Iron Metabolism in Cardiovascular Disease: Physiology, Mechanisms, and Therapeutic Targets

Nephrology: What You May Have Missed in 2023

This article highlights a selection of important nephrology studies published in 2023 that have relevance for nonnephrologist physicians. Four studies examined progression of chronic kidney disease or cardiovascular disease with respect to finerenone use, magnesium supplementation, iron markers, and COVID-19. Two studies examined treatments to improve specific aspects of chronic kidney disease management, including daprodustat to address anemia and patiromer to address hyperphosphatemia. One study showed that acetazolamide added to loop diuretics increased diuresis in acute decompensated heart failure across a wide range of renal function. Another study found that once-daily hydrochlorothiazide did not prevent kidney stone recurrence. Finally, an antibiotic stewardship intervention safely reduced antibiotic prescribing for suspected urinary tract infection in frail older adults.

Endothelial transferrin receptor 1 contributes to thrombogenesis through cascade ferroptosis

Oxidative stress and iron accumulation-induced ferroptosis occurs in injured vascular cells and can promote thrombogenesis. Transferrin receptor 1 (encoded by the TFRC gene) is an initial element involved in iron transport and ferroptosis and is highly expressed in injured vascular tissues, but its role in thrombosis has not been determined. To explore the potential mechanism and therapeutic effect of TFRC on thrombogenesis, a DVT model of femoral veins (FVs) was established in rats, and weighted correlation network analysis (WGCNA) was used to identify TFRC as a hub protein that is associated with thrombus formation. TFRC was knocked down by adeno-associated virus (AAV) or lentivirus transduction in FVs or human umbilical vein endothelial cells (HUVECs), respectively. Thrombus characteristics and ferroptosis biomarkers were evaluated. Colocalization analysis, molecular docking and coimmunoprecipitation (co-IP) were used to evaluate protein interactions. Tissue-specific TFRC knockdown alleviated iron overload and redox stress, thereby preventing ferroptosis in injured FVs. Loss of TFRC in injured veins could alleviate thrombogenesis, reduce thrombus size and attenuate hypercoagulability. The protein level of thrombospondin-1 (THBS1) was increased in DVT tissues, and silencing TFRC decreased the protein level of THBS1. In vitro experiments further showed that TFRC and THBS1 were sensitive to erastin-induced ferroptosis and that TFRC knockdown reversed this effect. TFRC can interact with THBS1 in the domain spanning from TSR1-2 to TSR1-3 of THBS1. Amino acid sites, including GLN320 of TFRC and ASP502 of THBS1, could be potential pharmacological targets. Erastin induced ferroptosis affected extracellular THBS1 levels and weakened the interaction between TFRC and THBS1 both in vivo and in vitro, and promoted the interaction between THBS1 and CD47. This study revealed a linked relationship between venous ferroptosis and coagulation cascades. Controlling TFRC and ferroptosis in endothelial cells can be an efficient approach for preventing and treating thrombogenesis.

Inhibition of CISD1 alleviates mitochondrial dysfunction and ferroptosis in mice with acute lung injury

The NET family member, CDGSH iron-sulfur domain-containing protein 1 (CISD1), is located in theoutermembrane of mitochondria, where it regulates energy and iron metabolism. CISD1 has vital functions in certain human diseases; however, its function in acute lung injury (ALI) is unknown. ALI pathogenesis critically involves mitochondrial dysfunction and ferroptosis, which might be regulated by CISD1. Therefore, we investigated CISD1's function in mitochondrial dysfunction and ferroptosis regulation in lipopolysaccharide (LPS)-induced ALI. We found that CISD1 was upregulated in LPS-induced ALI,and silencing Cisd1 prevented cell apoptosis and increased cell viability. When CISD1was inhibited by mitoNEET ligand-1 (NL-1) there was a significant mitigation of pathological injury and lung edema, and reduced numbers of total cells, polymorphonuclear leukocytes, and a decreased protein content in the bronchoalveolar lavage fluid (BALF). Moreover, inhibition of CISD1 markedly decreased the interleukin (IL)6, IL-1β, and tumor necrosis factor alpha (TNF-α) levels in the lungs and BALF of ALI-model mice. Silencing of Cisd1 prevented LPS-induced mitochondrial membrane potential depolarization, cellular ATP reduction, and reactive oxygen species (ROS) accumulation, suggesting mitochondrial protection. ALI activated ferroptosis, as evidenced by the increased lipid-ROS, intracellular Fe2+ level, reduced Gpx4 (glutathione peroxidase 4) expression, and the glutathione/glutathione disulfide ratio. Interestingly, inhibition of CISD1 reduced LPS-induced ferroptosis in vivo and in vitro. In conclusion, inhibition of CISD1 alleviated mitochondrial dysfunction and ferroptosis in LPS-induced ALI, identifying CISD1 as possible target for therapy of LPS-induced ALI.

The EAT-Lancet Diet Index, Plasma Proteins, and Risk of Heart Failure in a Population-Based Cohort

BACKGROUND

The landmark EAT-Lancet Commission proposed that a planetary health diet is comprised mainly of plant-based foods. However, studies examining whether this diet is associated with heart failure (HF) are currently lacking. In addition, the potential proteomics mechanism on the association between diet and HF warrants further elucidation.

OBJECTIVES

This study aims to both examine the association between the EAT-Lancet diet index and risk of HF and identify plasma proteins underlying such an association.

METHODS

This prospective cohort study included 23,260 participants. HF cases during the follow-up were identified through the Swedish national register. An EAT-Lancet diet index (score range: 0-42) was created to assess adherence to the EAT-Lancet reference diet. In a subcohort (n = 4,742), fasting plasma proteins were quantified.

RESULTS

During a median follow-up of 25.0 years, 1,768 incident HF cases were documented. After adjusting for sociodemographic, lifestyle, diabetes, hypertension, use of lipid-lowering drugs, and body mass index, the HR per 3-point increase of the EAT-Lancet diet index was 0.93 (95% CI: 0.88-0.97). This association was robust in several sensitivity analyses. Among the included 136 plasma proteins, a total of 8 proteins (AM, GDF15, IL6, TIM, CTSD, CCL20, FS, and FUR) were both inversely associated with the EAT-Lancet diet index and positively associated with risk of HF; the overall proteomic score mediated 9.4% (95% CI: 2.2%-32.1%) of the association.

CONCLUSIONS

Higher adherence to the EAT-Lancet diet was associated with a lower risk of HF. The identified eight plasma proteins provide information on potential pathways mediating such an association.

The deletion of ppr2 interferes iron sensing and leads to oxidative stress response in Schizosaccharomyces pombe

Pentatricopeptide repeat proteins are involved in mitochondrial both transcriptional and posttranscriptional regulation. Schizosaccharomyces pombe Ppr2 is a general mitochondrial translation factor that plays a critical role in the synthesis of all mitochondrial DNA-encoded oxidative phosphorylation subunits, which are essential for mitochondrial respiration. Our previous analysis showed that ppr2 deletion resulted in increased expression of iron uptake genes and caused ferroptosis-like cell death in S. pombe. In the present work, we showed that deletion of ppr2 reduced viability on glycerol- and galactose-containing media.Php4 is a transcription repressor that regulates iron homeostasis in fission yeast. We found that in the ppr2 deletion strain, Php4 was constitutively active and accumulated in the nucleus in the stationary phase. We also found that deletion of ppr2 decreased the ferroptosis-related protein Gpx1 in the mitochondria. Overexpression of Gpx1 improves the viability of Δppr2 cells. We showed that the deletion of ppr2 increased the production of ROS, downregulated heme synthesis and iron-sulfur cluster proteins, and induced stress proteins. Finally, we observed the nuclear accumulation of Pap1-GFP and Sty1-GFP, suggesting that Sty1 and Pap1 in response to cellular stress in the ppr2 deletion strain. These results suggest thatppr2 deletion may cause mitochondrial dysfunction, which is likely to lead to iron-sensing defect and iron starvation response, resulting in perturbation of iron homeostasis and increased hydroxyl radical production. The increased hydroxyl radical production triggers cellular responses in theppr2 deletion strain.

Relationship between serum iron level and physical function in heart failure patients is lost by presence of diabetes

AIMS

Iron deficiency (ID) is common in patients with heart failure (HF) and is reportedly associated with exercise intolerance and impaired quality of life. Iron supplementation therapy in HF patients with ID improves exercise capacity. Conversely, protective roles of iron depletion in the development of diabetes mellitus (DM) and its complications have been proposed. This study aimed to determine the impact of ID on physical function in HF patients with and without DM.

METHODS AND RESULTS

We enrolled consecutive patients who were admitted to our institute for HF diagnosis and management. The short physical performance battery (SPPB) was used to evaluate physical function, and low physical function was defined as an SPPB score of <10 points as individuals with SPPB scores of <10 points are most likely to be classified as frail and are at high risk for disability and future adverse events, including death. ID was defined as serum ferritin < 100 or 100-299 ng/mL when transferrin saturation (TSAT) was <20% according to the HF guidelines. Among the 562 HF patients (72 ± 14 years old; 56% male), 329 patients (58%) and 191 patients (34%) had ID and low physical function, respectively. Multivariate logistic regression analysis showed that TSAT as a continuous variable, but not ID, was a predictor of low physical function (odds ratio: 0.980, P = 0.024). Subgroup analysis showed that a significant association between low TSAT and low physical function was lost in HF patients with DM (P for interaction < 0.001). A spline dose-response curve for the relationship between TSAT and risk of low physical function with adjustments for covariates associated with low physical function in non-DM patients was almost linear with an increase in the risk of low physical function as the TSAT increased, but such a relationship was not found in the analyses of DM patients. A lack of close TSAT-SPPB relationship in HF patients with DM was confirmed also in a propensity-score-matched cohort.

CONCLUSIONS

TSAT as a continuous variable, but not ID, was independently associated with physical function in HF patients, and a significant association was lost in patients with HF and DM, suggesting a limited impact of iron supplementation therapy in HF patients with DM.

Pyridoxamine Limits Cardiac Dysfunction in a Rat Model of Doxorubicin-Induced Cardiotoxicity

The use of doxorubicin (DOX) chemotherapy is restricted due to dose-dependent cardiotoxicity. Pyridoxamine (PM) is a vitamin B6 derivative with favorable effects on diverse cardiovascular diseases, suggesting a cardioprotective effect on DOX-induced cardiotoxicity. The cardioprotective nature of PM was investigated in a rat model of DOX-induced cardiotoxicity. Six-week-old female Sprague Dawley rats were treated intravenously with 2 mg/kg DOX or saline (CTRL) weekly for eight weeks. Two other groups received PM via the drinking water next to DOX (DOX+PM) or saline (CTRL+PM). Echocardiography, strain analysis, and hemodynamic measurements were performed to evaluate cardiac function. Fibrotic remodeling, myocardial inflammation, oxidative stress, apoptosis, and ferroptosis were evaluated by various in vitro techniques. PM significantly attenuated DOX-induced left ventricular (LV) dilated cardiomyopathy and limited TGF-β1-related LV fibrotic remodeling and macrophage-driven myocardial inflammation. PM protected against DOX-induced ferroptosis, as evidenced by restored DOX-induced disturbance of redox balance, improved cytosolic and mitochondrial iron regulation, and reduced mitochondrial damage at the gene level. In conclusion, PM attenuated the development of cardiac damage after DOX treatment by reducing myocardial fibrosis, inflammation, and mitochondrial damage and by restoring redox and iron regulation at the gene level, suggesting that PM may be a novel cardioprotective strategy for DOX-induced cardiomyopathy.

Intravenous iron: an update

Iron deficiency is the most common nutritional deficiency worldwide, with significant adverse health consequences in the presence or absence of anaemia. Total dose intravenous iron replacement is recommended for replacement of iron in patients with severe iron deficiency, especially in the presence of anaemia, intolerance or inefficacy following oral iron, or states of inflammation where upregulation of hepcidin may impair gastrointestinal absorption of iron. Currently, available intravenous iron formulations have been demonstrated to have an excellent overall safety profile, but potential adverse effects, including skin staining, infusion-related reactions and hypophosphataemia, have been described. Knowledge of differences in administration and safety profiles of currently available iron formulations will allow appropriate prescription, counselling, as well as recognition and management of adverse events in patients requiring intravenous iron.

Elevated SLC40A1 impairs cardiac function and exacerbates mitochondrial dysfunction, oxidative stress, and apoptosis in ischemic myocardia

Iron homeostasis is crucial for optimal cardiac function. Iron deficiency and overload have been linked to the development of cardiomyopathy and heart failure (HF) via intricate mechanisms. Although the crucial role of SLC40A1 in iron metabolism by facilitating the efflux of cellular iron has been confirmed, its specific molecular functions in cardiovascular diseases remain poorly understood. In this study, we generated mice with inducible cardiomyocyte-specific overexpression of SLC40A1 for the first time. The overexpression of SLC40A1 in the cardiomyocytes of adult mice resulted in significant iron deficiency, leading to mitochondrial dysfunction, oxidative stress, and apoptosis, subsequently resulting in the development of fatal HF. Notably, SLC40A1 upregulation was observed in the ischemic region during the initial phase of myocardial infarction (MI), contributing to iron loss in the cardiomyocytes. Conversely, the cardiomyocyte-specific knockdown of SLC40A1 improved cardiac dysfunction after MI by enhancing mitochondrial function, suppressing oxidative stress, and reducing cardiomyocytes apoptosis. Mechanistically, Steap4 interacted with SLC40A1, facilitating SLC40A1-mediated iron efflux from cardiomyocytes. In short, our study presents evidence for the involvement of SLC40A1 in the regulation of myocardial iron levels and the therapeutic benefits of cardiomyocyte-specific knockdown of SLC40A1 in MI in mice.

Safety and Efficacy of Ferric Carboxymaltose in Heart Failure With Preserved Ejection Fraction and Iron Deficiency

Heart Failure with Preserved Ejection Fraction (HFpEF) is a prevalent cardiovascular condition characterized by a complex pathophysiology and limited therapeutic options. Coinciding iron deficiency often compounds the clinical picture, contributing to symptom burden and adverse outcomes. The review underscores the urgency for effective treatments in light of its increasing incidence and considerable healthcare burden. It highlights the clinical significance of addressing iron deficiency in HFpEF patients. FCM emerges as a promising therapeutic modality, demonstrating the ability to rapidly restore iron stores and enhance patients' quality of life while reducing hospitalization rates and mortality. The review thoroughly elucidates the impact of iron deficiency on HFpEF symptoms and outcomes, elucidating how FCM effectively mitigates these challenges. Detailed discussions encompass FCM's mechanism of action, pharmacokinetics, and safety profile. Notably, FCM's adaptability to diverse patient profiles and clinical settings is emphasized, reinforcing its clinical utility. Clinical evidence, including study designs, patient cohorts, and key findings, affirms FCM's potential as a valuable therapeutic option. Real-world data analysis further underscores FCM's practicality and safety beyond controlled clinical trials. The review concludes by addressing future research directions and critical research gaps, accentuating the need for mechanistic insights, long-term outcome studies, and refined patient selection criteria. As FCM increasingly integrates into clinical practice, it offers promise in revolutionizing HFpEF management, addressing an unmet need in this intricate cardiovascular condition.

The mechanism of ferroptosis and its related diseases

Ferroptosis, a regulated form of cellular death characterized by the iron-mediated accumulation of lipid peroxides, provides a novel avenue for delving into the intersection of cellular metabolism, oxidative stress, and disease pathology. We have witnessed a mounting fascination with ferroptosis, attributed to its pivotal roles across diverse physiological and pathological conditions including developmental processes, metabolic dynamics, oncogenic pathways, neurodegenerative cascades, and traumatic tissue injuries. By unraveling the intricate underpinnings of the molecular machinery, pivotal contributors, intricate signaling conduits, and regulatory networks governing ferroptosis, researchers aim to bridge the gap between the intricacies of this unique mode of cellular death and its multifaceted implications for health and disease. In light of the rapidly advancing landscape of ferroptosis research, we present a comprehensive review aiming at the extensive implications of ferroptosis in the origins and progress of human diseases. This review concludes with a careful analysis of potential treatment approaches carefully designed to either inhibit or promote ferroptosis. Additionally, we have succinctly summarized the potential therapeutic targets and compounds that hold promise in targeting ferroptosis within various diseases. This pivotal facet underscores the burgeoning possibilities for manipulating ferroptosis as a therapeutic strategy. In summary, this review enriched the insights of both investigators and practitioners, while fostering an elevated comprehension of ferroptosis and its latent translational utilities. By revealing the basic processes and investigating treatment possibilities, this review provides a crucial resource for scientists and medical practitioners, aiding in a deep understanding of ferroptosis and its effects in various disease situations.

Iron Status and Short-Term Recovery after Non-Severe Acute Myocarditis: A Prospective Observational Study

Pathomechanisms responsible for recovery from acute myocarditis (MCD) or progression to non-ischemic cardiomyopathy have not been comprehensively investigated. Iron, positioned at the crossroads of inflammation and the energy metabolism of cardiomyocytes, may contribute to the pathophysiology of inflammatory myocardial disease. The aim of this study was to evaluate whether systemic iron parameters are related to myocardial dysfunction in MCD patients. We prospectively enrolled 42 consecutive patients hospitalized for MCD. Their iron status and their clinical, laboratory, and echocardiographic indices were assessed during hospitalization and during ambulatory visits six weeks after discharge. A control group comprising healthy volunteers was recruited. The MCD patients had higher serum ferritin and hepcidin and lower serum iron concentration and transferrin saturation (TSAT) than the healthy controls (all p < 0.01). Six weeks after discharge, the iron status of the MCD patients was already comparable to that of the control group. During hospitalization, lower serum iron and TSAT correlated with higher NT-proBNP (both p < 0.05). In-hospital lower serum iron and TSAT correlated with both a lower left ventricular ejection fraction (LVEF) and worse left ventricular global longitudinal strain at follow-up visits (all p < 0.05). In conclusion, in patients with acute MCD, iron status is altered and normalizes within six weeks. Low serum iron and TSAT are related to greater in-hospital neurohormonal activation and subtle persistent left ventricular dysfunction.