Labaditin, a cyclic peptide with rich biotechnological potential: preliminary toxicological studies and structural changes in water and lipid membrane environment

Unearthing naturally-occurring cyclic antibacterial peptides and their structural optimization strategies

Natural products with antibacterial activity are highly desired globally to combat against multidrug-resistant (MDR) bacteria. Antibacterial peptide (ABP), especially cyclic ABP (CABP), is one of the abundant classes. Most of them were isolated from microbes, demonstrating excellent bactericidal effects. With the improved proteolytic stability, CABPs are normally considered to have better druggability than linear peptides. However, most clinically-used CABP-based antibiotics, such as colistin, also face the challenges of drug resistance soon after they reached the market, urgently requiring the development of next-generation succedaneums. We present here a detail review on the novel naturally-occurring CABPs discovered in the past decade and some of them are under clinical trials, exhibiting anticipated application potential. According to their chemical structures, they were broadly classified into five groups, including (i) lactam/lactone-based CABPs, (ii) cyclic lipopeptides, (iii) glycopeptides, (iv) cyclic sulfur-rich peptides and (v) multiple-modified CABPs. Their chemical structures, antibacterial spectrums and proposed mechanisms are discussed. Moreover, engineered analogs of these novel CABPs are also summarized to preliminarily analyze their structure-activity relationship. This review aims to provide a global perspective on research and development of novel CABPs to highlight the effectiveness of derivatives design in identifying promising antibacterial agents. Further research efforts in this area are believed to play important roles in fighting against the multidrug-resistance crisis.

Antibacterial activity of Betadine ( Jatropha multifida L.) stem extract on Pseudomonas aeruginosa growth invitro

Background

Today, people use plants to treat various types of diseases and improve human health. One of the medicinal plants is the Betadine plant ( Jatropha multifida L.). Betadine plants have many functions, especially the sap, leaves, fruit and seeds. The compound contents in Betadine stem sap, which is efficacious as an antimicrobial, are saponins, tannins, flavonoids and labaditin. One of the bacteria that cause infection is Pseudomonas aeruginosa. These bacteria can cause opportunistic and nosocomial infections.

Methods

This study was a true experimental laboratory with a post-test only control group design. This study used Betadine stem sap extract with concentrations of 25%, 50%, 75%, 100%, gentamicin cream 10% as positive control, and dimethyl sulfoxide (DMSO) solution as negative control. This study used the Kirby-Bauer diffusion method and the bacterium Pseudomonas aeruginosa was grown on nutrient agar media, then incubated for 24 hours and calculated using calipers. Research data were analyzed using one-way ANOVA test.

Results

The highest inhibition zone was group 50% (12.725 ± 0.2500 mm) while the lowest inhibition zone was group 100% (8.675 ± 0.5620 mm).

Conclusions

Betadine stem extract had antibacterial activity in inhibiting the growth of Pseudomonas aeruginosa bacteria, with the 50% concentration being the most effective in inhibiting the growth of Pseudomonas aeruginosa bacteria.

A frog-derived bionic peptide with discriminative inhibition of tumors based on integrin αvβ3 identification

Aureins, natural active peptides extracted from skin secretions of Australian bell frogs, have become a research focus due to the antitumor effects caused by lysing cell membranes. However, clinical translation of Aureins is still limited by non-selective toxicity between normal and cancer cells. Herein, by structure-activity relationship analysis and rational linker design, a dual-function fusion peptide RA3 is designed by tactically fusing Aurein peptide A1 with strong anticancer activity, with a tri-peptide with integrin αvβ3-binding ability which was screened in our previous work. Rational design and selection of fusion linkers ensures α-helical conformation and active functions of this novel fusion peptide, inducing effective membrane rupture and selective apoptosis of cancer cells. The integrin binding and tumor recognition ability of the fusion peptide is further validated by fluorescence imaging in cell and mouse models, in comparison with the non-selective A1 peptide. Meanwhile, increased stability and superior therapeutic efficacy are achieved in vivo for the RA3 fusion peptide. Our study highlights that aided by computational simulation technologies, the biomimetic fusion RA3 peptide has been successfully designed, surmounting the poor tumor-selectivity of the natural defensive peptide, serving as a promising therapeutic agent for cancer treatment.

Interfacial Self-Assembly of Antimicrobial Peptide GL13K into Non-Fibril Crystalline β-Sheets

The need for new and potent antibiotics in an era of increasing multidrug resistance in bacteria has driven the search for new antimicrobial agents, including the design of synthetic antimicrobial peptides (AMPs). While a number of β-sheet forming AMPs have been proposed, their similarity to β-amyloids raises a number of concerns associated with neurodegenerative states. GL13K is an effective, synthetic AMP that selectively folds into β-sheets at anionic interfaces. Moreover, it is one of relatively few AMPs that preferentially fold into β-sheets without bridging disulfides. The interfacial activity of GL13K and its propensity to form amyloid fibrils have not been investigated. Using structural studies at the air/water interface and in the absence of anionic lipids, we demonstrate that while GL13K does form crystalline β-sheets, it does not self-assemble into fibrils. This work emphasizes the requirement for a single charged amino acid in the hydrophobic face to prevent fibril formation in synthetic peptides.

Role of Toluidine Blue-O Binding Mechanism for Photooxidation in Bioinspired Bacterial Membranes

The alarming increase in bacterial resistance to antibiotics has demanded new strategies for microbial inactivation, which include photodynamic therapy whose activity relies on the photoreaction damage to the microorganism membrane. Herein, the binding mechanisms of the photosensitizer toluidine blue-O (TBO) on simplified models of bacterial membrane with Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) were correlated to the effects of the photoinduced lipid oxidation. Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were also used as a reference of mammalian membranes. The surface pressure isotherms combined with polarization-modulated infrared reflection absorption spectroscopy revealed that TBO expands DOPC, DOPE, and DOPG monolayers owing to electrostatic interactions with the negatively charged groups in the phospholipids, with a stronger adsorption on DOPG, which has a net surface charge. Light irradiation made the TBO-containing DOPC and DOPE monolayers less unstable as a result of the singlet oxygen (¹O₂) reaction with the chain unsaturation and hydroperoxide formation. In contrast, the decreased stability of the irradiated TBO-containing DOPG monolayer suggests the cleavage of carbon chains. The anionic nature of DOPG allowed a deeper penetration of TBO into the chain region, favoring contact-dependent reactions between the excited triplet state of TBO and lipid unsaturations or/and hydroperoxide groups, which is the key for the cleavage reactions and further membrane permeabilization.

The cyclic peptide labaditin does not alter the outer membrane integrity of Salmonella enterica serovar Typhimurium

Antimicrobial peptides are a promising class of new antibiotics with the ability to kill bacteria by disrupting their cell membrane, which is especially difficult for Gram-negative bacteria whose cell wall contains an outer layer of lipopolysaccharides (LPS). Here we show that the cyclic decapeptide Labaditin (Lo), with proven activity against the Gram-positive Staphylococcus aureus and Streptococcus mutans, is not able to kill the Gram-negative Salmonella enterica serovar Typhimurium (S.e.s. Typhimurium). We found that Lo induced significant changes in the surface pressure isotherms of Langmuir monolayers representing the Salmonella enterica serovar Typhimurium inner membrane (S.e.s. Typhimurium IM), and caused leakage in large unilamellar vesicles made with this IM lipid composition. On the basis of these results one should expect bactericidal activity against S.e.s. Typhimurium. However, Lo could not interact with a monolayer of LPS, causing no significant changes in either the surface pressure isotherms or in the polarization-modulated infrared reflection absorption spectra (PM-IRRAS). Therefore, the failure of Lo to kill S.e.s. Typhimurium is associated with the lack of interaction with LPS from the outer bacteria membrane. Our approach with distinct monolayer compositions and combined techniques to investigate molecular-level interactions is useful for drug design to fight antibiotic-resistant bacteria.

Biomedical applications of nanotechnology

The ability to investigate substances at the molecular level has boosted the search for materials with outstanding properties for use in medicine. The application of these novel materials has generated the new research field of nanobiotechnology, which plays a central role in disease diagnosis, drug design and delivery, and implants. In this review, we provide an overview of the use of metallic and metal oxide nanoparticles, carbon-nanotubes, liposomes, and nanopatterned flat surfaces for specific biomedical applications. The chemical and physical properties of the surface of these materials allow their use in diagnosis, biosensing and bioimaging devices, drug delivery systems, and bone substitute implants. The toxicology of these particles is also discussed in the light of a new field referred to as nanotoxicology that studies the surface effects emerging from nanostructured materials.

Isoleucine/leucine residues at "a" and "d" positions of a heptad repeat sequence are crucial for the cytolytic activity of a short anticancer lytic peptide

Many lytic peptides contain a heptad sequence with leucine or isoleucine residues at "a" and "d" positions. However, their roles in the peptide-induced cytolytic process remain unclear. We have recently reported an anticancer lytic peptide ZXR-2 (FKIGGFIKKLWRSLLA), which contains a shortened zipper-like sequence with Ile/Leu at "a" and "d" positions. To understand the roles of these Ile/Leu residues, a series of analogs were constructed by sequentially replacing the Ile or Leu residue with alanine (Ala). Significant reduction of the cytolytic activity was observed when the Ile (3rd and 7th) and Leu (10th and 14th) residues at the "a" and "d" positions were substituted, while the replacement of the separate Leu (15th) residue had less effect. Based on the quenching of the intrinsic fluorescence of the peptides and their induced surface pressure changes of lipid monolayer, it was conjectured that the peptide ZXR-2 might insert into cell membranes from the C-terminal and to a depth of the W₁₁ position. Accordingly, I₃, I₇, and L₁₀ residues which mainly exposed in aqueous solution were more responsible for the peptide self-association on cell membranes, while L₁₄, together with L₁₅, might help peptide insert and anchor to cell membranes. These results are significant to elucidate the crucial roles of such Ile/Leu residues at "a" and "d" positions in peptide-peptide and peptide-membrane interactions to exert the membrane disruption activity of lytic peptides. With further understanding about the structure-activity relationship of lytic peptides, it would be helpful for designing novel anticancer lytic peptides.

The importance of cyclic structure for Labaditin on its antimicrobial activity against Staphylococcus aureus

Antimicrobial resistance has reached alarming levels in many countries, thus leading to a search for new classes of antibiotics, such as antimicrobial peptides whose activity is exerted by interacting specifically with the microorganism membrane. In this study, we investigate the molecular-level mechanism of action for Labaditin (Lo), a 10-amino acid residue cyclic peptide from Jatropha multifida with known bactericidal activity against Streptococcus mutans. We show that Lo is also effective against Staphylococcus aureus (S. aureus) but this does not apply to its linear analogue (L₁). Using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we observed with that the secondary structure of Lo was preserved upon interacting with Langmuir monolayers from a phospholipid mixture mimicking S. aureus membrane, in contrast to L₁. This structure preservation for the rigid, cyclic Lo is key for the self-assembly of peptide nanotubes that induce pore formation in large unilamellar vesicles (LUVs), according to permeability assays and dynamic light scattering measurements. In summary, the comparison between Labaditin (Lo) and its linear analogue L₁ allowed us to infer that the bactericidal activity of Lo is more related to its interaction with the membrane. It does not require specific metabolic targets, which makes cyclic peptides promising for antibiotics without bacteria resistance.

Cytotoxic Orbitide from the Latex of Croton urucurana

The bioactive ethyl acetate phase obtained from the latex of Croton urucurana Baillon afforded a novel orbitide (1), [1-9-NαC]-crourorb A1, that proved active against NCI-ADR/RES (ovary, multidrug-resistance phenotype) cells with the same potency as doxorubicin (positive control) and inactive up to the highest concentration tested against nontumor NIH/3T3 cells. The structure elucidation was based on 1D and 2D NMR spectroscopy, further supported by HRESIMS data and by application of Marfey's method for determination of the absolute configuration of its amino acid residues. This is the first orbitide obtained from C. urucurana.

Liposomal systems as carriers for bioactive compounds

Since the revolutionary discovery that phospholipids can form closed bilayered structures in aqueous systems, the study of liposomes has become a very interesting area of research. The versatility and amazing biocompatibility of liposomes has resulted in their wide-spread use in many scientific fields, and many of their applications, especially in medicine, have yielded breakthroughs in recent decades. Specifically, their easy preparation and various structural aspects have given rise to broadly usable methodologies to internalize different compounds, with either lipophilic or hydrophilic properties. The study of compounds with potential biotechnological application(s) is generally related to evaluation and risk assessment of the possible cytotoxic or therapeutic effects of the compound under study. In most cases, undesirable side-effects are associated with an interaction of the liposome with the cell membrane and/or its absorption and subsequent interaction with a cellular biomolecule. Liposomal carrier systems have an unprecedented potential for delivering bioactive substances to specific molecular targets due to their biocompatibility, biodegradability and low toxicity. Liposomes are therefore considered to be an invaluable asset in applied biotechnology studies due to their potential for interaction with both hydrophilic and lipophilic compounds.

Syntheses of some α-cyclic tripeptides as potential inhibitors for HMG-CoA Reductase

α-Cyclic tripeptides (CtPs) are the most rigid members of the cyclic peptide family. However, due to their synthetic difficulty, biological activity has remained undisclosed. The incorporation of side-chain-protected natural amino acids into functional CtPs was performed to explore the potential biological functions. Several novel CtPs that consist of protected serine (S(Bn)) and/or glutamate (E(OBn)) were prepared from corresponding linear tripeptides by chemical synthesis. There is a strong possibility for CtPs that contain 3 phenyl groups to correlate with atorvastatin structure. The binding effects in human HMG-CoA reductase (hHMGR) activities were first evaluated by molecular docking. High docking scores were received with these CtPs for enzyme. Therefore, enzymatic assays were carried out and the compound cyclo(S(Bn))3 was indeed able to moderately inhibit hHMGR (IC50 = 110 μM).

Ribifolin, an orbitide from Jatropha ribifolia, and its potential antimalarial activity

A new orbitide named ribifolin was isolated and characterized from Jatropha ribifolia using mass spectrometry, NMR spectroscopy, quantitative amino acid analysis, molecular dynamics/simulated annealing, and Raman optical activity measurements and calculations. Ribifolin (1) and its linear form (1a) were synthesized by solid-phase peptide synthesis, followed by evaluation of its antiplasmodial and cytotoxicity activities. Compound 1 was moderately effective (IC50 = 42 μM) against the Plasmodium falciparum strain 3D7.

Interaction of cyclic and linear Labaditin peptides with anionic and zwitterionic micelles

Conformational changes of the cyclic (Lo) peptide Labaditin (VWTVWGTIAG) and its linear analogue (L1) promoted by presence of anionic sodium dodecyl sulfate (SDS) and zwitterionic L-α-Lysophosphatidylcholine (LPC) micelles were investigated. Results from λ(max) blue-shift of tryptophan fluorescence emission combined with Stern-Volmer constants values and molecular dynamics (MD) simulations indicated that L1 interacts with SDS micelles to a higher extent than does Lo. Further, the MD simulation demonstrated that both Lo and L1 interact similarly with LPC micelles, being preferentially located at the micelle/water interface. The peptide-micelle interaction elicits conformational changes in the peptides. Lo undergoes limited modifications and presents unordered structure in both LPC and SDS micelles. On the other hand, L1 displays a random-coil structure in aqueous medium, pH 7.0, and it acquires a β-structure upon interaction with SDS and LPC, albeit with structural differences in each medium.

Jatrophidin I, a cyclic peptide from Brazilian Jatropha curcas L.: isolation, characterization, conformational studies and biological activity

A cyclic peptide, jatrophidin I, was isolated from the latex of Jatropha curcas L. Its structure was elucidated by extensive 2D NMR spectroscopic analysis, with additional conformational studies performed using Molecular Dynamics/Simulated Annealing (MD/SA). Jatrophidin I had moderate protease inhibition activity when compared with pepstatin A; however, the peptide was inactive in antimalarial, cytotoxic and antioxidant assays.

Medicinal property, phytochemistry and pharmacology of several Jatropha species (Euphorbiaceae): a review

The genus Jatropha (Euphorbiaceae) comprises of about 170 species of woody trees, shrubs, subshrubs or herbs in the seasonally dry tropics of the Old and the New World. They are used in medicinal folklore to cure various diseases of 80% of the human population in Africa, Asia and Latin America. Species from this genus have been popular to cure stomachache, toothache, swelling, inflammation, leprosy, dysentery, dyscrasia, vertigo, anemia, diabetis, as well as to treat HIV and tumor, opthalmia, ringworm, ulcers, malaria, skin diseases, bronchitis, asthma and as an aphrodisiac. They are also employed as ornamental plants and energy crops. Cyclic peptides alkaloids, diterpenes and miscellaneous compounds have been reported from this genus. Extracts and pure compounds of plants from this genus are reported for cytotoxicity, tumor-promoting, antimicrobial, antiprotozoal, anticoagulant, immunomodulating, anti-inflammatory, antioxidant, protoscolicidal, insecticidal, molluscicidal, inhibition AChE and toxicity activities.

Proteoliposomes in nanobiotechnology

Proteoliposomes are systems that mimic lipid membranes (liposomes) to which a protein has been incorporated or inserted. During the last decade, these systems have gained prominence as tools for biophysical studies on lipid-protein interactions as well as for their biotechnological applications. Proteoliposomes have a major advantage when compared with natural membrane systems, since they can be obtained with a smaller number of lipidic (and protein) components, facilitating the design and interpretation of certain experiments. However, they have the disadvantage of requiring methodological standardization for incorporation of each specific protein, and the need to verify that the reconstitution procedure has yielded the correct orientation of the protein in the proteoliposome system with recovery of its functional activity. In this review, we chose two proteins under study in our laboratory to exemplify the steps necessary for the standardization of the reconstitution of membrane proteins in liposome systems: (1) alkaline phosphatase, a protein with a glycosylphosphatidylinositol anchor, and (2) Na,K-ATPase, an integral membrane protein. In these examples, we focus on the production of the specific proteoliposomes, as well as on their biochemical and biophysical characterization, with emphasis on studies of lipid-protein interactions. We conclude the chapter by highlighting current prospects of this technology for biotechnological applications, including the construction of nanosensors and of a multi-protein nanovesicular biomimetic to study the processes of initiation of skeletal mineralization.