CSF α-synuclein, tau, and amyloid β in Parkinson's disease

A rapid α-synuclein seed assay of Parkinson's disease CSF panel shows high diagnostic accuracy

BACKGROUND

Assays that specifically measure α-synuclein seeding activity in biological fluids could revolutionize the diagnosis of Parkinson's disease. Recent improvements in α-synuclein real-time quaking-induced conversion assays of cerebrospinal fluid have dramatically reduced reaction times from 5-13 days down to 1-2 days.

OBJECTIVE

To test our improved assay against a panel of cerebrospinal fluid specimens from patients with Parkinson's disease and healthy controls from the MJ Fox Foundation/NINDS BioFIND collection.

METHODS

Specimens collected from healthy controls and patients with clinically typical moderate-to-advanced Parkinson's disease were tested without prior knowledge of disease status. Correlative analyses between assay parameters and clinical measures were performed by an independent investigator.

RESULTS

BioFIND samples gave positive signals in 105/108 (97%) Parkinson's disease cases versus 11/85 (13%) healthy controls. Receiver operating characteristic analyses of diagnosis of cases versus healthy controls gave areas under the curve of 95%. Beyond binary positive/negative determinations, only weak correlations were observed between various assay response parameters and Parkinson's disease clinical measures or other cerebrospinal fluid analytes. Of note, REM sleep behavioral disorder questionnaire scores correlated with the reaction times needed to reach 50% maximum fluorescence. Maximum fluorescence was inversely correlated with Unified Parkinson's Disease Rating Scale motor scores, which was driven by the patients without REM sleep behavioral disorder.

CONCLUSIONS

Our improved α-synuclein seed amplification assay dramatically reduces the time needed to diagnose Parkinson's disease while maintaining the high-performance standards associated with previous α-synuclein seed assays, supporting the clinical utility of this assay for Parkinson's disease diagnosis.

A refined concept: α-synuclein dysregulation disease

α-synuclein (αSyn) still remains a mysterious protein even two decades after SNCA encoding it was identified as the first causative gene of familial Parkinson's disease (PD). Accumulation of αSyn causes α-synucleinopathies including PD, dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Recent advances in therapeutic approaches offer new antibody-, vaccine-, antisense-oligonucleotide- and small molecule-based options to reduce αSyn protein levels and aggregates in patient's brain. Gathering research information of other neurological disease particularly Alzheimer's disease, recent disappointment of an experimental amyloid plaques busting antibody in clinical trials underscores the difficulty of treating people who show even mild dementia as damage in their brain may already be too extensive. Prodromal intervention to inhibit the accumulation of pathogenic protein may advantageously provide a better outcome. However, treatment prior to onset is not ethically justified as standard practice at present. In this review, we initiate a refined concept to define early pathogenic state of αSyn accumulation before occurrence of brain damage as a disease criterion for αSyn dysregulation disease.

Diagnostic Values of Cerebrospinal Fluid T-Tau and Aβ₄₂ using Meso Scale Discovery Assays for Alzheimer's Disease

BACKGROUND

Meso Scale Discovery (MSD) recently established electrochemiluminescence-based assays to measure cerebrospinal fluid (CSF) levels of total tau (t-tau) and amyloid-β 1-42 peptide (Aβ42) that can aid in the diagnosis of Alzheimer's disease (AD). The goal of this investigation is to independently evaluate this platform and establish cut-off values of these biomarkers for AD diagnosis.

OBJECTIVE

To validate the analytical and clinical performance of the MSD t-tau and Aβ42 kits and propose diagnostic cut-off values for the field.

METHODS

The analytical performance of the CSF t-tau and Aβ42 assays was determined, followed by assessment of diagnostic performance of CSF t-tau, Aβ42, and t-tau/Aβ42 in three clinically characterized cohorts.

RESULTS

Both MSD assays demonstrated consistent and stable analytical performance, as well as resistance to several important pre-analytic variables. Diagnostically, t-tau/Aβ42 performed the best.

CONCLUSIONS

Our results independently confirm the analytical and clinical performance of the MSD CSF t-tau and Aβ42 assays. Based on a large, multi-center, clinically-diagnosed cohort, we propose for the first time candidate diagnostic cut-offs for MSD measured CSF t-tau, Aβ42, and t-tau/Aβ42. However, these values needs to be refined as more subjects are included and the assays are tested by other laboratories.

CSF tau and tau/Aβ42 predict cognitive decline in Parkinson's disease

INTRODUCTION

A substantial proportion of patients with Parkinson's disease (PD) have concomitant cognitive dysfunction. Identification of biomarker profiles that predict which PD patients have a greater likelihood for progression of cognitive symptoms is pressingly needed for future treatment and prevention approaches.

METHODS

Subjects were drawn from the Deprenyl and Tocopherol Antioxidative Therapy of Parkinsonism (DATATOP) study, a large clinical trial that enrolled initially untreated PD patients. For the current study, Phase One encompassed trial baseline until just prior to levodopa administration (n = 403), and Phase Two spanned the initiation of levodopa treatment until the end of cognitive follow-up (n = 305). Correlations and linear mixed models were performed to determine cross-sectional and longitudinal associations between baseline amyloid β1-42 (Aβ42), total tau (t-tau), and phosphorylated tau (p-tau) in cerebrospinal fluid (CSF) and measures of memory and executive function. Analyses also considered APOE genotype and tremor- vs. rigidity-dominant phenotype.

RESULTS

No association was found between baseline CSF biomarkers and cognitive test performance during Phase One. However, once levodopa treatment was initiated, higher p-tau and p-tau/Aβ42 predicted subsequent decline on cognitive tasks involving both memory and executive functions. The interactions between biomarkers and cognition decline did not appear to be influenced by levodopa dosage, APOE genotype or motor phenotype.

CONCLUSIONS

The current study has, for the first time, demonstrated the possible involvement of tau species, whose gene (MAPT) has been consistently linked to the risk of PD by genome-wide association studies, in the progression of cognitive symptoms in PD.

Cerebrospinal fluid biomarkers in parkinsonian conditions: an update and future directions

Parkinsonian diseases comprise a heterogeneous group of neurodegenerative disorders, which show significant clinical and pathological overlap. Accurate diagnosis still largely relies on clinical acumen; pathological diagnosis remains the gold standard. There is an urgent need for biomarkers to diagnose parkinsonian disorders, particularly in the early stages when diagnosis is most difficult. In this review, several of the most promising cerebrospinal fluid candidate markers will be discussed. Their strengths and limitations will be considered together with future developments in the field.

Longitudinal assessment of tau and amyloid beta in cerebrospinal fluid of Parkinson disease

Tau gene has been consistently associated with the risk of Parkinson disease in recent genome wide association studies. In addition, alterations of the levels of total tau, phosphorylated tau [181P], and amyloid beta 1-42 in cerebrospinal fluid have been reported in patients with sporadic Parkinson disease and asymptomatic carriers of leucine-rich repeat kinase 2 mutations, in patterns that clearly differ from those typically described for patients with Alzheimer disease. To further determine the potential roles of these molecules in Parkinson disease pathogenesis and/or in tracking the disease progression, especially at early stages, the current study assessed all three proteins in 403 Parkinson disease patients enrolled in the DATATOP (Deprenyl and tocopherol antioxidative therapy of parkinsonism) placebo-controlled clinical trial, the largest cohort to date with cerebrospinal fluid samples collected longitudinally. These initially drug-naive patients at early disease stages were clinically evaluated, and cerebrospinal fluid was collected at baseline and then at endpoint, defined as the time at which symptomatic anti-Parkinson disease medications were determined to be required. General linear models were used to test for associations between baseline cerebrospinal fluid biomarker levels or their rates of change and changes in the Unified Parkinson Disease Rating Scale (total or part III motor score) over time. Robust associations among candidate markers are readily noted. Baseline levels of amyloid beta were weakly but negatively correlated with baseline Unified Parkinson Disease Rating Scale total scores. Baseline phosphorylated tau/total tau and phosphorylated tau/amyloid beta were significantly and negatively correlated with the rates of the Unified Parkinson Disease Rating Scale change. While medications (deprenyl and/or tocopherol) did not appear to alter biomarkers appreciably, a weak but significant positive correlation between the rate of change in total tau or total tau/amyloid beta levels and the change of the Unified Parkinson Disease Rating Scale was observed. Notably, these correlations did not appear to be influenced by APOE genotype. These results are one of the very first pieces of evidence suggesting that tau and amyloid beta are critically involved in early Parkinson disease progression, potentially by a different mechanism than that in Alzheimer disease, although their applications as Parkinson disease progression markers will likely require the addition of other proteins.

Metal dyshomeostasis and inflammation in Alzheimer's and Parkinson's diseases: possible impact of environmental exposures

A dysregulated metal homeostasis is associated with both Alzheimer's (AD) and Parkinson's (PD) diseases; AD patients have decreased cortex and elevated serum copper levels along with extracellular amyloid-beta plaques containing copper, iron, and zinc. For AD, a putative hepcidin-mediated lowering of cortex copper mechanism is suggested. An age-related mild chronic inflammation and/or elevated intracellular iron can trigger hepcidin production followed by its binding to ferroportin which is the only neuronal iron exporter, thereby subjecting it to lysosomal degradation. Subsequently raised neuronal iron levels can induce translation of the ferroportin assisting and copper binding amyloid precursor protein (APP); constitutive APP transmembrane passage lowers the copper pool which is important for many enzymes. Using in silico gene expression analyses, we here show significantly decreased expression of copper-dependent enzymes in AD brain and metallothioneins were upregulated in both diseases. Although few AD exposure risk factors are known, AD-related tauopathies can result from cyanobacterial microcystin and β-methylamino-L-alanine (BMAA) intake. Several environmental exposures may represent risk factors for PD; for this disease neurodegeneration is likely to involve mitochondrial dysfunction, microglial activation, and neuroinflammation. Administration of metal chelators and anti-inflammatory agents could affect disease outcomes.

Inflammation and α-synuclein's prion-like behavior in Parkinson's disease--is there a link?

Parkinson's disease patients exhibit progressive spreading of aggregated α-synuclein in the nervous system. This slow process follows a specific pattern in an inflamed tissue environment. Recent research suggests that prion-like mechanisms contribute to the propagation of α-synuclein pathology. Little is known about factors that might affect the prion-like behavior of misfolded α-synuclein. In this review, we suggest that neuroinflammation plays an important role. We discuss causes of inflammation in the olfactory bulb and gastrointestinal tract and how this may promote the initial misfolding and aggregation of α-synuclein, which might set in motion events that lead to Parkinson's disease neuropathology. We propose that neuroinflammation promotes the prion-like behavior of α-synuclein and that novel anti-inflammatory therapies targeting this mechanism could slow disease progression.

β-Amyloid induced effects on cholinergic, serotonergic, and dopaminergic neurons is differentially counteracted by anti-inflammatory drugs

β-Amyloid (Aβ) is a small peptide that plays a potent role in synaptic plasticity as well as forms amyloid plaques in Alzheimer's disease (AD). Recent studies suggest that Aβ deposition is deleterious not only in AD, but also in Parkinson's disease (PD) and depression. This Aβ effect is associated with inflammatory processes. However, further evaluation is needed to understand how Aβ and inflammation interact and contribute to the regulation of the cholinergic, serotonergic, and dopaminergic neuronal populations. The aim of the present study was to investigate the effects of Aβ(1-42) on cholinergic neurons of the nucleus basalis of Meynert (which degenerate in AD), on serotonergic neurons of the dorsal raphe nucleus (which play a role in depression), and on dopaminergic neurons of the ventral mesencephalon (which degenerate in PD) in rat organotypic brain slices. Furthermore, we investigated whether anti-inflammatory drugs (celecoxib, citalopram, cyclooxygenase-2 inhibitor, ibuprofen, indomethacin, piclamilast) modulate or counteract Aβ-induced effects. Two-week-old organotypic brain slices of the nucleus basalis of Meynert, dorsal raphe nucleus, and ventral mesencephalon were incubated with 50 ng/ml Aβ(1-42) with or without anti-inflammatory agents for 3 days. Our results reveal that Aβ significantly decreased the number of choline acetyltransferase-positive cholinergic, tryptophan hydroxylase-positive serotonergic, and tyrosine hydroxylase-positive dopaminergic neurons and that anti-inflammatory drugs partially counteracted the Aβ-induced neuronal decline. This decline was not due to apoptotic processes (as evaluated by TUNEL, propidium iodide, caspase), oxidative stress (as measured by nitrite, catalase, or superoxide dismutase-2), or inflammation, but was most likely caused by a downregulation of these key enzymes.

Cerebrospinal fluid amyloid β and tau in LRRK2 mutation carriers

OBJECTIVE

The goal of the current investigation was to examine a cohort of symptomatic and asymptomatic LRRK2 mutation carriers, in order to address whether the reported alterations in amyloid β (Aβ) and tau species in the CSF of patients with sporadic Parkinson disease (PD) are a part of PD pathogenesis, the aging process, or a comorbid disease in patients with PD, and to explore the possibility of Aβ and tau as markers of early or presymptomatic PD.

METHODS

CSF Aβ42, total tau, and phosphorylated tau were measured with Luminex assays in 26 LRRK2 mutation carriers, who were either asymptomatic (n = 18) or had a phenotype resembling sporadic PD (n = 8). All patients also underwent PET scans with 18F-6-fluoro-l-dopa (FD), 11C-(±)-α-dihydrotetrabenazine (DTBZ), and 11C-d-threo-methylphenidate (MP) to measure dopaminergic function in the striatum. The levels of CSF markers were then compared to each PET measurement.

RESULTS

Reduced CSF Aβ42 and tau levels correlated with lower striatal dopaminergic function as determined by all 3 PET tracers, with a significant association between Aβ42 and FD uptake. When cases were restricted to carriers of the G2019S mutation, the most common LRRK2 variant in our cohort, significant correlations were also observed for tau.

CONCLUSIONS

The disposition of Aβ and tau is likely important in both LRRK2-related and sporadic PD, even during early phases of the disease. A better understanding of their production, aggregation, and degradation, including changes in their CSF levels, may provide insights into the pathogenesis of PD and the potential utility of these proteins as biomarkers.