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

Deciphering the interplay between LPS/TLR4 pathways, neurotransmitter, and deltamethrin-induced depressive-like behavior: Perspectives from the gut-brain axis

The improper use of deltamethrin (DM) can result in its accumulation in soil, water, food, and even the human body, which is associated with an elevated risk of neurotoxicity and behavioral abnormalities; however, the underlying mechanisms remain insufficiently investigated. Emerging evidence underscores the significance of the gut-brain axis in central nervous system (CNS) dysfunctions. Accordingly, this study investigates the role of the gut-brain axis in DM-induced behavioral anomalies in mice. The results showed that DM exposure induced depressive-like behavior, and the hippocampus, the region that is responsible for the modulation of emotional behavior, showed structural integrity disrupted (neuronal nuclear shrinkage and decreased tight junction protein expression). In addition, DM exposure led to compromised gut barrier integrity (disruptions on crypt surfaces and decreased tight junction protein expression), which might contribute to the gut bacterial-derived lipopolysaccharide (LPS) leakage into the bloodstream and reaching the brain, triggering LPS/toll-like receptor (TLR) 4 -mediated increases in brain pro-inflammatory cytokines. Subsequently, we observed a disturbance in neurotransmitter metabolic pathways following DM exposure, which inhibited the production of 5-hydroxytryptamine (5-HT). Additionally, DM exposure resulted in gut microbiota dysbiosis. Characteristic bacteria, such as Alistipes, Bifidobacterium, Gram-negative bacterium cTPY-13, and Odoribacter exhibited significant correlations with behavior, tight junction proteins, inflammatory response, and neurotransmitters. Further fecal microbiota transplantation (FMT) experiments suggested that DM-induced gut microbiota dysbiosis might contribute to depressive-like behavior. These results provide a new perspective on the toxicity mechanism of DM, indicating that its neurotoxicity may be partially regulated by the microbiota-gut-brain axis.

Fenpropathrin causes alterations in locomotion and social behaviors in zebrafish (Danio rerio)

Fenpropathrin is one of the widely used pyrethroid pesticides in agriculture and is frequently detected in the environment, groundwater, and food. While fenpropathrin was found to have neurotoxic effects in mammals, it remains unclear whether it has similar effects on fish. Here, we used adult zebrafish to investigate the impacts of fenpropathrin on fish social behaviors and neural activity. Exposure of adult zebrafish to 500 ppb of fenpropathrin for 72 h increased anxiety levels but decreased physical fitness, as measured by a novel tank diving test and swimming tunnel test. Fish exposed to fenpropathrin appeared to spend more time in the conspecific zone of the tank, possibly seeking greater comfort from their companions. Although learning, memory, and aggressive behavior did not change, fish exposed to fenpropathrin appeared to have shorter fighting durations. The immunocytochemical results showed the tyrosine hydroxylase antibody-labeled dopaminergic neurons in the teleost posterior tuberculum decreased in the zebrafish brain. According to a quantitative polymerase chain reaction (qPCR) analysis of the brain, exposure to fenpropathrin resulted in a decrease in the messenger (m)RNA expression of monoamine oxidase (mao), an enzyme that facilitates the deamination of dopamine. In contrast, the mRNA expression of the sncga gene, which may trigger Parkinson's disease, was found to have increased. There were no changes observed in expressions of genes related to antioxidants and apoptosis between the control and fenpropathrin-exposed groups. We provide evidence to demonstrate the defect of the neurotoxicity of fenpropathrin toward dopaminergic neurons in adult zebrafish.

Influence of bifenthrin exposure at different gestational stages on the neural development

Perinatal exposure to bifenthrin (BF) alters neurodevelopment. However, the most susceptible time period to BF exposure and the possible mechanisms are not clear. In the current study, pregnant female mice were treated with BF (0.5 mg/kg/d) at three different stages [gestational day (GD) 0-5, 6-15 and 16-birth (B)] and neurologic deficits were evaluated in offspring mice. BF exposure at GD 16-B significantly altered the locomotor activity and caused learning and memory impairments in 6-week-old offspring. Gestational BF exposure also caused neuronal loss in the region of cornu ammonis of hippocampi of 6-week-old offspring. Interestingly, neurobehavioral impairments and neuronal loss were not observed in offspring at 10-week-old. BF exposure at GD 16-B also decreased protein levels of VGluT1, NR1 and NR2A while increased the protein levels of NR2B and VGAT1, as well as the gene levels of Il-1β, Il-6 and Tnf-α in hippocampi of 6-week-old offspring. Collectively, these data demonstrate that gestational exposure to a low dose BF causes neurodevelopmental deficits that remit with the age and the late-stage of pregnancy is the most susceptible time window to BF exposure. Imbalance in excitatory/inhibitory neuronal transmission, altered expression levels of NMDA receptors and increased neural inflammation may be associated with BF prenatal exposure-triggered neurobehavioral impairments.

The Effect of the Pyrethroid Pesticide Fenpropathrin on the Cardiac Performance of Zebrafish and the Potential Mechanism of Toxicity

Fenpropathrin, a pyrethroid insecticide, has been widely used for many years in agricultural fields. It works by disturbing the voltage-gated sodium channel, leading to paralysis and the death of the target animal. While past studies have focused on neurodegeneration following fenpropathrin poisoning in humans, relatively few pieces of research have examined its effect on other peripheral organs. This study successfully investigated the potential toxicity of fenpropathrin on the cardiovascular system using zebrafish as an animal model. Zebrafish larvae exposed to varying doses of fenpropathrin underwent an evaluation of cardiac physiology by measuring the heart rate, stroke volume, cardiac output, and shortening fraction. The blood flow velocity and the dorsal aorta diameter were also measured to assess the impact of fenpropathrin exposure on the vascular system. Furthermore, molecular docking was performed to evaluate the pesticide binding affinity to various proteins associated with the cardiovascular system, revealing the potential mechanism of the fenpropathrin cardiotoxic effect. The findings demonstrated a significant dose-dependent increase in the heart rate stroke volume, cardiac output, shortening fraction, and ejection fraction of zebrafish larvae after 24 h of acute treatment with fenpropathrin. Additionally, zebrafish treated at a concentration of 1 ppm exhibited significantly larger blood vessels in diameter and an increased blood flow velocity compared to the control group. According to molecular docking, fenpropathrin showed a high affinity for various voltage-gated sodium channels like scn1lab, cacna1sb, and clcn3. Finally, from the results, we found that fenpropathrin caused cardiomegaly, which may have been induced by the voltage-gated sodium channel disruption. This study highlights the significant disruption of fenpropathrin in the cardiovascular system and emphasizes the need for further research on the health implications of this pesticide.

Effects of prenatal pesticide exposure on the fetal brain and placenta transcriptomes in a rodent model

Organophosphate and pyrethroid pesticides are among the most extensively used insecticides worldwide. Prenatal exposures to both classes of pesticides have been linked to a wide range of neurobehavioral deficits in the offspring. The placenta is a neuroendocrine organ and the crucial regulator of the intrauterine environment; early-life toxicant exposures could impact neurobehavior by disrupting placental processes. Female C57BL/6 J mice were exposed via oral gavage to an organophosphate, chlorpyrifos (CPF) at 5 mg/kg, a pyrethroid, deltamethrin (DM), at 3 mg/kg, or vehicle only control (CTL). Exposure began two weeks before breeding and continued every three days until euthanasia at gestational day 17. The transcriptomes of fetal brain (CTL n = 18, CPF n = 6, DM n = 8) and placenta (CTL n = 19, CPF n = 16, DM n = 12) were obtained through RNA sequencing, and resulting data was evaluated using weighted gene co-expression networks, differential expression, and pathway analyses. Fourteen brain gene co-expression modules were identified; CPF exposure disrupted the module related to ribosome and oxidative phosphorylation, whereas DM disrupted the modules related to extracellular matrix and calcium signaling. In the placenta, network analyses revealed 12 gene co-expression modules. While CPF exposure disrupted modules related to endocytosis, Notch and Mapk signaling, DM exposure dysregulated modules linked to spliceosome, lysosome and Mapk signaling pathways. Overall, in both tissues, CPF exposure impacted oxidative phosphorylation, while DM was linked to genes involved in spliceosome and cell cycle. The transcription factor Max involved in cell proliferation was overexpressed by both pesticides in both tissues. In summary, gestational exposure to two different classes of pesticide can induce similar pathway-level transcriptome changes in the placenta and the brain; further studies should investigate if these changes are linked to neurobehavioral impairments.

How the exposure to environmentally relevant pesticide formulations affects the expression of stress response genes and its relation to oxidative damage and genotoxicity in Caiman latirostris

This study aimed to analyze the molecular stress responses thought the expression levels of catalase (cat), superoxide dismutase (sod) and heat shock protein 70 (hsp70) genes, and how these relate with cellular stress response considering oxidative damage to lipids, DNA and genotoxicity in blood of Caiman latirostris hatchlings exposed to pesticide formulations under ex situ conditions. Treatments were: negative control (NC-tap water), glyphosate 2% (GLY), cypermethrin 0.12% (CYP), chlorpyrifos 0.8% (CPF), and their ternary mixture (Mx3). The concentrations and schedule of application were those recommended in soybean crops. Soil and water showed pesticides residues in all exposed groups. Results showed a statistically significant increase in the micronucleus frequency and DNA damage, with an important oxidation in all exposed groups. The expression level of cat gene was significantly higher in CYP while the expression of hsp70 was significantly lower in GLY, CYP and Mx3, compared to NC. Pesticides tested showed alterations in expression levels, growth parameters, DNA damage and base oxidation under realistic exposure conditions, and can threaten, in the long term, the health status of wild populations.

Pyrethroids and developmental neurotoxicity - A critical review of epidemiological studies and supporting mechanistic evidence

BACKGROUND

Pyrethroid metabolites are widely detectable in urine from the general population, including pregnant women and children. Pyrethroids are neurotoxic and suggested endocrine disruptors. Exposure during vulnerable developmental time windows may have long-term impacts on neurodevelopment.

OBJECTIVE

To evaluate the epidemiological evidence for neurodevelopmental effects related to prenatal and childhood pyrethroid exposure in a systematic review and to assess biological plausibility by evaluating mechanistic evidence.

METHODS

We searched PubMed and Web of Science up to September 1, 2021 and included original studies published in English in which pyrethroid exposure was measured or estimated during pregnancy or childhood and associations with neurodevelopmental outcomes in the children were investigated. The Navigation Guide Systematic Review Methodology was used to evaluate the epidemiological evidence. For mechanistic evidence, we focused on relevant key events (KEs) suggested in Adverse Outcome Pathways (AOPs) using the OECD-supported AOP-wiki platform. A systematic search combining the KEs with pyrethroids, including 26 individual compounds, was performed in the ToxCast database.

RESULTS

Twenty-five epidemiological studies met the inclusion criteria, 17 presented findings on prenatal exposure, 10 on childhood exposure and two on both exposure windows. The overall body of evidence was rated as "moderate quality" with "sufficient evidence" for an association between prenatal pyrethroid exposure and adverse neurodevelopment. For childhood exposure, the overall rating was "low quality" with "limited evidence" because of cross-sectional study design. Regarding mechanistic evidence, we found that pyrethroids are able to interfere with neurodevelopmental KEs included in established AOPs for adverse neurodevelopmental. The evidence was strongest for interference with thyroid hormone (TH) function.

CONCLUSION

Pyrethroids are probably human developmental neurotoxicants and adverse impacts of pyrethroid exposure on neurodevelopment are likely at exposure levels occurring in the general population. Preventive measures to reduce exposure among pregnant women and children are warranted.

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.

Influence of perinatal deltamethrin exposure at distinct developmental stages on motor activity, learning and memory

BACKGROUND

Perinatal exposure to deltamethrin (DM) causes attention-deficit/ hyperactivity disorder-like behaviors. However, the vulnerable time window to DM exposure and the possible mechanism are obscure. We aimed to identify the critical window(s) at perinatal stages for DM exposure and the possible mechanism.

METHOD

Pregnant mice were exposed to DM (0.5 mg/kg) at three different prenatal stages [gestational day (GD) 0-5, 6-15 and 16-birth (16-B)] and early postnatal stage (PD 0-10). Locomotor activity, learning and memory were evaluated using open field and Y-maze test, respectively. Nissl staining and western blots were used to examine the neuronal loss and the protein expression, respectively.

RESULTS

Perinatal exposures to DM had no effect on reproductive and growth index of offspring. However, mice receiving DM exposure during GD 16-B displayed significantly higher mortality suggesting GD 16-B is the most vulnerable time window to DM exposure. Prenatal but not early postnatal DM exposure impaired locomotor activity, learning and memory, and caused neuron loss in the dentate gyrus of male offspring. However, neither prenatal nor postnatal DM exposure affected mouse behavior of female offspring. Prenatal DM exposures decreased the protein levels of NR2A and NR2B in both hippocampi and cerebral cortices of male offspring. However, female mice receiving DM exposure at GD 16-B but not other stages displayed increased expression levels of NR2A and NR2B in hippocampi.

CONCLUSION

Prenatal but not early postnatal DM exposure impairs the neuron development in male but not female mice. Altered NMDA receptor expression may correlate to DM-induced behavioral deficits.

Agricultural surface water, imidacloprid, and chlorantraniliprole result in altered gene expression and receptor activation in Pimephales promelas

The toxicity of single pesticides is likely underestimated when considering complex pesticide mixtures found in agricultural runoff and this is especially true for newer pesticides with little toxicity data on non-target species. The goal of our study was to compare the toxicity of two newer pesticides, imidacloprid (IMI) and chlorantraniliprole (CHL), when an invertebrate and fish were exposed to single compounds, binary mixtures or surface water collected near agricultural fields. A secondary goal was to determine whether changes in select subcellular molecular pathways correspond to the insecticides' mechanisms of activity in aquatic organisms. We conducted acute (96 h) exposures using a dilution series of field water and environmentally relevant concentrations of single and binary mixtures of IMI and CHL. We then evaluated survival, gene expression and the activity of IMI toward the n-acetylcholine receptor (nAChR) and CHL activity toward the ryanodine receptor (RyR). Both IMI and CHL were detected at all sampling locations for May 2019 and September 2019 sampling dates and exposure to field water led to high invertebrate but not fish mortality. Fish exposed to field collected water had significant changes in the relative expression of genes involved with detoxification and neuromuscular function. Exposure of fish to single compounds or binary mixtures of IMI and CHL led to increased relative gene expression of RyR in fish. Furthermore, we found that IMI targets the nAChR in aquatic invertebrates and that CHL can cause overactivation of the RyR in invertebrates and fish. Overall, our finding suggests that IMI and CHL may impact neuromuscular health in fish. Expanding monitoring efforts to include sublethal and molecular assays would allow the detection of subcellular level effects due to complex mixtures present in surface water near agricultural areas.

Cypermethrin induces Sertoli cell apoptosis through mitochondrial pathway associated with calcium

Cypermethrin, one kind of pyrethroid pesticides, has been shown to act as endocrine-disrupting chemicals (EDCs). The purpose of this study was to explore the roles of Sertoli cell apoptosis through mitochondrial pathway associated with calcium (Ca²⁺) in cypermethrin-induced male reproductive toxicology. The mouse Sertoli cells TM4 were cultured with 0 μM, 10 μM, 20 μM, 40 μM and 80 μM of cypermethrin. We used flow cytometry, Fluo-4 AM, western blot and JC-1 Assay Kit to examine apoptosis, intracellular Ca²⁺, expressions of mitochondrial apoptotic pathway-related proteins and mitochondrial membrane potential. We found cypermethrin increased apoptosis rate of TM4 cells significantly and with a significant increase in intracellular Ca²⁺ concentration. Cypermethrin significantly decreased the protein expressions of cytosolic B-cell lymphoma-2 (Bcl-2) and mitochondrial cytochrome c (Cyt-c). The protein expressions of cytosolic Bcl-2-associated x (Bax), Cyt-c, cleaved caspase-3, calmodulin (CaM), Ca²⁺/CaM-dependent protein kinases II (CaMKII) and phosphorylated CaMKII were increased significantly in cypermethrin-exposed TM4 cells. Cypermethrin decreased mitochondrial membrane potential significantly. Then, Bcl-2 family and Ca²⁺/CaM/CaMKII pathway participate in cypermethrin-induced homeostasis. Ca²⁺ overload activates mitochondrial pathway by increasing permeability of mitochondrial membrane and decreasing mitochondrial membrane potential. We suggest cypermethrin induces Sertoli cell apoptosis involving mitochondrial pathway associated with Ca²⁺ regulated by Bcl-2 family and Ca²⁺/CaM/CaMKII pathway. The study provides a new insight into mechanisms involved in cypermethrin-induced male reproductive toxicology.

Dengue fever and insecticide resistance in Aedes mosquitoes in Southeast Asia: a review

Dengue fever is the most important mosquito-borne viral disease in Southeast Asia. Insecticides remain the most effective vector control approach for Aedes mosquitoes. Four main classes of insecticides are widely used for mosquito control: organochlorines, organophosphates, pyrethroids and carbamates. Here, we review the distribution of dengue fever from 2000 to 2020 and its associated mortality in Southeast Asian countries, and we gather evidence on the trend of insecticide resistance and its distribution in these countries since 2000, summarising the mechanisms involved. The prevalence of resistance to these insecticides is increasing in Southeast Asia, and the mechanisms of resistance are reported to be associated with target site mutations, metabolic detoxification, reduced penetration of insecticides via the mosquito cuticle and behavioural changes of mosquitoes. Continuous monitoring of the status of resistance and searching for alternative control measures will be critical for minimising any unpredicted outbreaks and improving public health. This review also provides improved insights into the specific use of insecticides for effective control of mosquitoes in these dengue endemic countries.

Effects of pyrethroids on brain development and behavior: Deltamethrin

Deltamethrin (DLM) is a Type II pyrethroid pesticide widely used in agriculture, homes, public spaces, and medicine. Epidemiological studies report that increased pyrethroid exposure during development is associated with neurobehavioral disorders. This raises concern about the safety of these chemicals for children. Few animal studies have explored the long-term effects of developmental exposure to DLM on the brain. Here we review the CNS effects of pyrethroids, with emphasis on DLM. Current data on behavioral and cognitive effects after developmental exposure are emphasized. Although, the acute mechanisms of action of DLM are known, how these translate to long-term effects is only beginning to be understood. But existing data clearly show there are lasting effects on locomotor activity, acoustic startle, learning and memory, apoptosis, and dopamine in mice and rats after early exposure. The most consistent neurochemical findings are reductions in the dopamine transporter and the dopamine D1 receptor. The data show that DLM is developmentally neurotoxic but more research on its mechanisms of long-term effects is needed.

Role of autophagy and oxidative stress to astrocytes in fenpropathrin-induced Parkinson-like damage

Fenpropathrin is an insecticide that is widely used in agriculture. It remains unknown whether fenpropathrin exposure increases the risk of Parkinson's disease. We found that fenpropathrin increased oxidative stress both in vitro and in vivo. Additionally, fenpropathrin increased production of ROS, NOS2, and HO-1, and decreased SOD and GSH in astrocytes. We further found that fenpropathrin-mediated oxidative stress might inhibit autophagic flow, including decreased expression of LC3A/B and enhanced expression of SQSTM1 via down-regulation of CDK-5, an upstream marker of autophagy. In mice, autophagy was slightly different from that found in astrocytes, as reflected in the increased expressions of LC3A/B and SQSTM1. Our findings elucidate the toxicological phenomena and pathogenic mechanisms of fenpropathrin and may provide guidance for improved pesticide control and environmental protection.

Human neuronal signaling and communication assays to assess functional neurotoxicity

Prediction of drug toxicity on the human nervous system still relies mainly on animal experiments. Here, we developed an alternative system allowing assessment of complex signaling in both individual human neurons and on the network level. The LUHMES cultures used for our approach can be cultured in 384-well plates with high reproducibility. We established here high-throughput quantification of free intracellular Ca2+ concentrations [Ca2+]i as broadly applicable surrogate of neuronal activity and verified the main processes by patch clamp recordings. Initially, we characterized the expression pattern of many neuronal signaling components and selected the purinergic receptors to demonstrate the applicability of the [Ca2+]i signals for quantitative characterization of agonist and antagonist responses on classical ionotropic neurotransmitter receptors. This included receptor sub-typing and the characterization of the anti-parasitic drug suramin as modulator of the cellular response to ATP. To exemplify potential studies on ion channels, we characterized voltage-gated sodium channels and their inhibition by tetrodotoxin, saxitoxin and lidocaine, as well as their opening by the plant alkaloid veratridine and the food-relevant marine biotoxin ciguatoxin. Even broader applicability of [Ca2+]i quantification as an end point was demonstrated by measurements of dopamine transporter activity based on the membrane potential-changing activity of this neurotransmitter carrier. The substrates dopamine or amphetamine triggered [Ca2+]i oscillations that were synchronized over the entire culture dish. We identified compounds that modified these oscillations by interfering with various ion channels. Thus, this new test system allows multiple types of neuronal signaling, within and between cells, to be assessed, quantified and characterized for their potential disturbance.

Fenpropathrin induces degeneration of dopaminergic neurons via disruption of the mitochondrial quality control system

The synthetic pyrethroid derivative, fenpropathrin, is a widely used insecticide. However, a variety of toxic effects in mammals have been reported. In particular, fenpropathrin induces degeneration of dopaminergic neurons and parkinsonism. However, the mechanism of fenpropathrin-induced parkinsonism has remained unknown. In the present study, we investigated the toxic effects and underlying mechanisms of fenpropathrin on perturbing the dopaminergic system both in vivo and in vitro. We found that fenpropathrin induced cellular death of dopaminergic neurons in vivo. Furthermore, fenpropathrin increased the generation of reactive oxygen species, disrupted both mitochondrial function and dynamic networks, impaired synaptic communication, and promoted mitophagy in vitro. In mice, fenpropathrin was administered into the striatum via stereotaxic (ST) injections. ST-injected mice exhibited poor locomotor function at 24 weeks after the first ST injection and the number of tyrosine hydroxylase (TH)-positive cells and level of TH protein in the substantia nigra pars compacta were significantly decreased, as compared to these parameters in vehicle-treated mice. Taken together, our results demonstrate that exposure to fenpropathrin induces a loss of dopaminergic neurons and partially mimics the pathologic features of Parkinson's disease. These findings suggest that fenpropathrin may induce neuronal degeneration via dysregulation of mitochondrial function and the mitochondrial quality control system.

BmK NSP, a new sodium channel activator from Buthus martensii Karsch, promotes neurite outgrowth in primary cultured spinal cord neurons

Scorpion venom is a rich source of bioactive compounds that affect neuronal excitability by modulating the activities of various channels/receptors. In the current study, guided by a Ca²⁺ mobilization assay, we purified a new neuroactive peptide designated as BmK NSP (Buthus martensii Karsch neurite-stimulating peptide, MW: 7064.30 Da). The primary structure of BmK NSP was determined by Edman degradation. BmK NSP concentration-dependently elevated intracellular Ca²⁺ concentration ([Ca²⁺]_i) with an EC₅₀ value of 4.18 μM in primary cultured spinal cord neurons (SCNs). Depletion of extracellular Ca²⁺ abolished BmK NSP-triggered Ca²⁺ response. Moreover, we demonstrated that BmK NSP-induced Ca²⁺ response was partially suppressed by the inhibitors of L-type Ca²⁺ channels, Na⁺-Ca²⁺ exchangers and NMDA receptors and was abolished by voltage-gated sodium channel (VGSC) blocker, tetrodotoxin. Whole-cell patch clamp recording demonstrated that BmK NSP delayed VGSC inactivation (EC₅₀ = 1.10 μM) in SCNs. BmK NSP enhanced neurite outgrowth in a non-monotonic manner that peaked at ~30 nM in SCNs. BmK NSP-promoted neurite outgrowth was suppressed by the inhibitors of L-type Ca²⁺ channels, NMDA receptors, and VGSCs. Considered together, these data demonstrate that BmK NSP is a new α-scorpion toxin that enhances neurite outgrowth through main routes of Ca²⁺ influx. Modulation of VGSC activity by α-scorpion toxin might represent a novel strategy to regulate the neurogenesis in SCNs.

Action of the insecticide cyfluthrin on Ca2+ signal transduction and cytotoxicity in human osteosarcoma cells

Cyfluthrin is a pyrethroid insecticide and common household pesticide. The effect of cyfluthrin on Ca²⁺-related physiology in human osteosarcoma is unclear. This study investigated the effect of cyfluthrin on cytosolic-free Ca²⁺ concentrations ([Ca²⁺]_i) and viability in MG63 human osteosarcoma cells. Cyfluthrin concentration-dependently induced [Ca²⁺]_i rises. Cyfluthrin-induced Ca²⁺ entry was confirmed by the Mn²⁺-induced quench of fura-2 fluorescence. Cyfluthrin at concentrations of 10-100 μM induced [Ca²⁺]_i rises. Ca²⁺ removal reduced the signal by approximately 50%. Cyfluthrin (100 μM) induced Mn²⁺ influx suggesting Ca²⁺ entry. Cyfluthrin-induced Ca²⁺ entry was inhibited 50% by protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate) and inhibitor (GF109203X) and also by three inhibitors of store-operated Ca²⁺ channels: nifedipine, econazole, and SKF96365. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin (TG) completely inhibited cyfluthrin-evoked [Ca²⁺]_i rises. Conversely, treatment with cyfluthrin abolished TG-evoked [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) with 1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dion abolished cyfluthrin-induced [Ca²⁺]_i rises. Cyfluthrin at 25-65 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester. Together, in MG63 cells, cyfluthrin induced [Ca²⁺]_i rises by evoking PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. Cyfluthrin also caused Ca²⁺-independent cell death.

Pagoamide A, a Cyclic Depsipeptide Isolated from a Cultured Marine Chlorophyte, Derbesia sp., Using MS/MS-Based Molecular Networking

A thiazole-containing cyclic depsipeptide with 11 amino acid residues, named pagoamide A (1), was isolated from laboratory cultures of a marine Chlorophyte, Derbesia sp. This green algal sample was collected from America Samoa, and pagoamide A was isolated using guidance by MS/MS-based molecular networking. Cultures were grown in a light- and temperature-controlled environment and harvested after several months of growth. The planar structure of pagoamide A (1) was characterized by detailed 1D and 2D NMR experiments along with MS and UV analysis. The absolute configurations of its amino acid residues were determined by advanced Marfey's analysis following chemical hydrolysis and hydrazinolysis reactions. Two of the residues in pagoamide A (1), phenylalanine and serine, each occurred twice in the molecule, once in the d- and once in the l-configuration. The biosynthetic origin of pagoamide A (1) was considered in light of other natural products investigations with coenocytic green algae.

Toxicokinetics of cis- and trans-Permethrin: Influence of Isomer, Maturation, and Sex

Permethrin exposure of children and adults is widespread in many populations, but knowledge of its relative toxicokinetics (TK) and health risks in immature age groups is lacking. Studies were conducted in rats to determine the influence of immaturity and sex (on plasma and target organ dosimetry of each of the insecticide’s 2 isomers, cis- and trans-permethrin [CIS and TRANS]). Postnatal day 15, 21, and 90 (adult), Sprague Dawley rats were orally administered a graduated series of doses of CIS and TRANS in corn oil. Serial sacrifices were conducted over 24 h to obtain plasma, brain, liver, skeletal muscle, and fat profiles of CIS and TRANS. Levels of TRANS decreased relatively rapidly, despite administration of relatively high doses. Concentrations of each isomer in plasma, brain, and other tissues monitored were inversely proportional to the animals’ age. The youngest pups exhibited 4-fold higher plasma and brain area under the curves than did adults. Little difference was observed in the TK of CIS or TRANS between adult male and female rats, other than higher initial plasma and liver CIS levels in females. Elevated exposure of the immature brain appears to be instrumental in increased susceptibility to the acute neurotoxicity of high-dose permethrin (Cantalamessa [1993]), but it remains to be established whether age-dependent TK is relevant to long-term, low-level risks.

Relationship Between the Dose Administered, Target Tissue Dose, and Toxicity Level After Acute Oral Exposure to Bifenthrin and Tefluthrin in Young Adult Rats

Most pyrethroid insecticides (PYRs) share a similar primary target site in mammals. However, the potency estimates of the lethal and sublethal effects of these compounds differ up to 103-fold. The aim of this study was to evaluate the relationship between the dose administered, the target tissue dose, and the effect of 2 highly toxic PYRs, tefluthrin (TEF; 0.1-9 mg/kg) and bifenthrin (BIF; 0.5-12 mg/kg), by using the oral route, a corn oil vehicle (1 ml/kg) and subcutaneous temperature (Tsc) monitoring assays in adult rats. The Tsc was determined at 30-min intervals for 5 h (TEF) or 4.5 h (BIF) after dosing. Rats were sacrificed at 6 h after dosing, and BIF and TEF concentrations were determined in blood (Bd), liver (Lv), and cerebellum (Cb) by using a GC-ECD system. The minimal effective dose of BIF (3 mg/kg) affecting Tsc was similar to that found in prior studies using other testing paradigms. Regarding TEF, a very steep relationship between the dose administered and toxicity was observed, with a near-threshold to low-effective range for Tsc at 0.1-6 mg/kg, and a near lethal syndrome at ≥ 7.5 mg/kg. At 6-7.5 mg/kg TEF, the Cb/Bd and Cb/Lv concentration ratios were both > 1. Conversely, for BIF, the Cb concentration was barely over the Bd concentration and the Cb/Lv concentration ratio remained < 1. Our results and previous findings call for more comprehensive consideration to establish the relevance of the distribution into target tissues and the tissue dosimetry for health risks through the exposure to PYRs in humans.

Ca2+ movement and cytotoxicity induced by the pyrethroid pesticide bifenthrin in human prostate cancer cells

Bifenthrin, a commonly used pyrethroid pesticide, evokes various toxicological effects in different models. However, the effect of bifenthrin on cytosolic-free Ca2+ level ([Ca2+] i) and cytotoxicity in human prostate cancer cells is unclear. This study examined whether bifenthrin altered Ca2+ homeostasis and cell viability in PC3 human prostate cancer cells. [Ca2+] i in suspended cells were measured using the fluorescent Ca2+-sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 assay. Bifenthrin (100–400 μM) concentration-dependently induced [Ca2+] i rises. Ca2+ removal reduced the signal by approximately 30%. In Ca2+-free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished bifenthrin-evoked [Ca2+] i rises. Conversely, treatment with bifenthrin abolished BHQ-evoked [Ca2+] i rises. Inhibition of phospholipase C (PLC) with U73122 significantly inhibited bifenthrin-induced [Ca2+] i rises. Mn2+ has been shown to enter cells through similar mechanisms as Ca2+ but quenches fura-2 fluorescence at all excitation wavelengths. Bifenthrin (400 μM)-induced Mn2+ influx implicates that Ca2+ entry occurred. Bifenthrin-induced Ca2+ entry was inhibited by 30% by protein kinase C (PKC) activator (phorbol 12-myristate 13 acetate) and inhibitor (GF109203X) and three inhibitors of store-operated Ca2+ channels: nifedipine, econazole, and SKF96365. Bifenthrin at 175–275 μM decreased cell viability, which was not reversed by pretreatment with the Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane- N, N, N′, N′-tetra acetic acid-acetoxymethyl ester. Together, in PC3 cells, bifenthrin-induced [Ca2+] i rises by evoking PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-sensitive store-operated Ca2+ entry. Bifenthrin also caused Ca2+-independent cell death.

Influence of Nanomolar Deltamethrin on the Hallmarks of Primary Cultured Cortical Neuronal Network and the Role of Ryanodine Receptors

BACKGROUND

The pyrethroid deltamethrin (DM) is broadly used for insect control. Although DM hyperexcites neuronal networks by delaying inactivation of axonal voltage-dependent [Formula: see text] channels, this mechanism is unlikely to mediate neurotoxicity at lower exposure levels during critical perinatal periods in mammals.

OBJECTIVES

We aimed to identify mechanisms by which acute and subchronic DM altered axonal and dendritic growth, patterns of synchronous [Formula: see text] oscillations (SCOs), and electrical spike activity (ESA) functions critical to neuronal network formation.

METHODS

Measurements of SCOs using [Formula: see text] imaging, ESA using microelectrode array (MEA) technology, and dendritic complexity using Sholl analysis were performed in primary murine cortical neurons from wild-type (WT) and/or ryanodine receptor 1 ([Formula: see text]) mice between 5 and 14 d in vitro (DIV). [Formula: see text] binding analysis and a single-channel voltage clamp were utilized to measure engagement of RyRs as a direct target of DM.

RESULTS

Neuronal networks responded to DM ([Formula: see text]) as early as 5 DIV, reducing SCO amplitude and depressing ESA and burst frequencies by 60-70%. DM ([Formula: see text]) enhanced axonal growth in a nonmonotonic manner. [Formula: see text] enhanced dendritic complexity. DM stabilized channel open states of RyR1, RyR2, and cortical preparations expressing all three isoforms. DM ([Formula: see text]) altered gating kinetics of RyR1 channels, increasing mean open time, decreasing mean closed time, and thereby enhancing overall open probability. SCO patterns from cortical networks expressing [Formula: see text] were more responsive to DM than WT. [Formula: see text] neurons showed inherently longer axonal lengths than WT neurons and maintained less length-promoting responses to nanomolar DM.

CONCLUSIONS

Our findings suggested that RyRs were sensitive molecular targets of DM with functional consequences likely relevant for mediating abnormal neuronal network connectivity in vitro. https://doi.org/10.1289/EHP4583.

The investigation of the pyrethroid insecticide lambda-cyhalothrin (LCT)-affected Ca2+ homeostasis and -activated Ca2+-associated mitochondrial apoptotic pathway in normal human astrocytes: The evaluation of protective effects of BAPTA-AM (a selective Ca2+ chelator)

Exposure to insecticides has been found to have deleterious effects on human health. Lambda-cyhalothrin (LCT), a mixture of isomers of cyhalothrin, is a pyrethroid insecticide routinely used in pest control programs. LCT was reported to cause neurotoxic effects in various models. However, the mechanism of underlying effect of LCT on cytotoxicity in normal human brain cells is still elusive. This study examined whether LCT affected Ca²⁺ homeostasis and Ca²⁺-related physiology in Gibco® Human Astrocytes (GHA cells), and explored whether BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid), a selective Ca²⁺ chelator, has protective effects on LCT-treated GHA cells. The data show that LCT (10-15 μM) concentration-dependently induced cytotoxicity in both GHA cells and DI TNC1 normal rat astrocytes but only induced intracellular Ca²⁺ concentration ([Ca²⁺]_i) rises in GHA cells. In terms of Ca²⁺ signaling in GHA cells, LCT-induced [Ca²⁺]_i rises were reduced by removing extracellular Ca²⁺ and were inhibited by store-operated Ca²⁺ channel modulators (2-APB, econazole or SKF96365). In Ca²⁺-free medium, pretreatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin abolished LCT-induced [Ca²⁺]_i rises. Conversely, incubation with LCT abolished thapsigargin-induced [Ca²⁺]_i rises. Regarding cytotoxicity, LCT evoked apoptosis by regulating apoptotic protein expressions (Bax, BCl-2, cleaved caspase-9/-3). This apoptotic response was significantly inhibited by prechelating cytosolic Ca²⁺ with BAPTA-AM. Together, in GHA cells, LCT induced [Ca²⁺]_i rises by inducing Ca²⁺ entry via store-operated Ca²⁺ channels and Ca²⁺ release from the endoplasmic reticulum. Moreover, BAPTA-AM has a protective effect on inhibiting LCT-activated mitochondrial apoptotic pathway. This study provided new insights into the molecular protective mechanism of LCT-induced cytotoxicity in normal human astrocytes.

Pyrethroid bifenthrin induces oxidative stress, neuroinflammation, and neuronal damage, associated with cognitive and memory impairment in murine hippocampus

Exposure to synthetic pyrethroid (SPs) pesticides such as bifenthrin (BF) has been associated with adverse neurodevelopmental outcomes and cognitive impairments, but the underlying neurobiological mechanism is poorly understood so far. The present study has been designed to evaluate changes in behavior and in biomarkers of oxidative stress and neuroinflammation in the hippocampus of rats subchronically treated with BF. Rats exposed daily to BF at doses of 0.6 and 2.1 mg/kg b. w. for 60 days exhibited spatial and cognitive impairments as well as memory dysfunction after 60 days. This repeated BF treatment also significantly increased mRNA expression of pro-inflammatory cytokines tumor necrosis factor (TNF-α), interleukin (IL-1β), (IL-6), nuclear factor erythroid-2 (Nrf2), cyclooxygenase-2 (COX-2), nuclear factor-kappaB pathway (NF-kappaB), and prostaglandin E₂ (PGE₂) in the hippocampus. It further resulted in a significant increase in protein levels of Nrf2, COX-2, microsomal prostaglandin synthase-1 (mPGES-1) and NF-kappaB. This was accompanied by oxidative/nitrosative stress in the hippocampus of treated rats, as shown by increased levels of malondialdehyde (MDA), protein carbonyls (PCO), and nitric oxide (NO), and reduced levels of enzymatic (catalase, superoxide dismutase, and glutathione peroxidase) and non-enzymatic (reduced glutathione) antioxidants. The data are in line with those obtained in organotypic hippocampal slice cultures (OHSCs) isolated from mouse brain and exposed to BF for 72 h, showing neuronal death only at the high dose of 20 μM when compared to controls. These findings suggest that exposure to BF induces neuronal damage, alters redox state, and causes neuroinflammation in the hippocampus, which might lead to cognitive and memory impairment.

Inflammatory and oxidative mechanisms potentiate bifenthrin-induced neurological alterations and anxiety-like behavior in adult rats

Bifenthrin (BF) is a synthetic pyrethroid pesticide widely used in several countries to manage insect pests on diverse agricultural crops. Growing evidence indicates that BF exposure is associated with an increased risk of developing neurodegenerative disorders. However, the mechanisms by which BF induces neurological and anxiety alterations in the frontal cortex and striatum are not well known. The present in vivo study was carried out to determine whether reactive oxygen species (ROS)-mediated oxidative stress (OS) and neuroinflammation are involved in such alterations. Thirty-six Wistar rats were thus randomly divided into three groups and were orally administered with BF (0.6 and 2.1 mg/kg body weight, respectively) or the vehicle (corn oil), on a daily basis for 60 days. Results revealed that BF exposure in rats enhanced anxiety-like behavior after 60 days of treatment, as assessed with the elevated plus-maze test by decreases in the percentage of time spent in open arms and frequency of entries into these arms. BF-treated rats also exhibited increased oxidation of lipids and carbonylated proteins in the frontal cortex and striatum, and decreased glutathione levels and antioxidant enzyme activities including superoxide dismutase, catalase and glutathione peroxidase. Treatment with BF also increased protein synthesis and mRNA expression of the inflammatory mediators cyclooxygenase-2 (COX-2), microsomal prostaglandin synthase-1 (mPGES-1) and nuclear factor-kappaBp65 (NF-kBp65), as well as the production of tumor necrosis factor-α (TNF-α) and ROS. Moreover, BF exposure significantly decreased protein synthesis and mRNA expression of nuclear factor erythroid-2 (Nrf2) and acetylcholinesterase (AChE), as well as gene expression of muscarinic-cholinergic receptors (mAchR) and choline acetyltransferase (ChAT) in the frontal cortex and striatum. These data suggest that BF induced neurological alterations in the frontal cortex and striatum of rats, and that this may be associated with neuroinflammation and oxidative stress via the activation of Nrf2/NF-kBp65 pathways, which might promote anxiety-like behavior.

Exposure to permethrin promotes high fat diet-induced weight gain and insulin resistance in male C57BL/6J mice

Permethrin is a pyrethroid pesticide that was previously reported to promote fat accumulation and insulin resistance in vitro. A recent study in female mice also found that permethrin could promote high fat-induced insulin resistance. The effects of permethrin on glucose and lipid metabolisms in male mice, however, remain unknown. The purpose of this study was to investigate the effects and interactions of permethrin exposure (50, 500, and 5000 μg/kg body weight/day) and dietary fat (low fat, 4% w/w; high fat, 20% w/w) on development of obesity and insulin resistance in male C57BL/6J mice. Our results showed that permethrin treatment significantly increased body weight, fat mass, and insulin resistance with high fat diet, but not with low fat diet, without influencing energy intake. Permethrin treatment also significantly increased serum levels of insulin, glucose, leptin, triglycerides and cholesterol. Further results showed that permethrin inhibited AMP-activated protein kinase in white adipose tissue. These results suggest that permethrin interacts with dietary fat to alter lipid and glucose metabolisms in male C57BL/6J mice.

Gas chromatography/negative chemical ionization mass spectrometry of transfluthrin in rat plasma and brain

RATIONALE

Transfluthrin is a relatively non-toxic rapid-acting synthetic pyrethroid insecticide. It is widely used in household and hygiene products. A sensitive and accurate bioanalytical method is required for quantification of its concentration in plasma and its potential target organ, the brain for studies to assess its health effects and toxicokinetics in mammals.

METHODS

The samples were prepared by liquid-liquid extraction. Gas chromatography mass spectrometry (GC/MS) analysis was performed for the determination of transfluthrin in biological samples with an overall method run time of 15 min. Transfluthrin was quantified using selected-ion monitoring (SIM) in the negative chemical ionization (NCI) mode. Chromatographic separation was achieved using a Zebron® ZB5-MS GC column operating with 1 mL/min constant flow helium. Cis-Permethrin was used as the internal standard.

RESULTS

The method was validated to be precise and accurate within the linear range of 1.0-400.0 ng/mL in plasma and 4.0-400.0 ng/mL in brain homogenate, based on a 100 μL sample volume for both matrices. This method was applied to samples following administration of a 10 mg/kg oral dose to male adult rats. The plasma concentrations were observed to be 11.70 ± 5.69 ng/mL and brain concentrations 12.09 ± 3.15 ng/g when measured 2 h post-dose.

CONCLUSIONS

A rapid GC/NCI-MS method was demonstrated to be sensitive, specific, precise and accurate for the quantification of transfluthrin in rat plasma and brain. The optimized method was successfully used to quantify the rat plasma and brain concentrations of transfluthrin 2 h after the oral dosing of Sprague-Dawley rats.

Pyrethroid Insecticide Cypermethrin Accelerates Pubertal Onset in Male Mice via Disrupting Hypothalamic-Pituitary-Gonadal Axis

Pyrethroids, a class of insecticides that are widely used worldwide, have been identified as endocrine-disrupting chemicals (EDCs). Our recent epidemiological study reported on an association of increased pyrethroids exposure with elevated gonadotropins levels and earlier pubertal development in Chinese boys. In this study, we further investigated the effects of cypermethrin (CP), one of the most ubiquitous pyrethroid insecticides, on hypothalamic-pituitary-gonadal (HPG) axis and pubertal onset in male animal models. Early postnatal exposure to CP at environmentally relevant doses (0.5, 5, and 50 μg/kg CP) significantly accelerated the age of puberty onset in male mice. Administration of CP induced a dose-dependent increase in serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone in male mice. CP did not affect gonadotropin-releasing hormone (GnRH) gene expression in the hypothalamus, but CP at higher concentrations stimulated GnRH pulse frequency. CP could induce the secretion of LH and FSH, as well as the expression of gonadotropin subunit genes [chorionic gonadotropin α (CGα), LHβ, and FSHβ] in pituitary gonadotropes. CP stimulated testosterone production and the expression of steroidogenesis-related genes [steroidogenic acute regulatory (StAR) and Cytochrome p 450, family 11, subfamily A, polypeptide 1 (CYP11A1)] in testicular Leydig cells. The interference with hypothalamic sodium channels as well as calcium channels in pituitary gonadotropes and testicular Leydig cells was responsible for CP-induced HPG axis maturation. Our findings established in animal models provide further evidence for the biological plausibility of pyrethroid exposure as a potentially environmental contributor to earlier puberty in males.

Modification of distinct ion channels differentially modulates Ca2+ dynamics in primary cultured rat ventricular cardiomyocytes

Primary cultured cardiomyocytes show spontaneous Ca²⁺ oscillations (SCOs) which not only govern contractile events, but undergo derangements that promote arrhythmogenesis through Ca²⁺ -dependent mechanism. We systematically examined influence on SCOs of an array of ion channel modifiers by recording intracellular Ca²⁺ dynamics in rat ventricular cardiomyocytes using Ca²⁺ specific fluorescence dye, Fluo-8/AM. Voltage-gated sodium channels (VGSCs) activation elongates SCO duration and reduces SCO frequency while inhibition of VGSCs decreases SCO frequency without affecting amplitude and duration. Inhibition of voltage-gated potassium channel increases SCO duration. Direct activation of L-type Ca²⁺ channels (LTCCs) induces SCO bursts while suppressing LTCCs decreases SCO amplitude and slightly increases SCO frequency. Activation of ryanodine receptors (RyRs) increases SCO duration and decreases both SCO amplitude and frequency while inhibiting RyRs decreases SCO frequency without affecting amplitude and duration. The potencies of these ion channel modifiers on SCO responses are generally consistent with their affinities in respective targets demonstrating that modification of distinct targets produces different SCO profiles. We further demonstrate that clinically-used drugs that produce Long-QT syndrome including cisapride, dofetilide, sotalol, and quinidine all induce SCO bursts while verapamil has no effect. Therefore, occurrence of SCO bursts may have a translational value to predict cardiotoxicants causing Long-QT syndrome.

Exploring poisonous mechanism of honeybee, Apis mellifera ligustica Spinola, caused by pyrethroids

As the important intracellular secondary messengers, calcium channel is the target of many neurotoxic pesticides as calcium homeostasis in the neuroplasm play important role in neuronal functions and behavior in insects. This study investigated the effect of deltamethrin (DM) on calcium channel in the brain nerve cells of adult workers of Apis mellifera ligustica Spinola that were cultured in vitro. The results showed that the intracellular calcium concentration was significantly elevated even with a very low concentration of the DM (3.125×10^-2mg/L). Further testing revealed that T-type voltage-gated calcium channels (VGCCs), except for sodium channels, was one of the target of DM on toxicity of Apis mellifera, while DM has no significant effect on the L-type VGCCs, N-methyl-d-aspartate receptor-gated calcium channels and calcium store. These results suggesting that the DM may act on T-type VGCCs in brain cells of honeybees and result in behavioral abnormalities including swarming, feeding, learning, and acquisition.

In vitro evaluation of pyrethroid-mediated changes on neuronal burst parameters using microelectrode arrays

Effects of pyrethroids (beta-cyfluthrin, bifenthrin, cypermethrin, deltamethrin, lambda-cyhalothrin, and permethrin) on the burst parameters (mean burst rate [MBR], percent spikes in burst [PSB], mean burst duration [MBD], mean spikes in burst [MSB], mean interspike interval in burst [MISIB], and mean interburst interval [MIBI]) have been investigated using the microelectrode array technique. Rat cortical neuronal networks (between 24 and 35 DIV) were exposed to the five accumulative concentrations of pyrethroids (0.01μM, 0.1μM, 1μM, 10μM, and 100μM) after initially recording the baseline activity. When compared to the baseline, the burst parameter that had undergone the most change (either increase/decrease) at the initial concentrations was MBR, followed by MIBI and PSB. The other burst parameters (MSB, MBD, and MISIB) did not undergo much change (either increase/decrease) by the pyrethroids at the initial concentrations when compared to the baseline. The MBR of all pyrethroids rose at initial concentrations followed by decrease at higher concentrations. A drop in the MIBI accompanied the rise in the MBR. The rank orders of relative potency of pyrethroids on the IC₅₀ of different burst parameters clearly distinguish type-1 pyrethroids (bifenthrin, permethrin) from the type-2 pyrethroids (beta-cyfluthrin, cypermethrin, deltamethrin, lambda-cyhalothrin), with type-2 being more potent. The rank order of relative potency of pyrethroids based on the IC₅₀ of MBR was beta-cyfluthrin>lambda-cyhalothrin>deltamethrin>cypermethrin>bifenthrin>permethrin.

Pyrethroid Insecticides Directly Activate Microglia Through Interaction With Voltage-Gated Sodium Channels

Microglia are considered to be the resident immune cells of the central nervous system and contribute significantly to ongoing neuroinflammation in a variety of neurodegenerative diseases. Recently, we and others identified that voltage-gated sodium channels (VGSC) are present on microglia cells and contribute to excessive accumulation of intracellular Na⁺and release of major pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α). Based on this finding and the fact that pyrethroid pesticides act on VGSC, we hypothesized that exposure of microglia to the pyrethroid pesticides, permethrin and deltamethrin, would activate microglia and increase the release of TNF-α. BV2 cells or primary microglia were treated with 0-5 µM deltamethrin or permethrin in the presence or absence of tetrodotoxin (TTX), a VGSC blocker for 24-48 h. Both pyrethroids caused a rapid Na⁺influx and increased accumulation of intracellular sodium [(Na⁺)i] in the microglia in a dose- and time-dependent manner, which was significantly reduced by TTX. Furthermore, deltamethrin and permethrin increased the release of TNF-α in a dose- and time-dependent manner, which was significantly reduced by pre-treatment of cells with TTX. These results demonstrate that pyrethroid pesticides may directly activate microglial cells through their interaction with microglial VGSC. Because neuroinflammation plays a key role in many neurodegenerative diseases, these data provide an additional mechanism by which exposure to pyrethroid insecticides may contribute to neurodegeneration.

Activation of sodium channels by α-scorpion toxin, BmK NT1, produced neurotoxicity in cerebellar granule cells: an association with intracellular Ca2+ overloading

Voltage-gated sodium channels (VGSCs) are responsible for the action potential generation in excitable cells including neurons and involved in many physiological and pathological processes. Scorpion toxins are invaluable tools to explore the structure and function of ion channels. BmK NT1, a scorpion toxin from Buthus martensii Karsch, stimulates sodium influx in cerebellar granule cells (CGCs). In this study, we characterized the mode of action of BmK NT1 on the VGSCs and explored the cellular response in CGC cultures. BmK NT1 delayed the fast inactivation of VGSCs, increased the Na⁺ currents, and shifted the steady-state activation and inactivation to more hyperpolarized membrane potential, which was similar to the mode of action of α-scorpion toxins. BmK NT1 stimulated neuron death (EC₅₀ = 0.68 µM) and produced massive intracellular Ca²⁺ overloading (EC₅₀ = 0.98 µM). TTX abrogated these responses, suggesting that both responses were subsequent to the activation of VGSCs. The Ca²⁺ response of BmK NT1 was primary through extracellular Ca²⁺ influx since reducing the extracellular Ca²⁺ concentration suppressed the Ca²⁺ response. Further pharmacological evaluation demonstrated that BmK NT1-induced Ca²⁺ influx and neurotoxicity were partially blocked either by MK-801, an NMDA receptor blocker, or by KB-R7943, an inhibitor of Na⁺/Ca²⁺ exchangers. Nifedipine, an L-type Ca²⁺ channel inhibitor, slightly suppressed both Ca²⁺ response and neurotoxicity. A combination of these three inhibitors abrogated both responses. Considered together, these data ambiguously demonstrated that activation of VGSCs by an α-scorpion toxin was sufficient to produce neurotoxicity which was associated with intracellular Ca²⁺ overloading through both NMDA receptor- and Na⁺/Ca²⁺ exchanger-mediated Ca²⁺ influx.

Identification of chemicals that mimic transcriptional changes associated with autism, brain aging and neurodegeneration

Environmental factors, including pesticides, have been linked to autism and neurodegeneration risk using retrospective epidemiological studies. Here we sought to prospectively identify chemicals that share transcriptomic signatures with neurological disorders, by exposing mouse cortical neuron-enriched cultures to hundreds of chemicals commonly found in the environment and on food. We find that rotenone, a pesticide associated with Parkinson's disease risk, and certain fungicides, including pyraclostrobin, trifloxystrobin, famoxadone and fenamidone, produce transcriptional changes in vitro that are similar to those seen in brain samples from humans with autism, advanced age and neurodegeneration (Alzheimer's disease and Huntington's disease). These chemicals stimulate free radical production and disrupt microtubules in neurons, effects that can be reduced by pretreating with a microtubule stabilizer, an antioxidant, or with sulforaphane. Our study provides an approach to prospectively identify environmental chemicals that transcriptionally mimic autism and other brain disorders.

This study presents gene expression responses of cultured brain cells to hundreds of chemicals found in the environment and in food. The authors identified chemicals that induce transcriptomic profiles that overlap those seen in human brains affected with autism, aging, and neurodegeneration.

Effects of Deltamethrin on crayfish motor axon activity and neuromuscular transmission

Deltamethrin (DM) is a widely used pesticide known to target sodium channels. Although this compound has been studied extensively at molecular and behavioral levels, the detailed action of DM on cellular and synaptic function is less well documented. In this report, we show that DM at nanomolar concentrations can silence tonic motor output of the crayfish ventral superficial flexor (VSF) within ∼10 min. Action potential (AP) amplitude was consistently reduced before silencing occurred, whereas AP duration and AP firing frequency did not change. In some synapses EPSP amplitude and synaptic delay were modified by DM, but the direction of change was not consistent. In order to better understand these diverse effects, intracellular recordings from motor axons of the crayfish opener were used for a detailed analysis. DM caused an initial, slow depolarization of resting membrane potential (Vm), which was accompanied by reduced AP amplitude but not AP duration. Resting Vm then underwent a step depolarization of ∼20 mV, which we propose corresponds to the onset of the depolarization block. In addition, DM shifted the AP initiation site in some opener axons during prolonged firing. This shift occurred concomitantly with a reduction in synaptic delay. A similar reduction in synaptic delay was also detected at some VSF axons, and can be attributed to the same mechanism. Results reported here suggest that DM at low concentrations result in: (i) depolarization block of motor axons before changes in network output can be detected, (ii) variable effects on synaptic transmission, with this variability presumably due to the diverse morphology and excitability of motor axons.

Plasma protein binding limits the blood brain barrier permeation of the pyrethroid insecticide, deltamethrin

Previous pharmacokinetic studies of deltamethrin (DLM) have revealed that brain levels of this highly lipophilic pyrethroid insecticide are only 15-20% of plasma levels. Experiments were performed to assess determinants limiting CNS access including plasma protein binding and the efflux transporter, P-gp. A human brain microvascular endothelial cell line, hCMEC/D3, was utilized as a model in vitro system to evaluate blood-brain barrier (BBB) permeation. Incubation of DLM with a series of human serum albumin (HSA) concentrations showed that unbound (fu) DLM ranged from 80% with 0.01% HSA to ∼20% at the physiologically-relevant 4% HSA. A positive correlation (R=0.987) was seen between fu and cellular uptake. Concentration-dependent uptake of DLM in 0.01% HSA was non-linear and was reduced at 4°C and by the P-gp inhibitor cyclosporine (CSA), indicative of a specific transport process. Cellular accumulation of [(3)H]-paclitaxel, a P-glycoprotein (P-gp) substrate, was increased by CSA but not by DLM, suggesting that DLM is neither a substrate nor an inhibitor of P-gp. The concentration-dependent uptake of DLM from 4% HSA was linear and not significantly impacted by temperature or CSA. In situ brain perfusion studies monitoring brain association of DLM at 0.01% and 4% HSA confirmed the aforementioned in vitro findings. This study demonstrates that brain uptake of DLM under normal physiological conditions appears to be a passive, non-saturable process, limited by the high protein binding of the pyrethroid.

Synthetic Cystine-Knot Miniproteins - Valuable Scaffolds for Polypeptide Engineering

Peptides with the cystine-knot architecture, often termed knottins, are promising scaffolds for biomolecular engineering. These unique molecules combine diverse bioactivities with excellent structural, thermal, and proteolytical stability. Being different in the composition and structure of their amino acid backbone, knottins share the same core element, namely cystine knot, which is built by six cysteine residues forming three disulfides upon oxidative folding. This motif ensures a notably rigid framework that highly tolerates both rational and combinatorial changes in the primary structure. Being accessible through recombinant production and total chemical synthesis, cystine-knot miniproteins can be endowed with novel bioactivities by variation of surface-exposed loops and incorporation of non-natural elements within their non-conserved regions towards the generation of tailor-made peptidic compounds. In this chapter the topology of cystine-knot peptides, their synthesis and applications for diagnostics and therapy is discussed.

The 28-day exposure to fenpropathrin decreases locomotor activity and reduces activity of antioxidant enzymes in mice brains

BACKGROUND

Fenpropathrin (Fen) is a pyrethroid (Pyr) insecticide. Pyrs are used in veterinary medicine, in agriculture and for domestic purposes. As their use increases, new questions about their side effects and mode of action in non-target organisms arise. The objective of this work was to characterize dose-response relationship for in vivo motor function and memory in mice exposed to Fen for 28 days and to assess its influence on activity of antioxidant enzymes in mice brains.

METHODS

The experiment was performed using 64 female mice. Fen at the dose of 11.9mg/kg of body mass, 5.95mg/kg or 2.38mg/kg was administered ip to the mice for 28 consecutive days. Motor function and spatial working memory were tested on days 7, 14 and 28. On day 29, the animals were sacrificed and brains were used to determine activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx).

RESULTS

Fen significantly decreased locomotor activity in mice receiving the highest dose at every stage of the experiment. Lower doses reduced locomotion on days 7 and 14. Fen did not produce memory impairment. A decrease in activities of SOD and GPx was recorded in mice brains.

CONCLUSIONS

The decrease of SOD activity in mice brains results from direct inhibition of the enzyme by Fen and/or increased utilization due to excessive free radical formation in conditions of Fen-induced oxidative stress. The reduction in GPx activity is probably due to limited glutathione availability. The reduced locomotor activity is a behavioral demonstration of Fen-induced damage in the dopaminergic system.