Does increased platelet release of Abeta peptide contribute to brain abnormalities in individuals with depression?

Under the umbrella of depression and Alzheimer's disease physiopathology: Can cannabinoids be a dual-pleiotropic therapy?

Depression and Alzheimer´s disease (AD) are two disorders highly prevalent worldwide. Depression affects more than 300 million people worldwide while AD affects 60-80% of the 55 million cases of dementia. Both diseases are affected by aging with high prevalence in elderly and share not only the main brain affected areas but also several physiopathological mechanisms. Depression disease is already ascribed as a risk factor to the development of AD. Despite the wide diversity of pharmacological treatments currently available in clinical practice for depression management, they remain associated to a slow recovery process and to treatment-resistant depression. On the other hand, AD treatment is essentially based in symptomatology relieve. Thus, the need for new multi-target treatments arises. Herein, we discuss the current state-of-art regarding the contribution of the endocannabinoid system (ECS) in synaptic transmission processes, synapses plasticity and neurogenesis and consequently the use of exogenous cannabinoids in the treatment of depression and on delaying the progression of AD. Besides the well-known imbalance of neurotransmitter levels, including serotonin, noradrenaline, dopamine and glutamate, recent scientific evidence highlights aberrant spine density, neuroinflammation, dysregulation of neurotrophic factor levels and formation of amyloid beta (Aβ) peptides, as the main physiopathological mechanisms compromised in depression and AD. The contribution of the ECS in these mechanisms is herein specified as well as the pleiotropic effects of phytocannabinoids. At the end, it became evident that Cannabinol, Cannabidiol, Cannabigerol, Cannabidivarin and Cannabichromene may act in novel therapeutic targets, presenting high potential in the pharmacotherapy of both diseases.

Platelet-Derived Amyloid-β Protein Precursor as a Biomarker of Alzheimer's Disease

BACKGROUND

Platelet proteins may be associated with Alzheimer's disease (AD) pathology.

OBJECTIVE

To investigate the relationship between platelet proteins and cerebrospinal fluid (CSF) biomarkers of AD and cognition in individuals with memory decline to identify effective screening methods for detecting the early stages of the disease.

METHODS

We classified 68 participants with subjective memory decline according to the ATN framework determined by CSF amyloid-β (A), CSF p-tau (T), and t-tau (N). All participants underwent Mini-Mental State Examination (MMSE) and platelet-related protein content testing.

RESULTS

Eighteen participants had normal AD biomarkers (NCs), 24 subjects had non-AD pathologic changes (non-AD), and 26 subjects fell within the Alzheimer's continuum (AD). The platelet amyloid-β protein precursor (AβPP) ratio in the AD group was significantly lower than in the non-AD and NCs groups, and positively correlated with MMSE scores and CSF amyloid-β42 level, which could affect MMSE scores through CSF amyloid-β42. Levels of platelet phosphorylated-tau 231 and ser396/404 phosphorylated tau were elevated in both AD and non-AD compared to NCs. Additionally, the receiver operating characteristic analysis demonstrated that the platelet AβPP ratio was a sensitive identifier for differentiating the AD from NCs (AUC = 0.846) and non-AD (AUC = 0.768). And ser396/404 phosphorylated tau could distinguish AD from NCs.

CONCLUSION

Our study was the first to find an association between platelet AβPP ratio and CSF biomarkers of AD, which contribute to the understanding of the peripheral changes in AD. These findings may help to discover potential feasible and effective screening tools for AD.

Platelet Function Is Associated With Dementia Risk in the Framingham Heart Study

Background Vascular function is compromised in Alzheimer disease (AD) years before amyloid and tau pathology are detected and a substantial body of work shows abnormal platelet activation states in patients with AD. The aim of our study was to investigate whether platelet function in middle age is independently associated with future risk of AD. Methods and Results We examined associations of baseline platelet function with incident dementia risk in the community-based FHS (Framingham Heart Study) longitudinal cohorts. The association between platelet function and risk of dementia was evaluated using the cumulative incidence function and inverse probability weighted Cox proportional cause-specific hazards regression models, with adjustment for demographic and clinical covariates. Platelet aggregation response was measured by light transmission aggregometry. The final study sample included 1847 FHS participants (average age, 53.0 years; 57.5% women). During follow-up (median, 20.5 years), we observed 154 cases of incident dementia, of which 121 were AD cases. Results from weighted models indicated that platelet aggregation response to adenosine diphosphate 1.0 µmol/L was independently and positively associated with dementia risk, and it was preceded in importance only by age and hypertension. Sensitivity analyses showed associations with the same directionality for participants defined as adenosine diphosphate hyper-responders, as well as the platelet response to 0.1 µmol/L epinephrine. Conclusions Our study shows individuals free of antiplatelet therapy with a higher platelet response are at higher risk of dementia in late life during a 20-year follow-up, reinforcing the role of platelet function in AD risk. This suggests that platelet phenotypes may be associated with the rate of dementia and potentially have prognostic value.

Is there a relationship between morphological and functional platelet changes and depressive disorder?

BACKGROUND

Blood platelets, due to shared biochemical and functional properties with presynaptic serotonergic neurons, constituted, over the years, an attractive peripheral biomarker of neuronal activity. Therefore, the literature strongly focused on the investigation of eventual structural and functional platelet abnormalities in neuropsychiatric disorders, particularly in depressive disorder. Given their impact in biological psychiatry, the goal of the present paper was to review and critically analyze studies exploring platelet activity, functionality, and morpho-structure in subjects with depressive disorder.

METHODS

According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to March 2020 with the search terms: (1) platelets in depression [Title/Abstract]"; (2) "(platelets[Title]) AND depressive disorder[Title/Abstract]"; (3) "(Platelet[Title]) AND major depressive disorder[Title]"; (4) (platelets[Title]) AND depressed[Title]"; (5) (platelets[Title]) AND depressive episode[Title]"; (6) (platelets[Title]) AND major depression[Title]"; (7) platelet activation in depression[All fields]"; and (8) platelet reactivity in depression[All fields]."

RESULTS

After a detailed screening analysis and the application of specific selection criteria, we included in our review a total of 106 for qualitative synthesis. The studies were classified into various subparagraphs according to platelet characteristics analyzed: serotonergic system (5-HT2A receptors, SERT activity, and 5-HT content), adrenergic system, MAO activity, biomarkers of activation, responsivity, morphological changes, and other molecular pathways.

CONCLUSIONS

Despite the large amount of the literature examined, nonunivocal and, occasionally, conflicting results emerged. However, the findings on structural and metabolic alterations, modifications in the expression of specific proteins, changes in the aggregability, or in the responsivity to different pro-activating stimuli, may be suggestive of potential platelet dysfunctions in depressed subjects, which would result in a kind of hyperreactive state. This condition could potentially lead to an increased cardiovascular risk. In line with this hypothesis, we speculated that antidepressant treatments would seem to reduce this hyperreactivity while representing a potential tool for reducing cardiovascular risk in depressed patients and, maybe, in other neuropsychiatric conditions. However, the problem of the specificity of platelet biomarkers is still at issue and would deserve to be deepened in future studies.

Can platelet activation result in increased plasma Aβ levels and contribute to the pathogenesis of Alzheimer's disease?

One of the central lesions in the brain of subjects with Alzheimer's disease (AD) is represented by aggregates of β-amyloid (Aβ), a peptide of 40-42 amino acids derived from the amyloid precursor protein (APP). The reasons why Aβ accumulates in the brain of individuals with sporadic forms of AD are unknown. Platelets are the primary source of circulating APP and, upon activation, 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. Increased platelet activity can stimulate platelet adhesion to endothelial cells, trigger the recruitment of leukocytes into the vascular wall and cause perivascular inflammation, which can spread inflammation in the brain. Neuroinflammation is fueled by activated microglial cells and reactive astrocytes that release neurotoxic cytokines and chemokines. Platelet activation is also associated with the progression of carotid artery disease resulting in an increased risk of cerebral hypoperfusion which may also contribute to the AD neurodegenerative process. Platelet activation may thus be a pathophysiological mechanism of AD and for the strong link between AD and cerebrovascular diseases. Interfering with platelet activation may represent a promising potential adjunct therapeutic approach for AD.

Different Sides of Depression in the Elderly: An In-depth View on the Role of Aβ Peptides

BACKGROUND

Late-onset depression (LOD) is the most common neuropsychiatric disorder associated with Alzheimer's disease (AD), often associated with structural and functional brain changes, neuropsychological impairments and negative family history for affective disorders. LOD could be a risk factor or a prodromal phase of AD; this has led to the investigation of the link between depression and amyloid-β (Aβ) peptides by measuring Aβ levels in plasma, cerebrospinal fluid (CSF) and brains of elderly depressed subjects.

OBJECTIVE

Clarify the complex relationship between depression, Aβ peptides and AD.

METHOD

We evaluated all articles published up to 2019 in PubMed in which Aβ was measured in serum (or plasma), CSF or brain in elderly with Major Depressive Disorder or depressive symptoms evaluated with standard scales.

RESULTS

Low plasma Aβ42 levels are strongly associated with depression severity. Plasma Aβ40 levels are higher in younger depressed, drug-resistant and those with more severe symptoms. CSF Aβ42 levels are lower in depressed than controls. PET-detected global and region-specific increases in Aβ deposition are sometimes associated with LOD, cognitive impairment, anxiety but not with Cardiovascular Diseases (CVDs)/CVD risk factors. Elderly depressed with CVDs/CVD risk factors have more frequently high plasma Aβ40 levels and drug-resistance; those without these co-morbidities have low plasma Aβ42 levels and a greater cognitive impairment.

CONCLUSION

Two specific Aβ profiles emerge in elderly depressed. One is associated with Aβ42 reductions in plasma and CSF, possibly reflecting increased brain amyloid deposition and prodromal AD. The other one is characterized by high plasma Aβ40 levels, cerebrovascular disease and clinically associated with increased AD risk.

CSF α-synuclein correlates with CSF neurogranin in late-life depression

Purpose/aim of the study: Major depressive disorder (MDD) in late life is linked to increased risk of subsequent dementia, but it is still unclear exactly what pathophysiological mechanisms underpin this link. A potential mechanism related to elevated risk of dementia in MDD is increased levels of α-synuclein (α-Syn), a protein found in presynaptic neuronal terminals.Materials and methods: In this study, we examined cerebrospinal fluid (CSF) levels of α-Syn in conjunction with biomarkers of neurodegeneration (amyloid-β 42, total and phospho tau) and synaptic dysfunction (neurogranin), and measures of memory ability, in 27 cognitively intact older individuals with MDD and 19 controls.Results: Our results show that CSF α-Syn levels did not significantly differ across depressed and control participants, but α-Syn was directly associated with neurogranin levels, and indirectly linked to poorer memory ability.Conclusions: All in all, we found that α-Syn may be implicated in the association between late life MDD and synaptic dysfunction, although further research is needed to confirm these results.

State-dependent alterations in cerebrospinal fluid Aβ42 levels in cognitively intact elderly with late-life major depression

Depression has been linked to Alzheimer's disease as either an increased risk factor for its development or as a prodromal symptom. The neurobiological basis for such an association, however, remains poorly understood. Numerous studies have examined whether changes in amyloid beta (Aβ) metabolism, which are implicated in the pathogenesis of Alzheimer's disease, are also found in depression. In this paper, we investigated the relationship between depressive symptoms and cerebrospinal fluid (CSF) Aβ indices in otherwise healthy, cognitively normal elderly with late-life major depression (LLMD) and controls using a longitudinal approach, which is a novel contribution toward the literature. Significantly lower levels of CSF Aβ42 were observed in the LLMD group at baseline and were associated with more severe depressive symptoms. During longitudinal follow-up, the depressed group remained cognitively unchanged, but was significantly less depressed than at baseline. A greater improvement in depressive symptoms was associated with increases in CSF Aβ42 levels in both groups. Increases in CSF Aβ42 and Aβ40 were also associated with increased CSF total-tau levels. Our results suggest that LLMD may be associated with state-dependent effects of CSF Aβ42 levels. Future studies should determine whether the association reflects state-dependent changes in neuronal activity and/or brain amyloid burden in depression.

Glucocorticoid may influence amyloid β metabolism in patients with depression

Epidemiological studies have demonstrated that depression may be a risk factor for Alzheimer's disease (AD); however, the biological mechanisms of the transition from depression to AD are still not clear. Changes of amyloid β protein (Aβ) metabolism and increased glucocorticoid (GC) levels have been found in both depression and AD. Moreover, several studies in animal models have demonstrated that GC administration changes Aβ metabolism. To reveal whether GC affects amyloid metabolism in patients with depression, we evaluated serum levels of Aβ40, Aβ42 and cortisol at admission in 187 inpatients with major depressive disorder (MDD) and 224 healthy comparisons. Additionally, we re-evaluated the serum levels of Aβs in 27 patients with MDD 1 year later. The results of multiple regression analyses revealed that serum cortisol and Aβ levels are not correlated at the time of admission. However, serum cortisol levels at admission correlated with serum Aβ42 levels and Aβ40/Aβ42 ratio 1 year later. These findings suggest that increased cortisol in patients with MDD may influence the metabolism of Aβ over prolonged periods of time.

Serum Levels of Albumin-β-Amyloid Complex in Patients with Depression

OBJECTIVE

Epidemiologic studies have demonstrated that suffering from depression may be a risk for Alzheimer disease (AD). As a possible biologic mechanism underlying the transition from depression to AD, it has been speculated that pathologic changes in β-amyloid (Aβ) metabolism are involved. To further understand the peripheral kinetics of amyloid in patients with depression, we investigated serum levels of free Aβ and albumin-bound Aβ.

METHODS

Seventy inpatients with DSM-IV major depressive disorder (MDD) and 81 healthy individuals (the comparison group) were recruited between June 2012 and February 2014. Serum Aβ40 and Aβ42 levels, Aβ40/Aβ42 ratio, and serum levels of albumin-Aβ complexes (SLAACs) were compared between the comparison group and patients in two age groups comprising younger (<60 years) and elderly (≥60 years) people.

RESULTS

SLAAC was decreased in older patients with MDD but not in younger patients. The serum-free Aβ40/Aβ42 ratio was higher in patients with depression, even in younger patients.

CONCLUSION

Our findings suggest that free Aβ and the albumin-bound Aβ reflect a different serum amyloid kinetics in depression. We speculate that serum-free Aβ reflects changes in amyloid metabolism in patients suffering from depression and albumin-bound Aβ reflects AD pathology and may be a potential predictor of the prodromal stage of AD.

High amyloid-β deposition related to depressive symptoms in older individuals with normal cognition: a pilot study

OBJECTIVE

Previous studies have reported depressive symptoms in the preclinical stages of Alzheimer's disease (AD). The objective of this study was to determine whether depressive symptoms are associated with cortical amyloid burden. In order to do this, we measured cortical amyloid via (11) C-labeled Pittsburgh Compound B ([(11) C]PIB) uptake using positron emission tomography (PET) in cognitively normal subjects.

METHODS

We performed [(11) C]PIB-PET in 29 cognitively normal, older participants. Depressive symptoms were assessed using the 15-item Geriatric Depression Scale (GDS). Aβ deposition was quantified by binding potential (BPND ), and the association between cortical mean BPND values and GDS scores was evaluated. Analysis of parametric BPND images was performed to examine the relationship between regional BPND and GDS scores.

RESULTS

We found a positive correlation between depressive symptoms and mean cortical PIB-BPND in groups of subjects with middle to high PIB-BPND . There was little change in GDS-depression score between subjects with low and middle PIB-BPND levels, while an increase in GDS was shown in the high PIB-BPND group. The main BPND increase was localized to the precuneus/posterior cingulate cortex (PCu/PCC) in subjects with high PIB-BPND , and we found a significant positive relationship between PIB-BPND in this area and depressive symptoms.

CONCLUSIONS

Emotional dysregulation because of Aβ neuropathology in the PCu/PCC may relate to depressive symptoms. More specifically, we found that older, cognitively normal patients with depressive episodes were more likely to have underlying AD pathology. Thus, depressive symptoms may increase the predictive ability of the identification of future AD cases. Copyright © 2016 John Wiley & Sons, Ltd.

Amyloid Hypothesis: Is There a Role for Antiamyloid Treatment in Late-Life Depression?

Antidepressants have modest efficacy in late-life depression (LLD), perhaps because various neurobiologic processes compromise frontolimbic networks required for antidepressant response. We propose that amyloid accumulation is an etiologic factor for frontolimbic compromise that predisposes to depression and increases treatment resistance in a subgroup of older adults. In patients without history of depression, amyloid accumulation during the preclinical phase of Alzheimer disease (AD) may result in the prodromal depression syndrome that precedes cognitive impairment. In patients with early-onset depression, pathophysiologic changes during recurrent episodes may promote amyloid accumulation, further compromise neurocircuitry required for antidepressant response, and increase treatment resistance during successive depressive episodes. The findings that support the amyloid hypothesis of LLD are (1) Depression is a risk factor, a prodrome, and a common behavioral manifestation of AD; (2) amyloid deposition occurs during a long predementia period when depression is prevalent; (3) patients with lifetime history of depression have significant amyloid accumulation in brain regions related to mood regulation; and (4) amyloid deposition leads to neurobiologic processes, including vascular damage, neurodegeneration, neuroinflammation, and disrupted functional connectivity, that impair networks implicated in depression. The amyloid hypothesis of LLD is timely because availability of ligands allows in vivo assessment of amyloid in the human brain, a number of antiamyloid agents are relatively safe, and there is evidence that some antidepressants may reduce amyloid production. A model of LLD introducing the role of amyloid may guide the design of studies aiming to identify novel antidepressant approaches and prevention strategies of AD.

Amyloid-associated depression and ApoE4 allele: longitudinal follow-up for the development of Alzheimer's disease

BACKGROUND

Amyloid-associated depression is associated with cognitive impairment cross sectionally. This follow-up study was to determine the relationship between amyloid-associated depression and the development of Alzheimer's disease (AD).

METHODS

Two hundred and twenty three subjects who did not have dementia at baseline were given a repeat cognitive evaluation for incident AD. Depression was defined by having a Center for Epidemiological Studies Depression (CES-D) score ≥ 16, and non-amyloid vs. amyloid-associated depression by having a low vs. high plasma amyloid-β peptide 40 (Aβ40)/Aβ42 ratio. Apolipoprotein E (ApoE) genotype was determined, and antidepressant usage was documented.

RESULTS

Fifteen subjects developed AD (7%) after an average follow-up time of 6.2 years. While none of those with non-amyloid depression developed AD, 9% of those with amyloid-associated depression developed AD. Further, among those with amyloid-associated depression, ApoE4 carriers tended to have a higher risk of AD than ApoE4 non-carriers (40% vs. 4%, p = 0.06). In contrast, 8% of those who did not have depression at baseline developed AD, but ApoE4 carriers and non-carriers did not show a difference in the AD risk. After adjusting for age, the interaction between ApoE4 and amyloid-associated depression (β = +0.113, SE = 0.047, P = 0.02) and the interaction between ApoE4 and antidepressant use (β = +0.174, SE = 0.064, P = 0.007) were associated with the AD risk.

CONCLUSIONS

Amyloid-associated depression may be prodromal depression of AD especially in the presence of ApoE4. Future studies with a larger cohort and a longer follow-up are warranted to further confirm this conclusion.

A systematic review of amyloid-β peptides as putative mediators of the association between affective disorders and Alzheimer׳s disease

BACKGROUND

Affective disorders are associated with an increased occurrence of cognitive deficits and have been linked to cognitive impairment and Alzheimer׳s disease. The putative molecular mechanisms involved in these associations are however not clear. The aim of this systematic review was to explore clinically founded evidence for amyloid-β peptides in cerebrospinal fluid and blood as putative biomarkers for affective disorders.

METHOD

Systematic searches in Embase and PubMed databases yielded 23 eligible, observational studies.

RESULTS

Despite inconsistencies that were partly ascribed to the application of different assay formats, study results indicate a potentially altered amyloid-β metabolism in affective disorder.

LIMITATIONS

Since most studies used a cross-sectional design, causality is difficult to establish. Moreover, methodological rigor of included studies varied and several studies were limited by very low sample numbers. Finally, different assays for amyloid-β were utilized in the different studies, thus hampering comparisons.

CONCLUSION

To unravel possible risk relations and causalities between affective disorder and Alzheimer׳s disease and to determine how amyloid-β concentrations change over time and are associated with cognition as well as affective symptomatology, future research should include prospective, longitudinal studies, implemented in large study populations, where peripheral and central amyloid-β ratios are quantified concomitantly and continuously across various affective phases. Also, to enable inter-survey comparisons, the use of standardized pre-analytical/analytical procedures is crucial.

Plasma amyloid-β levels in drug-resistant bipolar depressed patients receiving electroconvulsive therapy

AIMS

Alterations of plasma amyloid-β (Aβ) peptides have been related to a high risk for cognitive impairment and dementia. The present study aimed to measure plasma Aβ peptides (Aβ40, Aβ42) and the Aβ40/Aβ42 ratio in a sample of drug-resistant bipolar depressed patients, as well as to explore the possible correlation between biological parameters and clinical changes along an electroconvulsive therapy (ECT) course.

METHODS

Aβ40 and Aβ42 were measured by means of an ELISA assay in 25 drug-resistant bipolar depressed patients before (T0) and 1 week after (T1) the end of ECT. The patients were clinically evaluated by means of the Hamilton Rating Scale for Depression, 21-item (HRSD-21), the Mini-Mental State Examination, and the Clinical Global Impressions-Severity of Illness Scale.

RESULTS

Plasma Aβ levels and the Aβ40/Aβ42 ratio were similar at T0 and T1. The Aβ40/Aβ42 ratio correlated positively with the HRSD total score at both T0 and T1. At T0, a negative correlation was found between the Aβ40/Aβ42 ratio and the improvement of depressive and cognitive symptoms. Moreover, remitters (n = 9; HRSD ≤10) showed a significantly lower Aβ40/Aβ42 ratio at T0 than nonremitters.

CONCLUSION

The present data suggest that a low Aβ40/Aβ42 ratio might characterize a subgroup of depressed patients who respond to ECT, while higher values of this parameter seem to be typical of more severe cases of patients with cognitive impairment.

Soluble amyloid-β levels and late-life depression

Late-Life Major Depression (LLMD) is a complex heterogeneous disorder that has multiple pathophysiological mechanisms such as medical comorbidity, vascular-related factors and Alzheimer's disease (AD). There is an association between LLMD and AD, with LLMD possibly being a risk factor for, or early symptom of AD and vascular dementia. Whether depression is an etiologic risk factor for dementia, or part of the dementia prodrome remains controversial. AD has a long prodromal period with the neuropathologic features of the disease preceding the onset of clinical symptoms by as much as 15-20 years. Clinicopathological studies have provided robust support for the importance of Aβ42 in the pathogenesis of AD, but several other risk factors have also been identified. Given the relationship between Aβ42 and AD, a potential relationship between Aβ42 and LLMD would improve the understanding of the association between LLMD and AD. We reviewed 15 studies that analyzed the relationship between soluble Aβ42 and LLMD. For studies looking at plasma and/or cerebrospinal fluid (CSF) levels of Aβ42, the relationship between LLMD and soluble Aβ42 was equivocal, with some studies finding elevated Aβ42 levels associated with LLMD and others finding the opposite, decreased levels of Aβ42 associated with LLMD. It may be that there is poor reliability in the diagnosis of depression in late life, or variability in the criteria and the scales used, or subtypes of depression in late life such as early vs. late onset depression, vascular-related depression, and preclinical/comorbid depression in AD. The different correlations associated with each of these factors would be causing the inconsistent results for soluble Aβ42 levels in LLMD, but it is also possible that these patterns derive from disease stage-dependent differences in the trajectory of CSF Aβ42 during older age, or changes in neuronal activity or the sleep/wake cycle produced by LLMD that influence Aβ42 dynamics.

Heterogeneity of elderly depression: increased risk of Alzheimer's disease and Aβ protein metabolism

Epidemiological studies have proposed that depression may increase the risk for Alzheimer's disease (AD), even in patients with early-onset depression. Although metabolism of amyloid β protein (Aβ) in elderly depression received attention in terms of their correlation, there is a serious heterogeneity in elderly depression in terms of age at onset of depression. Moreover, it is unknown whether early-onset major depressive disorder (MDD) has a long-term effect on the involvement of Aβ metabolism and later development of AD. Thus, we evaluated serum Aβ40 and Aβ42 levels, the Aβ40/Aβ42 ratio in 89 elderly (≥60 years of age) inpatients with MDD and 81 age-matched healthy controls, and compared them among patients with early-onset (<60 years) and late-onset (≥60years) MDD and controls. The results showed that the serum Aβ40/Aβ42 ratio was significantly higher in patients with both early- and late-onset MDD than in controls (early-onset, p=0.010; late-onset, p=0.043), and it is of great interest that the serum Aβ40/Aβ42 ratio was negatively correlated with the age at MDD onset (R=-0.201, p=0.032). These results suggest that an earlier onset of MDD may have a more serious abnormality in Aβ metabolism, possibly explaining a biological mechanism underlying the link between depression and AD.

Protein binding in patients with late-life depression

CONTEXT

Depression has been identified as a risk factor and a prodrome of dementia. Common neurobiological mechanisms may underlie this clinical and phenomenologic overlap.

OBJECTIVE

To examine and compare protein (amyloid and tau) binding in critical brain regions in patients diagnosed as having late-life major depressive disorder (MDD) and healthy control individuals using 2-(1-{6-[(2-[(18)F]fluoroethyl)(methyl)-amino]-2-naphthyl}ethylidene) malononitrile ([(18)F]FDDNP) positron emission tomography.

DESIGN

A cross-section neuroimaging study using positron emission tomography.

SETTING

University of California, Los Angeles. Patients  Our samples comprised 20 patients diagnosed as having MDD and 19 healthy control individuals of comparable age, sex, and educational level. Main Outcome Measure  Relative distribution volume in regions of interest was used as the measure of [(18)F]FDDNP binding in all study participants.

RESULTS

When compared with controls, [(18)F]FDDNP binding was significantly higher overall and in the posterior cingulate and lateral temporal regions in the MDD group.

CONCLUSIONS

These findings suggest that neuronal injury associated with higher protein load in critical brain regions might provide a mechanism in the pathophysiologic manifestation of MDD in late life and have implications for the therapeutics of depression in elderly individuals.

The relationship between plasma amyloid-β peptides and the medial temporal lobe in the homebound elderly

BACKGROUND

The ratio of high amyloid-β peptide40 (Aβ40) and low Aβ42 in plasma predicts the risk of Alzheimer's disease (AD) and is associated with episodic recall in depression. We thus examined the relationship between plasma Aβ levels and brain volumes.

METHODS

Homebound elders (N = 352) who had undergone brain MRI were used. Plasma Aβ1-40 and Aβ1-42 were measured by ELISA. Volumes of medial temporal regions, including the amygdala and hippocampus, were manually measured.

RESULTS

Amygdala volume was associated with log(10) of plasma Aβ1-42 (β = +0.19, SE = 0.07, p = 0.005) after adjusting for AD, infarcts, white matter hyperintensities and demographics. In the absence of dementia, decreasing quartiles of plasma Aβ1-42 (Mean + SD ml: Q4 = 4.1 ± 0.8; Q3 = 3.9 ± 0.7; Q2 = 3.6 ± 0.8 and Q1 = 3.7 ± 0.8, p = 0.01) and increasing quartiles of plasma Aβ1-40/1-42 ratio were associated with smaller amygdala volume. Those depressed subjects with a high plasma Aβ1-40/1-42 ratio had smaller amygdala (Mean + SD ml: 3.3 ± 0.8 vs. 3.6 ± 0.8, p = 0.04) and total brain volume (Mean + SD liter: 0.95 ± 0.07 vs. 1.04 ± 0.12, p = 0.005), and had a higher rate of MCI (67 vs. 36%, p = 0.02) than those with a low plasma Aβ1-40/1-42 ratio.

CONCLUSIONS

The combination of low plasma Aβ1-42 concentration and atrophy of the medial temporal lobe structures, which regulates mood and cognition, may represent a biomarker for a prodromal stage of AD.

Plasma amyloid beta-42 independently predicts both late-onset depression and Alzheimer disease

OBJECTIVES

Depression in the elderly might represent a prodromal phase of Alzheimer disease (AD). High levels of plasma amyloid beta-42 (Aβ42) were found in prestages of AD and also in depressed patients in cross-sectional studies. This study examined the association of emerging late-onset depression (LOD) and AD with plasma Aβ42 in a sample of never depressed and not demented persons at baseline.

DESIGN

Prospective 5-year longitudinal study.

PARTICIPANTS

A community dwelling of older adults (N = 331) from the Vienna Transdanube Aging study.

MEASUREMENTS

Laboratory measurements, cognitive functioning, and depressive symptoms were assessed at baseline, 2.5, and 5 years follow-ups.

RESULTS

After exclusion of converters to AD, regression analysis revealed that higher plasma Aβ42 at baseline was a positive predictor for conversion to first episode of LOD. Independent of whether persons with mild cognitive impairment (MCI) at 2.5 years were included or excluded into regressions, higher plasma Aβ42 at baseline was a significant predictor for the development of probable or possible AD at 5 years. Higher conversion to AD was also associated with male gender but not with either higher scores on the Geriatric Depression Scale (GDS), with stroke or cerebral infarction nor apolipoprotein E ε4 allele. No association was found for an interaction between plasma Aβ42 levels and GDS.

CONCLUSIONS

Higher plasma Aβ42 at baseline predicted the development of first episode of LOD and conversion to probable or possible AD. Emerging depression as measured by scores on GDS at the 2.5-year follow-up, either alone or as an interaction factor with plasma Aβ42, failed to predict the conversion to AD at 5 years.

Amyloid-associated depression: a prodromal depression of Alzheimer disease?

CONTEXT

A high ratio of plasma amyloid-beta peptide 40 (Abeta(40)) to Abeta(42), determined by both high Abeta(40) and low Abeta(42) levels, increases the risk of Alzheimer disease. In a previous study, we reported that depression is also associated with low plasma Abeta(42) levels in the elderly population.

OBJECTIVE

To characterize plasma Abeta(40):Abeta(42) ratio and cognitive function in elderly individuals with and without depression.

DESIGN

Cross-sectional study.

SETTING

Homecare agencies.

PARTICIPANTS

A total of 995 homebound elderly individuals of whom 348 were defined as depressed by a Center for Epidemiological Studies Depression score of 16 or greater.

MAIN OUTCOME MEASURES

Cognitive domains of memory, language, executive, and visuospatial functions according to levels of plasma Abeta(40) and Abeta(42) peptides.

RESULTS

Subjects with depression had lower plasma Abeta(42) levels (median, 14.1 vs 19.2 pg/mL; P = .006) and a higher plasma Abeta(40):Abeta(42) ratio (median, 8.9 vs 6.4; P < .001) than did those without depression in the absence of cardiovascular disease and antidepressant use. The interaction between depression and plasma Abeta(40):Abeta(42) ratio was associated with lower memory score (beta = -1.9, SE = 0.7, P = .006) after adjusting for potentially confounders. Relative to those without depression, "amyloid-associated depression," defined by presence of depression and a high plasma Abeta(40):Abeta(42) ratio, was associated with greater impairment in memory, visuospatial ability, and executive function; in contrast, nonamyloid depression was not associated with memory impairment but with other cognitive disabilities.

CONCLUSION

Amyloid-associated depression may define a subtype of depression representing a prodromal manifestation of Alzheimer disease.