A biochemical, histochemical, and electron microscopic study on the effects of iron-loading on the hearts of mice

Iron chelation alleviates multiple pathophysiological pathways in a rat model of cardiac pressure overload

Iron dysmetabolism affects a great proportion of heart failure patients, while chronic hypertension is one of the most common risk factors for heart failure and death in industrialized countries. Serum data from reduced ejection fraction heart failure patients show a relative or absolute iron deficiency, whereas cellular myocardial analyses field equivocal data. An observed increase in organellar iron deposits was incriminated to cause reactive oxygen species formation, lipid peroxidation, and cell death. Therefore, we studied the effects of iron chelation on a rat model of cardiac hypertrophy. Suprarenal abdominal aortic constriction was achieved surgically, with a period of nine weeks to accommodate the development of chronic pressure overload. Next, deferiprone (100 mg/kg/day), a lipid-permeable iron chelator, was administered for two weeks. Pressure overload resulted in increased inflammation, fibrotic remodeling, lipid peroxidation, left ventricular hypertrophy and mitochondrial iron derangements. Deferiprone reduced cardiac inflammation, lipid peroxidation, mitochondrial iron levels, and hypertrophy, without affecting circulating iron levels or ejection fraction. In conclusion, metallic molecules may pose ambivalent effects within the cardiovascular system, with beneficial effects of iron redistribution, chiefly in the mitochondria.

The molecular mechanisms of ferroptosis and its role in cardiovascular disease

Ferroptosis is a programmed iron-dependent cell death characterized by accumulation of lipid peroxides (LOOH) and redox disequilibrium. Ferroptosis shows unique characteristics in biology, chemistry, and gene levels, compared to other cell death forms. The metabolic disorder of intracellular LOOH catalyzed by iron causes the inactivity of GPX4, disrupts the redox balance, and triggers cell death. Metabolism of amino acid, iron, and lipid, including associated pathways, is considered as a specific hallmark of ferroptosis. Epidemiological studies and animal experiments have shown that ferroptosis plays an important character in the pathophysiology of cardiovascular disease such as atherosclerosis, myocardial infarction (MI), ischemia/reperfusion (I/R), heart failure (HF), cardiac hypertrophy, cardiomyopathy, and abdominal aortic aneurysm (AAA). This review systematically summarized the latest research progress on the mechanisms of ferroptosis. Then we report the contribution of ferroptosis in cardiovascular diseases. Finally, we discuss and analyze the therapeutic approaches targeting for ferroptosis associated with cardiovascular diseases.

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

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

Arrhythmias and Sudden Cardiac Death in Beta-Thalassemia Major Patients: Noninvasive Diagnostic Tools and Early Markers

Beta-thalassemias are a group of inherited, autosomal recessive diseases, characterized by reduced or absent synthesis of beta-globin chains of the hemoglobin tetramer, resulting in variable phenotypes, ranging from clinically asymptomatic individuals to severe anemia. Three main forms have been described: heterozygotes, homozygotes β+, and homozygotes β°. Beta-thalassemia major (β-TM), the most serious form, is characterized by an absent synthesis of globin chains that are essential for hemoglobin formation, causing chronic hemolytic anemia. Cardiac complications represent a leading cause of mortality in β-TM patients, although an important and progressive increase of life expectancy has been demonstrated after the introduction of chelating therapies. Iron overload is the primary factor of cardiac damage resulting in thalassemic cardiomyopathy, in which diastolic dysfunction usually happens before systolic impairment and overt heart failure (HF). Although iron-induced cardiomyopathy is slowly progressive and it usually takes several decades for clinical and laboratory features of cardiac dysfunction to manifest, arrhythmias or sudden death may be present without signs of cardiac disease and only if myocardial siderosis is present. Careful analysis of electrocardiograms and other diagnostic tools may help in early identification of high-risk β-TM patients for arrhythmias and sudden cardiac death.

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-mercaptalbumin, Oxidized Form of Serum Albumin, Significantly Associated with Renal Function and Anemia in Chronic Kidney Disease Patients

Oxidative stress plays a major role in development of cardiovascular disease in patients with chronic kidney disease (CKD). Human mercaptalbumin (HMA), a reduced form of serum albumin, and non-mercaptalbumin (HNA), an oxidized form of serum albumin, are known as indicators for evaluating oxidative stress in systemic circulation, including end-stage renal disease cases. We investigated factors associated with fraction of HNA [f(HNA)] in 112 pre-dialysis CKD patients (63.6 ± 14.0 years old; 59 males, 53 females) using a newly established anion-exchange column packed with hydrophilic polyvinyl alcohol gel as well as high performance liquid chromatography. Mean f(HNA) in our CKD patients was 30.0 ± 6.1%, higher than that previously reported for healthy subjects. In multiple regression analysis, age (β = 0.200, p = 0.014), eGFR (β = −0.238, p = 0.009), hemoglobin (β = −0.346, p < 0.001), and ferritin (β = 0.200, p = 0.019) were significantly and independently associated with f(HNA) (R² = 0.356, p < 0.001). In addition, factors related to CKD-mineral and bone disorder (CKD-MBD), including intact-PTH (β = 0.218, p = 0.049) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) (β = −0.178, p = 0.040), were significantly and independently associated with serum f(HNA) (R² = 0.339, p < 0.001), whereas fibroblast growth factor-23 was not. These findings indicate the importance of management of hemoglobin and ferritin levels, as well as appropriate control of CKD-MBD factors for a better redox state of serum albumin in CKD patients.

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.

Comparative study of the protective effect between deferoxamine and deferiprone on chronic iron overload induced cardiotoxicity in rats

Patients with iron overload frequently suffer from hemochromatosis of major organs, such as the heart and liver. Heart affection is the most common cause of death in patients with iron overload. Although the beneficial effects of deferoxamine (DFO) on iron-associated mortality are well documented, the role of deferiprone in the management of transfusional iron overload is controversial. The aim of this study was to compare the protective effect of iron chelators (DFO and deferiprone) individually and in combination with the anti-oxidant (vitamin C) in the prevention of myocardial damage. Sixty albino rats were divided into six groups: two control groups (noniron-loaded and iron-loaded) and four iron-loaded groups classified as follows: DFO group, DFO combined with vitamin C group, deferiprone group and deferiprone combined with vitamin C group. Heart tissue and blood samples were taken for histopathological examination of the heart, determination of total iron-binding capacity, 8-OH-deoxyguanosine (8-OH-dG), myocardial lipid peroxidation and glutathione (GSH) content. Less histopathological cardiac changes and a significant decrease in all biochemical parameters, except myocardial GSH, were observed in the deferiprone group. The addition of vitamin C improves the biochemical and histopathological changes in comparison to those rats administered DFO or deferiprone individually.

Acute iron poisoning in adult female

We report a case of a 27-year-old female with anemia, treated with high dose oral and parenteral iron therapy (within 20 days, the patient received a total dose of 4 g Fe+2 orally and 700 mg Fe+2 iv and im), and developed clinical manifestations characteristic of acute iron poisoning. Initial gastrointestinal symptoms and hypotension were followed by signs of mitochondrial toxicity: high leucocytosis, shock, multi-organ failure and disseminated intravascular coagulation. We discuss the difficulties in diagnosing acute iron poisoning. The initial low total iron blood capacity and high ferritin level, as well as the typical sequence of symptoms, supported the diagnosis. The patient avoided fatal consequences, probably due to the administration of iron doses over an extended period of time. However, cumulative effects led to the apparent iron toxicity. After 2 weeks of treatment, the patient was discharged from hospital in good condition. Human & Experimental Toxicology (2007) 26, 663-666

Electrocardiographic Presentation, Cardiac Arrhythmias, and Their Management in β-Thalassemia Major Patients

Beta-thalassemia major (β-TM) is a genetic hemoglobin disorder characterized by an absent synthesis of globin chains that are essential for hemoglobin formation, causing chronic hemolytic anemia. Clinical management of thalassemia major consists in regular long-life red blood cell transfusions and iron chelation therapy to remove iron introduced in excess with transfusions. Iron deposition in combination with inflammatory and immunogenic factors is involved in the pathophysiology of cardiac dysfunction in these patients. Heart failure and arrhythmias, caused by myocardial siderosis, are the most important life-limiting complications of iron overload in beta-thalassemia patients. Cardiac complications are responsible for 71% of global death in the beta-thalassemia major patients. The aim of this review was to describe the most frequent electrocardiographic abnormalities and arrhythmias observed in β-TM patients, analyzing their prognostic impact and current treatment strategies.

Comparative study of the effect of verapamil and vitamin D on iron overload-induced oxidative stress and cardiac structural changes in adult male rats

The present study was designed to compare the effect of verapamil and vitamin D on the expression of the voltage-dependent LTCC alpha 1c subunit (Cav1.2) and thereby on iron overload-induced cardiac dysfunction in adult male rat. Forty rats were randomly divided into four groups. Control group received the vehicle, iron overload group received ferrous sulfate intraperitoneally (IP) for 4 weeks, iron overload+verapamil received ferrous sulfate and verapamil IP concurrently for 4 weeks and iron overload+vitamin D group received ferrous sulfate IP and vitamin D3 orally concurrently for 4 weeks. Serum ferritin, total antioxidant capacity (TAC), total peroxide (TP) and cardiac iron and calcium were determined. Oxidative stress index (OSI) was calculated. Histopathological studies using H&E, Masson trichrome and Prussian blue stains and immunohistochemical studies using Cav1.2 antibody were also carried out. Administration of ferrous sulfate induced a significant increase in serum ferritin, OSI, cardiac iron and calcium contents. Moreover, cardiomyocytes were degenerated and the expression of Cav1.2 protein was increased in iron overload group as compared to control. Verapamil decreased ferrous sulfate-induced increase in serum ferritin, OSI and cardiac iron deposition. In addition, verapamil improved myocardial degeneration and decreased the expression of Cav1.2 protein. In contrast, vitamin D produced insignificant changes in ferrous sulfate-induced increase in cardiac iron content, myocardial degeneration and the expression of Cav1.2 protein. These results indicate that verapamil has a protective effect against iron overload-induced cardiac dysfunction, oxidative stress and structural changes, while vitamin D has an insignificant effect on these parameters.

Iron distribution and histopathological characterization of the liver and heart of β-thalassemic mice with parenteral iron overload: Effects of deferoxamine and deferiprone

The liver and heart are the major target organs for iron accumulation and iron toxicity in β-thalassemia. To mimic the phenomenon of heavy iron overload resulting from repeated blood transfusions, a total of 180 mg of iron dextran was intraperitoneally injected into C57BL/6J mice (WT) and heterozygous β-globin knockout mice ((mu)β(th-3/+), BKO). The effects of deferiprone and deferoxamine in this model were investigated. The iron was distributed homogenously throughout the 4 liver lobes (left, caudate, right and median) and was present in hepatocytes, Kupffer cells and the sinusoidal space. Iron accumulation in phagocytic macrophages, recruitment of hepatic lymphocytes and nucleus membrane degeneration were observed as a result of iron overload in the WT and BKO mice. However, the expansion of hepatic extramedullary hematopoiesis was observed only in the BKO mice with iron overload. In the heart, the iron accumulated in the cardiac interstitium and myocytes, and moderate hypertrophy of the myocardial fibers and cardiac myocyte degeneration were observed. Although the total liver iron was not significantly altered by iron chelation therapy, image analysis demonstrated a difference in the efficacies of two iron chelators. The major site of chelation was the extracellular compartment, but treatment with deferiprone also resulted in intracellular iron chelation. Interestingly, iron chelators reversed the pathological changes resulting from iron overload in WT and BKO mice despite being used for only a short treatment period. We suggest that some of these effects may be secondary to the anti-inflammatory activity of the chelators.

Assessment of the relationship between fragmented QRS and cardiac iron overload in patients with beta-thalassemia major

Objective:

Beta-thalassemia major (TM) is a genetic hemoglobin disorder causing chronic hemolytic anemia. Since cardiac insufficiency and arrhythmias are the primary causes of mortality in such patients, monitoring of cardiac iron load is important in management of the disorder. The purpose of this study was to investigate the importance of fragmented QRS (fQRS) and its relation to the cardiac T2* value for the evaluation of cardiac iron load in TM patients.

Methods:

This retrospective study included 103 TM patients. The patients’ T2* values, measured by cardiac MRI and 12-lead surface ECGs, were interpreted. The cardiac T2* values under 20 were considered as cardiac iron overload. The relationship between the cardiac T2* value and fQRS in ECG was investigated.

Results:

The median age of the patients was 22.6±6.6 years. All patients were on regular blood transfusions and iron chelators. The patients had no risk factors for coronary artery disease. In 50 (48%) patients fQRS was detected, and in 37 (74%) of these the T2* values were low. 86% of patients with cardiac involvement (37) had fQRS, but 22% of patients with non-involvement (13) had fQRS (p<0.001).

Conclusion:

Since cardiac involvement is the primary cause of mortality in TM patients, the early diagnosis of cardiac dysfunction is of vital importance. The search for fQRS in the ECGs of these patients, particularly when cardiac T2* values cannot be determined and followed, is a non-expensive and easy-to-attain method for therapy management.

Adiponectin ameliorates iron-overload cardiomyopathy through the PPARα-PGC-1-dependent signaling pathway

Adiponectin is a circulating adipose-derived cytokine that may act as an antioxidative and anti-inflammatory protein. Although adiponectin has been reported to exert cytoprotective effects in acute cardiac diseases, its effects on chronic heart failure are less clear. Therefore, we aimed to investigate whether adiponectin would have a beneficial effect in iron-induced chronic heart failure and to elucidate its regulation in cardiomyocytes. Mice were first treated with iron dextran for 4 weeks to induce iron-overload cardiomyopathy. They exhibited decreased survival with impaired left ventricle contractility and decreased serum adiponectin levels. In vivo cardiac adiponectin gene (ADIPOQ) overexpression with adenoassociated virus (AAV)-ADIPOQ ameliorated cardiac iron deposition and restored cardiac function in iron-overloaded mice. In addition, AAV-ADIPOQ-treated iron-overload mice had lower expression of inflammatory markers, including myeloperoxidase activity, monocyte chemotactic protein-1, tumor necrosis factor-α, interleukin-6, and intercellular adhesion molecule-1, than iron-overloaded mice not treated with AAV-ADIPOQ. Our in vitro study showed that adiponectin induced heme oxygenase-1 (HO-1) expression through the peroxisome proliferator-activated receptor (PPAR)α-HO-1 signaling pathway. Furthermore, the adiponectin-mediated beneficial effects were PPARα-dependent as the adiponectin-mediated attenuation of iron deposition was abolished in PPARα-knockout mice. Finally, PPARα-HO-1 signaling involved PPARα and peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) binding and nuclear translocation, and their levels were increased by adiponectin therapy. Together, these findings suggest that adiponectin acts as an anti-inflammatory signaling molecule and induces the expression of HO-1 through the PPARα-PGC-1 complex-dependent pathway in cardiomyocytes, resulting in the attenuation of iron-induced cardiomyopathy. Using adiponectin for adjuvant therapies in iron-overload cardiac dysfunction may be an option in the future.

Transition metals and mitochondrial metabolism in the heart

Transition metals are essential to many biological processes in almost all organisms from bacteria to humans. Their versatility, which arises from an ability to undergo reduction-oxidation chemistry, enables them to act as critical cofactors of enzymes throughout the cell. Accumulation of metals, however, can also lead to oxidative stress and cellular damage. The importance of metals to both enzymatic reactions and oxidative stress makes them key players in mitochondria. Mitochondria are the primary energy-generating organelles of the cell that produce ATP through a chain of enzymatic complexes that require transition metals, and are highly sensitive to oxidative damage. Moreover, the heart is one of the most mitochondrially-rich tissues in the body, making metals of particular importance to cardiac function. In this review, we focus on the current knowledge about the role of transition metals (specifically iron, copper, and manganese) in mitochondrial metabolism in the heart. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

Disruption of ATP-binding cassette B8 in mice leads to cardiomyopathy through a decrease in mitochondrial iron export

Mitochondrial iron levels are tightly regulated, as iron is essential for the synthesis of Fe/S clusters and heme in the mitochondria, but high levels can cause oxidative stress. The ATP-binding cassette (ABC) transporter ABCB8 is a mitochondrial inner membrane protein with an unknown function. Here, we show that ABCB8 is involved in mitochondrial iron export and is essential for baseline cardiac function. Induced genetic deletion of ABCB8 in mouse hearts resulted in mitochondrial iron accumulation and cardiomyopathy, as assessed by echocardiography and invasive hemodynamics. Mice with ABCB8 deletion in the heart also displayed mitochondrial damage, and higher levels of reactive oxygen species and cell death. Down-regulation of ABCB8 in vitro resulted in decreased iron export from isolated mitochondria, whereas its overexpression had the opposite effect. Furthermore, ABCB8 is needed for the maturation of the cytosolic Fe/S proteins, as its deletion in vitro and in vivo led to decreased activity of cytosolic, but not mitochondrial, iron-sulfur-containing enzymes. These results indicate that ABCB8 is essential for normal cardiac function, maintenance of mitochondrial iron homeostasis and maturation of cytosolic Fe/S proteins. In summary, this report provides characterization of a protein involved in mitochondrial iron export.

Dispersion of repolarization and beta-thalassemia major: the prognostic role of QT and JT dispersion for identifying the high-risk patients for sudden death

BACKGROUND

Patients with beta-thalassemia major (β-TM) are at increased risk for sudden cardiac death (SCD). Heterogeneity of ventricular repolarization is considered to provide an electrophysiological substrate for malignant arrhythmias. QT dispersion (QTc-D) and JT dispersion (JTc-D) are electrocardiographic parameters indicative of heterogeneity of ventricular repolarization. The aim of our study was to evaluate the heterogeneity of ventricular repolarization in patients with beta-thalassemia and to test the hypothesis that an abnormal QTc and JTc dispersion may predict SCD in this population.

MATERIALS AND METHODS

 The study involved 51 patients with β-TM (age 33.9±8.4; 33M) and 51 healthy subjects used as controls, matched for age, gender, and body mass index (BMI). Among the β-TM group, 14 patients with β-TM (age 27±6.64; 11M) died from SCD during follow-up. For each patient, QTD and JTD intervals were calculated.

RESULTS

Compared to the healthy control group, β-TM group presented increased values of the QTc-D (65.36±33.95 vs. 37, 62±17.65; P<0.003) and JTc-D (74.64±33.27 vs. 40.32±12.45; P<0.001). In the β-TM sudden death group, QTc-D and JTc-D were significantly greater than in survived β-TM group (92.70±44.24 vs. 56.14±23.80, P=0.0001; 101.54±47.93 vs. 64.47±17.90, P=0.0001). A cutoff value of 70ms for QTc-D had a sensitivity and specificity of 77% in identifying patients at risk for SCD. A cutoff value of 100ms for JTc-D had a sensitivity of 65% and a specificity of 94% in identifying this category of patients.

CONCLUSION

β-TM is associated with significant changes in heterogeneity of ventricular repolarization. QTc and JTc dispersion are useful markers of risk of SCD in patients with β-TM.

Endoplasmic reticulum stress involved in heart and liver injury in iron-loaded rats

1. Iron overload contributes to the pathogenesis of various diseases and directly induces tissue injury. In the present study, we investigated the relationship between heart and liver injury induced by iron overload and cellular endoplasmic reticulum (ER) stress to explore the molecular mechanism of iron overload-induced cellular injury. 2. Iron overload in rats was generated by intraperitoneal injection of iron-dextran chronically (30 mg/kg per day for 9 weeks) or acutely (300 mg/kg once). Tissue injury was assessed by determining serum lactate dehydrogenase (LDH), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity, as well as malondialdehyde (MDA) content in the heart and liver. The ER stress response was analysed by expression of glucose-response protein 78 (GRP78) and activation of caspase 12. 3. In chronic iron-loaded rats, iron levels in the heart and liver were higher, by approximately 2- and 7.8-fold, respectively (P < 0.01), compared with control. Serum LDH, ALT and AST activity, as well as MDA content, GRP78 expression and caspase 12 activity in the heart and liver, were upregulated in chronically iron-loaded rats. In acute iron-loaded rats, iron content in the heart and liver was 51% and 63% higher than in controls (both P < 0.01). Serum LDH, ALT and AST activity, MDA content in the heart and liver and levels of ER stress markers were all increased in acute iron-loaded rats. N-Acetylcysteine (150 mg/kg, s.c.) lowered the levels of these parameters in acute iron-loaded rats. 4. The results of the present study indicate that ER stress may play an important role in iron-induced tissue injury and that reactive oxygen species may mediate the ER stress response in the pathogenesis of iron-overload cellular injury.

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.

Uncoupling and oxidative stress in liver mitochondria isolated from rats with acute iron overload

One hypothesis for the etiology of cell damage arising from iron overload is that its excess selectively affects mitochondria. Here we tested the effects of acute iron overload on liver mitochondria isolated from rats subjected to a single dose of i.p. 500 mg/kg iron-dextran. The treatment increased the levels of iron in mitochondria (from 21 +/- 4 to 130 +/- 7 nmol/mg protein) and caused both lipid peroxidation and glutathione oxidation. The mitochondria of iron-treated rats showed lower respiratory control ratio in association with higher resting respiration. The mitochondrial uncoupling elicited by iron-treatment did not affect the phosphorylation efficiency or the ATP levels, suggesting that uncoupling is a mitochondrial protective mechanism against acute iron overload. Therefore, the reactive oxygen species (ROS)/H+ leak couple, functioning as a mitochondrial redox homeostatic mechanism could play a protective role in the acutely iron-loaded mitochondria.

Haptoglobin Genotype– and Diabetes-Dependent Differences in Iron-Mediated Oxidative Stress In Vitro and In Vivo

We have recently demonstrated in multiple independent population-based longitudinal and cross sectional analyses that the haptoglobin 2-2 genotype is associated with an increased risk for diabetic cardiovascular disease. The chief function of haptoglobin (Hp) is to bind to hemoglobin and thereby prevent hemoglobin-induced oxidative tissue damage. This antioxidant function of haptoglobin is mediated in part by the ability of haptoglobin to prevent the release of iron from hemoglobin on its binding. We hypothesized that there may be diabetes- and haptoglobin genotype–dependent differences in the amount of catalytically active redox active iron derived from hemoglobin. We tested this hypothesis using several complementary approaches both in vitro and in vivo. First, measuring redox active iron associated with haptoglobin-hemoglobin complexes in vitro, we demonstrate a marked increase in redox active iron associated with Hp 2-2-glycohemoglobin complexes. Second, we demonstrate increased oxidative stress in tissue culture cells exposed to haptoglobin 2-2-hemoglobin complexes as opposed to haptoglobin 1-1-hemoglobin complexes, which is inhibitable by desferrioxamine by either a chelation or reduction mechanism. Third, we demonstrate marked diabetes-dependent differences in the amount of redox active iron present in the plasma of mice genetically modified expressing the Hp 2 allele as compared with the Hp 1 allele. Taken together these data implicate redox active iron in the increased susceptibility of individuals with the Hp 2 allele to diabetic vascular disease.

Intravenous iron administration induces oxidation of serum albumin in hemodialysis patients

BACKGROUND

Intravenous iron administration (IVIR) is effective for correcting anemia in hemodialysis (HD) patients. However, it may also enhance the generation of hydroxyl radicals. Recently, plasma proteins have been demonstrated to be extremely susceptible to oxidative stress. Therefore, we investigated the effect of IVIR on the oxidative status of albumin, a major plasma protein, in HD patients.

METHODS

Eleven hemodialysis (HD) patients were treated with 40 mg of saccharated ferric oxide intravenously after every dialysis session for four weeks, and 11 age-/gender-matched HD patients were treated with vehicle. We performed high performance liquid chromatography (HPLC) analysis of serum albumin and determined the levels of reduced and oxidized albumin. Carbonyl formation of plasma proteins were also measured using an anti-2,4 dinitrophenylhydrazine antibody in patients with or without IVIR.

RESULTS

IVIR resulted in an increase in both disulfide form (f(HNA-1)) and oxidized form (f(HNA-2)) of albumin in HD patients (36.0 +/- 6.03 vs. 41.7 +/- 6.27; 5.46 +/- 1.50 vs. 8.7 +/- 2.22, respectively, P < 0.05). The findings here also show that IVIR substantially increased plasma protein carbonyl content by oxidizing albumin. In addition, we found a strong correlation between plasma carbonyl content and the levels of oxidized albumin (f(HNA-1) and f(HNA-2)) in HD patients (R= 0.674 and R= 0.724, respectively, P < 0.01).

CONCLUSION

The results of this study indicate that the HPLC analysis of serum albumin represents a potentially useful method for the quantitative and qualitative evaluation of oxidative stress in HD patients, and strongly suggest the possibility that oxidative stress, generated by IVIR, enhances the oxidation of albumin in those patients.

Deferoxamine promotes survival and prevents electrocardiographic abnormalities in the gerbil model of iron-overload cardiomyopathy

We investigated the time course of electrocardiographic (ECG) changes in the Mongolian gerbil model of iron overload and the effects of the iron chelator deferoxamine (DFO) on these changes. Iron overload was produced with weekly subcutaneous injections of low doses (200 mg/kg/wk) or high doses (800 mg/kg/wk) of iron-dextran. DFO was administered subcutaneously at a dose of 200 mg/kg/day to high-dose animals. Our results show that (1) survival of iron-overloaded gerbils is dose-dependent, with median survival times of 68 and 14 weeks for low- and high-dose animals, respectively; (2) both low and high doses produce prolongation of the PR interval and bradycardia in early stages and prolongation of the QT interval, premature ventricular contractions, variable degrees of atrioventricular block, changes in the ST segment, and T-wave inversion at later stages coinciding with the development of heart failure; (3) DFO prevented death during 20 weeks of high-dose iron-dextran; (4) DFO prevented ECG changes, although delayed prolongation of PR intervals and QRS complexes occurred; and (5) despite marked prolongation of survival and prevention of ECG changes, DFO had modest effects on total cardiac iron content. We speculate that DFO chelates a small iron pool located within the cytoplasm of iron-overloaded cardiomyocytes.

Iron therapy, advanced oxidation protein products, and carotid artery intima-media thickness in end-stage renal disease

BACKGROUND

Increased common carotid artery intima-media thickness (CCA-IMT) is a marker of early atherosclerosis. Low-grade inflammation is associated with the pathogenesis of atherosclerosis. Low-grade inflammation and increased CCA-IMT are observed in end-stage renal disease (ESRD). Oxidative stress is involved in uremia-related inflammation. Advanced oxidation protein products (AOPP) are markers of oxidant-mediated protein damage in ESRD. Intravenous iron given to patients on hemodialysis (HD) might induce oxidative stress. We investigated the relationships between AOPP, iron therapy, and CCA-IMT in stable HD patients.

METHODS AND RESULTS

Plasma AOPP and blood chemistry, including iron status, were analyzed in a cohort of 79 ESRD patients on HD. Measurements of CCA-IMT and CCA diameter, as assessed by B-mode ultrasonography, were obtained in 60 patients. AOPP levels were elevated in ESRD patients, and in univariate (r=0.42, P<0.0001) and multivariate analyses (r=0.38, P<0.001), they correlated with serum ferritin and with the intravenous iron dose received during the 12 months preceding the study (ferritin, P<0001; AOPP, P<0.01). Univariate and multivariate analyses identified the AOPP concentration as being significantly associated with CCA-IMT (P=0.0197) and CCA wall-to-lumen ratio (r=0.560, P<0.0001). Independently of AOPP concentration, cumulative iron dose was positively related to CCA-IMT (P=0.015) in patients <60 years.

CONCLUSION

In ESRD patients, CCA-IMT and CCA wall-to-lumen ratio were associated with plasma AOPP, serum ferritin, and the annual intravenous iron dose administered. These findings support the concept of a role of oxidative stress in the early atherosclerosis of ESRD patients, which may be increased by the usually recommended doses of intravenous iron.

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.

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

Hereditary hemochromatosis is a disorder of iron metabolism, which is currently the most prevalent autosomal recessive disorder in the world, with an expression of the homozygous form occurring in approximately 1 in 200 individuals of European descent. Approximately one third of patients with hemochromatosis die of iron-induced cardiac complications. Although the exact mechanism is not known, it is believed that the toxicity of excess iron in biological systems is due to its ability to catalyze the generation of harmful reactive oxygen free radical species (ROS), which can damage proteins, lipids, and DNA. There is preliminary evidence to suggest that non-transferrin-bound iron uptake in the myocardium may occur through voltage-dependent L-type calcium channels, and that calcium channel blockers (CCBs) may possess antioxidant properties. Accordingly, the authors hypothesized that the administration of amlodipine besylate would (1) decrease iron uptake in the myocardium and (2) decrease oxygen free radical production as measured by cytotoxic aldehyde-derived peroxidation products in a murine model of iron overload cardiomyopathy. The findings show that the CCB amlodipine is partially effective in limiting iron uptake in the heart and significantly inhibits the production of ROS in chronically iron-loaded mice. These are important preliminary findings because they suggest that CCBs may have significance in the clinical management of genetic disorders of iron metabolism.

Decreasing effects of iron toxicosis on selenium and glutathione peroxidase activity

Heart failure due to chronic iron overload is a leading cause of cardiovascular mortality in the second and third decades of life worldwide, but its mechanism is not known. Deficiencies of selenium have been shown to result in damage to the myocardium and to the development of various cardiomyopathies. In the current investigation, the dose-dependent effects of chronic iron toxicosis on heart tissue concentrations of selenium and the protective antioxidant enzyme glutathione peroxidase (GPx) were investigated in a murine model of iron-overload cardiomyopathy (n = 20). Significant dose-dependent decreases in heart tissue selenium concentrations (r = -0.95, p < 0.001) and selenium-dependent GPx activity (r = -0.93, p < 0.001) were observed in chronically iron-loaded mice in comparison with placebo controls. These results suggest that dietary supplementation with selenium may be beneficial in the clinical management of disorders of iron metabolism.

Selenium and glutathione peroxidase with beta-thalassemia major

BACKGROUND

Chronic iron-overload is a major cause of organ failure and mortality worldwide, but its pathogenesis remains to be elucidated.

OBJECTIVES

To examine the relationship between various measures of body iron burden, selenium concentrations and glutathione peroxidase (GPx) activity in patients with beta-thalassemia major.

METHODS

An age- and gender-matched case control study was conducted to examine the relationship between various measures of body iron burden (serum ferritin, transferrin saturation, total serum iron), plasma concentrations of selenium and glutathione peroxidase (GPx) activity in patients with homozygous beta-thalassemia major (N = 20) and healthy controls (N = 10). Ten patients received the experimental oral chelator L1 and ten received chelation therapy with subcutaneous desferal.

RESULTS

Significantly decreased plasma concentrations of selenium (microg/L) were observed in patients chelated with L1 (1.4 +/- 0.2) or desferal (1.4 +/- 0.1), in comparison to healthy controls (1.8 +/- 0.1, p < 0.01). Significantly decreased plasma activity of GPx (microg/L) was observed in patients chelated with L1 (166 +/- 43) or desferal (178 +/- 46), in comparison to healthy controls (296 +/- 22, p < 0.001). Significantly increased concentrations of all measures of body iron burden were observed in beta-thalassemia patients, in comparison to healthy controls (p < 0.001).

CONCLUSION

Patients with beta-thalassemia major and chronic iron-overload have decreased concentrations of the essential element selenium and the protective selenium-dependent antioxidant enzyme GPx. Additional research examining the effects of dietary antioxidant supplementation with selenium on these aforementioned parameters in patients with beta-thalassemia major and iron-overload is warranted.

Systemic oxygen-free radical production in iron-loaded mice

Although iron is an essential element for normal cell metabolism, in excess quantities it is highly cytotoxic and lethal. In fact, acute iron poisoning is a leading cause of overdose mortality in young children. Hereditary hemochromatosis, a disorder of iron metabolism, is currently the most prevalent genetic disorder in the world, which results in organ failure and premature mortality. Hence, an enhanced understanding of its pathogenesis is critical for providing safe and effective nursing care to affected individuals and their families. Although the exact mechanism of iron's toxicity is not known, it was hypothesized that chronic iron loading would result in increased tissue (heart, liver, and spleen) concentrations of iron and increased free radical production in a murine model (n = 20). Our results show that chronic iron loading results in highly significant dose-dependent increases in tissue concentrations of iron and systemic free radical generation (p < 0.001).