A new pregnane glycoside from the root barks of Periploca sepium

Discovery of the Chlorinated and Ammoniated Derivatives of Vanillin as Potential Insecticidal Candidates Targeting V-ATPase: Structure-Based Virtual Screening, Synthesis, and Bioassay

Vacuolar-type H+-ATPases (V-ATPases) play a crucial role in the life cycle of agricultural pests and represent a promising target for the development of novel insecticides. In this study, S18, a derivative of vanillin acquired from Specs database using a structure-based virtual screening methodology, was first identified as a V-ATPase inhibitor. It binds to subunit A of the enzyme with a Kd of 1 nM and exhibits insecticidal activity against M. separata. Subsequently, using S18 as the lead compound, a new series of vanillin derivatives were rationally designed and efficiently synthesized. and their biological activities were assessed. Among them, compound 3b-03 showed the strongest insecticidal activity against M. separata by effectively targeting the V-ATPase subunit A with Kd of 0.803 μM. Isothermal titration calorimetric measurements and docking results provided insights into its interaction with subunit A of V-ATPase, which could facilitate future research aimed at the development of novel chemical insecticides.

Effects of periplocoside T isolated from Periploca sepium on behavior and sensory-CNS-motor circuits in Drosophila melanogaster larvae

Periplocoside T (PST) from Periploca sepium has insecticidal activity against some lepidopterans, which can significantly inhibit the activity of vacuolar-type H⁺-ATPases (V-ATPase). V-ATPase is involved in the release of neurotransmitters in vesicles during nerve signal transduction. However, there are actions of PST on behavior and sensory-central nervous system (CNS)-motor neural circuit which are commonly overlooked. After exposure to 500 mg/L PST for 48 h, the difference of the proportion of larvae responding to stimuli in the four Drosophila strains was not significant as compared to controls, but larval mouth hook movement and body wall motion were significantly decreased as compared to controls, and the decrease was more obvious in para^ts1; DSC1^-/- and DSC1^-/- strains, especially in para^ts1; DSC1^-/- strain. Compared with control (DMSO), the excitatory junction potential (EJP) frequencies of sensory-CNS-motor circuits in the four Drosophila strains after PST or bafiloymcin A1 (BA1, a V-ATPase specific inhibitor) treatment gradually decreased with time, and the decreasing amplitude of BA1 treatment was greater than that of PST treatment, but both were higher than that of the control. The decay amplitude of EJP frequency in two strains with DSC1 channel knockout was lower than that of w¹¹¹⁸ and para^ts1 strains without DSC1 channel knockout. Thus, the results indicated that PST, similar to BA1, could inhibit the transmission of sensory-CNS-motor circuit excitability of Drosophila larvae by inhibiting the activity of V-ATPase, and DSC1 channel play a role of in regulating the stability of nervous system.

Identification and mechanism of insecticidal periplocosides from the root bark of Periploca sepium Bunge

BACKGROUND

The Periploca sepium bark root (PSBR) has been regarded as a potential botanical insecticide because of its significant insecticidal activity of secondary metabolites. Several periplocosides were isolated from it as promising pesticides to control crop pests in agriculture.

RESULTS

In our research, two new periplocosides, along with four known periplocosides were isolated from PSBR. The names of new periplocosides were periplocoside T (PST) and periplocoside U (PSU) while another four periplocosides were known as follows: periplocoside A (PSA), periplocoside F (PSF), periplocoside E (PSE) and periplocoside D (PSD). All periplocosides were evalulated for insecticidal activity against 3rd Mythimna separata (Walker) and Plutella xylostella. The biometric data showed that periplocoside T, PSD and PSF had remarkable insecticidal activity against tested insects. Its values of LD₅₀ were 1.31, 3.94 and 3.42 μg·lavare^-1 against 3rd M. separata respectively, while the activity of those compounds against 3rd P. xylostella were 5.45, 12.17 and 13.95 μg·lavare^-1 , respectively. It was apparent after further study of the mechanism of action against M. separata was conducted that PST possessed the most significant insecticidal activity. The results of enzymatic activity displayed that powerful activation of tryptase, especially weak alkaline tryptase might be a dominant factor causing death of M. separata in vivo.

CONCLUSION

We herein report isolation and the mechanisms of action of insecticidal periplocosides, which established the fundamental development of natural agents to prevent pest damage to crops. © 2020 Society of Chemical Industry.

Genus Periploca (Apocynaceae): A Review of Its Classification, Phytochemistry, Biological Activities and Toxicology

The genus Periploca belongs to the family Apocynaceae, which is composed of approximately ten species of plants according to incomplete statistics. Most of these plants serve as folk medicines with a long history, especially Periploca sepium and Periploca forrestii. The botanical classifications, chemical constituents, biological activities and toxicities of the genus Periploca were summarized in the literature from 1897 to early 2019. Though the botanical classification of this genus is controversial, these species are well-known to be rich sources of diverse and complex natural products-above all, cardiac steroids and C₂₁ pregnane steroids with special structures and obvious pharmacological activities. The various crude extracts and 314 isolated metabolites from this genus have attracted much attention in intensive biological studies, indicating that they are equipped with cardiotonic, anti-inflammatory, immunosuppressive, antitumor, antimicrobial, antioxidant, insecticidal and other properties. It is noteworthy that some cardiac glycosides showed hepatotoxicity and cardiotoxicity at certain doses. Therefore, in view of the medical and agricultural value of the genus Periploca, in-depth investigations of the pharmacology in vivo, the mechanisms of biological actions, and the pharmacokinetics of the active ingredients should be carried out in the future. Moreover, in order to ensure the safety of clinical medication, the potential toxicities of cardiac glycosides or other compounds should also be paid attention. This systematic review provides an important reference base for applied research on pharmaceuticals and pesticides from this genus.

Comparative Proteomic Analysis of the Effect of Periplocoside P from Periploca sepium on Brush Border Membrane Vesicles in Midgut Epithelium of Mythimna separata Larvae

Periplocoside P (PSP), a novel compound isolated from Periploca sepium Bunge, possesses insecticidal activity against some lepidopterans, such as Mythimna separata. In M. separata, the brush border membrane vesicles of the midgut epithelium are the initial site of action of periplocosides. We conducted two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight/time of flight mass spectrometry analysis to analyze differentially expressed proteins (DEPs) from periplocoside P (PSP)-treated M. separata. We successfully isolated seven up-regulated and three down-regulated DEPs that have been previously identified, as well as a novel DEP. The DEPs are implicated in protein degradation, transporter, folding, and synthesis, and in juvenile hormone biosynthesis. DEPs involved in the oxidative phosphorylation energy metabolism pathway are enriched. Through real-time polymerase chain reaction assay, we confirmed that vma1 expression is significantly up-regulated expression levels in PSP-treated M. separata larvae. Enzymology validation further indicated that PSP can significantly inhibit V-type ATPase activity in a concentration-dependent manner. Given these results, we speculate that in M. separata, the V-type ATPase A subunit in the midgut epithelium is the putative target binding site of periplocosides. This finding provides preliminary evidence for the mode of action of periplocosides.

C21 steroidal glycosides and oligosaccharides from the root bark of Periploca sepium

Four new C₂₁ steroidal glycosides (1-4), named perisepiumosides FI (1-4) together with six known steroidal glycosides (5-10) and four oligosaccharides (11-14), were isolated from the root bark of Periploca sepium. Their structures were characterized on the basis of 1D and 2D-NMR spectroscopic data as well as HR-ESI-MS analysis. The evaluation of inhibition activity against human A-549 and HepG2 cell lines indicated that compounds 2, 8, 10 and 13 showed different levels of cytotoxic activities with IC₅₀ values ranging from 0.61 to 7.86μM.

Effects of Periplocoside P from Periploca sepium on the Midgut Transmembrane Potential of Mythimna separata Larvae

Periplocoside P (PSP) isolated from the root bark of Periploca sepium contains a pregnane glycoside skeleton and possesses high insecticidal properties. Preliminary studies indicated that PSP disrupts epithelial functions in the midgut of lepidopteran larvae. In the present study, we examined the effects of PSP on the apical and basolateral membrane voltages, V_a and V_bl, respectively, of cells from (1) midguts isolated from the larvae of the oriental armyworm Mythimna separata that were in vitro incubated with toxins and (2) midguts isolated from M. separata larvae force-fed with PSP. We compared the effects of PSP with the effects of the Bacillus thuringiensis toxin Cry1Ab and inactive periplocoside E (PSE) on the midgut epithelial cells. The results showed that V_a rapidly decreased in the presence of PSP in a time- and dose-dependent manner, similar to the effects of Cry1Ab. By contrast, PSE did not affect the V_a and V_bl. Additionally, PSP did not influence the V_bl. Given these results, we speculate that PSP may modulate transport mechanisms at the apical membrane of the midgut epithelial cells by inhibiting the V-type H⁺ ATPase.

Insecticidal Pregnane Glycosides from the Root Barks of Periploca sepium

To explore novel lead compounds for botanical pesticides from natural sources, a new pregnane glycoside (periplocoside) P2 as well as its isomer, a known pregnane glycoside P1, were isolated from the root barks of Periploca sepium using a bioactivity-guided method, and their structures were confirmed by 1D NMR, 2D NMR, IR, ESI-MSn and HRMS. Their insecticidal activities were evaluated against 3rd instar larvae of M. separata, and the results indicated that P2 exhibited excellent insecticidal activity with LC50 values of 2.9 and 2.2 mg/mL after 24 and 48 h, respectively, much lower than those of the positive control celangulin-V (24.7 and 21.0 mg/mL after 24 and 48 h, respectively). This work demonstrated that pregnane glycosides from Periploca sepium could be promising lead compounds for developing botanical pesticides urgently needed in agriculture.

Different Effects of Bacillus thuringiensis Toxin Cry1Ab on Midgut Cell Transmembrane Potential of Mythimna separata and Agrotis ipsilon Larvae

Bacillus thuringiensis (Bt) Cry toxins from the Cry1A family demonstrate significantly different toxicities against members of the family Noctuidae for unknown reasons. In this study, membrane potential was measured and analyzed in freshly isolated midgut samples from Mythimna separata and Agrotis ipsilon larvae under oral administration and in vitro incubation with Bt toxin Cry1Ab to elucidate the mechanism of action for further control of these pests. Bioassay results showed that the larvae of M. separata achieved a LD50 of 258.84 ng/larva at 24 h after ingestion; M. separata larvae were at least eightfold more sensitive than A. ipsilon larvae to Cry1Ab. Force-feeding showed that the observed midgut apical-membrane potential (V(am)) of M. separata larvae was significantly depolarized from -82.9 ± 6.6 mV to -19.9 ± 7.2 mV at 8 h after ingestion of 1 μg activated Cry1Ab, whereas no obvious changes were detected in A. ipsilon larvae with dosage of 5 μg Cry1Ab. The activated Cry1Ab caused a distinct concentration-dependent depolarization of the apical membrane; V(am) was reduced by 50% after 14.7 ± 0.2, 9.8 ± 0.4, and 7.6 ± 0.6 min of treatment with 1, 5, and 10 μg/mL Cry1Ab, respectively. Cry1Ab showed a minimal effect on A. ipsilon larvae even at 20 μg/mL, and V(am) decreased by 26.3% ± 2.3% after 15 min. The concentrations of Cry1Ab displayed no significant effect on the basolateral side of the epithelium. The V(am) of A. ipsilon (-33.19 ± 6.29 mV, n = 51) was only half that of M. separata (-80.94 ± 6.95 mV, n = 75). The different degrees of sensitivity to Cry1Ab were speculatively associated with various habits, as well as the diverse physiological or biochemical characteristics of the midgut cell membranes.