Nature of non-transferrin-bound iron: studies on iron citrate complexes and thalassemic sera

Stored RBC transfusions leads to the systemic inflammatory response syndrome in anemic murine neonates

OBJECTIVE

RBC transfusions (RBCT) are life-saving treatment for premature and critically ill infants. However, the procedure has been associated with the development of systemic inflammatory response syndrome (SIRS) and potentially multiple organ dysfunction syndrome (MODS) in neonates. The present study aimed to investigate the mechanisms of RBCT-related SIRS in severely anemic murine neonates.

METHODS

C57BL/6 (WT), TLR4-/- and myeloid-specific triggered myeloid receptor-1 (trem1)-/- mouse pups were studied in 4 groups (n = 6 each): (1) naïve controls, (2) transfused control, (3) anemic (hematocrit 20-24%) and (4) anemic with RBC transfused using our established murine model of phlebotomy-induced anemia (PIA) and RBC transfusion. Plasma was measured for quantifying inflammatory cytokines (IFN-γ, IL-1β, TNF-α, IL-6, MIP-1α, MIP-1β, MIP2 and LIX) using a Luminex assay. In vitro studies included (i) sensitization by exposing the cells to a low level of lipopolysaccharide (LPS; 500 ng/ml) and (ii) trem1-siRNA transfection with/without plasma supernatant from stored RBC to assess the acute inflammatory response through trem1 by qRT-PCR and immunoblotting.

RESULTS

Anemic murine pups developed cytokine storm within 2 h of receiving stored RBCs, which increased until 6 h post-transfusion, as compared to non-anemic mice receiving stored RBCTs ("transfusion controls"), in a TLR4-independent fashion. Nonetheless, severely anemic pups had elevated circulating endotoxin levels, thereby sensitizing circulating monocytes to presynthesize proinflammatory cytokines (IFN-γ, IL-1β, TNF-α, IL-6, MIP-1α, MIP-1β, MIP2, LIX) and express trem1. Silencing trem1 expression in Raw264.7 cells mitigated both endotoxin-associated presynthesis of proinflammatory cytokines and the RBCT-induced release of inflammatory cytokines. Indeed, myeloid-specific trem1-/- murine pups had significantly reduced evidence of SIRS following RBCTs.

CONCLUSION

Severe anemia-associated low-grade inflammation sensitizes monocytes to enhance the synthesis of proinflammatory cytokines and trem1. In this setting, RBCTs further activate these monocytes, thereby inducing SIRS. Inhibiting trem1 in myeloid cells, including monocytes, alleviates the inflammatory response associated with the combined effects of anemia and RBCTs in murine neonates.

Near UV and Visible Light-Induced Degradation of Bovine Serum Albumin and a Monoclonal Antibody Mediated by Citrate Buffer and Fe(III): Reduction vs Oxidation Pathways

Light exposure during manufacturing, storage, and administration can lead to the photodegradation of therapeutic proteins. This photodegradation can be promoted by pharmaceutical buffers or impurities. Our laboratory has previously demonstrated that citrate-Fe(III) complexes generate the •CO2- radical anion when photoirradiated under near UV (λ = 320-400 nm) and visible light (λ = 400-800 nm) [Subelzu, N.; Schöneich, C. Mol. Pharmaceutics 2020, 17 (11), 4163-4179; Zhang, Y. Mol. Pharmaceutics 2022, 19 (11), 4026-4042]. Here, we evaluated the impact of citrate-Fe(III) on the photostability and degradation mechanisms of disulfide-containing proteins (bovine serum albumin (BSA) and NISTmAb) under pharmaceutically relevant conditions. We monitored and localized competitive disulfide reduction and protein oxidation by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis depending on the reaction conditions. These competitive pathways were affected by multiple factors, including light dose, Fe(III) concentration, protein concentration, the presence of oxygen, and light intensity.

The iron(III) coordinating properties of citrate and α-hydroxycarboxylate containing siderophores

The iron(III) binding properties of citrate and rhizoferrin, a citrate containing siderophore, are compared. Citrate forms many oligonuclear complexes, whereas rhizoferrin forms a single mononuclear complex. The α-hydroxycarboxylate functional group, which is present in both citrate, and rhizoferrin, has a high affinity and selectivity for iron(III) under most biological conditions. The nature of the toxic form of iron found in the blood of patients suffering from many haemoglobinopathies and haemochromatosis is identified as a mixture of iron(III)citrate complexes. The significance of the presence of this iron pool to patients suffering from systemic iron overload is discussed. The wide utilisation of the α-hydroxycarboxylate functional group in siderophore structures is described, as is their photo-induced decarboxylation leading to the release of iron(II) ions. The importance of this facile dissociation to algal iron uptake is discussed.

Revealing the nuclearity of iron citrate complexes at biologically relevant conditions

Citric acid plays an ubiquitous role in the complexation of essential metals like iron and thus it has a key function making them biologically available. For this, iron(III) citrate complexes are considered among the most significant coordinated forms of ferric iron that take place in biochemical processes of all living organisms. Although these systems hold great biological relevance, their coordination chemistry has not been fully elucidated yet. The current study aimed to investigate the speciation of iron(III) citrate using Mössbauer and electron paramagnetic resonance spectroscopies. Our aim was to gain insights into the structure and nuclearity of the complexes depending on the pH and iron to citrate ratio. By applying the frozen solution technique, the results obtained directly reflect the iron speciation present in the aqueous solution. At 1:1 iron:citrate molar ratio, polynuclear species prevailed forming most probably a trinuclear structure. In the case of citrate excess, the coexistence of several monoiron species with different coordination environments was confirmed. The stability of the polynuclear complexes was checked in the presence of organic solvents.

Quantitative proteomics and RNA-sequencing of mouse liver endothelial cells identify novel regulators of BMP6 by iron

Hepcidin is the master hormone governing systemic iron homeostasis. Iron regulates hepcidin by activating bone morphogenetic protein (BMP)6 expression in liver endothelial cells (LECs), but the mechanisms are incompletely understood. To address this, we performed proteomics and RNA-sequencing on LECs from iron-adequate and iron-loaded mice. Gene set enrichment analysis identified transcription factors activated by high iron, including Nrf-2, which was previously reported to contribute to BMP6 regulation, and c-Jun. Jun (encoding c-Jun) knockdown blocked Bmp6 but not Nrf-2 pathway induction by iron in LEC cultures. Chromatin immunoprecipitation of mouse livers showed iron-dependent c-Jun binding to predicted sites in Bmp6 regulatory regions. Finally, c-Jun inhibitor blunted induction of Bmp6 and hepcidin, but not Nrf-2 activity, in iron-loaded mice. However, Bmp6 and iron parameters were unchanged in endothelial Jun knockout mice. Our data suggest that c-Jun participates in iron-mediated BMP6 regulation independent of Nrf-2, though the mechanisms may be redundant and/or multifactorial.

Plasma non-transferrin-bound iron uptake by the small intestine leads to intestinal injury and intestinal flora dysbiosis in an iron overload mouse model and Caco-2 cells

Iron overload often occurs during blood transfusion and iron supplementation, resulting in the presence of non-transferrin-bound iron (NTBI) in host plasma and damage to multiple organs, but effects on the intestine have rarely been reported. In this study, an iron overload mouse model with plasma NTBI was established by intraperitoneal injection of iron dextran. We found that plasma NTBI damaged intestinal morphology, caused intestinal oxidative stress injury and reactive oxygen species (ROS) accumulation, and induced intestinal epithelial cell apoptosis. In addition, plasma NTBI increased the relative abundance of Ileibacterium and Desulfovibrio in the cecum, while the relative abundance of Faecalibaculum and Romboutsia was reduced. Ileibacterium may be a potential microbial biomarker of plasma NTBI. Based on the function prediction analysis, plasma NTBI led to the weakening of intestinal microbiota function, significantly reducing the function of the extracellular structure. Further investigation into the mechanism of injury showed that iron absorption in the small intestine significantly increased in the iron group. Caco-2 cell monolayers were used as a model of the intestinal epithelium to study the mechanism of iron transport. By adding ferric ammonium citrate (FAC, plasma NTBI in physiological form) to the basolateral side, the apparent permeability coefficient (Papp) values from the basolateral to the apical side were greater than 3×10-6 cm s-1. Intracellular ferritin level and apical iron concentration significantly increased, and SLC39A8 (ZIP8) and SLC39A14 (ZIP14) were highly expressed in the FAC group. Short hairpin RNA (shRNA) was used to knock down ZIP8 and ZIP14 in Caco-2 cells. Transfection with ZIP14-specific shRNA decreased intracellular ferritin level and inhibited iron uptake. These results revealed that plasma NTBI may cause intestinal injury and intestinal flora dysbiosis due to the uptake of plasma NTBI from the basolateral side into the small intestine, which is probably mediated by ZIP14.

Non-transferrin-bound iron determination in blood serum using microsequential injection solid phase spectrometry- proof of concept

Non-transferrin-bound iron (NTBI) is a group of circulating toxic iron forms, which occur in iron overload or health conditions with dysregulation of iron metabolism. NTBI is responsible for increased oxidative stress and tissue iron loading. Despite its relevance as a biochemical marker in several diseases, a standardized assay is still lacking. Several methods were developed to quantify NTBI, but results show high inter-method and even inter-laboratory variability. Thus, the development of a consistent NTBI assay is a major goal in the management of iron overload and related clinical conditions. In this work, a micro sequential injection lab-on-valve (μSI-LOV) method in a solid phase spectrophotometry (SPS) mode was developed for the quantification of NTBI, using a bidentate 3,4-hydroxypyridinone (3,4-HPO) ligand anchored to sepharose beads as a chromogenic reagent. To attain SPS, the functionalized beads were packed into a column in the flow cell, and the analyte, NTBI retained as iron (III), formed a colored complex at the beads while eliminating the sample matrix. The dynamic concentration range was 1.62-7.16 μmol L^-1 of iron (III), with a limit of detection of 0.49 μmol L^-1 and a limit of quantification of 1.62 μmol L^-1. The proposed μSI-LOV-SPS method is a contribution to the development of an automatic method for the quantification of the NTBI in serum samples.

Putting square pegs in round holes: why traditional pharmacokinetic principles cannot universally be applied to iron-carbohydrate complexes

Intravenous iron-carbohydrate complexes are nanomedicines that are commonly used to treat iron deficiency and iron deficiency anemia of various etiologies. Many challenges remain regarding these complex drugs in the context of fully understanding their pharmacokinetic parameters. Firstly, the measurement of the intact iron nanoparticles versus endogenous iron concentration fundamentally limits the availability of data for computational modeling. Secondly, the models need to include several parameters to describe the iron metabolism which is not completely defined and those identified (e.g. ferritin) exhibit considerable interpatient variability. Additionally, modeling is further complicated by the lack of traditional receptor/enzyme interactions. The known parameters of bioavailability, distribution, metabolism, and excretion for iron-carbohydrate nanomedicines will be reviewed and future challenges that currently prevent the direct application of physiologically-based pharmacokinetic or other computational modeling techniques will be discussed.

Utilization of delactosed whey permeate for the synthesis of ethyl acetate with Kluyveromyces marxianus

Ethyl acetate is an important organic solvent and currently produced from fossil carbon resources. Microbial synthesis of this ester from sugar-rich waste could be an interesting alternative. Therefore, synthesis of ethyl acetate by Kluyveromyces marxinanus DSM 5422 from delactosed whey permeate (DWP) was studied in an aerated stirred bioreactor at 40 °C. DWP is mainly composed of residual lactose and minerals. The minerals inhibited yeast growth, as witnessed by an increased lag period, a reduced growth rate, and an extended process duration. All experiments were therefore carried out with diluted DWP. In a series of batch experiments, the pH of iron-deficient DWP medium varied between 4.8 and 5.9. The pH of the cultivation medium significantly influenced cell growth and product syntheses, with the highest ethyl acetate yield of 0.347 g g^-1 and lowest by-product formation achieved at pH 5.1. It is likely that this effect is due to pH-dependent iron chelation, which affects the iron bioavailability and the intracellular iron content, thus affecting growth and metabolite synthesis. The viability of yeast cells was always high despite the harsh conditions in DWP medium, which enabled extended usage of the biomass in repeated-batch and fed-batch cultivations. These two culture techniques increased the volume of DWP processed per time by 32 and 84% for the repeated-batch and the fed-batch cultivation, respectively, without a drop of the ester yield. KEY POINTS: • Delactosed whey permeate was converted to ethyl acetate with a high rate and yield. • The formation of ethyl acetate in DWP medium at iron limitation is pH-dependent. • Highly active yeasts from batch processes enabled extension as fed and repeated batch.

The clinical relevance of detectable plasma iron species in iron overload states and subsequent to intravenous iron-carbohydrate administration

Many disorders of iron homeostasis (e.g., iron overload) are associated with the dynamic kinetic profiles of multiple non-transferrin bound iron (NTBI) species, chronic exposure to which is associated with deleterious end-organ effects. Here we discuss the chemical nature of NTBI species, challenges with measuring NTBI in plasma, and the clinical relevance of NTBI exposure based on source (iron overload disorder vs. intravenous iron-carbohydrate complex administration). NTBI is not a single entity but consists of multiple, often poorly characterized species, some of which are kinetically non-exchangeable while others are relatively exchangeable. Prolonged presence of plasma NTBI is associated with excessive tissue iron accumulation in susceptible tissues, with consequences, such as endocrinopathy and heart failure. In contrast, intravenous iron-carbohydrate nanomedicines administration leads only to transient NTBI appearance and lacks evidence for association with adverse clinical outcomes. Assays to measure plasma NTBI are typically technically complex and remain chiefly a research tool. There have been two general approaches to estimating NTBI: capture assays and redox-activity assays. Early assays could not avoid capturing some iron from transferrin, thus overestimating NTBI. By contrast, some later assays may have promoted the donation of NTBI species to transferrin during the assay procedure, potentially underestimating NTBI levels. The levels of transferrin saturation at which NTBI species have been detectable have varied between different methodologies and between patient populations studied.

Increased Levels of Circulating Iron-Albumin Complexes in Peripheral Arterial Disease Patients

Under physiological conditions, extracellular iron circulates in the blood bound to transferrin. As a consequence of several pathologies, the circulating level of a Non-Transferrin Bound pool of Iron (NTBI) increases. The NTBI pool is biologically heterogeneous and represented by iron chelated either by small metabolites (citrate, amino acids, or cofactors) or by serum proteins. By promoting reactive oxygen species (ROS) and reactive nitrogen species (RNS) formation, NTBI causes oxidative stress and alteration of membrane lipids, seriously compromising the healthy state of organs and tissues. While NTBI involvement in several pathologies has been clarified, its contribution to vascular diseases remains to be investigated. Here we measure and analyze the pool of NTBI in the serum of a small group of peripheral arterial disease (PAD) patients. We show that: (i) the NTBI pool shifts from low molecular complexes to high-molecular ones in PAD patients compared to healthy controls; (ii) most of this NTBI is bound to the serum protein Albumin; (iii) this NTBI-Albumin complex can be isolated and quantitated following a simple immunoisolation procedure amenable to automation and suitable for clinical screening purposes.

Plasma Non-transferrin-Bound Iron Could Enter into Mice Duodenum and Negatively Affect Duodenal Defense Response to Virus and Immune Responses

Plasma non-transferrin-bound iron (NTBI) exists when the plasma iron content exceeds the carrying capacity of transferrin and can be quickly cleared by the liver, pancreas, and other organs. However, whether it could enter the small intestine and its effects still remain unclear. Herein, these issues were explored. Mice were intravenously administrated of ferric citrate (treatment) or citrate acid (control) 10 min after the saturation of the transferrin. Two hours later, hepatic, duodenal, and jejunal iron content and distribution were measured and duodenal transcriptome sequencing was performed. Significant increase of duodenal and hepatic iron content was detected, indicating that plasma NTBI could be absorbed by the duodenum as well as the liver. A total of 103 differentially expressed genes were identified in the duodenum of mice in the treatment group compared to the control group. Gene Ontology (GO) functional analysis of these genes showed that they were mainly involved in defense response to virus and immune response. The results of Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) analysis revealed that there were major changes in the hematopoietic cell lineage and some virus infection pathways between the two groups. Determination of 7 cytokines in the duodenum were further conducted, which demonstrated that the anti-inflammatory factors interferon (IL)-4 and IL-10 in the duodenum were significantly decreased after NTBI uptake. Our findings revealed that NTBI in plasma can enter the duodenum, which would change the duodenal hematopoietic cell lineage and have a negative impact on defense response to the virus and immune responses.

Functional role of endothelial transferrin receptor 1 in iron sensing and homeostasis

Systemic iron homeostasis is regulated by the hepatic hormone hepcidin to balance meeting iron requirements while limiting toxicity from iron excess. Iron-mediated induction of bone morphogenetic protein (BMP) 6 is a central mechanism for regulating hepcidin production. Liver endothelial cells (LECs) are the main source of endogenous BMP6, but how they sense iron to modulate BMP6 transcription and thereby hepcidin is uncertain. Here, we investigate the role of endothelial cell transferrin receptor 1 (TFR1) in iron uptake, BMP6 regulation, and systemic iron homeostasis using primary LEC cultures and endothelial Tfrc (encoding TFR1) knockout mice. We show that intracellular iron regulates Bmp6 expression in a cell-autonomous manner, and TFR1 mediates iron uptake and Bmp6 expression by holo-transferrin in primary LEC cultures. In addition, endothelial Tfrc knockout mice exhibit altered iron homeostasis compared with littermate controls when fed a limited iron diet, as evidenced by increased liver iron and inappropriately low Bmp6 and hepcidin expression relative to liver iron. However, endothelial Tfrc knockout mice have a similar iron phenotype compared to littermate controls when fed an iron-rich standard diet. Finally, ferritin and non-transferrin bound iron (NTBI) are additional sources of iron that mediate Bmp6 induction in primary LEC cultures via TFR1-independent mechanisms. Together, our data demonstrate a minor functional role for endothelial cell TFR1 in iron uptake, BMP6 regulation, and hepatocyte hepcidin regulation under iron limiting conditions, and suggest that ferritin and/or NTBI uptake by other transporters have a dominant role when iron availability is high.

Might nontransferrin-bound iron in blood plasma and sera be a nonproteinaceous high-molecular-mass FeIII aggregate?

The HFE (Homeostatic Fe regulator) gene is commonly mutated in hereditary hemochromatosis. Blood of (HFE)(-/-) mice and of humans with hemochromatosis contains toxic nontransferrin-bound iron (NTBI) which accumulates in organs. However, the chemical composition of NTBI is uncertain. To investigate, HFE(-/-) mice were fed iron-deficient diets supplemented with increasing amounts of iron, with the expectation that NTBI levels would increase. Blood plasma was filtered to obtain retentate and flow-through solution fractions. Liquid chromatography detected by inductively coupled plasma mass spectrometry of flow-through solutions exhibited low-molecular-mass iron peaks that did not increase intensity with increasing dietary iron. Retentates yielded peaks due to transferrin (TFN) and ferritin, but much iron in these samples adsorbed onto the column. Retentates treated with the chelator deferoxamine (DFO) yielded a peak that comigrated with the Fe-DFO complex and originated from iron that adhered to the column in the absence of DFO. Additionally, plasma from younger and older 57Fe-enriched HFE mice were separately pooled and concentrated by ultrafiltration. After removing contributions from contaminating blood and TFN, Mössbauer spectra were dominated by features due to magnetically interacting FeIII aggregates, with greater intensity in the spectrum from the older mice. Similar features were generated by adding 57FeIII to "pseudo plasma". Aggregation was unaffected by albumin or citrate at physiological concentrations, but DFO or high citrate concentrations converted aggregated FeIII into high-spin FeIII complexes. FeIII aggregates were retained by the cutoff membrane and adhered to the column, similar to the behavior of NTBI. A model is proposed in which FeII entering blood is oxidized, and if apo-TFN is unavailable, the resulting FeIII ions coalesce into FeIII aggregates, a.k.a. NTBI.

The (Bio)Chemistry of Non-Transferrin-Bound Iron

In healthy individuals, virtually all blood plasma iron is bound by transferrin. However, in several diseases and clinical conditions, hazardous non-transferrin-bound iron (NTBI) species occur. NTBI represents a potentially toxic iron form, being a direct cause of oxidative stress in the circulating compartment and tissue iron loading. The accumulation of these species can cause cellular damage in several organs, namely, the liver, spleen, and heart. Despite its pathophysiological relevance, the chemical nature of NTBI remains elusive. This has precluded its use as a clinical biochemical marker and the development of targeted therapies. Herein, we make a critical assessment of the current knowledge of NTBI speciation. The currently accepted hypotheses suggest that NTBI is mostly iron bound to citric acid and iron bound to serum albumin, but the chemistry of this system remains fuzzy. We explore the complex chemistry of iron complexation by citric acid and its implications towards NTBI reactivity. Further, the ability of albumin to bind iron is revised and the role of protein post-translational modifications on iron binding is discussed. The characterization of the NTBI species structure may be the starting point for the development of a standardized analytical assay, the better understanding of these species’ reactivity or the identification of NTBI uptake mechanisms by different cell types, and finally, to the development of new therapies.

Polystyrene nanoplastics change the functional traits of biofilm communities in freshwater environment revealed by GeoChip 5.0

There is an increasing concern regarding the potential effects of nanoplastics (NPs) on freshwater ecosystems. Considering the functional values of biofilms in freshwater, knowledge on whether and to what extent NPs can influence the ecosystem processes of biofilms were still limited. Herein, the freshwater biofilms cultured in lab were exposed to 100 nm polystyrene NPs (PS-NPs) of different dosages (1 and 10 mg/L) for 14 days. Confocal laser scanning microscope observation indicated that biofilms were dominated by filamentous, and spiral algae species and the intensity of extracellular polymeric substances increased under PS-NPs exposure. GeoChip 5.0 analysis revealed that PS-NPs exposure triggered a significant increase in functional genes α diversity (p < 0.05) and altered biofilms' functional structure. Furthermore, the abundance of genes involved in the total carbon and nitrogen cycling were increased under PS-NPs exposure. The abundance of nitrogen fixation genes experienced the most pronounced increase (24.4%) under 1 mg/L PS-NPs treatment, consistent with the increase of ammonium in overlying water. Whereas antibiotic resistance genes and those related to photosynthetic pigments production were suppressed. These results provided direct evidence for PS-NPs' effects on the biofilm functions in terms of biogeochemical cycling, improving our understanding of the potentials of NPs on freshwater ecosystems.

Current status of beta-thalassemia and its treatment strategies

Background

Thalassemia is an inherited hematological disorder categorized by a decrease or absence of one or more of the globin chains synthesis. Beta‐thalassemia is caused by one or more mutations in the beta‐globin gene. The absence or reduced amount of beta‐globin chains causes ineffective erythropoiesis which leads to anemia.

Methods

Beta‐thalassemia has been further divided into three main forms: thalassemia major, intermedia, and minor/silent carrier. A more severe form among these is thalassemia major in which individuals depend upon blood transfusion for survival. The high level of iron deposition occurs due to regular blood transfusion therapy.

Results

Overloaded iron raises the synthesis of reactive oxygen species (ROS) that are noxious and prompting the injury to the hepatic, endocrine, and vascular system. Thalassemia can be analyzed and diagnosed via prenatal testing (genetic testing of amniotic fluid), blood smear, complete blood count, and DNA analysis (genetic testing). Treatment of thalassemia intermediate is symptomatic; however; it can also be accomplished by folic supplementation and splenectomy.

Conclusion

Thalassemia major can be cured through regular transfusion of blood, transplantation of bone marrow, iron chelation management, hematopoietic stem cell transplantation, stimulation of fetal hemoglobin production, and gene therapy.

Iron Metabolism in Pancreatic Beta-Cell Function and Dysfunction

Iron is an essential element involved in a variety of physiological functions. In the pancreatic beta-cells, being part of Fe-S cluster proteins, it is necessary for the correct insulin synthesis and processing. In the mitochondria, as a component of the respiratory chain, it allows the production of ATP and reactive oxygen species (ROS) that trigger beta-cell depolarization and potentiate the calcium-dependent insulin release. Iron cellular content must be finely tuned to ensure the normal supply but also to prevent overloading. Indeed, due to the high reactivity with oxygen and the formation of free radicals, iron excess may cause oxidative damage of cells that are extremely vulnerable to this condition because the normal elevated ROS production and the paucity in antioxidant enzyme activities. The aim of the present review is to provide insights into the mechanisms responsible for iron homeostasis in beta-cells, describing how alteration of these processes has been related to beta-cell damage and failure. Defects in iron-storing or -chaperoning proteins have been detected in diabetic conditions; therefore, the control of iron metabolism in these cells deserves further investigation as a promising target for the development of new disease treatments.

Iron loading induces cholesterol synthesis and sensitizes endothelial cells to TNFα-mediated apoptosis

In plasma, iron is normally bound to transferrin, the principal protein in blood responsible for binding and transporting iron throughout the body. However, in conditions of iron overload when the iron-binding capacity of transferrin is exceeded, non-transferrin-bound iron (NTBI) appears in plasma. NTBI is taken up by hepatocytes and other parenchymal cells via NTBI transporters and can cause cellular damage by promoting the generation of reactive oxygen species. However, how NTBI affects endothelial cells, the most proximal cell type exposed to circulating NTBI, has not been explored. We modeled in vitro the effects of systemic iron overload on endothelial cells by treating primary human umbilical vein endothelial cells (HUVECs) with NTBI (ferric ammonium citrate [FAC]). We showed by RNA-Seq that iron loading alters lipid homeostasis in HUVECs by inducing sterol regulatory element-binding protein 2-mediated cholesterol biosynthesis. We also determined that FAC increased the susceptibility of HUVECs to apoptosis induced by tumor necrosis factor-α (TNFα). Moreover, we showed that cholesterol biosynthesis contributes to iron-potentiated apoptosis. Treating HUVECs with a cholesterol chelator hydroxypropyl-β-cyclodextrin demonstrated that depletion of cholesterol was sufficient to rescue HUVECs from TNFα-induced apoptosis, even in the presence of FAC. Finally, we showed that FAC or cholesterol treatment modulated the TNFα pathway by inducing novel proteolytic processing of TNFR1 to a short isoform that localizes to lipid rafts. Our study raises the possibility that iron-mediated toxicity in human iron overload disorders is at least in part dependent on alterations in cholesterol metabolism in endothelial cells, increasing their susceptibility to apoptosis.

Implication of Dietary Iron-Chelating Bioactive Compounds in Molecular Mechanisms of Oxidative Stress-Induced Cell Ageing

One of the prevailing perceptions regarding the ageing of cells and organisms is the intracellular gradual accumulation of oxidatively damaged macromolecules, leading to the decline of cell and organ function (free radical theory of ageing). This chemically undefined material known as "lipofuscin," "ceroid," or "age pigment" is mainly formed through unregulated and nonspecific oxidative modifications of cellular macromolecules that are induced by highly reactive free radicals. A necessary precondition for reactive free radical generation and lipofuscin formation is the intracellular availability of ferrous iron (Fe2+) ("labile iron"), catalyzing the conversion of weak oxidants such as peroxides, to extremely reactive ones like hydroxyl (HO•) or alcoxyl (RO•) radicals. If the oxidized materials remain unrepaired for extended periods of time, they can be further oxidized to generate ultimate over-oxidized products that are unable to be repaired, degraded, or exocytosed by the relevant cellular systems. Additionally, over-oxidized materials might inactivate cellular protection and repair mechanisms, thus allowing for futile cycles of increasingly rapid lipofuscin accumulation. In this review paper, we present evidence that the modulation of the labile iron pool distribution by nutritional or pharmacological means represents a hitherto unappreciated target for hampering lipofuscin accumulation and cellular ageing.

The Clinical Significance of Iron Overload and Iron Metabolism in Myelodysplastic Syndrome and Acute Myeloid Leukemia

Myelodysplasticsyndrome (MDS) and acute myeloid leukemia (AML) are clonal hematopoietic stem cell diseases leading to an insufficient formation of functional blood cells. Disease-immanent factors as insufficient erythropoiesis and treatment-related factors as recurrent treatment with red blood cell transfusions frequently lead to systemic iron overload in MDS and AML patients. In addition, alterations of function and expression of proteins associated with iron metabolism are increasingly recognized to be pathogenetic factors and potential vulnerabilities of these diseases. Iron is known to be involved in multiple intracellular and extracellular processes. It is essential for cell metabolism as well as for cell proliferation and closely linked to the formation of reactive oxygen species. Therefore, iron can influence the course of clonal myeloid disorders, the leukemic environment and the occurrence as well as the defense of infections. Imbalances of iron homeostasis may induce cell death of normal but also of malignant cells. New potential treatment strategies utilizing the importance of the iron homeostasis include iron chelation, modulation of proteins involved in iron metabolism, induction of leukemic cell death via ferroptosis and exploitation of iron proteins for the delivery of antileukemic drugs. Here, we provide an overview of some of the latest findings about the function, the prognostic impact and potential treatment strategies of iron in patients with MDS and AML.

Silencing of lipocalin-2 improves cardiomyocyte viability under iron overload conditions via decreasing mitochondrial dysfunction and apoptosis

This study aimed to investigate the mechanistic roles of LCN-2 and LCN-2 receptors (LCN-2R) as iron transporters in cardiomyocytes under iron overload condition. H9c2 cardiomyocytes were treated with either LCN-2 small interfering RNA (siRNA) or LCN-2R siRNA or L-type or T-type calcium channel (LTCC or TTCC) blockers, or iron chelator deferiprone (DFP). After the treatments, the cells were exposed to Fe³⁺ or Fe²⁺ , after that biological parameters were determined. Silencing of lipocalin-2 or its receptor improved cardiomyocyte viability via decreasing iron uptake, mitochondrial fission, mitophagy and cleaved caspase-3 only in the Fe³⁺ overload condition. In contrast, treatments with LTCC blocker and TTCC blocker showed beneficial effects on those parameters only in conditions of Fe²⁺ overload. Treatment with DFP has been shown beneficial effects both in Fe²⁺ and Fe³⁺ overload condition. All of these findings suggested that LTCC and TTCC play crucial roles in the Fe²⁺ uptake, whereas LCN-2 and LCN-2R were essential for Fe³⁺ uptake into the cardiomyocytes under iron overload conditions.

Acute Effects of Iron Sucrose and Iron Carboxymaltose on Endothelial Function in Nondialysis Chronic Kidney Disease Patients

BACKGROUND

Intravenous iron is commonly prescribed in chronic kidney disease (CKD) patients. Iron sucrose (IS) and ferric carboxymaltose (FCM) are 2 frequently used formulations. Experimental data showed that this 2 intravenous iron preparations have different potential to induce oxidative stress and by that endothelial dysfunction. Still, direct comparisons in clinical settings are rather scarce.

STUDY QUESTION

Are there any acute changes in endothelial function after single intravenous iron infusions of IS and FCM in nondialysis CKD patients?

STUDY DESIGN

This was a prospective, crossover study in which 31 patients with CKD stages 3-5 (80% stages 3 and 4, 81% female, 55% older than 60 years, 23% diabetes mellitus, and 94% arterial hypertension) who required intravenous iron as part of their routine medical care were enrolled.

MEASURES AND OUTCOMES

The effect of flow-mediated vasodilatation infusions containing 250-mL 10% glucose, 500-mg FCM, and 200-mg IS, both in 250-mL 0.9% saline solution, was compared. The infusions were administered over 30 minutes, 72 hours apart, in the mentioned order. Ultrasound measurement of the brachial artery flow-mediated vasodilation (FMD) performed 15 minutes before and after each infusion was used to assess endothelial function. The outcome was the post/preinfusion difference (Δ) in FMD.

RESULTS

The baseline FMD was similar before each study intervention. The arterial reactivity significantly decreased only after IS infusion [ΔFMD -2.3 (-5.65 to -0.33) vs. 1.0 (-1.49 to 1.80) after glucose, P = 0.01], but not after FCM [ΔFMD -0.8 (-2.50 to 0.65), P = 0.27 vs. glucose]. Moreover, the arterial reactivity was higher after IS as compared to FCM.

CONCLUSIONS

Endothelial dysfunction seems to be acutely induced by a single dose of intravenous IS, but not by FCM, in nondialysis CKD patients.

Liver Iron Retention Estimated from Utilization of Oral and Intravenous Radioiron in Various Anemias and Hemochromatosis in Humans

Patients with hereditary hemochromatosis and non-transfusion-dependent hereditary anemia develop predominantly liver iron-overload. We present a unique method allowing quantification of liver iron retention in humans during first-pass of ⁵⁹Fe-labeled iron through the portal system, using standard ferrokinetic techniques measuring red cell iron uptake after oral and intravenous ⁵⁹Fe administration. We present data from patients with iron deficiency (ID; N = 47), hereditary hemochromatosis (HH; N = 121) and non-transfusion-dependent hereditary anemia (HA; N = 40). Mean mucosal iron uptake and mucosal iron transfer (±SD) were elevated in patients with HH (59 ± 18%, 80 ± 15% respectively), HA (65 ± 17%, 74 ± 18%) and ID (84 ± 14%, 94 ± 6%) compared to healthy controls (43 ± 19%, 64 ± 18%) (p < 0.05) resulting in increased iron retention after 14 days compared to healthy controls in all groups (p < 0.01). The fraction of retained iron utilized for red cell production was 0.37 ± 0.17 in untreated HA, 0.55 ± 0.20 in untreated HH and 0.99 ± 0.22 in ID (p < 0.01). Interestingly, compared to red blood cell iron utilization after oral iron administration, red blood cell iron utilization was higher after injection of transferrin-bound iron in HA and HH. Liver iron retention was considerably higher in HH and HA compared to ID. We hypothesize that albumin serves as a scavenger of absorbed Fe(II) for delivering albumin-bound Fe(III) to hepatocytes.

The FeII(citrate) Fenton reaction under physiological conditions

The Fenton reaction of Fe^II(citrate) in the presence and absence of bicarbonate (HCO₃^-) is studied. It is found that the rate constant of the Fenton reaction (k_obs) increases with increasing [citrate]. k_obs also increase with increasing [HCO₃^-]; this effect is most significant at biological citrate concentrations. Methane and ethane gases are formed from (CH₃)₂SO when the Fenton reaction is carried out in the presence of large [citrate] due to the reaction of the citrate radical, (^-₂OC)CH₂C(OH)(CO₂^-)CH(CO₂^-)/(^-₂OC)CH₂C(O)(CO₂^-)CH₂(CO₂^-) with (CH₃)₂SO. In the absence of citrate (CH₃)₂SO₂ is the main product of the Fenton reaction. However, in the presence of 0.10 mM citrate, no (CH₃)₂SO₂ is formed, some (CH₃)SOOH is formed, along with a low yield of beta-ketoglutaric acid. Formation of (CH₃)SOOH and beta-ketoglutaric acid are due to the citrate radical and Fe^IV(citrate). In the presence of bicarbonate formation of abundant beta-ketoglutaric acid confirms the formation of carbonate radical anion (CO₃^-). Thus, bicarbonate affects the mechanism and kinetics of the reaction dramatically. Hydroxyl radicals (OH) are not formed in the presence of bicarbonate and probably also not in its absence. These results point out that hydroxyl radicals, formed by the Fenton reaction, do not initiate oxidative stress in biological systems.

Low-molecular-mass iron complexes in blood plasma of iron-deficient pigs do not originate directly from nutrient iron

Nutrient iron entering the blood binds transferrin (TFN)d, which delivers iron to cells in the body. In healthy individuals, ∼30% of TFN is iron-bound while the remainder is unbound (apo-TFN). TFN saturates the plasma of individuals with iron-overload diseases such as hereditary hemochromatosis, prompting release of a poorly-defined low-molecular-mass (LMM) iron species called non-transferrin-bound iron (NTBI). An experiment was devised to directly detect NTBI in plasma of iron-deficient pigs and to assess the role of the liver which is known to bind NTBI. Catheters were surgically installed in the portal vein (PV) and either the caudal vena cava or the cranial vena cava. After the animals recovered, 57Fe II ascorbate was injected into the stomach via a feeding tube. Blood was removed through the catheters before and after injection; plasma became 57Fe-enriched after injection. 57Fe-enriched plasma was passed through a 10 kDa cutoff membrane and the flow-through solution (FTS) was subjected to size-exclusion liquid chromatography (LC). The eluent flowed into an ICP-MS where 56Fe and 57Fe were detected. Low-intensity iron peaks with masses of 400-1600 Da were observed, but none became enriched in 57Fe after injection. Rather, the injected 57Fe bound to apo-TFN. Viewed naively, this implies that nutrient-derived 57Fe in healthy mammals passes from the intestines to apo-TFN without first entering the blood as a LMM intermediate. In this case, nutrient iron exported from intestinal enterocytes of healthy individuals may quickly bind apo-TFN such that LMM iron species do not accumulate in blood plasma. Some 57Fe from the FTS may have adsorbed onto the column. In any event, the LMM iron species in plasma that eluted from the column must have originated from iron stored within the body, perhaps in macrophages - not directly from nutrient iron absorption. The liver absorbed and released LMM iron species, but the effect was modest, consistent with its role as a dynamic iron buffer. Passage through the liver also altered the distribution of different forms of TFN present in the PV.

Low-molecular-mass iron in healthy blood plasma is not predominately ferric citrate

Blood contains a poorly characterized pool of labile iron called non-transferrin-bound iron (NTBI). In patients with iron-overload diseases such as hemochromatosis, NTBI accumulates in the liver, heart, and other organs. This material is probably nonproteinaceous and low molecular mass (LMM). However, the number, concentration, mass, and chemical composition of NTBI species remain unknown despite decades of effort. Here, solutions of plasma from humans, pigs, horses, and mice were passed through a 10 kDa cutoff membrane, affording flow-through solutions (FTSs) containing ∼1 μM iron. The FTSs were subjected to size-exclusion liquid chromatography at pH 8.5, 6.5, and 4.5. Iron was detected by an online inductively-coupled-plasma mass spectrometer. LC-ICP-MS chromatograms of the FTSs exhibited 2-6 iron-containing species with apparent masses between 400 and 2500 Da. Their approximate concentrations in plasma were 10-8-10-7 M. Not every FTS sample contained every LMM iron species, indicating individual variations. The most reproducible iron species had apparent masses of 400 and 500 Da. Chromatograms of the FTSs from established hemochromatosis patients exhibited no significant differences relative to controls. The peak positions and intensities depended on column pH. Some FTS iron adsorbed onto the column, especially at higher pH. Column-adsorbing-iron coordinated apo-transferrin whereas the more tightly coordinated iron species did not. Ferric citrate standards exhibited LMM iron peaks that were similar to but not the same as those obtained in FTSs. The results indicate that the LMM iron species in healthy blood plasma is not primarily ferric citrate; however, this may be one of many contributing complexes.

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.

A new ferrous diflunisal complex and its effects on biopools of labile iron

Drugs bearing metal-coordinating moieties can alter biological metal distribution. In this work, a complex between iron(II) and diflunisal was prepared in the solid state, exhibiting the following composition: [Fe(diflunisal)₂(H₂O)₂], (Fe(dif)₂). The ability of diflunisal to alter labile pools of both plasmatic and cellular iron was investigated in this work. We found out that diflunisal does not increase the levels of redox-active iron in plasma of iron overloaded patients. However, diflunisal efficiently carries iron into HeLa or HepG2 cells, inducing an iron-catalyzed oxidative stress.

Interaction of Transfusion and Iron Chelation in Thalassemias

The relationship between blood transfusion intensity, chelatable iron pools, and extrahepatic iron distribution is described in thalassemia. Risk factors for cardiosiderosis are discussed with particular reference to the balance of transfusional iron loading rate and transferrin-iron utilization rate as marked by plasma levels of soluble transferrin receptors. Low transfusion regimens increase residual erythropoiesis allowing for apotransferrin-dependent clearance of non-transferrin-bound iron species otherwise destined for myocardium. The impact of transfusion rates on chelation dosing required for iron balance is also shown.

Identification of a new high-molecular-weight Fe-citrate species at low citrate-to-Fe molar ratios: Impact on arsenic removal with ferric hydroxide

Ferric hydroxide precipitation and flocculation is the most commonly used method for the removal of arsenic in water treatment. However, citrate often interrupts the precipitation of ferric hydroxides and thus affects arsenic removal. To date, the mechanisms controlling the effects of citrate on arsenic removal with ferric hydroxide flocculation and precipitation at very low citrate-to-Fe molar ratios are not well understood. Herein, we report a new mechanism by which citrate inhibits arsenic removal using ferric hydroxide. At a substoichiometric citrate-to-Fe molar ratio of 0.28, citrate forms a high-molecular-weight Fe-citrate (Fe₄Cit) species. The optimized structure of the Fe₄Cit species was obtained by the density functional theory calculation. To the best of our knowledge, this study is the first to report the formation and to identify the structure of dominant Fe-citrate species at a very low citrate-to-Fe molar ratio.

Switching iron sucrose to ferric carboxymaltose associates to better control of iron status in hemodialysis patients

BACKGROUND

Although the efficacy of iron sucrose (IS) and ferric carboxymaltose (FCM) in treating anemia in hemodialysis (HD) patients has been studied individually, a comparison of these two intravenous iron formulations has not yet been performed in HD patients.

METHODS

We performed a retrospective audit on records of 221 stable HD patients from different HD centers in the Netherlands, who were switched from IS to FCM on a 1:1 ratio. To assess the effect of the switch on iron status parameters, data from 3 time points before and 3 time points after the switch were analyzed using linear mixed effects models. Subanalyses were done in 2 subgroups of patients anemic or iron deficient at baseline.

RESULTS

Hemoglobin increased in all groups (anemic [1.4 g/dL, P < 0.001] iron deficient [0.6 g/dL, P < 0.001]), while the weekly iron dose was significantly lower when patients received FCM compared to IS (48 vs 55 mg/week, P = 0.04). Furthermore, serum ferritin and transferrin saturation increased in all groups (anemic [64 μg/L, 5.0%, P < 0.001] iron deficient [76 μg/L, 3.6%, P < 0.001]). Finally, the darbepoetin α dose decreased significantly in all groups (anemic [- 16 μg/wk., P = 0.01] iron deficient [- 11 μg/wk., P < 0.001]).

CONCLUSIONS

In this real-life study in HD patients, a switch from IS to FCM resulted in an improvement of iron status parameters despite a lower weekly dose of FCM. Furthermore, the ESA dose was reduced during FCM, while hemoglobin levels increased.

Increased intracellular iron in mouse primary hepatocytes in vitro causes activation of the Akt pathway but decreases its response to insulin

BACKGROUND

An iron-overloaded state has been reported to be associated with insulin resistance. On the other hand, conditions such as classical hemochromatosis (where iron overload occurs primarily in the liver) have been reported to be associated with increased insulin sensitivity. The reasons for these contradictory findings are unclear. In this context, the effects of increased intracellular iron per se on insulin signaling in hepatocytes are not known.

METHODS

Mouse primary hepatocytes were loaded with iron in vitro by incubation with ferric ammonium citrate (FAC). Intracellular events related to insulin signaling, as well as changes in gene expression and hepatocyte glucose production (HGP), were studied in the presence and absence of insulin and/or forskolin (a glucagon mimetic).

RESULTS

In vitro iron-loading of hepatocytes resulted in phosphorylation-mediated activation of Akt and AMP-activated protein kinase. This was associated with decreased basal and forskolin-stimulated HGP. Iron attenuated forskolin-mediated induction of the key gluconeogenic enzyme, glucose-6-phosphatase. It also attenuated activation of the Akt pathway in response to insulin, which was associated with decreased protein levels of insulin receptor substrates 1 and 2, constituting insulin resistance.

CONCLUSIONS

Increased intracellular iron has dual effects on insulin sensitivity in hepatocytes. It increased basal activation of the Akt pathway, but decreased activation of this pathway in response to insulin.

GENERAL SIGNIFICANCE

These findings may help explain why both insulin resistance and increased sensitivity have been observed in iron-overloaded states. They are of relevance to a variety of disease conditions characterized by hepatic iron overload and increased risk of diabetes.

Protective effects of the mechanistic target of rapamycin against excess iron and ferroptosis in cardiomyocytes

Clinical studies have suggested that myocardial iron is a risk factor for left ventricular remodeling in patients after myocardial infarction. Ferroptosis has recently been reported as a mechanism of iron-dependent nonapoptotic cell death. However, ferroptosis in the heart is not well understood. Mechanistic target of rapamycin (mTOR) protects the heart against pathological stimuli such as ischemia. To define the role of cardiac mTOR on cell survival in iron-mediated cell death, we examined cardiomyocyte (CM) cell viability under excess iron and ferroptosis conditions. Adult mouse CMs were isolated from cardiac-specific mTOR transgenic mice, cardiac-specific mTOR knockout mice, or control mice. CMs were treated with ferric iron [Fe(III)]-citrate, erastin, a class 1 ferroptosis inducer, or Ras-selective lethal 3 (RSL3), a class 2 ferroptosis inducer. Live/dead cell viability assays revealed that Fe(III)-citrate, erastin, and RSL3 induced cell death. Cotreatment with ferrostatin-1, a ferroptosis inhibitor, inhibited cell death in all conditions. mTOR overexpression suppressed Fe(III)-citrate, erastin, and RSL3-induced cell death, whereas mTOR deletion exaggerated cell death in these conditions. 2',7'-Dichlorodihydrofluorescein diacetate measurement of reactive oxygen species (ROS) production showed that erastin-induced ROS production was significantly lower in mTOR transgenic versus control CMs. These findings suggest that ferroptosis is a significant type of cell death in CMs and that mTOR plays an important role in protecting CMs against excess iron and ferroptosis, at least in part, by regulating ROS production. Understanding the effects of mTOR in preventing iron-mediated cell death will provide a new therapy for patients with myocardial infarction. NEW & NOTEWORTHY Ferroptosis has recently been reported as a new form of iron-dependent nonapoptotic cell death. However, ferroptosis in the heart is not well characterized. Using cultured adult mouse cardiomyocytes, we demonstrated that the mechanistic target of rapamycin plays an important role in protecting cardiomyocytes against excess iron and ferroptosis.

Theoretical investigations on hydrogen peroxide decomposition in aquo

Hydrogen peroxide (H₂O₂) decomposition mechanisms in the absence and presence of iron ions in aqueous solution, which contain no OH radical formation, are theoretically determined. H₂O₂ decomposition in the presence of iron ions is driven by electron transfer to the iron ion and proceeds by hydrogen transfers in the hydrogen bond network around H₂O₂.

Labile plasma iron levels predict survival in patients with lower-risk myelodysplastic syndromes

Red blood cell transfusions remain one of the cornerstones in supportive care of lower-risk patients with myelodysplastic syndromes. We hypothesized that patients develop oxidant-mediated tissue injury through the formation of toxic iron species, caused either by red blood cell transfusions or by ineffective erythropoiesis. We analyzed serum samples from 100 lower-risk patients with myelodysplastic syndromes at six-month intervals for transferrin saturation, hepcidin-25, growth differentiation factor 15, soluble transferrin receptor, non-transferrin bound iron and labile plasma iron in order to evaluate temporal changes in iron metabolism and the presence of potentially toxic iron species and their impact on survival. Hepcidin levels were low in 34 patients with ringed sideroblasts compared to 66 patients without. Increases of hepcidin and non-transferrin bound iron levels were visible early in follow-up of all transfusion-dependent patient groups. Hepcidin levels significantly decreased over time in transfusion-independent patients with ringed sideroblasts. Increased soluble transferrin receptor levels in transfusion-independent patients with ringed sideroblasts confirmed the presence of ineffective erythropoiesis and suppression of hepcidin production in these patients. Detectable labile plasma iron levels in combination with high transferrin saturation levels occurred almost exclusively in patients with ringed sideroblasts and all transfusion-dependent patient groups. Detectable labile plasma iron levels in transfusion-dependent patients without ringed sideroblasts were associated with decreased survival. In conclusion, toxic iron species occurred in all transfusion-dependent patients and in transfusion-independent patients with ringed sideroblasts. Labile plasma iron appeared to be a clinically relevant measure for potential iron toxicity and a prognostic factor for survival in transfusion-dependent patients. clinicaltrials.gov Identifier: 00600860.

Eltrombopag: a powerful chelator of cellular or extracellular iron(III) alone or combined with a second chelator

Eltrombopag (ELT) is a thrombopoietin receptor agonist reported to decrease labile iron in leukemia cells. Here we examine the previously undescribed iron(III)-coordinating and cellular iron-mobilizing properties of ELT. We find a high binding constant for iron(III) (log β₂=35). Clinically achievable concentrations (1 µM) progressively mobilized cellular iron from hepatocyte, cardiomyocyte, and pancreatic cell lines, rapidly decreasing intracellular reactive oxygen species (ROS) and also restoring insulin secretion in pancreatic cells. Decrements in cellular ferritin paralleled total cellular iron removal, particularly in hepatocytes. Iron mobilization from cardiomyocytes exceeded that obtained with deferiprone, desferrioxamine, or deferasirox at similar iron-binding equivalents. When combined with these chelators, ELT enhanced cellular iron mobilization more than additive (synergistic) with deferasirox. Iron-binding speciation plots are consistent with ELT donating iron to deferasirox at clinically relevant concentrations. ELT scavenges iron citrate species faster than deferasirox, but rapidly donates the chelated iron to deferasirox, consistent with a shuttling mechanism. Shuttling is also suggested by enhanced cellular iron mobilization by ELT when combined with the otherwise ineffective extracellular hydroxypyridinone chelator, CP40. We conclude that ELT is a powerful iron chelator that decreases cellular iron and further enhances iron mobilization when combined with clinically available chelators.

Markers of oxidative/nitrosative stress and inflammation in lung tissue of rats exposed to different intravenous iron compounds

Iron deficiency anemia is a frequent complication in clinical conditions such as chronic kidney disease, chronic heart failure, inflammatory bowel disease, cancer, and excessive blood loss. Given the ability of iron to catalyze redox reactions, iron therapy can be associated with oxidative stress. The lung is uniquely susceptible to oxidative stress, and little is known about the effects of intravenous iron treatment in this organ. This study characterized changes in markers of oxidative/nitrosative stress and inflammation in the lung of non-iron deficient, non-anemic rats treated with five weekly doses (40 mg iron per kg body weight) of low molecular weight iron dextran (LMWID), iron sucrose (IS), ferric carboxymaltose (FCM), ferumoxytol (FMX), iron isomaltoside 1000 (IIM), or saline (control). Rats treated with LMWID, FMX, or IIM showed significant changes in most measures of oxidative/nitrosative stress, inflammation, and iron deposition compared to the saline-treated controls, with greatest changes in the LMWID treatment group. Increases in products of lipid peroxidation (thiobarbituric acid reactive substances) and protein nitrosation (nitrotyrosine) were consistent with increases in the activity of antioxidant enzymes (catalase, Cu,Zn-SOD, GPx), decreases in antioxidative capacity (reduced:oxidized GSH ratio), increased levels of transcription factors involved in the inflammatory pathway (NF-κB, HIF-1α), inflammatory cytokines (TNF-α, IL-6), adhesion molecules (VCAM-1), markers of macrophage infiltration (ED-1), and iron deposition (Prussian blue, ferritin). Since changes in measured parameters in FCM- or IS-treated rats were generally modest, the results suggest that FCM and IS have a low propensity to induce lung inflammation. The relevance of these findings to clinical safety profiles of the tested intravenous iron products requires further investigation.

The Impact of Iron Overload in Acute Leukemia: Chronic Inflammation, But Not the Presence of Nontransferrin Bound Iron is a Determinant of Oxidative Stress

In the literature, studies on the oxidant effects of nontransferrin bound iron [NTBI (eLPI assay)] during chemotherapy of acute lymphoblastic leukemia and acute myeloblastic leukemia are lacking. We established NTBI and oxidative stress determinants (OSD), iron parameters, high-sensitive C-reactive protein (hs-CRP) levels, liver tests, cumulative chemotherapeutic doses, and transfused blood in 36 children with acute leukemia throughout chemotherapy. These parameters were determined at the beginning and end of chemotherapy blocks (11 time points) and in 20 healthy children using enzyme-linked immunosorbent assay, and colorimetric and fluorometric enzymatic methods. In acute lymphoblastic leukemia, NTBI, OSD, and hs-CRP were higher than controls at 4/11, 7/11, and 9/11 time points (P<0.05). At 3 time points, NTBI and OSD concurrently increased. Ferritin, soluble transferrin receptor, serum iron, and transferrin saturation were higher than in controls at 5 to 11/11 time points (P<0.05). Those with NTBI had higher iron parameters than those without NTBI (P<0.05), but showed similar OSD, hs-CRP, liver enzymes, cumulative chemotherapeutics, and transfused blood (P>0.05). OSD did not correlate with NTBI, but correlated with hs-CRP. In conclusion, NTBI is a poor predictor of OSD in acute leukemia possibly because of the heterogeneity of NTBI and chronic inflammation. Further studies are needed to delineate the pathophysiology of these diseases.

Endogenous hepcidin and its agonist mediate resistance to selected infections by clearing non-transferrin-bound iron

The iron-regulatory hormone hepcidin is induced early in infection, causing iron sequestration in macrophages and decreased plasma iron; this is proposed to limit the replication of extracellular microbes, but could also promote infection with macrophage-tropic pathogens. The mechanisms by which hepcidin and hypoferremia modulate host defense, and the spectrum of microbes affected, are poorly understood. Using mouse models, we show that hepcidin was selectively protective against siderophilic extracellular pathogens (Yersinia enterocolitica O9) by controlling non-transferrin-bound iron (NTBI) rather than iron-transferrin concentration. NTBI promoted the rapid growth of siderophilic but not nonsiderophilic bacteria in mice with either genetic or iatrogenic iron overload and in human plasma. Hepcidin or iron loading did not affect other key components of innate immunity, did not indiscriminately promote intracellular infections (Mycobacterium tuberculosis), and had no effect on extracellular nonsiderophilic Y enterocolitica O8 or Staphylococcus aureus Hepcidin analogs may be useful for treatment of siderophilic infections.

First study on iron complexes in blood and organ samples from thalassaemic and normal laboratory mice using Mössbauer spectroscopy

Measurements of iron complexes and iron stores in the body are crucial for evaluation and management of chelation therapy targeted against iron accumulation or overload in blood and organs. In this work, blood and tissue samples from one normal and one thalassaemic laboratory mouse were studied using ⁵⁷Fe Mössbauer spectroscopy at 78 K for the first time. In contrast to human patients, these laboratory mice did not receive any medical treatment, thus the iron components present in the samples are not altered from their natural state. The Mössbauer spectra of blood, liver and spleen samples of the thalassaemic mouse were found to differ in shape and iron content compared with corresponding spectra of the normal mouse. These results demonstrate a basis for further exploitation of the thalassaemic mouse model to study thalassaemia and its treatment in more detail using Mössbauer spectroscopy.

Residual erythropoiesis protects against myocardial hemosiderosis in transfusion-dependent thalassemia by lowering labile plasma iron via transient generation of apotransferrin

Cardiosiderosis is a leading cause of mortality in transfusion-dependent thalassemias. Plasma non-transferrin-bound iron and its redox-active component, labile plasma iron, are key sources of iron loading in cardiosiderosis. Risk factors were identified in 73 patients with or without cardiosiderosis. Soluble transferrin receptor-1 levels were significantly lower in patients with cardiosiderosis (odds ratio 21). This risk increased when transfusion-iron loading rates exceeded the erythroid transferrin uptake rate (derived from soluble transferrin receptor-1) by >0.21 mg/kg/day (odds ratio 48). Labile plasma iron was >3-fold higher when this uptake rate threshold was exceeded, but non-transferrin-bound iron and transferrin saturation were comparable. The risk of cardiosiderosis was decreased in patients with low liver iron, ferritin and labile plasma iron, or high bilirubin, reticulocyte counts or hepcidin. We hypothesized that high erythroid transferrin uptake rate decreases cardiosiderosis through increased erythroid re-generation of apotransferrin. To test this, iron uptake and intracellular reactive oxygen species were examined in HL-1 cardiomyocytes under conditions modeling transferrin effects on non-transferrin-bound iron speciation with ferric citrate. Intracellular iron and reactive oxygen species increased with ferric citrate concentrations especially when iron-to-citrate ratios exceeded 1:100, i.e. conditions favoring kinetically labile monoferric rather than oligomer species. Excess iron-binding equivalents of apotransferrin inhibited iron uptake and decreased both intracellular reactive oxygen species and labile plasma iron under conditions favoring monoferric species. In conclusion, high transferrin iron utilization, relative to the transfusion-iron load rate, decreases the risk of cardiosiderosis. A putative mechanism is the transient re-generation of apotransferrin by an active erythron, rapidly binding labile plasma iron-detectable ferric monocitrate species.

Iron Therapy in Patients with Heart Failure and Iron Deficiency: Review of Iron Preparations for Practitioners

In patients with heart failure (HF), iron deficiency (ID) correlates with decreased exercise capacity and poor health-related quality of life, and predicts worse outcomes. Both absolute (depleted iron stores) and functional (where iron is unavailable for dedicated tissues) ID can be easily evaluated in patients with HF using standard laboratory tests (assessment of serum ferritin and transferrin saturation). Intravenous iron therapy in iron-deficient patients with HF and reduced ejection fraction has been shown to alleviate HF symptoms and improve exercise capacity and quality of life. In this paper, we provide information on how to diagnose ID in HF. Further we discuss pros and cons of different iron preparations and discuss the results of major trials implementing iron supplementation in HF patients, in order to provide practical guidance for clinicians on how to manage ID in patients with HF.

Hydroxypyridinone Chelators: From Iron Scavenging to Radiopharmaceuticals for PET Imaging with Gallium-68

Derivatives of 3,4-hydroxypyridinones have been extensively studied for in vivo Fe3+ sequestration. Deferiprone, a 1,2-dimethyl-3,4-hydroxypyridinone, is now routinely used for clinical treatment of iron overload disease. Hexadentate tris(3,4-hydroxypyridinone) ligands (THP) complex Fe3+ at very low iron concentrations, and their high affinities for oxophilic trivalent metal ions have led to their development for new applications as bifunctional chelators for the positron emitting radiometal, 68Ga3+, which is clinically used for molecular imaging in positron emission tomography (PET). THP-peptide bioconjugates rapidly and quantitatively complex 68Ga3+ at ambient temperature, neutral pH and micromolar concentrations of ligand, making them amenable to kit-based radiosynthesis of 68Ga PET radiopharmaceuticals. 68Ga-labelled THP-peptides accumulate at target tissue in vivo, and are excreted largely via a renal pathway, providing high quality PET images.