Planarian cholinesterase: molecular and functional characterization of an evolutionarily ancient enzyme to study organophosphorus pesticide toxicity

Organophosphate toxicity patterns: A new approach for assessing organophosphate neurotoxicity

Organophosphorus compounds or organophosphates (OPs) are widely used as flame retardants, plasticizers, lubricants and pesticides. This contributes to their ubiquitous presence in the environment and to the risk of human exposure. The persistence of OPs and their bioaccumulative characteristics raise serious concerns regarding environmental and human health impacts. To address the need for safer OPs, this study uses a New Approach Method (NAM) to analyze the neurotoxicity pattern of 42 OPs. The NAM consists of a 4-step process that combines computational modeling with in vitro and in vivo experimental studies. Using spherical harmonic-based cluster analysis, the OPs were grouped into four main clusters. Experimental data and quantitative structure-activity relationships (QSARs) analysis were used in conjunction to provide information on the neurotoxicity profile of each group. Results showed that one of the identified clusters had a favorable safety profile, which may help identify safer OPs for industrial applications. In addition, the 3D-computational analysis of each cluster was used to identify meta-molecules with specific 3D features. Toxicity was found to correspond to the level of phosphate surface accessibility. Substances with conformations that minimize phosphate surface accessibility caused less neurotoxic effect. This multi-assay NAM could be used as a guide for the classification of OP toxicity, helping to minimize the health and environmental impacts of OPs, and providing rapid support to the chemical regulators, whilst reducing reliance on animal testing.

How neurobehavior and brain development in alternative whole-organism models can contribute to prediction of developmental neurotoxicity

Developmental neurotoxicity (DNT) is not routinely evaluated in chemical risk assessment because current test paradigms for DNT require the use of mammalian models which are ethically controversial, expensive, and resource demanding. Consequently, efforts have focused on revolutionizing DNT testing through affordable novel alternative methods for risk assessment. The goal is to develop a DNT in vitro test battery amenable to high-throughput screening (HTS). Currently, the DNT in vitro test battery consists primarily of human cell-based assays because of their immediate relevance to human health. However, such cell-based assays alone are unable to capture the complexity of a developing nervous system. Whole organismal systems that qualify as 3 R (Replace, Reduce and Refine) models are urgently needed to complement cell-based DNT testing. These models can provide the necessary organismal context and be used to explore the impact of chemicals on brain function by linking molecular and/or cellular changes to behavioural readouts. The nematode Caenorhabditis elegans, the planarian Dugesia japonica, and embryos of the zebrafish Danio rerio are all suited to low-cost HTS and each has unique strengths for DNT testing. Here, we review the strengths and the complementarity of these organisms in a novel, integrative context and highlight how they can augment current cell-based assays for more comprehensive and robust DNT screening of chemicals. Considering the limitations of all in vitro test systems, we discuss how a smart combinatory use of these systems will contribute to a better human relevant risk assessment of chemicals that considers the complexity of the developing brain.

Comparative toxicity assessment of glyphosate and two commercial formulations in the planarian Dugesia japonica

Introduction: Glyphosate is a widely used, non-selective herbicide. Glyphosate and glyphosate-based herbicides (GBHs) are considered safe for non-target organisms and environmentally benign at currently allowed environmental exposure levels. However, their increased use in recent years has triggered questions about possible adverse outcomes due to low dose chronic exposure in animals and humans. While the toxicity of GBHs has primarily been attributed to glyphosate, other largely unstudied components of GBHs may be inherently toxic or could act synergistically with glyphosate. Thus, comparative studies of glyphosate and GBHs are needed to parse out their respective toxicity. Methods: We performed such a comparative screen using pure glyphosate and two popular GBHs at the same glyphosate acid equivalent concentrations in the freshwater planarian Dugesia japonica. This planarian has been shown to be a useful model for both ecotoxicology and neurotoxicity/developmental neurotoxicity studies. Effects on morphology and various behavioral readouts were obtained using an automated screening platform, with assessments on day 7 and day 12 of exposure. Adult and regenerating planarians were screened to allow for detection of developmentally selective effects. Results: Both GBHs were more toxic than pure glyphosate. While pure glyphosate induced lethality at 1 mM and no other effects, both GBHs induced lethality at 316 μM and sublethal behavioral effects starting at 31.6 μM in adult planarians. These data suggest that glyphosate alone is not responsible for the observed toxicity of the GBHs. Because these two GBHs also include other active ingredients, namely diquat dibromide and pelargonic acid, respectively, we tested whether these compounds were responsible for the observed effects. Screening of the equivalent concentrations of pure diquat dibromide and pure pelargonic acid revealed that the toxicity of either GBH could not be explained by the active ingredients alone. Discussion: Because all compounds induced toxicity at concentrations above allowed exposure levels, our data indicates that glyphosate/GBH exposure is not an ecotoxicological concern for D. japonica planarians. Developmentally selective effects were not observed for all compounds. Together, these data demonstrate the usefulness of high throughput screening in D. japonica planarians for assessing various types of toxicity, especially for comparative studies of several chemicals across different developmental stages.

Adult and regenerating planarians respond differentially to chronic drug exposure

There is a lack of data on the effects of chronic exposure to common drugs and stimulants on the developing nervous system. Freshwater planarians have emerged as a useful invertebrate model amenable to high-throughput behavioral phenotyping to assay chemical safety in adult and developing brains. Here, we leverage the unique strength of the system to test in parallel for effects on the adult and developing nervous system, by screening ten common drugs and stimulants (forskolin, clenbuterol, LRE-1, MDL-12,330A, adenosine, caffeine, histamine, mianserin, fluoxetine and sertraline) using the asexual freshwater planarian Dugesia japonica. The compounds were tested up to 100 μM nominal concentration for their effects on planarian morphology and behavior. Quantitative phenotypic assessments were performed on days 7 and 12 of exposure using an automated screening platform. The antidepressants sertraline and fluoxetine were the most potent to induce lethality, with significant lethality observed at 10 μM. All ten compounds caused sublethal morphological and/or behavioral effects, with the most effects, in terms of potency and breadth of endpoints affected, seen with mianserin and fluoxetine. Four of the compounds (forskolin, clenbuterol, mianserin, and fluoxetine) were developmentally selective, causing effects at lower concentrations in regenerating planarians. Of these, fluoxetine showed the greatest differences between the two developmental stages, inducing many behavioral endpoints in regenerating planarians but only a few in adult planarians. While some of these behavioral effects may be due to neuroefficacy, these results substantiate the need for better evaluation of the safety of these common drugs on the developing nervous system.

Toxicity of herbicide glyphosate to planarian Dugesia japonica and its potential molecular mechanisms

Glyphosate (GLY) is one of the most widely used agrochemicals in the world, and its exposure has become a public health concern. The freshwater planarian is an ideal test organism for detecting the toxicity of pollutants and has been an emerging animal model in toxicological studies. Nevertheless, the underlying toxicity mechanism of GLY to planarians has not been thoroughly explored. To elucidate the toxicity effects and molecular mechanism involved in GLY exposure of planarians, we studied the acute toxicity, histological change, and transcriptional response of Dugesia japonica subjected to GLY. Significant morphological malformations and histopathological changes were observed in planarians after GLY exposure for different times. Also, a number of differentially expressed genes (DEGs) were obtained at 1, 3 and 5 d after exposure; Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of these DEGs were performed, and a global and dynamic view was obtained in planarians upon GLY exposure at the transcriptomic level. Furthermore, real-time quantitative PCR (qRT-PCR) was conducted on nine DEGs associated with detoxification, apoptosis, stress response, DNA repair, etc. The expression patterns were well consistent with the RNA sequencing (RNA-seq) results at different time points, which confirmed the reliability and accuracy of the transcriptome data. Collectively, our results established that GLY could pose adverse effects on the morphology and histo-architecture of D. japonica, and the planarians are capable of responding to the disadvantageous stress by dysregulating the related genes and pathways concerning immune response, detoxification, energy metabolism, DNA damage repair, etc. To the best of our knowledge, this is the first report of transcriptomic analyses of freshwater planarians exposed to environmental pollutants, and it provided detailed sequencing data deriving from transcriptome profiling to deepen our understanding the molecular toxicity mechanism of GLY to planarians.

PBDEs disrupt homeostasis maintenance and regeneration of planarians due to DNA damage, proliferation and apoptosis anomaly

Polybrominated diphenyl ethers (PBDEs) are widely used as brominated flame retardants in the manufacturing industry, belonging to persistent organic pollutants in the environment. Planarians are the freshwater worms, with strong regenerative ability and extreme sensitivity to environmental toxicants. This study aimed to evaluate the potential acute comprehensive effects of PBDE-47/-209 on freshwater planarians. Methods to detect the effects include: detection of oxidative stress, observation of morphology and histology, detection of DNA fragmentation, and detection of cell proliferation and apoptosis. In the PBDE-47 treatment group, planarians showed increased oxidative stress intensity, severe tissue damage, increased DNA fragmentation level, and increased cell proliferation and apoptosis. In the PBDE-209 treatment group, planarians showed decreased oxidative stress intensity, slight tissue damage, almost unchanged DNA fragmentation level and apoptosis, proliferation increased only on the first day after treatment. In conclusion, both PBDE-47 and PBDE-209 are dangerous environmental hazardous material that can disrupt planarians homeostasis, while the toxicity of PBDE-47 is sever than PBDE-209 that PBDE-47 can lead to the death of planarians.

Bioactivation and detoxification of organophosphorus pesticides in freshwater planarians shares similarities with humans

Organophosphorus pesticides (OPs) are a chemically diverse class of insecticides that inhibit acetylcholinesterase (AChE). Many OPs require bioactivation to their active oxon form via cytochrome P450 to effectively inhibit AChE. OP toxicity can be mitigated by detoxification reactions performed by carboxylesterase and paraoxonase. The relative extent of bioactivation to detoxification varies among individuals and between species, leading to differential susceptibility to OP toxicity. Because of these species differences, it is imperative to characterize OP metabolism in model systems used to assess OP toxicity. We have shown that the asexual freshwater planarian Dugesia japonica is a suitable model to assess OP neurotoxicity and developmental neurotoxicity via rapid, automated testing of adult and developing organisms in parallel using morphological and behavioral endpoints. D. japonica has two cholinesterase enzymes with intermediate properties between AChE and butyrylcholinesterase that are sensitive to OP inhibition. Here, we demonstrate that D. japonica contains the major OP metabolic machinery to be a relevant model for OP neurotoxicity studies. Adult and regenerating D. japonica can bioactivate chlorpyrifos and diazinon into their respective oxons. Significant AChE inhibition was only observed after in vivo metabolic activation but not when the parent OPs were directly added to planarian homogenate using the same concentrations and timing. Using biochemical assays, we found that D. japonica has both carboxylesterase (24 nmol/(min*mg protein)) and paraoxonase (60 pmol/(min*mg protein)) activity. We show that planarian carboxylesterase activity is distinct from cholinesterase activity using benzil and tacrine. These results further support the use of D. japonica for OP toxicity studies.

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.

Cognitive Impairment and Neurodegenerative Diseases Development Associated with Organophosphate Pesticides Exposure: a Review Study

A significant body of literature emphasizes the role of insecticide, particularly organophosphates (OPs), as the major environmental factor in the etiology of neurodegenerative diseases. This review aims to study the relationship between OP insecticide exposure, cognitive impairment, and neurodegenerative disease development. Human populations, especially in developing countries, are frequently exposed to OPs due to their extensive applications. The involvement of various signaling pathways in OP neurotoxicity are reported, but the OP-induced cognitive impairment and link between OP exposure and the pathophysiology of neurodegenerative diseases are not clearly understood. In the present review, we have therefore aimed to come to new conclusions which may help to find protective and preventive strategies against OP neurotoxicity and may establish a possible link between organophosphate exposure, cognitive impairment, and OP-induced neurotoxicity. Moreover, we discuss the findings obtained from animal and human research providing some support for OP-induced cognitive impairment and neurodegenerative disorders.

Beyond the behavioural phenotype: Uncovering mechanistic foundations in aquatic eco-neurotoxicology

During the last decade, there has been an increase in awareness of how anthropogenic pollution can alter behavioural traits of diverse aquatic organisms. Apart from understanding profound ecological implications, alterations in neuro-behavioural indices have emerged as sensitive and physiologically integrative endpoints in chemical risk assessment. Accordingly, behavioural ecotoxicology and broader eco-neurotoxicology are becoming increasingly popular fields of research that span a plethora of fundamental laboratory experimentations as well as applied field-based studies. Despite mounting interest in aquatic behavioural ecotoxicology studies, there is, however, a considerable paucity in deciphering the mechanistic foundations underlying behavioural alterations upon exposure to pollutants. The behavioural phenotype is indeed the highest-level integrative neurobiological phenomenon, but at its core lie myriads of intertwined biochemical, cellular, and physiological processes. Therefore, the mechanisms that underlie changes in behavioural phenotypes can stem among others from dysregulation of neurotransmitter pathways, electrical signalling, and cell death of discrete cell populations in the central and peripheral nervous systems. They can, however, also be a result of toxicity to sensory organs and even metabolic dysfunctions. In this critical review, we outline why behavioural phenotyping should be the starting point that leads to actual discovery of fundamental mechanisms underlying actions of neurotoxic and neuromodulating contaminants. We highlight potential applications of the currently existing and emerging neurobiology and neurophysiology analytical strategies that should be embraced and more broadly adopted in behavioural ecotoxicology. Such strategies can provide new mechanistic discoveries instead of only observing the end sum phenotypic effects.

Let it rip: the mechanics of self-bisection in asexual planarians determines their population reproductive strategies

Asexual freshwater planarians reproduce by transverse bisection (binary fission) into two pieces. This process produces a head and a tail, which fully regenerate within 1-2 weeks. How planarians split into two offspring-using only their musculature and substrate traction-is a challenging biomechanics problem. We found that three different species,Dugesia japonica,Girardia tigrinaandSchmidtea mediterranea, have evolved three different mechanical solutions to self-bisect. Using time lapse imaging of the fission process, we quantitatively characterize the main steps of division in the three species and extract the distinct and shared key features. Across the three species, planarians actively alter their body shape, regulate substrate traction, and use their muscles to generate tensile stresses large enough to overcome the ultimate tensile strength of the tissue. Moreover, we show thathoweach planarian species divides dictates how resources are split among its offspring. This ultimately determines offspring survival and reproductive success. Thus, heterospecific differences in the mechanics of self-bisection of individual worms explain the observed differences in the population reproductive strategies of different planarian species.

Antioxidant responses and lipid peroxidation can be used as sensitive indicators for the heavy metals risk assessment of the Wei River: a case study of planarian Dugesia Japonica

PURPOSE

To verify antioxidant responses and lipid peroxidation can be used as sensitive indicators for the risk assessment of the Wei River.

MATERIAL AND METHODS

We investigate the effects of the Wei River on oxidative stress of planarian Dugesia japonica by antioxidant parameters, and use ICP-MS to measure the heavy metals in the Wei River. Then, we observe the effects of three common heavy metal ions (Cr³⁺, Hg²⁺, Pb²⁺) on the regeneration of planarians on morphological and histological levels.

RESULTS

The significant changes of antioxidant parameters (SOD, CAT, GPx, GST, T-AOC) and MDA content indicate that oxidative stress is induced after the Wei River exposure on planarians, though the heavy metals in the Wei River are not exceeding the standards. Then, the regeneration of planarians shows different degree of morphological and histological damage after Cr³⁺, Hg²⁺ and Pb²⁺ exposure.

CONCLUSION

We speculate that the heavy metal ions in the Wei River, especially Cr³⁺, Hg²⁺ and Pb²⁺, may give rise to oxidative damage on planarians. These findings illustrate that planarian can serve as an indicator of aquatic ecosystem pollution, antioxidant responses and lipid peroxidation can also be used as sensitive indicators and provide an excellent opportunity for urban river risk assessment.

Planarian toxicity fluorescent assay: A rapid and cheap pre-screening tool for potential skin irritants

Here we report a new planarian (Dugesia lugubris) fluorescent assay as a rapid and cheap pre-screening tool to predict strong skin irritants. Our aim was to provide a simple and cost-effective in vivo method that avoided use of higher vertebrates. Adapting previously reported methods for planaria mobility alongside an acute toxicity assay, different irritants at five concentrations (0.1%, 0.05%, 0.025%, 0.01% and 0.005% w/v) were tested but both methods failed to discriminate the irritation potential of the test compounds. Therefore, a new alternative fluorescence assay was developed, hypothesising that increasing damage from the irritant to the planarian outer protective membrane will increase accumulation of sodium fluorescein in the flatworm. Fourteen test chemicals were selected representing strong, moderate, mild and non-irritants. In general, results showed increasing sodium fluorescein accumulation within planaria following acute exposure to increasingly strong skin irritants; on exposure to the strong irritants, benzalkonium chloride, citronellal, methyl palmitate, 1-bromohexane and carvacrol, fluorescence within the planaria was significantly greater (P < 0.05) than the negative controls and the common non-irritants PEG-400, dipropylene glycol and isopropyl alcohol; fluorescence values of planaria tested with negative controls and non-irritants were not significantly different. For all test compounds, Fluorescence Intensity of the planaria was compared with literature Primary Irritation Index data and generated a statistically significant (P < 0.005) Pearson correlation (r) of 0.87. Thus, the planarian fluorescent assay is a promising tool for rapid early testing of potential strong skin irritants, and non-irritants, and avoids use of higher vertebrate models.

Dugesia japonica is the best suited of three planarian species for high-throughput toxicology screening

High-throughput screening (HTS) using new approach methods is revolutionizing toxicology. Asexual freshwater planarians are a promising invertebrate model for neurotoxicity HTS because their diverse behaviors can be used as quantitative readouts of neuronal function. Currently, three planarian species are commonly used in toxicology research: Dugesia japonica, Schmidtea mediterranea, and Girardia tigrina. However, only D. japonica has been demonstrated to be suitable for HTS. Here, we assess the two other species for HTS suitability by direct comparison with D. japonica. Through quantitative assessments of morphology and multiple behaviors, we assayed the effects of 4 common solvents (DMSO, ethanol, methanol, ethyl acetate) and a negative control (sorbitol) on neurodevelopment. Each chemical was screened blind at 5 concentrations at two time points over a twelve-day period. We obtained two main results: First, G. tigrina and S. mediterranea planarians showed significantly reduced movement compared to D. japonica under HTS conditions, due to decreased health over time and lack of movement under red lighting, respectively. This made it difficult to obtain meaningful readouts from these species. Second, we observed species differences in sensitivity to the solvents, suggesting that care must be taken when extrapolating chemical effects across planarian species. Overall, our data show that D. japonica is best suited for behavioral HTS given the limitations of the other species. Standardizing which planarian species is used in neurotoxicity screening will facilitate data comparisons across research groups and accelerate the application of this promising invertebrate system for first-tier chemical HTS, helping streamline toxicology testing.

Enzymatic decontamination of paraoxon-ethyl limits long-term effects in planarians

Organophosphorus compounds (OP) are highly toxic molecules used as insecticides that inhibit cholinesterase enzymes involved in neuronal transmission. The intensive use of OP for vector control and agriculture has led to environmental pollutions responsible for severe intoxications and putative long-term effects on humans and wild animals. Many in vivo models were studied over the years to assess OP acute toxicity, but the long-term effects are poorly documented. Planarian, a freshwater flatworm having a cholinergic system, has emerged as a new original model for addressing both toxicity and developmental perturbations. We used Schmidtea mediterranea planarians to evaluate long-term effects of paraoxon-ethyl at two sublethal concentrations over three generations. Toxicity, developmental perturbations and disruption of behavior were rapidly observed and higher sensitivity to paraoxon-ethyl of next generations was noticed suggesting that low insecticide doses can induce transgenerational effects. With the view of limiting OP poisoning, SsoPox, an hyperthermostable enzyme issued from the archaea Saccharolobus solfataricus, was used to degrade paraoxon-ethyl prior to planarian exposure. The degradation products, although not lethal to the worms, were found to decrease cholinesterase activities for the last generation of planarians and to induce abnormalities albeit in lower proportion than insecticides.

Pharmacological or genetic targeting of Transient Receptor Potential (TRP) channels can disrupt the planarian escape response

In response to noxious stimuli, planarians cease their typical ciliary gliding and exhibit an oscillatory type of locomotion called scrunching. We have previously characterized the biomechanics of scrunching and shown that it is induced by specific stimuli, such as amputation, noxious heat, and extreme pH. Because these specific inducers are known to activate Transient Receptor Potential (TRP) channels in other systems, we hypothesized that TRP channels control scrunching. We found that chemicals known to activate TRPA1 (allyl isothiocyanate (AITC) and hydrogen peroxide) and TRPV (capsaicin and anandamide) in other systems induce scrunching in the planarian species Dugesia japonica and, except for anandamide, in Schmidtea mediterranea. To confirm that these responses were specific to either TRPA1 or TRPV, respectively, we tried to block scrunching using selective TRPA1 or TRPV antagonists and RNA interference (RNAi) mediated knockdown. Unexpectedly, co-treatment with a mammalian TRPA1 antagonist, HC-030031, enhanced AITC-induced scrunching by decreasing the latency time, suggesting an agonistic relationship in planarians. We further confirmed that TRPA1 in both planarian species is necessary for AITC-induced scrunching using RNAi. Conversely, while co-treatment of a mammalian TRPV antagonist, SB-366791, also enhanced capsaicin-induced reactions in D. japonica, combined knockdown of two previously identified D. japonica TRPV genes (DjTRPVa and DjTRPVb) did not inhibit capsaicin-induced scrunching. RNAi of DjTRPVa/DjTRPVb attenuated scrunching induced by the endocannabinoid and TRPV agonist, anandamide. Overall, our results show that although scrunching induction can involve different initial pathways for sensing stimuli, this behavior’s signature dynamical features are independent of the inducer, implying that scrunching is a stereotypical planarian escape behavior in response to various noxious stimuli that converge on a single downstream pathway. Understanding which aspects of nociception are conserved or not across different organisms can provide insight into the underlying regulatory mechanisms to better understand pain sensation.

Evaluation of a robust engineered enzyme towards organophosphorus insecticide bioremediation using planarians as biosensors

Organophosphorus compounds (OPs) are neurotoxic molecules developed as insecticides and chemical warfare nerve agents (CWNAs). They are covalent inhibitors of acetylcholinesterase (AChE), a key enzyme in central and peripheral nervous systems and are responsible for numerous poisonings worldwide. Many animal models have been studied over the years but finding a suitable in vivo model to account for both acute toxicity and long-term exposure remains a topical issue. Recently, an emerging aquatic animal model harboring a mammalian-like cholinergic nervous system, the freshwater planarian from Platyhelminthes, has been used to investigate neurotoxicity and developmental disruption. Given the tremendous toxicity of OPs, various bioremediation strategies have been considered over the years to counter their poisonous effects. Among these, enzymes have been particularly highlighted as they can degrade OPs in a fast, non toxic and environmentally friendly manner. In this article we investigated the biotechnological potential for decontaminating OPs of the previously reported variant SsoPox-αsD6 from the hyperstable enzyme SsoPox, isolated from the archaea Sulfolobus solfataricus. The capacity to hydrolyze 4 new substrates (methyl-pirimiphos, quinalphos, triazophos and dibrom) was demonstrated and the degradation products generated by enzymatic hydrolysis were characterized. We further evaluated the capacity of SsoPox-αsD6 for in vivo protection of freshwater planarians Schmidtea mediterranea (Smed). The use of SsoPox-αsD6 drastically decreased mortality and enhanced mobility of planarians. Then, an enzyme-based filtration device was developed by immobilizing intact Escherichia coli cells expressing SsoPox-αsD6 into alginate beads. The efficacy of the device was demonstrated using planarians as biosensors.

Screening for neurotoxic potential of 15 flame retardants using freshwater planarians

Asexual freshwater planarians are an attractive invertebrate model for high-throughput neurotoxicity screening, because they possess multiple quantifiable behaviors to assess distinct neuronal functions. Planarians uniquely allow direct comparisons between developing and adult animals to distinguish developmentally selective effects from general neurotoxicity. In this study, we used our automated planarian screening platform to compare the neurotoxicity of 15 flame retardants (FRs), consisting of representative phased-out brominated (BFRs) and replacement organophosphorus FRs (OPFRs). OPFRs have emerged as a proposed safer alternative to BFRs; however, limited information is available on their health effects. We found 11 of the 15 FRs (3/6 BFRs, 7/8 OPFRs, and Firemaster 550) caused adverse effects in both adult and developing planarians with similar nominal lowest-effect-levels for BFRs and OPFRs. This suggests that replacement OPFRs are comparably neurotoxic to the phased-out compounds. BFRs were primarily systemically toxic, whereas OPFRs, except Tris(2-chloroethyl) phosphate, shared a behavioral phenotype in response to noxious heat at sublethal concentrations, indicating specific neurotoxic effects. We found this behavioral phenotype was correlated with cholinesterase inhibition, thus linking behavioral outcomes to molecular targets. By directly comparing effects on adult and developing planarians, we further found that one BFR (3,3',5,5'-Tetrabromobisphenol A) caused a developmental selective defect. Together, these results demonstrate that our planarian screening platform yields high content data from various behavioral and morphological endpoints, allowing us to distinguish selective neurotoxic effects and effects specific to the developing nervous system. Ten of these 11 bioactive FRs were previously found to be bioactive in other models, including cell culture and alternative animal models (nematodes and zebrafish). This level of concordance across different platforms emphasizes the urgent need for further evaluation of OPFRs in mammalian systems.

Neuropsychiatric Disorders in Farmers Associated with Organophosphorus Pesticide Exposure in a Rural Village of Northwest México

This study aims to determine the degree of acetylcholinesterase inhibition and neurological symptoms for each of the psychiatric disorders diagnosed in the farm workers of a rural population in the state of Baja California, Mexico. We conducted a cross-sectional study on 140 agricultural workers (exposed participants). The study was run using the Mini International Neuropsychiatric Interview Diagnostic Test (MINI), a pre-established questionnaire to diagnose the mental state of each agricultural worker. Analysis of enzymatic activity was carried out using the modified Ellman method. The results showed that, among agricultural workers with slightly inhibited enzymatic activity, 25% met the criteria for the diagnosis of major depression with suicidal attitudes, 23.9% with inhibited enzymatic activity showed generalized anxiety, 23.5% showed combined depression⁻anxiety, and 22% met the criteria for major depression and no psychiatric diagnosis disorder. These results suggest the need for the development of effective public-health strategies to inform farm workers about integrated pesticide management in order to prevent serious health complications.