Mechanisms of cardiac iron homeostasis and their importance to heart function

A New Perspective on the Role of Alterations in Mitochondrial Proteins Involved in ATP Synthesis and Mobilization in Cardiomyopathies

The heart requires a continuous energy supply to sustain its unceasing contraction-relaxation cycle. Mitochondria, a double-membrane organelle, generate approximately 90% of cellular energy as adenosine triphosphate (ATP) through oxidative phosphorylation, utilizing the electrochemical gradient established by the respiratory chain. Mitochondrial function is compromised by damage to mitochondrial DNA, including point mutations, deletions, duplications, or inversions. Additionally, disruptions to proteins associated with mitochondrial membranes regulating metabolic homeostasis can impair the respiratory chain's efficiency. This results in diminished ATP production and increased generation of reactive oxygen species. This review provides an overview of mutations affecting mitochondrial transporters and proteins involved in mitochondrial energy synthesis, particularly those involved in ATP synthesis and mobilization, and it examines their role in the pathogenesis of specific cardiomyopathies.

Combinatorial approach to treat iron overload cardiomyopathy in pediatric patients with thalassemia-major: A systematic review and meta-analysis

BACKGROUND

Iron overload cardiomyopathy is a significant cause of morbidity and mortality in transfusion-dependent thalassemia patients. Standard iron chelation therapy is less efficient in alleviating iron accumulation in many organs, especially when iron enters the cells via specific calcium channels.

AIM

To validate our hypothesis that adding amlodipine to the iron chelation regimen is more efficient in alleviating myocardial iron overload.

METHODS

Five databases, including PubMed, Cochrane Library, Embase, ScienceDirect, and ClinicalTrials.gov, were systematically searched, and three randomized controlled trials involving 144 pediatric patients with transfusion-dependent thalassemia were included in our meta-analysis based on the predefined eligibility criteria. The quality of the included studies was assessed based on the Cochrane collaboration tool for bias assessment. The primary outcome assessed was myocardial-T2 and myocardial iron concentration, while the secondary results showed serum ferritin level, liver iron concentration, and treatment adverse outcomes. Weighted mean difference and odds ratio were calculated to measure the changes in the estimated treatment effects.

RESULTS

During the follow-up period, Amlodipine treatment significantly improved cardiac T2 by 2.79 ms compared to the control group [95% confidence interval (CI): 0.34-5.24, P = 0.03, I 2 = 0%]. Additionally, a significant reduction of 0.31 in myocardial iron concentration was observed with amlodipine treatment compared to the control group [95%CI: -0.38-(-0.25), P < 0.00001, I 2 = 0%]. Liver iron concentration was slightly lower in the amlodipine group by -0.04 mg/g, but this difference was not statistically significant (95%CI: -0.33-0.24, P = 0.77, I 2 = 0%). Amlodipine also showed a non-significant trend toward a reduction in serum ferritin levels (-328.86 ng/mL, 95%CI: -1212.34-554.62, P = 0.47, I 2 = 90%). Regarding safety, there were no significant differences between the groups in the incidence of gastrointestinal upset, hypotension, or lower limb edema.

CONCLUSION

Amlodipine with iron chelation therapy significantly improved cardiac parameters, including cardiac-T2 and myocardial iron, in patients with transfusion-dependent thalassemia without causing significant adverse events but enhancing the efficacy of iron chelation therapy.

Inverted U-Shaped Association of Soluble Transferrin Receptor Concentrations with Risks of Cardiovascular Diseases in Overweight Individuals: A Cross-Sectional Study

Background

Iron metabolism may play a role in cardiovascular disease (CVD) pathogenesis. The association between iron metabolism and CVD has yet to be fully investigated. This study evaluated whether iron metabolism was associated with CVD risk and whether the body mass index (BMI) of US adults varied the association.

Methods

A cross-sectional study was performed using the National Health and Nutrition Examination Survey (NHANES), conducted from 2017 to 2018. Generalized additive models (GAMs) and multivariable logistic regression were adopted to analyze the association between iron metabolism (serum iron (SI), serum ferritin (SF), transferrin saturation (TSAT), and soluble transferrin receptor (sTfR)) and CVD risk. Further, stratified analysis was conducted to identify patients with high CVD risk.

Results

Participants with CVD tended to have significantly increased levels of sTfR (p < 0.001) and decreased levels of TSAT (p < 0.001) and SI (p < 0.001). After adjusting for confounding factors, sTfR levels had a significant positive association with CVD risk (Q1 as reference, Q4 odds ratio (OR) 2.1, 95% CI 1.54-2.87, p < 0.001). Notably, the association between sTfR and CVD risk differed in the BMI subgroup (p for interaction < 0.05). We identified an inverted U-shaped relationship between sTfR and the CVD risk in the group of overweight individuals (non-linear p < 0.001). When the sTfR level was below the turning point (sTfR = 5.35 mg/L), a per unit increase in the sTfR level was correlated with a 78% greater adjusted OR of CVD risk (OR, 1.78 [1.44, 2.19]).

Conclusions

Increased sTfR levels were non-linearly related to the CVD risk in the overweight population.

Dose-Dependent Relationship between Iron Metabolism and Perioperative Myocardial Injury in Cardiac Surgery with Cardiopulmonary Bypass: A Retrospective Analysis

INTRODUCTION

We sought to comprehensively explore the potential linear and nonlinear relationship between preoperative iron metabolism and perioperative myocardial injury (PMI) following cardiac surgery with cardiopulmonary bypass (CPB).

METHODS

Patients who underwent cardiac surgery with CPB between December 2018 and April 2021 were retrospectively collected. The measurements of iron metabolism included serum iron (SI), serum ferritin (SF), transferrin (TRF), transferrin saturation (TS), and total iron-binding capacity (TIBC). Logistic regression and restricted cubic spline (RCS) models were used for linear and nonlinear analysis. The primary outcome was PMI with a 100× upper reference limit.

RESULTS

Of 2,420 patients screened, 744 eligible patients were enrolled for the final analysis. The incidence of PMI was 25.7%. No significant linear relationship was observed. In the RCS models adjusted with age (median: 56), female, and history of diabetes, a statistically significant difference was detected between TRF (p for nonlinear 0.0152) or TIBC (p for nonlinear 0.0477) and PMI. The gentle U-shaped relationship observed between TRF, TIBC, and PMI suggests that when TRF and TIBC increase, the risk decreases, reaching its lowest point when TRF = 2.4 and TIBC = 54. Nevertheless, as TRF and TIBC continue to increase, the risk starts to rise again. Subgroup analyses yielded consistent findings, with a notable emphasis on older patients who were more susceptible to variations in iron metabolism.

CONCLUSION

Iron metabolism, including TRF, and TIBC, exhibited a nonlinear relationship with PMI by the RCS model adjusted by age, gender, and history of diabetes.

Cardiomyocyte-specific overexpression of FPN1 diminishes cardiac hypertrophy induced by chronic intermittent hypoxia

The significance of iron in myocardial mitochondria function cannot be underestimated, because deviations in iron levels within cardiomyocytes may have profound detrimental effects on cardiac function. In this study, we investigated the effects of ferroportin 1 (FPN1) on cardiac iron levels and pathological alterations in mice subjected to chronic intermittent hypoxia (CIH). The cTNT-FPN1 plasmid was administered via tail vein injection to induce the mouse with FPN1 overexpression in the cardiomyocytes. CIH was established by exposing the mice to cycles of 21%-5% FiO2 for 3 min, 8 h per day. Subsequently, the introduction of hepcidin resulted in a reduction in FPN1 expression, and H9C2 cells were used to establish an IH model to further elucidate the role of FPN1. First, FPN1 overexpression ameliorated CIH-induced cardiac dysfunction, myocardial hypertrophy, mitochondrial damage and apoptosis. Second, FPN1 overexpression attenuated ROS levels during CIH. In addition, FPN1 overexpression mitigated CIH-induced cardiac iron accumulation. Moreover, the administration of hepcidin resulted in a reduction in FPN1 levels, further accelerating the CIH-induced levels of ROS, LIP and apoptosis in H9C2 cells. These findings indicate that the overexpression of FPN1 in cardiomyocytes inhibits CIH-induced cardiac iron accumulation, subsequently reducing ROS levels and mitigating mitochondrial damage. Conversely, the administration of hepcidin suppressed FPN1 expression and worsened cardiomyocyte iron toxicity injury.

scRNA-seq reveals the diversity of the developing cardiac cell lineage and molecular players in heart rhythm regulation

We utilized scRNA-seq to delineate the diversity of cell types in the zebrafish heart. Transcriptome profiling of over 50,000 cells at 48 and 72 hpf defined at least 18 discrete cell lineages of the developing heart. Utilizing well-established gene signatures, we identified a population of cells likely to be the primary pacemaker and characterized the transcriptome profile defining this critical cell type. Two previously uncharacterized genes, atp1b3b and colec10, were found to be enriched in the sinoatrial cardiomyocytes. CRISPR/Cas9-mediated knockout of these two genes significantly reduced heart rate, implicating their role in cardiac development and conduction. Additionally, we describe other cardiac cell lineages, including the endothelial and neural cells, providing their expression profiles as a resource. Our results established a detailed atlas of the developing heart, providing valuable insights into cellular and molecular mechanisms, and pinpointed potential new players in heart rhythm regulation.

Herbal medicines provide regulation against iron overload in cardiovascular diseases: Informing future applications

ETHNOPHARMACOLOGICAL RELEVANCE

Iron is an essential micronutrient for maintaining physiological activities, especially for highly active cardiomyocytes. Inappropriate iron overload or deficiency has a significant impact on the incidence and severity of cardiovascular diseases (CVD). Iron overload exerts potentially deleterious effects on doxorubicin (DOX) cardiomyopathy, atherosclerosis, and myocardial ischemia-reperfusion injury (MI/RI) by participating in lipid peroxides production. Notably, iron overload-associated cell death has been defined as a possible mechanism for ferroptosis. At present, some traditional herbal medicines and extracts have been included in the study of regulating iron overload and the subsequent therapeutic effect on CVD.

AIM OF THE STUDY

To give an outline of iron metabolism and ferroptosis in cardiomyocytes and to focus on herbal medicines and extracts to prevent iron overload in CVD.

MATERIALS AND METHODS

Literature information was systematically collected from ScienceDirect, PubMed, Google Scholar, Web of Science, China National Knowledge Infrastructure, WanFang data, as well as classic books and clinical reports.

RESULTS

After understanding the mechanism of iron overload on CVD, this paper reviews the therapeutic function of various herbal medicines in eliminating iron overload in CVD. These include Chinese herbal compound prescriptions (Salvia miltiorrhiza injection, Gegen Qinlian decoction, Tongxinluo, Banxia-Houpu decoction), plant extracts, phenylpropanoids, flavonoids, terpenoids, and polyphenols. Among them, flavonoids are considered to be the most promising compounds because of their prominent iron chelation. Mechanically, these herbal medicines act on the Nrf2 signaling pathway, AMPK signaling pathway, and KAT5/GPX4 signaling pathway, thereby attenuating iron overload and lipid peroxidation in CVD.

CONCLUSION

Our review provides up-to-date information on herbal medicines that exert cardiovascular protective effects by modulating iron overload and ferroptosis. These herbal medicines hold promise as a template for preventing iron overload in CVD.

Endoplasmic reticulum stress-mediated cell death in cardiovascular disease

The endoplasmic reticulum (ER) plays a vital function in maintaining cellular homeostasis. Endoplasmic reticulum stress (ERS) can trigger various modes of cell death by activating the unfolded protein response (UPR) signaling pathway. Cell death plays a crucial role in the occurrence and development of diseases such as cancer, liver diseases, neurological diseases, and cardiovascular diseases. Several cardiovascular diseases including hypertension, atherosclerosis, and heart failure are associated with ER stress. ER stress-mediated cell death is of interest in cardiovascular disease. Moreover, an increasing body of evidence supports the potential of modulating ERS for treating cardiovascular disease. This paper provides a comprehensive review of the UPR signaling pathway, the mechanisms that induce cell death, and the modes of cell death in cardiovascular diseases. Additionally, we discuss the mechanisms of ERS and UPR in common cardiovascular diseases, along with potential therapeutic strategies.

Iron accumulation and lipid peroxidation: implication of ferroptosis in hepatocellular carcinoma

Ferroptosis is a type of controlled cell death caused by lipid peroxidation, which results in the rupture of the cell membrane. ferroptosis has been repeatedly demonstrated over the past ten years to be a significant factor in a number of diseases. The liver is a significant iron storage organ, thus ferroptosis will have great potential in the treatment of liver diseases. Ferroptosis is particularly prevalent in HCC. In the opening section of this article, we give a general summary of the pertinent molecular mechanisms, signaling pathways, and associated characteristics of ferroptosis. The primary regulating mechanisms during ferroptosis are then briefly discussed, and we conclude by summarizing the development of a number of novel therapeutic strategies used to treat HCC in recent years. Ferroptosis is a crucial strategy for the treatment of HCC and offers new perspectives on the treatment of liver cancer.

Iron Dysregulation in Cardiovascular Diseases

Iron metabolism plays a crucial role in various physiological functions of the human body, as it is essential for the growth and development of almost all organisms. Dysregulated iron metabolism-manifested either as iron deficiency or overload-is a significant risk factor for the development of cardiovascular disease (CVD). Moreover, emerging evidence suggests that ferroptosis, a form of iron-dependent programed cell death, may also contribute to CVD development. Understanding the regulatory mechanisms of iron metabolism and ferroptosis in CVD is important for improving disease management. By integrating different perspectives and expertise in the field of CVD-related iron metabolism, this overview provides insights into iron metabolism and CVD, along with approaches for diagnosing, treating, and preventing CVD associated with iron dysregulation.

Hydrogen Attenuates Chronic Intermittent Hypoxia-Induced Cardiac Hypertrophy by Regulating Iron Metabolism

The present study aimed to investigate the impact of hydrogen (H2) on chronic intermittent hypoxia (CIH)-induced cardiac hypertrophy in mice by modulating iron metabolism. C57BL/6N mice were randomly allocated into four groups: control (Con), CIH, CIH + H2, and H2. The mice were exposed to CIH (21-5% FiO2, 3 min/cycle, 8 h/d), and received inhalation of a hydrogen-oxygen mixture (2 h/d) for 5 weeks. Cardiac and mitochondrial function, levels of reactive oxygen species (ROS), and iron levels were evaluated. The H9C2 cell line was subjected to intermittent hypoxia (IH) and treated with H2. Firstly, we found H2 had a notable impact on cardiac hypertrophy, ameliorated pathological alterations and mitochondrial morphology induced by CIH (p < 0.05). Secondly, H2 exhibited a suppressive effect on oxidative injury by decreasing levels of inducible nitric oxide synthase (i-NOS) (p < 0.05) and 4-hydroxynonenal (4-HNE) (p < 0.01). Thirdly, H2 demonstrated a significant reduction in iron levels within myocardial cells through the upregulation of ferroportin 1 (FPN1) proteins (p < 0.01) and the downregulation of transferrin receptor 1 (TfR1), divalent metal transporter 1 with iron-responsive element (DMT1(+ire)), and ferritin light chain (FTL) mRNA or proteins (p < 0.05). Simultaneously, H2 exhibited the ability to decrease the levels of Fe2+ and ROS in H9C2 cells exposed to IH (p < 0.05). Moreover, H2 mediated the expression of hepcidin, hypoxia-inducible factor-1α (HIF-1α) (p < 0.01), and iron regulatory proteins (IRPs), which might be involved in the regulation of iron-related transporter proteins. These results suggested that H2 may be beneficial in preventing cardiac hypertrophy, a condition associated with reduced iron toxicity.

Space microgravity increases expression of genes associated with proliferation and differentiation in human cardiac spheres

Efficient generation of cardiomyocytes from human-induced pluripotent stem cells (hiPSCs) is important for their application in basic and translational studies. Space microgravity can significantly change cell activities and function. Previously, we reported upregulation of genes associated with cardiac proliferation in cardiac progenitors derived from hiPSCs that were exposed to space microgravity for 3 days. Here we investigated the effect of long-term exposure of hiPSC-cardiac progenitors to space microgravity on global gene expression. Cryopreserved 3D hiPSC-cardiac progenitors were sent to the International Space Station (ISS) and cultured for 3 weeks under ISS microgravity and ISS 1 G conditions. RNA-sequencing analyses revealed upregulation of genes associated with cardiac differentiation, proliferation, and cardiac structure/function and downregulation of genes associated with extracellular matrix regulation in the ISS microgravity cultures compared with the ISS 1 G cultures. Gene ontology analysis and Kyoto Encyclopedia of Genes and Genomes mapping identified the upregulation of biological processes, molecular function, cellular components, and pathways associated with cell cycle, cardiac differentiation, and cardiac function. Taking together, these results suggest that space microgravity has a beneficial effect on the differentiation and growth of cardiac progenitors.

Iron deficiency in myocardial ischaemia: molecular mechanisms and therapeutic perspectives

Systemic iron deficiency (SID), even in the absence of anaemia, worsens the prognosis and increases mortality in heart failure (HF). Recent clinical-epidemiological studies, however, have shown that a myocardial iron deficiency (MID) is frequently present in cases of severe HF, even in the absence of SID and without anaemia. In addition, experimental studies have shown a poor correlation between the state of systemic and myocardial iron. MID in animal models leads to severe mitochondrial dysfunction, alterations of mitophagy, and mitochondrial biogenesis, with profound alterations in cardiac mechanics and the occurrence of a fatal cardiomyopathy, all effects prevented by intravenous administration of iron. This shifts the focus to the myocardial state of iron, in the absence of anaemia, as an important factor in prognostic worsening and mortality in HF. There is now epidemiological evidence that SID worsens prognosis and mortality also in patients with acute and chronic coronary heart disease and experimental evidence that MID aggravates acute myocardial ischaemia as well as post-ischaemic remodelling. Intravenous administration of ferric carboxymaltose (FCM) or ferric dextrane improves post-ischaemic adverse remodelling. We here review such evidence, propose that MID worsens ischaemia/reperfusion injury, and discuss possible molecular mechanisms, such as chronic hyperactivation of HIF1-α, exacerbation of cytosolic and mitochondrial calcium overload, amplified increase of mitochondrial [NADH]/[NAD+] ratio, and depletion of energy status and NAD+ content with inhibition of sirtuin 1-3 activity. Such evidence now portrays iron metabolism as a core factor not only in HF but also in myocardial ischaemia.

An Alternative Mechanism of Subcellular Iron Uptake Deficiency in Cardiomyocytes

BACKGROUND

Systemic defects in intestinal iron absorption, circulation, and retention cause iron deficiency in 50% of patients with heart failure. Defective subcellular iron uptake mechanisms that are independent of systemic absorption are incompletely understood. The main intracellular route for iron uptake in cardiomyocytes is clathrin-mediated endocytosis.

METHODS

We investigated subcellular iron uptake mechanisms in patient-derived and CRISPR/Cas-edited induced pluripotent stem cell-derived cardiomyocytes as well as patient-derived heart tissue. We used an integrated platform of DIA-MA (mass spectrometry data-independent acquisition)-based proteomics and signaling pathway interrogation. We employed a genetic induced pluripotent stem cell model of 2 inherited mutations (TnT [troponin T]-R141W and TPM1 [tropomyosin 1]-L185F) that lead to dilated cardiomyopathy (DCM), a frequent cause of heart failure, to study the underlying molecular dysfunctions of DCM mutations.

RESULTS

We identified a druggable molecular pathomechanism of impaired subcellular iron deficiency that is independent of systemic iron metabolism. Clathrin-mediated endocytosis defects as well as impaired endosome distribution and cargo transfer were identified as a basis for subcellular iron deficiency in DCM-induced pluripotent stem cell-derived cardiomyocytes. The clathrin-mediated endocytosis defects were also confirmed in the hearts of patients with DCM with end-stage heart failure. Correction of the TPM1-L185F mutation in DCM patient-derived induced pluripotent stem cells, treatment with a peptide, Rho activator II, or iron supplementation rescued the molecular disease pathway and recovered contractility. Phenocopying the effects of the TPM1-L185F mutation into WT induced pluripotent stem cell-derived cardiomyocytes could be ameliorated by iron supplementation.

CONCLUSIONS

Our findings suggest that impaired endocytosis and cargo transport resulting in subcellular iron deficiency could be a relevant pathomechanism for patients with DCM carrying inherited mutations. Insight into this molecular mechanism may contribute to the development of treatment strategies and risk management in heart failure.

Magnetic resonance imaging of organ iron before and after correction of iron deficiency in patients with heart failure

AIMS

Intravenous iron therapy (IVIT) is known to improve functional status in chronic heart failure (CHF) patients. The exact mechanism is not completely understood. We correlated magnetic resonance imaging (MRI) patterns of T2* iron signal in various organs to systemic iron and exercise capacity (EC) in CHF before and after IVIT.

METHODS AND RESULTS

We prospectively analysed 24 patients with systolic CHF for T2* MRI pattern of the left ventricle (LV), small and large intestines, spleen, liver, skeletal muscle, and brain for iron. In 12 patients with iron deficiency (ID), we restored iron deficit by IVIT using ferric carboxymaltose. The effects after 3 months were analysed by spiroergometry and MRI. Patients with vs. without ID showed lower blood ferritin, haemoglobin (76 ± 63 vs. 196 ± 82 μg/L and 12.3 ± 1.1 vs. 14.2 ± 1.1 g/dL, all P < 0.002), and in trend a lower transferrin saturation (TSAT) (19.1 [13.1; 28.2] vs. 25.1 [21.3; 29.1] %, P = 0.05). Spleen and liver iron was lower as expressed by higher T2* value (71.8 [66.4; 93.1] vs. 36.9 [32.9; 51.7] ms, P < 0.002 and 33.5 ± 5.9 vs. 28.8 ± 3.9 ms, and P < 0.03). There was a strong trend for a lower cardiac septal iron content in ID (40.6 [33.0; 57.3] vs. 33.7 [31.3; 40.2] ms, P = 0.07). After IVIT, ferritin, TSAT, and haemoglobin increased (54 [30; 104] vs. 235 [185; 339] μg/L, 19.1 [13.1; 28.2] vs. 25.0 [21.0; 33.7] %, 12.3 ± 1.1 vs. 13.3 ± 1.3 g/L, all P < 0.04). Peak VO₂ improved (18.2 ± 4.2 vs. 20.9 ± 3.8 mL/min/kg^-1 , P = 0.05). Higher peak VO₂ at anaerobic threshold was associated with higher blood ferritin, reflecting higher metabolic exercise capacity after therapy (r = 0.9, P = 0.0009). Increase in EC was associated with haemoglobin increase (r = 0.7, P = 0.034). LV iron increased by 25.4% (48.5 [36.2; 64.8] vs. 36.2 [32.9; 41.9] ms, P < 0.04). Spleen and liver iron increased by 46.4 and 18.2%, respectively (71.8 [66.4; 93.1] vs. 38.5 [22.4; 76.9] ms, P < 0.04 and 33.5 ± 5.9 vs. 27.4 ± 8.6 ms, P < 0.007). Iron in skeletal muscle, brain, intestine, and bone marrow remained unchanged (29.6 [28.6; 31.2] vs. 30.4 [29.7; 30.7] ms, P = 0.7, 81.0 ± 6.3 vs. 82.9 ± 9.9 ms, P = 0.6, 34.3 ± 21.4 vs. 25.3 ± 14.1 ms, P = 0.2, 9.4 [7.5; 21.8] vs. 10.3 [6.7; 15.7] ms, P = 0.5 and 9.8 ± 1.5 vs. 13.7 ± 8.9 ms, P = 0.1).

CONCLUSIONS

CHF patients with ID showed lower spleen, liver, and in trend lower cardiac septal iron. After IVIT, iron signal of the left ventricle as well as spleen and liver increased. Improvement in EC was associated with increase in haemoglobin after IVIT. In ID, liver, spleen, and brain but not heart iron were associated with markers of systemic ID.

Ferroptosis in hepatocellular carcinoma: mechanisms and targeted therapy

Hepatocellular carcinoma is the most prevalent form of primary liver cancer with a multifactorial aetiology comprising genetic, environmental, and behavioural factors. Evading cell death is a defining hallmark of hepatocellular carcinoma, underpinning tumour growth, progression, and therapy resistance. Ferroptosis is a form of nonapoptotic cell death driven by an array of cellular events, including intracellular iron overload, free radical production, lipid peroxidation and activation of various cell death effectors, ultimately leading to rupture of the plasma membrane. Although induction of ferroptosis is an emerging strategy to suppress hepatocellular carcinoma, malignant cells manage to develop adaptive mechanisms, conferring resistance to ferroptosis and ferroptosis-inducing drugs. Herein, we aim at elucidating molecular mechanisms and signalling pathways involved in ferroptosis and offer our opinions on druggable targets and new therapeutic strategy in an attempt to restrain the growth and progression of hepatocellular carcinoma through induction of ferroptotic cell death.

Guanxin V attenuates myocardial ischaemia reperfusion injury through regulating iron homeostasis

CONTEXT

Guanxin V (GX), a traditional Chinese medicine formula, is safe and effective in the treatment of coronary artery disease. However, its protective effect on myocardial ischaemia reperfusion injury (MIRI) is unclear.

OBJECTIVE

To investigate the cardioprotective effect of GX on MIRI and explore the potential mechanism.

MATERIALS AND METHODS

Sprague-Dawley male rats were divided into Sham, MIRI and MIRI + GX groups. GX (6 g/kg) was administered to rats via intragastric administration for seven days before ischaemia reperfusion (IR) surgery. The infarct size, histopathology, serum enzyme activities, ultrastructure of the cardiac mitochondria were assessed. H9c2 cells were pre-treated with GX (0.5 mg/mL), and then exposed to hypoxia/reoxygenation (HR). The cell viability and LDH levels were measured. Network pharmacology was conducted to predict the potential mechanism. The related targets of GX were predicted using the TCMSP database, DrugBank database, etc. Finally, pharmacological experiments were used to validate the predicted results.

RESULTS

In vivo, GX significantly reduced the myocardial infarct size from 56.33% to 17.18%, decreased the levels of AST (239.32 vs. 369.18 U/L), CK-MB (1324.61 vs. 2066.47 U/L) and LDH (1245.26 vs. 1969.62 U/L), and reduced mitochondrial damage. In vitro, GX significantly increased H9c2 cell viability (IC50 = 3.913 mg/mL) and inhibited the release of LDH (207.35 vs. 314.33). In addition, GX could maintain iron homeostasis and reduce oxidative stress level by regulating iron metabolism-associated proteins.

CONCLUSIONS

GX can attenuate MIRI via regulating iron homeostasis, indicating that GX may act as a potential candidate for the treatment of MIRI.

Banxia-Houpu decoction diminishes iron toxicity damage in heart induced by chronic intermittent hypoxia

CONTEXT

Obstructive sleep apnoea (OSA) causes chronic intermittent hypoxia (CIH), which results in mitochondrial dysfunction and generates reactive oxygen species (ROS) in the heart. Excessive free iron could accelerate oxidative damage, which may be involved in this process. Banxia-Houpu decoction (BHD) was reported to improve the apnoea hypopnoea index in OSA patients, but the specific mechanism was still unclear.

OBJECTIVE

To investigate whether BHD could reduce CIH-induced heart damage by regulating iron metabolism and mitochondrial function.

MATERIALS AND METHODS

C57BL/6N mice were randomly divided into control, CIH and BHD groups. Mice were exposed to CIH (21 - 5% O2, 20 times/h, 8 h/d) and administered BHD (3.51, 7.01 and 14.02 g/kg, intragastrically) for 21 d. Cardiac and mitochondrial function, iron levels, apoptosis and mitophagy were determined.

RESULTS

BHD (7.01 g/kg) significantly improved cardiac dysfunction, pathological change and mitochondrial structure induced by CIH. BHD increased the Bcl-2/Bax ratio (1.4-fold) and inhibited caspase 3 cleavage in CIH mice (0.45-fold). BHD activated mitophagy by upregulating Parkin (1.94-fold) and PINK1 (1.26-fold), inhibiting the PI3K-AKT-mTOR pathway. BHD suppressed ROS generation by decreasing NOX2 (0.59-fold) and 4-HNE (0.83-fold). BHD reduced the total iron in myocardial cells (0.72-fold) and mitochondrial iron by downregulating Mfrn2 (0.81-fold) and MtFt (0.78-fold) proteins, and upregulating ABCB8 protein (1.33-fold). Rosmarinic acid, the main component of Perilla Leaf in BHD, was able to react with Fe2+ and Fe3+ in vitro.

DISCUSSION AND CONCLUSIONS

These findings encourage the use of BHD to resist cardiovascular injury and provide the theoretical basis for clinical treatment in OSA patients.

Melatonin: Potential avenue for treating iron overload disorders

Iron overload as a highly risk factor, can be found in almost all human chronic and common diseases. Iron chelators are often used to treat iron overload; however, patient adherence to these chelators is poor due to obvious side effects and other disadvantages. Numerous studies have shown that melatonin has a high iron chelation ability and direct free radical scavenging activity, and can inhibit the lipid peroxidation process caused by iron overload. Therefore, melatonin may become potential complementary therapy for iron overload-related disorders due to its iron chelating and antioxidant activities. Here, the research progress of iron overload is reviewed and the therapeutic potential of melatonin in the treatment of iron overload is analyzed. In addition, studies related to the protective effects of melatonin on oxidative damage induced by iron overload are discussed. This review provides a foundation for preventing and treating iron homeostasis disorders with melatonin.

Transferrin-mediated increase of labile iron Pool following simulated ischemia causes lipid peroxidation during the early phase of reperfusion

Heart ischemia/reperfusion (I/R) injury is related to iron content. However, the occurrence and mechanism of changes in labile iron pool (LIP) during I/R is debatable. Moreover, the identity of the iron form dominant in LIP during I/R is unclear. Herein, we measured changes of LIP during simulated ischemia (SI) and reperfusion (SR), in which ischemia was simulated in vitro with lactic acidosis and hypoxia. Total LIP did not change in lactic acidosis, whereas LIP, especially Fe³⁺, increased in hypoxia. Under SI, accompanied by hypoxia with acidosis, both Fe²⁺ and Fe³⁺ were significantly increased. Increased total LIP was maintained at 1 h post-SR. However, the Fe²⁺ and Fe³⁺ portion was changed. The increased Fe²⁺ was decreased, and conversely the Fe³⁺ was increased. BODIPY oxidized signal increased and through the time-course these changes correlated with blebbing of cell membrane and SR-induced LDH release. These data suggested lipid peroxidation occurred via Fenton's reaction. The experiments using bafilomycin A1 and zinc protoporphyrin suggested no role of ferritinophagy or heme oxidation in the increase of LIP during SI. The extracellular source, transferrin assessed using serum transferrin bound iron (TBI) saturation showed that the depletion of TBI reduced SR-induced cell damages and additive saturation of TBI accelerated SR-induced lipid peroxidation. Furthermore, Apo-Tf dramatically blocked the increase of LIP and SR-induced damages. In conclusion, Tf-mediated iron induces the increase of LIP during SI, and it causes Fenton reaction-mediated lipid peroxidation during the early phase of SR.

From Iron Metabolism to Ferroptosis: Pathologic Changes in Coronary Heart Disease

Coronary heart disease (CHD) is closely related to oxidative stress and inflammatory response and is the most common cardiovascular disease (CVD). Iron is an essential mineral that participates in many physiological and biochemical reactions in the human body. Meanwhile, on the negative side, iron has an active redox capacity, which leads to the accumulation of reactive oxygen species (ROS) and lipid peroxidation. There is growing evidence that disordered iron metabolism is involved in CHD's pathological progression. And the result of disordered iron metabolism is associated with iron overload-induced programmed cell death, often called ferroptosis. That features iron-dependent lipid peroxidation. Ferroptosis may play a crucial role in the development of CHD, and targeting ferroptosis may be a promising option for treating CHD. Here, we review the mechanisms of iron metabolism in cardiomyocytes (CMs) and explain the correlation between iron metabolism and ferroptosis. Meanwhile, we highlight the specific roles of iron metabolism and ferroptosis in the main pathological progression of CHD.

The underlying pathological mechanism of ferroptosis in the development of cardiovascular disease

Cardiovascular diseases (CVDs) have been attracting the attention of academic society for decades. Numerous researchers contributed to figuring out the core mechanisms underlying CVDs. Among those, pathological decompensated cellular loss posed by cell death in different kinds, namely necrosis, apoptosis and necroptosis, was widely regarded to accelerate the pathological development of most heart diseases and deteriorate cardiac function. Recently, apart from programmed cell death revealed previously, ferroptosis, a brand-new cellular death identified by its ferrous-iron-dependent manner, has been demonstrated to govern the occurrence and development of different cardiovascular disorders in many types of research as well. Therefore, clarifying the regulatory function of ferroptosis is conducive to finding out strategies for cardio-protection in different conditions and improving the prognosis of CVDs. Here, molecular mechanisms concerned are summarized systematically and categorized to depict the regulatory network of ferroptosis and point out potential therapeutic targets for diverse cardiovascular disorders.

Many-Body Study of Iron(III)-Bound Human Serum Transferrin

We present the very first density functional theory and dynamical mean field theory calculations of iron-bound human serum transferrin. Peaks in the optical conductivity at 250, 300, and 450 nm were observed, in line with experimental measurements. Spin multiplet analysis suggests that the ground state is a mixed state with high entropy, indicating the importance of strong electronic correlation in this system's chemistry.

Heart Ferroportin Protein Content Is Regulated by Heart Iron Concentration and Systemic Hepcidin Expression

The purpose of the study was to investigate the expression of ferroportin protein following treatments that affect systemic hepcidin. Administration of erythropoietin to C57BL/6J mice decreased systemic hepcidin expression; it also increased heart ferroportin protein content, determined by immunoblot in the membrane fraction, to approximately 200% of control values. This increase in heart ferroportin protein is very probably caused by a decrease in systemic hepcidin expression, in accordance with the classical regulation of ferroportin by hepcidin. However, the control of heart ferroportin protein by systemic hepcidin could apparently be overridden by changes in heart non-heme iron content since injection of ferric carboxymaltose to mice at 300 mg Fe/kg resulted in an increase in liver hepcidin expression, heart non-heme iron content, and also a threefold increase in heart ferroportin protein content. In a separate experiment, feeding an iron-deficient diet to young Wistar rats dramatically decreased liver hepcidin expression, while heart non-heme iron content and heart ferroportin protein content decreased to 50% of controls. It is, therefore, suggested that heart ferroportin protein is regulated primarily by the iron regulatory protein/iron-responsive element system and that the regulation of heart ferroportin by the hepcidin-ferroportin axis plays a secondary role.

Mutant CHCHD10 causes an extensive metabolic rewiring that precedes OXPHOS dysfunction in a murine model of mitochondrial cardiomyopathy

Mitochondrial cardiomyopathies are fatal diseases, with no effective treatment. Alterations of heart mitochondrial function activate the mitochondrial integrated stress response (ISR^mt), a transcriptional program affecting cell metabolism, mitochondrial biogenesis, and proteostasis. In humans, mutations in CHCHD10, a mitochondrial protein with unknown function, were recently associated with dominant multi-system mitochondrial diseases, whose pathogenic mechanisms remain to be elucidated. Here, in CHCHD10 knockin mutant mice, we identify an extensive cardiac metabolic rewiring triggered by proteotoxic ISR^mt. The stress response arises early on, before the onset of bioenergetic impairments, triggering a switch from oxidative to glycolytic metabolism, enhancement of transsulfuration and one carbon (1C) metabolism, and widespread metabolic imbalance. In parallel, increased NADPH oxidases elicit antioxidant responses, leading to heme depletion. As the disease progresses, the adaptive metabolic stress response fails, resulting in fatal cardiomyopathy. Our findings suggest that early interventions to counteract metabolic imbalance could ameliorate mitochondrial cardiomyopathy associated with proteotoxic ISR^mt.

Sayles et al. report that mutant CHCHD10 proteotoxicity activates the mitochondrial integrated stress response (ISR^mt) in a mouse model of mitochondrial cardiomyopathy. Chronic ISR^mt causes profound metabolic imbalances, culminating in oxidative stress and iron dysregulation, ultimately resulting in mitochondrial dysfunction and contributing to disease pathogenesis.

The Emerging Role of Ferroptosis in Cardiovascular Diseases

Ferroptosis is one type of programmed cell death discovered in recent years, which is characterized by iron-dependent lipid peroxidation and participating in iron, lipid and antioxidant metabolism. Ferroptosis is different from the traditional cell death types such as apoptosis, necroptosis and autophagy in morphology, biochemistry and genetics. Cardiovascular diseases are considered as an important cause of death from non-communicable diseases in the global population and poses a serious threat to human health. Apoptosis has long been thought to be the major type of cardiomyocyte death, but now ferroptosis has been shown to play a major role in cardiovascular diseases as well. This review will discuss related issues such as the mechanisms of ferroptosis and its effects on the occurrence and development of cardiovascular diseases, aiming to provide a novel target for the prevention and treatment of cardiovascular diseases.

Prevalence and determinants of iron deficiency in cardiac amyloidosis

Aims

Iron deficiency (ID) is common in patient with chronic heart failure (HF) and has been widely studied. In contrast, data concerning ID in cardiac amyloidosis (CA) are limited. Amyloidosis is a severe and fatal systemic disease, characterized by an accumulation of amyloid fibrils in various tissues/organs, including nerves, kidneys, gastrointestinal tract, and heart. Amyloid deposits in the heart eventually cause HF. The main subtypes of CA are light chain (AL), hereditary transthyretin (ATTRv), and wild‐type transthyretin (ATTRwt). We performed this study to determine the prevalence, clinical outcome (all‐cause mortality), and determinants of ID among the three main subtypes of CA.

Methods and results

Iron deficiency status were analysed in 816 CA patients enrolled at the French Referral Centre for Cardiac Amyloidosis: 271 (33%) had AL, 164 (20%) ATTRv, and 381 (47%) ATTRwt. ID affected 49% of CA patients, 45% with AL, 58% with ATTRv, and 48% with ATTRwt. We identified ATTR status (ATTRv P = 0.003, ATTRwt P = 0.037), diabetes (P = 0.003), aspirin treatment (P = 0.009), haemoglobin levels (P = 0.006), and altered global longitudinal strain (P = 0.02) as independent ID determinants. There is no difference in all‐cause mortality considering ID status.

Conclusions

Iron deficiency is common in patients with CA, irrespective of the subtype. Patients seem more likely to have ID if diagnosed with ATTR, if diabetic, and/or treated with aspirin. In CA, the benefit of intravenous iron therapy, for ID, on morbidity and mortality needs further study.

Triad role of hepcidin, ferroportin, and Nrf2 in cardiac iron metabolism: From health to disease

Iron is an essential trace element required for several vital physiological and developmental processes, including erythropoiesis, bone, and neuronal development. Iron metabolism and oxygen homeostasis are interlinked to perform a vital role in the functionality of the heart. The metabolic machinery of the heart utilizes almost 90 % of oxygen through the electron transport chain. To handle this tremendous level of oxygen, the iron metabolism in the heart is utmost crucial. Iron availability to the heart is therefore tightly regulated by (i) the hepcidin/ferroportin axis, which controls dietary iron absorption, storage, and recycling, and (ii) iron regulatory proteins 1 and 2 (IRP1/2) via hypoxia inducible factor 1 (HIF1) pathway. Despite iron being vital to the heart, recent investigations have demonstrated that iron imbalance is a common manifestation in conditions of heart failure (HF), since free iron readily transforms between Fe²⁺ and Fe³⁺via the Fenton reaction, leading to reactive oxygen species (ROS) production and oxidative damage. Therefore, to combat iron-mediated oxidative stress, targeting Nrf2/ARE antioxidant signaling is rational. The involvement of Nrf2 in regulating several genes engaged in heme synthesis, iron storage, and iron export is beginning to be uncovered. Consequently, it is possible that Nrf2/hepcidin/ferroportin might act as an epicenter connecting iron metabolism to redox alterations. However, the mechanism bridging the two remains obscure. In this review, we tried to summarize the contemporary insight of how cardiomyocytes regulate intracellular iron levels and discussed the mechanisms linking cardiac dysfunction with iron imbalance. Further, we emphasized the impact of Nrf2 on the interplay between systemic/cardiac iron control in the context of heart disease, particularly in myocardial ischemia and HF.

Fenton-like reaction of the iron(II)-histidine complex generates hydroxyl radicals: implications for oxidative stress and Alzheimer's disease

The hydroxyl radical (˙OH), generated from Fenton/Fenton-like reactions of iron(II) species in biology, can oxidatively damage biomolecules, inducing oxidative stress and diseases. However, this common understanding has been questioned recently after a carbonate radical was observed from the Fenton-like reaction of the iron(II)-carbonate complex. Herein, we report that the Fenton-like reaction of the iron(II)-histidine complex, one major iron(II) species in blood plasma, can occur at neutral pH to generate ˙OH, not iron(IV). Our findings and critical analyses on relevant studies clarify the above doubt, reveal a new pathway of causing oxidative stress by the iron(II) species, and have implications for Alzheimer's disease.

Dysregulation of iron metabolism in cardiovascular diseases: From iron deficiency to iron overload

Iron deficiency and iron overload are the most prevalent and opposite forms of dysregulated iron metabolism that affect approximately 30 percent of the world population, in particularly, elderly and patients with chronic diseases. Both iron deficiency and overload are frequently observed in a wide range of cardiovascular diseases, contributing to the onset and progression of these diseases. One of the devastating seqeulae for iron overload is the induction of ferroptosis, a newly defined form of regulated cell death which heavily impacts cardiac function through ferroptotic cell death in cardiomyocytes. In this review, we will aim to evaluate iron deficiency and iron overload in cardiovascular diseases. We will summarize current therapeutic strategies to tackle iron deficiency and iron overload, major pitfalls of current studies, and future perspectives.

Extracellular vesicles from thalassemia patients carry iron-containing ferritin and hemichrome that promote cardiac cell proliferation

Extracellular vesicles (EVs) are bioactive, submicron-sized membrane vesicles released from all cell types upon activation or apoptosis. EVs including microparticles (MPs) and exosomes have emerged as important mediators of cell-to-cell communication in both normal and pathological states including thalassemia (thal). However, the role of EVs derived from β-thal patients with iron overload (+ IO) and without iron overload (-IO) on cardiac cells is unclear. We hypothesized plasma EVs in thal patients containing ferritin (iron storage protein) and a denaturated hemoglobin-hemichrome that induce cardiac cell proliferation. The origins and numbers of EVs isolated from plasma of normal, thal (+ IO), and (- IO) patients were compared and determined for their iron and iron-containing proteins along with their effects on cardiac and endothelial cells. Data shows that MPs were originated from many cell sources with marked numbers of platelet origin. Only the number of RBC-derived MPs in thal (+ IO) patients was significantly high when compared to normal controls. Although MPs derived from both normal and thal patients promoted cardiac cell proliferation in a dose-dependent manner, only exosomes from thal patients promoted cardiac cell proliferation compared to the untreated. Moreover, the exosomes from thal (+ IO) potentially induce higher cardiac cell proliferation and angiogenesis in terms of tube number than thal (- IO) and normal controls. Interestingly, ferritin content in the exosomes isolated from thal (+ IO) was higher than that found in the MPs isolated from the same patient. The exosomes of thal patients with higher serum ferritin level also contained greater level of ferritin inside the exosomes. Apart from ferritin, there were trends of increasing hemichrome and iron presented in the plasma EVs and EV-treated H9C2 cells. Findings from this study support the hypothesis that EVs from β-thal patients carry iron-load proteins that leads to the induction of cardiac cell proliferation.

Systemic iron deficiency does not affect the cardiac iron content and progression of heart failure

Chronic heart failure (HF) is often accompanied by systemic iron deficiency (ID). However, effects of ID on cardiac iron status and progression of HF are unknown. To investigate these effects rats underwent LAD ligation to induce post-myocardial infarction HF or sham operation. After 3 weeks the animals from both groups were randomized into three subgroups: control, moderate ID and severe ID+anemia (IDA) by a combination of phlebotomy and low iron diet for 5 weeks. Serum and hepatic iron content were reduced by 55% and 70% (ID) and by 80% and 77% (IDA), respectively, while cardiac iron content was unchanged in HF rats. Changes in expression of all cardiomyocyte iron handling proteins indicating preserved cardiomyocytes iron status in HF and ID/IDA. Contractile function of LV cardiomyocytes, Ca²⁺ transient amplitude, sarcoplasmic reticulum Ca²⁺ release and SERCA2a function was augmented by ID and IDA and it was accompanied by an increase in serum catecholamines. Neither ID nor IDA affected left ventricular (LV) systolic or diastolic function or dimensions. To sum up, systemic ID does not result in cardiac ID and does not affect progression of HF and even improves contractile function and Ca²⁺ handling of isolated LV cardiomyocytes, however, at the cost of increased catecholamine level. This suggests that intravenous iron therapy should be considered as an additional therapeutic option in HF, preventing the increase of catecholaminergic drive with its well-known long-term adverse effects.

Neurohormonal activation induces intracellular iron deficiency and mitochondrial dysfunction in cardiac cells

Background

Iron deficiency (ID) is common in patients with heart failure (HF) and is associated with poor outcomes, yet its role in the pathophysiology of HF is not well-defined. We sought to determine the consequences of HF neurohormonal activation in iron homeostasis and mitochondrial function in cardiac cells.

Methods

HF was induced in C57BL/6 mice by using isoproterenol osmotic pumps and embryonic rat heart-derived H9c2 cells were subsequently challenged with Angiotensin II and/or Norepinephrine. The expression of several genes and proteins related to intracellular iron metabolism were assessed by Real time-PCR and immunoblotting, respectively. The intracellular iron levels were also determined. Mitochondrial function was analyzed by studying the mitochondrial membrane potential, the accumulation of radical oxygen species (ROS) and the adenosine triphosphate (ATP) production.

Results

Hearts from isoproterenol-stimulated mice showed a decreased in both mRNA and protein levels of iron regulatory proteins, transferrin receptor 1, ferroportin 1 and hepcidin compared to control mice. Furthermore, mitoferrin 2 and mitochondrial ferritin were also downregulated in the hearts from HF mice. Similar data regarding these key iron regulatory molecules were found in the H9c2 cells challenged with neurohormonal stimuli. Accordingly, a depletion of intracellular iron levels was found in the stimulated cells compared to non-stimulated cells, as well as in the hearts from the isoproterenol-induced HF mice. Finally, neurohormonal activation impaired mitochondrial function as indicated by the accumulation of ROS, the impaired mitochondrial membrane potential and the decrease in the ATP levels in the cardiac cells.

Conclusions

HF characteristic neurohormonal activation induced changes in the regulation of key molecules involved in iron homeostasis, reduced intracellular iron levels and impaired mitochondrial function. The current results suggest that iron could be involved in the pathophysiology of HF.

In-depth review: is hepcidin a marker for the heart and the kidney?

Iron is an essential trace element involved in oxidation-reduction reactions, oxygen transport and storage, and energy metabolism. Iron in excess can be toxic for cells, since iron produces reactive oxygen species and is important for survival of pathogenic microbes. There is a fine-tuning in the regulation of serum iron levels, determined by intestinal absorption, macrophage iron recycling, and mobilization of hepatocyte stores versus iron utilization, primarily by erythroid cells in the bone marrow. Hepcidin is the major regulatory hormone of systemic iron homeostasis and is upregulated during inflammation. Hepcidin metabolism is altered in chronic kidney disease. Ferroportin is an iron export protein and mediates iron release into the circulation from duodenal enterocytes, splenic reticuloendothelial macrophages, and hepatocytes. Systemic iron homeostasis is controlled by the hepcidin-ferroportin axis at the sites of iron entry into the circulation. Hepcidin binds to ferroportin, induces its internalization and intracellular degradation, and thus inhibits iron absorption from enterocytes, and iron release from macrophages and hepatocytes. Recent data suggest that hepcidin, by slowing or preventing the mobilization of iron from macrophages, may promote atherosclerosis and may be associated with increased cardiovascular disease risk. This article reviews the current data regarding the molecular and cellular pathways of systemic and autocrine hepcidin production and seeks the answer to the question whether changes in hepcidin translate into clinical outcomes of all-cause and cardiovascular mortality, and cardiovascular and renal end-points.

Clinician's Corner: Anemia at Altitude-Iron Deficiency and Other Acquired Anemias

DeLoughery, Thomas G. Clinician's corner: Anemia at altitude-Iron deficiency and other acquired anemias. High Alt Med Biol. 22:000-000, 2021.-Acquired anemias are common throughout the world. This article will discuss iron deficiency and other acquired causes of anemia such as inflammation and renal disease. Iron deficiency with or without anemia can detract from performance and may be a risk factor for altitude sickness. Anyone considering going to altitude should be screened for iron deficiency with a serum ferritin if they have risk factors for iron deficiency. The effects of other acquired anemias are less well defined. Several other diseases can also lead to anemia, and altitude challenges are more related to the underlying disease than to anemia.

Sorting nexin 3 induces heart failure via promoting retromer-dependent nuclear trafficking of STAT3

Sorting nexins (SNXs), the retromer-associated cargo binding proteins, have emerged as critical regulators of the trafficking of proteins involved in the pathogenesis of diverse diseases. However, studies of SNXs in the development of cardiovascular diseases, especially cardiac hypertrophy and heart failure, are lacking. Here, we ask whether SNX3, the simplest structured isoform in the SNXs family, may act as a key inducer of myocardial injury. An increased level of SNX3 was observed in failing hearts from human patients and mice. Cardiac-specific Snx3 knockout (Snx3-cKO) mice and Snx3 transgenic (Snx3-cTg) mice were generated to evaluate the role of Snx3 in myocardial hypertrophy, fibrosis, and heart function by morphology, echocardiography, histological staining, and hypertrophic biomarkers. We report that Snx3-cKO in mice significantly protected against isoproterenol (ISO)-induced cardiac hypertrophy at 12 weeks. Conversely, Snx3-cTg mice were more susceptible to ISO-induced cardiac hypertrophy at 12 weeks and showed aggravated cardiac injury even heart failure at 24 weeks. Immunoprecipitation-based mass spectrometry, immunofluorescent staining, co-immunoprecipitation, localized surface plasmon resonance, and proximity ligation assay were performed to examine the direct interaction of SNX3-retromer with signal transducer and activator of transcription 3 (STAT3). We discovered that STAT3 was a new interacting partner of SNX3-retromer, and SNX3-retromer served as an essential platform for assembling gp130/JAK2/STAT3 complexes and subsequent phosphorylation of STAT3 by direct combination at EE. SNX3-retromer and STAT3 complexes were transiently imported into the nucleus after hypertrophic stimuli. The pharmacological inhibition or knockdown of STAT3 reversed SNX3 overexpression-induced myocardial injury. STAT3 overexpression blunts the beneficial function of SNX3 knockdown on hypertrophic cardiomyocytes. We show that SNX3-retromer promoted importin α3-mediated STAT3 nuclear trafficking and ultimately leading to cardiac injury. Taken together, our study reveals that SNX3 plays a key role in cardiac function and implicates SNX3 as a potential therapeutic target for cardiac hypertrophy and heart failure.

Abnormal iron status is associated with an increased risk of mortality in patients on peritoneal dialysis

BACKGROUND AND AIMS

Iron deficiency is prevalent, but there is limited data about the relationship between iron status and poor outcomes in chronic kidney disease patients undergoing peritoneal dialysis (PD). We aimed to investigate the association between iron status and mortality in PD patients.

METHODS AND RESULTS

This retrospective study was conducted on incident PD patients from January 2006 to December 2016 and followed up until December 2018. Patients were categorized into four groups according to baseline serum transferrin saturation (percent) and ferritin levels (ng/ml): reference (20-30%, 100-500 ng/ml), absolute iron deficiency (<20%, <100 ng/ml), function iron deficiency (FID) (<20%, >100 ng/ml), and high iron (>30%, >500 ng/ml). Among the 1173 patients, 77.5% had iron deficiency. During a median follow-up period of 43.7 months, compared with the reference group, the FID group was associated with increased risk for all-cause [adjusted hazard ratio (aHR) 1.87, 95% confidence interval (95% CI) 1.05-3.31, P = 0.032], but not cardiovascular (CV) mortality. Additionally, the high iron group had a more than four-fold increased risk of both all-cause and CV mortality [aHR 4.32 (95% CI 1.90-9.81), P < 0.001; aHR 4.41 (95% CI 1.47-13.27), P = 0.008; respectively].

CONCLUSION

FID and high iron predict worse prognosis of patients on PD.

Iron Availability in Tissue Microenvironment: The Key Role of Ferroportin

Body iron levels are regulated by hepcidin, a liver-derived peptide that exerts its function by controlling the presence of ferroportin (FPN), the sole cellular iron exporter, on the cell surface. Hepcidin binding leads to FPN internalization and degradation, thereby inhibiting iron release, in particular from iron-absorbing duodenal cells and macrophages involved in iron recycling. Disruption in this regulatory mechanism results in a variety of disorders associated with iron-deficiency or overload. In recent years, increasing evidence has emerged to indicate that, in addition to its role in systemic iron metabolism, FPN may play an important function in local iron control, such that its dysregulation may lead to tissue damage despite unaltered systemic iron homeostasis. In this review, we focus on recent discoveries to discuss the role of FPN-mediated iron export in the microenvironment under both physiological and pathological conditions.

Ferroptosis and its emerging roles in cardiovascular diseases

Ferroptosis is a new form of regulated cell death (RCD) driven by iron-dependent lipid peroxidation, which is morphologically and mechanistically distinct from other forms of RCD including apoptosis, autophagic cell death, pyroptosis and necroptosis. Recently, ferroptosis has been found to participate in the development of various cardiovascular diseases (CVDs) including doxorubicin-induced cardiotoxicity, ischemia/reperfusion-induced cardiomyopathy, heart failure, aortic dissection and stroke. Cardiovascular homeostasis is indulged in delicate equilibrium of assorted cell types composing the heart or vessels, and how ferroptosis contributes to the pathophysiological responses in CVD progression is unclear. Herein, we reviewed recent discoveries on the basis of ferroptosis and its involvement in CVD pathogenesis, together with related therapeutic potentials, aiming to provide insights on fundamental mechanisms of ferroptosis and implications in CVDs and associated disorders.

HSF1 functions as a key defender against palmitic acid-induced ferroptosis in cardiomyocytes

Palmitic acid (PA)-induced myocardial injury is considered a critical contributor to the development of obesity and type 2 diabetes mellitus (T2DM)-related cardiomyopathy. However, the underlying mechanism has not been fully understood. Here, we demonstrated that PA induced the cell death of H9c2 cardiomyoblasts in a dose- and time-dependent manner, while different ferroptosis inhibitors significantly abrogated the cell death of H9c2 cardiomyoblasts and primary neonatal rat cardiomyocytes exposed to PA. Mechanistically, PA decreased the protein expression levels of both heat shock factor 1 (HSF1) and glutathione peroxidase 4 (GPX4) in a dose- and time-dependent manner, which were restored by different ferroptosis inhibitors. Overexpression of HSF1 not only alleviated PA-induced cell death and lipid peroxidation but also improved disturbed iron homeostasis by regulating the transcription of iron metabolism-related genes (e.g., Fth1, Tfrc, Slc40a1). Additionally, PA-blocked GPX4 protein expression was evidently restored by HSF1 overexpression. Inhibition of endoplasmic reticulum (ER) stress rather than autophagy contributed to HSF1-mediated GPX4 expression. Moreover, GPX4 overexpression protected against PA-induced ferroptosis, whereas knockdown of GPX4 reversed the anti-ferroptotic effect of HSF1. Consistent with the in vitro findings, PA-challenged Hsf1-/- mice exhibited more serious ferroptosis, increased Slc40a1 and Fth1 mRNA expression, decreased GPX4 and TFRC expression and enhanced ER stress in the heart compared with Hsf1+/+ mice. Altogether, HSF1 may function as a key defender against PA-induced ferroptosis in cardiomyocytes by maintaining cellular iron homeostasis and GPX4 expression.

Retene, pyrene and phenanthrene cause distinct molecular-level changes in the cardiac tissue of rainbow trout (Oncorhynchus mykiss) larvae, part 2 - Proteomics and metabolomics

Polycyclic aromatic hydrocarbons (PAHs) are global contaminants of concern. Despite several decades of research, their mechanisms of toxicity are not very well understood. Early life stages of fish are particularly sensitive with the developing cardiac tissue being a main target of PAHs toxicity. The mechanisms of cardiotoxicity of the three widespread model polycyclic aromatic hydrocarbons (PAHs) retene, pyrene and phenanthrene were explored in rainbow trout (Oncorhynchus mykiss) early life stages. Newly hatched larvae were exposed to sublethal doses of each individual PAH causing no detectable morphometric alterations. Changes in the cardiac proteome and metabolome were assessed after 7 or 14 days of exposure to each PAH. Phase I and II enzymes regulated by the aryl hydrocarbon receptor were significantly induced by all PAHs, with retene being the most potent compound. Retene significantly altered the level of several proteins involved in key cardiac functions such as muscle contraction, cellular tight junctions or calcium homeostasis. Those findings were quite consistent with previous reports regarding the effects of retene on the cardiac transcriptome. Significant changes in proteins linked to iron and heme metabolism were observed following exposure to pyrene. While phenanthrene also altered the levels of several proteins in the cardiac tissue, no clear mechanisms or pathways could be highlighted. Due to high variability between samples, very few significant changes were detected in the cardiac metabolome overall. Slight but significant changes were still observed for pyrene and phenanthrene, suggesting possible effects on several energetic or signaling pathways. This study shows that early exposure to different PAHs can alter the expression of key proteins involved in the cardiac function, which could potentially affect negatively the fitness of the larvae and later of the juvenile fish.

Cardiomyopathy in Thalassemia: Quick Review from Cellular Aspects to Diagnosis and Current Treatments

BACKGROUND

Cardiomyopathic manifestations induced by continuous blood transfusion are the leading cause of death among patients with thalassemia major (TM). Despite introduction of chelation therapy, heart failure after cardiomyopathic manifestations is still a major threat to patients.

METHODS

We performed a search of relevant English-language literature, retrieving publications from the PubMed database and the Google Scholar search engine (2005-2018). We used "thalassemia major", "cardiomyopathy", "iron overload", "cardiac magnetic resonance T2" "chelation therapy", and "iron burden" as keywords.

RESULTS

The results of the studies we found suggest that cardiac hepcidin is a major regulator of iron homeostasis in cardiac tissue. Unlike previous assumptions, the heart appears to have a limited regeneration capability, originating from a small population of hypoxic cardiomyocytes.

CONCLUSIONS

Oxygen levels determine cardiomyocyte gene-expression patterns. Upregulation of cardiac hepcidin in hypoxia preserves cardiomyocytes from forming out of reactive oxygen species catalyzed by free cellular iron in cardiomyocytes. Using the limited regeneration capacity of cardiac cells and gaining further understanding of the cellular aspects of cardiomyopathic manifestations may help health care professionals to develop new therapeutic strategies.

An Unbiased Proteomics Method to Assess the Maturation of Human Pluripotent Stem Cell-Derived Cardiomyocytes

RATIONALE

Human pluripotent stem cell (hPSC)-derived cardiomyocytes exhibit the properties of fetal cardiomyocytes, which limits their applications. Various methods have been used to promote maturation of hPSC-cardiomyocytes; however, there is a lack of an unbiased and comprehensive method for accurate assessment of the maturity of hPSC-cardiomyocytes.

OBJECTIVE

We aim to develop an unbiased proteomics strategy integrating high-throughput top-down targeted proteomics and bottom-up global proteomics for the accurate and comprehensive assessment of hPSC-cardiomyocyte maturation.

METHODS AND RESULTS

Utilizing hPSC-cardiomyocytes from early- and late-stage 2-dimensional monolayer culture and 3-dimensional engineered cardiac tissue, we demonstrated the high reproducibility and reliability of a top-down proteomics method, which enabled simultaneous quantification of contractile protein isoform expression and associated post-translational modifications. This method allowed for the detection of known maturation-associated contractile protein alterations and, for the first time, identified contractile protein post-translational modifications as promising new markers of hPSC-cardiomyocytes maturation. Most notably, decreased phosphorylation of α-tropomyosin was found to be associated with hPSC-cardiomyocyte maturation. By employing a bottom-up global proteomics strategy, we identified candidate maturation-associated markers important for sarcomere organization, cardiac excitability, and Ca2+ homeostasis. In particular, upregulation of myomesin 1 and transmembrane 65 was associated with hPSC-cardiomyocyte maturation and validated in cardiac development, making these promising markers for assessing maturity of hPSC-cardiomyocytes. We have further validated α-actinin isoforms, phospholamban, dystrophin, αB-crystallin, and calsequestrin 2 as novel maturation-associated markers, in the developing mouse cardiac ventricles.

CONCLUSIONS

We established an unbiased proteomics method that can provide accurate and specific assessment of the maturity of hPSC-cardiomyocytes and identified new markers of maturation. Furthermore, this integrated proteomics strategy laid a strong foundation for uncovering the molecular pathways involved in cardiac development and disease using hPSC-cardiomyocytes.

Iron and oxidizing species in oxidative stress and Alzheimer's disease

Iron species can participate in the Fenton or Fenton-like reaction to generate oxidizing species that can cause oxidative damages to biomolecules and induce oxidative stress in the body. Furthermore, iron accumulation and oxidative stress have been shown to associate with the pathological progression of neurodegenerative disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). In this review, the role of iron species in generating the most deleterious free radical species (ie, hydroxyl radical) and effects of this species in causing oxidative stress in vivo are described. The implications of oxidative stress and the recently recognized cell death pathway (ie, ferroptosis) to AD are addressed. Strategies to combat this neurodegenerative disease, such as iron chelation and antioxidant therapies, and future research directions on this aspect are also discussed.

Detection and identification of the oxidizing species generated from the physiologically important Fenton-like reaction of iron(II)-citrate with hydrogen peroxide

The Fenton-like reaction of iron(II)-citrate with hydrogen peroxide is physiologically important because it is associated with the oxidative stress and pathological processes induced by the redox-active iron pool in vivo. However, the oxidizing species generated from this reaction at neutral pH has not been convincingly identified because two extremely unstable and hard-to-differentiate species, the hydroxyl radical (^•OH) and iron(IV) (ferryl) species, can be produced. Identifying this species is essential for understanding the reaction mechanism. Although there were few data that reported the detection of ^•OH from this reaction by using the EPR and fluorescence techniques, most of these data were obtained without the necessary assessment with a ^•OH scavenger. Furthermore, these two techniques may not be able to differentiate the ^•OH and iron(IV) species. Thus, these reported data cannot lead to a convincing conclusion that the ^•OH, not the iron(IV) species, was generated. Therefore, in the study reported herein, we carried out systematic investigations first by using the EPR and fluorescence techniques combined with a ^•OH scavenger to detect the oxidizing species generated from this Fenton-like reaction. Then we utilized NMR spectroscopy and for the first time obtained convincing evidence to demonstrate that this oxidizing species is the ^•OH rather than iron(IV) species. We also determined the second-order rate constant of the reaction, 3.6 × 10³ M^-1s^-1 (pH7.0, 25 °C), by using the stopped-flow spectrophotometry. On the basis of these findings, a scheme is proposed for the mechanism of this physiologically important Fenton-like reaction.