Deferoxamine prevents cardiac hypertrophy and failure in the gerbil model of iron-induced cardiomyopathy

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.

Cardiac Chamber Quantification by Echocardiography in Adults With Sickle Cell Disease: Need Attention to Eccentric Hypertrophy

Introduction and aim

Sickle cell anemia (SCA) is the most common hemoglobinopathy worldwide, and cardiovascular diseases are the most common causes of death. In these patients, cardiac remodeling begins from childhood and leads to sickle cell cardiomyopathy in the following years. Concentric hypertrophy and eccentric hypertrophy are known to predict early cardiac events. This study aims to reveal the relationship between cardiac remodeling types and survival in patients with SCA and investigate the factors that may affect left ventricular mass.

Materials and methods

A total of 146 patients with SCA were included in the study, and the left ventricular mass index (LVMI) and relative wall thickness (RWT) of the patients were calculated according to echocardiographic measurements, and the patients were categorized into normal, concentric remodeling (CR), concentric hypertrophy (CH), and eccentric hypertrophy (EH) groups.

Results

The median age of the patients is 32 (18-72). In logistic regression analysis, hemoglobin S (HbS) and ferritin levels were independent predictors for LVMI (p = 0.01 and p < 0.001, respectively). It was observed that 56 (38.4%) of the patients had normal left ventricles, 24 (16.4%) had CR, 21 (14.4%) had CH, and 45 (30.8%) had EH. 31 (21.2%) of the patients died. When we look at the survival curves, there was a statistically significant difference between the four groups (log-rank p < 0.001). It was observed that patients with EH were the group with the lowest probability of survival.

Conclusion

Cardiac death is one of the most common causes of death in patients with SCA. Early detection of cardiac disorders and starting treatment may be important in reducing mortality in these patients.

A Glance on the Role of Bacterial Siderophore from the Perspectives of Medical and Biotechnological Approaches

Iron, which is described as the most basic component found in nature, is hard to be assimilated by microorganisms. It has become increasingly complicated to obtain iron from nature as iron (II) in the presence of oxygen oxidized to press (III) oxide and hydroxide, becoming unsolvable at neutral pH. Microorganisms appeared to produce organic molecules known as siderophores in order to overcome this condition. Siderophore's essential function is to connect with iron (II) and make it dissolvable and enable cell absorption. These siderophores, apart from iron particles, have the ability to chelate various other metal particles that have collocated away to focus the use of siderophores on wound care items. There is a severe clash between the host and the bacterial pathogens during infection. By producing siderophores, small ferric iron-binding molecules, microorganisms obtain iron. In response, host immune cells produce lipocalin 2 to prevent bacterial reuptake of siderophores loaded with iron. Some bacteria are thought to produce lipocalin 2-resistant siderophores to counter this risk. The aim of this article is to discuss the recently described roles and applications of bacterial siderophore.

Mass spectrometry and associated technologies delineate the advantageously biomedical capacity of siderophores in different pathogenic contexts

Siderophores are chemically diverse small molecules produced by microorganisms for chelation of irons to maintain their survival and govern some important biological functions, especially those cause that infections in hosts. Still, siderophores can offer new insight into a better understanding of the diagnosis and treatments of infectious diseases from the siderophore biosynthesis and regulation perspective. Thus, this review aims to summarize the biomedical value and applicability of siderophores in pathogenic contexts by briefly reviewing mass spectrometry (MS)-based chemical biology and translational applications that involve diagnosis, pathogenesis, and therapeutic discovery for a variety of infectious conditions caused by different pathogens. We highlight the advantages and disadvantages of siderophore discovery and applications in pathogenic contexts. Finally, we propose a panel of new and promising strategy as precision-modification metabolomics method, to rapidly advance the discovery of and translational innovations pertaining to these value compounds in broad biomedical niches. © 2018 Wiley Periodicals, Inc. Mass Spec Rev XX:XX-XX, 2018.

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.

N-acetylcysteine Plus Deferoxamine Improves Cardiac Function in Wistar Rats After Non-reperfused Acute Myocardial Infarction

The antioxidant N-acetycysteine can turn into a prooxidant molecule in presence of iron ions. Thus, our goal was to test if the association of N-acetylcysteine (NAC) and an iron chelator (deferoxamine--DFX) in a rodent model of acute myocardial infarction (AMI) improves cardiac function. Male Wistar rats were subjected to a SHAM surgery or AMI. The animals were randomized: vehicle, NAC (25 mg/kg for 28 days), DFX (40 mg/kg for 7 days), or NAC plus DFX (NAC plus DFX, respectively). Animals were killed 28 days after the AMI. Animals treated with NAC/DFX showed an increase in left ventricular ejection fraction at 28 days when compared with vehicle group (45.2 ± 10.9 % vs. 34.7 ± 8.7 %, p = 0.03). Antioxidant effect of NAC/DFX treatment decreased 4-hydroxynonenal when compared to AMI group (p = 0.06). In conclusion, we showed beneficial effect of NAC/DFX association in improving left ventricle function in an experimental AMI.

Effect of L-type calcium channel blocker (amlodipine) on myocardial iron deposition in patients with thalassaemia with moderate-to-severe myocardial iron deposition: protocol for a randomised, controlled trial

INTRODUCTION

Sideroblastic cardiomyopathy secondary to repeated blood transfusions is a feared complication in thalassaemia. Control of myocardial iron is thus becoming the cornerstone of thalassaemia management. Recent evidence suggests a role for L-type Ca(2+) channels in mediating iron uptake by the heart. Blocking the cellular iron uptake through these channels may add to the benefit of therapy to standard chelation in reducing myocardial iron. We aim to determine the efficacy of amlodipine (a calcium channel blocker) as an adjunct to standard aggressive chelation in retarding myocardial iron deposition in thalassaemics with or without cardiomyopathy.

OUTCOMES

The primary outcome is to compare the efficacy of amlodipine+chelation (intervention) versus standard chelation (control) in retarding myocardial iron deposition. Secondary outcomes include the effect of amlodipine therapy on systolic and diastolic function, strain and strain rate and liver iron content.

METHODS AND ANALYSIS

This is a single-centre, parallel-group, prospective randomised control trial. Twenty patients will be randomised in a 1:1 allocation ratio into the intervention and control arms. In addition to conventional echocardiography, MRI T2* values for assessment of cardiac and liver iron load will be obtained at baseline and at 6 and 12 months. Cardiac T2* will be reported as the geometric mean and per cent coefficient of variation, and an increase in cardiac T2* values from baseline will be used as an end point to compare the efficacy of therapy. A p Value of <0.05 will be considered significant.

STUDY SETTING

Department of Pediatric and Child Health, Aga Khan University Hospital, Karachi, Pakistan.

ETHICS AND DISSEMINATION

This study has been approved by the Ethics Review Committee and Clinical Trials Unit at The Aga Khan University with respect to scientific content and compliance with applicable research and human subjects regulations. Findings will be reported through scientific publications and research conferences and project summary papers for participants.

TRIAL REGISTRATION NUMBER

ClinicalTrials.Gov. Registration no: NCT02065492.

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.

Modulation of hypoxia-inducible factors (HIF) from an integrative pharmacological perspective

Oxygen homeostasis determines the activity and expression of a multitude of cellular proteins and the interplay of pathways that affect crucial cellular processes for development, physiology, and pathophysiology. Hypoxia-inducible factors (HIFs) are transcription factors that respond to changes in available oxygen in the cellular environment and drives cellular adaptation to such conditions. Selective gene expression under hypoxic conditions is the result of an exquisite regulation of HIF, from the pre-transcriptional stage of the HIF gene to the final transcriptional activity of HIF protein. We provide a dissected analysis of HIF modulation with special focus on hypoxic conditions and HIF pharmacological interventions that can guide the application of any future HIF-mediated therapy.

Calcium channels and iron uptake into the heart

Iron overload can lead to iron deposits in many tissues, particularly in the heart. It has also been shown to be associated with elevated oxidative stress in tissues. Elevated cardiac iron deposits can lead to iron overload cardiomyopathy, a condition which provokes mortality due to heart failure in iron-overloaded patients. Currently, the mechanism of iron uptake into cardiomyocytes is still not clearly understood. Growing evidence suggests L-type Ca(2+) channels (LTCCs) as a possible pathway for ferrous iron (Fe(2+)) uptake into cardiomyocytes under iron overload conditions. Nevertheless, controversy still exists since some findings on pharmacological interventions and those using different cell types do not support LTCC's role as a portal for iron uptake in cardiac cells. Recently, T-type Ca(2+) channels (TTCC) have been shown to play an important role in the diseased heart. Although TTCC and iron uptake in cardiomyocytes has not been investigated greatly, a recent finding indicated that TTCC could be an important portal in thalassemic hearts. In this review, comprehensive findings collected from previous studies as well as a discussion of the controversy regarding iron uptake mechanisms into cardiomyocytes via calcium channels are presented with the hope that understanding the cellular iron uptake mechanism in cardiomyocytes will lead to improved treatment and prevention strategies, particularly in iron-overloaded patients.

Iron overload decreases CaV1.3-dependent L-type Ca2+ currents leading to bradycardia, altered electrical conduction, and atrial fibrillation

BACKGROUND

Chronic iron overload (CIO) is associated with blood disorders such as thalassemias and hemochromatosis. A major prognostic indicator of survival in patients with CIO is iron-mediated cardiomyopathy characterized by contractile dysfunction and electrical disturbances, including slow heart rate (bradycardia) and heart block.

METHODS AND RESULTS

We used a mouse model of CIO to investigate the effects of iron on sinoatrial node (SAN) function. As in humans, CIO reduced heart rate (≈20%) in conscious mice as well as in anesthetized mice with autonomic nervous system blockade and in isolated Langendorff-perfused mouse hearts, suggesting that bradycardia originates from altered intrinsic SAN pacemaker function. Indeed, spontaneous action potential frequencies in SAN myocytes with CIO were reduced in association with decreased L-type Ca(2+) current (I(Ca,L)) densities and positive (rightward) voltage shifts in I(Ca,L) activation. Pacemaker current (I(f)) was not affected by CIO. Because I(Ca,L) in SAN myocytes (as well as in atrial and conducting system myocytes) activates at relatively negative potentials due to the presence of Ca(V)1.3 channels (in addition to Ca(V)1.2 channels), our data suggest that elevated iron preferentially suppresses Ca(V)1.3 channel function. Consistent with this suggestion, CIO reduced Ca(V)1.3 mRNA levels by ≈40% in atrial tissue (containing SAN) and did not lower heart rate in Ca(V)1.3 knockout mice. CIO also induced PR-interval prolongation, heart block, and atrial fibrillation, conditions also seen in Ca(V)1.3 knockout mice.

CONCLUSIONS

Our results demonstrate that CIO selectively reduces Ca(V)1.3-mediated I(Ca,L), leading to bradycardia, slowing of electrical conduction, and atrial fibrillation as seen in patients with iron overload.

Deferasirox protects against iron-induced hepatic injury in Mongolian gerbil

Iron overload is associated with an increased risk of liver complications including fibrosis, cirrhosis, and hepatocellular carcinoma. Deferasirox is a new oral chelator with high iron-binding potency and selectivity. Here we investigate the ability of deferasirox to remove excessive hepatic iron and prevent iron-induced hepatic injury. Adult male Mongolian gerbils were divided into 3 groups (n=5/group)-control, iron overload (100 mg iron-dextran/kg body weight/5 days; intraperitoneal for 10 weeks), and iron overload followed by deferasirox treatment (100 mg deferasirox/kg body weight/d; pulse oral for 1 or 3 months). Compared with the nontreated iron overload group, deferasirox reduced hepatic iron concentration by 44% after 3 months of treatment (P<0.05). Histological analysis of hepatic tissue from the iron overloaded group detected frequent iron deposition, evidence of hepatic damage, and an accumulation of lipid vacuoles. Iron deposition was significantly diminished with deferasirox treatment, and no evidence of lipid accumulation was observed. Immunoblotting demonstrated that iron overload caused approximately 2-fold increase in hepatic ferritin expression (P<0.05), which was 48% lower after 3 months of deferasirox treatment (P<0.05). Deferasirox treatment also was associated with reduced hepatic protein oxidation, superoxide abundance, and cell death. The percentage of terminal deoxynucleotidyl transferase dUTP nick end labeling positive cells in the deferasirox-treated livers was 41% lower than that of iron overloaded group (P<0.05). Similarly, an iron-related increase in the expression of Bax/Bcl2, Bad, and caspase-3 were significantly lower after deferasirox treatment. These findings suggest that deferasirox may confer protection against iron-induced hepatic toxicity.

Iron sufficient to cause hepatic fibrosis and ascites does not cause cardiac arrhythmias in the gerbil

Chronic iron overload associated with hereditary hemochromatosis or repeated red cell transfusions is known to cause cardiac failure. Cardiac arrhythmias have been incidentally noted in patients with iron overload, but they are often dismissed as being related to comorbid conditions. Studies with anesthetized iron-loaded gerbils using short recordings suggest a role for iron in the development of arrhythmias. Our goal was to characterize iron-induced arrhythmias in the chronically instrumented, untethered, telemetered gerbil. Electrocardiograms were recorded for 10 s every 30 min for approximately 6 months in iron-loaded (n=23) and control (n=8) gerbils. All gerbils in both groups showed evidence of frequent sinus arrhythmia. There was no difference in heart rate, electrocardiographic parameters, or number of arrhythmias per minute between groups. Gerbils rarely showed significant arrhythmias. Body weight and heart weight were not significantly different between groups, whereas liver weight increased with increasing iron dose in the treated group. Cardiac and hepatic iron concentrations were significantly increased in iron-loaded gerbils. Eight of 14 gerbils loaded to 6.2 g/kg body weight developed ascites. We conclude that an iron load sufficient to cause clinical liver disease does not cause cardiac arrhythmias in the gerbil model of iron overload.

Safety and efficacy of combined chelation therapy with deferasirox and deferoxamine in a gerbil model of iron overload

INTRODUCTION

Combined therapy with deferoxamine (DFO) and deferasirox (DFX) may be performed empirically when DFX monotherapy fails. Given the lack of published data on this therapy, the study goal was to assess the safety and efficacy of combined DFO/DFX therapy in a gerbil model.

METHODS

Thirty-two female Mongolian gerbils 8-10 weeks old were divided into 4 groups (sham chelated, DFO, DFX, DFO/DFX). Each received 10 weekly injections of 200 mg/kg iron dextran prior to initiation of 12 weeks of chelation. Experimental endpoints were heart and liver weights, iron concentration and histology.

RESULTS

In the heart, there was no significant difference among the treatment groups for wet-to-dry ratio, iron concentration and iron content. DFX-treated animals exhibited lower organ weights relative to sham-chelated animals (less iron-mediated hypertrophy). DFO-treated organs did not differ from sham-chelated organs in any aspects. DFX significantly cleared hepatic iron. No additive effects were observed in the organs of DFO/DFX-treated animals.

CONCLUSIONS

Combined DFO/DFX therapy produced no detectable additive effect above DFX monotherapy in either the liver or heart, suggesting competition with spontaneous iron elimination mechanisms for chelatable iron. Combined therapy was well tolerated, but its efficacy could not be proven due to limitations in the animal model.

Influence of iron chelation on R1 and R2 calibration curves in gerbil liver and heart

MRI is gaining increasing importance for the noninvasive quantification of organ iron burden. Since transverse relaxation rates depend on iron distribution as well as iron concentration, physiologic and pharmacologic processes that alter iron distribution could change MRI calibration curves. This article compares the effect of three iron chelators, deferoxamine, deferiprone, and deferasirox, on R1 and R2 calibration curves according to two iron loading and chelation strategies. Thirty-three Mongolian gerbils underwent iron loading (iron dextran 500 mg/kg/wk) for 3 weeks followed by 4 weeks of chelation. An additional 56 animals received less aggressive loading (200 mg/kg/week) for 10 weeks, followed by 12 weeks of chelation. R1 and R2 calibration curves were compared to results from 23 iron-loaded animals that had not received chelation. Acute iron loading and chelation-biased R1 and R2 from the unchelated reference calibration curves but chelator-specific changes were not observed, suggesting physiologic rather than pharmacologic differences in iron distribution. Long-term chelation deferiprone treatment increased liver R1 50% (P < 0.01), while long-term deferasirox lowered liver R2 30.9% (P < 0.0001). The relationship between R1 and R2 and organ iron concentration may depend on the acuity of iron loading and unloading as well as the iron chelator administered.

Deferasirox and deferiprone remove cardiac iron in the iron-overloaded gerbil

INTRODUCTION

Deferasirox effectively controls liver iron concentration; however, little is known regarding its ability to remove stored cardiac iron. Deferiprone seems to have increased cardiac efficacy compared with traditional deferoxamine therapy. Therefore, the relative efficacy of deferasirox and deferiprone were compared in removing cardiac iron from iron-loaded gerbils.

METHODS

Twenty-nine 8- to 10-week-old female gerbils underwent 10 weekly iron dextran injections of 200 mg/kg/week. Prechelation iron levels were assessed in 5 animals, and the remainder received deferasirox 100 mg/kg/D po QD (n = 8), deferiprone 375 mg/kg/D po divided TID (n = 8), or sham chelation (n = 8), 5 days/week for 12 weeks.

RESULTS

Deferasirox reduced cardiac iron content 20.5%. No changes occurred in cardiac weight, myocyte hypertrophy, fibrosis, or weight-to-dry weight ratio. Deferasirox treatment reduced liver iron content 51%. Deferiprone produced comparable reductions in cardiac iron content (18.6% reduction). Deferiprone-treated hearts had greater mass (16.5% increase) and increased myocyte hypertrophy. Deferiprone decreased liver iron content 24.9% but was associated with an increase in liver weight and water content.

CONCLUSION

Deferasirox and deferiprone were equally effective in removing stored cardiac iron in a gerbil animal model, but deferasirox removed more hepatic iron for a given cardiac iron burden.

Antioxidant and lysosomotropic properties of acute D-propranolol underlies its cardioprotection of postischemic hearts from moderate iron-overloaded rats

The benefits of acute D-propranolol (D-Pro, non-beta-adrenergic receptor blocker) pretreatment against enhanced ischemia/reperfusion (I/R) injury of hearts from moderate iron-overloaded rats were examined. Perfused hearts from iron-dextran-treated rats (450 mg/kg/week for 3 weeks, intraperitoneal administration) exhibited normal control function, despite iron treatment that elevated plasma iron and conjugated diene levels by 8.1-and 2.5-fold, respectively. However, these hearts were more susceptible to 25 mins of global I/R stress compared with non-loaded hearts; the coronary flow rate, aortic output, cardiac work, left ventricular systolic pressure, positive differential left ventricular pressure (dP/dt), and left ventricular developed pressure displayed 38%, 60%, 55%, 13%, 41%, and 15% lower recoveries, respectively, and a 6.5-fold increase in left ventricular end-diastolic pressure. Postischemic hearts from iron-loaded rats also exhibited 5.6-, 3.48-, 2.43-, and 3.45-fold increases in total effluent iron content, conjugated diene levels, lactate dehydrogenase (LDH) activity, and lysosomal N-acetyl-beta-glucosaminidase (NAGA) activity, respectively, compared with similarly stressed non-loaded hearts. A comparison of detection time profiles during reperfusion suggests that most of the oxidative injury (conjugated diene) in hearts from iron-loaded rats occurred at later times of reperfusion (8.5-15 mins), and this corresponded with heightened tissue iron and NAGA release. D-Pro (2 microM infused for 30 mins) pretreatment before ischemia protected all parameters compared with the untreated iron-loaded group; pressure indices improved 1.2- to 1.6-fold, flow parameters improved 1.70- to 2.96-fold, cardiac work improved 2.87-fold, and end-diastolic pressure was reduced 56%. D-Pro lowered total release of tissue iron, conjugated diene content, LDH activity, and NAGA activity 4.59-, 2.55-, 3.04-, and 4.14-fold, respectively, in the effluent of I/R hearts from the iron-loaded group. These findings suggest that the enhanced postischemic dysfunction and tissue injury of hearts from iron-loaded rats was caused by excessive iron-catalyzed free radical stress, and that the membrane antioxidant properties of D-Pro and its stabilization of sequestered lysosomal iron by D-Pro may contribute to the cardioprotective actions of D-Pro.

D-propranolol attenuates lysosomal iron accumulation and oxidative injury in endothelial cells

The influence of selected beta-receptor blockers on iron overload and oxidative stress in endothelial cells (ECs) was assessed. Confluent bovine ECs were loaded with iron dextran (15 muM) for 24 h and then exposed to dihydroxyfumarate (DHF), a source of reactive oxygen species, for up to 2 h. Intracellular oxidant formation, monitored by fluorescence of 2',7'-dichlorofluorescin (DCF; 30 microM), increased and peaked at 30 min; total glutathione decreased by 52 +/- 5% (p < 0.01) at 60 min. When the ECs were pretreated 30 min before iron loading with 1.25 to 10 microM d-propranolol, glutathione losses were attenuated 15 to 80%, with EC(50) = 3.1 microM. d-Propranolol partially inhibited the DCF intensity increase, but atenolol up to 10 microM was ineffective. At 2 h, caspase 3 activity was elevated 3.2 +/- 0.3-fold (p < 0.01) in the iron-loaded and DHF-treated ECs, and cell survival, determined 24 h later, decreased 47 +/- 6% (p < 0.01). Ten micromoles of d-propranolol suppressed the caspase 3 activation by 63% (p < 0.05) and preserved cell survival back to 88% of control (p < 0.01). In separate experiments, 24-h iron loading resulted in a 3.6 +/- 0.8-fold increase in total EC iron determined by atomic absorption spectroscopy; d-propranolol at 5 microM reduced this increase to 1.5 +/- 0.4-fold (p < 0.01) of controls. Microscopic observation by Perls' staining revealed that the excessive iron accumulated in vesicular endosomal/lysosomal structures, which were substantially diminished by d-propranolol. We previously showed that propranolol could readily concentrate into the lysosomes and raise the intralysosomal pH; it is suggested that the lysosomotropic properties of d-propranolol retarded the EC iron accumulation and thereby conferred the protective effects against iron load-mediated cytotoxicity.

New developments in iron chelators

PURPOSE OF REVIEW

For three decades, deferoxamine has been the only approved iron chelator. This drug has an extremely short-half life and is not orally absorbed; thus, a search has been ongoing for alternative chelators with less onerous delivery. Recently, several oral iron chelators and variations of deferoxamine to prolong the half-life have been developed. These and the methods of monitoring iron overload are the subjects of this review.

RECENT FINDINGS

New chelators, combinations of chelators and regimens for known chelators and their safety and efficacy are being studied in important preclinical and clinical trials.

SUMMARY

The care and clinical outcomes of patients with thalassemia and other iron-overload disorders may be markedly improved by recent discoveries and novel approaches to chelation therapy.