Platelet APP isoform ratios in asymptomatic young adults expressing an AD-related presenilin-1 mutation

β-Amyloid promotes platelet activation and activated platelets act as bridge between risk factors and Alzheimer's disease

Alzheimer's disease (AD) is an evolving challenge that places an enormous burden on families and society. The presence of obvious brain β-amyloid (Aβ) deposition is a premise to diagnose AD, which induces the subsequent tau hyperphosphorylation and neurodegeneration. Platelets are the primary source of circulating amyloid precursor protein (APP). Upon activation, they can secrete significant amounts of Aβ into the blood, which can be actively transported to the brain across the blood-brain barrier and promote amyloid deposition. In this review, we summarized the changes in the platelet APP metabolic pathway in patients with AD and further comprehensively explored the targets and downstream events of Aβ-activated platelets. In addition, we attempted to clarify whether patients with AD are in a state of general platelet activation, with inconsistent results. Considering the increasingly evident bidirectional relationship between AD and vascular events, we speculate that the AD pathology alone seems to be insufficient to induce the general activation of platelets; however, the intervention of third-party factors, such as atherosclerosis, exposes the extracellular matrix and leads to platelet activation, further promoting AD progression. Therefore, we proposed a framework in which the relationship between platelets and AD is indirect and mediated by vascular factors. Therapies targeting platelets and interventions for vascular risk factors are likely to contribute to the prevention and treatment of AD.

Effect of a Cognitive Training Program on the Platelet APP Ratio in Patients with Alzheimer's Disease

In patients with Alzheimer’s disease (AD), synaptic plasticity seems to be involved in cognitive improvement induced by cognitive training. The platelet amyloid precursor protein (APP) ratio (APPr), i.e., the ratio between two APP isoforms, may be a useful peripheral biomarker to investigate synaptic plasticity pathways. This study evaluates the changes in neuropsychological/cognitive performance and APPr induced by cognitive training in AD patients participating in the “My Mind Project”. Neuropsychological/cognitive variables and APPr were evaluated in the trained group (n = 28) before a two-month experimental protocol, immediately after its termination at follow-up 1 (FU1), after 6 months at follow-up 2 (FU2), and after 24 months at follow-up 3 (FU3). The control group (n = 31) received general psychoeducational training for two months. Some memory and attention parameters were significantly improved in trained vs. control patients at FU1 and FU2 compared to baseline (Δ values). At FU3, APPr and Mini Mental State Examination (MMSE) scores decreased in trained patients. Δ APPr correlated significantly with the Δ scores of (i) MMSE at FU1, (ii) the prose memory test at FU2, and (iii) Instrumental Activities of Daily Living (IADL), the semantic word fluency test, Clinical Dementia Rating (CDR), and the attentive matrices test at FU3. Our data demonstrate that the platelet APPr correlates with key clinical variables, thereby proving that it may be a reliable biomarker of brain function in AD patients.

Decreased platelet APP isoform ratios in autosomal dominant Alzheimer's disease: baseline data from a DIAN cohort subset

INTRODUCTION

This study examines platelet amyloid precursor protein (APP) isoform ratios of 120KDa to 110KDa (APPr) between mutation carriers (MC) carrying a mutation for autosomal dominant Alzheimer's disease (ADAD) and non-carriers (NC). Two previous studies reported no significant difference in APPr between ADAD MC and NC, which may have been due to the small sample size in both studies. The current study examines APPr in MC versus NC in a larger sample. In addition, it investigated whether APPr correlate with neuroimaging data, neuropsychological data and cerebrospinal fluid biomarkers in a cohort subset derived from the Dominantly Inherited Alzheimer Network (DIAN) study.

METHODS

APPr were quantified by western blotting. Fifteen MC (symptomatic and asymptomatic) were compared against twelve NC using univariate general linear model. All participants underwent neuroimaging and neuropsychological testing which were correlated with APPr using Pearson's correlation coefficient (r).

RESULTS

APPr were lower in MC compared to NC (p=0.003) while Mini-Mental State Examination (MMSE) scores were not significantly different (p>0.1). Furthermore, APPr inversely correlated with amyloid imaging in the Caudate Nucleus (r=-0.505; p<0.05) and Precuneus (r=-0.510; p<0.05).

CONCLUSION

APPr are lower in ADAD MC compared to NC, and inversely correlated with brain amyloid load prior to significant differences in cognitive health. However, the use of APPr as a biomarker needs to be explored further.

Differences of peripheral inflammatory markers between mild cognitive impairment and Alzheimer's disease

Multiple pathogenic factors may contribute to the pathophysiology of Alzheimer's disease (AD). Peripheral markers have been used to assess biochemical alterations associated with AD and mild cognitive impairment (MCI) involved in its pathophysiology. The present study was conducted to evaluate inflammatory peripheral markers in elderly patients with MCI, patients with AD and normal elderly subjects. We measured plasma levels of different cytokines (IL-6, TNF-alpha and IFN-alpha) and platelet levels of cyclooxigenase-2 (COX-2) from 34 patients with MCI, 45 patients with AD and 28 age-matched control subjects. MCI and AD patients showed similarities in TNF-alpha and COX-2 levels, and differences in IL-6 and INF-alpha. Whereas augmented IL-6 levels have been found in AD patients, a significant increase in INF-alpha has been detected only in patients with MCI possibly associated with the depression stage frequently found in cognitive impairment. In conclusion, inflammatory response may be an early factor in AD development and these changes in circulating markers are possibly related to the progression of MCI to AD.

Calcium dysregulation in Alzheimer's disease

Alzheimer disease (AD) is the most common form of adult dementia. Its pathological hallmarks are synaptic degeneration, deposition of amyloid plaques and neurofibrillary tangles, leading to neuronal loss. A few hypotheses have been proposed to explain AD pathogenesis. The beta-amyloid (Abeta) and hyperphosphorylated tau hypotheses suggest that these proteins are the main players in AD development. Another hypothesis proposes that the dysregulation of calcium homeostasis may be a key factor in accelerating other pathological changes. Although Abeta and tau have been extensively studied, recently published data provide a growing body of evidence supporting the critical role of calcium signalling in AD. For example, presenilins, which are mutated in familial cases of AD, were demonstrated to form low conductance calcium channels in the ER and elevated cytosolic calcium concentration increases amyloid generation. Moreover, memantine, an antagonist of the NMDA-calcium channel receptor, has been found to have a beneficial effect for AD patients offering novel possibilities for a calcium signalling targeted therapy of AD. This review underscores the growing importance of calcium ions in AD development and focuses on the relevant aspects of calcium homeostasis.

Vascular dementia in patients with immune thrombocytopenic purpura

INTRODUCTION

Platelets have been implicated in memory disorders but this has not been investigated in patients with immune or idiopathic thrombocytopenia (ITP). ITP is an autoimmune disorder in which autoantibodies bring about platelet destruction. We previously reported a group of ITP patients who manifested TIA-like syndrome and gradual memory loss leading to dementia: platelet microparticles (PMP), a marker of platelet activation, were often elevated, suggesting that procoagulant PMP released from stimulated platelets contributed to thrombosis in small vessels. We have expanded on those studies to better define the clinical, laboratory, and radiologic characteristics of this syndrome.

MATERIALS AND METHODS

Twenty ITP patients with this syndrome were studied in comparison to twenty-three ITP patients without it (patient controls). Clinical and laboratory features were compared and radiologic images were analyzed. Factors influencing the rate of progression to advanced dementia were also investigated.

RESULTS AND CONCLUSION

Recurring dizzy or weak spells, TIA-like syndrome, recent memory loss, and cognitive impairment were common initial complaints. In some, these symptoms progressed rapidly to dementia but was indolent in others. Progression was faster in those with splenectomy and higher platelet counts. MRI showed enhanced signal in subcortical, periventricular areas, consistent with ischemic small vessel disease. Compared to patient controls, bleeding was less frequent and platelet activation (increased PMP, CD62p) was more frequent in the study group. Thrombotic complications may occur in ITP, manifested as TIA-like syndrome or memory loss due to ischemic small vessel disease, progressing to vascular dementia. Memory disturbances associated with platelet disorders warrants further investigation.