Selenium induces cholinergic motor neuron degeneration in Caenorhabditis elegans

2,4,6-trinitrotoluene induces neurotoxicity by affecting the G protein pathways in Caenorhabditis elegans

2,4,6-trinitrotoluene (TNT) is a chemical widely used to make explosives, and its use of residues can lead to potential threats to both ecosystems and human health. A thorough understanding of the various toxic effects of TNT is essential for developing effective environmental protection and health safety measures. Thus, we employed Caenorhabditis elegans (C. elegans), a typical model organism, to explore the neurotoxic effects of TNT and the signaling pathways involved. The results showed that neurotoxicity induced by 10-100 ng/mL TNT was manifested in reduced behavioral capacity (head thrashes, body bends, and pharyngeal pumping rates), and inhibition of foraging behavior and ethanol avoidance behavior. Using fluorescence-labeled transgenic nematodes, it was found that TNT damaged dopaminergic and cholinergic neurons, which resulted in a significant decrease in the release of neurotransmitters and the expression of associated genes (dat-1 and unc-17). We studied the role of G protein signaling pathways and discovered that the related genes (egl-30, gsa-1, goa-1, and unc-13) were significantly down-regulated, resulting in reduced acetylcholine release, which in turn corresponded to the observed behavioral abnormality and damaged neurons in the worms. This study shed light on TNT's neurotoxic mechanisms and associated health risks.

Dietary interventions in mitigating the impact of environmental pollutants on Alzheimer's disease - A review

Numerous studies linking environmental pollutants to oxidative stress, inflammation, and neurotoxicity have assigned pollutants to several neurodegenerative disorders, including Alzheimer's disease (AD). Heavy metals, pesticides, air pollutants, and endocrine disruptor chemicals have been shown to play important roles in AD development, with some traditional functions in amyloid-β formation, tau kinase action, and neuronal degeneration. However, pharmacological management and supplementation have resulted in limited improvement. This raises the interesting possibility that activities usually considered preventive, including diet, exercise, or mental activity, might be more similar to treatment or therapy for AD. This review focuses on the effects of diet on the effects of environmental pollutants on AD. One of the primary issues addressed in this review is a group of specific diets, including the Mediterranean diet (MeDi), Dietary Approaches to Stop Hypertension (DASH), and Mediterranean-DASH intervention for Neurodegenerative Delay (MIND), which prevent exposure to these toxins. Such diets have been proven to decrease oxidative stress and inflammation, which are unfavorable for neuronal growth. Furthermore, they contribute to positive changes in the composition of the human gut microbiota and thus encourage interactions in the Gut-Brain Axis, reducing inflammation caused by pollutants. This review emphasizes a multi-professional approach with reference to nutritional activities that would lower the neurotoxic load in populations with a high level of exposure to pollutants. Future studies focusing on diet and environment association plans may help identify preventive measures aimed at enhancing current disease deceleration.

Selenium-Enriched E. coli Bacteria Mitigate the Age-Associated Degeneration of Cholinergic Neurons in C. elegans

Selenium (Se) is an essential trace element for humans and animals, but high-dose supplementation with Se compounds, most notably selenite, may exert cytotoxic and other adverse effects. On the other hand, bacteria, including Escherichia coli (E. coli), are capable of reducing selenite to red elemental Se that may serve as a safer Se source. Here, we examined how a diet of Se-enriched E. coli bacteria affected vital parameters and age-associated neurodegeneration in the model organism Caenorhabditis elegans (C. elegans). The growth of E. coli OP50 for 48 h in medium supplemented with 1 mM sodium selenite resulted in reddening of the bacterial culture, accompanied by Se accumulation in the bacteria. Compared to nematodes supplied with the standard E. coli OP50 diet, the worms fed on Se-enriched bacteria were smaller and slimmer, even though their food intake was not diminished. Nevertheless, given the choice, the nematodes preferred the standard diet. The fecundity of the worms was not affected by the Se-enriched bacteria, even though the production of progeny was somewhat delayed. The levels of the Se-binding protein SEMO-1, which serves as a Se buffer in C. elegans, were elevated in the group fed on Se-enriched bacteria. The occurrence of knots and ruptures within the axons of cholinergic neurons was lowered in aged nematodes provided with Se-enriched bacteria. In conclusion, C. elegans fed on Se-enriched E. coli showed less age-associated neurodegeneration, as compared to nematodes supplied with the standard diet.

In vitro exposure to PM2.5 of olfactory Ensheathing cells and SH-SY5Y cells and possible association with neurodegenerative processes

PM2.5 exposure represents a risk factor for the public health. PM2.5 is able to cross the blood-alveolar and blood-brain barriers and reach the brain through three routes: nasal olfactory pathway, nose-brain pathway, blood-brain barrier pathway. We evaluated the effect of PM2.5 to induce cytotoxicity and reduced viability on in vitro cultures of OECs (Olfactory Ensheathing Cells) and SH-SY5Y cells. PM2.5 samples were collected in the metropolitan area of Catania, and the gravimetric determination of PM2.5, characterization of 10 trace elements and 16 polycyclic aromatic hydrocarbons (PAHs) were carried out for each sample. PM2.5 extracts were exposed to cultures of OECs and SH-SY5Y cells for 24-48-72 h, and the cell viability assay (MTT) was evaluated. Assessment of mitochondrial and cytoskeleton damage, and the assessment of apoptotic process were performed in the samples that showed lower cell viability. We have found an annual average value of PM2.5 = 16.9 μg/m3 and a maximum value of PM2.5 = 27.6 μg/m3 during the winter season. PM2.5 samples collected during the winter season also showed higher concentrations of PAHs and trace elements. The MTT assay showed a reduction in cell viability for both OECs (44%, 62%, 64%) and SH-SY5Y cells (16%, 17%, 28%) after 24-48-72 h of PM2.5 exposure. Furthermore, samples with lower cell viability showed a decrease in mitochondrial membrane potential, increased cytotoxicity, and also impaired cellular integrity and induction of the apoptotic process after increased expression of vimentin and caspase-3 activity, respectively. These events are involved in neurodegenerative processes and could be triggered not only by the concentration and time of exposure to PM2.5, but also by the presence of trace elements and PAHs on the PM2.5 substrate. The identification of more sensitive cell lines could be the key to understanding how exposure to PM2.5 can contribute to the onset of neurodegenerative processes.

Neurotoxicity of bisphenol A exposure on Caenorhabditis elegans induced by disturbance of neurotransmitter and oxidative damage

Bisphenol A (BPA) is putatively regarded as an environmental neurotoxicant found in everyday plastic products and materials, however, the possible neurobehavioral adverse consequences and molecular mechanisms in animals have not been clearly characterized. The nematode Caenorhabditis elegans has become a promising animal model for neurotoxicological researches. To investigate the dose-effect relationships of BPA-induced neurotoxicity effects, the locomotion behavior and developmental parameters of the nematode were determined after BPA exposure. The present data demonstrated that BPA caused neurobehavioral toxicities, including head thrashes and body bends inhibition. In addition, when C. elegans was exposed to BPA at a concentration higher than 2 μM, growth and survival rate were decreased. The serotonergic, dopaminergic and GABAergic neurons were damaged by BPA. Furthermore, lower levels of mRNA expression related to dopamine, serotonin and GABA were detected in the worms exposed to 50 μM BPA. Increased SOD-3 expression might be adaptive response to BPA exposure. Moreover, oxidative damage triggered by BPA was manifested by changes in GST-4 expression, accompany with abnormity of ATP synthesis, but not nuclear localization of DAF-16/FOXO. Finally, we showed that epigallocatechin-3-gallate partially rescued BPA-induced reactive oxygen species (ROS) production and neurobehavioral toxicity. Altogether, the neurobehavioral and developmental toxicity of BPA may be induced by neurotransmission abnormity and oxidative damage. The present data imply that oxidative stress is linked to neuronal damage and neurobehavioral harm resulting from developmental BPA exposure.

Caenorhabditis elegans as a model system to evaluate neuroprotective potential of nano formulations

The impact of neurodegenerative illnesses on society is significant, but the mechanisms leading to neuronal malfunction and death in these conditions remain largely unknown despite identifying essential disease genes. To pinpoint the mechanisms behind the pathophysiology of neurodegenerative diseases, several researchers have turned to nematode C. elegans instead of using mammals. Since C. elegans is transparent, free-living, and amenable to culture, it has several benefits. As a result, all the neurons in C. elegans can be easily identified, and their connections are understood. Human proteins linked to Neurodegeneration can be made to express in them. It is also possible to analyze how C. elegans orthologs of the genes responsible for human neurodegenerative diseases function. In this article, we focused at some of the most important C. elegans neurodegeneration models that accurately represent many elements of human neurodegenerative illness. It has been observed that studies using the adaptable C. elegans have helped us in better understanding of human diseases. These studies have used it to replicate several aspects of human neurodegeneration. A nanotech approach involves engineering materials or equipments interacting with biological systems at the molecular level to trigger physiological responses by increasing stimulation, responding, and interacting with target sites while minimizing side effects, thus revolutionizing the treatment and diagnosis of neurodegenerative diseases. Nanotechnologies are being used to treat neurological disorders and deliver nanoscale drugs. This review explores the current and future uses of these nanotechnologies as innovative therapeutic modalities in treatment of neurodegenerative diseases using C elegans as an experimental model.

Oxidative Stress in Amyotrophic Lateral Sclerosis: Synergy of Genetic and Environmental Factors

Amyotrophic lateral sclerosis (ALS) is a grievous neurodegenerative disease whose survival is limited to only a few years. In spite of intensive research to discover the underlying mechanisms, the results are fairly inconclusive. Multiple hypotheses have been regarded, including genetic, molecular, and cellular processes. Notably, oxidative stress has been demonstrated to play a crucial role in ALS pathogenesis. In addition to already recognized and exhaustively studied genetic mutations involved in oxidative stress production, exposure to various environmental factors (e.g., electromagnetic fields, solvents, pesticides, heavy metals) has been suggested to enhance oxidative damage. This review aims to describe the main processes influenced by the most frequent genetic mutations and environmental factors concurring in oxidative stress occurrence in ALS and the potential therapeutic molecules capable of diminishing the ALS related pro-oxidative status.

Excessive selenium affects neural development and locomotor behavior of zebrafish embryos

Selenium is an essential micronutrient derived from daily diet to maintain the normal growth and development of vertebrates. Excessive selenium intake will induce cardiovascular toxicity, reproductive toxicity and neurotoxicity. However, there have been few studies of the toxic effects of selenium on neural development and locomotor behavior. In this study, newly fertilized zebrafish embryos were treated with selenium. As a result, selenium treatment at the concentration of 0.5 µM decreased the moving speed and distance and blunted the touch response of zebrafish embryos. TUNEL assay and immunofluorescence analysis revealed that selenium induced nervous system impairment including promoted cell apoptosis, proliferation and neuroinflammation, and decreased neurons in zebrafish embryos. RNA-seq and RT-PCR results indicated that selenium treatment significantly decreased the expression of the dopaminergic neuron, motor neuron, GABAergic neuron and neurotransmitter transport marker genes in zebrafish embryos. The expression of PPAR signaling pathway marker genes was significantly down-regulated in selenium-treated embryos. Two PPAR agonists (rosiglitazone and bezafibrate) and an anti-cancer drug (cisplatin) were tested for their effects to alleviate selenium-induced locomotor defects. Rosiglitazone and bezafibrate could restore the expression of some neural marker genes but could not fully rescue the selenium-induced locomotor behavior defects. The supplementation of cisplatin could restore the dysfunctional locomotor behavior and the abnormal expression of the PPAR and neural marker genes to almost the normal levels. In conclusion, the results of this study reveal that selenium-induced neural development and locomotor behavior defects are caused by multiple complex factors including PPAR signaling, and all the factors might be recovered by cisplatin through unknown mechanisms.

A perspective on persistent toxicants in veterans and amyotrophic lateral sclerosis: identifying exposures determining higher ALS risk

Multiple studies indicate that United States veterans have an increased risk of developing amyotrophic lateral sclerosis (ALS) compared to civilians. However, the responsible etiological factors are unknown. In the general population, specific occupational (e.g. truck drivers, airline pilots) and environmental exposures (e.g. metals, pesticides) are associated with an increased ALS risk. As such, the increased prevalence of ALS in veterans strongly suggests that there are exposures experienced by military personnel that are disproportionate to civilians. During service, veterans may encounter numerous neurotoxic exposures (e.g. burn pits, engine exhaust, firing ranges). So far, however, there is a paucity of studies investigating environmental factors contributing to ALS in veterans and even fewer assessing their exposure using biomarkers. Herein, we discuss ALS pathogenesis in relation to a series of persistent neurotoxicants (often emitted as mixtures) including: chemical elements, nanoparticles and lipophilic toxicants such as dioxins, polycyclic aromatic hydrocarbons and polychlorinated biphenyls. We propose these toxicants should be directly measured in veteran central nervous system tissue, where they may have accumulated for decades. Specific toxicants (or mixtures thereof) may accelerate ALS development following a multistep hypothesis or act synergistically with other service-linked exposures (e.g. head trauma/concussions). Such possibilities could explain the lower age of onset observed in veterans compared to civilians. Identifying high-risk exposures within vulnerable populations is key to understanding ALS etiopathogenesis and is urgently needed to act upon modifiable risk factors for military personnel who deserve enhanced protection during their years of service, not only for their short-term, but also long-term health.

Prenatal exposure to a mixture of elements and neurobehavioral outcomes in mid-childhood: Results from Project Viva

BACKGROUND

Lead (Pb), manganese (Mn), selenium (Se) and methylmercury (MeHg) can be neurotoxic individually, despite Mn and Se also being essential elements. Little is known about the joint effects of essential and non-essential elements on neurobehavior, particularly for prenatal exposures.

OBJECTIVES

To evaluate associations of prenatal exposure to multiple elements with executive function and neurobehavior in children.

METHODS

Participants included 1009 mother-child pairs from the Project Viva pre-birth cohort. We estimated maternal erythrocyte Pb, Mn, Se, and Hg concentrations prenatally. In 6-11-year old children (median 7.6 years), parents and teachers rated children's executive function-related behaviors using the Behavior Rating Inventory of Executive Function (BRIEF) Global Executive Composite score and behavioral difficulties using the Strengths and Difficulties Questionnaire (SDQ) total difficulties score. We evaluated associations of element mixtures with neurobehavior using Bayesian kernel machine regression (BKMR), multivariable linear regression, and quantile g-computation.

RESULTS

Median erythrocyte Pb, Mn, Se, and Hg concentrations were 1.1 μg/dL, 33.1 μg/L, 204.5 ng/mL, and 3.1 ng/g, respectively. Findings from BKMR and quantile g-computation models both showed worse (higher) parent-rated BRIEF and SDQ z-scores with higher concentrations of the mixture, although estimates were imprecise. When remaining elements were set at their median within BKMR models, increases in Pb and Se from the 25th to 75th percentile of exposure distributions were associated with 0.08 (95% CI: 0.02, 0.19) and 0.07 (95% CI: 0.03, 0.16) standard deviation increases in parent-rated BRIEF scores, and 0.08 (95% CI: 0.02, 0.17) and 0.05 (95% CI: 0.03, 0.13) standard deviation increases in SDQ scores, respectively. There was no evidence of element interactions.

DISCUSSION

Although associations were small in magnitude, we found a trend of worsening neurobehavioral ratings with increasing prenatal exposure to an element mixture. However, we may be observing a limited range of dose-dependent impacts given the levels of exposure within our population.

Neurobehavior and neuron damage following prolonged exposure of silver nanoparticles with/without polyvinylpyrrolidone coating in Caenorhabditis elegans

Silver nanoparticles (AgNPs) have become widespread in the environment with increasing industrial applications. But the studies about their potential health risks are far from enough, especially in neurotoxic effects. This study aimed to investigate the neurotoxic effects of longer-term exposure (prolonged exposure for 48 h and chronic exposure for 6 days) of 20nm AgNPs with/without polyvinylpyrrolidone (PVP) coating at low concentrations (0.01-10 mg·L^-1 ) to Caenorhabditis elegans. The results suggested that exposure to AgNPs induced damage to nematode survival, with the longest and relative average life span reduced. Exposure to AgNPs caused neurotoxicity on locomotion behaviors (head thrashes, body bends, pharyngeal pumping frequency, and defecation interval) and sensory perception behaviors (chemotaxis assay and thermotaxis assay), as well as impaired dopaminergic, GABAergic, and cholinergic neurons, except for glutamatergic, based on the alters fluorescence intensity, in a dose- and time-dependent manner. Further investigations suggested that the low-dose AgNPs (0.01-0.1 mg·L^-1 ) exposure raises receptors of GABAergic and dopamine in C. elegans at the genetic level, whereas opposite results were observed at higher doses (1-10 mg·L^-1 ), which implied that AgNPs could cause neurotoxicity by impairing neurotransmitter delivery. The PVP-AgNPs could cause a higher fatality rate and neurotoxicity at the same dose. Notably, AgNPs did not cause any deleterious effect on nematodes at the lowest dose of 0.01 mg·L^-1 . In general, these results suggested that AgNPs possess the neurotoxic potential in C. elegans and provided useful information to understand the neurotoxicity of AgNPs, which would offer an inspiring perspective on the safe application.

A comprehensive review on the neuropathophysiology of selenium

As an essential micronutrient, selenium (Se) exerts its biological function as a catalytic entity in a variety of enzymes. From a toxicological perspective, however, Se can become extremely toxic at concentrations slightly above its nutritional levels. Over the last few decades, there has been a growing level of concern worldwide regarding the adverse effects of both inorganic and organic Se compounds on a broad spectrum of neurological functions. A wealth of evidence has shown that exposure to excess Se may compromise the normal functioning of various key proteins, neurotransmitter systems (the glutamatergic, dopaminergic, serotonergic, and cholinergic systems), and signaling molecules involved in the control and regulation of cognitive, behavioral, and neuroendocrine functions. Elevated Se exposure has also been suspected to be a risk factor for the development of several neurodegenerative and neuropsychiatric diseases. Nonetheless, despite the various deleterious effects of excess Se on the central nervous system (CNS), Se neurotoxicity and negative behavioral outcomes are still disregarded at the expense of its beneficial health effects. This review focuses on the current state of knowledge regarding the neurobehavioral effects of Se and discusses its potential mode of action on different aspects of the central and peripheral nervous systems. This review also provides a brief history of Se discovery and uses, its physicochemical properties, biological roles in the CNS, environmental occurrence, and toxicity. We also review potential links between exposure to different forms of Se compounds and aberrant neurobehavioral functions in humans and animals, and identify key knowledge gaps and hypotheses for future research.

Metals associated neurodegeneration in Parkinson's disease: Insight to physiological, pathological mechanisms and management

Parkinson's disease (PD) is a deliberately progressive neurological disorder, arises due to degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The loss of dopaminergic nerves and dopamine deficiency leads to motor symptoms characterized by rigidity, tremor, and bradykinesia. Heavy metals and trace elements play various physiological and pathological roles in the nervous system. Excessive exposure to toxic metals like mercury (Hg), lead (Pb), copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), aluminium (Al), arsenic (As), cadmium(cd), and selenium (Se) cross the blood-brain barrier to enter into the brain and leads to dopaminergic neuronal degeneration. Excessive concentrations of heavy metals in the brain promote oxidative stress, mitochondrial dysfunction, and the formation of α-synuclein leads to dopaminergic neuronal damage. There is increasing evidence that heavy metals normally present in the human body in minute concentration also cause accumulation to initiate the free radical formation and affecting the basal ganglia signaling. In this review, we explored how these metals affect brain physiology and their roles in the accumulation of toxic proteins (α-synuclein and Lewy bodies). We have also discussed the metals associated with neurotoxic effects and their prevention as management of PD. Our goal is to increase the awareness of metals as players in the onset and progression of PD.

Use of C. elegans as a 3R-compliant in vivo model for the chemoprevention of cisplatin-induced neurotoxicity

Anticancer therapeutics can provoke severe side effects that impair the patient's quality of life. A frequent dose-limiting side effect of platinum-based anticancer therapy is neurotoxicity. Its pathophysiology is poorly understood, and effective preventive or therapeutic measures are missing. Therefore, elucidation of the molecular mechanism of platinating drug-induced neurotoxicity and the development of preventive strategies is urgently needed. To this end, we aim to use C. elegans as a 3R-compliant in vivo model. The 3R principles were conceived for animal welfare in science concerning animal experiments, which should be replaced, reduced or refined. We can analytically demonstrate dose-dependent uptake of cisplatin (CisPt) in C. elegans, as well as genotoxic and cytotoxic effects based on DNA adduct formation (i.e., 1,2-GpG intrastrand crosslinks), induction of apoptosis, and developmental toxicity. Measuring the impairment of pharyngeal pumping as a marker of neurotoxicity, we found that especially CisPt reduces the pumping frequency at concentrations where basal and touch-provoked movement were not yet affected. CisPt causes glutathione (GSH) depletion and RNAi-mediated knockdown of the glutamate-cysteine ligase GCS-1 aggravates the CisPt-induced inhibition of pharyngeal pumping. Moreover, N-acetylcysteine (NAC) mitigated CisPt-triggered toxicity, indicating that GSH depletion contributes to the CisPt-induced pharyngeal damage. In addition to NAC, amifostine (WR1065) also protected the pharynx of C. elegans from the toxic effects of CisPt. Measuring pharyngeal activity by the electrophysiological recording of neurotransmission in the pharynx, we confirmed that CisPt is neurotoxic in C. elegans and that NAC is neuroprotective in the nematode. The data support the hypothesis that monitoring the pharyngeal activity of C. elegans is a useful surrogate marker of CisPt-induced neurotoxicity. In addition, a low GSH pool reduces the resistance of neurons to CisPt treatment, and both NAC and WR1065 are capable of attenuating platinum-induced neurotoxicity during post-incubation in C. elegans. Overall, we propose C. elegans as a 3R-compliant in vivo model to study the molecular mechanisms of platinum-induced neurotoxicity and to explore novel neuroprotective therapeutic strategies to alleviate respective side effects of platinum-based cancer therapy.

Role of environmental pollutants in Alzheimer's disease: a review

Neurodegenerative disorders are commonly erratic influenced by various factors including lifestyle, environmental, and genetic factors. In recent observations, it has been hypothesized that exposure to various environmental factors enhances the risk of Alzheimer's disease (AD). The exact etiology of Alzheimer's disease is still unclear; however, the contribution of environmental factors in the pathology of AD is widely acknowledged. Based on the available literature, the review aims to culminate in the prospective correlation between the various environmental factors and AD. The prolonged exposure to the various well-known environmental factors including heavy metals, air pollutants (particulate matter), pesticides, nanoparticles containing metals, industrial chemicals results in accelerating the progression of AD. Common mechanisms have been documented in the field of environmental contaminants for enhancing amyloid-β (Aβ) peptide along with tau phosphorylation, resulting in the initiation of senile plaques and neurofibrillary tangles, which results in the death of neurons. This review offers a compilation of available data to support the long-suspected correlation between environmental risk factors and AD pathology. Graphical abstract .

Effect of environmental toxicants on neuronal functions

In the last few years, neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) have attracted attention due to their high prevalence worldwide. Environmental factors may be one of the biggest reasons for these diseases related to neuronal dysfunctions. Most of neuronal disorders are strongly associated with pre- and postnatal exposure to environmental toxins released from industries. Some of the neurotoxic metals such as lead, aluminum, mercury, manganese, cadmium, and arsenic as well as some pesticides and metal-based nanoparticles have been involved in AD and PD due to their ability to produce senile/amyloid plaques and NFTs which are the main feature of these neuronal dysfunctions. Exposure to solvents is also majorly responsible for neurodegenerative disorders. The present review highlights the impact of omnipresent heavy metals with some other neurotoxins on human health and how they give rise to neuronal dysfunctions which in turn causes socio-economic consequences due to increasing pollution worldwide. Graphical abstract.

The adverse effects of selenomethionine on skeletal muscle, liver, and brain in the steelhead trout (Oncorhynchus mykiss)

Juvenile Oncorhynchus mykiss (average weight: 22.3 g) were fed one of five selenomethionine diets (1.09, 8.79, 15.37, 30.79, or 61.58 mg Se/kg diet). After 4 weeks, hepatic catalase activity over 15.37 mg Se/kg diets was significantly decreased, and the glutathione peroxidase activity over 30.79 mg Se/kg diets was elevated compared to the controls. In the brain, the dopamine levels at 61.58 mg Se/kg diet and the serotonin levels over 15.37 mg Se/kg diets were significantly increased, whereas the 3,4-dihydroxyphenylacetic acid, homovanillic acid, and dopamine turnover, and the 5-hydroxyindoleacetic acid and serotonin turnover over 30.79 mg Se/kg diets were decreased. In muscle, the 3-nitrotyrosine level over 15.37 mg Se/kg diets, acetylcholine esterase activity over 30.79 mg Se/kg diets, and histological alterations over 8.79 mg Se/kg diets were increased. Our current results showed that selenomethionine disrupted dopamine and serotonin metabolism in the brain and damaged the neuromuscular system in skeletal muscle.

Deep learning-enabled analysis reveals distinct neuronal phenotypes induced by aging and cold-shock

BACKGROUND

Access to quantitative information is crucial to obtain a deeper understanding of biological systems. In addition to being low-throughput, traditional image-based analysis is mostly limited to error-prone qualitative or semi-quantitative assessment of phenotypes, particularly for complex subcellular morphologies. The PVD neuron in Caenorhabditis elegans, which is responsible for harsh touch and thermosensation, undergoes structural degeneration as nematodes age characterized by the appearance of dendritic protrusions. Analysis of these neurodegenerative patterns is labor-intensive and limited to qualitative assessment.

RESULTS

In this work, we apply deep learning to perform quantitative image-based analysis of complex neurodegeneration patterns exhibited by the PVD neuron in C. elegans. We apply a convolutional neural network algorithm (Mask R-CNN) to identify neurodegenerative subcellular protrusions that appear after cold-shock or as a result of aging. A multiparametric phenotypic profile captures the unique morphological changes induced by each perturbation. We identify that acute cold-shock-induced neurodegeneration is reversible and depends on rearing temperature and, importantly, that aging and cold-shock induce distinct neuronal beading patterns.

CONCLUSION

The results of this work indicate that implementing deep learning for challenging image segmentation of PVD neurodegeneration enables quantitatively tracking subtle morphological changes in an unbiased manner. This analysis revealed that distinct patterns of morphological alteration are induced by aging and cold-shock, suggesting different mechanisms at play. This approach can be used to identify the molecular components involved in orchestrating neurodegeneration and to characterize the effect of other stressors on PVD degeneration.

CSF neurotoxic metals/metalloids levels in amyotrophic lateral sclerosis patients: comparison between bulbar and spinal onset

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of the central nervous system (CNS) that causes progressive and irreversible damage in motor neurons. Different causal hypotheses include genetic, viral, traumatic and environmental mechanisms, such as exposure to heavy metals. The aim of this study was to compare metal/metalloid levels in cerebro-spinal fluid of ALS subtypes (spinal vs bulbar clinical onset).

MATERIAL AND METHODS

This observational study consecutively screened all ALS patients referring to the Neurology Clinic of the University of Catania (Italy). Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify magnesium (Mg), cuprum (Cu), selenium (Se), iron (Fe), manganese (Mn), vanadium (V), zinc (Zn), alluminium (Al), arsenic (As), cobalt (Co), nickel (Ni), mercury (Hg), lead (Pb), cadmium (Cd) and palladium (Pd) levels.

RESULTS

Thirty-seven patients were enrolled (62.2% females), median age of 65 years (IQR: 59-71 years). Thirty-one (83.8%) patients had a spinal onset and 6 (16.2%) a bulbar onset. Se and As levels were higher compared to the reference values (RV) both in spinal and bulbar onset, while Cu was higher than RV only in bulbar onset. Moreover, Cu (129.8 μg/L vs 29.8 μg/L), Fe (54.5 μg/L vs 33.3 μg/L), Mn (3.4 μg/L vs 1.8 μg/L), Zn (46.1 μg/L vs 35.7 μg/L), Al (12.2 μg/L vs 6.7 μg/L), Ni (2.80 μg/L vs 1.40 μg/L), and Pb (0.60 μg/L vs 0.30 μg/L) levels were higher in bulbar than in spinal onset, conversely As was slightly higher in spinal than in bulbar onset (1.40 μg/L vs 1.10 μg/L). Overall, Cu (129 μg/L vs 31 μg/L), Fe (92.2 μg/L vs 32.9 μg/L), Mn (3.35 μg/L vs 1.80 μg/L), Zn (56.5 μg/L vs 35.2 μg/L), Al (14.45 μg/L vs 6.70 μg/L), and Cd (0.40 μg/L vs 0.08 μg/L) levels were higher in patients with disease duration less than 19 months.

CONCLUSION

Our results supported the hypothesis that metals/metalloids with neurotoxic effects could be involved in the etiology of ALS, showing higher levels of Cu, Se and As. Relevant differences in Cu and Mn levels were found between bulbar and spinal onset patients.

HIF-1 Has a Central Role in Caenorhabditis elegans Organismal Response to Selenium

Selenium is a trace element for most organisms; its deficiency and excess are detrimental. Selenium beneficial effects are mainly due to the role of the 21^st genetically encoded amino acid selenocysteine (Sec). Selenium also exerts Sec-independent beneficial effects. Its harmful effects are thought to be mainly due to non-specific incorporation in protein synthesis. Yet the selenium response in animals is poorly understood. In Caenorhabditis elegans, Sec is genetically incorporated into a single selenoprotein. Similar to mammals, a 20-fold excess of the optimal selenium requirement is harmful. Sodium selenite (Na₂SeO₃) excess causes development retardation, impaired growth, and neurodegeneration of motor neurons. To study the organismal response to selenium we performed a genetic screen for C. elegans mutants that are resistant to selenite. We isolated non-sense and missense egl-9/EGLN mutants that confer robust resistance to selenium. In contrast, hif-1/HIF null mutant was highly sensitive to selenium, establishing a role for this transcription factor in the selenium response. We showed that EGL-9 regulates HIF-1 activity through VHL-1, and identified CYSL-1 as a key sensor that transduces the selenium signal. Finally, we showed that the key enzymes involved in sulfide and sulfite stress (sulfide quinone oxidoreductase and sulfite oxidase) are not required for selenium resistance. In contrast, knockout strains in the persulfide dioxygenase ETHE-1 and the sulfurtransferase MPST-7 affect the organismal response to selenium. In sum, our results identified a transcriptional pathway as well as enzymes possibly involved in the organismal selenium response.

Deficiency but Not Supplementation of Selenium Impairs the Hippocampal Long-Term Potentiation and Hippocampus-Dependent Learning

Among the chemical factors that have been implicated in the etiology of dementia, recent concern has focused on both increased and decreased exposure to the metalloid selenium (Se). This report describes the molecular, behavioral, and electrophysiological analysis of rats that were fed with Se-free chow and Se-enriched tap water for 21 days. Three groups were produced, feeding them on a deficient diet with different Selenium content. Hippocampus-dependent spatial learning was measured using the water maze. Long-term potentiation (LTP) was recorded in the hippocampal dentate gyrus to assess how memory is formed at the cellular level. Hippocampal Se levels were measured in trained rats by using inductively coupled plasma mass spectrometry. Phosphorylated and total tau levels were measured in whole hippocampus by Western blot. An impairment of learning of rats feeding with Se-deficient diet was accompanied by attenuated LTP, and increased ratio of p²³¹Tau-to- and decreased ratio of p⁴¹⁶Tau-to-Tau in the non-stimulated hippocampus, despite no significant change was observed in Se levels of hippocampus and plasma. Se supplementation resulted in an increase in both tissues and an increase in the ratio of p²³¹Tau-to-Tau in the non-stimulated hippocampus but did not change learning performance and LTP. Despite impaired learning and LTP, no group differed in probe trial and in the fraction of phosphorylated tau in LTP-induced hippocampus. Reduced level of selenium would probably result in reduced synaptic plasticity as well as impairment of learning ability, suggesting requirement of Se for normal synaptic function.

Amyotrophic lateral sclerosis incidence following exposure to inorganic selenium in drinking water: A long-term follow-up

Some studies have reported an association between overexposure to selenium and risk of amyotrophic lateral sclerosis (ALS), a rare degenerative disease of motor neurons. From 1986 through 2015, we followed a cohort in Northern Italy that had been inadvertently consuming tap water with unusually high concentrations of inorganic hexavalent selenium from 1974 to 1985. We had previously documented an excess incidence of ALS in this cohort during 1986-1994. Here, we report extended follow-up of the cohort for an additional 21 years, encompassing 50,100 person-years of the exposed cohort and 2,233,963 person-years of the unexposed municipal cohort. We identified 7 and 112 incident ALS cases in the exposed and unexposed cohorts, respectively, yielding crude incidence rates of 14 and 5 cases per 100,000 person-years. A Poisson regression analysis, adjusting for age, sex and calendar year, produced an overall incidence rate ratio (IRR) for ALS of 2.8 (95% confidence interval (CI) 1.3, 6), with a substantially stronger IRR in 1986-1994 (8.2, 95% CI 2.7, 24.7) than in 1995-2015 (1.5, 95% CI 0.5, 4.7), and among women (5.1, 95% CI 1.8, 14.3) than men (1.7, 95% CI 0.5, 5.4). Overall, these results indicate an association between high exposure to inorganic selenium, a recognized neurotoxicant, and ALS incidence, with declining rates after cessation of exposure and stronger effects among women.

LPS-induced sickness behavior is not affected by selenium but is switched off by psychogenic stress in rats

Sickness behavior (SB) is considered part of the adaptive behavioral and neuroimmune changes that occur in response to inflammatory processes. However, SB is a motivational state modulated by the environmental context. The objective of this study was to evaluate if selenium could ameliorate symptoms of SB and if stress would affect these responses. We induced SB in rats using lipopolysaccharide (LPS). We choose selenium based on our findings of LPS-exposure decreasing selenium levels in rats. We exposed these rats to a psychogenic stress and studied motivational modulation paradigms, such as cure of the organism, preservation of the species, and fight or flight. We studied ultrasonic vocalizations, open-field behaviors, body weight, and IL-1 beta and IFN-gamma serum levels. LPS-induced SB was evidenced by decreased motor/exploratory activity and increased proinflammatory mediators' levels. Selenium treatment did not exert beneficial effects on SB, revealing that probably the selenium deficiency was not related to SB. When analyzed with the stress paradigm, the behavior of rats was differentially affected. LPS did not affect behavior in the presence of stress. SB was abrogated during stressor events to prioritize survival behaviors, such as fight-or-flight. Contrarily, the association of LPS, selenium, and stress induced SB even during stressor events, revealing that this combination induced a cumulative toxic effect.

Neuron-specific toxicity of chronic acrylamide exposure in C. elegans

Acrylamide is a food-borne chemical with well-known neurotoxic properties. To date, the toxicity mechanisms of chronic acrylamide exposure are not fully understood. Using the genetic model Caenorhabditis elegans, we found that chronic acrylamide exposure induces a locomotor defect that is characterized by severe uncoordination of muscle movement that is distinct from an overall reduction in activity. C. elegans exhibiting chronic acrylamide-induced locomotor defects show significant degeneration to the dopaminergic and cholinergic, but not GABAergic motor neurons. Degeneration of the dopaminergic and cholinergic neurons are found in 58% to 67% of C. elegans after chronic acrylamide exposure, with the varying degrees of severity ranging from neuronal blebbing to complete dendrite loss. The observed pattern of neurotoxicity does not have a heritable effect, as parental exposure to chronic acrylamide does not lead to neurodegeneration in the developed offspring. Overall, these finding illustrate that chronic acrylamide exposure cause locomotor defects by inducing degeneration of specific neuron types in C. elegans.

Selenium Nanoparticles as an Efficient Nanomedicine for the Therapy of Huntington's Disease

Huntington's disease (HD) is an incurable disease with progressive loss of neural function, which is influenced by epigenetic, oxidative stress, metabolic, and nutritional factors. Targeting inhibition of huntingtin protein aggregation is a strategy for HD therapy, but the efficacy is unsatisfactory. Studies found that selenium (Se) levels in the brain are insufficient for HD disease individuals, while improvement in Se homeostasis in the brain may attenuate neuronal loss and dysfunction. In this study, we applied selenium nanoparticles (NPs) (Nano-Se) for the HD disease therapy by regulating HD-related neurodegeneration and cognitive decline based on transgenic HD models of Caenorhabditis elegans (C. elegans). At low dosages, Nano-Se NPs significantly reduced neuronal death, relieved behavioral dysfunction, and protected C. elegans from damages in stress conditions. The molecular mechanism further revealed that Nano-Se attenuated oxidative stress, inhibited the aggregation of huntingtin proteins, and downregulated the expression of histone deacetylase family members at mRNA levels. The results suggested that Nano-Se has great potential for Huntington's disease therapy. In conclusion, the mechanism about how Nano-Se NPs protect from damages in stress conditions and how they repair neural functions will benefit HD disease therapy. This study will also guide rational design of Nano-Se NPs or other selenium compounds to improve HD therapy in the future.

Altered dietary selenium influences brain iron content and behavioural outcomes

Selenium (Se) is an essential micronutrient that provides antioxidant defence through selenoproteins, but at high concentrations, deleterious effects have been reported. The present study examines the antioxidant response in brain regions and behavioural functions in mice under various dietary Se paradigms; Se-deficient, Se-adequate and Se-excess. Se levels were found to be reduced in the cortex and hippocampus of Se-deficient animals, whereas no change was observed in animals on Se-excess diet. In the hippocampus, iron (Fe) levels increased in animals on Se-deficient and Se-excess diets. Moreover, in Se-deficient animals, Fe levels increased in cortex also. Interestingly, Se content in the hair positively correlated with the dietary Se intake. Total and Se-dependent glutathione peroxidase activity decreased in the cortex, hippocampus and cerebellum of animals on Se-deficient diet. On the other hand, the activity of these enzymes decreased in the cortex of animals on Se-excess diet. Further, lipid peroxidation increased in the cortex of animals on Se-deficient diet and in the hippocampus of animals on Se-excess diet. Cognitive functions assessed by Morris water maze and Y-maze tests revealed deficits in Se-deficient state. However, in Se-excess state cognitive deficits were observed only in Y-maze test. These findings suggest that long-term dietary variation in Se influences oxidative stress that impacts cognitive functions. Therefore, it is suggested that maintenance of Se status during postnatal development may be crucial for mental health.

Selenium species-dependent toxicity, bioavailability and metabolic transformations in Caenorhabditis elegans

The essential micronutrient selenium (Se) is required for various systemic functions, but its beneficial range is narrow and overexposure may result in adverse health effects. Additionally, the chemical form of the ingested selenium contributes crucially to its health effects. While small Se species play a major role in Se metabolism, their toxicological effects, bioavailability and metabolic transformations following elevated uptake are poorly understood. Utilizing the tractable invertebrate Caenorhabditis elegans allowed for an alternative approach to study species-specific characteristics of organic and inorganic Se forms in vivo, revealing remarkable species-dependent differences in the toxicity and bioavailability of selenite, selenomethionine (SeMet) and Se-methylselenocysteine (MeSeCys). An inverse relationship was found between toxicity and bioavailability of the Se species, with the organic species displaying a higher bioavailability than the inorganic form, yet being less toxic. Quantitative Se speciation analysis with HPLC/mass spectrometry revealed a partial metabolism of SeMet and MeSeCys. In SeMet exposed worms, identified metabolites were Se-adenosylselenomethionine (AdoSeMet) and Se-adenosylselenohomocysteine (AdoSeHcy), while worms exposed to MeSeCys produced Se-methylselenoglutathione (MeSeGSH) and γ-glutamyl-MeSeCys (γ-Glu-MeSeCys). Moreover, the possible role of the sole selenoprotein in the nematode, thioredoxin reductase-1 (TrxR-1), was studied comparing wildtype and trxr-1 deletion mutants. Although a lower basal Se level was detected in trxr-1 mutants, Se toxicity and bioavailability following acute exposure was indistinguishable from wildtype worms. Altogether, the current study demonstrates the suitability of C. elegans as a model for Se species dependent toxicity and metabolism, while further research is needed to elucidate TrxR-1 function in the nematode.

The glutathione system and the related thiol network in Caenorhabditis elegans

Advances in the field of redox biology have contributed to the understanding of the complexity of the thiol-based system in mediating signal transduction. The redox environment is the overall spatiotemporal balance of oxidation-reduction systems within the integrated compartments of the cell, tissues and whole organisms. The ratio of the reduced to disulfide glutathione redox couple (GSH:GSSG) is a key indicator of the redox environment and its associated cellular health. The reaction mechanisms of glutathione-dependent and related thiol-based enzymes play a fundamental role in the function of GSH as a redox regulator. Glutathione homeostasis is maintained by the balance of GSH synthesis (de novo and salvage pathways) and its utilization through its detoxification, thiol signalling, and antioxidant defence functions via GSH-dependent enzymes and free radical scavenging. As such, GSH acts in concert with the entire redox network to maintain reducing conditions in the cell. Caenorhabditis elegans offers a simple model to facilitate further understanding at the multicellular level of the physiological functions of GSH and the GSH-dependent redox network. This review discusses the C. elegans studies that have investigated glutathione and related systems of the redox network including; orthologs to the protein-encoding genes of GSH synthesis; glutathione peroxidases; glutathione-S-transferases; and the glutaredoxin, thioredoxin and peroxiredoxin systems.

Chronic exposure to dietary selenomethionine dysregulates the genes involved in serotonergic neurotransmission and alters social and antipredator behaviours in zebrafish (Danio rerio)

Selenium (Se) is a metalloid of potential interest from both a toxicological and nutritional perspective, having a range of safe intake. The adverse neuro-behavioural effects of Se have been investigated in both humans and fishes, but little is known about its effects on social behaviours or the serotonergic signaling pathway in the brain. In the present study, we investigated the effects of chorionic dietary exposure to Se (as selenomethionine) at different concentrations (control, 2.1, 11.6 or 31.5 μg/g dry wt.) on antipredator avoidance, shoaling behaviour, and social group preferences in adult zebrafish (Danio rerio). In addition, we also measured the expression of important genes in the serotonergic pathway that influence social behaviours. After 60 days of exposure, the highest dose (31.5 μg/g dry wt.) caused the highest level of baseline fear behaviour, with fish swimming lower in the water column and in tighter shoals compared to fish in the other treatments. With high levels of baseline fear, these fish did not significantly intensify fear behaviours in response to predation risk in the form of exposure to chemical alarm cues. When individual fish were given an opportunity to shoal with groups of differing sizes (3 vs. 4 individuals), fish exposed to the high dose spent less time with groups in general, and only control fish showed a significant preference for the larger group. In the zebrafish brain, we found significant upregulation in the mRNA expression of serotonin receptors (htr1aa and htr1b), a transporter (slc6a4a), and tryptophan hydroxylase-2 (tph2), whereas there was a downregulation of the monoamine oxidase (mao) gene. The results of this study suggest that disruption of serotonergic neurotransmission might have been responsible for Se-induced impairment of antipredator and social behaviour in zebrafish.

The increasing importance of environmental conditions in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease affecting motor neurons (MNs). Although a small percentage of ALS has a familial origin, the vast majority of cases are sporadic in which genetic factors and environment interact with each other leading to disease onset in genetically predisposed individuals. In the current model of the disease, each individual has a determined genetic load, some degree of cell degeneration related to age and several risky environmental exposures. In this scenario, MN degeneration would occur when the sum of these factors reach a certain threshold. To date, an extensive list of environmental factors has been associated to ALS, including different categories, such as exposure to heavy metals and other toxicants, cyanotoxins or infectious agents. In addition, in recent years, lifestyle and other demographic parameters are gaining relevance in the genesis of the disease. Among them, physical activity, nutrition, body mass index, cardiovascular risk factors, autoimmune diseases and cancer are some of the conditions which have been related to the disease. In this review, we will discuss the potential mechanisms of environmental conditions in motor neuron degeneration. Understanding the role of each one of these factors as well as their interactions appears as a crucial step in order to develop new preventive, diagnostic and therapeutic approaches for ALS patients.

Stem Cells as Potential Targets of Polyphenols in Multiple Sclerosis and Alzheimer's Disease

Alzheimer's disease (AD) and multiple sclerosis are major neurodegenerative diseases, which are characterized by the accumulation of abnormal pathogenic proteins due to oxidative stress, mitochondrial dysfunction, impaired autophagy, and pathogens, leading to neurodegeneration and behavioral deficits. Herein, we reviewed the utility of plant polyphenols in regulating proliferation and differentiation of stem cells for inducing brain self-repair in AD and multiple sclerosis. Firstly, we discussed the genetic, physiological, and environmental factors involved in the pathophysiology of both the disorders. Next, we reviewed various stem cell therapies available and how they have proved useful in animal models of AD and multiple sclerosis. Lastly, we discussed how polyphenols utilize the potential of stem cells, either complementing their therapeutic effects or stimulating endogenous and exogenous neurogenesis, against these diseases. We suggest that polyphenols could be a potential candidate for stem cell therapy against neurodegenerative disorders.

Dopaminergic dysregulation and impaired associative learning behavior in zebrafish during chronic dietary exposure to selenium

A growing body of evidence indicates that exposure to selenium (Se) can cause neurotoxicity, and this can occur because of its interference with several neurotransmitter systems in humans and animals. Dopamine is a critical modulator of a variety of brain functions and a prime target for environmental neurotoxicants. However, effects of environmentally relevant concentrations of Se on dopaminergic system and its neurobehavioral effects are still largely unknown. For this purpose, we exposed zebrafish, a model organism, to different concentrations of dietary l-selenomethionine (control, 3.5, 11.1, 27.4, and 63.4 μg Se/g dry weight) for a period of 60 days. Cognitive performance of fish was evaluated using a plus maze associative learning paradigm. Oxidative stress, as the main driver of Se neurotoxicity, was assessed by measuring the ratio of reduced to oxidized glutathione (GSH:GSSG), lipid peroxidation (LPO) levels, and mRNA expression of several antioxidant enzymes in the zebrafish brain. Dopamine levels in the brain and the expression of genes involved in dopamine synthesis, storage, reuptake, metabolism, and receptor activation were examined. Moreover, transcription of several synaptic plasticity-related immediate-early and late response genes was determined. Overall, fish fed with the two highest concentrations of dietary Se displayed impaired associative learning. Se exposure also induced oxidative stress in the zebrafish brain, as indicated by a reduction in GSH:GSSG ratio, increased LPO levels, and up-regulation of antioxidant genes in fish treated with the two highest concentrations of Se. An increase in brain dopamine levels associated with altered expression of dopaminergic cell markers was evident in different treatment groups. Moreover, Se exposure led to the down-regulation of immediate-early and late response genes in fish that exhibiting learning impairment. Taken together, the results of this study imply that the induction of oxidative stress and dysregulation of dopaminergic neurotransmission may underlie Se-induced impairment of associative learning in zebrafish.

Toxicity evaluation of Wanzhou watershed of Yangtze Three Gorges Reservior in the flood season in Caenorhabditis elegans

Three Gorges Reservoir (TGR) in the upper stream of Yangtze River in China is a reservoir with the largest and the longest yearly water-level drop. Considering the fact that most of safety assessments of water samples collected from TGR region were based on chemical analysis, we here employed Caenorhabditis elegans to perform in vivo safety assessment of original surface water samples collected from TGR region in the flood season in Wanzhou, Chongqing. Among the examined five original surface water samples, only exposure to original surface water sample collected from backwater area could induce the significant intestinal ROS production, enhance the intestinal permeability, and decrease the locomotion behavior. Additionally, exposure to original surface water sample collected from backwater area altered the expressions of sod-2, sod-5, clk-1, and mev-1. Moreover, mutation of sod-2 or sod-5 was susceptible to the potential toxicity of original surface water sample collected from backwater area on nematodes. Together, our results imply that exposure to surface water sample from the backwater area may at least cause the adverse effects on intestinal function and locomotion behavior in nematodes.

Oral administration of grape seed polyphenol extract restores memory deficits in chronic cerebral hypoperfusion rats

Chronic cerebral hypoperfusion (CCH) has been recognized as an important cause of both vascular dementia and Alzheimer's disease (AD), the two most prominent neurodegenerative diseases causing memory impairment in the elderly. However, an effective therapy for CCH-induced memory impairment has not yet been established. Grape seed polyphenol extract (GSPE) has powerful antioxidant properties and protects neurons and glia during ischemic injury, but its potential use in the prevention of CCH-induced memory impairment has not yet been investigated. Here, CCH-related memory impairment was modeled in rats using permanent bilateral occlusion of the common carotid artery. A Morris water maze task was used to evaluate memory, the levels of acetylcholinesterase, choline acetyltransferase, acetylcholine were used to evaluate cholinergic function, and oxidative stress was assessed by measuring the enzyme activity of superoxide dismutase, glutathione peroxidase, malonic dialdehyde, and catalase. We found that oral administration of GSPE for 1 month can rescue memory deficits. We also found that GSPE restores cholinergic neuronal function and represses oxidative damage in the hippocampus of CCH rats. We propose that GSPE protects memory in CCH rats by reducing ischemia-induced oxidative stress and cholinergic dysfunction. These findings provide a novel application of GSPE in CCH-related memory impairments.

Chronic Dietary Selenomethionine Exposure Induces Oxidative Stress, Dopaminergic Dysfunction, and Cognitive Impairment in Adult Zebrafish (Danio rerio)

The present study was designed to investigate the effects of chronic dietary exposure to selenium (Se) on zebrafish cognition and also to elucidate possible mechanism(s) by which Se exerts its neurotoxicity. To this end, adult zebrafish were exposed to different concentrations of dietary l-selenomethionine (control, 2.3, 9.7, 32.5, or 57.7 μg Se/g dry weight) for 30 days. Cognitive performance of fish was tested using a latent learning paradigm in a complex maze. In addition, we also evaluated oxidative stress biomarkers and the expression of genes involved in dopaminergic neurotransmission in the zebrafish brain. Fish treated with higher dietary Se doses (32.5 and 57.5 μg Se/g) exhibited impaired performance in the latent learning task. The impaired learning was associated with the induction of oxidative stress and altered mRNA expression of dopamine receptors, tyrosine hydroxylase, and dopamine transporter genes in the zebrafish brain. Collectively, our results illustrate that cognitive impairment in zebrafish could be associated with Se-induced oxidative stress and altered dopaminergic neurotransmission in the brain.

Selenium in the Therapy of Neurological Diseases. Where is it Going?

Selenium (₃₄Se), an antioxidant trace element, is an important regulator of brain function. These beneficial properties that Se possesses are attributed to its ability to be incorporated into selenoproteins as an amino acid. Several selenoproteins are expressed in the brain, in which some of them, e.g. glutathione peroxidases (GPxs), thioredoxin reductases (TrxRs) or selenoprotein P (SelP), are strongly involved in antioxidant defence and in maintaining intercellular reducing conditions. Since increased oxidative stress has been implicated in neurological disorders, including Parkinson’s disease, Alzheimer’s disease, stroke, epilepsy and others, a growing body of evidence suggests that Se depletion followed by decreased activity of Se-dependent enzymes may be important factors connected with those pathologies. Undoubtedly, the remarkable progress that has been made in understanding the biological function of Se in the brain has opened up new potential possibilities for the treatment of neurological diseases by using Se as a potential drug. However, further research in the search for optimal Se donors is necessary in order to achieve an effective and safe therapeutic income.

Biological functions of selenium and its potential influence on Parkinson's disease

Parkinson's disease is characterized by the death of dopaminergic neurons, mainly in the substantia nigra, and causes serious locomotor dysfunctions. It is likely that the oxidative damage to cellular biomolecules is among the leading causes of neurodegeneration that occurs in the disease. Selenium is an essential mineral for proper functioning of the brain, and mainly due to its antioxidant activity, it is possible to exert a special role in the prevention and in the nutritional management of Parkinson's disease. Currently, few researchers have investigated the effects of selenium on Parkinson´s disease. However, it is known that very high or very low body levels of selenium can (possibly) contribute to the pathogenesis of Parkinson's disease, because this imbalance results in increased levels of oxidative stress. Therefore, the aim of this work is to review and discuss studies that have addressed these topics and to finally associate the information obtained from them so that these data and associations serve as input to new research.

Degenerin channel activation causes caspase-mediated protein degradation and mitochondrial dysfunction in adult C. elegans muscle

BACKGROUND

Declines in skeletal muscle structure and function are found in various clinical populations, but the intramuscular proteolytic pathways that govern declines in these individuals remain relatively poorly understood. The nematode Caenorhabditis elegans has been developed into a model for identifying and understanding these pathways. Recently, it was reported that UNC-105/degenerin channel activation produced muscle protein degradation via an unknown mechanism.

METHODS

Generation of transgenic and double mutant C. elegans, RNAi, and drug treatments were utilized to assess molecular events governing protein degradation. Western blots were used to measure protein content. Cationic dyes and adenosine triphosphate (ATP) production assays were utilized to measure mitochondrial function.

RESULTS

unc-105 gain-of-function mutants display aberrant muscle protein degradation and a movement defect; both are reduced in intragenic revertants and in let-2 mutants that gate the hyperactive UNC-105 channel. Degradation is not suppressed by interventions suppressing proteasome-mediated, autophagy-mediated, or calpain-mediated degradation nor by suppressors of degenerin-induced neurodegeneration. Protein degradation, but not the movement defect, is decreased by treatment with caspase inhibitors or RNAi against ced-3 or ced-4. Adult unc-105 muscles display a time-dependent fragmentation of the mitochondrial reticulum that is associated with impaired mitochondrial membrane potential and that correlates with decreased rates of maximal ATP production. Reduced levels of CED-4, which is sufficient to activate CED-3 in vitro, are observed in unc-105 mitochondrial isolations.

CONCLUSIONS

Constitutive cationic influx into muscle appears to cause caspase degradation of cytosolic proteins as the result of mitochondrial dysfunction, which may be relevant to ageing and sarcopenia.

The Functions of Antioxidants and Heat Shock Proteins Are Altered in the Immune Organs of Selenium-Deficient Broiler Chickens

Despite increasing evidence indicating the essential involvement of selenium (Se) in the immune system, the effect of Se deficiency on the regulation of oxidative stress and heat shock proteins (Hsps) in broiler chickens is still unclear. In the present study, we established an exudative diathesis (ED) broiler chicken model caused by Se deficiency. We then analyzed histological observations and detected the expression levels of Hsps and antioxidant indexes in immune tissues. The antioxidant function declined remarkably, and most of the Hsp expression levels increased significantly in the spleen, thymus, and bursa of Fabricius of the broiler chicks with ED (except the messenger RNA (mRNA) levels of Hsp27, Hsp40, and Hsp70, which decreased in thymus tissues from the treatment groups); therefore, constitutive oxidation resistance and higher Hsps in broiler chicks with ED caused defects in immune organ morphology and function, as evidenced by abnormal histological structures: red pulp broadening and lymphocytes in the cortex and medulla of the thymic lobule decreased distinctly and distributed loosely. These results underscore the importance of Se in establishing an immune organ microenvironment conducive to normal function.

Importance of selenium and selenoprotein for brain function: From antioxidant protection to neuronal signalling

Multiple biological functions of selenium manifest themselves mainly via 25 selenoproteins that have selenocysteine at their active centre. Selenium is vital for the brain and seems to participate in the pathology of disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and epilepsy. Since selenium was shown to be involved in diverse functions of the central nervous system, such as motor performance, coordination, memory and cognition, a possible role of selenium and selenoproteins in brain signalling pathways may be assumed. The aim of the present review is to analyse possible relations between selenium and neurotransmission. Selenoproteins seem to be of special importance in the development and functioning of GABAergic (GABA, γ-aminobutyric acid) parvalbumin positive interneurons of the cerebral cortex and hippocampus. Dopamine pathway might be also selenium dependent as selenium shows neuroprotection in the nigrostriatal pathway and also exerts toxicity towards dopaminergic neurons under higher concentrations. Recent findings also point to acetylcholine neurotransmission involvement. The role of selenium and selenoproteins in neurotransmission might not only be limited to their antioxidant properties but also to inflammation, influencing protein phosphorylation and ion channels, alteration of calcium homeostasis and brain cholesterol metabolism. Moreover, a direct signalling function was proposed for selenoprotein P through interaction with post-synaptic apoliprotein E receptors 2 (ApoER2).

In vitro dopaminergic neurotoxicity of pesticides: a link with neurodegeneration?

Around the globe, chemical compounds are used to treat or repel pests and plagues that pose a threat to food and feed production. From epidemiological studies, it is known that there is a link between exposure to certain chemical classes of these so-called pesticides and the prevalence of neurodegenerative disorders such as Parkinson's disease in humans. However, which particular compound(s) account for this link or what underlying mechanisms are involved is still largely unresolved. The degenerative process in Parkinson's disease is largely limited to the dopaminergic neurons in the basal ganglia. Cellular mechanisms that are implicated in parkinsonian neurodegeneration include mitochondrial dysfunction, oxidative stress, disturbance of intracellular calcium homeostasis and endoplasmic reticulum (ER) stress. A major characteristic that distinguishes the dopaminergic neurons in the basal ganglia from other dopaminergic neurons is a particular reliance on intracellular calcium for spontaneous activity. Considering the energy consuming nature of maintenance of the intracellular calcium homeostasis and its involvement in life and death of a neuron, this may explain the specific vulnerability of this neuronal population. Despite a large variation in primary mechanism of action it has been demonstrated that pesticides from different classes disturb intracellular calcium homeostasis, thus interfering with intracellular calcium signalling. This relates to altered dopaminergic signalling, disturbed protein homeostasis and increased oxidative stress. Therefore, effects of (mixtures of) pesticides on the intracellular calcium homeostasis may play a role in the development of Parkinson's disease in humans. Although human exposure to pesticides via e.g. food often occurs in complex mixtures, (human) risk assessment is largely based on the assessment of single compounds. The discovery of common modes of action across different classes of pesticides therefore underpins the urgency of development of new models and approaches in risk assessment.

Role of environmental contaminants in the etiology of Alzheimer's disease: a review

Alzheimer's dis ease (AD) is a leading cause of mortality in the developed world with 70% risk attributable to genetics. The remaining 30% of AD risk is hypothesized to include environmental factors and human lifestyle patterns. Environmental factors possibly include inorganic and organic hazards, exposure to toxic metals (aluminium, copper), pesticides (organochlorine and organophosphate insecticides), industrial chemicals (flame retardants) and air pollutants (particulate matter). Long term exposures to these environmental contaminants together with bioaccumulation over an individual's life-time are speculated to induce neuroinflammation and neuropathology paving the way for developing AD. Epidemiologic associations between environmental contaminant exposures and AD are still limited. However, many in vitro and animal studies have identified toxic effects of environmental contaminants at the cellular level, revealing alterations of pathways and metabolisms associated with AD that warrant further investigations. This review provides an overview of in vitro, animal and epidemiological studies on the etiology of AD, highlighting available data supportive of the long hypothesized link between toxic environmental exposures and development of AD pathology.

Behavioral and dopaminergic damage induced by acute iron toxicity in Caenorhabditis elegans

Iron (Fe) exposure, results in multiple biological defects in C. elegans, including reproductive and motor impairment, which may be related to oxidative stress and neuronal damage.

Selenium, selenoproteins and neurodegenerative diseases

A review of selenium's essential role in normal brain function and its potential involvement in neurodegenerative diseases.

Use of Caenorhabditis elegans as a model to study Alzheimer's disease and other neurodegenerative diseases

Advances in research and technology has increased our quality of life, allowed us to combat diseases, and achieve increased longevity. Unfortunately, increased longevity is accompanied by a rise in the incidences of age-related diseases such as Alzheimer’s disease (AD). AD is the sixth leading cause of death, and one of the leading causes of dementia amongst the aged population in the USA. It is a progressive neurodegenerative disorder, characterized by the prevalence of extracellular Aβ plaques and intracellular neurofibrillary tangles, derived from the proteolysis of the amyloid precursor protein (APP) and the hyperphosphorylation of microtubule-associated protein tau, respectively. Despite years of extensive research, the molecular mechanisms that underlie the pathology of AD remain unclear. Model organisms, such as the nematode, Caenorhabditis elegans, present a complementary approach to addressing these questions. C. elegans has many advantages as a model system to study AD and other neurodegenerative diseases. Like their mammalian counterparts, they have complex biochemical pathways, most of which are conserved. Genes in which mutations are correlated with AD have counterparts in C. elegans, including an APP-related gene, apl-1, a tau homolog, ptl-1, and presenilin homologs, such as sel-12 and hop-1. Since the neuronal connectivity in C. elegans has already been established, C. elegans is also advantageous in modeling learning and memory impairments seen during AD. This article addresses the insights C. elegans provide in studying AD and other neurodegenerative diseases. Additionally, we explore the advantages and drawbacks associated with using this model.

Assessment of selenium toxicity on the life cycle of Caenorhabditis elegans

Selenium (Se) is a growing problem of global concern. Se can cause adverse effects on reproductive systems, which have been linked to declines in animal populations. The soil nematode Caenorhabditis elegans (C. elegans) is a ubiquitous soil organism that is increasingly utilized as a model organism in aquatic and soil toxicology. In the present study, the experimental data for individual body length, survival rate, brood size, and hatching rate were used to evaluate the possible effects of selenite [Se(IV)] on C. elegans. A stage-classified matrix model was applied to the experimental data to provide information on the population dynamics of C. elegans and to assess the Se(IV)-affected asymptotic population growth rate. Estimates of the survival probability showed significant decreases in survival at all stages when C. elegans was exposed to Se(IV). The growth probability of C. elegans in the L1 stage showed the most significant decline, from 0.11 h(-1) (for the control) to 0.04 h(-1) [for exposure to 3 mM Se(IV)]. These results showed that Se(IV) has a profound impact on C. elegans population dynamics. The asymptotic population growth rate (λ) was found to range from 1.00 to 0.64 h(-1) for increasing Se(IV) concentrations, implying a potential risk of population decrease for C. elegans exposure to a Se(IV)-contaminated environment. Our study shows how a mechanistic view based on the Se(IV) effects on the soil nematode C. elegans can promote a life cycle toxicity assessment. An important implication of this analysis is that mathematical models can be used to produce a population stage structure, to give clarity to the analysis of the key population-level endpoint (the asymptotic population growth rate) of population dynamics, and to evaluate the influences for the response of other species to environmental Se. These models sequentially provide candidate environmental criteria for the evaluation of the population impact of Se.