Role of calcium in reactive oxygen species-induced apoptosis in Candida albicans: an antifungal mechanism of antimicrobial peptide, PMAP-23

Nerol as a Novel Antifungal Agent: In Vitro Inhibitory Effects on Fusarium oxysporum, Pestalotiopsis neglecta, and Valsa mali and Its Potential Mechanisms against F. oxysporum

This study explores the in vitro antifungal effects of nerol, a linear acyclic monoterpene alcohol of plant origin, on Fusarium oxysporum, Pestalotiopsis neglecta, and Valsa mali. To further investigate the antifungal mechanism of nerol against F. oxysporum, we examined changes in mycelial morphology and cell membrane integrity-related indices, as well as the activities of antioxidant and pathogenicity-related enzymes. The results demonstrated that nerol exhibited significant concentration-dependent inhibition of mycelial growth in all three fungi, with EC50 values of 0.46 μL/mL for F. oxysporum, 1.81 μL/mL for P. neglecta, and 1.26 μL/mL for V. mali, with the strongest antifungal activity observed against F. oxysporum. Scanning electron microscopy revealed that nerol severely disrupted the mycelial structure of F. oxysporum, causing deformation, swelling, and even rupture. Treatment with 0.04 μL/mL nerol led to significant leakage of soluble proteins and intracellular ions in F. oxysporum, and the Na+/K+-ATPase activity was reduced to 28.02% of the control, indicating enhanced membrane permeability. The elevated levels of hydrogen peroxide and malondialdehyde, along with propidium iodide staining of treated microconidia, further confirmed cell membrane disruption caused by nerol. Additionally, after 12 h of exposure to 0.04 μL/mL nerol, the activity of superoxide dismutase in F. oxysporum decreased to 55.81% of the control, and the activities of catalase and peroxidase were also significantly inhibited. Nerol markedly reduced the activities of pathogenicity-related enzymes, such as endo-1,4-β-D-glucanase, polygalacturonase, and pectin lyase, affecting fungal growth and virulence. In conclusion, nerol disrupts the cell membrane integrity and permeability of F. oxysporum, reduces its virulence, and ultimately inhibits fungal growth, highlighting its potential as an alternative to chemical fungicides for controlling F. oxysporum.

Antifungal Synergy: Mechanistic Insights into the R-1-R Peptide and Bidens pilosa Extract as Potent Therapeutics against Candida spp. through Proteomics

Previous reports have demonstrated that the peptide derived from LfcinB, R-1-R, exhibits anti-Candida activity, which is enhanced when combined with an extract from the Bidens pilosa plant. However, the mechanism of action remains unexplored. In this research, a proteomic study was carried out, followed by a bioinformatic analysis and biological assays in both the SC5314 strain and a fluconazole-resistant isolate of Candida albicans after incubation with R-1-R. The proteomic data revealed that treatment with R-1-R led to the up-regulation of most differentially expressed proteins compared to the controls in both strains. These proteins are primarily involved in membrane and cell wall biosynthesis, membrane transport, oxidative stress response, the mitochondrial respiratory chain, and DNA damage response. Additionally, proteomic analysis of the C. albicans parental strain SC5314 treated with R-1-R combined with an ethanolic extract of B. pilosa was performed. The differentially expressed proteins following this combined treatment were involved in similar functional processes as those treated with the R-1-R peptide alone but were mostly down-regulated (data are available through ProteomeXchange with identifier PXD053558). Biological assays validated the proteomic results, evidencing cell surface damage, reactive oxygen species generation, and decreased mitochondrial membrane potential. These findings provide insights into the complex antifungal mechanisms of the R-1-R peptide and its combination with the B. pilosa extract, potentially informing future studies on natural product derivatives.

Antifungal Activity and Mechanisms of 2-Ethylhexanol, a Volatile Organic Compound Produced by Stenotrophomonas sp. NAU1697, against Fusarium oxysporum f. sp. cucumerinum

Researchers often consider microorganisms from Stenotrophomonas sp. to be beneficial for plants. In this study, the biocidal effects and action mechanisms of volatile organic compounds (VOCs) produced by Stenotrophomonas sp. NAU1697 were investigated. The mycelial growth and spore germination of Fusarium oxysporum f. sp. cucumerinum (FOC), which is a pathogen responsible for cucumber wilt disease, were significantly inhibited by VOCs emitted from NAU1697. Among the VOCs, 33 were identified, 11 of which were investigated for their antifungal properties. Among the tested compounds, 2-ethylhexanol exhibited the highest antifungal activity toward FOC, with a minimum inhibitory volume (MIV) of 3.0 μL/plate (equal to 35.7 mg/L). Damage to the hyphal cell wall and cell membrane integrity caused a decrease in the ergosterol content and a burst of reactive oxygen species (ROS) after 2-ethylhexanol treatment. DNA damage, which is indicative of apoptosis-like cell death, was monitored in 2-ethylhexanol-treated FOC cells by using micro-FTIR analysis. Furthermore, the activities of mitochondrial dehydrogenases and mitochondrial respiratory chain complex III in 2-ethylhexanol-treated FOC cells were significantly decreased. The transcription levels of genes associated with redox reactions and the cell wall integrity (CWI) pathway were significantly upregulated, thus indicating that stress was caused by 2-ethylhexanol. The findings of this research provide a new avenue for the sustainable management of soil-borne plant fungal diseases.

Anti-Staphy Peptides Rationally Designed from Cry10Aa Bacterial Protein

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

Exploring the Therapeutic Potential of Scorpion-Derived Css54 Peptide Against Candida albicans

Candida albicans (C. albicans) is one of the most common opportunistic fungi worldwide, which is associated with a high mortality rate. Despite treatment, C. albicans remains the leading cause of life-threatening invasive infections. Consequently, antimicrobial peptides (AMPs) are potential alternatives as antifungal agents with excellent antifungal activity. We previously reported that Css54, found in the venom of Centrurodies suffusus suffusus (C. s. suffusus) showed antibacterial activity against zoonotic bacteria. However, the antifungal activity of Css54 has not yet been elucidated. The objective of this study was to identify the antifungal activity of Css54 against C. albicans and analyze its mechanism. Css54 showed high antifungal activity against C. albicans. Css54 also inhibited biofilm formation in fluconazole-resistant fungi. The antifungal mechanism of action of Css54 was investigated using membrane-related assays, including the membrane depolarization assay and analysis of the membrane integrity of C. albicans after treatment with Css54. Css54 induced reactive oxygen species (ROS) production in C. albicans, which affected its antifungal activity. Our results indicate that Css54 causes membrane damage in C. albicans, highlighting its value as a potential therapeutic agent against C. albicans infection.

Antimicrobial peptide LL-37 disrupts plasma membrane and calcium homeostasis in Candida albicans via the Rim101 pathway

IMPORTANCE

Candida albicans is a major human fungal pathogen, and antimicrobial peptides are key components of innate immunity. Studying the interplay between C. albicans and human antimicrobial peptides would enhance a better understanding of pathogen-host interactions. Moreover, potential applications of antimicrobial peptides in antifungal therapy have aroused great interest. This work explores new mechanisms of LL-37 against C. albicans and reveals the complex connection among calcium homeostasis, oxidative stress, signaling, and possibly organelle interaction. Notably, these findings support the possible use of antimicrobial peptides to prevent and treat fungal infections.

Chemical Insights into Oxidative and Nitrative Modifications of DNA

This review focuses on DNA damage caused by a variety of oxidizing, alkylating, and nitrating species, and it may play an important role in the pathophysiology of inflammation, cancer, and degenerative diseases. Infection and chronic inflammation have been recognized as important factors in carcinogenesis. Under inflammatory conditions, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from inflammatory and epithelial cells, and result in the formation of oxidative and nitrative DNA lesions, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-nitroguanine. Cellular DNA is continuously exposed to a very high level of genotoxic stress caused by physical, chemical, and biological agents, with an estimated 10,000 modifications occurring every hour in the genetic material of each of our cells. This review highlights recent developments in the chemical biology and toxicology of 2'-deoxyribose oxidation products in DNA.

Novel antimicrobial peptide DvAMP serves as a promising antifungal agent against Cryptococcus neoformans

Cryptococcus neoformans is an important opportunistic human fungal pathogen that causes cryptococcosis in immunocompromised patients. However, the number of drugs for the treatment of cryptococcosis is restricted, and the development of novel antifungal drugs and innovative strategies for the treatment of cryptococcosis is urgently needed. In this study, we validated that DvAMP is a novel antimicrobial peptide with antimicrobial activity and that it was obtained by pre-screening from the UniProt database of more than three million unknown functional sequences based on the quantitative structure-activity relationships (QSARs) protocol (http://www.chemoinfolab.com/antifungal). The peptide exhibited satisfactory biosafety and physicochemical properties, and relatively rapid fungicidal activity against C. neoformans. Meanwhile, DvAMP was able to inhibit the static biofilm of C. neoformans and cause a reduction in the thickness of the capsule. In addition, DvAMP exerts antifungal effects through membrane-mediated mechanisms (membrane permeability and depolarization) and mitochondrial dysfunction, involving a hybrid multi-hit mechanism. Furthermore, by using the C. neoformans-Galleria mellonella infection model, we demonstrated that DvAMP has significant therapeutic effects in vivo and that it significantly reduces the mortality and fungal burden of infected larvae. These results suggest that DvAMP may be a potential antifungal drug candidate for the treatment of cryptococcosis.

Antimicrobial mechanisms and secondary metabolite profiles of Streptomyces hygroscopicus subsp. hygroscopicus 5-4 against banana fusarium wilt disease using metabolomics

Fusarium wilt of bananas (FWB) is seriously affecting the sustainable development of the banana industry and is caused by the devastating soil-borne fungus Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4). Biological control is a promising strategy for controlling Fusarium wilt in bananas. We previously identified Streptomyces hygroscopicus subsp. hygroscopicus 5-4 with strong antifungal activity against the FWB. The most possible antimicrobial mechanism of strain 5-4 was explored using the metabolomics approach, light microscopy imaging, and transmission electron microscopy (TEM). The membrane integrity and ultrastructure of Foc TR4 was damaged after extract treatment, which was supported by the degradation of mycelium, soluble protein content, extracellular reducing sugar content, NADH oxidase activity, malondialdehyde content, mitochondrial membrane potential, and mitochondrial respiratory chain complex enzyme activity. The extracts of strain 5-4 cultivated at different times were characterized by a liquid chromatography-mass spectrometer (LC-MS). 647 known metabolites were detected in the extracts of strains 5-4. Hygromycin B, gluten exorphin B4, torvoside G, (z)-8-tetradecenal, piperitoside, sarmentosin, pubescenol, and other compounds were the main differential metabolites on fermentation culture for 7 days. Compared with strain 5-4 extracts, hygromycin B inhibited the mycelial growth of Foc TR4, and the EC₅₀ concentration was 7.4 μg/mL. These results showed that strain 5-4 could destroy the cell membrane of Foc TR4 to inhibit the mycelial growth, and hygromycin B may be the key antimicrobial active metabolite. Streptomyces hygroscopicus subsp. hygroscopicus 5-4 might be a promising candidate strain to control the FWB and provide a scientific basis for the practical application of hygromycin B as a biological control agent.

Cecropin-Loaded Zeolitic Imidazolate Framework Nanoparticles with High Biocompatibility and Cervical Cancer Cell Toxicity

Cecropins (CECs) are insect venom-derived amphiphilic peptides with numerous pharmacological effects, including anti-inflammatory, antibacterial, antiviral, and anti-tumor activities. Cecropins induce tumor cell death by disrupting phospholipid membrane integrity. However, non-specific cytotoxicity and in vivo rapid degradation limit clinical application. Nanotechnologies provide novel strategies for tumor eradication, including nanocarriers that can precisely target drugs to tumor tissue. We report the fabrication of CEC-encapsulated zeolitic imidazolate framework 8 (ZIF-8) nanoparticles (CEC@ZIF-8 NPs) via the preparation of CEC@ZIF-8 NPs in pure water by one-pot stirring. This method yielded morphologically uniform NPs with 20 wt% drug loading capacity and 9% loading efficiency. The NP formulation protected CECs from proteasome degradation, enhanced peptide bioavailability, promoted HeLa tumor cell uptake, and increased antitumor efficacy compared to free CECs. In conclusion, this ZIF-8 encapsulation strategy may enhance the clinical applicability of CECs and other antitumor peptides.

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.

Synergistic activity of dobutamine combined with azoles and its mechanism of action against strains of Candida glabrata

Aims: To evaluate the antifungal effect of dobutamine against Candida glabrata as well as its synergism with azoles and its action on biofilm. Methods: The M27-A3 protocol and flow cytometry were used for elucidation of the possible mechanism of action. Results: The tested isolates presented MICs ranging from 2 to 32 μg/ml for dobutamine, with fungistatic effect. A total of 82% of the strains showed synergism with fluconazole, with 90% showing synergism with itraconazole. The effect on biofilm formation was nonsignificant. Cytometry tests showed that dobutamine induced mitochondrial depolarization. Conclusion: Dobutamine has an antifungal effect on strains of C. glabrata and synergistic activity with azoles. This effect is probably mediated by increased oxidative damage to the membrane.

Aureoverticillactam, a Potent Antifungal Macrocyclic Lactam from Streptomyces aureoverticillatus HN6, Generates Calcium Dyshomeostasis-Induced Cell Apoptosis via the Phospholipase C Pathway in Fusarium oxysporum f. sp. cubense Race 4

Extensive efforts have been made to discover new biofungicides of high efficiency for control of Fusarium oxysporum f. sp. cubense race 4, a catastrophic soilborne phytopathogen causing banana Fusarium wilt worldwide. We confirmed for the first time that aureoverticillactam (YY3) has potent antifungal activity against F. oxysporum f. sp. cubense race 4, with effective dose for 50% inhibition (EC₅₀) of 20.80 μg/ml against hyphal growth and 12.62 μg/ml against spore germination. To investigate its mechanism of action, we observed the cellular ultrastructures of F. oxysporum f. sp. cubense race 4 with YY3 treatment and found that YY3 led to cell wall thinning, mitochondrial deformities, apoptotic degradation of the subcellular fractions, and entocyte leakage. Consistent with these variations, increased permeability of cell membrane and mitochondrial membrane also occurred after YY3 treatment. On the enzymatic level, the activity of mitochondrial complex III, as well as the ATP synthase, was significantly suppressed by YY3 at a concentration >12.50 μg/ml. Moreover, YY3 elevated the cytosolic Ca²⁺ level to promote mitochondrial reactive oxygen species (ROS) production. Cell apoptosis also occurred as expected. On the transcriptome level, key genes involved in the phosphatidylinositol signaling pathway were significantly affected, with the expression level of Plc1 increased approximately fourfold. The expression levels of two apoptotic genes, casA1 and casA2, were also significantly increased by YY3. Of note, phospholipase C activation was observed with YY3 treatment in F. oxysporum f. sp. cubense race 4. These findings indicate that YY3 exerts its antifungal activity by activating the phospholipase C calcium-dependent ROS signaling pathway, which makes it a promising biofungicide.

A Systematic Survey of Characteristic Features of Yeast Cell Death Triggered by External Factors

Cell death in response to distinct stimuli can manifest different morphological traits. It also depends on various cell death signaling pathways, extensively characterized in higher eukaryotes but less so in microorganisms. The study of cell death in yeast, and specifically Saccharomyces cerevisiae, can potentially be productive for understanding cell death, since numerous killing stimuli have been characterized for this organism. Here, we systematized the literature on external treatments that kill yeast, and which contains at least minimal data on cell death mechanisms. Data from 707 papers from the 7000 obtained using keyword searches were used to create a reference table for filtering types of cell death according to commonly assayed parameters. This table provides a resource for orientation within the literature; however, it also highlights that the common view of similarity between non-necrotic death in yeast and apoptosis in mammals has not provided sufficient progress to create a clear classification of cell death types. Differences in experimental setups also prevent direct comparison between different stimuli. Thus, side-by-side comparisons of various cell death-inducing stimuli under comparable conditions using existing and novel markers that can differentiate between types of cell death seem like a promising direction for future studies.

Antimicrobial Activity of the Peptide LfcinB15 against Candida albicans

Lactoferricin (Lfcin) is an amphipathic, cationic peptide derived from proteolytic cleavage of the N-lobe of lactoferrin (Lf). Lfcin and its derivatives possess broad-spectrum antibacterial and antifungal activities. However, unlike their antibacterial functions, the modes of action of Lfcin and its derivatives against pathogenic fungi are less well understood. In this study, the mechanisms of LfcinB15, a derivative of bovine Lfcin, against Candida albicans were, therefore, extensively investigated. LfcinB15 exhibited inhibitory activity against planktonic cells, biofilm cells, and clinical isolates of C. albicans and non-albicans Candida species. We further demonstrated that LfcinB15 is localized on the cell surface and vacuoles of C. albicans cells. Moreover, LfcinB15 uses several different methods to kill C. albicans, including disturbing the cell membrane, inducing reactive oxygen species (ROS) generation, and causing mitochondrial dysfunction. Finally, the Hog1 and Mkc1 mitogen-activated protein kinases were both activated in C. albicans cells in response to LfcinB15. These findings help us to obtain more insight into the complex mechanisms used by LfcinB15 and other Lfcin-derived peptides to fight fungal pathogens.

Porcine Myeloid Antimicrobial Peptides: A Review of the Activity and Latest Advances

Traditional antibiotics have made great contributions to human health and animal husbandry since the discovery of penicillin in 1928, but bacterial resistance and drug residues are growing threats to global public health due to the long-term uncontrolled application of antibiotics. There is a critical need to develop new antimicrobial drugs to replace antibiotics. Antimicrobial peptides (AMPs) are distributed in all kingdoms of life, presenting activity against pathogens as well as anticancer, anti-inflammatory, and immunomodulatory activities; consequently, they have prospects as new potential alternatives to antibiotics. Porcine myeloid antimicrobial peptides (PMAPs), the porcine cathelicidin family of AMPs, have been reported in the literature in recent years. PMAPs have become an important research topic due to their strong antibacterial activity. This review focuses on the universal trends in the biochemical parameters, structural characteristics and biological activities of PMAPs.

β-amyrin-induced apoptosis in Candida albicans triggered by calcium

The emergence of drug-resistant pathogens has urged researchers to discover alternatives for traditional antibiotics. β-amyrin, which is included in the category of triterpenoids extracted from plants, is known for its antimicrobial activity, although the underlying mechanism has not yet been revealed. This study was conducted to elucidate the antifungal mode of action of β-amyrin against Candida albicans. Based on the relevance between triterpenoids and oxidative molecules, reactive oxygen species (ROS) concentrations were detected, which showed a noticeable increment. Disruption of Ca²⁺ homeostasis in the cytosol was additionally analyzed, which was supported by interactions between two. Subsequently, decrease in mitochondrial membrane potential, increment of mitochondrial Ca²⁺, and ROS concentration were monitored, which suggested mitochondrial dysfunction modulated by Ca²⁺. Further investigation confirmed oxidative damage through glutathione reduction and DNA fragmentation. Accumulation of lethal damages resulted in the activation of caspases and externalization of phosphatidylserine, indicating the induction of yeast apoptosis by β-amyrin in C. albicans.

Antifungal effect of volatile organic compounds produced by Pseudomonas chlororaphis subsp. aureofaciens SPS-41 on oxidative stress and mitochondrial dysfunction of Ceratocystis fimbriata

Ceratocystis fimbriata is the pathogen of black rot disease, which widely exists in sweet potato producing areas all over the world. The antifungal activity of volatile organic compounds (VOCs) released by Pseudomonas chlororaphis subsp. aureofaciens SPS-41 against C. fimbriata was reported in our previous study. In this study, we attempted to reveal the underlying antifungal mechanism of SPS-41 volatiles. Our results showed that the VOCs released by SPS-41 caused the morphological change of hyphae, destroyed the integrity of cell membrane, reduced the content of ergosterol, and induced massive accumulation of reactive oxygen species in C. fimbriata cells. Furthermore, SPS-41 fumigation decreased the mitochondrial membrane potential, acetyl-CoA and pyruvate content of C. fimbriata cells, as well as the mitochondrial dehydrogenases activity. In addition, the VOCs generated by SPS-41 reduced the intracellular ATP content and increased the extracellular ATP content of C. fimbriata. In summary, SPS-41 fumigation exerted its antifungal activity by inducing oxidative stress and mitochondrial dysfunction in C. fimbriata.

Calcium homeostasis plays important roles in the internalization and activities of the small synthetic antifungal peptide PAF26

Fungal diseases are responsible for the deaths of over 1.5 million people worldwide annually. Antifungal peptides represent a useful source of antifungals with novel mechanisms-of-action, and potentially provide new methods of overcoming resistance. Here we investigate the mode-of-action of the small, rationally designed synthetic antifungal peptide PAF26 using the model fungus Neurospora crassa. Here we show that the cell killing activity of PAF26 is dependent on extracellular Ca²⁺ and the presence of fully functioning fungal Ca²⁺ homeostatic/signaling machinery. In a screen of mutants with deletions in Ca²⁺ -signaling machinery, we identified three mutants more tolerant to PAF26. The Ca²⁺ ATPase NCA-2 was found to be involved in the initial interaction of PAF26 with the cell envelope. The vacuolar Ca²⁺ channel YVC-1 was shown to be essential for its accumulation and concentration within the vacuolar system. The Ca²⁺ channel CCH-1 was found to be required to prevent the translocation of PAF26 across the plasma membrane. In the wild type, Ca²⁺ removal from the medium resulted in the peptide remaining trapped in small vesicles as in the Δyvc-1 mutant. It is, therefore, apparent that cell killing by PAF26 is complex and unusually dependent on extracellular Ca²⁺ and components of the Ca²⁺ -regulatory machinery.

Human Antimicrobial Peptide Hepcidin 25-Induced Apoptosis in Candida albicans

Hepcidin 25 (hep 25) is a cysteine-rich 25-amino acid antimicrobial peptide containing the amino-terminal Cu(II)/Ni(II)-binding (ATCUN) motif. Upon metal binding, the ATCUN motif is known to be involved in the generation of reactive oxygen species (ROS), especially hydrogen peroxide and hydroxyl radicals, which act against different bacterial species. However, the antifungal activity and its correlation to the Cu(II)-ATCUN complex of Hep 25 are still poorly understood. Here, we found that ROS accumulation plays an important role in the fungicidal activity of hep 25 against Candida albicans. In addition, Annexin V-FITC staining and TUNEL assay results provide clues about the apoptosis induced by hep 25. Moreover, hep 25 also increases the generation of ROS, possibly because of copper binding to the ATCUN motif, which is relevant to its activity against C. albicans. Finally, the C. albicans killing action of hep 25 is an energy- and temperature-dependent process that does not involve targeting the membrane. Taken together, our results provide new insights into the mechanisms of hep 25 against C. albicans cells and the potential use of hep 25 and its derivatives as novel antifungal agents.

Candidalysin Is a Potent Trigger of Alarmin and Antimicrobial Peptide Release in Epithelial Cells

Host released alarmins and antimicrobial peptides (AMPs) are highly effective as antifungal agents and inducers. Whilst some are expressed constitutively at mucosal tissues, the primary site of many infections, others are elicited in response to pathogens. In the context of Candida albicans, the fungal factors inducing the release of these innate immune molecules are poorly defined. Herein, we identify candidalysin as a potent trigger of several key alarmins and AMPs known to possess potent anti-Candida functions. We also find extracellular ATP to be an important activator of candidalysin-induced epithelial signalling responses, namely epidermal growth factor receptor (EGFR) and MAPK signalling, which mediate downstream innate immunity during oral epithelial infection. The data provide novel mechanistic insight into the induction of multiple key alarmins and AMPs, important for antifungal defences against C. albicans.

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

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