Beta-amlyoid 1-42 and tau-protein in cerebrospinal fluid of patients with Parkinson's disease dementia

Tau: a biomarker of Huntington's disease

Developing effective treatments for patients with Huntington's disease (HD)-a neurodegenerative disorder characterized by severe cognitive, motor and psychiatric impairments-is proving extremely challenging. While the monogenic nature of this condition enables to identify individuals at risk, robust biomarkers would still be extremely valuable to help diagnose disease onset and progression, and especially to confirm treatment efficacy. If measurements of cerebrospinal fluid neurofilament levels, for example, have demonstrated use in recent clinical trials, other proteins may prove equal, if not greater, relevance as biomarkers. In fact, proteins such as tau could specifically be used to detect/predict cognitive affectations. We have herein reviewed the literature pertaining to the association between tau levels and cognitive states, zooming in on Alzheimer's disease, Parkinson's disease and traumatic brain injury in which imaging, cerebrospinal fluid, and blood samples have been interrogated or used to unveil a strong association between tau and cognition. Collectively, these areas of research have accrued compelling evidence to suggest tau-related measurements as both diagnostic and prognostic tools for clinical practice. The abundance of information retrieved in this niche of study has laid the groundwork for further understanding whether tau-related biomarkers may be applied to HD and guide future investigations to better understand and treat this disease.

Fluid and Biopsy Based Biomarkers in Parkinson's Disease

Several advances in fluid and tissue-based biomarkers for use in Parkinson's disease (PD) and other synucleinopathies have been made in the last several years. While work continues on species of alpha-synuclein (aSyn) and other proteins which can be measured from spinal fluid and plasma samples, immunohistochemistry and immunofluorescence from peripheral tissue biopsies and alpha-synuclein seeding amplification assays (aSyn-SAA: including real-time quaking induced conversion (RT-QuIC) and protein misfolding cyclic amplification (PMCA)) now offer a crucial advancement in their ability to identify aSyn species in PD patients in a categorical fashion (i.e., of aSyn + vs aSyn -); to augment clinical diagnosis however, aSyn-specific assays that have quantitative relevance to pathological burden remain an unmet need. Alzheimer's disease (AD) co-pathology is commonly found postmortem in PD, especially in those who develop dementia, and dementia with Lewy bodies (DLB). Biofluid biomarkers for tau and amyloid beta species can detect AD co-pathology in PD and DLB, which does have relevance for prognosis, but further work is needed to understand the interplay of aSyn tau, amyloid beta, and other pathological changes to generate comprehensive biomarker profiles for patients in a manner translatable to clinical trial design and individualized therapies.

The associations of cerebrospinal fluid biomarkers with cognition, and rapid eye movement sleep behavior disorder in early Parkinson's disease

Background

In Parkinson's disease (PD), levels of cerebrospinal fluid (CSF) biomarkers and progression of non-motor symptoms are associated, but the specifics are not yet clear.

Objective

The aim of this study was to investigate the associations of non-motor symptoms with CSF biomarkers in PD.

Materials and methods

We assessed 487 individuals from the Parkinson's Progression Markers Initiative (PPMI), consisting of 155 healthy controls (HCs) and 332 individuals with PD. Patients with PD were grouped according to non-motor symptoms and compared CSF α-synuclein (α-syn), amyloid-beta 1-42 (Aβ_1-42), and total tau (t-tau) levels. Multiple linear regressions were used in baseline analysis and linear mixed-effects models in longitudinal analysis. Analyses of mediating effects between cognition and CSF biomarkers were also performed.

Results

At baseline, PD patients with cognitive impairment (PDCI) exhibited significantly lower CSF α-syn (β = -0.1244; P = 0.0469), Aβ (β = -0.1302; P = 0.0447), and t-tau (β = -0.1260; P = 0.0131) levels than PD patients without cognitive impairment (PDCU). Moreover, a faster decline of α-syn (β = -0.2152; P = 0.0374) and Aβ (β = -0.3114; P = 0.0023) and a faster rise of t-tau (β = -0.1534; P = 0.0274) have been found in longitudinal analysis. The Aβ positive group showed an earlier decline in cognitive performance (β = -0.5341; P = 0.0180) compared with the negative Aβ group in both analyses. In addition, we found that PD patients with probable rapid eye movement sleep behavior disorder (pRBD) showed decreased CSF α-syn (β = -0.1343; P = 0.0033) levels. Finally, mediation analysis demonstrated that olfactory function partially mediated the relationship between cognition and CSF biomarkers levels.

Conclusion

Our study shows that CSF biomarkers are associated with cognition at baseline and longitudinally. Cognitive impairment is more severe in patients with a heavier Aβ burden. CSF α-syn decreased in PD patients with pRBD. This study suggests that early recognition of the increased risk of non-motor symptoms is important for disease surveillance and may be associated with the pathological progression of CSF markers.

Neuropathological substrates of cognition in Parkinson's disease

Autopsy validation is still required for a definitive diagnosis of Parkinson's disease (Postuma et al., 2015), where the presence of Lewy bodies and Lewy neurites, composed primarily of alpha-synuclein, are observed in stereotyped patterns throughout regions of the brainstem, limbic, and neocortical regions of the brain (Braak et al., 2003). In spite of these relatively reliable observed patterns of alpha-synuclein pathology, there is a large degree of heterogeneity in the timing and features of neuropsychiatric and cognitive dysfunction in Parkinson's disease (Fereshtehnejad et al., 2015; Selikhova et al., 2009; Williams-Gray et al., 2013). Detailed studies of their neuropathological substrates of cognitive dysfunction and their associations with a variety of in vivo biomarkers have begun to disentangle this complex relationship, but ongoing multicentered, longitudinal studies of well-characterized and autopsy validated cases are still required.

Biomarkers of Cerebral Glucose Metabolism and Neurodegeneration in Parkinson's Disease: A Cerebrospinal Fluid-Based Study

BACKGROUND

Several biomarkers have been evaluated in Parkinson's disease (PD); cerebrospinal fluid (CSF) levels of lactate may reflect cerebral metabolism function and CSF amyloid-β42 (Aβ42), total tau (t-tau) and phosphorylated tau (p-tau) concentrations may detect an underlying neurodegenerative process.

OBJECTIVE

CSF levels of lactate, Aβ42, t-tau, and p-tau were measured in patients with mild to moderate PD. CSF levels of dopamine (DA) and its metabolite 3,4-Dihydroxyphenylacetic acid (DOPAC) were also assessed, exploring their relations with the other CSF biomarkers.

METHODS

101 drug-naive PD patients and 60 controls were included. Participants underwent clinical assessments and CSF biomarker analysis. Patients were divided into subgroups according to their Hoehn & Yahr stage (PD-1, PD-2, PD-3).

RESULTS

PD patients showed higher lactate levels (M = 1.91; p = 0.03) and lower Aβ42 (M = 595; p < 0.001) and DA levels (M = 0.32; p = 0.04) than controls (Mlactate = 1.72; MAβ42 = 837; MDA = 0.50), while no significant differences were found in t-tau, p-tau and DOPAC concentrations. Considering the subgroup analysis, PD-3 group had higher lactate (M = 2.12) and t-tau levels (M = 333) than both PD-1 (Mlactate = 1.75, p = 0.006; Mt - tau = 176, p = 0.008) and PD-2 groups (Mlactate = 1.91, p = 0.01; Mt - tau = 176, p = 0.03), as well as the controls (Mlactate = 1.72, p = 0.04; Mt - tau = 205, p = 0.04). PD-2 group showed higher lactate levels than PD-1 group (p = 0.04) and controls (p = 0.03). Finally, CSF lactate levels negatively correlated with DA (r = -0.42) and positively with t-tau CSF levels (r = 0.33).

CONCLUSION

This CSF-based study shows that lactate levels in PD correlated with both clinical disease progression and neurodegeneration biomarkers, such as tau proteins and DA. Further studies should explore the clinical potential of measuring CSF biomarkers for better understanding the role of brain energy metabolism in PD, for research and therapeutic options.

Alpha-Synuclein Protofibrils in Cerebrospinal Fluid: A Potential Biomarker for Parkinson's Disease

BACKGROUND

Currently, there is no established biomarker for Parkinson's disease (PD) and easily accessible biomarkers are crucial for developing disease-modifying treatments.

OBJECTIVE

To develop a novel method to quantify cerebrospinal fluid (CSF) levels of α-synuclein protofibrils (α-syn PF) and apply it to clinical cohorts of patients with PD and atypical parkinsonian disorders.

METHODS

A cohort composed of 49 patients with PD, 12 with corticobasal degeneration (CBD), 22 with progressive supranuclear palsy, and 33 controls, that visited the memory clinic but had no biomarker signs of Alzheimer's disease (AD, tau<350 pg/mL, amyloid-beta 42 (Aβ42)>530 pg/mL, and phosphorylated tau (p-tau)<60 pg/mL) was used in this study. The CSF samples were analyzed with the Single molecule array (Simoa) technology. Total α-synuclein (α-syn) levels were analyzed with a commercial ELISA-kit.

RESULTS

The assay is specific to α-syn PF, with no cross-reactivity to monomeric α-syn, or the β- and γ-synuclein variants. CSF α-syn PF levels were increased in PD compared with controls (62.1 and 40.4 pg/mL, respectively, p = 0.03), and CBD (62.1 and 34.2 pg/mL, respectively, p = 0.02). The accuracy of predicting PD using α-syn PF is significantly different from controls (area under the curve 0.68, p = 0.0097) with a sensitivity of 62.8% and specificity of 67.7%. Levels of total α-syn were significantly different between the PD and CBD groups (p = 0.04).

CONCLUSION

The developed method specifically quantifies α-syn PF in human CSF with increased concentrations in PD, but with an overlap with asymptomatic elderly controls.

The Cerebellum Is a Common Key for Visuospatial Execution and Attention in Parkinson's Disease

Cognitive decline affects the clinical course in patients with Parkinson's disease (PD) and contributes to a poor prognosis. However, little is known about the underlying network-level abnormalities associated with each cognitive domain. We aimed to identify the networks related to each cognitive domain in PD using resting-state functional magnetic resonance imaging (MRI). Forty patients with PD and 15 normal controls were enrolled. All subjects underwent MRI and the Mini-Mental State Examination. Furthermore, the cognitive function of patients with PD was assessed using the Montreal Cognitive Assessment (MoCA). We used independent component analysis of the resting-state functional MRI for functional segmentation, followed by reconstruction to identify each domain-related network, to predict scores in PD using multiple regression models. Six networks were identified, as follows: the visuospatial-executive-domain-related network (R² = 0.54, p < 0.001), naming-domain-related network (R² = 0.39, p < 0.001), attention-domain-related network (R² = 0.86, p < 0.001), language-domain-related network (R² = 0.64, p < 0.001), abstraction-related network (R² = 0.10, p < 0.05), and orientation-domain-related network (R² = 0.64, p < 0.001). Cerebellar lobule VII was involved in the visuospatial-executive-domain-related and attention-domain-related networks. These two domains are involved in the first three listed nonamnestic cognitive impairment in the diagnostic criteria for PD with dementia (PDD). Furthermore, Brodmann area 10 contributed most frequently to each domain-related network. Collectively, these findings suggest that cerebellar lobule VII may play a key role in cognitive impairment in nonamnestic types of PDD.

Cognitive Impairment in Parkinson's Disease: Epidemiology, Clinical Profile, Protective and Risk Factors

Cognitive impairment is a common non-motor symptom in Parkinson's Disease (PD) and an important source of patient disability and caregiver burden. The timing, profile and rate of cognitive decline varies widely among individuals with PD and can range from normal cognition to mild cognitive impairment (PD-MCI) and dementia (PDD). Beta-amyloid and tau brain accumulation, oxidative stress and neuroinflammation are reported risk factors for cognitive impairment. Traumatic brain injury and pesticide and tobacco exposure have also been described. Genetic risk factors including genes such as COMT, APOE, MAPT and BDNF may also play a role. Less is known about protective factors, although the Mediterranean diet and exercise may fall in this category. Nonetheless, there is conflicting evidence for most of the factors that have been studied. The use of inconsistent criteria and lack of comprehensive assessment in many studies are important methodological issues. Timing of exposure also plays a crucial role, although identification of the correct time window has been historically difficult in PD. Our understanding of the mechanism behind these factors, as well as the interactions between gene and environment as determinants of disease phenotype and the identification of modifiable risk factors will be paramount, as this will allow for potential interventions even in established PD.

Glycoproteins as diagnostic and prognostic biomarkers for neurodegenerative diseases: A glycoproteomic approach

Neurodegenerative diseases (NDs) are incurable and can develop progressively debilitating disorders, including dementia and ataxias. Alzheimer's disease and Parkinson's disease are the most common NDs that mainly affect the elderly people. There is an urgent need to develop new diagnostic tools so that patients can be accurately stratified at an early stage. As a common post-translational modification, protein glycosylation plays a key role in physiological and pathological processes. The abnormal changes in glycosylation are associated with the altered biological pathways in NDs. The pathogenesis-related proteins, like amyloid-β and microtubule-associated protein tau, have altered glycosylation. Importantly, specific glycosylation changes in cerebrospinal fluid, blood and urine are valuable for revealing neurodegeneration in the early stages. This review describes the emerging biomarkers based on glycoproteomics in NDs, highlighting the potential applications of glycoprotein biomarkers in the early detection of diseases, monitoring of the disease progression, and measurement of the therapeutic responses. The mass spectrometry-based strategies for characterizing glycoprotein biomarkers are also introduced.

Olfactory Dysfunction and Its Association With Neuropathologic Proteins in Cerebrospinal Fluid From Patients With Parkinson Disease

Background and Purpose: Olfactory dysfunction (OD) is a common non-motor symptom of Parkinson disease (PD). However, the relationship between OD and neuropathologic proteins in cerebrospinal fluid (CSF) from PD patients remains unclear.

Methods: 166 PD patients were included in the study. Overall olfactory function was assessed by summing up the scores of olfactory threshold, discrimination, and identification by a Sniffin' Sticks test, based on which, patients were divided into PD with OD (PD-OD) and PD with no OD (PD-NOD) groups. CSF samples were obtained from 76 PD patients. The levels of neuropathologic proteins, including α-Synuclein, Aβ1-42, total tau (T-tau), and multiple forms of phosphorylated tau (P-tau) in CSF were measured by an enzyme-linked immunosorbent assay.

Results: out of the 166 PD patients, 103 cases (62.0%) had OD. The scores of overall olfactory functions, and olfactory threshold, discrimination, and identification in the PD-OD group were all significantly lower than that in the PD-NOD group (P < 0.001). α-Synuclein level in CSF was significantly higher in the PD-OD group than the PD-NOD group (P < 0.05), and was significantly and negatively correlated with the scores of overall olfactory function, and olfactory discrimination and identification (P < 0.05). Aβ1-42 level in CSF was higher in the PD-OD group than the PD-NOD group, and was significantly and negatively correlated with the olfactory identification score (P < 0.05). T-tau level in CSF was significantly lower in the PD-OD group than the PD-NOD group (P < 0.05), and was significantly and positively correlated with the olfactory discrimination score (P < 0.05). There was no significant difference in P-tau level in CSF between the PD-OD and PD-NOD groups and no correlation between OD score and P-tau level in CSF.

Conclusions: PD-OD includes the impairments of olfactory threshold, discrimination, and identification, and is associated with the significant elevation of α-Synuclein and the decrease of the T-tau level in CSF.

Unraveling Pathophysiological Mechanisms of Parkinson's Disease: Contribution of CSF Biomarkers

Diagnosis of Parkinson's disease (PD) relies on clinical history and physical examination, but misdiagnosis is common in early stages. Identification of biomarkers for PD may allow for early and more precise diagnosis and provide information about prognosis. Developments in analytical chemistry allow for the detection of a large number of molecules in cerebrospinal fluid (CSF), which are known to be associated with the pathogenesis of PD. Given the pathophysiology of PD, CSF α-synuclein species have the strongest rationale for use, also providing encouraging preliminary results in terms of early diagnosis. In the field of classical Alzheimer's disease (AD) biomarkers, low CSF Aβ₄₂ levels have shown a robust prognostic value in terms of development of cognitive impairment. Other CSF biomarkers including lysosomal enzymes, neurofilament light chain, markers of neuroinflammation and oxidative stress, although promising, have not proved to be reliable for diagnostic and prognostic purposes yet. Overall, the implementation of CSF biomarkers may give a substantial contribution to the optimal use of disease-modifying drugs.

Prevalence and clinical associations of tau in Lewy body dementias: A systematic review and meta-analysis

INTRODUCTION

Alzheimer's disease neuropathologies (amyloid-β and tau) frequently co-exist to varying degrees in Lewy body dementias (LBD), which include dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD).

OBJECTIVES

To investigate the prevalence of tau in DLB and PDD, and its associations with clinical outcomes.

METHODS

We searched the major electronic databases using the search term: ("dementia with Lewy bodies" OR "diffuse Lewy body disease" OR "Lewy body variant of Alzheimer's disease") AND ("tau protein" OR "tauopathy" OR "neurofibrillary tangle"), for relevant studies which evaluated tau in LBD. Forty-nine articles met the inclusion criteria for data extraction. Where appropriate, a random-effect meta-analysis was performed to obtain pooled estimates for prevalence and risk ratios (RR) or standardized mean differences (SMD) for clinical features, diagnostic accuracy and cognition.

RESULTS

Braak neurofibrillary tangle stage ≥ III was observed in 66% (n = 1511, 95%CI 60%-73%) of DLB and 52% (n = 433, 95%CI 27%-76%) of PDD at autopsy. Abnormal CSF phosphorylated-tau levels were present in 28% (n = 925, 95%CI 25%-31%) of DLB and 15% (n = 172, 95%CI 5%-24%) of PDD cases. Higher tau burden in DLB was associated with reduced likelihood of manifesting visual hallucinations (RR 0.56; 95%CI 0.40-0.77) and motor parkinsonism (RR 0.62; 95%CI 0.40-0.98), lower diagnostic accuracy of DLB during life (RR 0.49; 95%CI 0.38-0.64) and worse cognition prior to death (SMD 0.63; 95%CI 0.46-0.81).

CONCLUSIONS

Tau is common in LBD and may reduce clinical diagnostic accuracy in people with DLB. Prospective longitudinal studies are needed to understand the roles of co-morbid neuropathologies in Lewy body dementias.

Cerebrospinal fluid markers analysis in the differential diagnosis of dementia with Lewy bodies and Parkinson's disease dementia

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) share a couple of clinical similarities that is often a source of diagnostic pitfalls. We evaluated the discriminatory potential of brain-derived CSF markers [tau, p-tau (181P), Aβ_1-42, NSE and S100B] across the spectrum of Lewy body disorders and assessed whether particular markers are associated with cognitive status in investigated patients. The tau CSF level, amyloid β_1-42 and p-tau/tau ratio were helpful in the distinction between DLB and PDD (p = 0.04, p = 0.002 and p = 0.02, respectively) as well as from PD patients (p < 0.001, p = 0.001 and p = 0.002, respectively). Furthermore, the p-tau/tau ratio enabled the differentiation of DLB with mild dementia from PDD patients (p = 0.02). The CSF tau and p-tau levels in DLB and CSF tau and p-tau/tau ratio in PDD patients reflected the severity of dementia. Rapid disease course was associated with the decrease of Aβ_1-42 in DLB but not in PDD. Elevation of S100B in DLB (p < 0.0001) as well as in PDD patients (p = 0.002) in comparison to controls was estimated. Hence, with the appropriate clinical context; the CSF marker profile could be helpful in distinguishing DLB from PDD patients even in early stages of dementia.

Pathological Influences on Clinical Heterogeneity in Lewy Body Diseases

PD, PD with dementia, and dementia with Lewy bodies are clinical syndromes characterized by the neuropathological accumulation of alpha-synuclein in the CNS that represent a clinicopathological spectrum known as Lewy body disorders. These clinical entities have marked heterogeneity of motor and nonmotor symptoms with highly variable disease progression. The biological basis for this clinical heterogeneity remains poorly understood. Previous attempts to subtype patients within the spectrum of Lewy body disorders have centered on clinical features, but converging evidence from studies of neuropathology and ante mortem biomarkers, including CSF, neuroimaging, and genetic studies, suggest that Alzheimer's disease beta-amyloid and tau copathology strongly influence clinical heterogeneity and prognosis in Lewy body disorders. Here, we review previous clinical biomarker and autopsy studies of Lewy body disorders and propose that Alzheimer's disease copathology is one of several likely pathological contributors to clinical heterogeneity of Lewy body disorders, and that such pathology can be assessed in vivo. Future work integrating harmonized assessments and genetics in PD, PD with dementia, and dementia with Lewy bodies patients followed to autopsy will be critical to further refine the classification of Lewy body disorders into biologically distinct endophenotypes. This approach will help facilitate clinical trial design for both symptomatic and disease-modifying therapies to target more homogenous subsets of Lewy body disorders patients with similar prognosis and underlying biology. © 2019 International Parkinson and Movement Disorder Society.

Predict cognitive decline with clinical markers in Parkinson's disease (PRECODE-1)

Over the course of the disease, about 80% of Parkinson’s disease patients will develop cognitive impairment. However, predictive factors associated with cognitive decline are still under investigation. Here, we investigated which clinically available markers are predictive of cognitive impairment in a cohort of early drug-naïve Parkinson’s disease patients. 294 drug-naïve Parkinson’s disease patients, who were cognitively normal at baseline, were recruited from the Parkinson’s Progression Markers Initiative. At 36-month follow-up, patients were diagnosed with cognitive impairment according to two levels: Level 1 diagnosis was defined as MoCA < 26 and Level 2 diagnosis was defined as MoCA < 26, alongside an impaired score on at least two neuropsychological tests. Predictive variables with a validated cut-off were divided into normal or abnormal measures, whilst others were divided into normal or abnormal measures based on the decile with the highest power of prediction. At 3 years’ follow-up, 122/294 Parkinson’s disease (41.5%) patients had cognitive decline. We found that age at Parkinson’s disease onset, MDS-UPDRS Part-III, Hopkin’s Learning Verbal Test-Revised Recall, Semantic Fluency Test and Symbol Digit Modalities Test were all predictors of cognitive decline. Specifically, age at Parkinson’s disease onset, Semantic Fluency Test and symbol Digit Modalities Test were predictors of cognitive decline defined by Level 2. The combination of three abnormal tests, identified as the most significant predictors of cognitive decline, gave a 63.6–86.7% risk of developing cognitive impairment defined by Level 2 and Level 1 criteria, respectively, at 36-month follow-up. Our findings show that these clinically available measures encompass the ability to identify drug-naïve Parkinson’s disease patients with the highest risk of developing cognitive impairment at the earliest stages. Therefore, by implementing this in a clinical setting, we can better monitor and manage patients who are at risk of cognitive decline.

Parkinson's disease: evolution of cognitive impairment and CSF Aβ1-42 profiles in a prospective longitudinal study

OBJECTIVE

To evaluate the evolution of cognitive impairment in relation to cerebrospinal fluid (CSF) profiles of amyloid-β (Aβ), total-Tau and phosphorylated-Tau in Parkinson's disease (PD).

METHODS

Prospective, longitudinal, observational study up to 10 years with follow-up every 2  years. We assessed CSF profiles in 415 patients with sporadic PD (median age 66; 63% men) and 142 healthy controls (median age 62; 43% men).

RESULTS

Patients with PD with low CSF Aβ_1-42 levels at baseline were more often cognitively impaired than patients with intermediate and high Aβ_1-42 levels. Sixty-seven per cent of the patients with low Aβ_1-42 levels at baseline and normal cognition developed cognitive impairment during follow-up, compared with 41% and 37% of patients having intermediate and high CSF Aβ_1-42 levels. Kaplan-Meier survival curves and Cox regression revealed that patients with low CSF Aβ_1-42 levels at baseline developed cognitive impairment more frequently and earlier during follow-up.

CONCLUSION

We conclude that in patients with sporadic PD, low levels of Aβ_1-42 are associated with a higher risk of developing cognitive impairment earlier in the disease process at least in a subgroup of patients.

Fractalkine/CX3CR1 is involved in the cross-talk between neuron and glia in neurological diseases

Fractalkine (CX3C chemokine ligand 1, CX3CL1) is an essential chemokine, for regulating adhesion and chemotaxis through binding to CX3CR1, which plays a critical role in the crosstalk between glial cells and neurons by direct or indirect ways in the central nervous system (CNS). Fractalkine/CX3CR1 axis regulates microglial activation and function, neuronal survival and synaptic function by controlling the release of inflammatory cytokines and synaptic plasticity in the course of the neurological disease. The multiple functions of fractalkine/CX3CR1 make it exert neuroprotective or neurotoxic effects, which determines the pathogenesis. However, the role of fractalkine/CX3CR1 in the CNS remains controversial. Whether it can be used as a therapeutic target for neurological diseases needs to be further investigated. In this review, we summarize the studies highlighting fractalkine/CX3CR1-mediated effects and discuss the potential neurotoxic and neuroprotective actions of fractalkine/CX3CR1 in brain injury for providing useful insights into the potential applications of fractalkine/CX3CR1 in neurological diseases.

Ratios of proteins in cerebrospinal fluid in Parkinson's disease cognitive decline: prospective study

BACKGROUND

There is a need for biomarkers of dementia in PD.

OBJECTIVES

To determine if the levels of the main CSF proteins and their ratios are associated with deterioration in cognition and progression to dementia in the short to mid term.

METHODS

The Parkinson's Progression Markers Initiative database was used as an exploratory cohort, and a center-based cohort was used as a replication cohort. Amyloid ß1-42, total tau, threonine-181 phosphorylated tau, and α-synuclein in the CSF and the ratios of these proteins were assessed.

RESULTS

In the Parkinson's Progression Markers Initiative cohort (n = 281), the total tau/amyloid ß1-42, total tau/α-synuclein, total tau/amyloid ß1-42+α-synuclein, and amyloid ß1-42/total tau ratios were associated with a risk of progression to dementia over a 3-year follow-up. In the replication cohort (n = 40), the total tau/α-synuclein and total tau/amyloid ß1-42+α-synuclein ratios were associated with progression to dementia over a 41-month follow-up.

CONCLUSION

Ratios of the main proteins found in PD patient brain inclusions that can be measured in the CSF appear to have value as short- to mid-term predictors of dementia. © 2018 International Parkinson and Movement Disorder Society.

Amyloid-β and Parkinson's disease

Parkinson's disease (PD) is the second commonest neurodegenerative disorder in the world with a rising prevalence. The pathophysiology is multifactorial but aggregation of misfolded α-synuclein is considered to be a key underpinning mechanism. Amyloid-β (Aβ) and tau deposition are also comorbid associations and especially Aβ deposition is associated with cognitive decline in PD. Some existing evidence suggests that low cerebrospinal fluid (CSF) Aβ₄₂ is predictive of future cognitive impairment in PD. Recent studies also show that CSF Aβ is associated with the postural instability and gait difficulties (PIGD) or the newly proposed cholinergic subtype of PD, a possible risk factor for cognitive decline in PD. The glial-lymphatic system, responsible for convective solute clearance driven by active fluid transport through aquaporin-4 water channels, may be implicated in brain amyloid deposition. A better understanding of the role of this system and more specifically the role of Aβ in PD symptomatology, could introduce new treatment and repurposing drug-based strategies. For instance, apomorphine infusion has been shown to promote the degradation of Aβ in rodent models. This is further supported in a post-mortem study in PD patients although clinical implications are unclear. In this review, we address the clinical implication of cerebral Aβ deposition in PD and elaborate on its metabolism, its role in cognition and motor function/gait, and finally assess the potential effect of apomorphine on Aβ deposition in PD.

Recent Advances in Biomarkers for Parkinson's Disease

Parkinson's disease (PD) is one of the common progressive neurodegenerative disorders with several motor and non-motor symptoms. Most of the motor symptoms may appear at a late stage where most of the dopaminergic neurons have been already damaged. In order to provide better clinical intervention and treatment at the onset of disease, it is imperative to find accurate biomarkers for early diagnosis, including prodromal diagnosis and preclinical diagnosis. At the same time, these reliable biomarkers can also be utilized to monitor the progress of the disease. In this review article, we will discuss recent advances in the development of PD biomarkers from different aspects, including clinical, biochemical, neuroimaging and genetic aspects. Although various biomarkers for PD have been developed so far, their specificity and sensitivity are not ideal when applied individually. So, the combination of multimodal biomarkers will greatly improve the diagnostic accuracy and facilitate the implementation of personalized medicine.

The impact of Apolipoprotein E alleles on cognitive performance in patients with Parkinson's disease

Apolipoprotein E (ApoE) is a vital component of several lipoproteins and plays a major role in lipid metabolism. APOE gene comprises of three alleles determined by two single nucleotide polymorphisms (rs429358 and rs7412) resulting in the protein isoforms, among which ApoE4 is a confirmed risk factor for Alzheimer's Disease. However, the impact of APOE genotypes on Parkinson's Disease Dementia (PDD) is still inconclusive. The PDD diagnostic criteria are very inconsistent, and could be complemented with genetic factors. Our study covers a total of 237 patients diagnosed with Parkinson's Disease (PD) according to UK PD Brain Bank criteria, who were classified as subjects with (PDD, n equals 73) and without (nPDD, n equals 164) dementia, using neuropsychological assessment tests. TaqMan real-time PCR assays were used to determine APOE allele. No statistically significant differences in APOE alleles frequencies between nPDD and PDD patients have been observed. The study results revealed that the APOE polymorphism is not associated with cognitive status in PD patients.

Correlations between CSF proteins and spontaneous neuronal activity in Parkinson's disease

The relationship between cerebrospinal fluid (CSF) proteins and brain function in Parkinson's disease (PD) is not explained clearly. We investigated the correlations between CSF proteins and spontaneous neuronal activity in PD patients via fractional amplitude of low-frequency fluctuation (fALFF) using the Parkinson's Progression Markers Initiative database. Twenty-eight PD patients underwent resting-state functional magnetic resonance imaging in "off" status and lumbar puncture within a month. Correlation analyses between CSF proteins and fALFF value in whole brain as well as clinical assessment scores were performed. We found CSF total tau (t-tau) level was negatively correlated with fALFF in posterior cingulate gyrus. And fALFF in posterior cingulate gyrus was positively correlated with Hopkins Verbal Learning Test-Revised recognition discrimination index. Besides, alpha-synuclein (α-syn) level was correlated with fALFF in bilateral inferior frontal gyrus. This study provides evidence that CSF proteins may have a relationship with brain function related to cognitive status in PD patients.

Baseline prevalence and longitudinal evolution of non-motor symptoms in early Parkinson's disease: the PPMI cohort

OBJECTIVE

To examine the baseline prevalence and longitudinal evolution in non-motor symptoms (NMS) in a prospective cohort of, at baseline, patients with de novo Parkinson's disease (PD) compared with healthy controls (HC).

METHODS

Parkinson's Progression Markers Initiative (PPMI) is a longitudinal, ongoing, controlled study of de novo PD participants and HC. NMS were rated using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part I score and other validated NMS scales at baseline and after 2 years. Biological variables included cerebrospinal fluid (CSF) markers and dopamine transporter imaging.

RESULTS

423 PD subjects and 196 HC were enrolled and followed for 2 years. MDS-UPDRS Part I total mean (SD) scores increased from baseline 5.6 (4.1) to 7.7 (5.0) at year 2 in PD subjects (p<0.001) versus from 2.9 (3.0) to 3.2 (3.0) in HC (p=0.38), with a significant difference between the groups (p<0.001). In the multivariate analysis, higher baseline NMS score was associated with female sex (p=0.008), higher baseline MDS-UPDRS Part II scores (p<0.001) and more severe motor phenotype (p=0.007). Longitudinal increase in NMS severity was associated with the older age (0.008) and lower CSF Aβ1-42 (0.005) at baseline. There was no association with the dose or class of dopaminergic therapy.

CONCLUSIONS

This study of NMS in early PD identified clinical and biological variables associated with both baseline burden and predictors of progression. The association of a greater longitudinal increase in NMS with lower baseline Aβ1-42 level is an important finding that will have to be replicated in other cohorts.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01141023.

APOE, thought disorder, and SPARE-AD predict cognitive decline in established Parkinson's disease

BACKGROUND

People with PD are at high risk of developing cognitive impairment and dementia. Cross-sectional studies have identified candidate biomarkers associated with cognitive decline. However, longitudinal studies on this topic are rarer, and few have investigated the use of biomarker panels encompassing multiple modalities. The objective of this study was to find baseline predictors of cognitive decline in longitudinally followed, nondemented Parkinson's disease patients.

METHODS

We performed a prospective cohort study of 100 PD patients with a median disease duration of 6.4 years. All participants were nondemented at baseline. We examined 16 baseline biomarkers from clinical, genetic, biochemical, and MRI-based imaging modalities for their association with longitudinal cognitive decline for up to 8 years. We investigated biomarkers individually, as well as in a multivariate linear mixed-effects model encompassing multimodal biomarkers, with change in the Mattis Dementia Rating Scale-2 over time as the primary outcome. Annual consensus process-derived cognitive diagnosis was used for Cox proportional hazards modeling of risk for cognitive decline.

RESULTS

In multivariate analysis, the presence of the APOE E4 allele, thought disorder, and an Alzheimer's disease pattern of brain atrophy (spatial pattern of abnormality for recognition of early Alzheimer's disease index) best predicted cognitive decline, with APOE E4 genotype exerting the greatest effect. The presence of the APOE E4 allele was associated with a 3.5 times higher risk of worsening cognitive diagnosis over time (HR, 3.53; 95% CI, 1.52-8.24; P < 0.05). The APOE genotype effect was not specific to any Mattis Dementia Rating Scale-2 domain.

CONCLUSIONS

Our results confirm the importance of Alzheimer's disease biomarkers as risk factors for cognitive decline in established Parkinson's disease. © 2017 International Parkinson and Movement Disorder Society.

SNPs in Aβ clearance proteins: Lower CSF Aβ1-42 levels and earlier onset of dementia in PD

OBJECTIVE

To evaluate whether genetic variants in β-amyloid (Aβ) clearance proteins are associated with CSF levels of Aβ_1-42 on a biological level and the onset of dementia on a clinical level in Parkinson disease (PD).

METHODS

We analyzed genetic variants known to be involved in Aβ clearance in a PD group comprising 456 patients, 103 of them with dementia. Single nucleotide polymorphisms in the genes APOE, cystatin C (CST), and membrane metalloendopeptidase (MME) were evaluated in relation to demographic variables, clinical phenotypes, and CSF Aβ_1-42 levels using a cross-sectional approach.

RESULTS

Risk variants in the genes APOE and CST were associated with lower CSF Aβ_1-42 levels. Clinically, patients with 2 risk alleles in CST tended to show a shorter interval from age at onset of PD to age at onset of dementia.

CONCLUSIONS

This study suggests that genetic variants associated with Aβ clearance are involved in the pathogenesis of dementia in PD and possibly influence the onset of dementia.

Tau protein (MAPT) as a possible biochemical marker of traumatic brain injury in postmortem examination

MAPT is a neuronal protein that plays an important role in axonal stabilization, neuronal development, and neuronal polarity. MAPT release into the CSF and blood has been interpreted as indicative of axonal injury as its elevated levels were observed in olympic boxers even after a mild head trauma suggesting minor CNS injuries. In our study we wanted to check the potential relevance of MAPT examination for forensic purposes. The study was carried out using cases of head injury group and cases of sudden death (cardiopulmonary failure, no injuries of the head - control group) provided by forensic pathologists at the Department of Forensic Medicine, Medical University of Warsaw. CSF and blood were collected within 24h after death using suboccipital puncture and femoral vein puncture. Serum and cerebrospinal fluid Tau protein concentrations were compared using an enzyme-linked immunosorbent assay (elisa). Brain specimens (frontal cortex) were collected during forensic autopsies. Sections were stained histologically (hematoxylin-eosin) and immunohistochemically with anti human Tau antibody, anti glial fibrillary acid protein (GFAP), anti human macrosialin (CD68) or anti human endothelial cells (CD34). In our study we documented that elevated levels of serum and CSF MAPT may also be considered a marker for mild traumatic brain injury and traumatic brain injury (mTBI and TBI). An increase in CSF and serum levels of MAPT in the absence of visible macroscopic traumatic CNS changes indicates that even minor head injuries may result in changes at the neuronal level that could remain undiagnosed during regular forensic autopsy and routine histopathological examination.

Changes of cerebrospinal fluid Aβ42, t-tau, and p-tau in Parkinson's disease patients with cognitive impairment relative to those with normal cognition: a meta-analysis

The cerebrospinal fluid (CSF) signature of reduced amyloid beta 1-42 (Aβ₄₂), elevated total tau (t-tau), and phosphorylated tau181 (p-tau) is important for the early diagnosis of Alzheimer's disease (AD). Aβ₄₂, t-tau, and p-tau have been reported in numerous studies to contribute to predicting cognitive impairment in Parkinson's disease (PDCI). However, no consistent conclusion can be drawn so far. Literatures regarding Aβ₄₂, t-tau, and p-tau in CSF were systematically reviewed, and a meta-analysis was thus performed to evaluate the changes of these biomarkers in PDCI patients, including PD with mild cognitive impairment (PDMCI) and PD dementia (PDD) patients, relative to PD with normal cognition (PDNC) patients. Databases of "PubMed," "EBSCO," and "Springer" were retrieved for articles concerning Aβ₄₂, t-tau, and p-tau in PDCI patients relative to those in PDNC patients published from January 1, 2000 to February 1, 2017. The following keywords were set, namely, "dementia" or "cognitive impairment" or "mild cognitive impairment" and "cerebrospinal fluid" and "Parkinson*." Sixteen articles comprising 590 PDCI patients and 1182 PDNC patients were included. The results showed that CSF Aβ₄₂ level in PDCI cohort was lower than that in PDNC cohort (pooled Std.MD = -0.44, 95% CI [-0.61, -0.26], p < 0.00001). Reduced Aβ₄₂ (pooled Std.MD = -0.60, 95% CI [-0.75, -0.45], p < 0.00001) as well as elevated t-tau (pooled Std.MD = 0.21, 95% CI [0.06, 0.35], p = 0.006) and p-tau (pooled Std.MD = 0.36, 95% CI [0.02, 0.69], p = 0.04) could be observed in PDD cohort compared with PDNC cohort. Therefore, amyloid pathology and tauopathy may participate in the development of PDD, which is similar to AD.

Latent Cognitive Phenotypes in De Novo Parkinson's Disease: A Person-Centered Approach

OBJECTIVES

Cognitive impairment is an important aspect of Parkinson's disease (PD), but there is considerable heterogeneity in its presentation. This investigation aims to identify and characterize latent cognitive phenotypes in early PD.

METHODS

Latent class analysis, a data-driven, person-centered, cluster analysis was performed on cognitive data from the Parkinson's Progressive Markers Initiative baseline visit. This analytic method facilitates identification of naturally occurring endophenotypes. Resulting classes were compared across biomarker, symptom, and demographic data.

RESULTS

Six cognitive phenotypes were identified. Three demonstrated consistent performance across indicators, representing poor ("Weak-Overall"), average ("Typical-Overall"), and strong ("Strong-Overall") cognition. The remaining classes demonstrated unique patterns of cognition, characterized by "Strong-Memory," "Weak-Visuospatial," and "Amnestic" profiles. The Amnestic class evidenced greater tremor severity and anosmia, but was unassociated with biomarkers linked with Alzheimer's disease. The Weak-Overall class was older and reported more non-motor features associated with cognitive decline, including anxiety, depression, autonomic dysfunction, anosmia, and REM sleep behaviors. The Strong-Overall class was younger, more female, and reported less dysautonomia and anosmia. Classes were unrelated to disease duration, functional independence, or available biomarkers.

CONCLUSIONS

Latent cognitive phenotypes with focal patterns of impairment were observed in recently diagnosed individuals with PD. Cognitive profiles were found to be independent of traditional biomarkers and motoric indices of disease progression. Only globally impaired class was associated with previously reported indicators of cognitive decline, suggesting this group may drive the effects reported in studies using variable-based analysis. Longitudinal and neuroanatomical characterization of classes will yield further insight into the evolution of cognitive change in the disease. (JINS, 2017, 23, 551-563).

Phenotype of postural instability/gait difficulty in Parkinson disease: relevance to cognitive impairment and mechanism relating pathological proteins and neurotransmitters

Parkinson disease (PD) is identified as tremor-dominant (TD) and postural instability and gait difficulty (PIGD) phenotypes. The relationships between motor phenotypes and cognitive impairment and the underlying mechanisms relating pathological proteins and neurotransmitters in cerebrospinal fluid (CSF) are unknown. We evaluated the motor symptoms and cognitive function by scales, and detected the levels of pathological proteins and neurotransmitters in CSF. TD group and PIGD group had significantly higher levels of total tau, tau phosphorylated at the position of threonine 181(P-tau181t), threonine 231, serine 396, serine 199 and lower β amyloid (Aβ)_1–42 level in CSF than those in control group; PIGD group had significantly higher P-tau181t level and lower Aβ_1–42 level than those in TD group. In PD group, PIGD severity was negatively correlated with MoCA score and Aβ_1–42 level in CSF, and positively correlated with Hoehn-Yahr stage and P-tau181t level in CSF. In PIGD group, PIGD severity was negatively correlated with homovanillic acid (HVA) level in CSF, and HVA level was positively correlated with Aβ_1–42 level in CSF. PIGD was significantly correlated with cognitive impairment, which underlying mechanism might be involved in Aβ_1–42 aggregation in brain and relevant neurochemical disturbance featured by the depletion of HVA in CSF.

Cerebrospinal Fluid Biomarkers of Cognitive Decline in Parkinson's Disease

Among the nonmotor symptoms in Parkinson's disease (PD), cognitive impairment is one of the most common and devastating. Over recent years, mild cognitive impairment (MCI) has become a recognized feature of PD (PD-MCI). The underlying mechanisms which influence onset, rate of decline, and conversion to dementia (PDD) are largely unknown. Adding to this uncertainty is the heterogeneity of cognitive domains affected. Currently there are no disease-modifying treatments that can slow or reverse this process. Identification of biomarkers that can predict rate and risk of cognitive decline is therefore an unmet need. Cerebrospinal fluid (CSF) is an ideal biomarker candidate as its constituents reflect the metabolic processes underlying the functioning of brain parenchyma. The pathological hallmark of PD is the presence of aggregated α-synuclein (α-Syn) in intracellular Lewy inclusions. In addition, there is concomitant Alzheimer's disease (AD) pathology. In AD, decreased CSF β-amyloid 1-42 (Aβ42) and increased CSF tau levels are predictive of future cognitive decline, setting a precedent for such studies to be carried out in PD. CSF studies in PD have focused on the classical AD biomarkers and α-Syn. Longitudinal studies indicate that low levels of CSF Aβ42 are predictive of cognitive decline; however, results for tau and α-Syn were not consistent. This chapter summarizes recent findings of CSF biomarker studies and cognitive dysfunction in PD.

Cerebellar Insulin/IGF-1 signaling in diabetic rats: Effects of exercise training

The Diabetes Mellitus (DM) is a chronic disease associated with loss of brain regions such as the cerebellum, increasing the risk of developing neurodegenerative diseases such as Parkinson's disease (PD). In the brain of diabetic and PD organisms the insulin/IGF-1 signaling is altered. Exercise training is an effective intervention for the prevention of neurodegerative diseases since it release neurotrophic factors and regulating insulin/IGF-1 signaling in the brain. This study aimed to evaluate the proteins involved in the insulin/IGF-1 pathway in the cerebellum of diabetic rats subjected to exercise training protocol. Wistar rats were distributed in four groups: sedentary control (SC), trained control (TC), sedentary diabetic (SD) and trained diabetic (TD). Diabetes was induced by Alloxan (ALX) (32mg/kgb.w.). The training program consisted in swimming 5days/week, 1h/day, during 6 weeks, supporting an overload corresponding to 90% of the anaerobic threshold. At the end, cerebellum was extracted to determinate the protein expression of GSK-3β, IRβ and IGF-1R and the phosphorylation of β-amyloid, Tau, ERK1+ERK2 by Western Blot analysis. All dependent variables were analyzed by one-way analysis of variance with significance level of 5%. Diabetes causes hyperglycemia in both diabetic groups; however, in TD, there was a reduction in hyperglycemia compared to SD. Diabetes increased Tau and β-amyloid phosphorylation in both SD and TD groups. Furthermore, aerobic exercise increased ERK1+ERK2 expression in TC. The data showed that in cerebellum of diabetic rats induced by alloxan there are some proteins expression like Parkinson cerebellum increased, and the exercise training was not able to modulate the expression of these proteins.

Longitudinal Measurements of Cerebrospinal Fluid Biomarkers in Parkinson's Disease

OBJECTIVE

The purpose of this study was to investigate whether cerebrospinal fluid (CSF) levels of tau, phosphorylated tau, β-amyloid42 , α-synuclein, neurofilament light, and YKL-40 change over time and if changes correlate with motor progression and/or cognitive decline in patients with PD and controls.

METHODS

We included 63 patients with PD (nondemented) and 21 neurologically healthy controls from the prospective and longitudinal Swedish BioFINDER study, all of whom had clinical assessments and lumbar punctures at baseline and after 2 years.

RESULTS

CSF tau levels correlated strongly with α-synuclein. The levels of CSF α-synuclein, tau, phosphorylated tau, neurofilament light, and YKL-40, but not β-amyloid42 , increased in CSF over 2 years in PD. No changes were seen in the control group. Studying patients with a short disease duration ( ≤ 5 years) and patients with a long disease duration ( > 5 years) separately, α-synuclein and tau only increased in the PD group with long disease duration. In the PD group, an increase in phosphorylated tau over 2 years correlated with faster motor progression and faster cognitive decline. An increase in YKL-40 over 2 years correlated with faster cognitive decline.

CONCLUSION

CSF biomarkers reflecting Lewy body pathology and neurodegeneration (α-synuclein), neuronal degeneration (tau, phosphorylated tau, and neurofilament light), and inflammation (YKL-40) increase significantly over 2 years in PD. CSF levels of α-synuclein and tau correlate and remain stable in the early symptomatic phase of PD but increase in the later phase. We hypothesize that CSF α-synuclein levels might increase as a result of more intense neurodegeneration in PD with long disease duration. © 2016 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Biomarkers for dementia and mild cognitive impairment in Parkinson's disease

Cognitive decline is one of the most frequent and disabling nonmotor features of Parkinson's disease. Around 30% of patients with Parkinson's disease experience mild cognitive impairment, a well-established risk factor for the development of dementia. However, mild cognitive impairment in patients with Parkinson's disease is a heterogeneous entity that involves different types and extents of cognitive deficits. Because it is not currently known which type of mild cognitive impairment confers a higher risk of progression to dementia, it would be useful to define biomarkers that could identify these patients to better study disease progression and possible interventions. In this sense, the identification among patients with Parkinson's disease and mild cognitive impairment of biomarkers associated with dementia would allow the early detection of this process. This review summarizes studies from the past 25 years that have assessed the potential biomarkers of dementia and mild cognitive impairment in Parkinson's disease patients. Despite the potential importance, no biomarker has as yet been validated. However, features such as low levels of epidermal and insulin-like growth factors or uric acid in plasma/serum and of Aß in CSF, reduction of cerebral cholinergic innervation and metabolism measured by PET mainly in posterior areas, and hippocampal atrophy in MRI might be indicative of distinct deficits with a distinct risk of dementia in subgroups of patients. Longitudinal studies combining the existing techniques and new approaches are needed to identify patients at higher risk of dementia. © 2016 International Parkinson and Movement Disorder Society.

Parkinson's Disease with Fatigue: Clinical Characteristics and Potential Mechanisms Relevant to α-Synuclein Oligomer

Background and Purpose

The aim of this study was to identify the clinical characteristics and potential mechanisms relevant to pathological proteins in Parkinson's disease (PD) patients who experience fatigue.

Methods

PD patients (n=102) were evaluated using a fatigue severity scale and scales for motor and nonmotor symptoms. The levels of three pathological proteins—α-synuclein oligomer, β-amyloid (Aβ)_1-42, and tau—were measured in 102 cerebrospinal fluid (CSF) samples from these PD patients. Linear regression analyses were performed between fatigue score and the CSF levels of the above-listed pathological proteins in PD patients.

Results

The frequency of fatigue in the PD patients was 62.75%. The fatigue group had worse motor symptoms and anxiety, depression, and autonomic dysfunction. The CSF level of α-synuclein oligomer was higher and that of Aβ_1-42 was lower in the fatigue group than in the non-fatigue group. In multiple linear regression analyses, fatigue severity was significantly and positively correlated with the α-synuclein oligomer level in the CSF of PD patients, after adjusting for confounders.

Conclusions

PD patients experience a high frequency of fatigue. PD patients with fatigue have worse motor and part nonmotor symptoms. Fatigue in PD patients is associated with an increased α-synuclein oligomer level in the CSF.

An Alzheimer's Disease-Derived Biomarker Signature Identifies Parkinson's Disease Patients with Dementia

Biomarkers from multiple modalities have been shown to correlate with cognition in Parkinson's disease (PD) and in Alzheimer's disease (AD). However, the relationships of these markers with each other, and the use of multiple markers in concert to predict an outcome of interest, are areas that are much less explored. Our objectives in this study were (1) to evaluate relationships among 17 biomarkers previously reported to associate with cognition in PD or AD and (2) to test performance of a five-biomarker classifier trained to recognize AD in identifying PD with dementia (PDD). To do this, we evaluated a cross-sectional cohort of PD patients (n = 75) across a spectrum of cognitive abilities. All PD participants had 17 baseline biomarkers from clinical, genetic, biochemical, and imaging modalities measured, and correlations among biomarkers were assessed by Spearman's rho and by hierarchical clustering. We found that internal correlation among all 17 candidate biomarkers was modest, showing a maximum pairwise correlation coefficient of 0.51. However, a five-marker subset panel derived from AD (CSF total tau, CSF phosphorylated tau, CSF amyloid beta 42, APOE genotype, and SPARE-AD imaging score) discriminated cognitively normal PD patients vs. PDD patients with 80% accuracy, when employed in a classifier originally trained to recognize AD. Thus, an AD-derived biomarker signature may identify PDD patients with moderately high accuracy, suggesting mechanisms shared with AD in some PDD patients. Based on five measures readily obtained during life, this AD-derived signature may prove useful in identifying PDD patients most likely to respond to AD-based crossover therapies.

Lewy body dementias

The broad importance of dementia is undisputed, with Alzheimer's disease justifiably getting the most attention. However, dementia with Lewy bodies and Parkinson's disease dementia, now called Lewy body dementias, are the second most common type of degenerative dementia in patients older than 65 years. Despite this, Lewy body dementias receive little attention and patients are often misdiagnosed, leading to less than ideal management. Over the past 10 years, considerable effort has gone into improving diagnostic accuracy by refining diagnostic criteria and using imaging and other biomarkers. Dementia with Lewy bodies and Parkinson's disease dementia share the same pathophysiology, and effective treatments will depend not only on successful treatment of symptoms but also on targeting the pathological mechanisms of disease, ideally before symptoms and clinical signs develop. We summarise the most pertinent progress from the past 10 years, outlining some of the challenges for the future, which will require refinement of diagnosis and clarification of the pathogenesis, leading to disease-modifying treatments.

CSF β-Amyloid 1-42 Predicts Progression to Cognitive Impairment in Newly Diagnosed Parkinson Disease

Low CSF β-amyloid 1-42 has been associated with cognitive decline in advanced Parkinson's disease; data from a single cohort suggest β-amyloid 1-42 may be an early marker of cognitive impairment. Newly diagnosed Parkinson's participants (mean duration, 6.9 months) in the Parkinson's Progression Markers Initiative (n = 341) were assessed at baseline (untreated state) and followed for 2 years. CSF β-amyloid 1-42, α-synuclein, total tau, and tau phosphorylated at threonine 181 were collected at baseline. Participants were classified as having cognitive impairment (CI) if scores on two of six cognitive tests were 1.5 standard deviations below the standardized mean based on published norms in healthy controls. Multivariable regression analyses were used to determine the association between baseline CSF markers with cognitive impairment, defined by neuropsychological testing performance at 2-year follow-up. Fifty-five participants (16.1 %) had CI at baseline and were not included in further analyses. Thirty-seven of the 286 participants without CI at baseline (12.9 %) developed CI at 2 years. Participants with CI at 2 years had significantly lower mean baseline CSF β-amyloid 1-42 levels than non-CI participants (343.8 vs. 380.4 pg/mL, p < 0.01); no significant difference was seen for α-synuclein, T-tau, or P-tau 181. In a regression model of 286 participants without baseline CI adjusted for age, gender, disease duration, education, motor severity, and depression status, lower baseline β-amyloid 1-42 levels were associated with higher odds of CI at 2 years. (OR(10pg/mL) = 1.04, 95 % CI 1.01-1.08, p < 0.05). CSF β-amyloid 1-42 level at disease onset is an independent predictor of cognitive impairment in early Parkinson's disease.

Correlates of excessive daytime sleepiness in de novo Parkinson's disease: A case control study

OBJECTIVE

This study was undertaken to determine the frequency and correlates of excessive daytime sleepiness in de novo, untreated Parkinson's disease (PD) patients compared with the matched healthy controls.

METHODS

Data were obtained from the Parkinson's Progression Markers Initiative, an international study of de novo, untreated PD patients and healthy controls. At baseline, participants were assessed with a wide range of motor and nonmotor scales, including the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). Excessive daytime sleepiness was assessed based on the Epworth Sleepiness scale (ESS), with a cutoff of 10.

RESULTS

Four hundred twenty-three PD subjects and 196 healthy controls were recruited into the study. Mean ESS (min, max) score was 5.8 (0, 20) for the PD subjects and 5.6 (0, 19) for healthy controls (P = 0.54). Sixty-six (15.6%) PD subjects and 24 (12%) healthy controls had ESS of at least 10 (P = 0.28). No difference was seen in demographic characteristics, age of onset, disease duration, PD subtype, cognitive status, or utilization of sedatives between the PD sleepiness-positive versus the negative group. The sleepiness-positive group had higher MDS-UPDRS Part I and II but not III scores, and higher depression and autonomic dysfunction scores. Sleepiness was associated with a marginal reduction of A-beta (P = 0.05) but not alpha-synuclein spinal fluid levels in PD.

CONCLUSIONS

This largest case control study demonstrates no difference in prevalence of excessive sleepiness in subjects with de novo untreated PD compared with healthy controls. The only clinical correlates of sleepiness were mood and autonomic dysfunction. Ongoing longitudinal analyses will be essential to further examine clinical and biological correlates of sleepiness in PD and specifically the role of dopaminergic therapy.

Cerebrospinal fluid Aβ42 levels and APP processing pathway genes in Parkinson's disease

BACKGROUND

Of recent interest is the finding that certain cerebrospinal fluid (CSF) biomarkers traditionally linked to Alzheimer's disease (AD), specifically amyloid beta protein (Aβ), are abnormal in PD CSF. The aim of this exploratory investigation was to determine whether genetic variation within the amyloid precursor protein (APP) processing pathway genes correlates with CSF Aβ42 levels in Parkinson's disease (PD).

METHODS

Parkinson's disease (n = 86) and control (n = 161) DNA were genotyped for 19 regulatory region tagging single-nucleotide polymorphisms (SNPs) within nine genes (APP, ADAM10, BACE1, BACE2, PSEN1, PSEN2, PEN2, NCSTN, and APH1B) involved in the cleavage of APP. The SNP genotypes were tested for their association with CSF biomarkers and PD risk while adjusting for age, sex, and APOE ɛ4 status.

RESULTS

Significant correlation with CSF Aβ42 levels in PD was observed for two SNPs, (APP rs466448 and APH1B rs2068143). Conversely, significant correlation with CSF Aβ42 levels in controls was observed for three SNPs (APP rs214484, rs2040273, and PSEN1 rs362344).

CONCLUSIONS

In addition, results of this exploratory investigation suggest that an APP SNP and an APH1B SNP are marginally associated with PD CSF Aβ42 levels in APOE ɛ4 noncarriers. Further hypotheses generated include that decreased CSF Aβ42 levels are in part driven by genetic variation in APP processing genes. Additional investigation into the relationship between these findings and clinical characteristics of PD, including cognitive impairment, compared with other neurodegenerative diseases, such as AD, are warranted. © 2015 International Parkinson and Movement Disorder Society.

Biomarkers of cognitive decline in Parkinson's disease

Cognitive impairment is a frequent and devastating non-motor symptom of Parkinson's disease (PD). Impaired cognition has a major impact on either quality of life or mortality in patients with PD. Notably, the rate of cognitive decline and pattern of early cognitive deficits in PD are highly variable between individuals. Given that the underlying mechanisms of cognitive decline or dementia associated with PD remain unclear, there is currently no mechanism-based treatment available. Identification of biological markers, including neuroimaging, biofluids and common genetic variants, that account for the heterogeneity of PD related cognitive decline could provide important insights into the pathological processes that underlie cognitive impairment in PD. These combined biomarker approaches will enable early diagnosis and provide indicators of cognitive progression in PD patients. This review summarizes recent advances in the development of biomarkers for cognitive impairments in PD.

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.

What can biomarkers tell us about cognition in Parkinson's disease?

Cognitive decline is common in Parkinson's disease (PD), even in the early motor stage, and this non-motor feature impacts quality of life and prognosis tremendously. In this article, we discuss marker candidates for cognitive decline in PD from different angles, including functional and structural imaging techniques, biological fluid markers in cerebrospinal fluid, and blood genetic predictors, as well as gait as a surrogate marker of cognitive decline. Specifically, imaging-based markers of cognitive impairment in PD include cortical atrophy, reduced cortical metabolism, loss of cortical cholinergic and frontal dopaminergic function, as well as an increased cortical amyloid load. Reduced β-amyloid(1-42) in cerebrospinal fluid and lower plasma levels of epidermal growth factor are predictors for cognitive decline in PD. In addition, genetic variation in the apolipoprotein E (APOE), catechol-O-methyltransferase (COMT), microtubule-associated protein tau (MAPT), and glucocerebrosidase (GBA) genes may confer risk for cognitive impairment in PD; and gait disturbance may also indicate an increased risk for dementia. Other marker candidates have been proposed and are discussed. All of the current studies are hampered by gaps in our knowledge about the molecular causes of cognitive decline, which will have to be considered in future biomarker studies.

CSF biomarkers and clinical progression of Parkinson disease

OBJECTIVE

To investigate whether certain CSF biomarkers at baseline can predict future progression of motor symptoms and cognitive decline in patients with Parkinson disease (PD).

METHODS

Patients and controls were recruited from hospitals in southern Sweden as part of the prospective and longitudinal Swedish BioFinder Study. In the present study, we included 42 patients with PD and 69 controls who had clinical assessment and lumbar puncture at baseline. Baseline CSF samples were analyzed for α-synuclein (αSyn), β-amyloid 1-42 (Aβ42), tau, phosphorylated tau, and neurofilament light. Associations between CSF markers at baseline and change in clinical characteristics after 2 years of follow-up were investigated using multivariate models adjusting for age, sex, disease duration, and levodopa-equivalent daily dose.

RESULTS

Higher levels of αSyn within the PD group were associated with progression of motor symptoms and cognitive decline over 2 years, indicated by significant relationships between αSyn and change in Hoehn and Yahr (β = 0.394, p = 0.043), Unified Parkinson's Disease Rating Scale, Part III (UPDRS-III) (β = 0.449, p = 0.013), Timed Up and Go (β = 0.406, p = 0.023), and A Quick Test of Cognitive Speed (β = 0.423, p = 0.018). Lower levels of Aβ42 were associated with worsening of performance on delayed memory recall (F = 5.834, p = 0.022). Finally, high levels of phosphorylated tau were associated with worsening in motor symptoms (UPDRS-III, β = 0.350, p = 0.045; Hoehn and Yahr, β = 0.366, p = 0.038).

CONCLUSION

We found evidence of a link between higher levels of αSyn at baseline and worsening of motor symptoms and cognitive speed over 2 years in PD. Increased αSyn might be a marker of more intense synaptic degeneration in PD. The results indicate that cortical amyloid pathology (low CSF Aβ42) is associated with memory decline.

Cerebrospinal fluid biochemical studies in patients with Parkinson's disease: toward a potential search for biomarkers for this disease

The blood-brain barrier supplies brain tissues with nutrients and filters certain compounds from the brain back to the bloodstream. In several neurodegenerative diseases, including Parkinson's disease (PD), there are disruptions of the blood-brain barrier. Cerebrospinal fluid (CSF) has been widely investigated in PD and in other parkinsonian syndromes with the aim of establishing useful biomarkers for an accurate differential diagnosis among these syndromes. This review article summarizes the studies reported on CSF levels of many potential biomarkers of PD. The most consistent findings are: (a) the possible role of CSF urate on the progression of the disease; (b) the possible relations of CSF total tau and phosphotau protein with the progression of PD and with the preservation of cognitive function in PD patients; (c) the possible value of CSF beta-amyloid 1-42 as a useful marker of further cognitive decline in PD patients, and (d) the potential usefulness of CSF neurofilament (NFL) protein levels in the differential diagnosis between PD and other parkinsonian syndromes. Future multicentric, longitudinal, prospective studies with long-term follow-up and neuropathological confirmation would be useful in establishing appropriate biomarkers for PD.