Toxicology of insecticides to mammals

Navigating the complexities of docking tools with nicotinic receptors and acetylcholine binding proteins in the realm of neonicotinoids

Molecular docking, pivotal in predicting small-molecule ligand binding modes, struggles with accurately identifying binding conformations and affinities. This is particularly true for neonicotinoids, insecticides whose impacts on ecosystems require precise molecular interaction modeling. This study scrutinizes the effectiveness of prominent docking software (Ledock, ADFR, Autodock Vina, CDOCKER) in simulating interactions of environmental chemicals, especially neonicotinoid-like molecules with nicotinic acetylcholine receptors (nAChRs) and acetylcholine binding proteins (AChBPs). We aimed to assess the accuracy and reliability of these tools in reproducing crystallographic data, focusing on semi-flexible and flexible docking approaches. Our analysis identified Ledock as the most accurate in semi-flexible docking, while Autodock Vina with Vinardo scoring function proved most reliable. However, no software consistently excelled in both accuracy and reliability. Additionally, our evaluation revealed that none of the tools could establish a clear correlation between docking scores and experimental dissociation constants (Kd) for neonicotinoid-like compounds. In contrast, a strong correlation was found with drug-like compounds, bringing to light a bias in considered software towards pharmaceuticals, thus limiting their applicability to environmental chemicals. The comparison between semi-flexible and flexible docking revealed that the increased computational complexity of the latter did not result in enhanced accuracy. In fact, the higher computational cost of flexible docking with its lack of enhanced predictive accuracy, rendered this approach useless for this class of compounds. Conclusively, our findings emphasize the need for continued development of docking methodologies, particularly for environmental chemicals. This study not only illuminates current software capabilities but also underscores the urgency for advancements in computational molecular docking as it is a relevant tool to environmental sciences.

EVALUATING BAITS WITH LUFENURON AND NITENPYRAM FOR FLEA CONTROL ON PRAIRIE DOGS (CYNOMYS SPP.) TO MITIGATE PLAGUE

Plague, caused by Yersinia pestis, is a widespread threat to endangered black-footed ferrets (Mustela nigripes) and their primary prey, prairie dogs (Cynomys spp.). Wildlife biologists most commonly manage plague using insecticides to control fleas, the primary vectors of Y. pestis. We tested edible baits containing the insecticides lufenuron and/or nitenpyram in prairie dogs. During a laboratory study, we treated 26 white-tailed prairie dogs (Cynomys leucurus) with lufenuron at 300 mg/kg body mass. All animals remained clinically healthy over the 9 wk monitoring period. Although serum lufenuron concentrations were >130 ppb in two treatment groups at week 1, concentrations declined to ≤60 ppb after 3 wk in non-torpid prairie dogs and after 7 wk in torpid prairie dogs. In a field experiment, we tested baits containing a combination of 75 mg lufenuron and 6 mg nitenpyram, respectively, in black-tailed prairie dogs (Cynomys ludovicianus). We uniformly distributed baits at 125 baits/ha on two plots (treated once) and 250 baits/ha on two plots (each treated twice 4.4 wk apart). Following treatments, flea abundance increased on prairie dogs and remained stable in burrows. Our findings indicate that baits containing lufenuron and nitenpyram, at the reported treatment rates, are ineffective tools for flea control on prairie dogs. Future experiments might evaluate efficacy of higher doses of lufenuron and nitenpyram, and repetitive treatments at differing intervals over time to evaluate potentially therapeutic treatments.

Lufenuron induces reproductive toxicity and genotoxic effects in pregnant albino rats and their fetuses

Insecticides and other agrochemicals have become indispensable components of the agricultural system to ensure a notable increase in crop yield and food production. As a natural consequence, chemical residues result in significantly increased contamination of both terrestrial and aquatic ecosystems. The present study evaluated the teratogenic, genotoxic, and oxidative stress effects of residual-level lufenuron exposure on pregnant rats during the organogenesis gestational period of both mother and fetus. The tested dams were divided into three groups; control (untreated), low-dose group (orally administered with 0.4 mg/kg lufenuron) and high-dose group (orally administered with 0.8 mg/kg lufenuron). The dams of the two treatment groups showed teratogenic abnormalities represented by the asymmetrical distribution of fetuses in both uterine horns, accompanied by observed resorption sites and intensive bleeding in the uterine horns, whereas their fetuses suffered from growth retardation, morphologic malformations, and skeletal deformations. Histologic examination of the liver and kidney tissues obtained from mothers and fetuses after lufenuron exposure revealed multiple histopathologic changes. DNA fragmentation and cell cycle perturbation were also detected in the liver cells of lufenuron-treated pregnant dams and their fetuses through comet assay and flow cytometry, respectively. Moreover, lufenuron-induced oxidative stress in the liver of mothers and fetuses was confirmed by the increased malondialdehyde levels and decreased levels of enzymatic antioxidants (glutathione peroxidase and superoxide dismutase). Taken together, it can be concluded that lufenuron has a great potential in exerting teratogenic, genotoxic, and oxidative stresses on pregnant rats and their fetuses upon chronic exposure to residual levels during the organogenesis gestational period. The obtained results in the present study imply that women and their fetuses may have the same risk.

Monitoring of adsorption and transfer of organochlorines in soybean seeds and sprouts with mass spectrometric imaging

Development of analytical techniques that can monitor the adsorption, transfer and in-situ distribution of environmental pollutants in agricultural products is essential to ensure the implementation of stringent food safety standards for consumer protection. A mass spectrometric imaging approach is described herein to investigate the dynamic changes and spatial distributions of 4, 4'-DDT (dichlorodiphenyltrichloroethane) in soybean seeds and sprouts during the growth. Soy beans seeds incubated in DDT containing water were sliced in every 20 μm and directly blotted on the surface of a compressed thin film of (Bi2O3)0.07(CoO)0.03(ZnO)0.9 nanoparticles. Endogenous molecules and exogenous DDT compounds in soy bean seeds were ionized and dissociated by photoelectrons that are generated on surfaces of semiconductor nanoparticles upon the irradiation of the 3rd harmonic (355 nm) of Nd3+:YAG laser. Structural identification is achieved by the interpretation of fragment ions resulting from electron-initiated specific bond cleavages or hole oxidization. Mass spectrometric images reveal increased quantities of DDT residues in soy bean seeds and sprouts during the growth. It provides an in situ way without extensive sample preparation to monitor the transfer and distribution of exogenous pollutants as well as the possible impacts on plant growth.

Polymer-Coated Hydroxyapatite Nanocarrier for Double-Stranded RNA Delivery

Conventional synthetic insecticides have limited success due to insect resistance and negative effects on off-target biota and the environment. Although RNA interference (RNAi) is a tool that is becoming more widely utilized in pest control products, naked dsRNA has limited success in most taxa. Nanocarriers have shown promising results in enhancing the efficacy of this tool. In this study, we used a layer-by-layer electrostatic assembly where we synthesized poly(acrylic acid) (PAA)-coated hydroxyapatite (HA) nanoparticles (PAA-HA NPs) as inorganic nanocarriers, which were then coated with a layer of a cationic poly(amino acid), 10 kDa poly-l-arginine (PLR₁₀), to allow for binding of a layer of negatively charged dsRNA. Binding of PLR₁₀-PAA-HA NPs to dsRNA was found to increase as the mass ratio of NPs to dsRNA increased. In vitro studies with transgenic SF9 cells (from Spodoptera frugiperda) expressing the firefly luciferase gene showed a significant gene silencing (35% decrease) at a 5:1 NP-to-dsRNA ratio, while naked dsRNA was ineffective at gene silencing. There was a significant concentration-response relationship in knockdown; however, cytotoxicity was observed at higher concentrations. Confocal microscopy studies showed that dsRNA from PLR₁₀-PAA-HA NPs was not localized within endosomes, while naked dsRNA appeared to be entrapped within the endosomes. Overall, polymer-functionalized HA nanocarriers enabled dsRNA to elicit gene knockdown in cells, whereas naked dsRNA was not effective in causing gene knockdown.

Analysis of Chromosomal Damage Caused by Acetamiprid

Different chemicals can have genotoxic effects on the body, as confirmed by chromosome damage detection. Using conventional cytogenetic analysis and fluorescence in situ hybridization, we tested the extent of chromosome damage caused by the acetamiprid-based insecticide Mospilan 20SP on bovine peripheral blood lymphocytes at concentrations of, 2.5, 5, 25 and 50 µg.ml−1 after a 24 h incubation period. During the experiment, the presence of unstable aberrations—chromosomal and chromatid breaks and gaps—were detected by conventional cyto-genetic analysis. With increasing insecticide concentrations, we observed a statistically significant increase in chromosome damage frequency after 24 hours of exposure. Fluorescence in situ hybridization was used to detect stable structural aberrations; whole-chromosome painting probes for bovine chromosomes 1 and 7 (BTA 1 and BTA 7) were used for this purpose. As a result of exposure to the insecticide, neither BTA 1/BTA 7 translocations nor other types of translocations were observed.

An evaluation of neonicotinoids' potential to inhibit human cholinesterases: Protein-ligand docking and interaction profiling studies

Many so-called neuroactive insecticides target invertebrate neurotransmitter systems, including the cholinergic system. With their relatively low toxicity to vertebrates, neonicotinoids represent a new class of neuroactive insecticides that bind to nicotinic receptors for acetylcholine in the insect central nervous system and result in paralysis and eventual death due to receptor overstimulation. On the understanding that, today, cholinesterase inhibitors are used to obtain the symptomatic relief of Alzheimer disease (AD), the aforementioned direct cholinomimetic action of neonicotinoids could, perhaps, confer anti-AD drug-like attributes to these compounds. It is shown here, using protein-ligand docking and interaction profiling, that neonicotinoids penetrate deep into the active-site gorge of both acetylcholinesterase and butyrylcholinesterase and that they form relatively strong noncovalent bonds with multiple critical residues that normally bind/hydrolyze choline esters. With their gorge-spanning shape and dual-binding specificity, neonicotinoids (first-generation compounds in particular) represent promising leads for the development of reversible, mixed-type cholinesterase inhibitors in the fight against AD.

The effect of chlorpyrifos upon ATPase activity of sarcoplasmic reticulum and biomechanics of skeleta l muscle contraction

We investigated the effect of chlorpyrifos, an organophosphate insecticide, on Ca2+,Mg2+-ATPase activity of sarcoplasmic reticulum and on contraction dynamics (force and length changes) of Rana temporaria m. tibialis anterior muscle fiber bundles. All of the used concentrations of chlorpyrifos (10-6 to 10-5 M) caused decrease of Ca2+,Mg2+-ATPase activity. The inhibition of Ca2+,Mg2+-ATPase activity by chlorpyriphos in concentrations of 10-6 M to 7.5·10-6 M is due to permeation of sarcoplasmic reticulum rather than due to direct enzyme inhibition by organophosphate insecticides. The inhibitory properties of the compound were higher at increased concentration and exposure timeframes. Chlorpyrifos in concentration range of 10-6 to 7.5·10-6 M causes changes in muscle fiber response force that were more pronounced than changes in contractile length. We demonstrated inhibition of Ca2+,Mg2+-ATPase activity caused by noncholinergic effects of chlorpyriphos. It is possible to conclude that influence of organophosphate insecticides happens not only in the neuromuscular transmission but also on the level of subcellular structures.

Using short-term bioassays to evaluate the endocrine disrupting capacity of the pesticides linuron and fenoxycarb

Several short-term whole-organism bioassays based on transgenic aquatic models are now under validation by the OECD (Organization for Economic Co-operation and Development) to become standardized test guidelines for the evaluation of the endocrine activity of substances. Evaluation of the endocrine disrupting capacity of pesticides will be a domain of applicability of these future reference tests. The herbicide linuron and the insecticide fenoxycarb are two chemicals commonly used in agricultural practices. While numerous studies indicate that linuron is likely to be an endocrine disruptor, there is little information available on the effect of fenoxycarb on vertebrate endocrine systems. Using whole-organism bioassays based on transgenic Xenopus laevis tadpoles and medaka fry we assessed the potential of fenoxycarb and linuron to disrupt thyroid, androgen and estrogen signaling. In addition we used in silico approach to simulate the affinity of these two pesticides to human hormone receptors. Linuron elicited thyroid hormone-like activity in tadpoles at all concentrations tested and, showed an anti-estrogenic activity in medaka at concentrations 2.5mg/L and higher. Our experiments suggest that, in addition to its previously established anti-androgenic action, linuron exhibits thyroid hormone-like responses, as well as acting at the estrogen receptor level to inhibit estrogen signaling. Fenoxycarb on the other hand, did not cause any changes in thyroid, androgen or estrogen signaling at the concentrations tested.

Ligand-binding characterization of simulated β-adrenergic-like octopamine receptor in Schistocerca gregaria via progressive structure simulation

It is important to design insecticides having both low drug resistance and less undesirable toxicity for desert locust control. Specific GPCRs of Schistocerca gregaria, especially β-adrenergic-like octopamine receptor (SgOctβR), can be considered as its potential effective insecticide targets. However, either the unavailability of SgOctβR's structure or the inadequate capability of its sequence lead the development of insecticide for Schistocerca gregaria meets its plateau. To relax this difficulty, this paper develops a promising progressive structure simulation from SgOctβR's sequence, to its predicted structure of SgOctβR in vacuum, to its conformation as well as its complex with endogenous ligand octopamine in a solvent-membrane system. The combined approach of multiple sequence alignment, static structural characterization, and dynamic process of conformational change during binding octopamine reveal three important aspects. The first one is the characterization of SgOctβR's active pocket, including the attending secondary structure elements, its hydrophobic residues and nonpolar surface. The second one is the interaction with octopamine, especially the involved hydrogen bonds and an aromatic stacking of pi-pi interactions. The third one is the potential binding sites, including six highly conserved residues and one highly variable residue for locust insecticide design. This work is definitely helpful for the further structure-based drug design for efficient and eco-friendly insecticides, as well as site-directed mutagenesis biochemical research of SgOctβR.

Fipronil-amitraz-S-methoprene-triggered pemphigus foliaceus in 21 dogs: clinical, histological and immunological characteristics

BACKGROUND

A recently launched topical ectoparasiticide containing fipronil, amitraz and S-methoprene has been associated with the development of an acantholytic pustular dermatitis similar to that of Promeris-triggered pemphigus foliaceus (PF).

HYPOTHESIS/OBJECTIVES

Our objectives were to describe the clinical, histological and immunological features of this PF-like cutaneous adverse drug reaction.

ANIMALS

Twenty-one dogs with a probable or definitive diagnosis of PF-like cutaneous adverse drug reaction were identified between May 2012 and February 2013.

MATERIAL AND METHODS

Histology, direct and indirect immunofluorescence were employed to address the study objectives.

RESULTS

Most dogs were middle-aged or older (median, 9 years) and of large size (median, 23 kg). In six dogs (29%), the PF-like lesions remained confined to the site of application, while 15 dogs (71%) exhibited lesions at distant sites. One or two applications of the ectoparasiticide were sufficient to trigger PF-like lesions in seven (33%) and six (29%) dogs, respectively. Systemic signs were reported in nine dogs (43%), all with lesions extending to sites distant from application areas. Tissue-bound antikeratinocyte IgG was detected in the lesional epidermis of eight of 19 (42%) cases by direct immunofluorescence, while serum antikeratinocyte IgG was detected in 10 of 14 (71%) cases by indirect immunofluorescence. Autoantibodies were found to target canine desmocollin-1 in 11 of 14 dogs (79%), but not canine desmoglein-1, by indirect immunofluorescence on transfected cells. These immunological findings were similar in cases with localized and distant disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

This new topical ectoparasiticide containing fipronil, amitraz and S-methoprene is capable of triggering the development of an acantholytic pustular dermatosis that is a clinical, histological and immunological close match for Promeris-triggered PF and naturally occurring autoimmune PF in dogs.

A single amino acid polymorphism in the Drosophila melanogaster Dα1 (ALS) subunit enhances neonicotinoid efficacy at Dα1-chicken β2 hybrid nicotinic acetylcholine receptor expressed in Xenopus laevis oocytes

Polymorphisms are sometimes observed in native insect nicotinic acetylcholine receptor (nAChR) subunits, which are important insecticide targets, yet little is known of their impact on insecticide actions. Here we investigated the effects of a polymorphism involving the substitution of histidine108 by leucine in the Drosophila melanogaster Dα1 subunit on the agonist actions of the neurotransmitter acetylcholine (ACh) and two commercial neonicotinoid insecticides (imidacloprid and clothianidin). There was no significant impact of the H108L substitution on either the ACh EC50, the concentration leading to a half maximal ACh response, or the maximum current amplitude in response at 10 μM ACh, of the Dα1-chicken β2 nAChR expressed in Xenopus laevis oocytes. However, the response amplitudes to imidacloprid and clothianidin were significantly enhanced, indicating a role of His108 in the selective interactions of Dα1 with these neonicotinoids.

Common Virulence Factors and Tissue Targets of Entomopathogenic Bacteria for Biological Control of Lepidopteran Pests

This review focuses on common insecticidal virulence factors from entomopathogenic bacteria with special emphasis on two insect pathogenic bacteria Photorhabdus (Proteobacteria: Enterobacteriaceae) and Bacillus (Firmicutes: Bacillaceae). Insect pathogenic bacteria of diverse taxonomic groups and phylogenetic origin have been shown to have striking similarities in the virulence factors they produce. It has been suggested that the detection of phage elements surrounding toxin genes, horizontal and lateral gene transfer events, and plasmid shuffling occurrences may be some of the reasons that virulence factor genes have so many analogs throughout the bacterial kingdom. Comparison of virulence factors of Photorhabdus, and Bacillus, two bacteria with dissimilar life styles opens the possibility of re-examining newly discovered toxins for novel tissue targets. For example, nematodes residing in the hemolymph may release bacteria with virulence factors targeting neurons or neuromuscular junctions. The first section of this review focuses on toxins and their context in agriculture. The second describes the mode of action of toxins from common entomopathogens and the third draws comparisons between Gram positive and Gram negative bacteria. The fourth section reviews the implications of the nervous system in biocontrol.

Aspergillus nidulans synthesize insect juvenile hormones upon expression of a heterologous regulatory protein and in response to grazing by Drosophila melanogaster larvae

Secondary metabolites are known to serve a wide range of specialized functions including communication, developmental control and defense. Genome sequencing of several fungal model species revealed that the majority of predicted secondary metabolite related genes are silent in laboratory strains, indicating that fungal secondary metabolites remain an underexplored resource of bioactive molecules. In this study, we combine heterologous expression of regulatory proteins in Aspergillus nidulans with systematic variation of growth conditions and observe induced synthesis of insect juvenile hormone-III and methyl farnesoate. Both compounds are sesquiterpenes belonging to the juvenile hormone class. Juvenile hormones regulate developmental and metabolic processes in insects and crustaceans, but have not previously been reported as fungal metabolites. We found that feeding by Drosophila melanogaster larvae induced synthesis of juvenile hormone in A. nidulans indicating a possible role of juvenile hormone biosynthesis in affecting fungal-insect antagonisms.