Antifungal activity of novel synthetic peptides by accumulation of reactive oxygen species (ROS) and disruption of cell wall against Candida albicans

Insights into the antifungal properties and modes of action of a recombinant hepcidin, rAd-Hep from the shrimp scad, Alepes djedaba (Forsskål, 1775)

Antimicrobial peptides are short, mostly cationic and amphipathic molecules crucial for host defence. Among these, hepcidins are a family of cysteine rich peptides, with HAMP1 hepcidins playing a dual role in iron metabolism and antimicrobial defense. Recently, recombinantly produced Alepes djedaba hepcidin, rAd-Hep was characterized and its antibacterial potential against various pathogens have been discerned. Herein, we investigated the antifungal nature and modes of action of rAd-Hep against some fungal pathogens. The peptide was found to be active against both filamentous fungi and yeasts viz., Aspergillus flavus, Aspergillus sydowii, Fusarium solani, Penicillium citrinum, Candida albicans and Saccharomyces cerevisiae. The peptide acted via membrane permeabilization creating pores of ∼0.7-1.4 nm radii, ROS generation, chromatin condensation and DNA binding. The recombinant hepcidin, rAd-Hep can be considered as a promising candidate for future endeavors in antifungal therapies.

Recent Advances in the Development of Antifungal Agents: Beyond Azoles, Polyenes, and Echinocandins

The escalating incidence of antimicrobial resistance to antifungal agents, alongside the emergence of drug-resistant fungal strains, constitutes a significant threat to a potential global fungal pandemic. In response, researchers are intensifying efforts to identify novel antifungal compounds through diverse methodologies. Emerging strategies focus on innovative therapeutic targets that may reduce the risk of resistance development while offering broad-spectrum efficacy against fungal infections. Additionally, these approaches present potential cost-effectiveness and accelerated development timelines. This review systematically categorizes a range of novel antifungal compounds, including antifungal peptides, cationic amphiphiles, small molecules, polymers, and repurposed drugs, based on their efficacy in inhibiting fungal growth and associated virulence factors. These compounds exhibit notable antimicrobial activity across in silico, in vitro, and in vivo systems against various pathogenic fungal strains, with several showing substantial promise for clinical application. Furthermore, the review highlights the limitations of standard antifungals and elucidates the mechanisms by which fungal strains develop resistance. This work aims to engage researchers in the distinctive field of fungal biology and foster the exploration of new antifungal strategies.

Antifungal Action of Valencene and Nootkatone Compounds in Association with Fluconazole and Their Mechanism of Action Against Candida spp. and Pichia kudriavzevii Strains

Candidemia is a public health challenge as it causes thousands of annual deaths and combating it has become difficult due to the development of resistance in Candida spp. Compounds derived from natural products may counter this resistance. Therefore, we evaluate the intrinsic and combined antifungal activity of valencene and nootkatone compounds and their possible mechanism of action against Candida spp. Using the microdilution method, the antifungal effect of sesquiterpenes and their combination with fluconazole was determined. The results comprised the yeast growth curve and its 50% Inhibitory Concentration (IC50). They showed that the compounds alone inhibited microbial growth at a concentration of 1024 µg/mL for valencene being able to kill the fungus Pichia kudriavzevii (Candida krusei), for nootkatone the inhibition occurred at 512 µg/mL and was able to kill the species P. kudriavzevii and Candida tropicalis. Combined with the antifungal, the inhibition occurred at low concentrations (2 and 4 µg/mL) against all strains except P. kudriavzevii, which the combination with nootkatone inhibited at 512 µg/mL. The IC50 revealed inhibition of the strains at higher concentrations in the compounds and fluconazole alone compared to the combination concentrations. In addition, both compounds acted through the production of reactive oxygen species, helping the antifungal against C. albicans and P. kudriavzevii, contributing minimally to compromising membrane viability. Thus, the compounds show promise for combined activity with fluconazole.

De novo design of Na+-activated lipopeptides with selective antifungal activity: A promising strategy for antifungal drug discovery

In recent years, invasive fungal infections have posed a significant threat to human health, particularly due to the limited availability of effective antifungal medications. This study responds to the urgent need for powerful and selective antifungal agents by designing and synthesizing a series of lipopeptides with lipoylation at the N-terminus of the antimicrobial peptide I6. Compared to the parent peptide I6, lipopeptides exhibited selective antifungal efficacy in the presence of Na+. Among the variants tested, C8-I6 emerged as the most effective, with an average effective concentration of 5.3 μM against 12 different fungal species. C8-I6 combated fungal infections by disrupting both cytoplasmic and mitochondrial membranes, impairing the proton motive force, generating reactive oxygen species, and triggering apoptosis in fungal cells. Importantly, C8-I6 exhibited minimal hemolysis and cytotoxicity while effectively inhibiting fungal biofilm formation. In vivo experiments further validated the safety and therapeutic potential of C8-I6 in treating fungal skin infections. These findings underscore the significance of lipoylation in enhancing the efficacy of antimicrobial peptides, positioning C8-I6 as a promising candidate in fighting against drug-resistant fungal infections.

Advancements in peptide-based antimicrobials: A possible option for emerging drug-resistant infections

In recent years, multidrug-resistant pathogenic microorganisms (MDROs) have emerged as a severe threat to human health, exhibiting robust resistance to traditional antibiotics. This has created a formidable challenge in modern medicine as we grapple with limited options to combat these resilient bacteria. Despite extensive efforts by scientists to develop new antibiotics targeting these pathogens, the quest for novel antibacterial molecules has become increasingly arduous. Fortunately, nature offers a potential solution in the form of cationic antimicrobial peptides (AMPs) and their synthetic counterparts. AMPs, naturally occurring peptides, have displayed promising efficacy in fighting bacterial infections by disrupting bacterial cell membranes, hindering their survival and reproduction. These peptides, along with their synthetic mimics, present an exciting alternative in combating antibiotic resistance. They hold the potential to emerge as a formidable tool against MDROs, offering hope for improved strategies to protect communities. Extensive research has explored the diversity, history, and structure-properties relationship of AMPs, investigating their amphiphilic nature for membrane disruption and mechanisms of action. However, despite their therapeutic promise, AMPs face several documented limitations. Among these challenges, poor pharmacokinetic properties stand out, impeding the attainment of therapeutic levels in the body. Additionally, some AMPs exhibit toxicity and susceptibility to protease cleavage, leading to a short half-life and reduced efficacy in animal models. These limitations pose obstacles in developing effective treatments based on AMPs. Furthermore, the high manufacturing costs associated with AMPs could significantly hinder their widespread use. In this review, we aim to present experimental and theoretical insights into different AMPs, focusing specifically on antibacterial peptides (ABPs). Our goal is to offer a concise overview of peptide-based drug candidates, drawing from a wide array of literature and peer-reviewed studies. We also explore recent advancements in AMP development and discuss the challenges researchers face in moving these molecules towards clinical trials. Our main objective is to offer a comprehensive overview of current AMP and ABP research to guide the development of more precise and effective therapies for bacterial infections.

A Novel Beta-Defensin Isoform from Malabar Trevally, Carangoides malabaricus (Bloch & Schneider, 1801), an Arsenal Against Fish Bacterial Pathogens: Molecular Characterization, Recombinant Production, and Mechanism of Action

Antimicrobial peptides (AMPs), including beta-defensin from fish, are a crucial class of peptide medicines. The focus of the current study is the molecular and functional attributes of CmDef, a 63-amino acid beta-defensin AMP from Malabar trevally, Carangoides malabaricus. This peptide demonstrated typical characteristics of AMPs, including hydrophobicity, amphipathic nature, and +2.8 net charge. The CmDef was recombinantly expressed and the recombinant peptide, rCmDef displayed a strong antimicrobial activity against bacterial fish pathogens with an MIC of 8 µM for V. proteolyticus and 32 µM for A. hydrophila. The E. tarda and V. harveyi showed an inhibition of 94% and 54%, respectively, at 32 µM concentration. No activity was observed against V. fluvialis and V. alginolyticus. The rCmDef has a multimode of action that exerts an antibacterial effect by membrane depolarization followed by membrane permeabilization and ROS production. rCmDef also exhibited anti-cancer activities in silico without causing hemolysis. The peptide demonstrated stability under various conditions, including different pH levels, temperatures, salts, and metal ions (KCl and CaCl2), and remained stable in the presence of proteases such as trypsin and proteinase K at concentrations up to 0.2 µg/100 µl. The strong antibacterial efficacy and non-cytotoxic nature suggest that rCmDef is a single-edged sword that can contribute significantly to aquaculture disease management.

Dual Antifungal and Antiproliferative Activities of a Novel Protein Fraction from a Medicinally Important Herb Trillium govanianum Wall. ex. D. Don

Antimicrobial resistance of microorganisms and the unwanted side effects of chemoradiation therapy in cancer are major issues in healthcare. In recent times, protein-based drugs have emerged as promising candidates due to their high specificity, less side effects, etc. In this context, the rhizome of Trillium govanianum was first explored for biologically active proteins/peptides. For this, three protein fractions namely Aqueous protein fraction (APF), Hexane-Methanol-treated aqueous protein fraction (HMAPF), and Methanol-treated aqueous protein fraction (MAPF) were prepared and evaluated for antimicrobial and antiproliferative activities. In antifungal activity, HMAPF showed the lowest MIC90 values of 1.56 µg/ml against Candida parapsilosis and Candida glabrata and 3.12 µg/ml against Candida albicans and Candida auris. The antifungal activity was further confirmed by a chitinase assay, a growth kinetics and a proteinase inhibitory assay. Surprisingly, none of the three protein fractions exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus. Moreover, APF exhibited potent antiproliferative and antioxidant activities with IC50 values of 18 µg/ml and 227 µg /ml, respectively. For HMAPF, an IC50 value of 70 µg/ml against the MDA-MB-231 cell line was observed. The present results demonstrate that the protein fractions, particularly HMAPF and APF, might serve as potential sources of a dual antifungal and antiproliferative protein-based drug.

Antibacterial Efficacy and Mechanisms of Action of a Novel Beta-Defensin from Snakehead Murrel, Channa striata

Beta-defensins, identified from fishes, constitute a crucial category of antimicrobial peptides important in combating bacterial fish pathogens. The present investigation centers on the molecular and functional characterization of CsDef, a 63-amino acid beta-defensin antimicrobial peptide derived from snakehead murrel (Channa striata). The physicochemical attributes of CsDef align with the distinctive characteristics observed in AMPs. CsDef was recombinantly produced, and the recombinant peptide, rCsDef, exhibited notable antibacterial efficacy against bacterial fish pathogens with an MIC of 16 μM for V. proteolyticus. A. hydrophila exhibited 91% inhibition, E. tarda 92%, and V. harveyi 53% at 32 μM of rCsDef. The rCsDef exhibited a multifaceted mechanism of action against bacteria, i.e., through membrane depolarization, membrane permeabilization, and generation of ROS. The rCsDef was non-hemolytic to hRBCs and non-cytotoxic to normal mammalian cell line CHO-K1. However, it exhibited anticancer properties in MCF-7. rCsDef demonstrated notable stability with respect to pH, temperature, salt, metal ions, and proteases. These findings suggest it is a potential candidate molecule for prospective applications in aquaculture.

Antifungal activity of a trypsin inhibitor from Salvia hispanica L. (chia) seeds against fluconazole-resistant strains of Candida spp. and evaluation of its toxicity in vitro

The incidence of Candida species resistant to traditional antifungal drugs is increasing globally. This issue significantly impacts patients' lives and increases healthcare expenses, confirming the need to develop novel therapeutic strategies. Recently, a thermostable trypsin inhibitor named ShTI (11.558 kDa), which has antibacterial effects on Staphylococcus aureus, was isolated from Salvia hispanica L. (chia) seeds. This study aimed to assess the antifungal effect of ShTI against Candida species and its synergism with fluconazole and to evaluate its mode of action. Preliminary toxicological studies on mouse fibroblasts were also performed. ShTI exhibited antifungal effects against C. parapsilosis (ATCC® 22,019), C. krusei (ATCC® 6258), and six clinical fluconazole-resistant strains of C. albicans (2), C. parapsilosis (2), and C. tropicalis (2). The minimum inhibitory concentration (MIC) values were 4.1 µM (inhibiting 50% of the isolates) and 8.2 µM (inhibiting 100% of the isolates). Additionally, when combined with fluconazole, ShTI had a synergistic effect on C. albicans, altering the morphological structure of the yeast. The mode of action of ShTI against C. krusei (ATCC® 6258) and C. albicans involves cell membrane permeabilization, the overproduction of reactive oxygen species, the formation of pseudohyphae, pore formation, and consequently, cell death. In addition, ShTI (8.65 and 17.3 µM) had noncytotoxic and nongenotoxic effects on L929 mouse fibroblasts. These findings suggest that ShTI could be a promising antimicrobial candidate, but further research is necessary to advance its application as a novel antifungal agent.

Globospiramine Exhibits Inhibitory and Fungicidal Effects against Candida albicans via Apoptotic Mechanisms

Candidiasis is considered an emerging public health concern because of the occurrence of drug-resistant Candida strains and the lack of an available structurally diverse antifungal drug armamentarium. The indole alkaloid globospiramine from the anticandidal Philippine medicinal plant Voacanga globosa exhibits a variety of biological activities; however, its antifungal properties remain to be explored. In this study, we report the in vitro anticandidal activities of globospiramine against two clinically relevant Candida species (C. albicans and C. tropicalis) and the exploration of its possible target proteins using in silico methods. Thus, the colony-forming unit (CFU) viability assay revealed time- and concentration-dependent anticandidal effects of the alkaloid along with a decrease in the number of viable CFUs by almost 50% at 60 min after treatment. The results of the MIC and MFC assays indicated inhibitory and fungicidal effects of globospiramine against C. albicans (MIC = 8 µg/mL; MFC = 8 µg/mL) and potential fungistatic effects against C. tropicalis at lower concentrations (MIC = 4 µg/mL; MFC > 64 µg/mL). The FAM-FLICA poly-caspase assay showed metacaspase activation in C. albicans cells at concentrations of 16 and 8 µg/mL, which agreed well with the MIC and MFC values. Molecular docking and molecular dynamics simulation experiments suggested globospiramine to bind strongly with 1,3-β-glucan synthase and Als3 adhesin-enzymes indirectly involved in apoptosis-driven candidal inhibition.

Pore-forming peptide C14R exhibits potent antifungal activity against clinical isolates of Candida albicans and Candida auris

Introduction

Invasive candidiasis is a global public health problem as it poses a significant threat in hospital-settings. The aim of this study was to evaluate C14R, an analog derived from peptide BP100, as a potential antimicrobial peptide against the prevalent opportunistic yeast Candida albicans and the emergent multidrug-resistant yeast Candida auris.

Methods

Antifungal susceptibility testing of C14R against 99 C. albicans and 105 C. auris clinical isolates from Colombia, was determined by broth microdilution. Fluconazole was used as a control antifungal. The synergy between C14R and fluconazole was assessed in resistant isolates. Assays against fungal biofilm and growth curves were also carried out. Morphological alterations of yeast cell surface were evaluated by scanning electron microscopy. A permeability assay verified the pore-forming ability of C14R.

Results

C. albicans and C. auris isolates had a geometric mean MIC against C14R of 4.42 µg/ml and 5.34 µg/ml, respectively. Notably, none of the isolates of any species exhibited growth at the highest evaluated peptide concentration (200 µg/ml). Synergistic effects were observed when combining the peptide and fluconazole. C14R affects biofilm and growth of C. albicans and C. auris. Cell membrane disruptions were observed in both species after treatment with the peptide. It was confirmed that C14R form pores in C. albicans' membrane.

Discussion

C14R has a potent antifungal activity against a large set of clinical isolates of both C. albicans and C. auris, showing its capacity to disrupt Candida membranes. This antifungal activity remains consistent across isolates regardless of their clinical source. Furthermore, the absence of correlation between MICs to C14R and resistance to fluconazole indicates the peptide's potential effectiveness against fluconazole-resistant strains. Our results suggest the potential of C14R, a pore-forming peptide, as a treatment option for fungal infections, such as invasive candidiasis, including fluconazole and amphotericin B -resistant strains.

Exploring the Fluconazole-Resistance Modifying Activity and Potential Mechanism of Action of Fixed Oil from Caryocar coriaceum Wittm. (Caryocaraceae) against Candida Species

The fixed oil from the inner mesocarp of Caryocar coriaceum Wittm. is used in the Chapada do Araripe region of Brazil for the treatment of genitourinary candidiasis. This study aimed to evaluate the chemical composition, antifungal activity, reduction of fungal virulence, and the preliminary toxicity of the fixed oil from the inner mesocarp of C. coriaceum tested against three Candida yeasts. The oil was characterized by gas chromatography (GC-MS and GC-FID). Antifungal activity was assessed using the serial microdilution method. Additionally, the potential of the oil as an enhancer of fluconazole action was tested at sub-inhibitory concentrations (MIC/8). The mechanism of action of C. coriaceum fixed oil was determined by evaluating the inhibition of morphological transition in Candida spp. The chemical composition of the fixed oil of C. coriaceum comprised both unsaturated and saturated fatty acids. Oleic (61 %) and palmitic (33 %) acids were the major constituents. Regarding its anti-Candida activity, the oil inhibited the growth of C. albicans (IC50 : 371 μg/mL) and C. tropicalis (IC50 : 830 μg/mL). Furthermore, the oil reversed the antifungal resistance of C. albicans and C. tropicalis, restoring the susceptibility to fluconazole and reducing their IC50 from 12.33 μg/mL and 362 μg/mL to 0.22 μg/mL and 13.93 μg/mL, respectively. The fixed oil of C. coriaceum completely inhibited the morphological transition of C. albicans and C. tropicalis at a concentration of 512 μg/mL, but exhibited limited low antifungal potential against C. krusei. The observed antifungal activity may be attributed to the overproduction of reactive oxygen species. Additionally, the oil showed no toxic effect on the Drosophila melanogaster in vivo model. The fixed oil from the inner mesocarp of C. coriaceum emerge as a strong candidate for the development of new pharmaceutical formulations to treat infections caused by Candida spp.

Antifungal Activity of Cedrol from Cunninghamia lanceolate var. konishii against Phellinus noxius and Its Mechanism

Phellinus noxius is a highly destructive fungus that causes brown root disease in trees, leading to decay and death. In Taiwan, five prized woods-Taiwania cryptomerioides, Calocedrus macrolepis var. formosana, Cunninghamia lanceolata var. konishii, Chamaecyparis formosensis, and Chamaecyparis obtusa var. formosana-are known for their fragrance and durability. This study aims to explore the anti-brown-root-rot-fungus activity of Cunninghamia lanceolata var. konishii (CL) essential oil (CLOL) and its primary components, while also delving into their mechanisms of action and inhibition pathways. The essential oil (CLOL) from CL wood demonstrated significant efficacy against P. noxius, with an inhibitory concentration (IC50) of 37.5 µg/mL. Cedrol, the major component (78.48%) in CLOL, emerged as a potent antifungal agent, surpassing the reference drug triflumizole. Further assays with cedrol revealed a stronger anti-brown-root-disease activity (IC50 = 15.7 µg/mL) than triflumizole (IC50 = 32.1 µg/mL). Scanning electron microscopy showed deformation and rupture of fungal hyphae treated with CLOL and cedrol, indicating damage to the fungal cell membrane. Cedrol-induced oxidative stress in P. noxius was evidenced by increased reactive oxygen species (ROS) levels, leading to DNA fragmentation, mitochondrial membrane potential reduction, and fungal apoptosis through the mitochondrial pathway. Gel electrophoresis confirmed cedrol-induced DNA fragmentation, whereas TUNEL staining demonstrated increased apoptosis with rising cedrol concentrations. Moreover, protein expression analysis revealed cedrol-triggered release of cytochrome c, activation of caspase-9, and subsequent caspase-3 activation, initiating a caspase cascade reaction. This groundbreaking study establishes cedrol as the first compound to induce apoptosis in P. noxius while inhibiting its growth through oxidative stress, an increase in mitochondrial membrane permeability, and activation of the mitochondrial pathway. The findings offer compelling evidence for cedrol's potential as an effective antifungal agent against the destructive brown root disease caused by P. noxius.

The elucidation of the multimodal action of the investigational anti-Candida lipopeptide (AF4) lead from Bacillus subtilis

Background: Candida species are the main etiological agents for candidiasis, and Candida albicans are the most common infectious species. Candida species' growing resistance to conventional therapies necessitates more research into novel antifungal agents. Antifungal peptides isolated from microorganisms have potential applications as novel therapeutics. AF4 a Bacillus-derived lipopeptide demonstrating broad-spectrum antifungal activity has been investigated for its ability to cause cell death in Candida species via membrane damage and oxidative stress. Methods: Using biophysical techniques, the secondary structure of the AF4 lipopeptide was identified. Scanning electron microscopy and confocal microscopy with fluorescent dyes were performed to visualise the effect of the lipopeptide. The membrane disruption and permeabilization were assessed using the 1,6-diphenyl hexatriene (DPH) fluorescence assay and flow cytometric (FC) assessment of propidium iodide (PI) uptake, respectively. The reactive oxygen species levels were estimated using the FC assessment. The induction of apoptosis and DNA damage were studied using Annexin V-FITC/PI and DAPI. Results: Bacillus-derived antifungal variant AF4 was found to have structural features typical of lipopeptides. Microscopy imaging revealed that AF4 damages the surface of treated cells and results in membrane permeabilization, facilitating the uptake of the fluorescent dyes. A loss of membrane integrity was observed in cells treated with AF4 due to a decrease in DPH fluorescence and a dose-dependent increase in PI uptake. Cell damage was also determined from the log reduction of viable cells treated with AF4. AF4 treatment also caused elevated ROS levels, induced phosphatidylserine externalisation, late-stage apoptosis, and alterations to nuclear morphology revealed by DAPI fluorescence. Conclusion: Collectively, the mode of action studies revealed that AF4 acts primarily on the cell membrane of C. albicans and has the potential to act as an antifungal drug candidate.

Antibacterial activity of peptides and bio-safety evaluation: in vitro and in vivo studies against bacterial and fungal pathogens

BACKGROUND

Antimicrobial peptides are promising alternatives to antibiotics to treat bacterial and fungal infections, especially drug-resistant clinical pathogens.

METHODS

Antimicrobial peptides (AMPs) were synthesized and antimicrobial activity was assayed. The antibacterial mechanism, ATP production, ROS generation and molecular mechanism were determined. Biofilm inhibition assay was performed in planktonic bacterial cells and biofilm degradation assay was performed using mature biofilm. The synthesized AMP2 was subjected to in vitro and in vivo analysis to analyze the safety.

RESULTS

The synthesized peptides AMP1, AMP2, AMP3 and AMP4 exhibited antimicrobial activity against Gram-positive and Gram-negative bacteria. The MIC values ranged from 1.5 ± 0.25-12.5 ± 1.25 µM and the MFC values range from 2.25 ± 0.12-25 ± 1.25 µM. F. solani showed fewer MFC values than other fungal strains. Time kill assay was performed and the AMP2 killed about 70 % of Acinetobacter baumannii at 1 × MIC concentration within 10 min incubation and killed 97 % of bacteria at 1 × MBC concentration within 15 min. The antimicrobial peptide AMP2 was highly effective against planktonic A. baumannii and L. monocytogenes. The tested AMP2 showed less toxicity to cell lines and Zebrafish.

CONCLUSIONS

Antimicrobial peptides have potential antimicrobial properties against Gram-positive and Gram-negative bacteria. The in silico studies of these antimicrobial peptides are useful for eradicating drug-resistant bacteria.

Antifungal Efficacy of Antimicrobial Peptide Octominin II against Candida albicans

Most clinically isolated Candida albicans strains are drug-resistant, emphasizing the urgent need to discover alternative therapies. In this study, the previously characterized Octominin was modified into a shorter peptide with an 18 amino acid sequence (1GWLIRGAIHAGKAIHGLI18) and named Octominin II. The secondary structure of Octominin II is a random coil with a helical turn and a positive charge (+2.46) with a hydrophobic ratio of 0.46. Octominin II inhibited C. albicans, C. auris, and C. glabrata with minimum inhibitory and fungicidal concentrations against C. albicans of 80 and 120 µg/mL, respectively. Field emission scanning electron microscopy confirmed that Octominin II treatment caused ultra-structural changes in C. albicans cells. Furthermore, membrane permeability results for the fluorescent indicator propidium iodide revealed modifications in cell wall integrity in Octominin II-treated C. albicans. Octominin II treatment increases the production of reactive oxygen species (ROS) in C. albicans. Gene expression studies revealed that Octominin II suppresses virulence genes of C. albicans such as CDR1, TUP1, AGE3, GSC1, SAP2, and SAP9. In addition, a nucleic acid binding assay revealed that Octominin II degraded genomic DNA and total RNA in a concentration-dependent manner. Additionally, Octominin II inhibited and eradicated C. albicans biofilm formation. Octominin II showed relatively less cytotoxicity on raw 264.7 cells (0-200 µg/mL) and hemolysis activity on murine erythrocytes (6.25-100 µg/mL). In vivo studies confirmed that Octominin II reduced the pathogenicity of C. albicans. Overall, the data suggests that Octominin II inhibits C. albicans by employing different modes of action and can be a promising candidate for controlling multidrug-resistant Candida infections.

Caryocar coriaceum fruits as a potential alternative to combat fungal and bacterial infections: In vitro evaluation of methanolic extracts

Caryocar coriaceum, commonly known as 'pequi', is a medicinal species used traditionally for the herbal treatment of infectious and parasitic diseases in the Brazilian Northeast region. In this study, we investigated whether the fruits of C. coriaceum have bioactive chemical constituents against etiological agents of infectious diseases. The methanolic extract of the internal mesocarp of the fruits of C. coriaceum (MECC) was chemically analyzed and evaluated for its antimicrobial and drug-enhancing activity against multidrug-resistant pathogenic bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus), and Candida spp. strains. The extract had flavones, flavonols, xanthones, catechins, and flavanones as major classes. A total of 11.26 mg GAE/g of phenolics, and 5.98 mg QE/g of flavonoids were found. No intrinsic antibacterial activity was observed; however, the extract was able to intensify the action of gentamicin and erythromycin against multi-resistant strains. The anti-Candida effect observed in this study was mainly due to the formation of reactive oxygen species. The extract was capable of causing damage to the plasmatic membrane of Candida tropicalis through pores formation. Our findings partially support the ethnopharmacological uses of the fruit pulp of C. coriaceum against infectious and parasitic diseases.

Physicochemical and Anti-fungal Studies of the Pharmaceutical Co-crystal/Salt of Fluconazole

Crystal engineering is one green alternative to organic synthesis that can be used to manipulate molecular behavior promptly and economically. We report the preparation and characterization of the pharmaceutical organic salt (FLC-C) of fluconazole (FLC) and organosulfonate (NDSA-2H), based on the sulfonate-pyridinium supramolecular synthon. Structural studies validate the crystallization of the two-component stoichiometric crystal with two molecules of water in the triclinic P1̅ space group. The anticipated proton transfer between the crystal forms leads to ionic interactions, augmenting the organic salt's thermal stability. Hirshfeld studies of FLC-C help to understand the role and significance of different types of intermolecular interactions responsible for crystal packing. The structural and theoretical studies indicate the absence of π-π interactions in FLC-C, which account for the incipience of solid-state emission in the product. The solubility studies establish augmented aqueous solubility of FLC-C over pristine FLC at physiological pH values of 2 and 7. Interestingly, in in vitro studies, FLC-C appears to serve as a potential alternative to FLC, displaying a wide spectrum of antifungal activity. FLC-C is active against several human pathogenic yeast strains, including the leading and emerging Candida strains (Candida albicans and Candida auris, respectively), at comparable and/or lower drug concentrations without showing any enhanced host cell toxicity. Interestingly, the pharmaceutical co-crystal also displays fluorescence properties inside the Candida cells.

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.

Synthetic amino acids-based short amphipathic peptides exhibit antifungal activity by targeting cell membrane disruption

Availability of a limited number of antifungal drugs created a necessity to develop new antifungals with distinct mode of action. Investigation on a new series of peptides led us to identify Boc-His-Trp-His[1-(4-tert-butylphenyl)] (10g) as the most promising inhibitor exhibiting IC₅₀ value of 4.4 µg/mL against Cryptococcus neoformans. Analog 10g exhibit high selectivity to fungal cells and was nonhemolytic and noncytotoxic at its minimum inhibitory concentration. 10g produced fungicidal effect on growing cryptococcal cells and displayed synergistic effect with amphotericin B. Overall cationic character of 10g resulted in interaction with negatively charged fungal membrane while hydrophobicity enhanced penetration inside the cryptococcal cells causing hole(s) formation and disruption to the membrane as evident by the scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy analyses. Flow cytometric investigation revealed rapid death of fungal cells by apopotic pathway.

Giving a Hand: Synthetic Peptides Boost the Antifungal Activity of Itraconazole against Cryptococcus neoformans

Cryptococcus neoformans is a multidrug-resistant pathogen responsible for infections in immunocompromised patients. Here, itraconazole (ITR), a commercial antifungal drug with low effectiveness against C. neoformans, was combined with different synthetic antimicrobial peptides (SAMPs), Mo-CBP3-PepII, RcAlb-PepII, RcAlb-PepIII, PepGAT, and PepKAA. The Mo-CBP3-PepII was designed based on the sequence of MoCBP3, purified from Moringa oleifera seeds. RcAlb-PepII and RcAlb-PepIII were designed using Rc-2S-Alb, purified from Ricinus communis seed cakes. The putative sequence of a chitinase from Arabidopsis thaliana was used to design PepGAT and PepKAA. All SAMPs have a positive liquid charge and a hydrophobic potential ranging from 41-65%. The mechanisms of action responsible for the combined effect were evaluated for the best combinations using fluorescence microscopy (FM). The synthetic peptides enhanced the activity of ITR by 10-fold against C. neoformans. Our results demonstrated that the combinations could induce pore formation in the membrane and the overaccumulation of ROS on C. neoformans cells. Our findings indicate that our peptides successfully potentialize the activity of ITR against C. neoformans. Therefore, synthetic peptides are potential molecules to assist antifungal agents in treating Cryptococcal infections.

Anticryptococcal activity and mechanistic studies of short amphipathic peptides

Cryptococcus neoformans, an opportunistic fungal pathogen, causes cryptococcosis in immunocompromised persons. A series of modified L-histidines-containing peptides are synthesized that exhibit promising activity against C. neoformans. Analog 11d [L-His(2-adamantyl)-L-Trp-L-His(2-phenyl)-OMe] produced potency with an IC₅₀ of 3.02 µg/ml (MIC = 5.49 µg/ml). This peptide is noncytotoxic and nonhaemolytic at the MIC and displays synergistic effects with amphotericin B at subinhibitory concentration. Mechanistic investigation of 11d using microscopic tools indicates cell wall and membrane disruption of C. neoformans, while flow cytometric analysis confirms cell death by apoptosis. This study indicates that 11d exhibits antifungal potential and acts via the rapid onset of action.

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.

Mechanisms of Action of the Antimicrobial Peptide Cecropin in the Killing of Candida albicans

The development of drug resistance has caused fungal infections to become a global health concern. Antimicrobial peptides (AMPs) offer a viable solution to these pathogens due to their resistance to drug resistance and their diverse mechanisms of actions, which include direct killing and immunomodulatory properties. The peptide Cecropin, which is expressed by genetically engineered bacteria, has antifungal effects on Candida albicans. The minimal inhibitory concentration (MIC) and the minimal fungicidal concentration (MFC) of Candida albicans were 0.9 μg/mL and 1.8 μg/mL, respectively, detected by the micro-broth dilution method. According to the killing kinetics, the MFC of Cecropin could kill Candida albicans in 40 min. The electron microscope indicated that Cecropin could cause the cell wall to become rough and nicked, eventually killing Candida albicans. The effects of Cecropin on the cell membrane of treated C. albicans, using the 1,6-diphenyl-1,3,5-hexatriene and propidium iodide protocol, showed that they could change the permeability and fluidity, destroy it, and lead to cell necrosis. In addition, Cecropin can also induce cells to produce excessive reactive oxygen species, causing changes in the mitochondrial membrane potential. Therefore, this study provides a certain theoretical basis for the antifungal infection of new antifungal agents.

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.

In vitro and in vivo Activity of Phibilin Against Candida albicans

The increase in the occurrence of antifungal-resistant Candida albicans infections necessitates more research to explore alternative effective and safe agents against this fungus. In this work, Phibilin, a new antimicrobial peptide obtained from Philomycus bilineatus and used in traditional Chinese medicine, effectively inhibits the growth and activities of C. albicans, including the clinical resistant strains. Phibilin is a fungicidal antimicrobial peptide that exhibited its antimicrobial effect against C. albicans mainly by disrupting the membrane and interacting with the DNA of the fungi. In particular, Phibilin induces the necrosis of C. albicans via the ROS-related pathway. Moreover, this antifungal compound inhibited the biofilm formation of C. albicans by preventing the development of hyphae in a dose-dependent manner. Furthermore, Phibilin and clotrimazole displayed a synergistic effect in inhibiting the growth of the fungi. In the mouse cutaneous infection model, Phibilin significantly inhibited the formation of skin abscesses and decreased the counts of C. albicans cells in the infected area. Overall, Phibilin is potentially an effective agent against skin infections caused by C. albicans.

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.

How do terminal modifications of short designed IIKK peptide amphiphiles affect their antifungal activity and biocompatibility?

HYPOTHESIS

The widespread and prolonged use of antifungal antibiotics has led to the rapid emergence of multidrug resistant Candida species that compromise current treatments. Natural and synthetic antimicrobial peptides (AMPs) offer potential alternatives but require further development to overcome some of their current drawbacks. AMPs kill pathogenic fungi by permeabilising their membranes but it remains unclear how AMPs can be designed to maximise their antifungal potency whilst minimising their toxicity to host cells.

EXPERIMENTS

We have designed a group of short (IIKK)₃ AMPs via selective terminal modifications ending up with different amphiphilicities. Their antifungal performance was assessed by minimum inhibition concentration (MICs) and dynamic killing to 4 Candida strains and Cryptococcus neoformans, and the minimum biofilm-eradicating concentrations to kill 95% of the C. albicans biofilms (BEC₉₅). Different antifungal actions were interpreted on the basis of structural disruptions of the AMPs to small unilamellar vesicles from fluorescence leakage, Zeta potential, small angle neutron scattering (SANS) and molecular dynamics simulations (MD).

FINDING

AMPs possess high antifungal activities against the Candida species and Cryptococcus neoformans; some of them displayed faster dynamic killing than antibiotics like amphotericin B. G(IIKK)₃I-NH₂ and (IIKK)₃II-NH₂ were particularly potent against not only planktonic microbes but also fungal biofilms with low cytotoxicity to host cells. It was found that their high selectivity and fast action were well correlated to their fast membrane lysis, evident from data measured from Zeta potential measurements, SANS and MD, and also consistent with the previously observed antibacterial and anticancer performance. These studies demonstrate the important role of colloid and interface science in further developing short, potent and biocompatible AMPs towards clinical treatments via structure design and optimization.

Alternative Treatment Strategies for Secondary Bacterial and Fungal Infections Associated with COVID-19

Antimicrobials are essential for combating infectious diseases. However, an increase in resistance to them is a major cause of concern. The empirical use of drugs in managing COVID-19 and the associated secondary infections have further exacerbated the problem of antimicrobial resistance. Hence, the situation mandates exploring and developing efficient alternatives for the treatment of bacterial and fungal infections in patients suffering from COVID-19 or other viral infections. In this review, we have described the alternatives to conventional antimicrobials that have shown promising results and are at various stages of development. An acceleration of efforts to investigate their potential as therapeutics can provide more treatment options for clinical management of drug-resistant secondary bacterial and fungal infections in the current pandemic and similar potential outbreaks in the future. The alternatives include bacteriophages and their lytic enzymes, anti-fungal enzymes, antimicrobial peptides, nanoparticles and small molecule inhibitors among others. What is required at this stage is to critically examine the challenges in developing the listed compounds and biomolecules as therapeutics and to establish guidelines for their safe and effective application within a suitable time frame. In this review, we have attempted to highlight the importance of rational use of antimicrobials in patients suffering from COVID-19 and boost the deployment of alternative therapeutics.

Unusual Pseudopeptides: Syntheses and Structural Analyses of Ethylenediprolyl Peptides and Their Metal Complexes with Cu(II) Ion

The synthetic unnatural amino acids and their peptides as peptidomimetics have shown remarkable structural and functional properties. In the repertoire of synthetic peptides, pseudopeptides have emerged as attractive small peptidomimetics that are capable of forming the characteristic secondary structures in the solid/solution phase, as in natural peptides. This report describes the synthesis and structural analyses of novel pseudopeptides as ethylenediprolyl (etpro) tetra/hexapeptides, comprising a chiral diaminedicarboxylate scaffold. Their NMR and CD spectral analyses strongly support the formation of the β-turn-type structures in organic solvents (ACN/MeOH). Further, the single-crystal X-ray studies of tetrapseudopeptide confirm the formation of a unique self-assembly structure as β-strand type in the solid state through hydrogen bonding. Importantly, their diamine moiety influences the formation of Cu-complexes with Cu(II) ions. A tetrapseudopeptide monocarboxylate-Cu(II) complex forms the single crystal that is studied by the single-crystal X-ray diffractometer. The crystal structure of the tetrapseudopeptide-Cu(II) complex confirms the formation of the distorted square planar geometry structure, almost like the amyloid β(Aβ)-peptide-Cu(II) complex structural geometry. Hence, these etpro-pseudopeptides are emerging peptidomimatics that form β-turn types of structures and metal complexes mainly with Cu(II) ions. These molecules could be considered for the development of peptide-based catalysts and peptide-based therapeutic drug candidates.

Characterization, Biological Activity, and Mechanism of Action of a Plant-Based Novel Antifungal Peptide, Cc-AFP1, Isolated From Carum carvi

Due to the increasing rate of invasive fungal infections and emerging antifungal resistance, development of novel antifungal drugs has been an urgent necessity. Antifungal peptides (AFPs) have recently attracted attention due to their unique ability to evade drug-resistant fungal pathogens. In this study, a novel AFP, Cc-AFP1, with a molecular weight of ~3.759 kDa, was isolated from Carum carvi L., purified by ammonium sulfate precipitation and reversed-phase HPLC and finally identified by sequence analysis using Edman degradation. Peptide sequence analysis revealed a fragment of 36 amino acid residues as RVCFRPVAPYLGVGVSGAVRDQIGVKLGSVYKGPRG for Cc-AFP1 with a net charge of +5 and a hydrophobicity ratio of 38%. The antifungal activity of Cc-AFP1 was confirmed against Aspergillus species with MIC values in the range of 8–16 µg/ml. Cc-AFP1 had less than 5% hemolytic activity at 8–16 µg/ml on human red blood cells with no obvious cytotoxicity against the HEK293 cell line. Stability analysis showed that the activity of Cc-AFP1 was maintained at different temperatures (20°C to 80°C) and pH (8 to 10). The results of a propidium iodide uptake and transmission electron microscopy showed that the antifungal activity of Cc-AFP1 could be attributed to alteration in the fungal cell membrane permeability. Taken together, these results indicate that Cc-AFP1 may be an attractive molecule to develop as a novel antifungal agent combating fungal infections cause by Aspergillus species.

Antifungal Activity of Linear and Disulfide-Cyclized Ultrashort Cationic Lipopeptides Alone and in Combination with Fluconazole against Vulvovaginal Candida spp

Vulvovaginal candidiasis (VVC) occurs in over 75% of women at least once during their lifetime and is an infection that significantly affects their health. Candida strains resistant to standard azole antifungal therapy and relapses of VVC are more and more common. Hypothetically, biofilm is one of the main reasons of relapses and failure of the therapy. Ultrashort cationic lipopeptides (USCLs) exhibit high antimicrobial activities. Our previous study on USCLs revealed that disulfide cyclization can result in selective antifungal compounds. Therefore, four USCL were selected and their antifungal activity were studied on 62 clinical strains isolated from VVC. The results confirmed previous premises that cyclic analogs have increased selectivity between fungal cells and keratinocytes and improved anticandidal activity compared to their linear analogs against both planktonic and biofilm cultures. On the other hand, linear lipopeptides in combination with fluconazole showed a synergistic effect. It was found that the minimum inhibitory concentrations of the tested compounds in combination with fluconazole were at least four times lower than when used separately. Our results indicate that combination therapy of VVC with USCLs and fluconazole at low non-toxic concentrations can be beneficial owing to the synergistic effect. However, further in vivo studies are needed to confirm this hypothesis.

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.

Anticandidal Activity of Omiganan and Its Retro Analog Alone and in Combination with Fluconazole

Vulvovaginal candidiasis (VVC) is a vaginal infection that manifests itself as several symptoms which can lead to various life-threatening complications. The majority of VVC is caused by Candida albicans strains, and it is estimated that approximately 75% of women worldwide would suffer from this condition at least once during their lifetime. Surprisingly, the detailed pathomechanism of yeast-like fungi invasions in vagina is not yet fully understood. However, the ability to form biofilm on vaginal mucosa is considered as one of the critical factors associated with failure of the therapy and recurrences of the disease. Antimicrobial peptides (AMPs) are a promising class of compounds that are receiving a growing interest owing to their antibacterial, antifungal, and antibiofilm properties. Omiganan is a synthetic analog of Indolicidin that is characterized by wide spectrum of antimicrobial and antibiofilm activities. Recent reports suggest improved activity of analogs with a reversed sequence (retro-analog concept). Therefore, Omiganan and its retro analog were tested against planktonic forms and biofilm of 18 Candida strains isolated from VVC. Moreover, the synergy between the AMPs and fluconazole was studied as well. The AMPs appeared to be effective against C. albicans biofilm, and the reversion of the sequence generally led to an improved antimicrobial activity. Furthermore, confocal and scanning electron microscopic visualizations revealed the effectiveness of AMPs-fluconazole combinations also against fluconazole-resistant strains.

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.

In Vitro and In Vivo Anti-Candida Activity and Structural Analysis of Killer Peptide (KP)-Derivatives

The previously described decapeptide AKVTMTCSAS (killer peptide, KP), derived from the variable region of a recombinant yeast killer toxin-like anti-idiotypic antibody, proved to exert a variety of antimicrobial, antiviral, and immunomodulatory activities. It also showed a peculiar self-assembly ability, likely responsible for the therapeutic effect in animal models of systemic and mucosal candidiasis. The present study analyzed the biological and structural properties of peptides derived from KP by substitution or deletion of the first residue, leaving unchanged the remaining amino acids. The investigated peptides proved to exert differential in vitro and/or in vivo anti-Candida activity without showing toxic effects on mammalian cells. The change of the first residue in KP amino acidic sequence affected the conformation of the resulting peptides in solution, as assessed by circular dichroism spectroscopy. KP-derivatives, except one, were able to induce apoptosis in yeast cells, like KP itself. ROS production and changes in mitochondrial transmembrane potential were also observed. Confocal and transmission electron microscopy studies allowed to establish that selected peptides could penetrate within C. albicans cells and cause gross morphological alterations. Overall, the physical and chemical properties of the first residue were found to be important for peptide conformation, candidacidal activity and possible mechanism of action. Small antimicrobial peptides could be exploited for the development of a new generation of antifungal drugs, given their relative low cost and ease of production as well as the possibility of devising novel delivery systems.

Evaluation of the antifungal activity in vitro of midazolam against fluconazole-resistant Candida spp. isolates

Aim: The purpose of this study was to evaluate the antifungal activity of midazolam, alone and in association with azoles, against isolates of clinical Candida spp. in planktonic and biofilm form. Materials & methods: The antifungal activity was observed using the broth microdilution technique. Flow cytometry tests were performed to investigate the probable mechanism of action and the comet test and cytotoxicity test were applied to evaluate DNA damage. Results: Midazolam (MIDAZ) showed antifungal activity against planktonic cells (125-250 μg/ml) and reduced the viability of Candida spp. biofilms (125 a 2500 μg/ml). The interaction of MIDAZ against Candida spp. biofilms was observed through scanning electron microscopy, causing alteration of their appearance. Therefore, MIDAZ has antifungal potential against Candida spp.

Antifungal activity of MAF-1A peptide against Candida albicans

Invasive candidiasis is a major threat to human health, and Candida albicans is the most common pathogenic species responsible for this condition. The incidence of drug-resistant strains of C. albicans is rising, necessitating the development of new antifungal drugs. Antimicrobial peptides (AMPs) have recently attracted attention due to their unique ability to evade the drug resistance of microorganisms. However, the mechanism of their activity has not yet been identified. The current study analyzed the mode of action of MAF-1A by confocal microscopy, scanning electron microscopy, fluorescent staining, flow cytometry, and qRT-PCR. The results indicate that MAF-1A disrupts the cell membrane of C. albicans and enters the cell where it binds and interacts with nucleic acids. qRT-PCR demonstrated that the expression of several sterol biosynthesis–related genes in C. albicans was increased after MAF-1A treatment. Together, these findings suggest that MAF-1A exerts antifungal action by affecting both the cell membrane and intracellular components. The antifungal mechanism of MAF-1A is unique, and its identification has great research and clinical significance.

Isolation of Antimicrobial Genes from Oryza rufipogon Griff by Using a Bacillus subtilis Expression System with Potential Antimicrobial Activities

Antimicrobial genes are distributed in all forms of life and provide a primary defensive shield due to their unique broad-spectrum resistance activities. To better isolate these genes, we used the Bacillus subtilis expression system as the host cells to build Oryza rufipogon Griff cDNA libraries and screen potential candidate genes from the library at higher flux using built-in indicator bacteria. We observed that the antimicrobial peptides OrR214 and OrR935 have strong antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria, as well as several fungal pathogens. Owing to their high thermal and enzymatic stabilities, these two peptides can also be used as field biocontrol agents. Furthermore, we also found that the peptide OrR214 (MIC 7.7-10.7 μM) can strongly inhibit bacterial growth compared to polymyxin B (MIC 5-25 μM) and OrR935 (MIC 33-44 μM). The cell flow analysis, reactive oxygen burst, and electron microscopy (scanning and transmission electron microscopy) observations showed that the cell membranes were targeted by peptides OrR214 and OrR935, which revealed the mode of action of bacteriostasis. Moreover, the hemolytic activity, toxicity, and salt sensitivity experiments demonstrated that these two peptides might have the potential to be used for clinical applications. Overall, OrR214 and OrR935 antimicrobial peptides have a high-throughput bacteriostatic activity that acts as a new form of antimicrobial agent and can be used as a raw material in the field of drug development.

Machaerium acutifolium lectin alters membrane structure and induces ROS production in Candida parapsilosis

Lectins are a group of widely distributed and structurally heterogeneous proteins of nonimmune origin. These proteins have the ability to interact with glycans present on cell surfaces and elicit diverse biological activities. Machaerium acutifolium lectin (MaL) is an N-acetyl-D-glucosamine-binding lectin that exhibits antinociceptive activity via transient receptor potential cation channel subfamily V member 1 (TRPV1). Lectins that have the ability to recognize and interact with N-acetyl-D-glucosamine residues are potential candidates for studies of fungicidal activity. In this work, we show that MaL has antifungal activity against Candida species, and we describe its mode of action towards Candida parapsilosis. MaL inhibited the growth of C. albicans and C. parapsilosis. However, MaL was more potent against C. parapsilosis. The candidacidal mode of action of MaL on C. parapsilosis involves enhanced cell permeabilization, alteration of the plasma membrane proton-pumping ATPase function (H+-ATPase), induction of oxidative stress, and DNA damage. MaL also exhibited antibiofilm activity and noncytotoxicity to Vero cells. These results indicate that MaL is a promising candidate for the future development of a new, natural, and safe drug for the treatment of infections caused by C. parapsilosis.

A synthetic coumarin derivative (4-flourophenylacetamide-acetyl coumarin) impedes cell cycle at G0/G1 stage, induces apoptosis, and inhibits metastasis via ROS-mediated p53 and AKT signaling pathways in A549 cells

New chemotherapeutic agents with minimum side effects are indispensable to treat non-small-cell lung cancer (NSCLC) since the mortality rate of patients suffering from NSCLC remains high despite receiving conventional medication. In our previous study, many coumarin derivatives were screened for their anticancer properties in A549, an in vitro NSCLC model. One of these, 4-flourophenylacetamide-acetyl coumarin (4-FPAC), induced cytotoxicity at a concentration as low as 0.16 nM. Herein, initially, the cytotoxic potential of 4-FPAC was tested on a noncancerous cell line NIH3T3 and was found safe at the selected dose of 0.16 nM. Further, we investigated the mechanism by which 4-FPAC induced cytotoxicity and arrested the progression of cell cycle as well as metastasis in A549. Results of ethidium bromide/acridine orange (EtBr/AO), 4,6-diamidino-2-phenylindole, comet, and lactate dehydrogenase assays revealed that 4-FPAC caused cytotoxicity via reactive oxygen species-induced p53-mediated mechanism, which involves both extrinsic and intrinsic pathways of apoptosis. Dichlorodihydrofluorescein diacetate, rhodamine 123, and AO staining confirmed the involvement of both mitochondria and lysosome in inducing apoptosis. However, flow cytometric analysis revealed that it causes cell cycle arrest at the G0/G1 phase by modulating p21, CDK2, and CDK4 expression. Aggregation, soft-agar, clonogenic, and scratch assays as well as gene expression analysis collectively confirmed that 4-FPAC minimizes the metastatic property of A549 by downregulating Snail, matrix metalloproteinase 9, and interleukin-8. Additional studies reaffirmed the above findings and substantiated the role of PI3K/AKT in achieving them. The cell-type-specific selective cytostatic and antimetastatic properties shown by 4-FPAC indicate its potential to emerge as a drug of choice against NSCLC in the future.