Expression of Iron-Related Proteins at the Neurovascular Unit Supports Reduction and Reoxidation of Iron for Transport Through the Blood-Brain Barrier

Chronic dietary iron overload affects hepatic iron metabolism and cognitive behavior in Wistar rats

BACKGROUND

Iron accumulation in organs affects iron metabolism, leading to deleterious effects on the body. Previously, it was studied that high dietary iron in various forms and concentrations influences iron metabolism, resulting in iron accumulation in the liver and spleen and cognitive impairment. However, the actual mechanism and impact of long-term exposure to high dietary iron remain unknown. As a result, we postulated that iron overload caused by chronic exposure to excessive dietary iron supplementation would play a role in iron dyshomeostasis and inflammation in the liver and brain of Wistar rats.

METHODS

Animals were segregated into control, low iron (FAC-Ferric Ammonium Citrate 5000 ppm), and high iron dose group (FAC 20,000 ppm). The outcome of dietary iron overload on Wistar rats was evaluated in terms of body weight, biochemical markers, histological examination of liver and brain tissue, and cognitive-behavioral studies. Also, gene expression of rat brain tissue involving iron transporters Dmt1, TfR1, iron storage protein Fpn1, inflammatory markers Nf-kB, Tnf-α, Il-6, and hepcidin was performed.

RESULTS

Our data indicate that excess iron supplementation for 30 weeks leads to decreased body weight, increased serum iron levels, and decreased RBC levels in iron fed Wistar rats. Morris water maze (MWM) studies after 30 weeks showed increased escape latency in the high iron dose group compared with the control group. Histological studies of the high iron dose group showed an iron accumulation in the liver and brain loss of cellular architecture, and cellular degeneration was observed. Excess iron treatment showed upregulation of the Dmt1 gene in iron metabolism and a remarkable increase in the Nf-kB gene in rat brain tissue.

CONCLUSION

The results show chronic excess iron supplementation leads to iron accumulation in the liver, leading to inflammation in Wistar rats.

Genome-wide meta-analyses of restless legs syndrome yield insights into genetic architecture, disease biology and risk prediction

Restless legs syndrome (RLS) affects up to 10% of older adults. Their healthcare is impeded by delayed diagnosis and insufficient treatment. To advance disease prediction and find new entry points for therapy, we performed meta-analyses of genome-wide association studies in 116,647 individuals with RLS (cases) and 1,546,466 controls of European ancestry. The pooled analysis increased the number of risk loci eightfold to 164, including three on chromosome X. Sex-specific meta-analyses revealed largely overlapping genetic predispositions of the sexes (rg = 0.96). Locus annotation prioritized druggable genes such as glutamate receptors 1 and 4, and Mendelian randomization indicated RLS as a causal risk factor for diabetes. Machine learning approaches combining genetic and nongenetic information performed best in risk prediction (area under the curve (AUC) = 0.82-0.91). In summary, we identified targets for drug development and repurposing, prioritized potential causal relationships between RLS and relevant comorbidities and risk factors for follow-up and provided evidence that nonlinear interactions are likely relevant to RLS risk prediction.

Iron imbalance in neurodegeneration

Iron is an essential element for the development and functionality of the brain, and anomalies in its distribution and concentration in brain tissue have been found to be associated with the most frequent neurodegenerative diseases. When magnetic resonance techniques allowed iron quantification in vivo, it was confirmed that the alteration of brain iron homeostasis is a common feature of many neurodegenerative diseases. However, whether iron is the main actor in the neurodegenerative process, or its alteration is a consequence of the degenerative process is still an open question. Because the different iron-related pathogenic mechanisms are specific for distinctive diseases, identifying the molecular mechanisms common to the various pathologies could represent a way to clarify this complex topic. Indeed, both iron overload and iron deficiency have profound consequences on cellular functioning, and both contribute to neuronal death processes in different manners, such as promoting oxidative damage, a loss of membrane integrity, a loss of proteostasis, and mitochondrial dysfunction. In this review, with the attempt to elucidate the consequences of iron dyshomeostasis for brain health, we summarize the main pathological molecular mechanisms that couple iron and neuronal death.

Ferroptosis regulation through Nrf2 and implications for neurodegenerative diseases

This article provides an overview of the background knowledge of ferroptosis in the nervous system, as well as the key role of nuclear factor E2-related factor 2 (Nrf2) in regulating ferroptosis. The article takes Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) as the starting point to explore the close association between Nrf2 and ferroptosis, which is of clear and significant importance for understanding the mechanism of neurodegenerative diseases (NDs) based on oxidative stress (OS). Accumulating evidence links ferroptosis to the pathogenesis of NDs. As the disease progresses, damage to the antioxidant system, excessive OS, and altered Nrf2 expression levels, especially the inhibition of ferroptosis by lipid peroxidation inhibitors and adaptive enhancement of Nrf2 signaling, demonstrate the potential clinical significance of Nrf2 in detecting and identifying ferroptosis, as well as targeted therapy for neuronal loss and mitochondrial dysfunction. These findings provide new insights and possibilities for the treatment and prevention of NDs.

Natural compounds efficacy in Ophthalmic Diseases: A new twist impacting ferroptosis

Ferroptosis, a distinct form of cell death, is characterized by the iron-mediated oxidation of lipids and is finely controlled by multiple cellular metabolic pathways. These pathways encompass redox balance, iron regulation, mitochondrial function, as well as amino acid, lipid, and sugar metabolism. Additionally, various disease-related signaling pathways also play a role in the regulation of ferroptosis. In recent years, with the introduction of the concept of ferroptosis and the deepening of research on its mechanism, ferroptosis is closely related to various biological conditions of eye diseases, including eye organ development, aging, immunity, and cancer. This article reviews the development of the concept of ferroptosis, the mechanism of ferroptosis, and its latest research progress in ophthalmic diseases and reviews the research on ferroptosis in ocular diseases within the framework of metabolism, active oxygen biology, and iron biology. Key regulators and mechanisms of ferroptosis in ocular diseases introduce important concepts and major open questions in the field of ferroptosis and related natural compounds. It is hoped that in future research, further breakthroughs will be made in the regulation mechanism of ferroptosis and the use of ferroptosis to promote the treatment of eye diseases. At the same time, natural compounds may be the direction of new drug development for the potential treatment of ferroptosis in the future. Open up a new way for clinical ophthalmologists to research and prevent diseases.

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

Iron in multiple sclerosis - Neuropathology, immunology, and real-world considerations

Iron is an essential element involved in a multitude of bodily processes. It is tightly regulated, as elevated deposition in tissues is associated with diseases such as multiple sclerosis (MS). Iron accumulation in the central nervous system (CNS) of MS patients is linked to neurotoxicity through mechanisms including oxidative stress, glutamate excitotoxicity, misfolding of proteins, and ferroptosis. In the past decade, the combination of MRI and histopathology has enhanced our understanding of iron deposition in MS pathophysiology, including in the pro-inflammatory and neurotoxicity of iron-laden rims of chronic active lesions. In this regard, iron accumulation may not only have an impact on different CNS-resident cells but may also promote the innate and adaptive immune dysfunctions in MS. Although there are discordant results, most studies indicate lower levels of iron but higher amounts of the iron storage molecule ferritin in the circulation of people with MS. Considering the importance of iron, there is a need for evidence-guided recommendation for dietary intake in people living with MS. Potential novel therapeutic approaches include the regulation of iron levels using next generation iron chelators, as well as therapies to interfere with toxic consequences of iron overload including antioxidants in MS.

Iron homeostasis imbalance and ferroptosis in brain diseases

Brain iron homeostasis is maintained through the normal function of blood-brain barrier and iron regulation at the systemic and cellular levels, which is fundamental to normal brain function. Excess iron can catalyze the generation of free radicals through Fenton reactions due to its dual redox state, thus causing oxidative stress. Numerous evidence has indicated brain diseases, especially stroke and neurodegenerative diseases, are closely related to the mechanism of iron homeostasis imbalance in the brain. For one thing, brain diseases promote brain iron accumulation. For another, iron accumulation amplifies damage to the nervous system and exacerbates patients' outcomes. In addition, iron accumulation triggers ferroptosis, a newly discovered iron-dependent type of programmed cell death, which is closely related to neurodegeneration and has received wide attention in recent years. In this context, we outline the mechanism of a normal brain iron metabolism and focus on the current mechanism of the iron homeostasis imbalance in stroke, Alzheimer's disease, and Parkinson's disease. Meanwhile, we also discuss the mechanism of ferroptosis and simultaneously enumerate the newly discovered drugs for iron chelators and ferroptosis inhibitors.

Ferroportin1 in the brain

Despite years of research, it remains unclear why certain brain regions of patients with neurodegenerative diseases (NDs) have abnormally high levels of iron, although it has long been suggested that disrupted expression of iron-metabolizing proteins due to genetic or non-genetic factors is responsible for the enhancement in brain iron contents. In addition to the increased expression of cell-iron importers lactoferrin (lactotransferrin) receptor (LfR) in Parkinson's disease (PD) and melanotransferrin (p97) in Alzheimer's disease (AD), some investigations have suggested that cell-iron exporter ferroportin 1 (Fpn1) may be also associated with the elevated iron observed in the brain. The decreased expression of Fpn1 and the resulting decrease in the amount of iron excreted from brain cells has been thought to be able to enhance iron levels in the brain in AD, PD and other NDs. Cumulative results also suggest that the reduction of Fpn1 can be induced by hepcidin-dependent and -independent pathways. In this article, we discuss the current understanding of Fpn1 expression in the brain and cell lines of rats, mice and humans, with emphasis on the potential involvement of reduced Fpn1 in brain iron enhancement in patients with AD, PD and other NDs.

The blood-brain barrier: structure, regulation, and drug delivery

Blood-brain barrier (BBB) is a natural protective membrane that prevents central nervous system (CNS) from toxins and pathogens in blood. However, the presence of BBB complicates the pharmacotherapy for CNS disorders as the most chemical drugs and biopharmaceuticals have been impeded to enter the brain. Insufficient drug delivery into the brain leads to low therapeutic efficacy as well as aggravated side effects due to the accumulation in other organs and tissues. Recent breakthrough in materials science and nanotechnology provides a library of advanced materials with customized structure and property serving as a powerful toolkit for targeted drug delivery. In-depth research in the field of anatomical and pathological study on brain and BBB further facilitates the development of brain-targeted strategies for enhanced BBB crossing. In this review, the physiological structure and different cells contributing to this barrier are summarized. Various emerging strategies for permeability regulation and BBB crossing including passive transcytosis, intranasal administration, ligands conjugation, membrane coating, stimuli-triggered BBB disruption, and other strategies to overcome BBB obstacle are highlighted. Versatile drug delivery systems ranging from organic, inorganic, and biologics-derived materials with their synthesis procedures and unique physio-chemical properties are summarized and analyzed. This review aims to provide an up-to-date and comprehensive guideline for researchers in diverse fields, offering perspectives on further development of brain-targeted drug delivery system.

The Role of Iron Metabolism, Lipid Metabolism, and Redox Homeostasis in Alzheimer's Disease: from the Perspective of Ferroptosis

In the development of Alzheimer's disease (AD), cell death is common. Novel cell death form-ferroptosis is discovered in recent years. Ferroptosis is an iron-regulated programmed cell death mechanism and has been identified in AD clinical samples. Typical characteristics of ferroptosis involve the specific changes in cell morphology, iron-dependent aggregation of reactive oxygen species (ROS) and lipid peroxides, loss of glutathione (GSH), inactivation of glutathione peroxidase 4 (GPX4), and a unique group of regulatory genes. Increasing evidence demonstrates that ferroptosis may be associated with neurological dysfunction in AD. However, the underlying mechanisms have not been fully elucidated. This article reviews the potential role of ferroptosis in AD, the involvement of ferroptosis in the pathological progression of AD through the mechanisms of iron metabolism, lipid metabolism, and redox homeostasis, as well as a range of potential therapies targeting ferroptosis for AD. Intervention strategies based on ferroptosis are promising for Alzheimer's disease treatment at present, but further researches are still needed.

Restoration of metal homeostasis: a potential strategy against neurodegenerative diseases

Metal homeostasis is critical to normal neurophysiological activity. Metal ions are involved in the development, metabolism, redox and neurotransmitter transmission of the central nervous system (CNS). Thus, disturbance of homeostasis (such as metal deficiency or excess) can result in serious consequences, including neurooxidative stress, excitotoxicity, neuroinflammation, and nerve cell death. The uptake, transport and metabolism of metal ions are highly regulated by ion channels. There is growing evidence that metal ion disorders and/or the dysfunction of ion channels contribute to the progression of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Therefore, metal homeostasis-related signaling pathways are emerging as promising therapeutic targets for diverse neurological diseases. This review summarizes recent advances in the studies regarding the physiological and pathophysiological functions of metal ions and their channels, as well as their role in neurodegenerative diseases. In addition, currently available metal ion modulators and in vivo quantitative metal ion imaging methods are also discussed. Current work provides certain recommendations based on literatures and in-depth reflections to improve neurodegenerative diseases. Future studies should turn to crosstalk and interactions between different metal ions and their channels. Concomitant pharmacological interventions for two or more metal signaling pathways may offer clinical advantages in treating the neurodegenerative diseases.

Intraperitoneal injection of iron dextran induces peripheral iron overload and mild neurodegeneration in the nigrostriatal system in C57BL/6 mice

AIMS

Elevated iron levels in the affected areas of brain are linked to several neurodegenerative diseases including Parkinson's disease (PD). This study investigated the influence of peripheral iron overload in peripheral tissues, as well as its entry into the brain regions on lysosomal functions. The survival of dopaminergic neurons in the nigrostriatal system and motor coordination were also investigated.

MAIN METHODS

An intraperitoneal injection of iron dextran (FeDx) mouse model was established. Western blot was used to detect iron deposition and lysosomal functions in the liver, spleen, hippocampal (HC), striatum (STR), substantia nigra (SN) and olfactory bulb (OB). Iron in serum and cerebrospinal fluid (CSF) was determined by an iron assay kit. Immunofluorescence and immunohistochemical staining were applied to detect dopaminergic neurons and fibers. Motor behavior was evaluated by gait analysis.

KEY FINDINGS

Iron was deposited consistently in the liver and spleen, and serum iron was elevated. While iron deposition occurred late in the HC, STR and SN, without apparently affecting CSF iron levels. Although cathepsin B (CTSB), cathepsin D (CTSD), glucocerebrosidase (GCase) and lysosome integrated membrane protein 2 (LIMP-2) protein levels were dramatically up-regulated in the liver and spleen, they were almost unchanged in the brain regions. However, CTSB was up-regulated in acute iron-overloaded OB and primary cultured astrocytes. The number of dopaminergic neurons in the SN remained unchanged, and mice did not exhibit significant motor incoordination.

SIGNIFICANCE

Intraperitoneal injection of FeDx in mice induces largely peripheral iron overload while not necessarily sufficient to cause severe disruption of the nigrostriatal system.

Curcumin and N-Acetylcysteine Nanocarriers Alone or Combined with Deferoxamine Target the Mitochondria and Protect against Neurotoxicity and Oxidative Stress in a Co-Culture Model of Parkinson's Disease

As the blood-brain barrier (BBB) prevents most compounds from entering the brain, nanocarrier delivery systems are frequently being explored to potentially enhance the passage of drugs due to their nanometer sizes and functional characteristics. This study aims to investigate whether Pluronic® F68 (P68) and dequalinium (DQA) nanocarriers can improve the ability of curcumin, n-acetylcysteine (NAC) and/or deferoxamine (DFO), to access the brain, specifically target mitochondria and protect against rotenone by evaluating their effects in a combined Transwell® hCMEC/D3 BBB and SH-SY5Y based cellular Parkinson’s disease (PD) model. P68 + DQA nanoformulations enhanced the mean passage across the BBB model of curcumin, NAC and DFO by 49%, 28% and 49%, respectively (p < 0.01, n = 6). Live cell mitochondrial staining analysis showed consistent co-location of the nanocarriers within the mitochondria. P68 + DQA nanocarriers also increased the ability of curcumin and NAC, alone or combined with DFO, to protect against rotenone induced cytotoxicity and oxidative stress by up to 19% and 14% (p < 0.01, n = 6), as measured by the MTT and mitochondrial hydroxyl radical assays respectively. These results indicate that the P68 + DQA nanocarriers were successful at enhancing the protective effects of curcumin, NAC and/or DFO by increasing the brain penetrance and targeted delivery of the associated bioactives to the mitochondria in this model. This study thus emphasises the potential effectiveness of this nanocarrier strategy in fully utilising the therapeutic benefit of these antioxidants and lays the foundation for further studies in more advanced models of PD.

Pathogenesis of α-Synuclein in Parkinson's Disease: From a Neuron-Glia Crosstalk Perspective

Parkinson's disease (PD) is a progressive neurodegenerative disorder. The classical behavioral defects of PD patients involve motor symptoms such as bradykinesia, tremor, and rigidity, as well as non-motor symptoms such as anosmia, depression, and cognitive impairment. Pathologically, the progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) and the accumulation of α-synuclein (α-syn)-composed Lewy bodies (LBs) and Lewy neurites (LNs) are key hallmarks. Glia are more than mere bystanders that simply support neurons, they actively contribute to almost every aspect of neuronal development and function; glial dysregulation has been implicated in a series of neurodegenerative diseases including PD. Importantly, amounting evidence has added glial activation and neuroinflammation as new features of PD onset and progression. Thus, gaining a better understanding of glia, especially neuron-glia crosstalk, will not only provide insight into brain physiology events but also advance our knowledge of PD pathologies. This review addresses the current understanding of α-syn pathogenesis in PD, with a focus on neuron-glia crosstalk. Particularly, the transmission of α-syn between neurons and glia, α-syn-induced glial activation, and feedbacks of glial activation on DA neuron degeneration are thoroughly discussed. In addition, α-syn aggregation, iron deposition, and glial activation in regulating DA neuron ferroptosis in PD are covered. Lastly, we summarize the preclinical and clinical therapies, especially targeting glia, in PD treatments.

The role of glutathione conjugation on the transcellular transport process of PEGylated liposomes across the blood brain barrier

Notwithstanding the growing evidence of improved drug delivery efficiency to the brain by ligand modification of PEGylated liposomes, the comprehensive knowledge of their transport processes and payload across the BBB is yet to be revealed. Herein, this study sought to understand the glutathione (GSH) ligand effect on transcellular transport mechanisms of liposomes through the blood-brain barrier (BBB) by comparing PEGylated liposomes (PEG-L) and GSH PEGylated liposomes (GSH-PEG-L). Endocytosis and exocytosis of liposomes including the role of secreted extracellular vesicles (EVs) of brain endothelial cells (BECs) were assessed. Further pharmacokinetics and brain distribution analysis of gemcitabine loaded liposomes were carried in healthy rats to ascertain the in vivo applicability. Our findings suggested that the presence of GSH increased the cellular uptake of liposomes by up to 3-fold in human brain microvascular endothelial cells depending on the dose but not in astrocytes. The cell exposure to liposomes particularly GSH-PEG-L dramatically increased the cell secretion of small and microvesicles with liposomal components, though different liposomes preferred different vesicles for exocytosis. This correlated with GSH-PEG-L transport efficiency of 4% across the in vitro BBB model in 24 h, 1.7-fold higher than that of PEG-L (p < 0.05). In rats, while PEG-L and GSH-PEG-L showed similar pharmacokinetic profiles and prolonged circulation properties, 3.8% of the total injected dose (ID) of gemcitabine was found in the brain of the GSH-PEG-L group at 8 h post-injection, compared with 2.8% ID in the PEG-L group. A brain: blood concentration ratio of 1.27 ± 0.12 indicated that an active transport mechanism to cross the BBB for GSH-PEG-L. Overall, this study revealed that GSH augmented the transcellular transport efficiency of liposomes through BBB to improve targeted brain delivery by enhancing cellular uptake and vesicular exocytosis route of BECs.

Electroacupuncture Reduces Cerebral Hemorrhage Injury in Rats by Improving Cerebral Iron Metabolism

Objective

To study the effects of electroacupuncture at Baihui and Dazhui points on the expression of hepcidin (Hepc), transferrin (Tf), transferrin receptor (TfR), and ferritin (Ft) in rats with cerebral hemorrhage to provide a theoretical basis for the treatment of cerebral hemorrhage with acupuncture.

Method

The model of cerebral hemorrhage in rats was established by autologous blood injection method and treated by electroacupuncture (EA) at the acupoints of Baihui and Dazhui. Hepc siRNA was injected into the lateral ventricle 30 min before model preparation to produce the cerebral hemorrhage model. The modified neurological severity score (mNSS) was used to assess the neurological function, and the total iron content in brain tissue was determined using atomic absorption spectrometry; the expression of Hepc, Ft, Tf, and TfR in perihematoma tissue was detected using immunohistochemistry; the interference efficiency of Hepc siRNA was detected using western blot and reverse transcription polymerase chain reaction (RT-PCR).

Results

The degree of neurological deficit showed a downward trend at 3 days, 7 days, and 14 days, and electroacupuncture significantly reduced the neurological deficit score at each time point (P < 0.01). Regarding total iron content in brain tissue, on the 3rd day, the 7th day, and the 14th day, the iron content of the hematoma tissue after intracerebral hemorrhage was reduced by electroacupuncture (P < 0.01). Regarding immunohistochemical results. Hepc, Ft, Tf, and TfR protein expressions on day 14 were significantly higher after cerebral hemorrhage (P < 0.01). After electroacupuncture, the expression of Hepc, Ft, Tf, and TfR protein was significantly reduced (P < 0.01). Western blot and RT-PCR revealed that the interference efficiency of Hepc siRNA was statistically significant (P < 0.01).

Conclusion

Electroacupuncture can reduce neurological severity scores in rats with cerebral hemorrhage and may exert cerebral protective effects by reducing Hepc protein and gene expression; lowering Ft, Tf, and TfR protein expression; and promoting iron metabolism in the brain of rats with cerebral hemorrhage.

Iron, Neuroinflammation and Neurodegeneration

Disturbance of the brain homeostasis, either directly via the formation of abnormal proteins or cerebral hypo-perfusion, or indirectly via peripheral inflammation, will activate microglia to synthesise a variety of pro-inflammatory agents which may lead to inflammation and cell death. The pro-inflammatory cytokines will induce changes in the iron proteins responsible for maintaining iron homeostasis, such that increased amounts of iron will be deposited in cells in the brain. The generation of reactive oxygen and nitrogen species, which is directly involved in the inflammatory process, can significantly affect iron metabolism via their interaction with iron-regulatory proteins (IRPs). This underlies the importance of ensuring that iron is maintained in a form that can be kept under control; hence, the elegant mechanisms which have become increasingly well understood for regulating iron homeostasis. Therapeutic approaches to minimise the toxicity of iron include N-acetyl cysteine, non-steroidal anti-inflammatory compounds and iron chelation.

Factors influencing the blood-brain barrier permeability

The blood-brain barrier (BBB) is a dynamic structure that protects the brain from harmful blood-borne, endogenous and exogenous substances and maintains the homeostatic microenvironment. All constituent cell types play indispensable roles in the BBB's integrity, and other structural BBB components, such as tight junction proteins, adherens junctions, and junctional proteins, can control the barrier permeability. Regarding the need to exchange nutrients and toxic materials, solute carriers, ATP-binding case families, and ion transporter, as well as transcytosis regulate the influx and efflux transport, while the difference in localisation and expression can contribute to functional differences in transport properties. Numerous chemical mediators and other factors such as non-physicochemical factors have been identified to alter BBB permeability by mediating the structural components and barrier function, because of the close relationship with inflammation. In this review, we highlight recently gained mechanistic insights into the maintenance and disruption of the BBB. A better understanding of the factors influencing BBB permeability could contribute to supporting promising potential therapeutic targets for protecting the BBB and the delivery of central nervous system drugs via BBB permeability interventions under pathological conditions.

Gestational and Lactational Iron Deficiency Anemia Impairs Myelination and the Neurovascular Unit in Infant Rats

Iron deficiency anemia is a prevalent health problem among pregnant women and infants, particularly in the developing countries that causes brain development deficits and poor cognitive outcomes. Since tissue iron depletion may impair myelination and trigger cellular hypoxic signaling affecting blood vessels, we studied myelination and the neurovascular unit (NVU) in infant rats born to mothers fed with an iron deficient (ID) or control diet from embryonic day 5 till weaning. Blood samples and brains of rat pups at postnatal day (PND) 14 and 30 were analyzed. PND 14 ID rats had severe microcytic hypochromic anemia that was almost reversed at PND 30 although hypomyelination and astrocyte immature phenotype in the corpus callosum were significant at that age. In CA1 hippocampal region, PND 14 and PND 30 ID rats showed significant reduced expression of the receptor β of the platelet-derived growth factor localized in pericytes and associated to aquaporin 4 (AQP4) immunopositive capillaries. Shorter AQP4 + capillaries and reduced AQP4 expression were also evidenced in PND 14 and PND 30 ID rats. In addition, pericyte membrane permeability through large-pore channels was transiently increased in ID rats at PND 14 but not at PND 30, while the blood-brain barrier permeability was not affected. Remarkably, transient increased pericyte permeability found in PND 14 ID rats was not directly related to iron depletion, suggesting the involvement of other iron deficiency anemia-induced mechanisms. In summary, severe ID during gestation and lactation produces persistent hypomyelination and significantly affects hippocampal pericytes and astrocytes in the NVU which may trigger impaired neurovascular function.

Iron Dyshomeostasis and Ferroptosis: A New Alzheimer’s Disease Hypothesis?

Iron plays a crucial role in many physiological processes of the human body, but iron is continuously deposited in the brain as we age. Early studies found iron overload is directly proportional to cognitive decline in Alzheimer’s disease (AD). Amyloid precursor protein (APP) and tau protein, both of which are related to the AD pathogenesis, are associated with brain iron metabolism. A variety of iron metabolism-related proteins have been found to be abnormally expressed in the brains of AD patients and mouse models, resulting in iron deposition and promoting AD progression. Amyloid β (Aβ) and hyperphosphorylated tau, two pathological hallmarks of AD, can also promote iron deposition in the brain, forming a vicious cycle of AD development-iron deposition. Iron deposition and the subsequent ferroptosis has been found to be a potential mechanism underlying neuronal loss in many neurodegenerative diseases. Iron chelators, antioxidants and hepcidin were found useful for treating AD, which represents an important direction for AD treatment research and drug development in the future. The review explored the deep connection between iron dysregulation and AD pathogenesis, discussed the potential of new hypothesis related to iron dyshomeostasis and ferroptosis, and summarized the therapeutics capable of targeting iron, with the expectation to draw more attention of iron dysregulation and corresponding drug development.

Role of endolysosome function in iron metabolism and brain carcinogenesis

Iron, the most abundant metal in human brain, is an essential microelement that regulates numerous cellular mechanisms. Some key physiological roles of iron include oxidative phosphorylation and ATP production, embryonic neuronal development, formation of iron-sulfur clusters, and the regulation of enzymes involved in DNA synthesis and repair. Because of its physiological and pathological importance, iron homeostasis must be tightly regulated by balancing its uptake, transport, and storage. Endosomes and lysosomes (endolysosomes) are acidic organelles known to contain readily releasable stores of various cations including iron and other metals. Increased levels of ferrous (Fe2+) iron can generate reactive oxygen species (ROS) via Fenton chemistry reactions and these increases can damage mitochondria and genomic DNA as well as promote carcinogenesis. Accumulation of iron in the brain has been linked with aging, diet, disease, and cerebral hemorrhage. Further, deregulation of brain iron metabolism has been implicated in carcinogenesis and may be a contributing factor to the increased incidence of brain tumors around the world. Here, we provide insight into mechanisms by which iron accumulation in endolysosomes is altered by pH and lysosome membrane permeabilization. Such events generate excess ROS resulting in mitochondrial DNA damage, fission, and dysfunction, as well as DNA oxidative damage in the nucleus; all of which promote carcinogenesis. A better understanding of the roles that endolysosome iron plays in carcinogenesis may help better inform the development of strategic therapeutic options for cancer treatment and prevention.

Quercetin attenuates neurotoxicity induced by iron oxide nanoparticles

Iron oxide nanoparticles (IONPs) have been proposed as targeted carriers to deliver therapeutic molecules in the central nervous system (CNS). However, IONPs may damage neural tissue via free iron accumulation, protein aggregation, and oxidative stress. Neuroprotective effects of quercetin (QC) have been proven due to its antioxidant and anti-inflammatory properties. However, poor solubility and low bioavailability of QC have also led researchers to make various QC-involved nanoparticles to overcome these limitations. We wondered how high doses or prolonged treatment with quercetin conjugated superparamagnetic iron oxide nanoparticles (QCSPIONs) could improve cognitive dysfunction and promote neurogenesis without any toxicity. It can be explained that the QC inhibits protein aggregation and acts against iron overload via iron-chelating activity, iron homeostasis genes regulation, radical scavenging, and attenuation of Fenton/Haber-Weiss reaction. In this review, first, we present brain iron homeostasis, molecular mechanisms of iron overload that induced neurotoxicity, and the role of iron in dementia-associated diseases. Then by providing evidence of IONPs neurotoxicity, we discuss how QC neutralizes IONPs neurotoxicity, and finally, we make a brief comparison between QC and conventional iron chelators. In this review, we highlight that QC as supplementation and especially in conjugated form reduces iron oxide nanoparticles neurotoxicity in clinical application.

Ferroptosis Mechanisms Involved in Hippocampal-Related Diseases

Ferroptosis is a newly recognized type of cell death that is different from traditional forms of cell death, such as apoptosis, autophagy, and necrosis. It is caused by the accumulation of intracellular iron, promoting lipid peroxidation and leading to cell death. Iron is essential as a redox metal in several physiological functions. The brain is one of the organs known to be affected by iron homeostatic balance disruption. An increased concentration of iron in the central nervous system has been associated with oxidative stress, lipid peroxidation of proteins, and cell death. The hippocampus is an important brain region for learning, memory, and emotional responses, and is also a sensitive part of the brain to the dysfunctional homeostasis of transition metals. Damage of hippocampal structure and function are intimately involved in the pathogenic mechanisms underlying neurodegenerative diseases. Currently, ferroptosis is playing an increasingly important role in treatment areas of central nervous system diseases. Thus, we provide an overview of ferroptosis regulatory mechanisms, such as lipid metabolism, glutathione metabolism, and iron metabolism in this review. We also highlight the role of ferroptosis in hippocampal-related diseases and investigate a theoretical basis for further research on the role of ferroptosis in nervous system disease treatment.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer’s disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-β (Aβ) have been proposed as one of the major causes of the disease, the mechanism of clearing Aβ is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aβ in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

High-fat diet exacerbates lead-induced blood-brain barrier disruption by disrupting tight junction integrity

Environmental exposure to lead (Pb) can damage to the central nervous system (CNS) in humans. High-fat diet (HFD) also has been suggested to impair neurocognitive function. Blood-brain barrier (BBB) is a rigorous permeability barrier for maintaining homeostasis of CNS. The damage of BBB caused by tight junctions (TJs) disruption is central to the etiology of various CNS disorders. This study aimed to investigate whether HFD could exacerbate Pb exposure induced the destruction of BBB integrity by TJs disruption. To this end, we measured cell viability assay, trans-endothelial electrical resistance assay, horseradish peroxidase flux measurement, Western blot analysis, and immunofluorescence experiments. The results showed that palmitic acid (PA), the most common saturated fatty acid found in the human body, can increase the permeability of the BBB in vitro which formed in bEnd.3 cells induced by Pb exposure, and decrease the expression of TJs, such as zonula occludins-1 (ZO-1) and occludin. Besides, we found that PA could promote the up-regulation of matrix metalloproteinase (MMP)-9 expression and activate the c-Jun N-terminal kinase (JNK) pathway induced by Pb. MMP-9 inhibitor or JNK inhibitor could increase BBB integrity and up-regulate the expressions of ZO-1 and occludin after treatment, respectively. Moreover, the JNK inhibitor could down-regulate the expression of MMP-9. In conclusion, these results suggested that HFD exacerbates Pb-induced BBB disruption by disrupting TJs integrity. This may be because PA promotes the activation of JNK pathway and then up-regulated the expression of MMP-9 after Pb-exposure. It is suggested that people with HFD exposed to environmental Pb may cause more serious damage to the CNS.

Ferroptosis as a New Mechanism in Parkinson's Disease Therapy Using Traditional Chinese Medicine

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. To date, among medications used to treat PD, only levodopa exhibits a limited disease-modifying effect on early-onset PD, but it cannot delay the progression of the disease. In 2018, for the first time, the World Health Organization included traditional Chinese medicine (TCM) in its influential global medical compendium. The use of TCM in the treatment of PD has a long history. At present, TCM can help treat and prevent PD. Iron metabolism is closely associated with PD. Ferroptosis, which is characterized by the accumulation of lipid peroxides, is a recently discovered form of iron-dependent cell death. The research literature indicates that ferroptosis in dopaminergic neurons is an important pathogenetic mechanism of PD. TCM may thus play unique roles in the treatment of PD and provide new ideas for the treatment of PD by regulating pathways associated with ferroptosis.

Micellar Nanocarriers of Hydroxytyrosol Are Protective against Parkinson's Related Oxidative Stress in an In Vitro hCMEC/D3-SH-SY5Y Co-Culture System

Hydroxytyrosol (HT) is a natural phenolic antioxidant which has neuroprotective effects in models of Parkinson’s disease (PD). Due to issues such as rapid metabolism, HT is unlikely to reach the brain at therapeutic concentrations required for a clinical effect. We have previously developed micellar nanocarriers from Pluronic F68^® (P68) and dequalinium (DQA) which have suitable characteristics for brain delivery of antioxidants and iron chelators. The aim of this study was to utilise the P68 + DQA nanocarriers for HT alone, or in combination with the iron chelator deferoxamine (DFO), and assess their physical characteristics and ability to pass the blood–brain barrier and protect against rotenone in a cellular hCMEC/D3-SH-SY5Y co-culture system. Both HT and HT + DFO formulations were less than 170 nm in size and demonstrated high encapsulation efficiencies (up to 97%). P68 + DQA nanoformulation enhanced the mean blood–brain barrier (BBB) passage of HT by 50% (p < 0.0001, n = 6). This resulted in increased protection against rotenone induced cytotoxicity and oxidative stress by up to 12% and 9%, respectively, compared to the corresponding free drug treatments (p < 0.01, n = 6). This study demonstrates for the first time the incorporation of HT and HT + DFO into P68 + DQA nanocarriers and successful delivery of these nanocarriers across a BBB model to protect against PD-related oxidative stress. These nanocarriers warrant further investigation to evaluate whether this enhanced neuroprotection is exhibited in in vivo PD models.

The Ferroxidase Hephaestin in Lung Cancer: Pathological Significance and Prognostic Value

Hephaestin (HEPH) belongs to a group of exocytoplasmic ferroxidases which contribute to cellular iron homeostasis by favouring its export. Down-regulation of HEPH expression, possibly by stimulating cell proliferation due to an increase in iron availability, has shown to correlate with poor survival in breast cancer. The lung is particularly sensitive to iron-induced oxidative stress, given the high oxygen tension present, however, HEPH distribution in lung cancer and its influence on prognosis have not been investigated yet. In this study we explored the prognostic value of HEPH and its expression pattern in the most prevalent histotypes of lung cancers, namely lung adenocarcinoma and lung squamous cell carcinoma. In silico analyses, based on UALCAN, Gene Expression Profiling Interactive Analysis (GEPIA) and Kaplan–Meier plotter bioinformatics, revealed a significant correlation between higher levels of HEPH expression and favorable prognosis, in both cancer histotypes. Moreover, TIMER web platform showed a statistically significant association between HEPH expression and cell elements belonging to the tumor microenvironment identified as endothelial cells and a subpopulation of cancer-associated fibroblasts, further confirmed by double immunohistochemical labeling with cell type specific markers. Taken together, these data shed a light on the complex mechanisms of local iron handling lung cancer can exploit to support tumorigenesis.

Alteration of Iron Concentration in Alzheimer's Disease as a Possible Diagnostic Biomarker Unveiling Ferroptosis

Proper functioning of all organs, including the brain, requires iron. It is present in different forms in biological fluids, and alterations in its distribution can induce oxidative stress and neurodegeneration. However, the clinical parameters normally used for monitoring iron concentration in biological fluids (i.e., serum and cerebrospinal fluid) can hardly detect the quantity of circulating iron, while indirect measurements, e.g., magnetic resonance imaging, require further validation. This review summarizes the mechanisms involved in brain iron metabolism, homeostasis, and iron imbalance caused by alterations detectable by standard and non-standard indicators of iron status. These indicators for iron transport, storage, and metabolism can help to understand which biomarkers can better detect iron imbalances responsible for neurodegenerative diseases.

Iron Accumulation and Lipid Peroxidation in the Aging Retina: Implication of Ferroptosis in Age-Related Macular Degeneration

Iron is an essential component in many biological processes in the human body. It is critical for the visual phototransduction cascade in the retina. However, excess iron can be toxic. Iron accumulation and reduced efficiency of intracellular antioxidative defense systems predispose the aging retina to oxidative stress-induced cell death. Age-related macular degeneration (AMD) is characterized by retinal iron accumulation and lipid peroxidation. The mechanisms underlying AMD include oxidative stress-mediated death of retinal pigment epithelium (RPE) cells and subsequent death of retinal photoreceptors. Understanding the mechanism of the disruption of iron and redox homeostasis in the aging retina and AMD is crucial to decipher these mechanisms of cell death and AMD pathogenesis. The mechanisms of retinal cell death in AMD are an area of active investigation; previous studies have proposed several types of cell death as major mechanisms. Ferroptosis, a newly discovered programmed cell death pathway, has been associated with the pathogenesis of several neurodegenerative diseases. Ferroptosis is initiated by lipid peroxidation and is characterized by iron-dependent accumulation. In this review, we provide an overview of the mechanisms of iron accumulation and lipid peroxidation in the aging retina and AMD, with an emphasis on ferroptosis.

The blood-brain barrier studied in vitro across species

The blood-brain barrier (BBB) is formed by brain capillary endothelial cells (BECs) supported by pericytes and astrocytes. The BBB maintains homeostasis and protects the brain against toxic substances circulating in the blood, meaning that only a few drugs can pass the BBB. Thus, for drug screening, understanding cell interactions, and pathology, in vitro BBB models have been developed using BECs from various animal sources. When comparing models of different species, differences exist especially in regards to the transendothelial electrical resistance (TEER). Thus, we compared primary mice, rat, and porcine BECs (mBECs, rBECs, and pBECs) cultured in mono- and co-culture with astrocytes, to identify species-dependent differences that could explain the variations in TEER and aid to the selection of models for future BBB studies. The BBB models based on primary mBECs, rBECs, and pBECs were evaluated and compared in regards to major BBB characteristics. The barrier integrity was evaluated by the expression of tight junction proteins and measurements of TEER and apparent permeability (Papp). Additionally, the cell size, the functionality of the P-glycoprotein (P-gp) efflux transporter, and the expression of the transferrin receptor were evaluated and compared. Expression and organization of tight junction proteins were in all three species influenced by co-culturing, supporting the findings, that TEER increases after co-culturing with astrocytes. All models had functional polarised P-gp efflux transporters and expressed the transferrin receptor. The most interesting discovery was that even though the pBECs had higher TEER than rBECs and mBECs, the Papp did not show the same variation between species, which could be explained by a significantly larger cell size of pBECs. In conclusion, our results imply that the choice of species for a given BBB study should be defined from its purpose, instead of aiming to reach the highest TEER, as the models studied here revealed similar BBB properties.

Hepcidin attenuates the iron-mediated secondary neuronal injury after intracerebral hemorrhage in rats

Iron plays a key role in secondary neuronal injury after intracerebral hemorrhage (ICH), and hepcidin is able to reduce brain iron in iron-overloaded rats by down-regulating iron transport proteins including ferroportin 1 and transferrin receptor 1. These led us to hypothesize that hepcidin might reduce iron-mediated neurotoxicity by inhibiting iron accumulation in ICH brain. Here, we examined effects of Ad-hepcidin (hepcidin expression adenovirus) on the nonheme iron contents, expression of hepcidin, ferritin and iron transport proteins, neuronal cell survival, water contents in the brain and/or cerebrospinal fluid (CSF), and ICH-induced apoptosis, neurological deficit by RT-PCR, Western blot analysis, NeuN Immunofluorescence, TUNEL, Fluoro-Jade B staining, behavioral performance and Morris water-maze tests in 510 rats. We demonstrated that hepcidin could significantly suppress the ICH-induced increase in iron and ferritin in brain tissues and CSF by inhibiting expression of iron transport proteins, increase neuronal survival by attenuating ICH-induced apoptosis, reactive oxygen species, neurodegeneration and brain edema, as well as effectively improve ICH-induced behavioral and cognitive deficit in rats. The findings collectively showed that hepcidin could effectively attenuate iron-mediated secondary neuronal injury after ICH in rats. This naturally existing protein can potentially be developed into a therapeutic drug for the treatment of ICH patients.

Inflaming the Brain with Iron

Iron accumulation and neuroinflammation are pathological conditions found in several neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Iron and inflammation are intertwined in a bidirectional relationship, where iron modifies the inflammatory phenotype of microglia and infiltrating macrophages, and in turn, these cells secrete diffusible mediators that reshape neuronal iron homeostasis and regulate iron entry into the brain. Secreted inflammatory mediators include cytokines and reactive oxygen/nitrogen species (ROS/RNS), notably hepcidin and nitric oxide (·NO). Hepcidin is a small cationic peptide with a central role in regulating systemic iron homeostasis. Also present in the cerebrospinal fluid (CSF), hepcidin can reduce iron export from neurons and decreases iron entry through the blood-brain barrier (BBB) by binding to the iron exporter ferroportin 1 (Fpn1). Likewise, ·NO selectively converts cytosolic aconitase (c-aconitase) into the iron regulatory protein 1 (IRP1), which regulates cellular iron homeostasis through its binding to iron response elements (IRE) located in the mRNAs of iron-related proteins. Nitric oxide-activated IRP1 can impair cellular iron homeostasis during neuroinflammation, triggering iron accumulation, especially in the mitochondria, leading to neuronal death. In this review, we will summarize findings that connect neuroinflammation and iron accumulation, which support their causal association in the neurodegenerative processes observed in AD and PD.

Brain-Targeted Delivery of Pre-miR-29b Using Lactoferrin-Stearic Acid-Modified-Chitosan/Polyethyleneimine Polyplexes

The efficacy of brain therapeutics is largely hampered by the presence of the blood–brain barrier (BBB), mainly due to the failure of most (bio) pharmaceuticals to cross it. Accordingly, this study aims to develop nanocarriers for targeted delivery of recombinant precursor microRNA (pre-miR-29b), foreseeing a decrease in the expression of the BACE1 protein, with potential implications in Alzheimer’s disease (AD) treatment. Stearic acid (SA) and lactoferrin (Lf) were successfully exploited as brain-targeting ligands to modify cationic polymers (chitosan (CS) or polyethyleneimine (PEI)), and its BBB penetration behavior was evaluated. The intracellular uptake of the dual-targeting drug delivery systems by neuronal cell models, as well as the gene silencing efficiency of recombinant pre-miR-29b, was analyzed in vitro. Labeled pre-miR-29b-CS/PEI-SA-Lf systems showed very strong fluorescence in the cytoplasm and nucleus of RBE4 cells, being verified the delivery of pre-miR-29b to neuronal cells after 1 h transfection. The experiment of transport across the BBB showed that CS-SA-Lf delivered 65% of recombinant pre-miR-29b in a period of 4 h, a significantly higher transport ratio than the 42% found for PEI-SA-Lf in the same time frame. Overall, a novel procedure for the dual targeting of DDS is disclosed, opening new perspectives in nanomedicines delivery, whereby a novel drug delivery system harvests the merits and properties of the different immobilized ligands.

Age-Related Changes and Sex-Related Differences in Brain Iron Metabolism

Iron is an essential element that participates in numerous cellular processes. Any disruption of iron homeostasis leads to either iron deficiency or iron overload, which can be detrimental for humans' health, especially in elderly. Each of these changes contributes to the faster development of many neurological disorders or stimulates progression of already present diseases. Age-related cellular and molecular alterations in iron metabolism can also lead to iron dyshomeostasis and deposition. Iron deposits can contribute to the development of inflammation, abnormal protein aggregation, and degeneration in the central nervous system (CNS), leading to the progressive decline in cognitive processes, contributing to pathophysiology of stroke and dysfunctions of body metabolism. Besides, since iron plays an important role in both neuroprotection and neurodegeneration, dietary iron homeostasis should be considered with caution. Recently, there has been increased interest in sex-related differences in iron metabolism and iron homeostasis. These differences have not yet been fully elucidated. In this review we will discuss the latest discoveries in iron metabolism, age-related changes, along with the sex differences in iron content in serum and brain, within the healthy aging population and in neurological disorders such as multiple sclerosis, Parkinson's disease, Alzheimer's disease, and stroke.

Intertwined mechanisms define transport of anti-ICAM nanocarriers across the endothelium and brain delivery of a therapeutic enzyme

The interaction of drug delivery systems with tissues is key for their application. An example is drug carriers targeted to endothelial barriers, which can be transported to intra-endothelial compartments (lysosomes) or transcellularly released at the tissue side (transcytosis). Although carrier targeting valency influences this process, the mechanism is unknown. We studied this using polymer nanocarriers (NCs) targeted to intercellular adhesion molecule-1 (ICAM-1), an endothelial-surface glycoprotein whose expression is increased in pathologies characterized by inflammation. A bell-shaped relationship was found between NC targeting valency and the rate of transcytosis, where high and low NC valencies rendered less efficient transcytosis rates than an intermediate valency formulation. In contrast, an inverted bell-shape relationship was found for NC valency and lysosomal trafficking rates. Data suggested a model where NC valency plays an opposing role in the two sub-processes involved in transcytosis: NC binding-uptake depended directly on valency and exocytosis-detachment was inversely related to this parameter. This is because the greater the avidity of the NC-receptor interaction the more efficient uptake becomes, but NC-receptor detachment post-transport is more compromised. Cleavage of the receptor at the basolateral side of endothelial cells facilitated NC transcytosis, likely by helping NC detachment post-transport. Since transcytosis encompasses both sets of events, the full process finds an optimum at the intersection of these inverted relationships, explaining the bell-shaped behavior. NCs also trafficked to lysosomes from the apical side and, additionally, from the basolateral side in the case of high valency NCs which are slower at detaching from the receptor. This explains the opposite behavior of NC valency for transcytosis vs. lysosomal transport. Anti-ICAM NCs were verified to traffic into the brain after intravenous injection in mice, and both cellular and in vivo data showed that intermediate valency NCs resulted in higher delivery of a therapeutic enzyme, acid sphingomyelinase, required for types A and B Niemann-Pick disease.

Epigenetic Regulation of Ferroportin in Primary Cultures of the Rat Blood-Brain Barrier

Ferroportin plays an essential role for iron transport through the blood-brain barrier (BBB), which is formed by brain capillary endothelial cells (BCECs). To maintain the integrity of the BBB, the BCECs gain support from pericytes and astrocytes, which together with neurons form the neurovascular unit (NVU). The objectives of the present study were to investigate ferroportin expression in primary cells of the NVU and to determine if ferroportin mRNA (Fpn) expression is epigenetically regulated. Primary rat BCECs, pericytes, astrocytes, and neurons all expressed ferroportin mRNA at varying levels, with BCECs exhibiting the highest expression of Fpn, peaking when co-cultured but examined separately from astrocytes. Conversely, Fpn expression was lowest in isolated astrocytes, which correlated with high DNA methylation in their Slc40a1 promoter. To provide further evidence for epigenetic regulation, mono-cultured BCECs, pericytes, and astrocytes were treated with the histone deacetylase inhibitors valproic acid (VPA) and sodium butyrate (SB), which significantly increased Fpn and ferroportin protein in BCECs and pericytes. Furthermore, ⁵⁹Fe export from BCECs was elevated after treatment with VPA. In conclusion, we present first time evidence stating that Fpn expression is epigenetically regulated in BCECs, which may have implications for pharmacological induction of iron transport through the BBB.

Potential role of iron in repair of inflammatory demyelinating lesions

Inflammatory destruction of iron-rich myelin is characteristic of multiple sclerosis (MS). Although iron is needed for oligodendrocytes to produce myelin during development, its deposition has also been linked to neurodegeneration and inflammation, including in MS. We report perivascular iron deposition in multiple sclerosis lesions that was mirrored in 72 lesions from 13 marmosets with experimental autoimmune encephalomyelitis. Iron accumulated mainly inside microglia/macrophages from 6 weeks after demyelination. Consistently, expression of transferrin receptor, the brain's main iron-influx protein, increased as lesions aged. Iron was uncorrelated with inflammation and postdated initial demyelination, suggesting that iron is not directly pathogenic. Iron homeostasis was at least partially restored in remyelinated, but not persistently demyelinated, lesions. Taken together, our results suggest that iron accumulation in the weeks after inflammatory demyelination may contribute to lesion repair rather than inflammatory demyelination per se.

Gene therapy to the blood-brain barrier with resulting protein secretion as a strategy for treatment of Niemann Picks type C2 disease

Treatment of many diseases affecting the central nervous system (CNS) is complicated by the inability of several therapeutics to cross the blood-brain barrier (BBB). Genetically modifying brain capillary endothelial cells (BCECs) denotes an approach to overcome the limitations of the BBB by turning BCECs into recombinant protein factories. This will result in protein secretion toward both the brain and peripheral circulation, which is particularly relevant in genetic diseases, like lysosomal storage diseases (LSD), where cells are ubiquitously affected both in the CNS and the periphery. Here we investigated transfection of primary rat brain capillary endothelial cells (rBCECs) for synthesis and secretion of recombinant NPC2, the protein deficient in the lysosomal cholesterol storage disease Niemann Pick type C2. We demonstrate prominent NPC2 gene induction and protein secretion in 21% of BCECs in non-mitotic monocultures with a biological effect on NPC2-deficient fibroblasts as verified from changes in filipin III staining of cholesterol deposits. By comparison the transfection efficiency was 75% in HeLa-cells, known to persist in a mitotic state. When co-cultured with primary rat astrocytes in conditions with maintained BBB properties 7% BCECs were transfected, clearly suggesting that induction of BBB properties with polarized conditions of the non-mitotic BCECs influences the transfection efficacy and secretion directionality. In conclusion, non-viral gene therapy to rBCECs leads to protein secretion and signifies a method for NPC2 to target cells inside the CNS otherwise inaccessible because of the presence of the BBB. However, obtaining high transfection efficiencies is crucial in order to achieve sufficient therapeutic effects. Cover Image for this issue: https://doi.org/10.1111/jnc.15050.

Effects of Cadmium on ZO-1 Tight Junction Integrity of the Blood Brain Barrier

Cadmium (Cd) is a highly toxic environmental pollutant released from the smelting and refining of metals and cigarette smoking. Oral exposure to cadmium may result in adverse effects on a number of tissues, including the central nervous system (CNS). In fact, its toxicity has been related to neurological disorders, as well as neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Under normal conditions, Cd barely reaches the brain in adults because of the presence of the blood-brain barrier (BBB); however, it has been demonstrated that Cd-dependent BBB alteration contributes to pathogenesis of neurodegeneration. However, the mechanism underlying Cd-dependent BBB alteration remain obscure. Here, we investigated the signaling pathway of Cd-induced tight junction (TJ), F-actin, and vimentin protein disassembly in a rat brain endothelial cell line (RBE4). RBE4 cells treated with 10 μM cadmium chloride (CdCl2) showed a dose- and time-dependent significant increase in reactive oxygen species (ROS) production. This phenomenon was coincident with the alteration of the TJ zonula occludens-1 (ZO-1), F-actin, and vimentin proteins. The Cd-dependent ROS increase elicited the upregulation of GRP78 expression levels, a chaperone involved in endoplasmic reticulum (ER) stress that induces caspase-3 activation. Further signal profiling by the pannexin-1 (PANX1) specific inhibitor 10Panx revealed a PANX1-independent increase in ATP spillage in Cd-treated endothelial cells. Our results point out that a ROS-dependent ER stress-mediated signaling pathway involving caspase-3 activation and ATP release is behind the BBB morphological alterations induced by Cd.

Evaluation of Targeted Delivery to the Brain Using Magnetic Immunoliposomes and Magnetic Force

Magnetic nanoparticles have great prospects for drug delivery purposes, as they can be designed with various surface coatings and conjugated with drugs and targeting moieties. They also have a unique potential for precise delivery when guided by magnetic force. The blood-brain barrier (BBB) denotes the interface between the blood and brain parenchyma and hinders the majority of drugs from entering the brain. Red fluorescent magnetic nanoparticles were encapsulated in liposomes and conjugated to antibodies targeting the rat transferrin receptor (OX26) to form magnetic immunoliposomes. These magnetic immunoliposomes enhanced the uptake by rat brain capillary endothelial cells (BCECs) in vitro. In situ brain perfusion in young rats high in the endogenous expression of transferrin receptors by BCECs, revealed enhanced uptake of magnetic immunoliposomes when compared to naked magnetic nanoparticles or non-targeted magnetic liposomes. When applying the external magnetic force, the magnetic nanoparticles were detected in the brain parenchyma, suggesting transport across the BBB. Ultrastructural examination of the immunoliposomes, unfortunately, was unable to confirm a complete encapsulation of all naked nanoparticles within the liposomes, suggesting that the data on the brain could derive from particles being released from the liposomes under influence of external magnetic force; hence hypothesizes on external magnetic force as a qualifier for dragging targeted magnetic immunoliposomes through the BBB. In conclusion, our results suggest that transport of magnetic nanoparticles present in BCECs by targeted delivery to the transferrin receptor may undergo further transport into the brain when applying magnetic force. While magnetic immunoliposomes are targetable to BCECs, their design to enable further transport across the BBB when applying external magnetic force needs further improvement.

Impairment of the Developing Human Brain in Iron Deficiency: Correlations to Findings in Experimental Animals and Prospects for Early Intervention Therapy

Due to the necessity of iron for a variety of cellular functions, the developing mammalian organism is vulnerable to iron deficiency, hence causing structural abnormalities and physiological malfunctioning in organs, which are particularly dependent on adequate iron stores, such as the brain. In early embryonic life, iron is already needed for proper development of the brain with the proliferation, migration, and differentiation of neuro-progenitor cells. This is underpinned by the widespread expression of transferrin receptors in the developing brain, which, in later life, is restricted to cells of the blood–brain and blood–cerebrospinal fluid barriers and neuronal cells, hence ensuring a sustained iron supply to the brain, even in the fully developed brain. In embryonic human life, iron deficiency is thought to result in a lower brain weight, with the impaired formation of myelin. Studies of fully developed infants that have experienced iron deficiency during development reveal the chronic and irreversible impairment of cognitive, memory, and motor skills, indicating widespread effects on the human brain. This review highlights the major findings of recent decades on the effects of gestational and lactational iron deficiency on the developing human brain. The findings are correlated to findings of experimental animals ranging from rodents to domestic pigs and non-human primates. The results point towards significant effects of iron deficiency on the developing brain. Evidence would be stronger with more studies addressing the human brain in real-time and the development of blood biomarkers of cerebral disturbance in iron deficiency. Cerebral iron deficiency is expected to be curable with iron substitution therapy, as the brain, privileged by the cerebral vascular transferrin receptor expression, is expected to facilitate iron extraction from the circulation and enable transport further into the brain.

Brain iron transport

Brain iron is a crucial participant and regulator of normal physiological activity. However, excess iron is involved in the formation of free radicals, and has been associated with oxidative damage to neuronal and other brain cells. Abnormally high brain iron levels have been observed in various neurodegenerative diseases, including neurodegeneration with brain iron accumulation, Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the key question of why iron levels increase in the relevant regions of the brain remains to be answered. A full understanding of the homeostatic mechanisms involved in brain iron transport and metabolism is therefore critical not only for elucidating the pathophysiological mechanisms responsible for excess iron accumulation in the brain but also for developing pharmacological interventions to disrupt the chain of pathological events occurring in these neurodegenerative diseases. Numerous studies have been conducted, but to date no effort to synthesize these studies and ideas into a systematic and coherent summary has been made, especially concerning iron transport across the luminal (apical) membrane of the capillary endothelium and the membranes of different brain cell types. Herein, we review key findings on brain iron transport, highlighting the mechanisms involved in iron transport across the luminal (apical) as well as the abluminal (basal) membrane of the blood-brain barrier, the blood-cerebrospinal fluid barrier, and iron uptake and release in neurons, oligodendrocytes, astrocytes and microglia within the brain. We offer suggestions for addressing the many important gaps in our understanding of this important topic, and provide new insights into the potential causes of abnormally increased iron levels in regions of the brain in neurodegenerative disorders.

DMT1 Expression and Iron Levels at the Crossroads Between Aging and Neurodegeneration

Iron homeostasis is an essential prerequisite for metabolic and neurological functions throughout the healthy human life, with a dynamic interplay between intracellular and systemic iron metabolism. The development of different neurodegenerative diseases is associated with alterations of the intracellular transport of iron and heavy metals, principally mediated by Divalent Metal Transporter 1 (DMT1), responsible for Non-Transferrin Bound Iron transport (NTBI). In addition, DMT1 regulation and its compartmentalization in specific brain regions play important roles during aging. This review highlights the contribution of DMT1 to the physiological exchange and distribution of body iron and heavy metals during aging and neurodegenerative diseases. DMT1 also mediates the crosstalk between central nervous system and peripheral tissues, by systemic diffusion through the Blood Brain Barrier (BBB), with the involvement of peripheral iron homeostasis in association with inflammation. In conclusion, a survey about the role of DMT1 and iron will illustrate the complex panel of interrelationship with aging, neurodegeneration and neuroinflammation.

Iron, Myelin, and the Brain: Neuroimaging Meets Neurobiology

Although iron is crucial for neuronal functioning, many aspects of cerebral iron biology await clarification. The ability to quantify specific iron forms in the living brain would open new avenues for diagnosis, therapeutic monitoring, and understanding pathogenesis of diseases. A modality that allows assessment of brain tissue composition in vivo, in particular of iron deposits or myelin content on a submillimeter spatial scale, is magnetic resonance imaging (MRI). Multimodal strategies combining MRI with complementary analytical techniques ex vivo have emerged, which may lead to improved specificity. Interdisciplinary collaborations will be key to advance beyond simple correlative analyses in the biological interpretation of MRI data and to gain deeper insights into key factors leading to iron accumulation and/or redistribution associated with neurodegeneration.