Antifungal Mechanism of Action of Lactoferrin: Identification of H+-ATPase (P3A-Type) as a New Apoptotic-Cell Membrane Receptor

The Antimicrobial Activity of Human Defensins at Physiological Non-Permeabilizing Concentrations Is Caused by the Inhibition of the Plasma Membrane H+-ATPases

Human defensins are cysteine-rich peptides (Cys-rich peptides) of the innate immune system. Defensins contain an ancestral structural motif (i.e., γ-core motif) associated with the antimicrobial activity of natural Cys-rich peptides. In this study, low concentrations of human α- and β-defensins showed microbicidal activity that was not associated with cell membrane permeabilization. The cell death pathway was similar to that previously described for human lactoferrin, also an immunoprotein containing a γ-core motif. The common features were (1) cell death not related to plasma membrane (PM) disruption, (2) the inhibition of microbicidal activity via extracellular potassium, (3) the influence of cellular respiration on microbicidal activity, and (4) the influence of intracellular pH on bactericidal activity. In addition, in yeast, we also observed (1) partial K+-efflux mediated via Tok1p K+-channels, (2) the essential role of mitochondrial ATP synthase in cell death, (3) the increment of intracellular ATP, (4) plasma membrane depolarization, and (5) the inhibition of external acidification mediated via PM Pma1p H+-ATPase. Similar features were also observed with BM2, an antifungal peptide that inhibits Pma1p H+-ATPase, showing that the above coincident characteristics were a consequence of PM H+-ATPase inhibition. These findings suggest, for the first time, that human defensins inhibit PM H+-ATPases at physiological concentrations, and that the subsequent cytosolic acidification is responsible for the in vitro microbicidal activity. This mechanism of action is shared with human lactoferrin and probably other antimicrobial peptides containing γ-core motifs.

Transcriptomic and biochemical analyses revealed antifungal mechanism of trans-anethole on Aspergillus flavus growth

Plant volatile compounds have great potential for preventing and controlling fungal spoilage in post-harvest grains. Recently, we have reported the antifungal effects of trans-anethole, the main volatile constituent of the Illicium verum fruit, on Aspergillus flavus. In this study, the inhibitory mechanisms of trans-anethole against the growth of A. flavus mycelia were investigated using transcriptomic and biochemical analyses. Biochemical and transcriptomic changes in A. flavus mycelia were evaluated after exposure to 0.2 μL/mL trans-anethole. Scanning electron microscopy showed that trans-anethole treatment resulted in the surface wrinkling of A. flavus mycelia, and calcofluor white staining confirmed that trans-anethole treatment disrupted the mycelial cell wall structure. Annexin V-fluorescein isothiocyanate/propidium iodide double staining suggested that trans-anethole induced apoptosis in A. flavus mycelia. Reduced mitochondrial membrane potential and DNA damage were observed in trans-anethole-treated A. flavus mycelia using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-imidacarbocyanine and 4',6-diamidino-2-phenylindole staining, respectively. 2',7'- Dichloro-dihydro-fluorescein diacetate staining and biochemical assays demonstrated that trans-anethole treatment cause the accumulation of reactive oxygen species in the A. flavus mycelia. Transcriptome results showed that 1673 genes were differentially expressed in A. flavus mycelia exposed to trans-anethole, which were mainly associated with multidrug transport, oxidative phosphorylation, citric acid cycle, ribosomes, and cyclic adenosine monophosphate signaling. We propose that trans-anethole can inhibit the growth of A. flavus mycelia by disrupting the cell wall structure, blocking the multidrug transport process, disturbing the citric acid cycle, and inducing apoptosis. This study provides new insights into the inhibitory mechanism of trans-anethole on A. flavus mycelia and will be helpful for the development of natural fungicides. KEY POINTS: • Biochemical analyses of A. flavus mycelia exposed to trans-anethole were performed • Transcriptomic changes in trans-anethole-treated A. flavus mycelia were analyzed • An inhibitory mechanism of trans-anethole on the growth of A. flavus mycelia was proposed.

Various Biomimetics, Including Peptides as Antifungals

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

Testing Antimicrobial Properties of Human Lactoferrin-Derived Fragments

Lactoferrin, an iron-binding glycoprotein, plays a significant role in the innate immune system, with antibacterial, antivirial, antifungal, anticancer, antioxidant and immunomodulatory functions reported. It is worth emphasizing that not only the whole protein but also its derived fragments possess antimicrobial peptide (AMP) activity. Using AmpGram, a top-performing AMP classifier, we generated three novel human lactoferrin (hLF) fragments: hLF 397-412, hLF 448-464 and hLF 668-683, predicted with high probability as AMPs. For comparative studies, we included hLF 1-11, previously confirmed to kill some bacteria. With the four peptides, we treated three Gram-negative and three Gram-positive bacterial strains. Our results indicate that none of the three new lactoferrin fragments have antimicrobial properties for the bacteria tested, but hLF 1-11 was lethal against Pseudomonas aeruginosa. The addition of serine protease inhibitors with the hLF fragments did not enhance their activity, except for hLF 1-11 against P. aeruginosa, which MIC dropped from 128 to 64 µg/mL. Furthermore, we investigated the impact of EDTA with/without serine protease inhibitors and the hLF peptides on selected bacteria. We stress the importance of reporting non-AMP sequences for the development of next-generation AMP prediction models, which suffer from the lack of experimentally validated negative dataset for training and benchmarking.

The application of lactoferrin in infant formula: The past, present and future

Human milk is universally regarded as the gold standard to fulfill nutrition needs of infants. Lactoferrin (LF) is a major multiple bioactive glycoprotein in human milk but little is presented in infant formula. LF can resist digestion in the infant gastrointestinal tract and is absorbed into the bloodstream in an intact form to perform physiological functions. Evidence suggest that LF prevents pathogen infection, promotes immune system development, intestinal development, brain development and bone health, as well as ameliorates iron deficiency anemia. However, more clinical studies of LF need to be further elucidated to determine an appropriate dosage for application in infant formula. LF is sensitive to denaturation induced by processing of infant formula such as heat treatments and spay drying. Thus, further studies should be focus on maximizing the retention of LF activity in the infant formula process. This review summarizes the structural features of LF. Then the digestion, absorption and metabolism of LF in infants are discussed, followed by the function of LF for infants. Further, we summarize LF in infant formula and effects of processing of infant formula on bioactivities of LF, as well as future perspectives of LF research.

Lactoferrin versus Long-Acting Penicillin in Reducing Elevated Anti-Streptolysin O Titer in Cases of Tonsillopharyngitis

Background

Beta-Hemolytic streptococci are the most frequent bacteria causing tonsillitis. Lactoferrin may play a role in the treatment of chronic tonsillitis due to its direct antimicrobial activity.

Objective

To assess the possible role of lactoferrin in reduction of raised serum Anti-Streptolysin O Titer (ASOT) in cases of chronic tonsillopharyngitis in comparison to long acting penicillin.

Methods

This study included 117 children with tonsillopharyngitis with high ASOT randomly divided into three groups; group 1 treated with lactoferrin, group 2 treated with long acting penicillin and group 3 treated with both drugs. For all patients ASOT was measured after three and six months of starting treatment.

Results

This study included 60 males and 57 females with the mean age (8.5 ± 2.4). There is statistically significant reduction in ASOT in all groups after three months of treatment. ASOT after 3 months was significantly lower in group1 (370±440) and group 3 (350±450) in comparison to group 2 (420±560) with p value 0.02, 0.004, respectively, with no significant difference in comparing group 1 to group 3 p value 0.4. Also, ASO titre after 6 months was significantly lower in group1 (350±420) and group 3 (340±440) in comparison to group 2 (420±550) with p value 0.02, 0.007, respectively, with no significant difference in comparing group 1 to group 3 p value 0.5. In comparing ASOT at three months and six months of treatment in the three studied groups; it decreased by 2% in group 1, and 1.6% in group 3 and no change in group 2.

Conclusion

Lactoferrin alone or in combination with long acting penicillin is safe and more effective than long acting penicillin alone in reducing ASOT. Treatment for six months with lactoferrin alone or in combination with long acting penicillin could offer a better response.

Lactoferrin as a Human Genome “Guardian”—An Overall Point of View

Structural abnormalities causing DNA modifications of the ethene and propanoadducts can lead to mutations and permanent damage to human genetic material. Such changes may cause premature aging and cell degeneration and death as well as severe impairment of tissue and organ function. This may lead to the development of various diseases, including cancer. In response to a damage, cells have developed defense mechanisms aimed at preventing disease and repairing damaged genetic material or diverting it into apoptosis. All of the mechanisms described above are part of the repertoire of action of Lactoferrin—an endogenous protein that contains iron in its structure, which gives it numerous antibacterial, antiviral, antifungal and anticancer properties. The aim of the article is to synthetically present the new and innovative role of lactoferrin in the protection of human genetic material against internal and external damage, described by the modulation mechanisms of the cell cycle at all its levels and the mechanisms of its repair.

A review on lactoferrin as a proton pump inhibitor

Lactoferrin (Lf) is a versatile natural milk-derived protein that exhibits multiple interesting biological activities. Since it is safe for human administration and currently manufactured using low cost and well-established large-scale processes, the Lf scientific community has been devoted at dissecting its mechanisms of action towards its more rational and efficient use for various applications. Emerging literature has identified proton pumping ATPases as molecular targets of Lf in different cellular models linked to distinct activities of this natural protein. Information on this subject has not been systematically analysed before, hence herein we review the current state of art on the effect of Lf on proton pumping ATPases. Though structurally different, we propose that Lf holds a proton pump inhibitor (PPI)-like activity based on the functional resemblance with the classical inhibitors of the stomach H⁺/K⁺-ATPase. The downstream events and outcomes of the PPI-like activity of Lf, as well as its impact for the development of improved Lf applications are also discussed.

Effect of fluocinolone acetonide (0.1%) treatment in oral lichen planus patients on salivary lactoferrin levels and Candida colonization: a prospective study

Background

Although topical steroids are an effective treatment for oral lichen planus, they can have suppressive effects on oral immunity and predispose the patients to Candida overgrowth. Lactoferrin is a crucial local immunity protein in the oral cavity with important antimicrobial activity. The aim of this study was to prospectively investigate salivary lactoferrin secretion levels and Candida colonization in oral lichen planus patients treated with fluocinolone acetonide 0.1% in orabase.

Methods

Saliva samples were collected from 15 oral lichen planus subjects who had never received topical steroid treatment prior to this study and 15 healthy volunteers to determine their salivary lactoferrin levels using an enzyme-linked immunosorbent assay and to investigate the presence of oral Candida species at baseline and 3 months after treatment with fluocinolone acetonide 0.1% in orabase. Statistical analysis was performed to compare lactoferrin secretion and Candida colonization levels between the groups using the Mann–Whitney U test for independent data or the Wilcoxon Signed-Rank test for paired data.

Results

The salivary lactoferrin secretion level was not significantly different between the control group and oral lichen planus patients or between before and after treatment with fluocinolone acetonide 0.1% in orabase (P > 0.05). Candida was detected in 11 (73.33%) healthy volunteers, 8 (53.33%) oral lichen planus patients before treatment, and 9 (60%) oral lichen planus patients after treatment with fluocinolone acetonide 0.1% in orabase. There was no significant difference in Candida counts between the groups (P > 0.05).

Conclusion

Our study indicates that using fluocinolone acetonide 0.1% in orabase to treat oral lichen planus for 3 months did not affect salivary lactoferrin protein secretion or Candida carriage.

Trial registration The trial was registered at the Thai Clinical Trials Registry (TCTR identifier: TCTR20200723002).

New 24-Membered Macrolactins Isolated from Marine Bacteria Bacillus siamensis as Potent Fungal Inhibitors against Sugarcane Smut

Sugarcane smut, caused by Sporisorium scitamineum, is one of the most devastating fungal diseases affecting sugarcane worldwide. To develop a potent sugarcane smut fungicide, secondary metabolites of marine-derived Bacillus siamensis were isolated and screened for inhibitory activities, which led to the discovery of five new 24-membered macrolactins, bamemacrolactins A-E (1-5), with 3 being the most potent inhibitor. The antifungal mechanism of 3 was studied by assessing its effects on mycelial morphology and the cell wall. Differential proteomics were used to analyze proteins in S. scitamineum upon treatment with bamemacrolactin C and to elucidate its antifungal mechanism. A total of 533 differentially expressed proteins were found. After the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses, eight target proteins were selected, and their functions were discussed. Six of the eight proteins were reported as antifungal targets. The target proteins are involved in the oxidative phosphorylation pathway. Therefore, the potent inhibition of S. scitamineum by compound 3 is most likely through oxidative phosphorylation and targeting a series of enzymes.

Bifunctional Inhibitors from Capsicum chinense Seeds with Antimicrobial Activity and Specific Mechanism of Action Against Phytopathogenic Fungi

BACKGROUND

Antimicrobial peptides (AMPs) are found in the defense system in virtually all life forms, being present in many, if not all, plant species.

OBJECTIVE

The present work evaluated the antimicrobial, enzymatic activity and mechanism of action of the PEF2 fraction from Capsicum chinense Jack. seeds against phytopathogenic fungi.

METHODS

Peptides were extracted from C. chinense seeds and subjected to reverse-phase chromatography on an HPLC system using a C18 column coupled to a C8 guard column, then the obtained PEF2 fraction was rechromatographed using a C2/C18 column. Two fractions, named PEF2A and PEF2B, were obtained. The fractions were tested for antimicrobial activity on Colletotrichum gloeosporioides, Colletotrichum lindemuthianum, Fusarium oxysporum and Fusarium solani. Trypsin inhibition assays, reverse zymographic detection of protease inhibition and α-amylase activity assays were also performed. The mechanism of action by which PEF2 acts on filamentous fungi was studied through analysis of membrane permeability and production of reactive oxygen species (ROS). Additionally, we investigated mitochondrial functionality and caspase activation in fungal cells.

RESULTS

It is possible to observe that PEF2 significantly inhibited trypsin activity and T. molitor larval α-amylase activity. The PEF2 fraction was able to inhibit the growth of C. gloeosporioides, C. lindemuthianum and F. oxysporum. PEF2A inhibited the growth of C. lindemuthianum (75%) and F. solani (43%). PEF2B inhibited C. lindemuthianum growth (66%) and F. solani (94%). PEF2 permeabilized F. solani cell membranes and induced ROS in F. oxysporum and F. solani. PEF2 could dissipate mitochondrial membrane potential but did not cause the activation of caspases in all studied fungi.

CONCLUSION

The results may contribute to the biotechnological application of these AMPs in the control of pathogenic microorganisms in plants of agronomic importance.

Membrane-Interacting Antifungal Peptides

The incidence of invasive fungal infections is increasing worldwide, resulting in more than 1.6 million deaths every year. Due to growing antifungal drug resistance and the limited number of currently used antimycotics, there is a clear need for novel antifungal strategies. In this context, great potential is attributed to antimicrobial peptides (AMPs) that are part of the innate immune system of organisms. These peptides are known for their broad-spectrum activity that can be directed toward bacteria, fungi, viruses, and/or even cancer cells. Some AMPs act via rapid physical disruption of microbial cell membranes at high concentrations causing cell leakage and cell death. However, more complex mechanisms are also observed, such as interaction with specific lipids, production of reactive oxygen species, programmed cell death, and autophagy. This review summarizes the structure and mode of action of antifungal AMPs, thereby focusing on their interaction with fungal membranes.

Lactoferrin perturbs lipid rafts and requires integrity of Pma1p-lipid rafts association to exert its antifungal activity against Saccharomyces cerevisiae

Lactoferrin (Lf) is a bioactive milk-derived protein with remarkable wide-spectrum antifungal activity. To deepen our understanding of the molecular mechanisms underlying Lf cytotoxicity, the role of plasma membrane ergosterol- and sphingolipid-rich lipid rafts and their association with the proton pump Pma1p was explored. Pma1p was previously identified as a Lf-binding protein. Results showed that bovine Lf (bLf) perturbs ergosterol-rich lipid rafts organization by inducing intracellular accumulation of ergosterol. Using yeast mutant strains lacking lipid rafts-associated proteins or enzymes involved in the synthesis of ergosterol and sphingolipids, we found that perturbations in the composition of these membrane domains increase resistance to bLf-induced yeast cell death. Also, when Pma1p-lipid rafts association is compromised in the Pma1-10 mutant and in the absence of the Pma1p-binding protein Ast1p, the bLf killing activity is impaired. Altogether, results showed that the perturbation of lipid rafts and the inhibition of both Pma1p and V-ATPase activities mediate the antifungal activity of bLf. Since it is suggested that the combination of conventional antifungals with lipid rafts-disrupting compounds is a powerful antifungal approach, our data will help to pave the way for the use of bLf alone or in combination for the treatment/eradication of clinically and agronomically relevant yeast pathogens/fungi.

The Effect of Honokiol on Ergosterol Biosynthesis and Vacuole Function in Candida albicans

Ergosterol, an essential constituent of membrane lipids of yeast, is distributed in both the cell membrane and intracellular endomembrane components such as vacuoles. Honokiol, a major polyphenol isolated from Magnolia officinalis, has been shown to inhibit the growth of Candida albicans. Here, we assessed the effect of honokiol on ergosterol biosynthesis and vacuole function in C. albicans. Honokiol could decrease the ergosterol content and upregulate the expression of genes related with the ergosterol biosynthesis pathway. The exogenous supply of ergosterol attenuated the toxicity of honokiol against C. albicans. Honokiol treatment could induce cytosolic acidification by blocking the activity of the plasma membrane Pma1p H⁺-ATPase. Furthermore, honokiol caused abnormalities in vacuole morphology and function. Concomitant ergosterol feeding to some extent restored the vacuolar morphology and the function of acidification in cells treated by honokiol. Honokiol also disrupted the intracellular calcium homeostasis. Amiodarone attenuated the antifungal effects of honokiol against C. albicans, probably due to the activation of the calcineurin signaling pathway which is involved in honokiol tolerance. In conclusion, this study demonstrated that honokiol could inhibit ergosterol biosynthesis and decrease Pma 1p H⁺-ATPase activity, which resulted in the abnormal pH in vacuole and cytosol.

Lactoferrin and Its Derived Peptides: An Alternative for Combating Virulence Mechanisms Developed by Pathogens

Due to the emergence of multidrug-resistant pathogens, it is necessary to develop options to fight infections caused by these agents. Lactoferrin (Lf) is a cationic nonheme multifunctional glycoprotein of the innate immune system of mammals that provides numerous benefits. Lf is bacteriostatic and/or bactericidal, can stimulate cell proliferation and differentiation, facilitate iron absorption, improve neural development and cognition, promote bone growth, prevent cancer and exert anti-inflammatory and immunoregulatory effects. Lactoferrin is present in colostrum and milk and is also produced by the secondary granules of polymorphonuclear leukocytes, which store this glycoprotein and release it at sites of infection. Lf is also present in many fluids and exocrine secretions, on the surfaces of the digestive, respiratory and reproductive systems that are commonly exposed to pathogens. Apo-Lf (an iron-free molecule) can be microbiostatic due to its ability to capture ferric iron, blocking the availability of host iron to pathogens. However, apo-Lf is mostly microbicidal via its interaction with the microbial surface, causing membrane damage and altering its permeability function. Lf can inhibit viral entry by binding to cell receptors or viral particles. Lf is also able to counter different important mechanisms evolved by microbial pathogens to infect and invade the host, such as adherence, colonization, invasion, production of biofilms and production of virulence factors such as proteases and toxins. Lf can also cause mitochondrial and caspase-dependent regulated cell death and apoptosis-like in pathogenic yeasts. All of these mechanisms are important targets for treatment with Lf. Holo-Lf (the iron-saturated molecule) can contain up to two ferric ions and can also be microbicidal against some pathogens. On the other hand, lactoferricins (Lfcins) are peptides derived from the N-terminus of Lf that are produced by proteolysis with pepsin under acidic conditions, and they cause similar effects on pathogens to those caused by the parental Lf. Synthetic analog peptides comprising the N-terminus Lf region similarly exhibit potent antimicrobial properties. Importantly, there are no reported pathogens that are resistant to Lf and Lfcins; in addition, Lf and Lfcins have shown a synergistic effect with antimicrobial and antiviral drugs. Due to the Lf properties being microbiostatic, microbicidal, anti-inflammatory and an immune modulator, it represents an excellent natural alternative either alone or as adjuvant in the combat to antibiotic multidrug-resistant bacteria and other pathogens. This review aimed to evaluate the data that appeared in the literature about the effects of Lf and its derived peptides on pathogenic bacteria, protozoa, fungi and viruses and how Lf and Lfcins inhibit the mechanisms developed by these pathogens to cause disease.

The role of fungi in fungal keratitis

Fungal keratitis (FK) accounts for approximately half of the microbial keratitis encountered in low middle income countries (LMICs) and predominantly affect the working rural-poor. FK causes significant morbidity with the majority of patients left with moderate or worse visual impairment and approximately 25% requiring expensive and often unsuccessful surgical interventions. The severity of FK and the resultant corneal damage or resolution can be attributed to i) the virulence and bioburden of the fungal pathogen, ii) the host defense mechanism and immune response and iii) sub-optimal diagnostics and anti-fungal treatment strategies. This review provides a comprehensive overview of the multifaceted components that drive FK progression and resolution, highlighting where knowledge gaps exist and areas that warrant further research.

The Biology of Lactoferrin, an Iron-Binding Protein That Can Help Defend Against Viruses and Bacteria

Lactoferrin is a nutrient classically found in mammalian milk. It binds iron and is transferred via a variety of receptors into and between cells, serum, bile, and cerebrospinal fluid. It has important immunological properties, and is both antibacterial and antiviral. In particular, there is evidence that it can bind to at least some of the receptors used by coronaviruses and thereby block their entry. Of importance are Heparan Sulfate Proteoglycans (HSPGs) and the host receptor angiotensin-converting enzyme 2 (ACE2), as based on other activities lactoferrin might prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from attaching to the host cells. Lactoferrin (and more specifically enteric-coated LF because of increased bioavailability) may consequently be of preventive and therapeutic value during the present COVID-19 pandemic.

Lactoferrin Is Broadly Active against Yeasts and Highly Synergistic with Amphotericin B

Lactoferrin (LF) is a multifunctional milk protein with antimicrobial activity against a range of pathogens. While numerous studies report that LF is active against fungi, there are considerable differences in the level of antifungal activity and the capacity of LF to interact with other drugs. Here we undertook a comprehensive evaluation of the antifungal spectrum of activity of three defined sources of LF across 22 yeast and 24 mold species and assessed its interactions with six widely used antifungal drugs. LF was broadly and consistently active against all yeast species tested (MICs, 8 to 64 μg/ml), with the extent of activity being strongly affected by iron saturation. LF was synergistic with amphotericin B (AMB) against 19 out of 22 yeast species tested, and synergy was unaffected by iron saturation but was affected by the extent of LF digestion. LF-AMB combination therapy significantly prolonged the survival of Galleria mellonella wax moth larvae infected with Candida albicans or Cryptococcus neoformans and decreased the fungal burden 12- to 25-fold. Evidence that LF directly interacts with the fungal cell surface was seen via scanning electron microscopy, which showed pore formation, hyphal thinning, and major cell collapse in response to LF-AMB synergy. Important virulence mechanisms were disrupted by LF-AMB treatment, which significantly prevented biofilms in C. albicans and C. glabrata, inhibited hyphal development in C. albicans, and reduced cell and capsule size and phenotypic diversity in Cryptococcus Our results demonstrate the potential of LF-AMB as an antifungal treatment that is broadly synergistic against important yeast pathogens, with the synergy being attributed to the presence of one or more LF peptides.

Role of membrane sterol and redox system in the anti-candida activity reported for Mo-CBP2, a protein from Moringa oleifera seeds

Plant proteins are emerging as an alternative to conventional treatments against candidiasis. The aim of this study was to better understand the mechanism of action of Mo-CBP₂ against Candida spp, evaluating redox system activity, lipid peroxidation, DNA degradation, cytochrome c release, medium acidification, and membrane interaction. Anti-candida activity of Mo-CBP₂ decreased in the presence of ergosterol, which was not observed with antioxidant agents. C. albicans treated with Mo-CBP₂ also had catalase and peroxidase activities inhibited, while superoxide dismutase was increased. Mo-CBP₂ increased the lipid peroxidation, but it did not alter the ergosterol profile in live cells. External medium acidification was strongly inhibited, and cytochrome c release and DNA degradation were detected. Mo-CBP₂ interacts with cell membrane constituents, changes redox system enzymes in C. albicans and causes lipid peroxidation by ROS overproduction. DNA degradation and cytochrome c release suggest apoptotic or DNAse activity. Lipid peroxidation and H⁺-ATPases inhibition may induce the process of apoptosis. Finally, Mo-CBP₂ did not have a cytotoxic effect in mammalian Vero cells. This study highlights the biotechnological potential of Mo-CBP₂ as a promising molecule with low toxicity and potent activity. Further studies should be performed to better understand its mode of action and toxicity.

Cytosolic Acidification Is the First Transduction Signal of Lactoferrin-induced Regulated Cell Death Pathway

In yeast, we reported the critical role of K⁺-efflux for the progress of the regulated cell death (RCD) induced by human lactoferrin (hLf), an antimicrobial protein of the innate immune system that blocks Pma1p H⁺-ATPase. In the present study, the K⁺ channel Tok1p was identified as the K⁺ channel-mediating K⁺-efflux, as indicated by the protective effect of extracellular K⁺ (30 mM), K⁺-channel blockers, and the greater hLf-resistance of TOK1-disrupted strains. K⁺-depletion was necessary but not sufficient to induce RCD as inferred from the effects of valinomycin, NH₄Cl or nigericin which released a percentage of K⁺ similar to that released by lactoferrin without affecting cell viability. Cytosolic pH of hLf-treated cells decreased transiently (0.3 pH units) and its inhibition prevented the RCD process, indicating that cytosolic acidification was a necessary and sufficient triggering signal. The blocking effect of lactoferrin on Pma1p H⁺-ATPase caused a transitory decrease of cytosolic pH, and the subsequent membrane depolarization activated the voltage-gated K⁺ channel, Tok1p, allowing an electrogenic K⁺-efflux. These ionic events, cytosolic accumulation of H⁺ followed by K⁺-efflux, constituted the initiating signals of this mitochondria-mediated cell death. These findings suggest, for the first time, the existence of an ionic signaling pathway in RCD.

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.

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.

Regulated Cell Death as a Therapeutic Target for Novel Antifungal Peptides and Biologics

The rise of microbial pathogens refractory to conventional antibiotics represents one of the most urgent and global public health concerns for the 21st century. Emergence of Candida auris isolates and the persistence of invasive mold infections that resist existing treatment and cause severe illness has underscored the threat of drug-resistant fungal infections. To meet these growing challenges, mechanistically novel agents and strategies are needed that surpass the conventional fungistatic or fungicidal drug actions. Host defense peptides have long been misunderstood as indiscriminant membrane detergents. However, evidence gathered over the past decade clearly points to their sophisticated and selective mechanisms of action, including exploiting regulated cell death pathways of their target pathogens. Such peptides perturb transmembrane potential and mitochondrial energetics, inducing phosphatidylserine accessibility and metacaspase activation in fungi. These mechanisms are often multimodal, affording target pathogens fewer resistance options as compared to traditional small molecule drugs. Here, recent advances in the field are examined regarding regulated cell death subroutines as potential therapeutic targets for innovative anti-infective peptides against pathogenic fungi. Furthering knowledge of protective host defense peptide interactions with target pathogens is key to advancing and applying novel prophylactic and therapeutic countermeasures to fungal resistance and pathogenesis.

In vitro and in vivo anticandidal activities of alginate-enclosed chitosan-calcium phosphate-loaded Fe-bovine lactoferrin nanocapsules

Aim:

To study the in vitro and in vivo anticandidal activity of nanocapsulated bovine lactoferrin.

Materials & methods:

In vitro and in vivo antimicrobial activities were conducted to study the anticandidal activities of nanocapsules (NCs).

Results:

The NCs showed good anticandidal activities. The disruption of cell wall and cell membrane was noted via microscopy studies. The NCs changed the normal growth profile of Candida albicans. NCs reduced the colony forming unit in kidney and blood samples. Histopathological examination showed better cell structure and coordination compared with untreated mice kidney. NCs also enhanced the natural killing properties of C. albicans by epithelial cells.

Conclusion:

NCs have effective anticandidal properties and have the potential as a therapeutic agent against candidiasis.

Previous study revealed that lactoferrin had potent anticandidal action against C. albicans. However, encapsulated lactoferrin has never been tested for anticandidal activity in detail. In the present study, we evaluate nanocapsulated lactoferrin for anticandidal effects. To observe the anticandidal properties of encapsulated lactoferrin, various studies were conducted. Our findings showed that encapsulated lactoferrin demonstrates remarkable efficacy against C. albicans.

Elucidation of antimicrobial activity and mechanism of action by N-substituted carbazole derivatives

Compounds belonging to a carbazole series have been identified as potent fungal plasma membrane proton adenosine triphophatase (H+-ATPase) inhibitors with a broad spectrum of antifungal activity. The carbazole compounds inhibit the adenosine triphosphate (ATP) hydrolysis activity of the essential fungal H+-ATPase, thereby functionally inhibiting the extrusion of protons and extracellular acidification, processes that are responsible for maintaining high plasma membrane potential. The compound class binds to and inhibits the H+-ATPase within minutes, leading to fungal death after 1-3h of compound exposure in vitro. The tested compounds are not selective for the fungal H+-ATPase, exhibiting an overlap of inhibitory activity with the mammalian protein family of P-type ATPases; the sarco(endo)plasmic reticulum calcium ATPase (Ca2+-ATPase) and the sodium potassium ATPase (Na+,K+-ATPase). The ion transport in the P-type ATPases is energized by the conversion of ATP to adenosine diphosphate (ADP) and phosphate and a general inhibitory mechanism mediated by the carbazole derivative could therefore be blocking of the active site. However, biochemical studies show that increased concentrations of ATP do not change the inhibitory activity of the carbazoles suggesting they act as allosteric inhibitors. Furthermore decreased levels of intracellular ATP would suggest that the compounds inhibit the H+-ATPase indirectly, but Candida albicans cells exposed to potent H+-ATPase-inhibitory carbazoles result in increased levels of intracellular ATP, indicating direct inhibition of H+-ATPase.

Identification of Antifungal H+-ATPase Inhibitors with Effect on Plasma Membrane Potential

The plasma membrane H⁺-ATPase (Pma1) is an essential fungal protein and a proposed target for new antifungal medications. The compounds in a small-molecule library containing ∼191,000 commercially available compounds were screened for their ability to inhibit Saccharomyces cerevisiae plasma membranes containing Pma1. The overall hit rate was 0.2%, corresponding to 407 compounds. These hit compounds were further evaluated for ATPase selectivity and broad-spectrum antifungal activity. Following this work, one Pma1 inhibitor series based on compound 14 and analogs was selected for further evaluation. This compound series was able to depolarize the membrane and inhibit extracellular acidification in intact fungal cells concomitantly with a significant increase in intracellular ATP levels. Collectively, we suggest that these effects may be a common feature of Pma1 inhibitors. Additionally, the work uncovered a dual mechanism for the previously identified cationic peptide BM2, revealing fungal membrane disruption, in addition to Pma1 inhibition. The methods presented here provide a solid platform for the evaluation of Pma1-specific inhibitors in a drug development setting. The present inhibitors could serve as a starting point for the development of new antifungal agents with a novel mode of action.

The Antifungal Activity of Lactoferrin and Its Derived Peptides: Mechanisms of Action and Synergy with Drugs against Fungal Pathogens

Lactoferrin is a multifunctional iron-binding glycoprotein belonging to the transferrin family. It is found abundantly in milk and is present as a major protein in human exocrine secretions where it plays a role in the innate immune response. Various antifungal functions of lactoferrin have been reported including a wide spectrum of activity across yeasts and molds and synergy with other antifungal drugs in combination therapy, and various modes of action have been proposed. Bioactive peptides derived from lactoferrin can also exhibit strong antifungal activity, with some surpassing the potency of the whole protein. This paper reviews current knowledge of the spectrum of activity, proposed mechanisms of action, and capacity for synergy of lactoferrin and its peptides, including the three most studied derivatives: lactoferricin, lactoferrampin, and Lf(1-11), as well as some lactoferrin-derived variants and modified peptides.