Modulation of in vitro fungicidal activity of human lactoferrin against Candida albicans by extracellular cation concentration and target cell metabolic activity

Combination of a pH-responsive peptide amphiphile and a conventional antibiotic in treating Gram-negative bacteria

BACKGROUND

Clinical treatments ofgastric infections using antibiotics suffer from the undesired killing of commensal bacteria and emergence of antibiotic resistance. It is desirable to develop pH-responsive antimicrobial peptides (AMPs) that kill pathogenic bacteria such as H. pyloriand resistant E. coli under acidic environment with minimal impact to commensal bacteria whilst not causing antibiotic resistance.

EXPERIMENTS

Using a combined approach of cell assays, molecular dynamics (MD) simulations and membrane models facilitating biophysical and biochemical measurements including small angle neutron scattering (SANS), we have characterized the pH-responsive physiochemical properties and antimicrobial performance of two amphiphilic AMPs, GIIKDIIKDIIKDI-NH2 and GIIKKIIDDIIKKI-NH2 (denoted as 3D and 2D, respectively), that were designed by selective substitutions of cationic residues of Lys (K) in the extensively studied AMP G(IIKK)3I-NH2 with anionic residue Asp (D).

FINDINGS

Whilst 2D kept non-ordered coils across the entire pH range studied, 3D displayed a range of secondary structures when pH was shifted from basic to acidic, with distinct self-assembly into nanofibers in aqueous environment. Further experimental and modeling studies revealed that the AMPs interacted differently with the inner and outer membranes of Gram-negative bacteria in a pH-responsive manner and that the structural features characterized by membrane leakage and intramembrane nanoaggregates revealed from fluorescence spectroscopy and SANS were well linked to antimicrobial actions. Different antimicrobial efficacies of 2D and 3D were underlined by the interplay between their ability to bind to the outer membrane lipid LPS (lipopolysaccharide), outer membrane permeability change and inner membrane depolarization and leakage. Furthermore, AMP's binding with the inner membrane under acidic condition caused both the dissipation of membrane potential (Δψ) and the continuous dissipation of transmembrane ΔpH, with Δψ and ΔpH being the key components of the proton motive force. Combinations of antibiotic (Minocycline) with the pH-responsive AMP generated the synergistic effects against Gram-negative bacteria only under acidic condition. These features are crucial to target applications to gastric infections, anti-acne and wound healing.

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).

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 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.

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.

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.

Intestinal amoebiasis: 160 years of its first detection and still remains as a health problem in developing countries

Amoebiasis is a parasitic disease caused by Entamoeba histolytica (E. histolytica), an extracellular enteric protozoan. This infection mainly affects people from developing countries with limited hygiene conditions, where it is endemic. Infective cysts are transmitted by the fecal-oral route, excysting in the terminal ileum and producing invasive trophozoites (amoebae). E. histolytica mainly lives in the large intestine without causing symptoms; however, possibly as a result of so far unknown signals, the amoebae invade the mucosa and epithelium causing intestinal amoebiasis. E. histolytica possesses different mechanisms of pathogenicity for the adherence to the intestinal epithelium and for degrading extracellular matrix proteins, producing tissue lesions that progress to abscesses and a host acute inflammatory response. Much information has been obtained regarding the virulence factors, metabolism, mechanisms of pathogenicity, and the host immune response against this parasite; in addition, alternative treatments to metronidazole are continually emerging. An accesible and low-cost diagnostic method that can distinguish E. histolytica from the most nonpathogenic amoebae and an effective vaccine are necessary for protecting against amoebiasis. However, research about the disease and its prevention has been a challenge due to the relationship between E. histolytica and the host during the distinct stages of the disease is multifaceted. In this review, we analyze the interaction between the parasite, the human host, and the colon microbiota or pathogenic microorganisms, which together give rise to intestinal amoebiasis.

PMAP-23 triggers cell death by nitric oxide-induced redox imbalance in Escherichia coli

BACKGROUND

Antibiotic resistance is a global problem and there is an urgent need to augment the arsenal against pathogenic bacteria. The emergence of different drug resistant bacteria is threatening human lives to be pushed toward the pre-antibiotic era. Antimicrobial peptides (AMPs) are a host defense component against infectious pathogens in response to innate immunity. PMAP-23, an AMP derived from porcine myeloid, possesses antibacterial activity. It is currently not clear how the antibacterial activity of PMAP-23 is manifested.

METHODS

The disruptive effect of nitric oxide (NO) on the catalase activity, reactive oxygen species (ROS) production, DNA oxidation and apoptosis-like death were evaluated using the NO generation inhibitor.

RESULTS

In this investigation, PMAP-23 generates NO in a dose dependent manner. NO deactivated catalase and this antioxidant could not protect Escherichia coli against ROS, especially hydroxyl radical. This redox imbalance was shown to induce oxidative stress, thus leading to DNA strand break. Consequently, PMAP-23 treated E. coli cells resulted in apoptosis-like death. These physiological changes were inhibited when NO generation was inhibited. In the ΔdinF mutant, the levels of DNA strand break sharply increased and the cells were more sensitive to PMAP-23 than wild type.

CONCLUSION

Our data strongly indicates that PMAP-23 mediates apoptosis-like cell death through affecting intracellular NO homeostasis. Furthermore, our results demonstrate that DinF functioned in protection from oxidative DNA damage.

GENERAL SIGNIFICANCE

The identification of PMAP-23 antibacterial activity and mechanism provides a promising antibacterial agent, supporting the role of NO in cell death regulation.

Ange K, Han X, Edsinger E, Sohn J, Linhardt RJ. Structural and Functional Components of the Skate Sensory Organ Ampullae of Lorenzini

The skate, a cartilaginous fish related to sharks and rays, possesses a unique electrosensitive sensory organ known as the ampullae of Lorenzini (AoL). This organ is responsible for the detection of weak electric field changes caused by the muscle contractions of their prey. While keratan sulfate (KS) is believed to be a component of a jelly that fills this sensory organ and has been credited with its high proton conductivity, modern analytical methods have not been applied to its characterization. Surprisingly, total glycosaminoglycan (GAG) analysis demonstrates that the KS from skate jelly is extraordinarily pure, containing no other GAGs. This KS had a molecular weight of 20 to 30 kDa, consisting primarily of N-linked KS comprised mostly of a monosulfated disaccharide repeating unit, →3) Gal (1→4) GlcNAc6S (1→. Proteomic analysis of AoL jelly suggests that transferrin, keratin, and mucin serve as KS core proteins. Actin and tropomyosin are responsible for assembling the macrostructure of the jelly, and parvalbumin α-like protein and calreticulin regulate calcium and potassium channels involved in the transduction of the electrical signal, once conducted down the AoL by the jelly, serving as the molecular basis for electroreception.

Role of Soluble Innate Effector Molecules in Pulmonary Defense against Fungal Pathogens

Fungal infections of the lung are life-threatening but rarely occur in healthy, immunocompetent individuals, indicating efficient clearance by pulmonary defense mechanisms. Upon inhalation, fungi will first encounter the airway surface liquid which contains several soluble effector molecules that form the first barrier of defense against fungal infections. These include host defense peptides, like LL-37 and defensins that can neutralize fungi by direct killing of the pathogen, and collectins, such as surfactant protein A and D, that can aggregate fungi and stimulate phagocytosis. In addition, these molecules have immunomodulatory activities which can aid in fungal clearance from the lung. However, existing observations are based on in vitro studies which do not reflect the complexity of the lung and its airway surface liquid. Ionic strength, pH, and the presence of mucus can have strong detrimental effects on antifungal activity, while the potential synergistic interplay between soluble effector molecules is largely unknown. In this review, we describe the current knowledge on soluble effector molecules that contribute to antifungal activity, the importance of environmental factors and discuss the future directions required to understand the innate antifungal defense in the lung.

Sweet whey as a raw material for the dietary supplements obtaining with immunomodulatory effect

This article presents the results of the study of literary sources to prove the viability of the idea of using sweet whey to deep its fractionation, and to obtain biologically active proteins with immunomodulatory effect. We demonstrated methods for fractionation of milk whey (membrane and chromatographic), as well as the technological scheme of concentration of sweet whey. We introduced the composition of sweet whey and protein content of immunomodulatory action. Modern methods of processing whey, which include, basically, only the process of dehydration and concentration of whey and its use in the complete component composition, which limits its use for food purposes are shown. The necessity of processing of secondary resources in a catastrophic ecological situation on the planet and full use of the composite processing of raw materials for food purposes, and also shows properties of proteins immunomodulating actions which are part of the whey are grounded.

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.

Transcriptome and network analyses in Saccharomyces cerevisiae reveal that amphotericin B and lactoferrin synergy disrupt metal homeostasis and stress response

Invasive fungal infections are difficult to treat. The few available antifungal drugs have problems with toxicity or efficacy, and resistance is increasing. To overcome these challenges, existing therapies may be enhanced by synergistic combination with another agent. Previously, we found amphotericin B (AMB) and the iron chelator, lactoferrin (LF), were synergistic against a range of different fungal pathogens. This study investigates the mechanism of AMB-LF synergy, using RNA-seq and network analyses. AMB treatment resulted in increased expression of genes involved in iron homeostasis and ATP synthesis. Unexpectedly, AMB-LF treatment did not lead to increased expression of iron and zinc homeostasis genes. However, genes involved in adaptive response to zinc deficiency and oxidative stress had decreased expression. The clustering of co-expressed genes and network analysis revealed that many iron and zinc homeostasis genes are targets of transcription factors Aft1p and Zap1p. The aft1Δ and zap1Δ mutants were hypersensitive to AMB and H₂O₂, suggesting they are key regulators of the drug response. Mechanistically, AMB-LF synergy could involve AMB affecting the integrity of the cell wall and membrane, permitting LF to disrupt intracellular processes. We suggest that Zap1p- and Aft1p-binding molecules could be combined with existing antifungals to serve as synergistic treatments.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era.

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

Human lactoferrin (hLf) is a protein of the innate immune system which induces an apoptotic-like process in yeast. Determination of the susceptibility to lactoferrin of several yeast species under different metabolic conditions, respiratory activity, cytoplasmic ATP levels, and external medium acidification mediated by glucose assays suggested plasma membrane Pma1p (P3A-type ATPase) as the hLf molecular target. The inhibition of plasma membrane ATPase activity by hLf and the identification of Pma1p as the hLf-binding membrane protein confirmed the previous physiological evidence. Consistent with this, cytoplasmic ATP levels progressively increased in hLf-treated Candida albicans cells. However, oligomycin, a specific inhibitor of the mitochondrial F-type ATPase proton pump (mtATPase), abrogated the antifungal activity of hLf, indicating a crucial role for mtATPase in the apoptotic process. We suggest that lactoferrin targeted plasma membrane Pma1p H(+)-ATPase, perturbing the cytoplasmic ion homeostasis (i.e., cytoplasmic H(+) accumulation and subsequent K(+) efflux) and inducing a lethal mitochondrial dysfunction. This initial event involved a normal mitochondrial ATP synthase activity responsible for both the ATP increment and subsequent hypothetical mitochondrial proton flooding process. We conclude that human lactoferrin inhibited Pma1p H(+)-ATPase, inducing an apoptotic-like process in metabolically active yeast. Involvement of mitochondrial H(+)-ATPase (nonreverted) was essential for the progress of this programmed cell death in which the ionic homeostasis perturbation seems to precede classical nonionic apoptotic events.

Changes in the hemolytic activity of Candida species by common electrolytes

Background

Hemolysins are crucial virulence factors which help pathogens to survive and persist in the host. This study investigated whether common electrolytes will affect the hemolysins of Candida species. The hemolysins from 25 Candida isolates were investigated using a plate specially designed for Candida species in the presence of three electrolytes, CaCl₂, NaCl and KCl, at different concentrations. The hemolytic activity was determined after 48 h and the hemolytic index was calculated.

Results

All three electrolytes caused a decrease in the hemolytic activity. Significant differences existed between varying concentrations of NaCl, while no significant differences existed for the CaCl₂ and KCl groups. Additionally, the peripheral hemolytic index was highly correlated with the hemolytic index (r = 0.656, p < 0.001).

Conclusions

Our findings indicate that electrolytes reduce hemolysis by Candida species and a correlation exists between the peripheral hemolytic index and the translucent hemolytic index.

Early childhood caries is associated with genetic variants in enamel formation and immune response genes

Early childhood caries (ECC) is a chronic, infectious disease that affects the primary dentition of young children. It is the result of an imbalance of risk factors and protective factors that influence the disease. The aim of this study was to assess genetic and environmental factors that may contribute to ECC. Two hundred and fifty-nine unrelated children were evaluated using a cross-sectional design. Data on oral habits were obtained through a questionnaire, and caries experience data were collected by clinical examination. Twenty-three markers in 10 genes were studied. Genotyping of the selected polymorphisms was carried out by real-time PCR. Regression analyses were performed comparing individuals with and without caries experience. Of 259 subjects, 123 were caries free. The genotype TT in ALOX15 (rs7217186) was a risk factor for ECC, whereas the genotypes GG in ENAM (rs1264848), AG and GG in KLK4 (rs198968), CT in LTF (rs4547741), and GG in TUFT1 (rs3790506) were protective for EEC. In conclusion, environmental factors and gene interactions can act as protective or risk factors for ECC. These factors together contribute to the presence and severity of the disease.

Iron binding modulates candidacidal properties of salivary histatin 5

Salivary protein histatin 5 (Hst 5) is fungicidal toward Candida albicans, the causative agent of oropharyngeal candidiasis. However, its activity in saliva is compromised by salivary protease-mediated degradation and interaction with salivary salts. Hst 5 has also been shown to bind various metals in saliva-namely, Zn, Cu, and Ni. Surprisingly, interactions of Hst 5 with Fe have not been studied, although iron is one of the most abundant metals present in saliva. Using circular dichroism, we show that Hst 5 can bind up to 10 equivalents of iron as measured by loss of its alpha-helical secondary structure that is normally observed for it in trifluoroethylene. A significant decrease in the candidacidal ability of Hst 5 was observed upon iron binding, with increasing iron concentrations being inversely proportional to Hst 5 killing activity. Binding assays showed that the decrease in killing was likely a result of reduced binding (10-fold reduction) of Fe-Hst 5 to C. albicans cells. Protease stability analysis showed that Fe-Hst 5 was completely resistant to trypsin digestion. In contrast, zinc binding had limited effects on Hst 5 fungicidal activity or protease susceptibility. RNA sequencing results identified changes in iron uptake genes in Hst 5-treated C. albicans cells. Our findings thus suggest that consequences of Hst 5 binding iron not only affect candidacidal ability and proteolyic stability of Hst 5, but may also contribute to a novel killing mechanism involving interference with cellular iron metabolism.

The intracellular inhibition of HCV replication represents a novel mechanism of action by the innate immune Lactoferrin protein

Hepatitis C virus (HCV) is a major public-health problem with 130-170 million individuals chronically infected worldwide. In order to halt the epidemic, therapy against HCV will need to be both effective and widely available. Studies focusing on safe and affordable natural product active against HCV have revealed the antiviral activity of the human Lactoferrin (hLF) protein which binds and neutralizes the circulating virion. In the current study, investigation of hLF activity on the HCV subgenomic replicon system, which is independent from viral entry and shedding, revealed a distinct antireplicative activity of hLF against HCV. Hepatocellular uptake of hLF was confirmed and correlated with qualitative HCV staining reduction. Quantitative dose-response inhibition assays confirmed an hLF-mediated and dose-dependent HCV replication reduction reaching up to 60%. The in cellulo anti-HCV activity of hLF was additive to both Ribavirin and Interferon-α-2b. Further investigation of hLF activity against the essential viral proteins involved in HCV genome replication revealed an inhibitory activity against the HCV ATPase/Helicase NS3 protein but not against the HCV RNA-dependent RNA polymerase (NS5B protein). NS3 inhibition was mediated by a direct and specific interaction between hLF and an allosteric binding site on NS3. Taken together, our findings reveal a new antiviral mechanism of action by which hLF inhibits intracellular HCV replication.

How does it kill?: understanding the candidacidal mechanism of salivary histatin 5

Histatins are salivary cationic peptides that provide the first line of defense against oral candidiasis caused by Candida albicans. This minireview presents a critical evaluation of our knowledge of the candidacidal mechanism of histatin 5 (Hst 5). Hst 5 is the most potent among all histatin family members with regard to its antifungal activity. The mode of action of Hst 5 has been a subject of intense debate. Unlike other classical host innate immune proteins, pore formation or membrane lysis by Hst 5 has largely been disproven, and it is now known that all targets of Hst 5 are intracellular. Hst 5 binds C. albicans cell wall proteins (Ssa1/2) and glycans and is taken up by the cells through fungal polyamine transporters in an energy-dependent manner. Once inside the fungal cells, Hst 5 may affect mitochondrial functions and cause oxidative stress; however, the ultimate cause of cell death is by volume dysregulation and ion imbalance triggered by osmotic stress. Besides these diverse targets, a novel mechanism based on the metal binding abilities of Hst 5 is discussed. Finally, translational approaches for Hst 5, based on peptide design and synergy with other known drugs, are considered a step forward for bench-to-bed application of Hst 5.

Lactoferrin and the newborn: current perspectives

Neonatal sepsis and necrotizing enterocolitis (NEC) are associated with significant mortality and morbidity. Inflammation secondary to sepsis and NEC increases morbidity, especially those related to the lung, brain and eye. Therapeutic strategies that target inflammation and decrease the emergence of antibiotic resistance are urgently needed. Lactoferrin (Lf) is a multifunctional protein that modulates inflammation, cell growth and differentiation and has broad antimicrobial activity. Studies evaluating the efficacy and safety of Lf in the prevention of neonatal sepsis and NEC are currently in progress, and one completed study shows significant promise. In this article, the functions of this multifunctional molecule and current clinical evidence for its use in the newborn are reviewed. Lf prophylaxis and therapy may have a significant impact in improving clinical outcomes of vulnerable preterm neonates.

Optimization of cellular uptake of zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine for maximal photoinactivation of Candida albicans

Cellular uptake and photodynamic action of zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc⁴⁺) was examined in Candida albicans. In vitro investigations showed that ZnPPc⁴⁺ was rapidly bound to C. albicans cells. The binding of phthalocyanine to cells was dependent on ZnPPc⁴⁺ concentrations (1-10 μM) and cells densities (10⁶-10⁸ cells mL⁻¹). A high amount of ZnPPc⁴⁺ retained in the cells after two washing steps, indicating a strong interaction between the photosensitizer and C. albicans. The uptake was temperature dependent, although the difference between 37 °C and 4 °C was about 10 %. Also, the amount of ZnPPc bound to C. albicans was affected when the cells were incubated for a longer time with azide and 2,4-dinitrophenol (DNP) prior to treatment with ZnPP⁴⁺. Cell survival after irradiation was dependent on the irradiation period, ZnPPc⁴⁺ concentration and cells density. Photoinactivation of C. albicans cells was elevated even after two washing steps. The strong dependence of uptake on cell density reveals the strength and avidity of the binding of ZnPPc⁴⁺ to C. albicans cells. The accumulation behaviour of ZnPPc⁴⁺ suggests that mainly an affinity-mediated binding mechanism can be involved. Therefore, ZnPPc⁴⁺ is an interesting phthalocyanine for photodynamic inactivation (PDI) of yeasts in liquid suspensions.

Lactoferrin: an alternative view of its role in human biological fluids

Lactoferrin is a major component of biologically important mucosal fluids and of the specific granules of neutrophils. Understanding its biological function is essential for understanding neutrophil- and mucosal-mediated immunity. In this review, we reevaluate the in vivo functions of human lactoferrin (hLF) emphasizing in vivo studies and in vitro studies performed in biologically relevant fluids. We discuss the evidence in the literature that supports (or does not support) proposed roles for hLF in mucosal immunity and in neutrophil function. We argue that the current literature supports a microbiostatic role, but not a microbicidal role, for hLF in vivo. The literature also supports a role for hLF in inhibiting colonization and infection of epithelial surfaces by microorganisms and in protecting tissues from neutrophil-mediated damage. Using this information, we briefly discuss hLF in the context of the complex biological fluids in which it is found.

Lactoferrin a multiple bioactive protein: an overview

BACKGROUND

Lactoferrin (Lf) is an 80kDa iron-binding glycoprotein of the transferrin family. It is abundant in milk and in most biological fluids and is a cell-secreted molecule that bridges innate and adaptive immune function in mammals. Its protective effects range from anticancer, anti-inflammatory and immune modulator activities to antimicrobial activities against a large number of microorganisms. This wide range of activities is made possible by mechanisms of action involving not only the capacity of Lf to bind iron but also interactions of Lf with molecular and cellular components of both hosts and pathogens.

SCOPE OF REVIEW

This review summarizes the activities of Lf, its regulation and potential applications.

MAJOR CONCLUSIONS

The extensive uses of Lf in the treatment of various infectious diseases in animals and humans has been the driving force in Lf research however, a lot of work is required to obtain a better understanding of its activity.

GENERAL SIGNIFICANCE

The large potential applications of Lf have led scientists to develop this nutraceutical protein for use in feed, food and pharmaceutical applications. This article is part of a Special Issue entitled Molecular Mechanisms of Iron Transport and Disorders.

In vivo function of airway epithelial TLR2 in host defense against bacterial infection

Decreased Toll-like receptor 2 (TLR2) expression has been reported in patients with chronic obstructive pulmonary disease and in a murine asthma model, which may predispose the hosts to bacterial infections, leading to disease exacerbations. Since airway epithelial cells serve as the first line of respiratory mucosal defense, the present study aimed to reveal the role of airway epithelial TLR2 signaling to lung bacterial [i.e., Mycoplasma pneumoniae (Mp)] clearance. In vivo TLR2 gene transfer via intranasal inoculation of adenoviral vector was performed to reconstitute TLR2 expression in airway epithelium of TLR2(-/-) BALB/c mice, with or without ensuing Mp infection. TLR2 and lactotransferrin (LTF) expression in airway epithelial cells and lung Mp load were assessed. Adenovirus-mediated TLR2 gene transfer to airway epithelial cells of TLR2(-/-) mice reconstituted 30-40% TLR2 expression compared with TLR2(+/+) cells. Such airway epithelial TLR2 reconstitution in TLR2(-/-) mice significantly reduced lung Mp load (an appropriate 45% reduction), coupled with elevated LTF expression. LTF expression in mice was shown to be mainly dependent on TLR2 signaling in response to Mp infection. Exogenous human LTF protein dose-dependently decreased lung bacterial load in Mp-infected TLR2(-/-) mice. In addition, human LTF protein directly dose-dependently decreased Mp levels in vitro. These data indicate that reconstitution of airway epithelial TLR2 signaling in TLR2(-/-) mice significantly restores lung defense against bacteria (e.g., Mp) via increased lung antimicrobial protein LTF production. Our findings may offer a deliverable approach to attenuate bacterial infections in airways of asthma or chronic obstructive pulmonary disease patients with impaired TLR2 function.

Antimicrobial mechanism of action of transferrins: selective inhibition of H+-ATPase

Two bacterial species with different metabolic features, namely, Pseudomonas aeruginosa and Lactococcus lactis, were used as a comparative experimental model to investigate the antimicrobial target and mechanism of transferrins. In anaerobiosis, P. aeruginosa cells were not susceptible to lactoferrin (hLf) or transferrin (hTf). In aerobiosis, the cells were susceptible but O(2) consumption was not modified, indicating that components of the electron transport chain (ETC) were not targeted. However, the respiratory chain inhibitor piericidin A significantly reduced the killing activity of both proteins. Moreover, 2,6-dichlorophenolindophenol (DCIP), a reducing agent that accepts electrons from the ETC coupled to H(+) extrusion, made P. aeruginosa susceptible to hLf and hTf in anaerobiosis. These results indicated that active cooperation of the cell was indispensable for the antimicrobial effect. For L. lactis cells lacking an ETC, the absence of a detectable transmembrane electrical potential in hLf-treated cells suggested a loss of H(+)-ATPase activity. Furthermore, the inhibition of ATPase activity and H(+) translocation (inverted membrane vesicles) provided direct evidence of the ability of hLf to inhibit H(+)-ATPase in L. lactis. Based on these data, we propose that hLf and hTf also inhibit the H(+)-ATPase of respiring P. aeruginosa cells. Such inhibition thereby interferes with reentry of H(+) from the periplasmic space to the cytoplasm, resulting in perturbation of intracellular pH and the transmembrane proton gradient. Consistent with this hypothesis, periplasmic H(+) accumulation was prevented by anaerobiosis or by piericidin A or was induced by DCIP in anaerobiosis. Collectively, these results indicate that transferrins target H(+)-ATPase and interfere with H(+) translocation, yielding a lethal effect in vitro.

Can lactoferrin prevent neonatal sepsis and necrotizing enterocolitis?

Despite the use of potent antimicrobials, neonatal sepsis and necrotizing enterocolitis are associated with significant mortality and morbidity. The emergence of microbial antibiotic resistance is a grave concern. Inflammation secondary to sepsis and necrotizing enterocolitis increases pulmonary and cerebral morbidity. New strategies that target inflammation and reduce the emergence of antibiotic resistance are urgently needed. Lactoferrin has broad-spectrum antimicrobial and immunomodulatory activities. In animal models of colitis, lactoferrin reduces inflammatory injury. Lactoferrin also induces the receptor-mediated proliferation and differentiation of intestinal cells. A randomized, controlled trial of lactoferrin in premature neonates to prevent late-onset sepsis is currently in progress. Lactoferrin is a promising agent in the prevention of neonatal sepsis and necrotizing enterocolitis but needs further evaluation to confirm its safety, tolerability and efficacy.

Lactoferrin as a natural regimen for selective decontamination of the digestive tract: recombinant porcine lactoferrin expressed in the milk of transgenic mice protects neonates from pathogenic challenge in the gastrointestinal tract

BACKGROUND

Nosocomial infection with antibiotic-resistant strains is a major threat to critical care medicine. Selective decontamination of the digestive tract (SDD) is one of the strategies used to reduce ventilator-associated pneumonia and sepsis in critically ill patients. In the present study, we performed pathogenic challenges of the digestive tract in a transgenic milk-fed animal model to test whether porcine lactoferrin (pLF) is an effective SDD regimen.

METHODS

Transgenic mice expressing recombinant pLF in their milk at a mean+/-SD concentration of 120+/-13.6 mg/L during the lactation stage fed normal CD-1 mice pups for 4 weeks. The pups were subsequently challenged with pathogenic Escherichia coli, Staphylococcus aureus, and Candida albicans.

RESULTS

Compared with the control groups fed wild-type (normal) milk, the groups fed pLF-enriched milk demonstrated statistically significant improvements in weight gain; lower bacterial numbers in intestinal fluid, blood, and liver; healthier microvilli in the small intestine; and alveoli in the lungs.

CONCLUSIONS

Our results showed that oral administration of pLF-enriched milk to mice led to broad-spectrum antimicrobial activity in the digestive tract and protected the mucosa of the small intestine from injury, implying that pLF can be used as an effective SDD regimen.

Lactoferrin as a natural immune modulator

Lactoferrin, an iron-binding glycoprotein, is a cell-secreted mediator that bridges innate and adaptive immune function in mammals. It is a pleiotropic molecule that directly assists in the influence of presenting cells for the development of T-helper cell polarization. The aim of this review is to provide an overview of research regarding the role of lactoferrin in maintaining immune homeostasis, in particular as a mediator of immune responses to infectious assault, trauma and injury. These findings are critically relevant in the development of both prophylactic and therapeutic interventions in humans. Understanding these particular effects of lactoferrin will provide a logical framework for determining its role in health and disease.

Effect of ethylenediaminetetraacetate and lysozyme on the antimicrobial activity of ovotransferrin against Listeria monocytogenes

This study evaluated the effect of EDTA and lysozyme on the antibacterial activities of activated ovotransferrin against 5 strains of Listeria monocytogenes. First, a disc test was performed to screen the concentrations of EDTA or lysozyme that showed antibacterial activities in ovotransferrin (O) or ovotransferrin in 100 mM NaHCO3 (OS) solution. Turbidity and viability tests were conducted using O or OS solution combined with either lysozyme (OL and OSL) or EDTA (OE and OSE). Also, OS combined with 2 mg/mL of lysozyme (OSL) or 1 mg/mL of EDTA (OSLE), or both, was applied on commercial hams to determine if the solutions show antibacterial activities on meat products. The effect of initial cell population on the antibacterial activities of ovotransferrin combined with either EDTA or lysozyme was also determined. The L. monocytogenes started to grow after 1 d of incubation in the presence of >2.0 mg/mL of lysozyme. The OL groups showed weak antibacterial activities against L. monocytogenes in brain heart infusion broth culture, and their activities were bacteriostatic. The OSL groups were bactericidal against L. monocytogenes, resulting in 1 log reduction from initial cell population. Even though OSL showed stronger antibacterial activity than OS, lysozyme had no significant effect on antibacterial activity of OS against L. monocytogenes. Also, EDTA itself at 1.0 and 2.0 mg/mL was bacteriostatic against 5 strains of L. monocytogenes. They were more susceptible to EDTA than lysozyme, and OSE1 and OSE2 had bactericidal activity against L. monocytogenes. There was a significant difference in the survivor cell populations between OS and OSE groups (P < 0.05). Therefore, EDTA enhanced the antibacterial activity of OS against L. monocytogenes. However, ovotransferrin plus either lysozyme or EDTA, or both, did not show any antibacterial effect in commercial hams during storage at 10 degrees C. In addition, the initial population of L. monocytogenes cells influenced the antibacterial activity of OSL or OSE.

Human lactoferrin induces apoptosis-like cell death in Candida albicans: critical role of K+-channel-mediated K+ efflux

Human lactoferrin (hLf) induced an apoptosis-like phenotype in Candida albicans cells, which includes phosphatidylserine externalization, nuclear chromatin condensation, DNA degradation, and increased reactive oxygen species (ROS) production. Intracellular ROS accumulation was seen to correlate with candidacidal activity in hLf-treated cells. Mitochondrial activity was involved as indicated by mitochondrial depolarization and increased hLf resistance of cells preincubated with sordarin or erythromycin, the latter of which inhibits protein synthesis in mitoribosomes. Interestingly, Cl(-)- and K(+)-channel blockers prevented the hLf antimicrobial activity, but only when cells were pretreated with the blocking agent (tetraethylammonium) prior to the hLf-induced K(+)-release period. These results indicate for the first time that K(+)-channel-mediated K(+) efflux is required for the progression of apoptosis-like process in yeast, suggesting that this essential apoptotic event of higher eukaryotes has been evolutionary conserved among species ranging from yeasts to humans.

Apical maxi-K (KCa1.1) channels mediate K+ secretion by the mouse submandibular exocrine gland

The exocrine salivary glands of mammals secrete K+ by an unknown pathway that has been associated with HCO3(-) efflux. However, the present studies found that K+ secretion in the mouse submandibular gland did not require HCO3(-), demonstrating that neither K+/HCO3(-) cotransport nor K+/H+ exchange mechanisms were involved. Because HCO3(-) did not appear to participate in this process, we tested whether a K channel is required. Indeed, K+ secretion was inhibited >75% in mice with a null mutation in the maxi-K, Ca2+-activated K channel (KCa1.1) but was unchanged in mice lacking the intermediate-conductance IKCa1 channel (KCa3.1). Moreover, paxilline, a specific maxi-K channel blocker, dramatically reduced the K+ concentration in submandibular saliva. The K+ concentration of saliva is well known to be flow rate dependent, the K+ concentration increasing as the flow decreases. The flow rate dependence of K+ secretion was nearly eliminated in KCa1.1 null mice, suggesting an important role for KCa1.1 channels in this process as well. Importantly, a maxi-K-like current had not been previously detected in duct cells, the theoretical site of K+ secretion, but we found that KCa1.1 channels localized to the apical membranes of both striated and excretory duct cells, but not granular duct cells, using immunohistochemistry. Consistent with this latter observation, maxi-K currents were not detected in granular duct cells. Taken together, these results demonstrate that the secretion of K+ requires and is likely mediated by KCa1.1 potassium channels localized to the apical membranes of striated and excretory duct cells in the mouse submandibular exocrine gland.

The gamma-core motif correlates with antimicrobial activity in cysteine-containing kaliocin-1 originating from transferrins

Kaliocin-1 is a 31-residue peptide derived from human lactoferrin, and with antimicrobial properties that recapitulate those of its 611 amino acid parent holoprotein. As kaliocin-1 is a cysteine-stabilized peptide, it was of interest to determine whether it contained a multidimensional gamma-core signature recently identified as common to virtually all classes of disulfide-stabilized antimicrobial peptides. Importantly, sequence and structural analyses identified an iteration of this multidimensional antimicrobial signature in kaliocin-1. Further, the gamma-core motif was found to be highly conserved in the transferrin family of proteins across the phylogenetic spectrum. Previous studies suggested that the mechanism by which kaliocin-1 exerts anti-candidal efficacy depends on mitochondrial perturbation without cell membrane permeabilization. Interestingly, results of a yeast two-hybrid screening analysis identified an interaction between kaliocin-1 and mitochondrial initiation factor 2 in a Saccharomyces cerevisiae model system. Taken together, these data extend the repertoire of antimicrobial peptides that contain gamma-core motifs, and suggest that the motif is conserved within large native as well as antimicrobial peptide subcomponents of transferrin family proteins. Finally, these results substantiate the hypothesis that antimicrobial activity associated with host defense effector proteins containing a gamma-core motif may correspond to targets common to fungal mitochondria or their bacterial ancestors.

The role of released ATP in killing Candida albicans and other extracellular microbial pathogens by cationic peptides

A unifying theme common to the action of many cationic peptides that display lethal activities against microbial pathogens is their specific action at microbial membranes that results in selective loss of ions and small nucleotides chiefly ATP. One model cationic peptide that induces non-lytic release of ATP from the fungal pathogen Candida albicans is salivary histatin 5 (Hst 5). The major characteristic of Hst 5-induced ATP release is that it occurs rapidly while cells are still metabolically active and have polarized membranes, thus precluding cell lysis as the means of release of ATP. Other cationic peptides that induce selective release of ATP from target microbes are lactoferricin, human neutrophil defensins, bactenecin, and cathelicidin peptides. The role of released extracellular ATP induced by cationic peptides is not known, but localized increases in extracellular ATP concentration may serve to potentiate cell killing, facilitate further peptide uptake, or function as an additional signal to activate the host innate immune system at the site of infection.

Microbicidal action of lactoferrin and lactoferricin and their synergistic effect with metronidazole in Entamoeba histolytica

Lactoferrin (Lf), in its iron-free form, has been shown to inhibit the growth of pathogenic microorganisms. In the light of new agents to control amoebiasis, the microbicidal activity of human and bovine Lf and bovine lactoferricin (bLfcin, fragment 4-14), and of each combined with metronidazole, the main drug used in amoebiasis, was evaluated in trophozoites of Entamoeba histolytica. Both lactoferrins and bLfcin were able to kill amoebas in a concentration-dependent manner. This killing effect was modulated according to the culture age, pH, and temperature. Parasites obtained from the stationary phase were more susceptible to Lf than those from the early exponential phase. The effect of Lf and its derived peptide, bLfcin, was prevented by both Fe2+ and Fe3+. However, the divalent cations Mg2+ and Ca2+ prevented the killing effect of Lf but not of bLfcin. A synergistic amoebicidal effect was found between metronidazole and human Lf, bovine Lf, or bLfcin. These data suggest that Lf and bLfcin might be used in amoebiasis if they are administered with a low dose of metronidazole to diminish the toxicity of this drug. Thus, Lf and bLfcin are therapeutically potential candidates for use as antiamoebics in patients.

Antimicrobial proteins and polypeptides in pulmonary innate defence

Inspired air contains a myriad of potential pathogens, pollutants and inflammatory stimuli. In the normal lung, these pathogens are rarely problematic. This is because the epithelial lining fluid in the lung is rich in many innate immunity proteins and peptides that provide a powerful anti-microbial screen. These defensive proteins have anti-bacterial, anti- viral and in some cases, even anti-fungal properties. Their antimicrobial effects are as diverse as inhibition of biofilm formation and prevention of viral replication. The innate immunity proteins and peptides also play key immunomodulatory roles. They are involved in many key processes such as opsonisation facilitating phagocytosis of bacteria and viruses by macrophages and monocytes. They act as important mediators in inflammatory pathways and are capable of binding bacterial endotoxins and CPG motifs. They can also influence expression of adhesion molecules as well as acting as powerful anti-oxidants and anti-proteases. Exciting new antimicrobial and immunomodulatory functions are being elucidated for existing proteins that were previously thought to be of lesser importance. The potential therapeutic applications of these proteins and peptides in combating infection and preventing inflammation are the subject of ongoing research that holds much promise for the future.

Different anti-Candida activities of two human lactoferrin-derived peptides, Lfpep and kaliocin-1

The synthetic peptides Lfpep and kaliocin-1 include the sequences from positions 18 to 40 and 153 to 183 of human lactoferrin, respectively. Lfpep is a cationic peptide with bactericidal and giardicidal effects, whereas kaliocin-1 is a novel bactericidal peptide that corresponds to a highly homologous sequence present in the transferrin family of proteins. Both peptides presented fungicidal activity against Candida spp., including fluconazole- and amphotericin B-resistant clinical isolates. Lfpep exhibited higher antifungal activity (8- to 30-fold) and salt resistance than kaliocin-1. The killing activity of Lfpep was mediated by its permeabilizing activity on Candida albicans cells, whereas kaliocin-1 was unable to disrupt the cytoplasmic membrane, as indicated by its inability to allow permeation of propidium iodide and the small amount of K+ released. The amino acid sequence of kaliocin-1 includes the "multidimensional antimicrobial signature" conserved in disulfide-containing antimicrobial peptides and a striking similarity to brevinin-1Sa, an antimicrobial peptide from frog skin secretions, exhibiting a "Rana box"-like sequence. These features may be of interest in the design of new antifungals.

Antibiotic tolerance induced by lactoferrin in clinical Pseudomonas aeruginosa isolates from cystic fibrosis patients

Lactoferrin-induced cell depolarization and a delayed tobramycin-killing effect on Pseudomonas aeruginosa cells were correlated. This antibiotic tolerance effect (ATE) reflects the ability of a defense protein to modify the activity of an antibiotic as a result of its modulatory effect on bacterial physiology. P. aeruginosa isolates from cystic fibrosis patients showed higher ATE values (< or = 6-fold) than other clinical strains.

Effects of human lactoferrin on the cytoplasmic membrane of Candida albicans cells related with its candidacidal activity

Human lactoferrin is an innate host defence protein with antimicrobial activity that exerts a candidacidal effect in a cation concentration-dependent manner. We investigated the ability of this cationic protein (with an isoelectric point of 8.7) to permeabilize the cytoplasmic membrane of Candida albicans cells. Despite minor K(+)-release in lactoferrin-treated C. albicans cells, the killing effect was not related to an extensive membrane permeabilization, as indicated by: (a) the non-release of macromolecular cytosolic constituents; (b) the non-permeabilization for extracellular propidium iodide nor for intracellular accumulated calcein; and (c) the inability to disrupt the phospholipid bilayer of 8-aminonaphthalene-1,3,6, trisulfonic acid/p-xylene-bis-pyridiniumbromide-loaded liposomes. These results suggest that lactoferrin exerts its candidacidal effect through a mechanism different from membrane permeabilization described for other cationic peptides.