Transformers enable accurate prediction of acute and chronic chemical toxicity in aquatic organisms.

Environmental hazard assessments are reliant on toxicity data that cover multiple organism groups. Generating experimental toxicity data is, however, resource-intensive and time-consuming. Computational methods are fast and cost-efficient alternatives, but the low accuracy and narrow applicability domains have made their adaptation slow. Here, we present a AI-based model for predicting chemical toxicity. The model uses transformers to capture toxicity-specific features directly from the chemical structures and deep neural networks to predict effect concentrations. The model showed high predictive performance for all tested organism groups-algae, aquatic invertebrates and fish-and has, in comparison to commonly used QSAR methods, a larger applicability domain and a considerably lower error. When the model was trained on data with multiple effect concentrations (EC50/EC10), the performance was further improved. We conclude that deep learning and transformers have the potential to markedly advance computational prediction of chemical toxicity.

Dataset on aquatic ecotoxicity predictions of 2697 chemicals, using three quantitative structure-activity relationship platforms.

Empirical and in silico data on the aquatic ecotoxicology of 2697 organic chemicals were collected in order to compile a dataset for assessing the predictive power of current Quantitative Structure Activity Relationship (QSAR) models and software platforms. This document presents the dataset and the data pipeline for its creation. Empirical data were collected from the US EPA ECOTOX Knowledgebase (ECOTOX) and the EFSA (European Food Safety Authority) report "Completion of data entry of pesticide ecotoxicology Tier 1 study endpoints in a XML schema - database". Only data for OECD recommended algae, daphnia and fish species were retained. QSAR toxicity predictions were calculated for each chemical and each of six endpoints using ECOSAR, VEGA and the Toxicity Estimation Software Tool (T.E.S.T.) platforms. Finally, the dataset was amended with SMILES, InChIKey, pKa and logP collected from webchem and PubChem.

Economic interests cloud hazard reductions in the European regulation of substances of very high concern.

Here we investigate how the conflicts between hazard reduction and economic interests have shaped the regulation of substances of very high concern (SVHCs) under the Authorization program of the European chemical regulation Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH). Since regulation starts with listing SVHCs on the Candidate List, we analyze the relative importance of toxicological properties, economic motivations, and available scientific knowledge on the probability of inclusion on the Candidate List. We find that the most important factor in whether a substance is listed is whether it is being produced in, or imported into, the European Economic Area (EEA), with the regulators less likely to place a substance on the list if it is currently being produced or imported in the EEA. This evidence suggests that regulators have listed chemicals of secondary importance leading to lesser than anticipated hazard reductions, either because production and imports had already ceased before the listing, or because the compound has never been produced or imported in the EEA at all.

Effects of pesticides and metals on penaeid shrimps in Maputo Bay, Mozambique - A field study.

Estuaries are important nursery areas for many species and these habitats are often affected by anthropogenic activities. We investigate possible negative effects of pesticides and metals on penaeid shrimps in Maputo Bay, Mozambique. Shrimps and water samples were collected in three estuaries and one coastal area for biomarker and chemical analysis. Acetylcholinesterase (AChE) and glutathione-S transferase activities were analysed as biomarkers for pollutants. 37 different pesticides were analysed in water samples and shrimp muscle tissue was analysed for 10 metals. Risk assessment showed that the environmental thresholds were exceeded for several herbicides in three of four of the assessed nursery areas. Lower AChE activities were detected in shrimps captured close to an agriculture area and this location had the lowest shrimp densities. Metal analysis in shrimp showed low levels. Despite localized effects, results highlight the need to improve the regulation of pollutants in the Espírito Santo estuary in Maputo bay.

Towards 'one substance - one assessment': An analysis of EU chemical registration and aquatic risk assessment frameworks.

With the Green Deal the EU aims to achieve a circular economy, restore biodiversity and reduce environmental pollution. As a part of the Green Deal a 'one-substance one-assessment' (OS-OA) approach for chemicals has been proposed. The registration and risk assessment of chemicals on the European market is currently fragmented across different legal frameworks, dependent on the chemical's use. In this review, we analysed the five main European chemical registration frameworks and their risk assessment procedures for the freshwater environment, covering 1) medicines for human use, 2) veterinary medicines, 3) pesticides, 4) biocides and 5) industrial chemicals. Overall, the function of the current frameworks is similar, but important differences exist between the frameworks' environmental protection goals and risk assessment strategies. These differences result in inconsistent assessment outcomes for similar chemicals. Chemicals are also registered under multiple frameworks due to their multiple uses, and chemicals which are not approved under one framework are in some instances allowed on the market under other frameworks. In contrast, an OS-OA will require a uniform hazard assessment between all different frameworks. In addition, we show that across frameworks the industrial chemicals are the least hazardous for the freshwater environment (median PNEC of 2.60E-2 mg/L), whilst biocides are the most toxic following current regulatory assessment schemes (median PNEC of 1.82E-4 mg/L). Finally, in order to facilitate a successful move towards a OS-OA approach we recommend a) harmonisation of environmental protection goals and risk assessment strategies, b) that emission, use and production data should be made publicly available and that data sharing becomes a priority, and c) an alignment of the criteria used to classify problematic substances.

Pesticide mixtures in the Swedish streams: Environmental risks, contributions of individual compounds and consequences of single-substance oriented risk mitigation.

This paper presents the ecotoxicological assessment and environmental risk evaluation of complex pesticide mixtures occurring in freshwater ecosystems in southern Sweden. The evaluation is based on exposure data collected between 2002 and 2013 by the Swedish pesticide monitoring program and includes 1308 individual samples, detecting mixtures of up to 53 pesticides (modal=8). Pesticide mixture risks were evaluated using three different scenarios for non-detects (best-case, worst-case and using the Kaplan-Meier method). The risk of each scenario was analyzed using Swedish Water Quality Objectives (WQO) and trophic-level specific environmental thresholds. Using the Kaplan-Meier method the environmental risk of 73% of the samples exceeded acceptable levels, based on an assessment using Concentration-Addition and WQOs for the individual pesticides. Algae were the most sensitive organism group. However, analytical detection limits, especially for insecticides, were insufficient to analyze concentrations at or near their WQO's. Thus, the risk of the analyzed pesticide mixtures to crustaceans and fish is systematically underestimated. Treating non-detects as being present at their individual limit of detection increased the estimated risk by a factor 100 or more, compared to the best-case or the Kaplan-Meier scenario. Pesticide mixture risks are often driven by only 1-3 compounds. However, the risk-drivers (i.e., individual pesticides explaining the largest share of potential effects) differ substantially between sites and samples, and 83 of the 141 monitored pesticides need to be included in the assessment to account for 95% of the risk at all sites and years. Single-substance oriented risk mitigation measures that would ensure that each individual pesticide is present at a maximum of 95% of its individual WQO, would also reduce the mixture risk, but only from a median risk quotient of 2.1 to a median risk quotient of 1.8. Also, acceptable total risk levels would still be exceeded in more than 70% of the samples.

Evaluating the environmental hazard of industrial chemicals from data collected during the REACH registration process.

Registration dossiers for 11,678 industrial chemicals were retrieved from the database of the European Chemicals Agency, of which 3566 provided a numerical entry for the corresponding predicted no effect concentration for the freshwater environment (PNEC). A distribution-based examination of 2244 of these entries reveals that the average PNEC of an industrial chemical in Europe is 238nmol/L, covering a span of 9 orders of magnitude. A comparison with biocides, pesticides, pharmaceuticals and WFD-priority pollutants reveals that, in average, industrial chemicals are least hazardous (hazard ranking: industrial chemicals≪pharmaceuticals

Toward a conceptual approach for assessing risks from chemical mixtures and other stressors to coastal ecosystem services.

Growth of human populations and increased human activity, particularly in coastal areas, increase pressure on coastal ecosystems and the ecosystem services (ES) they provide. As a means toward being able to assess the impact of multiple stressors on ES, in the present study we propose an 8-step conceptual approach for assessing effects of chemical mixtures and other stressors on ES in coastal areas: step A, identify the relevant problems and policy aims; step B, identify temporal and spatial boundaries; step C, identify relevant ES; step D, identify relevant stressors (e.g., chemicals); step E, translate impacts into ES units; step F, assess cumulative risk in ES units; step G, rank stressors based on their contribution to adverse effects on ES; and step H, implement regulation and management as appropriate and necessary. Two illustrative case studies (Swedish coastal waters and a coastal lagoon in Costa Rica) are provided; one focuses on chemicals that affect human food supply and the other addresses pesticide runoff and trade-offs among ES. The 2 cases are used to highlight challenges of such risk assessments, including use of standardized versus ES-relevant test species, data completeness, and trade-offs among ES. Lessons learned from the 2 case studies are discussed in relation to environmental risk assessment and management of chemical mixtures. Integr Environ Assess Manag 2017;13:376-386. © 2016 SETAC.

A quick and robust method for quantification of the hypersensitive response in plants.

One of the most studied defense reactions of plants against microbial pathogens is the hypersensitive response (HR). The HR is a complex multicellular process that involves programmed cell death at the site of infection. A standard method to quantify plant defense and the HR is to measure the release of cellular electrolytes into water after infiltration with pathogenic bacteria. In this type of experiment, the bacteria are typically delivered into the plant tissue through syringe infiltration. Here we report the development of a vacuum infiltration protocol that allows multiple plant lines to be infiltrated simultaneously and assayed for defense responses. Vacuum infiltration did not induce more wounding response in Arabidopsis leaf tissue than syringe inoculation, whereas throughput and reproducibility were improved. The method was used to study HR-induced electrolyte loss after treatment with the bacterium Pseudomonas syringae pv. tomato DC3000 harboring the effector AvrRpm1, AvrRpt2 or AvrRps4. Specifically, the influence of bacterial titer on AvrRpm1-induced HR was investigated. Not only the amplitude, but also the timing of the maximum rate of the HR reaction was found to be dose-dependent. Finally, using vacuum infiltration, we were able quantify induction of phospholipase D activity after AvrRpm1 recognition in leaves labeled with (33)PO4.

Formation of oxidized phosphatidylinositol and 12-oxo-phytodienoic acid containing acylated phosphatidylglycerol during the hypersensitive response in Arabidopsis.

Plant membranes are composed of a wide array of polar lipids. The functionality of these extends far beyond a pure structural role. Membrane lipids function as enzyme co-factors, establish organelle identity and as substrates for enzymes such as lipases and lipoxygenases. Enzymatic degradation or oxidation (enzymatic or non-enzymatic) of membrane lipids leads to the formation of a diverse group of bioactive compounds. Plant defense reactions provoked by pathogenic microorganisms are often associated with substantial modifications of the lipidome. In this study, we profiled changes in phospholipids during the hypersensitive response triggered by recognition of the bacterial effector protein AvrRpm1 in Arabidopsis thaliana. A simple and robust LC-MS based method for profiling plant lipids was designed to separate all the major species of glycerolipids extracted from Arabidopsis leaf tissue. The method efficiently separated several isobaric and near isobaric lipid species, which otherwise are difficult to quantify in direct infusion based profiling. In addition to the previously reported OPDA-containing galactolipids found to be induced during hypersensitive response in Arabidopsis, three OPDA-containing sulfoquinovosyl diacylglycerol species, one phosphatidylinositol species as well as two acylated OPDA-containing phosphatidylglycerol species were found to accumulate during the hypersensitive response in Arabidopsis. Our study confirms and extends on the notion that the hypersensitive response in Arabidopsis triggers a unique profile of Allene Oxide Synthase dependent oxidation of membrane lipids. Primary targets of this oxidation seem to be uncharged and anionic lipid species.

Cerebrospinal fluid biomarkers of ß-amyloid metabolism in multiple sclerosis.

BACKGROUND: Amyloid precursor protein (APP) and amyloid ß (Aß) peptides are intensely studied in neuroscience and their cerebrospinal fluid (CSF) measurements may be used to track the metabolic pathways of APP in vivo. Reduced CSF levels of Aß and soluble APP (sAPP) fragments are reported in inflammatory diseases, including multiple sclerosis (MS); but in MS, the precise pathway of APP metabolism and whether it can be affected by disease-modifying treatments remains unclear. OBJECTIVE: To characterize the CSF biomarkers of APP degradation in MS, including the effects of disease-modifying therapy. METHODS: CSF samples from 87 MS patients (54 relapsing-remitting (RR) MS; 33 secondary progressive (SP) MS and 28 controls were analyzed for sAPP and Aß peptides by immunoassays, plus a subset of samples was analyzed by immunoprecipitation and mass spectrometry (IP-MS). Patients treated with natalizumab or mitoxantrone were examined at baseline, and after 1-2 years of treatment. RESULTS: CSF sAPP and Aß peptide levels were reduced in MS patients; but they increased again towards normal, after natalizumab treatment. A multivariate model of IP-MS-measured Aß species separated the SPMS patients from controls, with RRMS patients having intermediate levels. CONCLUSIONS: We confirmed and extended our previous observations of altered CSF sAPP and Aß peptide levels in MS patients. We found that natalizumab therapy may be able to counteract the altered APP metabolism in MS. The CSF Aß isoform distribution was found to be distinct in SPMS patients, as compared to the controls.

Amyloid-ß metabolism in Niemann-Pick C disease models and patients.

Niemann-Pick type C (NPC) is a progressive neurodegenerative lysosomal disease with altered cellular lipid trafficking. The metabolism of amyloid-ß (Aß) - previously mainly studied in Alzheimer's disease - has been suggested to be altered in NPC. Here we aimed to perform a detailed characterization of metabolic products from the amyloid precursor protein (APP) in NPC models and patients. We used multiple analytical technologies, including immunoassays and immunoprecipitation followed by mass spectrometry (IP-MS) to characterize Aß peptides and soluble APP fragments (sAPP-α/ß) in cell media from pharmacologically (U18666A) and genetically (NPC1 ( -/- ) ) induced NPC cell models, and cerebrospinal fluid (CSF) from NPC cats and human patients. The pattern of Aß peptides and sAPP-α/ß fragments in cell media was differently affected by NPC-phenotype induced by U18666A treatment and by NPC1 ( -/- ) genotype. U18666A treatment increased the secreted media levels of sAPP-α, AßX-40 and AßX-42 and reduced the levels of sAPP-ß, Aß1-40 and Aß1-42, while IP-MS showed increased relative levels of Aß5-38 and Aß5-40 in response to treatment. NPC1 ( -/- ) cells had reduced media levels of sAPP-α and Aß1-16, and increased levels of sAPP-ß. NPC cats had altered CSF distribution of Aß peptides compared with normal cats. Cats treated with the potential disease-modifying compound 2-hydroxypropyl-ß-cyclodextrin had increased relative levels of short Aß peptides including Aß1-16 compared with untreated cats. NPC patients receiving ß-cyclodextrin had reduced levels over time of CSF Aß1-42, AßX-38, AßX-40, AßX-42 and sAPP-ß, as well as reduced levels of the axonal damage markers tau and phosphorylated tau. We conclude that NPC models have altered Aß metabolism, but with differences across experimental systems, suggesting that NPC1-loss of function, such as in NPC1 ( -/- ) cells, or NPC1-dysfunction, seen in NPC patients and cats as well as in U18666A-treated cells, may cause subtle but different effects on APP degradation pathways. The preliminary findings from NPC cats suggest that treatment with cyclodextrin may have an impact on APP processing pathways. CSF Aß, sAPP and tau biomarkers were dynamically altered over time in human NPC patients.

An online nano-LC-ESI-FTICR-MS method for comprehensive characterization of endogenous fragments from amyloid ß and amyloid precursor protein in human and cat cerebrospinal fluid.

Amyloid precursor protein (APP) is the precursor protein to amyloid ß (Aß), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aß peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aß peptides by low-energy collision-induced dissociation tandem mass spectrometry (MS/MS), mainly long b-fragments are observed, limiting the possibility to determine variations such as amino acid variants or post-translational modifications (PTMs) within the N-terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aß peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aß processing has also been described in the lysosomal storage disease Niemann-Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aß was identified. Further, sialylated core 1 like O-glycans at Tyr10, recently discovered in human Aß (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aß peptide species in CSF by using an online top-down MS-based method.

Longitudinal cerebrospinal fluid biomarkers over four years in mild cognitive impairment.

Cerebrospinal fluid (CSF) measurements of amyloid-ß42 (Aß42), total-tau (T-tau), and phosphorylated tau (P-tau) may be used to predict future Alzheimer's disease (AD) dementia in patients with mild cognitive impairment (MCI). The precise temporal development of these biomarkers in relation to clinical progression is unclear. Earlier studies have been hampered by short follow-up. In an MCI cohort, we selected 15 patients who developed AD (MCI-AD) and 15 who remained cognitively stable during 4 years of follow-up. CSF was sampled at three serial occasions from each patient and analyzed for Aß peptides, the soluble amyloid-ß protein precursor protein fragments sAßPPα and sAßPPß, T-tau, P-tau, and chromogranin B, which is a protein linked to regulated neuronal secretion. We also measured, for the first time in MCI patients, an extended panel of Aß peptides by matrix-assisted-laser-desorption/ionization time-of-flight mass spectrometry (MS). Most biomarkers were surprisingly stable over the four years with coefficients of variation below or close to 10%. However, MCI-AD patients decreased in CSF AßX₋40 and chromogranin B concentrations, which may indicate a reduced number of functional neurons or synapses with disease progression. The MS Aß peptide panel was more useful than any single Aß peptide to identify MCI-AD patients already at baseline. Knowledge on these biomarkers and their trajectories may facilitate early diagnosis of AD and be useful in future clinical trials to track effects of disease modifying drugs.

BACE1 inhibition induces a specific cerebrospinal fluid ß-amyloid pattern that identifies drug effects in the central nervous system.

BACE1 is a key enzyme for amyloid-ß (Aß) production, and an attractive therapeutic target in Alzheimer's disease (AD). Here we report that BACE1 inhibitors have distinct effects on neuronal Aß metabolism, inducing a unique pattern of secreted Aß peptides, analyzed in cell media from amyloid precursor protein (APP) transfected cells and in cerebrospinal fluid (CSF) from dogs by immunoprecipitation-mass spectrometry, using several different BACE1 inhibitors. Besides the expected reductions in Aß1-40 and Aß1-42, treatment also changed the relative levels of several other Aß isoforms. In particular Aß1-34 decreased, while Aß5-40 increased, and these changes were more sensitive to BACE1 inhibition than the changes in Aß1-40 and Aß1-42. The effects on Aß5-40 indicate the presence of a BACE1 independent pathway of APP degradation. The described CSF Aß pattern may be used as a pharmacodynamic fingerprint to detect biochemical effects of BACE1-therapies in clinical trials, which might accelerate development of novel therapies.

The amyloid-ß isoform pattern in cerebrospinal fluid in familial PSEN1 M139T- and L286P-associated Alzheimer's disease.

There are several familial forms of Alzheimer's disease (AD) most of which are caused by mutations in the genes that encode the presenilin enzymes involved in the production of amyloid-ß (Aß) from the amyloid precursor protein (APP). In AD, Aß forms fibrils that are deposited in the brain as plaques. Much of the fibrillar Aß found in the plaques consists of the 42 amino acid form of Aß (Aß1-42) and it is now widely accepted that Aß is related to the pathogenesis of AD and that Aß may both impair memory and be neurotoxic. In human cerebrospinal fluid (CSF) several C- and N-terminally truncated Aß isoforms have been detected and their relative abundance pattern is thought to reflect the production and clearance of Aß. By using immunoprecipitation and mass spectrometry, we have previously demonstrated that carriers of the familial AD (FAD)-associated PSEN1 A431E mutation have low CSF levels of C-terminally truncated Aß isoforms shorter than Aß1-40. Here we replicate this finding in symptomatic carriers of the FAD-causing PSEN1 L286P mutation. Furthermore, we show that preclinical carriers of the PSEN1 M139T mutation may overexpress Aß1-42 suggesting that this particular mutation may cause AD by stimulating γ-secretase-mediated cleavage at amino acid 42 in the Aß sequence.

Evaluation of the performance of novel Aß isoforms as theragnostic markers in Alzheimer's disease: from the cell to the patient.

BACKGROUND: Alzheimer's disease (AD) is the most common neurodegenerative disorder in the aging population and is characterized by extracellular plaques in the brain. The last decades have witnessed an explosion in studies of the role of amyloid-ß (Aß) metabolism and aggregation in the pathogenesis of AD which has been translated into novel promising therapies with putative disease-modifying effects. OBJECTIVE: The aim is to investigate the performance of truncated Aß isoforms as theragnostic markers in clinical trials. METHODS: Aß isoforms were immunoprecipitated from human, mouse and dog cerebrospinal fluid (CSF) or cell media and analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. RESULTS: Aß1-14, Aß1-15, and Aß1-16 are elevated in cell media and in CSF in response to γ-secretase inhibitor treatment. In a clinical trial including AD patients, Aß1-14, Aß1-15, and Aß1-16 increased dose-dependently in response to treatment with the γ-secretase inhibitor LY450139. In dogs, Aß1-37 was significantly increased in response to treatment with the γ-secretase modulator E2012. CONCLUSIONS: The results presented add to the current knowledge on APP processing and that Aß isoforms can be used as novel biomarkers to monitor anti-Aß treatments in clinical trials and may be valuable for making a go/no go decision for large and expensive phase 2 or 3 clinical trials.

Pyroglutamate amyloid ß (Aß) aggravates behavioral deficits in transgenic amyloid mouse model for Alzheimer disease.

Pyroglutamate-modified Aß peptides at amino acid position three (Aß(pE3-42)) are gaining considerable attention as potential key players in the pathogenesis of Alzheimer disease (AD). Aß(pE3-42) is abundant in AD brain and has a high aggregation propensity, stability and cellular toxicity. The aim of the present work was to study the direct effect of elevated Aß(pE3-42) levels on ongoing AD pathology using transgenic mouse models. To this end, we generated a novel mouse model (TBA42) that produces Aß(pE3-42). TBA42 mice showed age-dependent behavioral deficits and Aß(pE3-42) accumulation. The Aß profile of an established AD mouse model, 5XFAD, was characterized using immunoprecipitation followed by mass spectrometry. Brains from 5XFAD mice demonstrated a heterogeneous mixture of full-length, N-terminal truncated, and modified Aß peptides: Aß(1-42), Aß(1-40), Aß(pE3-40), Aß(pE3-42), Aß(3-42), Aß(4-42), and Aß(5-42). 5XFAD and TBA42 mice were then crossed to generate transgenic FAD42 mice. At 6 months of age, FAD42 mice showed an aggravated behavioral phenotype compared with single transgenic 5XFAD or TBA42 mice. ELISA and plaque load measurements revealed that Aß(pE3) levels were elevated in FAD42 mice. No change in Aß(x)(-42) or other Aß isoforms was discovered by ELISA and mass spectrometry. These observations argue for a seeding effect of Aß(pE-42) in FAD42 mice.

SILAC zebrafish for quantitative analysis of protein turnover and tissue regeneration.

Defective tissue regeneration is thought to contribute to several human diseases, including neurodegenerative disorders, heart failure and various lung diseases. Boosting the regenerative capacity has been suggested a possible therapeutic approach. Methods to metabolically label newly synthesized proteins in vivo with stable isotopic forms of amino acids holds promise for the study of protein turnover and tissue regeneration that are fundamental to the sustained life of all organisms. Here, we used the "stable isotope labeling with amino acids in cell culture" (SILAC) approach to explore normal protein turnover and tissue regeneration in adult zebrafish. The ratio of labeled and unlabeled proteins/peptides in specific organs of zebrafish fed a SILAC diet containing (13)C(6)-labeled lysine was determined by liquid chromatography and tandem mass spectrometry. Labeling was highest in tissues with high regenerative capacity, including intestine, liver, and fin, whereas brain and heart displayed the lowest labeling. Proteins with high degree of labeling were mainly involved in catalytic or transport activity pathways. The technique also verified increased protein synthesis during regeneration of the caudal fin following amputation. This newly developed SILAC zebrafish model constitutes a novel tool to analyze tissue regeneration in an animal model amenable to genetic and pharmacologic manipulation.

Characterization of the brain ß-amyloid isoform pattern at different ages of Tg2576 mice.

BACKGROUND: Although genetic and biochemical studies have suggested a cardinal role for ß-amyloid (Aß) in Alzheimer's disease, the underlying mechanism(s) of how Aß induces neurodegeneration is still unclear. Our objective was to investigate the consequences of Aß, especially on tau phosphorylation at specific epitopes important for Alzheimer's disease. METHODS: We used cortices from Tg2576 mice at 7 days to 15 months of age. RESULTS: MALDI-TOF MS revealed an age-dependent shift in the Aß isoform pattern. Young animals displayed high cortical levels of the shorter Aß isoforms (Aß1-16 and Aß1-17) compared to 15-month-old Tg2576 mice which mainly expressed Aß1-40 and Aß1-42. The Aß1-42 showed an age-dependent increase, whereas total Aß1-40 levels remained constant. The highest levels of TBS-soluble Aß oligomers were found at 90 days of age. Brain Aß build-up did not affect the phosphorylation of tau at the epitopes investigated. CONCLUSIONS: This study provides new information about age-dependent Aß isoforms and oligomers as well as their effect on site-specific tau phosphorylation in this transgenic mouse model. Our observations suggest that the different human Aß isoforms do not directly cause increased tau phosphorylation and that the cognitive deficits seen in this mouse model are only related to the Aß overexpression.