Striatal Aβ peptide deposition mirrors dementia and differentiates DLB and PDD from other Parkinsonian syndromes

α-Synuclein triggers cofilin pathology and dendritic spine impairment via a PrPC-CCR5 dependent pathway

Cognitive dysfunction and dementia are critical symptoms of Lewy Body dementias (LBD). Specifically, alpha-synuclein (αSyn) accumulation in the hippocampus leading to synaptic dysfunction is linked to cognitive deficits in LBD. Here, we investigated the pathological impact of αSyn on hippocampal neurons. We report that either αSyn overexpression or αSyn pre-formed fibrils (PFFs) treatment triggers the formation of cofilin-actin rods, synapse disruptors, in cultured hippocampal neurons and in the hippocampus of synucleinopathy mouse models and of LBD patients. In vivo, cofilin pathology is present concomitantly with synaptic impairment and cognitive dysfunction. Rods generation prompted by αSyn involves the co-action of the cellular prion protein (PrPC) and the chemokine receptor 5 (CCR5). Importantly, we show that CCR5 inhibition, with a clinically relevant peptide antagonist, reverts dendritic spine impairment promoted by αSyn. Collectively, we detail the cellular and molecular mechanism through which αSyn disrupts hippocampal synaptic structure and we identify CCR5 as a novel therapeutic target to prevent synaptic impairment and cognitive dysfunction in LBD.

The molecular spectrum of amyloid-beta (Aβ) in neurodegenerative diseases beyond Alzheimer's disease

This study investigated the molecular spectrum of amyloid-beta (Aβ) in neurodegenerative diseases beyond Alzheimer's disease (AD). We analyzed Aβ deposition in the temporal cortex and striatum in 116 autopsies, including Lewy body disease (LBD; N = 51), multiple system atrophy (MSA; N = 10), frontotemporal lobar degeneration-TDP-43 (FTLD-TDP; N = 16), and progressive supranuclear palsy (PSP; N = 39). The LBD group exhibited the most Aβ deposition in the temporal cortex and striatum (90/76%, respectively), followed by PSP (69/28%), FTLD-TDP (50/25%), and the MSA group (50/10%). We conducted immunohistochemical analysis using antibodies targeting eight Aβ epitopes in the LBD and PSP groups. Immunohistochemical findings were evaluated semi-quantitatively and quantitatively using digital pathology. Females with LBD exhibited significantly more severe Aβ deposition, particularly Aβ42 and Aβ43 , along with significantly more severe tau pathology. Furthermore, a quantitative analysis of all Aβ peptides in the LBD group revealed an association with the APOE-ε4 genotypes. No significant differences were observed between males and females in the PSP group. Finally, we compared striatal Aβ deposition in cases with LBD (N = 15), AD without α-synuclein pathology (N = 6), and PSP (N = 5). There were no differences in the pan-Aβ antibody (6F/3D)-immunolabeled deposition burden among the three groups, but the deposition burden of peptides with high aggregation capacity, especially Aβ43 , was significantly higher in the AD and LBD groups than in the PSP group. Furthermore, considerable heterogeneity was observed in the composition of Aβ peptides on a case-by-case basis in the AD and LBD groups, whereas it was relatively uniform in the PSP group. Cluster analysis further supported these findings. Our data suggest that the type of concomitant proteinopathies influences the spectrum of Aβ deposition, impacted also by sex and APOE genotypes.

Co-aggregation of α-synuclein with amyloid-β stabilizes β-sheet-rich oligomers and enhances the formation of β-barrels

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative diseases with markedly different pathological features of β-amyloid (Aβ) plaques and α-synuclein (αS) Lewy bodies (LBs), respectively. However, clinical overlaps in symptoms and pathologies between AD and PD are commonly observed caused by the cross-interaction between Aβ and αS. To uncover the molecular mechanisms behind their overlapping symptoms and pathologies, we computationally investigated the impact of αS on an Aβ monomer and dimerization using atomistic discrete molecular dynamics simulations (DMD). Our results revealed that αS could directly interact with Aβ monomers and dimers, thus forming β-sheet-rich oligomers, including potentially toxic β-barrel intermediates. The binding hotspot involved the second half of the N-terminal domain and NAC region in αS, along with residues 10-21 and 31-42 in Aβ. In their hetero-complex, the binding hotspot primarily assumed a β-sheet core buried inside, which was dynamically shielded by the highly charged, amyloid-resistant C-terminus of αS. Because the amyloid prion region was the same as the binding hotspot being buried, their fibrillization may be delayed, causing the toxic oligomers to increase. This study sheds light on the intricate relationship between Aβ and αS and provides insights into the overlapping pathology of AD and PD.

Morphological characteristics differentiate dementia with Lewy bodies from Parkinson disease with and without dementia

Dementia with Lewy bodies (DLB) and Parkinson disease (PD) with and without dementia are entities of a spectrum of Lewy body diseases. About 26.3% of all PD patients develop dementia increasing up to 83%. Parkinson disease-dementia (PDD) and DLB share many clinical and morphological features that separate them from non-demented PD (PDND). Clinically distinguished by the temporal sequence of motor and cognitive symptoms, the pathology of PDD and DLB includes variable combinations of Lewy body (LB) and Alzheimer (AD) lesions, both being more severe in DLB, but much less frequent and less severe in PDND. The objective of this study was to investigate the morphological differences between these three groups. 290 patients with pathologically confirmed PD were reviewed. 190 of them had clinical dementia; 110 met the neuropathological criteria of PDD and 80 of DLB. The major demographic and clinical data were obtained from medical records. Neuropathology included semiquantitative assessment of LB and AD pathologies including cerebral amyloid angiopathy (CAA). PDD patients were significantly older than PDND and DLB ones (83.9 vs 77.9 years, p < 0.05); the age of DLB patients was between them (80.0 years), while the disease duration was shortest in DLB. Brain weight was lowest in DLB, which showed higher Braak LB scores (mean 5.2 vs 4.2) and highest Braak tau stages (mean 5.2 vs 4.4 and 2.3, respectively). Thal Aβ phases were also highest in DLB (mean 4.1 vs 3.0 and 1.8, respectively). Major findings were frequency and degree of CAA, being highest in DLB (95% vs 50% and 24%, with scores 2.9 vs 0.7 and 0.3, respectively), whereas other small vessel lesions showed no significant differences. Striatal Aβ deposits also differentiated DLB from the other groups. This and other studies of larger cohorts of PD patients indicate that the association of CAA and cortical tau-but less-LB pathologies are associated with more severe cognitive decline and worse prognosis that distinguish DLB from PDD and PDND. The particular impact of both CAA and tau pathology supports the concept of a pathogenic continuum ranging from PDND to DLB + AD within the spectrum of age-related synucleinopathies.

Mixed pathology as a rule, not exception: Time to reconsider disease nosology

Parkinson's disease is a progressive neurodegenerative disorder that is associated with motor and nonmotor symptoms. Accumulation of misfolded α-synuclein is considered a key pathological feature during disease initiation and progression. While clearly deemed a synucleinopathy, the development of amyloid-β plaques, tau-containing neurofibrillary tangles, and even TDP-43 protein inclusions occur within the nigrostriatal system and in other brain regions. In addition, inflammatory responses, manifested by glial reactivity, T-cell infiltration, and increased expression of inflammatory cytokines, plus other toxic mediators derived from activated glial cells, are currently recognized as prominent drivers of Parkinson's disease pathology. However, copathologies have increasingly been recognized as the rule (>90%) and not the exception, with Parkinson's disease cases on average exhibiting three different copathologies. While microinfarcts, atherosclerosis, arteriolosclerosis, and cerebral amyloid angiopathy may have an impact on disease progression, α-synuclein, amyloid-β, and TDP-43 pathology do not seem to contribute to progression.

Effect of Amyloid on Cognitive Performance in Parkinson's Disease and Dementia with Lewy Bodies

BACKGROUND

Concomitant amyloid pathology contributes to the clinical heterogeneity of Lewy body diseases (LBDs).

OBJECTIVE

The objective of this study was to investigate the pattern and effect of amyloid accumulation on cognitive dysfunction in Parkinson's disease (PD) and dementia with Lewy bodies (DLB).

METHODS

We retrospectively assessed 205 patients with LBD (91 with DLB and 114 with PD) who underwent ¹⁸ F-florbetaben positron emission tomography and divided them into amyloid-positive and amyloid-negative groups depending on global standardized uptake value ratios (SUVRs). We investigated the effect of group on the regional and global SUVRs using general linear models (GLMs) after controlling for age, sex, cognitive status, and score on the Korean version of the Mini-Mental State Examination. Moreover, the effect of amyloid on cognitive function, depending on the type of LBD, was evaluated using GLMs with interaction analysis.

RESULTS

In all evaluated regions including the striatum, the DLB group showed a higher SUVR than the PD group. Among amyloid-positive patients, the DLB group had a higher regional SUVR than the PD group in the frontal and parietal cortices. There was a significant interaction effect between amyloid and disease groups in language and memory function. In patients with PD, global amyloid load was negatively associated with language (B = -2.03; P = 0.010) and memory functions (B = -1.96; P < 0.001). However, amyloid load was not significantly associated with cognitive performance in the DLB group.

CONCLUSIONS

Although the burden of amyloid was higher in the DLB group, amyloid accumulation was negatively associated with the memory and language functions in the PD group only. © 2022 International Parkinson and Movement Disorder Society.

Neocortical Lewy Body Pathology Parallels Parkinson's Dementia, but Not Always

OBJECTIVE

The objective of this study was to evaluate the relationship between Parkinson's disease (PD) with dementia and cortical proteinopathies in a large population of pathologically confirmed patients with PD.

METHODS

We reviewed clinical data from all patients with autopsy data seen in the Movement Disorders Center at Washington University, St. Louis, between 1996 and 2019. All patients with a diagnosis of PD based on neuropathology were included. We used logistic regression and multivariate analysis of covariance (MANCOVA) to investigate the relationship between neuropathology and dementia.

RESULTS

A total of 165 patients with PD met inclusion criteria. Among these, 128 had clinical dementia. Those with dementia had greater mean ages of motor onset and death but equivalent mean disease duration. The delay between motor symptom onset and dementia was 1 year or less in 14 individuals, meeting research diagnostic criteria for possible or probable dementia with Lewy bodies (DLB). Braak Lewy body stage was associated with diagnosis of dementia, whereas severities of Alzheimer's disease neuropathologic change (ADNC) and small vessel pathology did not. Pathology of individuals diagnosed with DLB did not differ significantly from that of other patients with PD with dementia. Six percent of individuals with PD and dementia did not have neocortical Lewy bodies; and 68% of the individuals with PD but without dementia did have neocortical Lewy bodies.

INTERPRETATION

Neocortical Lewy bodies almost always accompany dementia in PD; however, they also appear in most PD patients without dementia. In some cases, dementia may occur in patients with PD without neocortical Lewy bodies, ADNC, or small vessel disease. Thus, other factors not directly related to these classic neuropathologic features may contribute to PD dementia. ANN NEUROL 2023;93:184-195.

A meta-analysis of the diagnostic utility of biomarkers in cerebrospinal fluid in Parkinson's disease

Biomarkers play important roles in the diagnosis and differential diagnosis of Parkinson's disease (PD). Thus, we carried out a systematic review and meta-analysis evaluating the diagnostic utility of cerebrospinal fluid (CSF) biomarkers to distinguish PD from atypical parkinsonian syndromes (APSs) and controls. Data for PD and APS and controls were extracted from 123 studies that reported the concentration of CSF biomarkers. Comparisons were presented using pooled Hedges' g. Sources of heterogeneity were evaluated using meta-regression, and subgroup and sensitivity analyses. We found that compared with controls, PD patients had lower levels of amyloid beta 1-42, phosphorylated tau, total tau, total α-synuclein, Zn, DJ-1, and YKL-40, and higher levels of oligomeric and phosphorylated α-synuclein. Moreover, lower CSF levels of neurofilament light chain, t-tau, YKL-40, and C-reactive protein were found in PD patients compared to those with multiple system atrophy. PD patients also had lower levels of NFL and higher levels of Aβ42 compared with patients with progressive supranuclear palsy. Reduced levels of p-tau and t-tau and higher Aβ42 levels were found in PD patients compared with patients with dementia with Lewy bodies. Finally, reduced NFL levels were found in patients with PD compared with patients with cortical basal degeneration. Therefore, we believe that the combinations of t-α-syn, Aβ42, and NFL could be promising biomarkers for the differential diagnosis of PD and APSs.

Novel PSEN1 (P284S) Mutation Causes Alzheimer's Disease with Cerebellar Amyloid β-Protein Deposition

BACKGROUND/OBJECTIVE

AD-associated PSEN1 mutations exhibit high clinical heterogeneity. The discovery of these mutations and the analysis of their associations with cases such as EOAD should be critical to understanding AD's pathogenesis.

METHODS

We performed clinical analysis, neuroimaging, target region capture and high-throughput sequencing, and Sanger sequencing in a family of 3 generations. The underlying Alzheimer's pathology was evaluated using biomarker evidence obtained from cerebrospinal fluid (CSF) amyloid testing and ¹⁸F-florbetapir (AV-45) PET imaging.

RESULTS

Target region capture sequencing revealed a novel heterozygous C to T missense point mutation at the base position 284 (c.850 C>T) located in exon 8 of the PSEN1 gene, resulting in a Prolineto- Serine substitution (P284S) at codon position 850. The mutation was also identified by Sanger sequencing in 2 family members, including proband and her daughter and was absent in the other 4 unaffected family members and 50 control subjects. Cerebrospinal fluid (CSF) amyloid test exhibited biomarker evidence of underlying Alzheimer's pathology. ¹⁸F-florbetapir (AV-45) PET imaging indicated extensive cerebral cortex and cerebellar Aβ deposition.

CONCLUSIONS

We discovered a novel PSEN1 pathogenic mutation, P284S, observed for the first time in a Chinese family with early-onset AD.

Are there morphological differences between Parkinson's disease-dementia and dementia with Lewy bodies?

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are two major neurocognitive disorders in the spectrum of Lewy body diseases that overlap in many clinical and neuropathological features, although they show several differences. Clinically distinguished mainly based on the duration of parkinsonism prior to development of dementia, their morphology is characterized by a variable combination of Lewy body (LB) and Alzheimer's disease (AD) pathologies, the latter usually being more frequent and severe in DLB.

OBJECTIVE

The aims of the study were to investigate essential neuropathological differences between PDD and DLB in a larger cohort of autopsy cases.

METHODS

110 PDD autopsy cases were compared with 78 DLB cases. The major demographic, clinical (duration of illness, final MMSE) and neuropathological data were assessed retrospectively. Neuropathological studies used standardized methods and immunohistochemistry for phospho-tau, β-amyloid (Aß) and α-synuclein, with semiquantitative assessment of the major histological lesions.

RESULTS

PDD patients were significantly older at death than DLB ones (mean 83.9 vs. 79.8 years), with a significantly longer disease duration (mean 9.2 vs. 6.7 years). Braak LB scores and particularly neuritic Braak stages were significantly higher in the DLB group (mean 5.1and 5.1 vs. 4.2 and 4.4, respectively), as were Thal Aβ phases (mean 4.1 vs. 3.0). Diffuse striatal Aβ plaques were considerable in 55% and moderate in 45% of DLB cases, but were extremely rare in PDD. The most significant differences concerned the frequency and degree of cerebral amyloid angiopathy (CAA), being significantly higher in DLB (98.7 vs. 50%, and mean degree of 2.9 vs. 0.72, respectively). Worse prognosis in DLB than in PDD was linked to both increased Braak neuritic stages and more severe CAA.

INTERPRETATION

These and other recent studies imply the association of CAA, more severe concomitant AD pathology, and striatal Aβ load with cognitive decline and more rapid disease process that distinguishes DLB from PDD, while the influence of other cerebrovascular diseases or co-pathologies in both disorders was not specifically examined. The importance of both CAA and tau pathology in DLB and much less in PDD supports the concept of a pathogenetic continuum from Parkinson's disease (PD) - > PDD - > DLB - > DLB + AD and subtypes of AD with LB pathology within the spectrum of age-related proteinopathies.

Striatal Blood-Brain Barrier Opening in Parkinson's Disease Dementia: A Pilot Exploratory Study

BACKGROUND

Parkinson's disease (PD) exhibits a high prevalence of dementia as disease severity and duration progress. Focused ultrasound (FUS) has been applied for transient blood-brain barrier (BBB) opening of cortical regions in neurodegenerative disorders. The striatum is a primary target for delivery of putative therapeutic agents in PD.

OBJECTIVE

Here, we report a prospective, single-arm, nonrandomized, proof-of-concept, phase I clinical trial (NCT03608553 amended) in PD with dementia to test the safety and feasibility of striatal BBB opening in PD patients.

METHODS

Seven PD patients with cognitive impairment were treated for BBB opening in the posterior putamen. This was performed in two sessions separated by 2 to 4 weeks, where the second session included bilateral putamina opening in 3 patients. Primary outcome measures included safety and feasibility of focal striatal BBB opening. Changes in motor and cognitive functions, magnetic resonance imaging (MRI), ¹⁸ F-fluorodopa (FDOPA), and β-amyloid PET (positron emission tomography) images were determined.

RESULTS

The procedure was feasible and well tolerated, with no serious adverse events. No neurologically relevant change in motor and cognitive (battery of neuropsychological tests) functions was recognized at follow-up. MRI revealed putamen BBB closing shortly after treatment (24 hours to 14 days) and ruled out hemorrhagic and ischemic lesions. There was a discrete but significant reduction in β-amyloid uptake in the targeted region and no change in FDOPA PET.

CONCLUSIONS

These initial results indicate that FUS-mediated striatal BBB opening is feasible and safe and therefore could become an effective tool to facilitate the delivery of putative neurorestorative molecules in PD. © 2022 International Parkinson and Movement Disorder Society.

Collusion of α-Synuclein and Aβ aggravating co-morbidities in a novel prion-type mouse model

BACKGROUND

The misfolding of host-encoded proteins into pathological prion conformations is a defining characteristic of many neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and Lewy body dementia. A current area of intense study is the way in which the pathological deposition of these proteins might influence each other, as various combinations of co-pathology between prion-capable proteins are associated with exacerbation of disease. A spectrum of pathological, genetic and biochemical evidence provides credence to the notion that amyloid β (Aβ) accumulation can induce and promote α-synuclein pathology, driving neurodegeneration.

METHODS

To assess the interplay between α-synuclein and Aβ on protein aggregation kinetics, we crossed mice expressing human α-synuclein (M20) with APPswe/PS1dE9 transgenic mice (L85) to generate M20/L85 mice. We then injected α-synuclein preformed fibrils (PFFs) unilaterally into the hippocampus of 6-month-old mice, harvesting 2 or 4 months later.

RESULTS

Immunohistochemical analysis of M20/L85 mice revealed that pre-existing Aβ plaques exacerbate the spread and deposition of induced α-synuclein pathology. This process was associated with increased neuroinflammation. Unexpectedly, the injection of α-synuclein PFFs in L85 mice enhanced the deposition of Aβ; whereas the level of Aβ deposition in M20/L85 bigenic mice, injected with α-synuclein PFFs, did not differ from that of mice injected with PBS.

CONCLUSIONS

These studies reveal novel and unexpected interplays between α-synuclein pathology, Aβ and neuroinflammation in mice that recapitulate the pathology of Alzheimer's disease and Lewy body dementia.

Locus Coeruleus Pathology Indicates a Continuum of Lewy Body Dementia

BACKGROUND

Lewy body dementia (LBD) has two main phenotypes of LBD, Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB), separated by the 'one-year-rule'. They also show different symptom profiles: core DLB features include fluctuating cognition, REM-sleep behaviur disorder, and visual hallucinations. These symptoms are sometimes present in PDD, representing an intermediate 'PDD-DLB' phenotype.

OBJECTIVE

DLB-like features may reflect deficits in the functions of the noradrenergic nucleus locus coeruleus (LC). Therefore, we compared the LC in the LBD phenotypes, PD, and controls.

METHODS

38 PD, 56 PDD, 22 DLB, and 11 age-matched control cases from the Parkinson's UK tissue bank were included. LC tissue sections were immunostained for tyrosine-hydroxylase (TH), α-synuclein, tau, and amyloid-β. TH-neurons were quantified and pathologic burden calculated by %-coverage method.

RESULTS

The LC shows a stepwise reduction in neuron count from controls, PD, PDD, to DLB. PDD-DLB cases showed an intermediate clinical phenotype that was reflected pathologically. Cell counts were significantly reduced in DLB compared to PDD after correction for demographic factors. LC degeneration contributed significantly to the onset of all DLB symptoms. While α-synuclein was not significantly different between PDD and DLB cases, DLB exhibited significantly less tau pathology.

CONCLUSION

DLB and DLB-like symptoms represent noradrenergic deficits resulting from neuronal loss in the LC. PDD and DLB are likely to represent a clinical continuum based on the presence or absence of DLB-like symptoms mirrored by a pathological continuum in the LC.

Significance of cerebral amyloid angiopathy and other co-morbidities in Lewy body diseases

Lewy body dementia (LBD) and Parkinson's disease-dementia (PDD) are two major neurocognitive disorders with Lewy bodies (LB) of unknown etiology. There is considerable clinical and pathological overlap between these two conditions that are clinically distinguished based on the duration of Parkinsonism prior to development of dementia. Their morphology is characterized by a variable combination of LB and Alzheimer's disease (AD) pathologies. Cerebral amyloid angiopathy (CAA), very common in aged persons and particularly in AD, is increasingly recognized for its association with both pathologies and dementia. To investigate neuropathological differences between LB diseases with and without dementia, 110 PDD and 60 LBD cases were compared with 60 Parkinson's disease (PD) cases without dementia (PDND). The major demographic and neuropathological data were assessed retrospectively. PDD patients were significantly older than PDND ones (83.9 vs 77.8 years; p < 0.05); the age of LB patients was in between both groups (mean 80.2 years), while the duration of disease was LBD < PDD < PDND (mean 6.7 vs 12.5 and 14.3 years). LBD patients had higher neuritic Braak stages (mean 5.1 vs 4.5 and 4.0, respectively), LB scores (mean 5.3 vs 4.2 and 4.0, respectively), and Thal amyloid phases (mean 4.1 vs 3.0 and 2.3, respectively) than the two other groups. CAA was more common in LBD than in the PDD and PDND groups (93 vs 50 and 21.7%, respectively). Its severity was significantly greater in LBD than in PDD and PDND (p < 0.01), involving mainly the occipital lobes. Moreover, striatal Aβ deposition highly differentiated LBD brains from PDD. Braak neurofibrillary tangle (NFT) stages, CAA, and less Thal Aβ phases were positively correlated with LB pathology (p < 0.05), which was significantly higher in LBD than in PDD < PDND. Survival analysis showed worse prognosis in LBD than in PDD (and PDND), which was linked to both increased Braak tau stages and more severe CAA. These and other recent studies imply the association of CAA-and both tau and LB pathologies-with cognitive decline and more rapid disease progression that distinguishes LBD from PDD (and PDND).

Advances in Brain Amyloid Imaging

Amyloid-β (Aβ) PET imaging has now been available for over 15 years. The ability to detect Aβ in vivo has greatly improved the clinical and research landscape of Alzheimer's disease (AD) and other neurodegenerative conditions. Aβ imaging provides very reliable, accurate, and reproducible measurements of regional and global Aβ burden in the brain. It has proved invaluable in anti-Aβ therapy trials, and is now recognized as a powerful diagnostic tool. The appropriate use of Aβ PET, when combined with comprehensive clinical evaluation by a dementia-trained specialist, can improve the accuracy of a clinical diagnosis of AD and substantially alter management. It can assist in differentiating AD from other neurodegenerative conditions, often by its ability to rule out the presence of Aβ. When combined with tau imaging, further increase in specificity for the diagnosis of AD can be achieved. The integration of Aβ PET, in conjunction with biomarkers of tau, neurodegeneration and neuroinflammation, into large, longitudinal, observational cohort studies continues to increase our understanding of the development of AD. Its incorporation into clinical trials has been pivotal in defining the most effective anti-Aβ biological therapies and optimal dosing so that effective disease modifying therapy now appears imminent. Aβ deposition is a gradual and protracted process, permitting a wide treatment window for anti-Aβ therapies and Aβ PET has made trials in this preclinical AD period feasible. Continuing improvement in Aβ tracer target to background ratio is allowing trials in earlier AD that tailor drug dosage to Aβ level. The quest to standardize quantification and define universally applicable thresholds for all Aβ tracers has produced the Centiloid method. Centiloid values that correlate well with neuropathologic findings and prognosis have been identified. Rapid cloud-based automated individual scan analysis is now possible and does not require MRI. Challenges remain, particularly around cross camera standardized uptake value ratio variation that need to be addressed. This review will compare available Aβ radiotracers, discuss approaches to quantification, as well as the clinical and research applications of Aβ PET.

A/T/(N) Profile in Cerebrospinal Fluid of Parkinson's Disease with/without Cognitive Impairment and Dementia with Lewy Bodies

Neuropathological investigations report that in synucleinopathies with dementia, namely Parkinson's disease (PD) with dementia (PDD) and dementia with Lewy bodies (DLB), the histopathological hallmarks of Alzheimer's Disease (AD), in particular amyloid plaques, are frequently observed. In this study, we investigated the cerebrospinal fluid (CSF) AD biomarkers in different clinical phenotypes of synucleinopathies. CSF Aβ42/Aβ40 ratio, phosphorylated tau and total tau were measured as markers of amyloidosis (A), tauopathy (T) and neurodegeneration (N) respectively, in 98 PD (48 with mild cognitive impairment, PD-MCI; 50 cognitively unimpaired, PD-nMCI), 14 PDD and 15 DLB patients, and 48 neurological controls (CTRL). In our study, CSF AD biomarkers did not significantly differ between CTRL, PD-MCI and PD-nMCI patients. In PD-nMCI and PD-MCI groups, A-/T-/N- profile was the most represented. Prevalence of A+ was similar in PD-nMCI and PD-MCI (10% and 13%, respectively), being higher in PDD (64%) and in DLB (73%). DLB showed the lowest values of Aβ42/Aβ40 ratio. Higher total tau at baseline predicted a worse neuropsychological outcome after one year in PD-MCI. A+/T+, i.e., AD-like CSF profile, was most frequent in the DLB group (40% vs. 29% in PDD).

Molecular profiling in Parkinsonian syndromes: CSF biomarkers

An accurate and early diagnosis of degenerative parkinsonian syndromes is a major need for their correct and timely therapeutic management. The current diagnostic criteria are mostly based on clinical features and molecular imaging. However, diagnostic doubts often persist especially in the early stages of diseases when signs are slight, ambiguous and overlapping among different syndromes. Molecular imaging may not be altered in the early stages of diseases, also failing to discriminate among different syndromes. Cerebrospinal fluid (CSF) represents an ideal source of biomarkers reflecting different pathways of neuropathological changes taking place in the brain and preceding the clinical onset. The aim of this review is to provide un update on CSF biomarkers in parkinsonian disorders, discussing in detail their association with neuropathological correlates. Their potential contribution in differential diagnosis and prognostic assessment of different parkinsonian syndromes is also discussed. Before entering the clinical use both for diagnostic and prognostic purposes, these CSF biomarkers need to be thoroughly assessed in terms of pre-analytical and analytical variability, as well as to clinical validation in independent cohorts.

Neuropathology of dementia in patients with Parkinson's disease: a systematic review of autopsy studies

BACKGROUND

Dementia is a common, debilitating feature of late Parkinson's disease (PD). PD dementia (PDD) is associated with α-synuclein propagation, but coexistent Alzheimer's disease (AD) pathology may coexist. Other pathologies (cerebrovascular, transactive response DNA-binding protein 43 (TDP-43)) may also influence cognition. We aimed to describe the neuropathology underlying dementia in PD.

METHODS

Systematic review of autopsy studies published in English involving PD cases with dementia. Comparison groups included PD without dementia, AD, dementia with Lewy bodies (DLB) and healthy controls.

RESULTS

44 reports involving 2002 cases, 57.2% with dementia, met inclusion criteria. While limbic and neocortical α-synuclein pathology had the strongest association with dementia, between a fifth and a third of all PD cases in the largest studies had comorbid AD. In PD cases with dementia, tau pathology was moderate or severe in around a third, and amyloid-β pathology was moderate or severe in over half. Amyloid-β was associated with a more rapid cognitive decline and earlier mortality, and in the striatum, distinguished PDD from DLB. Positive correlations between multiple measures of α-synuclein, tau and amyloid-β were found. Cerebrovascular and TDP-43 pathologies did not generally contribute to dementia in PD. TDP-43 and amyloid angiopathy correlated with coexistent Alzheimer pathology.

CONCLUSIONS

While significant α-synuclein pathology is the main substrate of dementia in PD, coexistent pathologies are common. In particular, tau and amyloid-β pathologies independently contribute to the development and pattern of cognitive decline in PD. Their presence should be assessed in future clinical trials where dementia is a key outcome measure.

TRIAL REGISTRATION NUMBER

CRD42018088691.

Cholinergic deficits and galaninergic hyperinnervation of the nucleus basalis of Meynert in Alzheimer's disease and Lewy body disorders

AIMS

Galanin is a highly inducible neuroprotective neuropeptide and in Alzheimer's disease (AD), a network of galaninergic fibres has been reported to hypertrophy and hyperinnervate the surviving cholinergic neurons in the basal forebrain. We aimed to determine (i) the extent of galanin hyperinnervation in patients with AD and Lewy body disease and (ii) whether galanin expression relates to the neuropathological burden and cholinergic losses.

METHODS

Galanin immunohistochemistry was carried out in the anterior nucleus basalis of Meynert of 27 Parkinson's disease (PD) cases without cognitive impairment (mild cognitive impairment [MCI]), 15 with PD with MCI, 42 with Parkinson's disease dementia (PDD), 12 with Dementia with Lewy bodies (DLB), 19 with AD, 12 mixed AD/DLB and 16 controls. Galaninergic innervation of cholinergic neurons was scored semiquantitatively. For a subgroup of cases (n = 60), cholinergic losses were determined from maximum densities of choline acetyltransferase positive (ChAT+ve) neurons and their projection fibres. Quantitative data for α-synuclein, amyloid beta and tau pathology were obtained from tissue microarrays covering cortical/subcortical regions.

RESULTS

Significant losses of cholinergic neurons and their projection fibres were observed across all diseases. Galaninergic hyperinnervation was infrequent and particularly uncommon in established AD and DLB. We found that hyperinnervation frequencies are significantly higher in the transition between PD without MCI to PDD and that higher burdens of co-existent AD pathology impair this galaninergic response.

CONCLUSIONS

Our results suggest that galanin upregulation represents an intrinsic response early in Lewy body diseases but which fails with increasing burdens of AD related pathology.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

Imaging and Molecular Mechanisms of Alzheimer's Disease: A Review

Alzheimer's disease is the most common form of dementia and is a significant burden for affected patients, carers, and health systems. Great advances have been made in understanding its pathophysiology, to a point that we are moving from a purely clinical diagnosis to a biological one based on the use of biomarkers. Among those, imaging biomarkers are invaluable in Alzheimer's, as they provide an in vivo window to the pathological processes occurring in Alzheimer's brain. While some imaging techniques are still under evaluation in the research setting, some have reached widespread clinical use. In this review, we provide an overview of the most commonly used imaging biomarkers in Alzheimer's disease, from molecular PET imaging to structural MRI, emphasising the concept that multimodal imaging would likely prove to be the optimal tool in the future of Alzheimer's research and clinical practice.

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.

Serotonin, β-amyloid, and cognition in Parkinson disease

OBJECTIVE

Serotoninergic neurotransmission may modulate β-amyloid peptide (Aβ) metabolism through upregulation of α-secretase. Early Parkinson disease (PD) shows variable serotoninergic denervation, which may impact Aβ deposition.

METHODS

We conducted 3 analyses to explore associations between serotoninergic neurotransmission and cerebral Aβ burden in PD. The first was a cross-sectional imaging study of PD subjects (n = 23) using the serotoninergic transporter positron emission tomography (PET) ligand [11 C]3-amino-4-(2-dimethylaminomethyl-phenylsulfaryl)-benzonitrile (DASB) and amyloid PET Pittsburgh compound B ([11 C]PiB). The second was a baseline study of Parkinson's Progression Markers Initiative (PPMI) subjects exploring the influence of serotoninergic medications on cerebrospinal fluid (CSF) Aβ-42 levels (n = 389), controlling for age, sex, Geriatric Depression Scale, disease duration, and education. Third, we fit an interval censored proportional hazard model with longitudinal PPMI data (n = 367) to test whether serotoninergic medication use associates with reduced risk of PD cognitive decline, defined as time to reach a Montreal Cognitive Assessment score ≤ 20, adjusting for baseline caudate dopamine transporter [123 I]ioflupane single photon emission computed tomography and CSF Aβ-42 levels.

RESULTS

Serotoninergic DASB distribution volume ratio (DVR) inversely associated with PiB DVR in the cerebral cortex (Pearson r = -0.478, p = 0.021) but not the striatum (r = -0.264, p = 0.224). In the baseline PPMI analysis, serotoninergic medication use for ≥6 months associated with a lower level of CSF Aβ-42 (t = -2.20, p = 0.029). In the longitudinal PPMI model, baseline serotoninergic medication use associated with a reduced risk of cognitive decline (t = -2.03, p = 0.043) after controlling for covariates.

INTERPRETATION

Cortical Aβ burden in PD associates inversely with serotoninergic innervation. Serotoninergic medications may alter Aβ metabolism and reduce the risk of PD cognitive decline. Ann Neurol 2018;83:994-1002.

Dementia with Lewy bodies and Parkinson's disease-dementia: current concepts and controversies

Dementia with Lewy bodies (DLB) and Parkinson's disease-dementia (PDD), although sharing many clinical, neurochemical and morphological features, according to DSM-5, are two entities of major neurocognitive disorders with Lewy bodies of unknown etiology. Despite considerable clinical overlap, their diagnosis is based on an arbitrary distinction between the time of onset of motor and cognitive symptoms: dementia often preceding parkinsonism in DLB and onset of cognitive impairment after onset of motor symptoms in PDD. Both are characterized morphologically by widespread cortical and subcortical α-synuclein/Lewy body plus β-amyloid and tau pathologies. Based on recent publications, including the fourth consensus report of the DLB Consortium, a critical overview is given. The clinical features of DLB and PDD include cognitive impairment, parkinsonism, visual hallucinations, and fluctuating attention. Intravitam PET and post-mortem studies revealed more pronounced cortical atrophy, elevated cortical and limbic Lewy pathologies (with APOE ε4), apart from higher prevalence of Alzheimer pathology in DLB than PDD. These changes may account for earlier onset and greater severity of cognitive defects in DLB, while multitracer PET studies showed no differences in cholinergic and dopaminergic deficits. DLB and PDD sharing genetic, neurochemical, and morphologic factors are likely to represent two subtypes of an α-synuclein-associated disease spectrum (Lewy body diseases), beginning with incidental Lewy body disease-PD-nondemented-PDD-DLB (no parkinsonism)-DLB with Alzheimer's disease (DLB-AD) at the most severe end, although DLB does not begin with PD/PDD and does not always progress to DLB-AD, while others consider them as the same disease. Both DLB and PDD show heterogeneous pathology and neurochemistry, suggesting that they share important common underlying molecular pathogenesis with AD and other proteinopathies. Cognitive impairment is not only induced by α-synuclein-caused neurodegeneration but by multiple regional pathological scores. Recent animal models and human post-mortem studies have provided important insights into the pathophysiology of DLB/PDD showing some differences, e.g., different spreading patterns of α-synuclein pathology, but the basic pathogenic mechanisms leading to the heterogeneity between both disorders deserve further elucidation. In view of the controversies about the nosology and pathogenesis of both syndromes, there remains a pressing need to differentiate them more clearly and to understand the processes leading these synucleinopathies to cause one disorder or the other. Clinical management of both disorders includes cholinesterase inhibitors, other pharmacologic and nonpharmacologic strategies, but these have only a mild symptomatic effect. Currently, no disease-modifying therapies are available.

Molecular Imaging and Updated Diagnostic Criteria in Lewy Body Dementias

PURPOSE OF REVIEW

The aims of the study were to review recent advances in molecular imaging in the Lewy body dementias (LBD) and determine if these may support the clinical but contested temporal profile distinction between Parkinson disease (PD) with dementia (PDD) versus dementia with Lewy bodies (DLB).

RECENT FINDINGS

There do not appear to be major regional cerebral metabolic or neurotransmitter distinctions between PDD and DLB. However, recent studies highlight the relative discriminating roles of Alzheimer proteinopathies. PDD patients have lower cortical β-amyloid deposition than DLB. Preliminary tau PET studies suggest a gradient of increasing tau binding from cognitively normal PD (absent to lowest) to cognitively impaired PD (low) to DLB (intermediate) to Alzheimer disease (AD; highest). However, tau binding in DLB, including the medial temporal lobe, is substantially lower than in AD. Alzheimer-type proteinopathies appear to be more common in DLB compared to PDD with relative but no absolute differences. Given the spectrum of overlapping pathologies, future α-synuclein ligands are expected to have the best potential to distinguish the LBD from pure AD.

Interactions of pathological proteins in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease (AD), frontotemporal lobar degeneration (FTD), Lewy body disease (LBD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) have in common that protein aggregates represent pathological hallmark lesions. Amyloid β-protein, τ-protein, α-synuclein, and TDP-43 are the most frequently aggregated proteins in these disorders. Although they are assumed to form disease-characteristic aggregates, such as amyloid plaques and neurofibrillary tangles in AD or Lewy bodies in LBD/PD, they are not restricted to these clinical presentations. They also occur in non-diseased individuals and can co-exist in the same brain without or with a clinical picture of a distinct dementing or movement disorder. In this review, we discuss the co-existence of these pathologies and potential additive effects in the human brain as well as related functional findings on cross-seeding and molecular interactions between these aggregates/proteins. We conclude that there is evidence for interactions at the molecular level as well as for additive effects on brain damage by multiple pathologies occurring in different functionally important neurons. Based upon this information, we hypothesize a cascade of events that may explain general mechanisms in the development of neurodegenerative disorders: (1) distinct lesions are a prerequisite for the development of a distinct disease (e.g., primary age-related tauopathy for AD), (2) disease-specific pathogenic events further trigger the development of a specific disease (e.g., Aβ aggregation in AD that exaggerate further Aβ and AD-related τ pathology), (3) the symptomatic disease manifests, and (4) neurodegenerative co-pathologies may be either purely coincidental or (more likely) have influence on the disease development and/or its clinical presentation.

Regional Overlap of Pathologies in Lewy Body Disorders

Lewy body disorders (LBD) are common neurodegenerative diseases characterized by the presence of aggregated α-synuclein in Lewy bodies and Lewy neurites in the central and peripheral nervous systems. The brains of patients with LBD often display other comorbid pathologies, i.e. insoluble tau, β-amyloid aggregates, TAR DNA-binding protein 43 (TDP-43) deposits, and argyrophilic grain disease (AGD). The incidence and physiological relevance of these concurrent pathological findings remain controversial. We performed a semiquantitative detailed mapping of α-synuclein, tau, β-amyloid (Aβ), TDP-43, and AGD pathologies in 17 areas in 63 LBD cases (44 with Parkinson disease [PD], 28 with dementia, and 19 with dementia with Lewy bodies). APOE and MAPT genetic variants were also investigated. A majority of LBD cases had 2 or 3 concomitant findings, particularly Alzheimer disease-related pathology. Pathological stages of tau, β-amyloid and α-synuclein pathologies were increased in cases with dementia. Aβ score was the best correlate of the time to dementia in PD. In addition, β-amyloid deposition correlated with α-synuclein load in all groups. MAPT H1 haplotype did not influence any assessed pathology in PD. These results highlight the common concurrence of pathologies in patients with LBD that may have an impact on the clinical expression of the diseases.

Differential expression of galanin in the cholinergic basal forebrain of patients with Lewy body disorders

INTRODUCTION

Depletion of cholinergic neurons within the nucleus basalis of Meynert (nbM) is thought to contribute to the development of cognitive impairments in both Alzheimer's disease (AD) and Lewy body disorders (LBD). It has been reported that, in late stage AD, a network of fibres that contain the neuropeptide galanin displays significant hypertrophy and 'hyperinnervates' the surviving cholinergic neurons. Galanin is considered as a highly inducible neuroprotective factor and in AD this is assumed to be part of a protective tissue response. The aim of this study was to determine if a similar galanin upregulation is present in the nbM in post-mortem tissue from patients with LBD. Gallatin immunohistochemistry was carried out on anterior nbM sections from 76 LBD cases (27 PD, 15 PD with mild cognitive impairment (MCI), 34 PD with dementia (PDD) and 4 aged-matched controls. Galaninergic innervation of cholinergic neurons was assessed on a semi-quantitative scale.

RESULTS

The LBD group had significantly higher galaninergic innervation scores (p = 0.016) compared to controls. However, this difference was due to increased innervation density only in a subgroup of LBD cases and this correlated positively with choline acetyltransferase-immunopositive neuron density.

CONCLUSION

Galanin upregulation within the basal forebrain cholinergic system in LBD, similar to that seen in AD, may represent an intrinsic adaptive response to neurodegeneration that is consistent with its proposed roles in neurogenesis and neuroprotection.

Striatal and Cortical β-Amyloidopathy and Cognition in Parkinson's Disease

INTRODUCTION

Although most previous cognitive studies of β-amyloidopathy in PD focused on cortical plaque deposition, recent postmortem studies point to an important role of striatal β-amyloid plaque deposition. The aim of this study was to investigate the relative contributions of striatal and cortical β-amyloidopathy to cognitive impairment in PD.

METHODS

Patients with PD (n = 62; age, 68.9 ± 6.4 years; H & Y stage: 2.7 ± 0.5; MoCA score: 25.2 ± 3.0) underwent [(11) C]Pittsburgh compound B β-amyloid, [(11) C]dihydrotetrabenazine monoaminergic, and [(11) C]methyl-4-piperidinyl propionate acetylcholinesterase brain PET imaging and neuropsychological assessment. [(11) C]Pittsburgh compound B β-amyloid data from young to middle-aged healthy subjects were used to define elevated [(11) C]Pittsburgh compound B binding in patients.

RESULTS

Elevated cortical and striatal β-amyloid deposition were present in 37% and 16%, respectively, of this predominantly nondemented cohort of patients with PD. Increased striatal β-amyloid deposition occurred in half of all subjects with increased cortical β-amyloid deposition. In contrast, increased striatal β-amyloid deposition did not occur in the absence of increased cortical β-amyloid deposition. Analysis of covariance using global composite cognitive z scores as the outcome parameter showed significant regressor effects for combined striatal and cortical β-amyloidopathy (F = 4.18; P = 0.02) after adjusting for covariate effects of cortical cholinergic activity (F = 5.67; P = 0.02), caudate nucleus monoaminergic binding, duration of disease, and age (total model: F = 3.55; P = 0.0048). Post-hoc analysis showed significantly lower cognitive z score for combined striatal and cortical β-amyloidopathy, compared to cortical-only β-amyloidopathy and non-β-amyloidopathy subgroups.

CONCLUSIONS

The combined presence of striatal and cortical β-amyloidopathy is associated with greater cognitive impairment than cortical β-amyloidopathy alone in PD.

Regional Multiple Pathology Scores Are Associated with Cognitive Decline in Lewy Body Dementias

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) are characterized by the presence of α-synuclein-containing Lewy bodies and Lewy neurites. However, both dementias also show variable degrees of Alzheimer's disease (AD) pathology (senile plaques and neurofibrillary tangles), particularly in areas of the cortex associated with higher cognitive functions. This study investigates the contribution of the individual and combined pathologies in determining the rate of cognitive decline. Cortical α-synuclein, phosphorylated tau (phosphotau) and Aβ plaque pathology in 34 PDD and 55 DLB patients was assessed semi-quantitatively in four regions of the neocortex. The decline in cognition, assessed by Mini Mental State Examination, correlated positively with the cortical α-synuclein load. Patients also had varying degrees of senile Aβ plaque and phosphotau pathology. Regression analyses pointed to a combined pathology (Aβ plaque plus phosphotau plus α-synuclein-positive features), particularly in the prefrontal cortex (BA9) and temporal lobe neocortex with the superior and middle temporal gyrus (BA21, 22), being a major determining factor in the development of dementia. Thus, cognitive decline in Lewy body dementias is not a consequence of α-synuclein-induced neurodegeneration alone but senile plaque and phosphorylated tau pathology also contribute to the overall deficits.

Nucleus basalis of Meynert revisited: anatomy, history and differential involvement in Alzheimer's and Parkinson's disease

It has been well established that neuronal loss within the cholinergic nucleus basalis of Meynert (nbM) correlates with cognitive decline in dementing disorders such as Alzheimer's disease (AD). Friedrich Lewy first observed his eponymous inclusion bodies in the nbM of postmortem brain tissue from patients with Parkinson's disease (PD) and cell loss in this area can be at least as extensive as that seen in AD. There has been confusion with regard to the terminology and exact localisation of the nbM within the human basal forebrain for decades due to the diffuse and broad structure of this "nucleus". Also, while topographical projections from the nbM have been mapped out in subhuman primates, no direct clinicopathological correlations between subregional nbM and cortical pathology and specific cognitive profile decline have been performed in human tissue. Here, we review the evolution of the term nbM and the importance of standardised nbM sampling for neuropathological studies. Extensive review of the literature suggests that there is a caudorostral pattern of neuronal loss within the nbM in AD brains. However, the findings in PD are less clear due to the limited number of studies performed. Given the differing neuropsychiatric and cognitive deficits in Lewy body-associated dementias (PD dementia and dementia with Lewy bodies) as compared to AD, we hypothesise that a different pattern of neuronal loss will be found in the nbM of Lewy body disease brains. Understanding the functional significance of the subregions of the nbM could prove important in elucidating the pathogenesis of dementia in PD.

System-based approaches to decode the molecular links in Parkinson's disease and diabetes

A growing body of evidence indicates an increased risk for developing Parkinson's disease (PD) among people with type 2 diabetes (T2DM). The relationship between the etiology and development of both chronic diseases is beginning to be uncovered and recent studies show that PD and T2DM share remarkably similar dysregulated pathways. It has been proposed that a cascade of events including mitochondrial dysfunction, impaired insulin signaling, and metabolic inflammation trigger neurodegeneration in T2DM models. Network-based approaches have elucidated a potential molecular framework linking both diseases. Further, transcriptional signatures that modulate the neurodegenerative phenotype in T2DM have been identified. Here we contextualize the current experimental approaches to dissect the mechanisms underlying the association between PD and T2DM and discuss the existing challenges toward the understanding of the coexistence of these devastating aging diseases.

Evaluation of the cerebrospinal fluid amyloid-β1-42/amyloid-β1-40 ratio measured by alpha-LISA to distinguish Alzheimer's disease from other dementia disorders

BACKGROUND

The well-established core biomarkers used to identify Alzheimer's disease (AD) overlap with other dementia disorders such as dementia with Lewy bodies (DLB) and Parkinson's disease with dementia (PDD). This study aimed to evaluate whether the cerebrospinal fluid (CSF) amyloid-β (Aβ)1-42/Aβ1-40 ratio, measured by a novel method, could improve the differential diagnosis of AD, DLB and PDD.

METHOD

CSF levels of Aβ1-40 and Aβ1-42 in patients with PDD, DLB, AD, Parkinson's disease and controls were analyzed using an amplified luminescent proximity homogenous immunoassay along with conventional immunoassays.

RESULTS

The CSF Aβ1-42/Aβ1-40 ratio increased discrimination of AD from PDD and DLB compared with either of the two Aβ biomarkers individually.

CONCLUSION

The use of the Aβ1-42/Aβ1-40 ratio could improve the differentiation of AD from PDD and DLB.

Using Pittsburgh Compound B for in vivo PET imaging of fibrillar amyloid-beta

The development of Aβ-PET imaging agents has allowed for detection of fibrillar Aβ deposition in vivo and marks a major advancement in understanding the role of Aβ in Alzheimer's disease (AD). Imaging Aβ thus has many potential clinical benefits: early or perhaps preclinical detection of disease and accurately distinguishing AD from dementias of other non-Aβ causes in patients presenting with mild or atypical symptoms or confounding comorbidities (in which the distinction is difficult to make clinically). From a research perspective, imaging Aβ allows us to study relationships between amyloid pathology and changes in cognition, brain structure, and function across the continuum from normal aging to mild cognitive impairment (MCI) to AD; and to monitor the effectiveness of anti-Aβ drugs and relate them to neurodegeneration and clinical symptoms. Here, we will discuss the application of one of the most broadly studied and widely used Aβ imaging agents, Pittsburgh Compound-B (PiB).

Can we clinically diagnose dementia with Lewy bodies yet?

Dementia with Lewy Bodies (DLB) was initially identified and confirmed primarily by pathology, but is soon to be incorporated into the Diagnostic and Statistical Manual criteria as a clinical disease entity. Despite these advances over more than 20 years, current data suggest that the sensitivity of accurate clinical diagnosis of DLB is still very low, although there is mounting evidence that supportive features may increase diagnostic accuracy. Although DLB remains easy to identify pathologically with different cellular pathologies differentiating it from other dementia syndromes, pathological identification using only Lewy body pathology has been shown to be inaccurate due to overlap with patients without dementia symptoms. A number of studies now suggest that a combination of cellular pathologies, which include α-synuclein and β-amyloid deposition as well as dopamine denervation, assist with differentiating this dementia syndrome from others. The clinical and pathological overlap with the tauopathy of Alzheimer's disease still remains to be clarified. To determine more robust and independent clinicopathological correlates from Alzheimer's disease, longitudinal prospective studies, using specific clinical batteries on dementia patients reaching the proposed criteria for DLB, with post-mortem assessment of the multiple pathologies associated with dementia, are required. Identifying genetic causes for DLB is another approach to investigate the pathogenesis of DLB. However this approach has been hindered to date by difficulties with identifying DLB clinically. The use of novel techniques is likely to advance knowledge on the pathogenesis of DLB and assist with redefining clinical and pathologic diagnostic criteria. To achieve the goal of more accurate clinical diagnosis of DLB, breakthroughs are necessary on the pathogenesis of DLB.

Striatal amyloid plaque density predicts Braak neurofibrillary stage and clinicopathological Alzheimer's disease: implications for amyloid imaging

Amyloid imaging may revolutionize Alzheimer's disease (AD) research and clinical practice but is critically limited by an inadequate correlation between cerebral cortex amyloid plaques and dementia. Also, amyloid imaging does not indicate the extent of neurofibrillary tangle (NFT) spread throughout the brain. Currently, the presence of dementia as well as a minimal brain load of both plaques and NFTs is required for the diagnosis of AD. Autopsy studies suggest that striatal amyloid plaques may be mainly restricted to subjects in higher Braak NFT stages that meet clinicopathological diagnostic criteria for AD. Striatal plaques, which are readily identified by amyloid imaging, might therefore be used to predict the presence of a higher Braak NFT stage and clinicopathological AD in living subjects. This study determined the sensitivity and specificity of striatal plaques for predicting a higher Braak NFT stage and clinicopathological AD in a postmortem series of 211 elderly subjects. Subjects included 87 clinicopathologically classified as non-demented elderly controls and 124 with AD. A higher striatal plaque density score (moderate or frequent) had 95.8% sensitivity, 75.7% specificity for Braak NFT stage V or VI and 85.6% sensitivity, 86.2% specificity for the presence of dementia and clinicopathological AD (National Institute on Aging - Reagan Institute "intermediate" or "high"). Amyloid imaging of the striatum may be useful as a predictor, in living subjects, of Braak NFT stage and the presence or absence of dementia and clinicopathological AD. Validation of this hypothesis will require autopsy studies of subjects that had amyloid imaging during life.

CSF and clinical hallmarks of subcortical dementias: focus on DLB and PDD

Dementia has become a relevant problem associated with the elderly in our countries. Increased interest in the field has yielded a copious literature, so far mostly centered on Alzheimer's dementia. Cerebrospinal fluid (CSF) analysis combined with neuropsychology, even in absence of neuroimaging, represents the gold standard to reach a diagnosis when cortical cognitive impairment prevails. In view of this, low levels of CSF amyloid peptides β (Aβ) and high tau/Aβ protein ratio, despite prominent impairment of executive functions or concomitant vascular burden, facilitate the diagnosis of Alzheimer's disease. Conversely, an early cognitive impairment occurring in patients suffering from Parkinson's disease (PD) or Lewy body disorders (LBDs), both diagnoses posed on pure clinical grounds, remains quite elusive in term of biomarkers or neuropsychological assessment. Whether PD with dementia (PDD) and dementia with Lewy bodies (DLB) represent further steps along with a continuum of the same progressive degeneration due to Lewy bodies deposition, rather then the association of Lewy bodies and Aβ pathology, remains a challenging issue. Aim of this work is to set a state-of-the-art on the neuropsychological profiles of both or DLB. Then, we will focus on the ongoing controversies about the specificity of the standard CSF biomarkers if applied to extrapyramidal disorders. Our conclusions are that the CSF pattern, in PDD and DLB, can certainly be distinct from that in AD, though mechanisms leading to dementia could be shared among them. It is possible that, by combining imaging tracers, neuropsychologically careful assessment and renewed CSF biomarkers, DLB can be better distinguished in subgroups, depending on the presence or absence of a relevant amyloid burden. However, more complete data, possibly collected in fieri during the progressive derangement of cognitive abilities, are needed to improve our ability to decipher and treat these entities.

Presence of Striatal Amyloid Plaques in Parkinson's Disease Dementia Predicts Concomitant Alzheimer's Disease: Usefulness for Amyloid Imaging

Dementia is a frequent complication of Parkinson's disease (PD). About half of PD dementia (PDD) is hypothesized to be due to progression of the underlying Lewy body pathology into limbic regions and the cerebral cortex while the other half is thought to be due to coexistent Alzheimer's disease. Clinically, however, these are indistinguishable. The spread of amyloid plaques to the striatum has been reported to be a sensitive and specific indicator of dementia due to Alzheimer's disease (AD). The purpose of the present study was to determine if the presence of striatal plaques might also be a useful indicator of the presence of diagnostic levels of AD pathology within PD subjects. We analyzed neuropathologically-confirmed cases of PD without dementia (PDND, N = 31), PDD without AD (PDD, N = 31) and PD with dementia meeting clinicopathological criteria for AD (PDAD, N =40). The minimum diagnostic criterion for AD was defined as including a clinical history of dementia, moderate or frequent CERAD cortical neuritic plaque density and Braak neurofibrillary stage III-VI. Striatal amyloid plaque densities were determined using Campbell-Switzer and Thioflavine S stains. Striatal plaque densities were significantly higher in PDAD compared to PDD (p<0.001). The presence of striatal plaques was approximately 80% sensitive and 80% specific for predicting AD. In comparison, the presence of cerebral cortex plaques alone was highly sensitive (100%) but had poor specificity (48% to 55%). The results suggest that striatal amyloid imaging may be clinically useful for making the distinction between PDD and PDAD.