Current Alzheimer Research - Volume 18, Issue 9, 2021

Biological rhythms have become the research focus in recent years. Biological rhythm disruption is a common symptom of Alzheimer's disease (AD) patients, which is usually considered as the late consequence of AD. Recent studies have shown that biological rhythm disruption even occurs before the onset of clinical symptoms of AD. The causal relationship between AD and biological rhythm disruption is not clear. Delineating their relationship can help understand the disease mechanisms and make the early diagnosis of AD possible. This review integrates the research on the abnormal changes of the biological rhythm-related parameters in the clinical manifestations of AD patients and the roles of the biological rhythm disorders in AD. We will discuss the links between biological rhythms and AD, with the focus on the bidirectionality between biological rhythms and AD processes. Collectively, these updated research findings may provide the basis for further exploring the significance of rhythm in the diagnosis and treatment of AD.

Alzheimer’s Disease (AD) is the most prevalent form of dementia across the world. While its discovery and pathological manifestations are centered on protein aggregations of amyloid- beta (Aβ) and hyperphosphorylated tau protein, neuroinflammation has emerged in the last decade as a main component of the disease in terms of both pathogenesis and progression. As the main innate immune cell type in the central nervous system (CNS), microglia play a very important role in regulating neuroinflammation, which occurs commonly in neurodegenerative conditions, including AD. Under inflammatory response, microglia undergo morphological changes and status transition from homeostatic to activated forms. Different microglia subtypes displaying distinct genetic profiles have been identified in AD, and these signatures often link to AD risk genes identified from the genome-wide association studies (GWAS), such as APOE and TREM2. Furthermore, many AD risk genes are highly enriched in microglia and specifically influence the functions of microglia in pathogenesis, e.g. releasing inflammatory cytokines and clearing Aβ. Therefore, building up a landscape of these risk genes in microglia, based on current preclinical studies and in the context of their pathogenic or protective effects, would largely help us to understand the complex etiology of AD and provide new insight into the unmet need for effective treatment.

Background: Patients with dementia have an increased risk of developing epilepsy, especially in patients with vascular dementia and Alzheimer’s disease. In selecting the optimal anti- epileptic drug (AED), the possible side effects such as drowsiness and worsening of cognitive function should be taken into consideration, together with co-morbidities and type of epilepsy. Objective: The current systematic review investigates the efficacy, tolerability, and changes in cognitive function after administration of AED in patients with dementia and epilepsy. Methods: We searched six databases, including MEDLINE and CENTRAL, checked reference lists, contacted experts, and searched Google Scholar to identify studies reporting randomized trials. Studies identified were independently screened, data extracted, and quality appraised by two researchers. A narrative synthesis was used to report findings. Results: We included one study with 95 patients with Alzheimer’s disease randomized to either levetiracetam, lamotrigine, or phenobarbital. No significant differences were found for efficacy, but patients receiving levetiracetam showed an improvement in mini-mental state examination scores and had fewer adverse events. Conclusion: High-quality evidence in the form of randomized controlled trials to guide clinicians in choosing an AED in patients with dementia and concomitant epilepsy remains scarce. However, levetiracetam has previously been shown to possibly improve cognition in patients with both mild cognitive impairment and Alzheimer’s disease, is better tolerated in the elderly population, and has no clinically relevant interaction with either cholinesterase inhibitors or NMDA receptor antagonists.

Aims: There are several candidate biomarkers for AD and PD which differ in sensitivity, specificity, cost-effectiveness, invasiveness, logistical and technical demands. This study is aimed to test whether plasma concentration of unfolded p53 may help to discriminate among the neurodegenerative processes occurring in Mild Cognitive Impairment, Alzheimer’s disease and Parkinson’s disease. Methods: An electrochemical immunosensor was used to measure unfolded p53 in plasma samples of 20 Mild Cognitive Impairment (13 males/7 females; mean age 74.95±5.31), 20 Alzheimer’s (11 males/9 females; mean age: 77.25±7.79), 15 Parkinson’s disease patients (12 males/3 females; mean age: 68.60 ± 7.36) and its respective age/sex/studies-matched controls. Results: We observed a significantly higher concentration of unfolded p53 in the plasma of patients of each of the three pathologies with respect to their control groups (p=0.000). Furthermore, the plasma concentration of unfolded p53 was significantly higher in Alzheimer’s disease patients in comparison with Mild Cognitive Impairment patients (p=0.000) and Parkinson’s disease patients (p=0.006). No significant difference between Mild Cognitive Impairment and Parkinson’s disease patients was observed (p=0.524). Conclusion: Our results suggest that unfolded p53 concentration in the plasma may be a useful biomarker for an undergoing neuropathological process that may be common, albeit with different intensity, to different diseases.

Background: As the most basic material, synthetic human Amyloid-β (1-42) (Aβ42) peptide from different manufacturers have been widely used. Their aggregation ability is vital to the reliability, repeatability and comparability of studies on Aβ42 physiology and pathology. However, it has not been evaluated and compared. Objective: To analyze the consistency of the aggregation ability of 5 commercially available Aβ42 peptide. Methods: 5 Aβ42 peptide represented as A, B, C, D and E were pretreated by HFIP. The pretreated Aβ42 peptide were dissolved in Thioflavin T (ThT) solution, and their aggregation kinetics was monitored for 30 h with the aggregation kinetics test. Meanwhile, the pretreated peptide were aggregated in phosphate buffered saline. After aggregated for 12 h, they were detected by methods of ThT fluorescence, far-UV circular dichroism (CD), SDS-PAGE, western blot, and transmission electron microscopy (TEM), respectively. After aggregation for 8 h and 12 h, their cytotoxicity to SH-SY5Y cells was further evaluated using Cell Counting Kit-8. Results: For aggregation kinetics, peptide A, C and E remained low level curves, while peptide B and D presented typical sigmoidal kinetics curves. In CD measurement, the aggregates of peptide B and D showed relatively high negative CD peaks with the height of -8.09 mdeg and -14.37 mdeg, while the height of peptide A, C and E was -1.04, -3.55, and -3.88. In ThT assay, relative fluorescence intensity of the aggregates of peptide B and D were 7.79 and 8.82, higher than 1.19, 1.71, and 2.70 of peptide A, C and E, respectively. In SDS-PAGE, all aggregates contained monomers and eleven polymers. Moreover, peptide B-E presented a trapezoidal distribution from dimers to trimers, and peptide A aggregated to dimers. By western blot, the bands of monomers remained in all aggregates. Furthermore, peptide B and D aggregated to dimers and trimers, peptide A and C only aggregated to dimers, and peptide E showed a strong band of trimers. By TEM, protofibrils were observed only in peptide B, while substantial spherical aggregates were formed in other peptide. Additionally, peptide B, D and E exhibited higher cytotoxicity after aggregated for 8 h, whereas peptide A, B and D presented relatively high cytotoxicity after 12-hour aggregation. Conclusion: Commercially available Aβ42 peptide showed obvious differences in aggregation ability, which should arouse enough attention in the field of basic study related to Aβ42. The aggregation ability evaluation with the various assay methods has some discrepancies, and it is highly urgent to establish a reasonable and uniform measurement strategy.

Background: Reduced cerebrovascular function and accumulation of tau pathology are key components of cognitive decline in Alzheimer’s disease (AD). Recent multimodal neuroimaging studies show a correlation between cortical tau accumulation and reduced cerebral perfusion. However, animal models predict that tau exerts capillary-level changes that may not be fully captured by standard imaging protocols. Objective: Using newly-developed magnetic resonance imaging (MRI) technology to measure capillary- specific perfusion parameters, we examined a series of mild cognitive impairment (MCI) and AD patients with tau positron emission tomography (PET) to observe whole-brain capillary perfusion alterations and their association with tau deposition. Methods: Seven subjects with MCI or AD received Flortaucipir PET to measure tau deposition and spin-echo dynamic susceptibility contrast (SE-DSC) MRI to measure microvascular perfusion (<10μm radius vessels). Gradient-echo (GE) DSC and pseudocontinuous arterial spin labeling (PCASL) MRI were also acquired to assess macrovascular perfusion. Tau PET, microvascular perfusion, and cortical thickness maps were visually inspected in volumetric slices and on cortical surface projections. Results: High tau PET signal was generally observed in the lateral temporal and parietal cortices, with uptake in the occipital cortex in one subject. Global blood flow measured by PCASL was reduced with increasing tau burden, which was consistent with previous studies. Tau accumulation was spatially associated with variable patterns of microvascular cerebral blood flow (CBF) and oxygen extraction fraction (OEF) in the cortex and with increased capillary transit heterogeneity (CTH) in adjacent periventricular white matter, independent of amyloid-β status. Conclusion: Although macrovascular perfusion generally correlated with tau deposition at the whole-cortex level, regional changes in microvascular perfusion were not uniformly associated with either tau pathology or cortical atrophy. This work highlights the heterogeneity of AD-related brain changes and the challenges of implementing therapeutic interventions to improve cerebrovascular function.

Background: Mild cognitive impairment (MCI) is a state between normal cognition and dementia. However, MCI diagnosis does not necessarily guarantee the progression to dementia. Since no previous study investigated brain positron emission tomography (PET) imaging of MCI-- to-normal reversion, we provided PET imaging of MCI- to-normal reversion using the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Methods: We applied comprehensive neuropsychological criteria (NP criteria), consisting of memory, language, and attention/executive function domains, to include patients with a baseline diagnosis of MCI (n=613). According to the criteria, the year 1 status of the patients was categorized into three groups (reversion: n=105, stable MCI: n=422, conversion: n=86). Demographic, neuropsychological, genetic, CSF, and cognition biomarker variables were compared between the groups. Additionally, after adjustment for confounding variables, the deposition pattern of amyloid-β and cerebral glucose metabolism were compared between three groups via AV45- and FDG-PET modalities, respectively. Results: MCI reversion rate was 17.1% during one year of follow-up. The reversion group had the lowest frequency of APOE 4+ subjects, the highest CSF level of amyloid-β, and the lowest CSF levels of t-tau and p-tau. Neuropsychological assessments were also suggestive of better cognitive performance in the reversion group. Patients with reversion to normal state had higher glucose metabolism in bilateral angular and left middle/inferior temporal gyri, when compared to those with stable MCI state. Meanwhile, lower amyloid-β deposition at baseline was observed in the frontal and parietal regions of the reverted subjects. On the other hand, the conversion group showed lower cerebral glucose metabolism in bilateral angular and bilateral middle/inferior temporal gyri compared to the stable MCI group, whereas the amyloid-β accumulation was similar between the groups. Conclusion: This longitudinal study provides novel insight regarding the application of PET imaging in predicting MCI transition over time.