Exploring the Sequence Diversity of Cyclotides from Vietnamese Viola Species

Characterization and evaluation of cytotoxic and antimicrobial activities of cyclotides from Viola japonica

Cyclotides are a type of defense peptide most commonly found in the Violaceae family of plants, exhibiting various biological activities. In this study, we focused on the Viola japonica as our research subject and conducted transcriptome sequencing and analysis using high-throughput transcriptomics techniques. During this process, we identified 61 cyclotides, among which 25 were previously documented, while the remaining 36 were designated as vija 1 to vija 36. Mass spectrometry detection showed that 21 putative cyclotides were found in the extract of V. japonica. Through isolation, purification and tandem mass spectrometry, we characterized and investigated the activities of five cyclotides. Our results demonstrated inhibitory effects of these cyclotides on the growth of Acinetobacter baumannii and Bacillus subtilis, with minimum inhibitory concentrations (MICs) of 4.2 μM and 2.1 μM, respectively. Furthermore, time killing kinetic assays revealed that cyclotides at concentration of 4 MICs achieved completely bactericidal effects within 2 h. Additionally, fluorescence staining experiments confirmed that cyclotides disrupt microbial membranes. Moreover, cytotoxicity studies showed that cyclotides possess cytotoxic effects, with IC50 values ranging from 0.1 to 3.5 μM. In summary, the discovery of new cyclotide sequences enhances our understanding of peptide diversity and the exploration of their activity lays the foundation for a deeper investigation into the mechanisms of action of cyclotides.

Immunosuppressive Cyclotides: A Promising Approach for Treating Autoimmune Diseases

The immune system maintains constant surveillance to prevent the infiltration of both endogenous and exogenous threats into host organisms. The process is regulated by effector immune cells that combat external pathogens and regulatory immune cells that inhibit excessive internal body inflammation, ultimately establishing a state of homeostasis within the body. Disruption to this process could lead to autoimmunity, which is often associated with the malfunction of both T cells and B cells with T cells playing a more major role. A number of therapeutic mediators for autoimmune diseases are available, from conventional disease-modifying drugs to biologic agents and small molecule inhibitors. Recently, ribosomally synthesized peptides, specifically cyclotides from plants are currently attracting more attention as potential autoimmune disease therapeutics due to their decreased toxicity compared to small molecules inhibitors as well as their remarkable stability against a number of factors. This review provides a concise overview of various cyclotides exhibiting immunomodulatory properties and their potential as therapeutic interventions for autoimmune diseases.

Cyclotides derived from Viola dalatensis Gagnep: A novel approach for enrichment and evaluation of antimicrobial activity

Cyclotides, plant-derived cysteine-rich peptides, exhibit a wide range of beneficial biological activities and possess exceptional structural stability. Cyclotides are commonly distributed throughout the Violaceae family. Viola dalatensis Gagnep, a Vietnamese species, has not been well studied, especially for cyclotides. This pioneering research explores cyclotides from V. dalatensis as antimicrobials. This study used a novel approach to enhance cyclotides after extraction. The approach combined 30% ammonium sulfate salt precipitation and RP-HPLC. A comprehensive analysis was performed to ascertain the overall protein content, flavonoids content, polyphenol content, and free radical scavenging capacity of compounds derived from V. dalatensis. Six known cyclotides were sequenced utilizing MS tandem. Semi-purified cyclotide mixtures (M1, M2, and M3) exhibited antibacterial efficacy against Bacillus subtilis (inhibitory diameters: 19.67-23.50 mm), Pseudomonas aeruginosa (22.17-23.50 mm), and Aspergillus flavus (14.67-21.33 mm). The enriched cyclotide precipitate from the stem extract demonstrated a minimum inhibitory concentration (MIC) of 0.08 mg/mL against P. aeruginosa, showcasing significant antibacterial effectiveness compared to the stem extract (MIC: 12.50 mg/mL). Considerable advancements have been achieved in the realm of cyclotides, specifically in their application as antimicrobial agents.

Cysteine-rich peptides: From bioactivity to bioinsecticide applications

Greater levels of insect resistance and constraints on the use of current pesticides have recently led to increased crop losses in agricultural production. Further, the health and environmental impacts of pesticides now restrict their application. Biologics based on peptides are gaining popularity as efficient crop protection agents with low environmental toxicity. Cysteine-rich peptides (whether originated from venoms or plant defense substances) are chemically stable and effective as insecticides in agricultural applications. Cysteine-rich peptides fulfill the stability and efficacy requirements for commercial uses and provide an environmentally benign alternative to small-molecule insecticides. In this article, cysteine-rich insecticidal peptide classes identified from plants and venoms will be highlighted, focusing on their structural stability, bioactivity and production.

A comprehensive review of phytochemistry, pharmacology and quality control of plants from the genus Viola

OBJECTIVES

The genus Viola belongs to the family Violaceae, and the plants from this genus are essential folk herb medicine extensively used in many areas. The plants from the genus Viola are used to treat various diseases and exert a significant role in protecting people's health. This review summarized the genus Viola plants' phytochemistry, pharmacology, and quality control methods.

KEY FINDINGS

The information on chemical constituents and pharmacological effects of the genus Viola was obtained by searching the Web of Science, Pubmed, CNKI, and other databases. A total of 208 valuable articles were selected and analyzed in this review. The main chemical components of plants from the genus Viola consist of flavonoids, coumarins, alkaloids, lignans, sesquiterpenes, cyclotides, etc. The active chemical components of medicinal plants from this genus exert antibacterial, antiviral, antioxidant, anti-inflammatory, anti-tumor, neuroprotective, hepatoprotective activities, and so on. The quality control of these plants is not sufficient and needs further research.

SUMMARY

The chemical constituents, pharmacological effects, and quality control of plants from the genus Viola were systematically summarized in this paper, and this review provides a literature basis for the further research of plants from this genus.

The acyclotide ribe 31 from Rinorea bengalensis has selective cytotoxicity and potent insecticidal properties in Drosophila

Cyclotides and acyclic versions of cyclotides (acyclotides) are peptides involved in plant defense. These peptides contain a cystine knot motif formed by three interlocked disulfide bonds, with the main difference between the two classes being the presence or absence of a cyclic backbone, respectively. The insecticidal activity of cyclotides is well documented, but no study to date explores the insecticidal activity of acyclotides. Here, we present the first in vivo evaluation of the insecticidal activity of acyclotides from Rinorea bengalensis on the vinegar fly Drosophila melanogaster. Of a group of structurally comparable acyclotides, ribe 31 showed the most potent toxicity when fed to D. melanogaster. We screened a range of acyclotides and cyclotides and found their toxicity toward human red blood cells was substantially lower than toward insect cells, highlighting their selectivity and potential for use as bioinsecticides. Our confocal microscopy experiments indicated their cytotoxicity is likely mediated via membrane disruption. Furthermore, our surface plasmon resonance studies suggested ribe 31 preferentially binds to membranes containing phospholipids with phosphatidyl-ethanolamine headgroups. Despite having an acyclic backbone, we determined the three-dimensional NMR solution structure of ribe 31 is similar to that of cyclotides. In summary, our results suggest that, with further optimization, ribe 31 could have applications as an insecticide due to its potent in vivo activity against D. melanogaster. More broadly, this work advances the field by demonstrating that acyclotides are more common than previously thought, have potent insecticidal activity, and have the advantage of potentially being more easily manufactured than cyclotides.

Application of chloroplast genome in the identification of Traditional Chinese Medicine Viola philippica

BACKGROUND

Viola philippica Cav. is the only source plant of "Zi Hua Di Ding", which is a Traditional Chinese Medicine (TCM) that is utilized as an antifebrile and detoxicant agent for the treatment of acute pyogenic infections. Historically, many Viola species with violet flowers have been misused in "Zi Hua Di Ding". Viola have been recognized as a taxonomically difficult genera due to their highly similar morphological characteristics. Here, all common V. philippica adulterants were sampled. A total of 24 complete chloroplast (cp) genomes were analyzed, among these 5 cp genome sequences were downloaded from GenBank and 19 cp genomes, including 2 "Zi Hua Di Ding" purchased from a local TCM pharmacy, were newly sequenced.

RESULTS

The Viola cp genomes ranged from 156,483 bp to 158,940 bp in length. A total of 110 unique genes were annotated, including 76 protein-coding genes, 30 tRNAs, and four rRNAs. Sequence divergence analysis screening identified 16 highly diverged sequences; these could be used as markers for the identification of Viola species. The morphological, maximum likelihood and Bayesian inference trees of whole cp genome sequences and highly diverged sequences were divided into five monophyletic clades. The species in each of the five clades were identical in their positions within the morphological and cp genome tree. The shared morphological characters belonging to each clade was summarized. Interestingly, unique variable sites were found in ndhF, rpl22, and ycf1 of V. philippica, and these sites can be selected to distinguish V. philippica from samples all other Viola species, including its most closely related species. In addition, important morphological characteristics were proposed to assist the identification of V. philippica. We applied these methods to examine 2 "Zi Hua Di Ding" randomly purchased from the local TCM pharmacy, and this analysis revealed that the morphological and molecular characteristics were valid for the identification of V. philippica.

CONCLUSIONS

This study provides invaluable data for the improvement of species identification and germplasm of V. philippica that may facilitate the application of a super-barcode in TCM identification and enable future studies on phylogenetic evolution and safe medical applications.

Cyclotides Chemosensitize Glioblastoma Cells to Temozolomide

Glioblastoma multiforme (GBM) is the most aggressive cancer originating in the brain, with a median survival of 12 months. Most patients do not respond to or develop resistance to the only effective chemotherapeutic drug, temozolomide (TMZ), used to treat gliomas. Novel treatment methods are critically needed. Cyclotides are plant peptides that may be promising adjuvants to TMZ chemotherapy. They exhibit antitumor activity and chemosensitize cells to doxorubicin in breast cancer studies. During this research, we optimized cyclotide isolation techniques, and several cyclotides (CyO2, CyO13, kalata B1, and varv peptide A) exhibited dose-dependent cytotoxicity in MTT assays with IC₅₀ values of 2.15-7.92 μM against human brain astrocytoma cells (U-87 MG) and human bone marrow derived neuroblastoma cells (SH-SY5Y). CyO2 and varv peptide A increased TMZ-induced cell death in U-87 MG cultures alone and when coexposed with CyO2 or varv peptide A plus TMZ. Phase contrast microscopy of glioblastoma cells exposed to cyclotides alone and coexposed to TMZ indicated shrunken, granular cells with blebbing, and the most pronounced effects were observed with coexposure treatments of cyclotides and TMZ. Cumulative results provide the proof-of-concept that cyclotides may enhance TMZ chemotherapy, and in vivo pharmacokinetic investigations of cyclotides are warranted with respect to GBM.

In Planta Discovery and Chemical Synthesis of Bracelet Cystine Knot Peptides from Rinorea bengalensis

Cyclotides are plant-derived peptides that have attracted interest as biocides and scaffolds for the development of stable peptide therapeutics. Cyclotides are characterized by their cyclic backbone and cystine knot framework, which engenders them with remarkably high stability. This study reports the cystine knot-related peptidome of Rinorea bengalensis, a small rainforest tree in the Violaceae family that is distributed from Australia westward to India. Surprisingly, many more acyclic knotted peptides (acyclotides) were discovered than cyclic counterparts (cyclotides), with 32 acyclotides and 1 cyclotide sequenced using combined transcriptome and proteomic analyses. Nine acyclotides were isolated and screened against a panel of mammalian cell lines, showing they had the cytotoxic properties normally associated with cyclotide-like peptides. NMR analysis of the acyclotide ribes 21 and 22 and the cyclotide ribe 33 confirmed that these peptides contained the cystine knot structural motif. The bracelet-subfamily cyclotide ribe 33 was amenable to chemical synthesis in reasonable yield, an achievement that has long eluded previous attempts to synthetically produce bracelet cyclotides. Accordingly, ribe 33 represents an exciting new bracelet cyclotide scaffold that can be subject to chemical modification for future molecular engineering applications.

Evaluation of the in Vivo Aphrodisiac Activity of a Cyclotide Extract from Hybanthus enneaspermus

Hybanthus enneaspermus is an Indian folk medicinal herb that has been widely used as a libido enhancer. This plant belongs to the Violaceae plant family, which ubiquitously contains disulfide-rich cyclic peptides named cyclotides. Cyclotides are an expanding plant-derived peptide family with numerous interesting bioactivities, and their unusual stability against proteolysis has attracted much attention in drug design applications. Recently, H. enneaspermus has been reported to be a rich source of cyclotides, and hence, it was of interest to investigate whether cyclotides contribute to its aphrodisiac activity. In this study, we evaluated the in vivo aphrodisiac activity of the herbal powder, extract, and the most abundant cyclotide, hyen D, extracted from H. enneaspermus on rats in a single dose regimen. After dosing, the sexual behaviors of male rats were observed, recorded, analyzed, and compared with those of the vehicle group. The results show that the extract and hyen D significantly decreased the intromission latency of sexually naïve male rats and the extract improved a range of other measured sexual parameters. The results suggest that the extract could enhance libido as well as facilitate erectile function in male rats and that the cyclotide hyen D could contribute to the libido-enhancing activity of this ethnomedicinal herb.