Plasma α-synuclein in patients with Parkinson's disease with and without treatment

A user's guide for α-synuclein biomarker studies in biological fluids: Perianalytical considerations

Parkinson's disease biomarkers are needed to increase diagnostic accuracy, to objectively monitor disease progression and to assess therapeutic efficacy as well as target engagement when evaluating novel drug and therapeutic strategies. This article summarizes perianalytical considerations for biomarker studies (based on immunoassays) in Parkinson's disease, with emphasis on quantifying total α‐synuclein protein in biological fluids. Current knowledge and pitfalls are discussed, and selected perianalytical variables are presented systematically, including different temperature of sample collection and types of collection tubes, gradient sampling, the addition of detergent, aliquot volume, the freezing time, and the different thawing methods. We also discuss analytical confounders. We identify gaps in the knowledge and delineate specific areas that require further investigation, such as the need to identify posttranslational modifications of α‐synuclein and antibody‐independent reference methods for quantification, as well as the analysis of potential confounders, such as comorbidities, medication, and phenotypes of Parkinson's disease in larger cohorts. This review could be used as a guideline for future Parkinson's disease biomarker studies and will require regular updating as more information arises in this growing field, including new technical developments as they become available. In addition to reviewing best practices, we also identify the current technical limitations and gaps in the knowledge that should be addressed to enable accurate and quantitative assessment of α‐synuclein levels in the clinical setting. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Autoimmune antibody decline in Parkinson's disease and Multiple System Atrophy; a step towards immunotherapeutic strategies

Background

Parkinson’s’ disease (PD) and Multiple System Atrophy (MSA) are progressive brain disorders characterized by intracellular accumulations of α-synuclein and nerve cell loss in specific brain areas. This loss causes problems with movement, balance and/or autonomic functions. Naturally occurring autoantibodies (NAbs) play potentially an important role in clearing or/and blocking circulating pathological proteins. Little is known about the functional properties of anti-α-synuclein NAbs in PD and MSA, and there have been opposing reports regarding their plasma concentrations in these disorders.

Methods

We have investigated the apparent affinity of anti-α-synuclein NAbs in plasma samples from 46 PD patients, 18 MSA patients and 41 controls using competitive enzyme-linked immunosorbent assay (ELISA) and Meso Scale Discovery (MSD) set-ups.

Results

We found that the occurrence of high affinity anti-α-synuclein NAbs in plasma from PD patients is reduced compared to healthy controls, and nearly absent in plasma from MSA patients. Also, levels of α-synuclein/NAbs immunocomplexes is substantially reduced in plasma from both patient groups. Further, cross binding of anti-α-synuclein NAbs with β- and γ-synuclein monomers suggest, the high affinity anti-α-synuclein plasma component, seen in healthy individuals, is directed mainly against C-terminal epitopes. Furthermore, we also observed reduced occurrence of high affinity anti-phosphorylated-α-synuclein NAbs in plasma from PD and MSA patients.

Conclusions

One interpretation implies that these patients may have impaired ability to clear and/or block the effects of pathological α-synuclein due to insufficient/absent concentration of NAbs and as such provides a rationale for testing immune-based therapeutic strategies directed against pathological α-synuclein. Following this interpretation, we can hypothesize that high affinity autoantibodies efficiently bind and clear potentially pathological species of α-synuclein in healthy brain, and that this mechanism is impaired or absent in PD and MSA patients.

Potential biomarkers and novel pharmacological targets in protein aggregation-related neurodegenerative diseases

The aggregation of specific proteins plays a pivotal role in the etiopathogenesis of several neurodegenerative diseases (NDs). β-Amyloid (Aβ) peptide-containing plaques and intraneuronal neurofibrillary tangles composed of hyperphosphorylated protein tau are the two main neuropathological lesions in Alzheimer's disease. Meanwhile, Parkinson's disease is defined by the presence of intraneuronal inclusions (Lewy bodies), in which α-synuclein (α-syn) has been identified as a major protein component. The current literature provides considerable insights into the mechanisms underlying oligomeric-related neurodegeneration, as well as the relationship between protein aggregation and ND, thus facilitating the development of novel putative biomarkers and/or pharmacological targets. Recently, α-syn, tau and Aβ have been shown to interact each other or with other "pathological proteins" to form toxic heteroaggregates. These latest findings are overcoming the concept that each neurodegenerative disease is related to the misfolding of a single specific protein. In this review, potential opportunities and pharmacological approaches targeting α-syn, tau and Aβ and their oligomeric forms are highlighted with examples from recent studies. Protein aggregation as a biomarker of NDs, in both the brain and peripheral fluids, is deeply explored. Finally, the relationship between biomarker establishment and assessment and their use as diagnostics or therapeutic targets are discussed.

Dataset of total, oligomeric alpha-synuclein and hemoglobin levels in plasma in Parkinson׳s disease

This data article presents a dataset of total, oligomeric alpha-synuclein and hemoglobin levels in plasma of drug-naïve PD patients and controls. This is the first attempt to assess the effect of hemolysis rate on oligomeric alpha-synuclein levels in peripheral plasma. The data are associated with the research article “Oligomeric alpha-synuclein and glucocerebrosidase activity levels in GBA-associated Parkinson׳s disease” (Pchelina et al., 2016) [1].

Relationship between the plasma levels of neurodegenerative proteins and motor subtypes of Parkinson's disease

The aim of our study is to examine the plasma levels of the four kinds of neurodegenerative proteins in plasma: α-syn, T-tau, P-tau_181, and Aβ-42 in Parkinson's disease (PD) and to evaluate the relationship between their plasma levels and PD motor subtypes. 84 patients with PD were enrolled in our study, and finally, 73 of them were classified into the tremor-dominant subtype (TD) and the postural instability gait difficulty subtype (PIGD). Their motor performance was evaluated by a series of clinical assessments: Freezing of Gait Questionnaire (FOGQ), Timed Up and Go (TUGs), Tinetti balance, and Tinetti gait. Plasma levels of these proteins were measured by enzyme-linked immunosorbent assay (ELISA). The plasma level of α-syn was significantly higher in PD patients when compared to controls (p = 0.004), and significantly higher in the PIGD group when compared to the TD group (p = 0.03). While the plasma level of Aβ-42 was significantly lower in PD patients than in controls (p = 0.002), and significantly lower in the PIGD group than in the TD group (p = 0.05). In PD patients, the plasma level of α-syn (r = -0.355, p < 0.001) was significantly related to the severity of Tenitti Gait score, even after performing multiple linear regression (p = 0.002). While the plasma level of Aβ-42 (r = -0.261, p < 0.05) was significantly associated with the severity of PIGD score and remained correlate when performed multiple linear regression (p = 0.005). The patients with PIGD subtype are characterized with a lower level of plasma Aβ-42 and a higher plasma level of α-syn, which may be used as biomarkers for diagnosis and progression of the subtypes of PD.

Sensitive analysis of α-synuclein by nonlinear laser wave mixing coupled with capillary electrophoresis

Multi-photon nonlinear laser wave-mixing spectroscopy is a novel absorption-based technique that offers excellent detection sensitivity for biomedical applications, including early diagnosis and investigation of neurodegenerative diseases. α-Synuclein is linked to Parkinson's disease (PD), and characterization of its oligomers and quantification of the protein may contribute to understanding PD. The laser wave-mixing signal has a quadratic dependence on analyte concentration, and hence the technique is effective in monitoring small changes in concentration within biofluids. A wide variety of labels can be employed for laser wave-mixing detection due to its ability to detect both chromophores and fluorophores. In this investigation, two fluorophores and a chromophore are studied and used as labels for the detection of α-synuclein. Wave-mixing detection limits of PD-related protein conjugated with fluorescein isothiocyanate, QSY 35 acetic acid, succinimidyl ester, and Chromeo P503 were determined to be 1.4 × 10(-13) M, 1.4 × 10(-10) M, and 1.9 × 10(-13) M, respectively. Based on the laser probe volume used, the corresponding mass detection limits were determined to be 1.1 × 10(-23) mol, 1.1 × 10(-20) mol, and 1.5 × 10(-23) mol. This study also presents molecular-based separation and quantification of α-synuclein by laser wave mixing coupled with capillary electrophoresis.

The utility of α-synuclein as biofluid marker in neurodegenerative diseases: a systematic review of the literature

The discovery of α-synuclein (α-syn) as a major component of Lewy bodies, neuropathological hallmark of Parkinson's disease (PD), dementia with Lewy bodies and of glial inclusions in multiple system atrophy initiated the investigation of α-syn as a biomarker in cerebrospinal fluid (CSF). Due to the involvement of the periphery in PD the quantification of α-syn in peripheral fluids such as serum, plasma and saliva has been investigated as well. We review how the development of multiple assays for the quantification of α-syn has yielded novel insights into the variety of α-syn species present in the different fluids; the optimal preanalytical conditions required for robust quantification and the potential clinical value of α-syn as biomarker. We also suggest future approaches to use of CSF α-syn in neurodegenerative diseases.

Dopaminergic Toxin 1-Methyl-4-Phenylpyridinium, Proteins α-Synuclein and Glia Maturation Factor Activate Mast Cells and Release Inflammatory Mediators

Parkinson’s disease (PD) is characterized by the presence of Lewy bodies and degeneration of dopaminergic neurons. 1-methyl-4-phenylpyridinium (MPP+), a metabolite of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and Lewy body component α-synuclein activates glia in PD pathogenesis. Mast cells and glia maturation factor (GMF) are implicated in neuroinflammatory conditions including Multiple Sclerosis. However, the role of mast cells in PD is not yet known. We have analyzed the effect of recombinant GMF, MPP+, α-synuclein and interleukin-33 (IL-33) on mouse bone marrow-derived cultured mast cells (BMMCs), human umbilical cord blood-derived cultured mast cells (hCBMCs) and mouse brain-derived cultured astrocytes by quantifying cytokines/chemokines released using ELISA or by detecting the expression of co-stimulatory molecules CD40 and CD40L by flow cytometry. GMF significantly released chemokine (C-C motif) ligand 2 (CCL2) from BMMCs but its release was reduced in BMMCs from GMF knockout mice. GMF, α-synuclein and MPP+ released IL-1β, β-hexosaminidase from BMMCs, and IL-8 from hCBMCs. GMF released CCL5, and IL-33- induced the expression of GMF from hCBMCs. Novel GMF expression was detected in hCBMCs and BMMCs by immunocytochemistry. GMF released tumor necrosis factor-alpha (TNF-α) from mouse astrocytes, and this release was greater in BMMC- astrocyte coculture than in individual cultures. Flow cytometry results showed increased IL-33 expression by GMF and MPP+, and GMF-induced CD40 expression in astrocytes. Proinflammatory mediator release by GMF, MPP+ and α-synuclein, as well as GMF expression by mast cells indicate a potential therapeutic target for neurodegenerative diseases including PD.

Low alpha-synuclein levels in the blood are associated with insulin resistance

Mutations in the protein alpha-synuclein (SNCA) have been linked to Parkinson's disease. We recently reported that non-mutated SNCA enhanced glucose uptake through the Gab1-PI3 kinase-Akt pathway and elucidated its effects on glucose regulation. Here, we examined the association of SNCA with insulin resistance (IR), a condition that is characterized by decreased tissue glucose uptake. Our observations include those from a population study as well as a SNCA-deficient mouse model, which had not previously been characterized in an IR scenario. In 1,152 patients, we found that serum SNCA levels were inversely correlated with IR indicators--body mass index, homeostatic model assessment for IR (HOMA-IR) and immunoreactive insulin (IRI)--and, to a lesser extent, with blood pressure and age. Additionally, SNCA-deficient mice displayed alterations in glucose and insulin responses during diet-induced IR. Moreover, during euglycemic clamp assessments, SNCA knock-out mice fed a high-fat diet (HFD) showed severe IR in adipose tissues and skeletal muscle. These findings provide new insights into IR and diabetes and point to SNCA as a potential candidate for further research.

The potential of pathological protein fragmentation in blood-based biomarker development for dementia - with emphasis on Alzheimer's disease

The diagnosis of dementia is challenging and early stages are rarely detected limiting the possibilities for early intervention. Another challenge is the overlap in the clinical features across the different dementia types leading to difficulties in the differential diagnosis. Identifying biomarkers that can detect the pre-dementia stage and allow differential diagnosis could provide an opportunity for timely and optimal intervention strategies. Also, such biomarkers could help in selection and inclusion of the right patients in clinical trials of both Alzheimer’s disease and other dementia treatment candidates. The cerebrospinal fluid (CSF) has been the most investigated source of biomarkers and several candidate proteins have been identified. However, looking solely at protein levels is too simplistic to provide enough detailed information to differentiate between dementias, as there is a significant crossover between the proteins involved in the different types of dementia. Additionally, CSF sampling makes these biomarkers challenging for presymptomatic identification. We need to focus on disease-specific protein fragmentation to find a fragment pattern unique for each separate dementia type – a form of protein fragmentology. Targeting protein fragments generated by disease-specific combinations of proteins and proteases opposed to detecting the intact protein could reduce the overlap between diagnostic groups as the extent of processing as well as which proteins and proteases constitute the major hallmark of each dementia type differ. In addition, the fragments could be detectable in blood as they may be able to cross the blood–brain barrier due to their smaller size. In this review, the potential of the fragment-based biomarker discovery for dementia diagnosis and prognosis is discussed, especially highlighting how the knowledge from CSF protein biomarkers can be used to guide blood-based biomarker development.

Serological Analysis of Alpha-synuclein and NF-κB in Parkinson's Disease Patients

INTRODUCTION

Several investigations have been made to determine the level of alpha-synuclein in the peripheral blood of Parkinson's disease patients, but the results were very contradictory and inconclusive. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) was also found to be involved in Parkinson's disease, but there is a lack of studies investigating NF-κB in Parkinson's disease patients. As far as our knowledge goes, no study reported the level of NF-κB in serum of Parkinson's disease patients. In this context, present study was designed to make a baseline study in order to evaluate the levels of total alpha-synuclein and NF-κB in serum of Parkinson's disease patients.

MATERIALS AND METHODS

Serum samples were collected from Parkinson's disease patients (n=97) and healthy controls (n=97). Their levels were determined by using Enzyme linked immunosorbent assay.

RESULTS

The levels of total alpha-synuclein (patients=5.79±2.24 ng/ml, controls=6.20±1.61 ng/ml; p=0.14) and NF-κB (patients=1.38±0.99 ng/ml, controls=1.65±1.00 ng/ml; p=0.71) were lower in Parkinson's disease patients than controls, but the differences were not statistically significant. This difference was also failed to reach significance between males (alpha-synuclein (p)=0.70, NF-κB (p)=0.84) and females (alpha-synuclein (p)=0.06, NF-κB (p)=0.77) in both the groups as well as within the groups. The levels of total alpha-synuclein and NF-κB were also not associated with Parkinson's disease severity (alpha-synuclein (p) = 0.84, NF-κB (p) = 0.73).

CONCLUSION

A non-significant difference in the levels of total alpha-synuclein and NF-κB between Parkinson's disease patients and controls suggested that these are not valuable biomarkers for Parkinson's disease, more specifically in Indian population.

Decrease in plasma levels of α-synuclein is evident in patients with Parkinson's disease after elimination of heterophilic antibody interference

There is substantial biochemical, pathological, and genetic evidence that α-synuclein (A-syn) is a principal molecule in the pathogenesis of Parkinson disease (PD). We previously reported that total A-syn levels in cerebrospinal fluid (CSF), measured with the specific enzyme-linked immunosorbent assay (ELISA) developed by ourselves, were decreased in patients with PD, and suggested the usefulness of A-syn in CSF and plasma as a biomarker for the diagnosis of PD. After our report, a considerable number of studies have investigated the levels A-syn in CSF and in blood, but have reported inconclusive results. Such discrepancies have often been attributed not only to the use of different antibodies in the ELISAs but also to interference from hemolysis. In this study we measured the levels of A-syn in CSF and plasma by using our own sandwich ELISA with or without heterophilic antibody (HA) inhibitor in 30 patients with PD and 58 age-matched controls. We thereby revealed that HA interfered with ELISA measurements of A-syn and are accordingly considered to be an important confounder in A-syn ELISAs. HA produced falsely exaggerated signals in A-syn ELISAs more prominently in plasma samples than in CSF samples. After elimination of HA interference, it was found that hemolysis did not have a significant effect on the signals obtained using our A-syn ELISA. Furthermore, plasma levels of A-syn were significantly lower in the PD group compared with the control group following elimination of HA interference with an HA inhibitor. Our results demonstrate that HA was a major confounder that should be controlled in A-syn ELISAs, and that plasma A-syn could be a useful biomarker for the diagnosis of PD if adequately quantified following elimination of HA interference.

Alpha-synuclein levels in blood plasma decline with healthy aging

There is unequivocal evidence that alpha-synuclein plays a pivotal pathophysiological role in neurodegenerative diseases, and in particular in synucleinopathies. These disorders present with a variable extent of cognitive impairment and alpha-synuclein is being explored as a biomarker in CSF, blood serum and plasma. Considering key events of aging that include proteostasis, alpha-synuclein may not only be useful as a marker for differential diagnosis but also for aging per se. To explore this hypothesis, we developed a highly specific ELISA to measure alpha-synuclein. In healthy males plasma alpha-synuclein levels correlated strongly with age, revealing much lower concentrations in older (avg. 58.1 years) compared to younger (avg. 27.6 years) individuals. This difference between the age groups was enhanced after acidification of the plasmas (p<0.0001), possibly reflecting a decrease of alpha-synuclein-antibody complexes or chaperone activity in older individuals. Our results support the concept that alpha-synuclein homeostasis may be impaired early on, possibly due to disturbance of the proteostasis network, a key component of healthy aging. Thus, alpha-synuclein may be a novel biomarker of aging, a factor that should be considered when analyzing its presence in biological specimens.

Naturally occurring alpha-synuclein autoantibodies in Parkinson's disease: sources of (error) variance in biomarker assays

Alpha-synuclein (α-Syn) plays a pivotal role in the pathophysiology of Parkinson’s disease (PD), which can partly be modulated by innate and adaptive immune functions, and vice versa. Here, naturally occurring α-Syn autoantibodies (α-Syn-nAbs) may be effective against α-Syn pathoetiology and may serve as a PD biomarker. However, serum and cerebrospinal fluid α-Syn-nAbs levels still lack consistent evidence as required for a reliable PD biomarker. Serum and cerebrospinal fluid α-Syn-nAbs levels of 66 PD patients and 69 healthy controls were assessed using a validated ELISA assay. Moreover, potential sources of error variance including unspecific ELISA background signals, free serum hemoglobin concentrations, α-Syn plate coating procedures, and differences in α-Syn-nAbs standards, were investigated. PD patients and controls did not differ in serum (p = .49) nor cerebrospinal fluid (p = .29) α-Syn-nAbs levels. Interestingly, free serum hemoglobin concentrations were negatively correlated with α-Syn-nAbs levels in controls (Spearman  = −.41, p<.001), but not in PD patients ( = .16, p = .21). ELISA α-Syn plate coating procedures impacted inter-assay variability (same day coating: 8–16%; coating on different days: 16–58%). α-Syn-nAbs standards from different purification batches differed regarding optical density measured in ELISAs suggesting differences in α-Syn affinity. While α-Syn-nAbs levels may represent a potential PD biomarker, several methodological issues have to be considered to increase reproducibility of α-Syn-nAbs findings. Further studies using standardized protocols minimizing sources of error variance may be necessary to establish a reliable PD α-Syn-nAbs biomarker.

Plasma exosomal α-synuclein is likely CNS-derived and increased in Parkinson's disease

Extracellular α-synuclein is important in the pathogenesis of Parkinson's disease (PD) and also as a potential biomarker when tested in the cerebrospinal fluid (CSF). The performance of blood plasma or serum α-synuclein as a biomarker has been found to be inconsistent and generally ineffective, largely due to the contribution of peripherally derived α-synuclein. In this study, we discovered, via an intracerebroventricular injection of radiolabeled α-synuclein into mouse brain, that CSF α-synuclein was readily transported to blood, with a small portion being contained in exosomes that are relatively specific to the central nervous system (CNS). Consequently, we developed a technique to evaluate the levels of α-synuclein in these exosomes in individual plasma samples. When applied to a large cohort of clinical samples (267 PD, 215 controls), we found that in contrast to CSF α-synuclein concentrations, which are consistently reported to be lower in PD patients compared to controls, the levels of plasma exosomal α-synuclein were substantially higher in PD patients, suggesting an increased efflux of the protein to the peripheral blood of these patients. Furthermore, although no association was observed between plasma exosomal and CSF α-synuclein, a significant correlation between plasma exosomal α-synuclein and disease severity (r = 0.176, p = 0.004) was observed, and the diagnostic sensitivity and specificity achieved by plasma exosomal α-synuclein were comparable to those determined by CSF α-synuclein. Further studies are clearly needed to elucidate the mechanism involved in the transport of CNS α-synuclein to the periphery, which may lead to a more convenient and robust assessment of PD clinically.

Alpha-synuclein in peripheral tissues and body fluids as a biomarker for Parkinson's disease - a systematic review

Parkinson's disease (PD) is neuropathologically characterized as an alpha-synucleinopathy. Alpha-synuclein-containing inclusions are stained as Lewy bodies and Lewy neurites in the brain, which are the pathological hallmark of PD. However, alpha-synuclein-containing inclusions in PD are not restricted to the central nervous system, but are also found in peripheral tissues. Alpha-synuclein levels can also be measured in body fluids. The aim of this study was to conduct a systematic review of available evidence to determine the utility of alpha-synuclein as a peripheral biomarker of PD. We searched PubMed (1948 to 26 May 2013), Embase (1974 to 26 May 2013), the Cochrane Library (up to 26 May 2013), LILACS (up to 26 May 2013) and CINAHL (up to 26 May 2013) for the studies of alpha-synuclein in peripheral tissues or body fluids in PD. A total of 49 studies fulfilled the search criteria. Peripheral tissues such as colonic mucosa showed a sensitivity of 42-90% and a specificity of 100%; submandibular salivary glands showed sensitivity and specificity of 100%; skin biopsy showed 19% sensitivity and 80% specificity in detecting alpha-synuclein pathology. CSF alpha-synuclein had 71-94% sensitivity and 25-53% specificity for distinguishing PD from controls. Plasma alpha-synuclein had 48-53% sensitivity and 69-85% specificity. Neither plasma nor CSF alpha-synuclein is presently a reliable marker of PD. This differs from alpha-synuclein in solid tissue samples of the enteric and autonomic nervous system, which offer some potential as a surrogate marker of brain synucleinopathy.

Epitope Mapping of Antibodies to Alpha-Synuclein in LRRK2 Mutation Carriers, Idiopathic Parkinson Disease Patients, and Healthy Controls

Alpha-synuclein (Snca) plays a major role in Parkinson disease (PD). Circulating anti-Snca antibodies has been described in PD patients and healthy controls, but they have been poorly characterized. This study was designed to assess the prevalence of anti-Snca reactivity in human subjects carrying the LRRK2 mutation, idiopathic PD (iPD) patients, and healthy controls and to map the epitopes of the anti-Snca antibodies. Antibodies to Snca were detected by ELISA and immunoblotting using purified recombinant Snca in plasma from individuals carrying LRRK2 mutations (104), iPD patients (59), and healthy controls (83). Epitopes of antibodies were mapped using recombinant protein constructs comprising different regions of Snca. Clear positive anti-Snca reactivity showed no correlation with age, sex, years of evolution, or the disability scores for PD patients and anti-Snca reactivity was not prevalent in human patients with other neurological or autoimmune diseases. Thirteen of the positive individuals were carriers of LRRK2 mutations either non-manifesting (8 out 49 screened) or manifesting (5 positive out 55), three positive (out of 59) were iPD patients, and five positive (out of 83) were healthy controls. Epitope mapping showed that antibodies against the N-terminal (a.a. 1–60) or C-terminal (a.a. 109–140) regions of Snca predominate in LRRK2 mutation carriers and iPD patients, being N122 a critical amino acid for recognition by the anti-C-terminal directed antibodies. Anti-Snca circulating antibodies seem to cluster within families carrying the LRRK2 mutation indicating possible genetic or common environmental factors in the generation of anti-Snca antibodies. These results suggest that case-controls’ studies are insufficient and further studies in family cohorts of patients and healthy controls should be undertaken, to progress in the understanding of the possible relationship of anti-Snca antibodies and PD pathology.

Alpha-synuclein elicits glucose uptake and utilization in adipocytes through the Gab1/PI3K/Akt transduction pathway

Insulin is the main glucoregulator that promotes the uptake of glucose by tissues and the subsequent utilization of glucose as an energy source. In this paper, we describe a novel glucoregulator, the alpha-synuclein (SNCA) protein, that has previously been linked to Parkinson's disease. Treatment with recombinant SNCA promotes glucose uptake in vitro in preadipocytes and in vivo in the adipose tissues and skeletal muscles of mice through the LPAR2/Gab1/PI3K/Akt pathway; these effects occur independently of the insulin receptor. This function of SNCA represents a new mechanistic insight that creates novel avenues of research with respect to the process of glucose regulation.

Gender differences in Parkinson's disease: focus on plasma α-synuclein

Among promising biological markers proposed for Parkinson's disease (PD) and other disorders related to Lewy bodies, plasma alpha-synuclein assay has provided conflicting results mainly owing to the various laboratory assay techniques used and protein forms assayed. In this observational and exploratory cross-sectional study, using an immunoenzymatic technique, we assayed and compared total plasma alpha-synuclein concentrations in 69 patients with PD and 110 age-matched healthy control subjects. Two previously unreported findings concerned gender. First, plasma alpha-synuclein concentrations measured in the more advanced parkinsonian disease stages decreased in men, but not in women. Second, again only in men, plasma alpha-synuclein concentration was associated with cognitive impairments, hallucinations, and sleep disorders. These findings underline the gender-related differences in parkinsonian patients and indicate plasma alpha-synuclein expression as a potential biological marker for PD progression in men.

Αlpha-synuclein levels in blood plasma from LRRK2 mutation carriers

The diagnosis of Parkinson's disease (PD) remains primarily a clinical issue, based mainly on phenotypic patterns. The identification of biomarkers capable of permitting the preclinical detection of PD is critically needed. α-Synuclein is a key protein in PD, with missense and multiplication mutations in the gene encoding α-synuclein (SNCA) having been reported in familial cases of PD, and accumulation of the protein identified in Lewy bodies (LBs) and Lewy neurites (LNs) in affected brain regions. With the objective of validating the use of α-synuclein as a clinical or progressive biomarker in an accessible tissue, we used an enzyme-linked immunosorbent assay (ELISA) to measure α-synuclein levels in the peripheral blood plasma of idiopathic PD and LRRK2 mutation carrier patients and compared our findings with healthy control subjects. Compared to healthy controls, we found a significant decrease in plasma total α-synuclein levels in idiopathic PD (iPD) patients (n = 134, p = 0.010). However, the reduction was less significant in patients who were LRRK2 mutation carriers (n = 32, p = 0.133). This lack of significance could be due to the small number of individuals employed in this group. No predictive value of total α-synuclein in the diagnosis of PD was found in a receiver operating characteristic (ROC) curve analysis. Although this is a pilot study requiring corroboration on a larger cohort of patients, our results highlight the possible use of plasma α-synuclein as a biomarker for PD.

α-Synuclein and anti-α-synuclein antibodies in Parkinson's disease, atypical Parkinson syndromes, REM sleep behavior disorder, and healthy controls

α-synuclein is thought to play a key role in Parkinson’s disease (PD) because it is the major protein in Lewy bodies, and because its gene mutations, duplication, and triplication are associated with early-onset PD. There are conflicting reports as to whether serum and plasma concentrations of α-synuclein and anti-α-synuclein antibodies differ between PD and control subjects. The objectives of this study were to compare the levels of α-synuclein and its antibodies between individuals with typical PD (n = 14), atypical Parkinson syndromes (n = 11), idiopathic rapid eye movement sleep behavior disorder (n = 10), and healthy controls (n = 9), to assess the strength of association between these serum proteins, and to determine group sizes needed for a high probability (80% power) of detecting statistical significance for 25% or 50% differences between typical PD and control subjects for these measurements. Analysis of log-transformed data found no statistically significant differences between groups for either α-synuclein or its antibodies. The concentrations of these proteins were weakly correlated (Spearman rho = 0.16). In subjects with typical PD and atypical Parkinson syndromes, anti-α-synuclein antibody levels above 1.5 µg/ml were detected only in subjects with no more than four years of clinical disease. Power analysis indicated that 236 and 73 samples per group would be required for an 80% probability that 25% and 50% differences, respectively, in mean α-synuclein levels between typical PD and control subjects would be statistically significant; for anti-α-synuclein antibodies, 283 and 87 samples per group would be required. Our findings are consistent with those previous studies which suggested that serum concentrations of α-synuclein and its antibodies are not significantly altered in PD.

Antibody-aided clearance of extracellular α-synuclein prevents cell-to-cell aggregate transmission

Abnormal deposition and intercellular propagation of α-synuclein plays a central role in the pathogenesis of disorders such as Parkinson's Disease (PD) and dementia with Lewy bodies (DLB). Previous studies demonstrated that immunization against α-synuclein resulted in reduced α-synuclein accumulation and synaptic loss in a transgenic (tg) mouse model, highlighting the potential for immunotherapy. However, the mechanism by which immunization prevents synucleinopathy-associated deficits remains unknown. Here, we show that antibodies against α-synuclein specifically target and aid in clearance of extracellular α-synuclein proteins by microglia, thereby preventing their actions on neighboring cells. Antibody-assisted clearance occurs mainly in microglia through the Fcγ receptor, and not in neuronal cells or astrocytes. Stereotaxic administration of antibody into the brains of α-synuclein tg mice prevented neuron-to-astroglia transmission of α-synuclein and led to increased localization of α-synuclein and the antibody in microglia. Furthermore, passive immunization with α-synuclein antibody reduced neuronal and glial accumulation of α-synuclein and ameliorated neurodegeneration and behavioral deficits associated with α-synuclein overexpression. These findings provide an underlying mechanistic basis for immunotherapy for PD/DLB and suggest extracellular forms of α-synuclein as potential therapeutic targets.

α-Synuclein as CSF and Blood Biomarker of Dementia with Lewy Bodies

Dementia with Lewy bodies (DLB) is a common subtype of dementia in the elderly. DLB is neuropathologically characterized by the presence of Lewy bodies and Lewy neurites, both of which are composed of α-synuclein. Although α-synuclein was initially considered to be an exclusively intracellular protein, it has been found to be secreted into biological fluids. α-Synuclein in biological fluids such as cerebrospinal fluid (CSF) and blood has been discussed as a potential biomarker of DLB and α-synuclein-related disorders, because α-synuclein is characteristically accumulated in the brain of patients with these disorders. The α-synuclein level in CSF has been examined by several investigators, and the majority of studies have shown a reduction in CSF α-synuclein level in DLB and α-synuclein-related disorders. Discrepant findings of studies of plasma α-synuclein level in patients with DLB have been reported. Because the level of α-synuclein stored in red blood cells is considerably high, blood contamination and haemolysis during sample collection and processing should be considered as a confounding factor for quantification of α-synuclein. Here, the recent progress in the studies of α-synuclein as a biomarker of DLB and their potential clinical applications are reviewed.

Premotor biomarkers for Parkinson's disease - a promising direction of research

The second most serious neurodegenerative disease is Parkinson’s disease (PD). Over the past several decades, a strong body of evidence suggests that PD can begin years before the hallmark clinical motor symptoms appear. Biomarkers for PD are urgently needed to differentiate between neurodegenerative disorders, screen novel therapeutics, and predict eventual clinical PD before the onset of symptoms. Some clinical evaluations and neuroimaging techniques have been developed in the last several years with some success in this area. Moreover, other strategies have been utilized to identify biochemical and genetic markers associated with PD leading to the examination of PD progression and pathogenesis in cerebrospinal fluid, blood, or saliva. Finally, interesting results are surfacing from preliminary studies using known PD-associated genetic mutations to assess potential premotor PD biomarkers. The current review highlights recent advances and underscores areas of potential advancement.

Decreased α-synuclein serum levels in patients with Lewy body dementia compared to Alzheimer's disease patients and control subjects

BACKGROUND/AIMS

Detection and differentiation of neurodegenerative dementias, such as dementia with Lewy bodies (DLB) and Alzheimer's disease (AD), with blood-based biomarkers would facilitate diagnosis and treatment.

METHODS

By use of a commercially available ELISA kit, we measured α-synuclein levels in the serum of 40 DLB patients and controls, and of 80 AD patients.

RESULTS

We found significantly reduced α-synuclein serum levels in DLB compared to both AD (p = 0.006) and control subjects (p = 0.001), reaching an area under the curve of >0.70.

CONCLUSION

Although these results do not justify a definition of serum α-synuclein as a potential single biomarker, results may contribute to a multimarker strategy in DLB diagnosis.

Phosphorylated α-synuclein can be detected in blood plasma and is potentially a useful biomarker for Parkinson's disease

Parkinson's disease (PD) is characterized by the presence of Lewy bodies containing phosphorylated and aggregated α-synuclein (α-syn). α-Syn is present in human body fluids, including blood plasma, and is a potential biomarker for PD. Immunoassays for total and oligomeric forms of both normal and phosphorylated (at Ser-129) α-syn have been used to assay plasma samples from a longitudinal cohort of 32 patients with PD (sampled at mo 0, 1, 2, 3), as well as single plasma samples from a group of 30 healthy control participants. The levels of α-syn in plasma varied greatly between individuals, but were remarkably consistent over time within the same individual with PD. The mean level of phospho-α-syn was found to be higher (P=0.053) in the PD samples than the controls, whereas this was not the case for total α-syn (P=0.244), oligo-α-syn (P=0.221), or oligo-phospho-α-syn (P=0.181). Immunoblots of plasma revealed bands (at 21, 24, and 50-60 kDa) corresponding to phosphorylated α-syn. Thus, phosphorylated α-syn can be detected in blood plasma and shows more promise as a diagnostic marker than the nonphosphorylated protein. Longitudinal studies undertaken over a more extended time period will be required to determine whether α-syn can act as a marker of disease progression.

Enzyme-linked immunosorbent assays for α-synuclein with species and multimeric state specificities

Abnormal intracellular deposition of aggregated α-synuclein is the characteristic feature of a number of neurological disorders, including Parkinson's disease (PD). Although α-synuclein is typically known as a cytosolic protein, a small amount is secreted by exocytosis in both monomeric and aggregated forms. The extracellular forms of α-synuclein in human body fluids, such as cerebrospinal fluid (CSF) and blood plasma, might be a diagnostic target for PD and related diseases. Here, we characterized a new set of monoclonal antibodies against α-synuclein, and using different combinations of antibodies, we established ELISA systems to specifically detect human α-synuclein, mouse and human α-synuclein together, and multimeric forms of α-synuclein in biological samples. By employing the Tyramide signal amplification method, the sensitivity of the assay was significantly improved to detect a concentration as low as ∼12.5 pg/ml. These assays might be useful tools for quantitative analysis of α-synuclein in various forms and with high sensitivity in diverse biological samples.

α-Synuclein in Parkinson disease and other neurodegenerative disorders

With the aging population in the Western hemisphere, neurodegenerative parkinsonism and dementia will become two of the great public health challenges of this century. A major pillar in the effort to treat these conditions will be the shift from symptomatic treatment to disease modifying therapy. This step will absolutely require cheap and reliable biomarkers; patients will need to be diagnosed before irreversible change has occurred. α-Synuclein (αS) is a recent candidate biomarker for Lewy body neurodegeneration. It is a 140 amino acid protein that forms the pathological substrate in idiopathic Parkinson's disease (IPD), dementia with Lewy bodies (DLB), as well as multiple system atrophy (MSA), a group of disorders collectively known as the synucleopathies. Biomarker research has investigated αS in blood, skin and cerebrospinal fluid (CSF). Plasma assays have demonstrated inconsistent results but CSF assays show a higher degree of uniformity, mostly demonstrating lower levels of αS in patients with Lewy body disease compared to controls. These results are not yet accurate or reliable enough to use as screening tools or isolated diagnostic tests in established disease. It has become clear that factors other than neurodegeneration affect αS concentrations in these tissue samples, such as genetic and environmental influences. Future studies using standardized techniques and larger patient numbers are awaited to realise the full potential of αS as a more definitive diagnostic biomarker.

Biomarkers for prediction and targeted prevention of Alzheimer's and Parkinson's diseases: evaluation of drug clinical efficacy

Neurodegenerative diseases like Parkinson’s disease (PD) and Alzheimer’s disease (AD) are considered disorders of multifactorial origin, inevitably progressive and having a long preclinical period. Therefore, the availability of biological markers or biomarkers (BMs) for early disease diagnosis will impact the management of AD and PD in several dimensions; it will 1) help to capture high-risk individuals before symptoms develop, a stage where prevention efforts might be expected to have their greatest impact; 2) provide a measure of disease progression that can be evaluated objectively, while clinical measures are much less accurate; 3) help to discriminate between true AD or PD and other causes of a similar clinical syndrome; 4) delineate pathophysiological processes responsible for the disease; 5) determine the clinical efficacy of novel, disease-modifying (neuroprotective) strategies. In the long run the availability of reliable BMs will significantly advance the research and therapeutics of AD and PD.

Significance and confounders of peripheral DJ-1 and alpha-synuclein in Parkinson's disease

DJ-1 and alpha-synuclein are leading biomarkers for Parkinson's disease diagnosis and/or monitoring disease progression. A few recent investigations have determined DJ-1 and alpha-synuclein levels in plasma or serum, a more convenient sample source than cerebrospinal fluid; but the results were variable or even contradictory. Besides limitations in detection technology and limited number of cases in some studies, inadequate control of several important confounders likely has contributed to these inconsistent results. In this study, the relative contribution of each blood component to blood DJ-1 and alpha-synuclein was evaluated, followed by quantification of plasma levels of both markers in a larger cohort of patients/subjects ( approximately 300 cases) whose cerebrospinal fluid DJ-1 and alpha-synuclein levels have been determined recently. The results demonstrated that the DJ-1 and alpha-synuclein in blood resided predominantly in red blood cells (>95%), followed by platelets (1-4%), white blood cells and plasma (< or =1%), indicating that variations in hemolysis and/or platelet contamination could have a significant effect on plasma/serum DJ-1 and alpha-synuclein levels. Nonetheless, after adjusting for the age, although there was a trend of decrease in DJ-1 and alpha-synuclein in patients with Parkinson's or Alzheimer's disease compared with healthy controls, no statistical difference was observed in this cohort between any groups, even when the extent of hemolysis and platelet contamination were controlled for. Additionally, no correlation between DJ-1 or alpha-synuclein and Parkinson's disease severity was identified. In conclusion, unlike in cerebrospinal fluid, total DJ-1 or alpha-synuclein in plasma alone is not useful as biomarkers for Parkinson's disease diagnosis or progression/severity.

Perivascular nerve fiber α-synuclein regulates contractility of mouse aorta: a link to autonomic dysfunction in Parkinson's disease

Parkinson's disease and other neurodegenerative disorders associated to changes in alpha-synuclein often result in autonomic dysfunction, most of the time accompanied by abundant expression of this synaptic protein in peripheral autonomic neurons. Given that expression of alpha-synuclein in vascular elements has been previously reported, the present study was undertaken to determine whether alpha-synuclein directly participates in the regulation of vascular responsiveness. We detected by immunohistochemistry perivascular nerve fibers containing alpha-synuclein in the aorta of mice while aortic endothelial cells and muscular fibers themselves did not exhibit detectable levels of this protein. To assess the effect of alpha-synuclein on vascular reactivity, aortic ring preparations obtained from alpha-synuclein-deficient knockout mice and from transgenic mice overexpressing human wild-type alpha-synuclein under the control of the tyrosine hydroxylase-promoter were mounted and equilibrated in organ baths for isometric tension recording. Lack of alpha-synuclein did not modify the relaxant responses to the endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) vasodilators, but resulted in a greater than normal norepinephrine-induced vasoconstriction along with a lowered response to dopamine, suggesting potential presynaptic changes in dopamine and norepinephrine releases in knockout mice. Overexpression of alpha-synuclein in TH-positive fibers resulted in complex abnormal responses, characterized by lowered acetylcholine-induced relaxation and lowered norepinephrin-induced contraction. Taken together, our data show for the first time that alpha-synuclein is present in sympathetic fibers supplying the murine aorta and provide evidence that changes in alpha-synuclein levels in perivascular fibers play a physiological role in the regulation of vascular function.