Amlodipine decreases iron uptake and oxygen free radical production in the heart of chronically iron overloaded mice

Impact of amlodipine on clinical outcomes for heart failure in patients with dilated cardiomyopathy: a Korean nationwide cohort study

Introduction

Amlodipine, widely used as a first-line treatment for hypertension, has inconclusive clinical evidence regarding its efficacy in patients with heart failure. This retrospective cohort study aimed to investigate the clinical effectiveness of amlodipine treatment after hospitalization for heart failure in patients with dilated cardiomyopathy (DCMP).

Methods

A total of 20,851 patients who were diagnosed with DCMP and admitted for heart failure between 2005 and 2016 according to Korean nationwide medical insurance service database were enrolled. Amlodipine use was defined as its prescription at the time of discharge and for at least 180 days within a year. The primary outcome was all-cause death, and the secondary outcome was heart failure rehospitalization during a 5-year period. The outcomes between patients who received amlodipine (n = 6,798) and those who did not (n = 14,053) were compared.

Results

During the 5-year follow-up, the group treated with amlodipine exhibited a significantly lower risk of all-cause death and heart failure rehospitalization than the group not treated with amlodipine [all-cause death: adjusted hazard ratio (HR): 0.64, 95% confidence interval (CI): 0.59-0.70, p < 0.001; cardiovascular death: adjusted HR: 0.71, 95% CI: 0.62-0.81, p < 0.001; heart failure rehospitalization: adjusted HR: 0.92, 95% CI: 0.86-0.98, p = 0.006]. In a subgroup analysis, amlodipine had a significant impact on decreasing all-cause mortality in older adults, those with a higher systolic blood pressure, and those with a lower Charlson Comorbidity Index.

Conclusion

In summary, amlodipine use after hospitalization for heart failure in patients with DCMP was associated with a lower risk of all-cause death and readmission for heart failure.

Amlodipine: Can act as an antioxidant in patients with transfusion-dependent β-thalassemia? A double-blind, controlled, crossover trial

BACKGROUND AND AIM

This study aimed to assess the antioxidant effects of amlodipine in transfusion-dependent β-thalassemia (TDT) patients.

METHODS

This crossover trial consisted of two sequences (AP and PA). In the AP sequence, nine cases received amlodipine 5 mg daily (phase I) and then were switched to placebo (phase II). In PA sequence, 10 patients took the placebo (phase I) and were shifted to amlodipine (phase II). The washout period was 2 weeks. The length of each phase was 6 months. Serum malondialdehyde (MDA, μmol/L), carbonyl (protein CO, μM/L), glutathione (GSH, nM/L), and total antioxidant capacity (TAC, μmol FeSO4/L) were measured in the beginning and at the end of phases I and II. The clinical significance was viewed as a minimum change difference of 5% for each outcome between amlodipine and placebo.

RESULTS

Seventeen cases completed the study. According to the baseline MDA values, the adjusted Hedges's g for MDA was -0.59, 95% confidence interval [CI] -1.26 to 0.08. After controlling the baseline protein CO values, Hedges's g computed for protein CO was -0.11, 95% CI -0.76 to 0.55. The estimated values of the adjusted Hedges's g for GSH and TAC were also 0.26, 95% CI -0.40 to 0.91, and 0.42, 95% CI -0.24 to 1.09, respectively. The change difference for MDA was 8.3% (protein CO 2.2%, GSH 3.1%, and TAC 12.9%).

CONCLUSION

Clinically, amlodipine therapy is an efficacious adjuvant treatment with conventional iron chelators for improving the levels of MDA and TAC in patients with TDT.

Iron overload cardiomyopathy: Using the latest evidence to inform future applications

Iron overload can be the result of either dysregulated iron metabolism in the case of hereditary hemochromatosis or repeated blood transfusions in the case of secondary hemochromatosis (e.g. in β-thalassemia and sickle cell anemia patients). Under iron overload conditions, transferrin (Tf) saturation leads to an increase in non-Tf bound iron which can result in the generation of reactive oxygen species (ROS). These excess ROS can damage cellular components, resulting in the dysfunction of vital organs including iron overload cardiomyopathy (IOC). Multiple studies have demonstrated that L-type and T-type calcium channels are the main routes for iron uptake in the heart, and that calcium channel blockers, given either individually or in combination with standard iron chelators, confer cardioprotective effects under iron overload conditions. Treatment with antioxidants may also provide therapeutic benefits. Interestingly, recent studies have suggested that mitochondrial dynamics and regulated cell death (RCD) pathways are potential targets for pharmacological interventions against iron-induced cardiomyocyte injury. In this review, the potential therapeutic roles of iron chelators, antioxidants, iron uptake/metabolism modulators, mitochondrial dynamics modulators, and inhibitors of RCD pathways in IOC are summarized and discussed.

Expression of Iron Metabolism Proteins in Patients with Chronic Heart Failure

In heart failure, iron deficiency is a common comorbid disease that negatively influences exercise tolerance, number of hospitalizations and mortality rate, and this is why iron iv supplementation is recommended. Little is known about the changes in iron-related proteins in the human HF myocardium. The purpose of this study was to assess iron-related proteins in non-failing (NFH) vs. failing (FH) human myocardium. The study group consisted of 58 explanted FHs; control consisted of 31 NFHs unsuitable for transplantation. Myocardial proteins expressions: divalent metal transporter (DMT-1); L-type calcium channel (L-CH); transferrin receptors (TfR-1/TfR-2); ferritins: heavy (FT-H) or light (FT-L) chain, mitochondrial (FT-MT); ferroportin (FPN), regulatory factors and oxidative stress marker: 4-hydroxynonenal (4-HNE). In FH, the expression in almost all proteins responsible for iron transport: DMT-1, TfR-1, L-CH, except TfR-2, and storage: FT-H/-L/-MT were reduced, with no changes in FPN. Moreover, 4-HNE expression (pg/mg; NFH 10.6 ± 8.4 vs. FH 55.7 ± 33.7; p < 0.0001) in FH was increased. HNE-4 significantly correlated with DMT-1 (r = −0.377, p = 0.036), L-CH (r = −0.571, p = 0.001), FT-H (r = −0.379, p = 0.036), also FPN (r = 0.422, p = 0.018). Reducing iron-gathering proteins and elevated oxidative stress in failing hearts is very unfavorable for myocardiocytes. It should be taken into consideration before treatment with drugs or supplements that elevate free oxygen radicals in the heart.

Hereditary Hemochromatosis: A Cardiac Perspective

Hereditary hemochromatosis (HH) is a common genetic metabolic disorder characterized by excessive iron absorption and elevated serum iron levels, which accumulate in various organs, such as the heart, pancreas, gonads, and damage these organs. There are only a few articles and clinical studies describing the characteristics of cardiac involvement in HH along with the significance of early diagnosis and management in preventing complications. In this review article, we have reviewed multiple pieces of literature and gathered available information regarding the subject. We compiled the data to investigate the importance of early detection of symptoms, regular monitoring, and prompt management with strict adherence to reverse or prevent complications. This article has reviewed different aspects of cardiac hemochromatosis, such as pathogenesis, clinical presentation, diagnosis, and management. Recognition of early symptoms, diagnosis of cardiac involvement with various modalities, and implementation of early treatment are essentially the foundation of better outcomes in HH.

A double-blind, controlled, crossover trial of amlodipine on iron overload status in transfusion dependent β-thalassemia patients

BACKGROUND AND AIM

This study examined whether administration of amlodipine could improve myocardial iron loading status in patients with transfusion dependent β-thalassemia (TDT), through a placebo-controlled, crossover study.

METHODS

Amlodipine (5 mg, daily) or placebo were prescribed to all patients (n = 19) for 6 months, and after a 2-week washout period, patients were crossed over to the other group. The efficacy of amlodipine on iron loading was assessed by measuring myocardial T2*-weighted magnetic resonance imaging (MRI T2*, millisecond [ms]) and serum ferritin (ng/mL).

RESULTS

Seventeen patients completed the study. The mean ± standard deviation [SD] of myocardial MRI T2* at baseline was 9.83 ± 2.67 ms Myocardial MRI T2* value rose to 11.44 ± 4.14 ms post amlodipine treatment in all patients. After placebo, myocardial MRI T2* value reached 10.29 ± 4.01 ms After controlling the baseline measures, Hedges's g for ferritin and myocardial MRI T2* outcomes were estimated 3.84 (95% confidence interval [CI] 2.68 to 4.97) and -1.80 (95% CI -2.58 to -0.10), respectively.

CONCLUSION

Amlodipine might improve myocardial MRI T2* and serum ferritin level compared to placebo. However, larger clinical studies are needed to confirm the results.

Involvement of cytosolic and mitochondrial iron in iron overload cardiomyopathy: an update

Iron overload cardiomyopathy (IOC) is a major cause of death in patients with diseases associated with chronic anemia such as thalassemia or sickle cell disease after chronic blood transfusions. Associated with iron overload conditions, there is excess free iron that enters cardiomyocytes through both L- and T-type calcium channels thereby resulting in increased reactive oxygen species being generated via Haber-Weiss and Fenton reactions. It is thought that an increase in reactive oxygen species contributes to high morbidity and mortality rates. Recent studies have, however, suggested that it is iron overload in mitochondria that contributes to cellular oxidative stress, mitochondrial damage, cardiac arrhythmias, as well as the development of cardiomyopathy. Iron chelators, antioxidants, and/or calcium channel blockers have been demonstrated to prevent and ameliorate cardiac dysfunction in animal models as well as in patients suffering from cardiac iron overload. Hence, either a mono-therapy or combination therapies with any of the aforementioned agents may serve as a novel treatment in iron-overload patients in the near future. In the present article, we review the mechanisms of cytosolic and/or mitochondrial iron load in the heart which may contribute synergistically or independently to the development of iron-associated cardiomyopathy. We also review available as well as potential future novel treatments.

Non-transferrin-bound iron transporters

Most cells in the body acquire iron via receptor-mediated endocytosis of transferrin, the circulating iron transport protein. When cellular iron levels are sufficient, the uptake of transferrin decreases to limit further iron assimilation and prevent excessive iron accumulation. In iron overload conditions, such as hereditary hemochromatosis and thalassemia major, unregulated iron entry into the plasma overwhelms the carrying capacity of transferrin, resulting in non-transferrin-bound iron (NTBI), a redox-active, potentially toxic form of iron. Plasma NTBI is rapidly cleared from the circulation primarily by the liver and other organs (e.g., pancreas, heart, and pituitary) where it contributes significantly to tissue iron overload and related pathology. While NTBI is usually not detectable in the plasma of healthy individuals, it does appear to be a normal constituent of brain interstitial fluid and therefore likely serves as an important source of iron for most cell types in the CNS. A growing body of literature indicates that NTBI uptake is mediated by non-transferrin-bound iron transporters such as ZIP14, L-type and T-type calcium channels, DMT1, ZIP8, and TRPC6. This review provides an overview of NTBI uptake by various tissues and cells and summarizes the evidence for and against the roles of individual transporters in this process.

Management of cardiac hemochromatosis

Iron-overload syndromes may be hereditary or acquired. Patients may be asymptomatic early in the disease. Once heart failure develops, there is rapid deterioration. Cardiac hemochromatosis is characterized by a dilated cardiomyopathy with dilated ventricles, reduced ejection fraction, and reduced fractional shortening. Deposition of iron may occur in the entire cardiac conduction system, especially the atrioventricular node. Cardiac hemochromatosis should be considered in any patient with unexplained heart failure. Screening for systemic iron overload with serum ferritin and transferin saturation should be performed. If these tests are consistent with iron overload, further noninvasive and histologic confirmation is indicated to confirm organ involvement with iron overload. Cardiac magnetic resonance imaging is superior to other diagnostic tests since it can quantitatively assess myocardial iron load. Therapeutic phlebotomy is the therapy of choice in nonanemic patients with cardiac hemochromatosis. Therapeutic phlebotomy should be started in men with serum ferritin levels of 300 μg/l or more and in women with serum ferritin levels of 200 μg/l or more. Therapeutic phlebotomy consists of removing 1 unit of blood (450 to 500 ml) weekly until the serum ferritin level is 10 to 20 μg/l and maintenance of the serum ferritin level at 50 μg/l or lower thereafter by periodic removal of blood. Phlebotomy is not a treatment option in patients with anemia (secondary iron-overload disorders) nor in patients with severe congestive heart failure. In these patients, the treatment of choice is iron chelation therapy.

Roles of lipocalin 2 and adiponectin in iron overload cardiomyopathy

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

Ebselen Decreases Oxygen Free Radical Production and Iron Concentrations in the Hearts of Chronically Iron-Overloaded Mice

Chronic iron overload is a major cause of cardiac failure throughout the world, but its pathogenesis remains to be clarified. It is conjectured that the toxicity of iron is due to its ability to catalyze the formation of oxygen free radicals (OFR), which can damage cellular membranes, proteins, and DNA. The authors report on the cardioprotective effects of the glutathione peroxidase (GPx) mimic ebselen on iron concentrations in the heart and GPx activity, and on the production of the cytotoxic aldehydes hexanal, 4-hydroxyl-2-nonenal (HNE), and malondialdehyde (MDA). Fifteen B6D2F1 mice were randomized to 1 of 3 treatment groups for a total of 20 treatments: 1) control (0.1 mL normal saline i.p. per mouse, per day); 2) iron-only (10 mg iron dextran i.p. per mouse, per day); 3) iron plus ebselen (25 mg/kg p.o. per mouse, per day). In comparison to iron-only treated mice, the authors’ findings show that supplementation with ebselen can decrease both cytotoxic aldehyde and iron concentrations in heart tissue. Additionally, mice supplemented with ebselen had an increase in GPx activity level in comparison to iron-only treated mice. To the authors’knowledge, this is the first study to examine the cardioprotective effects of ebselen against OFR damage in a model of chronic iron overload. These findings suggest that ebselen may have significance in the management of disorders of iron overload.

Prooxidant mechanisms in iron overload cardiomyopathy

Iron overload cardiomyopathy (IOC), defined as the presence of systolic or diastolic cardiac dysfunction secondary to increased deposition of iron, is emerging as an important cause of heart failure due to the increased incidence of this disorder seen in thalassemic patients and in patients of primary hemochromatosis. At present, although palliative treatment by regular iron chelation was recommended; whereas IOC is still the major cause for mortality in patient with chronic heart failure induced by iron-overloading. Because iron is a prooxidant and the associated mechanism seen in iron-overload heart is still unclear; therefore, we intend to delineate the multiple signaling pathways involved in IOC. These pathways may include organelles such as calcium channels, mitochondria; paracrine effects from both macrophages and fibroblast, and novel mediators such as thromboxane A2 and adiponectin; with increased oxidative stress and inflammation found commonly in these signaling pathways. With further understanding on these complex and inter-related molecular mechanisms, we can propose potential therapeutic strategies to ameliorate the cardiac toxicity induced by iron-overloading.

The role of endocytic pathways in cellular uptake of plasma non-transferrin iron

BACKGROUND

In transfusional siderosis, the iron binding capacity of plasma transferrin is often surpassed, with concomitant generation of non-transferrin-bound iron. Although implicated in tissue siderosis, non-transferrin-bound iron modes of cell ingress remain undefined, largely because of its variable composition and association with macromolecules. Using fluorescent tracing of labile iron in endosomal vesicles and cytosol, we examined the hypothesis that non-transferrin-bound iron fractions detected in iron overloaded patients enter cells via bulk endocytosis.

DESIGN AND METHODS

Fluorescence microscopy and flow cytometry served as analytical tools for tracing non-transferrin-bound iron entry into endosomes with the redox-reactive macromolecular probe Oxyburst-Green and into the cytosol with cell-laden calcein green and calcein blue. Non-transferrin-bound iron-containing media were from sera of polytransfused thalassemia major patients and model iron substances detected in thalassemia major sera; cell models were cultured macrophages, and cardiac myoblasts and myocytes.

RESULTS

Exposure of cells to ferric citrate together with albumin, or to non-transferrin-bound iron-containing sera from thalassemia major patients caused an increase in labile iron content of endosomes and cytosol in macrophages and cardiac cells. This increase was more striking in macrophages, but in both cell types was largely reduced by co-exposure to non-transferrin-bound iron-containing media with non-penetrating iron chelators or apo-transferrin, or by treatment with inhibitors of endocytosis. Endosomal iron accumulation traced with calcein-green was proportional to input non-transferrin-bound iron levels (r(2) = 0.61) and also preventable by pre-chelation.

CONCLUSIONS

Our studies indicate that macromolecule-associated non-transferrin-bound iron can initially gain access into various cells via endocytic pathways, followed by iron translocation to the cytosol. Endocytic uptake of plasma non-transferrin-bound iron is a possible mechanism that can contribute to iron loading of cell types engaged in bulk/adsorptive endocytosis, highlighting the importance of its prevention by iron chelation.

The iron-regulatory peptide hepcidin is upregulated in the ischemic and in the remote myocardium after myocardial infarction

Recent evidence suggests that iron metabolism contributes to the ischemic damage after myocardial infarction. Hepcidin, a recently discovered peptide hormone, regulates iron uptake and metabolism, protecting the body from iron overload. In this study we analyzed the regulation of hepcidin in the heart and blood of rats after myocardial infarction. To induce a myocardial infarction in the rats, left anterior descending coronary artery ligation was performed. After 1-24h, biopsies from the ischemic and the non-ischemic myocardium were taken. In these biopsies, the mRNA levels and the protein expression of hepcidin were analyzed by quantitative RT-PCR and immunoblot analysis, respectively. In parallel, the serum levels of prohepcidin were measured by ELISA. Six hours after myocardial infarction, the hepcidin mRNA expression was temporally upregulated in the ischemic and in the non-ischemic myocardium. The upregulation was specific for hepcidin, since other iron-related genes (hemojuvelin, IREG-1) remained unchanged. Furthermore, the alteration of the hepcidin protein expression in the ischemic area was connected to the level of hepcidin in the serum of the infarcted rats, where hepcidin also raised up. Angiotensin receptor blockade with candesartan did not influence the mRNA regulation of hepcidin. Together, these data show a particular upregulation of the iron-regulatory peptide hepcidin in the ischemic and the non-ischemic myocardium after myocardial infarction. It is speculated that upregulation of hepcidin may reduce iron toxicity and thus infarct size expansion in an infarcted heart.

Iron overload thalassemic cardiomyopathy: iron status assessment and mechanisms of mechanical and electrical disturbance due to iron toxicity

Patients with thalassemia major have inevitably suffered from complications of the disease, due to iron overload. Among such complications, cardiomyopathy is the leading cause of morbidity and mortality (63.6% to 71%). The major causes of death in this group of patients are congestive heart failure and fatal cardiac tachyarrhythmias leading to sudden cardiac death. The free radical-mediated pathway is the principal mechanism of iron toxicity. The consequent series of events caused by iron overload lead to catastrophic cardiac effects. The authors review the electrophysiological and molecular mechanisms, pathophysiology and correlated clinical insight of heart failure and arrhythmias in iron overload thalassemic cardiomyopathy.

Voltage-gated calcium channels provide an alternate route for iron uptake in neuronal cell cultures

Recent studies suggest that iron enters cardiomyocytes via the L-type voltage-gated calcium channel (VGCC). The neuronal VGCC may also provide iron entry. As with calcium, extraneous iron is associated with the pathology and progression of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. VGCCs, ubiquitously expressed, may be an important route of excessive entry for both iron and calcium, contributing to cell toxicity or death. We evaluated the uptake of (45)Ca(2+) and (55)Fe(2+) into NGF-treated rat PC12, and murine N-2alpha cells. Iron not only competed with calcium for entry into these cells, but iron uptake (similar to calcium uptake) was inhibited by nimodipine, a specific L-type VGCC blocker, and enhanced by FPL 64176, an L-VGCC activator, in a dose-dependent manner. Taken together, these data suggest that voltage-gated calcium channels are an alternate route for iron entry into neuronal cells under conditions that promote cellular iron overload toxicity.

Investigations into the systemic production of aldehyde-derived peroxidation products in a murine model of acute iron poisoning: a dose response study

Acute iron poisoning remains a leading cause of morbidity and mortality in pre-school aged children in North America. Acute iron poisoning leads to organ damage, such as respiratory difficulties, cardiac arrhythmias, and possible death. The mechanism of iron toxicity is not fully understood, though it is thought that free iron is able to catalyze the production of harmful oxygen free radicals, which can damage all biochemical classes including lipid membranes, proteins, and DNA. Accordingly, we hypothesized that acute iron loading results in dose-dependent increases in oxygen free radical production, as quantified by the cytotoxic aldehydes hexanal, 4-hydroxynonenal, and malondialdehyde, in an experimental murine model. In support of our hypothesis, significant dose-dependent increases in all aldehydes investigated were reported in comparison to controls (p < 0.001). This murine model will assist in providing a better understanding of possible mechanism(s) of injury and organ dysfunction following acute iron poisoning, and for the development and evaluation of treatment regimes.