Neonatal exposure to the cyanobacterial toxin BMAA induces changes in protein expression and neurodegeneration in adult hippocampus

How does the neurotoxin β-N-methylamino-L-alanine exist in biological matrices and cause toxicity?

The neurotoxin β-N-methylamino-L-alanine (BMAA) has been deemed as a risk factor for some neurodegenerative diseases such as amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC). This possible link has been proved in some primate models and cell cultures with the appearance that BMAA exposure can cause excitotoxicity, formation of protein aggregates, and/or oxidative stress. The neurotoxin BMAA extensively exists in the environment and can be transferred through the food web to human beings. In this review, the occurrence, toxicological mechanisms, and characteristics of BMAA were comprehensively summarized, and proteins and peptides were speculated as its possible binding substances in biological matrices. It is difficult to compare the published data from previous studies due to the inconsistent analytical methods and components of BMAA. The binding characteristics of BMAA should be focused on to improve our understanding of its health risk to human health in the future.

Cryosectioning and Immunohistochemistry Using Frozen Adult Murine Brain Neural Tissue

Cryopreservation and immunohistochemistry offer a comprehensive, robust, and simple methodology to investigate neural patterning and cellular function. Rapid freezing of the whole brain allows excellent preservation of neural ultrastructure and tissue architecture without destroying sensitive protein epitopes that are often compromised following standard paraffin embedding histological techniques. Here, we present a rapid and simple protocol for employing cryosectioning and subsequent immunohistochemistry in the study of adult murine brain neural tissue.

The Effects of Long-term, Low-dose β-N-methylamino-L-alanine (BMAA) Exposures in Adult SODG93R Transgenic Zebrafish

β-N-Methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid produced by cyanobacteria, which has been implicated in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). It is postulated that chronic exposure to BMAA can lead to formation of protein aggregates, oxidative stress, and/or excitotoxicity, which are mechanisms involved in the etiology of ALS. While specific genetic mutations are identified in some instances of ALS, it is likely that a combination of genetic and environmental factors, such as exposure to the neurotoxin BMAA, contributes to disease. We used a transgenic zebrafish with an ALS-associated mutation, compared with wild-type fish to explore the potential neurotoxic effects of BMAA through chronic long-term exposures. While our results revealed low concentrations of BMAA in the brains of exposed fish, we found no evidence of decreased swim performance or behavioral differences that might be reflective of neurodegenerative disease. Further research is needed to determine if chronic BMAA exposure in adult zebrafish is a suitable model to study neurodegenerative disease initiation and/or progression.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance

Research interest in a non-protein amino acid β-N-methylamino-L-alanine (BMAA) arose due to the discovery of a connection between exposure to BMAA and the occurrence of neurodegenerative diseases. Previous reviews on this topic either considered BMAA as a risk factor for neurodegenerative diseases or focused on the problems of detecting BMAA in various environmental samples. Our review is devoted to a wide range of fundamental biological problems related to BMAA, including the molecular mechanisms of biological activity of BMAA and the complex relationships between producers of BMAA and the environment in various natural ecosystems. At the beginning, we briefly recall the most important facts about the producers of BMAA (cyanobacteria, microalgae, and bacteria), the pathways of BMAA biosynthesis, and reliable methods of identification of BMAA. The main distinctive feature of our review is a detailed examination of the molecular mechanisms underlying the toxicity of BMAA to living cells. A brand new aspect, not previously discussed in any reviews, is the effect of BMAA on cyanobacterial cells. These recent studies, conducted using transcriptomics and proteomics, revealed potent regulatory effects of BMAA on the basic metabolism and cell development of these ancient photoautotrophic prokaryotes. Exogenous BMAA strongly influences cell differentiation and primary metabolic processes in cyanobacteria, such as nitrogen fixation, photosynthesis, carbon fixation, and various biosynthetic processes involving 2-oxoglutarate and glutamate. Cyanobacteria were found to be more sensitive to exogenous BMAA under nitrogen-limited growth conditions. We suggest a hypothesis that this toxic diaminoacid can be used by phytoplankton organisms as a possible allelopathic tool for controlling the population of cyanobacterial cells during a period of intense competition for nitrogen and other resources in various ecosystems.

Systematic and state-of the science review of the role of environmental factors in Amyotrophic Lateral Sclerosis (ALS) or Lou Gehrig's Disease

The etiology of sporadic amyotrophic lateral sclerosis (ALS) is still unclear. We evaluate environmental factors suspected to be associated with ALS for their potential linkage to disease causality and to model geographic distributions of susceptible populations and expected cases worldwide. A PRISMA systematic literature review was performed 2021. Bradford Hill criteria were used to identify and rank environmental factors and a secondary review of ALS diagnoses in population studies and ALS case or cohort studies was conducted. Prevalence rate projection informed estimates of impacted regions and populations. Among 1710 papers identified, 258 met the inclusion criteria, of which 173 responded to at least one of nine Bradford Hill criteria among 83 literature-identified ALS environmental factors. Environmental determinants of ALS in order of decreasing significance were β-N-methylamino-L-alanine (BMAA), formaldehyde, selenium, and heavy metals including manganese, mercury, zinc, and copper. Murine animal models were the most common methodology for exploring environmental factors. Another line of investigation of 62 population exposure studies implicated the same group of environmental agents (mean odds ratios): BMAA (2.32), formaldehyde (1.54), heavy metals (2.99), manganese (3.85), mercury (2.74), and zinc (2.78). An age-adjusted incidence model estimated current total ALS cases globally at ~85,000 people compared to only ~1600 cases projected from the reported ALS incidence in the literature. Modeling with the prevalence microscope equation forecasted an increase in U.S. ALS cases from 16,707 confirmed in 2015 to ~22,650 projected for 2040. Two orthogonal methods employed implicate BMAA, formaldehyde, manganese, mercury, and zinc as environmental factors with strong ALS associations. ALS cases likely are significantly underreported globally, and high vulnerability exists in regions with large aging populations. Recent studies on other diseases with environmental determinants suggest the need to consider additional potential triggers and mechanisms, including exposures to microbial agents and epigenetic modifications.

Exploring Molecular Approaches in Amyotrophic Lateral Sclerosis: Drug Targets from Clinical and Pre-Clinical Findings

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease (MND) characterized by the death of upper and lower motor neurons (corticospinal tract) in the motor cortex, basal ganglia, brain stem, and spinal cord. The patient experiences the sign and symptoms between 55 to 75 years of age, which include impaired motor movement, difficulty in speaking and swallowing, grip loss, muscle atrophy, spasticity, and sometimes associated with memory and cognitive impairments. Median survival is 3 to 5 years after diagnosis and 5 to 10% of the patients live for more than 10 years. The limited intervention of pharmacologically active compounds, that are used clinically, is majorly associated with the narrow therapeutic index. Pre-clinically established experimental models, where neurotoxin methyl mercury mimics the ALS like behavioural and neurochemical alterations in rodents associated with neuronal mitochondrial dysfunctions and downregulation of adenyl cyclase mediated cAMP/CREB, is the main pathological hallmark for the progression of ALS in central as well in the peripheral nervous system. Despite the considerable investigation into neuroprotection, it still constrains treatment choices to strong care and organization of ALS complications. Therefore, this current review specially targeted the investigation of clinical and pre-clinical features available for ALS to understand the pathogenic mechanisms and to explore the pharmacological interventions associated with the up-regulation of intracellular adenyl cyclase/cAMP/ CREB and activation of mitochondrial-ETC coenzyme-Q10 as a future drug target in the amelioration of ALS mediated motor neuronal dysfunctions.

β-Methylamino-L-alanine-induced protein aggregation in vitro and protection by L-serine

The cyanobacterial non-protein amino acid α-amino-β-methylaminopropionic acid, more commonly known as BMAA, was first discovered in the seeds of the ancient gymnosperm Cycad circinalis (now Cycas micronesica Hill). BMAA was linked to the high incidence of neurological disorders on the island of Guam first reported in the 1950s. BMAA still attracts interest as a possible causative factor in amyotrophic lateral sclerosis (ALS) following the identification of ALS disease clusters associated with living in proximity to lakes with regular cyanobacterial blooms. Since its discovery, BMAA toxicity has been the subject of many in vivo and in vitro studies. A number of mechanisms of toxicity have been proposed including an agonist effect at glutamate receptors, competition with cysteine for transport system x_c^_ and other mechanisms capable of generating cellular oxidative stress. In addition, a wide range of studies have reported effects related to disturbances in proteostasis including endoplasmic reticulum stress and activation of the unfolded protein response. In the present studies we examine the effects of BMAA on the ubiquitin-proteasome system (UPS) and on chaperone-mediated autophagy (CMA) by measuring levels of ubiquitinated proteins and lamp2a protein levels in a differentiated neuronal cell line exposed to BMAA. The BMAA induced increases in oxidised proteins and the increase in CMA activity reported could be prevented by co-administration of L-serine but not by the two antioxidants examined. These data provide further evidence of a protective role for L-serine against the deleterious effects of BMAA.

Is Exposure to BMAA a Risk Factor for Neurodegenerative Diseases? A Response to a Critical Review of the BMAA Hypothesis

In a literature survey, Chernoff et al. (2017) dismissed the hypothesis that chronic exposure to β-N-methylamino-L-alanine (BMAA) may be a risk factor for progressive neurodegenerative disease. They question the growing scientific literature that suggests the following: (1) BMAA exposure causes ALS/PDC among the indigenous Chamorro people of Guam; (2) Guamanian ALS/PDC shares clinical and neuropathological features with Alzheimer’s disease, Parkinson’s disease, and ALS; (3) one possible mechanism for protein misfolds is misincorporation of BMAA into proteins as a substitute for L-serine; and (4) chronic exposure to BMAA through diet or environmental exposures to cyanobacterial blooms can cause neurodegenerative disease. We here identify multiple errors in their critique including the following: (1) their review selectively cites the published literature; (2) the authors reported favorably on HILIC methods of BMAA detection while the literature shows significant matrix effects and peak coelution in HILIC that may prevent detection and quantification of BMAA in cyanobacteria; (3) the authors build alternative arguments to the BMAA hypothesis, rather than explain the published literature which, to date, has been unable to refute the BMAA hypothesis; and (4) the authors erroneously attribute methods to incorrect studies, indicative of a failure to carefully consider all relevant publications. The lack of attention to BMAA research begins with the review’s title which incorrectly refers to BMAA as a “non-essential” amino acid. Research regarding chronic exposure to BMAA as a cause of human neurodegenerative diseases is emerging and requires additional resources, validation, and research. Here, we propose strategies for improvement in the execution and reporting of analytical methods and the need for additional and well-executed inter-lab comparisons for BMAA quantitation. We emphasize the need for optimization and validation of analytical methods to ensure that they are fit-for-purpose. Although there remain gaps in the literature, an increasingly large body of data from multiple independent labs using orthogonal methods provides increasing evidence that chronic exposure to BMAA may be a risk factor for neurological illness.

BMAA and MCLR interact to modulate behavior and exacerbate molecular changes related to neurodegeneration in larval zebrafish

Exposure to toxins produced by cyanobacteria (i.e., cyanotoxins) is an emerging health concern due to their increasing prevalence and previous associations with neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). The objective of this study was to evaluate the neurotoxic effects of a mixture of two co-occurring cyanotoxins, β-methylamino-L-alanine (BMAA) and microcystin leucine and arginine (MCLR), using the larval zebrafish model. We combined high-throughput behavior-based toxicity assays with discovery proteomic techniques to identify behavioral and molecular changes following 6 days of exposure. While neither toxin caused mortality, morphological defects, or altered general locomotor behavior in zebrafish larvae, both toxins increased acoustic startle sensitivity in a dose-dependent manner by at least 40% (p < 0.0001). Furthermore, startle sensitivity was enhanced by an additional 40% in larvae exposed to the BMAA/MCLR mixture relative to those exposed to the individual toxins. Supporting these behavioral results, our proteomic analysis revealed a 4-fold increase in the number of differentially expressed proteins (DEPs) in the mixture-exposed group. Additionally, prediction analysis reveals activation and/or inhibition of 8 enriched canonical pathways (enrichment p-value < 0.01; z-score ≥|2|), including ILK, Rho Family GTPase, RhoGDI, and calcium signaling pathways, which have been implicated in neurodegeneration. We also found that expression of TDP-43, of which cytoplasmic aggregates are a hallmark of ALS pathology, was significantly upregulated by 5.7-fold following BMAA/MCLR mixture exposure. Together, our results emphasize the importance of including mixtures of cyanotoxins when investigating the link between environmental cyanotoxins and neurodegeneration as we reveal that BMAA and MCLR interact in vivo to enhance neurotoxicity.

Hippocampal neural stem cells are more susceptible to the neurotoxin BMAA than primary neurons: effects on apoptosis, cellular differentiation, neurite outgrowth, and DNA methylation

Developmental exposure to the environmental neurotoxin β-N-methylamino-L-alanine (BMAA), a proposed risk factor for neurodegenerative disease, can induce long-term cognitive impairments and neurodegeneration in rats. While rodent studies have demonstrated a low transfer of BMAA to the adult brain, this toxin is capable to cross the placental barrier and accumulate in the fetal brain. Here, we investigated the differential susceptibility of primary neuronal cells and neural stem cells from fetal rat hippocampus to BMAA toxicity. Exposure to 250 µM BMAA induced cell death in neural stem cells through caspase-independent apoptosis, while the proliferation of primary neurons was reduced only at 3 mM BMAA. At the lowest concentrations tested (50 and 100 µM), BMAA disrupted neural stem cell differentiation and impaired neurite development in neural stem cell-derived neurons (e.g., reduced neurite length, the number of processes and branches per cell). BMAA induced no alterations of the neurite outgrowth in primary neurons. This demonstrates that neural stem cells are more susceptible to BMAA exposure than primary neurons. Importantly, the changes induced by BMAA in neural stem cells were mitotically inherited to daughter cells. The persistent nature of the BMAA-induced effects may be related to epigenetic alterations that interfere with the neural stem cell programming, as BMAA exposure reduced the global DNA methylation in the cells. These findings provide mechanistic understanding of how early-life exposure to BMAA may lead to adverse long-term consequences, and potentially predispose for neurodevelopmental disorders or neurodegenerative disease later in life.

Western Pacific ALS-PDC: Evidence implicating cycad genotoxins

Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex (ALS-PDC) is a disappearing neurodegenerative disorder of apparent environmental origin formerly hyperendemic among Chamorros of Guam-USA, Japanese residents of the Kii Peninsula, Honshu Island, Japan and Auyu-Jakai linguistic groups of Papua-Indonesia on the island of New Guinea. The most plausible etiology is exposure to genotoxins in seed of neurotoxic cycad plants formerly used for food and/or medicine. Primary suspicion falls on methylazoxymethanol (MAM), the aglycone of cycasin and on the non-protein amino acid β-N-methylamino-L-alanine, both of which are metabolized to formaldehyde. Human and animal studies suggest: (a) exposures occurred early in life and sometimes during late fetal brain development, (b) clinical expression of neurodegenerative disease appeared years or decades later, and (c) pathological changes in various tissues indicate the disease was not confined to the CNS. Experimental evidence points to toxic molecular mechanisms involving DNA damage, epigenetic changes, transcriptional mutagenesis, neuronal cell-cycle reactivation and perturbation of the ubiquitin-proteasome system that led to polyproteinopathy and culminated in neuronal degeneration. Lessons learned from research on ALS-PDC include: (a) familial disease may reflect common toxic exposures across generations, (b) primary disease prevention follows cessation of exposure to culpable environmental triggers; and (c) disease latency provides a prolonged period during which to intervene therapeutically. Exposure to genotoxic chemicals ("slow toxins") in the early stages of life should be considered in the search for the etiology of ALS-PDC-related neurodegenerative disorders, including sporadic forms of ALS, progressive supranuclear palsy and Alzheimer's disease.

The cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) targets the olfactory bulb region

Olfactory dysfunction is implicated in neurodegenerative disorders and typically manifests years before other symptoms. The cyanobacterial neurotoxin β-N-methylamino-l-alanine (BMAA) is suggested as a risk factor for neurodegenerative disease. Detection of BMAA in air filters has increased the concern that aerosolization may lead to human BMAA exposure through the air. The aim of this study was to determine if BMAA targets the olfactory system. Autoradiographic imaging showed a distinct localization of radioactivity in the right olfactory mucosa and bulb following a unilateral intranasal instillation of ³H-BMAA (0.018 µg) in mice, demonstrating a direct transfer of BMAA via the olfactory pathways to the brain circumventing the blood–brain barrier, which was confirmed by liquid scintillation. Treatment of mouse primary olfactory bulb cells with 100 µM BMAA for 24 h caused a disruption of the neurite network, formation of dendritic varicosities and reduced cell viability. The NMDA receptor antagonist MK-801 and the metabotropic glutamate receptor antagonist MCPG protected against the BMAA-induced alterations, demonstrating the importance of glutamatergic mechanisms. The ionotropic non-NMDA receptor antagonist CNQX prevented the BMAA-induced decrease of cell viability in mixed cultures containing both neuronal and glial cells, but not in cultures with neurons only, suggesting a role of neuron–glial interactions and glial AMPA receptors in the BMAA-induced toxicity. The results show that the olfactory region may be a target for BMAA following inhalation exposure. Further studies on the relations between environmental olfactory toxicants and neurodegenerative disorders are warranted.

Angiopoietin-1 and ανβ3 integrin peptide promote the therapeutic effects of L-serine in an amyotrophic lateral sclerosis/Parkinsonism dementia complex model

Amyotrophic lateral sclerosis (ALS) is an adult disorder of neurodegeneration that manifests as the destruction of upper and lower motor neurons. Beta-N-methylamino-L-alanine (L-BMAA), an amino acid not present in proteins, was found to cause intraneuronal protein misfolding and to induce ALS/Parkinsonism dementia complex (PDC), which presents symptoms analogous to those of Alzheimer’s-like dementia and Parkinsonism. L-serine suppresses the erroneous incorporation of L-BMAA into proteins in the human nervous system. In this study, angiopoietin-1, an endothelial growth factor crucial for vascular development and angiogenesis, and the integrin αvβ3 binding peptide C16, which inhibits inflammatory cell infiltration, were utilized to improve the local microenvironment within the central nervous system of an ALS/PDC rodent model by minimizing inflammation. Our results revealed that L-serine application yielded better effects than C16+ angiopoietin-1 treatment alone for alleviating apoptotic and autophagic changes and improving cognition and electrophysiological dysfunction, but not for improving the inflammatory micro-environment in the central nerve system, while further advances in attenuating the functional disability and pathological impairment induced by L-BMAA could be achieved by co-treatment with C16 and angiopoietin-1 in addition to L-serine. Therefore, C16+ angiopoietin-1 could be beneficial as a supplement to promote the effects of L-serine treatment.

Mitotically heritable effects of BMAA on striatal neural stem cell proliferation and differentiation

The widespread environmental contaminant β-methylamino-L-alanine (BMAA) is a developmental neurotoxicant that can induce long-term learning and memory deficits. Studies have shown high transplacental transfer of 3H-BMAA and a significant uptake in fetal brain. Therefore, more information on how BMAA may influence growth and differentiation of neural stem cells is required for assessment of the risk to the developing brain. The aim of this study was to investigate direct and mitotically inherited effects of BMAA exposure using primary striatal neurons and embryonic neural stem cells. The neural stem cells were shown to be clearly more susceptible to BMAA exposure than primary neurons. Exposure to 250 µM BMAA reduced neural stem cell proliferation through apoptosis and G2/M arrest. At lower concentrations (50–100 µM), not affecting cell proliferation, BMAA reduced the differentiation of neural stem cells into astrocytes, oligodendrocytes, and neurons through glutamatergic mechanisms. Neurons that were derived from the BMAA-treated neuronal stem cells demonstrated morphological alterations including reduced neurite length, and decreased number of processes and branches per cell. Interestingly, the BMAA-induced changes were mitotically heritable to daughter cells. The results suggest that early-life exposure to BMAA impairs neuronal stem cell programming, which is vital for development of the nervous system and may result in long-term consequences predisposing for both neurodevelopmental disorders and neurodegenerative disease later in life. More attention should be given to the potential adverse effects of BMAA exposure on brain development.

Genotoxic effects of neurotoxin ß-N-methylamino-l-alanine in human peripheral blood cells

The non-proteinogenic amino acid ß-N-methylamino-l-alanine (BMAA) is associated with the development of neurodegenerative diseases such as Alzheimer's disease, amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS-PDC) and amyotrophic lateral sclerosis. BMAA is known to induce neurotoxic effects leading to neurodegeneration via multiple mechanisms including misfolded protein accumulation, glutamate induced excitotoxicity, calcium dyshomeostasis, endoplasmic reticulum stress and oxidative stress. In the present study, for the first time, genotoxic activity of BMAA (2.5, 5, 10 and 20 μg/mL) was studied in human peripheral blood cells (HPBCs) using the comet and cytokinesis-block micronucleus cytome assays. In addition, the influence of BMAA on the oxidative stress was assessed. At non-cytotoxic concentrations BMAA did not induce formation of DNA strand breaks in HPBCs after 4 and 24 h exposure; however, it significantly increased the number of micronuclei after 24 and 48 h at 20 μg/mL and nucleoplasmic bridges after 48 h at 20 μg/mL. The frequency of nuclear buds was slightly though non-significantly increased after 48 h. Altogether, this indicates that in HPBCs BMAA is clastogenic and induces complex genomic alterations including structural chromosomal rearrangements and gene amplification. No influence on oxidative stress markers was noticed. These findings provide new evidence that environmental neurotoxin BMAA, in addition to targeting common pathways involved in neurodegeneration, can also induce genomic instability in non-target HPBCs suggesting that it might be involved in cancer development. Therefore, these data are important in advancing our current knowledge and opening new questions in the understanding of the mechanisms of BMAA toxicity, particularly in the context of genotoxicity.

Correlated Materials Characterization via Multimodal Chemical and Functional Imaging

Multimodal chemical imaging simultaneously offers high-resolution chemical and physical information with nanoscale and, in select cases, atomic resolution. By coupling modalities that collect physical and chemical information, we can address scientific problems in biological systems, battery and fuel cell research, catalysis, pharmaceuticals, photovoltaics, medicine, and many others. The combined systems enable the local correlation of material properties with chemical makeup, making fundamental questions of how chemistry and structure drive functionality approachable. In this Review, we present recent progress and offer a perspective for chemical imaging used to characterize a variety of samples by a number of platforms. Specifically, we present cases of infrared and Raman spectroscopies combined with scanning probe microscopy; optical microscopy and mass spectrometry; nonlinear optical microscopy; and, finally, ion, electron, and probe microscopies with mass spectrometry. We also discuss the challenges associated with the use of data originated by the combinatorial hardware, analysis, and machine learning as well as processing tools necessary for the interpretation of multidimensional data acquired from multimodal studies.

Molecular imaging mass spectrometry for probing protein dynamics in neurodegenerative disease pathology

Recent advances in the understanding of basic pathological mechanisms in various neurological diseases depend directly on the development of novel bioanalytical technologies that allow sensitive and specific chemical imaging at high resolution in cells and tissues. Mass spectrometry-based molecular imaging (IMS) has gained increasing popularity in biomedical research for mapping the spatial distribution of molecular species in situ. The technology allows for comprehensive, untargeted delineation of in situ distribution profiles of metabolites, lipids, peptides and proteins. A major advantage of IMS over conventional histochemical techniques is its superior molecular specificity. Imaging mass spectrometry has therefore great potential for probing molecular regulations in CNS-derived tissues and cells for understanding neurodegenerative disease mechanism. The goal of this review is to familiarize the reader with the experimental workflow, instrumental developments and methodological challenges as well as to give a concise overview of the major advances and recent developments and applications of IMS-based protein and peptide profiling with particular focus on neurodegenerative diseases. This article is part of the Special Issue "Proteomics".

The environmental neurotoxin β-N-methylamino-L-alanine inhibits melatonin synthesis in primary pinealocytes and a rat model

The environmental neurotoxin β-N-methylamino-L-alanine (BMAA) is a glutamate receptor agonist that can induce oxidative stress and has been implicated as a possible risk factor for neurodegenerative disease. Detection of BMAA in mussels, crustaceans, and fish illustrates that the sources of human exposure to this toxin are more abundant than previously anticipated. The aim of this study was to determine uptake of BMAA in the pineal gland and subsequent effects on melatonin production in primary pinealocyte cultures and a rat model. Autoradiographic imaging of 10-day-old male rats revealed a high and selective uptake in the pineal gland at 30 minutes to 24 hours after ¹⁴ C-L-BMAA administration (0.68 mg/kg). Primary pinealocyte cultures exposed to 0.05-3 mmol/L BMAA showed a 57%-93% decrease in melatonin synthesis in vitro. Both the metabotropic glutamate receptor 3 (mGluR3) antagonist Ly341495 and the protein kinase C (PKC) activator phorbol-12-myristate-13-acetate prevented the decrease in melatonin secretion, suggesting that BMAA inhibits melatonin synthesis by mGluR3 activation and PKC inhibition. Serum analysis revealed a 45% decrease in melatonin concentration in neonatal rats assessed 2 weeks after BMAA administration (460 mg/kg) and confirmed an inhibition of melatonin synthesis in vivo. Given that melatonin is a most important neuroprotective molecule in the brain, the etiology of BMAA-induced neurodegeneration may include mechanisms beyond direct excitotoxicity and oxidative stress.

A Simple Sonication Improves Protein Signal in Matrix-Assisted Laser Desorption Ionization Imaging

Proper matrix application is crucial in obtaining high quality matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI). Solvent-free sublimation was essentially introduced as an approach of homogeneous coating that gives small crystal size of the organic matrix. However, sublimation has lower extraction efficiency of analytes. Here, we present that a simple sonication step after the hydration in standard sublimation protocol significantly enhances the sensitivity of MALDI MSI. This modified procedure uses a common laboratory ultrasonicator to immobilize the analytes from tissue sections without noticeable delocalization. Improved imaging quality with additional peaks above 10 kDa in the spectra was thus obtained upon sonication treatment. Graphical Abstract ᅟ.

The environmental neurotoxin β-N-methylamino-l-alanine (l-BMAA) is deposited into birds' eggs

The neurotoxic amino acid β-N-methylamino-L-alanine (BMAA) has been implicated in the etiology of neurodegenerative disorders. BMAA is also a known developmental neurotoxin and research indicates that the sources of human and wildlife exposure may be more diverse than previously anticipated. The aim of the present study was therefore to examine whether BMAA can be transferred into birds' eggs. Egg laying quail were dosed with ¹⁴C-labeled BMAA. The distribution of radioactivity in the birds and their laid eggs was then examined at different time points by autoradiography and phosphoimaging analysis. To evaluate the metabolic stability of the BMAA molecule, the distribution of ¹⁴C-methyl- and ¹⁴C-carboxyl-labeled BMAA were compared. The results revealed a pronounced incorporation of radioactivity in the eggs, predominantly in the yolk but also in the albumen. Imaging analysis showed that the concentrations of radioactivity in the liver decreased about seven times between the 24h and the 72h time points, while the concentrations in egg yolk remained largely unchanged. At 72h the egg yolk contained about five times the concentration of radioactivity in the liver. Both BMAA preparations gave rise to similar distribution pattern in the bird tissues and in the eggs, indicating metabolic stability of the labeled groups. The demonstrated deposition into eggs warrants studies of BMAAs effects on bird development. Moreover, birds' eggs may be a source of human BMAA exposure, provided that the laying birds are exposed to BMAA via their diet.

A Single Neonatal Exposure to BMAA in a Rat Model Produces Neuropathology Consistent with Neurodegenerative Diseases

Although cyanobacterial β-N-methylamino-l-alanine (BMAA) has been implicated in the development of Alzheimer's Disease (AD), Parkinson's Disease (PD) and Amyotrophic Lateral Sclerosis (ALS), no BMAA animal model has reproduced all the neuropathology typically associated with these neurodegenerative diseases. We present here a neonatal BMAA model that causes β-amyloid deposition, neurofibrillary tangles of hyper-phosphorylated tau, TDP-43 inclusions, Lewy bodies, microbleeds and microgliosis as well as severe neuronal loss in the hippocampus, striatum, substantia nigra pars compacta, and ventral horn of the spinal cord in rats following a single BMAA exposure. We also report here that BMAA exposure on particularly PND3, but also PND4 and 5, the critical period of neurogenesis in the rodent brain, is substantially more toxic than exposure to BMAA on G14, PND6, 7 and 10 which suggests that BMAA could potentially interfere with neonatal neurogenesis in rats. The observed selective toxicity of BMAA during neurogenesis and, in particular, the observed pattern of neuronal loss observed in BMAA-exposed rats suggest that BMAA elicits its effect by altering dopamine and/or serotonin signaling in rats.

Β-N-Methylamino-L-Alanine (BMAA) Toxicity Is Gender and Exposure-Age Dependent in Rats

Cyanobacterial β-N-methylamino-L-alanine (BMAA) has been suggested as a causative or contributory factor in the development of several neurodegenerative diseases. However, no BMAA animal model has adequately shown clinical or behavioral symptoms that correspond to those seen in either Alzheimer's Disease (AD), Amyotrophic Lateral Sclerosis (ALS) or Parkinson's Disease (PD). We present here the first data that show that when neonatal rats were exposed to BMAA on postnatal days 3, 4 and 5, but not on gestational day 14 or postnatally on days 7 or 10, several AD and/or PD-related behavioral, locomotor and cognitive deficits developed. Male rats exhibited severe unilateral hindlimb splay while whole body tremors could be observed in exposed female rats. BMAA-exposed rats failed to identify and discriminate a learned odor, an early non-motor symptom of PD, and exhibited decreased locomotor activity, decreased exploration and increased anxiety in the open field test. Alterations were also observed in the rats' natural passive defense mechanism, and potential memory deficits and changes to the rat's natural height avoidance behavior could be observed as early as PND 30. Spatial learning, short-term working, reference and long-term memory were also impaired in 90-day-old rats that had been exposed to a single dose of BMAA on PND 3-7. These data suggest that BMAA is a developmental neurotoxin, with specific target areas in the brain and spinal cord.

Cellular and Molecular Aspects of the β-N-Methylamino-l-alanine (BMAA) Mode of Action within the Neurodegenerative Pathway: Facts and Controversy

The implication of the cyanotoxin β-N-methylamino-l-alanine (BMAA) in long-lasting neurodegenerative disorders is still a matter of controversy. It has been alleged that chronic ingestion of BMAA through the food chain could be a causative agent of amyotrophic lateral sclerosis (ALS) and several related pathologies including Parkinson syndrome. Both in vitro and in vivo studies of the BMAA mode of action have focused on different molecular targets, demonstrating its toxicity to neuronal cells, especially motoneurons, and linking it to human neurodegenerative diseases. Historically, the hypothesis of BMAA-induced excitotoxicity following the stimulation of glutamate receptors has been established. However, in this paradigm, most studies have shown acute, rather than chronic effects of BMAA. More recently, the interaction of this toxin with neuromelanin, a pigment present in the nervous system, has opened a new research perspective. The issues raised by this toxin are related to its kinetics of action, and its possible incorporation into cellular proteins. It appears that BMAA neurotoxic activity involves different targets through several mechanisms known to favour the development of neurodegenerative processes.

Aerosol Health Effects from Molecular to Global Scales

Poor air quality is globally the largest environmental health risk. Epidemiological studies have uncovered clear relationships of gaseous pollutants and particulate matter (PM) with adverse health outcomes, including mortality by cardiovascular and respiratory diseases. Studies of health impacts by aerosols are highly multidisciplinary with a broad range of scales in space and time. We assess recent advances and future challenges regarding aerosol effects on health from molecular to global scales through epidemiological studies, field measurements, health-related properties of PM, and multiphase interactions of oxidants and PM upon respiratory deposition. Global modeling combined with epidemiological exposure-response functions indicates that ambient air pollution causes more than four million premature deaths per year. Epidemiological studies usually refer to PM mass concentrations, but some health effects may relate to specific constituents such as bioaerosols, polycyclic aromatic compounds, and transition metals. Various analytical techniques and cellular and molecular assays are applied to assess the redox activity of PM and the formation of reactive oxygen species. Multiphase chemical interactions of lung antioxidants with atmospheric pollutants are crucial to the mechanistic and molecular understanding of oxidative stress upon respiratory deposition. The role of distinct PM components in health impacts and mortality needs to be clarified by integrated research on various spatiotemporal scales for better evaluation and mitigation of aerosol effects on public health in the Anthropocene.

Perinatal Exposure to the Cyanotoxin β-N-Méthylamino-L-Alanine (BMAA) Results in Long-Lasting Behavioral Changes in Offspring-Potential Involvement of DNA Damage and Oxidative Stress

We recently demonstrated that perinatal exposure to the glutamate-related herbicide, glufosinate ammonium, has deleterious effects on neural stem cell (NSC) homeostasis within the sub-ventricular zone (SVZ), probably leading to ASD-like symptoms in offspring later in life. In the present study, we aimed to investigate whether perinatal exposure to another glutamate-related toxicant, the cyanobacterial amino acid β-N-methylamino-L-alanine (BMAA), might also trigger neurodevelopmental disturbances. With this aim, female mice were intranasally exposed to low doses of BMAA, 50 mg kg^-1 three times a week from embryonic days 7-10 to postnatal day 21. Behavioral analyses were performed during the offspring's early life and during adulthood. Developmental analyses revealed that perinatal exposure to BMAA hastened the appearance of some reflexes and communicative skills. BMAA-exposed offspring displayed sex-dependent changes in emotional cognition shortly after exposure. Later in life, the female offspring continued to express emotional defects and to display abnormal sociability, while males were less affected. To assess whether early exposure to BMAA had deleterious effects on NSC homeostasis, we exposed mice NSCs to 1 and 3 mM BMAA during 24 h. We found that BMAA-exposed NSCs produced high levels of ROS, highlighting the ability of BMAA to induce oxidative stress. We also showed that BMAA exposure increased the number of γH2AX/53BP1 foci per nucleus, suggesting that BMAA-induced DNA damage in NSCs. Collectively, this data strongly suggests that perinatal exposure to the cyanobacteria BMAA, even at low doses, results in neurobehavioral disturbances during both the postnatal period and adulthood. This is considered to be underpinned at the cellular level through dysregulation of NSC homeostasis in the developing brain.

Creating a Simian Model of Guam ALS/PDC Which Reflects Chamorro Lifetime BMAA Exposures

The theory that β-N-methylamino-L-alanine (BMAA), a cyanobacterial toxin, contaminates traditional food supplies of the Chamorro people of Guam is supported by the recent finding that chronic dietary exposure to L-BMAA in vervets (Chlorocebus sabaeus) triggers the formation of neurofibrillary tangles (NFT) and β-amyloid plaques in the brain. In the first experiment, we found that all four vervets receiving a 210 mg/kg dose for 140 days developed NFT and sparse amyloid deposits. In the second experiment, all eight vervets receiving a 210 mg/kg dose for 140 days developed NFT and amyloid deposits, as well as all eight vervets that received only 21 mg/kg. Based on dietary surveys of the Chamorro people, we estimated lifetime chronic BMAA exposure at a high and a low level: 1) adult male Chamorros eating two flying foxes per month plus one 30 g serving of cycad flour per week; and 2) adult male Chamorros eating one 30 g serving of cycad flour per day combined with the consumption of eight flying foxes per month. The resultant cumulative lifetime Chamorro exposures ranged from 1 to 41 g/kg and are comparable to the total lifetime vervet exposures in our experiments of 2 and 22 g/kg, respectively. Furthermore, measured protein-bound BMAA concentrations of vervets fed L-BMAA powder are comparable to measured protein-bound BMAA concentrations in postmortem brain tissues of Chamorros who died with ALS/PDC.

Potential transfer of neurotoxic amino acid β-N-methylamino-alanine (BMAA) from mother to infant during breast-feeding: Predictions from human cell lines

β-N-methylamino-alanine (BMAA) is a non-protein amino acid produced by cyanobacteria, diatoms and dinoflagellates. BMAA has potential to biomagnify in a terrestrial food chain, and to bioaccumulate in fish and shellfish. We have reported that administration of [¹⁴C]l-BMAA to lactating mice and rats results in a mother to off-spring transfer via the milk. A preferential enantiomer-specific uptake of [¹⁴C]l-BMAA has also been demonstrated in differentiated murine mammary epithelium HC11 cells. These findings, together with neurotoxic effects of BMAA demonstrated both in vitro and in vivo, highlight the need to determine whether such transfer could also occur in humans. Here, we used four cell lines of human origin to examine and compare the transport of the two BMAA enantiomers in vitro. The uptake patterns of [¹⁴C]l- and [¹⁴C]d-BMAA in the human mammary MCF7 cell line were in agreement with the results in murine HC11 cells, suggesting a potential secretion of BMAA into human breast milk. The permeability coefficients for both [¹⁴C]l- and [¹⁴C]d-BMAA over monolayers of human intestinal Caco2 cells supported an efficient absorption from the human intestine. As a final step, transport experiments confirmed that [¹⁴C]l-and [¹⁴C]d-BMAA can be taken up by human SHSY5Y neuroblastoma cells and even more efficiently by human U343 glioblastoma cells. In competition experiments with various amino acids, the ASCT2 specific inhibitor benzylserine was the most effective inhibitor of [¹⁴C]l-BMAA uptake tested here. Altogether, our results suggest that BMAA can be transferred from an exposed mother, via the milk, to the brain of the nursed infant.

Clinical applications of MALDI imaging technologies in cancer and neurodegenerative diseases

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) imaging mass spectrometry (IMS) enables localization of analytes of interest along with histology. More specifically, MALDI-IMS identifies the distributions of proteins, peptides, small molecules, lipids, and drugs and their metabolites in tissues, with high spatial resolution. This unique capacity to directly analyze tissue samples without the need for lengthy sample preparation reduces technical variability and renders MALDI-IMS ideal for the identification of potential diagnostic and prognostic biomarkers and disease gradation. MALDI-IMS has evolved rapidly over the last decade and has been successfully used in both medical and basic research by scientists worldwide. In this review, we explore the clinical applications of MALDI-IMS, focusing on the major cancer types and neurodegenerative diseases. In particular, we re-emphasize the diagnostic potential of IMS and the challenges that must be confronted when conducting MALDI-IMS in clinical settings. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

A critical review of the postulated role of the non-essential amino acid, β-N-methylamino-L-alanine, in neurodegenerative disease in humans

The compound BMAA (β-N-methylamino-L-alanine) has been postulated to play a significant role in four serious neurological human diseases: Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC) found on Guam, and ALS, Parkinsonism, and dementia that occur globally. ALS/PDC with symptoms of all three diseases first came to the attention of the scientific community during and after World War II. It was initially associated with cycad flour used for food because BMAA is a product of symbiotic cycad root-dwelling cyanobacteria. Human consumption of flying foxes that fed on cycad seeds was later suggested as a source of BMAA on Guam and a cause of ALS/PDC. Subsequently, the hypothesis was expanded to include a causative role for BMAA in other neurodegenerative diseases including Alzheimer's disease (AD) through exposures attributed to proximity to freshwaters and/or consumption of seafood due to its purported production by most species of cyanobacteria. The hypothesis that BMAA is the critical factor in the genesis of these neurodegenerative diseases received considerable attention in the medical, scientific, and public arenas. This review examines the history of ALS/PDC and the BMAA-human disease hypotheses; similarities and differences between ALS/PDC and the other diseases with similar symptomologies; the relationship of ALS/PDC to other similar diseases, studies of BMAA-mediated effects in lab animals, inconsistencies and data gaps in the hypothesis; and other compounds and agents that were suggested as the cause of ALS/PDC on Guam. The review concludes that the hypothesis of a causal BMAA neurodegenerative disease relationship is not supported by existing data.

MALDI imaging delineates hippocampal glycosphingolipid changes associated with neurotoxin induced proteopathy following neonatal BMAA exposure

The environmental toxin β-N-methylamino-L-alanine (BMAA) has been proposed to contribute to neurodegenerative diseases. We have previously shown that neonatal exposure to BMAA results in dose-dependent cognitive impairments, proteomic alterations and progressive neurodegeneration in the hippocampus of adult rats. A high BMAA dose (460mg/kg) also induced intracellular fibril formation, increased protein ubiquitination and enrichment of proteins important for lipid transport and metabolism. The aim of this study was therefore to elucidate the role of neuronal lipids in BMAA-induced neurodegeneration. By using matrix assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS), we characterized the spatial lipid profile in the hippocampus of six month-old rats that were treated neonatally (postnatal days 9-10) with 460mg/kg BMAA. Multivariate statistical analysis revealed long-term changes in distinct ganglioside species (GM, GD, GT) in the dentate gyrus. These changes could be a consequence of direct effects on ganglioside biosynthesis through the b-series (GM3-GD3-GD2-GD1b-GT1b) and may be linked to astrogliosis. Complementary immunohistochemistry experiments towards GFAP and S100β further verified the role of increased astrocyte activity in BMAA-induced brain damage. This highlights the potential of imaging MS for probing chemical changes associated with neuropathological mechanisms in situ. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

Imaging mass spectrometry in drug development and toxicology

During the last decades, imaging mass spectrometry has gained significant relevance in biomedical research. Recent advances in imaging mass spectrometry have paved the way for in situ studies on drug development, metabolism and toxicology. In contrast to whole-body autoradiography that images the localization of radiolabeled compounds, imaging mass spectrometry provides the possibility to simultaneously determine the discrete tissue distribution of the parent compound and its metabolites. In addition, imaging mass spectrometry features high molecular specificity and allows comprehensive, multiplexed detection and localization of hundreds of proteins, peptides and lipids directly in tissues. Toxicologists traditionally screen for adverse findings by histopathological examination. However, studies of the molecular and cellular processes underpinning toxicological and pathologic findings induced by candidate drugs or toxins are important to reach a mechanistic understanding and an effective risk assessment strategy. One of IMS strengths is the ability to directly overlay the molecular information from the mass spectrometric analysis with the tissue section and allow correlative comparisons of molecular and histologic information. Imaging mass spectrometry could therefore be a powerful tool for omics profiling of pharmacological/toxicological effects of drug candidates and toxicants in discrete tissue regions. The aim of the present review is to provide an overview of imaging mass spectrometry, with particular focus on MALDI imaging mass spectrometry, and its use in drug development and toxicology in general.

Workers on transformation of the shelter object of the Chernobyl nuclear power plant into an ecologically-safe system show qEEG abnormalities and cognitive dysfunctions: A follow-up study

OBJECTIVES

The present study aimed at assessing bioelectric activity and cognitive functions in the workers on the conversion project of the "Shelter" object (SO) of the Chernobyl nuclear power plant into an environmentally safe system.

METHODS

A total of 196 men were included and examined before (t0) and after (t1) working on the SO in the period 2004-2008. They underwent a qEEG and a battery of neuropsychological and psychiatric assessments.

RESULTS

At t1, the organized type of qEEG shifted towards the disorganized one. An increase of spectral δ-power in the left frontotemporal area, of θ- and α-power in the left temporal area, with redistribution of α-activity to the front and reduction of dominant frequency in the left temporal area, were registered. Further, neurocognitive tests revealed the presence of mild cognitive disorders at t1. Interestingly, those subjects previously exposed to radiation with no consequences, were more resistant to these detrimental effects.

CONCLUSIONS

Taken together, the disturbances observed may be considered as cognitive symptoms of a chronic fatigue syndrome resulting from the exposure to ionizing radiation. Simple and non-invasive assessments, such as those performed by us, may be helpful to detect early brain changes caused by the presence of radiological risk factors.

Transfer of developmental neurotoxin β-N-methylamino-l-alanine (BMAA) via milk to nursed offspring: Studies by mass spectrometry and image analysis

The cyanobacterial non-proteinogenic amino acid β-N-methylamino-l-alanine (BMAA) is proposed to be involved in the etiology of amyotrophic lateral sclerosis/parkinsonism dementia complex. When administered as single doses to neonatal rats, BMAA gives rise to cognitive and neurodegenerative impairments in the adult animal. Here, we employed mass spectrometry (LC-MS/MS) and autoradiographic imaging to examine the mother-to-pup transfer of BMAA in rats. The results show that unchanged BMAA was secreted into the milk and distributed to the suckling pups. The concentration of BMAA in pup stomach milk and the neonatal liver peaked after 8h, while the concentration in the pup brain increased throughout the study period. About 1 and 6% of the BMAA recovered from adult liver and brain were released following hydrolysis, suggesting that this fraction was associated with protein. No association to milk protein was observed. Injection of rat pups with [methyl-(14)C]-l-BMAA or [carboxyl-(14)C]-l-BMAA resulted in highly similar distribution patterns, indicating no or low metabolic elimination of the methylamino- or carboxyl groups. In conclusion, BMAA is transported as a free amino acid to rat milk and suckling pups. The results strengthen the proposal that mothers' milk could be a source of exposure for BMAA in human infants.

Environmental neurotoxin interaction with proteins: Dose-dependent increase of free and protein-associated BMAA (β-N-methylamino-L-alanine) in neonatal rat brain

β-Methylamino-L-alanine (BMAA) is implicated in the aetiology of neurodegenerative disorders. Neonatal exposure to BMAA induces cognitive impairments and progressive neurodegenerative changes including intracellular fibril formation in the hippocampus of adult rats. It is unclear why the neonatal hippocampus is especially vulnerable and the critical cellular perturbations preceding BMAA-induced toxicity remains to be elucidated. The aim of this study was to compare the level of free and protein-associated BMAA in neonatal rat brain and peripheral tissues after different exposures to BMAA. Ultra-high performance liquid chromatography-tandem mass spectrometry analysis revealed that BMAA passed the neonatal blood-brain barrier and was distributed to all studied brain areas. BMAA was also associated to proteins in the brain, especially in the hippocampus. The level in the brain was, however, considerably lower compared to the liver that is not a target organ for BMAA. In contrast to the liver there was a significantly increased level of protein-association of BMAA in the hippocampus and other brain areas following repeated administration suggesting that the degradation of BMAA-associated proteins may be lower in neonatal brain than in the liver. Additional evidence is needed in support of a role for protein misincorporation in the neonatal hippocampus for long-term effects of BMAA.

Pyrylium Salts as Reactive Matrices for MALDI-MS Imaging of Biologically Active Primary Amines

Many neuroactive substances, including endogenous biomolecules, environmental compounds, and pharmaceuticals possess primary amine functional groups. Among these are catecholamine neurotransmitters (e.g., dopamine), many substituted phenethylamines (e.g., amphetamine), as well as amino acids and neuropeptides. In most cases, mass spectrometric (ESI and MALDI) analyses of trace amounts of such compounds are challenging because of their poor ionization properties. We present a method for chemical derivatization of primary amines by reaction with pyrylium salts that facilitates their detection by MALDI-MS and enables the imaging of primary amines in brain tissue sections. A screen of pyrylium salts revealed that the 2,4-diphenyl-pyranylium ion efficiently derivatizes primary amines and can be used as a reactive MALDI-MS matrix that induces both derivatization and desorption. MALDI-MS imaging with such matrix was used to map the localization of dopamine and amphetamine in brain tissue sections and to quantitatively map the distribution of the neurotoxin β-N-methylamino-L-alanine.

Spatial neuroproteomics using imaging mass spectrometry

The nervous system constitutes arguably the most complicated and least understood cellular network in the human body. This consequently manifests itself in the fact that the molecular bases of neurodegenerative diseases remain unknown. The limited understanding of neurobiological mechanisms relates directly to the lack of appropriate bioanalytical technologies that allow highly resolved, sensitive, specific and comprehensive molecular imaging in complex biological matrices. Imaging mass spectrometry (IMS) is an emerging technique for molecular imaging. The technique is characterized by its high chemical specificity allowing comprehensive, spatial protein and peptide profiling in situ. Imaging MS represents therefore a powerful approach for investigation of spatio-temporal protein and peptide regulations in CNS derived tissue and cells. This review aims to provide a concise overview of major developments and applications concerning imaging mass spectrometry based protein and peptide profiling in neurobiological and biomedical research. This article is part of a Special Issue entitled: Neuroproteomics: Applications in Neuroscience and Neurology.

Probing the lipid chemistry of neurotoxin-induced hippocampal lesions using multimodal imaging mass spectrometry

The environmental toxin β-N-methylamino-L-alanine (BMAA) has been causatively linked to neurodegenerative disease pathology. In a rat model, neonatal BMAA exposure resulted in selective uptake in the hippocampal formation and caused learning and memory impairments in adult animals. Moreover, high dose neonatal BMAA exposure resulted in formation of protein inclusions in the CA1 region of the adult hippocampus. However the mechanism underlying BMAA induced neuropathology remains elusive. Imaging mass spectrometry is a powerful method for spatial interrogation of biochemical distribution in biological tissue with high chemical specificity. The aim of this study was to therefore characterize the lipid microenvironment of BMAA-induced hippocampal lesions in adult rats using matrix-assisted laser desorption/ionization (MALDI) and time-of-flight SIMS (ToF-SIMS imaging). Multimodal imaging was carried out by ToF-SIMS scans of the hippocampal formation followed by whole tissue scans using MALDI imaging. Multivariate analysis was performed on the SIMS data in order to delineate the spatial biochemistry surrounding the lesions. The data show lesion-specific localization of phosphatidylcholine fragments, suggesting neuroinflammatory glial cell activation. Complementary MALDI imaging data showed increased levels of phosphoethanolamines colocalizing with the proteopathic lesions pointing to macroautophagic mechanisms associated with neurotoxin-induced protein accumulation. Multimodal IMS by means of ToF-SIMS and MALDI mass spectrometry proved to be a powerful technique for neurotoxicological research.

Searching for a link between the L-BMAA neurotoxin and amyotrophic lateral sclerosis: a study protocol of the French BMAALS programme

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is the most common motor neurone disease. It occurs in two forms: (1) familial cases, for which several genes have been identified and (2) sporadic cases, for which various hypotheses have been formulated. Notably, the β-N-methylamino-L-alanine (L-BMAA) toxin has been postulated to be involved in the occurrence of sporadic ALS. The objective of the French BMAALS programme is to study the putative link between L-BMAA and ALS.

METHODS AND ANALYSIS

The programme covers the period from 1 January 2003 to 31 December 2011. Using multiple sources of ascertainment, all the incident ALS cases diagnosed during this period in the area under study (10 counties spread over three French regions) were collected. First, the standardised incidence ratio will be calculated for each municipality under concern. Then, by applying spatial clustering techniques, overincidence and underincidence zones of ALS will be sought. A case-control study, in the subpopulation living in the identified areas, will gather information about patients' occupations, leisure activities and lifestyle habits in order to assess potential risk factors to which they are or have been exposed. Specimens of drinking water, food and biological material (brain tissue) will be examined to assess the presence of L-BMAA in the environment and tissues of ALS cases and controls.

ETHICS AND DISSEMINATION

The study has been reviewed and approved by the French ethical committee of the CPP SOOM IV (Comité de Protection des Personnes Sud-Ouest & Outre-Mer IV). The results will be published in peer-reviewed journals and presented at national and international conferences.

High resolution metabolite imaging in the hippocampus following neonatal exposure to the environmental toxin BMAA using ToF-SIMS

The environmental neurotoxin β-N-methylamino-L-alanine (BMAA) is suggested to be linked with neurodegenerative disease. In a rat model, neonatal exposure to BMAA induced selective uptake in the hippocampus and caused cell loss, mineralization and astrogliosis as well as learning and memory impairments in adulthood. Moreover, neonatal exposure resulted in increased protein ubiquitination in the cornus ammonis 1 (CA1) region of the adult hippocampus indicating that BMAA may induce protein aggregation. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) based imaging is a powerful technology for spatial profiling of small molecular weight compounds in biological tissues with high chemical specificity and high spatial resolution. The aim of this study was to characterize neurochemical changes in the hippocampus of six month-old rats treated neonatally (postnatal days 9-10) with BMAA. Multivariate data analysis of whole section ToF-SIMS scans was performed to delineate anatomical regions of interest based on their chemical distribution pattern. Further analysis of spectral data obtained from the outlined anatomical regions, including CA1 and dentate gyrus (DG) revealed BMAA-induced long-term changes. Increased levels of phospholipids and protein fragments in the histopathologically altered CA1 region as well as phosphate depletion in the DG were observed. Moreover, high resolution SIMS imaging revealed a specific localization of phosphatidylcholine lipids, protein signals and potassium in the histopathologically altered CA1. These findings demonstrate that ToF-SIMS based imaging is a powerful approach for probing biochemical changes in situ and might serve as promising technique for investigating neurotoxin-induced brain pathology.

Intracellular fibril formation, calcification, and enrichment of chaperones, cytoskeletal, and intermediate filament proteins in the adult hippocampus CA1 following neonatal exposure to the nonprotein amino acid BMAA

The environmental neurotoxin β-N-methylamino-l-alanine (BMAA) has been implicated in the etiology of neurodegenerative disease, and recent studies indicate that BMAA can be misincorporated into proteins. BMAA is a developmental neurotoxicant that can induce long-term learning and memory deficits, as well as regionally restricted neuronal degeneration and mineralization in the hippocampal CA1. The aim of the study was to characterize long-term changes (2 weeks to 6 months) further in the brain of adult rats treated neonatally (postnatal days 9–10) with BMAA (460 mg/kg) using immunohistochemistry (IHC), transmission electron microscopy, and laser capture microdissection followed by LC-MS/MS for proteomic analysis. The histological examination demonstrated progressive neurodegenerative changes, astrogliosis, microglial activation, and calcification in the hippocampal CA1 3–6 months after exposure. The IHC showed an increased staining for α-synuclein and ubiquitin in the area. The ultrastructural examination revealed intracellular deposition of abundant bundles of closely packed parallel fibrils in neurons, axons, and astrocytes of the CA1. Proteomic analysis of the affected site demonstrated an enrichment of chaperones (e.g., clusterin, GRP-78), cytoskeletal and intermediate filament proteins, and proteins involved in the antioxidant defense system. Several of the most enriched proteins (plectin, glial fibrillar acidic protein, vimentin, Hsp 27, and ubiquitin) are known to form complex astrocytic inclusions, so-called Rosenthal fibers, in the neurodegenerative disorder Alexander disease. In addition, TDP-43 and the negative regulator of autophagy, GLIPR-2, were exclusively detected. The present study demonstrates that neonatal exposure to BMAA may offer a novel model for the study of hippocampal fibril formation in vivo.