Direct cell penetration of the antifungal peptide, MMGP1, in Candida albicans

Marine-Derived Metabolites Act as Promising Antifungal Agents

The incidence of invasive fungal diseases (IFDs) is on the rise globally, particularly among immunocompromised patients, leading to significant morbidity and mortality. Current clinical antifungal agents, such as polyenes, azoles, and echinocandins, face increasing resistance from pathogenic fungi. Therefore, there is a pressing need for the development of novel antifungal drugs. Marine-derived secondary metabolites represent valuable resources that are characterized by varied chemical structures and pharmacological activities. While numerous compounds exhibiting promising antifungal activity have been identified, a comprehensive review elucidating their specific underlying mechanisms remains lacking. In this review, we have compiled a summary of antifungal compounds derived from marine organisms, highlighting their diverse mechanisms of action targeting various fungal cellular components, including the cell wall, cell membrane, mitochondria, chromosomes, drug efflux pumps, and several biological processes, including vesicular trafficking and the growth of hyphae and biofilms. This review is helpful for the subsequent development of antifungal drugs due to its summary of the antifungal mechanisms of secondary metabolites from marine organisms.

Clinical Applications and Anticancer Effects of Antimicrobial Peptides: From Bench to Bedside

Cancer is a multifaceted global health issue and one of the leading causes of death worldwide. In recent years, medical science has achieved great advances in the diagnosis and treatment of cancer. Despite the numerous advantages of conventional cancer therapies, there are major drawbacks including severe side effects, toxicities, and drug resistance. Therefore, the urgency of developing new drugs with low cytotoxicity and treatment resistance is increasing. Antimicrobial peptides (AMPs) have attracted attention as a novel therapeutic strategy for the treatment of various cancers, targeting tumor cells with less toxicity to normal tissues. In this review, we present the structure, biological function, and underlying mechanisms of AMPs. The recent experimental studies and clinical trials on anticancer peptides in different cancer types as well as the challenges of their clinical application have also been discussed.

Internalization and membrane activity of the antimicrobial peptide CGA-N12

Antimicrobial peptides (AMPs) are conventional antibiotic alternatives due to their broad-spectrum antimicrobial activities and special mechanisms of action against pathogens. The antifungal peptide CGA-N12 was originally derived from human chromogranin A (CGA) and consists of the 65th to 76th amino acids of the CGA N-terminal region. In the present study, we found that CGA-N12 had fungicidal activity and exhibited time-dependent inhibition activity against Candida tropicalis. CGA-N12 entered the cells to exert its antagonist activity. The internalization of CGA-N12 was energy-dependent and accompanied by actin cytoskeleton-, clathrin-, sulfate proteoglycan-, endosome-, and lipid-depleting agent-mediated endocytosis. Moreover, the CGA-N12 internalization pathway was related to the peptide concentration. The effects of CGA-N12 on the cell membrane were investigated. CGA-N12 at a low concentration less than 4 × MIC100 did not destroy the cell membrane. While with increasing concentration, the damage to the cell membrane caused by CGA-N12 became more serious. At concentrations greater than 4 × MIC100, CGA-N12 destroyed the cell membrane integrity. Therefore, the membrane activity of CGA-N12 is concentration dependant.

CGA-N9, an antimicrobial peptide derived from chromogranin A: direct cell penetration of and endocytosis by Candida tropicalis

CGA-N9 is a peptide derived from the N-terminus of human chromogranin A comprising amino acids 47–55. Minimum inhibitory concentration (MIC) assays showed that CGA-N9 had antimicrobial activity and exhibited time-dependent inhibition activity against Candida tropicalis, with high safety in human red blood cells (HRBCs) and mouse brain microvascular endothelial cells (bEnd.3). According to the results of transmission electron microscopy (TEM), flow cytometry and confocal microscopy, CGA-N9 accumulated in cells without destroying the integrity of the cell membrane; the peptide was initially localized to the cell membrane and subsequently internalized into the cytosol. An investigation of the cellular internalization mechanism revealed that most CGA-N9 molecules entered the yeast cells, even at 4°C and in the presence of sodium azide (NaN₃), both of which block all energy-dependent transport mechanisms. In addition, peptide internalization was affected by the endocytic inhibitors 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), cytochalasin D (CyD) and heparin; chlorpromazine (CPZ) also had some effect on CGA-N9 internalization. Similar results were obtained in the MIC assays, whereby the anticandidal activity of CGA-N9 was blocked to different degrees in the presence of EIPA, CyD, heparin or CPZ. Therefore, most CGA-N9 passes through the C. tropicalis cell membrane via direct cell penetration, whereas the remainder enters through macropinocytosis and sulfate proteoglycan-mediated endocytosis, with a slight contribution from clathrin-mediated endocytosis.

Peptide based antimicrobials: Design strategies and therapeutic potential

Therapeutic activity of antibiotics is noteworthy, as they are used in the treatment of microbial infections. Regardless of their utility, there has been a steep decrease in the number of drug candidates due to antibiotic resistance, an inevitable consequence of noncompliance with the full therapeutic regimen. A variety of resistant species like MDR (Multi-Drug Resistant), XDR (Extensively Drug-Resistant) and PDR (Pan Drug-Resistant) species have evolved, but discovery pipeline has already shown signs of getting dried up. Therefore, the need for newer antibiotics is of utmost priority to combat the microbial infections of future times. Peptides have some interesting features like minimal side effect, high tolerability and selectivity towards specific targets, which would help them successfully comply with the stringent safety standards set for clinical trials. In this review, we attempt to present the state of the art in the discovery of peptide-based antimicrobials from a design perspective.

Stereochemistry as a determining factor for the effect of a cell-penetrating peptide on cellular viability and epithelial integrity

Cell-penetrating peptides (CPPs) comprise efficient peptide-based delivery vectors. Owing to the inherent poor enzymatic stability of peptides, CPPs displaying partial or full replacement of l-amino acids with the corresponding d-amino acids might possess advantages as delivery vectors. Thus, the present study aims to elucidate the membrane- and metabolism-associated effects of l-Penetratin (l-PEN) and its corresponding all-d analog (d-PEN). These effects were investigated when exerted on hepatocellular (HepG2) or intestinal (Caco-2 and IEC-6) cell culture models. The head-to-head comparison of these enantiomeric CPPs included evaluation of their effects on cell viability and morphology, epithelial membrane integrity, and cellular ultrastructure. In all investigated cell models, a rapid decrease in cell viability, pronounced membrane perturbation and an altered ultrastructure were detected upon exposure to d-PEN. At equimolar concentrations, these observations were less pronounced or even absent for cells exposed to l-PEN. Both CPPs remained stable for at least 2 h during exposure to proliferating cells (cultured for 24 h), although d-PEN exhibited a longer half-life when compared with that of l-PEN when exposed to well-differentiated cell monolayers (cultured for 18-20 days). Thus, the stereochemistry of the CPP penetratin significantly influences its effects on cell viability and epithelial integrity when profiled against a panel of mammalian cells.

Chiloscyphenol A derived from Chinese liverworts exerts fungicidal action by eliciting both mitochondrial dysfunction and plasma membrane destruction

This study aimed to characterize the antifungal effects of chiloscyphenol A (CA), a natural small molecule isolated from Chinese liverworts, and investigate its mode of action. CA was effective against five tested Candida species with a minimal inhibitory concentration (MIC) of 8-32 μg/ml and exhibited fungicidal activity against Candida albicans in both the planktonic state and mature biofilms. The in vivo study using Caenorhabditis elegans showed that CA prolonged the survival of C. albicans infected worms. Further investigations revealed that CA resulted in mitochondrial dysfunction as indicated by mtΔψ hyperpolarization, increased ATP production and intracellular ROS accumulation, and aggregated distribution of Tom70. In addition, CA caused perturbation of the cell membrane and increased membrane permeability, as demonstrated by specific staining and confocal microscopic and transmission electron microscopy (TEM) observations and by calcein-leakage measurements. This conclusion was further confirmed by the decreased cell size of CA-treated cells via three-dimensional contour-plot analysis using flow cytometry. Taken together, these results suggest that CA exerts fungicidal activity by eliciting both mitochondrial dysfunction and plasma membrane destruction in C. albicans. The elucidated mechanism supports the potential application of CA against clinical fungal infections.

Protective effect of a novel antifungal peptide derived from human chromogranin a on the immunity of mice infected with Candida krusei

Invasive fungal infections threat the life of immunocompromised patients. Chromogranin A N-46 (CGA-N46), corresponding to the 31st to 76th amino acids of the N-terminus of human chromogranin A, is an antifungal peptide. In order to elucidate the antifungal effects of CGA-N46 in vivo, we studied its effects on cell-mediated immunity in Candida krusei-infected mice. The results showed that the treatment with CGA-N46 increased the average body weight and decreased the mortality of the immunocompromised mice model infected with Candida krusei. The spleen and thymus indices of treated mice has markedly increased compared with that of the control group (P<0.05), and the immune cell levels in peripheral blood also increased significantly (P<0.05). The immuno-modulatory effect of CGA-N46 (60 mg/kg/day) was found to be comparable to that of terbinafine. Additionally, CGA-N46 could alleviate or eliminate histopathological symptoms in the liver, spleen, kidney, and lung tissues. In conclusion, the present study suggests that CGA-N46 may offer a new strategy for antifungal therapeutic option. This study is an essential step in elucidating the effect of CGA-N46 in vivo.

Critical Evaluation and Compilation of Physicochemical Determinants and Membrane Interactions of MMGP1 Antifungal Peptide

A growing issue of pathogen resistance to antibiotics has fostered the development of innovative approaches for novel drug development. Here, we report the physicochemical and biological properties of an antifungal peptide, MMGP1, based on computational analysis. Computation of physicochemical properties has revealed that the natural biological activities of MMGP1 are coordinated by its intrinsic properties such as net positive charge (+5.04), amphipathicity, high hydrophobicity, low hydrophobic moment, and higher isoelectric point (11.915). Prediction of aggregation hot spots in MMGP1 had revealed the presence of potentially aggregation-prone segments that can nucleate in vivo aggregation (on the membrane), whereas no aggregating regions were predicted for in vitro aggregation (in solutions) of MMGP1. This ability of MMGP1 to form oligomeric aggregates on membrane further substantiates its direct-cell penetrating potency. Monte Carlo simulation of the interactions of MMGP1 in the aqueous phase and different membrane environments revealed that increasing the proportion of acidic lipids on membrane had led to increase in the peptide helicity. Furthermore, the peptide adopts energetically favorable transmembrane configuration, by inserting peptide loop and helix termini into the membrane containing >60% of anionic lipids. The charged lipid-based insertion of MMGP1 into membrane might be responsible for the selectivity of peptide toward fungal cells. Additionally, MMGP1 possessed DNA-binding property. Computational docking has identified DNA-binding residues (TRP3, SER4, MET7, ARG8, PHE10, ALA11, GLY20, THR21, ARG22, MET23, TRP34, and LYS36) in MMGP1 crucial for its DNA-binding property. Furthermore, computational mutation analysis revealed that aromatic amino acids are crucial for in vivo aggregation, membrane insertion, and DNA-binding property of MMGP1. These data provide new insight into the molecular determinants of MMGP1 antifungal activity and also serves as the template for the design of novel peptide antibiotics.

Antiproliferative effect and characterization of a novel antifungal peptide derived from human Chromogranin A

CGA-N46 is a novel antifungal peptide derived from the N-terminus of human Chromogranin A, corresponding to the 31st to 76th amino acids. Further research on its activities and characteristics may be helpful for the application of CGA-N46 in medical or other situations. In the present study, the antifungal spectrum and physicochemical characteristics of CGA-N46 were investigated using an antifungal assay, its antiproliferative effects on cancer and normal cells were assessed using MTT assay and its combinatorial effect with other antibiotics was analyzed using checkerboard analysis. The results showed that CGA-N46 exhibited antifungal activity against the tested Candidas (C. glabrata, C. parapsilosis, C. krusei, C. tropicalis and C. albicans) at a concentration of <0.8 mM, but had no effect on the growth of filamentous fungi or other types of fungi (Cryptococcus neoformans, Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger, Fusarium moniliforme, Microsporum canis, Microsporum gypseum, Trichophyton rubrum and Trichophyton mentagrophytes), even at a concentration of 3.2 mM. CGA-N46 had an inhibitory effect on the proliferation of lung cancer A549 cells and a reversible effect on the growth of normal primary chicken embryo fibroblast cells, but no hemolytic activity on human erythrocytes at the minimum inhibitory concentration of CGA-N46 against yeasts. The antifungal activity of CGA-N46 was stable at a temperature <40°C or within a broad pH range (pH 5.0-7.0). Its antifungal activity was enhanced when the peptide was used in combination with fluconazole and terbinafine. The present results indicate that CGA-N46 is a safe, physicochemically stable, antifungal peptide with anticancer cell activity that exhibits an additive effect with conventional antibiotics.

Anti-candidal activity of a novel peptide derived from human chromogranin A and its mechanism of action against Candida krusei

Candida species (Candida spp.) are important fungal pathogens, which cause numerous clinical diseases associated with significant mortality and morbidity in healthcare settings. In our previous study, we identified a recombinant peptide, chromogranin A (CGA)-N46, corresponding to the N-terminal Pro31-Gln76 sequence of human CGA, that exhibited antifungal activity against Candida albicans. The present study investigated the antifungal activity of CGA-N46, and its underlying mechanism, against numerous Candida spp. CGA-N46 inhibited the growth of all of the tested Candida spp., of which Candida krusei exhibited the greatest sensitivity. CGA-N46 was able to disrupt the stability of the phospholipid monolayer without damaging the integrity and permeability of the outer membrane of C. krusei cells, and induced cytoplasm vacuolization and mitochondrial damage. In addition, treatment of C. krusei with CGA-N46 was associated with decreased levels of intracellular reactive oxygen species, a reduction in the mitochondrial membrane potential, and DNA synthesis inhibition. The results of the present study suggested that CGA-N46 was able to pass through the cell membrane of Candida spp. by temporarily destabilizing the phospholipid membrane, which in turn led to mitochondrial dysfunction and inhibition of DNA synthesis. Therefore, CGA-N46 may be considered a novel antifungal compound for the treatment of patients with C. krusei infections.

Cm-p5: an antifungal hydrophilic peptide derived from the coastal mollusk Cenchritis muricatus (Gastropoda: Littorinidae)

Antimicrobial peptides form part of the first line of defense against pathogens for many organisms. Current treatments for fungal infections are limited by drug toxicity and pathogen resistance. Cm-p5 (SRSELIVHQRLF), a peptide derived from the marine mollusk Cenchritis muricatus peptide Cm-p1, has a significantly increased fungistatic activity against pathogenic Candida albicans (minimal inhibitory concentration, 10 µg/ml; EC50, 1.146 µg/ml) while exhibiting low toxic effects against a cultured mammalian cell line. Cm-p5 as characterized by circular dichroism and nuclear magnetic resonance revealed an α-helical structure in membrane-mimetic conditions and a tendency to random coil folding in aqueous solutions. Additional studies modeling Cm-p5 binding to a phosphatidylserine bilayer in silico and isothermal titration calorimetry using lipid monophases demonstrated that Cm-p5 has a high affinity for the phospholipids of fungal membranes (phosphatidylserine and phosphatidylethanolamine), only moderate interactions with a mammalian membrane phospholipid, low interaction with ergosterol, and no interaction with chitin. Adhesion of Cm-p5 to living C. albicans cells was confirmed by fluorescence microscopy with FITC-labeled peptide. In a systemic candidiasis model in mice, intraperitoneal administration of Cm-p5 was unable to control the fungal kidney burden, although its low amphiphaticity could be modified to generate new derivatives with improved fungicidal activity and stability.

Cellular Uptake and Cytotoxicity of β-Lactoglobulin Nanoparticles: The Effects of Particle Size and Surface Charge

It is necessary to understand the cellular uptake and cytotoxicity of food-grade delivery systems, such as β-lactoglobulin (β-lg) nanoparticles, for the application of bioactive compounds to functional foods. The objectives of this study were to investigate the relationships between the physicochemical properties of β-lg nanoparticles, such as particle size and zeta-potential value, and their cellular uptakes and cytotoxicity in Caco-2 cells. Physicochemical properties of β-lg nanoparticles were evaluated using particle size analyzer. Flow cytometry and confocal laser scanning microscopy were used to investigate cellular uptake and cytotoxicity of β-lg nanoparticles. The β-lg nanoparticles with various particle sizes (98 to 192 nm) and zeta-potential values (−14.8 to −17.6 mV) were successfully formed. A decrease in heating temperature from 70°C to 60°C resulted in a decrease in the particle size and an increase in the zeta-potential value of β-lg nanoparticles. Non-cytotoxicity was observed in Caco-2 cells treated with β-lg nanoparticles. There was an increase in cellular uptake of β-lg nanoparticles with a decrease in particle size and an increase in zeta-potential value. Cellular uptake β-lg nanoparticles was negatively correlated with particle size and positively correlated with zeta-potential value. Therefore, these results suggest that the particle size and zeta-potential value of β-lg nanoparticles play an important role in the cellular uptake. The β-lg nanoparticles can be used as a delivery system in foods due to its high cellular uptake and non-cytotoxicity.

Biomedical potential of natural products derived through metagenomic approaches

Microbes are ubiquitous, irrespective of the environment they thrive in. Only 1% of these are culturable in laboratory. Metagenomics is useful in exploring biomedically important small molecules using culture independent approaches.

Mechanisms of the antifungal action of marine metagenome-derived peptide, MMGP1, against Candida albicans

BACKGROUND

Development of resistant variants to existing antifungal drugs continues to be the serious problem in Candida albicans-induced fungal pathogenesis, which has a considerable impact on animal and human health. Identification and characterization of newer drugs against C. albicans is, therefore, essential. MMGP1 is a direct cell-penetrating peptide recently identified from marine metagenome, which was found to possess potent antifungal activity against C. albicans.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we investigated the mechanism of antifungal action of MMGP1 against C. albicans. Agarose gel shift assay found the peptide to be having a remarkable DNA-binding ability. The modification of the absorption spectra and fluorescence quenching of the tryptophyl residue correspond to the stacking between indole ring and nucleotide bases. The formation of peptide-DNA complexes was confirmed by fluorescence quenching of SYTO 9 probe. The interaction of peptide with plasmid DNA afforded protection of DNA from enzymatic degradation by DNase I. In vitro transcription of mouse β-actin gene in the presence of peptide led to a decrease in the level of mRNA synthesis. The C. albicans treated with MMGP1 showed strong inhibition of biosynthetic incorporation of uridine analog 5-ethynyluridine (EU) into nascent RNA, suggesting the peptide's role in the inhibition of macromolecular synthesis. Furthermore, the peptide also induces endogenous accumulation of reactive oxygen species (ROS) in C. albicans. MMGP1 supplemented with glutathione showed an increased viability of C. albicans cells. The hyper-produced ROS by MMGP1 leads to increased levels of protein carbonyls and thiobarbituric acid reactive substances and it also causes dissipation of mitochondrial membrane potential and DNA fragmentation in C. albicans cells.

CONCLUSION

And Significance: Therefore, the antifungal activity of MMGP1 could be attributed to its binding with DNA, causing inhibition of transcription followed by endogenous production of ROS, which triggers cascade of events that leads to cell death.

Antimicrobial peptides: versatile biological properties

Antimicrobial peptides are diverse group of biologically active molecules with multidimensional properties. In recent past, a wide variety of AMPs with diverse structures have been reported from different sources such as plants, animals, mammals, and microorganisms. The presence of unusual amino acids and structural motifs in AMPs confers unique structural properties to the peptide that attribute for their specific mode of action. The ability of these active AMPs to act as multifunctional effector molecules such as signalling molecule, immune modulators, mitogen, antitumor, and contraceptive agent makes it an interesting candidate to study every aspect of their structural and biological properties for prophylactic and therapeutic applications. In addition, easy cloning and recombinant expression of AMPs in heterologous plant host systems provided a pipeline for production of disease resistant transgenic plants. Besides these properties, AMPs were also used as drug delivery vectors to deliver cell impermeable drugs to cell interior. The present review focuses on the diversity and broad spectrum antimicrobial activity of AMPs along with its multidimensional properties that could be exploited for the application of these bioactive peptides as a potential and promising drug candidate in pharmaceutical industries.