients were divided into a COVID-19 cohort (n = 91) and a cohort with infections not caused by severe acute respiratory syndrome-coronavirus-2 (n = 34). NT-proBNP was determined from serum and fresh urine samples collected in the emergency department. Clinical endpoints were the development of AKI and a composite one consisting of AKI, intensive care unit admission, and in-hospital death. RESULTS: 11 (12.1%) COVID-19 patients developed AKI during hospitalization, whereas 15 (16.5%) reached the composite endpoint. Urinary NT-proBNP was significantly elevated in COVID-19 patients who suffered AKI or reached the composite endpoint (each p < 0.005). In a multivariate regression analysis adjusted for age, chronic kidney disease, chronic heart failure, and arterial hypertension, urinary NT-proBNP was identified as independent predictor of AKI (p = 0.017, OR = 3.91 [CI: 1.28-11.97] per standard deviation [SD]), as well as of the composite endpoint (p = 0.026, OR 2.66 [CI: 1.13-6.28] per SD). CONCLUSION: Urinary NT-proBNP might help identify patients at risk for AKI and severe disease progression in COVID-19.

SARS-CoV-2 infects human cardiomyocytes promoted by inflammation and oxidative stress.

INTRODUCTION: The respiratory illness triggered by severe acute respiratory syndrome virus-2 (SARS-CoV-2) is often particularly serious or fatal amongst patients with pre-existing heart conditions. Although the mechanisms underlying SARS-CoV-2-related cardiac damage remain elusive, inflammation (i.e. 'cytokine storm') and oxidative stress are likely involved. METHODS AND RESULTS: Here we sought to determine: 1) if cardiomyocytes are targeted by SARS-CoV-2 and 2) how inflammation and oxidative stress promote the viral entry into cardiac cells. We analysed pro-inflammatory and oxidative stress and its impact on virus entry and virus-associated cardiac damage from SARS-CoV-2 infected patients and compared it to left ventricular myocardial tissues obtained from non-infected transplanted hearts either from end stage heart failure or non-failing hearts (donor group). We found that neuropilin-1 potentiates SARS-CoV-2 entry into human cardiomyocytes, a phenomenon driven by inflammatory and oxidant signals. These changes accounted for increased proteases activity and apoptotic markers thus leading to cell damage and apoptosis. CONCLUSION: This study provides new insights into the mechanisms of SARS-CoV-2 entry into the heart and defines promising targets for antiviral interventions for COVID-19 patients with pre-existing heart conditions or patients with co-morbidities.

Enhanced Cardiac CaMKII Oxidation and CaMKII-Dependent SR Ca Leak in Patients with Sleep-Disordered Breathing.

BACKGROUND: Sleep-disordered breathing (SDB) is associated with increased oxidant generation. Oxidized Ca/calmodulin kinase II (CaMKII) can contribute to atrial arrhythmias by the stimulation of sarcoplasmic reticulum Ca release events, i.e., Ca sparks. METHODS: We prospectively enrolled 39 patients undergoing cardiac surgery to screen for SDB and collected right atrial appendage biopsies. RESULTS: SDB was diagnosed in 14 patients (36%). SDB patients had significantly increased levels of oxidized and activated CaMKII (assessed by Western blotting/specific pulldown). Moreover, SDB patients showed a significant increase in Ca spark frequency (CaSpF measured by confocal microscopy) compared with control subjects. CaSpF was 3.58 ± 0.75 (SDB) vs. 2.49 ± 0.84 (no SDB) 1/100 µm-1s-1 (p < 0.05). In linear multivariable regression models, SDB severity was independently associated with increased CaSpF (B [95%CI]: 0.05 [0.03; 0.07], p < 0.001) after adjusting for important comorbidities. Interestingly, 30 min exposure to the CaMKII inhibitor autocamtide-2 related autoinhibitory peptide normalized the increased CaSpF and eliminated the association between SDB and CaSpF (B [95%CI]: 0.01 [-0.1; 0.03], p = 0.387). CONCLUSIONS: Patients with SDB have increased CaMKII oxidation/activation and increased CaMKII-dependent CaSpF in the atrial myocardium, independent of major clinical confounders, which may be a novel target for treatment of atrial arrhythmias in SDB.

Cardiac Fibrosis Is a Risk Factor for Severe COVID-19.

Increased left ventricular fibrosis has been reported in patients hospitalized with coronavirus disease 2019 (COVID-19). It is unclear whether this fibrosis is a consequence of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection or a risk factor for severe disease progression. We observed increased fibrosis in the left ventricular myocardium of deceased COVID-19 patients, compared with matched controls. We also detected increased mRNA levels of soluble interleukin-1 receptor-like 1 (sIL1-RL1) and transforming growth factor ß1 (TGF-ß1) in the left ventricular myocardium of deceased COVID-19 patients. Biochemical analysis of blood sampled from patients admitted to the emergency department (ED) with COVID-19 revealed highly elevated levels of TGF-ß1 mRNA in these patients compared to controls. Left ventricular strain measured by echocardiography as a marker of pre-existing cardiac fibrosis correlated strongly with blood TGF-ß1 mRNA levels and predicted disease severity in COVID-19 patients. In the left ventricular myocardium and lungs of COVID-19 patients, we found increased neuropilin-1 (NRP-1) RNA levels, which correlated strongly with the prevalence of pulmonary SARS-CoV-2 nucleocapsid. Cardiac and pulmonary fibrosis may therefore predispose these patients to increased cellular viral entry in the lung, which may explain the worse clinical outcome observed in our cohort. Our study demonstrates that patients at risk of clinical deterioration can be identified early by echocardiographic strain analysis and quantification of blood TGF-ß1 mRNA performed at the time of first medical contact.

Detrimental proarrhythmogenic interaction of Ca2+/calmodulin-dependent protein kinase II and NaV1.8 in heart failure.

An interplay between Ca2+/calmodulin-dependent protein kinase IIδc (CaMKIIδc) and late Na+ current (INaL) is known to induce arrhythmias in the failing heart. Here, we elucidate the role of the sodium channel isoform NaV1.8 for CaMKIIδc-dependent proarrhythmia. In a CRISPR-Cas9-generated human iPSC-cardiomyocyte homozygous knock-out of NaV1.8, we demonstrate that NaV1.8 contributes to INaL formation. In addition, we reveal a direct interaction between NaV1.8 and CaMKIIδc in cardiomyocytes isolated from patients with heart failure (HF). Using specific blockers of NaV1.8 and CaMKIIδc, we show that NaV1.8-driven INaL is CaMKIIδc-dependent and that NaV1.8-inhibtion reduces diastolic SR-Ca2+ leak in human failing cardiomyocytes. Moreover, increased mortality of CaMKIIδc-overexpressing HF mice is reduced when a NaV1.8 knock-out is introduced. Cellular and in vivo experiments reveal reduced ventricular arrhythmias without changes in HF progression. Our work therefore identifies a proarrhythmic CaMKIIδc downstream target which may constitute a prognostic and antiarrhythmic strategy.

Enhanced Heart Failure in Redox-Dead Cys17Ser PKARIα Knock-In Mice.

Background PKARIα (protein kinase A type I-α regulatory subunit) is redox-active independent of its physiologic agonist cAMP. However, it is unknown whether this alternative mechanism of PKARIα activation may be of relevance to cardiac excitation-contraction coupling. Methods and Results We used a redox-dead transgenic mouse model with homozygous knock-in replacement of redox-sensitive cysteine 17 with serine within the regulatory subunits of PKARIα (KI). Reactive oxygen species were acutely evoked by exposure of isolated cardiac myocytes to AngII (angiotensin II, 1 µmol/L). The long-term relevance of oxidized PKARIα was investigated in KI mice and their wild-type (WT) littermates following transverse aortic constriction (TAC). AngII increased reactive oxygen species in both groups but with RIα dimer formation in WT only. AngII induced translocation of PKARI to the cell membrane and resulted in protein kinase A-dependent stimulation of ICa (L-type Ca current) in WT with no effect in KI myocytes. Consequently, Ca transients were reduced in KI myocytes as compared with WT cells following acute AngII exposure. Transverse aortic constriction-related reactive oxygen species formation resulted in RIα oxidation in WT but not in KI mice. Within 6 weeks after TAC, KI mice showed an enhanced deterioration of contractile function and impaired survival compared with WT. In accordance, compared with WT, ventricular myocytes from failing KI mice displayed significantly reduced Ca transient amplitudes and lack of ICa stimulation. Conversely, direct pharmacological stimulation of ICa using Bay K8644 rescued Ca transients in AngII-treated KI myocytes and contractile function in failing KI mice in vivo. Conclusions Oxidative activation of PKARIα with subsequent stimulation of ICa preserves cardiac function in the setting of acute and chronic oxidative stress.

Beneficial effect of voluntary physical exercise in Plakophilin2 transgenic mice.

Arrhythmogenic right ventricular cardiomyopathy is a hereditary, rare disease with an increased risk for sudden cardiac death. The disease-causing mutations are located within the desmosomal complex and the highest incidence is found in plakophilin2. However, there are other factors playing a role for the disease progression unrelated to the genotype such as inflammation or exercise. Competitive sports have been identified as risk factor, but the type and extend of physical activity as cofactor for arrhythmogenesis remains under debate. We thus studied the effect of light voluntary exercise on cardiac health in a mouse model. Mice with a heterozygous PKP2 loss-of-function mutation were given the option to exercise in a running wheel which was monitored 24 h/d. We analyzed structural and functional development in vivo by echocardiography which revealed that neither the genotype nor the exercise caused any significant structural changes. Ejection fraction and fractional shortening were not influenced by the genotype itself, but exercise did cause a drop in both parameters after 8 weeks, which returned to normal after 16 weeks of training. The electrophysiological analysis revealed that the arrhythmogenic potential was slightly higher in heterozygous animals (50% vs 18% in wt littermates) and that an additional stressor (isoprenaline) did not lead to an increase of arrhythmogenic events pre run or after 8 weeks of running but the vulnerability was increased after 16 weeks. Exercise-induced alterations in Ca handling and contractility of isolated myocytes were mostly abolished in heterozygous animals. No fibrofatty replacements or rearrangement of gap junctions could be observed. Taken together we could show that light voluntary exercise can cause a transient aggravation of the mutation-induced phenotype which is abolished after long term exercise indicating a beneficial effect of long term light exercise.

Kidney injury molecule-1: potential biomarker of acute kidney injury and disease severity in patients with COVID-19.

AIMS: The aim of the current study was to evaluate whether tubular markers kidney injury molecule-1 (KIM-1) and N-acetyl-ß-glucosaminidase (NAG) are related to acute kidney injury (AKI) and severe disease in patients with COVID-19. METHODS AND RESULTS: In this prospective observational clinical trial we examined a cohort of 80 patients with proof of acute respiratory infection and divided them into a COVID-19 cohort (n = 54) and a control cohort (n = 26). KIM-1 and NAG were measured from urine samples collected in the emergency department. We assessed the development of AKI, admission to the intensive care unit (ICU) and intrahospital death as clinical endpoints. Urinary KIM-1 and NAG were not significantly different between patients with SARS-CoV-2 and those with other respiratory infections (each p = n.s.). Eight patients from the COVID-19 cohort and five of the non-COVID-19-patients suffered from acute kidney injury during their stay. Nine COVID-19 patients and two non-COVID-19 patients were admitted to the ICU. KIM-1 was significantly elevated in COVID-19 patients with, compared to those without AKI (p = 0.005), as opposed to NAG and creatinine (each p = n.s.). Furthermore, KIM-1 was significantly elevated in the patients with COVID-19 that had to be transferred to the ICU (p = 0.015), in contrast to NAG and creatinine (each p = n.s.). CONCLUSION: Assessing KIM-1 in patients with COVID-19 might provide additional value in recognizing AKI at an early stage of disease. Further, KIM-1 might indicate higher risk for clinical deterioration as displayed by admission to the ICU.

Loss of CASK Accelerates Heart Failure Development.

[Figure: see text].

Decreased GLUT1/NHE1 RNA expression in whole blood predicts disease severity in patients with COVID-19.

AIMS: We aimed to assess whether expression of whole-blood RNA of sodium proton exchanger 1 (NHE1) and glucose transporter 1 (GLUT1) is associated with COVID-19 infection and outcome in patients presenting to the emergency department with respiratory infections. Furthermore, we investigated NHE1 and GLUT1 expression in the myocardium of deceased COVID-19 patients. METHODS AND RESULTS: Whole-blood quantitative assessment of NHE1 and GLUT1 RNA was performed using quantitative PCR in patients with respiratory infection upon first contact in the emergency department and subsequently stratified by SARS-CoV-2 infection status. Assessment of NHE1 and GLUT1 RNA using PCR was also performed in left ventricular myocardium of deceased COVID-19 patients. NHE1 expression is up-regulated in whole blood of patients with COVID-19 compared with other respiratory infections at first medical contact in the emergency department (control: 0.0021 ± 0.0002, COVID-19: 0.0031 ± 0.0003, P = 0.01). The ratio of GLUT1 to NHE1 is significantly decreased in the blood of COVID-19 patients who are subsequently intubated and/or die (severe disease) compared with patients with moderate disease (moderate disease: 0.497 ± 0.083 vs. severe disease: 0.294 ± 0.0336, P = 0.036). This ratio is even further decreased in the myocardium of patients who deceased from COVID-19 in comparison with the myocardium of non-infected donors. CONCLUSIONS: NHE1 and GLUT1 may be critically involved in the disease progression of SARS-CoV-2 infection. We show here that SARS-CoV-2 infection critically disturbs ion channel expression in the heart. A decreased ratio of GLUT1/NHE1 could potentially serve as a biomarker for disease severity in patients with COVID-19.

Long-term effects of empagliflozin on excitation-contraction-coupling in human induced pluripotent stem cell cardiomyocytes.

The SGLT2 inhibitor empagliflozin improved cardiovascular outcomes in patients with diabetes. As the cardiac mechanisms remain elusive, we investigated the long-term effects (up to 2 months) of empagliflozin on excitation-contraction (EC)-coupling in human cardiomyocytes derived from induced pluripotent stem cells (iPSC-CM) in a blinded manner. IPSC from 3 donors, differentiated into pure iPSC-CM (4 differentiations), were treated with a clinically relevant concentration of empagliflozin (0.5 µmol/l) or vehicle control. Treatment, data acquisition, and analysis were conducted externally blinded. Epifluorescence microscopy measurements in iPSC-CM showed that empagliflozin has neutral effects on Ca2+ transient amplitude, diastolic Ca2+ levels, Ca2+ transient kinetics, or sarcoplasmic Ca2+ load after 2 weeks or 8 weeks of treatment. Confocal microscopy determining possible effects on proarrhythmogenic diastolic Ca2+ release events showed that in iPSC-CM, Ca2+ spark frequency and leak was not altered after chronic treatment with empagliflozin. Finally, in patch-clamp experiments, empagliflozin did not change action potential duration, amplitude, or resting membrane potential compared with vehicle control after long-term treatment. Next-generation RNA sequencing (NGS) and mapped transcriptome profiles of iPSC-CMs untreated and treated with empagliflozin for 8 weeks showed no differentially expressed EC-coupling genes. In line with NGS data, Western blots indicate that empagliflozin has negligible effects on key EC-coupling proteins. In this blinded study, direct treatment of iPSC-CM with empagliflozin for a clinically relevant duration of 2 months did not influence cardiomyocyte EC-coupling and electrophysiology. Therefore, it is likely that other mechanisms independent of cardiomyocyte EC-coupling are responsible for the beneficial treatment effect of empagliflozin. KEY MESSAGES: This blinded study investigated the clinically relevant long-term effects (up to 2 months) of empagliflozin on cardiomyocyte excitation-contraction (EC)-coupling. Human cardiomyocytes derived from induced pluripotent stem cells (iPSC-CM) were used to study a human model including a high repetition number of experiments. Empagliflozin has neutral effects on cardiomyocyte Ca2+ transients, sarcoplasmic Ca2+ load, and diastolic sarcoplasmic Ca2+ leak. In patch-clamp experiments, empagliflozin did not change the action potential. Next-generation RNA sequencing, mapped transcriptome profiles, and Western blots of iPSC-CM untreated and treated with empagliflozin showed no differentially expressed EC-coupling candidates.

The oral Ca/calmodulin-dependent kinase II inhibitor RA608 improves contractile function and prevents arrhythmias in heart failure.

AIMS: Excessive activation of Ca/calmodulin-dependent kinase II (CaMKII) is of critical importance in heart failure (HF) and atrial fibrillation. Unfortunately, lack of selectivity, specificity, and bioavailability have slowed down development of inhibitors for clinical use. We investigated a novel CaMKIIδ/CaMKIIÉ£-selective, ATP-competitive, orally available CaMKII inhibitor (RA608) on right atrial biopsies of 119 patients undergoing heart surgery. Furthermore, we evaluated its oral efficacy to prevent deterioration of HF in mice after transverse aortic constriction (TAC). METHODS AND RESULTS: In human atrial cardiomyocytes and trabeculae, respectively, RA608 significantly reduced sarcoplasmic reticulum Ca leak, reduced diastolic tension, and increased sarcoplasmic reticulum Ca content. Patch-clamp recordings confirmed the safety of RA608 in human cardiomyocytes. C57BL6/J mice were subjected to TAC, and left ventricular function was monitored by echocardiography. Two weeks after TAC, RA608 was administered by oral gavage for 7 days. Oral RA608 treatment prevented deterioration of ejection fraction. At 3 weeks after TAC, ejection fraction was 46.1 ± 3.7% (RA608) vs. 34.9 ± 2.6% (vehicle), n = 9 vs. n = 12, P < 0.05, ANOVA, which correlated with significantly less CaMKII autophosphorylation at threonine 287. Moreover, a single oral dose significantly reduced inducibility of atrial and ventricular arrhythmias in CaMKIIδ transgenic mice 4 h after administration. Atrial fibrillation was induced in 6/6 mice for vehicle vs. 1/7 for RA608, P < 0.05, 'n - 1' χ2 test. Ventricular tachycardia was induced in 6/7 for vehicle vs. 2/7 for RA608, P < 0.05, 'n - 1' χ2 test. CONCLUSIONS: RA608 is the first orally administrable CaMKII inhibitor with potent efficacy in human myocytes. Moreover, oral administration potently inhibits arrhythmogenesis and attenuates HF development in mice in vivo.

Dantrolene reduces CaMKIIδC-mediated atrial arrhythmias.

AIMS: In atrial fibrillation (AF), an increased diastolic Ca2+ leak from the sarcoplasmic reticulum (SR) mediated by calcium/calmodulin-dependent-protein-kinaseIIδC (CaMKII) can serve as a substrate for arrhythmia induction and persistence. Dantrolene has been shown to stabilize the cardiac ryanodine-receptor. This study investigated the effects of dantrolene on arrhythmogenesis in human and mouse atria with enhanced CaMKII activity. METHODS AND RESULTS: Human atrial cardiomyocytes (CMs) were isolated from patients with AF. To investigate CaMKII-mediated arrhythmogenesis, atrial CMs from mice overexpressing CaMKIIδC (TG) and the respective wildtype (WT) were studied using confocal microscopy (Fluo-4), patch-clamp technique, and in vivo atrial catheter-based burst stimulations. Dantrolene potently reduced Ca2+ spark frequency (CaSpF) and diastolic SR Ca2+ leak in AF CMs. Additional CaMKII inhibition did not further reduce CaSpF or leak compared to dantrolene alone. While the increased SR CaSpF and leak in TG mice were reduced by dantrolene, no effects could be detected in WT. Dantrolene also potently reduced the pathologically enhanced frequency of diastolic SR Ca2+ waves in TG without having effects in WT. As an increased diastolic SR Ca2+ release can induce a depolarizing transient inward current, we could demonstrate that the incidence of afterdepolarizations in TG, but not in WT, mice was significantly diminished in the presence of dantrolene. To translate these findings into an in vivo situation we could show that dantrolene strongly suppressed the inducibility of AF in vivo in TG mice. CONCLUSION: Dantrolene reduces CaMKII-mediated atrial arrhythmogenesis and may therefore constitute an interesting antiarrhythmic drug for treating patients with atrial arrhythmias driven by an enhanced CaMKII activity, such as AF.