β-N-methylamino-L-alanine induces neurological deficits and shortened life span in Drosophila

Environmental Neurotoxin β-N-Methylamino-L-alanine (BMAA) as a Widely Occurring Putative Pathogenic Factor in Neurodegenerative Diseases

In the present review we have discussed the occurrence of β-N-methylamino-L-alanine (BMAA) and its natural isomers, and the organisms and sample types in which the toxin(s) have been detected. Further, the review discusses general pathogenic mechanisms of neurodegenerative diseases, and how modes of action of BMAA fit in those mechanisms. The biogeography of BMAA occurrence presented here contributes to the planning of epidemiological research based on the geographical distribution of BMAA and human exposure. Analysis of BMAA mechanisms in relation to pathogenic processes of neurodegeneration is used to critically assess the potential significance of the amino acid as well as to identify gaps in our understanding. Taken together, these two approaches provide the basis for the discussion on the potential role of BMAA as a secondary factor in neurodegenerative diseases, the rationale for further research and possible directions the research can take, which are outlined in the conclusions.

Shuttle craft Gene Affects Lifespan of Drosophila melanogaster by Controlling Early Development and Modifying Aging Program

Fundamental mechanisms underlying genetic control of lifespan are intensively studied and discussed due to the increasing importance of extending healthy human life. The stc gene of the model organism Drosophila melanogaster encodes a transcription factor, homolog of the human transcription factor NF-X1, involved in regulation of neuronal development and other processes, as well as in control of lifespan. In this work, we demonstrate that the stc knockdown in embryonic and nerve cells leads to changes in lifespan, with the nature of changes depending on the cell type and sex of individuals. Based on our results, we suggest that stc gene is involved in transcription regulation throughout life, and, as a result, also affects a complex integral trait, lifespan. At the same time, we show that the reduction of stc expression in neurons can alleviate the negative effect of glutamate on longevity, possibly preventing development of glutamate excitotoxicity, thus modifying the cell death program and preventing death of individuals due to phenoptosis.

Motor dysfunction in Drosophila melanogaster as a biomarker for developmental neurotoxicity

Adequate alternatives to conventional animal testing are needed to study developmental neurotoxicity (DNT). Here, we used kinematic analysis to assess DNT of known (toluene (TOL) and chlorpyrifos (CPS)) and putative (β-N-methylamino-L-alanine (BMAA)) neurotoxic compounds. Drosophila melanogaster was exposed to these compounds during development and evaluated for survival and adult kinematic parameters using the FlyWalker system, a kinematics evaluation method. At concentrations that do not induce general toxicity, the solvent DMSO had a significant effect on kinematic parameters. Moreover, while TOL did not significantly induce lethality or kinematic dysfunction, CPS not only induced developmental lethality but also significantly impaired coordination in comparison to DMSO. Interestingly, BMAA, which was not lethal during development, induced motor decay in young adult animals, phenotypically resembling aged flies, an effect later attenuated upon aging. Furthermore, BMAA induced abnormal development of leg motor neuron projections. Our results suggest that our kinematic approach can assess potential DNT of chemical compounds.

•

Alternatives to mammalian testing are needed to detect developmental neurotoxicity

•

The pesticide chlorpyrifos causes partial lethality and motor dysfunction

•

Non-lethal levels of BMAA induce motor dysfunction in a dose-dependent manner

•

Kinematic profiling of adult Drosophila can identify developmental neurotoxicity

Experimental evidence challenges the presumed defensive function of a "slow toxin" in cycads

[Formula: see text]-methylamino-L-alanine (BMAA) is a neurotoxic non-protein amino acid found in the tissues of cycad plants. The demonstrated toxicity of BMAA to diverse organisms, including humans, is widely assumed to imply a defensive function of BMAA against herbivores; however, this hypothesis has not previously been tested in an ecologically relevant system. We investigated the effects of dietary BMAA, across a range of dosages matching and exceeding levels typically present in cycad leaves, on the feeding preferences and performance of a generalist lepidopteran herbivore (Spodoptera littoralis).We observed no effects of dietary BMAA on the survival or development of S. littoralis larvae, nor any larval preference between BMAA-laced and control diets. These findings suggest that BMAA in cycad tissues does not deter feeding by insect herbivores, raising questions about other potential physiological or ecological functions of this compound.

Exposure to Aerosolized Algal Toxins in South Florida Increases Short- and Long-Term Health Risk in Drosophila Model of Aging

Harmful algal blooms (HABs) are a rising health and environmental concern in the United States, particularly in South Florida. Skin contact and the ingestion of contaminated water or fish and other seafood have been proven to have severe toxicity to humans in some cases. However, the impact of aerosolized HAB toxins is poorly understood. In particular, knowledge regarding either the immediate or long-term effects of exposure to aerosolized cyanotoxins produced by freshwater blue-green algae does not exist. The aim of this study was to probe the toxicity of aerosolized cyanobacterial blooms using Drosophila melanogaster as an animal model. The exposure of aerosolized HABs at an early age leads to the most severe long-term impact on health and longevity among all age groups. Young groups and old males showed a strong acute response to HAB exposure. In addition, brain morphological analysis using fluorescence imaging reveals significant indications of brain degeneration in females exposed to aerosolized HABs in early or late stages. These results indicate that one-time exposure to aerosolized HAB particles causes a significant health risk, both immediately and in the long-term. Interestingly, age at the time of exposure plays an important role in the specific nature of the impact of aerosol HABs. As BMAA and microcystin have been found to be the significant toxins in cyanobacteria, the concentration of both toxins in the water and aerosols was examined. BMAA and microcystin are consistently detected in HAB waters, although their concentrations do not always correlate with the severity of the health impact, suggesting the potential contribution from additional toxins present in the aerosolized HAB. This study demonstrates, for the first time, the health risk of exposure to aerosolized HAB, and further highlights the critical need and importance of understanding the toxicity of aerosolized cyanobacteria HAB particles and determining the immediate and long-term health impacts of HAB exposure.

Neuro- and hepatic toxicological profile of (S)-2,4-diaminobutanoic acid in embryonic, adolescent and adult zebrafish

(S)-2,4-Diaminobutanoic acid (DABA) is a noncanonical amino acid often co-produced by cyanobacteria along with β-N-methylamino-l-alanine (BMAA) in algal blooms. Although BMAA is a well-established neurotoxin, the toxicity of DABA remains unclear. As part of our development of biocompatible materials, we wish to make use of DABA as both a building block and as the end-product of enzymatically induced depolymerization; however, if it is toxic at very low concentrations, this would not be possible. We examined the toxicity of DABA using both in vivo embryonic and adult zebrafish models. At higher sublethal concentrations (700 μm), the fish demonstrated early signs of cardiotoxicity. Adolescent zebrafish were able to tolerate a higher concentration. Post-mortem histological analysis of juvenile zebrafish showed no liver or brain abnormalities associated with hepato- or neurotoxicity. Combined, these results show that DABA exhibits no overt toxicity at concentrations (100-300 μm) within an order of magnitude of those envisioned for its application. This study further highlights the low cost and ease of using zebrafish as an early-stage toxicological screening tool.

A high-fat diet impacts memory and gene expression of the head in mated female Drosophila melanogaster

Obesity predisposes humans to a range of life-threatening comorbidities, including type 2 diabetes and cardiovascular disease. Obesity also aggravates neural pathologies, such as Alzheimer's disease, but this class of comorbidity is less understood. When Drosophila melanogaster (flies) are exposed to high-fat diet (HFD) by supplementing a standard medium with coconut oil, they adopt an obese phenotype of decreased lifespan, increased triglyceride storage, and hindered climbing ability. The latter development has been previously regarded as a potential indicator of neurological decline in fly models of neurodegenerative disease. Our objective was to establish the obesity phenotype in Drosophila and identify a potential correlation, if any, between obesity and neurological decline through behavioral assays and gene expression microarray. We found that mated female w1118 flies exposed to HFD maintained an obese phenotype throughout adult life starting at 7 days, evidenced by increased triglyceride stores, diminished life span, and impeded climbing ability. While climbing ability worsened cumulatively between 7 and 14 days of exposure to HFD, there was no corresponding alteration in triglyceride content. Microarray analysis of the mated female w1118 fly head revealed HFD-induced changes in expression of genes with functions in memory, metabolism, olfaction, mitosis, cell signaling, and motor function. Meanwhile, an Aversive Phototaxis Suppression assay in mated female flies indicated reduced ability to recall an entrained memory 6 h after training. Overall, our results support the suitability of mated female flies for examining connections between diet-induced obesity and nervous or neurobehavioral pathology, and provide many directions for further investigation.

Neurotoxic Agent-Induced Injury in Neurodegenerative Disease Model: Focus on Involvement of Glutamate Receptors

Glutamate receptors play a crucial role in the central nervous system and are implicated in different brain disorders. They play a significant role in the pathogenesis of neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Although many studies on NDDs have been conducted, their exact pathophysiological characteristics are still not fully understood. In in vivo and in vitro models of neurotoxic-induced NDDs, neurotoxic agents are used to induce several neuronal injuries for the purpose of correlating them with the pathological characteristics of NDDs. Moreover, therapeutic drugs might be discovered based on the studies employing these models. In NDD models, different neurotoxic agents, namely, kainic acid, domoic acid, glutamate, β-N-Methylamino-L-alanine, amyloid beta, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridinium, rotenone, 3-Nitropropionic acid and methamphetamine can potently impair both ionotropic and metabotropic glutamate receptors, leading to the progression of toxicity. Many other neurotoxic agents mainly affect the functions of ionotropic glutamate receptors. We discuss particular neurotoxic agents that can act upon glutamate receptors so as to effectively mimic NDDs. The correlation of neurotoxic agent-induced disease characteristics with glutamate receptors would aid the discovery and development of therapeutic drugs for NDDs.

α-Lipoic acid attenuates oxidative stress and neurotoxicity via the ERK/Akt-dependent pathway in the mutant hSOD1 related Drosophila model and the NSC34 cell line of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a degenerative disease with a progressive loss of motor neurons in the central nervous system (CNS). However, there are unsolved problems with the therapies for this disease. α-Lipoic acid (LA) is a natural, universal antioxidant capable of scavenging hydroxyl radicals as well as regenerating a series of antioxidant enzymes that has been widely used in clinical settings. This study aimed to evaluate the antioxidant and neuroprotective effects of LA in ALS cell and Drosophila models with mutant G85R and G93A hSOD1 genes. The biological effects of LA and the protein levels of several antioxidant factors were examined, as were those of phospho-Akt and phospho-ERK. Furthermore, specific inhibitors of the PI3K/Akt and MEK/ERK signaling pathways were used to analyze their effects on LA-induced antioxidant expression in vivo and in vitro. Evidences showed that the mutant hSOD1 resulted in the increased oxidative stress, abnormal antioxidant signaling and pathological behaviors in motor performance and survival compared with non-mutant hSOD1 models, treatment with LA improved motor activity and survival in transgenic flies, prevented NSC34 cells from mutant hSOD1 or H₂O₂ induced decreased antioxidant enzymes as well as increased ROS levels. In addition, LA regulated the expression levels of antioxidant proteins in a dose- and periodical time-dependent manner, which might be mediated by ERK/Akt pathway activation and independent from the mutant hSOD1 gene. Our observations suggest that LA exerts strong and positive antioxidant and neuroprotective effects through the activation of the ERK-Akt pathway in hSOD1 ALS models.

Fisetin Exerts Antioxidant and Neuroprotective Effects in Multiple Mutant hSOD1 Models of Amyotrophic Lateral Sclerosis by Activating ERK

Oxidative stress exhibits a central role in the course of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease commonly found to include a copper/zinc superoxide dismutase (SOD1) gene mutation. Fisetin, a natural antioxidant, has shown benefits in varied neurodegenerative diseases. The possible effect of fisetin in ALS has not been clarified as of yet. We investigated whether fisetin affected mutant hSOD1 ALS models. Three different hSOD1-related mutant models were used: Drosophila expressing mutant hSOD1^G85R, hSOD1^G93A NSC34 cells, and transgenic mice. Fisetin treatment provided neuroprotection as demonstrated by an improved survival rate, attenuated motor impairment, reduced ROS damage and regulated redox homeostasis compared with those in controls. Furthermore, fisetin increased the expression of phosphorylated ERK and upregulated antioxidant factors, which were reversed by MEK/ERK inhibition. Finally, fisetin reduced the levels of both mutant and wild-type hSOD1 in vivo and in vitro, as well as the levels of detergent-insoluble hSOD1 proteins. The results indicate that fisetin protects cells from ROS damage and improves the pathological behaviors caused by oxidative stress in disease models related to SOD1 gene mutations probably by activating ERK, thereby providing a potential treatment for ALS.

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.

The Potential Role of BMAA in Neurodegeneration

Neurodegenerative diseases are a major public health issue throughout the world with devastating effects on patients and families. Sporadic forms of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis are generally thought to develop as a consequence of genetic susceptibility and environmental influences. A number of environmental triggers have been identified in association with amyotrophic lateral sclerosis and Parkinson's disease. We discuss the role of β-methylamino-L-alanine in the development of neurodegeneration and the potential importance of this neurotoxin as a risk for neurodegeneration.

The cyanobacterial neurotoxin β-N-methylamino-l-alanine (BMAA) induces neuronal and behavioral changes in honeybees

The cyanobacterially produced neurotoxin beta-N-methylamino-l-alanine (BMAA) is thought to induce amyotrophic lateral sclerosis/Parkinsonism dementia complex (ALS/PDC)-like symptoms. However, its mechanism of action and its pathway of intoxication are yet unknown. In vivo animal models suitable for investigating the neurotoxic effect of BMAA with applicability to the human are scarce. Hence, we used the honeybee (Apis mellifera) since its nervous system is relatively simple, yet having cognitive capabilities. Bees fed with BMAA-spiked sugar water had an increased mortality rate and a reduced ability to learn odors in a classical conditioning paradigm. Using (14)C-BMAA we demonstrated that BMAA is biologically available to the bee, and is found in the head, thorax and abdomen with little to no excretion. BMAA is also transferred from one bee to the next via trophallaxis resulting in an exposure of the whole beehive. BMAA bath application directly onto the brain leads to an altered Ca(2+) homeostasis and to generation of reactive oxygen species. These behavioral and physiological observations suggest that BMAA may have effects on bee brains similar to those assumed to occur in humans. Therefore the bee could serve as a surrogate model system for investigating the neurological effects of BMAA.

ALS-linked SOD1 in glial cells enhances ß-N-Methylamino L-Alanine (BMAA)-induced toxicity in Drosophila

Environmental factors have been implicated in the etiology of a number of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). However, the role of environmental agents in ALS remains poorly understood. To this end, we used transgenic fruit flies (Drosophila melanogaster) to explore the interaction between mutant superoxide dismutase 1 (SOD1) and chemicals such as ß-N-methylamino L-alanine (BMAA), the herbicide agent paraquat, and superoxide species. We expressed ALS-linked human SOD1 (hSOD1A4V, and hSOD1G85R), hSOD1wt as well as the Drosophila native SOD1 (dSOD1) in motoneurons (MNs) or in glial cells alone and simultaneously in both types of cells. We then examined the effect of BMAA (3 mM), paraquat (20 mM), and hydrogen peroxide (H2O2, 1%) on the lifespan of SOD1-expressing flies. Our data show that glial expression of mutant and wild type hSOD1s reduces the ability of flies to climb. Further, we show that while all three chemicals significantly shorten the lifespan of flies, mutant SOD1 does not have a significant additional effect on the lifespan of flies fed on paraquat, but further shortens the lifespan of flies fed on H2O2. Finally, we show that BMAA shows a dramatic cell-type specific effect with mutant SOD1. Flies with expression of mutant hSOD1 in MNs survived longer on BMAA compared to control flies. In contrast, BMAA significantly shortened the lifespan of flies expressing mutant hSOD1 in glia. Consistent with a neuronal protection role, flies expressing these mutant hSOD1s in both MNs and glia also lived longer. Hence, our studies reveal a synergistic effect of mutant SOD1 with H2O2 and novel roles for mutant hSOD1s in neurons to reduce BMAA toxicity and in glia to enhance the toxicity of BMAA in flies.

The physiological effect of ingested β-N-methylamino-L-alanine on a glutamatergic synapse in an in vivo preparation

The neurotoxin, BMAA (β-N-methylamino-L-alanine), may be a risk factor for amyotrophic lateral sclerosis (ALS), Parkinson's (PD) and Alzheimer's (AD) disease. In vivo experiments have demonstrated that BMAA can cause a number of motor dysfunctions if ingested or injected, and in vitro experiments show that this toxin binds to glutamate receptors with deleterious results. Also, BMAA exists in the human food chain worldwide, and has been detected in the brains of ALS and AD patients. This paper offers the first demonstration by intracellular recording of the effect of ingested BMAA on the postsynaptic response of an identified glutamatergic cell in a living, undissected organism (Drosophila melanogaster), and correlates these observations with the specific motor dysfunctions that result from ingestion. The results suggest that BMAA acts as a glutamate agonist, causing NMDA receptor channels to remain open for prolonged periods of time, thereby damaging the cell by excitotoxicity. The effect on the postsynaptic response became apparent days before the function of the postsynaptic cell (wing beat) became affected. Severely depolarized cells were able to fully recover with the removal of BMAA from the food source, suggesting that blocking BMAA binding in the brain might be a good treatment strategy.

A novel lenticular arena to quantify locomotor competence in walking fruit flies

Drosophila melanogaster has become an important invertebrate model organism in biological and medical research, for mutational and genetic analysis, and in toxicological screening. Many screening assays have been developed that assess the flies' mortality, reproduction, development, morphology, or behavioral competence. In this study, we describe a new assay for locomotor competence. It comprises a circular walking arena with a lenticular floor and a flat cover (the slope of the floor increases gradually from the center to the edge of the arena) plus automated fly tracking and statistical analysis. This simple modification of a flat arena presents a graduated physical challenge, with which we can assess fine gradations of motor ability, since a fly's time average radial distance from the arena center is a direct indicator of its climbing ability. The time averaged distribution of flies as a function of slope, activity levels, and walking speed, yields a fine grained picture of locomotory ability and motivation levels. We demonstrate the strengths and weaknesses of this assay (compared with a conventional tap-down test) by observing flies treated with a neurotoxin (BMAA) that acts as a glutamate agonist. The assay proves well suited to detect dose effects and progression effects with higher statistical power than the traditional tap-down, but it has a higher detection limit, making it less sensitive to treatment effects.