Molecular features and toxicological properties of four common pesticides, acetamiprid, deltamethrin, chlorpyriphos and fipronil

Nanoencapsulated deltamethrin combined with indoxacarb: An effective synergistic association against aphids

Widespread pesticide use for decades has caused environmental damage, biodiversity loss, serious human and animal health problems, and resistance to insecticides. Innovative strategies are needed to reduce treatment doses in pest management and to overcome insecticide resistance. In the present study, combinations of indoxacarb, an oxadiazine insecticide, with sublethal concentrations of deltamethrin encapsulated in lipid nanocapsules, have been tested on the crop pest Acyrthosiphon pisum. In vivo toxicological tests on A. pisum larvae have shown a synergistic effect of nanoencapsulated deltamethrin with a low dose of indoxacarb. Furthermore, the stability of deltamethrin nanoparticles has been demonstrated in vitro under different mimicking environmental conditions. In parallel, the integrity and stability of lipid nanoparticles in the digestive system of aphid larvae over time have been observed by Förster Resonance Energy Transfer (FRET) imaging. Thus, the deltamethrin nanocapsules/indoxacarb synergistic association is promising for the development of future formulations against pest insects to reduce insecticide doses.

Determination of Acetamiprid Residues in Vegetables by Indirect Competitive Chemiluminescence Enzyme Immunoassay

Acetamiprid (ACE) is widely used in various vegetables to control pests, resulting in residues and posing a threat to human health. For the rapid detection of ACE residues in vegetables, an indirect competitive chemiluminescence enzyme immunoassay (ic-CLEIA) was established. The optimized experimental parameters were as follows: the concentrations of coating antigen (ACE-BSA) and anti-ACE monoclonal antibody were 0.4 and 0.6 µg/mL, respectively; the pre-incubation time of anti-ACE monoclonal antibody and ACE (sample) solution was 30 min; the dilution ratio of goat anti-mouse-HRP antibody was 1:2500; and the reaction time of chemiluminescence was 20 min. The half-maximum inhibition concentration (IC₅₀), the detection range (IC₁₀–IC₉₀), and the detection limit (LOD, IC₁₀) of the ic-CLEIA were 10.24, 0.70–96.31, and 0.70 ng/mL, respectively. The cross-reactivity rates of four neonicotinoid structural analogues (nitenpyram, thiacloprid, thiamethoxam, and clothianidin) were all less than 10%, showing good specificity. The average recovery rates in Chinese cabbage and cucumber were 82.7–112.2%, with the coefficient of variation (CV) lower than 9.19%, which was highly correlated with the results of high-performance liquid chromatography (HPLC). The established ic-CLEIA has the advantages of simple pretreatment and detection process, good sensitivity and accuracy, and can meet the needs of rapid screening of ACE residues in vegetables.

Experimental and theoretical investigation of acetamiprid adsorption on nano carbons and novel PVC membrane electrode for acetamiprid measurement

Acetamiprid removal was investigated by synthesized Graphene oxide, multiwall nanotube and graphite from an aqueous solution. For this propose, FT-IR, XRD, UV–Vis, SEM and EDS were used to characterize the synthesized nano adsorbents and to determine the removal process. A novel PVC membrane electrode as selective electrode made for determining the concentration of acetamiprid. Batch adsorption studies were conducted to investigate the effect of temperature, initial acetamiprid concentration, adsorbent type and contact time as important adsorption parameters. The maximum equilibrium time was found to be 15 min for graphene oxide. The kinetics studies showed that the adsorption of acetamiprid followed the pseudo-second-order kinetics mechnism. All the adsorption equilibrium data were well fitted to the Langmuir isotherm model and maximum monolayer adsorption capacity 99 percent. Docking data of adsorption have resulted in the same as experimental data in good manner and confirmed the adsorption process.

4-oxo-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d]pyrimidine derivatives: design, synthesis, insecticidal assay and binding mode studies

A series of 4-oxo-4,5,6,7-tetrahydro-1 H -pyrazolo[3,4- d ]pyrimidine derivatives were designed and synthesized based on the fipronil low energy conformation by scaffold hopping strategy. Physicochemical properties calculation, insecticidal activities evaluation and binding mode studies were also performed. As a result, the insecticidal activities of the target compounds were lower than that of fipronil. The differences in binding mode between these compounds and fipronil may be the major reason for reduced insecticidal activities.

The use of insecticide mixtures containing neonicotinoids as a strategy to limit insect pests: Efficiency and mode of action

Synthetic insecticides continue to be the main strategy for managing insect pests, which are a major concern for both crop protection and public health. As nicotinic acetylcholine receptors play a central role in insect neurotransmission, they are the molecular target of neurotoxic insecticides such as neonicotinoids. These insecticides are used worldwide and have shown high efficiency in culture protection. However, the emergence of insect resistance mechanisms, and negative side-effects on non-target species have highlighted the need for a new control strategy. In this context, the use of insecticide mixtures with synergistic effects have been used in order to decrease the insecticide dose, and thus delay the selection of resistance-strains, and limit their negative impact. In this review, we summarize the available data concerning the mode of action of neonicotinoid mixtures, as well as their toxicity to various insect pests and non-target species. We found that insecticide mixtures containing neonicotinoids may be an effective strategy for limiting insect pests, and in particular resistant strains, although they could also negatively impact non-target species such as pollinating insects.

Development of pyrazole derivatives in the management of inflammation

The therapeutic limitations and poor management of inflammatory conditions are anticipated to impact patients negatively over the coming decades. Following the synthesis of the first pyrazole-antipyrine in 1887, several other derivatives have been screened for anti-inflammatory, analgesic, and antipyretic activities. Arguably, the pyrazole ring, as a major pharmacophore and central scaffold partly, defines the pharmacological profile of several derivatives. In this review, we explore the structural-activity relationship that accounts for the pharmacological profile of pyrazole derivatives and highlights future research perspectives capable of optimizing current advancement in the search for safe and efficacy anti-inflammatory drugs. The flourishing research into the pyrazole derivatives as drug candidates has advanced our understanding of inflammation-related diseases and treatment.

Assesment of hematotoxic, oxidative and genotoxic damage potentials of fipronil in rainbow trout Oncorhynchus mykiss, Walbaum

In this study, changes in the blood tissue of rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) caused by Fipronil (FP) insecticide were investigated using different biomarkers (Hematology parameters, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), malondialdehyde (MDA), paraoxonase (PON), arylesterase (ARE), myeleperoxidase (MPO), micronucleus (MN), 8-hydroxy-2-deoxyguanosine (8-OHdG)) level and caspase-3 activity. Statistically significant alterations in hematology parameters occurred with FP effect. In blood tissue, dose-dependent inhibition was determined in SOD-CAT-GPX-PON and ARE enzyme activities, but MDA and MPO were induced statistically significant. The results of MN assay were compared with the control group and it was obtained that genotoxicity of different dose groups was similar. The level of 8-OHdG and the activity and caspase-3 examined in blood tissue was increased depending on the dose. It was determined with different biomarkers that this insecticide caused physiological stress changes in the tissues examined.

Synergic effect of a quinuclidine benzamide complexed with borane, the LMA10233, in combination with seven pesticides

Some quinuclidine benzamide compounds have been found to modulate nicotinic acetylcholine receptors in both mammals and insects. In particular, the quaternarization of 3-amino quinuclidine benzamide derivatives with dichloromethane gave charged N-chloromethylated quinuclidine compounds, disclosing an antagonist profile on homomeric α7 nAChRs. Here, we synthesized and studied the toxicological effect of LMA10233, a quinuclidine-borane complex analogue, the LMA10233, on the pea aphid Acyrthosiphon pisum and found that LMA10233 only exhibit proper toxicity on A. pisum larvae when applied in concentrations of over 10 μg/ml. We assessed the ability of LMA10233 to enhance the toxicity of different insecticides. When a sublethal concentration of LMA10233 was combined with the LC₁₀ of each compound, we found a strong increase in toxicity at 24 h and 48 h of exposure for clothianidin, fipronil and chlorpyrifos, and only at 24 h for imidacloprid, acetamiprid and deltamethrin. However, when the pesticide was used at the LC₅₀, only acetamiprid showed a synergistic effect with LMA10233. When the concentration of LMA10233 was decreased, we found that up to 80-90% of mortality was obtained due to the synergism between acetamiprid and LMA10233. No similar effect was observed with other insecticides. We conclude that such quinuclidine-borane complex compounds could increase the toxic effect of insecticides at low concentrations.

Evaluation of toxicological responses and promising biomarkers of topmouth gudgeon (Pseudorasbora parva) exposed to fipronil at environmentally relevant levels

Fipronil is an insecticide commonly used in agriculture. We report here on the sublethal and sub-chronic effects of fipronil on non-target topmouth gudgeon (Pseudorasbora parva) at environmentally relevant levels. The results showed that fipronil did not cause significant changes in brain acetylcholinesterase activities, glutathione S-transferase (GST) activities in the intestine, and GST, glutamic pyruvic transaminase (GPT), and glutamic oxaloacetic transaminase (GOT) activities in the liver tissues at environmentally relevant levels for 96-h exposure. In the further test for a 12-day exposure, dose-dependent responses of the serum GPT and GOT activities were observed in all treated groups with sublethal concentrations of fipronil. Furthermore, fipronil could reduce the liver mitochondrial membrane fluidity of P. parva, especially with high concentration of fipronil at high temperature. The results suggest that serum GPT and GOT in P. parva might be useful biomarkers for effects of fipronil exposure at environmentally relevant level, and reducing fluidity of liver mitochondrial membrane may be one toxic mechanism of fipronil.

High foliar affinity cellulose for the preparation of efficient and safe fipronil formulation

In this work, fipronil was encapsulated within ethanediamine-modified carboxymethylcellulose (ACMC) to prepare an efficient and environmentally safe pesticide formulation (ACMCF). The chemical structure, morphology, foliar adhesion, bioactivity, and soil mobility of ACMCF were also systematically investigated. Results demonstrated that fipronil was encapsulated to form microcapsules successfully. Compared with the traditional fipronil emulsion (FE), ACMCF had a relatively high retention rate on cucumber and peanut leaves. The acute contact toxicity of ACMCF (LD₅₀ = 0.151 μg a.i./bee) toward Apis mellifera was far lower than that of FE (LD₅₀ = 0.00204 μg a.i./bee). Biological activity surveys confirmed that ACMCF has insecticidal ability against Plutella xylostella similar to that of FE. Moreover, the leaching and migration properties of ACMCF in three different kinds soils were weaker than those of FE. These results imply that ACMCF has promising application potential in increasing the effective utilization of fipronil and reducing risk to non-target organisms and the environment.

Design, Synthesis, Insecticidal Evaluation and Modeling Studies on 1,4,6,7- tetrahydropyrazolo[3,4-d][1,3]oxazine Derivatives: An Application of Scaffold Hopping Strategy on Fipronil

Background::

As the first phenylpyrazole pesticide, fipronil has been widely used in crop protection and public hygiene. In the low energy conformation of fipronil, a pseudo-six-membered ring is observed through an intramolecular hydrogen bond.

Methods: :

A scaffold hopping strategy was applied to mimic the pseudo-six-membered ring of fipronil by non-aromatic ring. All compounds were synthesized with a proper synthetic route and characterized by 1H NMR, 13C NMR and high-resolution mass spectra. Insecticidal activities of all target compounds against Plutella xylostella were assessed by a professional organization. Physicochemical property prediction and docking study of these compounds with GABA receptor were also performed.

Results::

A series of 1,4,6,7-tetrahydropyrazolo[3,4-d][1,3]oxazine derivatives containing twenty-five compounds were designed, synthesized and evaluated. Several compounds exhibited moderate activities against Plutella xylostella. The strong electron-withdrawing groups are conducive to improve activities of this series of compounds against Plutella xylostella. Docking study showed that the most active compound 10 with nitro group could bind within the TM2 domain of GABA receptor, in which a hydrogen bond was observed with residue 6’Thr. The activity of 10 was weaker than fipronil due to the differences in physicochemical properties.

Conclusion: :

More attention should be paid to physicochemical properties during novel pesticide hit or lead design through scaffold hopping.

Surface-Enhanced Raman Scattering Detection of Fipronil Pesticide Adsorbed on Silver Nanoparticles

This work presents a surface-enhanced Raman scattering (SERS) and density functional theory (DFT) study of a fipronil adsorbed on colloidal silver nanoparticles (AgNPs). A standard curve was established to quantify fipronil within a range of 0.0001⁻0.1 ppm (r² ≥ 0.985), relying on the unique fipronil Raman shift at ~2236 cm^-1 adsorbed on AgNPs. DFT calculations suggest that the nitrile moiety (C≡N) binding should be slightly more favorable, by 1.92 kcal/mol, than those of the nitrogen atom of the pyrazole in fipronil and Ag₆ atom clusters. The characteristic peaks of the SERS spectrum were identified, and both the calculated vibrational wavenumbers and the Raman intensity pattern were considered. The vibrational spectra of fipronil were obtained from the potential energy distribution (PED) analysis and selective Raman band enhancement.

A label-free triplex-to-G-qadruplex molecular switch for sensitive fluorescent detection of acetamiprid

The detection and monitoring of acetamiprid has drawn extensive attentions, due to their potential threat to human health. Herein, a simple, sensitive and label-free fluorescent assay based on triplex-to-G-qadruplex (TTGQ) molecular switch, was developed for the assay of acetamiprid in aqueous solution. In this detection, the proposed TTGQ molecule contained the acetamiprid aptamer sequence at its loop part and the triple-helix structure at its stem part. One single-stranded DNA grafted by two split G-rich DNA sequences at its two ends, participated in the assembly of the triplex part in TTGQ. In the presence of acetamiprid, TTGQ was dissociated, and the split G-rich DNA was released out to result in the fluorescent signal enhancement of a G-quadruplex's probe. By virtue of this TTGQ molecular switch, the proposed assay can sense acetamiprid at the concentration as low as 2.38 nM with excellent selectivity. Furthermore, the detection of acetamiprid in three kinds of foods extract demonstrated the high application potential of the detection platform in the field of food safety. Compared with the other reported strategies for acetamiprid assay, this triplex-to-G-qadruplex-based fluorescent molecular switch was just composed of two DNA probes without the labeling procedure, presenting a really simple and low-cost fluorescent detection for acetamiprid assay.

Assessment of the inhibitory activity of the pyrethroid pesticide deltamethrin against human placental glutathione transferase P1-1: A combined kinetic and docking study

Deltamethrin (DEL), which is a synthetic pyrethroid insecticide, has been used successfully all over the world to treat mosquito nets for the control of malaria. Glutathione S-transferases (GSTs; EC 2.5.1.18) catalyze the conjugation of reduced glutathione (GSH) to a variety of xenobiotics and are normally recognized as detoxification enzymes. Here, we used a colorimetric assay based on the human placental GSTP1-1 (hpGSTP1-1)-catalyzed reaction between GSH and the model substrate 1-chloro-2,4-dinitrobenzene (CDNB) as well as molecular docking to investigate the mechanistic and structural aspects of hpGSTP1-1 inhibition by DEL. We show that DEL is a potent, noncompetitive inhibitor of hpGSTP1-1 with an IC₅₀ value of 6.1 μM and K_i values of 5.61 ± 0.32 μM and 7.96 ± 0.97 μM at fixed [CDNB]-varied [GSH] and fixed [GSH]-varied [CDNB], respectively. DEL appears to be accommodated well in an eccentric cavity located at the interface of the hpGSTP1-1 homodimer, presumably causing conformational changes to the enzyme's substrate-binding sites such that the enzyme is no longer able to transform GSH and CDNB effectively. Correspondingly, considerable maternal exposure to and subsequent accumulation of DEL may interfere with the proper development of the vulnerable fetus, possibly increasing the risk of developing congenital defects.

Interactions of Fipronil within Fish and Insects: Experimental and Molecular Modeling Studies

Fipronil is an efficient phenylpyrazole insecticide that acts on insect γ-aminobutyric acid (GABA) receptors (GABARs) and has low toxicity to mammals but high toxicity to nontarget organisms such as fish. To develop novel efficient low-toxicity insecticides, it is necessary to determine the detailed toxic mechanism at the molecular target level. In this work, methods including affinity chromatography, fluorescent-labeled binding assays, and molecular modeling were integrated to explore the binding of fipronil to GABARs in fish ( Aristichthys nobilis) and insects ( Musca domestica). Affinity chromatography revealed that fipronil acts on two different subunits of GABARs in fish and M. domestica. Moreover, fluorescence assays revealed that fipronil exhibits similar affinity to the two GABARs. The K_d and B_max of fipronil binding to the A. nobilis GABAR were 346 ± 6 nmol/L and 40.6 ± 3.5 pmol/mg of protein, respectively. And the K_d and B_max of fipronil binding to the GABAR in M. domestica brain were 109 ± 9 nM and 21.3 ± 2.5 pmol/mg of protein, respectively. In addition, similar fipronil binding positions but different binding modes were observed in docking studies with Brachydanio rerio var. and M. domestica GABARs. These findings indicated similar interactions of fipronil with fish and insects, leading to high toxicity. The different binding features of fipronil between the two species might be helpful for the design and development of highly selective insecticides with low toxicity to fish.

Detection of Pesticide Residues in Food Using Surface-Enhanced Raman Spectroscopy: A Review

Pesticides directly pollute the environment and contaminate foods ultimately being absorbed by the human body. Their residues contain highly toxic substances that have been found to cause serious problems to human health even at very low concentrations. The gold standard method, gas/liquid chromatography combined with mass spectroscopy, has been widely used for the detection of pesticide residues. However, these methods have some drawbacks such as complicated pretreatment and cleanup steps. Recent technological advancements of surface-enhanced Raman spectroscopy (SERS) have promoted the creation of alternative detection techniques. SERS is a useful detection tool with ultrasensitivity and simpler protocols. Present SERS-based pesticide residue detection often uses standard solutions of target analytes in conjunction with theoretical Raman spectra calculated by density functional theory (DFT) and actual Raman spectra detected by SERS. SERS is quite a promising technique for the direct detection of pesticides at trace levels in liquid samples or on the surface of solid samples following simple extraction to increase the concentration of analytes. In this review, we highlight recent studies on SERS-based pesticide detection, including SERS for pesticide standard solution detection and for pesticides in/on food samples. Moreover, in-depth analysis of pesticide chemical structures, structural alteration during food processing, interaction with SERS substrates, and selection of SERS-active substrates is involved.

The Differential Effect of Low-Dose Mixtures of Four Pesticides on the Pea Aphid Acyrthosiphon pisum

The modes of action of most insecticides are known, but little information exists regarding the toxicological interactions involving insecticide mixtures at low doses. The effects of mixtures of four insecticides were investigated using LC₁₀ values (concentration leading to 10% mortality), acetamiprid (ACE, 0.235 µg/mL), chlorpyriphos (CHL, 107.0 µg/mL), deltamethrin (DEL, 5.831 µg/mL), and fipronil (FIP, 3.775 µg/mL) on the larvae of the pea aphid, Acyrthosiphon pisum. After 24 h exposure, 6 of the 11 tested combinations, DEL/FIP, ACE/DEL, CHL/FIP, ACE/DEL/FIP, ACE/CHL/FIP, and ACE/DEL/CHL/FIP, were toxic through an additive effect. Four combinations, ACE/FIP, DEL/CHL, ACE/CHL, and ACE/DEL/CHL had a synergistic effect, whereas only one DEL/CHL/FIP showed an antagonistic effect. The toxic effect of these mixtures was confirmed after 48 h of exposure, revealing an enhanced toxicity of CHL, DEL, and FIP in combination with ACE. We suggest that an insect pest management strategy should be evaluated in the future using different combinations of insecticides.

In vitro evaluation of the conjugations of neonicotinoids with transport protein: photochemistry, ligand docking and molecular dynamics studies

The flexibility of ligand structures and the property of substituents in neonicotinoids play a pivotal role in protein–neonicotinoid and this type of biorecognition may have a great impact on the potential toxicity of these widely used agrochemicals.

Molecular recognition of thiaclopride by Aplysia californica AChBP: new insights from a computational investigation

The binding of thiaclopride (THI), a neonicotinoid insecticide, with Aplysia californica acetylcholine binding protein (Ac-AChBP), the surrogate of the extracellular domain of insects nicotinic acetylcholine receptors, has been studied with a QM/QM' hybrid methodology using the ONIOM approach (M06-2X/6-311G(d):PM6). The contributions of Ac-AChBP key residues for THI binding are accurately quantified from a structural and energetic point of view. The importance of water mediated hydrogen-bond (H-bond) interactions involving two water molecules and Tyr55 and Ser189 residues in the vicinity of the THI nitrile group, is specially highlighted. A larger stabilization energy is obtained with the THI-Ac-AChBP complex compared to imidacloprid (IMI), the forerunner of neonicotinoid insecticides. Pairwise interaction energy calculations rationalize this result with, in particular, a significantly more important contribution of the pivotal aromatic residues Trp147 and Tyr188 with THI through CH···π/CH···O and π-π stacking interactions, respectively. These trends are confirmed through a complementary non-covalent interaction (NCI) analysis of selected THI-Ac-AChBP amino acid pairs.