Development of a new CERAD Total Score in Individuals with Parkinson’s Disease: Evidence from the LANDSCAPE Study

Introduction. The Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) is a renowned cognitive test battery for the assessment of cognitive functioning across various neurological conditions, including Parkinson’s Disease (PD). Its German extension, the CERAD-Plus, with additional subscales assessing executive functions and processing speed might offer additional diagnostic value as these two cognitive domains rank among the most vulnerable in individuals with PD. The most established CERAD total score (TS) proposed by Chandler and colleagues is based on arbitrarily selected raw values of the restricted CERAD test battery. Objective. The aim of the thesis project was the development of a new CERAD-TS in individuals with PD based on all available subtests of the extended CERAD-Plus test battery using age-, gender-, and education-corrected z-scores to ultimately test and compare its diagnostic utility with the established Chandler CERAD TS and common PD-screening tools. Methods. The present thesis project analyzed baseline data of 679 individuals with PD of varying cognitive abilities (67.6% male, n = 277 with normal cognition (PD-N), n = 307 with impaired cognition (PD-MCI), n = 95 with dementia (PD-D)) from the multicenter, prospective DEMPREAK/LANDSCAPE cohort. For the comparisons of four different TS based either on the original CERAD or the CERAD-Plus battery with varying weighting of subtests (e.g., rawscores, z-scores or factor-scores) receiver operating characteristics (ROC-) analyses were conducted. Comparisons of the areas under the curve (AUC) were run to identify the most parsimonious TS amongst the four tested TS. Results. The newly designed CERAD-Plus TS based on equally-weighted z-scores proved to be the most accurate and parsimonious TS when discriminating between individuals with PD of varying cognitive impairment (0.78 < AUC < 0.98). Not only was this TS superior to the Chandler CERAD-TS, but the new CERAD-Plus TS also outperformed cognitive screening instruments, such as the Mini Mental Status Examination (MMSE) or the PD-specific Parkinson Neuropsychometric Dementia Assessment (PANDA). Conclusion. Results of this thesis project highlight the importance of non-amnestic CERADPlus subscales (e.g., executive functions and processing speed) in the assessment of cognitive capacities in PD populations with different cognitive functioning, especially at an early stage of disease. An accurate and early diagnosis of PD is the prerequisite for early disease management and subsequent monitoring of disease progression. The new CERAD-Plus TS needs further validation and could prove to be of diagnostic value in non-PD populations as well

Redox proteomics of the inflammatory secretome identifies a common set of redoxins and other glutathionylated proteins released in inflammation, influenza virus infection and oxidative stress

Protein cysteines can form transient disulfides with glutathione (GSH), resulting in the production of glutathionylated proteins, and this process is regarded as a mechanism by which the redox state of the cell can regulate protein function. Most studies on redox regulation of immunity have focused on intracellular proteins. In this study we have used redox proteomics to identify those proteins released in glutathionylated form by macrophages stimulated with lipopolysaccharide (LPS) after pre-loading the cells with biotinylated GSH. Of the several proteins identified in the redox secretome, we have selected a number for validation. Proteomic analysis indicated that LPS stimulated the release of peroxiredoxin (PRDX) 1, PRDX2, vimentin (VIM), profilin1 (PFN1) and thioredoxin 1 (TXN1). For PRDX1 and TXN1, we were able to confirm that the released protein is glutathionylated. PRDX1, PRDX2 and TXN1 were also released by the human pulmonary epithelial cell line, A549, infected with influenza virus. The release of the proteins identified was inhibited by the anti-inflammatory glucocorticoid, dexamethasone (DEX), which also inhibited tumor necrosis factor (TNF)-α release, and by thiol antioxidants (N-butanoyl GSH derivative, GSH-C4, and N-acetylcysteine (NAC), which did not affect TNF-α production. The proteins identified could be useful as biomarkers of oxidative stress associated with inflammation, and further studies will be required to investigate if the extracellular forms of these proteins has immunoregulatory functions

Cysteine oxidation targets peroxiredoxins 1 and 2 for exosomal release through a novel mechanism of redox-dependent secretion

Non-classical protein secretion is of major importance as a number of cytokines and inflammatory mediators are secreted via this route. Current evidence indicates that there are several mechanistically distinct methods of non-classical secretion. We have recently shown that peroxiredoxin (Prdx) 1 and Prdx2 are released by various cells upon exposure to inflammatory stimuli such as LPS or TNF-α. The released Prdx then acts to induce production of inflammatory cytokines. However, Prdx1 and 2 do not have signal peptides and therefore must be secreted by alternative mechanisms as has been postulated for the inflammatory mediators IL-1β and HMGB1. We show here that circulating Prdx1 and 2 are present exclusively as disulphide-linked homodimers. Inflammatory stimuli also induce in vitro release of Prdx1 and 2 as disulfide-linked homodimers. Mutation of cysteines Cys51 or Cys172 (but not Cys70) in Prdx2, and Cys52 or Cys173 (but not Cys71 or Cys83) in Prdx1 prevented dimer formation and this was associated with inhibition of their TNF-α-induced release. Thus, the presence and oxidation of key cysteine residues in these proteins are a prerequisite for their secretion in response to TNF-α and this release can be induced with an oxidant. In contrast, the secretion of the nuclear-associated danger signal HMGB1 is independent of cysteine oxidation, as shown by experiments with a cysteine-free HMGB1 mutant. Release of Prdx1 and 2 is not prevented by inhibitors of the classical secretory pathway; instead, both Prdx1 and 2 are released in exosomes from both HEK cells and monocytic cells. Serum Prdx1 and 2 are also associated with the exosomes. These results describe a novel pathway of protein secretion mediated by cysteine oxidation that underlines the importance of redox-dependent signalling mechanisms in inflammation