Platelet of Alzheimer patients: increased counts and subnormal uptake and accumulation of [14C]5-hydroxytryptamine

Association of Peripheral Blood Cell Profile With Alzheimer's Disease: A Meta-Analysis

Background

Inflammation and immune dysfunction play significant roles in the pathogenesis of Alzheimer's disease (AD)-related dementia. Changes in peripheral blood cell profiles are a common manifestation of inflammation and immune dysfunction and have been reported in patients with AD or mild cognitive impairment (MCI). We systematically evaluated the association of peripheral blood cell counts and indices with AD or MCI through a meta-analysis.

Methods

We electronically searched sources to identify all case–control trials comparing peripheral blood cell counts and/or lymphocyte subsets between patients with AD or MCI and healthy controls (HCs). Meta-analyses were used to estimate the between-group standardized mean difference (SMD) and 95% confidence interval (CI).

Results

A total of 36 studies involving 2,339 AD patients, 608 MCI patients, and 8,352 HCs were included. AD patients had significantly decreased lymphocyte counts (SMD −0.345, 95% CI [−0.545, −0.146], P = 0.001) and significantly increased leukocyte counts (0.140 [0.039, 0.241], P = 0.006), neutrophil counts (0.309 [0.185, 0.434], P = 0.01), and neutrophil–lymphocyte ratio (NLR) (0.644 [0.310, 0.978], P < 0.001) compared to HCs. Similarly, significantly increased leukocyte counts (0.392 [0.206, 0.579], P < 0.001), NLR (0.579 [0.310, 0.847], P < 0.001), and neutrophil counts (0.248 [0.121, 0.376], P < 0.001) were found in MCI patients compared with HCs. A significantly decreased percentage of B lymphocytes (−1.511 [−2.775, −0.248], P = 0.019) and CD8⁺ T cells (−0.760 [−1.460, −0.061], P = 0.033) and a significantly increased CD4/CD8 ratio (0.615 [0.074, 1.156], P = 0.026) were observed in AD patients compared to HCs. Furthermore, significant changes in hemoglobin level and platelet distribution width were found in patients with AD or MCI compared with HCs. However, no significant difference was found between AD or MCI patients and HCs in terms of platelet counts, mean corpuscular volume, red cell distribution width, mean platelet volume, and CD4⁺ T, CD3⁺ T, or natural killer cell counts.

Conclusion

Changes in peripheral blood cell profiles, particularly involving leukocyte, lymphocyte, neutrophil, and CD8⁺ T cell counts, as well as the NLR and the CD4/CD8 ratio, are closely associated with AD. The diagnostic relevance of these profiles should be investigated in future.

Beyond Haemostasis and Thrombosis: Platelets in Depression and Its Co-Morbidities

Alongside their function in primary haemostasis and thrombo-inflammation, platelets are increasingly considered a bridge between mental, immunological and coagulation-related disorders. This review focuses on the link between platelets and the pathophysiology of major depressive disorder (MDD) and its most frequent comorbidities. Platelet- and neuron-shared proteins involved in MDD are functionally described. Platelet-related studies performed in the context of MDD, cardiovascular disease, and major neurodegenerative, neuropsychiatric and neurodevelopmental disorders are transversally presented from an epidemiological, genetic and functional point of view. To provide a complete scenario, we report the analysis of original data on the epidemiological link between platelets and depression symptoms suggesting moderating and interactive effects of sex on this association. Epidemiological and genetic studies discussed suggest that blood platelets might also be relevant biomarkers of MDD prediction and occurrence in the context of MDD comorbidities. Finally, this review has the ambition to formulate some directives and perspectives for future research on this topic.

Neuroinflammation and amyloid-beta 40 are associated with reduced serotonin transporter (SERT) activity in a transgenic model of familial Alzheimer's disease

Background

Discrepant and often contradictory results have accumulated regarding the antidepressant and pro-cognitive effects of serotonin transporter (SERT) antagonists in Alzheimer’s disease.

Methods

To address the discrepancy, we measured the activity and density of SERT in the neocortex of 3–24-month-old APP_swe/PS1_dE9 and wild-type littermate mice, by using [³H]DASB autoradiography and the [³H]5-HT uptake assay. Levels of soluble amyloid-β (Aβ), and pro-inflammatory cytokines that can regulate SERT function, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor (TNF), were measured in parallel. Neuroinflammation in aging APP_swe/PS1_dE9 mice was further evaluated by [³H]PK11195 autoradiography.

Results

Decreased SERT density was observed in the parietal and frontal cortex of 18–24-month-old APP_swe/PS1_dE9 mice, compared to age-matched, wild-type animals. The maximal velocity uptake rate (V_max) of [³H]5-HT was reduced in neocortical preparations from 20-month-old transgenic vs. wild-type mice. The reduction was observed when the proportion of soluble Aβ₄₀ in the Aβ_40/42 ratio increased in the aged transgenic brain. At concentrations compatible with those measured in 20-month-old APP_swe/PS1_dE9 mice, synthetic human Aβ₄₀, but not Aβ₄₂, reduced the baseline V_max of [³H]5-HT by ~ 20%. Neuroinflammation in APP_swe/PS1_dE9 vs. wild-type mice was evidenced by elevated [³H]PK11195 binding levels and increased concentration of IL-1β protein, which preceded the reductions in neocortical SERT density and activity. Age-induced increases in the levels of IL-1β, IL-6, and TNF were observed in both transgenic and wild-type animals.

Conclusions

The progression of cerebral amyloidosis is associated with neuroinflammation and decreased presynaptic markers of serotonergic integrity and activity. The Aβ₄₀-induced reduction in the uptake kinetics of [³H]5-HT suggests that the activity of SERT, and potentially the effects of SERT antagonism, depend on the levels of interstitial Aβ₄₀.

Platelet dysfunction in hypercholesterolemia mice, two Alzheimer's disease mouse models and in human patients with Alzheimer's disease

Alzheimer’s disease (AD) is a severe neurodegenerative disorder characterized mainly by accumulation of amyloid-β plaques and neurofibrillary tangles, synaptic and neuronal loss. Blood platelets contain the neurotransmitter serotonin and amyloid-precursor protein (APP), and may thus be useful as a peripheral biomarker for AD. The aim of the present study was to functionally characterize platelets by FACS, to examine alterations in APP expression and secretion, and to measure serotonin levels in hypercholesterolemia mice with AD-like pathology and in two AD mouse models, the triple transgenic AD model (3xTg) and the APP overexpressing AD model with the Swedish–Dutch–Iowa mutations (APP_SweDI). These data are supplemented with epidermal growth factor (EGF) levels and compared with changes observed in platelets of patients with AD. We observed decreased platelet APP isoforms in 3xTg mice and patients with AD when analysed by means of Western blot. In patients, a significant increase of APP levels was observed when assessed by ELISA. Secreted APPβ proved to be altered amongst all three animal models of AD at different time points and in human patients with AD. Serotonin levels were only reduced in 7 and 14 month old 3xTg mice. Moreover, we found significantly lower EGF levels in human AD patients and could thereby reproduce previous findings. Taken together, our data confirm that platelets are dysfunctional in AD, however, results from AD animal models do not coincide in all aspects, and markedly differ when compared to AD patients. We support previous data that APP, as well as EGF, could become putative biomarkers for diagnosing AD in human platelets.

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.

Assessment of platelet indices in patients with neurodegenerative diseases: mean platelet volume was increased in patients with Parkinson's disease

Platelets induce chronic inflammation which is a key step in atherosclerosis and may be involved in the progression of neurodegenerative diseases (NDD). We aimed to measure the mean platelet volume (MPV) and platelet count (PLC) in NDD patients. The present study was designed to investigate the platelet function by measuring MPV and PLC in NDD. A total of 182 outpatients with Alzheimer's (AD) or Parkinson's diseases (PD) were included. The control group consisted of 104 healthy subjects. Platelet count was similar between groups. MPV values of PD patients were higher than those of AD patients and controls (P < 0.001). MPV correlated negatively with Heohn and Yahr scale (HYS) score (P < 0.001). Increased MPV in patients with PD may point to a platelet dysfunction. High-grade inflammation presents with low levels of MPV as seen in PD patients with high HYS scores.

Proteomics analysis of plasma for potential biomarkers in the diagnosis of Alzheimer's disease

The objective of this study was to search for biological markers associated with Alzheimer's disease (AD). Plasma specimens obtained from ten pathologically diagnosed AD patients and ten non-demented (ND) control subjects were analyzed by a combination of 2-DE and MS. This strategy allowed us to identify six plasma proteins (alpha-1-antitrypsin, vitamin D-binding protein, inter-alpha-trypsin inhibitor family heavy chain-related protein, apolipoprotein J precursor, cAMP-dependent protein kinase catalytic subunit alpha 1, and an orf) whose 2-DE spot densities were different between the AD and ND groups. Due to their involvements in AD amyloid plaque formation, the plasma concentrations of alpha-1-antitrypsin and apolipoprotein J were further validated using either ELISA or Western blot. The results revealed that the plasma levels of alpha-1-antitrypsin in AD were higher than those of controls, confirming the 2-DE findings. However, no difference in total apolipoprotein J concentration was observed between the AD and ND groups. Considering the difference in resolving power to differentially quantitate protein isoforms provided by 2-DE and Western blot, 2-DE analysis combined with MS protein identification offers distinctive advantages when a disease-related protein isoform-specific variance is investigated.

Platelet serotonin in newborns and infants: ontogeny, heritability, and effect of in utero exposure to selective serotonin reuptake inhibitors

Ontogeny of platelet serotonin (5-hydroxytryptamine, 5-HT) during the first year of life was examined in newborns and infants. The effects of in utero exposure to selective serotonin reuptake inhibitors (SSRI, including fluoxetine, sertraline, and citalopram) were examined by comparing cord blood 5-HT levels in exposed and unexposed newborns. Heritability was assessed by correlation of the platelet 5-HT values observed for mother-infant pairs. No age effect was observed in 1-49 wk-old infants (r = 0.13, p = 0.49) and mean platelet 5-HT levels in infants (241 +/- 102 ng/mL, n = 33; 615 +/- 320 ng/10(9) platelets, n = 32) were similar to those reported for older children and adults. However, significantly lower blood 5-HT levels were observed in newborns (81.3 +/- 32.5 ng/mL, n = 16, p < 0.0001; 297 +/- 101 ng/10(9) platelets, n = 11, p = 0.0007) compared with the 1-49 wk-old infants. The mean cord blood 5-HT concentrations in newborns exposed in utero to SSRI (n = 8) were substantially lower than that seen in unexposed (n = 16) newborns (20.6 +/- 14.4 versus. 81.3 +/- 32.5 ng/mL, p = 0.0001; 90.7 +/- 55.4 versus. 297 +/- 101 ng/10(9) platelets, p = 0.0005). Platelet serotonin levels (ng/10(9) platelets) in mother-child pairs (n = 32) were significantly correlated (r = 0.415, p = 0.018). The results indicate that, although platelet 5-HT is low at birth, values quickly increase and stabilize at near-adult levels by 1 mo of age. Gestational exposure to SSRI appears to substantially reduce platelet 5-HT uptake in the fetus, strongly suggesting that such exposure has important physiologic effects. The observed mother-infant correlation agrees with a previous report of high heritability in a large adult population.

Peripheral blood abnormalities in Alzheimer disease: evidence for early endothelial dysfunction

Clinical and epidemiologic studies demonstrate that vascular risk factors may be involved in Alzheimer disease (AD). To evaluate whether vascular abnormalities are an early feature of AD, several parameters of coagulation and fibrinolysis were assessed. Thirty patients with mild AD and 30 age-matched control subjects entered the study. All subjects performed a standardized clinical and laboratory protocol. Persons with vascular risk factors and systemic diseases were excluded. AD patients present significant increased levels of thrombomodulin (p < 0.0001) and sE-selectin (p < 0.03). In contrast, no difference was found between the two diagnostic groups in the levels of beta-thromboglobulin, prothrombin fragment 1+2, fibrinogen, and von Willebrand factor. No other association but diagnosis was found with thrombomodulin and sE-selectin. These findings suggest that endothelial dysfunction is an early event in AD patients.

Neurodevelopmental evaluation of 9-month-old infants exposed to low levels of lead in utero: involvement of monoamine neurotransmitters

The objective of this work is to investigate the neurotoxicty of low-level lead exposure in utero on infants and the possible involvement of dopaminergic and serotonergic neurotransmitters. The correlation analysis for cord blood lead level, the concentrations of dopamine metabolite homovanillic acid (HVA) and serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cord plasma and the neurodevelopmental scales of infants were conducted on 244 9-month-old children. Both score of sociability subscale and 5-HIAA concentration were correlated with cord blood lead level. The sociability score was negatively correlated with the concentration of HVA, whereas both the coordination score and the global score were negatively correlated with the concentration of 5-HIAA. With partial correlation analysis, after taking HVA into account, the significant negative correlation between the sociability score and the cord blood lead level that existed in the linear correlation analysis disappeared, and the score of global scale correlated negatively with lead level in cord blood. When taking 5-HIAA into account, the scores of all the neurodevelopmental subscales except the language subscale were significantly negatively correlated with lead level in cord blood. The results indicated that low-level lead exposure in utero could produce a neurotoxic effect on the developing serotonergic system in infants. The neurotoxicity of low-level lead exposure in utero may affect the sociability of infants. Serotonergic activity was shown to have a potential effect on neurodevelopmental assessment. It may interfere with the association between low-level lead exposure in utero and other neurodevelopmental performances of 9-month-old children.

Altered oxidation and signal transduction systems in fibroblasts from Alzheimer patients

Abnormalities in calcium regulation, amyloid-beta-protein (A beta) production and oxidative metabolism have been implicated in Alzheimer's disease (AD). The use of cultured fibroblasts complement post-mortem and genetic approaches in clarifying the interaction of these processes and the underlying mechanism for the changes in AD. Definition of gene defects in particular Alzheimer families (FAD) permits elucidation of the role of those genetic abnormalities in altered signal transduction in cell lines from those families. Abnormalities in calcium regulation, ion channels, cyclic AMP, the phosphatidylinositide cascade and oxidative metabolism are well documented in fibroblasts from patients with primary genetic defects in the presenilins. Recent studies in AD fibroblasts that demonstrate abnormal secretion of A beta, a protein known to form the characteristic extracellular amyloid deposits in AD brain, further supports the use of these cells in AD research. Comparison of changes in calcium signaling, mitochondrial oxidation and A beta production in these cells suggests that changes in signal transduction including calcium may be a more consistent observation than altered A beta production in fibroblasts from some FAD families. An understanding of these abnormalities in fibroblasts may provide further insights into the pathophysiology of AD, new diagnostic measures and perhaps innovative therapeutic approaches.

Serotonin uptake and its kinetics in platelets of women with Alzheimer's disease

The uptake of serotonin (14C-5-hydroxytryptamine, 5HT) in platelets and its kinetic characteristics were investigated in a group of women (n = 20) with probable Alzheimer's Disease (mean age = 76.0, years, SD = 8.27, range = 63-88) and in healthy normal women (n = 18, mean age = 72.6 years, SD = 7.24, range = 61-84). Both the apparent affinity of binding of 5HT to the platelet membrane (Km) and the maximum velocity (Vmax) of the rate of transport of 14C-5HT into platelets were significantly higher in the Alzheimer's Disease group than in the normal comparison group. Initial velocity of 14C-5HT uptake not passive diffusion (nonspecific uptake of 14C-5HT at 4 degrees C) differed significantly in the two groups. Our findings suggest abnormalities in the kinetic mechanisms involved in the uptake of 14C-5HT by platelets in women with Alzheimer's Disease.