SN56 neuronal cell death after 24 h and 14 days chlorpyrifos exposure through glutamate transmission dysfunction, increase of GSK-3β enzyme, β-amyloid and tau protein levels

Decoding the Role of Neurotrophins in Glycogen Synthase Kinase 3-Beta Regulation in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most prevalent contributor to dementia in elderly individuals. Numerous signalling pathways influencing AD pathophysiology, involving glycogen synthase kinase-3β (Gsk-3β), have been investigated extensively as potential therapeutic targets. Gsk-3β is a critical factor in AD pathogenesis that affects several key hallmarks of the disease notably tau phosphorylation, amyloid-β generation, cognition, neurogenesis, and synaptic integrity. Neurotrophins are small proteins that are critical for maintaining neuronal health and function and may be used to treat neurodegenerative diseases. Notably, the dysregulation of certain neurotrophins and their receptors is also linked with AD which is a major contributor to neurodegeneration. Studies indicated that neurotrophins and their modulators are capable of protecting neurons by blocking the Gsk-3β activity suggesting a potential link for neuroprotection. Neurotrophins support the survival of neurons by regulating Gsk-3β activity. Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) signalling pathways activate Trk receptors that trigger downstream signalling cascades that subsequently inhibit Gsk-3β activity and reduce AD-related neuropathology. We also explore the role of modulators including phosphatases, kinase cascades, and other regulatory proteins that cross paths with neurotrophin-Gsk-3β signalling. In conclusion, this manuscript summarizes both direct and indirect regulatory roles of neurotrophins and modulators on Gsk-3β to understand the intricate mechanisms driving neurodegeneration in AD.

Analyzing the neurotoxic effects of anatoxin-a and saxitoxin in zebrafish larvae

Global warming due to climate change, as well as freshwater eutrophication caused by anthropogenic activities are responsible, among other factors, for an increasing occurrence of harmful algal blooms (HABs) in aquatic systems. These can lead to the generation of cyanotoxins, secondary metabolites coming from cyanobacteria, producing adverse effects in living organisms including death. This research aims to study the effects that two neurotoxins, anatoxin-a (ATX-a) and saxitoxin (STX), have on living organisms. Once the stability of both compounds in water was determined for a 24 h period using ultra-high-performance liquid chromatography coupled to a triple quadrupole mass spectrometer (UPLC-MS/MS), zebrafish larvae were exposed to different levels of toxins (1 ng L-1, 10 ng L-1, 100 ng L-1 and 1 μg L-1) during 24 h. Behavioral studies including vibrational startle response (VSR), habituation to vibrational stimuli, basal locomotor activity (BLM) and visual motor response (VMR) were performed using Danio Vision system, and neurotransmitters (NTs) from 15-head pools of control and exposed zebrafish larvae were extracted and analyzed by UPLC-MS/MS. Both compounds induced hypolocomotion in the individuals, while 10 and 100 ng L-1 of ATX-a significantly increased methionine (120 % and 126 %, respectively) and glutamate levels (118 % and 129 %, respectively). Saxitoxin enhanced 3-metoxytyramine (3-MT) levels at 1 ng L-1 by 185 %. The findings of this study show that both studied cyanotoxins influence the behavior of zebrafish larvae as well as their metabolism.

Increased Levels of Phosphorylated-P38α Induce WNT/β-Catenin and NGF/P75NTR/TrkA Pathways Disruption and SN56 Cell Death following Single and Repeated Chlorpyrifos Treatment

Chlorpyrifos (CPF) biocide, exposure to which is mainly produced in the human population through diet, induces several neurotoxic effects. CPF single and repeated exposure induces memory and learning disorders, although the mechanisms that produce these outcomes are complex and not well understood. CPF treatment (single and repeated) of cholinergic septal SN56 cells induced an increase in phosphorylated-P38α levels that led to WNT/β-Catenin and NGF/P75NTR/TrkA pathways disruption and cell death. These results provide new knowledge on the mechanisms that mediate CPF basal forebrain cholinergic neuronal loss induced by CPF single and repeated exposure and can help unravel the way through which this compound produces cognitive decline and develop efficient treatments against these effects.

Implications of organophosphate pesticides on brain cells and their contribution toward progression of Alzheimer's disease

The most widespread neurodegenerative disorder, Alzheimer's disease (AD) is marked by severe behavioral abnormalities, cognitive and functional impairments. It is inextricably linked with the deposition of amyloid β (Aβ) plaques and tau protein in the brain. Loss of white matter, neurons, synapses, and reactive microgliosis are also frequently observed in patients of AD. Although the causative mechanisms behind the neuropathological alterations in AD are not fully understood, they are likely influenced by hereditary and environmental factors. The etiology and pathogenesis of AD are significantly influenced by the cells of the central nervous system, namely, glial cells and neurons, which are directly engaged in the transmission of electrical signals and the processing of information. Emerging evidence suggests that exposure to organophosphate pesticides (OPPs) can trigger inflammatory responses in glial cells, leading to various cascades of events that contribute to neuroinflammation, neuronal damage, and ultimately, AD pathogenesis. Furthermore, there are striking similarities between the biomarkers associated with AD and OPPs, including neuroinflammation, oxidative stress, dysregulation of microRNA, and accumulation of toxic protein aggregates, such as amyloid β. These shared markers suggest a potential mechanistic link between OPP exposure and AD pathology. In this review, we attempt to address the role of OPPs on altered cell physiology of the brain cells leading to neuroinflammation, mitochondrial dysfunction, and oxidative stress linked with AD pathogenesis.

The susceptibility of humans to neurodegenerative and neurodevelopmental toxicities caused by organophosphorus pesticides

The toxicology field is concerned with the impact of organophosphorus (OP) compounds on human health. These compounds have been linked to an increased risk of neurological disorders, including neurodegenerative and neurodevelopmental diseases. This article aims to review studies on the role of OP compounds in developing these neurological disorders and explore how genetic variations can affect susceptibility to the neurotoxicity of these pesticides. Studies have shown that exposure to OP compounds can lead to the development of various neurological disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), attention deficit hyperactivity disorder (ADHD), autism, intellectual disability, and other developmental neurotoxicities. Apart from inhibiting the cholinesterase enzyme, OP compounds are believed to cause other pathological mechanisms at both the extracellular level (cholinergic, serotonergic, dopaminergic, glutamatergic, and GABAergic synapses) and the intracellular level (oxidative stress, mitochondrial dysfunction, inflammation, autophagy, and apoptosis) that contribute to these disorders. Specific genetic polymorphisms, including PON1, ABCB1, NOS, DRD4, GST, CYP, and APOE, have increased the risk of developing OP-related neurological disorders.

Effect of pesticides on phosphorylation of tau protein, and its influence on Alzheimer's disease

Alzheimer's disease (AD) is a progressive and neurodegenerative illness which results in alterations in cognitive development. It is characterized by loss/dysfunction of cholinergic neurons, and formation of amyloid plaques, and formation of neurofibrillary tangles, among other changes, due to hyperphosphorylation of tau-protein. Exposure to pesticides in humans occurs frequently due to contact with contaminated food, water, or particles. Organochlorines, organophosphates, carbamates, pyrethroids and neonicotinoids are associated with the most diagnosed incidents of severe cognitive impairment. The aim of this study was to determine the effects of these pesticides on the phosphorylation of tau protein, and its cognitive implications in the development of AD. It was found that exposure to pesticides increased the phosphorylation of tau protein at sites Ser198, Ser199, Ser202, Thr205, Ser396 and Ser404. Contact with these chemicals altered the enzymatic activities of cyclin-dependent kinase 5 and glycogen synthase kinase 3 beta, and protein phosphatase-2A. Moreover, it altered the expression of the microtubule associated protein tau gene, and changed levels of intracellular calcium. These changes affected tau protein phosphorylation and neuroinflammation, and also increased oxidative stress. In addition, the exposed subjects had poor level of performance in tests that involved evaluation of novelty, as test on verbal, non-verbal, spatial memory, attention, and problem-solving skills.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Bisphenol-A Neurotoxic Effects on Basal Forebrain Cholinergic Neurons In Vitro and In Vivo

The widely used plasticizer bisphenol-A (BPA) is well-known for producing neurodegeneration and cognitive disorders, following acute and long-term exposure. Although some of the BPA actions involved in these effects have been unraveled, they are still incompletely known. Basal forebrain cholinergic neurons (BFCN) regulate memory and learning processes and their selective loss, as observed in Alzheimer's disease and other neurodegenerative diseases, leads to cognitive decline. In order to study the BPA neurotoxic effects on BFCN and the mechanisms through which they are induced, 60-day old Wistar rats were used, and a neuroblastoma cholinergic cell line from the basal forebrain (SN56) was used as a basal forebrain cholinergic neuron model. Acute treatment of rats with BPA (40 µg/kg) induced a more pronounced basal forebrain cholinergic neuronal loss. Exposure to BPA, following 1- or 14-days, produced postsynaptic-density-protein-95 (PSD95), synaptophysin, spinophilin, and N-methyl-D-aspartate-receptor-subunit-1 (NMDAR1) synaptic proteins downregulation, an increase in glutamate content through an increase in glutaminase activity, a downregulation in the vesicular-glutamate-transporter-2 (VGLUT2) and in the WNT/β-Catenin pathway, and cell death in SN56 cells. These toxic effects observed in SN56 cells were mediated by overexpression of histone-deacetylase-2 (HDAC2). These results may help to explain the synaptic plasticity, cognitive dysfunction, and neurodegeneration induced by the plasticizer BPA, which could contribute to their prevention.

Bbc3 Loss Enhances Survival and Protein Clearance in Neurons Exposed to the Organophosphate Pesticide Chlorpyrifos

Exposure to environmental toxicants can increase the risk of developing age-related neurodegenerative disorders. Exposure to the widely used organophosphate pesticide chlorpyrifos (CPF) is associated with increased risk of developing Alzheimer's disease and Parkinson's disease, but the cellular mechanisms underlying CPF toxicity in neurons are not completely understood. We evaluated CPF toxicity in mouse primary cortical neuronal cultures, using RNA-sequencing to identify cellular pathways modulated by CPF. CPF exposure altered the expression of genes associated with intrinsic apoptosis, significantly elevating expression of the pro-apoptotic mediator Bbc3/Puma. Bbc3 loss attenuated CPF driven neurotoxicity, induction of other intrinsic apoptosis regulatory genes including Trp53 and Pmaip1 (encoding the NOXA protein), and cleavage of apoptosis executors caspase 3 and poly (ADP-ribose) polymerase (PARP). CPF exposure was associated with enhanced expression of endoplasmic reticulum stress-related genes and proteins and the accumulation of high molecular weight protein species in primary neuronal cultures. No evidence of alterations in the ubiquitin-proteosome system were observed, however, autophagy-related proteins were upregulated in CPF-treated Bbc3-/- neuronal cultures compared with identically exposed WT cultures. Elevated autophagy-related protein expression in Bbc3-/- neuronal cultures was associated with a reduction in CPF-induced high molecular weight alpha-synuclein and tau immunoreactive protein aggregates. Studies indicate that Bbc3-/- neuronal cultures enhance the endoplasmic reticulum stress response and upregulate protein clearance mechanisms as a component of resistance to CPF-mediated toxicity.

Chlorpyrifos induces cell proliferation in MCF-7 and MDA-MB-231 cells, through cholinergic and Wnt/β-catenin signaling disruption, AChE-R upregulation and oxidative stress generation after single and repeated treatment

Chlorpyrifos (CPF) biocide, is associated with breast cancer. The processes underlying this association have not been elucidated to date. CPF increases MCF-7 and MDA-MB-231 cell proliferation after acute and long-term treatment, partially through KIAA1363 overexpression and aryl-hydrocarbon receptor activation but also through estrogen receptor-alpha activation after 24 h exposure in MCF-7 cells, suggesting other mechanisms may be involved. CPF induces reactive oxygen species (ROS) generation, acetylcholine accumulation, and overexpression of acetylcholinesterase-R/S (AChE-R/S) variants, while it also alters the Wnt/β-catenin pathway, both in vitro and in vivo, in processes different from cancer. These latter mechanisms are also linked to cell proliferation and could mediate this effect induced by CPF. Our results show that CPF (0.01-100 μM), following one-day and fourteen-days treatment, respectively, induced ROS generation and lipid peroxidation, and acetylcholine accumulation due to AChE inhibition, Wnt/β-catenin up- or downregulation depending on the CPF treatment concentration, and AChE-R and AChE-S overexpression, with the latter being mediated through GSK-3β activity alteration. Finally, CPF promoted cell division through ACh and ROS accumulation, AChE-R overexpression, and Wnt/β-catenin signaling disruption. Our results provide novel information on the effect of CPF on human breast cancer cell lines that may help to explain its involvement in breast cancer.

Deltamethrin modulates the native structure of Hen Egg White Lysozyme and induces its aggregation at physiological pH

Deltamethrin, a type II pyrethroid pesticide was initially considered as safe for human use. Recent studies have reported several pathophysiological effects of deltamethrin on human and non-human species. However, its effect on structure and function of protein leading to progressive neurodegeneration is poorly understood. In present study, we investigated the interaction of deltamethrin with Hen Egg White Lysozyme (HEWL) at physiological pH and tried to understand the effect of pesticide on structure and function of protein. Employing different biophysical techniques, we shown that deltamethrin induces in vitro aggregation of HEWL in concentration dependent manner. Interaction of pesticide with different amino acids, followed by exposure of hydrophobic regions was driving force of aggregation process. Apart from modulating the hydrophobic domain, deltamethrin is observed to reduce α-helical and promote β-sheet content of lysozyme, eventually converting the globular protein into ThT sensitive amyloid fibrils and amorphous aggregates. Our study also indicate that deltamethrin induced aggregation reduces the catalytic activity of lysozyme.

Caffeic acid phenethyl ester reversed cadmium-induced cell death in hippocampus and cortex and subsequent cognitive disorders in mice: Involvements of AMPK/SIRT1 pathway and amyloid-tau-neuroinflammation axis

Exposure to nonbiodegradable cadmium (Cd) causes many health problems including the damage to the nervous system. This study aimed to increase knowledge about its neurotoxic effects and the neuroprotective potential of caffeic acid phenethyl ester (CAPE, a polyphenol abundant in honeybee propolis). In mice, CAPE (10 μmol/kg/day body weight) attenuated significantly learning and memory deficits induced by CdCl₂ (1.5 mg/kg/day body weight). For the CdCl₂-treated mice, CAPE increased crossing number in open field test, decreased the alternation in Y-maze test, and increased the latency time and error number in step down test. CAPE also inhibited CdCl₂-initiated Aβ accumulation and activation of pro-inflammatory factors and microglia in the brains. Therefore, CAPE could be a food-derived neuroprotective agent against Cd-induced neurotoxicity and neurodegenerative disorders, through attenuating neuronal apoptosis and neuroinflammation via the AMPK/SIRT1 pathway and amyloid-tau-neuroinflammation axis.

Neuropathological Mechanisms Associated with Pesticides in Alzheimer's Disease

Environmental toxicants have been implicated in neurodegenerative diseases, and pesticide exposure is a suspected environmental risk factor for Alzheimer’s disease (AD). Several epidemiological analyses have affirmed a link between pesticides and incidence of sporadic AD. Meanwhile, in vitro and animal models of AD have shed light on potential neuropathological mechanisms. In this paper, a perspective on neuropathological mechanisms underlying pesticides’ induction of AD is provided. Proposed mechanisms range from generic oxidative stress induction in neurons to more AD-specific processes involving amyloid-beta (Aβ) and hyperphosphorylated tau (p-tau). Mechanisms that are more speculative or indirect in nature, including somatic mutation, epigenetic modulation, impairment of adult neurogenesis, and microbiota dysbiosis, are also discussed. Chronic toxicity mechanisms of environmental pesticide exposure crosstalks in complex ways and could potentially be mutually enhancing, thus making the deciphering of simplistic causal relationships difficult.

Proteasome 20S and Rab5 Alteration after 24 h and 14 Days Chlorpyrifos Exposure Lead to β-Amyloid and Tau Protein Level Increases and SN56 Neuronal Cell Death

The biocide chlorpyrifos (CPF) was shown to produce cognition impairment following single and long-term exposure. The complete mechanisms that lead to the CPF induced cognitive disorders remain to be discovered. Aβ and tau proteins production was induced in basal forebrain SN56 cholinergic cells, by CPF, through proteasome 20S inhibition and Rab5 overexpression, leading to cell death both after acute and repeated administration, which was related with cognitive disorders induction. The results obtained in our study procure novel information related to the mechanisms involved in CPF neurodegeneration, which could be responsible for cognitive dysfunction and may lead to a promising alternative treatment of these effects.

Cadmium alters heat shock protein pathways in SN56 cholinergic neurons, leading to Aβ and phosphorylated Tau protein generation and cell death

Cadmium, a neurotoxic environmental compound, produces cognitive disorders, although the mechanism remains unknown. Cadmium induces a more pronounced cell death on cholinergic neurons from basal forebrain (BF), mediated, in part, by increase in Aβ and total and phosphorylated Tau protein levels, which may explain cadmium effects on learning and memory processes. Cadmium downregulates the expression of heat shock proteins (HSPs) HSP 90, HSP70 and HSP27, and of HSF1, the master regulator of the HSP pathway. HSPs proteins reduce the production of Aβ and phosphorylated Tau proteins and avoid cell death pathways induction. Thus, we hypothesized that cadmium induced the production of Aβ and Tau proteins by HSP pathway disruption through HSF1 expression alteration, leading to BF cholinergic neurons cell death. Our results show that cadmium downregulates HSF1, leading to HSP90, HSP70 and HSP27 gene expression downregulation in BF SN56 cholinergic neurons. In addition, cadmium induced Aβ and total and phosphorylated Tau proteins generation, mediated partially by HSP90, HSP70 and HSP27 disruption, leading to cell death. These results provide new understanding of the mechanisms contributing to cadmium harmful effects on cholinergic neurons.