Involvement of ApoE E4 and H63D in sporadic Alzheimer's disease in a folate-supplemented Ontario population

Imbalance of Essential Metals in Traumatic Brain Injury and Its Possible Link with Disorders of Consciousness

Dysfunction of the complex cerebral networks underlying wakefulness and awareness is responsible for Disorders of Consciousness (DoC). Traumatic Brain Injury (TBI) is a common cause of DoC, and it is responsible for a multi-dimensional pathological cascade that affects the proper functioning of the brainstem and brain consciousness pathways. Iron (Fe), Zinc (Zn), and Copper (Cu) have a role in the neurophysiology of both the ascending reticular activating system, a multi-neurotransmitter network located in the brainstem that is crucial for consciousness, and several brain regions. We aimed to summarize the role of these essential metals in TBI and its possible link with consciousness alterations. We found that TBI alters many neuronal molecular mechanisms involving essential metals, causing neurodegeneration, neural apoptosis, synaptic dysfunction, oxidative stress, and inflammation. This final pattern resembles that described for Alzheimer's disease (AD) and other neurological and psychiatric diseases. Furthermore, we found that amantadine, zolpidem, and transcranial direct current stimulation (tDCS)-the most used treatments for DoC recovery-seem to have an effect on essential metals-related pathways and that Zn might be a promising new therapeutic approach. This review summarizes the neurophysiology of essential metals in the brain structures of consciousness and focuses on the mechanisms underlying their imbalance following TBI, suggesting their possible role in DoC. The scenario supports further studies aimed at getting a deeper insight into metals' role in DoC, in order to evaluate metal-based drugs, such as metal complexes and metal chelating agents, as potential therapeutic options.

Age-Related Changes in Skeletal Muscle Iron Homeostasis

Sarcopenia is an age-related condition of slow, progressive loss of muscle mass and strength, which contributes to frailty, increased risk of hospitalization and mortality, and increased health care costs. The incidence of sarcopenia is predicted to increase to >200 million affected older adults worldwide over the next 40 years, highlighting the urgency for understanding biological mechanisms and developing effective interventions. An understanding of the mechanisms underlying sarcopenia remains incomplete. Iron in the muscle is important for various metabolic functions, including oxygen supply and electron transfer during energy production, yet these same chemical properties of iron may be deleterious to the muscle when either in excess or when biochemically unshackled (eg, in ferroptosis), it can promote oxidative stress and induce inflammation. This review outlines the mechanisms leading to iron overload in muscle with aging and evaluates the evidence for the iron overload hypothesis of sarcopenia. Based on current evidence, studies are needed to (a) determine the mechanisms leading to iron overload in skeletal muscle during aging; and (b) investigate whether skeletal muscles are functionally deficient in iron during aging leading to impairments in oxidative metabolism.

Iron in Alzheimer's Disease: From Physiology to Disease Disabilities

Reactive oxygen species (ROS) play a key role in the neurodegeneration processes. Increased oxidative stress damages lipids, proteins, and nucleic acids in brain tissue, and it is tied to the loss of biometal homeostasis. For this reason, attention has been focused on transition metals involved in several biochemical reactions producing ROS. Even though a bulk of evidence has uncovered the role of metals in the generation of the toxic pathways at the base of Alzheimer's disease (AD), this matter has been sidelined by the advent of the Amyloid Cascade Hypothesis. However, the link between metals and AD has been investigated in the last two decades, focusing on their local accumulation in brain areas known to be critical for AD. Recent evidence revealed a relation between iron and AD, particularly in relation to its capacity to increase the risk of the disease through ferroptosis. In this review, we briefly summarize the major points characterizing the function of iron in our body and highlight why, even though it is essential for our life, we have to monitor its dysfunction, particularly if we want to control our risk of AD.

Iron and Alzheimer's Disease: From Pathology to Imaging

Alzheimer's disease (AD) is a debilitating brain disorder that afflicts millions worldwide with no effective treatment. Currently, AD progression has primarily been characterized by abnormal accumulations of β-amyloid within plaques and phosphorylated tau within neurofibrillary tangles, giving rise to neurodegeneration due to synaptic and neuronal loss. While β-amyloid and tau deposition are required for clinical diagnosis of AD, presence of such abnormalities does not tell the complete story, and the actual mechanisms behind neurodegeneration in AD progression are still not well understood. Support for abnormal iron accumulation playing a role in AD pathogenesis includes its presence in the early stages of the disease, its interactions with β-amyloid and tau, and the important role it plays in AD related inflammation. In this review, we present the existing evidence of pathological iron accumulation in the human AD brain, as well as discuss the imaging tools and peripheral measures available to characterize iron accumulation and dysregulation in AD, which may help in developing iron-based biomarkers or therapeutic targets for the disease.

Hemochromatosis Mutations, Brain Iron Imaging, and Dementia in the UK Biobank Cohort

Background:

Brain iron deposition occurs in dementia. In European ancestry populations, the HFE p.C282Y variant can cause iron overload and hemochromatosis, mostly in homozygous males.

Objective:

To estimate p.C282Y associations with brain MRI features plus incident dementia diagnoses during follow-up in a large community cohort.

Methods:

UK Biobank participants with follow-up hospitalization records (mean 10.5 years). MRI in 206 p.C282Y homozygotes versus 23,349 without variants, including T2^* measures (lower values indicating more iron).

Results:

European ancestry participants included 2,890 p.C282Y homozygotes. Male p.C282Y homozygotes had lower T2^* measures in areas including the putamen, thalamus, and hippocampus, compared to no HFE mutations. Incident dementia was more common in p.C282Y homozygous men (Hazard Ratio HR = 1.83; 95% CI 1.23 to 2.72, p = 0.003), as was delirium. There were no associations in homozygote women or in heterozygotes.

Conclusion:

Studies are needed of whether early iron reduction prevents or slows related brain pathologies in male HFE p.C282Y homozygotes.

Regional brain iron associated with deterioration in Alzheimer's disease: A large cohort study and theoretical significance

OBJECTIVE

This paper is a proposal for an update of the iron hypothesis of Alzheimer's disease (AD), based on large-scale emerging evidence.

BACKGROUND

Iron featured historically early in AD research efforts for its involvement in the amyloid and tau proteinopathies, APP processing, genetics, and one clinical trial, yet iron neurochemistry remains peripheral in mainstream AD research. Much of the effort investigating iron in AD has focused on the potential for iron to provoke the onset of disease, by promoting proteinopathy though increased protein expression, phosphorylation, and aggregation.

NEW/UPDATED HYPOTHESIS

We provide new evidence from a large post mortem cohort that brain iron levels within the normal range were associated with accelerated ante mortem disease progression in cases with underlying proteinopathic neuropathology. These results corroborate recent findings that argue for an additional downstream role for iron as an effector of neurodegeneration, acting independently of tau or amyloid pathologies. We hypothesize that the level of tissue iron is a trait that dictates the probability of neurodegeneration in AD by ferroptosis, a regulated cell death pathway that is initiated by signals such as glutathione depletion and lipid peroxidation.

MAJOR CHALLENGES FOR THE HYPOTHESIS

While clinical biomarkers of ferroptosis are still in discovery, the demonstration of additional ferroptotic correlates (genetic or biomarker derived) of disease progression is required to test this hypothesis. The genes implicated in familial AD are not known to influence ferroptosis, although recent reports on APP mutations and apolipoprotein E allele (APOE) have shown impact on cellular iron retention. Familial AD mutations will need to be tested for their impact on ferroptotic vulnerability. Ultimately, this hypothesis will be substantiated, or otherwise, by a clinical trial of an anti-ferroptotic/iron compound in AD patients.

LINKAGE TO OTHER MAJOR THEORIES

Iron has historically been linked to the amyloid and tau proteinopathies of AD. Tau, APP, and apoE have been implicated in physiological iron homeostasis in the brain. Iron is biochemically the origin of most chemical radicals generated in biochemistry and thus closely associated with the oxidative stress theory of AD. Iron accumulation is also a well-established consequence of aging and inflammation, which are major theories of disease pathogenesis.

The roles of iron and HFE genotype in neurological diseases

Iron accumulation is a recurring pathological phenomenon in many neurological diseases including Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, and others. Iron is essential for normal development and functions of the brain; however, excess redox-active iron can also lead to oxidative damage and cell death. Especially for terminally differentiated cells like neurons, regulation of reactive oxygen species is critical for cell viability. As a result, cellular iron level is tightly regulated. Although iron accumulation related to neurological diseases has been well documented, the pathoetiological contributions of the homeostatic iron regulator (HFE), which controls cellular iron uptake, is less understood. Furthermore, a common HFE variant, H63D HFE, has been identified as a modifier of multiple neurological diseases. This review will discuss the roles of iron and HFE in the brain as well as their impact on various disease processes.

Iron Metabolism of the Skeletal Muscle and Neurodegeneration

Recent studies clearly indicate that the endocrine function of the skeletal muscle is essential for a long and healthy life. Regular exercise, which has been shown to stimulate the release of myokines, lowers the risk of many diseases, including Alzheimer’s and Parkinson’s disease, emphasizing the role of skeletal muscle in proper functioning of other tissues. In addition, exercise increases insulin sensitivity, which may also impact iron metabolism. Even though the role of iron in neurodegeneration is well established, the exact mechanisms of iron toxicity are not known. Interestingly, exercise has been shown to modulate iron metabolism, mainly by reducing body iron stores. Insulin signaling and iron metabolism are interconnected, as high tissue iron stores are associated with insulin resistance, and conversely, impaired insulin signaling may lead to iron accumulation in an affected tissue. Excess iron accumulation in tissue triggers iron-dependent oxidative stress. Further, iron overload in the skeletal muscle not only negatively affects muscle contractility but also might impact its endocrine function, thus possibly affecting the clinical outcome of diseases, including neurodegenerative diseases. In this review, we discuss possible mechanisms of iron dependent oxidative stress in skeletal muscle, its impact on muscle mass and endocrine function, as well as on neurodegeneration processes.

Could Alzheimer's Disease Originate in the Periphery and If So How So?

The classical amyloid cascade model for Alzheimer's disease (AD) has been challenged by several findings. Here, an alternative molecular neurobiological model is proposed. It is shown that the presence of the APOE ε4 allele, altered miRNA expression and epigenetic dysregulation in the promoter region and exon 1 of TREM2, as well as ANK1 hypermethylation and altered levels of histone post-translational methylation leading to increased transcription of TNFA, could variously explain increased levels of peripheral and central inflammation found in AD. In particular, as a result of increased activity of triggering receptor expressed on myeloid cells 2 (TREM-2), the presence of the apolipoprotein E4 (ApoE4) isoform, and changes in ANK1 expression, with subsequent changes in miR-486 leading to altered levels of protein kinase B (Akt), mechanistic (previously mammalian) target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3), all of which play major roles in microglial activation, proliferation and survival, there is activation of microglia, leading to the subsequent (further) production of cytokines, chemokines, nitric oxide, prostaglandins, reactive oxygen species, inducible nitric oxide synthase and cyclooxygenase-2, and other mediators of inflammation and neurotoxicity. These changes are associated with the development of amyloid and tau pathology, mitochondrial dysfunction (including impaired activity of the electron transport chain, depleted basal mitochondrial potential and oxidative damage to key tricarboxylic acid enzymes), synaptic dysfunction, altered glycogen synthase kinase-3 (GSK-3) activity, mTOR activation, impairment of autophagy, compromised ubiquitin-proteasome system, iron dyshomeostasis, changes in APP translation, amyloid plaque formation, tau hyperphosphorylation and neurofibrillary tangle formation.

No Genetic Overlap Between Circulating Iron Levels and Alzheimer's Disease

Iron deposition in the brain is a prominent feature of Alzheimer's disease (AD). Recently, peripheral iron measures have also been shown to be associated with AD status. However, it is not known whether these associations are causal: do elevated or depleted iron levels throughout life have an effect on AD risk? We evaluate the effects of peripheral iron on AD risk using a genetic profile score approach by testing whether variants affecting iron, transferrin, or ferritin levels selected from GWAS meta-analysis of approximately 24,000 individuals are also associated with AD risk in an independent case-control cohort (n∼10,000). Conversely, we test whether AD risk variants from a GWAS meta-analysis of approximately 54,000 account for any variance in iron measures (n∼9,000). We do not identify a genetic relationship, suggesting that peripheral iron is not causal in the initiation of AD pathology.

Serum Iron, Zinc, and Copper Levels in Patients with Alzheimer's Disease: A Replication Study and Meta-Analyses

To evaluate whether iron, zinc, and copper levels in serum are disarranged in Alzheimer's disease (AD), we performed meta-analyses of all studies on the topic published from 1984 to 2014 and contextually carried out a replication study in serum as well. Our meta-analysis results showed that serum zinc was significantly lower in AD patients. Our replication and meta-analysis results showed that serum copper was significantly higher in AD patients than in healthy controls, so our findings were consistent with the conclusions of four previously published copper meta-analyses. Even if a possible role of iron in the pathophysiology of the disease could not be ruled out, the results of our meta-analysis showed no change of serum iron levels in AD patients, but this conclusion was not robust and requires further investigation. The meta-regression analyses revealed that in some studies, differences in serum iron levels could be due to the different mean ages, while differences in zinc levels appeared to be due to the different sex ratios. However, the effect of sex ratio on serum zinc levels in our meta-analysis is subtle and needs further confirmation. Also, diverse demographic terms and methodological approaches appeared not to explain the high heterogeneity of our copper meta-analysis. Therefore, when investigating trace elements, covariants such as age and sex have to be taken into account in the analyses. In the light of these findings, we suggest that the possible alteration of serum zinc and copper levels are involved in the pathogenesis of AD.

Multi-Target Directed Donepezil-Like Ligands for Alzheimer's Disease

HIGHLIGHTS ASS234 is a MTDL compound containing a moiety from Donepezil and the propargyl group from the PF 9601N, a potent and selective MAO B inhibitor. This compound is the most advanced anti-Alzheimer agent for preclinical studies identified in our laboratory.Derived from ASS234 both multipotent donepezil-indolyl (MTDL-1) and donepezil-pyridyl hybrids (MTDL-2) were designed and evaluated as inhibitors of AChE/BuChE and both MAO isoforms. MTDL-2 showed more high affinity toward the four enzymes than MTDL-1.MTDL-3 and MTDL-4, were designed containing the N-benzylpiperidinium moiety from Donepezil, a metal- chelating 8-hydroxyquinoline group and linked to a N-propargyl core and they were pharmacologically evaluated.The presence of the cyano group in MTDL-3, enhanced binding to AChE, BuChE and MAO A. It showed antioxidant behavior and it was able to strongly complex Cu(II), Zn(II) and Fe(III).MTDL-4 showed higher affinity toward AChE, BuChE.MTDL-3 exhibited good brain penetration capacity (ADMET) and less toxicity than Donepezil. Memory deficits in scopolamine-lesioned animals were restored by MTDL-3.MTDL-3 particularly emerged as a ligand showing remarkable potential benefits for its use in AD therapy. Alzheimer's disease (AD), the most common form of adult onset dementia, is an age-related neurodegenerative disorder characterized by progressive memory loss, decline in language skills, and other cognitive impairments. Although its etiology is not completely known, several factors including deficits of acetylcholine, β-amyloid deposits, τ-protein phosphorylation, oxidative stress, and neuroinflammation are considered to play significant roles in the pathophysiology of this disease. For a long time, AD patients have been treated with acetylcholinesterase inhibitors such as donepezil (Aricept®) but with limited therapeutic success. This might be due to the complex multifactorial nature of AD, a fact that has prompted the design of new Multi-Target-Directed Ligands (MTDL) based on the "one molecule, multiple targets" paradigm. Thus, in this context, different series of novel multifunctional molecules with antioxidant, anti-amyloid, anti-inflammatory, and metal-chelating properties able to interact with multiple enzymes of therapeutic interest in AD pathology including acetylcholinesterase, butyrylcholinesterase, and monoamine oxidases A and B have been designed and assessed biologically. This review describes the multiple targets, the design rationale and an in-house MTDL library, bearing the N-benzylpiperidine motif present in donepezil, linked to different heterocyclic ring systems (indole, pyridine, or 8-hydroxyquinoline) with special emphasis on compound ASS234, an N-propargylindole derivative. The description of the in vitro biological properties of the compounds and discussion of the corresponding structure-activity-relationships allows us to highlight new issues for the identification of more efficient MTDL for use in AD therapy.

HFE gene variants, iron, and lipids: a novel connection in Alzheimer's disease

Iron accumulation and associated oxidative stress in the brain have been consistently found in several neurodegenerative diseases. Multiple genetic studies have been undertaken to try to identify a cause of neurodegenerative diseases but direct connections have been rare. In the iron field, variants in the HFE gene that give rise to a protein involved in cellular iron regulation, are associated with iron accumulation in multiple organs including the brain. There is also substantial epidemiological, genetic, and molecular evidence of disruption of cholesterol homeostasis in several neurodegenerative diseases, in particular Alzheimer's disease (AD). Despite the efforts that have been made to identify factors that can trigger the pathological events associated with neurodegenerative diseases they remain mostly unknown. Because molecular phenotypes such as oxidative stress, synaptic failure, neuronal loss, and cognitive decline, characteristics associated with AD, have been shown to result from disruption of a number of pathways, one can easily argue that the phenotype seen may not arise from a linear sequence of events. Therefore, a multi-targeted approach is needed to understand a complex disorder like AD. This can be achieved only when knowledge about interactions between the different pathways and the potential influence of environmental factors on them becomes available. Toward this end, this review discusses what is known about the roles and interactions of iron and cholesterol in neurodegenerative diseases. It highlights the effects of gene variants of HFE (H63D- and C282Y-HFE) on iron and cholesterol metabolism and how they may contribute to understanding the etiology of complex neurodegenerative diseases.

Metallostasis in Alzheimer's disease

2012 has been another year in which multiple large-scale clinical trials for Alzheimer's disease (AD) have failed to meet their clinical endpoints. With the social and financial burden of this disease increasing every year, the onus is now on the field of AD researchers to investigate alternative ideas to deliver outcomes for patients. Although several major clinical trials targeting Aβ have failed, three smaller clinical trials targeting metal interactions with Aβ have all shown benefit for patients. Here we review the genetic, pathological, biochemical, and pharmacological evidence that underlies the metal hypothesis of AD. The AD-affected brain suffers from metallostasis, or fatigue of metal trafficking, resulting in redistribution of metals into inappropriate compartments. The metal hypothesis is built upon a triad of transition elements: iron, copper, and zinc. The hypothesis has matured from early investigations showing amyloidogenic and oxidative stress consequences of these metals; recently, disease-related proteins, APP, tau, and presenilin, have been shown to have major roles in metal regulation, which provides insight into the pathway of neurodegeneration in AD and illuminates potential new therapeutic avenues.

Glutamate-mediated primary somatosensory cortex excitability correlated with circulating copper and ceruloplasmin

Objective. To verify whether markers of metal homeostasis are related to a magnetoencephalographic index representative of glutamate-mediated excitability of the primary somatosensory cortex. The index is identified as the source strength of the earliest component (M20) of the somatosensory magnetic fields (SEFs) evoked by right median nerve stimulation at wrist. Method. Thirty healthy right-handed subjects (51 ± 22 years) were enrolled in the study. A source reconstruction algorithm was applied to assess the amount of synchronously activated neurons subtending the M20 and the following SEF component (M30), which is generated by two independent contributions of gabaergic and glutamatergic transmission. Serum copper, ceruloplasmin, iron, transferrin, transferrin saturation, and zinc levels were measured. Results. Total copper and ceruloplasmin negatively correlated with the M20 source strength. Conclusion. This pilot study suggests that higher level of body copper reserve, as marked by ceruloplasmin variations, parallels lower cortical glutamatergic responsiveness.

Towards the prevention of potential aluminum toxic effects and an effective treatment for Alzheimer's disease

In 1991, treatment with low dose intramuscular desferrioxamine (DFO), a trivalent chelator that can remove excessive iron and/or aluminum from the body, was reported to slow the progression of Alzheimer's disease (AD) by a factor of two. Twenty years later this promising trial has not been followed up and why this treatment worked still is not clear. In this critical interdisciplinary review, we provide an overview of the complexities of AD and involvement of metal ions, and revisit the neglected DFO trial. We discuss research done by us and others that is helping to explain involvement of metal ion catalyzed production of reactive oxygen species in the pathogenesis of AD, and emerging strategies for inhibition of metal-ion toxicity. Highlighted are insights to be considered in the quests to prevent potentially toxic effects of aluminum toxicity and prevention and intervention in AD.

Association between HFE polymorphisms and susceptibility to Alzheimer's disease: a meta-analysis of 22 studies including 4,365 cases and 8,652 controls

Whether the variations in the hemochromatosis (HFE) gene increase Alzheimer's disease (AD) risk is still undetermined. We performed a meta-analysis in order to systematically summarize the possible association. Studies were identified by searching PUBMED, Web of Science and EMBASE databases complemented with screening the references of the retrieved studies. The association was measured using random-effect or fixed-effect odds ratio (OR) combined with 95% confidence intervals (CIs) according to the studies' heterogeneity. For C282Y polymorphism, we did not find any association using data from 22 studies including 4,365 cases and 8,652 controls. For H63D polymorphism, on the basis of 2,795 cases and 7,424 controls from 17 studies, we observed a significant association (allele contrast: OR = 0.902, 95% CI = 0.819-0.994, P = 0.037; minor-allele-dominant model: OR = 0.887, 95% CI = 0.790-0.996, P = 0.043). No publication bias was detected in this meta-analysis. The synthesis of available evidence supports mutant of HFE H63D polymorphism plays a protective role for AD risk.

The H63D HFE gene variant promotes activation of the intrinsic apoptotic pathway via mitochondria dysfunction following β-amyloid peptide exposure

Numerous epidemiological studies suggest that the expression of the HFE allelic variant H63D may be a risk factor or genetic modifier for Alzheimer's disease (AD). The H63D variant alters cellular iron homeostasis and increases baseline oxidative stress. The elevated cellular stress milieu, we have proposed, may alter cellular responses to genetic and environmental determinants of AD. Accumulation of β-amyloid peptides (Aβ) is one of the most prominent pathogenic characteristics of AD. Several studies have demonstrated that Aβ can induce neuronal cell death through apoptosis. In this study, we provide evidence that an Aβ(25-35) fragment, which contains the cytotoxic sequence of the amyloid peptide, activates the intrinsic apoptotic pathway in SH-SY5Y human neuroblastoma cells expressing the HFE allelic variant H63D to a greater extent than in cells with wild-type (WT) HFE. Specifically, Aβ(25-35) peptide exposure significantly induced Bax translocation from the cytosol to the mitochondria in H63D-expressing cells compared with WT cells. This translocation was associated with increased cytochrome c release from mitochondria and an increase in active caspase-9 and caspase-3 activity in H63D cells. Consequently, there is increased apoptosis in cells expressing the H63D variant as opposed to cells expressing WT HFE. We also found increased amyloid precursor protein (APP) and Aβ(1-42) peptide in the mitochondrial compartment as well as increased mitochondrial stress in H63D-expressing cells compared with WT. These findings support our hypothesis that the presence of the HFE H63D allele enables factors that trigger neurodegenerative processes associated with AD and predisposes cells to cytotoxcity.

Effects of hemochromatosis and transferrin gene mutations on iron dyshomeostasis, liver dysfunction and on the risk of Alzheimer's disease

It is now accepted that transition metals, such as iron and copper, are involved in the pathogenesis of the Alzheimer's disease (AD) through their participation in toxic oxidative phenomena. In this context, hemochromatosis (Hfe) and transferrin (Tf) genes are of particular importance, since they play a key role in iron homeostasis. Also, signs of liver distress which accompany metal dysmetabolisms have been shown to be linked to AD. In order to investigate whether and how all these factors are interconnected, in this study we have explored the relationship of the gene variants of Hfe H63D and C282Y and of Tf C2 with serum markers of iron status (iron, ferritin, TF, TF-saturation, ceruloplasmin -CP-, CP and TF serum concentrations (CP/TF) ratio), and of liver function (albumin, transaminases, prothrombin time-prothrombin time (PT)) in a sample of 160 AD patients and 79 healthy elderly controls. Albumin resulted in lower, PT longer and AST/ALT higher ratios in AD patients than in controls, indicating a distress of the liver. Also TF was lower and ferritin higher in AD. Multiple logistic regression backward analyses, performed to evaluate the effects of our biochemical variables upon the probability of developing AD, revealed that a one-unit TF serum-decrease increases the probability of AD by 80%, a one-unit albumin serum-decrease reduces this probability by 20%, and a one-unit increase of AST/ALT ratio generates a 4-fold probability increase. Patients who were carriers of the H63D mutation showed higher levels of iron, lower levels of TF and CP and higher CP/TF ratios, a panel resembling hemochromatosis. This picture was found neither in H63D non-carrier patients, nor in healthy controls. Our results suggest the existence of a link between Hfe mutations and iron abnormalities that increases the probability of developing AD when accompanied by a distress of the liver.

HFE gene variants affect iron in the brain

Iron accumulation in the brain and increased oxidative stress are consistent observations in many neurodegenerative diseases. Thus, we have begun examination into gene mutations or allelic variants that could be associated with loss of iron homeostasis. One of the mechanisms leading to iron overload is a mutation in the HFE gene, which is involved in iron metabolism. The 2 most common HFE gene variants are C282Y (1.9%) and H63D (8.9%). The C282Y HFE variant is more commonly associated with hereditary hemochromatosis, which is an autosomal recessive disorder, characterized by iron overload in a number of systemic organs. The H63D HFE variant appears less frequently associated with hemochromatosis, but its role in the neurodegenerative diseases has received more attention. At the cellular level, the HFE mutant protein resulting from the H63D HFE gene variant is associated with iron dyshomeostasis, increased oxidative stress, glutamate release, tau phosphorylation, and alteration in inflammatory response, each of which is under investigation as a contributing factor to neurodegenerative diseases. Therefore, the HFE gene variants are proposed to be genetic modifiers or a risk factor for neurodegenerative diseases by establishing an enabling milieu for pathogenic agents. This review will discuss the current knowledge of the association of the HFE gene variants with neurodegenerative diseases: amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, and ischemic stroke. Importantly, the data herein also begin to dispel the long-held view that the brain is protected from iron accumulation associated with the HFE mutations.

HFE H63D, C282Y and AGTR1 A1166C polymorphisms and brain white matter lesions in the aging brain

Incidental white matter lesions (WML) are a common neuroradiological finding in elderly people and have been linked to dementia and depression. Various mechanisms including hypoxia and increased production of reactive oxygen species (ROS) are implicated in the etiology of WML. The hemochromatosis (HFE) gene p.H63D and p.C282Y polymorphisms have been linked to dysregulation of iron metabolism and increased levels of ROS, whereas Angiotensin II receptor 1 (AGTR1) c.1166A → C polymorphism is known as a vascular risk factor. These genetic polymorphisms were characterized in brains donated to the UK MRC Cognitive Function and Ageing Study (CFAS) to assess their potential role in the risk for development of age-related WML. The study cohort comprised 258 brain donated to CFAS. WML severity was assessed in the postmortem brain donations using magnetic resonance imaging (MRI) scans and scored using the Scheltens' scale. Polymerase chain reaction (PCR) amplification of extracted DNA followed by restriction enzyme digestion was used to genotype the samples. Genotypes were validated using direct sequencing in a smaller sample. The results show that HFE p.H63D polymorphism is not associated with WML severity in the whole cohort. However, there is a significant association of the D allele with severity of WML in noncarriers of the APOE ε4 allele. No association is demonstrated between the HFE p.C282Y nor the AGTR1 c.1166A → C polymorphisms and WML severity. The HFE gene appears to be a genetic risk factor for severe aging WML independently of the APOE ε4 genotype. This would support the role of iron-related oxidative stress, in addition to previously studied factors, e.g., hypoxia as potential risk factors for developing prominent aging WML.

Independent component analysis of Alzheimer's DNA microarray gene expression data

BACKGROUND

Gene microarray technology is an effective tool to investigate the simultaneous activity of multiple cellular pathways from hundreds to thousands of genes. However, because data in the colossal amounts generated by DNA microarray technology are usually complex, noisy, high-dimensional, and often hindered by low statistical power, their exploitation is difficult. To overcome these problems, two kinds of unsupervised analysis methods for microarray data: principal component analysis (PCA) and independent component analysis (ICA) have been developed to accomplish the task. PCA projects the data into a new space spanned by the principal components that are mutually orthonormal to each other. The constraint of mutual orthogonality and second-order statistics technique within PCA algorithms, however, may not be applied to the biological systems studied. Extracting and characterizing the most informative features of the biological signals, however, require higher-order statistics.

RESULTS

ICA is one of the unsupervised algorithms that can extract higher-order statistical structures from data and has been applied to DNA microarray gene expression data analysis. We performed FastICA method on DNA microarray gene expression data from Alzheimer's disease (AD) hippocampal tissue samples and consequential gene clustering. Experimental results showed that the ICA method can improve the clustering results of AD samples and identify significant genes. More than 50 significant genes with high expression levels in severe AD were extracted, representing immunity-related protein, metal-related protein, membrane protein, lipoprotein, neuropeptide, cytoskeleton protein, cellular binding protein, and ribosomal protein. Within the aforementioned categories, our method also found 37 significant genes with low expression levels. Moreover, it is worth noting that some oncogenes and phosphorylation-related proteins are expressed in low levels. In comparison to the PCA and support vector machine recursive feature elimination (SVM-RFE) methods, which are widely used in microarray data analysis, ICA can identify more AD-related genes. Furthermore, we have validated and identified many genes that are associated with AD pathogenesis.

CONCLUSION

We demonstrated that ICA exploits higher-order statistics to identify gene expression profiles as linear combinations of elementary expression patterns that lead to the construction of potential AD-related pathogenic pathways. Our computing results also validated that the ICA model outperformed PCA and the SVM-RFE method. This report shows that ICA as a microarray data analysis tool can help us to elucidate the molecular taxonomy of AD and other multifactorial and polygenic complex diseases.