The Relevancy of Data Regarding the Metabolism of Iron to Our Understanding of Deregulated Mechanisms in ALS; Hypotheses and Pitfalls

Rethinking neurodegenerative diseases: neurometabolic concept linking lipid oxidation to diseases in the central nervous system

ABSTRACT

Currently, there is a lack of effective medicines capable of halting or reversing the progression of neurodegenerative disorders, including amyotrophic lateral sclerosis, Parkinson's disease, multiple sclerosis, or Alzheimer's disease. Given the unmet medical need, it is necessary to reevaluate the existing paradigms of how to target these diseases. When considering neurodegenerative diseases from a systemic neurometabolic perspective, it becomes possible to explain the shared pathological features. This innovative approach presented in this paper draws upon extensive research conducted by the authors and researchers worldwide. In this review, we highlight the importance of metabolic mitochondrial dysfunction in the context of neurodegenerative diseases. We provide an overview of the risk factors associated with developing neurodegenerative disorders, including genetic, epigenetic, and environmental factors. Additionally, we examine pathological mechanisms implicated in these diseases such as oxidative stress, accumulation of misfolded proteins, inflammation, demyelination, death of neurons, insulin resistance, dysbiosis, and neurotransmitter disturbances. Finally, we outline a proposal for the restoration of mitochondrial metabolism, a crucial aspect that may hold the key to facilitating curative therapeutic interventions for neurodegenerative disorders in forthcoming advancements.

Biochemical and Molecular Pathways in Neurodegenerative Diseases: An Integrated View

Neurodegenerative diseases (NDDs) like Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) are defined by a myriad of complex aetiologies. Understanding the common biochemical molecular pathologies among NDDs gives an opportunity to decipher the overlapping and numerous cross-talk mechanisms of neurodegeneration. Numerous interrelated pathways lead to the progression of neurodegeneration. We present evidence from the past pieces of literature for the most usual global convergent hallmarks like ageing, oxidative stress, excitotoxicity-induced calcium butterfly effect, defective proteostasis including chaperones, autophagy, mitophagy, and proteosome networks, and neuroinflammation. Herein, we applied a holistic approach to identify and represent the shared mechanism across NDDs. Further, we believe that this approach could be helpful in identifying key modulators across NDDs, with a particular focus on AD, PD, and ALS. Moreover, these concepts could be applied to the development and diagnosis of novel strategies for diverse NDDs.

Biofluid Biomarkers in the Prognosis of Amyotrophic Lateral Sclerosis: Recent Developments and Therapeutic Applications

Amyotrophic lateral sclerosis is a neurodegenerative disease characterized by the degeneration of motor neurons for which effective therapies are lacking. One of the most explored areas of research in ALS is the discovery and validation of biomarkers that can be applied to clinical practice and incorporated into the development of innovative therapies. The study of biomarkers requires an adequate theoretical and operational framework, highlighting the "fit-for-purpose" concept and distinguishing different types of biomarkers based on common terminology. In this review, we aim to discuss the current status of fluid-based prognostic and predictive biomarkers in ALS, with particular emphasis on those that are the most promising ones for clinical trial design and routine clinical practice. Neurofilaments in cerebrospinal fluid and blood are the main prognostic and pharmacodynamic biomarkers. Furthermore, several candidates exist covering various pathological aspects of the disease, such as immune, metabolic and muscle damage markers. Urine has been studied less often and should be explored for its possible advantages. New advances in the knowledge of cryptic exons introduce the possibility of discovering new biomarkers. Collaborative efforts, prospective studies and standardized procedures are needed to validate candidate biomarkers. A combined biomarkers panel can provide a more detailed disease status.

SPY1 inhibits neuronal ferroptosis in amyotrophic lateral sclerosis by reducing lipid peroxidation through regulation of GCH1 and TFR1

Ferroptosis is an iron-dependent cell death with the accumulation of lipid peroxidation and dysfunction of antioxidant systems. As the critical regulator, glutathione peroxidase 4 (GPX4) has been demonstrated to be down-regulated in amyotrophic lateral sclerosis (ALS). However, the mechanism of ferroptosis in ALS remains unclear. In this research, bioinformatics analysis revealed a high correlation between ALS, ferroptosis, and Speedy/RINGO cell cycle regulator family member A (SPY1). Lipid peroxidation of ferroptosis in hSOD1G93A cells and mice was generated by TFR1-imported excess free iron, decreased GSH, mitochondrial membrane dysfunction, upregulated ALOX15, and inactivation of GCH1, GPX4. SPY1 is a "cyclin-like" protein that has been proved to enhance the viability of hSOD1^G93A cells by inhibiting DNA damage. In our study, the decreased expression of SPY1 in ALS was resulted from unprecedented ubiquitination degradation mediated by MDM2 (a nuclear-localized E3 ubiquitin ligase). Further, SPY1 was identified as a novel ferroptosis suppressor via alleviating lipid peroxidation produced by dysregulated GCH1/BH4 axis (a resistance axis of ferroptosis) and transferrin receptor protein 1 (TFR1)-induced iron. Additionally, neuron-specific overexpression of SPY1 significantly delayed the occurrence and prolonged the survival in ALS transgenic mice through the above two pathways. These results suggest that SPY1 is a novel target for both ferroptosis and ALS.

Iron quantitative analysis of motor combined with bulbar region in M1 cortex may improve diagnosis performance in ALS

OBJECTIVES

To explore whether the combined analysis of motor and bulbar region of M1 on susceptibility-weighted imaging (SWI) can be a valid biomarker for amyotrophic lateral sclerosis (ALS).

METHODS

Thirty-two non-demented ALS patients and 35 age- and gender-matched healthy controls (HC) were retrospectively recruited. SWI and 3D-T1-MPRAGE images were obtained from all individuals using a 3.0-T MRI scan. The bilateral posterior band of M1 was manually delineated by three neuroradiologists on phase images and subdivided into the motor and bulbar regions. We compared the phase values in two groups and performed a stratification analysis (ALSFRS-R score, duration, disease progression rate, and onset). Receiver operating characteristic (ROC) curves were also constructed.

RESULTS

ALS group showed significantly increased phase values in M1 and the two subregions than the HC group, on the all and elderly level (p < 0.001, respectively). On all-age level comparison, negative correlations were found between phase values of M1 and clinical score and duration (p < 0.05, respectively). Similar associations were found in the motor region (p < 0.05, respectively). On both the total (p < 0.01) and elderly (p < 0.05) levels, there were positive relationships between disease progression rate and M1 phase values. In comparing ROC curves, the entire M1 showed the best diagnostic performance.

CONCLUSIONS

Combining motor and bulbar analyses as an integral M1 region on SWI can improve ALS diagnosis performance, especially in the elderly. The phase value could be a valuable biomarker for ALS evaluation.

KEY POINTS

• Integrated analysis of the motor and bulbar as an entire M1 region on SWI can improve the diagnosis performance in ALS. • Quantitative analysis of iron deposition by SWI measurement helps the clinical evaluation, especially for the elderly patients. • Phase value, when combined with the disease progression rate, could be a valuable biomarker for ALS.

Role of Iron in Aging Related Diseases

Iron progressively accumulates with age and can be further exacerbated by dietary iron intake, genetic factors, and repeated blood transfusions. While iron plays a vital role in various physiological processes within the human body, its accumulation contributes to cellular aging in several species. In its free form, iron can initiate the formation of free radicals at a cellular level and contribute to systemic disorders. This is most evident in high iron conditions such as hereditary hemochromatosis, when accumulation of iron contributes to the development of arthritis, cirrhosis, or cardiomyopathy. A growing body of research has further identified iron’s contributory effects in neurodegenerative diseases, ocular disorders, cancer, diabetes, endocrine dysfunction, and cardiovascular diseases. Reducing iron levels by repeated phlebotomy, iron chelation, and dietary restriction are the common therapeutic considerations to prevent iron toxicity. Chelators such as deferoxamine, deferiprone, and deferasirox have become the standard of care in managing iron overload conditions with other potential applications in cancer and cardiotoxicity. In certain animal models, drugs with iron chelating ability have been found to promote health and even extend lifespan. As we further explore the role of iron in the aging process, iron chelators will likely play an increasingly important role in our health.

Alterations of the serum and CSF ferritin levels and the diagnosis and prognosis of amyotrophic lateral sclerosis

Background

The ALS diagnostic challenges necessitate more robust diagnostic and prognostic methods. A potential biomarker in this regard is the alterations of ferritin levels in the serum and CSF of patients compared to controls.

Methods

The CSF and serum ferritin levels were measured in 50 ALS cases and 50 control patients with predefined exclusion criteria. The ELISA method was utilized for laboratory measurement and was statistically analyzed using the SPSS.

Results

Heightened serum ferritin levels in cases were not statistically significant. However, CSF ferritin levels were significantly higher in ALS patients (P < 0.001). Serum ferritin levels were significantly negatively correlated with the disease duration (P = 0.015) and were significantly positively correlated with the disease progression rate (DPR) (P = 0.012).

Conclusion

Heightened CSF ferritin levels can be used for the diagnosis of ALS. The correlation between the serum ferritin levels with the DPR and its correlation with the disease duration suggests potential prognostic utilities.

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Elevated serum ferritin level in patients with ALS is insignificant.

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CSF ferritin levels are significantly higher in ALS patients.

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Serum ferritin levels are negatively correlated with the disease duration.

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Serum ferritin levels are positively correlated with the disease progression rate.

The study of levels from redox-active elements in cerebrospinal fluid of amyotrophic lateral sclerosis patients carrying disease-related gene mutations shows potential copper dyshomeostasis

Amyotrophic lateral sclerosis is a progressive neurodegenerative disease characterized by a loss of function of motor neurons. The etiology of this disorder is still largely unknown. Gene-environment interaction arises as a possible key factor in the development of amyotrophic lateral sclerosis. We assessed the levels of trace metals, copper (Cu), iron (Fe), and manganese (Mn), of 9 amyotrophic lateral sclerosis cases and 40 controls by measuring their content in cerebrospinal fluid. The following trace element species were quantified using ion chromatography-inductively coupled plasma mass spectrometry: univalent copper (Cu-I), divalent Cu (Cu-II), divalent Fe (Fe-II), trivalent Fe (Fe-III), divalent Mn (Mn-II), trivalent Mn (Mn-III), and also unidentified Mn species (Mn-unknown) were present in some samples. When computing the relative risks for amyotrophic lateral sclerosis through an unconditional logistic regression model, we observed a weak and imprecise positive association for iron (Fe III, adjusted odds ratio 1.48, 95% CI 0.46-4.76) and manganese (total-Mn and Mn-II; adjusted odds ratio 1.11, 95% CI 0.74-1.67, and 1.13, 95% CI 0.79-1.61, respectively). Increased risk for copper was found both in the crude analysis (odds ratio 1.14, 95% CI 0.99-1.31) and in multivariable analysis after adjusting for sex, age, and year of storage (1.09, 95% CI 0.90-1.32). Our results suggest a possible positive association between Cu and genetic amyotrophic lateral sclerosis, while they give little indication of involvement of Fe and Mn in disease, though some correlations found also for these elements deserve further investigation.

Biomarkers in amyotrophic lateral sclerosis: a review of new developments

PURPOSE OF REVIEW

This review draws together the most recent findings in ALS biomarker research from biochemical, imaging and neurophysiology techniques.

RECENT FINDINGS

The potential of circulating RNA is highlighted, including new retrieval techniques. With ongoing genetic clinical trials, the need for pharmacodynamic biomarkers is essential. There is a strong case for neurofilament proteins being validated in ALS; their biomarker profile is discussed. Oxidative stress and neuroinflammation studies offer insight into disease mechanisms and offer good biomarker potential. Recent metabolic studies include investigation of lipid profiles, creatinine and ferritin. The potential of chitinase proteins as pharmacodynamic and prognostic biomarkers is highlighted. The role of tau and amyloidβ is debated, as evidenced by the articles presented here. Proteomic approaches provide unbiased discoveries of novel biomarkers, together with confirmation of previous findings. The use of imaging techniques is outlined to demonstrate selective atrophy, volume loss, muscle and tract involvement. In-vivo imaging is discussed with reference to histone deacetylase, oxidative stress, neuroinflammation and metabolic changes. New applications of electrophysiology demonstrate objective muscle biomarkers and brain network perturbations.

SUMMARY

The biomarker research field continues to provide insight into the disease. Multicentre collaborations are needed to validate these promising recent findings.

hTBK1-c.978T>A mutation promotes the ferroptosis in NSC-34 cells via mediation of KEAP1/NRF2/p62 signaling

BACKGROUND

Amyotrophic lateral sclerosis (ALS) can result in the dysfunction of upper and lower motor neurons. A previous study has indicated that TBK1 mutation (hTBK1-c.978T>A) is involved in progression of ALS. However, the mechanism by which TBK1 mutation mediates the progression of ALS remains unclear.

METHODS

NSC-34 cells with hTBK1-c.978T>A mutation (TBK1 mutation status) was used to mimic ALS in vitro. In addition, cell proliferation was detected by Ki67 staining. Gene and protein expressions in NSC-34 cells were detected by RT-qPCR and western blot, respectively. ROS and PGSK levels in NSC-34 cells were detected by flow cytometry.

RESULTS

hTBK1-c.978T>A mutation significantly inhibited the proliferation of NSC-34 cells via inducing cell ferroptosis, while the effect of TBK1 mutation was notably reversed by Ferrostatin-1 or p62 siRNA. Meanwhile, hTBK1-c.978T>A mutation significantly increased the expression of KEAP1 in NSC-34 cells, while this phenomenon was partially reversed by p62 knockdown.

CONCLUSION

hTBK1-c.978T>A mutation promoted promotes the ferroptosis in NSC-34 cells via regulation of KEAP1/NRF2/p62 signaling. Thus, hTBK1-c.978T>A mutation may serve as a possible target for the treatment of ALS.

Ferroptosis in Friedreich's Ataxia: A Metal-Induced Neurodegenerative Disease

Ferroptosis is an iron-dependent form of regulated cell death, arising from the accumulation of lipid-based reactive oxygen species when glutathione-dependent repair systems are compromised. Lipid peroxidation, mitochondrial impairment and iron dyshomeostasis are the hallmark of ferroptosis, which is emerging as a crucial player in neurodegeneration. This review provides an analysis of the most recent advances in ferroptosis, with a special focus on Friedreich's Ataxia (FA), the most common autosomal recessive neurodegenerative disease, caused by reduced levels of frataxin, a mitochondrial protein involved in iron-sulfur cluster synthesis and antioxidant defenses. The hypothesis is that the iron-induced oxidative damage accumulates over time in FA, lowering the ferroptosis threshold and leading to neuronal cell death and, at last, to cardiac failure. The use of anti-ferroptosis drugs combined with treatments able to activate the antioxidant response will be of paramount importance in FA therapy, such as in many other neurodegenerative diseases triggered by oxidative stress.

Lessons learned from CHMP2B, implications for frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS) are two neurodegenerative diseases with clinical, genetic and pathological overlap. As such, they are commonly regarded as a single spectrum disorder, with pure FTD and pure ALS representing distinct ends of a continuum. Dysfunctional endo-lysosomal and autophagic trafficking, leading to impaired proteostasis is common across the FTD-ALS spectrum. These pathways are, in part, mediated by CHMP2B, a protein that coordinates membrane scission events as a core component of the ESCRT machinery. Here we review how ALS and FTD disease causing mutations in CHMP2B have greatly contributed to our understanding of how endosomal-lysosomal and autophagic dysfunction contribute to neurodegeneration, and how in vitro and in vivo models have helped elucidate novel candidates for potential therapeutic intervention with implications across the FTD-ALS spectrum.

Overdosing on iron: Elevated iron and degenerative brain disorders

IMPACT STATEMENT

Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.

The role of alpha-synuclein as ferrireductase in neurodegeneration associated with Parkinson's disease

Misfolding of the protein α-synuclein contributes to the formation of the intracellular inclusion, Lewy bodies. Although these structures are not exclusive to Parkinson's disease, nevertheless, their presence in the substantia nigra is mandatory for the pathological diagnosis of the disorder. Therefore, there must be a focus on the pathological mechanisms responsible for Lewy body generation. Recent studies have suggested that α-synuclein has the potential to operate as the enzyme ferrireductase. Perhaps in the early diseased state, overexpression or mutation of alpha-synuclein/ferrireductase invokes the dyshomeostasis of iron (III)/(II) only, while in advanced stages, accumulation of iron in particular areas of the brain follows. Furthermore, the loss of an important iron chelator, neuromelanin (due to dopaminergic neuronal death), may then result in the release and increase in unbound free iron. Iron could generate reactive oxygen species, which could instigate a torrent of cellular deleterious processes. In addition, loss of energy supply may contribute to the alteration in activity of enzymes involved in the mitochondrial respiratory chain and would, therefore, confer a vulnerability to the dopaminergic neurons in the substantia nigra. Therefore, the ferrireductase alpha-synuclein may hold the key for major pathology of Parkinson's disease. In conclusion, we hypothesize that environmentally or genetically overexpressed and/or mutated α-synuclein/ferrireductase causes iron dyshomeostasis without increase of free iron concentration in the early phases of PD, while increased iron concentration accompanied by iron dyshomeostasis is a marker for progressed PD stages. It is essential to elucidate these degenerative mechanisms, so as to provide effective therapeutic treatment to halt or delay the progression of the illness already in the early phase of PD. The development of iron chelators seems to be a reasonable approach.

Soluble iron accumulation induces microglial glutamate release in the spinal cord of sporadic amyotrophic lateral sclerosis

Previous studies on sporadic amyotrophic lateral sclerosis (SALS) demonstrated iron accumulation in the spinal cord and increased glutamate concentration in the cerebrospinal fluid. To clarify the relationship between the two phenomena, we first performed quantitative and morphological analyses of substances related to iron and glutamate metabolism using spinal cords obtained at autopsy from 12 SALS patients and 12 age-matched control subjects. Soluble iron content determined by the Ferrozine method as well as ferritin (Ft) and glutaminase C (GLS-C) expression levels on Western blots were significantly higher in the SALS group than in the control group, while ferroportin (FPN) levels on Western blots were significantly reduced in the SALS group as compared to the control group. There was no significant difference in aconitase 1 (ACO1) and tumor necrosis factor-alpha (TNFα)-converting enzyme (TACE) levels on Western blots between the two groups. Immunohistochemically, Ft, ACO1, TACE, TNFα, and GLS-C were proven to be selectively expressed in microglia. Immunoreactivities for FPN and hepcidin were localized in neuronal and glial cells. Based on these observations, it is predicted that soluble iron may stimulate microglial glutamate release. To address this issue, cell culture experiments were carried out on a microglial cell line (BV-2). Treatment of BV-2 cells with ferric ammonium citrate (FAC) brought about significant increases in intracellular soluble iron and Ft expression levels and conditioned medium glutamate and TNFα concentrations. Glutamate concentration was also significantly increased in conditioned media of TNFα-treated BV-2 cells. While the FAC-driven increases in glutamate and TNFα release were completely canceled by pretreatment with ACO1 and TACE inhibitors, respectively, the TNFα-driven increase in glutamate release was completely canceled by GLS-C inhibitor pretreatment. Moreover, treatment of BV-2 cells with hepcidin resulted in a significant reduction in FPN expression levels on Western blots of the intracellular total protein extracts. The present results provide in vivo and in vitro evidence that microglial glutamate release in SALS spinal cords is enhanced by intracellular soluble iron accumulation-induced activation of ACO1 and TACE and by increased extracellular TNFα-stimulated GLS-C upregulation, and suggest a positive feedback mechanism to maintain increased intracellular soluble iron levels, involving TNFα, hepcidin, and FPN.

Hepcidin and its therapeutic potential in neurodegenerative disorders

Abnormally high brain iron, resulting from the disrupted expression or function of proteins involved in iron metabolism in the brain, is an initial cause of neuronal death in neuroferritinopathy and aceruloplasminemia, and also plays a causative role in at least some of the other neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich's ataxia. As such, iron is believed to be a novel target for pharmacological intervention in these disorders. Reducing iron toward normal levels or hampering the increases in iron associated with age in the brain is a promising therapeutic strategy for all iron-related neurodegenerative disorders. Hepcidin is a crucial regulator of iron homeostasis in the brain. Recent studies have suggested that upregulating brain hepcidin levels can significantly reduce brain iron content through the regulation of iron transport protein expression in the blood-brain barrier and in neurons and astrocytes. In this review, we focus on the discussion of the therapeutic potential of hepcidin in iron-associated neurodegenerative diseases and also provide a systematic overview of recent research progress on how misregulated brain iron metabolism is involved in the development of multiple neurodegenerative disorders.