Isabel Santana

Mitochondria dysfunction of Alzheimer's disease cybrids enhances Aβ toxicity

Alzheimers disease (AD) brain reveals high rates of oxygen consumption and oxidative stress, altered antioxidant defences, increased oxidized polyunsaturated fatty acids, and elevated transition metal ions. Mitochondrial dysfunction in AD is perhaps relevant to these observations, as such may contribute to neurodegenerative cell death through the formation of reactive oxygen species (ROS) and the release of molecules that initiate programmed cell death pathways. In this study, we analyzed the effects of beta‐amyloid peptide (Aβ) on human teratocarcinoma (NT2) cells expressing endogenous mitochondrial DNA (mtDNA), mtDNA from AD subjects (AD cybrids), and mtDNA from age‐matched control subjects (control cybrids). In addition to finding reduced cytochrome oxidase activity, elevated ROS, and reduced ATP levels in the AD cybrids, when these cell lines were exposed to Aβ 1–40 we observed excessive mitochondrial membrane potential depolarization, increased cytoplasmic cytochrome c, and elevated caspase‐3 activity. When exposed to Aβ, events associated with programmed cell death are activated in AD NT2 cybrids to a greater extent than they are in control cybrids or the native NT2 cell line, suggesting a role for mtDNA‐derived mitochondrial dysfunction in AD degeneration.

Cytochrome c oxidase is decreased in Alzheimer's disease platelets.

Cytochrome c oxidase (COX) activity reportedly is reduced in Alzheimers disease (AD) brain and platelets. The reasons for the defect in either tissue are unknown, but its presence in a non-degenerating tissue suggests it is not simply a consequence of neurodegeneration. We now offer confirmation of the AD platelet COX defect. Compared to age-matched controls, in mitochondria isolated from AD platelets there was a 15% decrease in COX activity despite the fact that COX subunits were present at normal levels. Platelet ATP levels were diminished in AD (from 11.33 +/- 0.52 to 9.11 +/- 0.72 nmol/mg), while reactive oxygen species (ROS) were increased (from 97.03 +/- 25.9 to 338.3 +/- 100 K/mg). Platelet membrane fluidity, Vitamin E, and cholesterol content were similar between groups. We conclude that COX catalytic activity is indeed diminished in AD platelet mitochondria, does not result from altered membrane fluidity, and is associated with ROS overproduction and ATP under-production.

A Pan-European Study of the C9orf72 Repeat Associated with FTLD: Geographic Prevalence, Genomic Instability, and Intermediate Repeats

We assessed the geographical distribution of C9orf72 G4C2 expansions in a pan‐European frontotemporal lobar degeneration (FTLD) cohort (n = 1,205), ascertained by the European Early‐Onset Dementia (EOD) consortium. Next, we performed a meta‐analysis of our data and that of other European studies, together 2,668 patients from 15 Western European countries. The frequency of the C9orf72 expansions in Western Europe was 9.98% in overall FTLD, with 18.52% in familial, and 6.26% in sporadic FTLD patients. Outliers were Finland and Sweden with overall frequencies of respectively 29.33% and 20.73%, but also Spain with 25.49%. In contrast, prevalence in Germany was limited to 4.82%. In addition, we studied the role of intermediate repeats (7–24 repeat units), which are strongly correlated with the risk haplotype, on disease and C9orf72 expression. In vitro reporter gene expression studies demonstrated significantly decreased transcriptional activity of C9orf72 with increasing number of normal repeat units, indicating that intermediate repeats might act as predisposing alleles and in favor of the loss‐of‐function disease mechanism. Further, we observed a significantly increased frequency of short indels in the GC‐rich low complexity sequence adjacent to the G4C2 repeat in C9orf72 expansion carriers (P < 0.001) with the most common indel creating one long contiguous imperfect G4C2 repeat, which is likely more prone to replication slippage and pathological expansion.

Montreal cognitive assessment: validation study for mild cognitive impairment and Alzheimer disease.

The Montreal Cognitive Assessment (MoCA) was recently proposed as a cognitive screening test for milder forms of cognitive impairment, having surpassed the well-known limitations of the Mini-Mental State Examination (MMSE). This study aims to validate the MoCA for screening Mild Cognitive Impairment (MCI) and Alzheimer disease (AD) through an analysis of diagnostic accuracy and the proposal of cut-offs. Patients were classified into 2 clinical groups according to standard criteria: MCI (n=90) and AD (n=90). The 2 control groups (C-MCI: n=90; C-AD: n=90) consisted of cognitively healthy community dwellers selected to match patients in sex, age, and education. The MoCA showed consistently superior psychometric properties compared with the MMSE, and higher diagnostic accuracy to discriminate between MCI (area under the curve=0.856; 95% confidence interval, 0.796-0.904) and AD patients (area under the curve=0.980; 95% confidence interval, 0.947-0.995). At an optimal cut-off of below 22 for MCI and below 17 for AD, the MoCA achieved significantly superior values in comparison with MMSE for sensitivity, specificity, positive predictive value, negative predictive value, and classification accuracy. Furthermore, the MoCA revealed higher sensitivity to cognitive decline in longitudinal monitoring. This study provides robust evidence that the MoCA is a better cognitive tool than the widely used MMSE for the screening and monitoring of MCI and AD in clinical settings.

Montreal Cognitive Assessment (MoCA): Normative study for the Portuguese population

The Montreal Cognitive Assessment (MoCA) is a brief cognitive screening instrument with good psychometric features and an excellent sensitivity in the early detection of mild cognitive decline. The MoCA was applied to a community-based sample of cognitively healthy adults (n = 650), stratified according to sociodemographic variables (age, gender, educational level, geographic region, geographic localization, and residence area), with a distribution similar to that observed in the Portuguese population. The normative data were determined according to age and education as these were the sociodemographic variables that most significantly contributed to the prediction of the MoCA scores, explaining 49% of their variance.

Peripheral inflammatory Cytokines as biomarkers in Alzheimer's disease and mild cognitive impairment

Background: Several lines of evidence in the literature have shown that inflammation is involved in the pathogenesis of Alzheimer’s disease (AD). However, the results from the evaluation of serum inflammatory markers in AD patients have been controversial. Objective: To determine if any differences exist in the monocytic secretion pattern of IL-1β, IL-6, IL-12 and TNF-α from mild cognitive impairment (MCI) and AD patients, when compared with healthy age-matched controls. Methods: To evaluate the percentage of peripheral monocytes secreting IL-1β, IL-6, IL-12 and TNF-α along with the relative levels of these proteins, a cytofluorimetric analysis was conducted under basal conditions and after lipopolysaccharide-induced cell activation. Results: We found, in AD and MCI patients, a significant raise in the percentage of monocytes producing the studied cytokines (under basal conditions and after the exposure to an inflammatory stimulus), as well as a decreased competence of these cells to respond to inflammatory challenges, when compared with controls. Conclusions: These results agree with a persistent inflammatory status in AD, reinforcing the hypothesis of a progressive impairment of the immune response in this disorder and suggesting that monocytes may be good targets to study the progression from MCI to AD.

Prevalence and prognosis of Alzheimer's disease at the mild cognitive impairment stage.

Three sets of research criteria are available for diagnosis of Alzheimers disease in subjects with mild cognitive impairment: the International Working Group-1, International Working Group-2, and National Institute of Aging-Alzheimer Association criteria. We compared the prevalence and prognosis of Alzheimers disease at the mild cognitive impairment stage according to these criteria. Subjects with mild cognitive impairment (n = 1607), 766 of whom had both amyloid and neuronal injury markers, were recruited from 13 cohorts. We used cognitive test performance and available biomarkers to classify subjects as prodromal Alzheimers disease according to International Working Group-1 and International Working Group-2 criteria and in the high Alzheimers disease likelihood group, conflicting biomarker groups (isolated amyloid pathology or suspected non-Alzheimer pathophysiology), and low Alzheimers disease likelihood group according to the National Institute of Ageing-Alzheimer Association criteria. Outcome measures were the proportion of subjects with Alzheimers disease at the mild cognitive impairment stage and progression to Alzheimers disease-type dementia. We performed survival analyses using Cox proportional hazards models. According to the International Working Group-1 criteria, 850 (53%) subjects had prodromal Alzheimers disease. Their 3-year progression rate to Alzheimers disease-type dementia was 50% compared to 21% for subjects without prodromal Alzheimers disease. According to the International Working Group-2 criteria, 308 (40%) subjects had prodromal Alzheimers disease. Their 3-year progression rate to Alzheimers disease-type dementia was 61% compared to 22% for subjects without prodromal Alzheimers disease. According to the National Institute of Ageing-Alzheimer Association criteria, 353 (46%) subjects were in the high Alzheimers disease likelihood group, 49 (6%) in the isolated amyloid pathology group, 220 (29%) in the suspected non-Alzheimer pathophysiology group, and 144 (19%) in the low Alzheimers disease likelihood group. The 3-year progression rate to Alzheimers disease-type dementia was 59% in the high Alzheimers disease likelihood group, 22% in the isolated amyloid pathology group, 24% in the suspected non-Alzheimer pathophysiology group, and 5% in the low Alzheimers disease likelihood group. Our findings support the use of the proposed research criteria to identify Alzheimers disease at the mild cognitive impairment stage. In clinical settings, the use of both amyloid and neuronal injury markers as proposed by the National Institute of Ageing-Alzheimer Association criteria offers the most accurate prognosis. For clinical trials, selection of subjects in the National Institute of Ageing-Alzheimer Association high Alzheimers disease likelihood group or the International Working Group-2 prodromal Alzheimers disease group could be considered.

Peripheral Oxidative Damage in Mild Cognitive Impairment and Mild Alzheimer's Disease

Oxidative stress has been shown to be a triggering event in the pathogenesis of Alzheimers disease (AD). However, little evidence exists on the role of oxidative imbalance in Mild Cognitive Impairment (MCI), a group with a high risk of progression to AD. We therefore assessed the peripheral blood levels of a broad spectrum of non-enzymatic and enzymatic antioxidant defenses, as well as lipid and protein oxidation markers and nitrogen oxidative species in 85 MCI patients, 42 mild AD patients and 37 age-matched controls. In mild AD patients, the plasma levels of vitamin E were significantly decreased, while the plasma concentration of oxidized glutathione was increased in both MCI and mild AD patients. An increase in plasmatic and erythrocytes oxidative markers was also observed in MCI and mild AD patients as compared to controls. In both patients groups, increased levels of plasma antioxidants were found in females, whereas apolipoprotein E epsilon4 allele carriers showed higher indices of intracellular oxidative markers. Moreover, in MCI patients, cognitive function positively correlates with antioxidant levels. This study shows that most of the oxidative changes found in mild AD patients are already present in the MCI group, and that progression to AD might be accompanied by antioxidant depletion.

Cerebrospinal fluid biomarkers in trials for Alzheimer and Parkinson diseases

Alzheimer disease (AD) and Parkinson disease (PD) are the most common neurodegenerative disorders. For both diseases, early intervention is thought to be essential to the success of disease-modifying treatments. Cerebrospinal fluid (CSF) can reflect some of the pathophysiological changes that occur in the brain, and the number of CSF biomarkers under investigation in neurodegenerative conditions has grown rapidly in the past 20 years. In AD, CSF biomarkers are increasingly being used in clinical practice, and have been incorporated into the majority of clinical trials to demonstrate target engagement, to enrich or stratify patient groups, and to find evidence of disease modification. In PD, CSF biomarkers have not yet reached the clinic, but are being studied in patients with parkinsonism, and are being used in clinical trials either to monitor progression or to demonstrate target engagement and downstream effects of drugs. CSF biomarkers might also serve as surrogate markers of clinical benefit after a specific therapeutic intervention, although additional data are required. It is anticipated that CSF biomarkers will have an important role in trials aimed at disease modification in the near future. In this Review, we provide an overview of CSF biomarkers in AD and PD, and discuss their role in clinical trials.

Exome sequencing reveals an unexpected genetic cause of disease: NOTCH3 mutation in a Turkish family with Alzheimer's disease

Alzheimers disease (AD) is a genetically complex disorder for which the definite diagnosis is only accomplished postmortem. Mutations in 3 genes (APP, PSEN1, and PSEN2) are known to cause AD, but a large number of familial cases do not harbor mutations in these genes and several unidentified genes that contain disease-causing mutations are thought to exist. We performed whole exome sequencing in a Turkish patient clinically diagnosed with Alzheimers disease from a consanguineous family with a complex history of neurological and immunological disorders and identified a mutation in NOTCH3 (p.R1231C), previously described as causing cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Complete screening of NOTCH3 in a cohort of 95 early onset AD cases and 95 controls did not reveal any additional pathogenic mutations. Although the complex history of disease in this family precluded us to establish segregation of the mutation found with disease, our results show that exome sequencing is a rapid, cost-effective and comprehensive tool to detect genetic mutations, allowing for the identification of unexpected genetic causes of clinical phenotypes. As etiological based therapeutics become more common, this method will be key in diagnosing and treating disease.