Increased amyloid beta protein levels in children and adolescents with Down syndrome

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

Intraneuronal accumulation of amyloid-β peptides as the pathomechanism linking autism and its co-morbidities: epilepsy and self-injurious behavior - the hypothesis

Autism spectrum disorder (ASD) is associated with enhanced processing of amyloid-β precursor protein (APP) by secretase-α, higher blood levels of sAPPα and intraneuronal accumulation of N-terminally truncated Aβ peptides in the brain cortex - mainly in the GABAergic neurons expressing parvalbumin - and subcortical structures. Brain Aβ accumulation has been also described in epilepsy-the frequent ASD co-morbidity. Furthermore, Aβ peptides have been shown to induce electroconvulsive episodes. Enhanced production and altered processing of APP, as well as accumulation of Aβ in the brain are also frequent consequences of traumatic brain injuries which result from self-injurious behaviors, another ASD co-morbidity. We discuss distinct consequences of accumulation of Aβ in the neurons and synapses depending on the Aβ species, their posttranslational modifications, concentration, level of aggregation and oligomerization, as well as brain structures, cell types and subcellular structures where it occurs. The biological effects of Aβ species which are discussed in the context of the pathomechanisms of ASD, epilepsy, and self-injurious behavior include modulation of transcription-both activation and repression; induction of oxidative stress; activation and alteration of membrane receptors' signaling; formation of calcium channels causing hyper-activation of neurons; reduction of GABAergic signaling - all of which lead to disruption of functions of synapses and neuronal networks. We conclude that ASD, epilepsy, and self-injurious behaviors all contribute to the enhanced production and accumulation of Aβ peptides which in turn cause and enhance dysfunctions of the neuronal networks that manifest as autism clinical symptoms, epilepsy, and self-injurious behaviors.

Blood Biomarkers for Alzheimer's Disease in Down Syndrome

Epidemiological evidence suggests that by the age of 40 years, all individuals with Down syndrome (DS) have Alzheimer's disease (AD) neuropathology. Clinical diagnosis of dementia by cognitive assessment is complex in these patients due to the pre-existing and varying intellectual disability, which may mask subtle declines in cognitive functioning. Cerebrospinal fluid (CSF) and positron emission tomography (PET) biomarkers, although accurate, are expensive, invasive, and particularly challenging in such a vulnerable population. The advances in ultra-sensitive detection methods have highlighted blood biomarkers as a valuable and realistic tool for AD diagnosis. Studies with DS patients have proven the potential blood-based biomarkers for sporadic AD (amyloid-β, tau, phosphorylated tau, and neurofilament light chain) to be useful in this population. In addition, biomarkers related to other pathologies that could aggravate dementia progression-such as inflammatory dysregulation, energetic imbalance, or oxidative stress-have been explored. This review serves to provide a brief overview of the main findings from the limited neuroimaging and CSF studies, outline the current state of blood biomarkers to diagnose AD in patients with DS, discuss possible past limitations of the research, and suggest considerations for developing and validating blood-based biomarkers in the future.

Assessment of dementia in a clinical sample of persons with intellectual disability

BACKGROUND

Assessment of age-associated disorders has become increasingly important.

METHODS

In a clinical setting, people with intellectual disability with and without dementia were assessed retrospectively using the Neuropsychological Test Battery (NTB) and the Dementia Questionnaire for People with Learning Disabilities (DLD) at two different times to analyse neuropsychological changes and diagnostic validity. One group (n = 44) was assessed with both instruments, while the DLD was applied in 71 patients.

RESULTS

In the NTB (n = 44), only patients with dementia (n = 26) showed a decline in the NTB total score and three subscales. Receiver operating characteristic analysis revealed a diagnostic sensitivity of .67, a specificity of .81, and an area under the curve (AUC) of .767. In the DLD group (n = 71), only those with dementia displayed a decrease in the cognitive and social scale; diagnostic sensitivity and specificity values were low (.61/.63) and the AUC was .704.

CONCLUSIONS

Neuropsychological assessment was sensitive to detect cognitive changes over time. Sensitivity values of both instruments suggest a reassessment at a later time point.

The BACH1/Nrf2 Axis in Brain in Down Syndrome and Transition to Alzheimer Disease-Like Neuropathology and Dementia

Down syndrome (DS) is the most common genetic cause of intellectual disability that is associated with an increased risk to develop early-onset Alzheimer-like dementia (AD). The brain neuropathological features include alteration of redox homeostasis, mitochondrial deficits, inflammation, accumulation of both amyloid beta-peptide oligomers and senile plaques, as well as aggregated hyperphosphorylated tau protein-containing neurofibrillary tangles, among others. It is worth mentioning that some of the triplicated genes encoded are likely to cause increased oxidative stress (OS) conditions that are also associated with reduced cellular responses. Published studies from our laboratories propose that increased oxidative damage occurs early in life in DS population and contributes to age-dependent neurodegeneration. This is the result of damaged, oxidized proteins that belong to degradative systems, antioxidant defense system, neuronal trafficking. and energy metabolism. This review focuses on a key element that regulates redox homeostasis, the transcription factor Nrf2, which is negatively regulated by BACH1, encoded on chromosome 21. The role of the Nrf2/BACH1 axis in DS is under investigation, and the effects of triplicated BACH1 on the transcriptional regulation of Nrf2 are still unknown. In this review, we discuss the physiological relevance of BACH1/Nrf2 signaling in the brain and how the dysfunction of this system affects the redox homeostasis in DS neurons and how this axis may contribute to the transition of DS into DS with AD neuropathology and dementia. Further, some of the evidence collected in AD regarding the potential contribution of BACH1 to neurodegeneration in DS are also discussed.

Cerebrospinal fluid and blood Aβ levels in Down syndrome patients with and without dementia: a meta-analysis study

Abnormal β-amyloid (Aβ) levels were found in patients with Down syndrome (DS). However, Aβ levels in patients with DS and DS with dementia (DSD) vary considerably across studies. Therefore, we performed a systematic literature review and quantitatively summarized the clinical Aβ data on the cerebrospinal fluid (CSF) and blood of patients with DS and those with DSD using a meta-analytical technique. We performed a systematic search of the PubMed and Web of Science and identified 27 studies for inclusion in the meta-analysis. Random-effects meta-analysis indicated that the levels of blood Aβ_1-40 and Aβ_1-42 were significantly elevated in patients with DS compared with those in healthy control (HC) subjects. In contrast, there were no significant differences between patients with DS and those with DSD in the blood Aβ_1-40 and Aβ_1-42 levels. The CSF Aβ_1-42 levels were significantly decreased in patients with DS compared to those in HC subjects. Further, CSF Aβ_1-42 levels were significantly decreased in patients with DSD compared to those with DS, with a large effect size. Taken together, our results demonstrated that blood Aβ_1-40 and Aβ_1-42 levels were significantly increased in patients with DS while CSF Aβ_1-42, but not Aβ_1-40 levels were significantly decreased in patients with DS.

Plasma amyloid and tau as dementia biomarkers in Down syndrome: Systematic review and meta-analyses

Individuals with Down syndrome (DS) are at high risk of developing Alzheimer's disease (AD). Discovering reliable biomarkers which could facilitate early AD diagnosis and be used to predict/monitor disease course would be extremely valuable. To examine if analytes in blood related to amyloid plaques may constitute such biomarkers, we conducted meta‐analyses of studies comparing plasma amyloid beta (Aβ) levels between DS individuals and controls, and between DS individuals with and without dementia. PubMed, Embase, and Google Scholar were searched for studies investigating the relationship between Aβ plasma concentrations and dementia in DS and 10 studies collectively comprising >1,600 adults, including >1,400 individuals with DS, were included. RevMan 5.3 was used to perform meta‐analyses. Meta‐analyses showed higher plasma Aβ₄₀ (SMD = 1.79, 95% CI [1.14, 2.44], Z = 5.40, p < .00001) and plasma Aβ₄₂ levels (SMD = 1.41, 95% CI [1.15, 1.68], Z = 10.46, p < .00001) in DS individuals than controls, and revealed that DS individuals with dementia had higher plasma Aβ₄₀ levels (SMD = 0.23, 95% CI [0.05, 0.41], Z = 2.54, p = .01) and lower Aβ₄₂/Aβ₄₀ ratios (SMD = −0.33, 95% CI [−0.63, −0.03], Z = 2.15, p = .03) than DS individuals without dementia. Our results indicate that plasma Aβ₄₀ levels may constitute a promising biomarker for predicting dementia status in individuals with DS. Further investigations using new ultra‐sensitive assays are required to obtain more reliable results and to investigate to what extent these results may be generalizable beyond the DS population.

EXPRESS: Angiogenic Profile Identifies Pulmonary Hypertension in Children with Down Syndrome

Past studies have shown that lung angiogenic signaling may be abnormal in children with Down syndrome, but whether differences in circulating angiogenic proteins can identify pulmonary hypertension in children with Down syndrome is unknown. A prospective study of 78 children from birth to 21 years of age was conducted to evaluate clinical data, echocardiograms, and cardiac catheterizations. Four patient populations were enrolled, including children with Down syndrome who have pulmonary hypertension (Down syndrome + pulmonary hypertension, n = 12); control children without Down syndrome who have pulmonary hypertension (C + pulmonary hypertension, n = 15); children with Down syndrome without a known diagnosis of pulmonary hypertension (Down syndrome − pulmonary hypertension, n = 26); and children without Down syndrome or a known diagnosis of pulmonary hypertension (C − pulmonary hypertension, n = 25). Blood samples were collected at enrollment and concentrations for 11 proteins were evaluated. A classification tree was created to identify angiogenic peptide signals that may be associated with pulmonary hypertension in children with Down syndrome compared with controls. Findings identified elevated endostatin levels (>4.98 log10 pg/ml) were associated with Down syndrome. Platelet-derived growth factor AA levels (>2.51 log10 pg/ml) were higher in non-Down syndrome patients with pulmonary hypertension (C + pulmonary hypertension), whereas lower angiogenin (<5.428 log10 pg/ml) or lower angiogenin with elevated angiopoietin-1 levels (>3.59 log10 pg/ml) distinguished pulmonary hypertension in those with Down syndrome from the other groups. This study suggests that children with Down syndrome have high endostatin levels, but low levels of angiogenin levels in children with Down syndrome more often identified pulmonary hypertension than Down syndrome subjects without pulmonary hypertension or non-Down syndrome children. We speculate that these changes in circulating peptides support the concept of dysregulated angiogenesis in children with Down syndrome and pulmonary hypertension, which may further support potential utility as biomarkers for identifying subjects with Down syndrome at risk for pulmonary hypertension in this population.

Plasma biomarkers for amyloid, tau, and cytokines in Down syndrome and sporadic Alzheimer's disease

BACKGROUND

Down syndrome (DS), caused by chromosome 21 trisomy, is associated with an ultra-high risk of dementia due to Alzheimer's disease (AD), driven by amyloid precursor protein (APP) gene triplication. Understanding relevant molecular differences between those with DS, those with sporadic AD (sAD) without DS, and controls will aid in understanding AD development in DS. We explored group differences in plasma concentrations of amyloid-β peptides and tau (as their accumulation is a characteristic feature of AD) and cytokines (as the inflammatory response has been implicated in AD development, and immune dysfunction is common in DS).

METHODS

We used ultrasensitive assays to compare plasma concentrations of the amyloid-β peptides Aβ40 and Aβ42, total tau (t-tau), and the cytokines IL1β, IL10, IL6, and TNFα between adults with DS (n = 31), adults with sAD (n = 27), and controls age-matched to the group with DS (n = 27), and explored relationships between molecular concentrations and with age within each group. In the group with DS, we also explored relationships with neurofilament light (NfL) concentration, due to its potential use as a biomarker for AD in DS.

RESULTS

Aβ40, Aβ42, and IL1β concentrations were higher in DS, with a higher Aβ42/Aβ40 ratio in controls. The group with DS showed moderate positive associations between concentrations of t-tau and both Aβ42 and IL1β. Only NfL concentration in the group with DS showed a significant positive association with age.

CONCLUSIONS

Concentrations of Aβ40 and Aβ42 were much higher in adults with DS than in other groups, reflecting APP gene triplication, while no difference in the Aβ42/Aβ40 ratio between those with DS and sAD may indicate similar processing and deposition of Aβ40 and Aβ42 in these groups. Higher concentrations of IL1β in DS may reflect an increased vulnerability to infections and/or an increased prevalence of autoimmune disorders, while the positive association between IL1β and t-tau in DS may indicate IL1β is associated with neurodegeneration. Finally, NfL concentration may be the most suitable biomarker for dementia progression in DS. The identification of such a biomarker is important to improve the detection of dementia and monitor its progression, and for designing clinical intervention studies.

Increased cerebral microbleeds and cortical superficial siderosis in pediatric patients with Down syndrome

BACKGROUND

Patients with Down syndrome carry a third copy of the amyloid precursor protein gene, which is localized on chromosome 21. Consequently, these patients are prone to develop early-onset Alzheimer disease and cerebral amyloid angiopathy. Post-mortem studies suggest increased amyloid deposition to be already detectable in children with Down syndrome. The aim of our study was to evaluate if amyloid-related changes in pediatric Down syndrome patients can be detected in vivo using MRI biomarkers of cerebral microbleeds and cortical superficial siderosis.

MATERIALS AND METHODS

This retrospective study included 12 patients with Down syndrome (mean age = 5.0 years) and 12 age-matched control subjects (mean age = 4.8 years). Frequency and location of microbleeds and siderosis were assessed on blood-sensitive MRI sequences in a consensus reading by two radiologists applying a modified Microbleed Anatomical Rating Scale.

RESULTS

Down syndrome patients showed a significantly higher mean microbleeds count and likelihood of siderosis than age-matched controls. Across groups, the highest microbleeds count was found in lobar regions (gray and white matter of frontal, parietal, temporal, and occipital lobes, and the insula), while fewer microbleeds were located in subcortical and infratentorial regions. The number of microbleeds increased over time in all three Down syndrome patients with a follow-up exam.

CONCLUSION

In vivo MRI biomarkers can support the diagnosis of early-onset cerebral amyloid angiopathy, which might already be present in pediatric Down syndrome patients. This might contribute to clinical decision-making and potentially to the development of therapeutic and prophylactic approaches, as cerebral amyloid angiopathy increases the risk for intracranial hemorrhage and may be associated with increased risk of developing Alzheimer disease.

The Role of Oxidative Stress in the Pathomechanism of Congenital Malformations

Congenital anomalies are significant causes of mortality and morbidity in infancy and childhood. Embryogenesis requires specific signaling pathways to regulate cell proliferation and differentiation. These signaling pathways are sensitive to endogenous and exogenous agents able to produce several structural changes of the developing fetus. Oxidative stress, due to an imbalance between the production of reactive oxygen species and antioxidant defenses, disrupts signaling pathways with a causative role in birth defects. This review provides a basis for understanding the role of oxidative stress in the pathomechanism of congenital malformations, discussing the mechanisms related to some congenital malformations. New insights in the knowledge of pathomechanism of oxidative stress-related congenital malformations, according to experimental and human studies, represent the basis of possible clinical applications in screening, prevention, and therapies.

Immunotherapy to improve cognition and reduce pathological species in an Alzheimer's disease mouse model

Background

Alzheimer’s disease (AD) is characterized by physiologically endogenous proteins amyloid beta (Aβ) and tau undergoing a conformational change and accumulating as soluble oligomers and insoluble aggregates. Tau and Aβ soluble oligomers, which contain extensive β-sheet secondary structure, are thought to be the most toxic forms. The objective of this study was to determine the ability of TWF9, an anti-β-sheet conformation antibody (aβComAb), to selectively recognize pathological Aβ and phosphorylated tau in AD human tissue compared with cognitively normal age-matched controls and to improve the performance of old 3xTg-AD mice with advanced pathology in behavioral testing after acute treatment with TWF9.

Methods

In this study, we used immunohistochemistry, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA) to characterize TWF9 specificity. We further assessed cognitive performance in old (18–22 months) 3xTg-AD mice using both a Barnes maze and novel object recognition after intraperitoneal administration of TWF9 (4 mg/kg) biweekly for 2 weeks before the start of behavioral testing. Injections continued for the duration of the behavioral testing, which lasted 2 weeks.

Results

Histological analysis of TWF9 in formalin-fixed paraffin-embedded human control and AD (ABC score: A3B3C3) brain tissue revealed preferential cytoplasmic immunoreactivity in neurons in the AD tissue compared with controls (p < 0.05). Furthermore, ELISA using oligomeric and monomeric Aβ showed a preferential affinity for oligomeric Aβ. Immunoprecipitation studies showed that TWF9 extracted both phosphorylated tau (p < 0.01) and Aβ (p < 0.01) from fresh frozen brain tissues. Results show that treated old 3xTg-AD mice have an enhanced novel object recognition memory (p < 0.01) and Barnes maze performance (p = 0.05) compared with control animals. Overall plaque burden, neurofibrillary tangles, microgliosis, and astrocytosis remained unchanged. Soluble phosphorylated tau was significantly reduced in TWF9-treated mice (p < 0.05), and there was a trend for a reduction in soluble Aβ levels in the brain homogenates of female 3xTg-AD mice (p = 0.06).

Conclusions

This study shows that acute treatment with an aβComAb can effectively improve performance in behavioral testing without reduction of amyloid plaque burden, and that peripherally administered IgG can affect levels of pathological species in the brain.

Clinical aspects and biomarkers of Alzheimer's disease in Down syndrome

Alzheimer's disease (AD) may affect in excess of 90% of individuals with Down syndrome (DS) after age 60, due to duplication of the APP gene in trisomy of chromosome 21, with neuropathology that is comparable to Sporadic AD and Familial AD (FAD). Previous literature suggested some unique features in clinical presentation of dementia in DS (DSd), which might be due to diagnostic difficulties, or represent a real difference compared to SAD or FAD. We review current knowledge on clinical diagnosis and presentation of dementia in DS in comparison with FAD due to APP mutations and APP duplication. We suggest that the clinical presentation in DS (prominent memory decline and behavioral symptoms, and early development of myoclonus and seizures) are similar to the clinical features associated with APP mutations that is known to have an increased Aβ42/ Aβ40 ratio, and highlight the relative lack of vascular complications associated with cerebral amyloid angiopathy in DS in comparison with those rare individuals with FAD due to duplication APP. We consider the biomarker evidence associated with DS and DSd with reference to Aβ peptide levels and oxidative stress, and suggest future directions for research to explore the potential mechanisms associated with the clinical presentation of DSd.

HNE-modified proteins in Down syndrome: Involvement in development of Alzheimer disease neuropathology

Down syndrome (DS), trisomy of chromosome 21, is the most common genetic form of intellectual disability. The neuropathology of DS involves multiple molecular mechanisms, similar to AD, including the deposition of beta-amyloid (Aβ) into senile plaques and tau hyperphosphorylationg in neurofibrillary tangles. Interestingly, many genes encoded by chromosome 21, in addition to being primarily linked to amyloid-beta peptide (Aβ) pathology, are responsible for increased oxidative stress (OS) conditions that also result as a consequence of reduced antioxidant system efficiency. However, redox homeostasis is disturbed by overproduction of Aβ, which accumulates into plaques across the lifespan in DS as well as in AD, thus generating a vicious cycle that amplifies OS-induced intracellular changes. The present review describes the current literature that demonstrates the accumulation of oxidative damage in DS with a focus on the lipid peroxidation by-product, 4-hydroxy-2-nonenal (HNE). HNE reacts with proteins and can irreversibly impair their functions. We suggest that among different post-translational modifications, HNE-adducts on proteins accumulate in DS brain and play a crucial role in causing the impairment of glucose metabolism, neuronal trafficking, protein quality control and antioxidant response. We hypothesize that dysfunction of these specific pathways contribute to accelerated neurodegeneration associated with AD neuropathology.

Aberrations in circulating inflammatory cytokine levels in patients with Down syndrome: a meta-analysis

Evidence suggests that immune system alterations in Down syndrome (DS) may be early events that drive neuropathological and cognitive changes of Alzheimer's disease. The primary objective of this meta-analysis was to investigate whether there is an abnormal cytokine profile in DS patients when compared with healthy control (HC) subjects. A systematic search of Pubmed and Web of Science identified 19 studies with 957 DS patients and 541 HC subjects for this meta-analysis. Random effects meta-analysis demonstrated that patients with DS had significantly increased circulating tumor necrosis factor-α (Hedges’ g = 1.045, 95% confidence interval (CI) = 0.192 to 1.898, p = 0.016), interleukin (IL)-1β (Hedges’ g = 0.696, 95% confidence CI = 0.149 to 1.242, p = 0.013), interferon-γ (Hedges’ g = 0.978, 95% CI = 0.417 to 1.539, p = 0.001) and neopterin (Hedges’ g = 0.815, 95% CI = 0.423 to 1.207, p < 0.001) levels compared to HC subjects. No significant differences were found between patients with DS and controls for concentrations of IL-4, IL-6, IL8 and IL-10. In addition, most of the cytokine data in this meta-analysis were from children with DS and HC, and subgroup analysis showed that children with DS had elevated tumor necrosis factor-α, IL-1β and interferon-γ levels when compared with controls. Taken together, these results demonstrated that patients (children) with DS are accompanied by increased circulating cytokine tumor necrosis factor-α, IL-1β and interferon-γ levels, strengthening the clinical evidence that patients (children) with DS are accompanied by an abnormal inflammatory response.

Prominent Intrapulmonary Bronchopulmonary Anastomoses and Abnormal Lung Development in Infants and Children with Down Syndrome

OBJECTIVES

To determine the frequency of histologic features of impaired lung vascular and alveolar development and to identify the presence of intrapulmonary bronchopulmonary anastomoses (IBA) in infants and children who died with Down syndrome.

STUDY DESIGN

A retrospective review of autopsy reports and lung histology from 13 children with Down syndrome (ages: 0-8 years) was performed. Histologic features of abnormal lung development were identified and semiquantified, including the presence of IBA. Three-dimensional reconstructions of IBA were also performed. Comparisons were made with 4 age-matched patients without Down syndrome with congenital heart defects who underwent autopsies during this time period.

RESULTS

Of the 13 subjects with Down syndrome, 69% died from cardiac events, 77% had a congenital heart defect, and 46% had a clinical diagnosis of pulmonary hypertension. Lung histology from all subjects with Down syndrome demonstrated alveolar simplification, and 92% had signs of persistence of a double capillary network in the distal lung. The lungs from the subjects with Down syndrome frequently had features of pulmonary arterial hypertensive remodeling (85%), and prominent bronchial vessels and IBA were observed in all subjects with Down syndrome. These features were more frequent in subjects with Down syndrome compared with control subjects.

CONCLUSIONS

Children with Down syndrome who died of cardiopulmonary diseases often have histologic evidence of impaired lung alveolar and vascular development, including the presence of prominent IBA and pulmonary hypertension. We speculate that children with Down syndrome are at risk for reduced lung surface area and recruitment of IBA, which may worsen gas exchange in subjects with Down syndrome.

Cognitive ability in Down syndrome and its relationship to urinary neopterin, a marker of activated cellular immunity

BACKGROUND

Neopterin is an unconjugated pteridine that is secreted in large quantities by activated macrophages and can be used as a clinical marker of activated cellular immunity and oxidative stress. We aimed to investigate whether urinary neopterin levels are associated with cognitive function in people with Down syndrome (DS).

METHODS

Out of 32 adults with DS who originally participated in a longitudinal study, 25 were followed up at 4 years. Informants rated their adaptive behavior (ABAS) and the adults with DS attempted assessments of language skills and memory at both baseline and follow-up time points (Modified Memory Object Task, MOMT), and receptive vocabulary (British Picture Vocabulary Scale, BPVS).

RESULTS

Neopterin/creatinine levels were negatively correlated with change in the MOMT total score (Spearman's Rho=-0.517, p=0.020) and change in the MOMT delayed recall score (Spearman's Rho=-0.577, p=0.008) over time, i.e. higher neopterin/creatinine level was associated with worse performance on a test of cognitive ability over time.

CONCLUSION

Urine neopterin may have potential as a biomarker for memory decline in Down syndrome, and could potentially also help to track progression of mild cognitive impairment (MCI) to Alzheimer's disease in other high risk populations.

Novel roles of amyloid-beta precursor protein metabolites in fragile X syndrome and autism

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and is associated with up to 5% of autism cases. Several promising drugs are in preclinical testing for FXS; however, bench-to-bedside plans for the clinic are severely limited due to lack of validated biomarkers and outcome measures. Published work from our laboratories has demonstrated altered levels of amyloid-beta (Aβ) precursor protein (APP) and its metabolites in FXS and idiopathic autism. Westmark and colleagues have focused on β-secretase (amyloidogenic) processing and the accumulation of Aβ peptides in adult FXS models, whereas Lahiri and Sokol have studied α-secretase (non-amyloidogenic or anabolic) processing and altered levels of sAPPα and Aβ in pediatric autism and FXS. Thus, our groups have hypothesized a pivotal role for these Alzheimer's disease (AD)-related proteins in the neurodevelopmental disorders of FXS and autism. In this review, we discuss the contribution of APP metabolites to FXS and autism pathogenesis as well as the potential use of these metabolites as blood-based biomarkers and therapeutic targets. Our future focus is to identify key underlying mechanisms through which APP metabolites contribute to FXS and autism condition-to-disease pathology. Positive outcomes will support utilizing APP metabolites as blood-based biomarkers in clinical trials as well as testing drugs that modulate APP processing as potential disease therapeutics. Our studies to understand the role of APP metabolites in developmental conditions such as FXS and autism are a quantum leap for the neuroscience field, which has traditionally restricted any role of APP to AD and aging.

Increased Lung Expression of Anti-Angiogenic Factors in Down Syndrome: Potential Role in Abnormal Lung Vascular Growth and the Risk for Pulmonary Hypertension

BACKGROUND AND AIMS

Infants with Down syndrome (DS) or Trisomy 21, are at high risk for developing pulmonary arterial hypertension (PAH), but mechanisms that increase susceptibility are poorly understood. Laboratory studies have shown that early disruption of angiogenesis during development impairs vascular and alveolar growth and causes PAH. Human chromosome 21 encodes known anti-angiogenic factors, including collagen18a1 (endostatin, ES), ß-amyloid peptide (BAP) and Down Syndrome Critical Region 1 (DSCR-1). Therefore, we hypothesized that fetal lungs from subjects with DS are characterized by early over-expression of anti-angiogenic factors and have abnormal lung vascular growth in utero.

METHODS

Human fetal lung tissue from DS and non-DS subjects were obtained from a biorepository. Quantitative reverse transcriptase PCR (qRT-PCR) was performed to assay 84 angiogenesis-associated genes and individual qRT-PCR was performed for ES, amyloid protein precursor (APP) and DSCR1. Western blot analysis (WBA) was used to assay lung ES, APP and DSCR-1 protein contents. Lung vessel density and wall thickness were determined by morphometric analysis.

RESULTS

The angiogenesis array identified up-regulation of three anti-angiogenic genes: COL18A1 (ES), COL4A3 (tumstatin) and TIMP3 (tissue inhibitor of metallopeptidase 3) in DS lungs. Single qRT-PCR and WBA showed striking elevations of ES and APP mRNA (p = 0.022 and p = 0.001) and protein (p = 0.040 and p = 0.002; respectively). Vessel density was reduced (p = 0.041) and vessel wall thickness was increased in DS lung tissue (p = 0.033) when compared to non-DS subjects.

CONCLUSIONS

We conclude that lung anti-angiogenic factors, including COL18A1 (ES), COL4A3, TIMP3 and APP are over-expressed and fetal lung vessel growth is decreased in subjects with DS. We speculate that increased fetal lung anti-angiogenic factor expression due to trisomy 21 impairs lung vascular growth and signaling, which impairs alveolarization and contributes to high risk for PAH during infancy.

Generation of Rabbit Monoclonal Antibody to Amyloid-β38 (Aβ38): Increased Plasma Aβ38 Levels in Down Syndrome

Secreted soluble amyloid-β (Aβ)38 is the second most prominent Aβ form next to Aβ40, and is found in cerebrospinal fluid (CSF) and blood. Recent studies have shown the importance of quantitation of CSF Aβ38 levels in combination with those of Aβ40 and Aβ42 to support the diagnosis of Alzheimer's disease (AD), and other neurodegenerative diseases, and to facilitate drug discovery studies. However, the availability of reliable and specific Aβ38 monoclonal antibody is limited. Our first aim was to generate and partially characterize rabbit monoclonal antibody (RabmAb) to Aβ38. The antibody was specific to Aβ38, since it did not react with Aβ37, Aβ39, Aβ40, or Aβ42 in ELISA or immunoblotting. The antibody was sensitive enough to measure Aβ38 levels in plasma. Our second aim was to quantitate Aβ38 levels in plasma from older Down syndrome (DS) persons and age-matched controls. Persons with DS (35 years and older) have neuropathological changes characteristic of AD. Studies have shown that plasma Aβ40 and Aβ42 levels are higher in older persons with DS than in controls. However, none examined Aβ38 levels in DS. Our quantitation data showed that, like Aβ40 and Aβ42 plasma levels, Aβ38 plasma levels were higher in DS than in controls. Longitudinal studies will determine whether plasma Aβ38 levels in combination with levels of Aβ40 and Aβ42 are useful to predict early signs of AD in DS.

Biomarkers of Alzheimer Disease in Children with Obstructive Sleep Apnea: Effect of Adenotonsillectomy

STUDY OBJECTIVE

Obese children are at increased risk for developing obstructive sleep apnea (OSA), and both of these conditions are associated with an increased risk for end-organ morbidities. Both OSA and obesity (OB) have been associated with increased risk for Alzheimer disease (AD). This study aimed to assess whether OSA and OB lead to increased plasma levels of 2 AD markers amyloid β protein 42 (Aβ42) and pre-senilin 1 (PS1).

METHODS

Fasting morning plasma samples from otherwise healthy children with a diagnosis of OB, OSA, or both (OSA+OB), and controls, and in a subset of children with OSA after adenotonsillectomy (T&A) were assayed for Aβ42 and PS1 levels using commercial enzyme-linked immunosorbent assay kits.

RESULTS

286 children (mean age of 7.2 ± 2.7 y) were evaluated. Compared to control subjects, OB children had similar Aβ42 (108.3 ± 31.7 pg/mL versus 83.6 ± 14.6 pg/mL) and PS1 levels (0.89 ± 0.44 ng/mL versus 0.80 ± 0.29 pg/mL). However, OSA children (Aβ42: 186.2 ± 66.7 pg/mL; P < 0.001; PS1: 3.42 ± 1.46 ng/mL; P < 0.001), and particularly OSA+OB children had significant elevations in both Aβ42 (349.4 ± 112.9 pg/mL; P < 0.001) and PS1 (PS1: 4.54 ± 1.16 ng/mL; P < 0.001) circulating concentrations. In a subset of 24 children, T&A resulted in significant reductions of Aβ42 (352.0 ± 145.2 versus 151.9 ± 81.4 pg/mL; P < 0.0001) and PS1 (4.82 ± 1.09 versus 2.02 ± 1.18 ng/mL; P < 0.0001).

CONCLUSIONS

Thus, OSA, and particularly OSA+OB, are associated with increased plasma levels of AD biomarkers, which decline upon treatment of OSA in a representative, yet not all- encompassing subset of patients, suggesting that OSA may accelerate AD-related processes even in early childhood. However, the cognitive and overall health-related implications of these findings remain to be defined.

Synthetic combinations of missense polymorphic genetic changes underlying Down syndrome susceptibility

Single nucleotide polymorphisms (SNPs) are important biomolecular markers in health and disease. Down syndrome, or Trisomy 21, is the most frequently occurring chromosomal abnormality in live-born children. Here, we highlight associations between SNPs in several important enzymes involved in the one-carbon folate metabolic pathway and the elevated maternal risk of having a child with Down syndrome. Our survey highlights that the combination of SNPs may be a more reliable predictor of the Down syndrome phenotype than single SNPs alone. We also describe recent links between SNPs in p53 and its related pathway proteins and Down syndrome, as well as highlight several proteins that help to associate apoptosis and p53 signaling with the Down syndrome phenotype. In addition to a comprehensive review of the literature, we also demonstrate that several SNPs reside within the same regions as these Down syndrome-linked SNPs, and propose that these closely located nucleotide changes may provide new candidates for future exploration.

Semantic Verbal Fluency Pattern, Dementia Rating Scores and Adaptive Behavior Correlate With Plasma Aβ42 Concentrations in Down Syndrome Young Adults

Down syndrome (DS) is an intellectual disability (ID) disorder in which language and specifically, verbal fluency are strongly impaired domains; nearly all adults show neuropathology of Alzheimer’s disease (AD), including amyloid deposition by their fifth decade of life. In the general population, verbal fluency deficits are considered a strong AD predictor being the semantic verbal fluency task (SVFT) a useful tool for enhancing early diagnostic. However, there is a lack of information about the association between the semantic verbal fluency pattern (SVFP) and the biological amyloidosis markers in DS. In the current study, we used the SVFT in young adults with DS to characterize their SVFP, assessing total generated words, clustering, and switching. We then explored its association with early indicators of dementia, adaptive behavior and amyloidosis biomarkers, using the Dementia Questionnaire for Persons with Intellectual Disability (DMR), the Adaptive Behavior Assessment System-Second Edition (ABAS-II), and plasma levels of Aβ peptides (Aβ₄₀ and Aβ₄₂), as a potent biomarker of AD. In DS, worse performance in SVFT and poorer communication skills were associated with higher plasma Aβ₄₂ concentrations, a higher DMR score and impaired communication skills (ABAS–II). The total word production and switching ability in SVFT were good indicators of plasma Aβ₄₂ concentration. In conclusion, we propose the SVFT as a good screening test for early detection of dementia and amyloidosis in young adults with DS.

The Ubiquitin-Proteasome System and Molecular Chaperone Deregulation in Alzheimer's Disease

One of the shared hallmarks of neurodegenerative diseases is the accumulation of misfolded proteins. Therefore, it is suspected that normal proteostasis is crucial for neuronal survival in the brain and that the malfunction of this mechanism may be the underlying cause of neurodegenerative diseases. The accumulation of amyloid plaques (APs) composed of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles (NFTs) composed of misfolded Tau proteins are the defining pathological markers of Alzheimer's disease (AD). The accumulation of these proteins indicates a faulty protein quality control in the AD brain. An impaired ubiquitin-proteasome system (UPS) could lead to negative consequences for protein regulation, including loss of function. Another pivotal mechanism for the prevention of misfolded protein accumulation is the utilization of molecular chaperones. Molecular chaperones, such as heat shock proteins (HSPs) and FK506-binding proteins (FKBPs), are highly involved in protein regulation to ensure proper folding and normal function. In this review, we elaborate on the molecular basis of AD pathophysiology using recent data, with a particular focus on the role of the UPS and molecular chaperones as the defensive mechanism against misfolded proteins that have prion-like properties. In addition, we propose a rational therapy approach based on this mechanism.

Assessing cognitive improvement in people with Down syndrome: important considerations for drug-efficacy trials

Experimental research over just the past decade has raised the possibility that learning deficits connected to Down syndrome (DS) might be effectively managed by medication. In the current chapter, we touch on some of the work that paved the way for these advances and discuss the challenges associated with translating them. In particular, we highlight sources of phenotypic variability in the DS population that are likely to impact performance assessments. Throughout, suggestions are made on how to detect meaningful changes in cognitive-adaptive function in people with DS during drug treatment. The importance of within-subjects evaluation is emphasized.

Erythrocyte phospholipid molecular species and fatty acids of Down syndrome children compared with non-affected siblings

The majority of children with Down syndrome (DS) develop Alzheimer's disease (AD) at an early age. Although long-chainn-3 fatty acids (FA) are protective of neurodegeneration, little is known about the FA status in DS. In the present study, we aimed to investigate whether children with DS presented altered plasma and erythrocyte membrane phospholipids (PL) FA composition, when compared with their non-affected siblings. Venous blood samples were analysed for plasma and erythrocyte membrane FA composition by TLC followed by GC techniques. Lipid molecular species were determined by electrospray ionisation/tandem MS (ESI-MS/MS). FA analysis measured by standard GC showed an increased concentration of MUFA and a decreased concentration of plasmalogens in major PL fractions, but there were no differences in the concentrations of arachidonic acid or DHA. However, as identified by ESI-MS/MS, children with DS had increased levels of the following erythrocyte PL molecular species: 16 : 0–16 : 0, 16 : 0–18 : 1 and 16 : 0–18 : 2n-6, with reduced levels of 16 : 0–20 : 4n-6 species. Children with DS presented significantly higher levels of MUFA in both plasma and erythrocyte membrane, as well as higher levels of saturated and monounsaturated molecular species. Of interest was the almost double proportion of 16 : 0–18 : 2n-6 and nearly half the proportion of 16 : 0–20 : 4n-6 of choline phosphoacylglycerol species in children with DS compared with their non-affected siblings. These significant differences were only revealed by ESI-MS/MS and were not observed in the GC analysis. Further investigations are needed to explore molecular mechanisms and to test the association between the pathophysiology of DS and the risk of AD.

Redox proteomics analysis to decipher the neurobiology of Alzheimer-like neurodegeneration: overlaps in Down's syndrome and Alzheimer's disease brain

Accumulation of oxidative damage is a common feature of neurodegeneration that, together with mitochondrial dysfunction, point to the fact that reactive oxygen species are major contributors to loss of neuronal homoeostasis and cell death. Among several targets of oxidative stress, free-radical-mediated damage to proteins is particularly important in aging and age-related neurodegenerative diseases. In the majority of cases, oxidative-stress-mediated post-translational modifications cause non-reversible modifications of protein structure that consistently lead to impaired function. Redox proteomics methods are powerful tools to unravel the complexity of neurodegeneration, by identifying brain proteins with oxidative post-translational modifications that are detrimental for protein function. The present review discusses the current literature showing evidence of impaired pathways linked to oxidative stress possibly involved in the neurodegenerative process leading to the development of Alzheimer-like dementia. In particular, we focus attention on dysregulated pathways that underlie neurodegeneration in both aging adults with DS (Down's syndrome) and AD (Alzheimer's disease). Since AD pathology is age-dependent in DS and shows similarities with AD, identification of common oxidized proteins by redox proteomics in both DS and AD can improve our understanding of the overlapping mechanisms that lead from normal aging to development of AD. The most relevant proteomics findings highlight that disturbance of protein homoeostasis and energy production are central mechanisms of neurodegeneration and overlap in aging DS and AD. Protein oxidation affects crucial intracellular functions and may be considered a 'leitmotif' of degenerating neurons. Therapeutic strategies aimed at preventing/reducing multiple components of processes leading to accumulation of oxidative damage will be critical in future studies.

Unraveling the complexity of neurodegeneration in brains of subjects with Down syndrome: insights from proteomics

Down syndrome (DS) is one of the most common genetic causes of intellectual disability characterized by multiple pathological phenotypes, among which neurodegeneration is a key feature. The neuropathology of DS is complex and likely results from impaired mitochondrial function, increased oxidative stress, and altered proteostasis. After the age of 40 years, many (most) DS individuals develop a type of dementia that closely resembles that of Alzheimer's disease with deposition of senile plaques and neurofibrillary tangles. A number of studies demonstrated that increased oxidative damage, accumulation of damaged/misfolded protein aggregates, and dysfunction of intracellular degradative systems are critical events in the neurodegenerative processes. This review summarizes the current knowledge that demonstrates a “chronic” condition of oxidative stress in DS pointing to the putative molecular pathways that could contribute to accelerate cognition and memory decline. Proteomics and redox proteomics studies are powerful tools to unravel the complexity of DS phenotypes, by allowing to identifying protein expression changes and oxidative PTMs that are proved to be detrimental for protein function. It is reasonable to suggest that changes in the cellular redox status in DS neurons, early from the fetal period, could provide a fertile environment upon which increased aging favors neurodegeneration. Thus, after a critical age, DS neuropathology can be considered a human model of early Alzheimer's disease and could contribute to understanding the overlapping mechanisms that lead from normal aging to development of dementia.

Detection of amyloid-β42 using a waveguide-coupled bimetallic surface plasmon resonance sensor chip in the intensity measurement mode

The waveguide-coupled bimetallic (WcBiM) surface plasmon resonance (SPR) chip had been utilized in the intensity interrogation detection mode to detect amyloid-β42 (Aβ42), a biomarker of the Alzheimer disease. The SPR reflectance curve of the WcBiM chip has the narrower full-width-at-half-maximum (FWHM) compared with the SPR reflectance curve of the conventional gold (Au) chip, resulting in the steeper gradient. For the enhancement of resolution, the light source was fixed at an angle where the slope of the reflectance curve is the steepest, and the change in the reflectance was monitored. For the detection of Aβ42, the antibody of Aβ42 (anti-Aβ42) was immobilized on the WcBiM SPR chip using the self-assembled monolayer. The SPR responses, the average changes in the reflectance to the Aβ42 at the concentrations of 100 pg/ml, 250 pg/ml, 500 pg/ml, 750 pg/ml, 1,000 pg/ml, and 2,000 pg/ml were 0.0111%, 0.0305%, 0.0867%, 0.1712%, 0.3021%, and 0.5577%, respectively, for the three replicates. From linear regression analysis, the calibration curve indicated that the SPR response had a linear relation with Aβ42 with the concentration in the range of 100 pg/ml to 2,000 pg/ml. A control experiment showed the anti-Aβ42-modified surface of the WcBiM chip had a high specificity to Aβ42. Thus, the enhanced resolution by utilizing the WcBiM SPR chip in the intensity interrogation detection mode aids the diagnosis of the Alzheimer disease by detecting the Aβ42 around the criteria concentration (500 pg/ml) without any labeling.

What's hAPPening at synapses? The role of amyloid β-protein precursor and β-amyloid in neurological disorders

Accumulating evidence suggests that dysregulated levels of amyloid β-protein precursor (APP) and its catabolites contribute to the impaired synaptic plasticity and seizure incidence observed in several neurological disorders, including Alzheimer's disease, fragile X syndrome, Down's syndrome, autism, epilepsy and Parkinson's disease as well as in brain injury. This review article summarizes what is known regarding the synaptic synthesis, processing and function of APP and amyloid-beta (Aβ), as well as discusses how these proteins could contribute to the altered synaptic plasticity and pathology of the aforementioned disorders. In addition, APP and its proteolytic fragments are emerging as biomarkers for neurological health, and pharmacological interventions that modulate their levels, such as secretase inhibitors, passive immunotherapy against Aβ and mGluR5 antagonists, are reviewed.

Gene regulation as a potential avenue for the treatment of neurodegenerative disorders

BACKGROUND

As more people live to an older age, the frequency of diseases associated with longer life begins to increase. Neurodegenerative disorders are the worst of these in that there is now no treatment that offers any real improvement. For this reason, any new avenue of research that could lead to a treatment needs to be rigorously pursued. In many cases, neurodegenerative diseases are associated with the expression of a protein with an altered conformation or that generates a breakdown product associated with the cause. Clearly, the prevention of this process is a key therapeutic target.

OBJECTIVE

In this review, the potential for regulating gene expression to prevent or reverse neurodegenerative disease is explored.

CONCLUSIONS

Whereas much research has been directed at the proteins associated with neurodegeneration, understanding what controls their expression presents a new way this issue could be studied.

Blood biomarkers of methylation in Down syndrome and metabolic simulations using a mathematical model

SCOPE

The study tests the metabolites of the methylation cycle in individuals with Down syndrome (DS) and applies a mathematical model in order to change this cycle by nutritional factors.

METHODS AND RESULTS

We measured concentrations of the metabolites related to the methylation cycle in the blood of 35 young individuals with DS and 47 controls of comparable age. Moreover, we applied a mathematical model to learn more about the regulation of the methylation cycle in DS. Concentrations of cystathionine, cysteine, betaine, choline, dimethylglycine, S-adenosylhomocysteine (SAH), S-adenosylmethionine (SAM), and holotranscobalamin were significantly higher in DS compared to the controls. The median SAM/SAH ratio was lower in DS and that of methionine and reduced glutathione did not differ significantly between the groups. The mathematical model showed that enhanced methionine turnover and accelerated Hcy-remethylation might explain the shift in the methylation cycle in DS.

CONCLUSION

In addition to the DS-related excess of cystathionine beta synthase (CBS) activity, increases in the activities of MS and betaine homocysteine methyl transferase, and in methionine input were necessary to account for the changes in metabolite levels observed in DS. A low-methionine diet might offer a perspective for reversing the metabolic imbalance in DS, but this awaits clinical investigations.

Plasma amyloid-β as a function of age, level of intellectual disability, and presence of dementia in Down syndrome

Adults with Down syndrome (DS) are at risk for developing Alzheimer's disease (AD). While plasma amyloid-β (Aβ) is known to be elevated in DS, its relationship to cognitive functioning is unknown. To assess this relationship, samples from two groups of subjects were used. In the first group, nondemented adults with DS were compared to: 1) a group of young and old individuals without DS and 2) to a group of patients with AD. Compared to these controls, there were significantly higher levels of plasma Aβ in nondemented adults with DS while AD patients showed lower levels of plasma Aβ. A larger second group included demented and nondemented adults with DS, in order to test the hypothesis that plasma Aβ may vary as a function of dementia and Apolipoprotein E (ApoE) genotype. Plasma Aβ levels alone did not dissociate DS adults with and without dementia. However, in demented adults with DS, ApoE4 was associated with higher Aβ40 but not Aβ42. After controlling for level of intellectual disability (mild, moderate, severe) and the presence or absence of dementia, there was an improved prediction of neuropsychological scores by plasma Aβ. In summary, plasma Aβ can help predict cognitive function in adults with DS independently of the presence or absence of dementia.

Oxidative Stress and Down Syndrome: A Route toward Alzheimer-Like Dementia

Down syndrome (DS) is one of the most frequent genetic abnormalities characterized by multiple pathological phenotypes. Indeed, currently life expectancy and quality of life for DS patients have improved, although with increasing age pathological dysfunctions are exacerbated and intellectual disability may lead to the development of Alzheimer's type dementia (AD). The neuropathology of DS is complex and includes the development of AD by middle age, altered free radical metabolism, and impaired mitochondrial function, both of which contribute to neuronal degeneration. Understanding the molecular basis that drives the development of AD is an intense field of research. Our laboratories are interested in understanding the role of oxidative stress as link between DS and AD. This review examines the current literature that showed oxidative damage in DS by identifying putative molecular pathways that play a central role in the neurodegenerative processes. In addition, considering the role of mitochondrial dysfunction in neurodegenerative phenomena, results demonstrating the involvement of impaired mitochondria in DS pathology could contribute a direct link between normal aging and development of AD-like dementia in DS patients.

Reversal of fragile X phenotypes by manipulation of AβPP/Aβ levels in Fmr1KO mice

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and the leading known genetic cause of autism. Fragile X mental retardation protein (FMRP), which is absent or expressed at substantially reduced levels in FXS, binds to and controls the postsynaptic translation of amyloid β-protein precursor (AβPP) mRNA. Cleavage of AβPP can produce β-amyloid (Aβ), a 39-43 amino acid peptide mis-expressed in Alzheimer's disease (AD) and Down syndrome (DS). Aβ is over-expressed in the brain of Fmr1(KO) mice, suggesting a pathogenic role in FXS. To determine if genetic reduction of AβPP/Aβ rescues characteristic FXS phenotypes, we assessed audiogenic seizures (AGS), anxiety, the ratio of mature versus immature dendritic spines and metabotropic glutamate receptor (mGluR)-mediated long-term depression (LTD) in Fmr1(KO) mice after removal of one App allele. All of these phenotypes were partially or completely reverted to normal. Plasma Aβ(1-42) was significantly reduced in full-mutation FXS males compared to age-matched controls while cortical and hippocampal levels were somewhat increased, suggesting that Aβ is sequestered in the brain. Evolving therapies directed at reducing Aβ in AD may be applicable to FXS and Aβ may serve as a plasma-based biomarker to facilitate disease diagnosis or assess therapeutic efficacy.

Plasma β amyloid and the risk of Alzheimer's disease in Down syndrome

Extracellular deposition of amyloid beta peptide (Aβ) has been implicated as a critical step in the pathogenesis of Alzheimer's disease (AD). In Down syndrome (DS), Alzheimer's disease is assumed to be caused by the triplication and overexpression of the gene for amyloid precursor protein (APP), located on chromosome 21. Plasma concentrations of Aβ1-40 and Aβ1-42 were determined in a population based study of 506 persons with DS, who were screened annually for dementia. We used Cox proportional hazards models to determine the risk of dementia. Demented persons with DS have a significantly higher plasma Aβ1-40 concentration than the nondemented (p = 0.05). Those with the highest concentrations of Aβ1-40 and Aβ1-42 have a higher risk to develop dementia. The risk to develop dementia during follow-up (mean 4.7 years) increased to 2.56 (95% confidence interval, 1.39-4.71) for Aβ1-42 and 2.16 (95% confidence interval, 1.14-4.10) for Aβ1-40. High plasma concentration of plasma Aβ1-40 and Aβ1-42 are determinants of the risk of dementia in persons with DS.

Comparison of conventional ELISA with electrochemiluminescence technology for detection of amyloid-β in plasma

Plasma amyloid-β (Aβ) level could be useful as a non-invasive biomarker in Alzheimer's disease research. We compared a multiplex electrochemiluminescence detection method with a well established ELISA method for plasma Aβ quantification. Compared to the ELISA method, the electrochemiluminescence detection method demonstrates a statistically significant, but modest correlation. The reasons for this may include the differences in the affinities of antibodies, and purity and source of Aβ peptides used as standards. However, the advantages of electrochemiluminescence detection technology include short processing time and small sample volume. This comparison demonstrates the need for a further study in optimizing this system.

Effect of Anticoagulants on Amyloid β-Protein Precursor and Amyloid Beta Levels in Plasma

Altered levels of amyloid β-protein precursor (AβPP) and/or amyloid beta (Aβ) are characteristic of several neurological disorders including Alzheimer's disease (AD), Down syndrome (DS), Fragile X syndrome (FXS), Parkinson's disease (PD), autism and epilepsy. Thus, these proteins could serve as valuable blood-based biomarkers for assessing disease severity and pharmacological efficacy. We have observed significant differences in Aβ_1-42 levels in human plasma dependent on the anticoagulant utilized during blood collection. Our data suggests that anticoagulants alter AβPP processing and that care needs to be used in comparing published studies that have not utilized the same blood collection methodology.

Direct exposure of guinea pig CNS to human luteinizing hormone increases cerebrospinal fluid and cerebral beta amyloid levels

BACKGROUND/AIMS

Luteinizing hormone (LH) has been shown to alter the metabolism of beta amyloid (Aβ), a key protein in Alzheimer's disease (AD) pathogenesis. While LH and components required for LH receptor signalling are present in the brain, their role in the CNS remains unclear. In vitro, LH has been shown to facilitate neurosteroid production and alter Aβ metabolism. However, whether LH can directly modulate cerebral Aβ levels in vivo has not previously been studied. In this study, we investigated the effect of chronic administration of LH to the guinea pig CNS on cerebral Aβ levels.

METHODS

Gonadectomised male animals were administered, via cortical placement, either placebo or LH slow-release pellets. At 14 and 28 days after treatment, animals were sacrificed. Brain, plasma and CSF were collected and Aβ levels measured via ELISA. Levels of the Aβ precursor protein (APP) and the neurosteroidogenic enzyme cytochrome P450 side-chain cleavage enzyme (P450scc) were also assayed.

RESULTS

An increase in CSF Aβ40 levels was observed 28 days following treatment. These CSF data also reflected changes in Aβ40 levels observed in brain homogenates. No change was observed in plasma Aβ40 levels but APP and its C-terminal fragments (APP-CTF) were significantly increased in response to LH exposure. Protein expression of P450scc was increased after 28 days of LH exposure, suggesting activation of the LH receptor.

CONCLUSION

These data indicate that direct exposure of guinea pig CNS to LH results in altered brain Aβ levels, perhaps due to altered APP expression/metabolism.

Assessment and rehabilitation of cognitive impairment in multiple sclerosis

Patients with multiple sclerosis (MS) have a substantial risk of cognitive dysfunction, even in the earliest stages of the disease, where there is minimum physical disability. Despite the high prevalence rates and the significant impact of cognitive dysfunction on quality of life in this population, cognitive functions are not routinely assessed due to the high cost and time consumption. This article provides an overview of the current state of knowledge related to cognition in MS and on the optimal approach to neuropsychological assessment of this population. It then focuses on the pharmacological and other treatment options available for MS patients with, or at risk for developing, cognitive impairment. The available immune-modulating agents may reduce the development of new lesions and therefore prevent or minimize the progression of cognitive decline. However, there is currently insufficient evidence concerning the efficiency of symptomatic treatment in MS. There is also currently no optimal non-pharmacological treatment strategy for cognitive decline in MS, as the studies published to date report heterogeneous results. Nevertheless, non-pharmacological treatments such as cognitive rehabilitation may benefit some MS patients. As cognition is increasingly recognized as a major feature of MS, its assessment and rehabilitation will become a greater priority.

Plasma beta-amyloid and duration of Alzheimer's disease in adults with Down syndrome

OBJECTIVES

To investigate the relation of plasma levels of Abeta peptides (Abeta1-40 and Abeta1-42) and apolipoprotein E (APOE) genotype to dementia status, and the duration of Alzheimer's disease (AD) in adults with Down syndrome (DS).

METHODS

Adults with DS were recruited from community settings and followed up for a mean period of 6.7 years. Plasma levels Abeta1-40 and Abeta1-42 and APOE genotype were determined at the last visit.

RESULTS

There were 83 nondemented participants and 44 participants with prevalent AD. Overall, plasma levels of Abeta1-42, Abeta1-40 and the ratio Abeta1-42/Abeta1-40 did not differ significantly between the adults with DS. Among demented participants, the mean level of Abeta1-40 was significantly lower (157.0 vs. 195.3) and the ratio of Abeta1-42/Abeta1-40 was significantly higher (0.28 vs. 0.16) in those with more than 4 years duration of dementia than in those with 4 or fewer years' duration of dementia. This pattern was generally similar in those with and without an APOE epsilon4 allele.

CONCLUSIONS

There is an association between plasma Abeta peptide levels and the duration of AD in older persons with DS. The predictive and diagnostic roles of Abeta1-42 and Abeta1-40 measurements for AD, however, remain controversial. Change in Abeta peptide levels with onset of AD and with the duration of dementia may account for a lack of difference between prevalent cases and nondemented individuals and for variation in the predictive power of Abeta peptide levels.

Amyloid beta concentrations in older people with Down syndrome and dementia

People with Down syndrome develop Alzheimer's disease with an early age of onset. Plasma amyloid beta (Abeta) levels were measured in individuals with Down syndrome who were over the age of 40. No associations between age and Abeta1-40 and Abeta1-42 concentrations were found and nor were Abeta1-40 and Abeta1-42 levels found to vary between those with Alzheimer's-type dementia and those without dementia. The APOE genotype was not found to have an impact upon Abeta1-40 or Abeta1-42 concentrations. These data suggest that other factors play important roles in determining the onset and progression of dementia in the Down syndrome population.

Biomarkers for cognitive impairment and dementia in elderly people

The threat of a looming pandemic of dementia in elderly people highlights the compelling need for the development and validation of biomarkers that can be used to identify pre-clinical and prodromal stages of disease in addition to fully symptomatic dementia. Although predictive risk factors and correlative neuroimaging measures will have important roles in these efforts, this Review describes recent progress in the discovery, validation, and standardisation of molecular biomarkers--small molecules and macromolecules whose concentration in the brain or biological fluids can aid diagnosis at different stages of the more common dementing diseases and in the assessment of disease progression and response to therapeutics. An approach that efficiently combines independent information from risk-factor assessment, neuroimaging measures, and biomarkers might soon guide clinicians in the early diagnosis and management of cognitive impairment in elderly people.

Gene expression variation increase in trisomy 21 tissues

Congenital development disorders with variable severity occur in trisomy 21. However, how these phenotypic abnormalities develop with variations remains elusive. We hypothesize that the differences in euploid gene expression variation among trisomy 21 tissues are caused by the presence of an extra copy of chromosome 21 and may contribute to the phenotypic variations in Down syndrome. We used DNA microarray to measure the differences in gene expression variance between four human trisomy 21 and six euploid amniocytes. The three publicly available data sets of fetal brains, adult brains, and fetal hearts were also analyzed. The numbers of euploid genes with greater variance were significantly higher in all four kinds of trisomy 21 tissues (p<0.01) than in the corresponding euploid tissues. Seventeen euploid genes with significantly different variance between trisomy 21 and euploid amniocytes were found using the F test. In summary, there is a set of euploid genes that shows greater variance of expression in human trisomy 21 tissues than in euploid tissues. This change may contribute to producing the variable phenotypic abnormalities observed in Down syndrome.

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.

Increase in beta-amyloid levels in cerebrospinal fluid of children with Down syndrome

BACKGROUND

Individuals with Down syndrome (DS) invariably develop Alzheimer's disease (AD) during their life span. It is therefore of importance to study young DS patients when trying to elucidate early events in AD pathogenesis.

AIM

To investigate how levels of different amyloid-beta (Abeta) peptides, as well as tau and phosphorylated tau, in cerebrospinal fluid (CSF) from children with DS change over time. The first CSF sample was taken at 8 months and the following two samples at 20-40 and 54 months of age.

RESULTS

Individual levels of the Abeta peptides, as well as total Abeta levels in CSF increased over time when measured with Western blot. Tau in CSF decreased whereas there was no change in levels of phosphorylated tau over time.

CONCLUSION

The increasing levels of Abeta in CSF during early childhood of DS patients observed in this study are probably due to the trisomy of the Abeta precursor APP, which leads to an overproduction of Abeta. Despite the increased CSF concentrations of Abeta, there were no signs of an AD-indicating tau pattern in CSF, since the levels of total tau decreased and phosphorylated tau remained unchanged. This observation further strengthens the theory of Abeta pathology preceding tau pathology in AD.