Examination of the mechanism(s) involved in doxorubicin-mediated iron accumulation in ferritin: studies using metabolic inhibitors, protein synthesis inhibitors, and lysosomotropic agents

Molecular Biology Mechanisms and Emerging Therapeutics of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that is conventionally characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2), accounting for approximately 15-20% of all breast cancers. Compared to other molecular phenotypes, TNBC is typically associated with high malignancy and poor prognosis. Cytotoxic agents have been the mainstay of treatment for the past few decades due to the lack of definitive targets and limited therapeutic interventions. However, recent developments have demonstrated that TNBC has peculiar molecular classifications and biomarkers, which provide the possibility of evolving treatment from basic cytotoxic chemotherapy to an expanding domain of targeted therapies. This review presents a framework for understanding the current clinical experience surrounding molecular biology mechanisms in TNBC (Figure 1). Including immunotherapy, polymerase (PARP) and PI3K/AKT pathway inhibitors, antibody-drug conjugates, and androgen receptor (AR) blockade. Additionally, the role of miRNA therapeutics targeting TNBC and potential strategies targeting cancer stem cells (CSCs) are discussed and highlighted. As more and more treatments arise on the horizon, we believe that patients with TNBC will have a new sense of hope.

Relevance of Ferroptosis to Cardiotoxicity Caused by Anthracyclines: Mechanisms to Target Treatments

Anthracyclines (ANTs) are a class of anticancer drugs widely used in oncology. However, the clinical application of ANTs is limited by their cardiotoxicity. The mechanisms underlying ANTs-induced cardiotoxicity (AIC) are complicated and involve oxidative stress, inflammation, topoisomerase 2β inhibition, pyroptosis, immunometabolism, autophagy, apoptosis, ferroptosis, etc. Ferroptosis is a new form of regulated cell death (RCD) proposed in 2012, characterized by iron-dependent accumulation of reactive oxygen species (ROS) and lipid peroxidation. An increasing number of studies have found that ferroptosis plays a vital role in the development of AIC. Therefore, we aimed to elaborate on ferroptosis in AIC, especially by doxorubicin (DOX). We first summarize the mechanisms of ferroptosis in terms of oxidation and anti-oxidation systems. Then, we discuss the mechanisms related to ferroptosis caused by DOX, particularly from the perspective of iron metabolism of cardiomyocytes. We also present our research on the prevention and treatment of AIC based on ferroptosis. Finally, we enumerate our views on the development of drugs targeting ferroptosis in this emerging field.

The role of iron in doxorubicin-induced cardiotoxicity: recent advances and implication for drug delivery

As an anthracycline antibiotic, doxorubicin (DOX) is one of the most potent and widely used chemotherapeutic agents for treating various types of tumors. Unfortunately, the clinical application of this drug results in severe side effects, particularly dose-dependent cardiotoxicity. There are multiple mechanisms involved with the cardiotoxicity caused by DOX, among which intracellular iron homeostasis plays an essential role based on a recent discovery. In this mini-review, we summarize the clinical features and symptoms of DOX-dependent cardiotoxicity, discuss the correlation between iron and cardiotoxicity, and highlight the involvement of iron-dependent ferroptotic cell death therein. Recent advances in this topic will aid the development of novel DOX delivery systems with reduced adverse effects, and expand the clinical application of anthracycline.

The Cardioprotective Mechanism of Phenylaminoethyl Selenides (PAESe) Against Doxorubicin-Induced Cardiotoxicity Involves Frataxin

Doxorubicin (DOX) is an anthracycline cancer chemotherapeutic that exhibits cumulative dose-limiting cardiotoxicity and limits its clinical utility. DOX treatment results in the development of morbid cardiac hypertrophy that progresses to congestive heart failure and death. Recent evidence suggests that during the development of DOX mediated cardiac hypertrophy, mitochondrial energetics are severely compromised, thus priming the cardiomyocyte for failure. To mitigate cumulative dose (5 mg/kg, QIW x 4 weeks with 2 weeks recovery) dependent DOX, mediated cardiac hypertrophy, we applied an orally active selenium based compound termed phenylaminoethyl selenides (PAESe) (QIW 10 mg/kg x 5) to our animal model and observed that PAESe attenuates DOX-mediated cardiac hypertrophy in athymic mice, as observed by MRI analysis. Mechanistically, we demonstrated that DOX impedes the stability of the iron-sulfur cluster biogenesis protein Frataxin (FXN) (0.5 fold), resulting in enhanced mitochondrial free iron accumulation (2.5 fold) and reduced aconitase activity (0.4 fold). Our findings further indicate that PAESe prevented the reduction of FXN levels and the ensuing elevation of mitochondrial free iron levels. PAESe has been shown to have anti-oxidative properties in part, by regeneration of glutathione levels. Therefore, we observed that PAESe can mitigate DOX mediated cardiac hypertrophy by enhancing glutathione activity (0.4 fold) and inhibiting ROS formation (1.8 fold). Lastly, we observed that DOX significantly reduced cellular respiration (basal (5%) and uncoupled (10%)) in H9C2 cardiomyoblasts and that PAESe protects against the DOX-mediated attenuation of cellular respiration. In conclusion, the current study determined the protective mechanism of PAESe against DOX mediated myocardial damage and that FXN is implicitly involved in DOX-mediated cardiotoxicity.

Passive Diffusion vs Active pH-Dependent Encapsulation of Tyrosine Kinase Inhibitors Vandetanib and Lenvatinib into Folate-Targeted Ferritin Delivery System

Introduction

The present study reports on examination of the effects of encapsulating the tyrosine kinase inhibitors (TKIs) vandetanib and lenvatinib into a biomacromolecular ferritin-based delivery system.

Methods

The encapsulation of TKIs was performed via two strategies: i) using an active reversible pH-dependent reassembly of ferritin´s quaternary structure and ii) passive loading of hydrophobic TKIs through the hydrophobic channels at the junctions of ferritin subunits. After encapsulation, ferritins were surface-functionalized with folic acid promoting active-targeting capabilities.

Results

The physico-chemical and nanomechanical analyses revealed that despite the comparable encapsulation efficiencies of both protocols, the active loading affects stability and rigidity of ferritins, plausibly due to their imperfect reassembly. Biological experiments with hormone-responsive breast cancer cells (T47-D and MCF-7) confirmed the cytotoxicity of encapsulated and folate-targeted TKIs to folate-receptor positive cancer cells, but only limited cytotoxic effects to healthy breast epithelium. Importantly, the long-term cytotoxic experiments revealed that compared to the pH-dependent encapsulation, the passively-loaded TKIs exert markedly higher anticancer activity, most likely due to undesired influence of harsh acidic environment used for the pH-dependent encapsulation on the TKIs’ structural and functional properties.

Conclusion

Since the passive loading does not require a reassembly step for which acids are needed, the presented investigation serves as a solid basis for future studies focused on encapsulation of small hydrophobic molecules.

The Role of NCOA4-Mediated Ferritinophagy in Ferroptosis

Nuclear receptor coactivator 4 (NCOA4) is a selective cargo receptor that mediates the autophagic degradation of ferritin, the cytosolic iron storage complex, in a process known as ferritinophagy. NCOA4-mediated ferritinophagy is required to maintain intracellular and systemic iron homeostasis and thereby iron-dependent physiologic processes such as erythropoiesis. Given this role of ferritinophagy in regulating iron homeostasis, modulating NCOA4-mediated ferritinophagic flux alters sensitivity to ferroptosis, a non-apoptotic iron-dependent form of cell death triggered by peroxidation of polyunsaturated fatty acids (PUFAs). A role for ferroptosis has been established in the pathophysiology of cancer and neurodegeneration; however, the importance of ferritinophagy in these pathologies remains largely unknown. Here, we review the available evidence on biochemical regulation of NCOA4-mediated ferritinophagy and its role in modulating sensitivity to innate and induced ferroptosis in neurodegenerative diseases and cancer. Finally, we evaluate the potential of modulating ferritinophagy in combination with ferroptosis inducers as a therapeutic strategy.

Classical and intermediate monocytes scavenge non-transferrin-bound iron and damaged erythrocytes

Myelomonocytic cells are critically involved in iron turnover as aged RBC recyclers. Human monocytes are divided in 3 subpopulations of classical, intermediate, and nonclassical cells, differing in inflammatory and migratory phenotype. Their functions in iron homeostasis are, however, unclear. Here, we asked whether the functional diversity of monocyte subsets translates into differences in handling physiological and pathological iron species. By microarray data analysis and flow cytometry we identified a set of iron-related genes and proteins upregulated in classical and, in part, intermediate monocytes. These included the iron exporter ferroportin (FPN1), ferritin, transferrin receptor, putative transporters of non-transferrin-bound iron (NTBI), and receptors for damaged erythrocytes. Consequently, classical monocytes displayed superior scavenging capabilities of potentially toxic NTBI, which were augmented by blocking iron export via hepcidin. The same subset and, to a lesser extent, the intermediate population, efficiently cleared damaged erythrocytes in vitro and mediated erythrophagocytosis in vivo in healthy volunteers and patients having received blood transfusions. To summarize, our data underline the physiologically important function of the classical and intermediate subset in clearing NTBI and damaged RBCs. As such, these cells may play a nonnegligible role in iron homeostasis and limit iron toxicity in iron overload conditions.

Human classical and intermediate monocytes mediate clearance of non-transferrin-bound iron and erythrophagocytosis.

Detection and quantitation of iron in ferritin, transferrin and labile iron pool (LIP) in cardiomyocytes using 55Fe and storage phosphorimaging

Dysregulated iron metabolism has a detrimental effect on cardiac function. The importance of iron homeostasis in cardiac health and disease warrants detailed studies of cardiomyocyte iron uptake, utilization and recycling at the molecular level. In this study, we have performed metabolic labeling of primary cultures of neonatal rat cardiomyocytes with radioactive iron coupled with separation of labeled iron-containing molecules by native electrophoresis followed by detection and quantification of incorporated radioiron by storage phosphorimaging. For the radiolabeling we used a safe and convenient beta emitter ⁵⁵Fe which enabled sensitive and simultaneous detection and quantitation of iron in cardiomyocyte ferritin, transferrin and the labile iron pool (LIP). The LIP is believed to represent potentially dangerous redox-active iron bound to uncharacterized molecules. Using size-exclusion chromatography spin micro columns, we demonstrate that iron in the LIP is bound to high molecular weight molecule(s) (≥5000 Da) in the neonatal cardiomyocytes.

Altered sterol metabolism in budding yeast affects mitochondrial iron-sulfur (Fe-S) cluster synthesis

Ergosterol synthesis is essential for cellular growth and viability of the budding yeast Saccharomyces cerevisiae, and intracellular sterol distribution and homeostasis are therefore highly regulated in this species. Erg25 is an iron-containing C4-methyl sterol oxidase that contributes to the conversion of 4,4-dimethylzymosterol to zymosterol, a precursor of ergosterol. The ERG29 gene encodes an endoplasmic reticulum (ER)-associated protein, and here we identified a role for Erg29 in the methyl sterol oxidase step of ergosterol synthesis. ERG29 deletion resulted in lethality in respiring cells, but respiration-incompetent (Rho^- or Rho⁰) cells survived, suggesting that Erg29 loss leads to accumulation of oxidized sterol metabolites that affect cell viability. Down-regulation of ERG29 expression in Δerg29 cells indeed led to accumulation of methyl sterol metabolites, resulting in increased mitochondrial oxidants and a decreased ability of mitochondria to synthesize iron-sulfur (Fe-S) clusters due to reduced levels of Yfh1, the mammalian frataxin homolog, which is involved in mitochondrial iron metabolism. Using a high-copy genomic library, we identified suppressor genes that permitted growth of Δerg29 cells on respiratory substrates, and these included genes encoding the mitochondrial proteins Yfh1, Mmt1, Mmt2, and Pet20, which reversed all phenotypes associated with loss of ERG29 Of note, loss of Erg25 also resulted in accumulation of methyl sterol metabolites and also increased mitochondrial oxidants and degradation of Yfh1. We propose that accumulation of toxic intermediates of the methyl sterol oxidase reaction increases mitochondrial oxidants, which affect Yfh1 protein stability. These results indicate an interaction between sterols generated by ER proteins and mitochondrial iron metabolism.

Alzheimer's disease: as it was in the beginning

Since Alzheimer's disease was first described in 1907, many attempts have been made to reveal its main cause. Nowadays, two forms of the disease are known, and while the hereditary form of the disease is clearly caused by mutations in one of several genes, the etiology of the sporadic form remains a mystery. Both forms share similar sets of neuropathological and molecular manifestations, including extracellular deposition of amyloid-beta, intracellular accumulation of hyperphosphorylated tau protein, disturbances in both the structure and functions of mitochondria, oxidative stress, metal ion metabolism disorders, impairment of N-methyl-D-aspartate receptor-related signaling pathways, abnormalities of lipid metabolism, and aberrant cell cycle reentry in some neurons. Such a diversity of symptoms led to proposition of various hypotheses for explaining the development of Alzheimer's disease, the amyloid hypothesis, which postulates the key role of amyloid-beta in Alzheimer's disease development, being the most prominent. However, this hypothesis does not fully explain all of the molecular abnormalities and is therefore heavily criticized. In this review, we propose a hypothetical model of Alzheimer's disease progression, assuming a key role of age-related mitochondrial dysfunction, as was postulated in the mitochondrial cascade hypothesis. Our model explains the connections between all the symptoms of Alzheimer's disease, with particular attention to autophagy, metal metabolism disorders, and aberrant cell cycle re-entry in neurons. Progression of the Alzheimer's disease appears to be a complex process involving aging and too many protective mechanisms affecting one another, thereby leading to even greater deleterious effects.

Gold-based drug encapsulation within a ferritin nanocage: X-ray structure and biological evaluation as a potential anticancer agent of the Auoxo3-loaded protein

Auoxo3, a cytotoxic gold(iii) compound, was encapsulated within a ferritin nanocage. Inductively coupled plasma mass spectrometry, circular dichroism, UV-Vis absorption spectroscopy and X-ray crystallography confirm the potential-drug encapsulation. The structure shows that naked Au(i) ions bind to the side chains of Cys48, His49, His114, His114 and Cys126, Cys126, His132, His147. The gold-encapsulated nanocarrier has a cytotoxic effect on different aggressive human cancer cells, whereas it is significantly less cytotoxic for non-tumorigenic cells.

Chemotherapy-Related Cardiac Dysfunction: A Systematic Review of Genetic Variants Modulating Individual Risk

Chemotherapy-related cardiac dysfunction is a significant side effect of anticancer treatment. Risk stratification is based on clinical- and treatment-related risk factors that do not adequately explain individual susceptibility. The addition of genetic variants may improve risk assessment. We conducted a systematic literature search in PubMed and Embase, to identify studies investigating genetic risk factors for chemotherapy-related cardiac dysfunction. Included were articles describing genetic variants in humans altering susceptibility to chemotherapy-related cardiac dysfunction. The validity of identified studies was assessed by 10 criteria, including assessment of population stratification, statistical methodology, and replication of findings. We identified 40 studies: 34 exploring genetic risk factors for anthracycline-induced cardiotoxicity (n=9678) and 6 studies related to trastuzumab-associated cardiotoxicity (n=642). The majority (35/40) of studies had a candidate gene approach, whereas 5 genome-wide association studies have been performed. We identified 25 genetic variants in 20 genes and 2 intergenic variants reported significant at least once. The overall validity of studies was limited, with small cohorts, failure to assess population ancestry and lack of replication. SNPs with the most robust evidence up to this point are CELF4 rs1786814 (sarcomere structure and function), RARG rs2229774 (topoisomerase-2β expression), SLC28A3 rs7853758 (drug transport), UGT1A6 rs17863783 (drug metabolism), and 1 intergenic variant (rs28714259). Existing evidence supports the hypothesis that genetic variation contributes to chemotherapy-related cardiac dysfunction. Although many variants identified by this systematic review show potential to improve risk stratification, future studies are necessary for validation and assessment of their value in a diagnostic and prognostic setting.

MRI-based evaluation of multiorgan iron overload is a predictor of adverse outcomes in pediatric patients undergoing allogeneic hematopoietic stem cell transplantation

The medical records of 44 pediatric patients who underwent allogeneic transplantation from 2011 to 2015 were retrospectively reviewed. Magnetic resonance imaging was used to measure iron concentrations in the liver, spleen, pancreas and bone. These patients were divided into two groups, 18 with non-elevated (< 100 μmol/g; Group 1) liver iron concentration before transplantation and 26 with elevated (> 100 μmol/g; Group 2) concentration . We compared transplant-related outcomes in the two groups. Iron overload was a negative prognostic risk factor for sinusoidal obstruction syndrome (OR = 17), osteoporosis (OR = 6.8), pancreatic insufficiency (OR = 17) and metabolic syndrome (OR = 15.1). No statistically significant differences in overall survival, disease-free survival, relapse incidence and incidence of acute or chronic graft-versus host disease were observed between the two groups. Mean times to engraftment of platelets (43.0 ± 35.3 days vs. 22.1 ± 9.5 days, p < 0.05) and neutrophils (23.1 ± 10.4 days vs. 17.8 ± 4.6 days, p < 0.05) appear significantly longer in Group 2 than in Group 1. Time to platelet engraftment showed statistically significant correlation with pre-transplant liver (r = 0.5775; p < 0.001) and bone iron concentration (r = 0.7305; p < 0.001). Post-transplant evaluation pointed out that iron concentration analyzed at the first follow-up peaked in all tissues. The iron accumulation was highest in bone, followed by the spleen, liver and pancreas. One year post transplant 9 of 18 (50%) patients in Group 1 and 6 of 22 (27%) in Group 2 presented with bone and/or spleen iron overload, but not with liver overload. Liver iron concentration is not always a reliable indicator of systemic siderosis or of the efficacy of chelation therapy.

Dual Role of ROS as Signal and Stress Agents: Iron Tips the Balance in favor of Toxic Effects

Iron is essential for life, while also being potentially harmful. Therefore, its level is strictly monitored and complex pathways have evolved to keep iron safely bound to transport or storage proteins, thereby maintaining homeostasis at the cellular and systemic levels. These sequestration mechanisms ensure that mildly reactive oxygen species like anion superoxide and hydrogen peroxide, which are continuously generated in cells living under aerobic conditions, keep their physiologic role in cell signaling while escaping iron-catalyzed transformation in the highly toxic hydroxyl radical. In this review, we describe the multifaceted systems regulating cellular and body iron homeostasis and discuss how altered iron balance may lead to oxidative damage in some pathophysiological settings.

Iron and Neurodegeneration: Is Ferritinophagy the Link?

Mounting evidence indicates that the lysosome-autophagy pathway plays a critical role in iron release from ferritin, the main iron storage cellular protein, hence in the distribution of iron to the cells. The recent identification of nuclear receptor co-activator 4 as the receptor for ferritin delivery to selective autophagy sheds further light on the understanding of the mechanisms underlying this pathway. The emerging view is that iron release from ferritin through the lysosomes is a general mechanism in normal and tumour cells of different tissue origins, but it has not yet been investigated in brain cells. Defects in the lysosome-autophagy pathway are often involved in the pathogenesis of neurodegenerative disorders, and brain iron homeostasis disruption is a hallmark of many of these diseases. However, in most cases, it has not been established whether iron dysregulation is directly involved in the pathogenesis of the diseases or if it is a secondary effect derived from other pathogenic mechanisms. The recent evidence of the crucial involvement of autophagy in cellular iron handling offers new perspectives about the role of iron in neurodegeneration, suggesting that autophagy dysregulation could cause iron dyshomeostasis. In this review, we recapitulate our current knowledge on the routes through which iron is released from ferritin, focusing on the most recent advances. We summarise the current evidence concerning lysosome-autophagy pathway dysfunctions and those of iron metabolism and discuss their potential interconnections in several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases; amyotrophic lateral sclerosis; and frontotemporal lobar dementia.

The role of iron in anthracycline cardiotoxicity

The clinical use of the antitumor anthracycline Doxorubicin is limited by the risk of severe cardiotoxicity. The mechanisms underlying anthracycline-dependent cardiotoxicity are multiple and remain uncompletely understood, but many observations indicate that interactions with cellular iron metabolism are important. Convincing evidence showing that iron plays a role in Doxorubicin cardiotoxicity is provided by the protecting efficacy of iron chelation in patients and experimental models, and studies showing that iron overload exacerbates the cardiotoxic effects of the drug, but the underlying molecular mechanisms remain to be completely characterized. Since anthracyclines generate reactive oxygen species, increased iron-catalyzed formation of free radicals appears an obvious explanation for the aggravating role of iron in Doxorubicin cardiotoxicity, but antioxidants did not offer protection in clinical settings. Moreover, how the interaction between reactive oxygen species and iron damages heart cells exposed to Doxorubicin is still unclear. This review discusses the pathogenic role of the disruption of iron homeostasis in Doxorubicin-mediated cardiotoxicity in the context of current and future pharmacologic approaches to cardioprotection.

Ferritin heavy chain as main mediator of preventive effect of metformin against mitochondrial damage induced by doxorubicin in cardiomyocytes

The efficacy of doxorubicin (DOX) as an antitumor agent is greatly limited by the induction of cardiomyopathy, which results from mitochondrial dysfunction and iron-catalyzed oxidative stress in the cardiomyocyte. Metformin (MET) has been seen to have a protective effect against the oxidative stress induced by DOX in cardiomyocytes through its modulation of ferritin heavy chain (FHC), the main iron-storage protein. This study aimed to assess the involvement of FHC as a pivotal molecule in the mitochondrial protection offered by MET against DOX cardiotoxicity. The addition of DOX to adult mouse cardiomyocytes (HL-1 cell line) increased the cytosolic and mitochondrial free iron pools in a time-dependent manner. Simultaneously, DOX inhibited complex I activity and ATP generation and induced the loss of mitochondrial membrane potential. The mitochondrial dysfunction induced by DOX was associated with the release of cytochrome c to the cytosol, the activation of caspase 3, and DNA fragmentation. The loss of iron homeostasis, mitochondrial dysfunction, and apoptosis induced by DOX were prevented by treatment with MET 24h before the addition of DOX. The involvement of FHC and NF-κB was determined through siRNA-mediated knockdown. Interestingly, the presilencing of FHC or NF-κB with specific siRNAs blocked the protective effect induced by MET against DOX cardiotoxicity. These findings were confirmed in isolated primary neonatal rat cardiomyocytes. In conclusion, these results deepen our knowledge of the protective action of MET against DOX-induced cardiotoxicity and suggest that therapeutic strategies based on FHC modulation could protect cardiomyocytes from the mitochondrial damage induced by DOX by restoring iron homeostasis.

Mobilization of stored iron in mammals: a review

From the nutritional standpoint, several aspects of the biochemistry and physiology of iron are unique. In stark contrast to most other elements, most of the iron in mammals is in the blood attached to red blood cell hemoglobin and transporting oxygen to cells for oxidative phosphorylation and other purposes. Controlled and uncontrolled blood loss thus has a major impact on iron availability. Also, in contrast to most other nutrients, iron is poorly absorbed and poorly excreted. Moreover, amounts absorbed (~1 mg/day in adults) are much less than the total iron (~20 mg/day) cycling into and out of hemoglobin, involving bone marrow erythropoiesis and reticuloendothelial cell degradation of aged red cells. In the face of uncertainties in iron bioavailability, the mammalian organism has evolved a complex system to retain and store iron not immediately in use, and to make that iron available when and where it is needed. Iron is stored innocuously in the large hollow protein, ferritin, particularly in cells of the liver, spleen and bone marrow. Our current understanding of the molecular, cellular and physiological mechanisms by which this stored iron in ferritin is mobilized and distributed-within the cell or to other organs-is the subject of this review.

The structure of anthracycline derivatives determines their subcellular localization and cytotoxic activity

The cytotoxic activities and subcellular localizations of clinically used and synthetic analogues of the anthracycline family of chemotherapeutic agents were studied. The structures of the anthracycline derivatives affected their cytotoxicity and the time required for these compounds to exert cytotoxic effects on tumor cells. Fluorescent DNA intercalator displacement experiments demonstrated that there was no correlation between the DNA intercalation properties and the cytotoxicity of the studied anthracycline derivatives. Confocal microscopy experiments indicated that structural differences led to differences in subcellular localization. All studied anthracycline derivatives were observed in lysosomes, suggesting that this organelle, which is involved in several processes leading to malignancy, may contain previously unidentified molecular targets for these antitumor agents.

Lysosomal iron, iron chelation, and cell death

SIGNIFICANCE

Lysosomes are acidic organelles containing more than fifty hydrolases that provide for the degradation of intracellular and endocytosed materials by autophagy and heterophagy, respectively. They digest a variety of macromolecules, as well as all organelles, and their integrity is crucial. As a result of the degradation of iron-containing macromolecules (e.g., ferritin and mitochondrial components) or endocytosed erythrocytes (by macrophages), lysosomes can accumulate large amounts of iron. This iron occurs often as Fe(II) due to the acidic and reducing lysosomal environment. Fe(II) is known to catalyze Fenton reactions, yielding extremely reactive hydroxyl radicals that may jeopardize lysosomal membrane integrity during oxidative stress. This results in the release of hydrolases and redox-active iron into the cytosol with ensuing damage or cell death. Lysosomes play key roles not only in apoptosis and necrosis but also in neurodegeneration, aging, and atherosclerosis.

RECENT ADVANCES

The damaging effect of intralysosomal iron can be hampered by endogenous or exogenous iron chelators that enter the lysosomal compartment by membrane permeation, endocytosis, or autophagy.

CRITICAL ISSUES

Cellular sensitivity to oxidative stress is enhanced by lysosomal redox-active iron or by lysosomal-targeted copper chelators binding copper (from degradation of copper-containing macromolecules) in redox-active complexes. Probably due to higher copper levels, lysosomes of malignant cells may be specifically sensitized by such chelators.

FUTURE DIRECTIONS

By increasing lysosomal redox-active iron or exposing cells to lysosomal-targeted copper chelators, it should be possible to enhance the sensitivity of cancer cells to radiation-induced oxidative stress or treatment with cytostatics that induce such stress.

Transferrin iron uptake is stimulated by ascorbate via an intracellular reductive mechanism

Although ascorbate has long been known to stimulate dietary iron (Fe) absorption and non-transferrin Fe uptake, the role of ascorbate in transferrin Fe uptake is unknown. Transferrin is a serum Fe transport protein supplying almost all cellular Fe under physiological conditions. We sought to examine ascorbate's role in this process, particularly as cultured cells are typically ascorbate-deficient. At typical plasma concentrations, ascorbate significantly increased (59)Fe uptake from transferrin by 1.5-2-fold in a range of cells. Moreover, ascorbate enhanced ferritin expression and increased (59)Fe accumulation in ferritin. The lack of effect of cycloheximide or the cytosolic aconitase inhibitor, oxalomalate, on ascorbate-mediated (59)Fe uptake from transferrin indicate increased ferritin synthesis or cytosolic aconitase activity was not responsible for ascorbate's activity. Experiments with membrane-permeant and -impermeant ascorbate-oxidizing reagents indicate that while extracellular ascorbate is required for stimulation of (59)Fe uptake from (59)Fe-citrate, only intracellular ascorbate is needed for transferrin (59)Fe uptake. Additionally, experiments with l-ascorbate analogs indicate ascorbate's reducing ene-diol moiety is necessary for its stimulatory activity. Importantly, neither N-acetylcysteine nor buthionine sulfoximine, which increase or decrease intracellular glutathione, respectively, affected transferrin-dependent (59)Fe uptake. Thus, ascorbate's stimulatory effect is not due to a general increase in cellular reducing capacity. Ascorbate also did not affect expression of transferrin receptor 1 or (125)I-transferrin cellular flux. However, transferrin receptors, endocytosis, vacuolar-type ATPase activity and endosomal acidification were required for ascorbate's stimulatory activity. Therefore, ascorbate is a novel modulator of the classical transferrin Fe uptake pathway, acting via an intracellular reductive mechanism.

Association of projected transfusional iron burden with treatment intensity in childhood cancer survivors

BACKGROUND

Packed red blood cell (PRBC) transfusion is a mainstay in childhood cancer treatment, but has potential for inducing iron overload. The purpose of this study was to determine whether treatment intensity is predictive of projected iron burden resulting from PRBC transfusions among survivors of several forms of childhood cancer.

PROCEDURE

This retrospective cohort study involved patients treated at Children's Hospital Los Angeles (CHLA) between June 1, 2004 and December 31, 2009. Clinical/demographic data were abstracted from medical records. Treatment Intensity Level was determined for each patient using a published scale. Adjusted cumulative PRBC transfusion volume for each patient (ml/kg) was used to compute the adjusted total iron burden (mg/kg) based upon the average hematocrit of the product.

RESULTS

Median age of the cohort (n = 214) was 7.9 years (range 0.2-20.2). One hundred and fourteen (53.3%) were male and 129 (60.3%) were Hispanic/Latino. Diagnoses included acute leukemia and six solid tumors, management of which represents a range of cancer treatment intensities. The number of transfusions, transfusion volumes, and projected iron burden were significantly increased and exceeded upper limits of normal among patients with higher treatment intensity. Multivariate analysis found younger age and lower hemoglobin at diagnosis to be associated with greater iron burden after adjusting for treatment intensity.

CONCLUSION

Greater treatment intensity is associated with need for more PRBC transfusions, and thus increased risk of iron overload among childhood cancer survivors. Iron overload may represent another clinically significant late effect following childhood cancer treatment.

Sustained expression of heme oxygenase-1 alters iron homeostasis in nonerythroid cells

Heme oxygenases initiate the catabolism of heme, releasing carbon monoxide, iron, and biliverdin. Sustained induction of heme oxygenase-1 (HO-1) in nonerythroid cells plays a key role in many pathological processes, yet the effect of long-term HO-1 expression on cellular iron metabolism in the absence of exogenous heme is poorly understood. Here we report that in a model nonerythroid cell, both transient and stable HO-1 expression increased heme oxygenase activity, but total cellular heme content was decreased only with transient enzyme expression. Sustained HO-1 activity increased the expression of both the mitochondrial iron importer mitoferrin-2 and the rate-limiting enzyme in heme synthesis, aminolevulinate synthase-1, and it augmented the mitochondrial content of heme. Also, the expression of transferrin receptor-1 and the activities of iron-regulatory proteins 1 and 2 decreased, whereas total labile iron and the regulatory activity of the heme-binding transcription factor Bach1 were unaltered. In addition, stable, but not transient, HO-1 expression decreased the activities of aconitase, as well as increasing proteasomal degradation of ferritin. Together, our results reveal a novel and coordinated adaptive response of nonerythroid cells to sustained HO-1 induction that has an impact on cellular iron homeostasis.

The role of lysosomes in iron metabolism and recycling

Iron is the most abundant transition metal in the earth's crust. It cycles easily between ferric (oxidized; Fe(III)) and ferrous (reduced; Fe(II)) and readily forms complexes with oxygen, making this metal a central player in respiration and related redox processes. However, 'loose' iron, not within heme or iron-sulfur cluster proteins, can be destructively redox-active, causing damage to almost all cellular components, killing both cells and organisms. This may explain why iron is so carefully handled by aerobic organisms. Iron uptake from the environment is carefully limited and carried out by specialized iron transport mechanisms. One reason that iron uptake is tightly controlled is that most organisms and cells cannot efficiently excrete excess iron. When even small amounts of intracellular free iron occur, most of it is safely stored in a non-redox-active form in ferritins. Within nucleated cells, iron is constantly being recycled from aged iron-rich organelles such as mitochondria and used for construction of new organelles. Much of this recycling occurs within the lysosome, an acidic digestive organelle. Because of this, most lysosomes contain relatively large amounts of redox-active iron and are therefore unusually susceptible to oxidant-mediated destabilization or rupture. In many cell types, iron transit through the lysosomal compartment can be remarkably brisk. However, conditions adversely affecting lysosomal iron handling (or oxidant stress) can contribute to a variety of acute and chronic diseases. These considerations make normal and abnormal lysosomal handling of iron central to the understanding and, perhaps, therapy of a wide range of diseases.

Novel tetrapeptide, RGDF, mediated tumor specific liposomal doxorubicin (DOX) preparations

Arginine-glycine-aspartate (RGD) has been shown to possess a strong affinity for the integrins overexpressed in tumor cells, especially during tumor invasion, angiogenesis and metasis. Based on work from others, a novel tetrapeptide, arginine-glycine-aspartate-phenylanaline (RGDF), has been designed and studied as a homing device to direct liposomal doxorubicin (DOX) to tumor cells in this work. In order to incorporate RGDF into liposomal DOX preparations, RGDF was conjugated with three different fatty alcohols to achieve RGDF-fatty alcohol conjugates. Glycine-glycine-aspartate-phenylanaline (GGDF)-lauryl alcohol conjugate was synthesized as a negative control. RGDF-fatty alcohol conjugates (RGDFO(CH(2))(n)CH(3)) and GGDF-lauryl alcohol conjugate (L-GGDFC12-DOX) incorporated liposomal preparations were obtained by first preparing liposomes using the film dispersion method followed by loading DOX using a transmembrane pH gradient method. Because of their amphipathic nature, RGDF- or GGDF-fatty alcohol conjugates are expected to be readily incorporated into liposomes with their fatty alkanyl chains being intercalated between fatty acyl chains of liposomal bilayers and the hydrophilic peptide moiety (RGDF or GGDF) being anchored on the surface of liposomes. The particle size and zeta potential of liposomal DOX preparations containing RGDF-fatty alcohol conjugate (L-RGDF-DOXs) or L-GGDFC12-DOX were measured, and their morphology was studied using transmission electron microscopy. In vitro DOX release profile from RGDF incorporated liposomal DOX was measured. The antitumor activities of RGDF incorporated liposomal DOX preparations were evaluated in ICR mice inoculated with sarcoma S(180), which is known to express α(v)β(3) integrin. Both conventional liposomal DOX preparation (L-DOX) without RGDFO(CH(2))(n)CH(3) and L-GGDFC12-DOX were used as negative controls. Our results showed improved tumor growth inhibition with L-RGDF-DOXs over doxorubicin hydrochloride solution, L-DOX and L-GGDFC12-DOX. Pathological examination of tumor biopsy demonstrated that L-RGDF-DOXs induced enhanced tumor cell death in comparison to negative controls. Pharmacokinetic studies showed that the concentrations of DOX found in tumor sites were increased by 1.7-4.5-fold when liposomal DOX preparation containing RGDF-lauryl alcohol conjugate (L-RGDFC12-DOX) was administered in comparison to when L-GGDFC12-DOX or doxorubicin hydrochloride solution was administered. The concentrations of DOX found in the heart, which is the main site of toxic effects of DOX, were significantly reduced when L-RGDFC12-DOX was administered in comparison to when L-GGDFC12-DOX or doxorubicin hydrochloride solution was administered.

Cell sensitivity to oxidative stress is influenced by ferritin autophagy

To test the consequences of lysosomal degradation of differently iron-loaded ferritin molecules and to mimic ferritin autophagy under iron-overload and normal conditions, J774 cells were allowed to endocytose heavily iron loaded ferritin, probably with some adventitious iron (Fe-Ft), or iron-free apo-ferritin (apo-Ft). When cells subsequently were exposed to a bolus dose of hydrogen peroxide, apo-Ft prevented lysosomal membrane permeabilization (LMP), whereas Fe-Ft enhanced LMP. A 4-h pulse of Fe-Ft initially increased oxidative stress-mediated LMP that was reversed after another 3h under standard culture conditions, suggesting that lysosomal iron is rapidly exported from lysosomes, with resulting upregulation of apo-ferritin that supposedly is autophagocytosed, thereby preventing LMP by binding intralysosomal redox-active iron. The obtained data suggest that upregulation of the stress protein ferritin is a rapid adaptive mechanism that counteracts LMP and ensuing apoptosis during oxidative stress. In addition, prolonged iron starvation was found to induce apoptotic cell death that, interestingly, was preceded by LMP, suggesting that LMP is a more general phenomenon in apoptosis than so far recognized. The findings provide new insights into aging and neurodegenerative diseases that are associated with enhanced amounts of cellular iron and show that lysosomal iron loading sensitizes to oxidative stress.

Distinct mechanisms of ferritin delivery to lysosomes in iron-depleted and iron-replete cells

Ferritin is a cytosolic protein that stores excess iron, thereby protecting cells from iron toxicity. Ferritin-stored iron is believed to be utilized when cells become iron deficient; however, the mechanisms underlying the extraction of iron from ferritin have yet to be fully elucidated. Here, we demonstrate that ferritin is degraded in the lysosome under iron-depleted conditions and that the acidic environment of the lysosome is crucial for iron extraction from ferritin and utilization by cells. Ferritin was targeted for degradation in the lysosome even under iron-replete conditions in primary cells; however, the mechanisms underlying lysosomal targeting of ferritin were distinct under depleted and replete conditions. In iron-depleted cells, ferritin was targeted to the lysosome via a mechanism that involved autophagy. In contrast, lysosomal targeting of ferritin in iron-replete cells did not involve autophagy. The autophagy-independent pathway of ferritin delivery to lysosomes was deficient in several cancer-derived cells, and cancer-derived cell lines are more resistant to iron toxicity than primary cells. Collectively, these results suggest that ferritin trafficking may be differentially regulated by cell type and that loss of ferritin delivery to the lysosome under iron-replete conditions may be related to oncogenic cellular transformation.

Clinical and genetic determinants of anthracycline-induced cardiac iron accumulation

BACKGROUND

The involvement of iron in anthracycline cardiotoxicity is supported by extensive experimental data, and by the preventive efficacy of dexrazoxane, an iron chelator. However, no clinical evidence of anthracycline-induced cardiac iron accumulation is available and the influence of previous iron overload or of genetic factors in human-induced heart disease is largely unknown. Our aim was to test the hypothesis that anthracyclines increase iron heart concentration and that HFE genotype modulates this iron deposit.

METHODS

We retrospectively evaluated cardiac events, cardiac iron and HFE genotype in 97 consecutive necropsies from patients with solid and hematological neoplasms. Heart and liver iron concentration was determined by atomic absorption spectroscopy. HFE gene mutations (C282Y and H63D) linked to hereditary hemochromatosis were analyzed by Fluorescence Resonance Energy Transfer (FRET) genotyping.

RESULTS

Heart iron concentration was increased in cases treated with a cumulative doxorubicin dose greater than 200mg/m(2) (490 vs 240 μg/g; p=0.01), independently of liver iron load or transfusion history. HFE mutated haplotypes 282C/63D (p=0.049) and 282Y/63H (p=0.027) were associated to higher cardiac iron deposits. The haplotype C282Y-Y/H63D-H interacted with anthracyclines for increasing cardiac iron load. In a multivariate linear regression analysis both HFE genotypes and anthracyclines contributed to heart iron concentration (R(2)=0.284).

CONCLUSIONS

Our data support the occurrence of an HFE-modulated heart iron accumulation in individuals treated with anthracyclines, independently of systemic iron load. If prospectively confirmed, iron-related parameters might be useful as predictive factors for anthracycline cardiotoxicity.

Lysosomal proteolysis is the primary degradation pathway for cytosolic ferritin and cytosolic ferritin degradation is necessary for iron exit

Cytosolic ferritins sequester and store iron, consequently protecting cells against iron-mediated free radical damage. However, the mechanisms of iron exit from the ferritin cage and reutilization are largely unknown. In a previous study, we found that mitochondrial ferritin (MtFt) expression led to a decrease in cytosolic ferritin. Here we showed that treatment with inhibitors of lysosomal proteases largely blocked cytosolic ferritin loss in both MtFt-expressing and wild-type cells. Moreover, cytosolic ferritin in cells treated with inhibitors of lysosomal proteases was found to store more iron than did cytosolic ferritins in untreated cells. The prevention of cytosolic ferritin degradation in MtFt-expressing cells significantly blocked iron mobilization from the protein cage induced by MtFt expression. These studies also showed that blockage of cytosolic ferritin loss by leupeptin resulted in decreased cytosolic ferritin synthesis and prolonged cytosolic ferritin stability, potentially resulting in diminished iron availability. Lastly, we found that proteasomes were responsible for cytosolic ferritin degradation in cells pretreated with ferric ammonium citrate. Thus, the current studies suggest that cytosolic ferritin degradation precedes the release of iron in MtFt-expressing cells; that MtFt-induced cytosolic ferritin decrease is partially preventable by lysosomal protease inhibitors; and that both lysosomal and proteasomal pathways may be involved in cytosolic ferritin degradation.

Cytosolic and mitochondrial ferritins in the regulation of cellular iron homeostasis and oxidative damage

BACKGROUND

Ferritin structure is designed to maintain large amounts of iron in a compact and bioavailable form in solution. All ferritins induce fast Fe(II) oxidation in a reaction catalyzed by a ferroxidase center that consumes Fe(II) and peroxides, the reagents that produce toxic free radicals in the Fenton reaction, and thus have anti-oxidant effects. Cytosolic ferritins are composed of the H- and L-chains, whose expression are regulated by iron at a post-transcriptional level and by oxidative stress at a transcriptional level. The regulation of mitochondrial ferritin expression is presently unclear.

SCOPE OF REVIEW

The scope of the review is to update recent progress regarding the role of ferritins in the regulation of cellular iron and in the response to oxidative stress with particular attention paid to the new roles described for cytosolic ferritins, to genetic disorders caused by mutations of the ferritin L-chain, and new findings on mitochondrial ferritin.

MAJOR CONCLUSIONS

The new data on the adult conditional knockout (KO) mice for the H-chain and on the hereditary ferritinopathies with mutations that reduce ferritin functionality strongly indicate that the major role of ferritins is to protect from the oxidative damage caused by iron deregulation. In addition, the study of mitochondrial ferritin, which is not iron-regulated, indicates that it participates in the protection against oxidative damage, particularly in cells with high oxidative activity.

GENERAL SIGNIFICANCE

Ferritins have a central role in the protection against oxidative damage, but they are also involved in non-iron-dependent processes.

Binding and uptake of H-ferritin are mediated by human transferrin receptor-1

Ferritin is a spherical molecule composed of 24 subunits of two types, ferritin H chain (FHC) and ferritin L chain (FLC). Ferritin stores iron within cells, but it also circulates and binds specifically and saturably to a variety of cell types. For most cell types, this binding can be mediated by ferritin composed only of FHC (HFt) but not by ferritin composed only of FLC (LFt), indicating that binding of ferritin to cells is mediated by FHC but not FLC. By using expression cloning, we identified human transferrin receptor-1 (TfR1) as an important receptor for HFt with little or no binding to LFt. In vitro, HFt can be precipitated by soluble TfR1, showing that this interaction is not dependent on other proteins. Binding of HFt to TfR1 is partially inhibited by diferric transferrin, but it is hindered little, if at all, by HFE. After binding of HFt to TfR1 on the cell surface, HFt enters both endosomes and lysosomes. TfR1 accounts for most, if not all, of the binding of HFt to mitogen-activated T and B cells, circulating reticulocytes, and all cell lines that we have studied. The demonstration that TfR1 can bind HFt as well as Tf raises the possibility that this dual receptor function may coordinate the processing and use of iron by these iron-binding molecules.

Specific iron chelators determine the route of ferritin degradation

Deferoxamine (DFO) is a high-affinity Fe (III) chelator produced by Streptomyces pilosus. DFO is used clinically to remove iron from patients with iron overload disorders. Orally administered DFO cannot be absorbed, and therefore it must be injected. Here we show that DFO induces ferritin degradation in lysosomes through induction of autophagy. DFO-treated cells show cytosolic accumulation of LC3B, a critical protein involved in autophagosomal-lysosomal degradation. Treatment of cells with the oral iron chelators deferriprone and desferasirox did not show accumulation of LC3B, and degradation of ferritin occurred through the proteasome. Incubation of DFO-treated cells with 3-methyladenine, an autophagy inhibitor, resulted in degradation of ferritin by the proteasome. These results indicate that ferritin degradation occurs by 2 routes: a DFO-induced entry of ferritin into lysosomes and a cytosolic route in which iron is extracted from ferritin before degradation by the proteasome.

Oxidative stress and autophagy in the regulation of lysosome-dependent neuron death

Lysosomes critically regulate the pH-dependent catabolism of extracellular and intracellular macromolecules delivered from the endocytic/heterophagy and autophagy pathways, respectively. The importance of lysosomes to cell survival is underscored not only by their unique ability effectively to degrade metalloproteins and oxidatively damaged macromolecules, but also by the distinct potential for induction of both caspase-dependent and -independent cell death with a compromise in the integrity of lysosome function. Oxidative stress and free radical damage play a principal role in cell death induced by lysosome dysfunction and may be linked to several upstream and downstream stimuli, including alterations in the autophagy degradation pathway, inhibition of lysosome enzyme function, and lysosome membrane damage. Neurons are sensitive to lysosome dysfunction, and the contribution of oxidative stress and free radical damage to lysosome dysfunction may contribute to the etiology of neurodegenerative disease. This review provides a broad overview of lysosome function and explores the contribution of oxidative stress and autophagy to lysosome dysfunction-induced neuron death. Putative signaling pathways that either induce lysosome dysfunction or result from lysosome dysfunction or both, and the role of oxidative stress, free radical damage, and lysosome dysfunction in pediatric lysosomal storage disorders (neuronal ceroid lipofuscinoses or NCL/Batten disease) and in Alzheimer's disease are emphasized.

Ferritins: a family of molecules for iron storage, antioxidation and more

Ferritins are characterized by highly conserved three-dimensional structures similar to spherical shells, designed to accommodate large amounts of iron in a safe, soluble and bioavailable form. They can have different architectures with 12 or 24 equivalent or non-equivalent subunits, all surrounding a large cavity. All ferritins readily interact with Fe(II) to induce its oxidation and deposition in the cavity in a mineral form, in a reaction that is catalyzed by a ferroxidase center. This is an anti-oxidant activity that consumes Fe(II) and peroxides, the reagents that produce toxic free radicals in the Fenton reaction. The mechanism of ferritin iron incorporation has been characterized in detail, while that of iron release and recycling has been less thoroughly studied. Generally ferritin expression is regulated by iron and by oxidative damage, and in vertebrates it has a central role in the control of cellular iron homeostasis. Ferritin is mostly cytosolic but is found also in mammalian mitochondria and nuclei, in plant plastids and is secreted in insects. In vertebrates the cytosolic ferritins are composed of H and L subunit types and their assembly in a tissues specific ratio that permits flexibility to adapt to cell needs. The H-ferritin can translocate to the nuclei in some cell types to protect DNA from iron toxicity, or can be actively secreted, accomplishing various functions. The mitochondrial ferritin is found in mammals, it has a restricted tissue distribution and it seems to protect the mitochondria from iron toxicity and oxidative damage. The various functions attributed to the cytosolic, nuclear, secretory and mitochondrial ferritins are discussed.

Heart protection by ischemic preconditioning: a novel pathway initiated by iron and mediated by ferritin

Ischemic preconditioning is a well-known procedure transiently protecting the heart against injury associated with prolonged ischemia, through mechanism/s only partly understood. The aim of this study was to test whether preconditioning-induced protection of the heart involves an iron-based mechanism, including the generation of an iron signal followed by accumulation of ferritin. In isolated rat hearts perfused in the Langendorff configuration, we measured heart contractility, ferritin levels, ferritin-iron content, and mRNA levels of ferritin subunits. Ischemic preconditioning caused rapid accumulation of ferritin, reaching 359% of the baseline value (set at 100%). This was accompanied by a parallel decline in ferritin-bound iron: from 2191+/-548 down to 760+/-34 Fe atoms/ferritin molecule, p<0.05. Ferritin levels remained high during the subsequent period of prolonged ischemia, and returned to nearly the baseline value during the reperfusion phase. Selective iron chelators (acetyl hydroxamate or Zn-desferrioxamine) abrogated the functional protection and suppressed ferritin accumulation, thus demonstrating the essentiality of an iron signal in the preconditioning-induced protective mechanism. Moreover, introduction of an iron-containing ternary complex, known to import iron into cells, caused a three-fold accumulation of ferritin and simulated the preconditioning-induced functional protection against prolonged myocardial ischemia. The ischemic preconditioning-and-ischemia-induced increase in ferritin levels correlated well with the accumulation of ferritin L-subunit mRNA: 5.44+/-0.47 vs 1.23+/-0.15 (units) in the baseline, p<0.05, suggesting that transcriptional control of ferritin L-subunit synthesis had been activated. Ischemic preconditioning initiates de novo synthesis of ferritin in the heart; the extra ferritin is proposed to serve a 'sink' for redox-active iron, thus protecting the heart from iron-mediated oxidative damage associated with ischemia-reperfusion injury. The present results substantiate a novel iron-based mechanism of ischemic preconditioning and could pave the way for the development of new modalities of heart protection.

Translational control of C-terminal Src kinase (Csk) expression by PRL3 phosphatase

Phosphatase of regenerating liver 3 (PRL3) is up-regulated in cancer metastases. However, little is known of PRL3-mediated cellular signaling pathways. We previously reported that elevated PRL3 expression increases Src kinase activity, which likely contributes to the increased tumorigenesis and metastasis potential of PRL3. PRL3-induced Src activation is proposed to be indirect through down-regulation of Csk, a negative regulator of Src. Given the importance of PRL3 in tumor metastasis and the role of Csk in controlling Src activity, we addressed the mechanism by which PRL3 mediates Csk down-regulation. PRL3 is shown to exert a negative effect on Csk protein synthesis, rather than regulation of Csk mRNA levels or protein turnover. Interestingly, the preferential decrease in Csk protein synthesis is a consequence of increased eIF2 phosphorylation resulting from PRL3 expression. Reduced Csk synthesis also occurs in response to cellular stress that induces eIF2 phosphorylation, indicating that this regulatory mechanism may occur in response to a wider spectrum of cellular conditions known to direct translational control. Thus, we have uncovered a previously uncharacterized role for PRL3 in the gene-specific translational control of Csk expression.

Cardioprotective Effects of Fullerenol C60(Oh)24 on a Single Dose Doxorubicin-induced Cardiotoxicity in Rats with Malignant Neoplasm

The therapeutic utility of the anthracycline antibiotic doxorubicin is limited due to its cardiotoxicity. Our aim was to investigate the efficacy of fullerenol C60(OH)24 in preventing single, high-dose doxorubicin-induced cardiotoxicity in rats with malignant neoplasm. Experiment was performed on adult female Sprague Dawley rats with chemically induced mammary carcinomas. The animals were sacrificed two days after the application of doxorubicin and/or fullerenol, and the serum activities of CK, LDH and α-HBDH, as well as the levels of MDA, GSH, GSSG, GSH-Px, SOD, CAT, GR, and TAS in the heart, were determined. The results obtained from the enzymatic activity in the serum show that the administration of a single dose of 8 mg/kg in all treated groups induces statistically significant damage. There are significant changes in the enzymes of LDH and CK (p < 0.05), after an i.p. administration of doxorubicin/fullerenol and fullerenol. Comparing all groups with untreated control group, point to the conclusion that in the case of a lower α-HBDH/LDH ratio, results in more serious the liver parenchymal damage. The results revealed that doxorubicin induced oxidative damage and that the fullerenol antioxidative influence caused significant changes in MDA, GSH, GSSG, GSH-Px, SOD, CAT, GR, and TAS level in the heart (p < 0.05). Therefore, it is suggested that fullerenol might be a potential cardioprotector in doxorubicin-treated individuals.

Intracellular free iron and acidic pathways mediate TNF-induced death of rat hepatoma cells

Rat hepatoma HTC cells are intrinsically resistant to various apoptosis-inducing agents. Strategies to induce death in hepatoma cells are needed and the present experimental study was aimed to investigate the sensitivity of HTC cells to TNF and to clarify the mechanisms of action of this cytokine. Cells were treated with TNF and death mechanisms characterized employing an integration of morphological and biochemical techniques. HTC cells, sensitized to TNF toxicity with cycloheximide, died in a caspase-independent apoptosis-like manner. Although we found no evidence for a direct involvement of lysosomal cathepsins, bafilomycin A1 and ammonium chloride significantly attenuated TNF toxicity. Also desferrioxamine mesylate, an iron chelator, partly protected the cells from TNF, while a complete protection was afforded by combining ammonium chloride and iron chelator. Moreover, HTC were protected from TNF also by lipophylic antioxidants and diphenylene iodonium chloride, a NADPH oxidase inhibitor. These data depict a novel mechanism of TNF-mediated cytotoxicity in HTC cells, in which the endo-lysosomal compartment, NADPH oxidase and an iron-mediated pro-oxidant status contribute in determining a caspase-independent, apoptosis-like cell death.

Iron chelation by clinically relevant anthracyclines: alteration in expression of iron-regulated genes and atypical changes in intracellular iron distribution and trafficking

Anthracyclines are effective anticancer agents. However, their use is limited by cardiotoxicity, an effect linked to their ability to chelate iron and to perturb iron metabolism (Mol Pharmacol 68:261-271, 2005). These effects on iron-trafficking remain poorly understood, but they are important to decipher because treatment for anthracycline cardiotoxicity uses the chelator, dexrazoxane. Incubation of cells with doxorubicin (DOX) up-regulated mRNA levels of the iron-regulated genes transferrin receptor-1 (TfR1) and N-myc downstream-regulated gene-1 (Ndrg1). This effect was mediated by iron depletion, because it was reversed by adding iron and it was prevented by saturating the anthracycline metal binding site with iron. However, DOX did not act like a typical chelator, because it did not induce cellular iron mobilization. In the presence of DOX and (59)Fe-transferrin, iron-trafficking studies demonstrated ferritin-(59)Fe accumulation and decreased cytosolic-(59)Fe incorporation. This could induce cytosolic iron deficiency and increase TfR1 and Ndrg1 mRNA. Up-regulation of TfR1 and Ndrg1 by DOX was independent of anthracycline-mediated radical generation and occurred via hypoxia-inducible factor-1alpha-independent mechanisms. Despite increased TfR1 and Ndrg1 mRNA after DOX treatment, this agent decreased TfR1 and Ndrg1 protein expression. Hence, the effects of DOX on iron metabolism were complex because of its multiple effector mechanisms.

An introduction to the metabolic determinants of anthracycline cardiotoxicity

Antitumor therapy with doxorubicin and other anthracyclines is limited by the possible development of cardiomyopathy upon chronic administration. Several lines of evidence suggest that a close link exists between cardiotoxicity and the amount of anthracycline that accumulates in the heart and then undergoes one- or two- electron reduction to toxic metabolites or by-products. Alternative metabolic pathways lead to an oxidative degradation of anthracyclines, possibly counteracting anthracycline accumulation and reductive bioactivation; unfortunately, however, the actual role of anthracycline oxidation is only partially characterized. Here, we briefly review the biochemical foundations of reductive versus oxidative anthracycline metabolism. We show that multiple links exist between one pathway of toxic biactivation and another, limiting the search and clinical development of "better anthracyclines" that retain antitumor activity but induce less cardiotoxicity than the available analogues.

Flavonoids as protectors against doxorubicin cardiotoxicity: Role of iron chelation, antioxidant activity and inhibition of carbonyl reductase

Anthracycline antibiotics (e.g. doxorubicin and daunorubicin) are among the most effective and widely used anticancer drugs. Unfortunately, their clinical use is limited by the dose-dependent cardiotoxicity. Flavonoids represent a potentially attractive class of compounds to mitigate the anthracycline cardiotoxicity due to their iron-chelating, antioxidant and carbonyl reductase-inhibitory effects. The relative contribution of various characteristics of the flavonoids to their cardioprotective activity is, however, not known. A series of ten flavonoids including quercetin, quercitrin, 7-monohydroxyethylrutoside (monoHER) and seven original synthetic compounds were employed to examine the relationships between their inhibitory effects on carbonyl reduction, iron-chelation and antioxidant properties with respect to their protective potential against doxorubicin-induced cardiotoxicity. Cardioprotection was investigated in the neonatal rat ventricular cardiomyocytes whereas the H9c2 cardiomyoblast cells were used for cytotoxicity testing. Iron chelation was examined via the calcein assay and antioxidant effects and site-specific scavenging were quantified by means of inhibition of lipid peroxidation and hydroxyl radical scavenging activity, respectively. Inhibition of carbonyl reductases was assessed in cytosol from human liver. None of the flavonoids tested had better cardioprotective action than the reference cardioprotector, monoHER. However, a newly synthesized quaternary ammonium analog with comparable cardioprotective effects has been identified. No direct correlation between the iron-chelating and/or antioxidant effect and cardioprotective potential has been found. A major role of carbonyl reductase inhibition seems unlikely, as the best two cardioprotectors of the series are only weak reductase inhibitors.

Iron chelation-afforded cardioprotection against chronic anthracycline cardiotoxicity: A study of salicylaldehyde isonicotinoyl hydrazone (SIH)

Pyridoxal-derived aroylhydrazone iron chelators have been previously shown as effective cardioprotectants against chronic anthracycline cardiotoxicity. In this study we focused on a novel salicylaldehyde analogue (salicylaldehyde isonicotinoyl hydrazone, SIH), which has been recently demonstrated to possess marked and dose-dependent protective effects against oxidative injury of cardiomyocytes. Therefore, in the present study the cardioprotective potential of SIH against daunorubicin (DAU) cardiotoxicity was assessed in vitro (isolated rat ventricular cardiomyocytes; DAU 10 microM, 48 h exposure) as well as in vivo (chronic DAU-induced cardiomyopathy in rabbits; DAU 3mg/kg, i.v. weekly, 10 weeks). In vitro, SIH (3-100 microM) was able to partially, but significantly decrease the LDH leakage from cardiomyocytes. In vivo, SIH co-administration was capable to reduce (SIH dose of 0.5mg/kg, i.v.) or even to completely prevent (1.0mg/kg, i.v.) the DAU-induced mortality. Moreover, the latter dose of the chelator significantly improved the left ventricular function (LV dP/dt(max)=1185+/-80 kPa/s versus 783+/-53 kPa/s in the DAU group; P<0.05) and decreased the severity of the myocardial morphological changes as well as the plasma levels of cardiac troponin T. Unfortunately, further escalation of the SIH dose (to 2.5mg/kg) resulted in a nearly complete reversal of the protective effects as judged by the overall mortality, functional, morphological as well as biochemical examinations. Hence, this study points out that aroylhydrazone iron chelators can induce a significant cardioprotection against anthracycline cardiotoxicity; however, they share the curious dose-response relationship which is unrelated to the chemical structure or the route of the administration of the chelator.

Crucial role of lysosomal iron in the formation of dinitrosyl iron complexes in vivo

Dinitrosyl non-heme-iron complexes (DNIC) are found in many nitric oxide producing tissues. A prerequisite of DNIC formation is the presence of nitric oxide, iron and thiol/imidazole groups. The aim of this study was to investigate the role of the cellular labile iron pool in the formation of DNIC in erythroid K562 cells. The cells were treated with a nitric oxide donor in the presence of a permeable (salicylaldehyde isonicotinoyl hydrazone) or a nonpermeable (desferrioxamine mesylate) iron chelator and DNIC formation was recorded using electron paramagnetic resonance. Both chelators inhibited DNIC formation up to 50% after 6 h of treatment. To further investigate the role of lysosomal iron in DNIC formation, we prevented lysosomal proteolysis by pretreatment of whole cells with NH4Cl. Pretreatment with NH4Cl inhibited the formation of DNIC in a time-dependent manner that points to the importance of the degradation of iron metalloproteins in DNIC formation in vivo. Fractionation of the cell content after treatment with the nitric oxide donor revealed that DNIC is formed predominantly in the endosomal/lysosomal fraction. Taken together, these data indicate that lysosomal iron plays a crucial role in DNIC formation in vivo. Degradation of iron-containing metalloproteins seems to be important for this process.

Ferroportin-mediated mobilization of ferritin iron precedes ferritin degradation by the proteasome

Ferritin is a cytosolic molecule comprised of subunits that self-assemble into a nanocage capable of containing up to 4500 iron atoms. Iron stored within ferritin can be mobilized for use within cells or exported from cells. Expression of ferroportin (Fpn) results in export of cytosolic iron and ferritin degradation. Fpn-mediated iron loss from ferritin occurs in the cytosol and precedes ferritin degradation by the proteasome. Depletion of ferritin iron induces the monoubiquitination of ferritin subunits. Ubiquitination is not required for iron release but is required for disassembly of ferritin nanocages, which is followed by degradation of ferritin by the proteasome. Specific mammalian machinery is not required to extract iron from ferritin. Iron can be removed from ferritin when ferritin is expressed in Saccharomyces cerevisiae, which does not have endogenous ferritin. Expressed ferritin is monoubiquitinated and degraded by the proteasome. Exposure of ubiquitination defective mammalian cells to the iron chelator desferrioxamine leads to degradation of ferritin in the lysosome, which can be prevented by inhibitors of autophagy. Thus, ferritin degradation can occur through two different mechanisms.