Deficiency of mitochondrial calcium uniporter abrogates iron overload-induced cardiac dysfunction by reducing ferroptosis.

Iron overload associated cardiac dysfunction remains a significant clinical challenge whose underlying mechanism(s) have yet to be defined. We aim to evaluate the involvement of the mitochondrial Ca2+ uniporter (MCU) in cardiac dysfunction and determine its role in the occurrence of ferroptosis. Iron overload was established in control (MCUfl/fl) and conditional MCU knockout (MCUfl/fl-MCM) mice. LV function was reduced by chronic iron loading in MCUfl/fl mice, but not in MCUfl/fl-MCM mice. The level of mitochondrial iron and reactive oxygen species were increased and mitochondrial membrane potential and spare respiratory capacity (SRC) were reduced in MCUfl/fl cardiomyocytes, but not in MCUfl/fl-MCM cardiomyocytes. After iron loading, lipid oxidation levels were increased in MCUfl/fl, but not in MCUfl/fl-MCM hearts. Ferrostatin-1, a selective ferroptosis inhibitor, reduced lipid peroxidation and maintained LV function in vivo after chronic iron treatment in MCUfl/fl hearts. Isolated cardiomyocytes from MCUfl/fl mice demonstrated ferroptosis after acute iron treatment. Moreover, Ca2+ transient amplitude and cell contractility were both significantly reduced in isolated cardiomyocytes from chronically Fe treated MCUfl/fl hearts. However, ferroptosis was not induced in cardiomyocytes from MCUfl/fl-MCM hearts nor was there a reduction in Ca2+ transient amplitude or cardiomyocyte contractility. We conclude that mitochondrial iron uptake is dependent on MCU, which plays an essential role in causing mitochondrial dysfunction and ferroptosis under iron overload conditions in the heart. Cardiac-specific deficiency of MCU prevents the development of ferroptosis and iron overload-induced cardiac dysfunction.

Acetylcholinesterase inhibitor ameliorates doxorubicin-induced cardiotoxicity through reducing RIP1-mediated necroptosis.

Doxorubicin is an effective chemotherapeutic drug, but causes cardiotoxicity which limits its use. Oxidative stress, mitochondrial dysfunction, and inflammation are closely implicated in doxorubicin-induced cardiotoxicity (DIC). Necroptosis, a new form of programmed cell death, was also upregulated by doxorubicin, leading to cardiomyocyte death and cardiac dysfunction. Donepezil, an acetylcholinesterase inhibitor, exerted cardioprotection against various heart diseases. However, its cardioprotective effects in DIC are still unknown. We hypothesized that donepezil reduces reactive oxygen species (ROS) production, mitochondrial dysfunction, mitochondrial dynamics imbalance, necroptosis, and apoptosis in DIC rats. Male Wistar rats were assigned to receive either normal saline solution (n = 8) or doxorubicin (3 mg/kg, 6 doses, n = 16) via intraperitoneal injection. The doxorubicin-treated rats were further subdivided to receive either sterile drinking water (n = 8) or donepezil (5 mg/kg/day, p.o., n = 8) for 30 days. At the end of the experiment, the left ventricular (LV) function was determined. Serum and heart tissue were collected to evaluate histological and biochemical parameters. Doxorubicin-treated rats exhibited higher levels of inflammatory cytokines and ROS production. Doxorubicin also impaired mitochondrial function, mitochondrial dynamics balance, mitophagy, and autophagy, which culminated in apoptosis. Furthermore, doxorubicin increased necroptosis as evidenced by increased phosphorylation of receptor-interacting protein kinase 1, receptor-interacting protein kinase 3, and mixed-lineage kinase domain-like. All of these mechanisms led to LV dysfunction. Interestingly, donepezil alleviated mitochondrial injury, mitophagy, autophagy, and cardiomyocyte death, leading to improved LV function in DIC. In conclusion, donepezil attenuated DIC-induced LV dysfunction by reducing mitochondrial damage, mitophagy, autophagy, apoptosis, and necroptosis.

Calcium and Heart Failure: How Did We Get Here and Where Are We Going?

The occurrence and prevalence of heart failure remain high in the United States as well as globally. One person dies every 30 s from heart disease. Recognizing the importance of heart failure, clinicians and scientists have sought better therapeutic strategies and even cures for end-stage heart failure. This exploration has resulted in many failed clinical trials testing novel classes of pharmaceutical drugs and even gene therapy. As a result, along the way, there have been paradigm shifts toward and away from differing therapeutic approaches. The continued prevalence of death from heart failure, however, clearly demonstrates that the heart is not simply a pump and instead forces us to consider the complexity of simplicity in the pathophysiology of heart failure and reinforces the need to discover new therapeutic approaches.

The mechanistic insights of the arrhythmogenic effect of trastuzumab.

Cardiovascular diseases and cancers are the leading causes of deaths globally, and an increasing proportion of cancer patients is suffering from cardiac adverse effects of chemotherapeutic drugs. Trastuzumab, a monoclonal antibody that inhibits the activity of the human epidermal growth factor receptor 2 (HER2), is a potent targeted therapy for HER2-positive malignancies. Despite the impressive antineoplastic efficacy, the cardiotoxicity of trastuzumab frequently limits its use. Trastuzumab-induced cardiac contractile dysfunction has been extensively studied, yet the electrophysiological side effect of trastuzumab remains poorly characterized. Growing evidence from basic and clinical studies supports the link between trastuzumab treatment and arrhythmias. This review comprehensively summarizes relevant information from those reports, discusses their limitations, and suggests future research directions. We aim to encourage further investigations that will provide valuable insights to devise cardioprotective strategies against trastuzumab-induced cardiotoxicity.

Activation of TRPC (Transient Receptor Potential Canonical) Channel Currents in Iron Overloaded Cardiac Myocytes.

BACKGROUND: Arrhythmias and heart failure are common cardiac complications leading to substantial morbidity and mortality in patients with hemochromatosis, yet mechanistic insights remain incomplete. We investigated the effects of iron (Fe) on electrophysiological properties and intracellular Ca2+ (Ca2+i) handling in mouse left ventricular cardiomyocytes. METHODS: Cardiomyocytes were isolated from the left ventricle of mouse hearts and were superfused with Fe3+/8-hydroxyquinoline complex (5-100 µM). Membrane potential and ionic currents including TRPC (transient receptor potential canonical) were recorded using the patch-clamp technique. Ca2+i was evaluated by using Fluo-4. Cell contraction was measured with a video-based edge detection system. The role of TRPCs in the genesis of arrhythmias was also investigated by using a mathematical model of a mouse ventricular myocyte with the incorporation of the TRPC component. RESULTS: We observed prolongation of the action potential duration and induction of early and delayed afterdepolarizations in myocytes superfused with 15 µmol/L Fe3+/8-hydroxyquinoline complex. Iron treatment decreased the peak amplitude of the L-type Ca2+ current and total K+ current, altered Ca2+i dynamics, and decreased cell contractility. During the final phase of Fe treatment, sustained Ca2+i waves and repolarization failure occurred and ventricular cells became unexcitable. Gadolinium abolished Ca2+i waves and restored the resting membrane potential to the normal range. The involvement of TRPC activation was confirmed by TRPC channel current recordings in the absence or presence of functional TRPC channel antibodies. Computer modeling captured the same action potential and Ca2+i dynamics and provided additional mechanistic insights. CONCLUSIONS: We conclude that iron overload induces cardiac dysfunction that is associated with TRPC channel activation and alterations in membrane potential and Ca2+i dynamics.

Silencing of lipocalin-2 improves cardiomyocyte viability under iron overload conditions via decreasing mitochondrial dysfunction and apoptosis.

This study aimed to investigate the mechanistic roles of LCN-2 and LCN-2 receptors (LCN-2R) as iron transporters in cardiomyocytes under iron overload condition. H9c2 cardiomyocytes were treated with either LCN-2 small interfering RNA (siRNA) or LCN-2R siRNA or L-type or T-type calcium channel (LTCC or TTCC) blockers, or iron chelator deferiprone (DFP). After the treatments, the cells were exposed to Fe3+ or Fe2+ , after that biological parameters were determined. Silencing of lipocalin-2 or its receptor improved cardiomyocyte viability via decreasing iron uptake, mitochondrial fission, mitophagy and cleaved caspase-3 only in the Fe3+ overload condition. In contrast, treatments with LTCC blocker and TTCC blocker showed beneficial effects on those parameters only in conditions of Fe2+ overload. Treatment with DFP has been shown beneficial effects both in Fe2+ and Fe3+ overload condition. All of these findings suggested that LTCC and TTCC play crucial roles in the Fe2+ uptake, whereas LCN-2 and LCN-2R were essential for Fe3+ uptake into the cardiomyocytes under iron overload conditions.

The effects of iron overload on mitochondrial function, mitochondrial dynamics, and ferroptosis in cardiomyocytes.

Excessive iron accumulation in the heart can lead to iron overload cardiomyopathy (IOC), the leading cause of death in hemochromatosis patients. Current understanding regarding the mechanism by which iron overload causes a deterioration in cardiac performance, mitochondrial dysfunction, and impaired mitochondrial dynamics remains limited. Ferroptosis, a newly identified form of regulated cell death, has recently been revealed influencing the pathophysiological process of IOC. Nevertheless, the direct effect of cardiac iron overload on ferroptotic cell death is incompletely characterized. This review article comprehensively summarizes and discusses the effects of iron overload on cardiac mitochondrial function, cardiac mitochondrial dynamics, ferroptosis of cardiomyocytes, and left ventricular function in in vitro and in vivo reports. This review also provides relevant consistent and controversial information which can facilitate further mechanistic investigation into iron-induced cardiac dysfunction in the clinical setting in the near future.

Doxorubicin and its proarrhythmic effects: A comprehensive review of the evidence from experimental and clinical studies.

The cancer burden on health and socioeconomics remains exceedingly high, with more than ten million new cases reported worldwide in 2018. The financial cost of managing cancer patients has great economic impact on both an individual and societal levels. Currently, many chemotherapeutic agents are available to treat various malignancies. One of these agents is doxorubicin, which was isolated from Streptomyces peucetius in the 1960s. Doxorubicin is frequently administered in combination with other agents as a mainstay chemotherapeutic regimen in many settings, since there is well-documented evidence that it is effective in eliminating malignant cells. Doxorubicin exerts its anti-tumor properties through DNA intercalation and topoisomerase inhibition. It also contains a quinone moiety which is susceptible to redox reactions with certain intracellular molecules, thereby leading to the production of reactive oxygen species. The oxidative stress following doxorubicin exposure is responsible for its well-documented cardiotoxicity, impairing cardiac contractility, ultimately resulting in congestive heart failure. Despite the cumulative evidence noting its adverse effects on the heart, limited information is available regarding the mechanistic association between doxorubicin and cardiac arrhythmias. There is compelling evidence to suggest that doxorubicin also causes proarrhythmic effects. Several case reports and studies in cancer patients have attributed many arrhythmic events to doxorubicin, some of which are life-threatening such as complete heart block and ventricular fibrillation. In this review, reports regarding the potential arrhythmic complications associated with doxorubicin from previous studies investigating the effects of doxorubicin on cardiac electrophysiological properties are comprehensively summarized and discussed. Consistencies and controversial findings from in vitro, in vivo, ex vivo, and clinical studies are presented and mechanistic insights regarding the effects of doxorubicin are also discussed.

Combined iron chelator with N-acetylcysteine exerts the greatest effect on improving cardiac calcium homeostasis in iron-overloaded thalassemic mice.

The morbidity and mortality in thalassemia patients are predominantly caused by iron overload cardiomyopathy (IOC). Iron-induced cardiac intracellular Ca2+ ([Ca2+]i) dysregulation is among the core pathophysiological processes in IOC-related heart failure. Although cardioprotective roles of deferiprone (DFP) and N-acetylcysteine (NAC) have been reported, their effect on cardiac [Ca2+]i transients and Ca2+-regulatory protein expression in thalassemic mice is unknown. In the present study, iron overload condition was induced in wild-type (WT) and heterozygous ß-thalassemic (HT) mice by a high-iron diet. The iron-overloaded mice subsequently received a vehicle, DFP, NAC, or DFP plus NAC co-therapy. In both WT and HT iron-overloaded mice, DFP and NAC had similar efficacy in decreasing plasma non-transferrin-bound iron, decreasing cardiac iron concentration (CIC) and relieving systolic dysfunction. DFP plus NAC co-therapy, however, was better than the monotherapy in reducing CIC and restoring cardiac [Ca2+]i transient amplitude and rising rate. All regimens produced no change in cardiac Ca2+-regulatory protein expression. We provided the first evidence regarding the synergistic effect of combined iron chelator-antioxidant therapy on cardiac [Ca2+]i homeostasis in iron-overloaded thalassemic mice, with consistent improvement of cardiac contractility.

Cellular Electrophysiology of Iron-Overloaded Cardiomyocytes.

Iron, the most abundant transition metal element in the human body, plays an essential role in many physiological processes. However, without a physiologically active excretory pathway, iron is subject to strict homeostatic processes acting upon its absorption, storage, mobilization, and utilization. These intricate controls are perturbed in primary and secondary hemochromatoses, leading to a deposition of excess iron in multiple vital organs including the heart. Iron overload cardiomyopathy is the leading cause of mortality in patients with iron overload conditions. Apart from mechanical deterioration of the siderotic myocardium, arrhythmias reportedly contribute to a substantial portion of cardiac death associated with iron overload. Despite this significant impact, the cellular mechanisms of electrical disturbances in an iron-overloaded heart are still incompletely characterized. This review article focuses on cellular electrophysiological studies that directly investigate the effects of iron overload on the function of cardiac ion channels, including trans-sarcolemmal and sarcoplasmic reticulum Ca2+ fluxes, as well as cardiac action potential morphology. Our ultimate aim is to provide a comprehensive summary of the currently available information that will encourage and facilitate further mechanistic elucidation of iron-induced pathoelectrophysiological changes in the heart.

Diagnosis and treatment of cardiac iron overload in transfusion-dependent thalassemia patients.

INTRODUCTION: Thalassemia is among the most common genetic diseases. Patients with severe forms of the disease are transfusion-dependent, leading to iron overload. A condition which can eventually develop in the iron-loaded heart is iron overload cardiomyopathy, a debilitating disease that accounts for the majority of deaths in thalassemia patients. Areas covered: This review article provides a comprehensive summary of the diagnosis and treatment of cardiac iron overload in transfusion-dependent thalassemia patients, with discussion covering current weak points and potential improvements of the relevant diagnostic and therapeutic strategies. Expert commentary: Current limitations of various diagnostic techniques for iron overload cardiomyopathy include suboptimal accuracy, untimely detection, or inadequate accessibility, and novel modalities are required to overcome these shortcomings. Treatment should address key pathophysiologic mechanisms of iron overload cardiomyopathy, which include cardiac iron mishandling and iron-induced oxidative injury. Apart from the promotion of iron removal by chelators, prevention of cardiac iron deposition and attenuation of oxidative damage should also be rigorously investigated on a cell-to-bedside basis.

Roles of lipocalin 2 and adiponectin in iron overload cardiomyopathy.

Thalassemia is among the most common genetic diseases worldwide. Ineffective erythropoiesis, chronic hemolysis, and regular blood transfusion in thalassemia patients lead to increased iron burden. Iron overload cardiomyopathy is the most severe co-morbidity and most common cause of mortality in thalassemia patients. Although its associated mechanisms are still not completely understood, cellular iron mishandling, chronic inflammation, and oxidative stress appear to be the key processes involved. In order to acquire a more comprehensive insight of the impact of cardiac iron overload, these alterations need to be intensively investigated. This comprehensive mini-review focuses on two emergent molecules which have been shown to potentially play significant roles in iron overload cardiomyopathy. These two molecules are an iron-transporting protein, lipocalin 2, and an anti-inflammatory adipokine, adiponectin. Reports from in vitro and in vivo studies are comprehensively summarized. Clinical studies examining the roles of these molecules in thalassemia patients are also presented and discussed.

Heart Rate Variability as an Alternative Indicator for Identifying Cardiac Iron Status in Non-Transfusion Dependent Thalassemia Patients.

BACKGROUND: Iron-overload cardiomyopathy is a major cause of death in thalassemia patients due to the lack of an early detection strategy. Although cardiac magnetic resonance (CMR) T2* is used for early detection of cardiac iron accumulation, its availability is limited. Heart rate variability (HRV) has been used to evaluate cardiac autonomic function and found to be depressed in thalassemia. However, its direct correlation with cardiac iron accumulation has never been investigated. We investigated whether HRV can be used as an alternative indicator for early identification of cardiac iron deposition in thalassemia patients. METHODS: Ninety-nine non-transfusion dependent thalassemia patients (23.00 (17.00, 32.75) years, 35 male) were enrolled. The correlation between HRV recorded using 24-hour Holter monitoring and non-transferrin bound iron (NTBI), hemoglobin (Hb), serum ferritin, LV ejection fraction (LVEF), and CMR-T2* were determined. RESULTS: The median NTBI value was 3.15 (1.11, 6.59) µM. Both time and frequency domains of HRV showed a significant correlation with the NTBI level, supporting HRV as a marker of iron overload. Moreover, the LF/HF ratio showed a significant correlation with CMR-T2* with the receiver operating characteristic (ROC) curve of 0.684±0.063, suggesting that it could represent the cardiac iron deposit in thalassemia patients. HRV was also significantly correlated with serum ferritin and Hb. CONCLUSIONS: This novel finding regarding the correlation between HRV and CMR-T2* indicates that HRV could be a potential marker in identifying early cardiac iron deposition prior to the development of LV dysfunction, and may be used as an alternative to CMR-T2* for screening cardiac iron status in thalassemia patients.