Permethrin, but not deltamethrin, increases spontaneous glutamate release from hippocampal neurons in culture☆

Acetylcholinesterase biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine neurotransmitter: A literature review

Neurotoxic pesticides are a group of chemicals that pose a severe threat to both human health and the environment. These molecules are also known to accumulate in the food chain and persist in the environment, which can lead to long-term exposure and adverse effects on non-target organisms. The detrimental effects of these pesticides on neurotransmitter levels and function can lead to a range of neurological and behavioral symptoms, which are closely associated with neurodegenerative diseases. Hence, the accurate and reliable detection of these neurotoxic pesticides and associated neurotransmitters is essential for clinical applications, such as diagnosis and treatment. Over the past few decades, acetylcholinesterase (AchE) biosensors have emerged as a sensitive and reliable tool for the electrochemical detection of neurotoxic pesticides and acetylcholine. These biosensors can be tailored to utilize the high specificity and sensitivity of AchE, enabling the detection of these chemicals. Additionally, enzyme immobilization and the incorporation of nanoparticles have further improved the detection capabilities of these biosensors. AchE biosensors have shown tremendous potential in various fields, including environmental monitoring, clinical diagnosis, and pesticide residue analysis. This review summarizes the advancements in AchE biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine over the past two decades.

Tefluthrin: metabolism, food residues, toxicity, and mechanisms of action

Tefluthrin is a Type I pyrethroid insecticide widely used all over the world. Residues of tefluthrin in various agricultural and animal-derived products may be related to potential human health risks. Tefluthrin metabolism in mammals involves hydrolysis of the ester bond to form cyclopropane acid and 4-methylbenzyl alcohol moieties, followed by oxidation. In this review manuscript, we provide crucial information regarding the toxicity of pyrethroids and propose natural antioxidants for amelioration poisoning in humans and animals. We call for the rational use of tefluthrin as an agrochemical product and for greater attention to the residual toxicity caused by tefluthrin in primary and succeeding crops. This greater attention is required given the global use of tefluthrin.

Exposure to Sub-Lethal Doses of Permethrin Is Associated with Neurotoxicity: Changes in Bioenergetics, Redox Markers, Neuroinflammation and Morphology

Permethrin (PERM) is a member of the class I family of synthetic pyrethroids. Human use has shown that it affects different systems, with wide health dysfunctions. Our aim was to determine bioenergetics, neuroinflammation and morphology changes, as redox markers after subacute exposure to PERM in rats. We used MDA determination, protein carbonyl assay, mitochondrial O₂ consumption, expression of pro-inflammatory cytokines and a deep histopathological analysis of the hippocampus. PERM (150 mg/kg and 300 mg/kg body weight/day, o.v.) increased lipoperoxidation and carbonylated proteins in a dose-dependent manner in the brain regions. The activities of antioxidant enzymes glutathione peroxidase, reductase, S-transferase, catalase, and superoxide dismutase showed an increase in all the different brain areas, with dose-dependent effects in the cerebellum. Cytokine profiles (IL-1β, IL-6 and TNF-α) increased in a dose-dependent manner in different brain tissues. Exposure to 150 mg/kg of permethrin induced degenerated and/or dead neurons in the rat hippocampus and induced mitochondrial uncoupling and reduction of oxidative phosphorylation and significantly decreased the respiratory parameters state 3-associated respiration in complex I and II. PERM exposure at low doses induces reactive oxygen species production and imbalance in the enzymatic antioxidant system, increases gene expression of pro-inflammatory interleukins, and could lead to cell damage mediated by mitochondrial functional impairment.

Emerging role of glutamate in the pathophysiology and therapeutics of Gulf War illness

Gulf War illness (GWI) is a chronic and multi-symptomatic disorder affecting veterans who served in the Gulf War. The commonly reported symptoms in GWI veterans include mood problems, cognitive impairment, muscle and joint pain, migraine/headache, chronic fatigue, gastrointestinal complaints, skin rashes, and respiratory problems. Neuroimaging studies have revealed significant brain structure alterations in GWI veterans, including subcortical atrophy, decreased volume of the hippocampus, reduced total grey and white matter, and increased brain white matter axial diffusivity. These brain changes may contribute to or increase the severities of the GWI-related symptoms. Epidemiological studies have revealed that neurotoxic exposures and stress may be significant contributors to the development of GWI. However, the mechanism underlying how the exposure and stress could contribute to the multi-symptomatic disorder of GWI remains unclear. We and others have demonstrated that rodent models exposed to GW-related agents and stress exhibited higher extracellular glutamate levels, as well as impaired structure and function of glutamatergic synapses. Restoration of the glutamatergic synapses ameliorated the GWI-related pathological and behavioral deficits. Moreover, recent studies showed that a low-glutamate diet reduced multiple symptoms in GWI veterans, suggesting an important role of the glutamatergic system in GWI. Currently, growing evidence has indicated that abnormal glutamate neurotransmission may contribute to the GWI symptoms. This review summarizes the potential roles of glutamate dyshomeostasis and dysfunction of the glutamatergic system in linking the initial cause to the multi-symptomatic outcomes in GWI and suggests the glutamatergic system as a therapeutic target for GWI.

Restoring tripartite glutamatergic synapses: A potential therapy for mood and cognitive deficits in Gulf War illness

Gulf War illness is associated with a combination of exposure to war-related chemical agents and traumatic stress. Currently, there are no effective treatments, and the pathophysiology remains elusive. Neurological problems are among the most commonly reported symptoms. In this study, we investigated the glutamatergic system in the hippocampi of mice exposed to war-related chemical agents and stress. Mice developed Gulf War illness-like symptoms, including mood deficits, cognitive impairments, and fatigue. They exhibited the following pathological changes in hippocampi: elevated extracellular glutamate levels, impaired glutamatergic synapses, astrocyte atrophy, loss of interneurons, and decreased neurogenesis. LDN/OSU-215111 is a small-molecule that can strengthen the structure and function of both the astrocytic processes and the glutamatergic synapses that together form the tripartite synapses. We found that LDN/OSU-215111 effectively prevented the development of mood and cognitive deficits in mice when treatment was implemented immediately following the exposure. Moreover, when symptoms were already present, LDN/OSU-215111 still significantly ameliorated these deficits; impressively, benefits were sustained one month after treatment cessation, indicating disease modification. LDN/OSU-215111 effectively normalized hippocampal pathological changes. Overall, this study provides strong evidence that restoration of tripartite glutamatergic synapses by LDN/OSU-215111 is a potential therapy for Gulf War illness.

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Exposure to Gulf War-related agents and stress causes long-term hippocampal glutamatergic synapses impairment.

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LDN/OSU-215111, a small-molecule that enhances tripartite synapses, normalizes hippocampal deficits in a mouse model of GWI.

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LDN/OSU-215111 effectively ameliorates mood deficits, cognitive impairments, and fatigue in a mouse model of GWI.

Relative toxicity for indoor semi volatile organic compounds based on neuronal death

BACKGROUND

Semi Volatile Organic Compounds (SVOCs) are contaminants commonly found in dwellings as a result of their use as plasticizers, flame retardants, or pesticides in building materials and consumer products. Many SVOCs are suspected of being neurotoxic, based on mammal experimentation (impairment of locomotor activity, spatial learning/memory or behavioral changes), raising the question of cumulative risk assessment. The aim of this work is to estimate the relative toxicity of such SVOCs, based on neuronal death.

METHOD

SVOCs fulfilling the following conditions were included: detection frequency >10% in dwellings, availability of data on effects or mechanism of action for neurotoxicity, and availability of dose-response relationships based on cell viability assays as a proxy of neuronal death. Benchmark concentration values (BMC) were estimated using a Hill model, and compared to assess relative toxicity.

RESULTS

Of the 58 SVOCs selected, 28 were suspected of being neurotoxic in mammals, and 21 have been documented as inducing a decrease in cell viability in vitro. 13 have at least one dose-response relationship that can be used to derive a BMC based on a 10% fall in neuronal viability. Based on this in vitro endpoint, PCB-153 appeared to be the most toxic compound, having the lowest BMC₁₀ (0.072μM) and diazinon the least toxic compound, having the highest BMC₁₀ (94.35μM). We showed that experimental designs (in particular choice of cell lines) had a significant influence on BMC calculation.

CONCLUSION

For the first time, the relative in vitro toxicity of 13 indoor contaminants belonging to different chemical families has been assessed on the basis of neuronal cell viability. Lack of comparable toxicity datasets limits the number of SVOCs that can be included. More standardized protocols in terms of cell lines, species and exposure duration should be developed with a view to cumulative risk assessment.

Deltamethrin affects the expression of voltage-gated calcium channel α1 subunits and the locomotion, egg-laying, foraging behavior of Caenorhabditis elegans

Deltamethrin belongs to the class of synthetic pyrethroids, which are being widely used as insecticides in agricultural practices. Voltage-gated sodium channels (VGSCs) are the primary targets of these chemicals for toxicity to insects. Caenorhabditis elegans (C. elegans) does not have VGSCs but is susceptible to deltamethrin. Recent findings have suggested that pyrethroids can affect voltage-gated calcium channels (VGCCs). However, it remains elusive whether deltamethrin induces toxicity to C. elegans via modulating the activity of VGCCs. To identify the potential target of deltamethrin, we exposed C. elegans to different concentrations of deltamethrin and Ca²⁺ channel blockers for different times, characterized the behavioral toxicity of deltamethrin on C. elegans, and determined the expression of egl-19, unc-2, and cca-1, which encode the α1-subunit of the L-, R/N/P/Q-, and T-type VGCC, respectively. We found that deltamethrin inhibited the locomotion, egg-laying and foraging ability of C. elegans in a concentration dependent manner. We also showed that body length of worms on agar plates containing 200mgL^-1 deltamethrin for 12h was not significantly different from controls, whereas the cholinesterase inhibitor carbofuran caused hypercontraction which is a characteristic of organophosphates and carbamates, suggesting that deltamethrin's mode of action is distinct from those nematicides. In addition, unc-2 was significantly up-regulated following 0.05mgL^-1 deltamethrin exposure for 24h; while egl-19 and cca-1 were significantly up-regulated following 5 and 50mgL^-1 deltamethrin exposure for 24h. Further tests of worms' sensitivity and expression of three α1-subunits of VGCC to Ca²⁺ channel blockers indicate that deltamethrin may induce toxic behavior C. elegans via modulation of the expression of the α1-subunits of VGCC. This study provides insights into the linkage between deltamethrin-induced toxic behavior and the regulation of α1-subunits of VGCC in C. elegans.

This can't be stressed enough: The contribution of select environmental toxicants to disruption of the stress circuitry and response

Integration of the hypothalamic-pituitary-adrenal (HPA) axis and the limbic system through glucocorticoid signaling is imperative in initiating and regulating a suitable stress response following real or perceived threats. Dysfunction of these circuits that results in a persistent or inhibited glucocorticoid secretion can severely affect processing of stressful experiences and lead to risk for developing further psychiatric pathology. Exposure to toxic chemicals found in our environment, including pesticides, metals, and industrial compounds, have been shown to have significant impact on neurological health and disease. Indeed, studies have begun to identify the HPA axis and limbic system as potential targets of many of these environmental chemicals, suggesting a possible environmental risk for damage to the stress circuit and response to stressful stimuli. This review will focus on our current understanding of the impact exposure to environmental toxicants, including bisphenol A and lead, has on the synaptic physiology of the HPA axis and limbic system and how this contributes to an alteration in behavior output. Further, this discussion will provide a starting point to continue to couple novel toxicological and neurological approaches to elaborate our understanding of the influence of environmental chemicals on the stress response and pathology.

Effects of monoterpenes on ion channels of excitable cells

Monoterpenes are a structurally diverse group of phytochemicals and a major constituent of plant-derived 'essential oils'. Monoterpenes such as menthol, carvacrol, and eugenol have been utilized for therapeutical purposes and food additives for centuries and have been reported to have anti-inflammatory, antioxidant and analgesic actions. In recent years there has been increasing interest in understanding the pharmacological actions of these molecules. There is evidence indicating that monoterpenes can modulate the functional properties of several types of voltage and ligand-gated ion channels, suggesting that some of their pharmacological actions may be mediated by modulations of ion channel function. In this report, we review the literature concerning the interaction of monoterpenes with various ion channels.

Attenuation of γ-aminobutyric acid (GABA) transaminase activity contributes to GABA increase in the cerebral cortex of mice exposed to β-cypermethrin

The current study investigated the γ-aminobutyric acid (GABA) levels and GABA metabolic enzymes (GABA transaminase (GABAT) and glutamate decarboxylase (GAD)) activities at 2 and 4 h after treatment, using a high-performance liquid chromatography with ultraviolet detectors and colorimetric assay, in the cerebral cortex of mice treated with 20, 40 or 80 mg/kg β-cypermethrin by a single oral gavage, with corn oil as vehicle control. In addition, GABA protein (4 h after treatment), GABAT protein (2 h after treatment) and GABA receptors messenger RNA (mRNA) expression were detected by immunohistochemistry, Western blot and real-time quantitative reverse transcriptase polymerase chain reaction, respectively. β-Cypermethrin (80 mg/kg) significantly increased GABA levels in the cerebral cortex of mice, at both 2 and 4 h after treatment, compared with the control. Also, GABA immunohistochemistry results suggested that the number of positive granules was increased in the cerebral cortex of mice 4 h after exposure to 80 mg/kg β-cypermethrin when compared with the control. Furthermore, the results also showed that GABAT activity detected was significantly decreased in the cerebral cortex of mice 2 h after β-cypermethrin administration (40 or 80 mg/kg). No significant changes were found in GAD activity, or the expression of GABAT protein and GABAB receptors mRNA, in the cerebral cortex of mice, except that 80 mg/kg β-cypermethrin caused a significant decrease, compared with the vehicle control, in GABAA receptors mRNA expression 4 h after administration. These results suggested that attenuated GABAT activity induced by β-cypermethrin contributed to increased GABA levels in the mouse brain. The downregulated GABAA receptors mRNA expression is most likely a downstream event.

Permethrin modulates cholinergic mini-synaptic currents by partially blocking the calcium channel

Pyrethroid insecticide modulation of the voltage-gated sodium channel (VGSC) is proposed to underlie their effects on neuronal excitability by inhibiting channel inactivation and increasing channel open time. However, some in vitro evidences indicate that target sites other than VGSCs could contribute to pyrethroid disruption of neuronal activity. Cholinergic excitability in Drosophila, as in other insects and mammals, is important for activity in the central nervous system. The effects of permethrin, a putative calcium antagonist, on calcium current and cholinergic mini-synaptic transmission were investigated in the Drosophila brain. At concentration of 2.5μM, permethrin significantly decreased the calcium current and cholinergic mini-synaptic current. However, the permethrin could not antagonize the calcium current completely. Removal of calcium from the external solution produced a significant decrease of cholinergic mini-synaptic transmission. The results are consistent with the hypothesis that permethrin may modulate cholinergic mini-synaptic currents by partially blocking the calcium channel.

Mechanisms of pyrethroid insecticide-induced stimulation of calcium influx in neocortical neurons

Pyrethroid insecticides bind to voltage-gated sodium channels (VGSCs) and modify their gating kinetics, thereby disrupting neuronal function. Pyrethroids have also been reported to alter the function of other channel types, including activation of voltage-gated calcium channels. Therefore, the present study compared the ability of 11 structurally diverse pyrethroids to evoke Ca(2+) influx in primary cultures of mouse neocortical neurons. Nine pyrethroids (tefluthrin, deltamethrin, λ-cyhalothrin, β-cyfluthrin, esfenvalerate, S-bioallethrin, fenpropathrin, cypermethrin, and bifenthrin) produced concentration-dependent elevations in intracellular calcium concentration ([Ca(2+)](i)) in neocortical neurons. Permethrin and resmethrin were without effect on [Ca(2+)](i). These pyrethroids displayed a range of efficacies on Ca(2+) influx; however, the EC(50) values for active pyrethroids all were within one order of magnitude. Tetrodotoxin blocked increases in [Ca(2+)](i) caused by all nine active pyrethroids, indicating that the effects depended on VGSC activation. The pathways for deltamethrin- and tefluthrin-induced Ca(2+) influx include N-methyl-D-aspartic acid receptors, L-type Ca(2+) channels, and reverse mode of operation of the Na(+)/Ca(2+) exchanger inasmuch as antagonists of these sites blocked deltamethrin-induced Ca(2+) influx. These data demonstrate that pyrethroids stimulate Ca(2+) entry into neurons subsequent to their actions on VGSCs.

Allethrin differentially modulates voltage-gated calcium channel subtypes in rat PC12 cells

Pyrethroid insecticides are one of the most widely used classes of insecticides. Previous studies revealed that pyrethroids potently affect the insect voltage-gated sodium (Na(+)) channel (VGSC), resulting in prolonged channel open time. However, recent findings have suggested that pyrethroids may affect targets other than the VGSC. In particular, several studies have shown that pyrethroids can modulate the activity of voltage-gated calcium (Ca(2+)) channels (VGCCs). However, these studies often reported conflicting results; some studies observed stimulatory effects, whereas others observed inhibitory effects of pyrethroids on VGCCs. This study investigated whether allethrin (AL), a well-characterized type I pyrethroid, altered VGCC characteristics measured by whole-cell recording in rat pheochromocytoma cells (PC12) differentiated with nerve growth factor (NGF). AL (5 microM) increased peak, end, and tail composite VGCC current independent of its effects on VGSCs. After blocking VGCC subtype-specific current with omega-conotoxin GVIA (GVIA, an N-type VGCC antagonist) or nimodipine (NIM, an L-type VGCC antagonist), our data further suggest that AL differentially affects VGCC subtypes. Thus, AL apparently stimulated GVIA-insensitive current while inhibiting NIM-insensitive current. AL also significantly altered the voltage dependency of activation and inactivation of L-type VGCCs. The differential modulation of VGCC subtypes by AL may explain some of the conflicting observations of other studies.