Opposing synaptic regulation of amyloid-β metabolism by NMDA receptors in vivo

The concentration of amyloid-β (Aβ) within the brain extracellular space is one determinant of whether the peptide will aggregate into toxic species that are important in Alzheimer’s disease (AD) pathogenesis. Some types of synaptic activity can regulate Aβ levels. Here we demonstrate two distinct mechanisms that are simultaneously activated by NMDA receptors and regulate brain interstitial fluid (ISF) Aβ levels in opposite directions in the living mouse. Depending on the dose of NMDA administered locally to the brain, ISF Aβ levels either increase or decrease. Low doses of NMDA increase action potentials and synaptic transmission which leads to an elevation in synaptic Aβ generation. In contrast, high doses of NMDA activate signaling pathways that lead to ERK (extracellular-regulated kinase) activation, which reduces processing of APP into Aβ. This depression in Aβ via APP processing occurs despite dramatically elevated synaptic activity. Both of these synaptic mechanisms are simultaneously active, with the balance between them determining whether ISF Aβ levels will increase or decrease. NMDA receptor antagonists increase ISF Aβ levels, suggesting that basal activity at these receptors normally suppresses Aβ levels in vivo. This has implications for understanding normal Aβ metabolism as well as AD pathogenesis

Rapid in vivo measurement of B-amyloid reveals biphasic clearance kinetics in an Alzheimer\u27s mouse model

Accumulation of ?-amyloid peptide is a key step in Alzheimer?s disease pathogenesis. Yuede et al. propose a novel method to track ?-amyloid levels in vivo

In vivo measurement of apolipoprotein E from the brain interstitial fluid using microdialysis

BACKGROUND: The APOE4 allele variant is the strongest known genetic risk factor for developing late-onset Alzheimer’s disease. The link between apolipoprotein E (apoE) and Alzheimer’s disease is likely due in large part to the impact of apoE on the metabolism of amyloid β (Aβ) within the brain. Manipulation of apoE levels and lipidation within the brain has been proposed as a therapeutic target for the treatment of Alzheimer’s disease. However, we know little about the dynamic regulation of apoE levels and lipidation within the central nervous system. We have developed an assay to measure apoE levels in the brain interstitial fluid of awake and freely moving mice using large molecular weight cut-off microdialysis probes. RESULTS: We were able to recover apoE using microdialysis from human cerebrospinal fluid (CSF) in vitro and mouse brain parenchyma in vivo. Microdialysis probes were inserted into the hippocampus of wild-type mice and interstitial fluid was collected for 36 hours. Levels of apoE within the microdialysis samples were determined by ELISA. The levels of apoE were found to be relatively stable over 36 hours. No apoE was detected in microdialysis samples from apoE KO mice. Administration of the RXR agonist bexarotene increased ISF apoE levels while ISF Aβ levels were decreased. Extrapolation to zero-flow analysis allowed us to determine the absolute recoverable concentration of apoE3 in the brain ISF of apoE3 KI mice. Furthermore, analysis of microdialysis samples by non-denaturing gel electrophoresis determined lipidated apoE particles in microdialysis samples were consistent in size with apoE particles from CSF. Finally, we found that the concentration of apoE in the brain ISF was dependent upon apoE isoform in human apoE KI mice, following the pattern apoE2>apoE3>apoE4. CONCLUSIONS: We are able to collect lipidated apoE from the brain of awake and freely moving mice and monitor apoE levels over the course of several hours from a single mouse. Our technique enables assessment of brain apoE dynamics under physiological and pathophysiological conditions and in response to therapeutic interventions designed to affect apoE levels and lipidation within the brain

Acute dosing of latrepirdine (Dimebon), a possible Alzheimer therapeutic, elevates extracellular amyloid-beta levels in vitro and in vivo.

BACKGROUND: Recent reports suggest that latrepirdine (Dimebon, dimebolin), a retired Russian antihistamine, improves cognitive function in aged rodents and in patients with mild to moderate Alzheimer's disease (AD). However, the mechanism(s) underlying this benefit remain elusive. AD is characterized by extracellular accumulation of the amyloid-beta (Abeta) peptide in the brain, and Abeta-lowering drugs are currently among the most popular anti-amyloid agents under development for the treatment of AD. In the current study, we assessed the effect of acute dosing of latrepirdine on levels of extracellular Abeta using in vitro and in vivo experimental systems. RESULTS: We evaluated extracellular levels of Abeta in three experimental systems, under basal conditions and after treatment with latrepirdine. Mouse N2a neuroblastoma cells overexpressing Swedish APP were incubated for 6 hr in the presence of either vehicle or vehicle + latrepirdine (500pM-5 muM). Synaptoneurosomes were isolated from TgCRND8 mutant APP-overexpressing transgenic mice and incubated for 0 to 10 min in the absence or presence of latrepirdine (1 muM or 10 muM). Drug-naïve Tg2576 Swedish mutant APP overexpressing transgenic mice received a single intraperitoneal injection of either vehicle or vehicle + latrepirdine (3.5 mg/kg). Picomolar to nanomolar concentrations of acutely administered latrepirdine increased the extracellular concentration of Abeta in the conditioned media from Swedish mutant APP-overexpressing N2a cells by up to 64% (p = 0.01), while a clinically relevant acute dose of latrepirdine administered i.p. led to an increase in the interstitial fluid of freely moving APP transgenic mice by up to 40% (p = 0.01). Reconstitution of membrane protein trafficking and processing is frequently inefficient, and, consistent with this interpretation, latrepirdine treatment of isolated TgCRND8 synaptoneurosomes involved higher concentrations of drug (1-10 muM) and led to more modest increases in extracellular Abeta(x-42 )levels (+10%; p = 0.001); of note, however, was the observation that extracellular Abeta(x-40 )levels did not change. CONCLUSIONS: Here, we report the surprising association of acute latrepirdine dosing with elevated levels of extracellular Abeta as measured in three independent neuron-related or neuron-derived systems, including the hippocampus of freely moving Tg2576 mice. Given the reported association of chronic latrepirdine treatment with improvement in cognitive function, the effects of chronic latrepirdine treatment on extracellular Abeta levels must now be determined.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Prevalence of patient-reported dysphagia in multiple sclerosis patients: an Italian multicenter study (using the DYMUS questionnaire).

OBJECTIVE: Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) with a chronic course. Dysphagia represents one of the current challenges in clinical practice for the management of MS patients. Dysphagia starts to appear in mildly impaired MS subjects (EDSS 2-3) and becomes increasingly common in the most severely disabled subjects (EDSS 8-9). The aim of the present study was to evaluate the frequency and characteristics of patient-reported dysphagia in MS patients with a multicenter study using the recently developed DYMUS (DYsphagia in MUltiple Sclerosis) questionnaire. DESIGN: Data were collected in a multi-centre, cross-sectional study using a face-to-face structured questionnaire for clinical characteristics and the DYMUS questionnaire. RESULTS: 1875 patients were interviewed. The current study has shown a correlation between patient-reported dysphagia and EDSS and disease course but not with age, gender and disease duration. Questionnaires were divided into "patient-reported dysphagia-yes" (587, 31.3%) and "patient-reported dysphagia-no" (1288, 68.7%). Compared with the patient-reported dysphagia-no group, patients in patient-reported dysphagia-yes group had higher EDSS score (mean EDSS 4.6 vs. 2.8; p<0.001) and had a longer disease duration (mean duration 13years vs. 11years; p<0.001), while there was no significant difference in gender (32.7% vs. 30.5% male and 67.3% vs. 69.5% female) and in age composition (46.18 vs. 42.05). CONCLUSIONS: This study represents the largest, multi-centre sample of MS patients evaluated for patient-reported dysphagia utilizing an ad-hoc questionnaire for this condition

Validation of the DYMUS questionnaire for the assessment of dysphagia in multiple sclerosis

Swallowing problems can complicate the course of multiple sclerosis (MS). However, no validated questionnaire for the assessment of dysphagia in MS is currently available. We previously developed a 10-item DYsphagia in Multiple Sclerosis questionnaire (DYMUS). In the present study, this questionnaire was submitted to a validation process. Thirteen Italian MS centres took part in this research in which DYMUS was administered to 1734 consecutive MS patients during routine checkups outside relapse. The questionnaire showed very good internal consistency (Cronbach's alpha = 0.914). It was then subdivided into two subscales, both of which also showed very good internal consistency: Cronbach's alpha was 0.885 for the 'dysphagia for solids' subscale and 0.864 for the 'dysphagia for liquids' subscale. The DYMUS questionnaire was found to be an easy and reliable tool for detecting dysphagia and also for the preliminary selection of patients requiring more specific instrumental analyses, and those suitable for aspiration prevention programmes