Iron metabolism

Identification and characterization of a clam ferritin from Sinonovacula constricta

Ferritin, a major iron storage protein of most living organisms, plays a crucial role in iron metabolism. Here we reported the isolation and characterization of a cDNA of ferritin gene from Sinonovacula constricta (denoted as ScFER). The full-length cDNA of ScFER was of 996 bp, consisting of a 5'-UTR of 120 bp, a 3'-UTR of 360 bp, and a complete open reading frame of 516 bp encoding a polypeptide with 171 amino acid residues. The predicted molecular mass of deduced amino acid of ScFER was 19.76 kDa and the theoretical pI was 5.07. Quantitative real-time PCR was employed to analyze the expression profiles of ScFER mRNA in muscle, mantle and visceral mass after iron exposure. The peak expression level of ScFER in the three tissues was 1.79-fold, 1.31-fold and 3.51-fold increases in muscle, mantle and visceral mass, respectively. The polyclonal antibodies generated from the recombinant product of ScFER could be specifically identified not only the recombinant product, but also the native protein from muscle. All these results strongly suggested that ScFER was involved in the iron metabolism regulation in S. constricta.

Structural diversity of class I MHC-like molecules and its implications in binding specificities

The binding groove of class I major histocompatibility complex (MHC) class is essentially important for antigen binding and presentation on T cells. There are several molecules that have analogous conformations to class I MHC. However, they bind specifically to varying types of ligands and cell-surface receptors in order to elicit an immune response. To elucidate how such recognition is achieved in classical MHC-I like molecules, we have extensively analyzed the structure of human leukocyte antigen (HLA-1), neonatal Fc receptor (FcRn), hereditary hemochromatosis protein (HFE), cluster of differentiation 1 (CD1), gamma delta T cell receptor ligand (Τ22), zinc-α2-glycoprotein (ZAG), and MHC class I chain-related (MIC-A) proteins. All these molecules have analogous structural anatomy, divided into three distinct domains, where α1-α2 superdomains form a groove-like structure that potentially bind to certain ligand, while the α3 domain adopts a fold resembling immunoglobulin constant domains, and holds this α1-α2 platform and the light chain. We have observed many remarkable features of α1-α2 platform, which provide specificities to these proteins toward a particular class of ligands. The relative orientation of α1, α2, and α3 domains is primarily responsible for the specificity to the light chain. Interestingly, light chain of all these proteins is β₂-microglobulin (β₂M), except ZAG which has prolactin-induced protein (PIP). However, MIC-A is devoid of any light chain. Residues on β₂M recognize a sequence motif on the α3 domain that is essentially restricted to specific heavy chain of MHC class I molecules. Our analysis suggests that the structural features of class I molecules determine the recognition of different ligands and light chains, which are responsible for their corresponding functions through an inherent mechanism.

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

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

Gender-related variations in iron metabolism and liver diseases

The regulation of iron metabolism involves multiple organs including the duodenum, liver and bone marrow. The recent discoveries of novel iron-regulatory proteins have brought the liver to the forefront of iron homeostasis. The iron overload disorder, genetic hemochromatosis, is one of the most prevalent genetic diseases in individuals of Caucasian origin. Furthermore, patients with non-hemochromatotic liver diseases, such as alcoholic liver disease, chronic hepatitis C or nonalcoholic steatohepatitis, often exhibit elevated serum iron indices (ferritin, transferrin saturation) and mild to moderate hepatic iron overload. Clinical data indicate significant differences between men and women regarding liver injury in patients with alcoholic liver disease, chronic hepatitis C or nonalcoholic steatohepatitis. The penetrance of genetic hemochromatosis also varies between men and women. Hepcidin has been suggested to act as a modifier gene in genetic hemochromatosis. Hepcidin is a circulatory antimicrobial peptide synthesized by the liver. It plays a pivotal role in the regulation of iron homeostasis. Hepcidin has been shown to be regulated by iron, inflammation, oxidative stress, hypoxia, alcohol, hepatitis C and obesity. Sex and genetic background have also been shown to modulate hepcidin expression in mice. The role of gender in the regulation of human hepcidin gene expression in the liver is unknown. However, hepcidin may play a role in gender-based differences in iron metabolism and liver diseases. Better understanding of the mechanisms associated with gender-related differences in iron metabolism and chronic liver diseases may enable the development of new treatment strategies.

Antioxidant activities of flavonol derivatives from the leaves and stem bark of Scutia buxifolia Reiss

This study evaluated the antioxidant activities in the leaves and stem bark fractions of Scutia buxifolia. Cerebral lipid peroxidation (TBARS) was induced by Fe(II) and radical-scavenging activity was determined by DPPH method. Folin-Ciocalteu was used to determine phenolic contents. Quercetin, quercitrin, isoquercitrin and rutin were isolated from leaf ethyl acetate fraction and their levels were measured by high performance liquid chromatography-photodiode array detector. IC(50) (DPPH) varied from 4.35+/-1.30 to 29.55+/-0.54 microg/mL for stem bark and from 6.50+/-0.40 to 30.54+/-1.14 in the leaves. Ethyl acetate and butanolic fractions caused a sharp fall in TBARS production with IC(50) from 2.93+/-2.17 to 40.46+/-2.51 microg/mL for the leaves and 0.66+/-0.17 to 27.3+/-1.23 for the stem bark. Results obtained indicated that S. buxifolia has a great potential to prevent disease caused by the overproduction of free radicals and also it might be used as a potential source of natural antioxidant agents.

Contribution of STAT3 and SMAD4 pathways to the regulation of hepcidin by opposing stimuli

Hepcidin, a key regulator of iron metabolism, is a small antimicrobial peptide produced by the liver that regulates intestinal iron absorption and iron recycling by macrophages. Hepcidin is stimulated when iron stores increase and during inflammation and, conversely, is inhibited by hypoxia and augmented erythropoiesis. In many pathologic situations, such as in the anemia of chronic disease (ACD) and iron-loading anemias, several of these factors may be present concomitantly and may generate opposing signaling to regulate hepcidin expression. Here, we address the question of dominance among the regulators of hepcidin expression. We show that erythropoiesis drive, stimulated by erythropoietin but not hypoxia, down-regulates hepcidin in a dose-dependent manner, even in the presence of lipopolysaccharide (LPS) or dietary iron-loading, which may act additively. These effects are mediated through down-regulation of phosphorylation of Stat3 triggered by LPS and of Smad1/5/8 induced by iron. In conclusion, hepcidin expression levels in the presence of opposing signaling are determined by the strength of the individual stimuli rather than by an absolute hierarchy among signaling pathways. Our findings also suggest that erythropoietic drive can inhibit both inflammatory and iron-sensing pathways, at least in part, via the suppression of STAT3 and SMAD4 signaling in vivo.

A novel ratiometric fluorescent Fe3+ sensor based on a phenanthroimidazole chromophore

Phenanthroimidazole derivative 1 has been developed as a rare example of ratiometric fluorescent sensors for Fe(3+). Interestingly, upon treatment with Fe(3+), the sensor displayed a ratiometric fluorescent response with an enhancement of the ratios of emission intensities at 440 and 500 nm from 0.36 to 3.24. The detection range of the sensor for Fe(3+) is in the 1.0x10(-5)-1.5x10(-4) M concentration range and the detection limit is 5.26x10(-6) M. In addition, the sensor showed good selectivity to Fe(3+) with the selectivity coefficients (K(Fe3+) = S(Fe3+)/S(0) of Fe(3+) over other metal ions tested in the range of 5-68.

Efflux of iron from the cerebrospinal fluid to the blood at the blood-CSF barrier: effect of manganese exposure

The blood-cerebrospinal fluid (CSF) barrier (BCB) resides within the choroid plexus, with the apical side facing the CSF and the basolateral side towards the blood. Previous studies demonstrate that manganese (Mn) exposure in rats disrupts iron (Fe) homeostasis in the blood and CSF. The present study used a primary culture of rat choroidal epithelial cells grown in the two-chamber Transwell system to investigate the transepithelial transport of Fe across the BCB. Free, unbound Fe as [(59)Fe] was added to the donor chamber and the radioactivity in the acceptor chamber was quantified to determine the direction of Fe fluxes. Under the normal condition, the [(59)Fe] efflux (from the CSF to the blood) was 128% higher than that of the influx (P < 0.01). Mn exposure significantly increased the efflux rate of [(59)Fe] (P < 0.01) and the effect was inhibited when the cells were pre-incubated with the antibody against divalent metal transport 1 (DMT1). Moreover, when the siRNA knocked down the cellular DMT1 expression, the elevated Fe uptake caused by Mn exposure in the choroidal epithelial Z310 cells was completely abolished, indicating that Mn may facilitate Fe efflux via a DMT1-mediated transport mechanism. In vivo subchronic exposure to Mn in rats reduced Fe clearance from the CSF, as demonstrated by the ventriculo-cisternal brain perfusion, along with up-regulated mRNAs encoding DMT1 and transferrin receptor (TfR) in the same animals. Taken together, these data suggest that free Fe appears to be favorably transported from the CSF toward the blood by DMT1 and this process can be facilitated by Mn exposure. Enhanced TfR-mediated influx of Fe from the blood and ferroportin-mediated expelling Fe toward the CSF may compromise DMT1-mediated efflux, leading to an increased Fe concentration in the CSF as seen in Mn-exposed animals.

Antioxidant effects of different extracts from Melissa officinalis, Matricaria recutita and Cymbopogon citratus

Considering the important role of oxidative stress in the pathogenesis of several neurological diseases, and the growing evidence of the presence of compounds with antioxidant properties in the plant extracts, the aim of the present study was to investigate the antioxidant capacity of three plants used in Brazil to treat neurological disorders: Melissa officinalis, Matricaria recutita and Cymbopogon citratus. The antioxidant effect of phenolic compounds commonly found in plant extracts, namely, quercetin, gallic acid, quercitrin and rutin was also examined for comparative purposes. Cerebral lipid peroxidation (assessed by TBARS) was induced by iron sulfate (10 microM), sodium nitroprusside (5 microM) or 3-nitropropionic acid (2 mM). Free radical scavenger properties and the chemical composition of plant extracts were assessed by 1'-1' Diphenyl-2' picrylhydrazyl (DPPH) method and by Thin Layer Chromatography (TLC), respectively. M. officinalis aqueous extract caused the highest decrease in TBARS production induced by all tested pro-oxidants. In the DPPH assay, M. officinalis presented also the best antioxidant effect, but, in this case, the antioxidant potencies were similar for the aqueous, methanolic and ethanolic extracts. Among the purified compounds, quercetin had the highest antioxidant activity followed by gallic acid, quercitrin and rutin. In this work, we have demonstrated that the plant extracts could protect against oxidative damage induced by various pro-oxidant agents that induce lipid peroxidation by different process. Thus, plant extracts could inhibit the generation of early chemical reactive species that subsequently initiate lipid peroxidation or, alternatively, they could block a common final pathway in the process of polyunsaturated fatty acids peroxidation. Our study indicates that M. officinalis could be considered an effective agent in the prevention of various neurological diseases associated with oxidative stress.

Expression of iron-related proteins during infection by bovine herpes virus type-1

Bovine herpesvirus 1 (BHV-1), a dsDNA animal virus, is an economically important pathogen of cattle and the aetiological agent of many types of disease. The efficient replication of a DNA virus is strictly dependent on iron since this metal plays a crucial role in the catalytic center of viral ribonucleotide reductase. Consequently, iron metabolism is an important area for virus/host interaction and a large body of evidence suggests that viral infection is potentially influenced by the iron status of the host. The aim of the present study was to address the effects of BHV-1 on iron metabolism in Madin-Darby bovine kidney (MDBK) cells at different times of post-infection. For this purpose, cell viability, iron regulatory proteins (IRPs) activity and levels, transferrin receptor 1 (TfR-1), ferritin expression and LIP were evaluated. Our data demonstrate that a productive BHV-1 infection in MDBK cells determines an overall decrease of IRPs RNA-binding activity without affecting their expression. As consequence of this modulation, an increased ferritin mRNA translation and a decreased TfR-1 mRNA translation were also observed. Moreover, the LIP level was decreased following viral infection. These results are consistent with the hypothesis that by reducing the iron up-take and by enhancing the sequestration of free iron, animal cells will limit the iron availability for virus proliferation. Therefore, the results presented herein support the view that iron metabolism could be critical for the interaction between DNA viruses, such as BHV-1, and mammalian cells. Delineation of the interplay among pathogen and host may provide new antimicrobial agents.

Neuroprotective effect of aminoguanidine on iron-induced neurotoxicity

Iron is a commonly used metal to induce neuronal hyperactivity and oxidative stress. Iron levels rise in the brain in some neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. A body of evidence indicates a link between neuronal death and nitric oxide. The present study was performed to investigate whether nitric oxide produced by inducible nitric oxide synthase is involved in iron-induced neuron death. For this purpose rats were divided into four groups: control, iron, aminoguanidine and iron+aminoguanidine. Animals in iron and iron+aminoguanidine groups received intracerebroventricular FeCl3 injection (200 mM, 2.5 microl). Rats belonging to control and aminoguanidine groups received the same amount of saline into the cerebral ventricles. All animals were kept alive for 10 days following the operation and animals in aminoguanidine and iron+aminoguanidine groups received intraperitoneal aminoguanidine injections once a day (100mg/kg day) during this period. After 10 days, rats were perfused intracardially under deep urethane anesthesia. Removed brains were processed using the standard histological techniques. The total numbers of neurons in hippocampus of all rats were estimated with the unbiased stereological techniques. It was found that aminoguanidine decreased mean neuron loss from 43.4% to 20.3%. Results of the present study suggest that aminoguanidine may attenuate the neurotoxic effects of iron by inhibiting inducible nitric oxide synthase.

Role of alcohol in the regulation of iron metabolism

Patients with alcoholic liver disease frequently exhibit increased body iron stores, as reflected by elevated serum iron indices (transferrin saturation, ferritin) and hepatic iron concentration. Even mild to moderate alcohol consumption has been shown to increase the prevalence of iron overload. Moreover, increased hepatic iron content is associated with greater mortality from alcoholic cirrhosis, suggesting a pathogenic role for iron in alcoholic liver disease. Alcohol increases the severity of disease in patients with genetic hemochromatosis, an iron overload disorder common in the Caucasian population. Both iron and alcohol individually cause oxidative stress and lipid peroxidation, which culminates in liver injury. Despite these observations, the underlying mechanisms of iron accumulation and the source of the excess iron observed in alcoholic liver disease remain unclear. Over the last decade, several novel iron-regulatory proteins have been identified and these have greatly enhanced our understanding of iron metabolism. For example, hepcidin, a circulatory antimicrobial peptide synthesized by the hepatocytes of the liver is now known to play a central role in the regulation of iron homeostasis. This review attempts to describe the interaction of alcohol and iron-regulatory molecules. Understanding these molecular mechanisms is of considerable clinical importance because both alcoholic liver disease and genetic hemochromatosis are common diseases, in which alcohol and iron appear to act synergistically to cause liver injury.

Brain iron metabolism: neurobiology and neurochemistry

New findings obtained during the past years, especially the discovery of mutations in the genes associated with brain iron metabolism, have provided key insights into the homeostatic mechanisms of brain iron metabolism and the pathological mechanisms responsible for neurodegenerative diseases. The accumulated evidence demonstrates that misregulation in brain iron metabolism is one of the initial causes for neuronal death in some neurodegenerative disorders. The errors in brain iron metabolism found in these disorders have a multifactorial pathogenesis, including genetic and nongenetic factors. The disturbances of iron metabolism might occur at multiple levels, including iron uptake and release, storage, intracellular metabolism and regulation. It is the increased brain iron that triggers a cascade of deleterious events, leading to neuronal death in these diseases. In the article, the recent advances in studies on neurochemistry and neuropathophysiology of brain iron metabolism were reviewed.

Ferritin accumulation in dystrophic microglia is an early event in the development of Huntington's disease

Huntington's Disease (HD) is characterized primarily by neuropathological changes in the striatum, including loss of medium-spiny neurons, nuclear inclusions of the huntingtin protein, gliosis, and abnormally high iron levels. Information about how these conditions interact, or about the temporal order in which they appear, is lacking. This study investigated if, and when, iron-related changes occur in the R6/2 transgenic mouse model of HD and compared the results with those from HD patients. Relative to wild-type mice, R6/2 mice had increased immunostaining for ferritin, an iron storage protein, in the striatum beginning at 2-4 weeks postnatal and in cortex and hippocampus starting at 5-7 weeks. The ferritin staining was found primarily in microglia, and became more pronounced as the mice matured. Ferritin-labeled microglia in R6/2 mice appeared dystrophic in that they had thick, twisted processes with cytoplasmic breaks; some of these cells also contained the mutant huntingtin protein. Brains from HD patients (Vonsattel grades 0-4) also had increased numbers of ferritin-containing microglia, some of which were dystrophic. The cells were positive for Perl's stain, indicating that they contained abnormally high levels of iron. These results provide the first evidence that perturbations to iron metabolism in HD are predominately associated with microglia and occur early enough to be important contributors to HD progression.

Studies on resistance characteristic and cDNA sequence conservation of transferrin from crucian carp, Carassius auratus

Transferrin (Tf) is a kind of non-heme beta-globulin with two iron ions (Fe(3+))-binding sites. To prove Tf's physiological functions, Fe(3+)-proteins, serum iron contents, and total iron-binding capabilities were tested for Tfs of crucian carps (Carassius auratus) and sliver carps (Hypophthalmichthys molitrix). The above results demonstrated that sliver carps shared 1/3 Tf alleles with crucian carps; Tf of crucian carps had stronger Fe(3+)-binding ability and transportation ability in plasma than that of sliver carps. In addition, the results of oxygen consumption experiments indicated that crucian carps had the higher oxygen utility rate than sliver carps. For acute hypoxia exposure assay, normoxic gas mixture, hypoxic gas mixture A, and hypoxic gas mixture B were used to induce oxygen-regulated gene expression of crucian carps in acute hypoxia. The results of quantitative real-time PCR revealed that mRNA levels of Tf gene, Tfr gene and ATPase gene were down-regulated in acute hypoxia but mRNA level of LDHa gene was up-regulated in acute hypoxia. The results of crucian carp Tf-cDNA sequence analysis showed that cDNA regions of two Fe(3+)-binding sites were T(747)-T(1026) and T(1737)-A(1884) based on the principle of bioinformatics. The sequence conservation of two Fe(3+)-binding sites was higher than that of the other five regions, which were confirmed according to the subregion model of Tf-cDNA sequence.

Voltage-gated calcium channels provide an alternate route for iron uptake in neuronal cell cultures

Recent studies suggest that iron enters cardiomyocytes via the L-type voltage-gated calcium channel (VGCC). The neuronal VGCC may also provide iron entry. As with calcium, extraneous iron is associated with the pathology and progression of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. VGCCs, ubiquitously expressed, may be an important route of excessive entry for both iron and calcium, contributing to cell toxicity or death. We evaluated the uptake of (45)Ca(2+) and (55)Fe(2+) into NGF-treated rat PC12, and murine N-2alpha cells. Iron not only competed with calcium for entry into these cells, but iron uptake (similar to calcium uptake) was inhibited by nimodipine, a specific L-type VGCC blocker, and enhanced by FPL 64176, an L-VGCC activator, in a dose-dependent manner. Taken together, these data suggest that voltage-gated calcium channels are an alternate route for iron entry into neuronal cells under conditions that promote cellular iron overload toxicity.

Brain Iron Toxicity: Differential Responses of Astrocytes, Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson's and Alzheimer's diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain's highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron.

Oogenesis: Single cell development and differentiation

Oocytes express a unique set of genes that are essential for their growth, for meiotic recombination and division, for storage of nutrients, and for fertilization. We have utilized the newly sequenced genome of Strongylocentrotus purpuratus to identify genes that help the oocyte accomplish each of these tasks. This study emphasizes four classes of genes that are specialized for oocyte function: (1) Transcription factors: many of these factors are not significantly expressed in embryos, but are shared by other adult tissues, namely the ovary, testis, and gut. (2) Meiosis: A full set of meiotic genes is present in the sea urchin, including those involved in cohesion, in synaptonemal complex formation, and in meiotic recombination. (3) Yolk uptake and storage: Nutrient storage for use during early embryogenesis is essential to oocyte function in most animals; the sea urchin accomplishes this task by using the major yolk protein and a family of accessory proteins called YP30. Comparison of the YP30 family members across their conserved, tandem fasciclin domains with their intervening introns reveals an incongruence in the evolution of its major clades. (4) Fertilization: This set of genes includes many of the cell surface proteins involved in sperm interaction and in the physical block to polyspermy. The majority of these genes are active only in oocytes, and in many cases, their anatomy reflects the tandem repeating interaction domains essential for the function of these proteins. Together, the expression profile of these four gene classes highlights the transitions of the oocyte from a stem cell precursor, through stages of development, to the clearing and re-programming of gene expression necessary to transition from oocyte, to egg, to embryo.

Effect of metal ions on HIF-1α and Fe homeostasis in human A549 cells

Several metals are carcinogenic but little is known about the mechanisms by which they cause cancer. A pathway that may contribute to metal ion induced carcinogenesis is by hypoxia signaling, which involves a disruption of cellular iron homeostasis by competition with iron transporters or iron-regulated enzymes. To examine the involvement of iron in the hypoxia signaling activity of these metal ions we investigated HIF-1alpha protein stabilization, IRP-1 activity, and ferritin protein levels in human lung carcinoma A459 cells exposed to various agents in serum- and iron-free salt-glucose medium (SGM) or in normal complete medium. We also studied the effects of excess exogenous iron on these responses induced by nickel ion exposure. Our results show the following: (1) SGM enhanced metals-induced HIF-1alpha stabilization and IRP-1 activation (e.g., nickel and cobalt ions). (2) If SGM was reconstituted with a slight excess level (25 microM of FeSO(4)) of iron, this enhancing ability was significantly decreased. (3) The effect of a high level of exogenous iron (500 microM of FeSO(4)) on metal-induced hypoxia and iron metabolism was highly dependent on the order of addition. If treatment with the Fe and metal ions was simultaneous (co-treatment), the effects of nickel ion exposure were overwhelmed, since the added Fe reversed HIF-1alpha stabilization, decreased IRP-1 activity, and increased ferritin level. Pre-treatment with iron was not able to reverse the responses caused by nickel ion exposure. These results imply that it is important to consider the available iron concentration and suitable exposure design when studying metal-induced hypoxia or metal-induced disruption of Fe homeostasis.

Metabolic analysis of mouse brains that have compromised iron storage

Iron is a critical component of the CNS that must be tightly regulated; too little iron can result in energy insufficiency and too much iron can result in oxidative stress. The intracellular iron storage protein ferritin is central to the regulation of iron. In this study, we determined the neurochemical profile of brains of animals deficient in heavy-chain ferritin (H-ferritin) using high-resolution magic angle spin proton magnetic resonance spectroscopy (HR-MAS (1)H MRS). Spectra of 2 mm-thick coronal tissue punches ( approximately 4 mg) were obtained using a CPMG pulse sequence on Bruker Avance 500 and quantified (nmol/mg tissue) using customized LCModel software (16 metabolites). In H-ferritin deficient mice, we found significant increases in striatal glutamate, hippocampal choline, and N-acetyl-aspartyl-glutamate in both the cortex and the hippocampus (t-test, p < 0.05). Neurochemical profiling with principal component analysis (PCA) revealed increased glutamate in the hippocampus, striatum, and ventral tegmental area (VTA) in H-ferritin deficient animals as compared to wild-type. While lactate was increased in the VTA of deficient animals, it was decreased in the striatum. Also, GABA was increased in both cortical and striatal regions of deficient mice. These changes reveal the importance of proper iron management for maintaining neurochemical balance and provide new evidence for region specific differences in neurochemical profiles as a result of compromised ability of neurons to store iron while overall iron status is normal. Because H-ferritin is predominantly expressed in neurons, the neurochemical profile is suggestive of neuronal iron deficiency and may have relevance to the functional consequences associated with brain iron deficiency.

Distinct requirements for Hfe in basal and induced hepcidin levels in iron overload and inflammation

Hepcidin is a negative regulator of iron absorption produced mainly by the liver in response to changes in iron stores and inflammation, and its levels have been shown to regulate the intestinal basolateral iron transporter ferroportin1 (Fp1). Hereditary hemochromatosis patients and Hfe-deficient mice show inappropriate expression of hepcidin but, in apparent contradiction, still retain the ability to regulate iron absorption in response to alterations of iron metabolism. To further understand the molecular relationships among Hfe, hepcidin, and Fp1, we investigated hepcidin and Fp1 regulation in Hfe-deficient mice (Hfe-/- and beta2m-/-) in response to iron deprivation, iron loading, and acute inflammation. We found that whereas basal hepcidin levels were manifestly dependent on the presence of Hfe and on the mouse background, all Hfe-deficient mice were still able to regulate hepcidin in situations of altered iron homeostasis. In the liver, Fp1 was modulated in opposite directions by iron and LPS, and its regulation in Hfe-deficient mice was similar to that observed in wild-type mice. In addition, we found that iron-deprived mice were able to mount a robust response after LPS challenge and that Toll-like receptor 4 (TLR-4)-deficient mice fail to regulate hepcidin expression in response to LPS. In conclusion, these results suggest that although Hfe is necessary for the establishment of hepcidin basal levels, it is dispensable for hepcidin regulation through both the iron-sensing and inflammatory pathways, and hepatic Fp1 regulation is largely independent of hepcidin and Hfe. The inflammatory pathway overrides the iron-sensing pathway and is TLR-4 dependent.

In vivo tumor growth is inhibited by cytosolic iron deprivation caused by the expression of mitochondrial ferritin

Mitochondrial ferritin (MtFt) is a mitochondrial iron-storage protein whose function and regulation is largely unknown. Our previous results have shown that MtFt overexpression markedly affects intracellular iron homeostasis in mammalian cells. Using tumor xenografts, we examined the effects of MtFt overexpression on tumor iron metabolism and growth. The expression of MtFt dramatically reduced implanted tumor growth in nude mice. Mitochondrial iron deposition in MtFt-expressing tumors was directly observed by transmission electron microscopy. A cytosolic iron starvation phenotype in MtFt-expressing tumors was revealed by increased RNA-binding activity of iron regulatory proteins, and concomitantly both an increase in transferrin receptor levels and a decrease in cytosolic ferritin. MtFt overexpression also led to decreases in total cellular heme content and heme oxygenase-1 levels. In addition, elevated MtFt in tumors was also associated with a decrease in total aconitase activity and lower frataxin protein level. In conclusion, our study shows that high MtFt levels can significantly affect tumor iron homeostasis by shunting iron into mitochondria; iron scarcity resulted in partially deficient heme and iron-sulfur cluster synthesis. It is likely that deprivation of iron in the cytosol is the cause for the significant inhibition of xenograft tumor growth.

A New Rhodamine-Based Chemosensor Exhibiting Selective FeIII-Amplified Fluorescence

[structure: see text] A new fluorescent probe 3 was synthesized, and it exhibited high selectivity for Fe(III) over other commonly coexistent metal ions in both ethanol and water. Upon the addition of Fe(III), the spirocyclic ring of 3 was opened and a significant enhancement of visible color and fluorescence in the range of 500-600 nm was observed.

A calcium channel blocker flunarizine attenuates the neurotoxic effects of iron

Iron is a metal highly concentrated in liver and brain tissue, and known to induce neuronal hyperactivity and oxidative stress. It has been established that iron levels rise in the brain in some neurodegenerative diseases such as Parkinson's and Alzheimer's diseases (AD). A body of evidence indicates a link between neuronal death and intracellular excessive calcium accumulation. The aim of the present study was to investigate the effects of a calcium antagonist, flunarizine, on neurotoxicity induced by intracerebroventricular (i.c.v.) iron injection. For this reason rats were divided into three groups as control, iron and iron+flunarizine groups. Animals in iron and iron+flunarizine groups received i.c.v. FeCl(3) injection (200 mM, 2.5 microl), while control rats received the same amount of saline into the cerebral ventricles. Rats in iron+flunarizine group also received i.c.v. flunarizine (1 microM, 2 microl) following FeCl(3) injection. All animals were kept alive for ten days following the operation and animals in iron+flunarizine group received intraperitoneal (i.p.) flunarizine injections once a day (10 mg/kg/day) during this period. After ten days, rats were sacrificed. The total numbers of neurons in hippocampus of all rats were estimated with the latest, unbiased stereological techniques. Findings of the present study suggest that flunarizine may attenuate the neurotoxic effects of iron injection by inhibiting the cellular influx of excessive calcium ions.

Heat shock protein 27 downregulates the transferrin receptor 1-mediated iron uptake

It has been reported that over-expression of human heat shock protein 27 (hsp27) in murine cells decreased the intracellular iron level [Arrigo, A. P., Virot, S., Chaufour, S., Firdaus, W., Kretz-Remy, C., & Diaz-Latoud, C. (2005). Hsp27 consolidates intracellular redox homeostasis by upholding glutathione in its reduced form and by decreasing iron intracellular levels. Antioxidants & Redox Signalling, 7, 412-422]. However, the mechanism involved is unknown. In this study, the regulation of transferrin receptor 1 (TfR1)-mediated iron uptake by human hsp27 was investigated in CCL39 cells by overexpression of human hsp27 and its dominant-negative mutant (hsp27-3G). The results showed that overexpression of hsp27 diminished intracellular labile iron pool, increased the binding activity of iron regulatory protein (IRP) to iron responsive element (IRE) and the cell surface-expressed TfR1s. However, the increased surface-expressed TfR1s resulted in decrease rather than increase of iron uptake. Further study revealed that overexpression of hsp27 decelerated transferrin endocytosis and recycling, while overexpressed hsp27-3G had a reversal effect. Moreover, flowcytometric analysis showed an enhanced actin polymerization in the cells overexpressing hsp27. In particular, fluorescence imaging of cytoskeleton displayed highly stabilized microfilaments and preferential localization of hsp27 in cortical area of the actin cytoskeleton. In contrast, disruption of actin cytoskeleton by cytochalasin B resulted in acceleration of the endocytosis and recycling of Tf, as well as increase of iron uptake. Meanwhile, the possible involvement of ferroportin 1 in down-regulation of intracellular iron level by overexpression of hsp27 was checked. However, the outcome was negative. Our findings indicate that hsp27 down-regulates TfR1-mediated iron uptake via stabilization of the cortical actin cytoskeleton rather than the classical IRP/IRE mode. The study may also imply that hsp27 protects cells from oxidative stress by reducing cellular iron uptake.

Potential sources of increased iron in the substantia nigra of parkinsonian patients

Histopathological, biochemical and in vivo brain imaging techniques, such as magnetic resonance imaging and transcranial sonography, revealed a consistent increase of substantia nigra (SN) iron in Parkinson's disease (PD). Increased iron deposits in the SN may have genetic and non-genetic causes. There are several rare movement disorders associated with neurodegeneration, and genetic abnormalities in iron regulation resulting in iron deposition in the brain. Non-genetic causes of increased SN iron may be the result of a disturbed or open blood-brain-barrier, local changes in the normal iron-regulatory systems, intraneuronal transportation of iron from iron-rich area into the SN and release of iron from intracellular iron storage molecules. Major iron stores are ferritin and haemosiderin in glial cells as well as neuromelanin in neurons. Age- and disease dependent overload of iron storage proteins may result in iron release upon reduction. Consequently, the low molecular weight chelatable iron complexes may trigger redox reactions leading to damage of biomolecules. Additionally, upon neurodegeneration there is strong microglial activation which can be another source of high iron concentrations in the brain.

A model of lysosomal metabolism of dextran coated superparamagnetic iron oxide (SPIO) nanoparticles: implications for cellular magnetic resonance imaging

Ferumoxides, dextran-coated superparamagnetic iron oxide (SPIO) particles, form ferumoxide-transfection agent (FE-TA) complexes that are internalized into endosomes/lysosomes and have been used to label cells for in vivo MRI tracking and localization studies. A better understanding of the physical state of the FE-TA complexes during endocytosis could improve their use. The purpose of this study was to measure the rate of the degradation of iron particles under varying physiological conditions. FE-TA complexes were incubated in seven different buffers containing different chelates with different pH. Reducible iron concentrations, T2 relaxation rates and gradient echo (GRE) magnetic resonance images (MRI) were obtained from each condition immediately after incubation and at 6, 24, 48, 72 and 96 h and days 7, 14 and 21. The dynamics of FE-TA in the endosome/lysosomes within the cells were visualized with electron microscopy. Sodium citrate buffer at pH 4.5 rapidly dissolved FE-TA complexes. However, FE-TA complexes were less soluble in the same buffer at pH 5.5. Similarly, FE-TA complexes were not readily soluble in any of the other buffers with or without chelates, regardless of pH. Electron microscopic images showed degraded FE-TA in some intracellular endosome/lysosomes between days 3 and 5. In the cellular environment, some of the FE-TA-containing endosomes were found to fuse with lysosomes, causing rapid dissociation at low pH and exposing the iron core to chelates that resulted in soluble Fe(III) within the lysosomes. The studies presented represent a first step in identifying the important cellular environmental parameters affecting the integrity of FE-TA complexes.