Characterization of brain-derived extracellular vesicle lipids in Alzheimer's disease.

Lipid dyshomeostasis is associated with the most common form of dementia, Alzheimer's disease (AD). Substantial progress has been made in identifying positron emission tomography and cerebrospinal fluid biomarkers for AD, but they have limited use as front-line diagnostic tools. Extracellular vesicles (EVs) are released by all cells and contain a subset of their parental cell composition, including lipids. EVs are released from the brain into the periphery, providing a potential source of tissue and disease specific lipid biomarkers. However, the EV lipidome of the central nervous system is currently unknown and the potential of brain-derived EVs (BDEVs) to inform on lipid dyshomeostasis in AD remains unclear. The aim of this study was to reveal the lipid composition of BDEVs in human frontal cortex, and to determine whether BDEVs have an altered lipid profile in AD. Using semi-quantitative mass spectrometry, we describe the BDEV lipidome, covering four lipid categories, 17 lipid classes and 692 lipid molecules. BDEVs were enriched in glycerophosphoserine (PS) lipids, a characteristic of small EVs. Here we further report that BDEVs are enriched in ether-containing PS lipids, a finding that further establishes ether lipids as a feature of EVs. BDEVs in the AD frontal cortex offered improved detection of dysregulated lipids in AD over global lipid profiling of this brain region.  AD BDEVs had significantly altered glycerophospholipid and sphingolipid levels, specifically increased plasmalogen glycerophosphoethanolamine and decreased polyunsaturated fatty acyl containing lipids, and altered amide-linked acyl chain content in sphingomyelin and ceramide lipids relative to CTL. The most prominent alteration was a two-fold decrease in lipid species containing anti-inflammatory/pro-resolving docosahexaenoic acid. The in-depth lipidome analysis provided in this study highlights the advantage of EVs over more complex tissues for improved detection of dysregulated lipids that may serve as potential biomarkers in the periphery.

Cerebral quantitative susceptibility mapping predicts amyloid-ß-related cognitive decline.

See Derry and Kent (doi:10.1093/awx167) for a scientific commentary on this article.The large variance in cognitive deterioration in subjects who test positive for amyloid-ß by positron emission tomography indicates that convergent pathologies, such as iron accumulation, might combine with amyloid-ß to accelerate Alzheimer's disease progression. Here, we applied quantitative susceptibility mapping, a relatively new magnetic resonance imaging method sensitive to tissue iron, to assess the relationship between iron, amyloid-ß load, and cognitive decline in 117 subjects who underwent baseline magnetic resonance imaging and amyloid-ß positron emission tomography from the Australian Imaging, Biomarkers and Lifestyle study (AIBL). Cognitive function data were collected every 18 months for up to 6 years from 100 volunteers who were either cognitively normal (n = 64) or diagnosed with mild cognitive impairment (n = 17) or Alzheimer's disease (n = 19). Among participants with amyloid pathology (n = 45), higher hippocampal quantitative susceptibility mapping levels predicted accelerated deterioration in composite cognition tests for episodic memory [ß(standard error) = -0.169 (0.034), P = 9.2 × 10-7], executive function [ß(standard error) = -0.139 (0.048), P = 0.004), and attention [ß(standard error) = -0.074 (0.029), P = 0.012]. Deteriorating performance in a composite of language tests was predicted by higher quantitative susceptibility mapping levels in temporal lobe [ß(standard error) = -0.104 (0.05), P = 0.036] and frontal lobe [ß(standard error) = -0.154 (0.055), P = 0.006]. These findings indicate that brain iron might combine with amyloid-ß to accelerate clinical progression and that quantitative susceptibility mapping could be used in combination with amyloid-ß positron emission tomography to stratify individuals at risk of decline.

The APOE ε4 Allele Is Associated with Lower Selenium Levels in the Brain: Implications for Alzheimer's Disease.

The antioxidant activity of selenium, which is mainly conferred by its incorporation into dedicated selenoproteins, has been suggested as a possible neuroprotective approach for mitigating neuronal loss in Alzheimer's disease. However, there is inconsistent information with respect to selenium levels in the Alzheimer's disease brain. We examined the concentration and cellular compartmentalization of selenium in the temporal cortex of Alzheimer's disease and control brain tissue. We found that Alzheimer's disease was associated with decreased selenium concentration in both soluble (i.e., cytosolic) and insoluble (i.e., plaques and tangles) fractions of brain homogenates. The presence of the APOE ε4 allele correlated with lower total selenium levels in the temporal cortex and a higher concentration of soluble selenium. Additionally, we found that age significantly contributed to lower selenium concentrations in the peripheral membrane-bound and vesicular fractions. Our findings suggest a relevant interaction between APOE ε4 and selenium delivery into brain, and show changes in cellular selenium distribution in the Alzheimer's disease brain.

Selenium Levels in Serum, Red Blood Cells, and Cerebrospinal Fluid of Alzheimer's Disease Patients: A Report from the Australian Imaging, Biomarker & Lifestyle Flagship Study of Ageing (AIBL).

Selenium (Se) protects cells against oxidative stress damage through a range of bioactive selenoproteins. Increased oxidative stress is a prominent feature of Alzheimer's disease (AD), and previous studies have shown that Se deficiency is associated with age-related cognitive decline. In this study, we assessed Se status in different biofluids from a subgroup of participants in the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing. As Se in humans can either be an active component of selenoproteins or inactive via non-specific incorporation into other proteins, we used both size exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) and tandem mass spectrometry to characterize selenoproteins in serum. We observed no differences in total Se concentration in serum or cerebrospinal fluid of AD subjects compared to mildly cognitively impairment patients and healthy controls. However, Se levels in erythrocytes were decreased in AD compared to controls. SEC-ICP-MS analysis revealed a dominant Se-containing fraction. This fraction was subjected to standard protein purification and a bottom-up proteomics approach to confirm that the abundant Se in the fraction was due, in part, to selenoprotein P. The lack of change in the Se level is at odds with our previous observations in a Brazilian population deficient in Se, and we attribute this to the Australian cohort being Se-replete.

Laser ablation-inductively coupled plasma-mass spectrometry imaging of white and gray matter iron distribution in Alzheimer's disease frontal cortex.

Iron deposition in the brain is a feature of normal aging, though in several neurodegenerative disorders, including Alzheimer's disease, the rate of iron accumulation is more advanced than in age-matched controls. Using laser ablation-inductively coupled plasma-mass spectrometry imaging we present here a pilot study that quantitatively assessed the iron content of white and gray matter in paraffin-embedded sections from the frontal cortex of Alzheimer's and control subjects. Using the phosphorus image as a confirmed proxy for the white/gray matter boundary, we found that increased intrusion of iron into gray matter occurs in the Alzheimer's brain compared to controls, which may be indicative of either a loss of iron homeostasis in this vulnerable brain region, or provide evidence of increased inflammatory processes as a response to chronic neurodegeneration. We also observed a trend of increasing iron within the white matter of the frontal cortex, potentially indicative of disrupted iron metabolism preceding loss of myelin integrity. Considering the known potential toxicity of excessive iron in the brain, our results provide supporting evidence for the continuous development of novel magnetic resonance imaging approaches for assessing white and gray matter iron accumulation in Alzheimer's disease.

Peripheral α-defensins 1 and 2 are elevated in Alzheimer's disease.

Biomarkers enabling the preclinical identification of Alzheimer's disease (AD) remain one of the major unmet challenges in the field. The blood cellular fractions offer a viable alternative to current cerebrospinal fluid and neuroimaging modalities. The current study aimed to replicate our earlier reports of altered binding within the AD-affected blood cellular fraction to copper-loaded immobilized metal affinity capture (IMAC) arrays. IMAC and anti-amyloid-ß (Aß) antibody arrays coupled with mass spectrometry were used to analyze blood samples collected from 218 participants from within the AIBL Study of Aging. Peripheral Aß was fragile and prone to degradation in the AIBL samples, even when stored at -80°C. IMAC analysis of the AIBL samples lead to the isolation and identification of alpha-defensins 1 and 2 at elevated levels in the AD periphery, validating earlier findings. Alpha-defensins 1 and 2 were elevated in AD patients indicating that an inflammatory phenotype is present in the AD periphery; however, peripheral Aß levels are required to supplement their prognostic power.

Among vitamin B12 deficient older people, high folate levels are associated with worse cognitive function: combined data from three cohorts.

BACKGROUND: Folate fortification of food aims to reduce the number of babies born with neural tube defects, but has been associated with cognitive impairment when vitamin B12 levels are deficient. Given the prevalence of low vitamin B12 levels among the elderly, and the global deployment of food fortification programs, investigation of the associations between cognitive impairment, vitamin B12, and folate are needed. OBJECTIVE: To investigate the associations of serum vitamin B12, red cell folate, and cognitive impairment. METHODS: Data were collected on 1,354 subjects in two studies investigating cognitive impairment, and from patients attending for assessment or management of memory problems in the Barwon region of south eastern Australia between 2001 and 2011. Eligible subjects who had blood measurements of vitamin B12 and red cell folate taken within six months of cognitive testing were included. Subjects with stroke or neurodegenerative diseases other than Alzheimer's disease were excluded. A Mini-Mental State Examination score of <24 was used to define impaired cognitive function. RESULTS: Participants with low serum vitamin B12 (<250 pmol/L) and high red cell folate (>1,594 nmol/L) levels were more likely to have impaired cognitive performance (adjusted odds ratio (AOR) 3.45, 95% confidence interval (CI): 1.60-7.43, p = 0.002) when compared to participants with biochemical measurements that were within the normal ranges. Participants with high folate levels, but normal serum vitamin B12, were also more likely to have impaired cognitive performance (AOR 1.74, 95% CI: 1.03-2.95, p = 0.04). CONCLUSIONS: High folate or folic acid supplements may be detrimental to cognition in older people with low vitamin B12 levels. This topic is of global significance due to the wide distribution of food fortification programs, so prospective studies should be a high priority.

Utility of an improved model of amyloid-beta (Aß1₋42) toxicity in Caenorhabditis elegans for drug screening for Alzheimer's disease.

BACKGROUND: The definitive indicator of Alzheimer's disease (AD) pathology is the profuse accumulation of amyloid-ß (Aß) within the brain. Various in vitro and cell-based models have been proposed for high throughput drug screening for potential therapeutic benefit in diseases of protein misfolding. Caenorhabditis elegans offers a convenient in vivo system for examination of Aß accumulation and toxicity in a complex multicellular organism. Ease of culturing and a short life cycle make this animal model well suited to rapid screening of candidate compounds. RESULTS: We have generated a new transgenic strain of C. elegans that expresses full length Aß1₋42. This strain differs from existing Aß models that predominantly express amino-truncated Aß3₋42. The Aß1₋42 is expressed in body wall muscle cells, where it oligomerizes, aggregates and results in severe, and fully penetrant, age progressive-paralysis. The in vivo accumulation of Aß1₋42 also stains positive for amyloid dyes, consistent with in vivo fibril formation. The utility of this model for identification of potential protective compounds was examined using the investigational Alzheimer's therapeutic PBT2, shown to be neuroprotective in mouse models of AD and significantly improve cognition in AD patients. We observed that treatment with PBT2 provided rapid and significant protection against the Aß-induced toxicity in C. elegans. CONCLUSION: This C. elegans model of full length Aß1₋42 expression can now be adopted for use in screens to rapidly identify and assist in development of potential therapeutics and to study underlying toxic mechanism(s) of Aß.

Manganese chelation therapy extends survival in a mouse model of M1000 prion disease.

Previous in vitro and in vivo investigations have suggested manganese (Mn(2+)) may play a role in pathogenesis through facilitating refolding of the normal cellular form of the prion protein into protease resistant, pathogenic isoforms (PrP(Sc)), as well as the subsequent promotion of higher order aggregation of these abnormal conformers. To further explore the role of Mn(2+) in pathogenesis, we undertook a number of studies, including an assessment of the disease modifying effects of chelation therapy in a well-characterized mouse model of prion disease. The di-sodium, calcium derivative of the chelator, cyclohexanediaminetetraacetic acid (Na(2)CaCDTA), was administered intraperitoneally to mice inoculated intra-cerebrally with either high or low-dose inocula, with treatment beginning early (shortly after inoculation) or late (at the usual mid-survival point of untreated mice). Analyses by inductively coupled plasma-mass spectrometry demonstrated brain Mn(2+) levels were selectively reduced by up to 50% in treated mice compared with untreated controls, with copper, iron, zinc and cobalt levels unchanged. In mice administered high-dose inocula, none of the treatment groups displayed an increase in survival although western blot analyses of early intensively treated mice showed reduced brain PrP(Sc) levels; mice infected using low-dose inocula however, showed a significant prolongation of survival (p = 0.002). Although our findings support a role for Mn(2+) in prion disease, further studies are required to more precisely delineate the extent of pathogenic involvement.

Behavioural phenotype of APPC100.V717F transgenic mice over-expressing a mutant Abeta-bearing fragment is associated with reduced NMDA receptor density.

The aim of this study was to characterize APPC100.V717F transgenic (TgC100.V717F) mice which over-express a mutant C100 fragment of the amyloid precursor protein. The mice were compared to TgC100 wild type mice (TgC100.WT) and non-transgenic controls at 4-9 and 16-22 months of age. TgC100.V717F mice showed behavioural hyperactivity, particularly at a younger age, as shown by increased numbers of elevated plus maze arm entries and Y-maze arm entries, enhanced baseline locomotor activity in the open field, and enhanced amphetamine-induced hyperlocomotion. This hyperactivity was less pronounced in TgC100.WT which only displayed significant differences to non-transgenic controls at a younger age for the number of Y-maze arm entries and baseline locomotor activity in the open field. In addition, TgC100.V717F mice, but not TgC100.WT, demonstrated cognitive deficits, as shown by reduced spontaneous alternation in the Y-maze and markedly reduced retention in a passive avoidance test. At an older age, TgC100.V717F mice showed enhanced startle and increased immobility time in the forced swim test. In the TgC100.V717F mice, but not TgC100.WT, the behavioural changes were paralleled by a significant reduction in the expression of hippocampal NMDA receptor subunits types 1 and 2A. Concomitantly, we detected axonal disruption and apoptosis in the hippocampus of TgC100.V717F mice. In conclusion, these data demonstrate that the mutant C100 fragment is an effector of biochemical and both cognitive and non-cognitive behaviours. These transgenic mice may be a model for the psychotic features associated with early Alzheimer's disease.

Therapeutic interventions ameliorating prion disease.

Of the many unresolved issues in relation to prion diseases, effective treatments remain an elusive exigency, although some progress has been made. This review describes disease-ameliorating therapeutic strategies reported to date in animal models of prion disease, as well as providing a brief overview of selected completed human treatment trials. Included in vivo studies have been broadly dichotomized according to the time of introduction of the treatment in relation to animal inoculation and also according to their possible principal mechanism of action, although the latter is not always entirely clear, and often there is likely to be more than one mechanism. Consequent to the pathogenic primacy of cellular prion protein (PrP(c))-to-scrapie PrP(c) (PrP(sc)) conversion, most reported treatments appear to directly target this replication process, although various other strategies, such as depletion of reaction substrates and abrogation of downstream effector pathways, have been utilized. Many factors, including experimental design, militate against reliable extrapolation of study results to the routine clinical setting or limit easy translational application to human disease. Notably problematic are approaches wherein benefit has been shown but the treatment was initiated before, at or soon after inoculation of experimental animals.

Paradoxical condensation of copper with elevated beta-amyloid in lipid rafts under cellular copper deficiency conditions: implications for Alzheimer disease.

Redox-active copper is implicated in the pathogenesis of Alzheimer disease (AD), beta-amyloid peptide (Abeta) aggregation, and amyloid formation. Abeta.copper complexes have been identified in AD and catalytically oxidize cholesterol and lipid to generate H2O2 and lipid peroxides. The site and mechanism of this abnormality is not known. Growing evidence suggests that amyloidogenic processing of the beta-amyloid precursor protein (APP) occurs in lipid rafts, membrane microdomains enriched in cholesterol. beta- and gamma-secretases, and Abeta have been identified in lipid rafts in cultured cells, human and rodent brains, but the role of copper in lipid raft amyloidogenic processing is presently unknown. In this study, we found that copper modulates flotillin-2 association with cholesterol-rich lipid raft domains, and consequently Abeta synthesis is attenuated via copper-mediated inhibition of APP endocytosis. We also found that total cellular copper is associated inversely with lipid raft copper levels, so that under intracellular copper deficiency conditions, Abeta.copper complexes are more likely to form. This explains the paradoxical hypermetallation of Abeta with copper under tissue copper deficiency conditions in AD.

beta-Amyloid as a molecular therapeutic target in Alzheimer's disease.

Alzheimer's disease is the most common form of dementia, primarily affecting individuals during or after their sixth decade of life. Despite decades of research, there are still no effective disease-modifying drugs available to treat this neurodegenerative disorder. Current FDA-approved medications primarily offer symptomatic relief and are based upon known neurotransmitter deficits. There are, however, many drugs in preclinical and clinical development which target other aspects of AD pathogenesis. Principal among these are drugs which modulate beta-amyloid, a protein that is believed to be central to the cascade which leads to the development of Alzheimer's disease. This article will outline the metabolism of beta-amyloid and review a number of different strategies, including pitfalls and future directions of such methods that are directed towards the modulation of this protein. It will become clear that beta-amyloid represents a potent molecular target for pharmacological manipulation to perhaps prevent the onset and progression of Alzheimer's disease.

Selective intracellular release of copper and zinc ions from bis(thiosemicarbazonato) complexes reduces levels of Alzheimer disease amyloid-beta peptide.

Copper and zinc play important roles in Alzheimer disease pathology with recent reports describing potential therapeutics based on modulation of metal bioavailability. We examined the ability of a range of metal bis(thiosemicarbazonato) complexes (MII(btsc), where M=CuII or ZnII) to increase intracellular metal levels in Chinese hamster ovary cells overexpressing amyloid precursor protein (APP-CHO) and the subsequent effect on extracellular levels of amyloid-beta peptide (Abeta). The CuII(btsc) complexes were engineered to be either stable to both a change in oxidation state and dissociation of metal or susceptible to intracellular reduction and dissociation of metal. Treatment of APP-CHO cells with stable complexes resulted in elevated levels of intracellular copper with no effect on the detected levels of Abeta. Treatment with complexes susceptible to intracellular reduction increased intracellular copper levels but also resulted in a dose-dependent reduction in the levels of monomeric Abeta. Treatment with less stable ZnII(btsc) complexes increased intracellular zinc levels with a subsequent dose-dependent depletion of monomeric Abeta levels. The increased levels of intracellular bioavailable copper and zinc initiated a signaling cascade involving activation of phosphoinositol 3-kinase and c-Jun N-terminal kinase. Inhibition of these enzymes prevented Abeta depletion induced by the MII(btsc) complexes. Inhibition of metalloproteases also partially restored Abeta levels, implicating metal-driven metalloprotease activation in the extracellular monomeric Abeta depletion. However, a role for alternative metal-induced Abeta metabolism has not been ruled out. These studies demonstrate that MII(btsc) complexes have potential for Alzheimer disease therapy.