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

Iron Overload in Brain: Transport Mismatches, Microbleeding Events, and How Nanochelating Therapies May Counteract Their Effects

Iron overload in many brain regions is a common feature of aging and most neurodegenerative diseases. In this review, the causes, mechanisms, mathematical models, and possible therapies are summarized. Indeed, physiological and pathological conditions can be investigated using compartmental models mimicking iron trafficking across the blood-brain barrier and the Cerebrospinal Fluid-Brain exchange membranes located in the choroid plexus. In silico models can investigate the alteration of iron homeostasis and simulate iron concentration in the brain environment, as well as the effects of intracerebral iron chelation, determining potential doses and timing to recover the physiological state. Novel formulations of non-toxic nanovectors with chelating capacity are already tested in organotypic brain models and could be available to move from in silico to in vivo experiments.

Developing Iron Nanochelating Agents: Preliminary Investigation of Effectiveness and Safety for Central Nervous System Applications

Excessive iron levels are believed to contribute to the development of neurodegenerative disorders by promoting oxidative stress and harmful protein clustering. Novel chelation treatments that can effectively remove excess iron while minimizing negative effects on the nervous system are being explored. This study focuses on the creation and evaluation of innovative nanobubble (NB) formulations, shelled with various polymers such as glycol-chitosan (GC) and glycol-chitosan conjugated with deferoxamine (DFO), to enhance their ability to bind iron. Various methods were used to evaluate their physical and chemical properties, chelation capacity in diverse iron solutions and impact on reactive oxygen species (ROS). Notably, the GC-DFO NBs demonstrated the ability to decrease amyloid-β protein misfolding caused by iron. To assess potential toxicity, in vitro cytotoxicity testing was conducted using organotypic brain cultures from the substantia nigra, revealing no adverse effects at appropriate concentrations. Additionally, the impact of NBs on spontaneous electrical signaling in hippocampal neurons was examined. Our findings suggest a novel nanochelation approach utilizing DFO-conjugated NBs for the removal of excess iron in cerebral regions, potentially preventing neurotoxic effects.

Emerging roles and therapeutic potentials of ferroptosis: from the perspective of 11 human body organ systems

Since ferroptosis was first described as an iron-dependent cell death pattern in 2012, there has been increasing interest in ferroptosis research. In view of the immense potential of ferroptosis in treatment efficacy and its rapid development in recent years, it is essential to track and summarize the latest research in this field. However, few writers have been able to draw on any systematic investigation into this field based on human body organ systems. Hence, in this review, we provide a comprehensive description of the latest progress in unveiling the roles and functions, as well as the therapeutic potential of ferroptosis, in treating diseases from the aspects of 11 human body organ systems (including the nervous system, respiratory system, digestive system, urinary system, reproductive system, integumentary system, skeletal system, immune system, cardiovascular system, muscular system, and endocrine system) in the hope of providing references for further understanding the pathogenesis of related diseases and bringing an innovative train of thought for reformative clinical treatment.

Visualization of ferroptosis in brain diseases and ferroptosis-inducing nanomedicine for glioma

A remarkable body of new data establishes that many degenerative brain diseases and some acute injury situations in the brain may be associated with ferroptosis. In recent years, ferroptosis has also attracted great interest in the cancer research community, partly because it is a unique mode of cell death distinct from other forms and thus has great therapeutic potential for brain cancer. Glioblastoma is a highly aggressive and fatal human cancer, accounting for 60% of all primary brain tumors. Despite the development of various pharmacological and surgical modalities, the survival rates of high-grade gliomas have remained poor over the past few decades. Recent evidence has revealed that ferroptosis is involved in tumor initiation, progression, and metastasis, and manipulating ferroptosis could offer a novel strategy for glioma management. Nanoparticles have been exploited as multifunctional platforms that can cross the blood-brain barrier and deliver therapeutic agents to the brain to address the pressing need for accurate visualization of ferroptosis and glioma treatment. To create efficient and durable ferroptosis inducers, many researchers have engineered nanocomposites to induce a more effective ferroptosis for therapy. In this review, we present the mechanism of ferroptosis and outline the current strategies of imaging and nanotherapy of ferroptosis in brain diseases, especially glioma. We aim to provide up-to-date information on ferroptosis and emphasize the potential clinical implications of ferroptosis for glioma diagnosis and treatment. However, regulation of ferroptosis in vivo remains challenging due to a lack of compounds.

Ferroptosis in Neurological Disease

Iron accumulation in the CNS occurs in many neurological disorders. It can contribute to neuropathology as iron is a redox-active metal that can generate free radicals. The reasons for the iron buildup in these conditions are varied and depend on which aspects of iron influx, efflux, or sequestration that help maintain iron homeostasis are dysregulated. Iron was shown recently to induce cell death and damage via lipid peroxidation under conditions in which there is deficient glutathione-dependent antioxidant defense. This form of cell death is called ferroptosis. Iron chelation has had limited success in the treatment of neurological disease. There is therefore much interest in ferroptosis as it potentially offers new drugs that could be more effective in reducing iron-mediated lipid peroxidation within the lipid-rich environment of the CNS. In this review, we focus on the molecular mechanisms that induce ferroptosis. We also address how iron enters and leaves the CNS, as well as the evidence for ferroptosis in several neurological disorders. Finally, we highlight biomarkers of ferroptosis and potential therapeutic strategies.

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.

lncRNA-associated ceRNA network revealing the potential regulatory roles of ferroptosis and immune infiltration in Alzheimer's disease

Background

Alzheimer's disease (AD) is the most common form of dementia characterized by a prominent cognitive deterioration of sufficient magnitude to impair daily living. Increasing studies indicate that non-coding RNAs (ncRNAs) are involved in ferroptosis and AD progression. However, the role of ferroptosis-related ncRNAs in AD remains unexplored.

Methods

We obtained the intersection of differentially expressed genes in GSE5281 (brain tissue expression profile of patients with AD) from the GEO database and ferroptosis-related genes (FRGs) from the ferrDb database. Least absolute shrinkage and selection operator model along with weighted gene co-expression network analysis screened for FRGs highly associated with AD.

Results

A total of five FRGs were identified and further validated in GSE29378 (area under the curve = 0.877, 95% confidence interval = 0.794-0.960). A competing endogenous RNA (ceRNA) network of ferroptosis-related hub genes (EPT1, KLHL24, LRRFIP1, CXCL2 and CD44) was subsequently constructed to explore the regulatory mechanism between hub genes, lncRNAs and miRNAs. Finally, CIBERSORT algorithms were used to unravel the immune cell infiltration landscape in AD and normal samples. M1 macrophages and mast cells were more infiltrated whereas memory B cells were less infiltrated in AD samples than in normal samples. Spearman's correlation analysis revealed that LRRFIP1 was positively correlated with M1 macrophages (r = -0.340, P < 0.001) whereas ferroptosis-related lncRNAs were negatively correlated with immune cells, wherein miR7-3HG correlated with M1 macrophages and NIFK-AS1, EMX2OS and VAC14-AS1 correlated with memory B cells (|r| > 0.3, P < 0.001).

Conclusion

We constructed a novel ferroptosis-related signature model including mRNAs, miRNAs and lncRNAs, and characterized its association with immune infiltration in AD. The model provides novel ideas for the pathologic mechanism elucidation and targeted therapy development of AD.

The contribution of an imbalanced redox signalling to neurological and neurodegenerative conditions

Nitric oxide and other redox active molecules such as oxygen free radicals provide essential signalling in diverse neuronal functions, but their excess production and insufficient scavenging induces cytotoxic redox stress which is associated with numerous neurodegenerative and neurological conditions. A further component of redox signalling is mediated by a homeostatic regulation of divalent metal ions, the imbalance of which contributes to neuronal dysfunction. Additional antioxidant molecules such as glutathione and enzymes such as super oxide dismutase are involved in maintaining a physiological redox status within neurons. When cellular processes are perturbed and generation of free radicals overwhelms the antioxidants capacity of the neurons, a resulting redox damage leads to neuronal dysfunction and cell death. Cellular sources for production of redox-active molecules may include NADPH oxidases, mitochondria, cytochrome P450 and nitric oxide (NO)-generating enzymes, such as endothelial, neuronal and inducible NO synthases. Several neurodegenerative and developmental neurological conditions are associated with an imbalanced redox state as a result of neuroinflammatory processes leading to nitrosative and oxidative stress. Ongoing research aims at understanding the causes and consequences of such imbalanced redox homeostasis and its role in neuronal dysfunction.

Redox stress and metal dys-homeostasis appear as hallmarks of early prion disease pathogenesis in mice

Neurodegenerative diseases are associated with a multitude of dysfunctional cellular pathways. One major contributory factor is a redox stress challenge during the development of several protein misfolding conditions including Alzheimer's (AD), Parkinson's disease (PD), and less common conditions such as Creutzfeldt Jakob disease (CJD). CJD is caused by misfolding of the neuronal prion protein and is characterised by a neurotoxic unfolded protein response involving chronic endoplasmic reticulum stress, reduced protein translation and spongiosis leading subsequently to synaptic and neuronal loss. Here we have characterised prion disease in mice to assess redox stress components including nitrergic and oxidative markers associated with neuroinflammatory activation. Aberrant regulation of the homeostasis of several redox metals contributes to the overall cellular redox stress and we have identified altered levels of iron, copper, zinc, and manganese in the hippocampus of prion diseased mice. Our data show that early in disease, there is evidence for oxidative stress in conjunction with reduced antioxidant superoxide dismutase mRNA and protein expression. Moreover, expression of divalent metal transporter proteins was reduced for Atp7b, Atox1, Slc11a2, Slc39a14 at 6-7 weeks but increased for Slc39a14 and Mt1 at 10 weeks of disease. Our data present evidence for a strong pro-oxidant environment and altered redox metal homeostasis in early disease pathology which both may be contributory factors to aggravating this protein misfolding disease.

Iron Deposition in Brain: Does Aging Matter?

The alteration of iron homeostasis related to the aging process is responsible for increased iron levels, potentially leading to oxidative cellular damage. Iron is modulated in the Central Nervous System in a very sensitive manner and an abnormal accumulation of iron in the brain has been proposed as a biomarker of neurodegeneration. However, contrasting results have been presented regarding brain iron accumulation and the potential link with other factors during aging and neurodegeneration. Such uncertainties partly depend on the fact that different techniques can be used to estimate the distribution of iron in the brain, e.g., indirect (e.g., MRI) or direct (post-mortem estimation) approaches. Furthermore, recent evidence suggests that the propensity of brain cells to accumulate excessive iron as a function of aging largely depends on their anatomical location. This review aims to collect the available data on the association between iron concentration in the brain and aging, shedding light on potential mechanisms that may be helpful in the detection of physiological neurodegeneration processes and neurodegenerative diseases such as Alzheimer's disease.

Blood-Based Biomarkers for Alzheimer's Disease Diagnosis and Progression: An Overview

Alzheimer’s Disease (AD) is a progressive neurodegenerative disease characterized by amyloid-β (Aβ) plaque deposition and neurofibrillary tangle accumulation in the brain. Although several studies have been conducted to unravel the complex and interconnected pathophysiology of AD, clinical trial failure rates have been high, and no disease-modifying therapies are presently available. Fluid biomarker discovery for AD is a rapidly expanding field of research aimed at anticipating disease diagnosis and following disease progression over time. Currently, Aβ_1–42, phosphorylated tau, and total tau levels in the cerebrospinal fluid are the best-studied fluid biomarkers for AD, but the need for novel, cheap, less-invasive, easily detectable, and more-accessible markers has recently led to the search for new blood-based molecules. However, despite considerable research activity, a comprehensive and up-to-date overview of the main blood-based biomarker candidates is still lacking. In this narrative review, we discuss the role of proteins, lipids, metabolites, oxidative-stress-related molecules, and cytokines as possible disease biomarkers. Furthermore, we highlight the potential of the emerging miRNAs and long non-coding RNAs (lncRNAs) as diagnostic tools, and we briefly present the role of vitamins and gut-microbiome-related molecules as novel candidates for AD detection and monitoring, thus offering new insights into the diagnosis and progression of this devastating disease.

Current research status of blood biomarkers in Alzheimer's disease: Diagnosis and prognosis

Alzheimer's disease (AD), which mainly occurs in the elderly, is a neurodegenerative disease with a hidden onset, which leads to progressive cognitive and behavioral changes. The annually increasing prevalence rate and number of patients with AD exert great pressure on the society. No effective disease-modifying drug treatments are available; thus, there is no cure yet. The disease progression can only be delayed through early detection and drug assistance. Therefore, the importance of exploring associated biomarkers for the early diagnosis and prediction of the disease progress is highlighted. The National Institute on Aging- Alzheimer's Association (NIA-AA) proposed A/T/N diagnostic criteria in 2018, including Aβ42, p-tau, t-tau in cerebrospinal fluid (CSF), and positron emission tomography (PET). However, the invasiveness of lumbar puncture for CSF assessment and non-popularity of PET have prompted researchers to look for minimally invasive, easy to collect, and cost-effective biomarkers. Therefore, studies have largely focused on some novel molecules in the peripheral blood. This is an emerging research field, facing many obstacles and challenges while achieving some promising results.

Iron intake and multiple health outcomes: Umbrella review

Iron is an essential trace element, while excess iron can lead to different levels of physical abnormalities or diseases. This umbrella review aimed to conduct a systematic evaluation of the possible relationships between iron intake and various health outcomes. We retrieved PubMed, Embase, Web of Science, Scopus, and the Cochrane Database of Systematic Reviews from inception through May 2021. A total of 34 meta-analyses with 46 unique health outcomes were identified. Heme iron intake was positively associated with nine outcomes, including colorectal cancer, type 2 diabetes mellitus, and cardiovascular disease mortality, while dietary total iron intake could decrease the risk of colorectal adenoma, esophageal cancer, coronary heart disease, and depression. Iron supplementation was a protective factor against eight outcomes. However, it was associated with decreased length and weight gain. The quality of evidence for most outcomes was "low" or "very low" with the remaining eleven as "high" or "moderate". All outcomes were categorized as class III, IV, or NS based on evidence classification. Although high iron intake has been identified to be significantly associated with a range of outcomes, firm universal conclusions about its beneficial or negative effects cannot be drawn given the low quality of evidence for most outcomes.

Ferroptosis as a mechanism of neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia, with complex pathophysiology that is not fully understood. While β-amyloid plaque and neurofibrillary tangles define the pathology of the disease, the mechanism of neurodegeneration is uncertain. Ferroptosis is an iron-mediated programmed cell death mechanism characterised by phospholipid peroxidation that has been observed in clinical AD samples. This review will outline the growing molecular and clinical evidence implicating ferroptosis in the pathogenesis of AD, with implications for disease-modifying therapies.

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.