Histopathological effects of Pedunsaponin A on Pomacea canaliculata

Molluscicide screening and identification of novel targets against Pomacea canaliculata

BACKGROUND

Owing to the nonavailability of any clear targets for molluscicides against Pomacea canaliculata, target-based screening strategy cannot be employed. In this study, the molluscicidal effects of typical pesticides on P. canaliculata were evaluated to obtain the molluscicide target. A series of arylpyrrole compounds were synthesized based on the discovered target, and their structure-activity relationships explored. A preliminary strategy for screening molluscicides based on specific targets was also developed.

RESULTS

A laboratory colony of P. canaliculata was developed, which showed no difference in sensitivity to niclosamide compared with the wild group, while exhibiting a higher stability against pesticide response. Mitochondrial adenosine triphosphate (ATP) synthase inhibitors and mitochondrial membrane potential uncouplers were identified and validated as potential targets for molluscicide screening against P. canaliculata. A series of arylpyrrole compounds were designed and synthesized. The median lethal concentration of 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile (Compound 102) was 10-fold lower than that of niclosamide.

CONCLUSION

New molluscicide targets were discovered and validated, and preliminary strategies were explored for pesticide screening based on these targets. Compound 102 exhibited a high molluscicidal activity and had a great potential value for exploring a molluscicide to control P. canaliculata. © 2024 Society of Chemical Industry.

The Eco-Immunological Relevance of the Anti-Oxidant Response in Invasive Molluscs

Reactive oxygen species (ROS) are volatile and short-lived molecules playing important roles in several physiological functions, including immunity and physiological adaptation to unsuitable environmental conditions. In an eco-immunological view, the energetic costs associated with an advantageous metabolic apparatus able to cope with wide changes in environmental parameters, e.g., temperature range, water salinity or drought, could be further balanced by the advantages that this apparatus may also represent in other situations, e.g., during the immune response. This review provides an overview of molluscs included in the IUCN list of the worst invasive species, highlighting how their relevant capacity to manage ROS production during physiologically challenging situations can also be advantageously employed during the immune response. Current evidence suggests that a relevant capacity to buffer ROS action and their damaging consequences is advantageous in the face of both environmental and immunological challenges, and this may represent a trait for potential invasiveness. This should be considered in order to obtain or update information when investigating the potential of the invasiveness of emerging alien species, and also in view of ongoing climate changes.

Study on the Synergistic Molluscicidal Effect of Pedunsaponin A and Niclosamide

Niclosamide (NI) is the main molluscicide used to control Pomacea canaliculata (Lamarck) (Architaenioglossa: Ampullariidae). However, NI failed to inhibit snail climbing during the treatment process. In this study, we examined the effect of NI combined with pedunsaponin A at an ineffective concentration. The molluscicidal effect of Pedunsaponin A on NI was evidently synergistic after 48 h, and the synergism ratio (SR) was 1.82 after treatment for 72 h at 0.8 mg·L^-1. Examination of the climbing adhesion effect showed that a high concentration of Pedunsaponin A (0.4 mg·L^-1 and 0.8 mg·L^-1) combined with NI significantly inhibited the climbing of P. canaliculata. We further studied the synergism mechanism; the results of histopathological observation showed that the siphon appeared cavities, the muscle fibers of the ventricular were severely dissolved, and kidney tubule arrangement was distorted after NI adding Pedunsaponin A. In addition, the hemocyte survival rate and the content of hemocyanin decreased significantly. According to the results of our study, the synergism mechanism may hinder oxygen transport of P. canaliculata, influencing the supply of energy; the ability of immune defense and excretion and metabolic detoxification decreased, prolonging the action time of NI in the body.

Research on the molluscicidal activity and molecular mechanisms of arecoline against Pomacea canaliculata

Pomacea canaliculata, as an invasive snail in China, can adversely affect agricultural crop yields, ecological environment, and human health. In this paper, we studied the molluscicidal activity and mechanisms of arecoline against P. canaliculata. The molluscicidal activity tests showed that arecoline exhibits strong toxicity against P. canaliculata, and the LC₅₀ value (72 h) was 1.05 mg/L (15 ± 2 mm shell diameter). Additionally, Molluscicidal toxicity were negatively correlated with the size of snails. Snails (25 ± 2 mm shell diameter) were choosed for mechanisms research and the result of microstructure and biochemistry showed that arecoline (4 mg/L, 20 ℃) had strong toxic effect on the gill, and the main signs were the loss of cilia in the gill filaments. Moreover, arecoline significantly decreased the oxygen consumption rate, ammonia excretion rate and inhibited acetylcholinesterase (AChE). Then, the changes in protein expression were studied by iTRAQ, and 526 downregulated proteins were found. Among these, cilia and flagella-associated 157-like (PcCFP) and rootletin-like (PcRoo) were selected as candidate target proteins through bioinformatics analysis, and then RNA interference (RNAi) was adopted to verify the function of PcCFP and PcRoo. The results showed that after arecoline treated, the mortality and the cilia shedding rate of PcRoo RNAi treated group was significantly lower than control group. The above results indicate that arecoline can bind well with protein PcRoo, and then leads to the drop of gill cilia, affect respiratory metabolism, accelerate its entry into hemolymph, inhibit AChE and finally leads to the death of P. canaliculata.

Study on the relationship of Hsp70 with the temperature sensitivity of pedunsaponin A poisoning Pomacea canaliculata

Previous studies have found that temperature influences molluscicidal the activity of pedunsaponin A (PA), which may be related to the expression of Hsp70, a cold-tolerance gene in Pomacea canaliculata. We determined the temperature effect of PA and the relationship between Hsp70 and temperature sensitivity of P. canaliculata poisoned by PA. Toxicity tests resulted in LC₅₀ values of 17.7239 mg⋅L^-1 at 10 °C, which decreased to 2.5774 mg⋅L^-1 at 30 °C, implying a positive correlation between toxicity of PA and temperature. After Hsp70 being interfered, the mortality rate of P. canaliculata treated with PA for 72 h was 70%, which was significantly higher than that of snails treated with PA for 72 h without interfering (56.7%). Meanwhile, immune enzyme activities such as SOD, ACP and AKP were significantly increased in the interfered group and expression level of PcAdv in the gill was also significantly increased. These results suggest that deletion of Hsp70 promotes the activation of some immune enzymes of P. canaliculata and elevates the content of target proteins to cope with the dual stresses of low temperatures and molluscicides. These findings indicate that the Hsp70 plays an important role in influencing the temperature sensitivity of P. canaliculata when treated with PA.

Pharmacophore identification, virtual screening and activity verification of pedunsaponin A on target proteins PcAdv and PcnWAS of Pomacea canaliculata

Target-protein-based pesticide screening has attracted wide-ranging attention on pesticide science. Pedunsaponin A (PA) is a compound isolated from the root of Pueraria peduncularis, and it has a strong toxic effect on Pomacea canaliculata. Previous studies found that Advlin (PcAdv) and neural Wiskott-Aldrich syndrome isoform X1(PcnWAS) are target proteins of PA when interacted with P. canaliculata. In this study, we modeled the two target proteins through I-Tasser and identified the pharmacophore of PA binding to the two target proteins by molecular docking. Furthermore, through virtual screening, potassium alginate was found to strongly bind to the target proteins in theory. In vivo bioassay showed that, similar to PA treatment, potassium alginate was able to induce typical poisoning symptoms on P. canaliculata, which were characterized by abnormal increase of excreta, weakening of climbing capacity, loss of gill cilia and decrease in hemocyanin content, and even cause death of P. canaliculata with a 13.33% mortality rate under 100 mg L^-1 concentration. Furthermore, the treatment of potassium alginate also decreased the gene expression level of PcAdv and PcnWAS. These findings indicate that potassium alginate can affect the living state of P. canaliculata, and that it is feasible to develop new molluscicides based on PcAdv and PcnWAS by virtual screening. © 2022 Society of Chemical Industry.

Identification and functional verification of the target protein of pedunsaponin A in the gills of Pomacea canaliculata

BACKGROUND

Based on previous research indicating that pedunsaponin A (PA) can destroy the gills of Pomacea canaliculata, we chose the gill as the main research object, and identified the target protein of PA in the gills of P. canaliculata through proteomics and RNA interference (RNAi).

RESULTS

Proteomics showed that 180 proteins were downregulated after PA treatment in P. canaliculata. Among them, we chose advillin (PcAdv), receptor type tyrosine protein phosphatase (PcRT) and unconventional myosin heavy chain 6 (PcUM) as candidate target proteins through bioinformatics analysis. The small interfering RNA (siRNA) with the best interference effect was identified through further screening. Gene interference rates were 97%, 98% and 82% for PcAdv, PcRT and PcUM, respectively. The results showed that after RNAi treatment, the mortality of P. canaliculata treated with PcAdv (60.0%) was significantly lower than that for the control (93.3%); histological analysis showed that the structure of the gill was intact, cilia shedding was reduced, and the survival rate of hemocytes had increased.

CONCLUSION

These findings indicate that, when the protein was absent or suppressed, the channel for entry of PA into the hemocytes of P. canaliculata was blocked, which reduced PA binding to hemocytes, and that there is a close relationship between shedding of gill cilia and PA entry into hemocytes. PcAdv is thus the key protein in PA destruction of gill cilia. Locating the proteins in gills that interact with drugs and investigating their mode of action is of great importance in the development of new molluscicides to control P. canaliculata populations.

Screening and functional verification of the target protein of pedunsaponin A in the killing of Pomacea canaliculata

Previous study found that pedunsaponin A (PA) influenced the cytoskeleton of Pomacea canaliculata hemocytes, leading to depolarization and haemocyte destruction and eventually to snail death. In this study, we analysed the changes in protein expression by iTRAQ-mediated proteomics and identified 51 downregulated proteins. Among these, we focused on proteins related to cytoskeletal function and identified neural Wiskott-Aldrich syndrome isoform X1 (PcnWAS). The full-length PcnWAS gene contains 9791 bp and includes an open reading frame of 1401 bp that encodes 735 amino acids with a predicted molecular mass of 49.83 kD. PcnWAS exhibited a relatively distant genetic relationship with known species; the closest homologue is Biomphalaria glabrata (57%). RNA interference (RNAi) was adopted to verify the function of PcnWAS after screening the siRNA sequence with an efficiency of 97%. Interference with the gene expression of PcnWAS did not lead to snail death, but the depolarization level increased, which demonstrated that PcnWAS is an important depolarization-related protein. The results of PA treatment of snails subjected to RNAi proved that interfering with PcnWAS gene expression decreased the molluscicidal activity of PA toward P. canaliculata; snail mortality after RNAi was significantly lower (40%) than that in PA-treated snails without RNAi (54%), while the survival rate and depolarization level in haemocytes were not significant, indicating that PcnWAS is only one of the important target proteins of PA in P. canaliculata. This study lays the foundation for further exploration of the molecular mechanism by which PA kills this harmful snail.

Study of the Differentially Expressed Genes in the Pomacea canaliculata Transcriptome after Treatment with Pedunsaponin A

Transcriptomes, genomes, and proteomes have played important roles in the search for drug targets. To determine the molluscicidal mechanism of pedunsaponin A against Pomacea canaliculata, RNA-seq technology was adopted to analyze the differentially expressed genes (DEGs) in the P. canaliculata transcriptome after treatment with pedunsaponin A. As a result, 533 DEGs were identified, among which 255 genes were significantly upregulated and 278 genes were significantly downregulated. According to the analysis of Gene Ontology (GO) functions, we found that the DEGs were significantly enriched in the viral life cycle, UDP-glucose 4-epimerase activity, guanylate cyclase activity, the cyclic guanosine monophosphate (cGMP) biosynthetic process, and the cGMP metabolic process. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway results showed that the DEGs were mainly involved in the hedgehog signaling pathway, phagosome, cytosolic DNA-sensing pathway, retinoic acid-inducible gene I like (RIG-I-like) receptor signaling pathway, bacterial secretion system, and nuclear factor-kappa B (NF-kappa B) signaling pathway. The above results indicated that pedunsaponin A causes a metabolic disorder, anomalous opening of membrane ion channels, and an imbalance in osmotic pressure between the interior and exterior of cells, eventually resulting in the death of cells involved in immune defense and influencing the immune response of P. canaliculata.

The Damaging Effects of Pedunsaponin A on Pomacea canaliculata Hemocytes

Pomacea canaliculata hemocytes are the main functional cells in the immune defense system, and hemocyte destruction disrupts the immune response mechanism of P. canaliculata, resulting in abnormal growth, development, reproduction, and even death. Our previous study found that Pedunsaponin A significantly affects P. canaliculata hemocyte structure. This study further investigated the damaging effects of Pedunsaponin A on P. canaliculata hemocytes. The cell mortality rate results showed that the hemocyte mortality was significantly increased after treatment with Pedunsaponin A, and the mortality rate exhibited a significant positive correlation with treatment time and dose. The membrane potential results showed that the cell membranes of P. canaliculata hemocytes exhibited time-dependent membrane depolarization after 40 mg/L Pedunsaponin A treatment. At 36 h, the cell depolarization rate in the Pedunsaponin A treatment group was 41.43%, which was significantly greater than the control group (6.24%). The cytoskeleton results showed that Pedunsaponin A led to disordered and dispersed arrangement of microfilaments and changes in the cytoskeletal structure. The apoptosis and cell cycle results showed that Pedunsaponin A induced apoptosis and influenced the cell cycle to some extent. These results showed that the cell membrane and cytoskeleton of P. canaliculata hemocytes were damaged after treatment with Pedunsaponin A, which led to an increase in cell mortality, dysfunction, cell cycle abnormalities and apoptosis. This study provides a foundation for further identification of the site of Pedunsaponin A activity on hemocytes.