Concomitant protein pathogenesis in Parkinson's disease and perspective mechanisms

Evaluating the Diagnostic Potential of Combined Salivary and Skin Biomarkers in Parkinson's Disease

Oligomeric alpha-synuclein (α-syn) in saliva and phosphorylated α-syn deposits in the skin have emerged as promising diagnostic biomarkers for Parkinson's disease (PD). This study aimed to assess and compare the diagnostic value of these biomarkers in discriminating between 38 PD patients and 24 healthy subjects (HSs) using easily accessible biological samples. Additionally, the study sought to determine the diagnostic potential of combining these biomarkers and to explore their correlations with clinical features. Salivary oligomeric α-syn levels were quantified using competitive ELISA, while skin biopsies were analyzed through immunofluorescence to detect phosphorylated α-syn at Ser129 (p-S129). Both biomarkers individually were accurate in discriminating PD patients from HSs, with a modest agreement between them. The combined positivity of salivary α-syn oligomers and skin p-S129 aggregates differentiated PD patients from HSs with an excellent discriminative ability with an AUC of 0.9095. The modest agreement observed between salivary and skin biomarkers individually suggests that they may reflect different aspects of PD pathology, thus providing complementary information when combined. This study's results highlight the potential of utilizing a multimodal biomarker approach to enhance diagnostic accuracy in PD.

Pathobiology of Cognitive Impairment in Parkinson Disease: Challenges and Outlooks

Cognitive impairment (CI) is a characteristic non-motor feature of Parkinson disease (PD) that poses a severe burden on the patients and caregivers, yet relatively little is known about its pathobiology. Cognitive deficits are evident throughout the course of PD, with around 25% of subtle cognitive decline and mild CI (MCI) at the time of diagnosis and up to 83% of patients developing dementia after 20 years. The heterogeneity of cognitive phenotypes suggests that a common neuropathological process, characterized by progressive degeneration of the dopaminergic striatonigral system and of many other neuronal systems, results not only in structural deficits but also extensive changes of functional neuronal network activities and neurotransmitter dysfunctions. Modern neuroimaging studies revealed multilocular cortical and subcortical atrophies and alterations in intrinsic neuronal connectivities. The decreased functional connectivity (FC) of the default mode network (DMN) in the bilateral prefrontal cortex is affected already before the development of clinical CI and in the absence of structural changes. Longitudinal cognitive decline is associated with frontostriatal and limbic affections, white matter microlesions and changes between multiple functional neuronal networks, including thalamo-insular, frontoparietal and attention networks, the cholinergic forebrain and the noradrenergic system. Superimposed Alzheimer-related (and other concomitant) pathologies due to interactions between α-synuclein, tau-protein and β-amyloid contribute to dementia pathogenesis in both PD and dementia with Lewy bodies (DLB). To further elucidate the interaction of the pathomechanisms responsible for CI in PD, well-designed longitudinal clinico-pathological studies are warranted that are supported by fluid and sophisticated imaging biomarkers as a basis for better early diagnosis and future disease-modifying therapies.

Evolution and Predictive Role of Plasma Alzheimer's Disease-related Pathological Biomarkers in Parkinson's Disease

Plasma Alzheimer's disease-related pathological biomarkers' role in Parkinson's disease (PD) remains unknown. We aimed to determine whether plasma Alzheimer's disease-related biomarkers can predict PD progression. A total of 184 PD patients and 86 healthy controls were included and followed up for 5 years. Plasma phosphorylated tau181 (p-tau181), Aβ40, and Aβ42 were measured at baseline and the 1- and 2-year follow-ups using the Quanterix-single-molecule array. Global cognitive function and motor symptoms were assessed using the Montreal Cognitive Assessment and Unified Parkinson's Disease Rating Scale part III. Genetic analyses were conducted to identify APOE and MAPT genotypes. Plasma p-tau181 levels were higher in PD than healthy controls. APOE-ε4 carriers had lower plasma Aβ42 levels and Aβ42/Aβ40 ratio. The linear mixed-effects models showed that Montreal Cognitive Assessment scores were associated with plasma p-tau181/Aβ42 ratio (β -1.719 [-3.398 to -0.040], p = .045). Higher baseline plasma p-tau181 correlated with faster cognitive decline and motor symptoms deterioration in total patients (β -0.170 [-0.322 to -0.018], p = .029; β 0.329 [0.032 to 0.626], p = .030) and APOE-ε4 carriers (β -0.318 [-0.602 to -0.034], p = .030; β 0.632 [0.017 to 1.246], p = .046), but not in the noncarriers. Higher baseline plasma Aβ40 correlated with faster cognitive decline in total patients (β -0.007 [-0.015 to -0.0001], p = .047) and faster motor symptoms deterioration in total patients (β 0.026 [0.010 to 0.041], p = .001) and APOE-ε4 carriers (β 0.044 [-0.026 to 0.049], p = .020), but not in the noncarriers. The plasma p-tau181/Aβ2 ratio monitors the cognitive status of PD. Higher baseline plasma p-tau181 and Aβ40 predict faster cognitive decline and motor symptoms deterioration in PD, especially in APOE-ε4 carriers.