Iron overload and arrhythmias: Influence of confounding factors

Hereditary hemochromatosis with homozygous C282Y HFE mutation: possible clinical model to assess effects of elevated reactive oxygen species on the development of cardiovascular disease

Hereditary hemochromatosis with the homozygous C282Y HFE mutation (HH-282H) is a genetic condition which causes iron overload (IO) and elevated reactive oxygen species (ROS) secondary to the IO. Interestingly, even after successful iron removal therapy, HH-282H subjects demonstrate chronically elevated ROS. Raised ROS are also associated with the development of multiple cardiovascular diseases and HH-282H subjects may be at risk to develop these complications. In this narrative review, we consider HH-282H subjects as a clinical model for assessing the contribution of elevated ROS to the development of cardiovascular diseases in subjects with fewer confounding clinical risk factors as compared to other disease conditions with high ROS. We identify HH-282H subjects as a potentially unique clinical model to assess the impact of chronically elevated ROS on the development of cardiovascular disease and to serve as a clinical model to detect effective interventions for anti-ROS therapy.

A novel tsRNA-5008a promotes ferroptosis in cardiomyocytes that causes atrial structural remodeling predisposed to atrial fibrillation

Atrial fibrillation (AF) is an extremely common clinical arrhythmia disease, but whether its mechanism is associated with ferroptosis remains unclear. The tRNA-derived small RNAs (tsRNAs) are involved in a variety of cardiovascular diseases, however, their role and mechanism in atrial remodeling in AF have not been studied. We aimed to explore whether tsRNAs mediate ferroptosis in AF progression. The AF models were constructed to detect ferroptosis-related indicators, and Ferrostatin-1 (Fer-1) was introduced to clarify the relationship between ferroptosis and AF. Atrial myocardial tissue was used for small RNA sequencing to screen potential tsRNAs. tsRNA functioned on ferroptosis and AF was explored. Atrial fibrosis and changes in the cellular structures and arrangement were observed in AF mice model, and these alterations were accompanied by ferroptosis occurrence, exhibited by the accumulation of Fe2+ and MDA levels and the decrease of expression of FTH1, GPX4, and SLC7A11. Blocking above ferroptosis activation with Fer-1 resulted in a significant improvement for AF. A total of 7 tsRNAs were upregulated (including tsRNA-5008a) and 2 tsRNAs were downregulated in atrial myocardial tissue in the AF group compared with the sham group. We constructed a tsRNA-mRNA regulated network, which showed tsRNA-5008a targeted 16 ferroptosis-related genes. Knockdown of tsRNA-5008a significantly suppressed ferroptosis through targeting SLC7A11 and diminished myocardial fibrosis both in vitro and in vivo. On the contrary, tsRNA-5008a mimics promoted ferroptosis in cardiomyocytes. Collectively, tsRNA-5008a involved in AF through ferroptosis. Our study provides novel insights into the role of tsRNA-5008a mediated ferroptosis in AF progression.

Paroxysmal atrial fibrillation and hemochromatosis: a narrative review

Paroxysmal atrial fibrillation (PAF) and hemochromatosis have a complex relationship. This review explores its mechanisms, prevalence, correlations, and clinical manifestations. Hereditary hemochromatosis (HH) involves iron overload due to HFE protein mutations, while atrial fibrillation (AF) is characterized by irregular heart rhythms. Iron overload in hemochromatosis can promote cardiac arrhythmias. AF is prevalent in developed countries and may be linked to cryptogenic strokes. Genetic variations and demographic factors influence the occurrence of both conditions. HH affects multiple organ systems, including the heart, while AF causes palpitations and reduced exercise tolerance. Diagnosis involves iron markers, genotypic testing, and electrocardiogram (ECG) findings. Treatment strategies focus on reducing iron levels in hemochromatosis and managing AF through antithrombotic therapy and rhythm control. Untreated hemochromatosis carries a higher risk of complications, and PAF is associated with increased cardiovascular-related mortality. For better understanding of the mechanisms and to improve management, additional studies are required. Tailored approaches and combined treatments may enhance patient outcomes.

Heteroatom-engineered multicolor lignin carbon dots enabling bimodal fluorescent off-on detection of metal-ions and glutathione

Carbon dots (CDs) have emerged as a promising subclass of optical nanomaterials with versatile functions in multimodal biosensing. Howbeit the rapid, reliable and reproducible fabrication of multicolor CDs from renewable lignin with unique groups (e.g., -OCH3, -OH and -COOH) and alterable moieties (e.g., β-O-4, phenylpropanoid structure) remains challenging due to difficult-to-control molecular behavior. Herein we proposed a scalable acid-reagent strategy to engineer a family of heteroatom-doped multicolor lignin carbon dots (LCDs) that are functioned as the bimodal fluorescent off-on sensing of metal-ions and glutathione (GSH). Benefiting from the modifiable photophysical structure via heteroatom-doping (N, S, W, P and B), the multicolor LCDs (blue, green and yellow) with a controllable size distribution of 2.06-2.22 nm deliver the sensing competences to fluorometric probing the distinctive metal-ion systems (Fe3+, Al3+ and Cu2+) under a broad response interval (0-500 μM) with excellent sensitivity and limit of detection (LOD, 0.45-3.90 μM). Meanwhile, we found that the addition of GSH can efficiently restore the fluorescence of LCDs by forming a stable Fe3+-GSH complex with a LOD of 0.97 μM. This work not only sheds light on evolving lignin macromolecular interactions with tunable luminescent properties, but also provides a facile approach to synthesize multicolor CDs with advanced functionalities.

The potential for the use of leghemoglobin and plant ferritin as sources of iron

Iron is an essential component for the body, but it is also a major cause for the development of many diseases such as cancer, cardiovascular diseases, and autoimmune diseases. It has been suggested that a diet rich in meat products, especially red meat and highly processed products, constitute a nutritional model that increases the risk of developing. In this context, it is indicated that people on an elimination diet (vegetarians and vegans) may be at risk of deficiencies in iron, because this micronutrient is found mainly in foods of animal origin and has lower bioavailability in plant foods. This article reviews the knowledge on the use of leghemoglobin and plant ferritin as sources of iron and discusses their potential for use in vegetarian and vegan diets.

Iron Overload in Chronic Kidney Disease: Less Ferritin, More T2*MRI

To date, there is no consensus on the most reliable marker of iron status in patients with chronic kidney disease (CKD). Serum ferritin is used routinely, although it may be a misleading marker for iron overload. The success of T2^* MRI in monitoring iron overload in patients with hemoglobinopathies can be beneficial to monitoring patients with CKD.

Relevance of mitochondrial oxidative stress to arrhythmias: Innovative concepts to target treatments

Cardiac arrhythmia occurs frequently worldwide, and in severe cases can be fatal. Mitochondria are the power plants of cardiomyocytes. In recent studies, mitochondria under certain stimuli produced excessive reactive oxygen species (ROS), which affect the normal function of cardiomyocytes through ion channels and related proteins. Mitochondrial oxidative stress (MOS) plays a key role in diseases with multifactorial etiopathogenesis, such as arrhythmia; MOS can lead to arrhythmias such as atrial fibrillation and ventricular tachycardia. This review discusses the mechanisms of arrhythmias caused by MOS, particularly of ROS produced by mitochondria. MOS can cause arrhythmias by affecting the activities of Ca²⁺-related proteins, the mitochondrial permeability transition pore protein, connexin 43, hyperpolarization-activated cyclic nucleotide-gated potassium channel 4, and ion channels. Based on these mechanisms, we discuss possible new treatments for arrhythmia. Targeted treatments focusing on mitochondria may reduce the progression of arrhythmias, as well as the occurrence of severe arrhythmias, and may be effective for personalized disease prevention.

Blocking effect of ferritin on the ryanodine receptor-isoform 2

Iron, an essential element for most living organism, participates in a wide variety of physiological processes. Disturbance in iron homeostasis has been associated with numerous pathologies, particularly in the heart and brain, which are the most susceptible organs. Under iron-overload conditions, the generation of reactive oxygen species leads to impairment in Ca2+ signaling, fundamentally implicated in cardiac and neuronal physiology. Since iron excess is accompanied by increased expression of iron-storage protein, ferritin, we examined whether ferritin has an effect on the ryanodine receptor - isoform 2 (RYR2), which is one of the major components of Ca2+ signaling. Using the method of planar lipid membranes, we show that ferritin induced an abrupt, permanent blockage of the RYR2 channel. The ferritin effect was strongly voltage dependent and competitively antagonized by cytosolic TEA+, an impermeant RYR2 blocker. Our results collectively indicate that monomeric ferritin highly likely blocks the RYR2 channel by a direct electrostatic interaction within the wider region of the channel permeation pathway.

Cardiovascular manifestations in hospitalized patients with hemochromatosis in the United States

BACKGROUND

Heart complications are the main cause of morbidity and mortality in hemochromatosis, but the liver is the main site for iron deposition in these patients. Large multicenter studies have described cardiovascular (CV) manifestations in patients with secondary hemochromatosis. However, the overall prevalence and risk of CV manifestations in patients with hemochromatosis at the population level are unknown.

OBJECTIVE

To examine the prevalence and risk of CV manifestations in patients with hemochromatosis.

METHODS

A retrospective cohort from the National Inpatient Sample database between 2012 and 2014 was studied. We identified hemochromatosis using ICD-9-CM diagnostic codes. CV manifestations were defined by the presence of conduction disorders, arrhythmias, congestive heart failure (CHF), pulmonary hypertension, and non-ischemic cardiomyopathy (NISCM).

RESULTS

Of the 63,846,188 weighted hospitalizations that met the inclusion criteria, 64,590 (0.1%) had hemochromatosis and 13,200,000 (20.7%) had one or more CV manifestations. Of those with hemochromatosis, 5.3% had primary and 94.7% had secondary hemochromatosis. 27.8% of all hemochromatosis patients had one or more CV manifestations, 16% cardiac arrhythmias, 10.6% supraventricular arrhythmias (SVA), 0.8% ventricular arrhythmias, 9.3% CHF, 7.4% pulmonary hypertension, 4.2% NISCM, 2% conduction disorders, and 0.4% cardiac arrest. SVA (14.6% vs 10.4%, P < 0.001) was more prevalent in primary hemochromatosis compared to secondary while pulmonary hypertension (7.7% vs 2.6%, P < 0.001) was more prevalent in secondary hemochromatosis compared to primary. In multivariate modelling, only the adjusted odds of composite CV manifestations (odds ratio [OR] 1.24, 95% confidence interval [CI]: 1.03-1.48, P < 0.05) and SVA (OR 1.59, 95% CI: 1.28-1.96, P < 0.001) were significantly higher in patients with primary hemochromatosis compared with patients without hemochromatosis. In patients with secondary hemochromatosis, the adjusted odds of composite CV manifestations (OR 1.84, 95% CI: 1.74-1.95, P < 0.001), CHF (OR 1.46, 95% CI: 1.35-1.57, P < 0.001), conduction disorder (OR 1.52, 95% CI: 1.33-1.73, P < 0.001), pulmonary hypertension (OR 4.43, 95% CI: 3.97-4.94, P < 0.001), SVA (OR 1.39, 95% CI: 1.29-1.48, P < 0.001), and NISCM (OR 1.98, 95% CI: 1.79-2.20, P < 0.001) were significantly higher compared with patients without hemochromatosis.

CONCLUSION

Supraventricular arrhythmias, congestive heart failure, and pulmonary hypertension were the most common CV disorders in hemochromatosis patients. Risk-adjusted burden of supraventricular arrhythmias was significantly higher in primary and secondary hemochromatosis while patients with secondary hemochromatosis had a higher risk of congestive heart failure, pulmonary hypertension, conduction disorders, and non-ischemic cardiomyopathy.

Advancement of echocardiography for surveillance of iron overload cardiomyopathy: comparison to cardiac magnetic resonance imaging

The prevalence of iron overload cardiomyopathy (IOC) is increasing. Patients with transfusion-dependent anemias or conditions associated with increased iron absorption over time are at a significant risk for the development of iron-overloaded states such as IOC. Current guidelines regarding the diagnostic evaluation and follow-up of patients at risk for IOC exist, and are composed of multiple components, including such as echocardiography, genetic testing, magnetic resonance imaging of liver, and cardiac magnetic resonance imaging (CMR). While these are considered reliable for the evaluation of patients at risk for an iron-overloaded state, there is an access challenge associated with initial and serial CMR scanning in this patient population. Furthermore, there are other limiting factors, such as patient characteristics that may preclude the use of CMR as a viable diagnostic imaging modality for these patients. On the other hand, recent evidence in the literature suggests that transthoracic echocardiography, which has had significant technological advances, can equal or even outperform CMR to identify cardiac functional abnormalities such as subclinical left ventricular strain and left atrial functional abnormalities in iron overload conditions. Therefore, there is a potential role of more frequent use of echocardiography for surveillance of the development of IOC. Our purpose with this narrative review is to describe recent advances in echocardiography and propose a potential increased use of echocardiography in the surveillance of the development of IOC.

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.

Iron Overload, Oxidative Stress and Calcium Mishandling in Cardiomyocytes: Role of the Mitochondrial Permeability Transition Pore

Iron (Fe) plays an essential role in many physiological processes. Hereditary hemochromatosis or frequent blood transfusions often cause iron overload (IO), which can lead to cardiomyopathy and arrhythmias; however, the underlying mechanism is not well defined. In the present study, we assess the hypothesis that IO promotes arrhythmias via reactive oxygen species (ROS) production, mitochondrial membrane potential (∆Ψm) depolarization, and disruption of cytosolic Ca dynamics. In ventricular myocytes isolated from wild type (WT) mice, both cytosolic and mitochondrial Fe levels were elevated following perfusion with the Fe3+/8-hydroxyquinoline (8-HQ) complex. IO promoted mitochondrial superoxide generation (measured using MitoSOX Red) and induced the depolarization of the ΔΨm (measured using tetramethylrhodamine methyl ester, TMRM) in a dose-dependent manner. IO significantly increased the rate of Ca wave (CaW) formation measured in isolated ventricular myocytes using Fluo-4. Furthermore, in ex-vivo Langendorff-perfused hearts, IO increased arrhythmia scores as evaluated by ECG recordings under programmed S1-S2 stimulation protocols. We also carried out similar experiments in cyclophilin D knockout (CypD KO) mice in which the mitochondrial permeability transition pore (mPTP) opening is impaired. While comparable cytosolic and mitochondrial Fe load, mitochondrial ROS production, and depolarization of the ∆Ψm were observed in ventricular myocytes isolated from both WT and CypD KO mice, the rate of CaW formation in isolated cells and the arrhythmia scores in ex-vivo hearts were significantly lower in CypD KO mice compared to those observed in WT mice under conditions of IO. The mPTP inhibitor cyclosporine A (CsA, 1 µM) also exhibited a protective effect. In conclusion, our results suggest that IO induces mitochondrial ROS generation and ∆Ψm depolarization, thus opening the mPTP, thereby promoting CaWs and cardiac arrhythmias. Conversely, the inhibition of mPTP ameliorates the proarrhythmic effects of IO.

Role of Oxidative Stress in the Genesis of Ventricular Arrhythmias

Ventricular arrhythmias, mainly lethal arrhythmias, such as ventricular tachycardia and fibrillation, may lead to sudden cardiac death. These are triggered as a result of cardiac injury due to chronic ischemia, acute myocardial infarction and various stressful conditions associated with increased levels of circulating catecholamines and angiotensin II. Several mechanisms have been proposed to underlie electrical instability of the heart promoting ventricular arrhythmias; however, oxidative stress which adversely affects ion homeostasis due to changes in the ion channel structure and function, seems to play a critical role in eliciting different types of ventricular arrhythmias. Prevention or mitigation of the severity of ventricular arrhythmias due to antioxidants has been indicated as the fundamental contribution in the field of preventive cardiology; however, novel interventions have to be developed for greater effectiveness and specificity in attenuating the adverse effects of oxidative stress. In this review, we have attempted to discuss proarrhythmic effects of oxidative stress differing in time and concentration dependence and highlight a molecular and cellular concept how it alters cardiac cell automaticity and conduction velocity sensitizing the probability of ventricular arrhythmias with resultant sudden cardiac death due to ischemic heart disease and other stressful situations. It is concluded that pharmacological approaches targeting multiple mechanisms besides oxidative stress might be more effective in the treatment of ventricular arrhythmias than current antiarrhythmic therapy.

Controversies on the Consequences of Iron Overload and Chelation in MDS

Many patients with MDS are prone to develop systemic and tissue iron overload in part as a consequence of disease-immanent ineffective erythropoiesis. However, chronic red blood cell transfusions, which are part of the supportive care regimen to correct anemia, are the major source of iron overload in MDS. Increased systemic iron levels eventually lead to the saturation of the physiological systemic iron carrier transferrin and the occurrence of non-transferrin-bound iron (NTBI) together with its reactive fraction, the labile plasma iron (LPI). NTBI/LPI-mediated toxicity and tissue iron overload may exert multiple detrimental effects that contribute to the pathogenesis, complications and eventually evolution of MDS. Until recently, the evidence supporting the use of iron chelation in MDS was based on anecdotal reports, uncontrolled clinical trials or prospective registries. Despite not fully conclusive, these and more recent studies, including the TELESTO trial, unravel an overall adverse action of iron overload and therapeutic benefit of chelation, ranging from improved hematological outcome, reduced transfusion dependence and superior survival of iron-loaded MDS patients. The still limited and somehow controversial experimental and clinical data available from preclinical studies and randomized trials highlight the need for further investigation to fully elucidate the mechanisms underlying the pathological impact of iron overload-mediated toxicity as well as the effect of classic and novel iron restriction approaches in MDS. This review aims at providing an overview of the current clinical and translational debated landscape about the consequences of iron overload and chelation in the setting of MDS.

Ferrous iron binding to epinephrine promotes the oxidation of iron and impedes activation of adrenergic receptors

Upon release in response to stress, epinephrine (Epi) may interact with labile iron pool in human plasma with potentially important (patho)physiological consequences. We have shown that Epi and Fe³⁺ build stable 1:1 high-spin bidentate complex at physiological pH, and that Epi does not undergo degradation in the presence of iron. However, the interactions of Epi with the more soluble Fe²⁺, and the impact of iron on biological activity of Epi are still not known. Herein we showed that Epi and Fe²⁺ build colorless complex which is stable under anaerobic conditions. In the presence of O₂, Epi promoted the oxidation of Fe²⁺ and the formation of Epi-Fe³⁺ complex. Cyclic voltammetry showed that mid-point potential of Epi-Fe²⁺ complex is very low (-582 mV vs. standard hydrogen electrode), which explains catalyzed oxidation of Fe²⁺. Next, we examined the impact of iron binding on biological performance of Epi using patch clamping in cell culture with constitutive expression of adrenergic receptors. Epi alone evoked an increase of outward currents, whereas Epi in the complex with Fe³⁺ did not. This implies that the binding of Epi to adrenergic receptors and their activation is prevented by the formation of complex with iron. Pro-oxidative activity of Epi-Fe²⁺ complex may represent a link between chronic stress and cardiovascular problems. On the other hand, labile iron could serve as a modulator of biological activity of ligands. Such interactions may be important in human pathologies that are related to iron overload or deficiency.