Oxidative stress by antimicrobial peptide pleurocidin triggers apoptosis in Candida albicans

Nanopore-based full-length transcriptome sequencing of the skin in Pseudopleuronectes yokohamae identifies novel antimicrobial peptide genes

The marbled flounder (Pseudopleuronectes yokohamae) is highly esteemed for its exceptional nutritional value and delicious taste. However, this species has extremely limited transcriptome data, which can offer priceless information for disease protection. In the study, the skin transcriptomic sequencing of P. yokohamae revealed 7.72 GB of clean data using the Nanopore sequencing platform. The results revealed 30,498 transcripts of functional annotations in the P. yokohamae transcriptome. All transcripts were searched in eight functional databases. A total of 10,337 ORFs were obtained, of which 6081 complete ORFs accounted for 58.83% of all predicted CDS. Moreover, 10,195 SSRs were detected. Meanwhile, the non-pecific immunity pathways were investigated for better understanding of the immunological reaction in P. yokohamae, and seven innate immune pathways were identified. The innate-immune related genes were highly expressed in the NOD-like receptor signaling pathway, followed by the C-type lectin receptor signaling pathway, Toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway and Cytosolic DNA-sensing pathway. In this study, four families of antimicrobial peptides (AMPs) in P. yokohamae were analysed for the first time, including piscidins, hepcidins, liver-expressed antimicrobial peptide and defensins. Seven AMPs, including Pypleurocidin-like WF3, Pypleurocidin-like WFX, Pyhepcidin 1, Pyhepcidin-like 1, PyLEAP-2, Pybeta-defensin and Pybeta-defensin-like 1, were further identified. The seven AMPs showed a highly identity in their cDNA and genomic structures and an inducible expression pattern preferable to skin in response to pathogens. The transcriptomic data and investigation of AMPs from P. yokohamae promote a deeper awareness of fish mucosal immunity and provide information in the prevention of fish diseases.

Unveiling novel insights: geraniol's enhanced anti-candida efficacy and mechanistic innovations against multidrug-resistant candida strains

OBJECTIVES

This study addressed the need for new treatments for severe Candida infections, especially resistant strains. It evaluated the antifungal potential of geraniol alone and with fluconazole against various Candida spp., including resistant strains, and investigated geraniol's mechanism of action using flow cytometry.

METHODS

The research assessed the inhibitory effects of geraniol on the growth of various Candida species at concentrations ranging from 110 to 883 µg/ml. The study also explored the potential synergistic effects when geraniol was combined with fluconazole. The mechanism of action was investigated through flow cytometry, with a particular emphasis on key enzymes associated with plasma membrane synthesis, membrane permeability changes, mitochondrial membrane depolarization, reactive oxygen species (ROS) induction, and genotoxicity.

RESULTS

Geraniol demonstrated significant antifungal activity against different Candida species, inhibiting growth at concentrations within the range of 110 to 883 µg/ml. The mechanism of action appeared to be multifactorial. Geraniol was associated with the inhibition of crucial enzymes involved in plasma membrane synthesis, increased membrane permeability, induction of mitochondrial membrane depolarization, elevated ROS levels, and the presence of genotoxicity. These effects collectively contributed to cell apoptosis.

CONCLUSIONS

Geraniol, alone and in combination with fluconazole, shows promise as a potential therapeutic option for Candida spp.

INFECTIONS

Its diverse mechanism of action, impacting crucial cellular processes, highlights its potential as an effective antifungal agent. Further research into geraniol's therapeutic applications may aid in developing innovative strategies to address Candida infections, especially those resistant to current therapies.

Antifungal activity of human antimicrobial peptides targeting apoptosis in Candida auris

Introduction. Innovative antifungal therapies are of crucial importance to combat the potentially life-threatening infections linked to the multidrug-resistant fungal pathogen Candida auris. Induction of regulated cell death, apoptosis, could provide an outline for future therapeutics. Human antimicrobial peptides (AMPs), well-known antifungal compounds, have shown the ability to induce apoptosis in pathogenic fungi.Hypothesis/Gap Statement . Although it is known that AMPs possess antifungal activity against C. auris, their ability to induce apoptosis requires further investigations.Aim. This study evaluated the effects of AMPs on the induction of apoptosis in C. auris.Methods. Human neutrophil peptide-1 (HNP-1), human β-Defensins-3 (hBD-3) and human salivary histatin 5 (His 5) were assessed against two clinical C. auris isolates. Apoptosis hallmarks were examined using FITC-Annexin V/PI double labelling assay and terminal deoxynucleotidyl transferase deoxynucleotidyl transferase nick-end labelling (TUNEL) to detect phosphatidylserine externalization and DNA fragmentation, respectively. Then, several intracellular triggers were studied using JC-10 staining, spectrophotometric assay and 2',7'-dichlorofluorescin diacetate staining to measure the mitochondrial membrane potential, cytochrome-c release and reactive oxygen species (ROS) production, respectively.Results and conclusion. FITC-Annexin V/PI staining and TUNEL analysis revealed that exposure of C. auris cells to HNP-1 and hBD-3 triggered both early and late apoptosis, while His 5 caused significant necrosis. Furthermore, HNP-1 and hBD-3 induced significant mitochondrial membrane depolarization, which resulted in substantial cytochrome c release. In contrast to His 5, which showed minimal mitochondrial depolarization and no cytochrome c release. At last, all peptides significantly increased ROS production, which is related to both types of cell death. Therefore, these peptides represent promising and effective antifungal agents for treating invasive infections caused by multidrug-resistant C. auris.

Specifically Targeting Metacaspases of Candida: A New Therapeutic Opportunity

The World Health Organization (WHO) recently published a list of fungal priority pathogens, including Candida albicans and C. auris. The increased level of resistance of Candida is raising concern, considering the availability of only four classes of medicine. The WHO is seeking novel agent classes with different targets and mechanisms of action. Targeting Candida metacaspases to control intrinsic cell death could provide new therapeutic opportunities for invasive candidiasis. In this review, we provide the available evidence for Candida cell death, describe Candida metacaspases, and discuss the potential of Candida metacaspases to offer a new specific target. Targeting Candida cell death has good scientific rationale given that the fungicidal activity of many marketed antifungals is mediated, among others, by cell death triggering. But none of the available antifungals are specifically activating Candida metacaspases, making this target a new therapeutic opportunity for non-susceptible isolates. It is expected that antifungals based on the activation of fungi metacaspases will have a broad spectrum of action, as metacaspases have been described in many fungi, including filamentous fungi. Considering this original mechanism of action, it could be of great interest to combine these new antifungal candidates with existing antifungals. This approach would help to avoid the development of antifungal resistance, which is especially increasing in Candida.

Exploring the frontiers of therapeutic breadth of antifungal peptides: A new avenue in antifungal drugs

The growing prevalence of fungal infections alongside rising resistance to antifungal drugs poses a significant challenge to public health safety. At the close of the 2000s, major pharmaceutical firms began to scale back on antimicrobial research due to repeated setbacks and diminished economic gains, leaving only smaller companies and research labs to pursue new antifungal solutions. Among various natural sources explored for novel antifungal compounds, antifungal peptides (AFPs) emerge as particularly promising. Despite their potential, AFPs receive less focus than their antibacterial counterparts. These peptides have been sourced extensively from nature, including plants, animals, insects, and especially bacteria and fungi. Furthermore, with advancements in recombinant biotechnology and computational biology, AFPs can also be synthesized in lab settings, facilitating peptide production. AFPs are noted for their wide-ranging efficacy, in vitro and in vivo safety, and ability to combat biofilms. They are distinguished by their high specificity, minimal toxicity to cells, and reduced likelihood of resistance development. This review aims to comprehensively cover AFPs, including their sources-both natural and synthetic-their antifungal and biofilm-fighting capabilities in laboratory and real-world settings, their action mechanisms, and the current status of AFP research.

ONE-SENTENCE SUMMARY

This comprehensive review of AFPs will be helpful for further research in antifungal research.

Sertraline has fungicidal activity against Candida spp. and acts by inhibiting membrane and cell wall biosynthesis

Aim: Our study evaluated the activity of sertraline (SER) alone and associated with antifungal drugs in planktonic Candida spp. strains, and investigated its mechanism of action. Materials & methods: Broth microdilution method and minimum fungicidal concentration/MIC ratio were used to assess SER anticandidal activity, and the interaction with antifungals was determined by fractional inhibitory concentration index. The mechanism of action was investigated by flow cytometry and in silico tests. Results: SER inhibited Candida spp. strains at low concentrations by the fungicidal effect and showed no loss of effectiveness when combined. Its action seemed to be related to the membrane and cell wall biosynthesis inhibition. Conclusion: SER has activity against Candida spp. isolated and associated with antifungals, and acts by causing cell wall and membrane damage.

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.

Combating fungal phytopathogens with human salivary antimicrobial peptide histatin 5 through a multi-target mechanism

Blast disease caused by Magnaporthe oryzae is a major contributor to decreased crop yield and rice production globally. The use of chemical fungicides to combat crop pathogens is not only unsafe but also promotes the emergence of pathogenic variants, leading to recurrent host infections. To address plant diseases, antimicrobial peptides have emerged as a promising alternative as they are effective, safe, and biodegradable antifungal agents. This study examines the antifungal activity and mechanism of action of the human salivary peptide histatin 5 (Hst5) on M. oryzae. Hst5 causes morphogenetic defects in the fungus, including non-uniform chitin distribution on the fungal cell wall and septa, deformed hyphal branching, and cell lysis. Importantly, a pore-forming mechanism of Hst5 in M. oryzae was ruled out. Furthermore, the interaction of Hst5 with the M. oryzae genomic DNA suggests that the peptide may also influence gene expression in the blast fungus. In addition to its effects on morphogenetic defects and cell lysis, Hst5 also inhibits conidial germination, appressorium formation, and the appearance of blast lesions on rice leaves. The elucidated multi-target antifungal mechanism of Hst5 in M. oryzae provides an environmentally friendly alternative to combating blast infections in rice by preventing fungal pathogenicity. The promising antifungal characteristics of the AMP peptide may also be explored for other crop pathogens, making it a potential biofungicide for the future.

A pilot study on ultrashort peptide with fluconazole: A promising novel anticandidal combination

Background and Aim

Human infections caused by Candida albicans are common and range in severity from relatively treatable skin and mucosal conditions to systemic, fatal invasive candidiasis. The treatment of fungal infections is challenged by major obstacles, including the scarcity of effective therapeutic options, the toxicity of available medications, and the escalating antifungal resistance. Hence, there exists an urgent need to develop new classes of antimicrobial agents. This study was conducted to investigate the effect of KW-23 peptide against standard and resistant strains of C. albicans alone and in combination with fluconazole.

Materials and Methods

A conjugated ultrashort antimicrobial peptide (KW-23) was designed and synthesized. KW-23 was challenged against standard and multidrug-resistant C. albicans alone and in combination with fluconazole using standard antimicrobial and checkerboard assays. The toxicity of the peptide was examined using hemolytic assays.

Results

KW-23 positively affected the standard and resistant Candidal strains (at 5 and 15 μg/mL respectively), exhibiting potent synergistic antimicrobial activity against the standard strain when combined with fluconazole. The effect of the combination was additive against the resistant strain (0.6 μg/mL). Furthermore, the peptide exhibited negligible toxicity on human erythrocytes.

Conclusion

KW-23 and its combination with fluconazole could be a promising candidate for developing anticandidal agents.

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.

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.

Electrochemical detection of gram-negative bacteria through mastoparan-capped magnetic nanoparticle

The increasing number of multidrug resistance microorganisms is an alarming threat, and their rapid detection is essential to prevent nosocomial, foodborne, or waterborne infections. Many peptides derived from the venom of wasp Synoeca surinama have antimicrobial activity against Gram-positive and Gram-negative bacteria. Synoeca-MP, an antimicrobial peptide (AMP) from mastoparan family, seems to increase bacterial membrane permeability, promoting cytotoxicity and membrane disruption. Here Synoeca-MP was evaluated as biorecognition element tethered over chitosan-coated magnetic nanoparticles (Fe₃O₄-Chit). The transducing layer of the biosensor was developed from the self-assembling of 4-mercaptobenzoic acid (4-MBA) monolayer onto gold substrate. Atomic force microscopy (AFM) analyses confirmed the biointeraction between AMP and different pathogens membranes. The fabrication and performance of the biosensing assembly were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Detection of Enterococcus faecalis (G+), Klebsiella pneumoniae (G-), Pseudomonas aeruginosa (G-), and Candida tropicalis was assessed in a recognition range from 10¹ to 10⁵ CFU.mL^-1. An instrumental limit of detection of 10 CFU.mL^-1 was obtained for each specimen. However, the device presented a preferential selectivity towards Gram-negative bacteria. The proposed biosensor is a sensitive, fast, and straightforward platform for microbial detection in aqueous samples, envisaged for environmental monitoring applications.

Antibacterial and Anticancer Activities of Pleurocidin-Amide, a Potent Marine Antimicrobial Peptide Derived from Winter Flounder, Pleuronectes americanus

The extensive use of conventional antibiotics has led to the growing emergence of many resistant strains of pathogenic bacteria. Evidence suggests that cationic antimicrobial peptides (AMPs) have the greatest potential to serve as traditional antibiotic substitutes. Recent studies have also reported that certain AMPs have selective toxicity toward various types of cancer cells. The electrostatic attraction between the negatively charged membrane components and AMPs is believed to play a crucial role in the disruption of bacterial and cancer cell membranes. In the current study, we used a potent AMP called Pleurocidin (Ple) derived from winter flounder Pleuronectes americanus and its C-terminal-amidated derivative Pleurocidin-amide (Ple-a), and evaluated their antibacterial and anticancer activities. Our results indicated that both Ple and Ple-a exhibited significant antibacterial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, especially marine pathogens, with MIC values ranging from 0.25 to 32 μg/mL. These peptides are also potent against several multidrug-resistant (MDR) bacterial strains, with MIC values ranging from 2 to 256 μg/mL. When used in combination with certain antibiotics, they exhibited a synergistic effect against MDR E. coli. Ple and Ple-a also showed notable cytotoxicity toward various cancer cell lines, with IC₅₀ values ranging from 11 to 340 μM, while normal mouse fibroblast 3T3 cells were less susceptible to these peptides. Ple-a was then selected to study its anticancer mechanism toward A549 human lung adenocarcinoma cells. Western blot analysis and confocal microscopy showed that Ple-a could inhibit autophagy of A549 cells, and induce apoptosis 48 h after treatment. Our findings provided support for the future application of Ple-a as potential therapeutic agent for bacterial infections and cancer treatment.

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.

Antifungal activity of puroindoline protein from soft wheat against grain molds and its potential as a biocontrol agent

Mold growth reduces the quality of stored grains, besides producing toxins that pose a potential threat to human health. Therefore, prevention of grain mold growth during storage is important to ensure a safe and high-quality product, preferably using an eco-friendly antifungal agent. The Puroindoline (PIN) protein was extracted by Triton X-114, and identified by QE mass spectrometry. A. flavus has attracted much attention because of its toxic secondary metabolites, and PIN protein showed a significant inhibition on A. flavus growth. Scanning electron microscopy revealed altered spore morphology of A. flavus following PIN protein treatment, and propidium iodide staining showed incomplete spore cell membranes. The disruption and deformation of A. flavus spores suggest that the cell walls and cell membranes were compromised. Decreased mitochondrial membrane potential and increased levels of intracellular reactive oxygen species (ROS) were detected using JC-1 and 2,7-dichlorodihydrofluorescein diacetate staining, respectively. PIN protein could effectively inhibit the growth and aflatoxins B1 production of A. flavus in stored grains, such as wheat and rice. PIN proteins can inhibit the growth of many common grain storage molds, including Penicillium, Aspergillus spp. (A. flavus, A. glaucus, A. kawachii, A. ochraceus, A. niger), Alternaria, and Fusarium graminearum, in a dose-dependent manner. PIN protein has a significant inhibitory effect on the growth of grain molds, with a stronger inhibitory effect noted in wheat and rice. Our study provides a novel and simple theoretical basis for the selection and storage of mold-resistant in grains and food during storage.

Antifungal Activity of ToAP2D Peptide Against Sporothrix globosa

Improving clinical efficacy and reducing treatment time have been the focus of sporotrichosis therapy. Antimicrobial peptides ToAP2A, ToAP2C, and ToAP2D were synthesized on the basis of ToAP2 (AP02759), a peptide derived from the antimicrobial peptide database by the database filtering technology, and their physicochemical characteristics were analyzed. Compared with template peptide ToAP2, the modified peptides had much shorter length, lower molecular weight but significantly greater stability, which in return resulted in increases in the aliphatic index, hydrophilicity, and protein binding ability. Here, we show that the three derived peptides inhibit the growth of Sporothrix globosa, among which ToAP2D had the strongest anti-fungal activity. ToAP2D showed good serum stability without acute toxicity. The ToAP2D treatment inhibited the growth of S. globosa and enhanced apoptosis, which was evidenced by the upregulation of apoptosis-related protein caspase-3. The scanning electron microscopy analysis revealed deformation and rupture of S. globosa. The levels of mitochondrial membrane potential were decreased and that of the reactive oxygen species (ROS) were increased in S. globosa upon ToAP2D treatment. Moreover, ToAP2D activated metacaspase. In the in vivo study, we further demonstrated that ToAP2D inhibited the S. globosa infection of mice footpads, and its efficiency was nearly comparable to itraconazole. In summary, our results suggest that antimicrobial peptide ToAP2D has the potential for sporotrichosis therapy.

A Novel Antimicrobial Peptide Sparamosin26-54 From the Mud Crab Scylla paramamosain Showing Potent Antifungal Activity Against Cryptococcus neoformans

Due to the increasing prevalence of drug-resistant fungi and the limitations of current treatment strategies to fungal infections, exploration and development of new antifungal drugs or substituents are necessary. In the study, a novel antimicrobial peptide, named Sparamosin, was identified in the mud crab Scylla paramamosain, which contains a signal peptide of 22 amino acids and a mature peptide of 54 amino acids. The antimicrobial activity of its synthetic mature peptide and two truncated peptides (Sparamosin1-25 and Sparamosin26-54) were determined. The results showed that Sparamosin26-54 had the strongest activity against a variety of Gram-negative bacteria, Gram-positive bacteria and fungi, in particular had rapid fungicidal kinetics (killed 99% Cryptococcus neoformans within 10 min) and had potent anti-biofilm activity against C. neoformans, but had no cytotoxic effect on mammalian cells. The RNA-seq results showed that after Sparamosin26-54 treatment, the expression of genes involved in cell wall component biosynthesis, cell wall integrity signaling pathway, anti-oxidative stress, apoptosis and DNA repair were significantly up-regulated, indicating that Sparamosin26-54 might disrupt the cell wall of C. neoformans, causing oxidative stress, DNA damage and cell apoptosis. The underlying mechanism was further confirmed. Sparamosin26-54 could bind to several phospholipids in the cell membrane and effectively killed C. neoformans through disrupting the integrity of the cell wall and cell membrane observed by electron microscope and staining assay. In addition, it was found that the accumulation of reactive oxygen species (ROS) increased, the mitochondrial membrane potential (MMP) was disrupted, and DNA fragmentation was induced after Sparamosin26-54 treatment, which are all hallmarks of apoptosis. Taken together, Sparamosin26-54 has a good application prospect as an effective antimicrobial agent, especially for C. neoformans infections.

Investigating Potential Applications of the Fish Anti-Microbial Peptide Pleurocidin: A Systematic Review

The anti-microbial peptide (AMP) pleurocidin is found in winter flounder (Pseudopleuronectes americanus), an Atlantic flounder species. There is promising evidence for clinical, aquaculture, and veterinary applications of pleurocidin. This review provides an overview of the current literature available on pleurocidin to guide future research directions. By fully elucidating pleurocidin’s mechanism of action and developing novel treatments against pathogenic microbes, populations of flatfish and humans can be protected. This review consulted publications from PubMed and Environment Complete with search terms such as “pleurocidin”, “winter flounder”, and “antimicrobial”. The fish immune system includes AMPs as a component of the innate immune system. Pleurocidin, one of these AMPs, has been found to be effective against various Gram-positive and Gram-negative bacteria. More investigations are required to determine pleurocidin’s suitability as a treatment against antibiotic-resistant pathogens. There is promising evidence for pleurocidin as a novel anti-cancer therapy. The peptide has been found to display potent anti-cancer effects against human cancer cells. Research efforts focused on pleurocidin may result in novel treatment strategies against antibiotic-resistant bacteria and cancer. More research is required to determine if the peptide is a suitable candidate to be developed into a novel anti-microbial treatment. Some of the microbes susceptible to the peptide are also pathogens of fish, suggesting its suitability as a therapeutic treatment for fish species.

Reactive oxygen mediated apoptosis as a therapeutic approach against opportunistic Candida albicans

Candida albicans are polymorphic fungal species commonly occurs in a symbiotic association with the host's usual microflora. Certain specific changes in its usual microenvironment can lead to diseases ranging from external mucosal to severally lethal systemic infections like invasive candidiasis hospital-acquired fatal infection caused by different species of Candida. The patient acquired with this infection has a high mortality and morbidity rate, ranging from 40% to 60%. This is an ill-posed problem by its very nature. Hence, early diagnosis and management is a crucial part. Antifungal drug resistance against the first and second generation of antifungal drugs has made it difficult to treat such fatal diseases. After a few dormant years, recently, there has been a rapid turnover of identifying novel drugs with low toxicity to limit the problem of drug resistance. After an initial overview of related work, we examine specific prior work on how a change in oxidative stress can facilitate apoptosis in C. albicans. Subsequently, it was investigated that Candida spp. suppresses the production of ROS mediated host defense system. Here, we have reviewed possibly all the small molecule inhibitors, natural products, antimicrobial peptide, and some naturally derived semi-synthetic compounds which are known to influence oxidative stress, to generate a proper apoptotic response in C. albicans and thus might be a novel therapeutic approach to augment the current treatment options.

Novel antifungal mechanism of oligochitosan by triggering apoptosis through a metacaspase-dependent mitochondrial pathway in Ceratocystis fimbriata

The antifungal effects of oligochitosan (OCS) against Ceratocystis fimbriata that causes black rot disease in sweet potato and its apoptosis mechanism were evaluated. OCS restrained the mycelial growth and spores germination of C. fimbriata, and decreased the ergosterol content of cell membrane. Transmission electron microscopy observation and flow cytometry analysis revealed that OCS induced morphology changes with smaller size and increased granularity of C. fimbriata, which was the typical feature of apoptosis. To clarify the apoptosis mechanism induced by OCS, a series of apoptosis-related parameters were analyzed. Results showed that OCS induced reactive oxygen species accumulation, Ca²⁺ homeostasis dysregulation, mitochondrial dysfunction and metacaspase activation, coupled with hallmarks of apoptosis including phosphatidylserine externalization, DNA fragmentation, and nuclear condensation. In summary, OCS triggered apoptosis through a metacaspase-dependent mitochondrial pathway in C. fimbriata. These findings have important implications for the application of OCS to control pathogens in food and agriculture.

Role of AMP-activated protein kinase during postovulatory aging of mouse oocytes†

Studies suggested that postovulatory oocyte aging might be prevented by maintaining a high maturation-promoting factor (MPF) activity. Whether AMP-activated protein kinase (AMPK) plays any role in postovulatory oocyte aging is unknown. Furthermore, while activation of AMPK stimulates meiotic resumption in mouse oocytes, it inhibits meiotic resumption in pig and bovine oocytes. Thus, the species difference in AMPK regulation of oocyte MPF activities is worth in-depth studies. This study showed that AMPK activation with metformin or 5-aminoimidazole- 4-carboxamide- 1-beta-d- ribofuranoside and inactivation with compound C significantly increased and decreased, respectively, the activation susceptibility (AS) and other aging parameters in aging mouse oocytes. While AMPK activity increased, MPF activity and cyclic adenosine monophosphate (cAMP) decreased significantly with time post ovulation. In vitro activation and inactivation of AMPK significantly decreased and increased the MPF activity, respectively. MPF upregulation with MG132 or downregulation with roscovitine completely abolished the effects of AMPK activation or inactivation on AS of aging oocytes, respectively. AMPK facilitated oocyte aging with increased reactive oxygen species (ROS) and cytoplasmic calcium. Furthermore, treatment with Ca2+/calmodulin-dependent protein kinase (CaMK) inhibitors significantly decreased AS and AMPK activation. Taken together, the results suggested that AMPK facilitated oocyte aging through inhibiting MPF activities, and postovulatory oocyte aging activated AMPK with decreased cAMP by activating CaMKs via increasing ROS and cytoplasmic calcium.

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.

Cellular apoptosis and necrosis as therapeutic targets for novel Eugenol Tosylate Congeners against Candida albicans

Despite the rise of new Candida species, Candida albicans tops the list with high morbidity and mortality rates. To tackle this problem there is a need to explore new antifungals that could replace or augment the current treatment options. We previously reported that tosylation of eugenol on hydroxyl group resulted in molecules with enhanced antifungal potency. In line with that work, we synthesized new eugenol tosylate congeners (ETC-1–ETC-7) with different substituents on pendent sulfonyl group and tested their susceptibility against different fluconazole susceptible and resistant C. albicans strains. We evaluated physiology and mode of cell death in response to the most active derivatives by analyzing major apoptotic markers in yeast such as phosphatidylserine externalization, DNA fragmentation, mitochondrial depolarization and decrease in cytochrome c oxidase activity. The results demonstrated that all C. albicans strains were variably susceptible to the test compounds with MIC ranging from 0.125–512 µg/ml, and the most active compounds (ETC-5, ETC-6 and ETC-7) actuate apoptosis and necrosis in Candida cells in a dose-dependent manner via metacaspase-dependent pathway. Furthermore haemolytic assay showed low cytotoxicity effect of these ETCs. Overall the results indicated that ETCs exhibit potential antifungal activity against C. albicans by activating apoptotic and necrotic pathways.

The Antifungal Peptide MCh-AMP1 Derived From Matricaria chamomilla Inhibits Candida albicans Growth via Inducing ROS Generation and Altering Fungal Cell Membrane Permeability

The rise of antifungal drug resistance in Candida species responsible for life threatening candidiasis is considered as an increasing challenge for the public health. MCh-AMP1 has previously been reported as a natural peptide from Matricaria chamomilla L. flowers with broad-spectrum antifungal activity against human pathogenic molds and yeasts. In the current study, the mode of action of synthetic MCh-AMP1 was investigated against Candida albicans, the major etiologic agent of life-threatening nosocomial candidiasis at cellular and molecular levels. Candida albicans ATCC 10231 was cultured in presence of various concentrations of MCh-AMP1 (16-64 μg/mL) and its mode of action was investigated using plasma membrane permeabilization assays, reactive oxygen species (ROS) induction, potassium ion leakage and ultrastructural analyses by electron microscopy. MCh-AMP1 showed fungicidal activity against Candida albicans at the concentrations of 32 and 64 μg/mL. The peptide increased fungal cell membrane permeability as evidenced by elevating of PI uptake and induced potassium leakage from the yeast cells. ROS production was induced by the peptide inside the fungal cells to a maximum of 64.8% at the concentration of 64 μg/mL. Scanning electron microscopy observations showed cell deformation as shrinkage and folding of treated yeast cells. Transmission electron microscopy showed detachment of plasma membrane from the cell wall, cell depletion and massive destruction of intracellular organelles and cell membrane of the fungal cells. Our results demonstrated that MCh-AMP1 caused Candida albicans cell death via increasing cell membrane permeability and inducing ROS production. Therefore, MCh-AMP1 could be considered as a promising therapeutic agent to combat Candida albicans infections.

Restraint stress of male mice triggers apoptosis in spermatozoa and spermatogenic cells via activating the TNF-α system

Studies have indicated that psychological stress impairs human fertility and that various stressors can induce apoptosis of testicular cells. However, the mechanisms by which psychological stress on males reduces semen quality and stressors induce apoptosis in testicular cells are largely unclear. Using a psychological (restraint) stress mouse model, we tested whether male psychological stress triggers apoptosis of spermatozoa and spermatogenic cells through activating tumour necrosis factor (TNF)-α signalling. Wild-type or TNF-α-/- male mice were restrained for 48 h before examination for apoptosis and expression of TNF-α and TNF receptor 1 (TNFR1) in spermatozoa, epididymis, seminiferous tubules and spermatogenic cells. The results showed that male restraint significantly decreased fertilization rate and mitochondrial membrane potential, while increasing levels of malondialdehyde, active caspase-3, TNF-α and TNFR1 in spermatozoa. Male restraint also increased apoptosis and expression of TNF-α and TNFR1 in caudae epididymides, seminiferous tubules and spermatogenic cells. Sperm quality was also significantly impaired when spermatozoa were recovered 35 days after male restraint. The restraint-induced damage to spermatozoa, epididymis and seminiferous tubules was significantly ameliorated in TNF-α-/- mice. Furthermore, incubation with soluble TNF-α significantly reduced sperm motility and fertilizing potential. Taken together, the results demonstrated that male psychological stress induces apoptosis in spermatozoa and spermatogenic cells through activating the TNF-α system and that the stress-induced apoptosis in spermatogenic cells can be translated into impaired quality in future spermatozoa.

Effects of the antifungal peptide Skh-AMP1 derived from Satureja khuzistanica on cell membrane permeability, ROS production, and cell morphology of conidia and hyphae of Aspergillus fumigatus

Skh-AMP1 (GRTSKQELCTWERGSVRQADKTIAG) is an antifungal peptide isolated from Satureja khuzistanica which has been shown to have strong antifungal activity against Aspergillus and Candida species, but no obvious hemolytic effects or cell cytotoxicity in vitro. In the present study, Skh-AMP1 was synthesized, and its mode of action on the plasma membrane, mitochondria, and morphological and ultrastructural changes against conidia and hyphae of Aspergillus fumigatus were evaluated. The results indicated that Skh-AMP1 had sporicidal activities against the non-germinated conidia of A. fumigatus at concentrations of 40 and 80 μM. Skh-AMP1 induced the release of K⁺ and the uptake of propidium iodide and enhanced reactive oxygen species (ROS) production in the conidia and hyphae of the fungus. Scanning and transmission electron microscopy showed deformation and shrinkage of the hyphae and conidia, cell membrane disruption and detachment from the cell wall, microvesicle formation, vacuolation and depletion of cytoplasm and organelles of the hyphae of A. fumigatus exposed to 40-80 μM of the peptide. The results further demonstrated that the antifungal activity of Skh-AMP1 may be related to its ability to disrupt fungal cell membrane permeabilization and induce enhanced ROS production. Therefore, Skh-AMP1 can be introduced as a novel antifungal candidate for developing new therapeutic agents.

RcAlb-PepII, a synthetic small peptide bioinspired in the 2S albumin from the seed cake of Ricinus communis, is a potent antimicrobial agent against Klebsiella pneumoniae and Candida parapsilosis

Antimicrobial peptides (AMPs) are important constituents of the innate immunity system of all living organisms. They participate in the first line of defense against invading pathogens such as viruses, bacteria, and fungi. In view of the increasing difficulties to treat infectious diseases due to the emergence of antibiotic-resistant bacterial strains, AMPs have great potential to control infectious diseases in humans and animals. In this study, two small peptides, RcAlb-PepI and RcAlb-PepII, were designed based on the primary structure of Rc-2S-Alb, a 2S albumin from the seed cake of Ricinus communis, and their antimicrobial activity assessed. RcAlb-PepII strongly inhibited the growth of Klebsiella pneumoniae and Candida parapsilosis, and induced morphological alterations in their cell surface. C. parapsilosis exposed to RcAlb-PepII presented higher cell membrane permeabilization and elevated content of reactive oxygen species. RcAlb-PepII also degraded and reduced the biofilm formation in C. parapsilosis and in K. pneumonia cells. Experimentally, RcAlb-PepII was not hemolytic and had low toxicity to mammalian cells. These are advantageous characteristics, which suggest that RcAlb-PepII is safe and apparently effective for its intended use and has great potential for the future development of an antimicrobial agent with the ability to kill or inhibit K. pneumoniae and C. parapsilosis cells.

Bioactive Peptides Against Fungal Biofilms

Infections caused by invasive fungal biofilms have been widely associated with high morbidity and mortality rates, mainly due to the advent of antibiotic resistance. Moreover, fungal biofilms impose an additional challenge, leading to multidrug resistance. This fact, along with the contamination of medical devices and the limited number of effective antifungal agents available on the market, demonstrates the importance of finding novel drug candidates targeting pathogenic fungal cells and biofilms. In this context, an alternative strategy is the use of antifungal peptides (AFPs) against fungal biofilms. AFPs are considered a group of bioactive molecules with broad-spectrum activities and multiple mechanisms of action that have been widely used as template molecules for drug design strategies aiming at greater specificity and biological efficacy. Among the AFP classes most studied in the context of fungal biofilms, defensins, cathelicidins and histatins have been described. AFPs can also act by preventing the formation of fungal biofilms and eradicating preformed biofilms through mechanisms associated with cell wall perturbation, inhibition of planktonic fungal cells’ adhesion onto surfaces, gene regulation and generation of reactive oxygen species (ROS). Thus, considering the critical scenario imposed by fungal biofilms and associated infections and the application of AFPs as a possible treatment, this review will focus on the most effective AFPs described to date, with a core focus on antibiofilm peptides, as well as their efficacy in vivo, application on surfaces and proposed mechanisms of action.

Programmed cell death in human pathogenic fungi - a possible therapeutic target

INTRODUCTION

Diseases caused by pathogenic fungi are increasing because of antibiotic overuse, the rise of immunosuppressive therapies, and climate change. The limited variety of antimycotics and the rapid adaptation of pathogenic fungi to antifungal agents serve to exacerbate this issue. Unfortunately, about 1.6 million people are killed by fungal infections annually. Areas covered: The discovery of the small antimicrobial proteins produced by microorganisms, animals, humans, and plants will hopefully overcome challenges in the treatment of fungal infections. These small proteins are highly stable and any resistance to them rarely evolves; therefore, they are potentially good candidates for the treatment and prevention of infections caused by pathogenic fungi. Some of these proteins target the programmed cell death machinery of pathogenic fungi; this is potentially a novel approach in antimycotic therapies. In this review, we highlight the elements of apoptosis in human pathogenic fungi and related model organisms and discuss the possible therapeutic potential of the apoptosis-inducing, small, antifungal proteins. Expert opinion: Small antimicrobial proteins may establish a new class of antimycotics in the future. The rarity of resistance and their synergistic effects with other frequently used antifungal agents may help pave the way for their use in the clinic.

Rifampin- or Capreomycin-Induced Remodeling of the Mycobacterium smegmatis Mycolic Acid Layer Is Mitigated in Synergistic Combinations with Cationic Antimicrobial Peptides

The mycobacterial cell wall affords natural resistance to antibiotics. Antimicrobial peptides (AMPs) modify the surface properties of mycobacteria and can act synergistically with antibiotics from differing classes. Here, we investigate the response of Mycobacterium smegmatis to the presence of rifampin or capreomycin, either alone or in combination with two synthetic, cationic, α-helical AMPs that are distinguished by the presence (D-LAK120-HP13) or absence (D-LAK120-A) of a kink-inducing proline. Using a combination of high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) metabolomics, diphenylhexatriene (DPH) fluorescence anisotropy measurements, and laurdan emission spectroscopy, we show that M. smegmatis responds to challenge with rifampin or capreomycin by substantially altering its metabolism and, in particular, by remodeling the cell envelope. Overall, the changes are consistent with a reduction of trehalose dimycolate and an increase of trehalose monomycolate and are associated with increased rigidity of the mycolic acid layer observed following challenge by capreomycin but not rifampin. Challenge with D-LAK120-A or D-LAK120-HP13 induced no or modest changes, respectively, in mycomembrane metabolites and did not induce a significant increase in the rigidity of the mycolic acid layer. Furthermore, the response to rifampin or capreomycin was significantly reduced when these were combined with D-LAK120-HP13 and D-LAK120-A, respectively, suggesting a possible mechanism for the synergy of these combinations. The remodeling of the mycomembrane in M. smegmatis is therefore identified as an important countermeasure deployed against rifampin or capreomycin, but this can be mitigated and the efficacy of rifampin or capreomycin potentiated by combining the drug with AMPs.IMPORTANCE We have used a combined NMR metabolomics/biophysical approach to better understand differences in the mechanisms of two closely related antimicrobial peptides, as well as the response of the model organism Mycobacterium smegmatis to challenge with first- or second-line antibiotics used against mycobacterial pathogens. We show that, in addition to membrane damage, the triggering of oxidative stress may be an important part of the mechanism of action of one AMP. The metabolic shift that accompanied rifampin and, particularly, capreomycin challenge was associated with modest and more dramatic changes, respectively, in the mycomembrane, providing a rationale for how the response to one antibiotic may affect bacterial penetration and, hence, the action of another. This study presents the first insights into how antimicrobial peptides may operate synergistically with existing antibiotics whose efficacy is waning or sensitize MDR mycobacteria and/or latent mycobacterial infections to them, prolonging the useful life of these drugs.

Programmed cell death in yeast by thionin-like peptide from Capsicum annuum fruits involving activation of caspases and extracellular H+ flux

CaThi is a thionin-like peptide isolated from fruits of Capsicum annuum, which has strong antimicrobial activity against bacteria, yeasts and filamentous fungi, and induced reactive oxygen species (ROS) in fungi. ROS are molecules that appear in the early stages of programmed cell death or apoptosis in fungi. Due to this fact, in this work we analyzed some events that may be related to process of apoptosis on yeast induced by CaThi. To investigate this possibility, we evaluated phosphatidylserine (PS) externalization, presence of active caspases and the ability of CaThi to bind to DNA in Candida tropicalis cells. Additionally, we investigated mitochondrial membrane potential, cell surface pH, and extracellular H⁺ fluxes in C. tropicalis cells after treatment with CaThi. Our results showed that CaThi induced PS externalization in the outer leaflet of the cell membrane, activation of caspases, and it had the ability for DNA binding and to dissipate mitochondrial membrane potential. In addition, the cell surface pH increased significantly when the C. tropicalis cells were exposed to CaThi which corroborates with ~96% inhibition on extracellular H⁺ efflux. Taking together, these data suggest that this peptide is capable of promoting an imbalance in pH homeostasis during yeast cell death playing a modulatory role in the H⁺ transport systems. In conclusion, our results strongly indicated that CaThi triggers apoptosis in C. tropicalis cells, involving a pH signaling mechanism.

Teleosts Genomics: Progress and Prospects in Disease Prevention and Control

Genome wide studies based on conventional molecular tools and upcoming omics technologies are beginning to gain functional applications in the control and prevention of diseases in teleosts fish. Herein, we provide insights into current progress and prospects in the use genomics studies for the control and prevention of fish diseases. Metagenomics has emerged to be an important tool used to identify emerging infectious diseases for the timely design of rational disease control strategies, determining microbial compositions in different aquatic environments used for fish farming and the use of host microbiota to monitor the health status of fish. Expounding the use of antimicrobial peptides (AMPs) as therapeutic agents against different pathogens as well as elucidating their role in tissue regeneration is another vital aspect of genomics studies that had taken precedent in recent years. In vaccine development, prospects made include the identification of highly immunogenic proteins for use in recombinant vaccine designs as well as identifying gene signatures that correlate with protective immunity for use as benchmarks in optimizing vaccine efficacy. Progress in quantitative trait loci (QTL) mapping is beginning to yield considerable success in identifying resistant traits against some of the highly infectious diseases that have previously ravaged the aquaculture industry. Altogether, the synopsis put forth shows that genomics studies are beginning to yield positive contribution in the prevention and control of fish diseases in aquaculture.

A Trypsin Inhibitor from Tecoma stans Leaves Inhibits Growth and Promotes ATP Depletion and Lipid Peroxidation in Candida albicans and Candida krusei

Tecoma stans (yellow elder) has shown medicinal properties and antimicrobial activity. Previous reports on antifungal activity of T. stans preparations and presence of trypsin inhibitor activity from T. stans leaves stimulated the investigation reported here. In this work, we proceeded to the purification and characterization of a trypsin inhibitor (TesTI), which was investigated for anti-Candida activity. Finally, in order to determine the potential of TesTI as a new natural chemotherapeutic product, its cytotoxicity to human peripheral blood mononuclear cells (PBMCs) was evaluated. TesTI was isolated from saline extract by ammonium sulfate fractionation followed by ion exchange and gel filtration chromatographies. Antifungal activity was evaluated by determining the minimal inhibitory (MIC) and fungicide (MFC) concentrations using fungal cultures containing only yeast form or both yeast and hyphal forms. Candida cells treated with TesTI were evaluated for intracellular ATP levels and lipid peroxidation. Cytotoxicity of TesTI to PBMCs was evaluated by MTT assay. TesTI (39.8 kDa, pI 3.41, K_i 43 nM) inhibited similarly the growth of both C. albicans and C. krusei culture types at MIC of 100 μg/mL. The MFCs were 200 μg/mL for C. albicans and C. krusei. Time-response curves revealed that TesTI (at MIC) was more effective at inhibiting the replication of C. albicans cells. At MIC, TesTI promoted reduction of ATP levels and lipid peroxidation in the Candida cells, being not cytotoxic to PBMCs. In conclusion, TesTI is an antifungal agent against C. albicans and C. krusei, without toxicity to human cells.

Dynamic monitoring of cellular metabolic activity in combination with live cell imaging

We present an automated analysis of the cellular dynamic metabolic activity in combination with live cell imaging, an essential factor for understanding the fundamental cellular physiological responses. For that purpose, we utilized the Intelligent Microplate Reader, a new analysis platform for marker-free cell-based assays in real-time. To demonstrate the benefit of the platform, we analyzed the relationship between various dynamic cell parameters (extracellular acidification, oxygen uptake, cell morphology, cell density and cell migration) of L929, a mouse fibroblast cell line, under the influence of sodium dodecyl sulfate. The dynamic kinetics of the monitored parameters are consistent and revealing much information about the activity occurring in the cells.

Micafungin induced apoptosis in Candida parapsilosis independent of its susceptibility to micafungin

We hypothesized that the cell wall inhibitor micafungin (MICA) induces apoptosis in both MICA-susceptible (MICA-S) and MICA-non-susceptible (MICA-NS) Candida parapsilosis. Antifungal activity and apoptosis were analyzed in MICA-S and MICA-NS C. parapsilosis strains following exposure to micafungin for 3 h at 37°C in RPMI 1640 medium. Apoptosis was characterized by detecting phosphatidylserine externalization (PS), plasma membrane integrity, reactive oxygen species (ROS) generation, mitochondrial membrane potential changes, adenosine triphosphate (ATP) release, and caspase-like activity. Apoptosis was detected in MICA exposed (0.25 to 1 mg/L) susceptible C. parapsilosis strains and was associated with apoptosis of 20-52% of analyzed cells versus only 5-30% of apoptosis in MICA-NS cells exposed to micafungin (0.5 to 2 mg/L; P = 0.001). The MICA antifungal activity was correlated with apoptotic cells showing increased dihydrorhodamine-123 staining (indicating ROS production), Rh-123 staining (decreased mitochondrial membrane potential), elevated ATP, and increased metacaspase activity. In conclusion, MICA is pro-apoptotic in MICA-S cells, but still exerts apoptotic effects in MICA -NS C. parapsilosis.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

The Use of a Liposomal Formulation Incorporating an Antimicrobial Peptide from Tilapia as a New Adjuvant to Epirubicin in Human Squamous Cell Carcinoma and Pluripotent Testicular Embryonic Carcinoma Cells

This study aims to explore the effects and mechanisms of hepcidin, a potential antimicrobial peptide from Tilapia, and epirubicin (Epi), an antineoplastic agent, on the generation of reactive oxygen species (ROS) and link the ROS levels to the reversal mechanisms of multidrug resistance (MDR) by epirubicin and hepcidin in human squamous cell carcinoma SCC15 and human embryonal carcinoma NT2D1 cells. The cells, pretreated with hepcidin, epirubicin, or a combination of these compounds in PEGylated liposomes, were used to validate the molecular mechanisms involved in inhibiting efflux transporters and inducing apoptosis as evaluated by cytotoxicity, intracellular accumulation, mRNA levels, cell cycle distribution, and caspase activity of this combination. We found that hepcidin significantly enhanced the cytotoxicity of epirubicin in liposomes. The co-incubation of epirubicin with hepcidin in liposomes intensified the ROS production, including hydrogen peroxide and superoxide free radicals. Hepcidin significantly increased epirubicin intracellular uptake into NT2D1 and SCC15 cells, as supported by the diminished mRNA expressions of MDR1, MDR-associated protein (MRP) 1, and MRP2. Hepcidin and/or epirubicin in liposomes triggered apoptosis, as verified by the reduced mitochondrial membrane potential, increased sub-G1 phase of cell cycle, incremental populations of apoptosis using annexin V/PI assay, and chromatin condensation. As far as we know, this is the first example showing that PEGylated liposomal TH1-5 and epirubicin gives rise to cell death in human squamous carcinoma and testicular embryonic carcinoma cells through the reduced epirubicin efflux via ROS-mediated suppression of P-gp and MRPs and concomitant initiation of mitochondrial apoptosis pathway. Hence, hepcidin in PEGylated liposomes may function as an adjuvant to anticancer drugs, thus demonstrating a novel strategy for reversing MDR.

Heat shock protein 90 and calcineurin pathway inhibitors enhance the efficacy of triazoles against Scedosporium prolificans via induction of apoptosis

Scedosporium prolificans is a pathogenic mold resistant to current antifungals, and infection results in high mortality. Simultaneous targeting of both ergosterol biosynthesis and heat shock protein 90 (Hsp90) or the calcineurin pathway in S. prolificans may be an important strategy for enhancing the potency of antifungal agents. We hypothesized that the inactive triazoles posaconazole (PCZ) and itraconazole (ICZ) acquire fungicidal activity when combined with the calcineurin inhibitor tacrolimus (TCR) or Hsp90 inhibitor 17-demethoxy-17-(2-propenylamino) geldanamycin (17AAG). PCZ, ICZ, TCR and 17AAG alone were inactive in vitro against S. prolificans spores (MICs > 128 μg/ml). In contrast, MICs for PCZ or ICZ in combination with TCR or 17AAG (0.125-0.50 μg/ml) were much lower compared with drug alone. In addition PCZ and ICZ in combination with TCR or 17AAG became fungicidal. Because apoptosis is regulated by the calcineurin pathway in fungi and is under the control of Hsp90, we hypothesized that this synergistic fungicidal effect is mediated via apoptosis. This observed fungicidal activity was mediated by increased apoptosis of S. prolificans germlings, as evidenced by reactive oxygen species accumulation, decreased mitochondrial membrane potential, phosphatidylserine externalization, and DNA fragmentation. Furthermore, induction of caspase-like activity was correlated with TCR or 17AAG + PCZ/ICZ-induced cell death. In conclusion, we report for the first time that PCZ or ICZ in combination with TCR or 17AAG renders S. prolificans exquisitely sensitive to PCZ or ICZ via apoptosis. This finding may stimulate the development of new therapeutic strategies for patients infected with this recalcitrant fungus.

Antifungal activity of naphthoquinoidal compounds in vitro against fluconazole-resistant strains of different Candida species: a special emphasis on mechanisms of action on Candida tropicalis

In recent decades, the incidence of candidemia in tertiary hospitals worldwide has substantially increased. These infections are a major cause of morbidity and mortality; in addition, they prolong hospital stays and raise the costs associated with treatment. Studies have reported a significant increase in infections by non-albicans Candida species, especially C. tropicalis. The number of antifungal drugs on the market is small in comparison to the number of antibacterial agents available. The limited number of treatment options, coupled with the increasing frequency of cross-resistance, makes it necessary to develop new therapeutic strategies. The objective of this study was to evaluate and compare the antifungal activities of three semisynthetic naphthofuranquinone molecules against fluconazole-resistant Candida spp. strains. These results allowed to us to evaluate the antifungal effects of three naphthofuranquinones on fluconazole-resistant C. tropicalis. The toxicity of these compounds was manifested as increased intracellular ROS, which resulted in membrane damage and changes in cell size/granularity, mitochondrial membrane depolarization, and DNA damage (including oxidation and strand breakage). In conclusion, the tested naphthofuranquinones (compounds 1-3) exhibited in vitro cytotoxicity against fluconazole-resistant Candida spp. strains.

Antimicrobial peptides from fish

Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.

Phenoptosis in yeasts

The current view on phenoptosis and apoptosis as genetic programs aimed at eliminating potentially dangerous organisms and cells, respectively, is given. Special emphasis is placed on apoptosis (phenoptosis) in yeasts: intracellular defects and a plethora of external stimuli inducing apoptosis in yeasts; distinctive morphological and biochemical hallmarks accompanying apoptosis in yeasts; pro- and antiapoptotic factors involved in yeast apoptosis signaling; consecutive stages of apoptosis from external stimulus to the cell death; a prominent role of mitochondria and other organelles in yeast apoptosis; possible pathways for release of apoptotic factors from the intermembrane mitochondrial space into the cytosol are described. Using some concrete examples, the obvious physiological importance and expediency of altruistic death of yeast cells is shown. Poorly known aspects of yeast apoptosis and prospects for yeast apoptosis study are defined.

Reactive oxygen species-inducing antifungal agents and their activity against fungal biofilms

Invasive fungal infections are associated with very high mortality rates ranging from 20–90% for opportunistic fungal pathogens such as Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. Fungal resistance to antimycotic treatment can be genotypic (due to resistant strains) as well as phenotypic (due to more resistant fungal lifestyles, such as biofilms). With regard to the latter, biofilms are considered to be critical in the development of invasive fungal infections. However, there are only very few antimycotics, such as miconazole (azoles), echinocandins and liposomal formulations of amphotericin B (polyenes), which are also effective against fungal biofilms. Interestingly, these antimycotics all induce reactive oxygen species (ROS) in fungal (biofilm) cells. This review provides an overview of the different classes of antimycotics and novel antifungal compounds that induce ROS in fungal planktonic and biofilm cells. Moreover, different strategies to further enhance the antibiofilm activity of such ROS-inducing antimycotics will be discussed.

The calcineurin pathway inhibitor tacrolimus enhances the in vitro activity of azoles against Mucorales via apoptosis

The calcineurin pathway regulates antifungal drug resistance and the virulence of several major human-pathogenic fungi, including the recalcitrant Mucorales. We hypothesized that the fungistatic triazoles posaconazole (PCZ) and itraconazole (ICZ) become fungicidal in the setting of the calcineurin inhibitor tacrolimus (TCR) and that such an effect is mediated through apoptosis. Fungicidal activity and apoptosis were studied using standard microbiological techniques and hyphal metabolic and vital dye reduction assays at 37°C in RPMI 1640. Apoptosis was characterized by detecting intracellular Ca(2+), phosphatidylserine (PS) externalization, DNA fragmentation, plasma membrane integrity, chromatin condensation, reactive oxygen species (ROS) generation, caspase-like activity, ATP, and cytochrome c release. MICs for PCZ and ICZ alone were significantly higher (8 to 128 μg/ml) than those of PCZ or ICZ plus TCR (0.25 to 4 μg/ml) for Rhizopus oryzae, Cunninghamella bertholletiae, and Mucor circinelloides. Both PCZ and ICZ in combination with TCR became fungicidal, and their activity was mediated through increased apoptotic cell death of R. oryzae (10 to 50%), C. bertholletiae (5 to 50%), and M. circinelloides (5 to 55%) germlings, with morphological apoptotic changes characterized by externalization of PS, nuclear condensation, and DNA fragmentation. Moreover, activation of the caspase-like activity was correlated with cell death induced by TCR plus PCZ or ICZ. These changes correlated with elevated intracellular Ca(2+) and ROS levels and disturbance of mitochondrial potential. We found that PCZ or ICZ in combination with TCR renders Mucorales sensitive to triazoles via apoptotic death. These observations could serve as a new paradigm for the development of new therapeutic strategies.

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.

Mitochondrial respiratory pathways inhibition in Rhizopus oryzae potentiates activity of posaconazole and itraconazole via apoptosis

The incidence of mucormycosis has increased drastically in immunocompromised patients. Also the array of targets whose inhibition results in Mucorales death is limited. Recently, researchers identified mitochondria as important regulators of detoxification and virulence mechanisms in fungi. In this context, targeting the mitochondrial respiratory chain may provide a new platform for antifungal development. We hypothesized that targeting respiratory pathways potentiates triazoles activity via apoptosis. We found that simultaneous administration of antimycin A (AA) and benzohydroxamate (BHAM), inhibitors of classical and alternative mitochondrial pathways respectively, resulted in potent activity of posaconazole (PCZ) and itraconazole (ICZ) against Rhizopus oryzae. We observed cellular changes characteristic of apoptosis in R. oryzae cells treated with PCZ or ICZ in combination with AA and BHAM. The fungicidal activity of this combination against R. oryzae was correlated with intracellular reactive oxygen species accumulation (ROS), phosphatidylserine externalization, mitochondrial membrane depolarization, and increased caspase like activity. DNA fragmentation and condensation assays also revealed apoptosis of R. oryzae cells. These apoptotic features were prevented by the addition of the ROS scavenger N-acetyl-cysteine. Taken together, these findings suggest that the use of PCZ or ICZ in combination with AA and BHAM makes R. oryzae exquisitely sensitive to treatment with triazoles via apoptosis. This strategy may serve as a new model for the development of improved or novel antifungal agents.

Caspofungin kills Candida albicans by causing both cellular apoptosis and necrosis

Caspofungin exerts candidacidal activity by inhibiting cell wall (1,3)-β-d-glucan synthesis. We investigated the physiologic mechanisms of caspofungin-induced Candida albicans cell death. Apoptosis (programmed cell death) and necrosis were studied after C. albicans SC5314 cells were exposed to caspofungin at 0.06, 0.125, and 0.5 μg/ml (0.5×, 1×, and 4× the MIC, respectively) for 3 h. Caspofungin at 0.125 and 0.5 μg/ml reduced cellular viability by >50%, as measured by colony counts and methylene blue exclusion. Apoptosis and necrosis were demonstrated by annexin V and propidium iodide staining for phosphatidylserine externalization and loss of membrane integrity, respectively. At all concentrations of caspofungin, 20 to 25% and 5 to 7% of C. albicans cells exhibited early apoptosis and late apoptosis/necrosis, respectively (P value was not significant [NS]). Necrosis, on the other hand, was significantly greater at 0.125 (43%) and 0.5 (48%) μg/ml than at 0.06 μg/ml (26%) (P values of 0.003 and 0.003, respectively). The induction of apoptosis at concentrations less than or equal to the MIC was corroborated by dihydrorhodamine 123 (DHR-123) and dihydroethidium (DHE) staining (reactive oxygen species production), JC-1 staining (mitochondrial membrane potential dissipation), and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) and 4',6-diamidino-2-phenylindole dihydrochloride (DAPI) staining (DNA damage and nuclear fragmentation). Moreover, electron microscopy of cells exposed to 0.125 μg/ml of caspofungin showed hallmark apoptotic features like chromatin margination and condensation and nuclear blebs. Apoptosis was associated with metacaspase 1 activation, as demonstrated by D2R staining. Caspofungin exerts activity against C. albicans by directly killing cells (resulting in necrosis) and causing others to undergo programmed cell death (apoptosis). Apoptosis is initiated at subinhibitory concentrations, suggesting that strategies to target this process may augment the benefits of antifungal agents.