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

Knockdown of microglial iron import gene, DMT1, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease

Background

Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer's disease (AD). In vitro, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of microglial-specific knockdown of Slc11a2 on AD-related cognitive decline and microglial transcriptional phenotype.

Methods

In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1 Cre - ERT2 ;Slc11a2 flfl;APP/PS1 + or - mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b + microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted.

Results

DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2 KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2 KD APP/PS1 females displayed significant increases in Enpp2, Ttr, and the iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2 KD cells from APP/PS1 females also exhibited decreased expression of markers associated with disease-associated microglia (DAMs), such as Apoe, Ctsb, Csf1, and Hif1α.

Conclusions

This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in microglia and cognitive deficits in Slc11a2 KD APP/PS1 female mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

Ebselen: A Review on its Synthesis, Derivatives, Anticancer Efficacy and Utility in Combating SARS-COV-2

Ebselen is a selenoorganic chiral compound with antioxidant properties comparable to glutathione peroxidase. It is also known as 2-phenyl-1,2-benzisoselenazol-3(2H)-one. In studies examining its numerous pharmacological activities, including antioxidant, anticancer, antiviral, and anti- Alzheimer's, ebselen has demonstrated promising results. This review's primary objective was to emphasize the numerous synthesis pathways of ebselen and their efficacy in fighting cancer. The data were collected from multiple sources, including Scopus, PubMed, Google Scholar, Web of Science, and Publons. The starting reagents for the synthesis of ebselen are 2-aminobenzoic acid and N-phenyl benzamide. It was discovered that ebselen has the ability to initiate apoptosis in malignant cells and prevent the formation of new cancer cells by scavenging free radicals. In addition, ebselen increases tumor cell susceptibility to apoptosis by inhibiting TNF-α mediated NF-kB activation. Ebselen can inhibit both doxorubicin and daunorubicin-induced cardiotoxicity. Allopurinol and ebselen administered orally can be used to suppress renal ototoxicity and nephrotoxicity. Due to excessive administration, diclofenac can induce malignancy of the gastrointestinal tract, which ebselen can effectively suppress. Recent research has demonstrated ebselen to inhibit viral function by binding to cysteinecontaining catalytic domains of various viral proteases. It was discovered that ebselen could inhibit the catalytic dyad function of Mpro by forming an irreversible covalent bond between Se and Cys145, thereby altering protease function and inhibiting SARS-CoV-2. Ebselen may also inhibit the activation of endosomal NADPH oxidase of vascular endothelial cells, which is believed to be required for thrombotic complications in COVID-19. In this review, we have included various studies conducted on the anticancer effect of ebselen as well as its inhibition of SARS-CoV-2.

Ebselen, an Active Seleno-Organic Compound, Alleviates Articular Cartilage Degeneration in a Rat Model of Knee Osteoarthritis

Osteoarthritis (OA) is a prevalent articular disease mainly characterized by extracellular matrix degradation, apoptosis, and inflammation, which lead to cartilage destruction and abnormal bone metabolism. With undesirable side effects, current limited symptomatic treatments are aimed at relieving pain and improving joint mobility in patients with OA. Intra-articular (IA) hyaluronic acid (HA) injection, as a nonsurgical therapy, is commonly used in the clinical management of knee OA, but the efficacy of this therapeutic option remains controversial. Ebselen has tremendous pharmacological importance for some diseases due to its antioxidant, antiapoptotic, and anti-inflammatory features. However, there is no research examining the therapeutic effect of Ebselen in OA using the rat OA model. Therefore, we aimed to investigate the therapeutic effect of Ebselen on cartilage degeneration and its role in bone morphogenetic protein 2 (BMP2) and nuclear factor kappa B (NF-κB) signaling in the molecular pathogenesis of OA. We induced a knee OA model in rats with an IA injection of monosodium-iodoacetate (MIA). After the treatment of Ebselen, we evaluated its chondroprotective effects by morphological, histopathological, and immunohistochemical methods and an enzyme-linked immunosorbent assay. We report for the first time that Ebselen treatment alleviated articular cartilage degeneration in the rat knee OA model and reduced MIA-induced BMP2 and NF-κB expressions. In addition, our results unveiled that Ebselen decreased IL-β and IL-6 levels but did not affect COMP levels in the rat serum. Ebselen could be a promising therapeutic drug for the prevention and treatment of OA by alleviating cartilage degeneration and regulating BMP2 and NF-κB expressions.

Ebselen: A promising therapy protecting cardiomyocytes from excess iron in iron-overloaded thalassemia patients

Iron-overload-associated cardiomyopathy has been one of the primary causes of mortality in thalassemia patients with iron burden. There is growing evidence citing the beneficial effects of ebselen as an antioxidant selectively blocking the divalent metal transporter 1 (DMT-1) to deter iron ingress into cardiomyocytes, raising internets in viewing this component in this population in order to treat and even prevent cardiomyopathy occurring from iron surplus. In this article, we reviewed the potential advantageous effects of ebselen in thalassemia patients who suffer from iron excess, susceptible to cardiomyopathy induced by iron overload. A systematic search in several databases, including PubMed, Scopus, and Web of Science, was conducted to explore the role of ebselen in controlling iron-overload-related cardiomyopathy in thalassemia patients by the keywords of Ebselen AND iron. The inclusion criteria were English-written preclinical and clinical studies investigating the efficacy and side effects of ebselen in an iron-overload context. After searching the databases, 44 articles were found. Next, of 19 published articles, 3 were included in this article. After reviewing the references of the included studies, no articles were added. In conclusion ebselen can be a promising adjuvant therapy in patients with thalassemia alongside the standard treatment with iron chelators, particularly in severe cases with cardiomyopathy, due to falling iron inflow by inhibiting DMT-1 and increasing ferroportin-1 expression and antioxidant properties. However, clinical studies need to be carried out to reach a definite conclusion.

Inflammation, dysregulated iron metabolism, and cardiovascular disease

Iron is an essential trace element associated with both pathologic deficiency and toxic overload. Thus, systemic and cell iron metabolism are highly controlled processes regulated by protein expression and localization, as well as turnover, through the action of cytokines and iron status. Iron metabolism in the heart is challenging because both iron overload and deficiency are associated with cardiac disease. Also associated with cardiovascular disease is inflammation, as many cardiac diseases are caused by or include an inflammatory component. In addition, iron metabolism and inflammation are closely linked. Hepcidin, the master regulator of systemic iron metabolism, is induced by the cytokine IL-6 and as such is among the acute phase proteins secreted by the liver as part of the inflammatory response. In an inflammatory state, systemic iron homeostasis is dysregulated, commonly resulting in hypoferremia, or low serum iron. Less well characterized is cardiac iron metabolism in general, and even less is known about how inflammation impacts heart iron handling. This review highlights what is known with respect to iron metabolism in the heart. Expression of iron metabolism-related proteins and processes of iron uptake and efflux in these cell types are outlined. Evidence for the strong co-morbid relationship between inflammation and cardiac disease is also reviewed. Known connections between inflammatory processes and iron metabolism in the heart are discussed with the goal of linking inflammation and iron metabolism in this tissue, a connection that has been relatively under-appreciated as a component of heart function in an inflammatory state. Therapeutic options connecting inflammation and iron balance are emphasized, with the main goal of this review being to bring attention to alterations in iron balance as a component of inflammatory diseases of the cardiovascular system.

Amlodipine rescues advanced iron overload cardiomyopathy in hemojuvelin knockout murine model: Clinical implications

Background

Iron overload cardiomyopathy (IOC) is a major co-morbidity of genetic hemochromatosis and secondary iron overload with limited therapeutic options. We aim to investigate mechanisms of rescue action of amlodipine in the murine model of iron overload, characterize changes in human cardiac tissue due to IOC, and compare them to the changes in the animal model of IOC.

Methods and results

As an animal model, we used male hemojuvelin knockout (HJVKO) mice, which lacked hemojuvelin (a co-receptor protein for hepcidin expression). The mice were fed a high-iron diet from 4 weeks to 1 year of age. As a rescue, iron-fed mice received the Ca²⁺ channel blocker, amlodipine, from 9 to 12 months. Iron overload resulted in systolic and diastolic dysfunctions and changes in the cardiac tissue similar to the changes in the explanted human heart with IOC. An IOC patient (β-thalassemia) with left-ventricular ejection fraction (LVEF) 25% underwent heart transplantation. The murine model and the explanted heart showed intra-myocyte iron deposition, fibrosis, hypertrophy, oxidative stress, remodeling of Ca²⁺ cycling proteins, and metabolic kinases typical of heart failure. Single-myocyte contractility and Ca²⁺ release were diminished in the murine model. The amlodipine-treated group exhibited normalization of cellular function and reversed fibrosis, hypertrophy, oxidative stress, and metabolic remodeling. We also report a clinical case of primary hemochromatosis successfully treated with amlodipine.

Conclusions

The aged HJVKO murine model on the iron-rich diet reproduced many features of the human case of IOC. The use of amlodipine in the murine model and clinical case reversed IOC remodeling, demonstrating that amlodipine is effective adjuvant therapy for IOC.

Iron homeostasis in the heart: Molecular mechanisms and pharmacological implications

Iron is necessary for the life of practically all living things, yet it may also harm people toxically. Accordingly, humans and other mammals have evolved an effective and tightly regulatory system to maintain iron homeostasis in healthy tissues, including the heart. Iron deficiency is common in patients with heart failure, and is associated with worse prognosis in this population; while the prevalence of iron overload-related cardiovascular disorders is also increasing. Therefore, enhancing the therapy of patients with cardiovascular disorders requires a thorough understanding of iron homeostasis. Here, we give readers an overview of the fundamental mechanisms governing systemic iron homeostasis as well as the most recent knowledge about the intake, storage, use, and export of iron from the heart. Genetic mouse models used for investigation of iron metabolism in various in vivo scenarios are summarized and highlighted. We also go through different clinical conditions and therapeutic approaches that target cardiac iron dyshomeostasis. Finally, we conclude the review by outlining the present knowledge gaps and important open questions in this field in order to guide future research on cardiac iron metabolism.

Hepcidin Promoted Ferroptosis through Iron Metabolism which Is Associated with DMT1 Signaling Activation in Early Brain Injury following Subarachnoid Hemorrhage

Iron metabolism disturbances play an important role in early brain injury (EBI) after subarachnoid hemorrhage (SAH), and hepcidin largely influences iron metabolism. Importantly, iron metabolism may be associated with ferroptosis, recently a nonapoptotic iron-dependent form of cell death that may have a great impact on brain injury after SAH. We investigated hepcidin on iron metabolism and ferroptosis involving divalent metal transporter 1 (DMT1), and ferroportin-1 (FPN1) in a rat model of SAH. Male Sprague-Dawley rats were subjected to the endovascular perforation to induce SAH, and treated with heparin (inhibitor of hepcidin), or oncostatin M (OSM, inducer of hepcidin), or ebselen (inhibitor of DMT1) by intracerebroventricular injections. Hepcidin, DMT1, FPN1 and glutathione peroxidase 4 (GPX4), were detected by western blot and immunofluorescence. Iron metabolism was detected through Perl's iron staining and iron content assay. Ferroptosis, the ROS production, lipid peroxidation (LPO) was evaluated by monitoring methane dicarboxylic aldehyde (MDA), glutathione (GSH), glutathione peroxidase 4 (GPX4) activity, and transmission electron microscopy. Neurological deficit scores, Evans blue staining and brain water content were also determined to detect EBI 72 h after SAH. Our results showed that inhibition of DMT1 by ebselen could suppress iron accumulation and lipid peroxidation, and thereby alleviate ferroptosis and EBI in SAH rats. Heparin downregulated the expression of hepcidin and DMT1, increased FPN1, and exerted protective effects that were equivalent to those of ebselen on ferroptosis and EBI. In addition, OSM increased the expression of hepcidin and DMT1, decreased FPN1, and aggravated ferroptosis and EBI, while the effect on ferroptosis was reversed by ebselen. Therefore, the study revealed that hepcidin could regulate iron metabolism and contribute to ferroptosis via DMT1 signaling activation in rats with EBI after SAH.

Ebselen, a multi-target compound: its effects on biological processes and diseases

Ebselen is a well-known synthetic compound mimicking glutathione peroxidase (GPx), which catalyses some vital reactions that protect against oxidative damage. Based on a large number of in vivo and in vitro studies, various mechanisms have been proposed to explain its actions on multiple targets. It targets thiol-related compounds, including cysteine, glutathione, and thiol proteins (e.g., thioredoxin and thioredoxin reductase). Owing to this, ebselen is a unique multifunctional agent with important effects on inflammation, apoptosis, oxidative stress, cell differentiation, immune regulation and neurodegenerative disease, with anti-microbial, detoxifying and anti-tumour activity. This review summarises the current understanding of the multiple biological processes and molecules targeted by ebselen, and its pharmacological applications.

Mechanisms of ebselen as a therapeutic and its pharmacology applications

Ebselen is a synthetic organoselenium radical scavenger compound that possesses glutathione peroxidase-like activity and its own unique bioactivity by reacting with thiols, hydroperoxides and peroxynitrites. Owing to its high affinity toward several essential reactions, ebselen protects cellular components from oxidative and free radical damage, and it has been employed as a useful tool for studying redox-related mechanisms. Based on numerous in vitro and in vivo research, mechanisms are proposed to understand the biomedical and molecular actions of ebselen in health and disease, and it is currently under clinical trials for the prevention and treatment of various human disorders. Based on these outstanding discoveries, this review summarizes the current understanding of the biochemical and molecular characteristics, pharmacological applications and future directions of ebselen.

Ebselen rescues oxidative-stress-suppressed osteogenic differentiation of bone-marrow-derived mesenchymal stem cells via an antioxidant effect and the PI3K/Akt pathway

BACKGROUND

Patients with metabolic bone diseases often have high risk of titanium implant failure due to compromised bone regeneration ability. Clinical evidence indicates that the poor osteogenic ability is partly because of excessive oxidative stress. To date, specific treatments for these patients are urgently needed. Ebselen, a non-toxic organoselenium compound, is reported to be a potent antioxidant agent. In this study, we hypothesized that ebselen exerted protective effects on osteogenic differentiation of bone-marrow-derived mesenchymal stem cells (BMSCs) under oxidative stress.

METHODS

BMSCs were isolated from SD rats, and their morphology and multiple differentiation abilities were characterized. Proliferation rates of BMSCs treated with different concentrations of ebselen were analyzed. Then BMSCs were pretreated by hydrogen peroxide (H₂O₂), after which ebselen at different concentrations (0, 1, 5, 10 μM) was added, alkaline phosphatase (ALP) activity, mineralization and osteogenic-related protein levels were evaluated and an optimum concentration of ebselen was selected. Subsequently, intracellular reactive oxygen species (ROS) generation and the role of the PI3K/AKT pathway were also investigated.

RESULTS

Ebselen within a proper range could promote the proliferation of BMSCs. H₂O₂-induced oxidative stress suppressed osteogenic differentiation of BMSCs, which was verified by the decrease in ALP activity, calcium deposition, Runx2 and β-catenin expression. However, ebselen could alleviate osteogenic dysfunction of BMSCs. We also observed that ebselen reduced ROS accumulation in H₂O₂-pretreated BMSCs. Moreover, the pro-osteogenic effects afforded by ebselen were almost abolished by the Akt inhibitor.

CONCLUSION

We concluded that ebselen could attenuate osteogenic dysfunction of BMSCs induced by H₂O₂ through an antioxidant effect and the activation of the PI3K/Akt pathway, suggesting that ebselen has a potential therapeutic effect for patients with metabolic bone diseases.

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

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

Non-transferrin-bound iron transporters

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

The Central Role of Biometals Maintains Oxidative Balance in the Context of Metabolic and Neurodegenerative Disorders

Traditionally, oxidative stress as a biological aspect is defined as an imbalance between the free radical generation and antioxidant capacity of living systems. The intracellular imbalance of ions, disturbance in membrane dynamics, hypoxic conditions, and dysregulation of gene expression are all molecular pathogenic mechanisms closely associated with oxidative stress and underpin systemic changes in the body. These also include aspects such as chronic immune system activation, the impairment of cellular structure renewal, and alterations in the character of the endocrine secretion of diverse tissues. All of these mentioned features are crucial for the correct function of the various tissue types in the body. In the present review, we summarize current knowledge about the common roots of metabolic and neurodegenerative disorders induced by oxidative stress. We discuss these common roots with regard to the way that (1) the respective metal ions are involved in the maintenance of oxidative balance and (2) the metabolic and signaling disturbances of the most important biometals, such as Mg²⁺, Zn²⁺, Se²⁺, Fe²⁺, or Cu²⁺, can be considered as the central connection point between the pathogenesis of both types of disorders and oxidative stress.

Targeting iron metabolism in drug discovery and delivery

Iron fulfils a central role in many essential biochemical processes in human physiology; thus, proper processing of iron is crucial. Although iron metabolism is subject to relatively strict physiological control, numerous disorders, such as cancer and neurodegenerative diseases, have recently been linked to deregulated iron homeostasis. Consequently, iron metabolism constitutes a promising and largely unexploited therapeutic target for the development of new pharmacological treatments for these diseases. Several iron metabolism-targeted therapies are already under clinical evaluation for haematological disorders, and these and newly developed therapeutic agents are likely to have substantial benefit in the clinical management of iron metabolism-associated diseases, for which few efficacious treatments are currently available.

Effects of iron overload condition on liver toxicity and hepcidin/ferroportin expression in thalassemic mice

AIMS

Although iron-overload conditions can be found in β-thalassemic patients, resulting in cellular damage, particularly in the liver, the mechanism for this iron-mediated hepatic injury specifically in β-thalassemic (HT) mice is unclear. This study aimed to investigate the roles of L-type calcium channels (LTCC), T-type calcium channels (TTCC) and divalent metal transporter1 (DMT1) in iron-mediated hepatic injury in HT mice.

MAIN METHODS

Iron chelator deferoxamine (DFO), LTCC blocker, TTCC blocker and DMT1 blocker were used to determine the roles of these channels regarding liver iron accumulation, apoptosis and iron regulatory protein expression in HT mice.

KEY FINDINGS

TTCC and DMT1 blockers and DFO decreased liver iron and malondialdehyde (MDA) in HT mice indicating their antioxidant effects, whereas LTCC blocker produced no decrease in liver iron or MDA. However, only DFO decreased liver apoptosis through the reduced Bax/Bcl-2 ratio in wild type (WT) mice. The levels of iron regulatory hormone hepcidin were markedly higher in HT mice even before iron loading while ferroportin levels did not alter. Each of the pharmacological interventions increased ferroportin protein back to normal levels only in WT while HT mice showed no difference.

SIGNIFICANCE

Thalassemic mice have different hepcidin/ferroportin and apoptotic protein expression as a defense mechanism to iron-overload compared with those in WT mice. DFO was the most effective intervention in preventing liver apoptosis under iron-overload conditions in WT but did not have the same effect in HT mice.

Pharmacology of iron transport

Elucidating the molecular basis for the regulation of iron uptake, storage, and distribution is necessary to understand iron homeostasis. Pharmacological tools are emerging to identify and distinguish among different iron transport pathways. Stimulatory or inhibitory small molecules with effects on iron uptake can help characterize the mechanistic elements of iron transport and the roles of the transporters involved in these processes. In particular, iron chelators can serve as potential pharmacological tools to alleviate diseases of iron overload. This review focuses on the pharmacology of iron transport, introducing iron transport membrane proteins and known inhibitors.

Novel pathways and therapies in experimental diabetic atherosclerosis

Diabetic subjects are at a greater risk of developing major vascular complications due to abnormalities pertinent to the diabetic milieu. Current treatment options achieve significant improvements in glucose levels and blood pressure control, but do not necessarily prevent or retard diabetes-mediated macrovascular disease. In this review, we highlight several pathways that are increasingly being appreciated as playing a significant role in diabetic vascular injury. We focus particularly on the advanced glycation end product/receptor for advanced glycation end product (AGE/RAGE) axis and its interplay with the nuclear protein HMGB1. We discuss evidence implicating a significant role for the renin-angiotensin system, urotensin II and PPAR, as well as the importance of proinflammatory mediators and oxidative stress in cardiovascular complications. The specific targeting of these pathways may lead to novel therapies to reduce the burden of diabetic vascular complications.

T-type calcium channel blockade improves survival and cardiovascular function in thalassemic mice

OBJECTIVES

Iron-overload cardiomyopathy is a major cause of morbidity and mortality in patients with thalassemia. However, the precise mechanisms of iron entry and sequestration in the heart are still unclear. Our previous study showed that Fe(2+) uptake in thalassemic cardiomyocytes are mainly mediated by T-type calcium channels (TTCC). Nevertheless, the role of TTCC as well as other transporters such as divalent metal transporter1 (DMT1) and L-type calcium channels (LTCC) as possible portals for iron entry into the heart in in vivo thalassemic mice under an iron-overload condition has not been investigated.

METHODS

An iron-overload condition was induced in genetically altered β-thalassemic mice and adult wild-type mice by feeding them with an iron diet (0.2% ferrocene w/w) for 3 months. Then, blockers for LTCC (verapamil and nifedipine), TTCC (efonidipine), and DMT1 (ebselen) as well as iron chelator desferoxamine (DFO) were given for 1 month with continuous iron feeding.

RESULTS

Treatment with LTCC, TTCC, DMT1 blockers, and DFO reduced cardiac iron deposit, cardiac malondialdehyde (MDA), plasma non-transferrin-bound iron, and improved heart rate variability and left ventricular (LV) function in thalassemic mice with iron overload. Only TTCC and DMT1 blockers and DFO reduced liver iron accumulation, liver MDA, plasma MDA, and decreased mortality rate in iron-overloaded thalassemic mice.

CONCLUSIONS

DMT1, LTCC, and TTCC played important roles for iron entry in the thalassemic heart under an iron-overloaded condition. Unlike LTCC blocker, TTCC blocker provided all benefits including attenuating iron deposit in both the heart and liver, reduced oxidative stress, and decreased mortality in iron-overloaded mice.

T-type calcium channel as a portal of iron uptake into cardiomyocytes of beta-thalassemic mice

OBJECTIVES

Iron-overload condition can be found in β-thalassemic patients with regular blood transfusion, leading to iron deposition in various organs including the heart. Elevated cardiac iron causes iron-overload cardiomyopathy, a condition that provokes mortality because of heart failure in patients with thalassemia. Previous studies demonstrated that myocardial iron uptake may occur via L-type calcium channels (LTCCs). However, direct evidence regarding the claimed pathway in thalassemic cardiomyocytes has never been investigated.

METHODS

Hearts from genetic-altered β-thalassemic mice and adult wild-type mice were used for cultured ventricular cardiomyocytes. Blockers for LTCC, T-type calcium channel (TTCC), transferrin receptor1 (TfR1), and divalent metal transporter1 (DMT1) were used, and quantification of cellular iron uptake under various iron loading conditions was performed by Calcein-AM fluorescence assay. Microarray analysis was performed to investigate gene expressions in the hearts of these mice.

RESULTS

This study demonstrated that iron uptake under iron-overload conditions in the cultured ventricular myocytes of thalassemic mice was greater than that of wild-type cells (P <0.01). TTCC blocker, efonidipine, and an iron chelator, deferoxamine, could prevent iron uptake into cultured cardiomyocytes, whereas blockers of TfR1, DMT1, and LTCC could not. Microarray analysis from thalassemic hearts demonstrated highly up-regulated genes of TTCC, zinc transporter, and transferrin receptor2.

CONCLUSIONS

Our findings indicated that iron uptake mechanisms in cultured thalassemic cardiomyocytes are mainly mediated by TTCC, suggesting that TTCC is the important pathway for iron uptake in this cultured thalassemic cardiomyocyte model.

Antiatherosclerotic and renoprotective effects of ebselen in the diabetic apolipoprotein E/GPx1-double knockout mouse

OBJECTIVE

To investigate the effect of the GPx1-mimetic ebselen on diabetes-associated atherosclerosis and renal injury in a model of increased oxidative stress.

RESEARCH DESIGN AND METHODS

The study was performed using diabetic apolipoprotein E/GPx1 (ApoE(-/-)GPx1(-/-))-double knockout (dKO) mice, a model combining hyperlipidemia and hyperglycemia with increased oxidative stress. Mice were randomized into two groups, one injected with streptozotocin, the other with vehicle, at 8 weeks of age. Groups were further randomized to receive either ebselen or no treatment for 20 weeks.

RESULTS

Ebselen reduced diabetes-associated atherosclerosis in most aortic regions, with the exception of the aortic sinus, and protected dKO mice from renal structural and functional injury. The protective effects of ebselen were associated with a reduction in oxidative stress (hydroperoxides in plasma, 8-isoprostane in urine, nitrotyrosine in the kidney, and 4-hydroxynonenal in the aorta) as well as a reduction in VEGF, CTGF, VCAM-1, MCP-1, and Nox2 after 10 weeks of diabetes in the dKO aorta. Ebselen also significantly reduced the expression of proteins implicated in fibrosis and inflammation in the kidney as well as reducing related key intracellular signaling pathways.

CONCLUSIONS

Ebselen has an antiatherosclerotic and renoprotective effect in a model of accelerated diabetic complications in the setting of enhanced oxidative stress. Our data suggest that ebselen effectively repletes the lack of GPx1, and indicate that ebselen may be an effective therapeutic for the treatment of diabetes-related atherosclerosis and nephropathy. Furthermore, this study highlights the feasibility of addressing two diabetic complications with one treatment regimen through the unifying approach of targeted antioxidant therapy.

Methylmercury neurotoxicity is associated with inhibition of the antioxidant enzyme glutathione peroxidase

In this study, we investigated the involvement of glutathione peroxidase-GPx in methylmercury (MeHg)-induced toxicity using three models: (a) in mouse brain after treatment with MeHg (40 mg/L in drinking water), (b) in mouse brain mitochondrial-enriched fractions isolated from MeHg-treated animals, and (c) in cultured human neuroblastoma SH-SY5Y cells. First, adult male Swiss mice exposed to MeHg for 21 days showed a significant decrease in GPx activity in the brain and an increase in poly(ADP-ribose) polymerase cleavage, an index of apoptosis. Second, in mitochondrial-enriched fractions isolated from MeHg-treated mice, there was a significant reduction in GPx activity and a concomitant decrease in mitochondrial activity and increases in ROS formation and lipid peroxidation. Incubation of mitochondrial-enriched fractions with mercaptosuccinic acid, a GPx inhibitor, significantly augmented the toxic effects of MeHg administered in vivo. Incubation of mitochondrial-enriched fractions with exogenous GPx completely blocked MeHg-induced mitochondrial lipid peroxidation. Third, SH-SY5Y cells treated for 24 h with MeHg showed a significant reduction in GPx activity. There was a concomitant significant decrease in cell viability and increase in apoptosis. Inhibition of GPx substantially enhanced MeHg toxicity in the SH-SY5Y cells. These results suggest that GPx is an important target for MeHg-induced neurotoxicity, presumably because this enzyme is essential for counteracting the pro-oxidative effects of MeHg both in vitro and in vivo.

Small-molecule screening identifies the selanazal drug ebselen as a potent inhibitor of DMT1-mediated iron uptake

HEK293T cells overexpressing divalent metal transporter-1 (DMT1) were established to screen for small-molecule inhibitors of iron uptake. Using a fluorescence-based assay, we tested 2000 known bioactive compounds to find 3 small molecules that potently block ferrous iron uptake. One of the inhibitors, ebselen, is a seleno compound used in clinical trials as a protective agent against ischemic stroke. Ebselen inhibited Fe(II) uptake (IC(50) of approximately 0.22 microM), but did not influence Fe(III) transport or DMT1-mediated manganese uptake. An unrelated antioxidant, pyrrolidine dithiobarbamate (PDTC), also inhibited DMT1 activity (IC(50) of approximately 1.54 microM). Both ebselen and PDTC increased cellular levels of reduced glutathione. These observations indicate that Fe(II) transport by DMT1 can be modulated by cellular redox status and suggest that ebselen may act therapeutically to limit iron-catalyzed damage due to transport inhibition.