Block of neuronal nicotinic acetylcholine receptors by organophosphate insecticides

Effects of DDT and DDE on placental cholinergic receptors

The placental cholinergic system; known as an important factor in intracellular metabolic activities, regulation of placental vascular tone, placental development, and neurotransmission; can be affected by persistent organic pesticides, particularly organochlorine pesticides(OCPs), which can influence various epigenetic regulations and molecular pathways. Although OCPs are legally prohibited, trace amounts of the persistent dichlorodiphenyltrichloroethane(DDT) are still found in the environment, making prenatal exposure inevitable. In this study, the effects of 2,4'-DDT and 4,4'-DDT; and its breakdown product 4,4'-DDE in the environment on placental cholinergic system were evaluated with regards to cholinergic genes. 40 human placentas were screened, where 42,50% (17 samples) were found to be positive for the tested compounds. Average concentrations were 10.44 μg/kg; 15.07 μg/kg and 189,42 μg/kg for 4,4'-DDE; 2,4'-DDT and 4,4'-DDT respectively. RNA-Seq results revealed 2396 differentially expressed genes in positive samples; while an increase in CHRM1,CHRNA1,CHRNG and CHRNA2 genes at 1.28, 1.49, 1.59 and 0.4 fold change were found(p<0028). The increase for CHRM1 was also confirmed in tissue samples with immunohistochemistry. In vitro assays using HTR8/SVneo cells; revealed an increase in mRNA expression of CHRM1, CHRM3 and CHRN1 in DDT and DDE treated groups; which was also confirmed through western blot assays. An increase in the expression of CHRM1,CHRNA1, CHRNG(p<0001) and CHRNA2(p<0,05) were found from the OCPs exposed and non exposed groups.The present study reveals that intrauterine exposure to DDT affects the placental cholinergic system mainly through increased expression of muscarinic receptors. This increase in receptor expression is expected to enhance the sensitivity of the placental cholinergic system to acetylcholine.

Recent advances in cholinergic mechanisms as reactions to toxicity, stress, and neuroimmune insults

This review presents recent studies of the chemical and molecular regulators of acetylcholine (ACh) signaling and the complexity of the small molecule and RNA regulators of those mechanisms that control cholinergic functioning in health and disease. The underlying structural, neurochemical, and transcriptomic concepts, including basic and translational research and clinical studies, shed new light on how these processes inter-change under acute states, age, sex, and COVID-19 infection; all of which modulate ACh-mediated processes and inflammation in women and men and under diverse stresses. The aspect of organophosphorus (OP) compound toxicity is discussed based on the view that despite numerous studies, acetylcholinesterase (AChE) is still a vulnerable target in OP poisoning because of a lack of efficient treatment and the limitations of oxime-assisted reactivation of inhibited AChE. The over-arching purpose of this review is thus to discuss mechanisms of cholinergic signaling dysfunction caused by OP pesticides, OP nerve agents, and anti-cholinergic medications; and to highlight new therapeutic strategies to combat both the acute and chronic effects of these chemicals on the cholinergic and neuroimmune systems. Furthermore, OP toxicity was examined in view of cholinesterase inhibition and beyond in order to highlight improved small molecules and RNA therapeutic strategies and assess their predicted pitfalls to reverse the acute toxicity and long-term deleterious effects of OPs.

Optical Biosensors and Their Applications for the Detection of Water Pollutants

The correct detection and quantification of pollutants in water is key to regulating their presence in the environment. Biosensors offer several advantages, such as minimal sample preparation, short measurement times, high specificity and sensibility and low detection limits. The purpose of this review is to explore the different types of optical biosensors, focusing on their biological elements and their principle of operation, as well as recent applications in the detection of pollutants in water. According to our literature review, 33% of the publications used fluorescence-based biosensors, followed by surface plasmon resonance (SPR) with 28%. So far, SPR biosensors have achieved the best results in terms of detection limits. Although less common (22%), interferometers and resonators (4%) are also highly promising due to the low detection limits that can be reached using these techniques. In terms of biological recognition elements, 43% of the published works focused on antibodies due to their high affinity and stability, although they could be replaced with molecularly imprinted polymers. This review offers a unique compilation of the most recent work in the specific area of optical biosensing for water monitoring, focusing on both the biological element and the transducer used, as well as the type of target contaminant. Recent technological advances are discussed.

The scleractinian coral Pocillopora damicornis relies on neuroendocrine regulation to cope with polycyclic aromatic hydrocarbons under heat stress

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic environmental pollutants and are threatening scleractinian corals. In this study, PAHs treatment did not induce significant physiological responses of the coral Pocillopora damicornis and its algal symbionts, but biological processes including response to toxin, drug metabolic, and oxidation reduction were triggered at the mRNA level. These results implied that PAHs could be a group of slow-acting environmental toxicants, whose effects were moderate but persistent. Besides, it was interesting to find that PAHs activated the neuroendocrine system in the coral by triggering the expression of monoaminergic and acetylcholinergic system related genes, indicating that PAHs might function as environmental hormones. Moreover, the combined treatments of PAHs and heat caused a much obvious effect on the coral and its algal symbionts by elevating antioxidant activity and suppressing photosynthesis in the symbionts. Results from the transcriptome data further indicated that corals might perform stress responses upon PAHs and heat challenges through the TNF and apoptosis pathways, which perhaps was modulated by the neuroendocrine system of corals. Collectively, our survey demonstrates that the PAHs can function as environmental hormones and activate the neuroendocrine regulation in scleractinian corals, which may contribute to the stress responses of symbiotic association by modulating photosynthesis, antioxidation, and apoptosis.

Data-driven learning of narcosis mode of action identifies a CNS transcriptional signature shared between whole organism Caenorhabditis elegans and a fish gill cell line

With the large numbers of man-made chemicals produced and released in the environment, there is a need to provide assessments on their potential effects on environmental safety and human health. Current regulatory frameworks rely on a mix of both hazard and risk-based approaches to make safety decisions, but the large number of chemicals in commerce combined with an increased need to conduct assessments in the absence of animal testing makes this increasingly challenging. This challenge is catalysing the use of more mechanistic knowledge in safety assessment from both in silico and in vitro approaches in the hope that this will increase confidence in being able to identify modes of action (MoA) for the chemicals in question. Here we approach this challenge by testing whether a functional genomics approach in C. elegans and in a fish cell line can identify molecular mechanisms underlying the effects of narcotics, and the effects of more specific acting toxicants. We show that narcosis affects the expression of neuronal genes associated with CNS function in C. elegans and in a fish cell line. Overall, we believe that our study provides an important step in developing mechanistically relevant biomarkers which can be used to screen for hazards, and which prevent the need for repeated animal or cross-species comparisons for each new chemical.

Behavioral and biochemical alterations induced by acute clothianidin and imidacloprid exposure in the killer shrimp, Dikerogammarus villosus

Neonicotinoids are widely used insecticides around the world and are preserved permanently in soils and appear in surface waters posing an increased threat to ecosystems. In the present study, we exposed adult specimens of amphipod Dikerogammarus villosus to environmentally relevant and higher concentrations of two widely used agricultural neonicotinoids, clothianidin (CLO) and imidacloprid (IMI), for 2 days. The acute effects were investigated at the behavioral (immobility time and swimming activity) and biochemical (glutathione S-transferase [GST] and acetylcholine esterase [AchE] activity) levels. All CLO concentrations used (64 nM, 128 nM, 192 nM) significantly decreased the immobility time and swimming activity. In the case of IMI, the immobility time decreased significantly only at the highest concentration applied (977 nM), but the distance travelled by the animals significantly decreased even at lower concentrations (78 nM and 313 nM). The GST enzyme activity did not change in the CLO-treated groups, however, the 626 nM and 977 nM IMI concentrations significantly increased the GST activity. Similarly, to the behavioral level, all CLO concentrations significantly decreased the AchE activity. In contrast, IMI has a significant stimulating effect on the AchE activity at the 313 nM, 626 nM, and 977 nM concentrations. Based on the authors' best knowledge, this is the first study to investigate the effects of CLO and IMI at environmentally-relevant concentrations on D. villosus. Our findings contribute to the understanding of the physiological effects of neonicotinoids.

Differences in neurotoxic outcomes of organophosphorus pesticides revealed via multi-dimensional screening in adult and regenerating planarians

Organophosphorus pesticides (OPs) are a chemically diverse class of commonly used insecticides. Epidemiological studies suggest that low dose chronic prenatal and infant exposures can lead to life-long neurological damage and behavioral disorders. While inhibition of acetylcholinesterase (AChE) is the shared mechanism of acute OP neurotoxicity, OP-induced developmental neurotoxicity (DNT) can occur independently and/or in the absence of significant AChE inhibition, implying that OPs affect alternative targets. Moreover, different OPs can cause different adverse outcomes, suggesting that different OPs act through different mechanisms. These findings emphasize the importance of comparative studies of OP toxicity. Freshwater planarians are an invertebrate system that uniquely allows for automated, rapid and inexpensive testing of adult and developing organisms in parallel to differentiate neurotoxicity from DNT. Effects found only in regenerating planarians would be indicative of DNT, whereas shared effects may represent neurotoxicity. We leverage this unique feature of planarians to investigate potential differential effects of OPs on the adult and developing brain by performing a comparative screen to test 7 OPs (acephate, chlorpyrifos, dichlorvos, diazinon, malathion, parathion and profenofos) across 10 concentrations in quarter-log steps. Neurotoxicity was evaluated using a wide range of quantitative morphological and behavioral readouts. AChE activity was measured using an Ellman assay. The toxicological profiles of the 7 OPs differed across the OPs and between adult and regenerating planarians. Toxicological profiles were not correlated with levels of AChE inhibition. Twenty-two "mechanistic control compounds" known to target pathways suggested in the literature to be affected by OPs (cholinergic neurotransmission, serotonin neurotransmission, endocannabinoid system, cytoskeleton, adenyl cyclase and oxidative stress) and 2 negative controls were also screened. When compared with the mechanistic control compounds, the phenotypic profiles of the different OPs separated into distinct clusters. The phenotypic profiles of adult vs. regenerating planarians exposed to the OPs clustered differently, suggesting some developmental-specific mechanisms. These results further support findings in other systems that OPs cause different adverse outcomes in the (developing) brain and build the foundation for future comparative studies focused on delineating the mechanisms of OP neurotoxicity in planarians.

Organophosphorus Pesticides as Modulating Substances of Inflammation through the Cholinergic Pathway

Organophosphorus pesticides (OPs) are widespread insecticides used for pest control in agricultural activities and the control of the vectors of human and animal diseases. However, OPs’ neurotoxic mechanism involves cholinergic components, which, beyond being involved in the transmission of neuronal signals, also influence the activity of cytokines and other pro-inflammatory molecules; thus, acute and chronic exposure to OPs may be related to the development of chronic degenerative pathologies and other inflammatory diseases. The present article reviews and discusses the experimental evidence linking inflammatory process with OP-induced cholinergic dysregulation, emphasizing the molecular mechanisms related to the role of cytokines and cellular alterations in humans and other animal models, and possible therapeutic targets to inhibit inflammation.

Alterations in the non-neuronal cholinergic system induced by in-vitro exposure to diazoxon in spleen mononuclear cells of Nile tilapia (O. niloticus)

Organophosphate pesticides as diazinon disrupt the neuroimmune communication, affecting the innate and adaptive immune response of the exposed organisms. Since the target molecule of diazinon is typically the acetylcholinesterase enzyme (AChE), the existence of a non-neuronal cholinergic system in leukocytes makes them susceptible to alterations by diazinon. Therefore, the aim of this work was to evaluate the activity of AChE, acetylcholine (ACh) concentration, and the expression of nicotinic ACh receptors (nAChR) and muscarinic ACh receptors (mAChR) in spleen mononuclear cells (SMNC) of Nile tilapia (O. niloticus) exposed in vitro to diazoxon, a diazinon metabolite. SMNC were exposed in-vitro to 1 nM, 1 μM, and 10 μM diazoxon for 24 h. The enzyme activity of AChE was then evaluated by spectrophotometry, followed by ACh quantification by ultra-performance liquid chromatography. Finally, mAChR and nAChR expression was evaluated by RT-qPCR. The results indicate that AChE levels are significantly inhibited at 1 and 10 μM diazoxon, while the relative expression of (M3, M4, and M5) mAChR and (β2) nAChR is reduced significantly as compared against SMNC not exposed to diazoxon. However, ACh levels show no significant difference with respect to the control group. The data indicate that diazoxon directly alters elements in the cholinergic system of SMNC by AChE inhibition or indirectly through the interaction with AChR, which is likely related to the immunotoxic properties of diazinon and its metabolites.

Adrenaline is effective in reversing the inadequate heart rate response in atropine treated organophosphorus and carbamate poisoning

BACKGROUND

In acute organophosphorus (OP) or carbamate poisoning, some patients require high dose atropine to counteract the effects on heart rate (HR) and blood pressure (BP). This study describes the factors associated with high dose atropine therapy and the use of adrenaline to reverse the inadequate HR response to atropine.

METHODS

Consecutive patients admitted to the intensive care unit (ICU) were prospectively recruited. Demographic data, treatment and outcomes of patients who failed to achieve target HR (100/min) or systolic BP >90 mm Hg with either a cumulative atropine dose of 100-mg within 6-h following admission or an infusion of 30 mg/h for at least 3-h were compared with patients who achieved the targets. Factors associated with high dose atropine therapy were explored using logistic regression analysis and expressed as odds ratio (OR) with 95% confidence intervals (CIs).

RESULTS

Of the 181 patients admitted with OP or carbamate poisoning, 155 patients fulfilled inclusion criteria. The mean (SD) age was 35.7 (15.8) years; admission APACHE-II score was 14.6 (7.5). Heart rate and/or BP target was not achieved in 13.6%. In these patients, target HR was achieved after adding adrenaline infusion at 2-4 μg/min. Ventilation duration (11.6 ± 6.3 vs. 8.4 ± 6.9 days, p = 0.05) and ICU stay (12.3 ± 5.8 vs. 8.9 ± 5.8 days, p = 0.01) were longer in patients requiring high dose atropine when compared with others. On multivariate logistic regression analysis, shorter time to presentation to hospital (p = 0.04) was associated with need for high dose atropine. Overall mortality was 9% and similar in both groups (p = 0.41).

CONCLUSIONS

High dose atropine therapy is required in a subset of patients with OP and carbamate poisoning and was associated with longer ventilation duration and ICU stay. Adrenaline infusion improved hemodynamics in these patients.

Neonicotinoids: Spreading, Translocation and Aquatic Toxicity

Various environmental and ecotoxicological aspects related to applications of neonicotinoid insecticides are assessed. Dosages of neonicotinoids applied in seed coating materials were determined and are compared to other applications (spray and granule). Environmental levels in soils and affecting factors in translocation are discussed. Excretion of neonicotinoids via guttation from coated maize seeds up to two months upon emergence, as well as cross-contamination of plants emerged from non-coated seeds or weeds nearby have been demonstrated. Contamination of surface waters is discussed in scope of a worldwide review and the environmental fate of the neonicotinoid active ingredients and the formulating surfactant appeared to be mutually affected by each other. Toxicity of neonicotinoid active ingredients and formulations on Daphnia magna completed with some investigations of activity of the detoxifying glutathione S-transferase enzyme demonstrated the modified toxicity due to the formulating agents. Electrophysiological results on identified central neurons of the terrestrial snail Helixpomatia showed acetylcholine antagonist (inhibitory) effects of neonicotinoid insecticide products, but no agonist (ACh-like) effects were recorded. These data also suggested different molecular targets (nicotinergic acetylcholine receptors and acetylcholine esterase enzyme) of neonicotinoids in the snail central nervous system.

Two opposite dose-dependent effects of diazinon on the motor activity of the rat ileum

Acute poisoning with OPs may lead to a range of neurological effects, which cannot be explained by AChE inhibition alone. Several OPs interact directly with cholinergic receptors in mammals, but such data does not exist for invertebrates. The aim of current study was to investigate the direct and indirect effects of diazinon on the contractions of rat ileum and to compare those effects on the nervemuscle preparation of the Ascaris suum. In the presence of increasing concentrations of diazinon (3, 10 and 30nM), EFS-induced ileal contractions were increased significantly. In the same preparation, diazinon 3nM, significantly increased contractions induced by EFS, but did not affect the contractions caused by 5MFI. Contrarily, 1μM of diazinon significantly and reversibly inhibited the EFS-induced ileal contractions. Diazinon exhibited competitive and non-competitive inhibitions of 5MFI induced contractions. The control EC₅₀ of 5MFI was 2.48μM with R_max=1.88g. In the presence of diazinon, EC₅₀ was 12.45μM, while R_max was reduced to 0.43g. After washing, the EC₅₀ and R_max values were again closer to the control level (3.80μM and 1.04g). Diazinon 1μM did not inhibit Ascaris suum contractions caused by ACh, but it increased the R_max. Diazinon in our study exhibits two opposite effects on the motor activity of the ileum. In low nanomolar concentrations the dominat is its effect on AChE and the stimulation of contractions. Furthermore, in concentrations that approach micromolar values diazinon has a direct inhibitory effect on muscarinic receptors. The direct inhibitory effect of diazinon on A. suum contractions was not found.

DEET potentiates the development and persistence of anticholinesterase dependent chronic pain signs in a rat model of Gulf War Illness pain

Exposure to DEET (N,N-diethyl-meta-toluamide) may have influenced the pattern of symptoms observed in soldiers with GWI (Gulf War Illness; Haley and Kurt, 1997). We examined how the addition of DEET (400mg/kg; 50% topical) to an exposure protocol of permethrin (2.6mg/kg; topical), chlorpyrifos (CP; 120mg/kg), and pyridostigmine bromide (PB;13mg/kg) altered the emergence and pattern of pain signs in an animal model of GWI pain (Nutter et al., 2015). Rats underwent behavioral testing before, during and after a 4week exposure: 1) hindlimb pressure withdrawal threshold; 2) ambulation (movement distance and rate); and 3) resting duration. Additional studies were conducted to assess the influence of acute DEET (10-100μM) on muscle and vascular nociceptor K_v7, K_DR, Na_v1.8 and Na_v1.9. We report that a 50% concentration of DEET enhanced the development and persistence of pain-signs. Rats exposed to all 4 compounds exhibited ambulation deficits that appeared 5-12weeks post-exposure and persisted through weeks 21-24. Rats exposed to only three agents (CP or PB excluded), did not fully develop ambulation deficits. When PB was excluded, rats also developed rest duration pain signs, in addition to ambulation deficits. There was no evidence that physiological doses of DEET acutely modified nociceptor K_v7, K_DR, Na_v1.8 or Na_v1.9 activities. Nevertheless, DEET augmented protocols decreased the conductance of K_v7 expressed in vascular nociceptors harvested from chronically exposed rats. We concluded that DEET enhanced the development and persistence of pain behaviors, but the anticholinesterases CP and PB played a determinant role.

Chlorpyrifos Toxicity in Mouse Cultured Cerebellar Granule Neurons at Different Stages of Development: Additive Effect on Glutamate-Induced Excitotoxicity

OBJECTIVE

Chlorpyrifos (CPF) is a neurotoxic organophosphorus (OP) insecticide. Its mechanism of action includes oxidative stress, excitotoxicity, and inhibition of the acetylcholinesterase enzyme (AChE). The aim of the present study is to investigate CPF toxicity in mature and immature cerebellar granule neurons (CGNs), as well as its effect on glutamate induced excitotoxicity.

MATERIALS AND METHODS

This study was an in vitro experimental study performed on mice cultured CGNs. Immature and mature neurons were exposed to different concentrations of CPF (1-1000 µM) and glutamate (10-600 µM) for 48 hours after which we used the MTT assay to measure cytotoxicity. Immature neurons had exposure to CPF for 5 days in order to evaluate the cytotoxic effect on developing neurons. Mature neurons received sub-lethal concentrations of CPF (10, 100 µM) combined with different concentrations of glutamate. AChE activity and reactive oxygen species (ROS) generation were assessed after treatments.

RESULTS

Immature CGNs had increased sensitivity to CPF toxicity compared to mature neurons. We observed significantly greater ROS production in immature compared to mature neurons, however AChE activity was more inhibited in mature neurons. Although CPF toxicity was not well correlated with AChE inhibition, it correlated well with ROS production. Glutamate toxicity was potentiated by sub-lethal concentration of CPF, however glutamate induced ROS production was not affected. The results suggested that CPF potentiated glutamate toxicity by mechanisms other than oxidative stress.

CONCLUSION

CPF toxicity differed in mature and immature neurons. Potentiated glutamate toxicity by CPF implied that CPF exposure might be a risk factor for neurodegenerative disease.

Transcriptome mining: Multigene panel to test delousing drug response in the sea louse Caligus rogercresseyi

Controlling infestations of copepodid ectoparasites in the salmon industry is increasingly problematic given higher instances of drug resistance or loss of sensitivity. Despite the importance of this issue, the molecular mechanisms and genes implicated in resistance/susceptibility are only scarcely understood. The objective of the present study was to identify and evaluate the expression levels of candidate genes associated with delousing drug response in the sea louse Caligus rogercresseyi. From RNA-seq data obtained for adult male and female sea lice, 62.48 M reads were assembled in 70,349 high-quality contigs. BLASTX analysis against UniprotKB/Swiss-Prot and the ESTs available for crustaceans in the NCBI database identified 870 transcripts previously related to genes associated with delousing drug response. Furthermore, 14 candidate genes were validated through RT-qPCR and were evaluated with deltamethrin and azamethiphos bioassays. The results evidenced an overregulation of genes involved in ion transport in salmon lice treated with deltamethrin, while those treated with azamethiphos evidenced an overregulation of genes such as cytochrome P450, Carboxylesterase, and acetylcholine receptors. The present study provides a multigene panel to test delousing drug response to pyrethroids and organophosphates in a highly prevalent pathogen of the Chilean salmon industry.

Health risk assessment of exposure to TriCresyl Phosphates (TCPs) in aircraft: a commentary

Possible exposure to TriCresyl Phosphates (TCPs) has led to concerns among airline crew members. One isomer, Tri-ortho-Cresyl Phosphate (ToCP) is known to be neurotoxic and exposure to ToCP via contaminated cabin air has been suggested to be associated with the alleged Aerotoxic syndrome. The symptoms associated with Aerotoxic syndrome are diverse, including headaches, loss of balance, numbness and neurobehavioral abnormalities such as emotional instability, depression and cognitive dysfunction. Other ortho-isomers are toxic as well, but the non-ortho isomers are regarded as less toxic. In a collaborative effort to increase insight into the possible association between exposure to TCPs via contaminated cabin air and Aerotoxic syndrome, we performed an exposure- and toxicological risk assessment. Measurements in KLM 737 aircraft have demonstrated the presence of non-ortho isomers in low concentrations, though ToCP and other ortho-isomers could not be detected. Based on this exposure assessment, we established a toxicological risk model that also takes into account human differences in bioactivation and detoxification to derive a hazard quotient. From this model it appears unlikely that the health effects and alleged Aerotoxic syndrome are due to exposure to ToCP. Alternative explanations for the reported symptoms are discussed, but evaluation of the current findings in light of the criteria for occupational disease leads to the conclusion that the Aerotoxic Syndrome cannot be regarded as such. Additional research is thus required to unravel the underlying causes for the reported health complaints.

Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees

Pesticides that target cholinergic neurotransmission are highly effective, but their use has been implicated in insect pollinator population decline. Honeybees are exposed to two widely used classes of cholinergic pesticide: neonicotinoids (nicotinic receptor agonists) and organophosphate miticides (acetylcholinesterase inhibitors). Although sublethal levels of neonicotinoids are known to disrupt honeybee learning and behaviour, the neurophysiological basis of these effects has not been shown. Here, using recordings from mushroom body Kenyon cells in acutely isolated honeybee brain, we show that the neonicotinoids imidacloprid and clothianidin, and the organophosphate miticide coumaphos oxon, cause a depolarization-block of neuronal firing and inhibit nicotinic responses. These effects are observed at concentrations that are encountered by foraging honeybees and within the hive, and are additive with combined application. Our findings demonstrate a neuronal mechanism that may account for the cognitive impairments caused by neonicotinoids, and predict that exposure to multiple pesticides that target cholinergic signalling will cause enhanced toxicity to pollinators.

Exposure to pesticides can disrupt foraging and navigation behaviour in bees. Palmer et al. use electrophysiology to show that two neonicotinoids and an organophosphate miticide cause neuronal dysfunction in the honeybee brain at environmentally relevant concentrations.

Acetylcholinesterase inhibitors: pharmacology and toxicology

Acetylcholinesterase is involved in the termination of impulse transmission by rapid hydrolysis of the neurotransmitter acetylcholine in numerous cholinergic pathways in the central and peripheral nervous systems. The enzyme inactivation, induced by various inhibitors, leads to acetylcholine accumulation, hyperstimulation of nicotinic and muscarinic receptors, and disrupted neurotransmission. Hence, acetylcholinesterase inhibitors, interacting with the enzyme as their primary target, are applied as relevant drugs and toxins. This review presents an overview of toxicology and pharmacology of reversible and irreversible acetylcholinesterase inactivating compounds. In the case of reversible inhibitors being commonly applied in neurodegenerative disorders treatment, special attention is paid to currently approved drugs (donepezil, rivastigmine and galantamine) in the pharmacotherapy of Alzheimer's disease, and toxic carbamates used as pesticides. Subsequently, mechanism of irreversible acetylcholinesterase inhibition induced by organophosphorus compounds (insecticides and nerve agents), and their specific and nonspecific toxic effects are described, as well as irreversible inhibitors having pharmacological implementation. In addition, the pharmacological treatment of intoxication caused by organophosphates is presented, with emphasis on oxime reactivators of the inhibited enzyme activity administering as causal drugs after the poisoning. Besides, organophosphorus and carbamate insecticides can be detoxified in mammals through enzymatic hydrolysis before they reach targets in the nervous system. Carboxylesterases most effectively decompose carbamates, whereas the most successful route of organophosphates detoxification is their degradation by corresponding phosphotriesterases.

Entomotoxicity and biosafety assessment of PEGylated acephate nanoparticles: a biologically safe alternative to neurotoxic pesticides

This is a report of an experimental study on a nanoencapsulation of the organophosphate acephate. Acephate was encapsulated in polyethylene glycol, using a simple, easy-to-replicate method that required no special equipment or conditions. The nanoencapsulation (nanoacephate) was characterized and its bioefficacy as compared to the regular commercial acephate was tested. The biosafety of the new compound was also tested on a murine model. Our new nanoencapsulation scored over the regular variety on all counts. It was found to successfully incorporate the active pesticidal component, acephate and this compound retained greater functional integrity over time as a nanoencapsulation. It was significantly more efficacious than the regular variety. It was biosafe when tested on murine model. We have reason to believe that this nanoencapsulation would allow the use of an organophosphate in a more targeted manner, thereby making it a cost-effective and eco-friendly alternative to the regular variety in use now.

Genome-wide study of DNA methylation alterations in response to diazinon exposure in vitro

Pesticide exposure has repeatedly been associated with cancers. However, molecular mechanisms are largely undetermined. In this study, we examined whether exposure to diazinon, a common organophosphate that has been associated with cancers, could induce DNA methylation alterations. We conducted genome-wide DNA methylation analyses on DNA samples obtained from human hematopoietic K562 cell exposed to diazinon and ethanol using the Illumina Infinium HumanMethylation27 BeadChip. Bayesian-adjusted t-tests were used to identify differentially methylated gene promoter CpG sites. We identified 1069 CpG sites in 984 genes with significant methylation changes in diazinon-treated cells. Gene ontology analysis demonstrated that some genes are tumor suppressor genes, such as TP53INP1 (3.0-fold, q-value <0.001) and PTEN (2.6-fold, q-value <0.001), some genes are in cancer-related pathways, such as HDAC3 (2.2-fold, q-value=0.002), and some remain functionally unknown. Our results provided direct experimental evidence that diazinon may modify gene promoter DNA methylation levels, which may play a pathological role in cancer development.

Modulation of human α4β2 nicotinic acetylcholine receptors by brominated and halogen-free flame retardants as a measure for in vitro neurotoxicity

Brominated flame retardants (BFRs) are abundant persistent organic pollutants with well-studied toxicity. The toxicological and ecological concern associated with BFRs argues for replacement by safer alternatives. However, the (neuro)toxic potential of alternative halogen-free flame retardants (HFFRs) is unknown. Previous research identified the nervous system as a sensitive target organ for BFRs, with modulation of excitatory nicotinic acetylcholine (nACh) receptors as one of the modes of action. Since it is essential to assess the (neuro)toxic potential of HFFRs before large scale use, we measured the effects of three BFRs and 13 HFFRs on the function of human α(4)β(2) nACh receptors, expressed in Xenopus oocytes, using the two-electrode voltage-clamp technique. The results demonstrate that some BFRs (TBBPA and to a lesser extent BDE-209) and HFFRs (TPP, Alpi, APP, MMT and to a lesser extent ATH, ATO, MHO, MPP, RDP and ZHS) act as nACh receptor antagonists. Contrary, BPS, BDP, DOPO and ZS were unable to modulate nACh receptors. Despite the lack of toxicological data on HFFRs and the need for additional studies to perform a full (neuro)toxic risk assessment, the current data on antagonistic effects on nACh receptors could be an important step in prioritizing viable HFFRs for substitution of BFRs.

Acute exposure to the insecticide O,S-dimethyl phosphoramidothioate (methamidophos) leads to impairment of cardiovascular reflexes in rats

Poisoning by organophosphorus insecticides is often accompanied by cardiac complications which may be serious and even fatal. However, the effects of these compounds on the cardiovascular mechanisms involved in blood pressure regulation are not known. The aim of this study was to evaluate the effects of a sublethal dose (8 mg/kg, i.p.) of the organophosphorus methamidophos on chemoreceptor (CR) and Bezold-Jarisch (BJR) cardiovascular reflexes. Male Wistar rats were treated with single intraperitoneal injections of methamidophos in saline (n=23) or saline (0.9 percent, n=20) and underwent catheterization of femoral artery and vein one day after the injections. Cardiovascular recordings were performed 24h after the catheterization procedure. Plasma cholinesterase (ChE) activity was measured 24h after similar treatments in separate groups (n=10/group). The bradycardic component of CR and BJR was significantly attenuated in animals treated with methamidophos. The ChE activity was 80 percent reduced in the methamidophos-treated animals. Methamidophos impairment of the bradycardic component of two important cardiovascular reflexes may contribute to the cardiovascular toxicity associated with acute organophosphorus insecticides exposure.

Central respiratory effects on motor nerve activities after organophosphate exposure in a working heart brainstem preparation of the rat

The impact of organophosphorus compound (OP) intoxication on the activity of central respiratory circuitry, causing acetylcholinesterase (AChE) inhibition and accumulation of acetylcholine in the respiratory brainstem circuits, is not understood. We investigated the central effect of the OP Crotylsarin (CRS) on respiratory network activity using the working heart brainstem preparation, which specifically allows for the analysis of central drug effects without changes in brainstem oxygenation possibly caused by drug effects on peripheral cardio-respiratory activity. Respiratory network activity was determined from phrenic and hypoglossal or vagal nerve activities (PNA, HNA, VNA). To investigate combined central and peripheral CRS effects hypo-perfusion was used mimicking additional peripheral cardiovascular collapse. Systemic CRS application induced a brief central apnea and complete AChE-inhibition in the brainstem. Subsequently, respiration was characterised by highly significant reduced PNA minute activity, while HNA showed expiratory related extra bursting indicative for activation of un-specified oro-pharyngeal behaviour. During hypo-perfusion CRS induced significantly prolonged apnoea. In all experiments respiratory activity fully recovered after 1h. We conclude that CRS mediated AChE inhibition causes only transient central breathing disturbance. Apparently intrinsic brainstem mechanisms can compensate for cholinergic over activation. Nevertheless, combination of hypo-perfusion and CRS exposure evoke the characteristic breathing arrests associated with OP poisoning.

Repeated exposures to low-level chlorpyrifos results in impairments in sustained attention and increased impulsivity in rats

Organophosphates such as chlorpyrifos (CPF) are among the most commonly used pesticides in the world. Therefore, it is not surprising that measurable levels of organophosphates (including CPF) are found in over 50% of fresh fruits, vegetables and grains that we consume and that approximately 80% of adults in the US have detectable levels of CPF metabolites in their urine. It is well known that acute exposure to organophosphates can cause cognitive deficits; however, the effects of daily or intermittent contact with low levels of organophosphates (often reflective of environmental exposures) are not well understood. The objective of this study was to determine if repeated low-level exposures to CPF impaired the performance of the 5-Choice Serial Reaction Time Task (5C-SRTT), an animal model of sustained attention. Adult rats were trained to stably perform the 5C-SRTT, then treated with vehicle or CPF 18.0 mg/kg daily for 14 consecutive days or every other day for 30 days. Behavioral testing occurred daily during the CPF-exposure period and throughout a 30 day washout period to assess recovery. All CPF-treated animals exhibited deficits in percent correct, an increase in omissions and premature responses without signs of impaired motivation or overt toxicity. Deficits in 5C-SRTT accuracy were apparent well into the 30 day washout period despite significant recovery of cholinesterase activity. These results indicate that repeated exposures to relatively low levels of chlorpyrifos lead to protracted impairments of sustained attention and an increase in impulsive behaviors in rats.

Mass spectrometry identifies multiple organophosphorylated sites on tubulin

Acute toxicity of organophosphorus poisons (OP) is explained by inhibition of acetylcholinesterase in nerve synapses. Low-dose effects are hypothesized to result from modification of other proteins, whose identity is not yet established. The goal of the present work was to obtain information that would make it possible to identify tubulin as a target of OP exposure. Tubulin was selected for study because live mice injected with a nontoxic dose of a biotinylated organophosphorus agent appeared to have OP-labeled tubulin in brain as determined by binding to avidin beads and mass spectrometry. The experiments with live mice were not conclusive because binding to avidin beads could be nonspecific. To be convincing, it is necessary to find and characterize the OP-labeled tubulin peptide. The search for OP-labeled tubulin peptides was begun by identifying residues capable of making a covalent bond with OP. Pure bovine tubulin (0.012 mM) was treated with 0.01-0.5 mM chlorpyrifos oxon for 24 h at 37 degrees C in pH 8.3 buffer. The identity of labeled amino acids and percent labeling was determined by mass spectrometry. Chlorpyrifos oxon bound covalently to tyrosines 83, 103, 108, 161, 224, 262, 272, 357, and 399 in bovine alpha tubulin, and to tyrosines 50, 51, 59, 106, 159, 281, 310, and 340 in bovine beta tubulin. The most reactive were tyrosine 83 in alpha and tyrosine 281 in beta tubulin. In the presence of 1 mM GTP, percent labeling increased 2-fold. Based on the crystal structure of the tubulin heterodimer (PDB 1jff) tyrosines 83 and 281 are well exposed to solvent. In conclusion seventeen tyrosines in tubulin have the potential to covalently bind chlorpyrifos oxon. These results will be useful when searching for OP-labeled tubulin in live animals.

Rare missense variants of neuronal nicotinic acetylcholine receptor altering receptor function are associated with sporadic amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (SALS) is a motor neuron degenerative disease of unknown etiology. Current thinking on SALS is that multiple genetic and environmental factors contribute to disease liability. Since neuronal acetylcholine receptors (nAChRs) are part of the glutamatergic pathway, we searched for sequence variants in CHRNA3, CHRNA4 and CHRNB4 genes, encoding neuronal nicotinic AChR subunits, in 245 SALS patients and in 450 controls. We characterized missense variants by in vitro mutagenesis, cell transfection and electrophysiology. Sequencing the regions encoding the intracellular loop of AChRs subunits disclosed 15 missense variants (6.1%) in 14 patients compared with only six variants (1.3%) in controls (P = 0.001; OR 4.48, 95% CI 1.7-11.8). The frequency of variants in exons encoding extracellular and transmembrane domains and in intronic regions did not differ. NAChRs formed by mutant alpha3 and alpha4 and wild-type (WT) beta4 subunits exhibited altered affinity for nicotine (Nic), reduced use-dependent rundown of Nic-activated currents (I(Nic)) and reduced desensitization leading to sustained intracellular Ca(2+) concentration, in comparison with WT-nAChR. The cellular loop has a crucial importance for receptor trafficking and regulating ion channel properties. Missense variants in this domain are significantly over-represented in SALS patients and alter functional properties of nAChR in vitro, resulting in increased Ca(2+) entry into the cells. We suggest that these gain-of-function variants might contribute to disease liability in a subset of SALS because Ca(2+) signals mediate nAChR's neuromodulatory effects, including regulation of glutamate release and control of cell survival.

Oxidative and excitatory mechanisms of developmental neurotoxicity: transcriptional profiles for chlorpyrifos, diazinon, dieldrin, and divalent nickel in PC12 cells

BACKGROUND

Oxidative stress and excitotoxicity underlie the developmental neurotoxicity of numerous chemicals.

OBJECTIVES

We compared the effects of organophosphates (chlorpyrifos and diazinon), an organo-chlorine (dieldrin), and a metal [divalent nickel (Ni2+)] to determine how these mechanisms contribute to similar or dissimilar neurotoxic outcomes.

METHODS

We used PC12 cells as a model of developing neurons and evaluated transcriptional profiles for genes for oxidative stress responses and glutamate receptors.

RESULTS

Chlorpyrifos had a greater effect on oxidative-stress-related genes in differentiating cells compared with the undifferentiated state. Chlorpyrifos and diazinon showed significant concordance in their effects on glutathione-related genes, but they were negatively correlated for effects on catalase and superoxide dismutase isoforms and had no concordance for effects on ionotropic glutamate receptors. Surprisingly, the correlations were stronger between diazinon and dieldrin than between the two organophosphates. The effects of Ni2+ were the least similar for genes related to oxidative stress but had significant concordance with dieldrin for effects on glutamate receptors.

CONCLUSIONS

Our results point to underlying mechanisms by which different organophosphates produce disparate neurotoxic outcomes despite their shared property as cholinesterase inhibitors. Further, apparently unrelated neurotoxicants may produce similar outcomes because of convergence on oxidative stress and excitotoxicity. The combined use of cell cultures and microarrays points to specific end points that can distinguish similarities and disparities in the effects of diverse developmental neurotoxicants.

Effects of nicotine exposure on in vitro metabolism of chlorpyrifos in male Sprague-Dawley rats

The routine use of tobacco products may modify key metabolizing systems, which will further impact the metabolism of environmental contaminants. The objective of this study was to quantify the effect of repeated in vivo exposures to nicotine, a major pharmacologically active component of cigarette smoke, on in vitro metabolism of chlorpyrifos (CPF). CPF is an organophosphorus (OP) insecticide that is metabolized by cytochrome P-450 (CYP450) to its major metabolites, chlorpyrifos-oxon (CPF-oxon) and 3,5,6-trichloro-2-pyridinol (TCP). Male Sprague-Dawley rats were dosed subcutaneously with 1 mg nicotine/kg for 1, 7, or 10 d. Rats were sacrificed 4 or 24 h after the last nicotine treatment, and liver microsomes were prepared. The microsomes were incubated with varying concentrations of CPF and the production of the metabolites CPF-oxon and TCP were measured. The metabolism of CPF to the active oxon metabolite did not show significant changes following repeated nicotine treatments, evidenced by the unchanged pseudo first-order clearance rate of V(max)/K(mapp). The V(max) describing the metabolism of CPF to the inactive metabolite, TCP was increased in 24-h postdosing groups, after both single and repeated treatments of nicotine. In contrast, the metabolism to TCP was unchanged in groups evaluated at 4 h (single or repeated) post nicotine dosing. Some basic marker substrate activities were also investigated to ensure that nicotine exerted effects on CYP450 activities. Total P450 reduced spectra were not altered by nicotine treatment, but marker substrate activities for CYP1A and CYP2E1 were increased at 24 h after the single treatment, and marker substrate activity for CYP2B was decreased 4 h after 7 d of treatment. Results of this in vitro study suggest that repeated nicotine exposure may result in altered metabolism of CPF. Future in vivo experiments based on these results need to be conducted to ascertain the impact of in vivo nicotine exposures on CPF metabolism in rats.

Amyloid precursor protein 96-110 and beta-amyloid 1-42 elicit developmental anomalies in sea urchin embryos and larvae that are alleviated by neurotransmitter analogs for acetylcholine, serotonin and cannabinoids

Amyloid precursor protein (APP) is overexpressed in the developing brain and portions of its extracellular domain, especially amino acid residues 96-110, play an important role in neurite outgrowth and neural cell differentiation. In the current study, we evaluated the developmental abnormalities caused by administration of exogenous APP(96-110) in sea urchin embryos and larvae, which, like the developing mammalian brain, utilize acetylcholine and other neurotransmitters as morphogens; effects were compared to those of beta-amyloid 1-42 (Abeta42), the neurotoxic APP fragment contained within neurodegenerative plaques in Alzheimer's Disease. Although both peptides elicited dysmorphogenesis, Abeta42 was far more potent; in addition, whereas Abeta42 produced abnormalities at developmental stages ranging from early cleavage divisions to the late pluteus, APP(96-110) effects were restricted to the intermediate, mid-blastula stage. For both agents, anomalies were prevented or reduced by addition of lipid-permeable analogs of acetylcholine, serotonin or cannabinoids; physostigmine, a carbamate-derived cholinesterase inhibitor, was also effective. In contrast, agents that act on NMDA receptors (memantine) or alpha-adrenergic receptors (nicergoline), and that are therapeutic in Alzheimer's Disease, were themselves embryotoxic, as was tacrine, a cholinesterase inhibitor from a different chemical class than physostigmine. Protection was also provided by agents acting downstream from receptor-mediated events: increasing cyclic AMP with caffeine or isobutylmethylxanthine, or administering the antioxidant, a-tocopherol, were all partially effective. Our findings reinforce a role for APP in development and point to specific interactions with neurotransmitter systems that act as morphogens in developing sea urchins as well as in the mammalian brain.

Tyrosines of human and mouse transferrin covalently labeled by organophosphorus agents: a new motif for binding to proteins that have no active site serine

The expectation from the literature is that organophosphorus (OP) agents bind to proteins that have an active site serine. However, transferrin, a protein with no active site serine, was covalently modified in vitro by 0.5mM 10-fluoroethoxyphosphinyl-N-biotinamido pentyldecanamide, chlorpyrifos oxon, diisopropylfluorophosphate, dichlorvos, sarin, and soman. The site of covalent attachment was identified by analyzing tryptic peptides in the mass spectrometer. Tyr 238 and Tyr 574 in human transferrin and Tyr 238, Tyr 319, Tyr 429, Tyr 491, and Tyr 518 in mouse transferrin were labeled by OP. Tyrosine in the small synthetic peptide ArgTyrThrArg made a covalent bond with diisopropylfluorophosphate, chlorpyrifos oxon, and dichlorvos at pH 8.3. These results, together with our previous demonstration that albumin and tubulin bind OP on tyrosine, lead to the conclusion that OP bind covalently to tyrosine, and that OP binding to tyrosine is a new OP-binding residue. The OP-reactive tyrosines are activated by interaction with Arg or Lys. It is suggested that many proteins in addition to those already identified may be modified by OP on tyrosine. The extent to which tyrosine modification by OP can occur in vivo and the toxicological implications of such modifications require further investigation.

Protective effects of mecamylamine and atropine against α(4)β(2) nicotinic receptor expression and functional toxicity in paraoxon-treated rats

Chronic and acute exposure to organophosphate pesticides or related nerve agents may lead to persistent neurological and neurobehavioral effects, which cannot be explained by acetylcholinesterase (AChE) inhibition alone. In the present study, the effects of mecamylamine (2mg/kg), or atropine (10mg/kg) alone, or in combination, on the expression of nicotinic acetylcholine receptors (nAChRs) subunits, functional signs of toxicity and lethality in paraoxon-treated rats were investigated. Surviving animals were sacrificed after 48h of paraoxon administration. Paraoxon, at dosage of 1× LD50, significantly reduced expression of α(4) and β(2) nAChR subunits mRNA and protein in rat brain homogenates. Mecamylamine, efficiently prevented reduction of the α(4) and β(2) nAChR mRNA and protein in paraoxon exposed rat brains, but atropine was not efficient. Concurrent treatment with mecamylamine and atropine restored nAChRs mRNA and protein level and prevented lethality and severe involuntary movements induced by paraoxon. Nicotinic receptors antagonists may be included in the cocktail of therapeutic agents targeting the various mechanisms for neuronal injury by organophosphates.

Fetal effects of environmental exposure of pregnant women to organophosphorus compounds in a rural farming community in Sri Lanka

BACKGROUND

The possible deleterious effects of low-grade, chronic environmental and occupational exposure to organophosphorus compounds (OPCs) are not well documented.

OBJECTIVE

To investigate the possible effects of low-level, chronic exposure of pregnant mothers to OPCs on the fetus by measuring OPC levels, and using markers of OPC exposure, oxidative stress and oxidative tissue damage.

METHODS

Toxicity was assessed by measuring (i) OPC levels in breast milk and plasma from maternal and cord blood using gas chromatography, (ii) maternal and fetal butyrylcholinesterase (BChE) activity using inhibition assays, (iii) antioxidant status of the fetus using superoxide dismutase activity assays, (iv) oxidative stress in the fetus by determining malondialdehyde (MDA) concentrations, and (v) examining for fetal DNA fragmentation using electrophoresis. Samples were obtained from consenting mothers living in a farming community in southern Sri Lanka at the end of the pesticide spray season (study group) and just before the commencement of the spray season (in-between spray season; control group).

RESULTS

Organophosphate residues were detected in only two subjects (chlorpyrifos in maternal and cord blood of one during the spray season and dimethoate in breast milk of another during the in between spray season), but the test employed was capable of only detecting concentrations above 0.05 mg/l. However, cord blood obtained during the spray season showed significant inhibition of BChE activity, increased oxidative stress and more DNA fragmentation when compared with cord blood obtained during the in-between spray season.

CONCLUSIONS

Inhibition of cord blood BChE activity indicates fetal exposure to organophosphorus compounds during times when there is a high probability of environmental drift. This provides a plausible explanation for the increased oxidative stress and high DNA fragmentation in the fetus. Long-term outcomes of such exposures are unknown.

Evaluation of nicotinic receptors agonists and antagonists against paraoxon exposed PC12 cells

Chronic and acute exposure to organophosphate pesticides may lead to persistent neurological and neurobehavioral effects, which cannot be explained by acetylcholinesterase (AChE) inhibition alone. In an attempt to elucidate the mechanism by which paraoxon affects the nicotinic receptors gene expression, the effects of exposure of PC12 cells to 100μM concentrations of paraoxon for 48h in the presence and the absence of nicotinic acetylcholine receptors (nAChRs) agonists and antagonists were characterized. Paraoxon at 100μM significantly inhibited AChE activity. On the mRNA level, the α(4) and β(2) subunits of nAChR mRNA were significantly decreased in the cells exposed to paraoxon. On the protein level, α(4) and β(2) subunits of nAChR protein were also significantly reduced. Mecamylamine (10μM), dihydro-β-erythroidine (DHβE) (5μM) and nicotine (10μM) efficiently prevented the decrease of α(4) and β(2) nAChR mRNA and protein in PC12 cells, but carbamaylcholine a weak agonist of nAChR was not efficient. These observations suggest that α(4)β(2) nAChRs are involved in paraoxon related toxicity and nicotinic receptors antagonists could play some protective role against organophosphate related damages.

Changes in mRNA and protein levels of nicotinic acetylcholine receptors in Diazoxon exposed pC12 cells

Effects of diazoxon on the gene and protein expression of nicotinic acetylcholine receptors (nAChR) were evaluated in PC12 cells. Cells were exposed to 100 microM diazoxon for 48 h in the presence versus absence of nAChR agonists or antagonists. Diazoxon significantly inhibited AChE activity in the cells. At the mRNA level, transcripts of the alpha4 and beta2 subunits of nAChR were significantly reduced in cells exposed to diazoxon, but there was no change in alpha7 subunit mRNA content. Diazoxon exposure also significantly reduced the protein levels of both alpha4 and beta2 nAChR subunits. Treatment with nicotine (10 microM) or with the nicotinic receptor antagonists, mecamylamine (10 microM) or dihydro-beta-erythroidine (DHbetaE) (5 microM) efficiently prevented the diazoxon-induced reduction in alpha4 and beta2 nAChR mRNA and protein in PC12 cells, but carbamaylcholine, a weak nAChR agonist, was ineffective. These data suggest that alpha4beta2 nAChRs are involved in diazoxon-related toxicity and that nicotinic receptor antagonists could play a protective role against organophosphate-related damage.

Noncholinesterase effects induced by organophosphate pesticides and their relationship to cognitive processes: implication for the action of acylpeptide hydrolase

Organophosphate pesticides have been classically described as inhibitors of acetylcholinesterase (AChE) activity in insects and invertebrates. However, there is now more evidence supporting the hypothesis that these compounds also act through noncholinergic pathways, especially those related to cognitive processes. The enzyme acylpeptide hydrolase was identified as a new target for organophosphate pesticides. This enzyme is more sensitive than AChE to some organophosphates (OP), including dichlorvos, which is the parent compound for metrifonate, a therapeutic agent used in the treatment of cognitive impairment associated to Alzheimer's disease. Therefore, there is some doubt as to whether the mechanism of action of this drug is mediated by a potentiation of cholinergic transmission. However, the direct action of acylpeptide hydrolase in cognitive processes and the physiological and molecular mechanisms underlying subacute exposure to OP have yet to be demonstrated. This review deals with evidence demonstrating the existence of mechanisms of actions of OP, which are independent of cholinergic pathway potentiation and which have an effect on cognitive processes. In addition, the possible participation of the enzyme acylpeptide hydrolase in these processes is also discussed. Finally, the possibility of using this enzyme activity as a new biomarker for exposure to OP is considered.

Differential protein adduction by seven organophosphorus pesticides in both brain and thymus

There is a need for mechanistic understanding of the lasting ill health reported in several studies of workers exposed to organophosphorus (OP) pesticide. Although the acute toxicity is largely explicable by acetylcholinesterase inhibition and the lasting effects of frank poisoning by direct excitotoxicity or indirect consequences of the cholinergic syndrome, effects at lower levels of exposure would not be predicted from these mechanisms. Similarly, reversible interactions with nicotinic and muscarinic receptors in adults would not predict continuing ill health. Many OP pesticides produce protein adduction, and the lasting nature of this makes it a candidate mechanism for the production of continuing ill health. We found significant adduction of partially characterized protein targets in both rat brain and thymus by azamethiphos, chlorfenvinphos, chlorpyrifos-oxon, diazinon-oxon, dichlorvos and malaoxon, in vitro and pirimiphos-methyl in vivo. The diversity in the adduction pattern seen across these agents at low dose levels means that any longer term effects of adduction would be specific to specific organophosphates, rather than generic. This presents a challenge to epidemiology, as most exposures are to different agents over time. However, some adducted proteins are also expressed in blood, notably albumin, and so may provide exposure measures to increase the power of future epidemiological studies.

Fluorescence-based sensing of p-nitrophenol and p-nitrophenyl substituent organophosphates

A novel detection method for organophosphate neurotoxins has been described, based on the fluorescence quenching of a Coumarin derivative. These dyes are similar in structure to some organophosphates (OPs), and they fluoresce in the blue-green region of the spectra. This methodology has been utilized for the detection of organophosphates whose hydrolysis product is p-nitrophenol by using an enzyme, organophosphorus hydrolase (OPH). Coumarin1 in the presence of p-nitrophenol results in a quenching of fluorescence, providing a direct measure of the concentration of p-nitrophenol present in the sample. The decrease in fluorescence intensity is proportional to the paraoxon concentration in the range of 7.0x10(-7)-1.7x10(-4) M. The specificity of this sensing application for p-nitrophenyl substituent OPs has also been demonstrated. OPs are a class of synthetic organic pesticides which generally have a short residual life and can cause numerous acute and chronic health effects. They have been an integral part of the agricultural industry for the past several decades due to their target specificities and selectable toxicities. The toxic nature of these compounds can be attributed to the species-specific inhibition of acetylcholinesterase (AChE), an important enzyme responsible for the regeneration of neural synaptic function. In addition to their wide agricultural and urban usage, they have also been exploited for the development of neurological chemical warfare agents. Currently available technologies for OP detection include sol-gel thin films, screen printed electrodes, acoustic patterning, gas chromatography-mass spectrometry, and various other intricate techniques that have limited field applicabilities. This optically-based approach promises much simpler and more direct detection capabilities.