Iron-export ferroxidase activity of ß-amyloid precursor protein is inhibited by zinc in Alzheimer's disease.

Alzheimer's Disease (AD) is complicated by pro-oxidant intraneuronal Fe(2+) elevation as well as extracellular Zn(2+) accumulation within amyloid plaque. We found that the AD ß-amyloid protein precursor (APP) possesses ferroxidase activity mediated by a conserved H-ferritin-like active site, which is inhibited specifically by Zn(2+). Like ceruloplasmin, APP catalytically oxidizes Fe(2+), loads Fe(3+) into transferrin, and has a major interaction with ferroportin in HEK293T cells (that lack ceruloplasmin) and in human cortical tissue. Ablation of APP in HEK293T cells and primary neurons induces marked iron retention, whereas increasing APP695 promotes iron export. Unlike normal mice, APP(-/-) mice are vulnerable to dietary iron exposure, which causes Fe(2+) accumulation and oxidative stress in cortical neurons. Paralleling iron accumulation, APP ferroxidase activity in AD postmortem neocortex is inhibited by endogenous Zn(2+), which we demonstrate can originate from Zn(2+)-laden amyloid aggregates and correlates with Aß burden. Abnormal exchange of cortical zinc may link amyloid pathology with neuronal iron accumulation in AD.

Loss-of-function and gain-of-function studies refute the hypothesis that tau protein is causally involved in the pathogenesis of Huntington's disease.

Tubulin-associated unit (Tau) is a microtubule-associated protein, whose abnormal phosphorylation and deposition in the brain characterizes a range of neurodegenerative diseases called tauopathies. Recent clinical (post-mortem) and pre-clinical evidence suggests that Huntington's disease (HD), an autosomal dominant neurodegenerative disorder, could be considered as a tauopathy. Studies have found the presence of hyperphosphorylated tau, altered tau isoform ratio and aggregated tau in HD brains. However, little is known about the implication of tau in the development of HD pathophysiology, which includes motor, cognitive and affective symptoms. To shine a light on the involvement of tau in HD, our present study aimed at (i) knocking out tau expression and (ii) expressing a transgene encoding mutant human tau in the R6/1 mouse model of HD. We hypothesized that expression of the mutant human tau transgene in HD mice would worsen the HD phenotype, while knocking out endogenous mouse tau in HD mice would improve some behavioral deficits displayed by HD mice. Our data suggest that neither the expression of a tau transgene nor the ablation of tau expression impacted the progression of the HD motor, cognitive and affective phenotypes. Supporting these behavioral findings, we also found that modulating tau expression had no effect on brain weights in HD mice. We also report that expression of the tau transgene increased the weight of WT and HD male mice, whereas tau ablation increased the weight of HD females only. Together, our results indicate that tau might not be as important in regulating the onset and progression of HD symptomatology as previously proposed.

Exploring the significance of lipids in Alzheimer's disease and the potential of extracellular vesicles.

Lipids play a significant role in maintaining central nervous system (CNS) structure and function, and the dysregulation of lipid metabolism is known to occur in many neurological disorders, including Alzheimer's disease. Here we review what is currently known about lipid dyshomeostasis in Alzheimer's disease. We propose that small extracellular vesicle (sEV) lipids may provide insight into the pathophysiology and progression of Alzheimer's disease. This stems from the recognition that sEV likely contributes to disease pathogenesis, but also an understanding that sEV can serve as a source of potential biomarkers. While the protein and RNA content of sEV in the CNS diseases have been studied extensively, our understanding of the lipidome of sEV in the CNS is still in its infancy.

Isolated rapid eye movement sleep behaviour disorder (iRBD) in the Island Study Linking Ageing and Neurodegenerative Disease (ISLAND) Sleep Study: protocol and baseline characteristics.

Isolated rapid eye movement (REM) sleep behaviour disorder (iRBD) is a sleep disorder that is characterised by dream enactment episodes during REM sleep. It is the strongest known predictor of α-synuclein-related neurodegenerative disease (αNDD), such that >80% of people with iRBD will eventually develop Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy in later life. More research is needed to understand the trajectory of phenoconversion to each αNDD. Only five 'gold standard' prevalence studies of iRBD in older adults have been undertaken previously, with estimates ranging from 0.74% to 2.01%. The diagnostic recommendations for video-polysomnography (vPSG) to confirm iRBD makes prevalence studies challenging, as vPSG is often unavailable to large cohorts. In Australia, there have been no iRBD prevalence studies, and little is known about the cognitive and motor profiles of Australian people with iRBD. The Island Study Linking Ageing and Neurodegenerative Disease (ISLAND) Sleep Study will investigate the prevalence of iRBD in Tasmania, an island state of Australia, using validated questionnaires and home-based vPSG. It will also explore several cognitive, motor, olfactory, autonomic, visual, tactile, and sleep profiles in people with iRBD to better understand which characteristics influence the progression of iRBD to αNDD. This paper details the ISLAND Sleep Study protocol and presents preliminary baseline results.

Modification of Biodistribution and Brain Uptake of Copper Bis(thiosemicarbazonato) Complexes by the Incorporation of Amine and Polyamine Functional Groups.

The synthesis of new bis(thiosemicarbazonato)copper(II) complexes featuring polyamine substituents via selective transamination reactions is presented. Polyamines of different lengths, with different ionizable substituent groups, were used to modify and adjust the hydrophilic/lipophilic balance of the copper complexes. The new analogues were radiolabeled with copper-64 and their lipophilicities estimated using distribution coefficients. The cell uptake of the new polyamine complexes was investigated with preliminary in vitro biological studies using a neuroblastoma cancer cell line. The in vivo biodistribution of three of the new analogues was investigated in vivo in mice using positron-emission tomography imaging, and one of the new complexes was compared to [64Cu]Cu(atsm) in an A431 squamous cell carcinoma xenograft model. Modification of the copper complexes with various amine-containing functional groups alters the biodistribution of the complexes in mice. One complex, with a pendent ( N, N-dimethylamino)ethane functional group, displayed tumor uptake similar to that of [64Cu]Cu(atsm) but higher brain uptake, suggesting that this compound has the potential to be of use in the diagnostic brain imaging of tumors and neurodegenerative diseases.

Amyloid-ß Peptide Aß3pE-42 Induces Lipid Peroxidation, Membrane Permeabilization, and Calcium Influx in Neurons.

Pyroglutamate-modified amyloid-ß (pE-Aß) is a highly neurotoxic amyloid-ß (Aß) isoform and is enriched in the brains of individuals with Alzheimer disease compared with healthy aged controls. Pyroglutamate formation increases the rate of Aß oligomerization and alters the interactions of Aß with Cu(2+) and lipids; however, a link between these properties and the toxicity of pE-Aß peptides has not been established. We report here that Aß3pE-42 has an enhanced capacity to cause lipid peroxidation in primary cortical mouse neurons compared with the full-length isoform (Aß(1-42)). In contrast, Aß(1-42) caused a significant elevation in cytosolic reactive oxygen species, whereas Aß3pE-42 did not. We also report that Aß3pE-42 preferentially associates with neuronal membranes and triggers Ca(2+) influx that can be partially blocked by the N-methyl-d-aspartate receptor antagonist MK-801. Aß3pE-42 further caused a loss of plasma membrane integrity and remained bound to neurons at significantly higher levels than Aß(1-42) over extended incubations. Pyroglutamate formation was additionally found to increase the relative efficiency of Aß-dityrosine oligomer formation mediated by copper-redox cycling.

Characterization and Identification of Dityrosine Cross-Linked Peptides Using Tandem Mass Spectrometry.

The use of mass spectrometry coupled with chemical cross-linking of proteins has become a powerful tool for proteins structure and interactions studies. Unlike structural analysis of proteins using chemical reagents specific for lysine or cysteine residues, identification of gas-phase fragmentation patterns of endogenous dityrosine cross-linked peptides have not been investigated. Dityrosine cross-linking in proteins and peptides are clinical markers of oxidative stress, aging, and neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. In this study, we investigated and characterized the fragmentation pattern of a synthetically prepared dityrosine cross-linked dimer of Aß(1-16) using ESI tandem mass spectrometry. We then detailed the fragmentation pattern of dityrosine cross-linked Aß(1-16), using collision induced dissociation (CID), higher-energy collision induced dissociation (HCD), electron transfer dissociation (ETD), and electron capture dissociation (ECD). Application of these generic fragmentation rules of dityrosine cross-linked peptides allowed for the identification of dityrosine cross-links in peptides of Aß and α-synuclein generated in vitro by enzymatic peroxidation. We report, for the first time, the dityrosine cross-linked residues in human hemoglobin and α-synuclein under oxidative conditions. Together these tools open up the potential for automated analysis of this naturally occurring post-translation modification in neurodegenerative diseases as well as other pathological conditions.

Stabilization of nontoxic Aß-oligomers: insights into the mechanism of action of hydroxyquinolines in Alzheimer's disease.

The extracellular accumulation of amyloid ß (Aß) peptides is characteristic of Alzheimer's disease (AD). However, formation of diffusible, oligomeric forms of Aß, both on and off pathways to amyloid fibrils, is thought to include neurotoxic species responsible for synaptic loss and neurodegeneration, rather than polymeric amyloid aggregates. The 8-hydroxyquinolines (8-HQ) clioquinol (CQ) and PBT2 were developed for their ability to inhibit metal-mediated generation of reactive oxygen species from Aß:Cu complexes and have both undergone preclinical and Phase II clinical development for the treatment of AD. Their respective modes of action are not fully understood and may include both inhibition of Aß fibrillar polymerization and direct depolymerization of existing Aß fibrils. In the present study, we find that CQ and PBT2 can interact directly with Aß and affect its propensity to aggregate. Using a combination of biophysical techniques, we demonstrate that, in the presence of these 8-HQs and in the absence of metal ions, Aß associates with two 8-HQ molecules and forms a dimer. Furthermore, 8-HQ bind Aß with an affinity of 1-10 µm and suppress the formation of large (>30 kDa) oligomers. The stabilized low molecular weight species are nontoxic. Treatment with 8-HQs also reduces the levels of in vivo soluble oligomers in a Caenorhabditis elegans model of Aß toxicity. We propose that 8-HQs possess an additional mechanism of action that neutralizes neurotoxic Aß oligomer formation through stabilization of small (dimeric) nontoxic Aß conformers.

Synthesis of Oxorhenium(V) and Oxotechnetium(V) Complexes That Bind to Amyloid-ß Plaques.

Alzheimer's disease is characterized by the presence of amyloid plaques in the brain. The primary constituents of the plaques are aggregated forms of the amyloid-ß (Aß) peptide. With the goal of preparing technetium-99(m) complexes that bind to Aß plaques with the potential to be diagnostic imaging agents for Alzheimer's disease, new tetradentate ligands capable of forming neutral and lipophilic complexes with oxotechentium(V) and oxorhenium(V) were prepared. Nonradioactive isotopes of technetium are not available so rhenium was used as a surrogate for exploratory chemistry. Two planar tetradentate N3O ligands were prepared that form charge-neutral complexes with oxorhenium(v) as well as a ligand featuring a styrylpyridyl functional group designed to bind to Aß plaques. All three ligands formed complexes with oxorhenium(V), and each complex was characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The oxorhenium(V) complex with a styrylpyridyl functional group binds to Aß plaques present in post-mortem human brain tissue. The chemistry was extrapolated to technetium-99(m) at the tracer level for two of the ligands. The resulting oxotechnetium(V) complexes were sufficiently lipophilic and charge-neutral to suggest that they have the potential to cross the blood-brain barrier but exhibited modest stability with respect to exchange with histidine. The chemistry presented here identifies a strategy to integrate styrylpyridyl functional groups into tetradentate ligands capable of forming complexes with [M═O](3+) cores (M = Re or Tc).

Oral treatment with Cu(II)(atsm) increases mutant SOD1 in vivo but protects motor neurons and improves the phenotype of a transgenic mouse model of amyotrophic lateral sclerosis.

Mutations in the metallo-protein Cu/Zn-superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS) in humans and an expression level-dependent phenotype in transgenic rodents. We show that oral treatment with the therapeutic agent diacetyl-bis(4-methylthiosemicarbazonato)copper(II) [Cu(II)(atsm)] increased the concentration of mutant SOD1 (SOD1G37R) in ALS model mice, but paradoxically improved locomotor function and survival of the mice. To determine why the mice with increased levels of mutant SOD1 had an improved phenotype, we analyzed tissues by mass spectrometry. These analyses revealed most SOD1 in the spinal cord tissue of the SOD1G37R mice was Cu deficient. Treating with Cu(II)(atsm) decreased the pool of Cu-deficient SOD1 and increased the pool of fully metallated (holo) SOD1. Tracking isotopically enriched (65)Cu(II)(atsm) confirmed the increase in holo-SOD1 involved transfer of Cu from Cu(II)(atsm) to SOD1, suggesting the improved locomotor function and survival of the Cu(II)(atsm)-treated SOD1G37R mice involved, at least in part, the ability of the compound to improve the Cu content of the mutant SOD1. This was supported by improved survival of SOD1G37R mice that expressed the human gene for the Cu uptake protein CTR1. Improving the metal content of mutant SOD1 in vivo with Cu(II)(atsm) did not decrease levels of misfolded SOD1. These outcomes indicate the metal content of SOD1 may be a greater determinant of the toxicity of the protein in mutant SOD1-associated forms of ALS than the mutations themselves. Improving the metal content of SOD1 therefore represents a valid therapeutic strategy for treating ALS caused by SOD1.

PBT2 inhibits glutamate-induced excitotoxicity in neurons through metal-mediated preconditioning.

Excitotoxicity is the pathological process by which neuronal death occurs as a result of excessive stimulation of receptors at the excitatory synapse such as the NMDA receptor (NMDAR). Excitotoxicity has been implicated in the acute neurological damage from ischemia and traumatic brain injury and in the chronic neurodegeneration in Alzheimer's disease (AD) and Huntington's disease (HD). As a result NMDAR antagonists have become an attractive therapeutic strategy for the potential treatment of multiple neurodegenerative diseases. However NMDAR signaling is dichotomous in nature, with excessive increases in neuronal intracellular calcium through excessive NMDAR activity being lethal but moderate increases to intracellular calcium levels during normal synaptic function providing neuroprotection. Subsequently indiscriminant inhibition of this receptor is best avoided as was concluded from previous clinical trials of NMDAR antagonists. We show that the metal chaperone, PBT2, currently in clinical trials for HD, is able to protect against glutamate-induced excitotoxicity mediated through NMDARs. This was achieved by PBT2 inducing Zn(2+)-dependent increases in intracellular Ca(2+) levels resulting in preconditioning of neurons and inhibition of Ca(2+)-induced neurotoxic signaling cascade involving calpain-activated cleavage of calcineurin. Our study demonstrates that modulating intracellular Ca(2+) levels by a zinc ionophore is a valid therapeutic strategy to protect against the effects of excitotoxicity thought to underlie both acute and chronic neurodegenerative diseases.

Pathogenic mutations within the hydrophobic domain of the prion protein lead to the formation of protease-sensitive prion species with increased lethality.

UNLABELLED: Prion diseases are a group of fatal and incurable neurodegenerative diseases affecting both humans and animals. The principal mechanism of these diseases involves the misfolding the host-encoded cellular prion protein, PrP(C), into the disease-associated isoform, PrP(Sc). Familial forms of human prion disease include those associated with the mutations G114V and A117V, which lie in the hydrophobic domain of PrP. Here we have studied the murine homologues (G113V and A116V) of these mutations using cell-based and animal models of prion infection. Under normal circumstances, the mutant forms of PrP(C) share similar processing, cellular localization, and physicochemical properties with wild-type mouse PrP (MoPrP). However, upon exposure of susceptible cell lines expressing these mutants to infectious prions, very low levels of protease-resistant aggregated PrP(Sc) are formed. Subsequent mouse bioassay revealed high levels of infectivity present in these cells. Thus, these mutations appear to limit the formation of aggregated PrP(Sc), giving rise to the accumulation of a relatively soluble, protease sensitive, prion species that is highly neurotoxic. Given that these mutations lie next to the glycine-rich region of PrP that can abrogate prion infection, these findings provide further support for small, protease-sensitive prion species having a significant role in the progression of prion disease and that the hydrophobic domain is an important determinant of PrP conversion. IMPORTANCE: Prion diseases are transmissible neurodegenerative diseases associated with an infectious agent called a prion. Prions are comprised of an abnormally folded form of the prion protein (PrP) that is normally resistant to enzymes called proteases. In humans, prion disease can occur in individuals who inherited mutations in the prion protein gene. Here we have studied the effects of two of these mutations and show that they influence the properties of the prions that can be formed. We show that the mutants make highly infectious prions that are more sensitive to protease treatment. This study highlights a certain region of the prion protein as being involved in this effect and demonstrates that prions are not always resistant to protease treatment.

Synthesis of 2-pyridyl-benzimidazole iridium(III), ruthenium(II), and platinum(II) complexes. study of the activity as inhibitors of amyloid-ß aggregation and neurotoxicity evaluation.

The design of small molecules that can target the aggregation of Aß as potential therapeutic agents for Alzheimer's disease is an area of study that has attracted a lot of attention recently. The novel ligand methyl 1-butyl-2-pyridyl-benzimidazole carboxylate was prepared for the synthesis of a series of new iridium(III), ruthenium(II), and platinum(II) 2-pyridyl-benzimidazole complexes. The crystal structure of the half-sandwich iridium(III) complex was established by X-ray diffraction. An arrangement of two cationic complexes in the unit cell is observed, and it seems to be organized by weak π···π interactions that are taking place between two symmetry-related benzimidazole ring systems. All new compounds inhibited aggregation of Aß1-42 in vitro as shown by both thioflavin T fluorescence assay and transmission electron microscopy. Among them the Ir compound rescued the toxicity of Aß1-42 in primary cortical neurons effectively.

C-terminal peptides modelling constitutive PrPC processing demonstrate ameliorated toxicity predisposition consequent to α-cleavage.

Misfolding of PrPC (cellular prion protein) to ß-strand-rich conformations constitutes a key event in prion disease pathogenesis. PrPC can undergo either of two constitutive endoproteolytic events known as α- and ß-cleavage, yielding C-terminal fragments known as C1 and C2 respectively. It is unclear whether C-terminal fragments generated through α- and ß-cleavage, especially C2, influence pathogenesis directly. Consequently, we compared the biophysical properties and neurotoxicity of recombinant human PrP fragments recapitulating α- and ß-cleavage, namely huPrP-(112-231) (equating to C1) and huPrP-(90-231) (equating to C2). Under conditions we employed, huPrP-(112-231) could not be induced to fold into a ß-stranded isoform and neurotoxicity was not a feature for monomeric or multimeric assemblies. In contrast, huPrP-(90-231) easily adopted a ß-strand conformation, demonstrated considerable thermostability and was toxic to neurons. Synthetic PrP peptides modelled on α- and ß-cleavage of the unique Y145STOP (Tyr145→stop) mutant prion protein corroborated the differential toxicity observed for recombinant huPrP-(112-231) and huPrP-(90-231) and suggested that the persistence of soluble oligomeric ß-strand-rich conformers was required for significant neurotoxicity. Our results additionally indicate that α- and ß-cleavage of PrPC generate biophysically and biologically non-equivalent C-terminal fragments and that C1 generated through α-cleavage appears to be pathogenesis-averse.

Biological metals and metal-targeting compounds in major neurodegenerative diseases.

Multiple abnormalities occur in the homeostasis of essential endogenous brain biometals in age-related neurodegenerative disorders, Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. As a result, metals both accumulate in microscopic proteinopathies, and can be deficient in cells or cellular compartments. Therefore, bulk measurement of metal content in brain tissue samples reveal only the "tip of the iceberg", with most of the important changes occurring on a microscopic and biochemical level. Each of the major proteins implicated in these disorders interacts with biological transition metals. Tau and the amyloid protein precursor have important roles in normal neuronal iron homeostasis. Changes in metal distribution, cellular deficiencies, or sequestration in proteinopathies all present abnormalities that can be corrected in animal models by small molecules. These biochemical targets are more complex than the simple excess of metals that are targeted by chelators. In this review we illustrate some of the richness in the science that has developed in the study of metals in neurodegeneration, and explore its novel pharmacology.

A Functional Role for Aß in Metal Homeostasis? N-Truncation and High-Affinity Copper Binding.

Accumulation of the ß-amyloid (Aß) peptide in extracellular senile plaques rich in copper and zinc is a defining pathological feature of Alzheimer's disease (AD). The Aß1-x (x=16/28/40/42) peptides have been the primary focus of Cu(II) binding studies for more than 15 years; however, the N-truncated Aß4-42 peptide is a major Aß isoform detected in both healthy and diseased brains, and it contains a novel N-terminal FRH sequence. Proteins with His at the third position are known to bind Cu(II) avidly, with conditional log K values at pH 7.4 in the range of 11.0-14.6, which is much higher than that determined for Aß1-x peptides. By using Aß4-16 as a model, it was demonstrated that its FRH sequence stoichiometrically binds Cu(II) with a conditional Kd value of 3×10(-14) M at pH 7.4, and that both Aß4-16 and Aß4-42 possess negligible redox activity. Combined with the predominance of Aß4-42 in the brain, our results suggest a physiological role for this isoform in metal homeostasis within the central nervous system.

Guanidine hydrochloride denaturation of dopamine-induced α-synuclein oligomers: a small-angle X-ray scattering study.

Alpha-synuclein (α-syn) forms the amyloid-containing Lewy bodies found in the brain in Parkinson's disease. The neurotransmitter dopamine (DA) reacts with α-syn to form SDS-resistant soluble, non-amyloid, and melanin-containing oligomers. Their toxicity is debated, as is the nature of their structure and their relation to amyloid-forming conformers of α-syn. The small-angle X-ray scattering technique in combination with modeling by the ensemble optimization method showed that the un-reacted native protein populated three broad classes of conformer, while reaction with DA gave a restricted ensemble range suggesting that the rigid melanin molecule played an important part in their structure. We found that 6 M guanidine hydrochloride did not dissociate α-syn DA-reacted dimers and trimers, suggesting covalent linkages. The pathological significance of covalent association is that if they are non-toxic, the oligomers would act as a sink for toxic excess DA and α-syn; if toxic, their stability could enhance their toxicity. We argue it is essential, therefore, to resolve the question of whether they are toxic or not.

Do current therapeutic anti-Aß antibodies for Alzheimer's disease engage the target?

Reducing amyloid-ß peptide (Aß) burden at the pre-symptomatic stages of Alzheimer's disease (AD) is currently the advocated clinical strategy for treating this disease. The most developed method for targeting Aß is the use of monoclonal antibodies including bapineuzumab, solanezumab and crenezumab. We have synthesized these antibodies and used surface plasmon resonance (SPR) and mass spectrometry to characterize and compare the ability of these antibodies to target Aß in transgenic mouse tissue as well as human AD tissue. SPR analysis showed that the antibodies were able to bind Aß with high affinity. All of the antibodies were able to bind Aß in mouse tissue. However, significant differences were observed in human brain tissue. While bapineuzumab was able to capture a variety of N-terminally truncated Aß species, the Aß detected using solanezumab was barely above detection limits while crenezumab did not detect any Aß. None of the antibodies were able to detect any Aß species in human blood. Immunoprecipitation experiments using plasma from AD subjects showed that both solanezumab and crenezumab have extensive cross-reactivity with non-Aß related proteins. Bapineuzumab demonstrated target engagement with brain Aß, consistent with published clinical data. Solanezumab and crenezumab did not, most likely as a result of a lack of specificity due to cross-reactivity with other proteins containing epitope overlap. This lack of target engagement raises questions as to whether solanezumab and crenezumab are suitable drug candidates for the preventative clinical trials for AD.

Changes in plasma amyloid beta in a longitudinal study of aging and Alzheimer's disease.

BACKGROUND: A practical biomarker is required to facilitate the preclinical diagnosis of Alzheimer's disease (AD). METHODS: Plasma amyloid beta (Aß)1-40, Aß1-42, Aßn-40, and Aßn-42 peptides were measured at baseline and after 18 months in 771 participants from the Australian Imaging Biomarkers and Lifestyle (AIBL) study of aging. Aß peptide levels were compared with clinical pathology, neuroimaging and neuropsychological measurements. RESULTS: Although inflammatory and renal function covariates influenced plasma Aß levels significantly, a decrease in Aß1-42/Aß1-40 was observed in patients with AD, and was also inversely correlated with neocortical amyloid burden. During the 18 months, plasma Aß1-42 decreased in subjects with mild cognitive impairment (MCI) and in those transitioning from healthy to MCI. CONCLUSION: Our findings are consistent with a number of published plasma Aß studies and, although the prognostic value of individual measures in any given subject is limited, the diagnostic contribution of plasma Aß may demonstrate utility when combined with a panel of peripheral biomarkers.

Do Bacterial Outer Membrane Vesicles Contribute to Chronic Inflammation in Parkinson's Disease?

Parkinson's disease (PD) is an increasingly common neurodegenerative disease. It has been suggested that the etiology of idiopathic PD is complex and multifactorial involving environmental contributions, such as viral or bacterial infections and microbial dysbiosis, in genetically predisposed individuals. With advances in our understanding of the gut-brain axis, there is increasing evidence that the intestinal microbiota and the mammalian immune system functionally interact. Recent findings suggest that a shift in the gut microbiome to a pro-inflammatory phenotype may play a role in PD onset and progression. While there are links between gut bacteria, inflammation, and PD, the bacterial products involved and how they traverse the gut lumen and distribute systemically to trigger inflammation are ill-defined. Mechanisms emerging in other research fields point to a role for small, inherently stable vesicles released by Gram-negative bacteria, called outer membrane vesicles in disease pathogenesis. These vesicles facilitate communication between bacteria and the host and can shuttle bacterial toxins and virulence factors around the body to elicit an immune response in local and distant organs. In this perspective article, we hypothesize a role for bacterial outer membrane vesicles in PD pathogenesis. We present evidence suggesting that these outer membrane vesicles specifically from Gram-negative bacteria could potentially contribute to PD by traversing the gut lumen to trigger local, systemic, and neuroinflammation. This perspective aims to facilitate a discussion on outer membrane vesicles in PD and encourage research in the area, with the goal of developing strategies for the prevention and treatment of the disease.