Mo-CBP3-PepI, Mo-CBP3-PepII, and Mo-CBP3-PepIII are synthetic antimicrobial peptides active against human pathogens by stimulating ROS generation and increasing plasma membrane permeability

Anti-Staphy Peptides Rationally Designed from Cry10Aa Bacterial Protein

Bacterial infections pose a significant threat to human health, constituting a major challenge for healthcare systems. Antibiotic resistance is particularly concerning in the context of treating staphylococcal infections. In addressing this challenge, antimicrobial peptides (AMPs), characterized by their hydrophobic and cationic properties, unique mechanism of action, and remarkable bactericidal and immunomodulatory capabilities, emerge as promising alternatives to conventional antibiotics for tackling bacterial multidrug resistance. This study focuses on the Cry10Aa protein as a template for generating AMPs due to its membrane-penetrating ability. Leveraging the Joker algorithm, six peptide variants were derived from α-helix 3 of Cry10Aa, known for its interaction with lipid bilayers. In vitro, antimicrobial assays determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) required for inhibiting the growth of Staphylococcus aureus, Escherichia coli, Acinetobacter baummanii, Enterobacter cloacae, Enterococcus facallis, Klebsiella pneumonia, and Pseudomonas aeruginosa. Time-kill kinetics were performed using the parental peptide AMPCry10Aa, as well as AMPCry10Aa_1 and AMPCry10Aa_5, against E. coli ATCC, S. aureus 111 and S. aureus ATCC strains showing that AMPCry10Aa_1 and AMPCry10Aa_5 peptides can completely reduce the initial bacterial load with less than 2 h of incubation. AMPCry10Aa_1 and AMPCry 10Aa_5 present stability in human serum and activity maintenance up to 37 °C. Cytotoxicity assays, conducted using the MTT method, revealed that all of the tested peptides exhibited cell viability >50% (IC50). The study also encompassed evaluations of the structure and physical-chemical properties. The three-dimensional structures of AMPCry10Aa and AMPCry10Aa_5 were determined through nuclear magnetic resonance (NMR) spectroscopy, indicating the adoption of α-helical segments. Electron paramagnetic resonance (EPR) spectroscopy elucidated the mechanism of action, demonstrating that AMPCry10Aa_5 enters the outer membranes of E. coli and S. aureus, causing substantial increases in lipid fluidity, while AMPCry10Aa slightly increases lipid fluidity in E. coli. In conclusion, the results obtained underscore the potential of Cry10Aa as a source for developing antimicrobial peptides as alternatives to conventional antibiotics, offering a promising avenue in the battle against antibiotic resistance.

An alkaloidal fraction of Annona tomentosa possesses anthelmintic activity and induces surface modifications in Haemonchus contortus

The nematode Haemonchus contortus is, as a parasite, responsible for most mortality of small ruminants, causing significant economic losses. Numerous plant-derived compounds have exhibited promising anthelmintic activities against this nematode. Notably, the Annona genus stands out for demonstrated anthelmintic effects by extracts from several of its species against different nematodes. This study aimed to assess the effect of an Annona tomentosa fraction, rich in alkaloids, on H. contortus. This fraction, named Alk.F, is derived from the methanolic extract of the plant's stem bark. Chemical characterization of Alk.F was performed by liquid chromatography coupled with mass spectrometry. Among the nine predominant peaks obtained, seven alkaloids were identified: reticuline, reticuline N-oxide, reticuline N-oxide isomer, cyclanoline, asimilobine, tetrahydropalmatine and anonaine. Alk.F inhibited the larval development of H. contortus with an IC50 of 0.026 mg/mL, inhibited larval exsheathment with an IC50 of 0.38 mg/mL, and displayed low hemolytic activity towards sheep erythrocytes. Furthermore, atomic force microscopy revealed that Alk.F altered adhesive forces and the height profile on the surface of H. contortus larvae. In conclusion, A. tomentosa alkaloids alter the cuticle structure of H. contortus, inhibiting larval development and exsheathment, thus offering possibilities for contributing to the development of new anthelmintic drugs.

Development strategies and application of antimicrobial peptides as future alternatives to in-feed antibiotics

The use of in-feed antibiotics has been widely restricted due to the significant environmental pollution and food safety concerns they have caused. Antimicrobial peptides (AMPs) have attracted widespread attention as potential future alternatives to in-feed antibiotics owing to their demonstrated antimicrobial activity and environment friendly characteristics. However, the challenges of weak bioactivity, immature stability, and low production yields of natural AMPs impede practical application in the feed industry. To address these problems, efforts have been made to develop strategies for approaching the AMPs with enhanced properties. Herein, we summarize approaches to improving the properties of AMPs as potential alternatives to in-feed antibiotics, mainly including optimization of structural parameters, sequence modification, selection of microbial hosts, fusion expression, and industrially fermentation control. Additionally, the potential for application of AMPs in animal husbandry is discussed. This comprehensive review lays a strong theoretical foundation for the development of in-feed AMPs to achieve the public health globally.

Peptide Dendrimer-Based Antibacterial Agents: Synthesis and Applications

Pathogenic bacteria cause the deaths of millions of people every year. With the development of antibiotics, hundreds and thousands of people's lives have been saved. Nevertheless, bacteria can develop resistance to antibiotics, rendering them insensitive to antibiotics over time. Peptides containing specific amino acids can be used as antibacterial agents; however, they can be easily degraded by proteases in vivo. To address these issues, branched peptide dendrimers are now being considered as good antibacterial agents due to their high efficacy, resistance to protease degradation, and low cytotoxicity. The ease with which peptide dendrimers can be synthesized and modified makes them accessible for use in various biological and nonbiological fields. That is, peptide dendrimers hold a promising future as antibacterial agents with prolonged efficacy without bacterial resistance development. Their in vivo stability and multivalence allow them to effectively target multi-drug-resistant strains and prevent biofilm formation. Thus, it is interesting to have an overview of the development and applications of peptide dendrimers in antibacterial research, including the possibility of employing machine learning approaches for the design of AMPs and dendrimers. This review summarizes the synthesis and applications of peptide dendrimers as antibacterial agents. The challenges and perspectives of using peptide dendrimers as the antibacterial agents are also discussed.

Interaction and simulation studies suggest the possible molecular targets of intrinsically disordered amyloidogenic antimicrobial peptides in Acinetobacter baumannii

Acinetobacter baumannii is one of the causing agents of nosocomial infections. A wide range of antibiotics fails to work against these pathogens. Hence, there is an urgent requirement to develop other therapeutics to solve this problem. Antimicrobial peptides (AMPs) are a diverse group of naturally occurring peptides that have the ability to kill diverse groups of microorganisms. The major challenge of using AMPs as therapeutics is their unstable nature and the fact that most of their molecular targets are still unknown. In this study, we have selected intrinsically disordered and amyloidogenic AMPs, showing activity against A. baumannii, that is, Bactenecin, Cath BF, Citropin 1.1, DP7, NA-CATH, Tachyplesin, and WAM-1. To identify the probable target of these AMPs in A. baumannii, calculation of docking score, binding energy, dissociation constant, and molecular dynamics analysis was performed with selected seventeen possible molecular targets. The result showed that the most probable molecular targets of most of the intrinsically disordered amyloidogenic AMPs were UDP-N-acetylenol-pyruvoyl-glucosamine reductase (MurB), followed by 33-36 kDa outer membrane protein (Omp 33-36), UDP-N-acetylmuramoyl-l-alanyl-d-glutamate-2,6-diaminopimelate ligase (MurE), and porin Subfamily Protein (PorinSubF). Further, molecular dynamics analysis concluded that the target of antimicrobial peptide Bactenecin is MurB of A. baumannii, and identified other molecular targets of selected AMPs. Additionally, the oligomerization capacity of the selected AMPs was also investigated, and it was shown that the selected AMPs form oligomeric states, and interact with their molecular targets in that state. Experimental validation using purified AMPs and molecular targets needs to be done to confirm the interaction.Communicated by Ramaswamy H. Sarma.

Computer-made peptide RQ18 acts as a dual antifungal and antibiofilm peptide though membrane-associated mechanisms of action

The spread of fungi resistant to conventional drugs has become a threatening problem. In this context, antimicrobial peptides (AMPs) have been considered as one of the main alternatives for controlling fungal infections. Here, we report the antifungal and antibiofilm activity and some clues about peptide RQ18's mechanism of action against Candida and Cryptococcus. This peptide inhibited yeast growth from 2.5 μM and killed all Candida tropicalis cells within 2 h incubation. Moreover, it showed a synergistic effect with antifungal agent the amphotericin b. RQ18 reduced biofilm formation and promoted C. tropicalis mature biofilms eradication. RQ18's mechanism of action involves fungal cell membrane damage, which was confirmed by the results of RQ18 in the presence of free ergosterol in the medium and fluorescence microscopy by Sytox green. No toxic effects were observed in murine macrophage cell lines and Galleria mellonella larvae, suggesting fungal target selectivity. Therefore, peptide RQ18 represents a promising strategy as a dual antifungal and antibiofilm agent that contributes to infection control without damaging mammalian cells.

In-vitro antimicrobial activity of AF-DP protein and in-silico approach of cell membrane disruption

Microbial resistance against common antibiotics has become one of the most serious threats to human health. The increasing statistics on this problem show the necessity of finding a way to deal with it. In recent years, antimicrobial peptides with unique properties and the capability of targeting a wide range of pathogens, have been considered as a potential for replacing common antibiotics. A small chitin-binding protein with anticandidal activity was isolated from Moringa oleifera seeds by Neto and colleagues in 2017, which very much resembled antimicrobial peptides. In this study, the antimicrobial protein 'AF-DP' was identified and characterized. AF-DP was heterologously expressed, purified, and characterized, and its 3D structure was predicted. Six molecular dynamic simulations were performed to investigate how the protein interacts with Gram-negative inner and outer, Gram-positive, fungal, cancerous, and normal mammalian membranes. Also, its antimicrobial and anticancer activity was assessed in vitro via minimum inhibition concentration (MIC) and MTT assays, respectively. This protein with 111 amino acids and a total net charge (of 10.5) has been predicted to be mainly composed of alpha helix and random coils. Its MIC affecting the growth of Escherichia coli, Staphylococcus aureus, and Candida albicans was 30 µg/ml, 100 µg/ml, and 100 µg/ml, respectively; AF-DP showed anticancer activity against MCF-7 breast cancer cell line. Scanning electron microscopic analysis confirmed the creation of pores and scratches on the surface of the bacterial membrane. The results of this research show that AF-DP can be a candidate for the production of new drugs as an AMP with antimicrobial activity.Communicated by Ramaswamy H. Sarma.

Various Biomimetics, Including Peptides as Antifungals

Biomimetics, which are similar to natural compounds that play an important role in the metabolism, manifestation of functional activity and reproduction of various fungi, have a pronounced attraction in the current search for new effective antifungals. Actual trends in the development of this area of research indicate that unnatural amino acids can be used as such biomimetics, including those containing halogen atoms; compounds similar to nitrogenous bases embedded in the nucleic acids synthesized by fungi; peptides imitating fungal analogs; molecules similar to natural substrates of numerous fungal enzymes and quorum-sensing signaling molecules of fungi and yeast, etc. Most parts of this review are devoted to the analysis of semi-synthetic and synthetic antifungal peptides and their targets of action. This review is aimed at combining and systematizing the current scientific information accumulating in this area of research, developing various antifungals with an assessment of the effectiveness of the created biomimetics and the possibility of combining them with other antimicrobial substances to reduce cell resistance and improve antifungal effects.

DVL, lectin from Dioclea violacea seeds, has multiples mechanisms of action against Candida spp via carbohydrate recognition domain

Lectins are proteins of non-immunological origin with the ability to bind to carbohydrates reversibly. They emerge as an alternative to conventional antifungals, given the ability to interact with carbohydrates in the fungal cell wall inhibiting fungal growth. The lectin from D. violacea (DVL) already has its activity described as anti-candida in some species. Here, we observed the anti-candida effect of DVL on C. albicans, C. krusei and C. parapsilosis and its multiple mechanisms of action toward the yeasts. Additionally, it was observed that DVL induces membrane and cell wall damage and ROS overproduction. DVL was also able to cause an imbalance in the redox system of the cells, interact with ergosterol, inhibit ergosterol biosynthesis, and induce cytochrome c release from the mitochondrial membrane. These results endorse the potential application of DVL in developing a new antifungal drug to fight back against fungal resistance.

United we stand, divided we fall: in-depth proteomic evaluation of the synergistic effect of Mo-CBP3-PepI and Ciprofloxacin against Staphylococcus aureus biofilms

Staphylococcus aureus forms biofilms, a structure that protects bacterial cells, conferring more resistance to difficult treatment. Synthetic peptides surge as an alternative to overcome the biofilm of multidrug-resistant pathogens. Mo-CBP3-PepI, when combined with Ciprofloxacin, reduced preformed S. aureus biofilm by 50% at low concentrations (0.2 and 6.2 μg. mL-1, respectively). The goal of this study was to evaluate the proteomic profile of biofilms after treatment with the Mo-CBP3-PepI combined with ciprofloxacin. Here, proteomic analysis confirmed with more depth previously described mechanisms and revealed changes in the accumulation of proteins related to DNA and protein metabolism, cell wall biosynthesis, redox metabolism, quorum sensing, and biofilm formation. Some proteins related to DNA and protein metabolism were reduced, while other proteins, like redox system proteins, disappeared in Ciprofloxacin+Mo-CBP3-PepI treatment. Our results indicated a synergistic effect of these two molecules with several mechanisms against S. aureus biofilm and opened new doors for combined treatments with other drugs.

Antimicrobial Activity the Essential Oil from Croton pluriglandulosus Carn. Leaves against Microorganisms of Clinical Interest

Multiresistant pathogens pose a serious threat to human health. The genus Candida is one class of human pathogenic yeasts responsible for infections affecting healthy and immunocompromised patients. In this context, plant essential oils emerged as a future natural alternative to control the diseases caused by these pathogens. Based on that, the present study aimed to evaluate the antimicrobial potential of essential oil from C. pluriglandulosus and understand the mechanism of action. Here, it highlighted antimicrobial activity and the mechanisms of action of the essential oil extracted from C. pluriglandulosus Carn.-Torres & Riina (CpEO) leaves on human pathogenic microorganisms in planktonic and biofilm lifestyles. In addition, for the first time, the oil composition was revealed by GC-MS analysis and the toxicity to human red blood cells (HRBC). Twenty-six chemical compounds were identified in CpEO, elemicin, bicyclogermacrene, caryophyllene, brevifolin, and 2,4,6-trimethoxy-styrene. Through hemolytic assay, it was shown that CpEO has no toxicity to human RBCs. At the concentration of 50 μg mL^-1, CpEO did not show great antibacterial potential. However, promising data were found for C. krusei and C. parapsilosis inhibiting by 89.3% and 80.7% of planktonic cell growth and 83.5% and 77.9% the biofilm formation, respectively. Furthermore, the mechanisms of action CpEO were elucidated by fluorescence. Scanning electron microscopy revealed damage to the cell membrane and pore formation, ROS overproduction, and induction of apoptosis in candida cells. Our results reinforce the potential of CpEO as an effective alternative molecule of pharmaceutical interest.

Rational design of HJH antimicrobial peptides to improve antimicrobial activity

Antimicrobial peptides (AMPs) have attracted considerable interest in the past decade due to their advantages for tackling antibiotic resistance. They exhibit potential antimicrobial activity through unique cell membrane destruction mechanism based on their net charge, hydrophobic properties, and α-helix. In this work, a series of HJH peptides was rationally designed and synthesized. The antimicrobial activity and cytotoxicity assays indicated that HJH-5 and HJH-6 containing hydrophobic residues and helices displayed prominent antimicrobial activity and mild cytotoxicity, respectively. These peptides may be developed for combatting microbial infections.

No Chance to Survive: Mo-CBP3-PepII Synthetic Peptide Acts on Cryptococcus neoformans by Multiple Mechanisms of Action

Multidrug-resistant Cryptococcus neoformans is an encapsulated yeast causing a high mortality rate in immunocompromised patients. Recently, the synthetic peptide Mo-CBP₃-PepII emerged as a potent anticryptococcal molecule with an MIC₅₀ at low concentration. Here, the mechanisms of action of Mo-CBP₃-PepII were deeply analyzed to provide new information about how it led C. neoformans cells to death. Light and fluorescence microscopies, analysis of enzymatic activities, and proteomic analysis were employed to understand the effect of Mo-CBP₃-PepII on C. neoformans cells. Light and fluorescence microscopies revealed Mo-CBP₃-PepII induced the accumulation of anion superoxide and hydrogen peroxide in C. neoformans cells, in addition to a reduction in the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) in the cells treated with Mo-CBP₃-PepII. In the presence of ascorbic acid (AsA), no reactive oxygen species (ROS) were detected, and Mo-CBP₃-PepII lost the inhibitory activity against C. neoformans. However, Mo-CBP₃-PepII inhibited the activity of lactate dehydrogenase (LDH) ergosterol biosynthesis and induced the decoupling of cytochrome c (Cyt c) from the mitochondrial membrane. Proteomic analysis revealed a reduction in the abundance of proteins related to energetic metabolism, DNA and RNA metabolism, pathogenicity, protein metabolism, cytoskeleton, and cell wall organization and division. Our findings indicated that Mo-CBP₃-PepII might have multiple mechanisms of action against C. neoformans cells, mitigating the development of resistance and thus being a potent molecule to be employed in the production of new drugs against C. neoformans infections.

Chitosan-graphene quantum dot based active film as smart wound dressing

Graphene quantum dots (GQDs), are biocompatible materials, with mechanical strength and stability. Chitosan, has antibacterial and anti-inflammatory properties, and biocompatibility. Wound healing is a challenging process especially in chronic diseases and infection. In this study, films consisting of chitosan and graphene quantum dots were developed for application in infected wounds. The chitosan-graphene films were prepared in the acidic solution followed by slow solvent evaporation and drying. The chitosan-graphene films were characterized by the scanning electron microscopy, x-ray diffraction, atomic force microscopy, Raman spectroscopy and thermogravimetric analysis. The films' was evaluated by the wound healing assays, hemolytic potential, and nitrite production, cytokine production and swelling potential. The obtained films were flexible and well-structured, promoting cell migration, greater antibacterial activity, lower hemolytic activity, and maintaining wound moisture. Our data suggested that the use of graphene quantum dot-containing chitosan films would be an efficient and promising way in combating wounds.

A Novel Peptide with Antifungal Activity from Red Swamp Crayfish Procambarus clarkii

The defense system of freshwater crayfish Procambarus clarkii as a diversified source of bioactive molecules with antimicrobial properties was studied. Antimicrobial activity of two polypeptide-enriched extracts obtained from hemocytes and hemolymph of P. clarkii were assessed against Gram positive (Staphylococcus aureus, Enterococcus faecalis) and Gram negative (Pseudomonas aeruginosa, Escherichia coli) bacteria and toward the yeast Candida albicans. The two peptide fractions showed interesting MIC values (ranging from 11 to 700 μg/mL) against all tested pathogens. Polypeptide-enriched extracts were further investigated using a high-resolution mass spectrometry and database search and 14 novel peptides were identified. Some peptides and their derivatives were chemically synthesized and tested in vitro against the bacterial and yeast pathogens. The analysis identified a synthetic derivative peptide, which showed an interesting antifungal (MIC and MFC equal to 31.2 μg/mL and 62.5 μg/mL, respectively) and antibiofilm (BIC₅₀ equal to 23.2 μg/mL) activities against Candida albicans and a low toxicity in human cells.

New Insights into the Mechanism of Antibacterial Action of Synthetic Peptide Mo-CBP3-PepI against Klebsiella pneumoniae

Klebsiella pneumoniae is a multidrug-resistant opportunistic human pathogen related to various infections. As such, synthetic peptides have emerged as potential alternative molecules. Mo-CBP₃-PepI has presented great activity against K. pneumoniae by presenting an MIC₅₀ at a very low concentration (31.25 µg mL^-1). Here, fluorescence microscopy and proteomic analysis revealed the alteration in cell membrane permeability, ROS overproduction, and protein profile of K. pneumoniae cells treated with Mo-CBP₃-PepI. Mo-CBP₃-PepI led to ROS overaccumulation and membrane pore formation in K. pneumoniae cells. Furthermore, the proteomic analysis highlighted changes in essential metabolic pathways. For example, after treatment of K. pneumoniae cells with Mo-CBP₃-PepI, a reduction in the abundance of protein related to DNA and protein metabolism, cytoskeleton and cell wall organization, redox metabolism, regulation factors, ribosomal proteins, and resistance to antibiotics was seen. The reduction in proteins involved in vital processes for cell life, such as DNA repair, cell wall turnover, and protein turnover, results in the accumulation of ROS, driving the cell to death. Our findings indicated that Mo-CBP₃-PepI might have mechanisms of action against K. pneumoniae cells, mitigating the development of resistance and thus being a potent molecule to be employed in producing new drugs against K. pneumoniae infections.

Ornamental tobacco floral nectar is a rich source of antimicrobial peptides

Although floral nectar is a rich source of nutrients, it is rarely infected by microorganisms. Defense molecules such as proteins have been identified in this fluid, but defense peptides have been largely overlooked. Thus, the aim of this study was to perform an extensive peptidomic analysis of the ornamental tobacco floral nectar to seek peptides involved in nectar defense. Using LC-MS/MS, 793 peptides were sequenced and characterized. After extensive bioinformatics analysis, six peptides were selected for further characterization, synthesis, and evaluation of their antimicrobial properties against phytopathogenic fungi and bacteria. All six peptides had antimicrobial activity to some extent. However, the activity varied by peptide concentration and microorganism tested. An analysis of the action mechanism revealed damage in the cell membrane induced by peptides. The results show that floral nectar is rich in peptides and that, together with proteins and hydrogen peroxide, they contribute to plant defense against microorganisms during pollination.

Essential Oil from Croton blanchetianus Leaves: Anticandidal Potential and Mechanisms of Action

Antimicrobial drugs are becoming ineffective given the resistance acquired by microorganisms. As such, it is imperative to seek new antimicrobial molecules that could provide a basis for the development of new drugs. Therefore, this work aimed to evaluate the antimicrobial potential and the mechanisms of action of the essential oil extracted from leaves of Croton blanchetianus (named CbEO) on different fungi and bacteria of clinical importance in both planktonic and biofilm lifestyles. GC-MS/MS analysis revealed the presence of twenty-two different compounds in the CbEO, which were identified using the Kovats retention index. Among these, the most abundant were amorphene (20.03%), spathulenol (5%), bicyclogermacrene (1.49%), caryophyllene oxide (4.55%), and eucalyptol (5.62%). CbOE (50 µg mL^-1) barely inhibited the growth of Bacillus subtilis (23%), Pseudomonas aeruginosa (27%), and Salmonella enterica (28%), and no inhibition was obtained against Enterobacter aerogenes and Klebsiella pneumoniae. Additionally, no activity against bacterial biofilm was detected. In contrast, CbEO was active against Candida species. C. albicans and C. parapsilosis were inhibited by 78 and 75%, respectively. The antibiofilm potential also was favorable against C. albicans and C. parapsilosis, inhibiting 44 and 74% of biofilm formation and reducing around 41 and 27% of the preformed biofilm, respectively. CbOE caused membrane damage and pore formation, overproduction of ROS, and apoptosis on C. albicans and C. parapsilosis cells, as well as not inducing hemolysis in human red cells. The results obtained in this work raise the possibility of using the essential oil of C. blanchetianus leaves as an alternative to fight infections caused by C. albicans and C. parapsilosis.

Redox Impact on Bacterial Macromolecule: A Promising Avenue for Discovery and Development of Novel Antibacterials

Antibiotic resistance in bacteria has remained a serious public health concern, resulting in substantial deaths and morbidity each year. Factors such as mutation and abuse of currently available antibiotics have contributed to the bulk of the menace. Hence, the introduction and implementation of new therapeutic strategies are imperative. Of these strategies, data supporting the role of reactive oxygen species (ROS) in bacterial lethality are intriguing, with several antimicrobials, including antibiotics such as fluoroquinolones, β-lactams, and aminoglycosides, as well as natural plant compounds, being remarkably implicated. Following treatment with ROS-inducing antimicrobials, ROS such as O₂^•-, ^•OH, and H₂O₂ generated in bacteria, which the organism is unable to detoxify, damage cellular macromolecules such as proteins, lipids, and nucleic acids and results in cell death. Despite the unique mechanism of action of ROS-inducing antibacterials and significant studies on ROS-mediated means of bacterial killing, the field remains a topical one, with contradicting viewpoints that require frequent review. Here, we appraised the antibacterial agents (antibiotics, natural and synthetic compounds) implicated in ROS generation and the safety concerns associated with their usage. Further, background information on the sources and types of ROS in bacteria, the mechanism of bacterial lethality via oxidative stress, as well as viewpoints on the ROS hypothesis undermining and solidifying this concept are discussed.

Important Roles and Potential Uses of Natural and Synthetic Antimicrobial Peptides (AMPs) in Oral Diseases: Cavity, Periodontal Disease, and Thrush

Numerous epithelial cells and sometimes leukocytes release AMPs as their first line of defense. AMPs encompass cationic histatins, defensins, and cathelicidin to encounter oral pathogens with minimal resistance. However, their concentrations are significantly below the effective levels and AMPs are unstable under physiological conditions due to proteolysis, acid hydrolysis, and salt effects. In parallel to a search for more effective AMPs from natural sources, considerable efforts have focused on synthetic stable and low-cytotoxicy AMPs with significant activities against microorganisms. Using natural AMP templates, various attempts have been used to synthesize sAMPs with different charges, hydrophobicity, chain length, amino acid sequence, and amphipathicity. Thus far, sAMPs have been designed to target Streptococcus mutans and other common oral pathogens. Apart from sAMPs with antifungal activities against Candida albicans, future endeavors should focus on sAMPs with capabilities to promote remineralization and antibacterial adhesion. Delivery systems using nanomaterials and biomolecules are promising to stabilize, reduce cytotoxicity, and improve the antimicrobial activities of AMPs against oral pathogens. Nanostructured AMPs will soon become a viable alternative to antibiotics due to their antimicrobial mechanisms, broad-spectrum antimicrobial activity, low drug residue, and ease of synthesis and modification.

Synergistic Antibiofilm Activity between Synthetic Peptides and Ciprofloxacin against Staphylococcus aureus

Staphylococcus aureus is a human pathogen known to be resistant to antibiotics since the mid-20th century and is constantly associated with hospital-acquired infections. S. aureus forms biofilms, which are complex surface-attached communities of bacteria held together by a self-produced polymer matrix consisting of proteins, extracellular DNA, and polysaccharides. Biofilms are resistance structures responsible for increasing bacterial resistance to drugs by 1000 times more than the planktonic lifestyle. Therefore, studies have been conducted to discover novel antibacterial molecules to prevent biofilm formation and/or degrade preformed biofilms. Synthetic antimicrobial peptides (SAMPs) have appeared as promising alternative agents to overcome increasing antibiotic resistance. Here, the antibiofilm activity of eight SAMPs, in combination with the antibiotic ciprofloxacin, was investigated in vitro. Biofilm formation by S. aureus was best inhibited (76%) by the combination of Mo-CBP3-PepIII (6.2 µg mL−1) and ciprofloxacin (0.39 µg mL−1). In contrast, the highest reduction (60%) of the preformed biofilm mass was achieved with RcAlb-PepII (1.56 µg mL−1) and ciprofloxacin (0.78 µg mL−1). Fluorescence microscopy analysis reinforced these results. These active peptides formed pores in the cellular membrane of S. aureus, which may be related to the enhanced ciprofloxacin’s antibacterial activity. Our findings indicated that these peptides may act with ciprofloxacin and are powerful co-adjuvant agents for the treatment of S. aureus infections.

Luffa operculata seed proteins: Identification by LC-ESI-MS/MS and biotechnological potential against Candida albicans and C. krusei

L: operculata is a plant commonly found in the North and Northeast of Brazil. Although the regional population knows its medicinal potential, there are few scientific studies about its antimicrobial potential. Thus, this study aimed to characterize the proteins from L. operculata seeds extracted using different solutions and evaluate their antimicrobial potentials. The protein extracts obtained with NaCl and sodium acetate buffer presented the best inhibitory activities against Candida albicans and C. krusei. The study of the mechanism of action revealed proteins from L. operculata seeds induced pore formation on the membrane and ROS overaccumulation. Scanning Electron Microscopy images also showed severe morphological changes in Candida albicans and C. krusei. Proteins from L.operculata seeds did not show antibacterial activity. The enzymatic assays revealed the presence of proteolytic enzymes, serine and cysteine protease inhibitors, and chitinases in both protein extracts. Proteomic analysis by LC-ESI-MS/MS identified 57 proteins related to many biological processes, such as defense to (a)biotic stress, energetic metabolism, protein folding, and nucleotide metabolism. In conclusion, the L. operculata seed proteins have biotechnological potential against the human pathogenic yeasts Candida albicans and C. krusei.

Antifungal Potential of Synthetic Peptides against Cryptococcus neoformans: Mechanism of Action Studies Reveal Synthetic Peptides Induce Membrane-Pore Formation, DNA Degradation, and Apoptosis

Cryptococcus neoformans is a human-pathogenic yeast responsible for pneumonia and meningitis, mainly in patients immunocompromised. Infections caused by C. neoformans are a global health concern. Synthetic antimicrobial peptides (SAMPs) have emerged as alternative molecules to cope with fungal infections, including C. neoformans. Here, eight SAMPs were tested regarding their antifungal potential against C. neoformans and had their mechanisms of action elucidated by fluorescence and scanning electron microscopies. Five SAMPs showed an inhibitory effect (MIC₅₀) on C. neoformans growth at low concentrations. Fluorescence microscope (FM) revealed that SAMPs induced 6-kDa pores in the C. neoformans membrane. Inhibitory assays in the presence of ergosterol revealed that some peptides lost their activity, suggesting interaction with it. Furthermore, FM analysis revealed that SAMPs induced caspase 3/7-mediated apoptosis and DNA degradation in C. neoformans cells. Scanning Electron Microscopy (SEM) analysis revealed that peptides induced many morphological alterations such as cell membrane, wall damage, and loss of internal content on C. neoformans cells. Our results strongly suggest synthetic peptides are potential alternative molecules to control C. neoformans growth and treat the cryptococcal infection.

Combined antibiofilm activity of synthetic peptides and antifungal drugs against Candida spp

Introduction: Candida krusei and Candida albicans are biofilm-forming drug-resistant yeasts that cause bloodstream infections that can lead to death. Materials & methods: nystatin and itraconazole were combined with two synthetic peptides, PepGAT and PepKAA, to evaluate the synergistic effect against Candida biofilms. Additionally, scanning electron and fluorescence microscopies were employed to understand the mechanism behind the synergistic activity. Results: Peptides enhanced the action of drugs to inhibit the biofilm formation of C. krusei and C. albicans and the degradation of mature biofilms of C. krusei. In combination with antifungal drugs, peptides' mechanism of action involved cell wall and membrane damage and overproduction of reactive oxygen species. Additionally, in combination, the peptides reduced the toxicity of drugs to red blood cells. Conclusion: These results reveal that the synthetic peptides enhanced the antibiofilm activity of drugs, in addition to reducing their toxicity. Thus, these peptides have strong potential as adjuvants and to decrease the toxicity of drugs.

A new bioinspired peptide on defensin from C. annuum fruits: Antimicrobial activity, mechanisms of action and therapeutical potential

BACKGROUND

Antimicrobial peptides, natural or synthetic, appear as promising molecules for antimicrobial therapy because of their both broad antimicrobial activity and mechanism of action. Herein, we determine the anti-Candida and antimycobacterial activities, mechanism of action on yeasts, and cytotoxicity on mammalian cells in the presence of the bioinspired peptide CaDef2.1_G27-K44.

METHODS

CaDef2.1_G27-K44 was designed to attain the following criteria: high positive net charge; low molecular weight (<3000 Da); Boman index ≤2.5; and total hydrophobic ratio ≥ 40%. The mechanism of action was studied by growth inhibition, plasma membrane permeabilization, ROS induction, mitochondrial functionality, and metacaspase activity assays. The cytotoxicity on macrophages, monocytes, and erythrocytes were also determined.

RESULTS

CaDef2.1_G27-K44 showed inhibitory activity against Candida spp. with MIC₁₀₀ values ranging from 25 to 50 μM and the standard and clinical isolate of Mycobacterium tuberculosis with MIC₅₀ of 33.2 and 55.4 μM, respectively. We demonstrate that CaDef2.1_G27-K44 is active against yeasts at different salt concentrations, induced morphological alterations, caused membrane permeabilization, increased ROS, causes loss of mitochondrial functionality, and activation of metacaspases. CaDef2.1_G27-K44 has low cytotoxicity against mammalian cells.

CONCLUSIONS

The results obtained showed that CaDef2.1_G27-K44 has great antimicrobial activity against Candida spp. and M. tuberculosis with low toxicity to host cells. For Candida spp., the treatment with CaDef2.1_G27-K44 induces a process of regulated cell death with apoptosis-like features.

GENERAL SIGNIFICANCE

We show a new AMP bioinspired with physicochemical characteristics important for selectivity and antimicrobial activity, which is a promising candidate for drug development, mainly to control Candida infections.

Plant Antimicrobial Peptides (PAMPs): Features, Applications, Production, Expression, and Challenges

The quest for an extraordinary array of defense strategies is imperative to reduce the challenges of microbial attacks on plants and animals. Plant antimicrobial peptides (PAMPs) are a subset of antimicrobial peptides (AMPs). PAMPs elicit defense against microbial attacks and prevent drug resistance of pathogens given their wide spectrum activity, excellent structural stability, and diverse mechanism of action. This review aimed to identify the applications, features, production, expression, and challenges of PAMPs using its structure–activity relationship. The discovery techniques used to identify these peptides were also explored to provide insight into their significance in genomics, transcriptomics, proteomics, and their expression against disease-causing pathogens. This review creates awareness for PAMPs as potential therapeutic agents in the medical and pharmaceutical fields, such as the sensitive treatment of bacterial and fungal diseases and others and their utilization in preserving crops using available transgenic methods in the agronomical field. PAMPs are also safe to handle and are easy to recycle with the use of proteases to convert them into more potent antimicrobial agents for sustainable development.

JcTI-PepI, a synthetic peptide bioinspired in the trypsin inhibitor from Jatropha curcas, presents potent inhibitory activity against C. krusei, a neglected pathogen

Antimicrobial resistance has been increasing globally, posing a global public health risk. It has prompted the scientific community to look for alternatives to traditional drugs. Antimicrobial Peptides (AMPs) have stood out in this context because they have the potential to control infectious diseases while causing no or little harm to mammalian cells. In the present study, three peptides, JcTI-PepI, JcTI-PepII, and JcTI-PepIII, were designed and tested for antimicrobial activity based on the primary sequence of JcTI-I, a 2S albumin with trypsin inhibitory activity from Jatropha curcas. JcTI-PepI strongly inhibited C. krusei growth, and it caused severe disruptions in cellular processes and cell morphology. C. krusei cells treated with JcTI-PepI showed indicative of membrane permeabilization and overproduction of Reactive Oxygen Species. Moreover, the yeast's ability to acidify the medium was severely compromised. JcTI-PepI was also effective against pre-formed biofilm and did not harm human erythrocytes and Vero cells. Overall, these characteristics indicate that JcTI-PepI is both safe and effective against C. krusei, an intrinsically resistant strain that causes serious health problems and is frequently overlooked. It implies that this peptide has a high potential for use as a new antimicrobial agent in the future.

Neutralizing Effect of Synthetic Peptides toward SARS-CoV-2

The outbreak caused by SARS-CoV-2 has taken many lives worldwide. Although vaccination has started, the development of drugs to either alleviate or abolish symptoms of COVID-19 is still necessary. Here, four synthetic peptides were assayed regarding their ability to protect Vero E6 cells from SARS-CoV-2 infection and their toxicity to human cells and zebrafish embryos. All peptides had some ability to protect cells from infection by SARS-CoV-2 with the D614G mutation. Molecular docking predicted the ability of all peptides to interact with and induce conformational alterations in the spike protein containing the D614G mutation. PepKAA was the most effective peptide, by having the highest docking score regarding the spike protein and reducing the SARS-CoV-2 plaque number by 50% (EC₅₀) at a concentration of 0.15 mg mL^-1. Additionally, all peptides had no toxicity to three lines of human cells as well as to zebrafish larvae and embryos. Thus, these peptides have potential activity against SARS-CoV-2, making them promising to develop new drugs to inhibit cell infection by SARS-CoV-2.

Synergistic Antifungal Activity of Synthetic Peptides and Antifungal Drugs against Candida albicans and C. parapsilosis Biofilms

C. albicans and C. parapsilosis are biofilm-forming yeasts responsible for bloodstream infections that can cause death. Synthetic antimicrobial peptides (SAMPs) are considered to be new weapons to combat these infections, alone or combined with drugs. Here, two SAMPs, called Mo-CBP₃-PepI and Mo-CBP₃-PepIII, were tested alone or combined with nystatin (NYS) and itraconazole (ITR) against C. albicans and C. parapsilosis biofilms. Furthermore, the mechanism of antibiofilm activity was evaluated by fluorescence and scanning electron microscopies. When combined with SAMPs, the results revealed a 2- to 4-fold improvement of NYS and ITR antibiofilm activity. Microscopic analyses showed cell membrane and wall damage and ROS overproduction, which caused leakage of internal content and cell death. Taken together, these results suggest the potential of Mo-CBP₃-PepI and Mo-CBP₃-PepIII as new drugs and adjuvants to increase the activity of conventional drugs for the treatment of clinical infections caused by C. albicans and C. parapsilosis.

Latex peptidases produce peptides capable of delaying fungal growth in bread

Antimicrobial peptides (AMPs) have been reported to be promising alternatives to chemical preservatives. Thus, this study aimed to characterise AMPs generated from the hydrolysis of wheat gluten proteins using latex peptidases of Calotropis procera, Cryptostegia grandiflora, and Carica papaya. The three hydrolysates (obtained after 16 h at 37 °C, using a 1: 25 enzyme:  substrate ratio) inhibited the growth of Aspergillus niger, A. chevalieri, Trichoderma reesei, Pythium oligandrum, Penicillium sp., and Lasiodiplodia sp. by 60-90%, and delayed fungal growth on bread by 3 days when used at 0.3 g/kg. Moreover, the specific volume and expansion factor of bread were not affected by the hydrolysates. Of 28 peptides identified, four were synthesised and exhibited activity against Penicillium sp. Fluorescence and scanning electron microscopy suggested that the peptides damaged the fungal plasma membrane. Bioinformatics analysis showed that no peptide was toxic and that the antigenic ones had cleavage sites for trypsin or pepsin.

Combination of Amphiphilic Cyclic Peptide [R4W4] and Levofloxacin against Multidrug-Resistant Bacteria

Bacterial resistance is a growing global concern necessitating the discovery and development of antibiotics effective against the drug-resistant bacterial strain. Previously, we reported a cyclic antimicrobial peptide [R4W4] containing arginine (R) and tryptophan (W) with a MIC of 2.67 µg/mL (1.95 µM) against methicillin-resistant Staphylococcus aureus (MRSA). Herein, we investigated the cyclic peptides [R4W4] or linear (R4W4) and their conjugates (covalent or noncovalent) with levofloxacin (Levo) with the intent to improve their potency to target drug-resistant bacteria. The physical mixture of the Levo with the cyclic [R4W4] proved to be significantly effective against all strains of bacteria used in the study as compared to covalent conjugation. Furthermore, the checkerboard assay revealed the significant synergistic effect of the peptides against all studied strains except for the wild type S. aureus, in which the partial synergy was observed. The hemolysis assay revealed less cytotoxicity of the physical mixture of the Levo with [R4W4] (22%) as compared to [R4W4] alone (80%). The linear peptide (R4W4) and the cyclic [R4W4] demonstrated ~90% and 85% cell viability at 300 µg/mL in the triple-negative breast cancer cells (MDA-MB-231) and the normal kidney cells (HEK-293), respectively. Similar trends were also observed in the cell viability of Levo-conjugates on these cell lines. Furthermore, the time-kill kinetic study of the combination of [R4W4] and Levo demonstrate rapid killing action at 4 h for MRSA (ATCC BAA-1556) and 12 h for E. coli (ATCC BAA-2452), P. aeruginosa (ATCC BAA-1744), and K. pneumoniae (ATCC BAA-1705). These results provide the effectiveness of a combination of Levo with cyclic [R4W4] peptide, which may provide an opportunity to solve the intriguing puzzle of treating bacterial resistance.

The characteristics and roles of antimicrobial peptides as potential treatment for antibiotic-resistant pathogens: a review

The emergence of antibiotic-resistant bacteria has become a significant and ever-increasing threat to global public health, increasing both morbidity and mortality rates, and the financial burden on health services. Infection by drug-resistant bacteria is anticipated to contribute to the demise of almost 10 million people by the year 2050 unless a competent and effective response is devised to engage with this issue. The emergence and spread of resistance are commonly caused by the excessive or inappropriate use of antibiotics and substandard pharmaceuticals. It arises when pathogens adapt to different conditions and develop self-defence mechanisms. Currently, novel antimicrobial peptides (AMPs) have been reported to be the sole cure for some clinical cases of infectious diseases such as sepsis and skin infections, although these agents may, on occasion, require administration together with an adjunctive low-dose antibiotic. Although AMPs are a promising alternative form of anti-microbial therapy and easily applied in the medical sector, they still have limitations that should not be taken lightly. Hence, this review explores the characteristics, advantages and disadvantages of AMPs for their potential in treating antibiotic-resistant pathogens.

Anticancer potential of limonoids from Swietenia macrophylla: Genotoxic, antiproliferative and proapoptotic effects towards human colorectal cancer

AIMS

Swietenia macrophylla have been considered for the treatment of various diseases, including anticancer activity. This study aimed to investigate the anticancer activity of S. macrophylla leaves extract and its isolated compound towards human colorectal cancer cell line.

MAIN METHODS

Hexanic extract of S. macrophylla leaves demonstrated relevant cytotoxicity only against colon cancer cell line HCT116.

KEY FINDINGS

Our results showed significant DNA damage and apoptosis after treatment with the hexanic extract of S. macrophylla. Moreover, no toxicity was noticed for the animal model. The isolated compound limonoid L1 showed potent cytotoxicity against cancer cell lines with IC₅₀ at 55.87 μg mL^-1. Limonoid L1 did not trigger any cell membrane rupture in the mice erythrocytes suggesting no toxicity. The antiproliferative effect of L1 was confirmed in colorectal cancer cells by clonogenic assay, inducing G2/M arrest, apoptosis, and DNA damage in cancer-type cells.

SIGNIFICANCE

L1 reduced BCL2 and increased ATM, CHK2, TP53, ARF, CDK1, CDKN1A, and CASP3 in the colorectal cancer cell line. These findings suggest that limonoid L1 isolated from S. macrophylla can be a promising anticancer agent in managing colorectal cancer.

Synthetic antimicrobial peptides control Penicillium digitatum infection in orange fruits

Fungal contamination is among the main reasons for food spoilage, affecting food safety and the economy. Among fungi, Penicillium digitatum is a major agent of this problem. Here, the in vitro activity of eight synthetic antimicrobial peptides was assessed against P. digitatum, and their action mechanisms were evaluated. All peptides were able to inhibit fungal growth. Furthermore, atomic force and fluorescence microscopies revealed that all peptides targeted the fungal membrane leading to pore formation, loss of internal content, and death. The induction of high levels of reactive oxygen species (ROS) was also a mechanism employed by some peptides. Interestingly, only three peptides (PepGAT, PepKAA, and Mo-CBP₃-PepI) effectively control P. digitatum colonization in orange fruits, at a concentration (50 µg mL^-1) 20-fold lower than the commercial food preservative (sodium propionate). Altogether, PepGAT, PepKAA, and Mo-CBP₃-PepI showed high biotechnological potential as new food preservatives to control food infection by P. digitatum.

New Insights into Anthelmintic Mechanisms of Action of a Synthetic Peptide: An Ultrastructural and Nanomechanical Approach

Resistant nematodes are not affected by the most common drugs commercially available. In the search for new anthelmintics, peptides have been investigated. Here, a linear synthetic peptide named RcAlb-PepIII bioinspired from the antimicrobial protein Rc-2S-Alb was designed, synthesized, and tested against barber pole worm Haemonchus contortus. The physicochemical properties of the peptide, the 3D structure model, the egg hatch inhibition, and larval development inhibition of H. contortus were carried out. Additionally, the ultrastructure of the nematode after treatment with the peptide was evaluated by atomic force microscopy. The RcAlb-PepIII inhibited the larval development of H. contortus with an EC₅₀ of 90 µM and did not affect egg hatch. Atomic force microscopy reveals the high affinity of RcAlb-PepIII with the cuticle of H. contortus in the L2 stage. It also shows the deposition of RcAlb-PepIII onto the surface of the cuticle, forming a structure similar to a film that reduces the roughness and mean square roughness (Rq) of it. In conclusion, the bioinspired RcAlb-PepIII has the potential to be used as a new anthelmintic compound to control gastrointestinal nematode parasites.

Computational approach, scanning electron and fluorescence microscopies revealed insights into the action mechanisms of anticandidal peptide Mo-CBP3-PepIII

AIMS

The Candida genus is composed of opportunistic pathogens that threaten public health. Given the increase in resistance to current drugs, it is necessary to develop new drugs to treat infections by these pathogens. Antimicrobial peptides are promising alternative molecules with low cost, broad action spectrum and low resistance induction. This study aimed to clarify the action mechanisms of synthetic peptides against Candida albicans.

MAIN METHODS

The mode of action of the anticandidal peptides Mo-CBP₃-PepIII were analyzed through molecular dynamics and quantum biochemistry methods against Exo-β-1,3-glucanase (EXG), vital to cell wall metabolism. Furthermore, scanning electron (SEM) and fluorescence (FM) microscopies were employed to corroborate the in silico data.

KEY FINDINGS

Mo-CBP₃-PepIII strongly interacted with EXG (-122.2 kcal mol^-1) at the active site, higher than the commercial inhibitor pepstatin. Also, molecular dynamics revealed the insertion of Mo-CBP₃-PepIII into the yeast membrane. SEM analyses revealed that Mo-CBP₃-PepIII induced cracks and scars of the cell wall and FM analyses confirmed the pore formation on the Candida membrane.

SIGNIFICANCE

Mo-CBP₃-PepIII has strong potential as a new drug with a broad spectrum of action, given its different mode of action compared to conventional drugs.

Synthetic antimicrobial peptides: Characteristics, design, and potential as alternative molecules to overcome microbial resistance

Recently, the dramatic emergence of antimicrobial resistance has received attention from World Health Organization. Synthetic antimicrobial peptides (SAMPs) are considered new weapons to fight against infections caused by multi-drug resistant pathogens. Here, the authors provide an overview of the current research on SAMPs. The focus is SAMPs, how to design them, which features must be considered during design, and comparison with natural peptides. This review also includes a discussion about the natural AMPs, mechanisms of action and applications as new drugs or even as adjuvants molecules to enhance commercial drugs activity. The advances in chemical synthesis have reduced the cost to produce synthetic peptides open ways to achieve new antimicrobial agents. Therefore, synthetic peptides are new promising molecules to safeguard human and animal health.

Quantum biochemistry, molecular docking, and dynamics simulation revealed synthetic peptides induced conformational changes affecting the topology of the catalytic site of SARS-CoV-2 main protease

The recent outbreak caused by SARS-CoV-2 continues to threat and take many lives all over the world. The lack of an efficient pharmacological treatments are serious problems to be faced by scientists and medical staffs worldwide. In this work, an in silico approach based on the combination of molecular docking, dynamics simulations, and quantum biochemistry revealed that the synthetic peptides RcAlb-PepI, PepGAT, and PepKAA, strongly interact with the main protease (Mpro) a pivotal protein for SARS-CoV-2 replication. Although not binding to the proteolytic site of SARS-CoV-2 Mpro, RcAlb-PepI, PepGAT, and PepKAA interact with other protein domain and allosterically altered the protease topology. Indeed, such peptide-SARS-CoV-2 Mpro complexes provoked dramatic alterations in the three-dimensional structure of Mpro leading to area and volume shrinkage of the proteolytic site, which could affect the protease activity and thus the virus replication. Based on these findings, it is suggested that RcAlb-PepI, PepGAT, and PepKAA could interfere with SARS-CoV-2 Mpro role in vivo. Also, unlike other antiviral drugs, these peptides have no toxicity to human cells. This pioneering in silico investigation opens up opportunity for further in vivo research on these peptides, towards discovering new drugs and entirely new perspectives to treat COVID-19.Communicated by Ramaswamy H. Sarma.

Current and novel therapeutic strategies for the management of cystic fibrosis

Introduction: Cystic fibrosis (CF), is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and affects thousands of people throughout the world. Lung disease is the leading cause of death in CF patients. Despite the advances in treatments, the management of CF mainly targets symptoms. Recent CFTR modulators however target common mutations in patients, alleviating symptoms of CF. Unfortunately, there is still no approved treatments for patients with rare mutations to date.Areas covered: This paper reviews current treatments of CF that mitigate symptoms and target genetic defects. The use of gene and drug delivery systems such as viral or non-viral vectors and nano-compounds to enhance CFTR expression and the activity of antimicrobials against chronic pulmonary infections respectively, will also be discussed.Expert opinion: Nano-compounds tackle biological barriers to drug delivery and revitalize antimicrobials, anti-inflammatory drugs and even genes delivery to CF patients. Gene therapy and gene editing are of particular interest because they have the potential to directly target genetic defects. Nanoparticles should be formulated to more specifically target epithelial cells, and biofilms. Finally, the development of more potent gene vectors to increase the duration of gene expression and reduce inflammation is a promising strategy to eventually cure CF.

Potent Anti-Candida Fraction Isolated from Capsicum chinense Fruits Contains an Antimicrobial Peptide That is Similar to Plant Defensin and is Able to Inhibit the Activity of Different α-Amylase Enzymes

Antimicrobial peptides (AMPs) are molecules present in several life forms, possess broad-spectrum of inhibitory activity against pathogenic microorganisms, and are a promising alternative to combat the multidrug resistant pathogens. The aim of this work was to identify and characterize AMPs from Capsicum chinense fruits and to evaluate their inhibitory activities against yeasts of the genus Candida and α-amylases. Initially, after protein extraction from fruits, the extract was submitted to anion exchange chromatography resulting two fractions. Fraction D1 was further fractionated by molecular exclusion chromatography, and three fractions were obtained. These fractions showed low molecular mass peptides, and in fraction F3, only two protein bands of approximately 6.5 kDa were observed. Through mass spectrometry, we identified that the lowest molecular mass protein band of fraction F3 showed similarity with AMPs from plant defensin family. We named this peptide CcDef3 (Capsicum chinense defensin 3). The antifungal activity of these fractions was analyzed against yeasts of the genus Candida. At 200 μg/mL, fraction F1 inhibited the growth of C. tropicalis by 26%, fraction F2 inhibited 35% of the growth of C. buinensis, and fraction F3 inhibited all tested yeasts, exhibiting greater inhibition activity on the growth of the yeast C. albicans (86%) followed by C. buinensis (69%) and C. tropicalis (21%). Fractions F1 and F2 promoted membrane permeabilization of all tested yeasts and increased the endogenous induction of reactive oxygen species (ROS) in C. buinensis and C. tropicalis, respectively. We also observed that fraction F3 at a concentration of 50 µg/mL inhibited the α-amylase activities of Tenebrio molitor larvae by 96% and human salivary by 100%. Thus, our results show that fraction F3, which contains CcDef3, is a very promising protein fraction because it has antifungal potential and is able to inhibit the activity of different α-amylase enzymes.

The forgotten 2S albumin proteins: Importance, structure, and biotechnological application in agriculture and human health

2S albumin proteins are a group of important seed storage proteins (SSPs) essential to seeds at early and late developmental stages, by providing amino acids and other nutrients during germination and for seed defense. 2S albumins possess a well-conserved cysteine supporting the stability of temperature, pH, and proteolysis. The 3D structure rich in alpha-helices and positively charged is particularly suited for antibacterial and antifungal activity, which is presented by many 2S albumins. However, the hypervariable region present in 2S albumins induces allergenic reactions. Because of that, 2S albumins have never been recognized for their biotechnological potential. However, the development of servers used for the rational design of antimicrobial molecules has now brought a new application to 2S albumins, acting as a model to design antimicrobial molecules without the toxic or allergenic effects of 2S albumins. Therefore, this review is focused on discussing the importance of 2S albumins to seed development and defense and the biochemical, structural and functional properties of these proteins thought to play a role in their antimicrobial activity. Additionally, the application of 2S albumins to design synthetic antimicrobial peptides is discussed, potentially bringing new functions to these forgotten proteins.

Synthetic peptides against Trichophyton mentagrophytes and T. rubrum: Mechanisms of action and efficiency compared to griseofulvin and itraconazole

AIMS

According to the WHO, 20-25% of people worldwide are affected by skin infections caused by dermatophytes, such as those of the Trichophyton genus. Additionally, several dermatophytes have developed resistance to drugs such as griseofulvin and itraconazole. This study tested 2S albumins-derived antimicrobial peptides (AMPs) as alternative antidermatophytic molecules.

MAIN METHODS

Membrane pore formation assays, tests to detect overproduction of ROS, scanning electron microscopy (SEM) and fluorescence microscopy (FM) were carried out to provide insight into the mechanisms of antidermatophytic action.

KEY FINDINGS

All AMPs (at 50 μg mL^-1) tested reduced the mycelial growth of T. mentagrophytes and T. rubrum by up to 95%. In contrast, using a concentration 20-fold higher, griseofulvin only inhibited T. mentagrophytes by 35%, while itraconazole was not active against both dermatophytes. Scanning electron and fluorescence microscopies revealed that the six AMPs caused severe damage to hyphal morphology by inducing cell wall rupture, hyphal content leakage, and death. Peptides also induced membrane pore formation and oxidative stress by overproduction of ROS. Based on the stronger activity of peptides than the commercial drugs and the mechanism of action, all six peptides have the potential to be either employed as models to develop new antidermatophytic drugs or as adjuvants to existing ones.

SIGNIFICANCE

The synthetic peptides are more efficient than conventional drug to treat infection caused by dermatophytes being potential molecules to develop new drugs.

A molecular docking study revealed that synthetic peptides induced conformational changes in the structure of SARS-CoV-2 spike glycoprotein, disrupting the interaction with human ACE2 receptor

The global outbreak of COVID-19 (Coronavirus Disease 2019) caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome caused by Coronavirus 2) began in December 2019. Its closest relative, SARS-CoV-1, has a slightly mutated Spike (S) protein, which interacts with ACE2 receptor in human cells to start the infection. So far, there are no vaccines or drugs to treat COVID-19. So, research groups worldwide are seeking new molecules targeting the S protein to prevent infection by SARS-CoV-2 and COVID-19 establishment. We performed molecular docking analysis of eight synthetic peptides against SARS-CoV-2 S protein. All interacted with the protein, but Mo-CBP₃-PepII and PepKAA had the highest affinity with it. By binding to the S protein, both peptides led to conformational alterations in the protein, resulting in incorrect interaction with ACE2. Therefore, given the importance of the S protein-ACE2 interaction for SARS-CoV-2 infection, synthetic peptides could block SARS-CoV-2 infection. Moreover, unlike other antiviral drugs, peptides have no toxicity to human cells. Thus, these peptides are potential molecules to be tested against SARS-CoV-2 and to develop new drugs to treat COVID-19.

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Synthetic peptides bind to SARS-CoV-2 Spike protein.

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Synthetic peptides induced conformational changes on SARS-CoV-2 spike protein structure.

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Synthetic peptides bind to ACE2 protein but did not affect its structure.

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Synthetic peptides induced the wrong interaction of SARS-CoV-2 with ACE2 receptor.

Antidermatophytic activity of synthetic peptides: Action mechanisms and clinical application as adjuvants to enhance the activity and decrease the toxicity of Griseofulvin

BACKGROUND

Dermatophytes belonging to the Trichophyton genus are important human pathogens, but they have developed resistance to griseofulvin, the most common antifungal drug used to treat dermatophytosis.

OBJECTIVE

This study was aimed to evaluate the antidermatophytic activity of synthetic peptides, as well as mechanisms of action and synergistic effect with griseofulvin.

METHODS

Scanning electron microscopy (SEM), atomic force microscopy (AFM) and fluorescence microscopy (FM) were employed to understand the activity and the mechanism of action of peptides.

RESULTS

Here we report that synthetic peptides at 50 μg/mL, a concentration 20-fold lower than griseofulvin, reduced the microconidia viability of T. mentagrophytes and T. rubrum by 100%, whereas griseofulvin decreased their viability by only 50% and 0%, respectively. The action mechanism of peptides involved cell wall damage, membrane pore formation and loss of cytoplasmic content. Peptides also induced overproduction of reactive oxygen species (ROS) and enhanced the activity of griseofulvin 10-fold against both fungi, suggesting synergistic effects, and eliminated the toxicity of this drug to human erythrocytes. Docking analysis revealed ionic and hydrophobic interactions between peptides and griseofulvin, which may explain the decline of griseofulvin toxicity when mixed with peptides.

CONCLUSION

Therefore, our results strongly suggest six peptides with high potential to be employed alone as new drugs or as adjuvants to enhance the activity and decrease the toxicity of griseofulvin.

The role of reactive oxygen species in the biological activity of antimicrobial agents: An updated mini review

Antimicrobial resistance remains a serious problem that results in high mortality and increased healthcare costs globally. One of the major issues is that resistant pathogens decrease the efficacy of conventional antimicrobials. Accordingly, development of novel antimicrobial agents and therapeutic strategies is urgently needed to overcome the challenge of antimicrobial resistance. A potential strategy is to kill pathogenic microorganisms via the formation of reactive oxygen species (ROS). ROS are defined as a number of highly reactive molecules that comprise molecular oxygen (O₂), superoxide anion (O₂^•-), hydrogen peroxide (H₂O₂) and hydroxyl radicals (^•OH). ROS exhibit antimicrobial actions against a broad range of pathogens through the induction of oxidative stress, which is an imbalance between ROS and the ability of the antioxidant defence system to detoxify ROS. ROS-dependent oxidative stress can damage cellular macromolecules, including DNA, lipids and proteins. This article reviews the antimicrobial action of ROS, challenges to ROS hypothesis, work to solidify ROS-mediated antimicrobial lethality hypothesis, recent developments in antimicrobial agents using ROS as an antimicrobial strategy, safety concerns related to ROS, and future directions in ROS research.

Mo-CBP4, a purified chitin-binding protein from Moringa oleifera seeds, is a potent antidermatophytic protein: In vitro mechanisms of action, in vivo effect against infection, and clinical application as a hydrogel for skin infection

Dermatophytes belonging to Trichophyton ssp. are important anthropophilic and zoophilic pathogens, which developed resistance to griseofulvin, the common antifungal drug used to treat dermatophytosis. In this context, Moringa oleifera seed proteins have been described as antifungal agents with potential applications. Thus, this work aimed to evaluate the antidermatophytic in vitro, focusing on mechanisms, and in vivo potential of Mo-CBP₄, purified from M. oleifera seeds. Mo-CBP₄was purified after protein extraction with 50 mM Tris-HCl buffer, pH 8.0, and chromatography on chitin and CM Sepharose™ columns and antidermatophytic potential of Mo-CBP₄ evaluated in vitro and in vivo. In vitro, Mo-CBP₄ reduced in 50% the germination of microconidia of Trichophyton mentagrophytes at 45 μM; but did not show inhibition of mycelial growth. Mo-CBP₄ (45 μM) presents the inhibitory activity even when incubated with N-acetyl-d-glucosamine (NAG). Analysis of the mechanisms of Mo-CBP₄ revealed an increase in membrane permeability, ROS overproduction and damage to cell wall leading to microconidia death. Furthermore, using in vivo models, Mo-CBP₄ (5, 10 and 20 mg g^-1) reduced the severity and time of dermatophytosis. Altogether, these findings indicate that Mo-CBP₄ has great potential for the development of novel antifungal drugs for the clinical treatment of dermatophytosis.

Identification, characterization, and antifungal activity of cysteine peptidases from Calotropis procera latex

Cysteine peptidases (EC 3.4.22) are the most abundant enzymes in latex fluids. However, their physiological functions are still poorly understood, mainly related to defense against phytopathogens. The present study reports the cDNA cloning and sequencing of five undescribed cysteine peptidases from Calotropis procera (Aiton) Dryand (Apocynaceae) as well as some in silico analyses. Of these, three cysteine peptidases (CpCP1, CpCP2, and CpCP3) were purified. Their enzymatic kinetics were determined and they were assayed for their efficacy in inhibiting the hyphal growth of phytopathogenic fungi. The mechanism of action was investigated by fluorescence and atomic force microscopy as well as by induction of reactive oxygen species (ROS). The deduced amino acid sequences showed similar biochemical characteristics and high sequence homology with several other papain-like cysteine peptidases. Three-dimensional models showed two typical cysteine peptidase domains (L and R domains), forming a "V-shaped" active site containing the catalytic triad (Cys, His, and Asn). Proteolysis of CpCP1 was higher at pH 7.0, whereas for CpCP2 and CpCP3 it was higher at 7.5. All peptidases exhibited optimum activity at 35 °C and followed Michaelis-Menten kinetics. However, the major difference among them was that CpCP1 exhibited highest V_max, K_m, K_cat and catalytic efficiency. All peptidases were deleterious to the two fungi tested, with IC₅₀ of around 50 μg/mL. The peptidases promoted membrane permeabilization, morphological changes with leakage of cellular content, and induction of ROS in F. oxysporum spores. These results corroborate the hypothesis that latex cysteine peptidases play a role in defense against fungi.