Avermectin Derivatives, Pharmacokinetics, Therapeutic and Toxic Dosages, Mechanism of Action, and Their Biological Effects

Evaluation of the toxicity of translaminar insecticides against the soybean tentiform leafminer (Lepidoptera: Gracillariidae), a potential new pest of soybean

Macrosaccus morrisella (Fitch) (Lepidoptera: Gracillariidae) is a leaf-mining microlepidopteran native to North America recently reported feeding on soybean in the United States and Canada. Control methods for the management of this pest remain unknown. The insecticides Agri-Mek SC (abamectin) and Endigo ZXC (lambda-cyhalothrin + thiamethoxam) were evaluated for: (i) effects against immature stages of M. morrisella in potted soybean plants; (ii) effects against adults of M. morrisella through different routes of exposure; and (iii) efficacy of field applications against M. morrisella. In the experiment with immature stages, when either insecticide was applied to potted plants with M. morrisella in serpentine or blotch mines, significantly fewer adults emerged compared to the untreated plants. In contrast, adult emergence from potted plants treated with either insecticide when M. morrisella was in tentiform mines did not differ from untreated plants. In the experiment with adults, the survival of M. morrisella exposed to either insecticide through oral exposure or residual contact + oral exposure was significantly lower than that for residual contact exposure alone, which in turn was lower than the untreated control. Within each exposure route, the response to the 2 insecticides did not differ. In the field experiment, at 21 days after insecticide application, the mean percentage of leaf area mined was significantly lower in plots treated with Endigo ZCX compared to plots treated with Agri-Mek SC or those left untreated. These results suggest that Endigo ZXC and to a lesser extent Agri-Mek SC may have potential for management of M. morrisella.

Ferulic acid alleviates cardiac injury by inhibiting avermectin-induced oxidative stress, inflammation and apoptosis

Avermectin (AVM) is a broad-spectrum antibiotic from the macrolide class, extensively employed in fisheries and aquaculture. Nevertheless, its indiscriminate utilisation has resulted in a substantial accumulation of remnants in the aquatic ecosystem, potentially inflicting significant harm to the cardiovascular system of aquatic species. Ferulic acid (FA) is a naturally occurring compound in wheat grain husks. It possesses potent anti-inflammatory and antioxidant properties, which can help reduce cardiovascular damage. Additionally, its affordability makes it an excellent option for aquaculture usage as a feed additive. This article explored the potential of FA as a feed additive to protect against AVM-induced heart damage in carp. We subjected carp to AVM for 30 days and provided them with a diet of 400 mg/kg of FA. FA substantially reduced the pathogenic damage to heart tissue caused by AVM, as shown through hematoxylin-eosin staining. The biochemical analysis revealed that FA markedly enhanced the activity of antioxidant enzymes catalase (CAT), glutathione (GSH), and total antioxidant capacity (T-AOC) while reducing the malondialdehyde (MDA) content. Furthermore, qPCR analysis demonstrated a substantial increase in the mRNA levels of transforming growth factor-β1 (tgf-β1) and interleukin-10 (il-10) simultaneously, significantly reducing the expression levels of interleukin-10 (il-6), interleukin-1β (il-1β), tumor necrosis factor-α (tnf-α) and inductible nitric oxide synthase (inos). Through the mitochondrial apoptotic route, FA reduced AVM-induced cell death in carp heart cells by upregulating bcl-2 while downregulating the mRNA expression levels of bax, fas, caspase8 and caspase9. In summary, FA alleviated cardiac injury by inhibiting AVM-induced oxidative stress, inflammatory response, and apoptosis in carp heart tissue.

Avermectin induced vascular damage in zebrafish larvae: association with mitochondria-mediated apoptosis and VEGF/Notch signaling pathway

Avermectin is a highly effective insecticide that has been widely used in agriculture since the 1990s. In recent years, the safety of avermectin for non-target organisms has received much attention. The vasculature is important organs in the body and participate in the composition of other organs. However, studies on the vascular safety of avermectin are lacking. The vasculature of zebrafish larvae is characterized by ease of observation and it is a commonly used model for vascular studies. Therefore, zebrafish larvae were used to explore the potential risk of avermectin on the vasculature. The results showed that avermectin induced vascular damage throughout the body of zebrafish larvae, including the head, eyes, intestine, somite, tail and other vasculature. The main forms of damage are reduction in vascular diameter, vascular area and vascular abundance. Meanwhile, avermectin induced a decrease in the number of endothelial cells and apoptosis within the vasculature. In addition, vascular damage may be related to impairment of mitochondrial function and mitochondria-mediated apoptosis. Finally, exploration of the molecular mechanisms revealed abnormal alterations in the expression of genes related to the VEGF/Notch signaling pathway. Therefore, the VEGF/Notch signaling pathway may be an important mechanism for avermectin-induced vascular damage in zebrafish larvae. This study demonstrates the vascular toxicity of avermectin in zebrafish larvae and reveals the possible molecular mechanism, which would hopefully draw more attention to the safety of avermectin in non-target organisms.

Ivermectin-induced toxicity in HepG2 cells and the protective effect of tetrahydrocurcumin and vitamin C

Ivermectin (IVM) is a semi-synthetic antiparasitic derived from abamectin, one of the natural avermectins. The liver promotes metabolism and excretion of IVM, representing a risk of toxicity to this organ. The use of antioxidants to alleviate damage caused by chemicals has been increasingly studied. Thus, the aim of this study was to evaluate the effects of IVM on HepG2 cells to elucidate the mechanisms related to its toxicity and the possible protection provided by tetrahydrocurcumin (THC) and vitamin C. HepG2 cells were treated with IVM (1-25 μM) for 24 and 48 h. IVM was cytotoxic to HepG2 cells, denoted by a dose-dependent decrease in cell proliferation and metabolic activity. In addition, IVM induced damage to the cell membrane at all tested concentrations and for both incubation times. IVM significantly decreased the mitochondrial membrane potential from concentrations of 5 μM (24 h) and 1 μM (48 h). Additionally, IVM showed a time- and dose-dependent decrease in cellular adenosine triphosphate levels. The levels of reduced glutathione were decreased in a time- and dose-dependent manner, while IVM stimulated the production of reactive oxygen and nitrogen species (RONS) at all tested doses, reaching rates above 50% following treatment at 7.5 μM (24 h) or 5 μM (48 h). Treatment with THC (50 μM) and vitamin C (50 μM) protected against IVM-induced cytotoxicity and RONS production. These results suggest that oxidative damage is involved in IVM-induced toxicity in HepG2 cells, and that THC and vitamin C can mitigate the toxic effects caused by the compound.

Pesticides in the environment: Degradation routes, pesticide transformation products and ecotoxicological considerations

Among rising environmental concerns, emerging contaminants constitute a variety of different chemicals and biological agents. The composition, residence time in environmental media, chemical interactions, and toxicity of emerging contaminants are not fully known, and hence, their regulation becomes problematic. Some of the important groups of emerging contaminants are pesticides and pesticide transformation products (PTPs), which present a considerable obstacle to maintaining and preserving ecosystem health. This review article aims to thoroughly comprehend the occurrence, fate, and ecotoxicological importance of pesticide transformation products (PTPs). The paper provides an overview of pesticides and PTPs as contaminants of emerging concern and discusses the modes of degradation of pesticides, their properties and associated risks. The degradation of pesticides, however, does not lead to complete destruction but can instead lead to the generation of PTPs. The review discusses the properties and toxicity of PTPs and presents the methods available for their detection. Moreover, the present study examines the existing regulatory framework and suggests the need for the development of new technologies for easy, routine detection of PTPs to regulate them effectively in the environment.

Potential of Streptomyces avermitilis: A Review on Avermectin Production and Its Biocidal Effect

Secondary metabolites produced by the fermentation of Streptomyces avermitilis bacterium are powerful antiparasitic agents used in animal health, agriculture and human infection treatments. Avermectin is a macrocyclic lactone with four structural components (A1, A2, B1, B2), each of them containing a major and a minor subcomponent, out of which avermectin B1a is the most effective parasitic control compound. Avermectin B1a produces two homologue avermectins (B1 and B2) that have been used in agriculture as pesticides and antiparasitic agents, since 1985. It has a great affinity with the Cl-channels of the glutamate receptor, allowing the constant flow of Cl- ions into the nerve cells, causing a phenomenon of hyperpolarization causing death by flaccid paralysis. The purpose of this work was to gather information on the production of avermectins and their biocidal effects, with special emphasis on their role in the control of pests and phytopathogenic diseases. The literature showed that S. avermitilis is an important producer of macrocyclic lactones with biocidal properties. In addition, avermectin contributes to the control of ectoparasites and endoparasites in human health care, veterinary medicine and agriculture. Importantly, avermectin is a compound that is harmless to the host (no side effects), non-target organisms and the environment.

Detection and Eradication of a Demodex Infestation in Specific Pathogen-free High-barrier Laboratory Mouse Facility Housing Immunocompromised Animals

Demodex mites are a common ectoparasite in nonlaboratory Mus musculus (mouse) populations. While infrequently reported in laboratory research mice, the prevalence is thought to be as high as 35% of all colonies. Here, we discuss an outbreak of Demodex within an SPF high-barrier vivarium housing laboratory mice first identified through commercial sentinel-free PCR testing. Consequently, in-house PCR-mediated identification of individually infected cages was conducted, and a successful method for eradication of secondary reemergent infection was generated via recurrent testing and empirical 12-wk treatment with 3 mg/kg moxidectin and 13 mg/kg imidacloprid. While we were unable to determine the source of our primary outbreak, the secondary outbreak was traced to nongenetically modified C57B6/J immunocompetent mice, which were capable of harboring subclinical infection below our PCR threshold. Our eventual successful eradication of Demodex confirmed, first, that in-house PCR detection is a cost-effective means of monitoring an outbreak; second, that treatment with 3 mg/kg moxidectin and 13 mg/kg imidacloprid does kill Demodex mites in laboratory mice; and third, that treatment of only PCR-positive mice is an insufficient way to control an outbreak. Taken together, our methodological approach for infestations such as Demodex suggests it is possible to eradicate them but that it requires a thorough, systematic, and aggressive treatment regimen. Moreover, we recommend that all cages derived from infected animals be treated as positive, regardless of PCR positivity, to prevent recurrent and/or persistent infections within an animal colony.

Comparative transcriptome analysis of doramectin-producing Streptomyces avermitilis N72 and its mutant strains

Doramectin, an essential animal anthelmintic, is synthesized through the fermentation process of Streptomyces avermitilis. This study delves into the transcriptomic profiles of two strains, namely the doramectin-producing wild-type S. avermitilis N72 and its highly doramectin-producing mutant counterpart, S. avermitilis XY-62. Comparative analysis revealed 860 up-regulated genes and 762 down-regulated genes in the mutant strain, notably impacting the expression of key genes pivotal in doramectin biosynthesis, including aveA1, aveA2, aveA3, aveA4, aveE, and aveBI. These findings shed light on the molecular mechanisms underpinning the heightened doramectin production in S. avermitilis XY-62, presenting promising avenues for optimizing doramectin production processes.

Ferulic acid alleviates avermectin induced renal injury in carp by inhibiting inflammation, oxidative stress and apoptosis

Avamectin (AVM), a macrolide antibiotic, is widely used in fisheries, agriculture, and animal husbandry, however, its irrational use poses a great danger to aquatic organisms. Ferulic acid (FA) is a natural chemical found in the cell walls of plants. It absorbs free radicals from the surrounding environment and acts as an antioxidant. However, the protective effect of FA against kidney injury caused by AVM has not been demonstrated. In this study, 60 carp were divided into the control group, AVM group (2.404 μg/L), FA+AVM group and FA group (400 mg/kg). Pathological examination, quantitative real-time PCR (qPCR), reactive oxygen species (ROS) and western blot were used to evaluate the preventive effect of FA on renal tissue injury after AVM exposure. Histological findings indicated that FA significantly reduced the swelling and infiltration of inflammatory cells in the kidney tissues of carp triggered by AVM. Dihydroethidium (DHE) fluorescent probe assay showed that FA inhibited the accumulation of kidney ROS. Biochemical results showed that FA significantly increased glutathione (GSH) content, total antioxidant capacity (T-AOC) and catalase (CAT) activity, and decreased intracellular malondialdehyde (MDA) content. In addition, western blot results revealed that the protein expression levels of Nrf2 and p-NF-κBp65 in the carp kidney were inhibited by AVM, but reversed by the FA. The qPCR results exhibited that FA significantly increased the mRNA levels of tgf-β1 and il-10, while significantly down-regulated the gene expression levels of tnf-α, il-6 and il-1β. These data suggest that FA can reduce oxidative stress and renal tissue inflammation induced by AVM. At the same time, FA inhibited the apoptosis of renal cells induced by AVM by decreasing the transcription level and protein expression level of Bax, and increasing the transcription level and protein expression level of Bcl2, PI3K and AKT. This study provides preliminary evidence for the theory that FA reduces the level of oxidative stress, inflammation response and kidney tissue damage caused by apoptosis in carp, providing a theoretical basis for the prevention and treatment of the AVM.

Evaluation of genotoxic effect via expression of DNA damage responsive gene induced by ivermectin on MDBK cell line

Ivermectin (IVM) is an anti-parasitic drug which is used for treating parasitic infestations. It has been used in humans for treating intestinal strongyloidiasis and onchocerciasis however, currently researchers are investigating its potential for treating coronavirus SARS-CoV-2. Due to its broad-spectrum activities, IVM is being used excessively in animals which has generated an interest for researchers to investigate its toxic effects. Cytotoxic and genotoxic effects have been reported in animals due to excessive usage of IVM. Therefore, this study aims to evaluate the cytotoxic and genotoxic effects of IVM on the Madin-Darby-Bovine-Kidney (MDBK) cell line by examining the expression of a DNA damage-responsive gene (OGG1). Cytotoxicity of IVM was tested using an assay (MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), whereas the genotoxicity was evaluated using comet assay along with micronucleus assay. Moreover, the gene expression of DNA damage response gene (OGG1) was measured by qRT-PCR, after extraction of RNA from the MDBK cell line using the TRIzol method and its conversion to cDNA by reverse-transcriptase PCR. During the experiment, cell viability percentage was measured at different doses of IVM i.e., 25%, 50%, 75%, along with LC50/2, LC50 and LC50*2. It was observed that the gene expression of OGG1 increased as the concentration of IVM increased. It was concluded that IVM has both cytotoxic and genotoxic effects on the MDBK cell line. Furthermore, it is recommended that studies related to the toxic effects of IVM at molecular level and on other model organisms should be conducted to combat its hazardous effects.

Enhancement of acyl-CoA precursor supply for increased avermectin B1a production by engineering meilingmycin polyketide synthase and key primary metabolic pathway genes

Avermectins (AVEs), a family of macrocyclic polyketides produced by Streptomyces avermitilis, have eight components, among which B1a is noted for its strong insecticidal activity. Biosynthesis of AVE "a" components requires 2-methylbutyryl-CoA (MBCoA) as starter unit, and malonyl-CoA (MalCoA) and methylmalonyl-CoA (MMCoA) as extender units. We describe here a novel strategy for increasing B1a production by enhancing acyl-CoA precursor supply. First, we engineered meilingmycin (MEI) polyketide synthase (PKS) for increasing MBCoA precursor supply. The loading module (using acetyl-CoA as substrate), extension module 7 (using MMCoA as substrate) and TE domain of MEI PKS were assembled to produce 2-methylbutyrate, providing the starter unit for B1a production. Heterologous expression of the newly designed PKS (termed Mei-PKS) in S. avermitilis wild-type (WT) strain increased MBCoA level, leading to B1a titer 262.2 μg/mL - 4.36-fold higher than WT value (48.9 μg/mL). Next, we separately inhibited three key nodes in essential pathways using CRISPRi to increase MalCoA and MMCoA levels in WT. The resulting strains all showed increased B1a titer. Combined inhibition of these key nodes in Mei-PKS expression strain increased B1a titer to 341.9 μg/mL. Overexpression of fatty acid β-oxidation pathway genes in the strain further increased B1a titer to 452.8 μg/mL - 8.25-fold higher than WT value. Finally, we applied our precursor supply strategies to high-yield industrial strain A229. The strategies, in combination, led to B1a titer 8836.4 μg/mL - 37.8% higher than parental A229 value. These findings provide an effective combination strategy for increasing AVE B1a production in WT and industrial S. avermitilis strains, and our precursor supply strategies can be readily adapted for overproduction of other polyketides.

Discovery of Antifungal Norsesquiterpenoids from a Soil-Derived Streptomyces microflavus: Targeting Biofilm Formation and Synergistic Combination with Amphotericin B against Yeast-like Fungi

Thirty-five norsesquiterpenoids were isolated from the fermentation broth of Streptomyces microflavus from the forest soil of Ailaoshan in China. The structures of new compounds (1-5, 10-26) were elucidated by comprehensive spectroscopic analysis including data from experimental and calculated ECD spectra, as well as Mosher's reagent derivatives method. Norsesquiterpenoids showed different levels of antifungal activity with MIC80 values ranging from 25 to 200 μg/mL against Candida albicans, Candida parapsilosis, and Cryptococcus neoformans. The combining isolated norsesquiterpenoids with amphotericin B resulted in a synergistic interaction against test yeast-like fungi with a fractional inhibitory concentration index < 0.5. Compound 33 significantly inhibited biofilm formation and destroyed the preformed biofilm of fungi. Moreover, 33 downregulated the expression of adhesion-related genes HWP1, ALS1, ALS3, ECE1, EAP1, and BCR1 to inhibit the adhesion of C. albicans. Findings from the current study highlight the potential usage of norsesquiterpenoids from soil-derived Streptomyces for antifungal leads discovery.

Citrus reticulata peel extract mitigates oxidative stress and liver injury induced by abamectin in rats

The prevalent use of abamectin (ABM) has latterly raised safety attention as it has different toxicities to non-target living organisms. Citrus fruits are widely renowned for their nutritional and health-promoting qualities, and their peels are full of phenolic constituents. The purpose of the current study was to evaluate the modulatory effectiveness of Citrus reticulata peel extract (CPE) against abamectin-induced hepatotoxicity and oxidative injury. Rats were distributed into 4 groups as follows: control, CPE (400 mg/kg bw orally for 14 days), ABM (2 mg/kg bw for 5 days), and CPE + ABM at the doses mentioned above. Results revealed that GC-MS analysis of CPE has 19 identified components with significant total phenolic and flavonoid contents. Treatment with ABM in rats displayed significant variations in enzymatic and non-enzymatic antioxidants, oxidative stress markers (MDA, H2O2, PCC), liver and kidney function biomarkers, hematological parameters, lipids, and protein profile as well as histopathological abnormalities, inflammation and apoptosis (TNF-α, Caspase-3, NF-κB, and Bcl-2 genes) in rats' liver. Supplementation of CPE solo dramatically improved the antioxidant state and reduced oxidative stress. C. reticulata peel extract pretreatment alleviated ABM toxicity by modulating most of the tested parameters compared to the ABM group. Conclusively, CPE had potent antioxidant activity and could be used in the modulation of ABM hepatotoxicity presumably due to its antioxidant, anti-inflammatory, and gene-regulating capabilities.

Marine Natural Products as Novel Treatments for Parasitic Diseases

Parasitic diseases including malaria, leishmaniasis, and trypanosomiasis have received significant attention due to their severe health implications, especially in developing countries. Marine natural products from a vast and diverse range of marine organisms such as sponges, corals, molluscs, and algae have been found to produce unique bioactive compounds that exhibit promising potent properties, including antiparasitic, anti-Plasmodial, anti-Leishmanial, and anti-Trypanosomal activities, providing hope for the development of effective treatments. Furthermore, various techniques and methodologies have been used to investigate the mechanisms of these antiparasitic compounds. Continued efforts in the discovery and development of marine natural products hold significant promise for the future of novel treatments against parasitic diseases.

Co-Processed Crystalline Solids of Ivermectin with Span® 60 as Solubility Enhancers of Ivermectin in Natural Oils

Despite being discovered over five decades ago, little is still known about ivermectin. Ivermectin has several physico-chemical properties that can result in it having poor bioavailability. In this study, polymorphic and co-crystal screening was used to see if such solid-state modifications can improve the oil solubility of ivermectin. Span® 60, a lipophilic non-ionic surfactant, was chosen as co-former. The rationale behind attempting to improve oil solubility was to use ivermectin in future topical and transdermal preparations to treat a range of skin conditions like scabies and head lice. Physical mixtures were also prepared in the same molar ratios as the co-crystal candidates, to serve as controls. Solid-state characterization was performed using X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR spectra of the co-crystal candidates showed the presence of Span® 60's alkyl chain peaks, which were absent in the spectra of the physical mixtures. Due to the absence of single-crystal X-ray data, co-crystal formation could not be confirmed, and therefore these co-crystal candidates were referred to as co-processed crystalline solids. Following characterization, the solid-state forms, physical mixtures and ivermectin raw material were dissolved in natural penetration enhancers, i.e., avocado oil (AVO) and evening primrose oil (EPO). The co-processed solids showed increased oil solubility by up to 169% compared to ivermectin raw material. The results suggest that co-processing of ivermectin with Span® 60 can be used to increase its oil solubility and can be useful in the development of oil-based drug formulations.

A phenotypic screen of the Global Health Priority Box identifies an insecticide with anthelmintic activity

BACKGROUND

Infection with parasitic nematodes (helminths), particularly those of the order Strongylida (such as Haemonchus contortus), can cause significant and burdensome diseases in humans and animals. Widespread drug (anthelmintic) resistance in livestock parasites, the absence of vaccines against most of these nematodes, and a lack of new and effective chemical entities on the commercial market demands the discovery of new anthelmintics. In the present study, we searched the Global Health Priority Box (Medicines for Malaria Venture) for new candidates for anthelmintic development.

METHODS

We employed a whole-organism, motility-based phenotypic screening assay to identify compounds from the Global Health Priority Box with activity against larvae of the model parasite H. contortus, and the free-living comparator nematode Caenorhabditis elegans. Hit compounds were further validated via dose-response assays, with lead candidates then assessed for nematocidal activity against H. contortus adult worms, and additionally, for cytotoxic and mitotoxic effects on human hepatoma (HepG2) cells.

RESULTS

The primary screen against H. contortus and C. elegans revealed or reidentified 16 hit compounds; further validation established MMV1794206, otherwise known as 'flufenerim', as a significant inhibitor of H. contortus larval motility (half-maximal inhibitory concentration [IC50] = 18 μM) and development (IC50 = 1.2 μM), H. contortus adult female motility (100% after 12 h of incubation) and C. elegans larval motility (IC50 = 0.22 μM). Further testing on a mammalian cell line (human hepatoma HepG2 cells), however, identified flufenerim to be both cytotoxic (half-maximal cytotoxic concentration [CC50] < 0.7 μM) and mitotoxic (half-maximal mitotoxic concentration [MC50] < 0.7 μM).

CONCLUSIONS

The in vitro efficacy of MMV1794206 against the most pathogenic stages of H. contortus, as well as the free-living C. elegans, suggests the potential for development as a broad-spectrum anthelmintic compound; however, the high toxicity towards mammalian cells presents a significant hindrance. Further work should seek to establish the protein-drug interactions of MMV1794206 in a nematode model, to unravel the mechanism of action, in addition to an advanced structure-activity relationship investigation to optimise anthelmintic activity and eliminate mammalian cell toxicity.

Developing a novel magnetic organic polymer for selective extraction and determination of 16 macrolides in water and honey samples

A novel magnetic organic polymer Fe3O4@SiO2@Tb-PDAN was designed and synthesized, which was used as an adsorbent for magnetic solid-phase extraction (MSPE) of 16 macrolides (MALs) in water and honey. The synthesized adsorbent was characterized using techniques including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Then several parameters of the extraction process were further optimized. Under the optimized conditions, an MSPE-LC-MS/MS method was established for extraction and determination of 16 MALs, which showed good linearity (r ≥ 0.999), low limits of detection (0.001-0.012 μg L-1 for water and 0.001-0.367 μg kg-1 for honey) and satisfactory recoveries (70.02-118.91%) with the relative standard deviations (RSDs) lower than 10.0%. This established method was then successfully applied to detect MALs in real samples, which suggested that Fe3O4@SiO2@Tb-PDAN was a potential magnetic adsorbent for efficient extraction and analysis of MALs.

Fabrication of Eco-Friendly Hydrolyzed Ethylene-Maleic Anhydride Copolymer-Avermectin Nanoemulsion with High Stability, Adhesion Property, pH, and Temperature-Responsive Releasing Behaviors

In this study, novel amphiphilic polymer emulsifiers for avermectin (Avm) were synthesized facilely via the hydrolysis of ethylene-maleic anhydride copolymer (EMA) with different agents, and their structures were confirmed by various techniques. Then, water-based Avm-nanoemulsions were fabricated with the emulsifiers via phase inversion emulsification process, and superior emulsifier was selected via the emulsification effects. Using the superior emulsifier, an optimal Avm-nanoemulsion (defined as Avm@HEMA) with satisfying particle size of 156.8 ± 4.9 nm, encapsulation efficiency (EE) of 69.72 ± 4.01% and drug loading capacity (DLC) of 54.93 ± 1.12% was constructed based on response surface methodology (RSM). Owing to the emulsifier, the Avm@HEMA showed a series of advantages, including high stability, ultraviolet resistance, low surface tension, good spreading and high affinity to different leaves. Additionally, compared to pure Avm and Avm-emulsifiable concentrate (Avm-EC), Avm@HEMA displayed a controlled releasing feature. The encapsulated Avm was released quite slowly at normal conditions (pH 7.0, 25 °C or 15 °C) but could be released at an accelerated rate in weak acid (pH 5.5) or weak alkali (pH 8.5) media or at high temperature (40 °C). The drug releasing profiles of Avm@HEMA fit the Korsmeyer-Peppas model quite well at pH 7.0 and 25 °C (controlled by Fickian diffusion) and at pH 7.0 and 10 °C (controlled by non-Fickian diffusion), while it fits the logistic model under other conditions (pH 5.5 and 25 °C, pH 8.5 and 25 °C, pH 7.0 and 40 °C).

Effects of chronic abamectin stress on growth performance, digestive capacity, and defense systems in red swamp crayfish (Procambarus clarkii)

Abamectin is a globally used pesticide, which is one of 16-member macrocyclic lactones compound. As an environmental contaminant, pesticide residues pose a great threat to the health and survival of aquatic animals. Procambarus clarkii is one of the most important economic aquatic animals in China. It is necessary to explore the toxic mechanism of abamectin to P. clarkii. In this study, the toxic mechanism of abamectin to P. clarkii was investigated by 0, 3 and 6 μg/L abamectin stress for 28 days. The digestive-, antioxidant- and immune- related enzymes activities, genes expression levels, and histological observations were analytical indicators of growth performance, digestive capacity, and defense systems. The results in this study showed that with abamectin concentration increasing, the growth of P. clarkii was stunted significantly, and the mortality rate increased significantly. With exposure time and abamectin concentration increasing, the expression levels of related genes, the activities of digestive-, antioxidant-, and immune- related enzymes decreased ultimately. Moreover, through histological observation, it was found that with abamectin concentration increasing, the hepatopancreas, muscle, and intestine were damaged. As elucidated by the results, once abamectin exists in the environment for a long time, even low doses will threaten to healthy growth and survival of P. clarkii. This study explored the potential toxicity and the toxic mechanism of abamectin to P. clarkii, and provides a theoretical basis for further study on the toxicity of pesticides to aquatic animals.

The natural polycyclic tetramate macrolactam HSAF inhibit Fusarium graminearum through altering cell membrane integrity by targeting FgORP1

Fusarium graminearum is a dominant phytopathogenic fungus causing Fusarium head blight (FHB) in cereal crops. Heat-stable antifungal factor (HSAF) is a polycyclic tetramate macrolactam (PoTeM) isolated from Lysobacter enzymogenes that exhibits strong antifungal activity against F. graminearum. HSAF significantly reduces the DON production and virulence of F. graminearum. Importantly, HSAF exhibited no cross-resistance to carbendazim, phenamacril, tebuconazole and pydiflumetofen. However, the target protein of HSAF in F. graminearum is unclear. In this study, the oxysterol-binding protein FgORP1 was identified as the potential target of HSAF using surface plasmon resonance (SPR) combined with RNA-sequence (RNA-seq). The RNA-seq results showed cell membrane and ergosterol biosynthesis were significantly impacted by HSAF in F. graminearum. Molecular docking showed that HSAF binds with arginine 1205 and glutamic acid 1212, which are located in the oxysterol-binding domain of FgORP1. The two amino acids in FgORP1 are responsible for HSAF resistance in F. graminearum though site-directed mutagenesis. Furthermore, deletion of FgORP1 led to significantly decreased sensitivity to HSAF. Additionally, FgORP1 regulates the mycelial growth, conidiation, DON production, ergosterol biosynthesis and virulence in F. graminearum. Overall, our findings revealed the mode of action of HSAF against F. graminearum, indicating that HSAF is a promising fungicide for controlling FHB.

Drosophila suzukii in Argentina: State of the Art and Further Perspectives

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), commonly known as spotted-wing drosophila or SWD, is an invasive, severe, and damaging pest, which is able to inflict huge economic losses on soft thin-skinned fruits worldwide. Argentina was not excluded from the rapid invasion of this new and aggressive pest. Berries and cherries are among the most economically important fruits, showing an increasing demand from both domestic and export markets, which make necessary the application of effective and early protection measures. Although SWD is currently established almost everywhere in Argentina, the scarcity of research on and rapid regulatory actions against this pest have probably contributed to its fast spread throughout the country. In view of that, the article reviews first the current threat status of SWD in Argentina, provides summarized information on crop and non-crop host fruits, seasonal variation and population dynamics, resident natural enemy assemblages, and describes control actions implemented to date. Finally, the need to focus local control actions within an integrated national SWD management program is emphasized. The development and application of complementary eco-friendly strategies, such as Sterile Insect Technique, biological control, mass trapping, and the use of innovative lactone-derived synthetic insecticides with extremely low toxicity for SWD parasitoids, in environmentally distinguishable Argentinian regions is also highlighted.

In-vitro susceptibility and ex-vivo evaluation of macrocyclic lactone endectocides sub-lethal concentrations against Plasmodium vivax oocyst development in Anopheles arabiensis

BACKGROUND

Asymptomatic malaria transmission has become a public health concern across malaria-endemic Africa including Ethiopia. Specifically, Plasmodium vivax is more efficient at transmitting earlier in the infection and at lower densities than Plasmodium falciparum. Consequently, a greater proportion of individuals infected with P. vivax can transmit without detectable gametocytaemia. Mass treatment of livestock with macrocyclic lactones (MLs), e.g., ivermectin and doramectin, was suggested as a complementary malaria vector tool because of their insecticidal effects. However, the effects of MLs on P. vivax in Anopheles arabiensis has not yet been fully explored. Hence, comparative in-vitro susceptibility and ex-vivo studies were conducted to evaluate the effects of ivermectin, doramectin and moxidectin sub-lethal concentrations on P. vivax oocyst development in An. arabiensis.

METHODS

The 7-day sub-lethal concentrations of 25% (LC25) and 5% (LC5) were determined from in-vitro susceptibility tests on female An. arabiensis in Hemotek® membrane feeding assay. Next, an ex-vivo study was conducted using P. vivax gametocytes infected patient's blood spiked with the LC25 and LC5 of the MLs. At 7-days post-feeding, each mosquito was dissected under a dissection stereo microscope, stained with 0.5% (w/v) mercurochrome solution, and examined for the presence of P. vivax oocysts. Statistical analysis was based on a generalized mixed model with binomially distributed error terms.

RESULTS

A 7-day lethal concentration of 25% (LC25, in ng/mL) of 7.1 (95% CI: [6.3;8.0]), 20.0 (95%CI:[17.8;22.5]) and 794.3 (95%CI:[716.4;1516.3]) were obtained for ivermectin, doramectin and moxidectin, respectively. Similarly, a lethal concentration of 5% (LC5, in ng/mL) of 0.6 (95% CI: [0.5;0.7]), 1.8 (95% CI:[1.6;2.0]) and 53.7 (95% CI:[ 48.4;102.5]) were obtained respectively for ivermectin, doramectin and moxidectin. The oocyst prevalence in treatment and control groups did not differ significantly (p > 0.05) from each other. Therefore, no direct effect of ML endectocides on P. vivax infection in An. arabiensis mosquitoes was observed at the sub-lethal concentration (LC25 and LC5).

CONCLUSIONS

The effects of ivermectin and doramectin on malaria parasite is more likely via indirect effects, particularly by reducing the vectors lifespan and causing mortality before completing the parasite's sporogony cycle or reducing their vector capacity as it affects the locomotor activity of the mosquito.

An Overview of Julia-lythgoe Olefination

Julia-Lythgoe olefination (or simply Julia olefination) is an olefination process between phenyl sulfones and aldehydes (or ketones) to give alkenes after alcohol functionalization and reductive elimination using sodium amalgam or SmI2. It is mainly used to synthesize E-alkenes and is a key step in numerous total syntheses of many natural products. This review exclusively deals with the Julia-Lythgoe olefination and concentrates mainly on the applications of this reaction in natural product synthesis covering literature up to 2021.

Biocontrol Potential of Streptomyces odonnellii SZF-179 toward Alternaria alternata to Control Pear Black Spot Disease

Pear black spot disease, caused by Alternaria alternata, is a devastating disease in pears and leads to enormous economic losses worldwide. In this investigation, we isolated a Streptomyces odonnellii SZF-179 from the rhizosphere soil of pear plants in China. Indoor confrontation experiments results showed that both SZF-179 and its aseptic filtrate had excellent inhibitory effects against A. alternata. Afterwards, the main antifungal compound of SZF-179 was identified as polyene, with thermal and pH stability in the environment. A microscopic examination of A. alternata mycelium showed severe morphological abnormalities caused by SZF-179. Protective studies showed that SZF-179 fermentation broth could significantly reduce the diameter of the necrotic lesions on pear leaves by 42.25%. Furthermore, the potential of fermentation broth as a foliar treatment to control black leaf spot was also evaluated. Disease indexes of 'Hosui' and 'Wonwhang' pear plants treated with SZF-179 fermentation broth were lower than that of control plants. Overall, SZF-179 is expected to be developed into a safe and broad-spectrum biocontrol agent. No studies to date have evaluated the utility of S. odonnellii for the control of pear black spot disease; our study fills this research gap. Collectively, our findings provide new insights that will aid the control of pear black spot disease, as well as future studies of S. odonnellii strains.

Population pharmacokinetics of ivermectin after mass drug administration in lymphatic filariasis endemic communities of Tanzania

Ivermectin (IVM) is a drug of choice used with albendazole for mass drug administration (MDA) to halt transmission of lymphatic filariasis. We investigated IVM pharmacokinetic (PK) variability for its dose optimization during MDA. PK samples were collected at 0, 2, 4, and 6 h from individuals weighing greater than 15 kg (n = 468) receiving IVM (3-, 6-, 9-, or 12 mg) and ALB (400 mg) during an MDA campaign in Tanzania. Individual characteristics, including demographics, laboratory/clinical parameters, and pharmacogenetic variations were assessed. IVM plasma concentrations were quantified by liquid-chromatography tandem mass spectrometry and analyzed using population-(PopPK) modeling. A two-compartment model with transit absorption kinetics, and allometrically scaled oral clearance (CL/F) and central volume (Vc /F) was adapted. Fitting of the model to the data identified 48% higher bioavailability for the 3 mg dose compared to higher doses and identified a subpopulation with 97% higher mean transit time (MTT). The final estimates for CL/F, Vc /F, intercompartment clearance, peripheral volume, MTT, and absorption rate constant for a 70 kg person (on dose other than 3 mg) were 7.7 L/h, 147 L, 20.4 L/h, 207 L, 1.5 h, and 0.71/h, respectively. Monte-Carlo simulations indicated that weight-based dosing provides comparable exposure across weight bands, but height-based dosing with capping IVM dose at 12 mg for individuals with height greater than 160 cm underdoses those weighing greater than 70 kg. Variability in IVM PKs is partly explained by body weight and dose. The established PopPK model can be used for IVM dose optimization. Height-based pole dosing results in varying IVM exposure in different weight bands, hence using weighing scales for IVM dosing during MDA is recommended.

Eucalyptol alleviates avermectin exposure-induced apoptosis and necroptosis of grass carp hepatocytes by regulating ROS/NLRP3 axis

The wide application of Avermectin (AVM) has caused pollution of surface water and damage to non-target organisms. A growing body of evidence supports the most prominent role of Eucalyptol (EUC) is antioxidation. To the purpose of explore the injury mechanism of Avermectin on grass carp hepatocytes and the antagonistic effect of Eucalyptol, 5.7 μM AVM and/or 20 μM EUC were used to treat grass carp hepatocytes for 24 h to establish hepatocyte exposure model. The results showed that Avermectin exposure significantly increased the contents of reactive oxygen species (ROS) and malondialdehyde (MDA) in cells, reduced the activities of superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC). Also, the expressions of NLRP3 inflammasome-related genes including NLRP3, ASC, and Caspase-1, the necroptosis-related genes including RIPK1, RIPK3, and MLKL and apoptotic genes including Bax, Caspase-3, and Caspase-9 were all up-regulated. Meanwhile, the expressions of Caspase-8 and Bcl-2 were significantly decreased upon exposure to Avermectin. However, the toxicity was significantly alleviated with the treatment of EUC or N-acetyl-l-cysteine (NAC). The above results indicated that eucalyptol alleviated AVM exposure-induced apoptosis and necroptosis of grass carp hepatocytes by regulating the ROS/NLRP3 signaling pathway.

Actinomycins produced by endophyte Streptomyces sp. GLL-9 from navel orange plant exhibit high antimicrobial effect against Xanthomonas citri susp. citri and Penicillium italicum

BACKGROUND

Citrus canker and citrus blue mold are two severe diseases in citrus plants, which are mainly caused by Xanthomonas citri susp. citri (Xcc) and Penicillium italicum, respectively. The currently widely used pesticides for these two diseases are harmful to human health and the environment. Therefore, searching for novel antimicrobial agents, especially from natural resources, is getting increasing interest.

RESULTS

In this study, the crude extract of Streptomyces sp. GLL-9, an endophyte from a navel orange tree, was found to exhibit excellent antimicrobial effects against Xcc and P. italicum. Bioassay-guided isolation led to the discovery of three actinomycins (Acts), actinomycin X2 (Act-X2 ), actinomycin D (ActD), and actinomycin XOβ (Act-XOβ ). The MIC (minimum inhibitory concentration) values of Act-X2 , ActD, and Act-XOβ were 31.25, 62.50, and 62.50 μg mL-1 against Xcc, respectively, while 62.50 (Act-X2 ) and 125.00 μg mL-1 (ActD) against P. italicum, being better or comparable to the positive controls. The highest yield of Acts was obtained by solid-state fermentation with rice containing 1% L-tryptophan as a culture medium, being 6.03, 3.07, and 1.02 mg g-1 , for Act-X2 , ActD, and Act-XOβ , respectively. The ethyl acetate extract of Streptomyces sp. GLL-9 cultivated under the optimal fermentation conditions (EAE-1) can efficiently control these two citrus diseases by excessively producing reactive oxygen species (ROS) in both pathogens, damaging the cell membranes of P. italicum, and inhibiting the growth of Xcc. In addition, Act-X2 , ActD, and EAE-1 displayed broad-spectrum antifungal activity.

CONCLUSION

EAE-1 and Acts produced by Streptomyces sp. GLL-9 have high potential as novel antimicrobial agents against plant pathogens. © 2023 Society of Chemical Industry.

Effects of abamectin on nonspecific immunity, antioxidation, and apoptosis in red swamp crayfish (Procambarus clarkii)

Abamectin, a pesticide of 16-member macrocyclic lactones, is widely applied in agriculture. As an important environmental factor, pesticides pose a great threat to defense system in aquatic animals. Procambarus clarkii is one of the most important economic aquatic animals in China. It is necessary to explore the defense mechanism of P. clarkii to abamectin. In this study, P. clarkii were exposed to 0, 0.2, 0.4, 0.6 mg/L abamectin, immune- and antioxidant-related enzymes activities, genes expression levels, and histological observations were used to analyze the defense capacity of P. clarkii to abamectin. With increasing abamectin concentration, reactive oxygen species (ROS) level and malondiadehyde (MDA) content increased significantly. Meanwhiile, acid phosphate (ACP), alkaline phosphatase (AKP) activities, total haemocyte counts (THC), and Crustin expression level decreased significantly, superoxide dismutase (SOD), catalase (CAT) activities, total antioxidant capacity (T-AOC), and GPX expression level also decreased significantly. Hematoxylin & eosin (H&E) observation showed that with increasing abamectin concentration, hepatopancreas were damaged, especially membrane structure. Through TUNEL observation and apoptosis-related genes (PcCTSL, Bcl-2, Bax, BI-1, PcCytc, caspase-3) expression levels, with increasing abamectin concentration, apoptosis rate increased significantly. Results of this study indicated that abamectin caused oxidative damage to P. clarkii, resulting in damage to defense system, suppression of nonspecific immunity and antioxidation, and promotion of apoptosis. It provided theoretical basis for healthy P. clarkii culture, and for further study on defense mechanism of aquatic animals to pesticides.

Coadministration of ivermectin and abamectin affects milk pharmacokinetics of the antiparasitic clorsulon in Assaf sheep

In veterinary field, drug exposure during milk production in dairy cattle is considered a major health problem which concerns dairy consumers. The induced expression of the ABC transporter G2 (ABCG2) in the mammary gland during lactation plays a significant role in the active secretion of many compounds into milk. The main objective of this study was to determine the involvement of ABCG2 in the secretion into milk of the antiparasitic clorsulon in sheep as well as the possible effect of the coadministration of model ABCG2 inhibitors such as macrocyclic lactones on this process. Cells transduced with the ovine variant of ABCG2 were used to carry out in vitro transepithelial transport assays in which we showed that clorsulon is a substrate of the ovine transporter. In addition, ivermectin and abamectin significantly inhibited clorsulon transport mediated by ovine ABCG2. In vivo interactions were studied in Assaf sheep after coadministration of clorsulon (in DMSO, 2 mg/kg, s.c.) with ivermectin (Ivomec®, 0.2 mg/kg, s.c.) or abamectin (in DMSO, 0.2 mg/kg, s.c.). After ivermectin and abamectin treatment, no relevant statistically significant differences in plasma levels of clorsulon were reported between the experimental groups since there were no differences in the area under the plasma concentration-curve (AUC) between clorsulon treatment alone and coadministration with macrocyclic lactones. With regard to milk, total amount of clorsulon, as percentage of dose excreted, did not show statistically significant differences when macrocyclic lactones were coadministered. However, the AUC for clorsulon significantly decreased (p < 0.05) after coadministration with ivermectin (15.15 ± 3.17 μg h/mL) and abamectin (15.30 ± 3.25 μg h/mL) compared to control group (20.73 ± 4.97 μg h/mL). Moreover, milk parameters such as half-life (T1/2) and mean residence time (MRT) were significantly lower (p < 0.05) after coadministration of macrocyclic lactones. This research shows that the milk pharmacokinetics of clorsulon is affected by the coadministration of ABCG2 inhibitors, reducing drug persistence in milk.

Pharmacokinetics of macrocyclic lactone endectocides in indigenous Zebu cattle and their insecticidal efficacy on Anopheles arabiensis

Outdoor biting, outdoor resting, and early evening biting of Anopheles arabiensis is a challenge in current malaria control and elimination efforts in Africa. Zooprophylaxis using livestock treated with macrocyclic lactones is a novel approach to control zoophilic vectors. Therefore, the present study aimed to investigate the pharmacokinetics and insecticidal efficacy of ivermectin (IVER), doramectin (DORA), and moxidectin (MOXI) subcutaneous (SC) formulations in treated calves. The study was conducted using indigenous (Bos indicus) calves treated with SC formulation at a dosage of 0.5, 0.2 or 0.05 mg/kg body weight (BW) IVER or DORA and 0.2 or 0.05 mg/kg BW MOXI. Direct skin feeding of mosquitoes and animal blood sampling were performed at 4, 8, 12, and 24 h and on days 2, 3, 5, 7, 10, 14, 21, 28, and 35 post treatment. The survival of fully fed A. arabiensis mosquitoes was monitored for 10 days. Plasma samples were analyzed using UHPLC-MS/MS. A. arabiensis mortality percentages in the 0.5 mg/kg BW DORA and IVER groups were 65.74% (95% CI: [54.98; 76.50]) and 64.53% (95% CI: [53.77; 75.29]), respectively, over 35 days post treatment. At the recommended dose (0.2 mg/kg BW), promising overall A. arabiensis mortality rates of 61.79% (95% CI: [51.55; 72.03]) and 61.78% (95% CI: [51.02; 72.54]) were observed for IVER and DORA, respectively. In contrast, A. arabiensis mortality in the MOXI group was 50.23% (95% CI: [39.87, 60.58]). At 0.2 mg/kg BW dose, area under the plasma concentration versus time curve (AUC0-inf) values for IVER, DORA, and MOXI were 382.53 ± 133.25, 395.41 ± 132.12, and 215.85 ± 63.09 ng day/mL, respectively. An extended elimination half-life (T1/2el) was recorded for DORA (4.28 ± 0.93 d), at 0.2 mg/kg BW dose level, compared to that for IVER (3.16 ± 1.47 d). The T1/2el of MOXI was 2.17 ± 0.44 day. A maximum plasma concentration (Cmax) was recorded earlier for MOXI (10 h) than for IVER (1.6 days) and longer for DORA (3.0 days). For DORA and IVER, significant differences were found in T1/2el (P<0.05), Cmax (P<0.01), and AUC0-inf (P<0.01) between the higher 0.5 mg/kg BW and the lower 0.05 mg/kg BW doses. The T1/2el and AUC0-inf of DORA and IVER in the present study were significantly (p < 0.05) correlated with the observed insecticidal efficacy against A. arabiensis mosquitoes at 0.2 mg/kg a dose. Therefore, treating cattle with IVER or DORA could complement the malaria vector control interventions, especially in Ethiopia, where the zoophilic malaria vector A. arabiensis majorly contribute for residual malaria transmission.

Ameliorative effects of silybin against avermectin-triggered carp spleen mitochondrial dysfunction and apoptosis through inhibition of PERK-ATF4-CHOP signaling pathway

The aim of this study was to investigate the splenic tissue damage of environmental biological drug avermectin to freshwater cultured carp and to evaluate the effect of silybin on the splenic tissue damage of carp induced by avermectin. A total of 60 carp were divided into 4 groups with 15 carp in each group, including the control group fed with basic diet, experimental group fed with basal diet and exposed to avermectin (avermectin group), experimental group fed with basal diet supplement silybin (silybin group), and experimental group fed with basal diet supplement silybin and exposed to avermectin (silybin + avermectin group). The whole test period lasted for 30 days, and spleen tissue was collected for analysis. In this study, H&E staining, mitochondrial purification and membrane potential detection, ATP detection, DHE staining, biochemical tests, qPCR, immunohistochemistry, and apoptosis staining were used to evaluate the biological processes of spleen tissue injury, mitochondrial function, oxidative stress, apoptosis, and endoplasmic reticulum stress. The results show that silybin protected carp splenic tissue damage caused by chronic avermectin exposure, decreased mitochondrial membrane potential, decreased ATP content, ROS accumulation, oxidative stress, apoptosis, and endoplasmic reticulum stress. Silybin may ameliorate the splenic tissue damage of cultured freshwater carp caused by environmental biopesticide avermectin by alleviating mitochondrial dysfunction and inhibiting PERK-ATF4-CHOP-driven mitochondrial apoptosis. Adding silybin into the diet becomes a feasible strategy to resist the pollution of avermectin and provides a theoretical basis for creating a good living environment for freshwater carp.

Repurposing Selamectin as an Antimicrobial Drug against Hospital-Acquired Staphylococcus aureus Infections

The emergence of multidrug-resistant strains requires the urgent discovery of new antibacterial drugs. In this context, an antibacterial screening of a subset of anthelmintic avermectins against gram-positive and gram-negative strains was performed. Selamectin completely inhibited bacterial growth at 6.3 μg/mL concentrations against reference gram-positive strains, while no antibacterial activity was found against gram-negative strains up to the highest concentration tested of 50 μg/mL. Given its relevance as a community and hospital pathogen, further studies have been performed on selamectin activity against Staphylococcus aureus (S. aureus), using clinical isolates with different antibiotic resistance profiles and a reference biofilm-producing strain. Antibacterial studies have been extensive on clinical S. aureus isolates with different antibiotic resistance profiles. Mean MIC90 values of 6.2 μg/mL were reported for all tested S. aureus strains, except for the macrolide-resistant isolate with constitutive macrolide-lincosamide-streptogramin B resistance phenotype (MIC90 9.9 μg/mL). Scanning Electron Microscopy (SEM) showed that selamectin exposure caused relevant cell surface alterations. A synergistic effect was observed between ampicillin and selamectin, dictated by an FIC value of 0.5 against methicillin-resistant strain. Drug administration at MIC concentration reduced the intracellular bacterial load by 81.3%. The effect on preformed biofilm was investigated via crystal violet and confocal laser scanning microscopy. Selamectin reduced the biofilm biomass in a dose-dependent manner with minimal biofilm eradication concentrations inducing a 50% eradication (MBEC50) at 5.89 μg/mL. The cytotoxic tests indicated that selamectin exhibited no relevant hemolytic and cytotoxic activity at active concentrations. These data suggest that selamectin may represent a timely and promising macrocyclic lactone for the treatment of S. aureus infections.

Disruption of the intestinal barrier by avermectin in carp involves oxidative stress and apoptosis and leads to intestinal inflammation

Avermectin (AVM) is a widely used insecticide. Due to its sensitive toxicity to aquatic organisms, the toxicology of AVM on fish intestines remains unclear. Here, we established a 96 h AVM acute toxicity model to explore the effects of AVM on the intestinal tract of carp. The 96 h LC50 of carps exposed to AVM was 24.04 μg/L, 12.02 μg/L was selected as the high-dose group and 3.005 μg/L was selected as the low-dose group. After 96 h of exposure, intestinal tissues were collected and subsequently analyzed for histopathology, the activities of antioxidant oxidases (CAT, SOD, GSH-Px), and the expression of mRNA associated with oxidative stress, inflammation, and apoptosis. Our study showed that AVM exposure caused intestinal damage in carp, decreased the expression of the tight junction protein gene, activated oxidative stress, induced apoptosis, and induced intestinal inflammation in carp. Therefore, we demonstrated that AVM exposure compromised the integrity of the intestinal barrier in carp, activated oxidative stress, induced endogenous apoptosis, and induced intestinal inflammatory responses. These results indicate that AVM, as a drug-sensitive to aquatic organisms, has a much more complex toxic effect on the fish intestinal tract, which provides a new perspective for studying the toxicology of AVM on the fish intestinal tract.

Novel Lactone-Based Insecticides and Drosophila suzukii Management: Synthesis, Potential Action Mechanisms and Selectivity for Non-Target Parasitoids

Drosophila suzukii, an invasive insect pest, poses a significant threat to various fruit crops. The use of broad-spectrum insecticides to control this pest can reduce the effectiveness of biological control agents, such as the parasitoid Trichopria anastrephae. Here, we evaluated the toxicity of newly synthesized lactone derivatives on D. suzukii and their selectivity towards T. anastrephae. We used in silico approaches to identify potential targets from the most promising molecules in the D. suzukii nervous system and to understand potential differences in susceptibilities between D. suzukii and its parasitoid. Of the nine molecules tested, (rac)-8 and compound 4 demonstrated efficacy against the fly. Exposure to the estimated LC90 of (rac)-8 and compound 4 resulted in a mortality rate of less than 20% for T. anastrephae without impairing the parasitoid's functional parasitism. The in silico predictions suggest that (rac)-8 and compound 4 target gamma amino butyric acid (GABA) receptors and transient receptor potential (TRP) channels of D. suzukii. However, only the reduced interaction with TRP channels in T. anastrephae demonstrated a potential reason for the selectivity of these compounds on the parasitoid. Our findings suggest the potential for integrating (rac)-8 and compound 4 into D. suzukii management practices.

Avermectin B1a Shows Potential Anti-Proliferative and Anticancer Effects in HCT-116 Cells via Enhancing the Stability of Microtubules

Avermectins are a group of macrocyclic lactones that are commonly used as pesticides to treat pests and parasitic worms. Some members of the avermectin family, such as ivermectin, have been found to exhibit anti-proliferative activity toward cancer cells. This study aimed to investigate the potential anti-cancer activities of avermectin B1a using the HCT-116 colon cancer cell line. The MTT assay was used to calculate the IC50 by incubating cells with increasing doses of avermectin B1a for 24, 48, and 72 h. Flow cytometry was used to evaluate apoptosis following the 24 h incubation of cells. The migration capacity of the HCT-116 cells in the absence or presence of avermectin B1a was also investigated. Finally, tubulin polymerization in the presence of avermectin B1a was evaluated. Avermectin B1a presented anti-proliferative activity with an IC50 value of 30 μM. Avermectin B1a was found to promote tubulin polymerization at 30 μM. In addition, avermectin B1a induced apoptosis in HCT-116 cells and substantially diminished their ability to migrate. Avermectin B1a exhibits significant anti-cancer activity and enhances tubulin polymerization, suggesting that it can be used as a promising microtubule-targeting agent for the development of future anticancer drugs.

Crosstalk between primary and secondary metabolism: Interconnected fatty acid and polyketide biosynthesis in prokaryotes

In primary metabolism, fatty acid synthases (FASs) biosynthesize fatty acids via sequential Claisen-like condensations of malonyl-CoA followed by reductive processing. Likewise, polyketide synthases (PKSs) share biosynthetic logic with FAS which includes utilizing the same precursors and cofactors. However, PKS biosynthesize structurally diverse, complex secondary metabolites, many of which are pharmaceutically relevant. This digest covers examples of interconnected biosynthesis between primary and secondary metabolism in fatty acid and polyketide metabolism. Taken together, further understanding the biosynthetic linkage between polyketide biosynthesis and fatty acid biosynthesis may lead to improved discovery and production of novel drug leads from polyketide metabolites.

Application of nematicide avermectin enriched antibiotic-resistant bacteria and antibiotic resistance genes in farmland soil

The extensive use of antibiotics in medicine and agriculture has resulted in the accumulation of antibiotic-resistant microorganisms and antibiotic resistance genes (ARGs) in environments, which threaten human health and contaminate environment. Nematicide avermectin is widely applied to control root-knot nematodes. The effect of five-years application of avermectin on rhizosphere microbiome and resistome of sick tobacco plants in farmland were investigated in present study. The environmental risks of avermectin was assessed adequately. Metagenomic method was used to analyze antibiotic-resistant bacteria and antibiotic resistance genes in the avermectin-treated soil. The abundance and distribution of antibiotic-resistant bacteria and their antibiotic resistance genes were affected by avermectin application. The antibiotic resistant Proteobacteria occupied the highest percentage (36%) in rhizosphere soil and carried 530 ARGs. Opportunistic human pathogens carrying antibiotic resistance genes were enriched in the avermectin-treated soil. Avermectin application increased the counts of many types of antibiotic resistance genes. The relative abundances of genes adeF, BahA, fusH, ileS, and tlrB in the avermectin-treated soil were significantly greater than in the untreated control soil. Different resistance mechanisms were revealed in the avermectin-treated soil. The efflux of antibiotic (670 ARGs), inactivation of antibiotic (475 ARGs), and alteration of antibiotic target (267 ARGs) were the main resistance mechanisms. Rigid control the avermectin dose and use frequency and other pesticides can decrease soil antibiotic resistance genes and protect agricultural products' safety and public health. Overall, application of nematicide avermectin enriched antibiotic-resistant bacteria and antibiotic resistance genes in farmland soil, which should be on the alert for environment protection.

Toxic encephalopathy and peripheral neuropathy of poisoning by Avermectin Pyridine: a case report and a review of the literature

Background

Avermectin Pyridaben (AVP) is an insecticide with extreme neurotoxicity in human, causing critical symptoms such as nausea, vomiting, coma and respiratory failure within a short time after oral ingestion. Neurological sequelae or even death may occur because of delayed treatment or excessive toxic dose.

Case presentation

We report a 15-year-old girl who presented with coma, respiratory failure, limb weakness, ataxia symptoms after ingestion of a toxic dose of AVP. Soon after the poisoning, the patient was treated with life-saving mechanical ventilation and haemodialysis. Subsequently brain Magnetic Resonance Imaging (MRI) and nerve conduction study (NCS) and electromyography (EMG) demonstrated toxic encephalopathy and peripheral nerve injury. Over the next 2 months the patient's limb function gradually recovered under treatment with hyperbaric oxygen, glucocorticoid pulses and neurotrophic drugs.

Conclusion

This case documents a rare presentation of toxic encephalopathy complicated with peripheral neuropathy following AVP poisoning. Seven other similar cases of poisoning in terms of common symptoms and effective treatment have also been summarised for providing clinicians with experience in diagnosis and therapy.

Protective effect of quercetin on avermectin induced splenic toxicity in carp: Resistance to inflammatory response and oxidative damage

Avermectin pollution is an important problem that cannot be ignored in aquatic system in recent years. It has brought great trouble to freshwater aquaculture, especially fishery aquaculture. Plant-derived quercetin has anti-inflammatory and antioxidant properties and is widely used as a dietary additive, but its protective effect on immune damage induced by avermectin in freshwater carp remains unclear. This study evaluated the role of dietary additive quercetin supplementation in chronic avermectin exposure of carp spleen. Sixty carp were divided into 4 groups (n = 15/ group), including control group, avermectin treatment group, quercetin treatment group, quercetin and avermectin co-treatment group. Carp were exposed to a 1/10 96 h LC₅₀ dose of avermectin for 30 d and fed a carp diet containing 400 mg/kg quercetin twice a day (3% body weigh/ carp). The results showed that chronic avermectin exposure caused the loose parenchymal structure of carp spleen tissue and the increase of inflammatory cells, accompanied by increased transcription levels of pro-inflammatory il-1β, il-6, tnf-α and decreased levels of anti-inflammatory factors il-10 and tgf-β1, ROS accumulation in spleen tissue. MDA content increased and T-AOC, CAT and GSH levels decreased. Quercetin down-regulates the NF-κB pathway by inhibiting the expression of iNOS and activating p38 MAPK, blocking the transcription of inflammatory factors, and alleviating the inflammation of carp spleen caused by chronic avermectin exposure. In addition, quercetin inhibits the over-activation of Nrf2/Keap-1 signaling axis, blocks ROS accumulation, and restores the spleen REDOX homeostasis. In conclusion, quercetin, as a dietary additive for carp feed, can effectively improve the immune damage caused by avermectin pollution in aquatic environment, resist spleen inflammation and oxidative stress, and provide a theoretical basis for clinical development of freshwater carp feed.

Efficacy and safety of single-dose ivermectin in mild-to-moderate COVID-19: the double-blind, randomized, placebo-controlled CORVETTE-01 trial

Background

To investigate whether ivermectin inhibits SARS-CoV-2 proliferation in patients with mild-to-moderate COVID-19 using time to a negative COVID-19 reverse transcription-polymerase chain reaction (RT-PCR) test.

Methods

CORVETTE-01 was a double-blind, randomized, placebo-controlled study (August 2020-October 2021) conducted in Japan. Overall, 248 patients diagnosed with COVID-19 using RT-PCR were assessed for eligibility. A single oral dose of ivermectin (200  μg/kg) or placebo was administered under fasting. The primary outcome was time to a negative COVID-19 RT-PCR test result for SARS-CoV-2 nucleic acid, assessed using stratified log-rank test and Cox regression models.

Results

Overall, 112 and 109 patients were randomized to ivermectin and placebo, respectively; 106 patients from each group were included in the full analysis set (male [%], mean age: 68.9%, 47.9 years [ivermectin]; 62.3%, 47.5 years [placebo]). No significant difference was observed in the occurrence of negative RT-PCR tests between the groups (hazard ratio, 0.96; 95% confidence interval [CI] 0.70-1.32; p = 0.785). Median (95% CI) time to a negative RT-PCR test was 14.0 (13.0-16.0) and 14.0 (12.0-16.0) days for ivermectin and placebo, respectively; 82.1% and 84% of patients achieved negative RT-PCR tests, respectively.

Conclusion

In patients with COVID-19, single-dose ivermectin was ineffective in decreasing the time to a negative RT-PCR test.

Clinical Trial Registration

ClinicalTrials.gov, NCT04703205.

The role of intercellular junction proteins in the penetration resistance of Drosophila larvae to avermectin

Insecticide resistance has become an increasingly serious challenge for agriculture in the world. To reveal the mechanisms of insecticide resistance, majority of studies have been carried out on the insensitivity of insecticide targets and the metabolism of insecticides. However, the mechanism of the insecticide penetration resistance in insects remains unclear. This study aimed to reveal the mechanism underlying the penetration resistance of Drosophila larvae to insecticide avermectin (AVM). Levels of intercellular junction proteins (IJPs) in the larvae were determined by Western blotting analysis and immunofluorescence assay. The result showed that the expression of IJPs septate junction and adherens junction proteins increased in the AVM-resistant insects compared with those in the AVM-susceptible ones, and the upregulation of the IJPs was mediated by the activation of protein kinase C (PKC) pathway. That AVM induced the activation of PKC was found not only in the Drosophila larvae but also in Drosophila S2 cells. These findings revealed that AVM could activate PKC pathway in Drosophila larvae, which mediated the upregulation of the IJPs and then led to the resistance to AVM, suggesting that the chemicals that can disrupt PKC activation may potentially be used to circumvent the resistance to AVM in insects.

Nemacol is a small molecule inhibitor of C. elegans vesicular acetylcholine transporter with anthelmintic potential

Nematode parasites of humans and livestock pose a significant burden to human health, economic development, and food security. Anthelmintic drug resistance is widespread among parasites of livestock and many nematode parasites of humans lack effective treatments. Here, we present a nitrophenyl-piperazine scaffold that induces motor defects rapidly in the model nematode Caenorhabditis elegans. We call this scaffold Nemacol and show that it inhibits the vesicular acetylcholine transporter (VAChT), a target recognized by commercial animal and crop health groups as a viable anthelmintic target. We demonstrate that it is possible to create Nemacol analogs that maintain potent in vivo activity whilst lowering their affinity to the mammalian VAChT 10-fold. We also show that Nemacol enhances the ability of the anthelmintic Ivermectin to paralyze C. elegans and the ruminant nematode parasite Haemonchus contortus. Hence, Nemacol represents a promising new anthelmintic scaffold that acts through a validated anthelmintic target.

The potential effect of Moringa oleifera ethanolic leaf extract against oxidative stress, immune response disruption induced by abamectin exposure in Oreochromis niloticus

Abamectin (ABM), a naturally fermented product of Streptomyces avermitilis, is applied to pest control in livestock and agriculture fields. The aim of the current study is to evaluate the protective effects of Moringa oleifera leaf ethanolic extract (MOE) on biochemical changes including oxidative stress indices, immune response marker, lipid profiles as well as mRNA expression of immune related genes, and abamectin (ABM, 5% EC) residue levels in Nile tilapia (Oreochromis niloticus) exposed to a sub-lethal concentration (0.5 µg/l) for 28 days. Disturbance in liver and kidney biomarkers was markedly increased in ABM-exposed fish compared to the control group. Malondialdehyde levels in the liver and brain tissues, as well as the activities of glutathione-s-transferase, superoxide dismutase, and glutathione peroxides, all increased significantly in ABM group. Additionally, ABM exposure increased the levels of interleukin 10 beta and growth factor gene expression. On the other hand, fish exposed to ABM had significantly lower serum alkaline phosphatase, creatinine, high-density lipoprotein, glutathione peroxides in brain, glutathione in liver and brain tissues, lysozyme activity, nitric oxide, immunoglobulin M, tumor necrosis factor, and interleukin 1 beta as compared to the control group. The recorded detrimental effects of ABM on tilapia have been overcome by the addition of MOE to the diet (1%) and ameliorating hepato-renal damage and enhancing antioxidant activity, innate immune responses, and upregulating the anti-inflammatory gene expression. Therefore, it could be concluded that MOE dietary supplementation at 1% could be used to counteract the oxidative stress, immune response disruption induced by abamectin exposure in Oreochromis niloticus, and reduce its accumulation in fish tissues.

Toward anthelmintic drug candidates for toxocariasis: Challenges and recent developments

Infections caused by parasitic helminths rank among the most prevalent infections of humans and animals. Toxocariasis, caused by nematodes of the genus Toxocara, is one of the most widespread and economically important zoonotic parasitic infections that humans share with dogs and cats. Despite the completion of the Toxocara canis draft genome project, which has been an important step towards advancing the understanding of this parasite and the search for drug targets, the treatment of toxocariasis has been dependent on a limited set of drugs, necessitating the search for novel anthelmintic agents, specially against Toxocara larvae in tissues. Given that research, development, and innovation are crucial to finding appropriate solutions in the fight against helminthiasis, this paper reviews the progress made in the discovery of anthelmintic drug candidates for toxocariasis. The main compounds reported in the recent years regards on analogues of albendazole, reactive quinone derivatives and natural produts and its analogues. Nanoparticles and formulations were also reviewed. The in vitro and/or in vivo anthelmintic properties of such alternatives are herein discussed as well as the opportunities and challenges for treatment of human toxocariasis. The performed review clarify that the scarcity of validated molecular targets and limited chemical space explored are the main bottlenecks for advancing in the field of anti-Toxocara agents.

Season-Long Simplification of Insect Communities in Dung From Cattle Treated With an Extended-Release Formulation of the Parasiticide Eprinomectin

Cattle treated with LongRange®, an injectable formulation of the parasiticide eprinomectin, fecally excrete insecticidal residues for an extended period post application. We examined the nontarget effect of these residues by comparing insect communities developing in dung of untreated cattle (week 0) with those developing in dung of cattle treated 1, 2, 4, 8, 12, 16, 20, and 24 or 25 weeks previously. Chemical analyses of dung showed that eprinomectin concentrations peaked at 1 week post application and were still detectable at 25 weeks. Results from two separate experiments showed that dung of untreated cattle supported more total insects (beetles, flies, parasitoid wasps) and insect species than did dung of cattle treated for ≤12 weeks (Experiment 1) and ≤25 weeks (Experiment 2) previously. For the two experiments, an effect of residue on individual taxa was either not detected (nine cases) or was determined to suppress insect development in dung of cattle treated for 8-12 weeks (two cases), 12-16 weeks (three cases), 16-20 weeks (two cases), or 24 or 25 weeks (six cases) previously. Flies and their parasitoid wasps were particularly sensitive to residues with suppression often at or near 100%. These results show that cattle treated with LongRange in spring will fecally excrete residues for the entire grazing season with an associated simplification of the dung insect community. The effect of this simplification on the long-term health on dung-breeding populations of insects on pastures and dung degradation was not examined in the present study, but merits future research. Environ Toxicol Chem 2023;42:684-697. © 2023 His Majesty the King in Right of Canada. Environmental Toxicology and Chemistry © 2023 SETAC. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Abamectin causes cardiac dysfunction in carp via inhibiting redox equilibrium and resulting in immune inflammatory response and programmed cell death

This study aims to investigate the effects of environmentally relevant concentrations of abamectin on the cardiac function of carp and the potential mechanisms. Here, male carp were exposed to abamectin, and cardiac function-related enzymatic markers were examined. Cardiac histopathology, redox equilibrium, inflammation, and cell death were evaluated. Abamectin exposure caused cardiac dysfunction by upregulating lactate dehydrogenase (LDH), aspartate aminotransferase (AST), creatine kinase (CK), creatine Kinase MB isoenzyme (CK-MB) and white blood cells (WBCs), and decreasing red blood cells (RBCs) and hemoglobin (Hb). DHE staining and biochemical assays revealed that abamectin caused ROS release and oxidative stress by inhibiting Nrf2-ARE pathway. Histopathological and real-time fluorescence quantitative PCR (RT-qPCR) assays revealed that abamectin caused myocardial fiber swelling and inflammatory cell infiltration, enhanced pro-inflammatory cytokines tumor necrosis factor-α (Tnf-α), interleukin-1 beta (Il-1β), and Il-6 levels and attenuated anti-inflammatory cytokines Il-10 and transforming growth factor beta 1 (Tgf-β1) through activating NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome and nuclear factor kappa-B (NF-κB) pathway. Tunel staining showed that abamectin triggered cardiac apoptosis via activating p53-mediated mitochondrial apoptosis with elevated bcl2-associated X (Bax), reduced B-cell lymphoma-2 (Bcl-2), and activated Caspase-9 and Caspase-3. Immunoblot analysis revealed that abamectin activated autophagic flow by inhibiting mammalian target of rapamycin (mTOR), resulting in the conversion of LC3B from LC3-I to LC3-II, elevation of autophagy protein 5 (Atg5), and reduction of p62. Overall, abamectin caused cardiac dysfunction in carp via inhibiting redox equilibrium and resulting in immune inflammatory response and programmed cell death.

Small molecule inducers of actinobacteria natural product biosynthesis

Actinobacteria are a large and diverse group of bacteria that are known to produce a wide range of secondary metabolites, many of which have important biological activities, including antibiotics, anti-cancer agents, and immunosuppressants. The biosynthesis of these compounds is often highly regulated with many natural products (NPs) being produced at very low levels in laboratory settings. Environmental factors, such as small molecule elicitors, can induce the production of secondary metabolites. Specifically, they can increase titers of known NPs as well as enabling discovery of novel NPs typically produced at undetectable levels. These elicitors can be NPs, including antibiotics or hormones, or synthetic compounds. In recent years, there has been a growing interest in the use of small molecule elicitors to induce the production of secondary metabolites from actinobacteria, especially for the discovery of NPs from "silent" biosynthetic gene clusters. This review aims to highlight classes of molecules that induce secondary metabolite production in actinobacteria and to describe the potential mechanisms of induction.

ONE-SENTENCE SUMMARY

This review describes chemical elicitors of actinobacteria natural products described to date and the proposed mechanisms of induction.

Modular polyketide synthase-derived insecticidal agents: from biosynthesis and metabolic engineering to combinatorial biosynthesis for their production

Covering: up to 2022Polyketides derived from actinomycetes are a valuable source of eco-friendly biochemical insecticides. The development of new insecticides is urgently required, as the number of insects resistant to more than one drug is rapidly increasing. Moreover, significant enhancement of the production of such biochemical insecticides is required for economical production. There has been considerable improvement in polyketide insecticidal agent production and development of new insecticides. However, most commercially important biochemical insecticides are synthesized by modular type I polyketide synthases (PKSs), and their structural complexities make chemical modification challenging. A detailed understanding of the biosynthetic mechanisms of potent polyketide insecticides and the structure-activity relationships of their analogs will provide insight into the comprehensive design of new insecticides with improved efficacies. Further metabolic engineering and combinatorial biosynthesis efforts, reinvigorated by synthetic biology, can eventually produce designed analogs in large quantities. This highlight reviews the biosynthesis of representative insecticides produced by modular type I PKSs, such as avermectin, spinosyn, and spectinabilin, and their insecticidal properties. Metabolic engineering and combinatorial biosynthetic strategies for the development of high-yield strains and analogs with insecticidal activities are emphasized, proposing a way to develop a next-generation insecticide.

Screening of a high-yield strain of avermectin B1a by colony analysis in situ

Avermectin, an agricultural antibiotic, is widely used as an agricultural insecticide and an important lead compound of antibiotics. It is manufactured by Streptomyces avermitilis through fermentation. Manufacturers pay special attention to screening for strains with high fermentation capacity based on morphological properties of the colony and by the result of shake flask fermentation. These traditional screening methods are time-consuming and labor-intensive and require specialized equipment. Moreover, evaluation of colony appearance is highly subjective. To improve and accelerate the screening process, we developed a rapid in situ screening method. Forty-four strains isolated naturally from the spores of industrial high-yielding strains were studied. The data show that the colony fermentation titer is highly correlated with the yield from the shake flask fermentation of avermectin, and the Pearson's R is 0.990. The total titer of avermectins by shake flask fermentation is also highly correlated with the B_1a titer (Pearson's R is 0.994). This result also shows that strains can be quickly screened by analyzing the colony titer. Pigment rings of the colonies that appeared after growing and maturing on the new medium plate were analyzed. The chosen colonies were directly marked and punched and then extracted with methanol. The fermentation ability can be evaluated by measuring the absorbance at 245 nm. This methodology can be applied in both natural breeding and mutation breeding conditions. By continuously breeding from 2008 to 2020, the flask titer of avermectin B_1a increased from 4582 ± 483 to 9197 ± 1134 μg/mL.

Identification of novel nematode succinate dehydrogenase inhibitors: Virtual screening based on ligand-pocket interactions

To discover new nematicidal succinate dehydrogenase (SDH) inhibitors with novel structures, we conducted a virtual screening of the ChemBridge library with 1.7 million compounds based on ligand-pocket interactions. The homology model of Caenorhabditis elegans SDH was established, along with a pharmacophore model based on ligand-pocket interactions. After the pharmacophore-based and docking-based screening, 19 compounds were selected for the subsequent enzymatic assays. The results showed that compound 1 (ID: 7607321) exhibited inhibitory activity against SDH with a determined IC₅₀ value of 19.6 μM. Structural modifications and nematicidal activity studies were then carried out, which provided further evidence that compound 1 exhibited excellent nematicidal activity. Molecular dynamics simulations were then conducted to investigate the underlying molecular basis for the potency of these inhibitors against SDH. This work provides a reliable strategy and useful information for the future design of nematode SDH inhibitors.