Study on Absorption, Distribution, Metabolism, and Excretion Properties of Novel Insecticidal GABA Receptor Antagonist, Pyraquinil, in Diamondback Moth Combining MALDI Mass Spectrometry Imaging and High-Resolution Mass Spectrometry

Assessing earthworm exposure to a multi-pharmaceutical mixture in soil: unveiling insights through LC-MS and MALDI-MS analyses, and impact of biochar on pharmaceutical bioavailability

In the European circular economy, agricultural practices introduce pharmaceutical (PhAC) residues into the terrestrial environment, posing a potential risk to earthworms. This study aimed to assess earthworm bioaccumulation factors (BAFs), the ecotoxicological effects of PhACs, the impact of biochar on PhAC bioavailability to earthworms, and their persistence in soil and investigate earthworm uptake mechanisms along with the spatial distribution of PhACs. Therefore, earthworms were exposed to contaminated soil for 21 days. The results revealed that BAFs ranged from 0.0216 to 0.329, with no significant ecotoxicological effects on earthworm weight or mortality (p > 0.05). Biochar significantly influenced the uptake of 14 PhACs on the first day (p < 0.05), with diminishing effects over time, and affected significantly the soil-degradation kinetics of 16 PhACs. Moreover, MALDI-MS analysis revealed that PhAC uptake occurs through both the dermal and oral pathways, as pharmaceuticals were distributed throughout the entire earthworm tissue without specific localization. In conclusion, this study suggests ineffective PhAC accumulation in earthworms, highlights the influence of biochar on PhAC degradation rates in soil, and suggests that uptake can occur through both earthworm skin and oral ingestion.

Design, One-Step Highly Selective Synthesis and Enhancing Insecticidal Activity and Photo-Self-Degradation of Phenylpyrazole Esterified Derivatives as GABA and nACh Receptor Inhibitors

In the pursuit of novel insecticides with high activity and a unique mode of action on the GABA receptor, a series of phenylpyrazole esterified derivatives (PEs) were synthesized using an improved Pinner reaction with high selectivity. Lewis acid catalysis was employed in a one-step solvent-thermal method to convert the cyano group of fipronil into an ester unit. FeCl3 was found to exhibit the highest selectivity for PEs synthesis, yielding PEs at 96.4%, with the byproduct being phenylpyrazole amide (PE0) at 2.1%. Initial biological assays indicated superior insecticidal activity of the target compounds against Plutella xylostella and Mythimna separata compared to fipronil. Particularly, the smaller and shorter ester units, PE3, PE5, and PE8, demonstrated 2-2.5 times higher insecticidal activity against P. xylostella than fipronil. The higher activity of ester units compared to amide and acylhydrazone units can be attributed to the enhanced lipid solubility of PEs. Additionally, it may be due to the impact of PEs on the neurotransmitter nACh or the coordination of calcium and chloride ions with the ester's -C═O and -O- bonds, blocking the chloride ion channel. Hydrophobic parameters were confirmed by reversed-phase high-performance liquid chromatography (HPLC), indicating the enhanced lipophilicity conferred by the ester units of PEs. Molecular docking and CoMFA analysis preliminarily validated the strong interactions and structure-activity relationships between PEs and the GABA receptor and nACh receptor in P. xylostella. Furthermore, under simulated natural sunlight, PEs exhibited photodegradation capabilities, transforming back into fipronil parent fragments and enhancing their insecticidal activity. Moreover, PEs displayed excellent fluorescent properties, enabling self-detection of residues. These research findings provide new insights and directions for the development of efficient pesticides, with potential wide applications in the fields of medicine and biosensors.

Degradation of the Novel Heterocyclic Insecticide Pyraquinil in Water: Kinetics, Degradation Pathways, Transformation Products Identification, and Toxicity Assessment

As new pesticides are continuously introduced into agricultural systems, it is essential to investigate their environmental behavior and toxicity effects to better evaluate their potential risks. In this study, the degradation kinetics, pathways, and aquatic toxicity of the new fused heterocyclic insecticide pyraquinil in water under different conditions were investigated for the first time. Pyraquinil was classified as an easily degradable pesticide in natural water, and hydrolyzes faster in alkaline conditions and at higher temperatures. The formation trends of the main transformation products (TPs) of pyraquinil were also quantified. Fifteen TPs were identified in water using ultrahigh-performance liquid chromatography coupled to quadrupole Orbitrap high-resolution mass spectrometry (UHPLC-Orbitrap-HRMS) and Compound Discoverer software, which adopted suspect and nontarget screening strategies. Among them, twelve TPs were reported for the first time and 11 TPs were confirmed by synthesis of their standards. The proposed degradation pathways have demonstrated that the 4,5-dihydropyrazolo[1,5-a]quinazoline skeleton of pyraquinil is stable enough to retain in its TPs. ECOSAR prediction and laboratory tests showed that pyraquinil was "very toxic" or "toxic" to aquatic organisms, while the toxicities of all of the TPs are substantially lower than that of pyraquinil except for TP484, which was predicted to pose a higher toxicity. The results are important for elucidating the fate and assessing the environmental risks of pyraquinil, and provide guidance for scientific and reasonable use.

Metabolism of an insecticide fipronil by soil fungus Cunninghamella elegans ATCC36112

In this study, the metabolic pathway of the phenylpyrazole insecticide fipronil in Cunninghamella elegans (C. elegans) was investigated. Approximately 92% of fipronil was removed within 5 days, and seven metabolites were accumulated simultaneously. The structures of the metabolites were completely or tentatively identified by GC-MS and ¹H, ¹³C NMR. To determine the oxidative enzymes involved in metabolism, piperonyl butoxide (PB) and methimazole (MZ) were used, and the kinetic responses of fipronil and its metabolites were determined. PB strongly inhibited fipronil metabolism, while MZ weakly inhibited its metabolism. The results suggest that cytochrome P450 (CYP) and flavin-dependent monooxygenase (FMO) may participate in fipronil metabolism. Integrated metabolic pathways can be inferred from the control and inhibitor experiments. Several novel products from the fungal transformation of fipronil were identified, and similarities between C. elegans transformation and mammalian metabolism of fipronil were compared. Therefore, these results will help to gain insight into the fungal degradation of fipronil and potential applications in fipronil bioremediation. At present, microbial degradation of fipronil is the most promising approach and maintains environmental sustainability. In addition, the ability of C. elegans to mimic mammalian metabolism will assist in illustrating the metabolic fate of fipronil in mammalian hepatocytes and assess its toxicity and potential adverse effects.

Structural Diversity Design, Synthesis, and Insecticidal Activity Analysis of Ester-Containing Isoxazoline Derivatives Acting on the GABA Receptor

To explore insecticides targeting the γ-aminobutyric acid (GABA) receptor, two series of novel isoxazoline derivatives containing sulfonic and carboxylic esters were designed and synthesized. Their insecticidal activities against Plutella xylostella, Mythimna separata, and Aedes aegypti larvae and their structure-activity relationship were investigated. The sulfonate-containing isoxazoline derivatives (10k-q) exhibited promising insecticidal activities against the three insect larvae. Compound 10o displayed excellent activities with LC50 values of 8.32, 5.23, and 0.35 μg/mL at 48 h against P. xylostella, M. separata, and A. aegypti larvae, respectively, which were better than or similar to those of avermectin. Furthermore, compound 10o exhibited a faster insecticidal effect than avermectin against M. separata. The mode of action of 10o was preliminarily verified by molecular docking, theoretical calculations, and measurement of glutamate decarboxylase and glutamic pyruvic transaminase activities. Compound 10o is a novel insecticidal candidate acting on GABA receptors, which could guide the discovery of isoxazoline insecticides.

Mechanism of Rotenone Toxicity against Plutella xylostella: New Perspective from a Spatial Metabolomics and Lipidomics Study

The botanical pesticide rotenone can effectively control target pest Plutella xylostella, yet insights into in situ metabolic regulation of P. xylostella toward rotenone remain limited. Herein, we demonstrated metabolic expression levels and spatial distribution of rotenone-treated P. xylostella using spatial metabolomics and lipidomics. Specifically, rotenone significantly affected purine and amino acid metabolisms, indicating that adenosine monophosphate and inosine were distributed in the whole body of P. xylostella with elevated levels, while guanosine 5'-monophosphate and tryptophan were significantly downregulated. Spatial lipidomics results indicated that rotenone may significantly destroy glycerophospholipids in cell membranes of P. xylostella, inhibit fatty acid biosynthesis, and consume diacylglycerol to enhance fat oxidation. These findings revealed that high toxicity of rotenone toward P. xylostella may be ascribed to negative effects on energy production and amino acid synthesis and damage to cell membranes, providing guidelines for the toxicity mechanism of rotenone on target pests and rational development of botanical pesticide candidates.