Cardioprotective effects of dantrolene in doxorubicin-induced cardiomyopathy in mice

Ryanodine receptor 2 inhibition reduces dispersion of cardiac repolarization, improves contractile function, and prevents sudden arrhythmic death in failing hearts

Sudden cardiac death (SCD) from ventricular tachycardia/fibrillation (VT/VF) is a leading cause of death, but current therapies are limited. Despite extensive research on drugs targeting sarcolemmal ion channels, none have proven sufficiently effective for preventing SCD. Sarcoplasmic ryanodine receptor 2 (RyR2) Ca2+ release channels, the downstream effectors of sarcolemmal ion channels, are underexplored in this context. Recent evidence implicates reactive oxygen species (ROS)-mediated oxidation and hyperactivity of RyR2s in the pathophysiology of SCD. We tested the hypothesis that RyR2 inhibition of failing arrhythmogenic hearts reduces sarcoplasmic Ca2+ leak and repolarization lability, mitigates VT/VF/SCD and improves contractile function. We used a guinea pig model that replicates key clinical aspects of human nonischemic HF, such as a prolonged QT interval, a high prevalence of spontaneous arrhythmic SCD, and profound Ca2+ leak via a hyperactive RyR2. HF animals were randomized to receive dantrolene (DS) or placebo in early or chronic HF. We assessed the incidence of VT/VF and SCD (primary outcome), ECG heart rate and QT variability, echocardiographic left ventricular (LV) structure and function, immunohistochemical LV fibrosis, and sarcoplasmic RyR2 oxidation. DS treatment prevented VT/VF and SCD by decreasing dispersion of repolarization and ventricular arrhythmias. Compared to placebo, DS lowered resting heart rate, preserved chronotropic competency during transient β-adrenergic challenge, and improved heart rate variability and cardiac function. Inhibition of RyR2 hyperactivity with dantrolene mitigates the vicious cycle of sarcoplasmic Ca2+ leak-induced increases in diastolic Ca2+ and ROS-mediated RyR2 oxidation, thereby reducing repolarization lability and protecting against VT/VF/SCD. Moreover, the consequent increase in sarcoplasmic Ca2+ load improves contractile function. These potentially life-saving effects of RyR2 inhibition warrant further investigation, such as clinical studies of repurposing dantrolene as a potential new therapy for heart failure and/or SCD.

Restoration of calcium release synchrony: A novel target for heart failure and ventricular arrhythmia

Myocardial calcium (Ca2+) signaling plays a crucial role in contractile function and membrane electrophysiology. An abnormal myocardial Ca2+ transient is linked to heart failure and ventricular arrhythmias. At the subcellular level, the synchronous release of Ca2+ sparks from sarcoplasmic Ca2+ release units determines the configuration and amplitude of the global Ca2+ transient. This narrative review evaluates the role of aberrant Ca2+ release synchrony in the pathophysiology of cardiomyopathies and ventricular arrhythmias. The potential therapeutic benefits of restoration of Ca2+ release synchrony in heart failure and ventricular arrhythmias are also discussed.

Cellular shortening and calcium dynamics are improved by noisy stimulus in a model of cardiomyopathy

Noise is present in cell biology. The capability of cells to respond to noisy environment have become essential. This study aimed to investigate whether noise can enhance the contractile response and Ca2+ handling in cardiomyocytes from a cardiomyopathy model. Experiments were conducted in an experimental setup with Gaussian white noise, frequency, and amplitude control to stimulate myocytes. Cell shortening, maximal shortening velocity, time to peak shortening, and time to half relaxation variables were recorded to cell shortening. Ca2+ transient amplitude and raise rate variables were registered to measure Ca2+ transients. Our results for cell shortening, Ca2+ transient amplitude, and raise rate suggest that cell response improve when myocytes are noise stimulated. Also, cell shortening, maximal shortening velocity, Ca2+ transient amplitude, and raise improves in control cells. Altogether, these findings suggest novel characteristics in how cells improve their response in a noisy environment.

Molecular Aspects Implicated in Dantrolene Selectivity with Respect to Ryanodine Receptor Isoforms

Dantrolene is an intra-cellularly acting skeletal muscle relaxant used for the treatment of the rare genetic disorder, malignant hyperthermia (MH). In most cases, MH susceptibility is caused by dysfunction of the skeletal ryanodine receptor (RyR1) harboring one of nearly 230 single-point MH mutations. The therapeutic effect of dantrolene is the result of a direct inhibitory action on the RyR1 channel, thus suppressing aberrant Ca2+ release from the sarcoplasmic reticulum. Despite the almost identical dantrolene-binding sequence exits in all three mammalian RyR isoforms, dantrolene appears to be an isoform-selective inhibitor. Whereas RyR1 and RyR3 channels are competent to bind dantrolene, the RyR2 channel, predominantly expressed in the heart, is unresponsive. However, a large body of evidence suggests that the RyR2 channel becomes sensitive to dantrolene-mediated inhibition under certain pathological conditions. Although a consistent picture of the dantrolene effect emerges from in vivo studies, in vitro results are often contradictory. Hence, our goal in this perspective is to provide the best possible clues to the molecular mechanism of dantrolene’s action on RyR isoforms by identifying and discussing potential sources of conflicting results, mainly coming from cell-free experiments. Moreover, we propose that, specifically in the case of the RyR2 channel, its phosphorylation could be implicated in acquiring the channel responsiveness to dantrolene inhibition, interpreting functional findings in the structural context.

Dantrolene and ryanodine receptors in COVID-19: The daunting task and neglected warden

Dantrolene (DTN) is a ryanodine receptor (RyR) antagonist that inhibits Ca²⁺ release from stores in the sarcoplasmic reticulum. DTN is mainly used in the management of malignant hyperthermia. RyRs are highly expressed in immune cells and are involved in different viral infections, including severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), because Ca²⁺ is necessary for viral replication, maturation and release. DTN can inhibit the proliferation of SARS-CoV-2, indicating its potential role in reducing entry and pathogenesis of SARS-CoV-2. DTN may increase clearance of SARS-CoV-2 and promote coronavirus disease 2019 (COVID-19) recovery by shortening the period of infection. DTN inhibits N-methyl-D-aspartate (NMDA) mediated platelets aggregations and thrombosis. Therefore, DTN may inhibit thrombosis and coagulopathy in COVID-19 through suppression of platelet NMDA receptors. Moreover, DTN has a neuroprotective effect against SARS-CoV-2 infection-induced brain injury through modulation of NMDA receptors, which are involved in excitotoxicity, neuronal injury and the development of neuropsychiatric disorders. In conclusion, DTN by inhibiting RyRs may attenuate inflammatory disorders in SARS-CoV-2 infection and associated cardio-pulmonary complications. Therefore, DNT could be a promising drug therapy against COVID-19. Preclinical and clinical studies are warranted in this regards.

Statins Protect Against Early Stages of Doxorubicin-induced Cardiotoxicity Through the Regulation of Akt Signaling and SERCA2

Background

Doxorubicin-induced cardiomyopathy (DICM) is one of the complications that can limit treatment for a significant number of cancer patients. In animal models, the administration of statins can prevent the development of DICM. Therefore, the use of statins with anthracyclines potentially could enable cancer patients to complete their chemotherapy without added cardiotoxicity. The precise mechanism mediating the cardioprotection is not well understood. The purpose of this study is to determine the molecular mechanism by which rosuvastatin confers cardioprotection in a mouse model of DICM.

Methods

Rosuvastatin was intraperitoneally administered into adult male mice at 100 μg/kg daily for 7 days, followed by a single intraperitoneal doxorubicin injection at 10 mg/kg. Animals continued to receive rosuvastatin daily for an additional 14 days. Cardiac function was assessed by echocardiography. Optical calcium mapping was performed on retrograde Langendorff perfused isolated hearts. Ventricular tissue samples were analyzed by immunofluorescence microscopy, Western blotting, and quantitative polymerase chain reaction.

Results

Exposure to doxorubicin resulted in significantly reduced fractional shortening (27.4% ± 1.11% vs 40% ± 5.8% in controls; P < 0.001) and re-expression of the fetal gene program. However, we found no evidence of maladaptive cardiac hypertrophy or adverse ventricular remodeling in mice exposed to this dose of doxorubicin. In contrast, rosuvastatin-doxorubicin-treated mice maintained their cardiac function (39% ± 1.26%; P < 0.001). Mechanistically, the effect of rosuvastatin was associated with activation of Akt and phosphorylation of phospholamban with preserved sarcoplasmic/endoplasmic reticulum Ca²⁺ transporting 2 (SERCA2)-mediated Ca²⁺ reuptake. These effects occurred independently of perturbations in ryanodine receptor 2 function.

Conclusions

Rosuvastatin counteracts the cardiotoxic effects of doxorubicin by directly targeting sarcoplasmic calcium cycling.

Rhynchophylline Regulates Calcium Homeostasis by Antagonizing Ryanodine Receptor 2 Phosphorylation to Improve Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is a serious complication of diabetes that can lead to heart failure and death, for which there is no effective treatment. Rhynchophylline (Rhy) is the main effective component of the Chinese herbal medicine Uncaria rhynchophylla, which mainly acts on the cardiovascular and nervous systems. However, its role in protecting against DCM remains unexplored. The present study sought to reveal the mechanism of Rhy in improving type 2 diabetes mellitus (T2DM) myocardial lesions from the perspective of regulating calcium homeostasis in cardiomyocytes. We prepared a mouse model of T2DM using a high-fat diet combined with low doses of streptozotocin. The T2DM mice were given 40 mg/kg of Rhy for 8 weeks. The results showed that Rhy can attenuate cardiac pathological changes, slow down the heart rate, decrease serum cardiac enzyme levels, reduce cardiomyocyte apoptosis, enhance cardiomyocyte contractility, and raise the calcium transient amplitude in T2DM mice. Further, Rhy downregulated the phosphorylation level of ryanodine receptor 2, upregulated the phosphorylation level of phospholamban, protected mitochondrial structure and function, and increased adenosine triphosphate levels in the cardiac tissue of T2DM mice. Our results demonstrated that Rhy may protect against myocardial damage in T2DM mice and promote cardiomyocyte contraction, and its mechanism of action seems to be related to the regulation of intracellular calcium homeostasis.