Immunomodulatory effects of cyclotides isolated from Viola odorata in an experimental autoimmune encephalomyelitis animal model of multiple sclerosis

Advances in cyclotide research: bioactivity to cyclotide-based therapeutics

Cyclotides are a class of plant-derived cyclic peptides having a distinctive structure with a cyclic cystine knot (CCK) motif. They are stable molecules that naturally play a role in plant defense. Till date, more than 750 cyclotides have been reported among diverse plant taxa belonging to Cucurbitaceae, Violaceae, Rubiaceae, Solanaceae, and Fabaceae. These native cyclotides exhibit several bioactivities, such as anti-bacterial, anti-HIV, anti-fungal, pesticidal, cytotoxic, and hemolytic activities which have immense significance in agriculture and therapeutics. The general mode of action of cyclotides is related to their structure, where their hydrophobic face penetrates the cell membrane and disrupts it to exhibit anti-microbial, cytotoxic, or hemolytic activities. Thus, the structure-activity relationship is of significance in cyclotides. Further, owing to their, small size, stability, and potential to interact and cross the membrane barrier of cells, they make promising choices for developing peptide-based biologics. However, challenges, such as production complexity, pharmacokinetic limitations, and off-target effects hinder their development. Advancements in cyclotide engineering, such as peptide grafting, ligand conjugation, and nanocarrier integration, heterologous production along with computational design optimization, can help overcome these challenges. Given the potential of these cyclic peptides, the present review focuses on the diversity, bioactivities, and structure-activity relationships of cyclotides, and advancements in cyclotides engineering emphasizing their unique attributes for diverse medical and biotechnological applications.

Plant Antimicrobial Peptides and Their Main Families and Roles: A Review of the Literature

Antimicrobial peptides (AMPs) are constituent molecules of the innate defense system and are naturally produced by all organisms. AMPs are characterized by a relatively low molecular weight (less than 10 kDa) and a variable number of cysteine residues that form disulfide bonds and contribute to the stabilization of the tertiary structure. In addition, there is a wide repertoire of antimicrobial agents against bacteria, viruses, fungi, and protozoa that can provide a large number of prototype peptides for study and biochemical manipulation. In this sense, plant AMPs stand out because they have a wide range of biological functions against microorganisms and potential applications in medicine and agriculture. Herein, we describe a mini-review of the principal AMP families, such as defensins, lipid transfer proteins (LTPs), thionins, heveins, and cyclotides. The objective of this work was to present the main discoveries regarding the biological activities of these plant AMP families, especially in the last 20 years. We also discuss the current knowledge of their biological activities, gene expression, and possible uses as antimicrobial molecules and in plant biotechnology.

New Insights into Involvement of Low Molecular Weight Proteins in Complex Defense Mechanisms in Higher Plants

Dynamic climate changes pose a significant challenge for plants to cope with numerous abiotic and biotic stressors of increasing intensity. Plants have evolved a variety of biochemical and molecular defense mechanisms involved in overcoming stressful conditions. Under environmental stress, plants generate elevated amounts of reactive oxygen species (ROS) and, subsequently, modulate the activity of the antioxidative enzymes. In addition, an increase in the biosynthesis of important plant compounds such as anthocyanins, lignin, isoflavonoids, as well as a wide range of low molecular weight stress-related proteins (e.g., dehydrins, cyclotides, heat shock proteins and pathogenesis-related proteins), was evidenced. The induced expression of these proteins improves the survival rate of plants under unfavorable environmental stimuli and enhances their adaptation to sequentially interacting stressors. Importantly, the plant defense proteins may also have potential for use in medical applications and agriculture (e.g., biopesticides). Therefore, it is important to gain a more thorough understanding of the complex biological functions of the plant defense proteins. It will help to devise new cultivation strategies, including the development of genotypes characterized by better adaptations to adverse environmental conditions. The review presents the latest research findings on selected plant defense proteins.

Structure and Activity of Reconstructed Pseudo-Ancestral Cyclotides

Cyclotides are cyclic peptides that are promising scaffolds for the design of drug candidates and chemical tools. However, despite there being hundreds of reported cyclotides, drug design studies have commonly focussed on a select few prototypic examples. Here, we explored whether ancestral sequence reconstruction could be used to generate new cyclotides for further optimization. We show that the reconstructed 'pseudo-ancestral' sequences, named Ancy-m (for the ancestral cyclotide of the Möbius sub-family) and Ancy-b (for the bracelet sub-family), have well-defined structures like their extant members, comprising the core structural feature of a cyclic cystine knot. This motif underpins efforts to re-engineer cyclotides for agrochemical and therapeutic applications. We further show that the reconstructed sequences are resistant to temperatures approaching boiling, bind to phosphatidyl-ethanolamine lipid bilayers at micromolar affinity, and inhibit the growth of insect cells at inhibitory concentrations in the micromolar range. Interestingly, the Ancy-b cyclotide had a higher oxidative folding yield than its comparator cyclotide cyO2, which belongs to the bracelet cyclotide subfamily known to be notoriously difficult to fold. Overall, this study provides new cyclotide sequences not yet found naturally that could be valuable starting points for the understanding of cyclotide evolution and for further optimization as drug leads.

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.

Development and Challenges of Cyclic Peptides for Immunomodulation

Cyclic peptides are polypeptide chains formed by cyclic sequences of amide bonds between protein-derived or non-protein-derived amino acids. Compared to linear peptides, cyclic peptides offer several unique advantages, such as increased stability, stronger affinity, improved selectivity, and reduced toxicity. Cyclic peptide has been proved to have a promising application prospect in the medical field. In addition, this paper mainly describes that cyclic peptides play an important role in anti-cancer, anti-inflammatory, anti-virus, treatment of multiple sclerosis and membranous nephropathy through immunomodulation. In order to know more useful information about cyclic peptides in clinical research and drug application, this paper also summarizes cyclic peptides currently in the clinical trial stage and cyclic peptide drugs approved for marketing in the recent five years. Cyclic peptides have many advantages and great potential in treating various diseases, but there are still many challenges to be solved in the development process of cyclic peptides.

High-throughput microfluidic chip with silica gel-C18 channels for cyclotide separation

Over the past two decades, microfluidic-based separations have been used for the purification, isolation, and separation of biomolecules to overcome difficulties encountered by conventional chromatography-based methods including high cost, long processing times, sample volumes, and low separation efficiency. Cyclotides, or cyclic peptides used by some plant families as defense agents, have attracted the interest of scientists because of their biological activities varying from antimicrobial to anticancer properties. The separation process has a critical impact in terms of obtaining pure cyclotides for drug development strategies. Here, for the first time, a mimic of the high-performance liquid chromatography (HPLC) on microfluidic chip strategy was used to separate the cyclotides. In this regard, silica gel-C18 was synthesized and characterized by Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H-NMR) and then filled inside the microchannel to prepare an HPLC C18 column-like structure inside the microchannel. Cyclotide extract was obtained from Viola ignobilis by a low voltage electric field extraction method and characterized by HPLC and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). The extract that contained vigno 1, 2, 3, 4, 5, and varv A cyclotides was added to the microchannel where distilled water was used as a mobile phase with 1 µL/min flow rate and then samples were collected in 2-min intervals until 10 min. Results show that cyclotides can be successfully separated from each other and collected from the microchannel at different periods of time. These findings demonstrate that the use of microfluidic channels has a high impact on the separation of cyclotides as a rapid, cost-effective, and simple method and the device can find widespread applications in drug discovery research.

Emodin attenuates inflammation and demyelination in experimental autoimmune encephalomyelitis

Emodin, a substance extracted from herbs such as rhubarb, has a protective effect on the central nervous system. However, the potential therapeutic effect of emodin in the context of multiple sclerosis remains unknown. In this study, a rat model of experimental autoimmune encephalomyelitis was established by immune induction to simulate multiple sclerosis, and the rats were intraperitoneally injected with emodin (20 mg/kg/d) from the day of immune induction until they were sacrificed. In this model, the nucleotide-binding domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome and the microglia exacerbated neuroinflammation, playing an important role in the development of multiple sclerosis. In addition, silent information regulator of transcription 1 (SIRT1)/peroxisome proliferator-activated receptor-alpha coactivator (PGC-1α) was found to inhibit activation of the NLRP3 inflammasome, and SIRT1 activation reduced disease severity in experimental autoimmune encephalomyelitis. Furthermore, treatment with emodin decreased body weight loss and neurobehavioral deficits, alleviated inflammatory cell infiltration and demyelination, reduced the expression of inflammatory cytokines, inhibited microglial aggregation and activation, decreased the levels of NLRP3 signaling pathway molecules, and increased the expression of SIRT1 and PGC-1α. These findings suggest that emodin improves the symptoms of experimental autoimmune encephalomyelitis, possibly through regulating the SIRT1/PGC-1α/NLRP3 signaling pathway and inhibiting microglial inflammation. These findings provide experimental evidence for treatment of multiple sclerosis with emodin, enlarging the scope of clinical application for emodin.

Cyclotide Nanotubes as a Novel Potential Drug-Delivery System: Characterization and Biocompatibility

Cyclotides are a class of cyclic peptides that can be self-assembled. This study aimed to discover the properties of cyclotide nanotubes. We performed differential scanning calorimetric (DSC) to characterize their properties. Then, we incorporated the coumarin as a probe and identified the morphology of nanostructures. The stability of cyclotide nanotubes after 3 months of keeping at -20 °C was determined by field emission scanning electron microscopy (FESEM). The cytocompatibility of cyclotide nanotubes was evaluated on peripheral blood mononuclear cells. In vivo, studies were also conducted on female C57BL/6 mice by intraperitoneally administration of nanotubes at 5, 50, and 100 mg/kg doses. Blood sampling was done before and 24 h after nanotube administration and complete blood count tests were conducted. DSC thermogram showed that the cyclotide nanotubes were stable after heating until 200 °C. Fluorescence microscopy images proved that the self-assembled structures of cyclotide can encapsulate the coumarin. FESEM proved that these nanotubes were stable even after 3 months. The results of the cytotoxicity assay and in-vivo study confirmed that these novel prepared nanotubes were biocompatible. These results suggested that the cyclotide nanotubes could be considered as a new carrier in biological fields while they are biocompatible.

Effects of Asparagus officinalis on immune system mediated EAE model of multiple sclerosis

Background

About 5 to 10 percent of the population in developed countries are affected by autoimmune diseases. One of the most important autoimmune disease with high prevalence rate is Multiple sclerosis in which there is currently no definitive cure for it, and most medications such as interferons are used only to limit the disease. The present study aims to investigate the effect of using Asparagus Officinalis fractions in an immune system mediated model of multiple sclerosis.

Material and Methods

Fractionation was performed by maceration using n-hexane, chloroform, chloroform-methanol (9: 1), n-Butanol and methanol solvents from aerial parts of Asparagus Officinalis. Thin layer chromatography, NMR and phenolic component measurement were done and two fractions were selected for checking in MS induced in vivo model.

Results

It was observed that chloroform-methanolic and N-Butanol fractions had higher content of saponin in comparison of other extracts. Also, it was showed that the methanolic and n-Butanol extracts contains the highestportion of glycosylic steroid saponins in comparison to other fractions. Regarding experimental autoimmune encephalomyelitis (EAE) score, Butanolic and methanolic fractions with doses higher that 100mg/kg showed a potent supportive effects as long as locomotor activity protection even in lower dose in comparison to phosphate buffered saline (PBS) group.

Conclusion

Considering the proved different effects of saponin compounds on the immune system we observed that those fractions altered the circulatory peripheral blood cells and also remit the clinical signs after EAE induction along with enhanced myelin sheath content in the median region of corpus callusom. It could be inferred that this fractions are promising candidates for further investigation as dose-dependent immune system regulating compounds in multiple sclerosis patients.

Morphological studies of self-assembled cyclotides extracted from Viola odorata as novel versatile platforms in biomedical applications

Self-assembling peptides have attracted researchers' attention recently. They are classified as biomedical materials with unique properties formed in response to environmental conditions. Cyclotides are macrocyclic plant-derived peptides containing 28-37 amino acids that have the ability to self-assemble. Herein, we investigated the effect of pH, time, and temperature on the self-assembling properties of the cyclotides extracted from Viola odorata. For this purpose, the cyclotides were dispersed in aqueous trifluoroacetic acid at pH 2, 4, or 6 and incubated at 25 or 37 °C for 1, 2, 3, 5, 7 or 10 days, and the morphology of the self-assembled structures was identified by optical microscopy, polarized optical microscopy, scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. At pH 2 and 4, the self-assembly process of cyclotides comprises a number of steps, starting with the formation of spherical peptide nanostructures followed by hierarchically assembled nanotubes, and then shifting to nanofibers after 10 days. At pH 6, amorphous structures were produced even after 10 days. The temperature also could affect the self-assembly mechanism of the cyclotides. At 25 °C, the spherical peptide micelles formed firstly and then merged to form nanotubes, while at 37 °C the cyclotides showed crystallization followed by an increase in length with time. The fluorescence microscopy images showed that the nanotubes could efficiently entrap the hydrophobic molecules of coumarin. This comparative study on the self-assembly of the cyclotides extracted from Viola odorata is the first example exploring the capacity of these cyclotides to adopt precise nanostructures. The nanotubes and nanofibers obtained with these cyclotides might find interesting applications in drug delivery and tissue engineering.