Platelet phospholipase A2 activity in patients with Alzheimer’s disease, vascular dementia and ischemic stroke

Blood biomarkers for post-stroke cognitive impairment: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Post-stroke cognitive impairment (PSCI) is a frequent consequence of stroke, which affects the quality of life and prognosis of stroke survivors. Numerous studies have indicated that blood biomarkers may be the key determinants for predicting and diagnosing cognitive impairment, but the results remain varied. Therefore, this meta-analysis aims to summarize potential biomarkers associated with PSCI.

METHODS

PubMed, Web of Science, Embase, and Cochrane Library were comprehensively searched for studies exploring blood biomarkers associated with PSCI from inception to 15 April 2022.

RESULTS

63 studies were selected from 4,047 references, which involves 95 blood biomarkers associated with the PSCI. We meta-analyzed 20 potential blood biomarker candidates, the results shown that the homocysteine (Hcy) (SMD = 0.35; 95 %CI: 0.20-0.49; P < 0.00001), c-reactive protein (CRP) (SMD = 0.49; 95 %CI: 0.20-0.78; P = 0.0008), uric acid (UA) (SMD = 0.41; 95 %CI: 0.06-0.76; P = 0.02), interleukin 6 (IL-6) (SMD = 0.92; 95 % CI: 0.27-1.57; P = 0.005), cystatin C (Cys-C) (SMD = 0.58; 95 %CI: 0.28-0.87; P = 0.0001), creatinine (SMD = 0.39; 95 %CI: 0.23-0.55; P < 0.00001) and tumor necrosis factor alpha (TNF-α) (SMD = 0.45; 95 %CI: 0.08-0.82; P = 0.02) levels were significantly higher in patients with PSCI than in the non-PSCI group.

CONCLUSION

Based on our findings, we recommend that paramedics focus on the blood biomarkers levels of Hcy, CRP, UA, IL-6, Cys-C, creatinine and TNF-α in conjunction with neuroimaging and neuropsychological assessment to assess the risk of PSCI, which may help with early detection and timely preventive measures. At the same time, other potential blood biomarkers should be further validated in future studies.

Comparative Use of Contralateral and Sham-Operated Controls Reveals Traces of a Bilateral Genetic Response in the Rat Brain after Focal Stroke

Ischemic stroke is a multifactorial disease with a complex etiology and global consequences. Model animals are widely used in stroke studies. Various controls, either brain samples from sham-operated (SO) animals or symmetrically located brain samples from the opposite (contralateral) hemisphere (CH), are often used to analyze the processes in the damaged (ipsilateral) hemisphere (IH) after focal stroke. However, previously, it was shown that focal ischemia can lead to metabolic and transcriptomic changes not only in the IH but also in the CH. Here, using a transient middle cerebral artery occlusion (tMCAO) model and genome-wide RNA sequencing, we identified 1941 overlapping differentially expressed genes (DEGs) with a cutoff value >1.5 and Padj < 0.05 that reflected the general transcriptome response of IH subcortical cells at 24 h after tMCAO using both SO and CH controls. Concomitantly, 861 genes were differentially expressed in IH vs. SO, whereas they were not vs. the CH control. Furthermore, they were associated with apoptosis, the cell cycle, and neurotransmitter responses. In turn, we identified 221 DEGs in IH vs. CH, which were non-DEGs vs. the SO control. Moreover, they were predominantly associated with immune-related response. We believe that both sets of non-overlapping genes recorded transcriptome changes in IH cells associated with transhemispheric differences after focal cerebral ischemia. Thus, the specific response of the CH transcriptome should be considered when using it as a control in studies of target brain regions in diseases that induce a global bilateral genetic response, such as stroke.

Platelet total PLA2 activity, serum oxidative level and plasma Cu/Zn ratio: a vicious cycle with a potential role to monitor MCI and Alzheimer's disease progression

Alzheimer's disease (AD) has no cure, mainly because of late diagnosis. Early diagnostic biomarkers are crucial. Phospholipases A2 (PLA2) are hydrolases with several functions in the brain, nevertheless their deregulation contributes to neurodegeneration. We evaluated platelet total PLA2 activity (ptotPLA2) in healthy elderly subjects (HE, n = 102), patients suffering from Mild Cognitive Impairment (MCI, n = 90) and AD (n = 91). Platelets are considered "circulating neurons" and ptotPLA2 seems to mirror the cerebral activity. ptotPLA2 of the three cohorts was similar, but in MCI the higher ptotPLA2 the worse the global cognitive status (Mini Mental State Examination score, MMSE) and in AD the lower ptotPLA2 the more severe the pathology stage (Clinical Dementia Rating, CDR). Accordingly, MCI with MMSE ≥ 26 overlapped HE, in MCI with MMSE < 26 and in AD with CDR 1 ptotPLA2 increased, in AD with CDR 2 ptotPLA2 decreased. In MCI ptotPLA2 positively correlated with blood oxidation and inflammation, in AD it was the opposite. Finally, Discrimination Index (DI) - calculated multiplying ptotPLA2, oxidative level and Cu/Zn ratio (an inflammation parameter) - differentiated MCI patients who progressed to dementia in the following 24 months and AD patients with the worse pathology development. Summarizing, ptotPLA2 changes during MCI and AD progression, is linked, in opposite way, to oxidative/inflammatory status in MCI and AD and might help, when included in DI, to identify MCI converters to dementia and AD patients with the more severe prognosis. ptotPLA2 may have a diagnostic/prognostic value and be a potential therapeutic target.

C-type lectin-like receptor 2 and zonulin are associated with mild cognitive impairment and Alzheimer's disease

OBJECTIVE

Increased permeability and changes in gut microbiota contributed to the pathogenesis of Alzheimer's disease (AD). Zonulin is a key modulator that regulates intestinal barrier function. Peripheral platelet alterations have been involved in AD pathology. C-type lectin-like receptor 2 (CLEC-2) is a receptor on the platelet surface for activation. The purpose of this study was to determine zonulin and CLEC-2 levels in mild cognitive impairment (MCI) and AD, and investigate the relationship between zonulin and CLEC-2.

METHODS

In this study, CLEC-2 and zonulin levels were measured using ELISA assay in 110 AD patients, 110 MCI patients, and 110 non-demented control subjects.

RESULTS

Increased CLEC-2 and zonulin levels were observed in MCI and AD patients. Furthermore, AD patients had higher CLEC-2 and zonulin levels compared with MCI patients. In addition, CLEC-2 levels were positively correlated with zonulin levels, after adjusting confounding factors (r = .592, P < .001). Multivariate analysis revealed that increased CLEC-2 and zonulin levels were significantly associated with reduced Mini-Mental State Examination (MMSE) score.

CONCLUSIONS

C-type lectin-like receptor 2 is correlated with zonulin after adjusting confounding covariates. Moreover, increased CLEC-2 and zonulin are the significant factors for reduced MMSE score in MCI and AD. Further studies are needed.

Platelets: Peripheral Biomarkers of Dementia?

Dementia continues to be the most burdening neurocognitive disorder, having a negative impact on the lives of millions. The search for biomarkers to improve the clinical diagnosis of dementia is ongoing, with the focus on effective use of readily accessible peripheral markers. In this review, we concentrate on platelets as biomarkers of dementia and analyze their potential as easily-accessible clinical biomarkers for various subtypes of dementia. Current platelet protein biomarkers that have been investigated for their clinical utility in the diagnosis of dementia, in particular Alzheimer's disease, include amyloid-β protein precursor (AβPP), the AβPP secretases (BACE1 and ADAM10), α-synuclein, tau protein, serotonin, cholesterol, phospholipases, clusterin, IgG, surface receptors, MAO-B, and coated platelets. Few of them, i.e., platelet tau, AβPP (particularly with regards to coated platelets) and secreted ADAM10 and BACE1 show the most promise to be taken forward into clinical setting to diagnose dementia. Aside from protein biomarkers, changes in factors such as mean platelet volume have the potential to play a very specific role in both the dementia diagnosis and prognosis. This review raises a number of research questions for consideration before application of the above biomarkers to routine clinical setting. It is without doubt that there is a need for more clarification on the effects of dementia on platelet morphology and protein content before these changes can be clinically applied as dementia biomarkers and explored further in differentiating distinct dementia subtypes.

Cognitive Stimulation Modulates Platelet Total Phospholipases A2 Activity in Subjects with Mild Cognitive Impairment

We evaluated the effect of cognitive stimulation (CS) on platelet total phospholipases A2 activity (tPLA2A) in patients with mild cognitive impairment (MCI_P). At baseline, tPLA2A negatively correlated with Mini-Mental State Examination score (MMSE_s): patients with MMSE_s <26 (Subgroup 1) had significantly higher activity than those with MMSE_s ≥26 (Subgroup 2), who had values similar to the healthy elderly. Regarding CS effect, Subgroup 1 had a significant tPLA2A reduction, whereas Subgroup 2 did not significantly changes after training. Our results showed for the first time that tPLA2A correlates with the cognitive conditions of MCI_P, and that CS acts selectively on subjects with a dysregulated tPLA2A.

Platelets, a reliable source for peripheral Alzheimer's disease biomarkers?

Peripheral biomarkers play an indispensable role in quick and reliable diagnoses of any kind of disease. With the population ageing, the number of people suffering from age-related diseases is expected to rise dramatically over the coming decades. In particular, all types of cognitive deficits, such as Alzheimer's disease, will increase. Alzheimer's disease is characterised mainly by coexistence of amyloid plaques and neurofibrillary tangles in brain. Reliable identification of such molecular characteristics antemortem, however, is problematic due to restricted availability of appropriate sample material and definitive diagnosis is only possible postmortem. Currently, the best molecular biomarkers available for antemortem diagnosis originate from cerebrospinal fluid. Though, this is not convenient for routine diagnosis because of the required invasive lumbar puncture. As a consequence, there is a growing demand for additional peripheral biomarkers in a more readily accessible sample material. Blood platelets, due to shared biochemical properties with neurons, can constitute an attractive alternative as discussed here. This review summarises potential platelet Alzheimer's disease biomarkers, their role, implication, and alteration in the disease. For easy comparison of their performance, the Hedge effect size was calculated whenever data were available.

Mean platelet volume and platelet distribution width in vascular dementia and Alzheimer's disease

Activated platelets play a substantial role in Alzheimer's disease (AD) and atherothrombosis. Mean platelet volume (MPV) is an early marker of platelet activation, which is linked to a variety of pro-thrombotic and pro-inflammatory diseases. This study is to examine the association between platelet indices and vascular dementia (VaD) and AD. In this cross-sectional study, we investigated the levels of platelet count, MPV, and platelet distribution width (PDW) in 150 VaD patients, 110 AD patients, and 150 non-demented controls. MPV and PDW were significantly lower in patients with VaD and AD as compared with controls. The decrease in PDW for AD patients as compared with VaD patients was also significant (p < 0.001). In addition, there was a positive correlation between Mini-Mental State Examination (MMSE) and MPV and PDW, after adjusting confounding factors (r = 0.532 for MPV and r = 0.425 for PDW, p < 0.001 for both). Multivariate regression analysis showed that MPV and PDW were significantly associated with MMSE (β = 0.366 for MPV and β = 0.273 for PDW, p < 0.001 for both). In conclusion, MPV and PDW were both decreased in VaD and AD. PDW levels were significantly lower in AD as compared to those in VaD. Our findings suggest that PDW in combination with MMSE scores could be potential indicators for distinguishing VaD from AD.

Decreased mean platelet volume and platelet distribution width are associated with mild cognitive impairment and Alzheimer's disease

Neuroinflammation is a critical driving force underlying mild cognitive impairment (MCI) and Alzheimer's disease (AD) pathologies. Activated platelets play an important role in neuroinflammation and have been implicated in AD pathogenic mechanisms. Mean platelet volume (MPV), a marker of platelet activation, is involved in the pathophysiology of a variety of pro-inflammatory diseases. However, little research has been conducted to investigate the relationship between platelet indices and MCI and AD pathogenesis. In this cross-sectional study, we investigated the levels of platelet count, MPV and platelet distribution width (PDW) in 120 AD patients, 120 MCI patients, and 120 non-demented controls. Our study showed that MPV and PDW were significantly lower in patients with AD as compared with either MCI or controls. Moreover, MCI patients had lower MPV and PDW values compared with the controls (P < 0.001). In addition, there is a positive correlation between mini-mental state examination (MMSE) and MPV and PDW, after adjusting age, gender, and body mass index (r = 0.576, P < 0.001 for MPV; r = 0.465, P < 0.001 for PDW, respectively). Multivariate analysis showed that MPV and PDW were significantly associated with MMSE (β = 0.462; P < 0.001 for MPV; β = 0.245; P < 0.001 for PDW; respectively). In conclusion, MPV and PDW were decreased in MCI and AD patients. Further prospective research is warranted to determine the potential clinical application of MPV and PDW as biomarkers in the early diagnosis of AD.

Alzheimer disease and platelets: how's that relevant

Alzheimer Disease (AD) is the most common neurodegenerative disorder worldwide, and account for 60% to 70% of all cases of progressive cognitive impairment in elderly patients. At the microscopic level distinctive features of AD are neurons and synapses degeneration, together with extensive amounts of senile plaques and neurofibrillars tangles. The degenerative process probably starts 20-30 years before the clinical onset of the disease. Senile plaques are composed of a central core of amyloid β peptide, Aβ, derived from the metabolism of the larger amyloid precursor protein, APP, which is expressed not only in the brain, but even in non neuronal tissues. More than 30 years ago, some studies reported that human platelets express APP and all the enzymatic activities necessary to process this protein through the same pathways described in the brain. Since then a large number of evidence has been accumulated to suggest that platelets may be a good peripheral model to study the metabolism of APP, and the pathophysiology of the onset of AD. In this review, we will summarize the current knowledge on the involvement of platelets in Alzheimer Disease. Although platelets are generally accepted as a suitable model for AD, the current scientific interest on this model is very high, because many concepts still remain debated and controversial. At the same time, however, these still unsolved divergences mirror a difficulty to establish constant parameters to better defined the role of platelets in AD.

Impacts of membrane biophysics in Alzheimer's disease: from amyloid precursor protein processing to aβ Peptide-induced membrane changes

An increasing amount of evidence supports the notion that cytotoxic effects of amyloid-β peptide (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD), are strongly associated with its ability to interact with membranes of neurons and other cerebral cells. Aβ is derived from amyloidogenic cleavage of amyloid precursor protein (AβPP) by β- and γ-secretase. In the nonamyloidogenic pathway, AβPP is cleaved by α-secretases. These two pathways compete with each other, and enhancing the non-amyloidogenic pathway has been suggested as a potential pharmacological approach for the treatment of AD. Since AβPP, α-, β-, and γ-secretases are membrane-associated proteins, AβPP processing and Aβ production can be affected by the membrane composition and properties. There is evidence that membrane composition and properties, in turn, play a critical role in Aβ cytotoxicity associated with its conformational changes and aggregation into oligomers and fibrils. Understanding the mechanisms leading to changes in a membrane's biophysical properties and how they affect AβPP processing and Aβ toxicity should prove to provide new therapeutic strategies for prevention and treatment of AD.

Peripheral inflammatory biomarkers of Alzheimer's disease: the role of platelets

Alzheimer's disease is an age-dependent neurodegenerative disorder characterized by loss of neurons, synaptic degeneration, senile plaques and neurofibrillary tangles. Besides these hallmarks, increased accumulation of activated microglia, astrocytes and leukocytes adhering to postcapillary venules are observed in the affected brain areas, suggesting the presence of an ongoing inflammatory process. As neuroinflammation triggers the activation of peripheral immune system, many studies have analyzed circulating inflammatory biomarkers, including basal or stimulated levels of cytokines and related molecules in blood of Alzheimer's patients, but with conflicting results. Platelets are an important source of amyloid-ss (Ass) in the circulatory system and play an important pro-inflammatory role. Upon activation, they adhere to leukocytes and endothelial cells by means of adhesive proteins like P-selectin, platelet endothelial cell adhesion molecule-1 (PECAM) and intercellular adhesion molecule-1 and -2 (ICAM-1 and -2) and secrete inflammatory mediators (chemokines, interleukins). In addition, platelets contain important enzymes involved in inflammatory intermediary synthesis like phospholipase A(2) (PLA(2)) and cyclooxygenase-2 (COX-2), and recent reports demonstrated significant changes in platelet levels and activities in Alzheimer's disease. Thus, as platelets represent an important link between Ass deposition and inflammatory reactions especially at endothelial level, they can be considered a valuable cellular model to evaluate potential peripheral inflammatory biomarkers in Alzheimer's disease.

Biomarkers for early diagnosis of Alzheimer disease: 'ALZheimer ASsociated gene'--a new blood biomarker?

Simple, non-invasive tests for an early detection of degenerative dementia by use of biomarkers are urgently required. However, up to the present, no validated extracerebral diagnostic markers (plasma/serum, platelets, urine, connective tissue) for the early diagnosis of Alzheimer disease (AD) are available. In disease stages with evident cognitive disturbances, the clinical diagnosis of probable AD is made with around 90% accuracy using modern clinical, neuropsychological and imaging methods. Diagnostic sensitivity and specificity even in early disease stages are improved by CSF markers, in particular combined tau and amyloid beta peptides (Abeta) and plasma markers (eg, Abeta-42/Abeta-40 ratio). Recently, a novel gene/protein--ALZAS (Alzheimer Associated Protein)--with a 79 amino acid sequence, containing the amyloid beta-42 fragment (Abeta-42), the amyloid precursor protein (APP) transmembrane signal and a 12 amino acid C-terminal, not present in any other known APP alleles, has been discovered on chromosome 21 within the APP region. Reverse transcriptase-PCR revealed the expression of the transcript of this protein in the cortex and hippocampal regions as well as in lymphocytes of human AD patients. The expression of ALZAS is mirrored by a specific autoimmune response in AD patients, directed against the ct-12 end of the ALZAS-peptide but not against the Abeta-sequence. ELISA studies of plasma detected highest titers of ALZAS in patients with mild cognitive impairment (presymptomatic AD), but only moderately increased titers in autopsy-confirmed AD, whereas low or undetectable ct-12 titers were found in cognitively intact age-matched subjects and young controls. The antigen, ALZAS protein, was detected in plasma in later clinical stages of AD. It is suggested that ALZAS represents an indicator in a dynamic equilibrium between both peripheral and brain degenerative changes in AD and may become a useful "non-invasive" diagnostic marker via a simple blood test.