Systemic iron metabolism: a review and implications for brain iron metabolism

Mechanistic Insight into the Binding of Huperzine a with Human Transferrin: Computational, Spectroscopic and Calorimetric Approaches

Huperzine A (HupA), an alkaloid found in the club moss Huperzia Serrata, has been in use for centuries in Chinese traditional medicine to treat dementia owing to its ability to inhibit the cholinergic enzyme acetylcholinesterase (AChE), thus acting as an acetylcholinesterase inhibitor (AChEI). An imbalance of metal ions in the brain is linked to Alzheimer's disease (AD) pathology. Transferrin (Tf) is a crucial player in iron homeostasis, thus highlighting its significance in AD. This study explores the plausible binding of HupA with Tf using molecular docking, molecular dynamics (MD) simulation, and free energy landscape (FEL) analyses. The docking results show that HupA binds to the functionally active region of Tf by forming three hydrogen bonds with Thr392, Glu394, and Ser688 and several hydrophobic interactions. The MD simulation analyses show that HupA binding is stable with Tf, causing minimal changes to the protein conformation. Moreover, principal component analysis (PCA) and FEL also depict the stable binding of HupA with Tf without any significant fluctuations. Further, fluorescence-based binding suggested excellent binding affinity of HupA with Tf affirming in silico observations. Isothermal titration calorimetry (ITC) advocated the spontaneous binding of HupA with Tf. This study provides an insight into the binding mechanism of HupA with Tf, and overall, the results show that HupA, after required experimentations, can be a better therapeutic agent for treating AD while targeting Tf.

Intranasal administration of α-synuclein preformed fibrils triggers microglial iron deposition in the substantia nigra of Macaca fascicularis

Iron deposition is present in main lesion areas in the brains of patients with Parkinson's disease (PD) and an abnormal iron content may be associated with dopaminergic neuronal cytotoxicity and degeneration in the substantia nigra of the midbrain. However, the cause of iron deposition and its role in the pathological process of PD are unclear. In the present study, we investigated the effects of the nasal mucosal delivery of synthetic human α-synuclein (α-syn) preformed fibrils (PFFs) on the pathogenesis of PD in Macaca fascicularis. We detected that iron deposition was clearly increased in a time-dependent manner from 1 to 17 months in the substantia nigra and globus pallidus, highly contrasting to other brain regions after treatments with α-syn PFFs. At the cellular level, the iron deposits were specifically localized in microglia but not in dopaminergic neurons, nor in other types of glial cells in the substantia nigra, whereas the expression of transferrin (TF), TF receptor 1 (TFR1), TF receptor 2 (TFR2), and ferroportin (FPn) was increased in dopaminergic neurons. Furthermore, no clear dopaminergic neuron loss was observed in the substantia nigra, but with decreased immunoreactivity of tyrosine hydroxylase (TH) and appearance of axonal swelling in the putamen. The brain region-enriched and cell-type-dependent iron localizations indicate that the intranasal α-syn PFFs treatment-induced iron depositions in microglia in the substantia nigra may appear as an early cellular response that may initiate neuroinflammation in the dopaminergic system before cell death occurs. Our data suggest that the inhibition of iron deposition may be a potential approach for the early prevention and treatment of PD.

Iron and Ferroptosis as Therapeutic Targets in Alzheimer's Disease

Alzheimer's disease (AD), one of the most common neurodegenerative diseases worldwide, has a devastating personal, familial, and societal impact. In spite of profound investment and effort, numerous clinical trials targeting amyloid-β, which is thought to have a causative role in the disease, have not yielded any clinically meaningful success to date. Iron is an essential cofactor in many physiological processes in the brain. An extensive body of work links iron dyshomeostasis with multiple aspects of the pathophysiology of AD. In particular, regional iron load appears to be a risk factor for more rapid cognitive decline. Existing iron-chelating agents have been in use for decades for other indications, and there are preliminary data that some of these could be effective in AD. Many novel iron-chelating compounds are under development, some with in vivo data showing potential Alzheimer's disease-modifying properties. This heretofore underexplored therapeutic class has considerable promise and could yield much-needed agents that slow neurodegeneration in AD.

Airborne, Vehicle-Derived Fe-Bearing Nanoparticles in the Urban Environment: A Review

Airborne particulate matter poses a serious threat to human health. Exposure to nanosized (<0.1 μm), vehicle-derived particulates may be hazardous due to their bioreactivity, their ability to penetrate every organ, including the brain, and their abundance in the urban atmosphere. Fe-bearing nanoparticles (<0.1 μm) in urban environments may be especially important because of their pathogenicity and possible association with neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. This review examines current knowledge regarding the sources of vehicle-derived Fe-bearing nanoparticles, their chemical and mineralogical compositions, grain size distribution and potential hazard to human health. We focus on data reported for the following sources of Fe-bearing nanoparticles: exhaust emissions (both diesel and gasoline), brake wear, tire and road surface wear, resuspension of roadside dust, underground, train and tram emissions, and aircraft and shipping emissions. We identify limitations and gaps in existing knowledge as well as future challenges and perspectives for studies of airborne Fe-bearing nanoparticles.

Peroxiredoxin 5 prevents iron overload-induced neuronal death by inhibiting mitochondrial fragmentation and endoplasmic reticulum stress in mouse hippocampal HT-22 cells

Iron is an essential element for neuronal as well as cellular functions. However, Iron overload has been known to cause neuronal toxicity through mitochondrial fission, dysregulation of Ca²⁺, endoplasmic reticulum (ER) stress, and reactive oxygen species (ROS) production. Nevertheless, the precise mechanisms of iron-induced oxidative stress and mitochondria- and ER-related iron toxicity in neuronal cells are not fully understood. In this study, we demonstrated that iron overload induces ROS production earlier in the ER than in the mitochondria, and peroxiredoxin 5 (Prx5), which is a kind of antioxidant induced by iron overload, prevents iron overload-induced mitochondrial fragmentation mediated by contact with ER and translocation of Drp1, by inhibiting ROS production and calcium/calcineurin pathway in HT-22 mouse hippocampal neuronal cells. Moreover, Prx5 also prevented iron overload-induced ER-stress and cleavage of caspase-3, which consequently attenuated neuronal cell death. Therefore, we suggested that iron overload induces oxidative stress in the ER earlier than in the mitochondria, thereby increasing ER stress and calcium levels, and consequently causing mitochondrial fragmentation and neuronal cell death. So we thought that this study is essential for understanding iron toxicity in neurons, and Prx5 may serve as a new therapeutic target to prevent iron overload-induced diseases and neurodegenerative disorders.

Development of an iron-selective antioxidant probe with protective effects on neuronal function

Iron accumulation, oxidative stress and calcium signaling dysregulation are common pathognomonic signs of several neurodegenerative diseases, including Parkinson´s and Alzheimer’s diseases, Friedreich ataxia and Huntington’s disease. Given their therapeutic potential, the identification of multifunctional compounds that suppress these damaging features is highly desirable. Here, we report the synthesis and characterization of N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetamide, named CT51, which exhibited potent free radical neutralizing activity both in vitro and in cells. CT51 bound Fe²⁺ with high selectivity and Fe³⁺ with somewhat lower affinity. Cyclic voltammetric analysis revealed irreversible binding of Fe³⁺ to CT51, an important finding since stopping Fe²⁺/Fe³⁺ cycling in cells should prevent hydroxyl radical production resulting from the Fenton-Haber-Weiss cycle. When added to human neuroblastoma cells, CT51 freely permeated the cell membrane and distributed to both mitochondria and cytoplasm. Intracellularly, CT51 bound iron reversibly and protected against lipid peroxidation. Treatment of primary hippocampal neurons with CT51 reduced the sustained calcium release induced by an agonist of ryanodine receptor-calcium channels. These protective properties of CT51 on cellular function highlight its possible therapeutic use in diseases with significant oxidative, iron and calcium dysregulation.

Modulatory potential of resveratrol during lung inflammatory disease

Neutrophils are the first cells to achieve the sites of infection or inflammation in the lungs. The massive accumulation of these cells is associated with acute and chronic lung injury. Therefore, they have been implicated in the pathogenesis of many lung diseases through the release of reactive oxygen intermediates, proteolytic enzymes and Neutrophil Extracellular Traps (NETs). The excessive and continuous release of NETs, fibers composed by decondensed chromatin coated with neutrophil proteins, are associated to the impairment of lung function in different pathological settings. Flavonoids inhibit the respiratory burst of neutrophils in mammals. However, one of these flavonoids, resveratrol has a particular chemical property. It reduce Cu(II) to Cu(I) form with concomitant formation of reactive oxygen species, which can produce DNA breakage as reported in several in vitro models. We hypothesize that direct resveratrol administration in lungs can cleave DNA in NETs, improving lung function during acute airway infections or chronic inflammatory lung diseases. If the hypothesis is correct, the control of NET formation can be used to reduce the inflammatory environment in lung after neutrophil stimuli. Additionally, the production of proinflammatory cytokines by neutrophils could be also diminished by resveratrol administration. In this sense, this flavonoid provides a multifaceted opportunity for treatment of lung diseases with strong or chronic neutrophil activation.

Iron overload-induced calcium signals modulate mitochondrial fragmentation in HT-22 hippocampal neuron cells

Iron is necessary for neuronal functions; however, excessive iron accumulation caused by impairment of iron balance could damage neurons. Neuronal iron accumulation has been observed in several neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Nevertheless, the precise mechanisms underlying iron toxicity in neuron cells are not fully understood. In this study, we investigated the mechanism underlying iron overload-induced mitochondrial fragmentation in HT-22 hippocampal neuron cells that were incubated with ferric ammonium citrate (FAC). Mitochondrial fragmentation via dephosphorylation of Drp1 (Ser637) and increased apoptotic neuronal death were observed in FAC-stimulated HT-22 cells. Furthermore, the levels of intracellular calcium (Ca(2+)) were increased by iron overload. Notably, chelation of intracellular Ca(2+) rescued mitochondrial fragmentation and neuronal cell death. In addition, iron overload activated calcineurin through the Ca(2+)/calmodulin and Ca(2+)/calpain pathways. Pretreatment with the calmodulin inhibitor W13 and the calpain inhibitor ALLN attenuated iron overload-induced mitochondrial fragmentation and neuronal cell death. Therefore, these findings suggest that Ca(2+)-mediated calcineurin signals are a key player in iron-induced neurotoxicity by regulating mitochondrial dynamics. We believe that our results may contribute to the development of novel therapies for iron toxicity related neurodegenerative disorders.

Magnetic resonance imaging (MRI) to study striatal iron accumulation in a rat model of Parkinson's disease

Abnormal accumulation of iron is observed in neurodegenerative disorders. In Parkinson's disease, an excess of iron has been demonstrated in different structures of the basal ganglia and is suggested to be involved in the pathogenesis of the disease. Using the 6-hydroxydopamine (6-OHDA) rat model of Parkinson's disease, the edematous effect of 6-OHDA and its relation with striatal iron accumulation was examined utilizing in vivo magnetic resonance imaging (MRI). The results revealed that in comparison with control animals, injection of 6-OHDA into the rat striatum provoked an edematous process, visible in T2-weighted images that was accompanied by an accumulation of iron clearly detectable in T2*-weighted images. Furthermore, Prussian blue staining to detect iron in sectioned brains confirmed the existence of accumulated iron in the areas of T2* hypointensities. The presence of ED1-positive microglia in the lesioned striatum overlapped with this accumulation of iron, indicating areas of toxicity and loss of dopamine nerve fibers. Correlation analyses demonstrated a direct relation between the hyperintensities caused by the edema and the hypointensities caused by the accumulation of iron.

The antidepressant drug carbamazepine induces differential transcriptome expression in the brain of Atlantic salmon, Salmo salar

Concerns are being expressed recently over possible environmental effects of human pharmaceuticals. Although the likelihood of acute toxicity is low, the continuous discharge of pharmaceuticals into the aquatic environment means that sublethal effects on non-target organisms need to be seriously considered. One-year-old Atlantic salmon parr were exposed to 7.85±0.13μgL(-1) of the antidepressant drug Carbamazepine (CBZ) for five days to investigate changes of mRNA expression in the brain by means of a custom 17k Atlantic salmon cDNA microarray. The selected concentration is similar to upper levels that can be found in hospital and sewage treatment plant effluents. After treatment, 373 features were differently expressed with 26 showing up- or down-regulation of ≥2-fold (p≤0.05). Among the mRNAs showing the highest change were the pituitary hormones encoding features somatolactin, prolactin and somatotropin, or growth hormone. Functional enrichment and network analyses of up- and down-regulated genes showed that CBZ induced a highly different gene expression profile in comparison to untreated organisms. CBZ induced expression of essential genes of the focal adhesion and extracellular matrix - receptor interaction pathways most likely through integrin alpha-6 (itga6) activation. Negative regulation of apoptotic process, extracellular matrix organization and heme biosynthesis were the most enriched biological process related GO-terms, with the simultaneous enrichment of collagen and extracellular region related cellular component GO-terms, and extracellular matrix structural constituent, hormone activity and chromatin binding molecular function related GO-terms. These results show that relatively low doses of CBZ may affect brain physiology in exposed salmon parr, targeting similar processes as in human, indicating a high degree of conservation of targets of CBZ action. However, and since the mRNAs showing most changes in expression are critical for adaptation to different stressors and life history transitions in Atlantic salmon, more research should be undertaken to assess CBZ effects to avoid impairment of normal development and maintenance of natural populations.

Iron dysregulation in Huntington's disease

Huntington's disease (HD) is one of many neurodegenerative diseases with reported alterations in brain iron homeostasis that may contribute to neuropathogenesis. Iron accumulation in the specific brain areas of neurodegeneration in HD has been proposed based on observations in post-mortem tissue and magnetic resonance imaging studies. Altered magnetic resonance imaging signal within specific brain regions undergoing neurodegeneration has been consistently reported and interpreted as altered levels of brain iron. Biochemical studies using various techniques to measure iron species in human samples, mouse tissue, or in vitro has generated equivocal data to support such an association. Whether elevated brain iron occurs in HD, plays a significant contributing role in HD pathogenesis, or is a secondary effect remains currently unclear.

Iron and intracerebral hemorrhage: from mechanism to translation

Intracerebral hemorrhage (ICH) is a leading cause of morbidity and mortality around the world. Currently, there is no effective medical treatment available to improve functional outcomes in patients with ICH due to its unknown mechanisms of damage. Increasing evidence has shown that the metabolic products of erythrocytes are the key contributor of ICH-induced secondary brain injury. Iron, an important metabolic product that accumulates in the brain parenchyma, has a detrimental effect on secondary injury following ICH. Because the damage mechanism of iron during ICH-induced secondary injury is clear, iron removal therapy research on animal models is effective. Although many animal and clinical studies have been conducted, the exact metabolic pathways of iron and the mechanisms of iron removal treatments are still not clear. This review summarizes recent progress concerning the iron metabolism mechanisms underlying ICH-induced injury. We focus on iron, brain iron metabolism, the role of iron in oxidative injury, and iron removal therapy following ICH, and we suggest that further studies focus on brain iron metabolism after ICH and the mechanism for iron removal therapy.

Copper interactions with DNA of chromatin and its role in neurodegenerative disorders

In this study, we have demonstrated the conformational changes to DNA induced by abnormal interactions of copper using circular dichroism, in combination with UV-absorbance and fluorescence spectroscopy. Results confirm that binding of copper to bases of DNA in chromatin is concentration dependent. Binding efficiency of Cu²⁺ ions to DNA is increased in proportion to the degree of unwinding of the double helix induced by denaturation. Altered B-DNA conformation will alter the integrity of DNA which may affect the normal process of DNA replication and transcription. Copper induced DNA damage in the brain may cause neurotoxicity and the neuronal cell death and is implicated in Alzheimer's disease and other neurological disorders.

Expression and localization of duodenal cytochrome b in the rat hippocampus after kainate-induced excitotoxicity

Brain iron accumulation and oxidative stress are common features of many neurodegenerative diseases, and could be due in part to increased iron influx across the blood-brain interface. The iron transport protein, divalent metal transporter 1 (DMT1) is found in reactive astrocytes of the lesioned hippocampal CA fields after excitotoxicity induced by the glutamate analog kainate (KA), but in order for iron to be transported by DMT1, it must be converted from the ferric to the ferrous form. The present study was carried out to investigate the expression of a ferric reductase, duodenal cytochrome b (DCYTB), in the rat hippocampus after KA injury. Quantitative reverse transcriptase-polymerase chain reaction showed significant increases in DCYTB mRNA expression of 2.5, 2.7, and 5.2-fold in the hippocampus at 1week, 2weeks and 1month post-KA lesions respectively compared to untreated controls, and 3.0-fold compared to 1month post-saline injection. DCYTB-positive cells were double labeled with glial fibrillary acidic protein, and electron microscopy showed that the DCYTB-positive cells had dense bundles of glial filaments, characteristic of astrocytes, and were present as end-feet around unlabeled brain capillary endothelial cells. DMT1 labeling in astrocytes and increased iron staining were also observed in the lesioned hippocampus. Together, the present findings of DCYTB and DMT1 localization in astrocytes suggest that DCYTB is a ferric reductase for reduction of ferric iron, for transport by DMT1 into the brain. We postulate that the coordinated action of these two proteins could be important in iron influx across the blood-brain interface, in areas undergoing neurodegeneration.

Iron-induced damage in corpus striatal cells of neonatal rats: attenuation by folic acid

BACKGROUND

Iron supplementation is recommended during pregnancy to meet the needs of the rapidly growing fetus. However, its intake is associated with the generation of destructive free radicals, i.e., oxidative damage to the fetal brain. Folic acid supplementation is needed during pregnancy to reduce the risk of neural tube defects.

HYPOTHESIS

Intake of folic acid can ameliorate the morphological features of cell damage in the striatal tissue (brain of neonatal rats) associated with the intake of iron.

OBJECTIVES AND METHODS

To test this hypothesis, an animal model (pregnant Albino rats) was established. The animals were divided into three groups: group A, control animals treated with saline only; group B, animals treated with iron gluconate; and group C, animals treated concomitantly with iron gluconate and folic acid. The striatal brain tissues of the neonates were examined for features of cellular damage, using immunohistological and ultrastructural methods.

RESULTS

The authors found significant variations among the three groups. The intake of iron (group B) and its deposition in the striatal tissue (neurons and glial cells) was associated with changes indicative of both cellular injury and regeneration. The former includes neuronal apoptosis and necrosis, and destruction of the organelles, including the mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes of the neurons and glial cells. The latter includes microgliosis, astrogliosis, upregulation of glial fibrillary acidic protein, and inducible nitric oxide synthase. These changes were absent in the striatal tissue of the control group (group A) and in animals treated concomitantly with both iron gluconate and folic acid (group C).

CONCLUSION

Intake of folic acid can protect the neonatal striatal tissue against iron-induced oxidative stress damage.

Olfactory ferric and ferrous iron absorption in iron-deficient rats

The absorption of metals from the nasal cavity to the blood and the brain initiates an important route of occupational exposures leading to health risks. Divalent metal transporter-1 (DMT1) plays a significant role in the absorption of intranasally instilled manganese, but whether iron uptake would be mediated by the same pathway is unknown. In iron-deficient rats, blood (59)Fe levels after intranasal administration of the radioisotope in the ferrous form were significantly higher than those observed for iron-sufficient control rats. Similar results were obtained when ferric iron was instilled intranasally, and blood levels of (59)Fe were even greater in the iron-deficient rats compared with the amount of ferrous iron absorbed. Experiments with Belgrade (b/b) rats showed that DMT1 deficiency limited ferric iron uptake from the nasal cavity to the blood compared with +/b controls matched for iron deficiency. These results indicate that olfactory uptake of ferric iron by iron-deficient rats involves DMT1. Western blot experiments confirmed that DMT1 levels are significantly higher in iron-deficient rats compared with iron-sufficient controls in olfactory tissue. Thus the molecular mechanism of olfactory iron absorption is regulated by body iron status and involves DMT1.

The role of iron as a mediator of oxidative stress in Alzheimer disease

Iron is both essential for maintaining a spectrum of metabolic processes in the central nervous system and elsewhere, and potent source of reactive oxygen species. Redox balance with respect to iron, therefore, may be critical to human neurodegenerative disease but is also in need of better understanding. Alzheimer disease (AD) in particular is associated with accumulation of numerous markers of oxidative stress; moreover, oxidative stress has been shown to precede hallmark neuropathological lesions early in the disease process, and such lesions, once present, further accumulate iron, among other markers of oxidative stress. In this review, we discuss the role of iron in the progression of AD.

Influence of Iron Deficiency on Olfactory Behavior in Weanling Rats

Chronically high occupational exposure to airborne metals like iron can impair olfactory function, but little is known about how low iron status modifies olfactory behavior. To investigate the influence of body iron status, weanling rats were fed a diet with low iron content (4 - 7 ppm) to induce iron deficiency anemia and olfactory behavior was compared to control rats fed an isocaloric diet sufficient in iron (210 - 220 ppm). Iron-deficient rats had prolonged exploratory time for attractive odorants in behavioral olfactory habituation/dis-habituation tests, olfactory preference tests and olfactory sensitivity tests compared with control rats. No significant differences were observed for aversive odorants between the two groups. These findings suggest that iron-dependent functions may be involved in controlling and processing of olfactory signal transduction via self and lateral inhibition such that odorant signal remains stronger for longer times prolonging exploratory activity on attractive odorants in the behavioral tests. These findings establish that iron deficiency can modify olfactory behavior.

A pilot trial of deferiprone for neurodegeneration with brain iron accumulation

Deferiprone was shown to reverse iron deposition in Friedreich's ataxia. This multi-center, unblinded, single-arm pilot study evaluated safety and efficacy of deferiprone for reducing cerebral iron accumulation in neurodegeneration with brain iron accumulation. Four patients with genetically-confirmed pantothenate kinase-associated neurodegeneration, and 2 with parkinsonism and focal dystonia, but inconclusive genetic tests, received 15 mg/kg deferiprone bid. Magnetic resonance imaging and neurological examinations were conducted at baseline, six and 12 months. Chelation treatment caused no apparent hematologic or neurological side effects. Magnetic resonance imaging revealed decreased iron accumulation in the globus pallidus of 2 patients (one with pantothenate kinase-associated neurodegeneration). Clinical rating scales and blinded video rating evaluations documented mild-to-moderate motor improvement in 3 patients (2 with pantothenate kinase-associated neurodegeneration). These results underline the safety and tolerability of deferiprone, and suggest that chelating treatment might be effective in improving neurological manifestations associated with iron accumulation. (Clinicaltrials.gov Identifier: NTC00907283).

Iron and mechanisms of neurotoxicity

The accumulation of transition metals (e.g., copper, zinc, and iron) and the dysregulation of their metabolism are a hallmark in the pathogenesis of several neurodegenerative diseases. This paper will be focused on the mechanism of neurotoxicity mediated by iron. This metal progressively accumulates in the brain both during normal aging and neurodegenerative processes. High iron concentrations in the brain have been consistently observed in Alzheimer's (AD) and Parkinson's (PD) diseases. In this connection, metalloneurobiology has become extremely important in establishing the role of iron in the onset and progression of neurodegenerative diseases. Neurons have developed several protective mechanisms against oxidative stress, among them, the activation of cellular signaling pathways. The final response will depend on the identity, intensity, and persistence of the oxidative insult. The characterization of the mechanisms mediating the effects of iron-induced increase in neuronal dysfunction and death is central to understanding the pathology of a number of neurodegenerative disorders.

Iron, the retina and the lens: a focused review

This review is focused on iron metabolism in the retina and in the lens and its relation to their respective age-related pathologies, macular degeneration (AMD) and cataract (ARC). Several aspects of iron homeostasis are considered first in the retina and second in the lens, paying particular attention to the transport of iron through the blood-retinal barrier and through the lens epithelial cell barrier, to the immunochemistry of iron-related proteins and their expression in both the retina and the lens, and to the nature of the photochemical damage caused by UV light on both tissues. A comparative overview of some iron related parameters (total iron, transferrin (Tf), transferrin saturation and total iron binding capacity), in plasma and ocular tissues and fluids of three animal species is also presented. Based on results selected from the literature reviewed, and our own results, a scheme for the overall circulation of iron within and out of the eye is proposed, in which, (i) iron is pumped from the retina to the vitreous body by a ferroportin/ferroxidase-mediated process at the endfeet of Müller cells, (ii) vitreal Tf binds this iron and the complex diffuses towards the lens, (iii) the iron/Tf complex is incorporated into the lens extracellular space probably at the lens equator and moves to the epithelial-fiber interface, (iv) upon interaction with Tf receptors of the apical pole of lens epithelial cells, the iron/Tf complex is endocytosed and iron is exported as Fe(3+) by a ferroportin/ferroxidase-mediated process taking place at the basal pole of the epithelial cells, and (v) Fe(3+) is bound to aqueous humor Tf and drained with the aqueous humor into systemic blood circulation for recycling. The proposed scheme represents an example of close cooperation between the retina and the lens to maintain a constant flow of iron within the eye that provides an adequate supply of iron to ocular tissues and secures the systemic recycling of this element. It does not discount the existence of additional ways for iron to leave the eye through the blood-retinal barrier. In this review both AMD and ARC are recognized as multifactorial diseases with an important photoxidative component, and exhibiting a remarkable similitude of altered local iron metabolism. The epidemiological relationship between ARC and ferropenic anemia is explained on the basis that hepcidin, the hormone responsible for the anemia of chronic inflammation, could paradoxically cause intracellular iron overload in the lens by interfering with the proposed ferroportin/ferroxidase-mediated export of iron at the basal side of the anterior lens epithelium. Other authors have suggested that a similar situation is created in the retina in the case of AMD.

Metabolic crossroads of iron and copper

Interactions between the essential dietary metals, iron and copper, have been known for many years. This review highlights recent advances in iron-copper interactions with a focus on tissues and cell types important for regulating whole-body iron and copper homeostasis. Cells that mediate dietary assimilation (enterocytes) and storage and distribution (hepatocytes) of iron and copper are considered, along with the principal users (erythroid cells) and recyclers of red cell iron (reticuloendothelial macrophages). Interactions between iron and copper in the brain are also discussed. Many unanswered questions regarding the role of these metals and their interactions in health and disease emerge from this synopsis, highlighting extensive future research opportunities.

Human hephaestin expression is not limited to enterocytes of the gastrointestinal tract but is also found in the antrum, the enteric nervous system, and pancreatic {beta}-cells

Hephaestin (Hp) is a membrane protein with ferroxidase activity that converts Fe(II) to Fe(III) during the absorption of nutritional iron in the gut. Using anti-peptide antibodies to predicted immunogenic regions of rodent Hp, previous immunocytochemical studies in rat, mouse, and human gut tissues localized Hp to the basolateral membranes of the duodenal enterocytes where the Hp was predicted to aid in the transfer of Fe(III) to transferrin in the blood. We used a recombinant soluble form of human Hp to obtain a high-titer polyclonal antibody to Hp. This antibody was used to identify the intracellular location of Hp in human gut tissue. Our immunocytochemical studies confirmed the previous localization of Hp in human enterocytes. However, we also localized Hp to the entire length of the gastrointestinal tract, the antral portion of the stomach, and to the enteric nervous system (both the myenteric and submucous plexi). Hp was also localized to human pancreatic beta-cells. In addition to its expression in the same cells as Hp, ferroportin was also localized to the ductal cells of the exocrine pancreas. The localization of the ferroxidase Hp to the neuronal plexi and the pancreatic beta cells suggests a role for the enzymatic function of Hp in the protection of these specialized cell types from oxidative damage.

mRNA expression of proteins involved in iron homeostasis in brain regions is altered by age and by iron overloading in the neonatal period

Abnormally high levels of iron are observed in the brain of patients suffering from neurodegenerative disorders. The mechanisms involved in iron accumulation in neurodegenerative disorders remain poorly understood. In the present study we investigated the effects of aging and neonatal iron overload on the mRNA expression of proteins critically involved in controlling iron homeostasis. Wistar rat pups received a single daily dose of vehicle or iron (10 mg/kg of b.w. of Fe(2+)), at postnatal days 12-14. The expression of Transferrin Receptor (TfR), H-Ferritin, and IRP2 were analyzed by a semi-quantitative reverse transcriptase polymerase chain reaction assay in cortex, hippocampus and striatum of rats sacrificed at three different ages (15-day-old; 90-day-old and 2-year old rats). Results indicate that TfR, H-ferritin, and IRP2 mRNA expression was differentially affected by aging and by neonatal iron treatment in all three brain regions. These findings might have implications for the understanding of iron homeostasis misregulation associated with neurodegenerative disorders.

Brain and retinal ferroportin 1 dysregulation in polycythaemia mice

Disruption of iron homeostasis within the central nervous system (CNS) can lead to profound abnormalities during both development and aging in mammals. The radiation-induced polycythaemia (Pcm) mutation, a 58-bp microdeletion in the promoter region of ferroportin 1 (Fpn1), disrupts transcriptional and post-transcriptional regulation of this pivotal iron transporter. This regulatory mutation induces dynamic alterations in peripheral iron homeostasis such that newborn homozygous Pcm mice exhibit iron deficiency anemia with increased duodenal Fpn1 expression while adult homozygotes display decreased Fpn1 expression and anemia despite organismal iron overload. Herein we report the impact of the Pcm microdeletion on iron homeostasis in two compartments of the central nervous system: brain and retina. At birth, Pcm homozygotes show a marked decrease in brain iron content and reduced levels of Fpn1 expression. Upregulation of transferrin receptor 1 (TfR1) in brain microvasculature appears to mediate the compensatory iron uptake during postnatal development and iron content in Pcm brain is restored to wild-type levels by 7 weeks of age. Similarly, changes in expression are transient and expression of Fpn1 and TfR1 is indistinguishable between Pcm homozygotes and wild-type by 12 weeks of age. Strikingly, the adult Pcm brain is effectively protected from the peripheral iron overload and maintains normal iron content. In contrast to Fpn1 downregulation in perinatal brain, the retina of Pcm homozygotes reveals increased levels of Fpn1 expression. While retinal morphology appears normal at birth and during early postnatal development, adult Pcm mice demonstrate a marked, age-dependent loss of photoreceptors. This phenotype demonstrates the importance of iron homeostasis in retinal health.

Genetic analysis of heme oxygenase-1 (HO-1) in German Parkinson's disease patients

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons and the presence of intracytoplasmic inclusions (Lewy bodies). Iron, which is elevated in the substantia nigra (SN) of PD patients, seems to be of pivotal importance, because of its capacity to enhance the amplification of reactive-oxygen species. Therefore, it is tempting that the iron-releasing key enzyme in heme catabolism, heme oxygenase-1 (HO-1), may represent a candidate for a genetic susceptibility to PD. In the current study, we examined a (GT)n fragment length polymorphism in the promoter region, as well as three coding SNPs in the HO-1 gene in order to assess if certain genotypes are associated with PD. Furthermore, peripheral blood expression levels of HO-1 in PD patients and healthy probands were compared. However, our analyses did not reveal a significant association of these genetic markers in the HO-1 gene with an increased susceptibility to PD.

A model for the analysis of competitive relaxation effects of manganese and iron in vivo

Manganese (Mn) and iron (Fe) are both paramagnetic species that can affect magnetic resonance relaxation rates. They also share common transport systems in vivo and thus in experimental models of metal exposure their effects on relaxation rates may interact in a complex fashion. Here we present a novel model to interpret the combined effects of Mn and Fe on MRI relaxation rates. To achieve varying levels of both metals, adult rats were separated into four groups; a control group and three groups treated with weekly intravenous injections of 3 mg Mn/kg body for 14 weeks. The three treated groups were fed either a normal diet, Fe deficient or Fe enriched diet. All rats were scanned using MRI at the 14th week to measure regional water relaxation rates. Rat brains were removed at the end of the study (14th week) and dissected into regions for measurement of Mn and Fe by atomic absorption spectroscopy. For the normal diet groups, R(1) was strongly correlated with tissue Mn concentrations. However, the slopes of the linear regression fits varied significantly among different brain regions, and a simple linear model failed to explain the changes in relaxation rate when both Mn and Fe contents changed. We propose a competition model, which is based on the ability of Mn and Fe to compete in vivo for common binding sites. The combined effect of Mn and Fe on the relaxation rates is complicated and additional studies will be necessary to explain how MRI signals are affected when the levels of both metals are varied.

Ceruloplasmin alters the tissue disposition and neurotoxicity of manganese, but not its loading onto transferrin

Manganese (Mn) is a redox-active element, and whereas its uptake, disposition, and toxicity in mammals may depend in part on its oxidation state, the proteins affecting manganese oxidation state and speciation in vivo are not well known. Studies have suggested that the oxidase protein ceruloplasmin (Cp) mediates iron and manganese oxidation and loading onto plasma transferrin (Tf), as well as cellular iron efflux. We hypothesized that ceruloplasmin may also affect the tissue distribution and eventual neurotoxicity of manganese. To test this, aceruloplasminemic versus wild-type mice were treated with a single i.p. (54)Mn tracer dose, or elevated levels of manganese subchronically (0, 7.5, or 15 mg Mn/kg s.c., three doses per week for 4 weeks), and evaluated for transferrin-bound manganese, blood manganese partitioning, tissue manganese disposition, and levels of brain glutathione, thiobarbituric acid reactive substances (TBARS), and protein carbonyls as measures of oxidative stress, and open arena activity. Results show that ceruloplasmin does not play a role in the loading of manganese onto plasma transferrin in vivo, or in the partitioning of manganese between the plasma and cellular fractions of whole blood. Ceruloplasmin did, however, affect the retention of manganese in blood and its distribution to tissues, most notably kidney and to a lesser extent brain and lung. Results also indicate that ceruloplasmin interacted with chronic elevated manganese exposures to produce greater levels of brain oxidative stress. These results provide evidence that metal oxidase proteins play an important role in altering neurotoxicity arising from elevated manganese exposures.

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.

Iron: the Redox-active center of oxidative stress in Alzheimer disease

Although iron is essential in maintaining the function of the central nervous system, it is a potent source of reactive oxygen species. Excessive iron accumulation occurs in many neurodegenerative diseases including Alzheimer disease (AD), Parkinson's disease, and Creutzfeldt-Jakob disease, raising the possibility that oxidative stress is intimately involved in the neurodegenerative process. AD in particular is associated with accumulation of numerous markers of oxidative stress; moreover, oxidative stress has been shown to precede hallmark neuropathological lesions early in the disease process, and such lesions, once present, further accumulate iron, among other markers of oxidative stress. In this review, we discuss the role of iron in the progression of AD.

Hypoxia inducible factor prolyl 4-hydroxylase enzymes: center stage in the battle against hypoxia, metabolic compromise and oxidative stress

Studies of adaptive mechanisms to hypoxia led to the discovery of the transcription factor called hypoxia inducible factor (HIF). HIF is a ubiquitously expressed, heterodimeric transcription factor that regulates a cassette of genes that can provide compensation for hypoxia, metabolic compromise, and oxidative stress including erythropoietin, vascular endothelial growth factor, or glycolytic enzymes. Diseases associated with oxygen deprivation and consequent metabolic compromise such as stroke or Alzheimer's disease may result from inadequate engagement of adaptive signaling pathways that culminate in HIF activation. The discovery that HIF stability and activation are governed by a family of dioxygenases called HIF prolyl 4 hydroxylases (PHDs) identified a new target to augment the transcriptional activity of HIF and thus the adaptive machinery that governs neuroprotection. PHDs lose activity when cells are deprived of oxygen, iron or 2-oxoglutarate. Inhibition of PHD activity triggers the cellular homeostatic response to oxygen and glucose deprivation by stabilizing HIF and other proteins. Herein, we discuss the possible role of PHDs in regulation of both HIF-dependent and -independent cell survival pathways in the nervous system with particular attention to the co-substrate requirements for these enzymes. The emergence of neuroprotective therapies that modulate genes capable of combating metabolic compromise is an affirmation of elegant studies done by John Blass and colleagues over the past five decades implicating altered metabolism in neurodegeneration.

Iron metabolism in Parkinsonian syndromes

Growing evidence suggests an involvement of iron in the pathophysiology of neurodegenerative diseases. Several of the diseases are associated with parkinsonian syndromes, induced by degeneration of basal ganglia regions that contain the highest amount of iron within the brain. The group of neurodegenerative disorders associated with parkinsonian syndromes with increased brain iron content can be devided into two groups: (1) parkinsonian syndromes associated with brain iron accumulation, including Parkinson's disease, diffuse Lewy body disease, parkinsonian type of multiple system atrophy, progressive supranuclear palsy, corticobasal ganglionic degeneration, and Westphal variant of Huntington's disease; and (2) monogenetically caused disturbances of brain iron metabolism associated with parkinsonian syndromes, including aceruloplasminemia, hereditary ferritinopathies affecting the basal ganglia, and panthotenate kinase associated neurodegeneration type 2. Although it is still a matter of debate whether iron accumulation is a primary cause or secondary event in the first group, there is no doubt that iron-induced oxidative stress contributes to neurodegeneration. Parallels concerning pathophysiological as well as clinical aspects can be drawn between disorders of both groups. Results from animal models and reduction of iron overload combined with at least partial relief of symptoms by application of iron chelators in patients of the second group give hope that targeting the iron overload might be one possibility to slow down the neurodegenerative cascade also in the first group of inevitably progressive neurodegenerative disorders.

NMDA receptor-nitric oxide transmission mediates neuronal iron homeostasis via the GTPase Dexras1

Dexras1 is a 30 kDa G protein in the Ras subfamily whose discovery was based on its pronounced inducibility by the glucocorticoid dexamethasone. It binds to neuronal nitric oxide synthase (nNOS) via the adaptor protein CAPON, eliciting S-nitrosylation and activation of Dexras1. We report that Dexras1 binds to the peripheral benzodiazepine receptor-associated protein (PAP7), a protein of unknown function that binds to cyclic AMP-dependent protein kinase and the peripheral benzodiazepine receptor. PAP7 in turn binds to the divalent metal transporter (DMT1), an iron import channel. We have identified a signaling cascade in neurons whereby stimulation of NMDA receptors activates nNOS, leading to S-nitrosylation and activation of Dexras1, which, via PAP7 and DMT1, physiologically induces iron uptake. As selective iron chelation prevents NMDA neurotoxicity in cortical cultures, the NMDA-NO-Dexras1-PAP7-DMT1-iron uptake signaling cascade also appears to mediate NMDA neurotoxicity.

Upregulation of DMT1 expression in choroidal epithelia of the blood-CSF barrier following manganese exposure in vitro

Divalent metal transporter 1 (DMT1), whose mRNA possesses a stem-loop structure in 3'-untranslated region, has been identified in most organs and responsible for transport of various divalent metal ions. Previous work from this laboratory has shown that manganese (Mn) exposure alters the function of iron regulatory protein (IRP) and increases iron (Fe) concentrations in the cerebrospinal fluid (CSF). This study was designed to test the hypothesis that Mn treatment, by acting on protein-mRNA binding between IRP and DMT1 mRNA, altered the expression of DMT1 in an immortalized choroidal epithelial Z310 cell line which was derived from rat choroid plexus epithelia, leading to a compartmental shift of Fe from the blood to the CSF. Immunocytochemistry confirmed the presence of DMT1 in Z310 cell. Following in vitro exposure to Mn at 100 microM for 24 and 48 h, the expression of DMT1 mRNA in Z310 cells was significantly increased by 45.4% (P < 0.05) and 78.1% (P < 0.01), respectively, as compared to controls. Accordingly, Western blot analysis revealed a significant increase of DMT1 protein concentrations at 48 h after Mn exposure (100 microM). Electrophoretic mobility shift assay (EMSA) showed that Mn exposure increased binding of IRP to DMT1 mRNA in cultured choroidal Z310 cells. Moreover, real-time RT-PCR revealed no changes in DMT1 heterogeneous nuclear RNA (hnRNA) levels following Mn exposure. These data suggest that Mn appears to stabilize the binding of IRP to DMT1 mRNA, thereby increasing the expression of DMT1. The facilitated transport of Fe by DMT1 at the blood-CSF barrier may partly contribute to Mn-induced neurodegenerative Parkinsonism.

Neurochemical investigations of dopamine neuronal systems in iron-regulatory protein 2 (IRP-2) knockout mice

Abnormal iron accumulations are frequently observed in the brains of patients with Parkinson's disease and in normal aging. Iron metabolism is regulated in the CNS by iron regulatory proteins (IRP-1 and IRP-2). Mice engineered to lack IRP-2 develop abnormal motoric behaviors including tremors at rest, abnormal gait, and bradykinesia at middle to late age (18 to 24 months). To further characterize the dopamine (DA) systems of IRP-2 -/- mice, we harvested CNS tissue from age-matched wild type and IRP-2 -/- (16-19 months) and analyzed the protein levels of tyrosine hydroxylase (TH), dopamine transporter (DAT), vesicular monoamine transporter (VMAT2), and DA levels in dorsal striatum, ventral striatum (including the core and shell of nucleus accumbens), and midbrain. We further analyzed the phosphorylation of TH in striatum at serine 40, serine 31, and serine 19. In both dorsal and ventral striatum of IRP-2 knockout mice, there was a 20-25% loss of TH protein and accompanied by a approximately 50% increase in serine 40 phosphorylation above wild-type levels. No change in serine 31 phosphorylation was observed. In the ventral striatum, there was also a significant loss (approximately 40%) of DAT and VMAT2. Levels of DA were decreased (approximately 20%) in dorsal striatum, but turnover of DA was also elevated ( approximately 30%) in dorsal striatum of IRP-2 -/- mice. We conclude that iron misregulation associated with the loss of IRP-2 protein affects DA regulation in the striatum. However, the modest loss of DA and DA-regulating proteins does not reflect the pathology of PD or animal models of PD. Instead, these observations support that the IRP-2 -/- genotype may enable neurobiological events associated with aging.

NADPH oxidase inhibitor diphenyliodonium abolishes lipopolysaccharide-induced down-regulation of transferrin receptor expression in N2a and BV-2 cells

The activation of cellular inflammatory response is tightly linked to induced production of reactive oxygen species (ROS) and nitric oxide (NO), which in turn have been identified as important regulators of cellular iron metabolism. In the present study, we have used the microglia cell line BV-2 and the neuroblastoma cell line N2a to study the regulatory effects of the microbial agent lipopolysaccharide (LPS) on the expression of the transferrin receptor (TfR) and ferritin in cell lines with different characteristics. The receptor mainly responsible for LPS recognition is the Toll-like receptor 4 (TLR4) that triggers a variety of intracellular signalling cascades leading to the induction of transcription of target genes involved in the innate immune response. Among the pathways to be activated is the MAPK cascade leading to the activation of nuclear factor-kappaB that induces transcription of a variety of genes, e.g., inducible nitric oxide synthase (iNOS). The TLR4-mediated LPS response also induces the production of ROS through a mechanism(s) suggested to involve the activation of NADPH oxidase(s). This study shows that exposure of BV-2 and N2a cells to LPS results in decreased TfR protein levels and increased H-ferritin mRNA levels. The LPS down-regulatory effect on TfR protein expression is abolished by the NADPH oxidase inhibitor diphenyliodonium (DPI) but is not affected by the free radical scavenger N-acetyl-L-cysteine (NAC) or the iNOS inhibitor aminoguanidine (AG). The increased H-ferritin mRNA levels in response to LPS are not affected by DPI, NAC, or AG.

Upregulation of iron regulatory proteins and divalent metal transporter-1 isoforms in the rat hippocampus after kainate induced neuronal injury

Iron regulatory proteins (IRP1 and IRP2) bind to iron response elements (IRE) on specific mRNAs, to affect the translation of many proteins involved in iron metabolism. An increase in iron levels and divalent metal transporter-1 (DMT1) expression have been observed in the rat hippocampus after excitotoxic injury induced by kainate, but thus far, it is not known whether these could be associated with changes in IRPs. The present study was therefore carried out to elucidate the expression of IRP1 or IRP2 and the IRE or non-IRE forms of DMT1 (DMT1 or -IRE DMT1) in the hippocampus after neuronal injury induced by kainate. A sustained upregulation of IRP1, IRP2, DMT1 and -IRE DMT1 protein was detected in the lesioned hippocampus by western blot and immunohistochemical analyses up to 2 months post-injection. Double immunofluorescence labeling showed that IRP1, IRP2, DMT1 and -IRE DMT1 were mostly expressed in GFAP positive astrocytes. The increased IRP expression could lead to increased expression of the +IRE form of DMT1. On the other hand, the increased expression of the -IRE DMT1 indicates that IRPs are unlikely to be only factor determining the expression of DMT1. It is postulated that transcription factors acting on putative AP-1, NF-kappaB binding sites, or gamma-interferon responsive elements on the DMT1 promoter may also play a role in upregulating the expression of the transporter. This could lead to increased iron influx into the brain areas undergoing neurodegeneration, and might be a factor contributing to neuronal damage after the initial excitotoxic injury.

Iron loading inhibits ferroportin1 expression in PC12 cells

Ferroportin1 (FP1 or MTP1/IREG1), the product of the SLC40A1 gene, is a main iron export protein in mammals. Its mRNA contains an iron response element (IRE) in its 5' untranslated region, but the way this gene is regulated by iron is still unclear. The existence of FP1 in the brain has been recently confirmed. To better understand the role of this important transmembrane iron exporter in brain iron homeostasis, we investigated the effects of iron and nitric oxide (NO) on FP1 expression and that of a FP1 antibody on iron release in nerve growth factor-treated rat PC12 cells. We found that FP1 expression was down-regulated by iron loading but stimulated by iron chelation and treatment with a NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In addition, a significant decrease in iron release was found in cells treated with a FP1 antibody. Our findings imply that regulation of FP1 by iron in the cells is at the transcriptional level, rather than by an IRE/IRP-mediated pathway. Based on our results and published data, it is suggested that the transcriptional and translational (IRP/IRE pathway) mechanisms of FP1 expression might both operate in a tissue-specific manner and that FP1 might have a role in iron export from PC12 cells.

Heme regulation in traumatic brain injury: relevance to the adult and developing brain

Intracranial bleeding is one of the most prominent aspects in the clinical diagnosis and prognosis of traumatic brain injury (TBI). Substantial amounts of blood products, such as heme, are released because of traumatic subarachnoid hemorrhages, intraparenchymal contusions, and hematomas. Despite this, surprisingly few studies have directly addressed the role of blood products, in particular heme, in the setting of TBI. Heme is degraded by heme oxygenase (HO) into three highly bioactive products: iron, bilirubin, and carbon monoxide. The HO isozymes, in particular HO-1 and HO-2, exhibit significantly different expression patterns and appear to have specific roles after injury. Developmentally, differences between the adult and immature brain have implications for endogenous protection from oxidative stress. The aim of this paper is to review recent advances in the understanding of heme regulation and metabolism after brain injury and its specific relevance to the developing brain. These findings suggest novel clinical therapeutic options for further translational study.

Increased expression of ferritin, an iron-storage protein, in specific regions of the parahippocampal cortex of epileptic rats

PURPOSE

Iron accumulation in the brain has been associated with neurodegenerative disorders, including epilepsy. In our previous SAGE study, we showed that ferritin, an iron-storage protein, was one of the genes (Ferritin-H) that showed overexpression before the chronic epileptic phase. In this study we used ferritin as indicator for disturbed iron homeostasis to acquire insight into whether this could play a role in the pathogenesis of temporal lobe epilepsy.

METHODS

With immunocytochemistry, we studied the regional and cellular distribution of ferritin protein in an animal model for temporal lobe epilepsy in which spontaneous seizures develop a few weeks after electrically induced status epilepticus (SE).

RESULTS

Increased ferritin expression was observed in regions known to be vulnerable to cell death, mainly in reactive microglial cells of epileptic rats. Ferritin expression after SE was initially high, especially throughout the hippocampus, but decreased over time. In the chronic epileptic phase, it was still upregulated in regions where extensive cell loss occurs during the early acute and latent period. Within the parahippocampal region, the most persistent ferritin overexpression was present in microglial cells in layer III of the medial entorhinal area. The upregulation was most extensive in rats that had developed a progressive form of epilepsy with frequent seizures (approximately five to 10 seizures per day).

CONCLUSIONS

The fact that ferritin upregulation is still present in specific limbic regions in chronic epileptic rats, when neuronal loss is absent or minimal, suggests a role of iron in the pathogenesis and progression of epilepsy.

Expression of the sulfhydryl oxidase ALR (Augmenter of Liver Regeneration) in adult rat brain

Mammalian Augmenter of Liver Regeneration protein (ALR) was first identified as a secondary growth factor involved in liver regeneration. Its sulfhydryl oxidase activity and involvement in iron homeostasis have been recently demonstrated. ALR is expressed in a broad range of peripheral organs, and initial experiments gave also evidence for the occurrence of this protein in brain. In the present study, we investigated in detail the expression of ALR in rat brain sections and determined its cellular and subcellular localizations using biomolecular and immunohistochemical procedures. As shown by Northern blot, ALR is differentially expressed throughout the rat brain, with the highest mRNA levels in the cerebellum and diencephalon. High protein levels were also detected in the brain and cerebellum by Western blot. ALR immunoreactivity was found in neurons and glial cells throughout brain rostrocaudal extent. Labeled astrocytes were particularly abundant in the white matter, and immunoreactive neurons were observed in several regions including the olfactory bulb, isocortex, hippocampal formation, amygdala, thalamus, hypothalamus, some nuclei of the brainstem and cerebellum. In neurons, immunoelectron microscopy showed the protein in the nucleus and mainly in mitochondria. These subcellular localizations may correlate with the occurrence of two ALR protein isoforms in the brain. In the central nervous system, the enzyme might be of importance in heavy metal homeostasis whose dysregulation can induce neurodegenerative disorders.

Differential expression of divalent metal transporter DMT1 (Slc11a2) in the spermatogenic epithelium of the developing and adult rat testis

Iron is essential for male fertility, and disruptions in iron balance lead to impairment of testicular function. The divalent metal transporter DMT1 is a key modulator of transferrin- and non-transferrin-bound iron homeostasis. As a first step in determining the role of DMT1 in the testis, we have characterized the pattern of DMT1 expression in the developing and adult rat testis. Northern blot analysis and RT-PCR of testis polyadenylated RNA revealed the presence of iron-responsive element (IRE) and non-IRE transcripts. Semiquantitative immunoblotting of immature and adult rat testis uncovered the expression of two distinct DMT1 protein species. Immunohistochemistry showed that DMT1 was widespread throughout each seminiferous tubule and was expressed in the intracellular compartment. In the adult rat testis, DMT1 was immunolocalized to both the Sertoli and germ cells. In contrast to the immature testis, expression was dependent on the stage of the spermatogenic cycle. DMT1 was not detected on any plasma membranes in either the developing or the adult testis, suggesting that DMT1 is not primarily responsible for translocating iron across this epithelium. Our data suggest an important role for DMT1 in intracellular iron handling during spermatogenesis and imply that germ cells have a need for a precisely targeted and timed supply of iron. We suggest that DMT1 may, as it does in other tissues, play a role in transporting iron between intracellular compartments and thus may play an important role in male fertility.

Hereditary haemochromatosis is unlikely to cause movement disorders--a critical review

Hereditary haemochromatosis (HH) is a common autosomal recessive systemic iron overload disorder in which CNS manifestations, particularly movement disorders, have been reported. We report a 63-year-old woman with familial HH with a four-year history of progressive gait disturbance, chorea, and mild cervical and laryngeal dystonia. Her movement disorder was thought to be related to the haemochromatosis. On further investigation, analysis for the Huntington's disease expansion was positive. A review of the seven published cases of movement disorders associated with HH as well as data concerning brain iron deposition in this condition leads us to debate the causal link between movement disorders and HH. We suggest that movement disorders are rare in association with HH, and that such patients should be thoroughly investigated for another cause for their movement disorder.

Genetic contributions to Parkinson's disease

Sporadic Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [alpha-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin-proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinson's disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinson's disease. The identification of multiple genes predisposing to Parkinson's disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.

Neurodegenerative disease and iron storage in the brain

PURPOSE OF REVIEW

Iron is very important for normal regulation of various metabolic pathways. Neurons store iron in the form of ferrous ion or neuromelanin. In specific disorders the axonal transport of iron is impaired, leading to iron deposition which in the presence of reactive oxygen species results in neurodegeneration.

RECENT FINDINGS

Recent developments in genetics, including the finding of mutations in the pantothenate kinase gene and ferritin light chain gene, have demonstrated a direct relationship between the presence of a mutation in the iron-regulatory pathways and iron deposition in the brain resulting in neurodegeneration. These two disorders now add to our understanding of the mechanism of disease due to dysfunction of iron-regulatory pathways. In addition to these disorders there may be several other mutations of iron-regulatory genes or related genes that are yet to be found. The animal models of disease have also added value to this area.

SUMMARY

In this review we provide a summary of recent developments in the field of movement disorders with abnormalities in iron transport, and the current evidence in neurodegenerative disorders such as Parkinson's disease.