Chronic exposure to dietary sterol glucosides is neurotoxic to motor neurons and induces an ALS-PDC phenotype

Mitochondrial Dyshomeostasis as an Early Hallmark and a Therapeutic Target in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal multisystem disease characterized by progressive death of motor neurons, loss of muscle mass, and impaired energy metabolism. More than 40 genes are now known to be associated with ALS, which together account for the majority of familial forms of ALS and only 10% of sporadic ALS cases. To date, there is no consensus on the pathogenesis of ALS, which makes it difficult to develop effective therapy. Accumulating evidence indicates that mitochondria, which play an important role in cellular homeostasis, are the earliest targets in ALS, and abnormalities in their structure and functions contribute to the development of bioenergetic stress and disease progression. Mitochondria are known to be highly dynamic organelles, and their stability is maintained through a number of key regulatory pathways. Mitochondrial homeostasis is dynamically regulated via mitochondrial biogenesis, clearance, fission/fusion, and trafficking; however, the processes providing "quality control" and distribution of the organelles are prone to dysregulation in ALS. Here, we systematically summarized changes in mitochondrial turnover, dynamics, calcium homeostasis, and alterations in mitochondrial transport and functions to provide in-depth insights into disease progression pathways, which may have a significant impact on current symptomatic therapies and personalized treatment programs for patients with ALS.

In Vitro Models of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is one of the commonest neurodegenerative diseases of adult-onset, which is characterized by the progressive death of motor neurons in the cerebral cortex, brain stem and spinal cord. The dysfunction and death of motor neurons lead to the progressive muscle weakness, atrophy, fasciculations, spasticity and ultimately the whole paralysis of body. Despite the identification of several genetic mutations associated with the pathogenesis of ALS, including mutations in chromosome 9 open reading frame 72 leading to the abnormal expansion of GGGGCC repeat sequence, TAR DNA-binding protein 43, fused in sarcoma/translocated in liposarcoma, copper/zinc superoxide dismutase 1 (SOD1) and TANK-binding kinase 1, the exact mechanisms underlying the specific degeneration of motor neurons that causes ALS remain incompletely understood. At present, since the transgenic model expressed SOD1 mutants was established, multiple in vitro models of ALS have been developed for studying the pathology, pathophysiology and pathogenesis of ALS as well as searching the effective neurotherapeutics. This review reviewed the details of present established in vitro models used in studying the pathology, pathophysiology and pathogenesis of ALS. Meanwhile, we also discussed the advantages, disadvantages, cost and availability of each models.

Swimming against ALS: How to model disease in zebrafish for pathophysiological and behavioral studies

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease that leads to progressive disability and motor impairment. Existing therapies provide modest improvements in patient survival, raising a need for new treatments for ALS. Zebrafish is a promising model animal for translational and fundamental research in ALS - it is an experimentally tractable vertebrate, with high homology to humans and an ample experimental toolbox. These advantages allow high-throughput study of behavioral and pathophysiological phenotypes. The last decade saw an increased interest in modelling ALS in zebrafish, leading to the current abundance and variety of available methods and models. Additionally, the rise of gene editing techniques and toxin combination studies has created novel opportunities for ALS studies in zebrafish. In this review, we address the relevance of zebrafish as a model animal for ALS studies, the strategies for model induction and key phenotypical evaluation. Furthermore, we discuss established and emerging zebrafish models of ALS, analyzing their validity, including their potential for drug testing, and highlighting research opportunities in this area.

Mechanistic insights into the role of plant polyphenols and their nano-formulations in the management of depression

Depression is a condition characterized by low mood and an aversion to activity, that causes behavioral problems, poor quality of life and limits daily life activities. It is considered as the fourth leading cause of disability worldwide. Selective Serotonin Reuptake Inhibitors (SSRIs) Monoamine Oxidase (MAO) inhibitors, Tricyclic Antidepressants (TCAs), and atypical antidepressants are some of the conventional medications used to treat depression. However, only about half of patients with major depressive disorder (MDD) respond effectively to first-line antidepressant therapy. Additionally, there are a number of drawbacks to standard antidepressants, such as anti-cholinergic side effects, drug-drug interactions, and food-drug interactions, which prompts researchers to look at alternative approaches to the treatment of depression. Medicinal plants and their metabolites are extensively tested for their efficacy against depression. Electronic databases such as Google scholar, Science Direct, SciFinder and PubMed were used to search relevant literature on the role of polyphenols in depression. Plants-derived Polyphenols represent a major class of compounds extensively distributed in plants. Number of polyphenols have demonstrated antidepressant activity, among which berberine, piperine, curcumin, naringenin, ascorbic acid and ginsenosides are extensively evaluated. The medicinal plants and their derived compounds mediated synthesized green nanoparticles have also exhibited considerable efficacy in the management of depression. The therapeutic effects of these phytochemicals is mediated via differentiation and inhibition of neuronal cell apoptosis, promotion of neuronal cell survival and modulation of key neurotransmitters. The aim of this study is to review compressively the chemical, pharmacological and neurological evidence showing the potential of polyphenols in depression.

MicroRNA expression in animal models of amyotrophic lateral sclerosis and potential therapeutic approaches

A review of recent animal models of amyotrophic lateral sclerosis showed a large number of miRNAs had altered levels of expression in the brain and spinal cord, motor neurons of spinal cord and brainstem, and hypoglossal, facial, and red motor nuclei and were mostly upregulated. Among the miRNAs found to be upregulated in two of the studies were miR-21, miR-155, miR-125b, miR-146a, miR-124, miR-9, and miR-19b, while those downregulated in two of the studies included miR-146a, miR-29, miR-9, and miR-125b. A change of direction in miRNA expression occurred in some tissues when compared (e.g., miR-29b-3p in cerebellum and spinal cord of wobbler mice at 40 days), or at different disease stages (e.g., miR-200a in spinal cord of SOD1(G93A) mice at 95 days vs. 108 and 112 days). In the animal models, suppression of miR-129-5p resulted in increased lifespan, improved muscle strength, reduced neuromuscular junction degeneration, and tended to improve motor neuron survival in the SOD1(G93A) mouse model. Suppression of miR-155 was also associated with increased lifespan, while lowering of miR-29a tended to improve lifespan in males and increase muscle strength in SOD1(G93A) mice. Overexpression of members of miR-17~92 cluster improved motor neuron survival in SOD1(G93A) mice. Treatment with an artificial miRNA designed to target hSOD1 increased lifespan and improved muscle strength in SOD1(G93A) animals. Further studies with animal models of amyotrophic lateral sclerosis are warranted to validate these findings and identify specific miRNAs whose suppression or directed against hSOD1 results in increased lifespan, improved muscle strength, reduced neuromuscular junction degeneration, and improved motor neuron survival in SOD1(G93A) animals.

Longitudinal Assessment of Behaviour and Associated Bio-Markers Following Chronic Consumption of β-Sitosterol β-D-Glucoside in Rats: A Putative Model of Parkinson’s Disease

The consumption of cycad (Cycas circinalis) seeds has been linked to the development of Amyotrophic Lateral Sclerosis-Parkinsonism Dementia Complex (ALS-PDC) in humans. ALS-PDC is a clinically variable disease presenting as a combination of symptoms typical of PD and/or ALS. Chronic consumption of β-sitosterol β-D-glucoside (BSSG), a component of the cycad seed, by rats (Rattus norvegicus) has been previously reported to initiate a progressive pathology that develops over several months and manifests as behavioural and histopathological changes that resemble characteristic features of Parkinson’s disease. As part of an independent multi-site validation study, we have tried to replicate and further characterize the BSSG model with a focus on motor function, and associated immunohistochemical markers. Beginning at 3 months of age, male CD^® (Sprague Dawley) rats (N = 80) were dosed orally with either a flour pellet or a flour pellet containing BSSG (3 mg) daily (5×/week) for 16 weeks consistent with previous reports of the model. Following BSSG intoxication, separate cohorts of animals (n = 10/treatment) were exposed to a behavioural test battery at 16, 24, 32, or 40 weeks post-initial BSSG feeding. The test battery consisted of the open field test, cylinder test, and ultrasonic vocalization (USV) assessment. No changes in behaviour were observed at any time point. Following behavioural testing, animals were processed for immunohistochemical markers of substantia nigra integrity. Immunohistochemistry of brain tissue revealed no differences in the microglial marker, Iba1, or the dopaminergic integrity marker, tyrosine hydroxylase (TH), in the substantia nigra at any assessment point. The absence of any group differences in behaviour and immunhistochemistry indicates an inability to replicate previous reports. Further investigation into the sources of variability in the model is necessary prior to further utilization of the BSSG model in preclinical studies.

Protective effects of apigenin on methylmercury-induced behavioral/neurochemical abnormalities and neurotoxicity in rats

Methylmercury (MeHg) is a neurotoxin that induces neurotoxicity and cell death in neurons. MeHg increases oligodendrocyte death, glial cell activation, and motor neuron demyelination in the motor cortex and spinal cord. As a result, MeHg plays an important role in developing neurocomplications similar to amyotrophic lateral sclerosis (ALS). Recent research has implicated c-JNK and p38MAPK overactivation in the pathogenesis of ALS. Apigenin (APG) is a flavonoid having anti-inflammatory, antioxidant, and c-JNK/p38MAPK inhibitory activities. The purpose of this study is to determine whether APG possesses neuroprotective effects in MeHg-induced neurotoxicity in adult rats associated with ALS-like neuropathological alterations. In the current study, the neurotoxin MeHg causes an ALS-like phenotype in Wistar rats after 21 days of oral administration at a dose of 5 mg/kg. Prolonged administration of APG (40 and 80 mg/kg) improved neurobehavioral parameters such as learning memory, cognition, motor coordination, and grip strength. This is mainly associated with the downregulation of c-JNK and p38MAPK signaling as well as the restoration of myelin basic protein within the brain. Furthermore, APG inhibited neuronal apoptotic markers (Bax, Bcl-2, and caspase-3), restored neurotransmitter imbalance, decreased inflammatory markers (TNF- and IL-1), and alleviated oxidative damage. As a result, the current study shows that APG has neuroprotective potential as a c-JNK and p38MAPK signaling inhibitor against MeHg-induced neurotoxicity in adult rats. Based on these promising findings, we suggested that APG could be a potential new therapeutic approach over other conventional therapeutic approaches for MeHg-induced neurotoxicity in neurobehavioral, molecular, and neurochemical abnormalities.

Phytosterols: Potential Metabolic Modulators in Neurodegenerative Diseases

Phytosterols constitute a class of natural products that are an important component of diet and have vast applications in foods, cosmetics, and herbal medicines. With many and diverse isolated structures in nature, they exhibit a broad range of biological and pharmacological activities. Among over 200 types of phytosterols, stigmasterol and β-sitosterol were ubiquitous in many plant species, exhibiting important aspects of activities related to neurodegenerative diseases. Hence, this mini-review presented an overview of the reported studies on selected phytosterols related to neurodegenerative diseases. It covered the major phytosterols based on biosynthetic considerations, including other phytosterols with significant in vitro and in vivo biological activities.

DNA damage as a mechanism of neurodegeneration in ALS and a contributor to astrocyte toxicity

Increasing evidence supports the involvement of DNA damage in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Elevated levels of DNA damage are consistently observed in both sporadic and familial forms of ALS and may also play a role in Western Pacific ALS, which is thought to have an environmental cause. The cause of DNA damage in ALS remains unclear but likely differs between genetic subgroups. Repeat expansion in the C9ORF72 gene is the most common genetic cause of familial ALS and responsible for about 10% of sporadic cases. These genetic mutations are known to cause R-loops, thus increasing genomic instability and DNA damage, and generate dipeptide repeat proteins, which have been shown to lead to DNA damage and impairment of the DNA damage response. Similarly, several genes associated with ALS including TARDBP, FUS, NEK1, SQSTM1 and SETX are known to play a role in DNA repair and the DNA damage response, and thus may contribute to neuronal death via these pathways. Another consistent feature present in both sporadic and familial ALS is the ability of astrocytes to induce motor neuron death, although the factors causing this toxicity remain largely unknown. In this review, we summarise the evidence for DNA damage playing a causative or secondary role in the pathogenesis of ALS as well as discuss the possible mechanisms involved in different genetic subtypes with particular focus on the role of astrocytes initiating or perpetuating DNA damage in neurons.

Phytosterols: Targeting Neuroinflammation in Neurodegeneration

Plant-derived sterols, phytosterols, are well known for their cholesterol-lowering activity in serum and their anti-inflammatory activities. Recently, phytosterols have received considerable attention due to their beneficial effects on various non-communicable diseases, and recommended use as daily dietary components. The signaling pathways mediated in the brain by phytosterols have been evaluated, but little is known about their effects on neuroinflammation, and no clinical studies have been undertaken on phytosterols of interest. In this review, we discuss the beneficial roles of phytosterols, including their attenuating effects on inflammation, blood cholesterol levels, and hallmarks of the disease, and their regulatory effects on neuroinflammatory disease pathways. Despite recent advancements made in phytosterol pharmacology, some critical questions remain unanswered. Therefore, we have tried to highlight the potential of phytosterols as viable therapeutics against neuroinflammation and to direct future research with respect to clinical applications.

Structure, metabolism and biological functions of steryl glycosides in mammals

Steryl glycosides (SGs) are sterols glycosylated at their 3β-hydroxy group. They are widely distributed in plants, algae, and fungi, but are relatively rare in bacteria and animals. Glycosylation of sterols, resulting in important components of the cell membrane SGs, alters their biophysical properties and confers resistance against stress by freezing or heat shock to cells. Besides, many biological functions in animals have been suggested from the observations of SG administration. Recently, cholesteryl glucosides synthesized via the transglycosidation by glucocerebrosidases (GBAs) were found in the central nervous system of animals. Identification of patients with congenital mutations in GBA genes or availability of respective animal models will enable investigation of the function of such endogenously synthesized cholesteryl glycosides by genetic approaches. In addition, mechanisms of the host immune responses against pathogenic bacterial SGs have partially been resolved. This review is focused on the biological functions of SGs in mammals taking into consideration their therapeutic applications in the future.

Rewarding compounds identified from the medicinal plant Rhodiola rosea

Preparations of Rhodiola rosea root are widely used in traditional medicine. They can increase life span in worms and flies, and have various effects related to nervous system function in different animal species and humans. However, which of the compounds in R. rosea is mediating any one of these effects has remained unknown in most cases. Here, an analysis of the volatile and non-volatile low-molecular-weight constituents of R. rosea root samples was accompanied by an investigation of their behavioral impact on Drosophila melanogaster larvae. Rhodiola rosea root samples have an attractive smell and taste to the larvae, and exert a rewarding effect. This rewarding effect was also observed for R. rosea root extracts, and did not require activity of dopamine neurons that mediate known rewards such as sugar. Based on the chemical profiles of R. rosea root extracts and resultant fractions, a bioactivity-correlation analysis (AcorA) was performed to identify candidate rewarding compounds. This suggested positive correlations for - among related compounds - ferulic acid eicosyl ester (FAE-20) and β-sitosterol glucoside. A validation using these as pure compounds confirmed that the correlations were causal. Their rewarding effects can be observed even at low micromolar concentrations and thus at remarkably lower doses than for any known taste reward in the larva. We discuss whether similar rewarding effects, should they be observed in humans, would indicate a habit-forming or addictive potential.

Unilateral intranigral administration of β-sitosterol β-D-glucoside triggers pathological α-synuclein spreading and bilateral nigrostriatal dopaminergic neurodegeneration in the rat

The spreading and accumulation of α-synuclein and dopaminergic neurodegeneration, two hallmarks of Parkinson’s disease (PD), have been faithfully reproduced in rodent brains by chronic, oral administration of β-sitosterol β-D-glucoside (BSSG). We investigated whether a single injection of BSSG (6 μg BSSG/μL DMSO) in the left substantia nigra of Wistar rats causes the same effects. Mock DMSO injections and untreated rats formed control groups. We performed immunostainings against the pathological α-synuclein, the dopaminergic marker tyrosine hydroxylase (TH), the neuroskeleton marker β-III tubulin, the neurotensin receptor type 1 (NTSR1) as non-dopaminergic phenotype marker and Fluro-Jade C (F-J C) label for neurodegeneration. Using β-galactosidase (β-Gal) assay and active caspase-3 immunostaining, we assessed cell death mechanisms. Golgi-Cox staining was used to measure the density and types of dendritic spines of striatal medium spiny neurons. Motor and non-motor alterations were also evaluated. The study period comprised 15 to 120 days after the lesion. In the injured substantia nigra, BSSG caused a progressive α-synuclein aggregation and dopaminergic neurodegeneration caused by senescence and apoptosis. The α-synuclein immunoreactivity was also present within microglia cells. Decreased density of dopaminergic fibers and dendritic spines also occurred in the striatum. Remarkably, all the histopathological changes also appeared on the contralateral nigrostriatal system, and α-synuclein aggregates were present in other brain regions. Motor and non-motor behavioral alterations were progressive. Our data show that the stereotaxic BSSG administration reproduces PD α-synucleinopathy phenotype in the rat. This approach will aid in identifying the spread mechanism of α-synuclein pathology and validate anti-synucleinopathy therapies.

Glucocerebrosidases catalyze a transgalactosylation reaction that yields a newly-identified brain sterol metabolite, galactosylated cholesterol

β-Glucocerebrosidase (GBA) hydrolyzes glucosylceramide (GlcCer) to generate ceramide. Previously, we demonstrated that lysosomal GBA1 and nonlysosomal GBA2 possess not only GlcCer hydrolase activity, but also transglucosylation activity to transfer the glucose residue from GlcCer to cholesterol to form β-cholesterylglucoside (β-GlcChol) in vitro β-GlcChol is a member of sterylglycosides present in diverse species. How GBA1 and GBA2 mediate β-GlcChol metabolism in the brain is unknown. Here, we purified and characterized sterylglycosides from rodent and fish brains. Although glucose is thought to be the sole carbohydrate component of sterylglycosides in vertebrates, structural analysis of rat brain sterylglycosides revealed the presence of galactosylated cholesterol (β-GalChol), in addition to β-GlcChol. Analyses of brain tissues from GBA2-deficient mice and GBA1- and/or GBA2-deficient Japanese rice fish (Oryzias latipes) revealed that GBA1 and GBA2 are responsible for β-GlcChol degradation and formation, respectively, and that both GBA1 and GBA2 are responsible for β-GalChol formation. Liquid chromatography-tandem MS revealed that β-GlcChol and β-GalChol are present throughout development from embryo to adult in the mouse brain. We found that β-GalChol expression depends on galactosylceramide (GalCer), and developmental onset of β-GalChol biosynthesis appeared to be during myelination. We also found that β-GlcChol and β-GalChol are secreted from neurons and glial cells in association with exosomes. In vitro enzyme assays confirmed that GBA1 and GBA2 have transgalactosylation activity to transfer the galactose residue from GalCer to cholesterol to form β-GalChol. This is the first report of the existence of β-GalChol in vertebrates and how β-GlcChol and β-GalChol are formed in the brain.

Plant Glycosides and Glycosidases: A Treasure-Trove for Therapeutics

Plants contain numerous glycoconjugates that are metabolized by specific glucosyltransferases and hydrolyzed by specific glycosidases, some also catalyzing synthetic transglycosylation reactions. The documented value of plant-derived glycoconjugates to beneficially modulate metabolism is first addressed. Next, focus is given to glycosidases, the central theme of the review. The therapeutic value of plant glycosidases is discussed as well as the present production in plant platforms of therapeutic human glycosidases used in enzyme replacement therapies. The increasing knowledge on glycosidases, including structure and catalytic mechanism, is described. The novel insights have allowed the design of functionalized highly specific suicide inhibitors of glycosidases. These so-called activity-based probes allow unprecedented visualization of glycosidases cross-species. Here, special attention is paid on the use of such probes in plant science that promote the discovery of novel enzymes and the identification of potential therapeutic inhibitors and chaperones.

A sequential methodology for integral evaluation of motor and non-motor behaviors in parkinsonian rodents

An animal model, suitable for resembling Parkinson's disease (PD) progress, should show both, motor and non-motor alterations. However, these features have been scarcely evaluated or developed in parkinsonian models induced by neurotoxins. This protocol provides modifications to original methods, allowing six different motor and non-motor behavior tests, which adequately and timely emulate the main parkinsonian sensorimotor alterations in the rat or mouse: (1) bilateral sensorimotor alterations, examined by the vibrissae test; (2) balance and motor coordination, evaluated by the uncoordinated gait test; (3) locomotor asymmetry, analyzed by the cylinder test; (4) bradykinesia, as a locomotor alteration evidenced by the open field test; (5) depressive-like behavior, judged by the forced swimming test; and (6) hyposmia, assessed by the olfactory asymmetry test. Some advantages of using these behavioral tests over others include:•No sophisticated materials or equipment are required for their application and evaluation.•They are used in rodent models for parkinsonian research, but they can also be helpful for studying other movement disorders.•These tests can accurately discriminate the affected side from the healthy one, after unilateral injury of one hemisphere, resulting in sensorimotor, olfactory or locomotor asymmetry.

Neuroprotective effect of CuATSM on neurotoxin-induced motor neuron loss in an ALS mouse model

CuATSM is a PET-imaging agent that has recently received attention for its success in extending the lifespan in animals in several neurodegenerative disease models. In the SOD1^G93A model of ALS, CuATSM prolonged mouse longevity far longer than any previously tested therapeutic agents. The mechanism underlying this outcome has not been fully understood, but studies suggest that this copper complex contributes to maintaining copper homeostasis in mitochondria. More specifically for the SOD1 model, the molecule supplies copper back to the SOD1 protein. Additionally, CuATSM demonstrated similar protective effects in various in vivo Parkinson's disease mouse models. In the current pilot study, we utilized a neurodegenerative mouse model of motor neuron degeneration induced by the neurotoxin β-sitosterol β-D-glucoside. In this model, slow but distinct and progressive features of sporadic ALS occur. Treatment with CuATSM kept animal behavioural performance on par with the controls and prevented the extensive motor neuron degeneration and microglia activation seen in the untreated animals. These outcomes support a broader neuroprotective role for CuATSM beyond mutant SOD models of ALS.

Essential Dietary Bioactive Lipids in Neuroinflammatory Diseases

SIGNIFICANCE

Under physiological conditions, neurons and glia are in a healthy, redox-balanced environment; when injury perturbs this equilibrium, a neuroinflammatory state is established by activated microglia that triggers pro-inflammatory responses and alters the oxidant/antioxidant balance, thus leading to neuronal loss and neurodegeneration. In neurodegenerative diseases (such as Alzheimer's disease, Parkinson's disease, amyothrophic lateral sclerosis, and multiple sclerosis), the brain is in a constitutively self-sustaining cycle of inflammation and oxidative stress that prompts and amplifies brain damage. Recent Advances: Recently, an increasing amount of scientific data highlight the ability of specific nutrients to cross the blood-brain barrier, and to modulate inflammatory and oxidative pathways. Therefore, nutritional approaches may contribute to restore the lost equilibrium among factors accounting for neurodegeneration.

CRITICAL ISSUES

Herein, we critically examine how essential lipids (including fatty acids, liposoluble vitamins and phytosterols) might contribute to accelerate or prevent the onset and progression of such pathologies. In particular, we highlight that experimental and clinical findings, although promising, are still inadequate to draw definitive conclusions.

FUTURE DIRECTIONS

More research is warranted in order to establish the real impact of lipid intake on brain health, especially when redox balance and inflammatory responses have been already compromised. In the future, it would be hoped to gain a detailed knowledge of chemical modifications and dynamic properties of such nutrients, before planning to exploit them as potential therapeutics. Antioxid. Redox Signal. 29, 37-60.

Glucocerebrosidase Mutations and Synucleinopathies. Potential Role of Sterylglucosides and Relevance of Studying Both GBA1 and GBA2 Genes

Gaucher's disease (GD) is the most prevalent lysosomal storage disorder. GD is caused by homozygous mutations of the GBA1 gene, which codes for beta-glucocerebrosidase (GCase). Although GD primarily affects peripheral tissues, the presence of neurological symptoms has been reported in several GD subtypes. GBA1 mutations have recently deserved increased attention upon the demonstration that both homo- and heterozygous GBA1 mutations represent the most important genetic risk factor for the appearance of synucleinopathies like Parkinson's disease (PD) and dementia with Lewy bodies (LBD). Although reduced GCase activity leads to alpha-synuclein aggregation, the mechanisms sustaining a role for GCase in alpha-synuclein homeostasis still remain largely unknown. Furthermore, the role to be played by impairment in the physiological function of endoplasmic reticulum, mitochondria and other subcellular membranous components is currently under investigation. Here we focus on the impact of GCase loss-of-function that impact on the levels of sterylglucosides, molecules that are known to trigger a PD-related synucleinopathy upon administration in rats. Moreover, the concurrence of another gene also coding for an enzyme with GCase activity (GBA2 gene) should also be taken into consideration, bearing in mind that in addition to a hydrolytic function, both GCases also share transglycosylation as a second catalytic activity. Accordingly, sterylglycoside levels should also be considered to further assess their impact on the neurodegenerative process. In this regard-and besides GBA1 genotyping-we suggest that screening for GBA2 mutations should be considered, together with analytical measurements of cholesterol glycosides in body fluids, as biomarkers for both PD risk and disease progression.

Animal models of amyotrophic lateral sclerosis: A comparison of model validity

Animal models are necessary to investigate the pathogenic features underlying motor neuron degeneration and for therapeutic development in amyotrophic lateral sclerosis (ALS). Measures of model validity allow for a critical interpretation of results from each model and caution from over-interpretation of experimental models. Face and construct validity refer to the similarity in phenotype and the proposed causal factor to the human disease, respectively. More recently developed models are restricted by limited phenotype characterization, yet new models hold promise for novel disease insights, thus highlighting their importance. In this article, we evaluate the features of face and construct validity of our new zebrafish model of environmentally-induced motor neuron degeneration and discuss this in the context of current environmental and genetic ALS models, including C9orf72, mutant Cu/Zn superoxide dismutase 1 and TAR DNA-binding protein 43 mouse and zebrafish models. In this mini-review, we discuss the pros and cons to validity criteria in each model. Our zebrafish model of environmentally-induced motor neuron degeneration displays convincing features of face validity with many hallmarks of ALS-like features, and weakness in construct validity. However, the value of this model may lie in its potential to be more representative of the pathogenic features underlying sporadic ALS cases, where environmental factors may be more likely to be involved in disease etiology than single dominant gene mutations. It may be necessary to compare findings between different strains and species modeling specific genes or environmental factors to confirm findings from ALS animal models and tease out arbitrary strain- and overexpression-specific effects.

Constrained Versus Free Cholesterol in DPPC Membranes: A Comparison of Chain Ordering Ability Using Deuterium NMR

We report here the first exploration of the nature of the hydrophobic region of bilayer membranes formed from sterol-modified phospholipids [Huang, Z.; Szoka, F. C., Sterol-Modified Phospholipids: Cholesterol and Phospholipid Chimeras with Improved Biomembrane Properties. J. Am. Chem. Soc. 2008, 130 (46), 15702-15712] & [Ding, J.; Starling, A. P.; East, J. M.; Lee, A. G., Binding Sites for Cholesterol on Ca(2+)-ATPase Studied by Using a Cholesterol-Containing Phospholipid. Biochemistry 1994, 33 (16), 4974-4979]. Using ²H NMR spectroscopy, we present our results for the phase behavior and acyl chain ordering of multilamellar vesicles (MLVs) of a sterol-modified phospholipid, 1-cholesterylhemisuccinoyl-2-palmitoyl(d₃₁)-sn-glycero-3-phosphocholine (hereafter referred to as CholPPC-d₃₁). We compared our results with the conformational order induced by cholesterol at various concentrations in 1-palmitoyl,2-palmitoyl(d₃₁)-sn-glycero-3-phosphocholine (DPPC-d₃₁)/cholesterol membranes. On the basis of the existing literature [Foglia, F.; Barlow, D. J.; Szoka, F. C.; Huang, Z.; Rogers, S. E.; Lawrence, M. J., Structural Studies of the Monolayers and Bilayers Formed by a Novel Cholesterol-Phospholipid Chimera. Langmuir 2011, 27 (13), 8275-8281], we expected to find that the deuterated palmitoyl chain in CholPPC-d₃₁ membranes had an order parameter profile similar to the deuterated palmitoyl chain of sn-2 labeled DPPC-d₃₁ in MLVs of a mixture of DPPC-d₃₁ with 40 mol % unconstrained cholesterol. Our data indicate that the ordering ability of cholesterol in CholPPC is significantly reduced compared to free cholesterol in DPPC. This result emphasizes that cholesterol molecules must be free to move in the bilayers to reach their maximum ordering ability. In other words, when compared to unconstrained cholesterol, the constrained cholesterol moiety in CholPPC causes nonoptimal chain packing.

The BSSG rat model of Parkinson's disease: progressing towards a valid, predictive model of disease

ABSTRACT

Parkinson's disease (PD) is a neurodegenerative disorder, classically considered a movement disorder. A great deal is known about the anatomical connections and neuropathology and pharmacological changes of PD, as they relate to the loss of dopaminergic function and the appearance of cardinal motor symptoms. Our understanding of the role of dopamine in PD has led to the development of effective pharmacological treatments of the motor symptoms in the form of dopamine replacement therapy using levodopa and dopaminergic agonists. Much of the information concerning these drug treatments has been obtained using classical neurotoxic models that mimic dopamine depletion (e.g., 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine or MPTP, 6-hydroxydopamine, reserpine). However, PD is more than a disorder of the nigrostriatal dopamine pathway. Our understanding of the neuropathology of PD has undergone massive changes, with the discovery that mutations in α-synuclein cause a familial form of PD and that PD pathology may spread, affecting multiple neurotransmitter systems and brain regions. These new developments in our understanding of PD demand that we reconsider our animal models. While classic neurotoxin models have been useful for the development of effective symptomatic treatments for motor manifestations, the paucity of a valid animal model exhibiting the progressive development of multiple key features of PD pathophysiology and phenotype has impeded the search for neuroprotective therapies, capable of slowing or halting disease progression.

RELEVANCE OF THE ARTICLE FOR PREDICTIVE PREVENTIVE AND PERSONALISED MEDICINE

What characteristics would a good animal model of human PD have? In so much as is possible, a good model would exhibit as many behavioral, anatomical, biochemical, immunological, and pathological changes as are observed in the human condition, developing progressively, with clear, identifiable biomarkers along the way. Here, we review the BSSG rat model of PD, a novel environmental model of PD, with strong construct, face, and predictive validity. This model offers an effective tool for the screening of preventive therapies that may prove to be more predictive of their effects in human patients.

A novel function for glucocerebrosidase as a regulator of sterylglucoside metabolism

BACKGROUND

Sterols are major cell membrane lipids, and in many organisms they are modified with glucose to generate sterylglucosides. Glucosylation dramatically changes the functional properties of sterols. The formation of sterylglucosides from sterols in plants, fungi, and bacteria uses UDP-glucose as a glucose donor. By contrast, sterylglucoside biosynthesis in mammals is catalyzed by the transglucosylation activity of glucocerebrosidases, with glucosylceramide acting as the glucose donor. Recent success in isolation and structural determination of sterylglucosides in the vertebrate central nervous system shows that transglucosylation also occurs in vivo. These analyses also revealed that sterylglucoside aglycons are composed of several cholesterol-related metabolites, including a plant-type sitosteryl.

SCOPE OF REVIEW

In this review, we discuss the biological functions and metabolism of sterylglucosides. We also summarize new findings from studies on the metabolism of vertebrate sterylglucosides and review the circumstances underlying the recent discovery of sterylglucosides in vertebrate brain. Finally, we discuss the role of sterylglucosides in a variety of neurodegenerative disorders such as Gaucher disease and Parkinson's disease.

MAJOR CONCLUSIONS

The biological significance of UDP-glucose-independent sterol glucosylation is still unknown, but it is plausible that glucosylation may provide sterols with novel biological functions. Even though sterol glucosylation is a simple reaction, it can dramatically change the physical properties of sterols.

GENERAL SIGNIFICANCE

Sterylglucosides may play roles in various physiological processes and in the pathogenesis of different diseases. Arriving at a better understanding of them at the organ and cellular level may open up new approaches to developing therapeutics for a variety of diseases. This article is part of a Special Issue entitled Neuro-glycoscience, edited by Kenji Kadomatsu and Hiroshi Kitagawa.

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.

Aglycon diversity of brain sterylglucosides: structure determination of cholesteryl- and sitosterylglucoside

To date, sterylglucosides have been reported to be present in various fungi, plants, and animals. In bacteria, such as Helicobacter pylori, proton NMR spectral analysis of isolated 1-O-cholesteryl-β-d-glucopyranoside (GlcChol) demonstrated the presence of an α-glucosidic linkage. By contrast, in animals, no detailed structural analysis of GlcChol has been reported, in part because animal-derived samples contain a high abundance of glucosylceramides (GlcCers)/galactosylceramides, which exhibit highly similar chromatographic behavior to GlcChol. A key step in vertebrate GlcChol biosynthesis is the transglucosylation reaction catalyzed by glucocerebrosidase (GBA)1 or GBA2, utilizing GlcCer as a glucose donor. These steps are expected to produce a β-glucosidic linkage. Impaired GBA1 and GBA2 function is associated with neurological disorders, such as cerebellar ataxia, spastic paraplegia, and Parkinson's disease. Utilizing a novel three-step chromatographic procedure, we prepared highly enriched GlcChol from embryonic chicken brain, allowing complete structural confirmation of the β-glucosidic linkage by ¹H-NMR analysis. Unexpectedly, during purification, two additional sterylglucoside fractions were isolated. NMR and GC/MS analyses confirmed that the plant-type sitosterylglucoside in vertebrate brain is present throughout embryonic development. The aglycon structure of the remaining sterylglucoside (GSX-2) remains elusive due to its low abundance. Together, our results uncovered unexpected aglycon heterogeneity of sterylglucosides in vertebrate brain.

WITHDRAWN: Behavioral abnormalities in young female mice following administration of aluminum adjuvants and the human papillomavirus (HPV) vaccine Gardasil

This article has been withdrawn at the request of the Editor-in-Chief due to serious concerns regarding the scientific soundness of the article. Review by the Editor-in-Chief and evaluation by outside experts, confirmed that the methodology is seriously flawed, and the claims that the article makes are unjustified. As an international peer-reviewed journal we believe it is our duty to withdraw the article from further circulation, and to notify the community of this issue. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

The Progressive BSSG Rat Model of Parkinson's: Recapitulating Multiple Key Features of the Human Disease

The development of effective neuroprotective therapies for Parkinson's disease (PD) has been severely hindered by the notable lack of an appropriate animal model for preclinical screening. Indeed, most models currently available are either acute in nature or fail to recapitulate all characteristic features of the disease. Here, we present a novel progressive model of PD, with behavioural and cellular features that closely approximate those observed in patients. Chronic exposure to dietary phytosterol glucosides has been found to be neurotoxic. When fed to rats, β-sitosterol β-d-glucoside (BSSG) triggers the progressive development of parkinsonism, with clinical signs and histopathology beginning to appear following cessation of exposure to the neurotoxic insult and continuing to develop over several months. Here, we characterize the progressive nature of this model, its non-motor features, the anatomical spread of synucleinopathy, and response to levodopa administration. In Sprague Dawley rats, chronic BSSG feeding for 4 months triggered the progressive development of a parkinsonian phenotype and pathological events that evolved slowly over time, with neuronal loss beginning only after toxin exposure was terminated. At approximately 3 months following initiation of BSSG exposure, animals displayed the early emergence of an olfactory deficit, in the absence of significant dopaminergic nigral cell loss or locomotor deficits. Locomotor deficits developed gradually over time, initially appearing as locomotor asymmetry and developing into akinesia/bradykinesia, which was reversed by levodopa treatment. Late-stage cognitive impairment was observed in the form of spatial working memory deficits, as assessed by the radial arm maze. In addition to the progressive loss of TH+ cells in the substantia nigra, the appearance of proteinase K-resistant intracellular α-synuclein aggregates was also observed to develop progressively, appearing first in the olfactory bulb, then the striatum, the substantia nigra and, finally, hippocampal and cortical regions. The slowly progressive nature of this model, together with its construct, face and predictive validity, make it ideal for the screening of potential neuroprotective therapies for the treatment of PD.

Daucosterol protects neurons against oxygen-glucose deprivation/reperfusion-mediated injury by activating IGF1 signaling pathway

We previously reported that daucosterol (a sterolin) up-regulates the expression of insulin-like growth factor I (IGF1)(1) protein in neural stem cells. In this study, we investigated the effects of daucosterol on the survival of cultured cortical neurons after neurons were subjected to oxygen and glucose deprivation and simulated reperfusion (OGD/R)(2), and determined the corresponding molecular mechanism. The results showed that post-treatment of daucosterol significantly reduced neuronal loss, as well as apoptotic rate and caspase-3 activity, displaying the neuroprotective activity. We also found that daucosterol increased the expression level of IGF1 protein, diminished the down-regulation of p-AKT(3) and p-GSK-3β(4), thus activating the AKT(5) signal pathway. Additionally, it diminished the down-regulation of the anti-apoptotic proteins Mcl-1(6) and Bcl-2(7), and decreased the expression level of the pro-apoptotic protein Bax(8), thus raising the ratio of Bcl-2/Bax. The neuroprotective effect of daucosterol was inhibited in the presence of picropodophyllin (PPP)(9), the inhibitor of insulin-like growth factor I receptors (IGF1R)(10). Our study provided information about daucosterol as an efficient and inexpensive neuroprotectants, to which the IGF1-like activity of daucosterol contributes. Daucosterol could be potentially developed as a medicine for ischemic stroke treatment.

ALS as a distal axonopathy: molecular mechanisms affecting neuromuscular junction stability in the presymptomatic stages of the disease

Amyotrophic Lateral Sclerosis (ALS) is being redefined as a distal axonopathy, in that many molecular changes influencing motor neuron degeneration occur at the neuromuscular junction (NMJ) at very early stages of the disease prior to symptom onset. A huge variety of genetic and environmental causes have been associated with ALS, and interestingly, although the cause of the disease can differ, both sporadic and familial forms of ALS show a remarkable similarity in terms of disease progression and clinical manifestation. The NMJ is a highly specialized synapse, allowing for controlled signaling between muscle and nerve necessary for skeletal muscle function. In this review we will evaluate the clinical, animal experimental and cellular/molecular evidence that supports the idea of ALS as a distal axonopathy. We will discuss the early molecular mechanisms that occur at the NMJ, which alter the functional abilities of the NMJ. Specifically, we focus on the role of axon guidance molecules on the stability of the cytoskeleton and how these molecules may directly influence the cells of the NMJ in a way that may initiate or facilitate the dismantling of the neuromuscular synapse in the presymptomatic stages of ALS.

Panax ginseng is neuroprotective in a novel progressive model of Parkinson's disease

Panax ginseng has been used in traditional Chinese medicine for centuries. Among its various benefits is a pluripotent targeting of the various events involved in neuronal cell death. This includes anti-inflammatory, anti-oxidant, and anti-apoptotic effects. Indeed, ginseng extract and its individual ginsenosides have been demonstrated to influence a number of biochemical markers implicated in Parkinson's disease (PD) pathogenesis. We have reported previously that administration of the ginseng extract, G115, afforded robust neuroprotection in two rodent models of PD. However, these traditional rodent models are acute in nature and do accurately recapitulate the progressive nature of the disease. Chronic exposure to the dietary phytosterol glucoside, β-sitosterol β-d-glucoside (BSSG) triggers the progressive development of neurological deficits, with behavioral and cellular features that closely approximate those observed in PD patients. Clinical signs and histopathology continue to develop for several months following cessation of exposure to the neurotoxic insult. Here, we utilized this model to further characterize the neuroprotective effects of the ginseng extract, G115. Oral administration of this extract significantly reduced dopaminergic cell loss, microgliosis, and accumulation of α-synuclein aggregates. Further, G115 administration fully prevented the development of locomotor deficits, in the form of reduced locomotor activity and coordination. These results suggest that ginseng extract may be a potential neuroprotective therapy for the treatment of PD.

Animal models of brain maldevelopment induced by cycad plant genotoxins

Cycads are long-lived tropical and subtropical plants that contain azoxyglycosides (e.g., cycasin, macrozamin) and neurotoxic amino acids (notably β-N-methylamino-l-alanine l-BMAA), toxins that have been implicated in the etiology of a disappearing neurodegenerative disease, amyotrophic lateral sclerosis and parkinsonism-dementia complex that has been present in high incidence among three genetically distinct populations in the western Pacific. The neuropathology of amyotrophic lateral sclerosis/parkinsonism-dementia complex includes features suggestive of brain maldevelopment, an experimentally proven property of cycasin attributable to the genotoxic action of its aglycone methylazoxymethanol (MAM). This property of MAM has been exploited by neurobiologists as a tool to study perturbations of brain development. Depending on the neurodevelopmental stage, MAM can induce features in laboratory animals that model certain characteristics of epilepsy, schizophrenia, or ataxia. Studies in DNA repair-deficient mice show that MAM perturbs brain development through a DNA damage-mediated mechanism. The brain DNA lesions produced by systemic MAM appear to modulate the expression of genes that regulate neurodevelopment and contribute to neurodegeneration. Epigenetic changes (histone lysine methylation) have also been detected in the underdeveloped brain after MAM administration. The DNA damage and epigenetic changes produced by MAM and, perhaps by chemically related substances (e.g., nitrosamines, nitrosoureas, hydrazines), might be an important mechanism by which early-life exposure to genotoxicants can induce long-term brain dysfunction.

Identification of receptors and enzymes for endocannabinoids in NSC-34 cells: relevance for in vitro studies with cannabinoids in motor neuron diseases

NSC-34 cells, a hybridoma cell line derived from the fusion of neuroblastoma cells with mice spinal cord cells, have been widely used as an in vitro model for the study of motor neuron diseases [i.e. amyotrophic lateral sclerosis (ALS)]. In the present study, they were used to characterize different elements of the cannabinoid signaling system, which have been reported to serve as targets for the neuroprotective action of different natural and synthetic cannabinoid compounds. Using RT-PCR, Western blotting and immunocytochemistry, we first identified the presence of the cannabinoid CB(1) receptor in these cells. As expected, CB(2) receptor is not expressed in this neuronal cell line, a result that is concordant with the idea that this receptor type is preferentially expressed in glial elements. Diacylglycerol-lipase (DAGL) and N-arachidonoylphosphatidylethanolamine-phospholipase D (NAPE-PLD), the enzymes that synthesize endocannabinoids, have also been detected in these cells using RT-PCR, and the same happened with the endocannabinoid-degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol-lipase (MAGL). The presence of the CB(1) receptor in these cells supports the idea that this receptor may play a role in the regulation of cellular survival face to excitotoxic injury. Interestingly, the expression of CB(1) receptor (and also the FAAH enzyme) was strongly up-regulated after differentiation of these cells, as previously reported with glutamate receptors. No changes were found for NAPE-PLD, DAGL and MAGL. Assuming that glutamate toxicity is one of the major causes of neuronal damage in ALS and other motor neurons diseases, the differentiated NSC-34 cells might serve as a useful model for studying neuroprotection with cannabinoids in conditions of excitotoxic injury, mitochondrial malfunctioning and oxidative stress.

Pathobiochemical effect of acylated steryl-β-glucoside on aggregation and cytotoxicity of α-synuclein

Cycad seed consumption by the native islanders of Guam is frequently associated with high rates of amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS/PDC); furthermore, accompanying pathological examination often exhibits α-synuclein inclusions in the neurons of the affected brain. Acylated steryl-β-glucoside (ASG) contained in cycad seeds is considered as causative environmental risk factor. We aimed to investigate whether ASG influences aggregation and cell toxicity of α-synuclein. To understand whether ASG is a causative factor in the development of ALS/PDC, soybean-derived ASG was tested for its effect on in vitro aggregation of α-synuclein using Thioflavin-T. ASG was also tested to determine whether it modulates α-synuclein cytotoxicity in yeast cells. In addition, we determined whether an interaction between ASG and α-synuclein occurs in the plasma membrane or cytoplasm using three factors: GM1 ganglioside, small unilamellar vesicles, and ATP. In the present study, we found that ASG-mediated acceleration of α-synuclein aggregation is influenced by the presence of ATP, but not by the presence of GM1. ASG accelerated the α-synuclein aggregation in the cytoplasm. ASG also enhanced α-synuclein-induced cytotoxicity in yeast cells. This study demonstrated that ASG directly enhances aggregation and cytotoxicity of α-synuclein, which are often observed in patients with ALS/PDC. These results, using assays that replicate cytoplasmic conditions, are consistent with the molecular mechanism that cytotoxicity is caused by intracellular α-synuclein fibril formation in neuronal cells.

Does α-amino-β-methylaminopropionic acid (BMAA) play a role in neurodegeneration?

The association of α-amino-β-methylaminopropionic acid (BMAA) with elevated incidence of amyotrophic lateral sclerosis/Parkinson’s disease complex (ALS/PDC) was first identified on the island of Guam. BMAA has been shown to be produced across the cyanobacterial order and its detection has been reported in a variety of aquatic and terrestrial environments worldwide, suggesting that it is ubiquitous. Various in vivo studies on rats, mice, chicks and monkeys have shown that it can cause neurodegenerative symptoms such as ataxia and convulsions. Zebrafish research has also shown disruption to neural development after BMAA exposure. In vitro studies on mice, rats and leeches have shown that BMAA acts predominantly on motor neurons. Observed increases in the generation of reactive oxygen species (ROS) and Ca²⁺ influx, coupled with disruption to mitochondrial activity and general neuronal death, indicate that the main mode of activity is via excitotoxic mechanisms. The current review pertaining to the neurotoxicity of BMAA clearly demonstrates its ability to adversely affect neural tissues, and implicates it as a potentially significant compound in the aetiology of neurodegenerative disease. When considering the potential adverse health effects upon exposure to this compound, further research to better understand the modes of toxicity of BMAA and the environmental exposure limits is essential.

Environmental neurotoxin-induced progressive model of parkinsonism in rats

OBJECTIVE

Exposure to a number of drugs, chemicals, or environmental factors can cause parkinsonism. Epidemiologic evidence supports a causal link between the consumption of flour made from the washed seeds of the plant Cycas micronesica by the Chamorro population of Guam and the development of amyotrophic lateral sclerosis/parkinsonism dementia complex.

METHODS

We now report that consumption of washed cycad flour pellets by Sprague-Dawley male rats induces progressive parkinsonism.

RESULTS

Cycad-fed rats displayed motor abnormalities after 2 to 3 months of feeding such as spontaneous unilateral rotation, shuffling gait, and stereotypy. Histological and biochemical examination of brains from cycad-fed rats revealed an initial decrease in the levels of dopamine and its metabolites in the striatum (STR), followed by neurodegeneration of dopaminergic (DAergic) cell bodies in the substantia nigra (SN) pars compacta (SNc). alpha-Synuclein (alpha-syn; proteinase K-resistant) and ubiquitin aggregates were found in the DAergic neurons of the SNc and neurites in the STR. In addition, we identified alpha-syn aggregates in neurons of the locus coeruleus and cingulate cortex. No loss of motor neurons in the spinal cord was found after chronic consumption of cycad flour. In an organotypic slice culture of the rat SN and the striatum, an organic extract of cycad causes a selective loss of dopamine neurons and alpha-syn aggregates in the SN.

INTERPRETATION

Cycad-fed rats exhibit progressive behavioral, biochemical, and histological hallmarks of parkinsonism, coupled with a lack of fatality.

New animal models of progressive neurodegeneration: tools for identifying targets in predictive diagnostics and presymptomatic treatment

Mental and neurological disorders are increasingly prevalent and constitute a major societal and economic burden worldwide. Many of these diseases and disorders are characterized by progressive deterioration over time, that ultimately results in identifiable symptoms that in turn dictate therapy. Disease-specific symptoms, however, often occur late in the degenerative process. A better understanding of presymptomatic events could allow for the development of new diagnostics and earlier interventions that could slow or stop the disease process. Such studies of progressive neurodegeneration require the use of animal models that are characterized by delayed or slowly developing disease phenotype(s). This brief review describes several examples of such animal models that have recently been developed with relevance to various neurological diseases and disorders, and delineates the potential of such models to aid in predictive diagnosis, early intervention and disease prevention.

Development and application of a comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry method for the analysis of L-beta-methylamino-alanine in human tissue

L-Beta-methylamino-alanine (BMAA) has been proposed as a worldwide contributor to neurodegenerative diseases, including Parkinson dementia complex (PDC) of Guam and Alzheimer's disease (AD). Recent conflicting reports of the presence of this amino acid in human brain from patients affected by these diseases have made it necessary to develop methods that provide unambiguous detection in complex samples. Comprehensive two-dimensional gas chromatography coupled with time-of-flight-mass-spectrometry analysis (GCxGC-TOFMS) followed by a targeted Parallel Factor Analysis (PARAFAC) deconvolution method has been used recently in metabolomic investigations to separate, identify, and quantify components of complex biological specimens. We have extended and applied this methodology to the toxicological problem of detecting BMAA in extracts of brain tissue. Our results show that BMAA can be isolated from closely eluting compounds and detected in trace amounts in extracts of brain tissue spiked with low levels of this analyte, ranging from 2.5ppb to 50ppb, with a limit of detection (LOD) of 0.7ppb. This new method was sufficiently sensitive to detect BMAA in cerebral extracts of mice fed BMAA. This optimized approach was then applied to analyze tissue from humans; however, no BMAA was detected in the brain extracts from controls or patients with PDC or AD. Our results demonstrate the application of multidimensional chromatography-mass spectrometry methods and computational deconvolution analysis to the problem of detecting trace amounts of a potential toxin in brain extracts from mice and humans.

Beyond Guam: the cyanobacteria/BMAA hypothesis of the cause of ALS and other neurodegenerative diseases

Excitement about neurogenetics in the last two decades has diverted attention from environmental causes of sporadic ALS. Fifty years ago endemic foci of ALS with a frequency one hundred times that in the rest of the world attracted attention since they offered the possibility of finding the cause for non-endemic ALS throughout the world. Research on Guam suggested that ALS, Parkinson's disease and dementia (the ALS/PDC complex) was due to a neurotoxic non-protein amino acid, beta-methylamino-L-alanine (BMAA), in the seeds of the cycad Cycas micronesica. Recent discoveries that found that BMAA is produced by symbiotic cyanobacteria within specialized roots of the cycads; that the concentration of protein-bound BMAA is up to a hundred-fold greater than free BMAA in the seeds and flour; that various animals forage on the seeds (flying foxes, pigs, deer), leading to biomagnification up the food chain in Guam; and that protein-bound BMAA occurs in the brains of Guamanians dying of ALS/PDC (average concentration 627 microg/g, 5 mM) but not in control brains have rekindled interest in BMAA as a possible trigger for Guamanian ALS/PDC. Perhaps most intriguing is the finding that BMAA is present in brain tissues of North American patients who had died of Alzheimer's disease (average concentration 95 microg/g, 0.8mM); this suggests a possible etiological role for BMAA in non-Guamanian neurodegenerative diseases. Cyanobacteria are ubiquitous throughout the world, so it is possible that all humans are exposed to low amounts of cyanobacterial BMAA, that protein-bound BMAA in human brains is a reservoir for chronic neurotoxicity, and that cyanobacterial BMAA is a major cause of progressive neurodegenerative diseases including ALS worldwide. Though Montine et al., using different HPLC method and assay techniques from those used by Cox and colleagues, were unable to reproduce the findings of Murch et al., Mash and colleagues using the original techniques of Murch et al. have recently confirmed the presence of protein-bound BMAA in the brains of North American patients dying with ALS and Alzheimer's disease (concentrations >100 microg/g) but not in the brains of non-neurological controls or Huntington's disease. We hypothesize that individuals who develop neurodegenerations may have a genetic susceptibility because of inability to prevent BMAA accumulation in brain proteins and that the particular pattern of neurodegeneration that develops depends on the polygenic background of the individual.

Distribution of free and glycosylated sterols within Cycas micronesica plants

Flour derived from Cycas micronesica seeds was once the dominant source of starch for Guam's residents. Cycad consumption has been linked to high incidence of human neurodegenerative diseases. We determined the distribution of the sterols stigmasterol and β-sitosterol and their derived glucosides stigmasterol β-d-glucoside and β-sitosterol β-d-glucoside among various plant parts because they have been identified in cycad flour and have been shown to elicit neurodegenerative outcomes. All four compounds were common in seeds, sporophylls, pollen, leaves, stems, and roots. Roots contained the greatest concentration of both free sterols, and photosynthetic leaflet tissue contained the greatest concentration of both steryl glucosides. Concentration within the three stem tissue categories was low compared to other organs. Reproductive sporophyll tissue contained free sterols similar to seeds, but greater concentration of steryl glucosides than seeds. One of the glucosides was absent from pollen. Concentration in young seeds was higher than old seeds as reported earlier, but concentration did not differ among age categories of leaf, sporophyll, or vascular tissue. The profile differences among the various tissues within these organs may help clarify the physiological role of these compounds.

The primary locus of motor neuron death in an ALS-PDC mouse model

A mouse model of amyotrophic lateral sclerosis-parkinsonism-dementia complex based on the consumption of cycad seed flour was used to determine whether the observed pathology of motor neuron loss begins in the distal axons or the spinal cord. Assessments of neuromuscular junction integrity and motor neurons were performed at multiple time points. Mice fed cycad pellets performed worse on the wire hang than controls. Microglial activation in cycad-fed mice was observed with motor neuron degeneration at 12 weeks, but reactive astrocyte proliferation was not observed. After 33 weeks of cycad feeding, motor neuron loss had stabilized, with no evidence of neuromuscular junction endplate denervation. These data suggest that neuronal pathology begins at the soma and proceeds distally in a 'dying forward' pattern.

Aluminum hydroxide injections lead to motor deficits and motor neuron degeneration

Gulf War Syndrome is a multi-system disorder afflicting many veterans of Western armies in the 1990-1991 Gulf War. A number of those afflicted may show neurological deficits including various cognitive dysfunctions and motor neuron disease, the latter expression virtually indistinguishable from classical amyotrophic lateral sclerosis (ALS) except for the age of onset. This ALS "cluster" represents the second such ALS cluster described in the literature to date. Possible causes of GWS include several of the adjuvants in the anthrax vaccine and others. The most likely culprit appears to be aluminum hydroxide. In an initial series of experiments, we examined the potential toxicity of aluminum hydroxide in male, outbred CD-1 mice injected subcutaneously in two equivalent-to-human doses. After sacrifice, spinal cord and motor cortex samples were examined by immunohistochemistry. Aluminum-treated mice showed significantly increased apoptosis of motor neurons and increases in reactive astrocytes and microglial proliferation within the spinal cord and cortex. Morin stain detected the presence of aluminum in the cytoplasm of motor neurons with some neurons also testing positive for the presence of hyper-phosphorylated tau protein, a pathological hallmark of various neurological diseases, including Alzheimer's disease and frontotemporal dementia. A second series of experiments was conducted on mice injected with six doses of aluminum hydroxide. Behavioural analyses in these mice revealed significant impairments in a number of motor functions as well as diminished spatial memory capacity. The demonstrated neurotoxicity of aluminum hydroxide and its relative ubiquity as an adjuvant suggest that greater scrutiny by the scientific community is warranted.

Free and glycosylated sterol bioaccumulation in developing Cycas micronesica seeds

The bioaccumulation of free and glycosylated forms of stigmasterol and β-sitosterol were determined from Cycas micronesica K.D. Hill seeds throughout seed ontogeny. Per-seed pool of the four compounds increased linearly from 2 to 24 months, indicating no developmental period elicited a major shift in the rate of bioaccumulation. The slopes were not homogeneous, signifying a change in relative sterol profile concomitant with seed maturation. This shift was in favour of the glucosides, as their rate of accumulation exceeded that of the free sterols. Stigmasterol content exceeded that of β-sitosterol, but ontogeny did not influence the ratio of these dominant sterols. The quantity and quality of sterol exposure during consumption of foods prepared from gametophytes by humans is strongly influenced by age of harvested seeds. Results are critical for a further understanding of the link between human neurodegenerative diseases and historical consumption of foods derived from the seed gametophyte tissue.

Beta-N-methylaminoalanine (BMAA): metabolism and metabolic effects in model systems and in neural and other tissues of the rat in vitro

The non-protein amino acid, beta-N-methylaminoalanine (BMAA), is neurotoxic and has been implicated in the amyotrophic lateral sclerosis-Parkinsonism-dementia (ALS-PD) complex of Guam. This concept remains controversial, in part because of the lack of a convincing animal model. The neuropharmacology of BMAA is well established, but little is known of its metabolism. This paper reports aspects of the metabolism, and metabolic effects, of BMAA in rat tissues. BMAA changed the distribution of taurine, glycine and serine between rat brain slices and their incubation medium; the glutamate/glutamine cycle between neurones and glia was also compromised. In model experiments BMAA reacted non-enzymatically with pyridoxal-5'-phosphate, releasing methylamine. Rat liver and kidney homogenates, but not brain homogenates, also formed methylamine and 2,3-diaminopropanoic acid when incubated with BMAA. These results provide evidence that several biochemical mechanisms are involved in the neurotoxicity of BMAA. The novel discovery that methylamine is formed from BMAA in rat liver and kidney preparations may be significant since chronic administration of methylamine to rats causes oxidative stress. The extent to which this reaction occurs in different animal species might be a decisive factor in selecting an animal model.