Human milk lactoferrin binds two DNA molecules with different affinities

DNA-based molecular recognition system for lactoferrin biosensing

The paper describes the development of a novel DNA oligonucleotide-based affinity bioreceptor that binds to lactoferrin, a glycoprotein-type immunomodulator. The research was performed using surface plasmon resonance method to investigate affinity of various types of oligonucleotides to the target protein. The 72 base pair-long 5'[(TAGAGGATCAAA)AAA]4TAGAGGATCAAA3' sequence with the highest affinity to lactoferrin was selected for further investigations. Kinetic analysis of the interaction between selected DNA and lactoferrin provided rate and equilibrium constants: ka = (2.49 ± 0.03)∙104 M-1∙s-1, kd = (1.89 ± 0.02)∙10-3 s-1, KA = (0.13 ± 0.05)∙108 M-1, and KD = (7.61 ± 0.18)∙10-8 M. Thermodynamic study conducted to determine the ΔH0, ΔS0, and ΔG0 for van't Hoff characteristic in the temperature range of 291.15-305.15 K, revealed the complex formation as endothermic and entropically driven. The chosen DNA sequence's selectivity towards lactoferrin was confirmed with interferents' response constituting <3 % of the response to lactoferrin. SPR analysis justified utility of the designed DNA oligonucleotide for Lf determination, with LOD of 4.42∙10-9 M. Finally, the interaction between lactoferrin and DNA was confirmed by electrochemical impedance spectroscopy, providing the basis for further quantitative assay of lactoferrin using the developed DNA-based bioreceptor. The interactions were performed under immobilized DNA ligand conditions, thus reflecting the sensor's surface, which facilitates their transfer to other label-free biosensor technologies.

Time to Kill and Time to Heal: The Multifaceted Role of Lactoferrin and Lactoferricin in Host Defense

Lactoferrin is an iron-binding glycoprotein present in most human exocrine fluids, particularly breast milk. Lactoferrin is also released from neutrophil granules, and its concentration increases rapidly at the site of inflammation. Immune cells of both the innate and the adaptive immune system express receptors for lactoferrin to modulate their functions in response to it. On the basis of these interactions, lactoferrin plays many roles in host defense, ranging from augmenting or calming inflammatory pathways to direct killing of pathogens. Complex biological activities of lactoferrin are determined by its ability to sequester iron and by its highly basic N-terminus, via which lactoferrin binds to a plethora of negatively charged surfaces of microorganisms and viruses, as well as to mammalian cells, both normal and cancerous. Proteolytic cleavage of lactoferrin in the digestive tract generates smaller peptides, such as N-terminally derived lactoferricin. Lactoferricin shares some of the properties of lactoferrin, but also exhibits unique characteristics and functions. In this review, we discuss the structure, functions, and potential therapeutic uses of lactoferrin, lactoferricin, and other lactoferrin-derived bioactive peptides in treating various infections and inflammatory conditions. Furthermore, we summarize clinical trials examining the effect of lactoferrin supplementation in disease treatment, with a special focus on its potential use in treating COVID-19.

The Influence of Proteins on Fate and Biological Role of Circulating DNA

Circulating DNA has already proven itself as a valuable tool in translational medicine. However, one of the overlooked areas of circulating DNA research is its association with different proteins, despite considerable evidence that this association might impact DNA’s fate in circulation and its biological role. In this review, we attempt to shed light on current ideas about circulating DNA origins and forms of circulation, known biological effects, and the clinical potential of circulating tumor deoxyribonucleoprotein complexes.

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.

How Enzymes, Proteins, and Antibodies Recognize Extended DNAs; General Regularities

X-ray analysis cannot provide quantitative estimates of the relative contribution of non-specific, specific, strong, and weak contacts of extended DNA molecules to their total affinity for enzymes and proteins. The interaction of different enzymes and proteins with long DNA and RNA at the quantitative molecular level can be successfully analyzed using the method of the stepwise increase in ligand complexity (SILC). The present review summarizes the data on stepwise increase in ligand complexity (SILC) analysis of nucleic acid recognition by various enzymes-replication, restriction, integration, topoisomerization, six different repair enzymes (uracil DNA glycosylase, Fpg protein from Escherichia coli, human 8-oxoguanine-DNA glycosylase, human apurinic/apyrimidinic endonuclease, RecA protein, and DNA-ligase), and five DNA-recognizing proteins (RNA helicase, human lactoferrin, alfa-lactalbumin, human blood albumin, and IgGs against DNA). The relative contributions of structural elements of DNA fragments "covered" by globules of enzymes and proteins to the total affinity of DNA have been evaluated. Thermodynamic and catalytic factors providing discrimination of unspecific and specific DNAs by these enzymes on the stages of primary complex formation following changes in enzymes and DNAs or RNAs conformations and direct processing of the catalysis of the reactions were found. General regularities of recognition of nucleic acid by DNA-dependent enzymes, proteins, and antibodies were established.

Functional analysis of recombinant buffalo lactoferrin and monoferric lobes and their cytotoxic effect on buffalo mammary epithelial cells

Lactoferrin (Lf) has been involved in diverse type of cellular activities and its biochemical properties are species specific. Lf is a bilobal molecule in which each lobe binds with one Fe²⁺/Fe³⁺ ion. A lot of physiological effects of Lf are regulated by its iron binding and release properties; however these properties are species-specific. To understand the iron-binding, thermal stability and cytotoxic effect of buffalo Lf (buLf) and contribution of individual N- and C-terminal lobes therein, buLf and the truncated monoferric lobes were expressed in Kluyveromyces lactis or Pichia pastoris yeast expression systems. The iron-uptake/release behavior and thermal stability of recombinant buLf was observed similar to the Lf purified from buffalo milk. Supplementation of recombinant buLf to the buffalo mammary epithelial cells (BuMEC) culture decreased their proliferation and the cell viability in a dose dependent manner. The cell growth decreased by 37% at 1.0 mg/ml Lf. C-lobe decreased the viability of BuMEC by 15% at 1 mg/ml. The C-lobe showed greater cytotoxic effect against BuMEC in comparison to N-lobe. buLf caused a reduced expression of the casein in BuMEC. At 1.0 mg/ml of buLf, CSN2 transcript level was reduced by 74% and 78% in the normal and hormone free media, respectively. The expression of IL-1β gene in BuMEC increased by 4-5 fold in the presence of 1.0 mg/ml of Lf. The effect was similar to that observed in the involutory mammary gland, suggesting the role of elevated level of Lf in remodeling of buffalo mammary tissue during involution.

Cow Milk Lactoferrin Possesses Several Catalytic Activities

Lactoferrin (LF) is a Fe³⁺-binding glycoprotein, that was first recognized in milk and then in other epithelial secretions and barrier body fluids to which many different functions have been attributed to LF including protection from iron-induced lipid peroxidation, immunomodulation, cell growth regulation, DNA and RNA binding, as well as transcriptional activation, еtс. The polyfunctional physiological role of LF is still unclear, but it has been suggested to be responsible for primary defense against microbial and viral infections. It was shown previously that human milk LF possesses several enzymatic activities: DNase, RNase, ATPase, phosphatase, and amylase. Analysis of human, cow, horse, buffalo and camel LF showed a highly conserved three-dimensional (3D) structure including only detail differences in the species. Recently, it was shown that similar to human cow LF possesses DNase and RNase activities. Using different methods here we have shown for the first time that LFs from the milk of seven cows of different breeds possess high peroxidase, protease, amylase, protease, and phosphatase activities. Protease activity of cow LFs was activated by Mg²⁺ and Ca²⁺ ions. In contrast to human LFs, ATPase activity was revealed only in three of seven cow LF preparations. The discovery that LF possesses these activities may contribute to understanding the multiple physiological functions of this extremely polyfunctional protein including its protective role against microbial and viral infections.

Cell-surface-bound circulating DNA in the blood: Biology and clinical application

Cell-surface-bound extracellular DNA (csbDNA) is present on the outer membrane of blood cells, including both red blood cells and leukocytes. Although less well characterized than cell-free DNA (cfDNA) in plasma and serum, leukocyte and red blood cell csbDNA form a considerable fraction of the blood extracellular nucleic acids pool, with typically at least comparable amount of DNA occurring bound to the outer surface of cells as compared with circulating free DNA in plasma. The cellular origin of csbDNA is not clear; however, as with cfDNA, in patients with cancer a proportion is derived from the tumor, thus making it potentially a useful source of DNA for cancer diagnosis, prognosis, and monitoring. © 2019 IUBMB Life, 71(9):1201-1210, 2019.

Visualization of Neutrophil Extracellular Traps and Fibrin Meshwork in Human Fibrinopurulent Inflammatory Lesions: III. Correlative Light and Electron Microscopic Study

Neutrophil extracellular traps (NETs) released from dead neutrophils at the site of inflammation represent webs of neutrophilic DNA stretches dotted with granule-derived antimicrobial proteins, including lactoferrin, and play important roles in innate immunity against microbial infection. We have shown the coexistence of NETs and fibrin meshwork in varied fibrinopurulent inflammatory lesions at both light and electron microscopic levels. In the present study, correlative light and electron microscopy (CLEM) employing confocal laser scanning microscopy and scanning electron microscopy was performed to bridge light and electron microscopic images of NETs and fibrin fibrils in formalin-fixed, paraffin-embedded, autopsied lung sections of legionnaire’s pneumonia. Lactoferrin immunoreactivity and 4'-6-diamidino-2-phenylindole (DAPI) reactivity were used as markers of NETs, and fibrin was probed by fibrinogen gamma chain. Of note is that NETs light microscopically represented as lactoferrin and DAPI-colocalized dots, 2.5 μm in diameter. CLEM gave super-resolution images of NETs and fibrin fibrils: “Dotted” NETs were ultrastructurally composed of fine filaments and masses of 58 nm-sized globular materials. A fibrin fibril consisted of clusters of smooth-surfaced filaments. NETs filaments (26 nm in diameter) were significantly thinner than fibrin filaments (295 nm in diameter). Of note is that CLEM was applicable to formalin-fixed, paraffin-embedded sections of autopsy material.

Visualization of Neutrophil Extracellular Traps and Fibrin Meshwork in Human Fibrinopurulent Inflammatory Lesions: I. Light Microscopic Study

Neutrophil extracellular traps (NETs) are extracellular fibrillary structures composed of degraded chromatin and granules of neutrophil origin. In fibrinopurulent inflammation such as pneumonia and abscess, deposition of fibrillar eosinophilic material is a common histopathological finding under hematoxylin-eosin staining. Expectedly, not only fibrin fibrils but also NETs consist of the fibrillar material. The aim of the present study is to analyze immunohistochemically how NETs are involved in the inflammatory process. Archival formalin-fixed, paraffin-embedded sections accompanying marked neutrophilic infiltration were the target of analysis. Neutrophil-associated substances (citrullinated histone H3, lactoferrin, myeloperoxidase and neutrophil elastase) were evaluated as NETs markers, while fibrinogen gamma chain was employed as a fibrin marker. Light microscopically, the fibrils were categorized into three types: thin, thick and clustered thick. Lactoferrin represented a good and stable NETs marker. Thin fibrils belonged to NETs. Thick fibrils are composed of either mixed NETs and fibrin or fibrin alone. Clustered thick fibrils were solely composed of fibrin. Neutrophils were entrapped within the fibrilllar meshwork of the thin and thick types. Apoptotic cells immunoreactive to cleaved caspase 3 and cleaved actin were dispersed in the NETs. In conclusion, NETs and fibrin meshwork were consistently recognizable by immunostaining for lactoferrin and fibrinogen gamma chain.

Visualization of Neutrophil Extracellular Traps and Fibrin Meshwork in Human Fibrinopurulent Inflammatory Lesions: II. Ultrastructural Study

Neutrophil extracellular traps (NETs) represent an extracellular, spider’s web-like structure resulting from cell death of neutrophils. NETs play an important role in innate immunity against microbial infection, but their roles in human pathological processes remain largely unknown. NETs and fibrin meshwork both showing fibrillar structures are observed at the site of fibrinopurulent inflammation, as described in our sister paper [Acta Histochem. Cytochem. 49; 109–116, 2016]. In the present study, immunoelectron microscopic study was performed for visualizing NETs and fibrin fibrils (thick fibrils in our tongue) in formalin-fixed, paraffin-embedded sections of autopsied lung tissue of legionnaire’s pneumonia. Lactoferrin and fibrinogen gamma chain were utilized as markers of NETs and fibrin, respectively. Analysis of immuno-scanning electron microscopy indicated that NETs constructed thin fibrils and granular materials were attached onto the NETs fibrils. The smooth-surfaced fibrin fibrils were much thicker than the NETs fibrils. Pre-embedding immunoelectron microscopy demonstrated that lactoferrin immunoreactivities were visible as dots on the fibrils, whereas fibrinogen gamma chain immunoreactivities were homogeneously observed throughout the fibrils. Usefulness of immunoelectron microscopic analysis of NETs and fibrin fibrils should be emphasized.

Lactoferrin, a Pleiotropic Protein in Health and Disease

SIGNIFICANCE

Lactoferrin (Lf) is a nonheme iron-binding glycoprotein strongly expressed in human and bovine milk and it plays many functions during infancy such as iron homeostasis and defense against microorganisms. In humans, Lf is mainly expressed in mucosal epithelial and immune cells. Growing evidence suggests multiple physiological roles for Lf after weaning.

RECENT ADVANCES

The aim of this review is to highlight the recent advances concerning multifunctional Lf activities.

CRITICAL ISSUES

First, we will provide an overview of the mechanisms related to Lf intrinsic synthesis or intestinal absorption as well as its interaction with a wide spectrum of mammalian receptors and distribution in organs and cell types. Second, we will discuss the large variety of its physiological functions such as iron homeostasis, transportation, immune regulation, oxidative stress, inflammation, and apoptosis while specifying the mechanisms of action. Third, we will focus on its recent physiopathology implication in metabolic disorders, including obesity, type 2 diabetes, and cardiovascular diseases. Additional efforts are necessary before suggesting the potential use of Lf as a diagnostic marker or as a therapeutic tool.

FUTURE DIRECTIONS

The main sources of Lf in human cardiometabolic disorders should be clarified to identify new perspectives for future research and develop new strategies using Lf in therapeutics. Antioxid. Redox Signal. 24, 813-836.

Features of hydrolysis of specific and nonspecific globular proteins and oligopeptides by antibodies against viral integrase from blood of HIV-infected patients

It was shown previously that, as differentiated from canonical proteases, abzymes against myelin basic protein (MBP) from blood of patients with multiple sclerosis and systemic lupus erythematosus effectively cleaved only MBP, while antibodies (ABs) against integrase (IN) from blood of HIV-infected patients specifically hydrolyzed only IN. In this work, all sites of effective hydrolysis by anti-IN antibodies (IgG and IgM) of 25-mer oligopeptide (OP25) corresponding to MBP were identified using reversed-phase and thin-layer chromatographies and MALDI mass spectrometry. It was found that amino acid sequences of OP25 and other oligopeptides hydrolyzed by anti-MBP abzymes were partially homologous to some fragments of the full sequence of IN. Sequences of IN oligopeptides cleavable by anti-IN abzymes were homologous to some fragments of MBP, but anti-MBP abzymes could not effectively hydrolyze OPs corresponding to IN. The common features of the cleavage sites of OP25 and other oligopeptides hydrolyzed by anti-MBP and anti-IN abzymes were revealed. The literature data on hydrolysis of specific and nonspecific proteins and oligopeptides by abzymes against different protein antigens were analyzed. Overall, the literature data suggest that short OPs, including OP25, mainly interact with light chains of polyclonal ABs, which had lower affinity and specificity to the substrate than intact ABs. However, it seems that anti-IN ABs are the only one example of abzymes capable of hydrolyzing various oligopeptides with high efficiency (within some hours but not days). Possible reasons for the efficient hydrolysis of foreign oligopeptides by anti-IN abzymes from HIV-infected patients are discussed.

Recognition of specific and nonspecific DNA by human lactoferrin

The general principles of recognition of nucleic acids by proteins are among the most exciting problems of molecular biology. Human lactoferrin (LF) is a remarkable protein possessing many independent biological functions, including interaction with DNA. In human milk, LF is a major DNase featuring two DNA-binding sites with different affinities for DNA. The mechanism of DNA recognition by LF was studied here for the first time. Electrophoretic mobility shift assay and fluorescence measurements were used to probe for interactions of the high-affinity DNA-binding site of LF with a series of model-specific and nonspecific DNA ligands, and the structural determinants of DNA recognition by LF were characterized quantitatively. The minimal ligands for this binding site were orthophosphate (K(i)  = 5 mM), deoxyribose 5'-phosphate (K(i)  = 3 mM), and different dNMPs (K(i)  = 0.56-1.6 mM). LF interacted additionally with 9-12 nucleotides or nucleotide pairs of single- and double-stranded ribo- and deoxyribooligonucleotides of different lengths and sequences, mainly through weak additive contacts with internucleoside phosphate groups. Such nonspecific interactions of LF with noncognate single- and double-stranded d(pN)(10) provided ~6 to ~7.5 orders of magnitude of the enzyme affinity for any DNA. This corresponds to the Gibbs free energy of binding (ΔG(0)) of -8.5 to -10.0 kcal/mol. Formation of specific contacts between the LF and its cognate DNA results in an increase of the DNA affinity for the enzyme by approximately 1 order of magnitude (K(d)  = 10 nM; ΔG(0)  ≈ -11.1 kcal/mol). A general function for the LF affinity for nonspecific d(pN)(n) of different sequences and lengths was obtained, giving the K(d) values comparable with the experimentally measured ones. A thermodynamic model was constructed to describe the interactions of LF with DNA.

Mini-review: Lactoferrin: a bioinspired, anti-biofilm therapeutic

Medically relevant biofilms have gained a significant level of interest, in part because of the epidemic rise in obesity and an aging population in the developed world. The associated comorbidities of chronic wounds such as pressure ulcers, venous leg ulcers, and diabetic foot wounds remain recalcitrant to the therapies available currently. Development of chronicity in the wound is due primarily to an inability to complete the wound healing process owing to the presence of a bioburden, specifically bacterial biofilms. New therapies are clearly needed which specifically target biofilms. Lactoferrin is a multifaceted molecule of the innate immune system found primarily in milk. While further investigation is warranted to elucidate mechanisms of action, in vitro analyses of lactoferrin and its derivatives have demonstrated that these complex molecules are structurally and functionally well suited to address the heterogeneity of bacterial biofilms. In addition, use of lactoferrin and its derivatives has proven promising in the clinic.

Lactoferrin, a bird’s eye view

Lactoferrin is an abundant iron-binding protein in milk. This 80 kDa bilobal glycoprotein is also present in several other secreted bodily fluids, as well as in the secondary granules of neutrophils. The potent iron-binding properties of lactoferrin can locally create iron deficiency, and this is an important factor in host defense as it prevents bacteria from growing and forming biofilms. In addition to having antibacterial activity, lactoferrin is now known to have a long list of other beneficial biological properties. It has direct antiviral, antifungal, and even some anticancer activities. It can also promote wound healing and bone growth, or it can act as an iron carrier. Moreover, lactoferrin displays a cytokine-like “alarmin” activity, and it activates the immune system. Simultaneously, it can bind endotoxin (lipopolysaccharide), and in doing so, it modulates the activity of the host immune response. The majority of these intriguing biological activities reside in the unique positively charged N-terminal region of the protein. Interestingly, several peptides, which retain many of the beneficial activities, can be released from this region of lactoferrin. An isoform of the human protein, known as delta-lactoferrin, is expressed inside many cells, where it acts as a transcription factor. Lactoferrin purified from human and bovine milk have very similar but not completely identical properties. Lactoferrin receptors have been identified on the surface of various cells, and some of these can bind both the human and the bovine protein. Because of the extensive health-promoting effects of lactoferrin, there has been considerable interest in the use of bovine or human lactoferrin as a “protein nutraceutical” or as a therapeutic protein. When lactoferrin is used as a “biologic drug”, it seems to be orally active in contrast to most other therapeutic proteins.

Therapeutic approaches using host defence peptides to tackle herpes virus infections

One of the most common viral infections in humans is caused by herpes simplex virus (HSV). It can easily be treated with nucleoside analogues (e.g., acyclovir), but resistant strains are on the rise. Naturally occurring antimicrobial peptides have been demonstrated to possess antiviral activity against HSV. New evidence has also indicated that these host defence peptides are able to selectively stimulate the innate immune system to fight of infections. This review will focus on the anti-HSV activity of such peptides (both natural and synthetic), describe their mode of action and their clinical potential.

DNA, oligosaccharides, and mononucleotides stimulate oligomerization of human lactoferrin

Using small-angle X-ray scattering (SAXS), light scattering (LS), and soft laser ablation we have shown that lactoferrin (LF) in solution at neutral pH is oligomerized in the absence of salt or at physiological salt concentrations. The level of oligomerization depends on the concentration of LF, KCl or NaCl, and on the duration of the protein storage in solution. At the concentrations comparable with those in human milk (1-6 mg/ml), the average radius of gyration (R(g)) values of LF can attain 400-480 A, while fresh solution of previously lyophylized LF demonstrate a lower average R(g) (50-100 A), and R(g) value characterizing the LF monomer formed at 1 M NaCl is 26.7 A. The addition of oligonucleotides, oligosaccharides, or mononucleotides to LF in the presence or in the absence of KCl with different level of initial oligomerization accelerates the oligomerization rate and increases the R(g) values up to approximately 600-700 A, which correspond to associates containing ten or more protein molecules. During gel filtration on Sepharose 4B, high-degree LF oligomers dissociate nearly completely forming different degraded complexes, but in some cases it is possible to reveal small amount of a decamer. A possible role for oligomerization of LF, a highly polyfunctional protein, for its different biological activities is discussed.

Effect of lactoferrin on the growth performance, intestinal morphology, and expression of PR-39 and protegrin-1 genes in weaned piglets

A total of 90 weaned female pigs (Duroc x Landrace x Yorkshire) were used in a 15-d growth experiment to investigate the effect of lactoferrin on growth performance, intestinal morphology, and expression of PR-39 and protegrin-1 genes. The pigs were allocated on the basis of BW and litter to 3 dietary treatments in a randomized complete block design. There were 3 replicate pens per treatment, and the pigs were grouped with 10 pigs per pen. The dietary treatments were (1) basal diet; (2) basal diet + 20 mg of flavomycin/kg + 110 mg of aureomycin/kg; (3) basal diet + 1.0 g of lactoferrin/kg. Six pigs, randomly selected from each treatment (2 piglets/pen) were slaughtered for intestinal morphology and expression of PR-39 and protegrin-1 genes at the end of the experiment. Supplementation with lactoferrin improved growth performance; it increased ADG by 41.80% (P < 0.01) and efficiency of gain (G:F) by 17.20% (P < 0.05). Intestinal villus height was increased by 15.30% (P < 0.05), and crypt depth was decreased by 9.60% (P < 0.05). Supplemental lactoferrin increased the relative abundance of mRNA for PR-39 and protegrin-1 by 143% (P < 0.01) and 217% (P < 0.01), respectively. The use of lactoferrin as an additive to improve nonspecific immunity and strengthen host defenses would be good a method of defending weaned pigs from infections and weanling stress.

Human delta-lactoferrin is a transcription factor that enhances Skp1 (S-phase kinase-associated protein) gene expression

Delta-lactoferrin is a cytoplasmic lactoferrin isoform that can locate to the nucleus, provoking antiproliferative effects and cell cycle arrest in S phase. Using macroarrays, the expression of genes involved in the G(1)/S transition was examined. Among these, Skp1 showed 2-3-fold increased expression at both the mRNA and protein levels. Skp1 (S-phase kinase-associated protein) belongs to the Skp1/Cullin-1/F-box ubiquitin ligase complex responsible for the ubiquitination of cellular regulators leading to their proteolysis. Skp1 overexpression was also found after delta-lactoferrin transient transfection in other cell lines (HeLa, MDA-MB-231, HEK 293) at comparable levels. Analysis of the Skp1 promoter detected two sequences that were 90% identical to those previously known to interact with lactoferrin, the secretory isoform of delta-lactoferrin (GGCACTGTAC-S1(Skp1), located at - 1067 bp, and TAGAAGTCAA-S2(Skp1), at - 646 bp). Both gel shift and chromatin immunoprecipitation assays demonstrated that delta-lactoferrin interacts in vitro and in vivo specifically with these sequences. Reporter gene analysis confirmed that delta-lactoferrin recognizes both sequences within the Skp1 promoter, with a higher activity on S1(Skp1). Deletion of both sequences totally abolished delta-lactoferrin transcriptional activity, identifying them as delta-lactoferrin-responsive elements. Delta-lactoferrin enters the nucleus via a short bipartite RRSDTSLTWNSVKGKK(417-432) nuclear localization signal sequence, which was demonstrated to be functional using mutants. Our results show that delta-lactoferrin binds to the Skp1 promoter at two different sites, and that these interactions lead to its transcriptional activation. By increasing Skp1 gene expression, delta-lactoferrin may regulate cell cycle progression via control of the proteasomal degradation of S-phase actors.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

The antimicrobial peptide, lactoferricin B, is cytotoxic to neuroblastoma cellsin vitro and inhibits xenograft growthin vivo

Antimicrobial peptides have been shown to exert cytotoxic activity towards cancer cells through their ability to interact with negatively charged cell membranes. In this study the cytotoxic effect of the antimicrobial peptide, LfcinB was tested in a panel of human neuroblastoma cell lines. LfcinB displayed a selective cytotoxic activity against both MYCN-amplified and non-MYCN-amplified cell lines. Non-transformed fibroblasts were not substantially affected by LfcinB. Treatment of neuroblastoma cells with LfcinB induced rapid destabilization of the cytoplasmic membrane and formation of membrane blebs. Depolarization of the mitochondria membranes and irreversible changes in the mitochondria morphology was also evident. Immuno- and fluorescence-labeled LfcinB revealed that the peptide co-localized with mitochondria. Furthermore, treatment of neuroblastoma cells with LfcinB induced cleavage of caspase-6, -7 and -9 followed by cell death. However, neither addition of the pan-caspase inhibitor, zVAD-fmk, or specific caspase inhibitors could reverse the cytotoxic effect induced by LfcinB. Treatment of established SH-SY-5Y neuroblastoma xenografts with repeated injections of LfcinB resulted in significant tumor growth inhibition. These results revealed a selective destabilizing effect of LfcinB on two important targets in the neuroblastoma cells, the cytoplasmic- and the mitochondria membrane.

Breast milk lactoferrin regulates gene expression by binding bacterial DNA CpG motifs but not genomic DNA promoters in model intestinal cells

High-affinity binding of DNA by lactoferrin (LF) is an established phenomenon, but the biologic function of this interaction remains unclear. LF is an abundant breast milk protein (12.5-87.5 micromol/L) and is resistant to digestion in the infant gut. Regulation of gene expression by LF appears to be a major activity, particularly in modulating immune responses. We hypothesized that LF binding to DNA is a mechanism of gene regulation and aimed to identify the mechanism and physiologic sites of this activity. Our studies focused on two major biologic compartments of DNA: LF binding to proinflammatory bacterial DNA sequences (CpG motifs) in extracellular compartments and LF binding to genomic DNA promoters in the nucleus. LF 0.5 mmol/L inhibited CpG motif-induced nuclear factor-kappaB (NF-kappaB) activation and interleukin (IL)-8 and IL-12 cytokine gene transcription in B cells. Intestinal epithelial cells were unresponsive to CpG motifs. However, significant LF transferred across M cell-like monolayers, specialized epithelial cells that transcytose intact macromolecules to underlying B-cell follicles in the intestine. LF did not activate gene expression by binding to putative response elements in epithelial and lymphoid cells. Nor did LF bind to putative response elements specifically in gel-shift assays. No nuclear localization of LF was detected in green fluorescent protein (GFP) tagging experiments. We conclude that breast milk LF regulates gene expression by binding CpG motifs extracellularly, with follicular B cells in the infant intestine a likely target.

Structural studies and model membrane interactions of two peptides derived from bovine lactoferricin

The powerful antimicrobial properties of bovine lactoferricin (LfcinB) make it attractive for the development of new antimicrobial agents. An 11-residue linear peptide portion of LfcinB has been reported to have similar antimicrobial activity to lactoferricin itself, but with lower hemolytic activity. The membrane-binding and membrane-perturbing properties of this peptide were studied together with an amidated synthetic version with an added disulfide bond, which was designed to confer increased stability and possibly activity. The antimicrobial and cytotoxic properties of the peptides were measured against Staphylococcus aureus and Escherichia coli and by hemolysis assays. The peptides were also tested in an anti-cancer assay against neuroblastoma cell lines. Vesicle disruption caused by these LfcinB derivatives was studied using the fluorescent reporter molecule calcein. The extent of burial of the two Trp residues in membrane mimetic environments were quantitated by fluorescence. Finally, the solution NMR structures of the peptides bound to SDS micelles were determined to provide insight into their membrane bound state. The cyclic peptide was found to have greater antimicrobial potency than its linear counterpart. Consistent with this property, the two Trp residues of the modified peptide were suggested to be embedded deeper into the membrane. Although both peptides adopt an amphipathic structure without any regular alpha-helical or beta-sheet conformation, the 3D-structures revealed a clearer partitioning of the cationic and hydrophobic faces for the cyclic peptide.

Lactoferrin Expression by Bovine Ocular Surface Epithelia: A Primary Cell Culture Model to Study Lactoferrin Gene Promoter Activity

Tear lactoferrin, mainly secreted by the lachrymal glands, exerts a protective effect on the ocular surface, and an abnormal decrease of its production may lead to an increased risk of infection and pathological alterations of ocular surface epithelia. In this study we analyzed whether corneal and conjunctival epithelia could be an additional source of tear lactoferrin, and whether conjunctival epithelial cells in culture could be a suitable model system to address regulation of lactoferrin gene expression. Real-time PCR and Western immunoblotting showed that in bovines lactoferrin is indeed produced by these epithelia, and that the human lactoferrin promoter can direct the expression of a CAT reporter gene, thus indicating that these cells are a true source of lactoferrin, and may be used in vitro to study the regulation of lactoferrin expression.

Stochastic-based descriptors studying biopolymers biological properties: Extended MARCH-INSIDE methodology describing antibacterial activity of lactoferricin derivatives

Lactoferricin are a number of related peptides derived from the enzymatic cleavage of lactoferrin, an iron-binding protein. These peptides, and other peptides derived from them by simple amino acid substitutions, have shown interesting antibacterial activity. In this paper we applied the MARCH-INSIDE methodology extended to peptide and proteins, to a QSAR study related to antibacterial activity of 31 derivatives of lactoffericin against E. Coli and S. Aureus by means of Linear Discriminant (LDA) and Multiple Linear Regression Analysis (MLR). In the case of LDA we obtained models that classify correctly more than 80% of all cases (85.7% for E. Coli antibacterial activity and 83.9 for S. Aureus). With the application of a Leave-One-Out Cross Validation Procedure, the percentage of good classification of both classification models remained near the above reported values (87.1% for E. Coli antibacterial activity and 83.9 for S. Aureus). We obtained several linear regression models taking into account total and local descriptors. The inclusion of those local descriptors improved the correlation parameters, the statistical quality, and the predictive power of the former model obtained only with total descriptors. The best models explained more than 80% of the experimental variance in the antimicrobial activity of those compounds. These results are comparable with those reported previously by Strom (Strom, M. B.; Rekdal, O.; Svendesen, J. S. J Peptide Res 2001, 57, 127-139.) and Tore-Lejon (Lejon, T.; Strom, M.; Svendsen, S. J Protein Sci 2001, 7, 74-78.; Lejon, T.; Svendsen J. S.; Haug, B. E. J Peptide Sci 2002, 8, 302-306.) in a smaller dataset applying Z-scales and volume-based descriptors and PLS as statistical techniques.

The Low-Density Lipoprotein Receptor-Related Protein 1 Is a Mitogenic Receptor for Lactoferrin in Osteoblastic Cells

Lactoferrin induces osteoblast proliferation and survival in vitro and is anabolic to bone in vivo. The molecular mechanisms by which lactoferrin exerts these biological actions are not known, but lactoferrin is known to bind to two members of the low-density lipoprotein receptor family, low- density lipoprotein receptor-related proteins 1 (LRP1) and 2 (LRP2). We have examined the role(s) of these receptors in the actions of lactoferrin on osteoblasts. We show that lactoferrin binds to cultured osteoblastic cells, and that LRP1 and LRP2 are expressed in several osteoblastic cell types. In primary rat osteoblastic cells, the LRP1/2 inhibitor receptor associated protein blocks endocytosis of lactoferrin and abrogates lactoferrin-induced p42/44 MAPK signaling and mitogenesis. Lactoferrin-induced mitogenesis is also inhibited by an antibody to LRP1. Lactoferrin also induces receptor associated protein-sensitive activation of p42/44 MAPK signaling and proliferation in osteoblastic human SaOS-2 cells, which express LRP1 but not LRP2. The mitogenic response of LRP1-null fibroblastic cells to lactoferrin is substantially reduced compared with that of cells expressing wild-type LRP1. The endocytic and signaling functions of LRP1 are independent of each other, because lactoferrin can activate mitogenic signaling in conditions in which endocytosis is inhibited. Taken together, these results 1) suggest that mitogenic signaling through LRP1 to p42/44 MAPKs contributes to the anabolic skeletal actions of lactoferrin; 2) demonstrate growth-promoting actions of a third LRP family member in osteoblasts; and 3) provide further evidence that LRP1 functions as a signaling receptor in addition to its recognized role in ligand endocytosis.

The prospects of modifying the antimicrobial properties of milk

Milk contains a variety of substances, which inhibit the infection of pathogens. This is of benefit to the mother, safeguarding the integrity of the lactating mammary gland, but also of huge importance for protection of the suckling offspring. The antimicrobial substances in milk can be classified into two categories. First, nonspecific, broad-spectrum defense substances, which have evolved over long periods of time, and secondly, substances like antibodies, which are specifically directed against particular pathogens and have developed during the mother's lifetime. Substances in both categories may be targets for biological intervention and manipulation with the goal of improving the antimicrobial properties of milk. These alterations of milk composition have applications in human as well as in animal health.

Lactoferrin against Staphylococcus aureus Mastitis. Lactoferrin alone or in combination with penicillin G on bovine polymorphonuclear function and mammary epithelial cells colonisation by Staphylococcus aureus

Antibiotics should combine good antibacterial activity and the capacity to work in association with the host defence system. In this study, we have investigated the effects of bovine lactoferrin alone or in combination with penicillin G on the phagocytic activity of bovine polymorphonuclear leukocytes against Staphylococcus aureus. We have shown that susceptibility of S. aureus to phagocytosis was decreased in the presence of penicillin in the medium. In a kinetic study, lactoferrin alone did not affect phagocytosis but, when used with penicillin, it reversed the negative effect of this antibiotic on phagocytosis. In addition, in an epithelial invasion assay, lactoferrin alone or in combination with penicillin reduced the invasion of mammary epithelial cells in culture by S. aureus. Lactating female CD-1 mice were infected by intra-mammary delivery of a virulent penicillin-susceptible S. aureus strain and were then randomly assigned to treatments according to a 2 x 2 factorial design. In this mouse mastitis model, 2 days of systemic treatments with lactoferrin and/or penicillin did not lead to a total clearance of infection by S. aureus, but bacterial number was significantly reduced by treatments with lactoferrin or penicillin. These data suggest that bovine lactoferrin, alone or in combination with penicillin G, enhances S. aureus susceptibility to immuno-defense mechanisms, which can be beneficial in the treatment of S. aureus infections.

Multiple enzymic activities of human milk lactoferrin

Lactoferrin (LF) is a Fe3+-binding glycoprotein, first recognized in milk and then in other human epithelial secretions and barrier fluids. Many different functions have been attributed to LF, including protection from iron-induced lipid peroxidation, immunomodulation and cell growth regulation, DNA binding, and transcriptional activation. Its physiological role is still unclear, but it has been suggested to be responsible for primary defense against microbial and viral infection. We present evidence that different subfractions of purified human milk LF possess five different enzyme activities: DNase, RNase, ATPase, phosphatase, and malto-oligosaccharide hydrolysis. LF is the predominant source of these activities in human milk. Some of its catalytically active subfractions are cytotoxic and induce apoptosis. The discovery that LF possesses these activities may help to elucidate its many physiological functions, including its protective role against microbial and viral infection.

The bovine lactoferrin region responsible for promoting the collagen gel contractile activity of human fibroblasts

We have reported that bovine lactoferrin (bLf) promotes the contractile activity of collagen gels by WI-38 human fibroblasts via the phosphorylation of myosin light chain (MLC). To identify the region of bLf that is responsible for this activity, we prepared bLf fragments by limited proteolysis using trypsin and investigated the effects of each fragment on gel contractile activity. Lf consists of a single polypeptide chain containing two lobes that are independent globular structures termed the N- and C-lobes. The fragment corresponding to the C-lobe of bLf (amino acids 341-689) had a more prominent effect on collagen gel contractile activity than did that of either native bLf or its N-lobe (1-284). Further hydrolysis of the C-lobe with either pepsin or trypsin resulted in a loss of this activity. The effect of the C-lobe on collagen gel contraction by fibroblasts was dose-dependent and was associated with the elevation of MLC phosphorylation.

Towards a structure-function analysis of bovine lactoferricin and related tryptophan- and arginine-containing peptides

The iron-binding protein lactoferrin is a multifunctional protein that has antibacterial, antifungal, antiviral, antitumour, anti-inflammatory, and immunoregulatory properties. All of these additional properties appear to be related to its highly basic N-terminal region. This part of the protein can be released in the stomach by pepsin cleavage at acid pH. The 25-residue antimicrobial peptide that is released is called lactoferricin. In this work, we review our knowledge about the structure of the peptide and attempt to relate this to its many functions. Microcalorimetry and fluorescence spectroscopy data regarding the interaction of the peptide with model membranes show that binding to net negatively charged bacterial and cancer cell membranes is preferred over neutral eukaryotic membranes. Binding of the peptide destabilizes the regular membrane bilayer structure. Residues that are of particular importance for the activity of lactoferricin are tryptophan and arginine. These two amino acids are also prevalent in "penetratins", which are regions of proteins or synthetic peptides that can spontaneously cross membranes and in short hexapeptide antimicrobial peptides derived through combinatorial chemistry. While the antimicrobial, antifungal, antitumour, and antiviral properties of lactoferricin can be related to the Trp/Arg-rich portion of the peptide, we suggest that the anti-inflammatory and immunomodulating properties are more related to a positively charged region of the molecule, which, like the alpha- and beta-defensins, may act as a chemokine. Few small peptides are involved in as wide a range of host defense functions as bovine and human lactoferricin.

Effect of lactoferrin in combination with penicillin on the morphology and the physiology of Staphylococcus aureus isolated from bovine mastitis

The objective of the present study was to evaluate the therapeutic potential of bovine lactoferrin or lactoferricin in combination with penicillin G against Staphylococcus aureus. Minimal inhibitory concentrations of lactoferrin, lactoferricin, penicillin, and combinations of lactoferrin or lactoferricin with penicillin were determined for 15 S. aureus strains including several strains resistant to beta-lactam antibiotics. The fractional inhibitory concentration index indicated a synergistic effect between lactoferrin and penicillin. Combination of lactoferrin with penicillin increased the inhibitory activity of penicillin by two- to fourfold and reduced the growth rate in S. aureus strains tested, whereas the increase in the inhibitory activity of lactoferrin by penicillin was 16- to 64-fold. The addition of iron to the medium containing a combination of penicillin and lactoferrin had no effect on growth inhibition. Electron microscopy revealed that concentration below the minimal inhibitory concentrations of penicillin induced important ultrastructure alterations, which were further enhanced by the presence of lactoferrin. When S. aureus cells were grown in the presence of a combination of penicillin and lactoferrin, changes in the protein profile of the bacteria, including the disappearance of several protein bands due to the presence of lactoferrin, were observed. These data suggest that bovine lactoferrin or lactoferricin in combination with beta-lactam antibiotics can increase the antibacterial activity of these antibiotics against S. aureus resistant to antibiotics.

Human lactoferrin activates transcription of IL-1beta gene in mammalian cells

Lactoferrin (Lf) has been suggested to play roles in primary defense against microbial infection and other cellular processes including immunomodulation. Lf is known to bind to DNA and implicated to activate transcription. In the present study, we demonstrated that Lf stimulated transcription of IL-1beta gene, one of natural genes containing putative Lf binding site (LBS) in the 5'-flanking sequences. K562 cells treated with a combination of Lf and PMA showed a synergistic induction in the level of IL-1beta mRNA over treatment with PMA alone. Synergistic stimulation of IL-1beta expression by Lf and PMA was also confirmed by IL-1beta/Luc reporter gene assays. Analysis of Lf domains revealed that the transcriptional domain of Lf is located within the N-terminal 90 amino acids, termed NIa and that the C-terminal half lobe lacked the transactivating activity. The NIa, the N-terminal half lobe as well as intact Lf stimulated transcription of IL-1beta gene in the transfected K562 cells along with PMA, while the C-terminal half lobe did not. Our results suggest that Lf may play some roles in transcription of IL-1beta gene and may also regulate transcription of other natural genes containing LBS.

Lactoferrin binds CpG-containing oligonucleotides and inhibits their immunostimulatory effects on human B cells

Unmethylated CpG dinucleotide motifs in bacterial DNA, as well as oligodeoxynucleotides (ODN) containing these motifs, are potent stimuli for many host immunological responses. These CpG motifs may enhance host responses to bacterial infection and are being examined as immune activators for therapeutic applications in cancer, allergy/asthma, and infectious diseases. However, little attention has been given to processes that down-modulate this response. The iron-binding protein lactoferrin is present at mucosal surfaces and at sites of infection. Since lactoferrin is known to bind DNA, we tested the hypothesis that lactoferrin will bind CpG-containing ODN and modulate their biological activity. Physiological concentrations of lactoferrin (regardless of iron content) rapidly bound CpG ODN. The related iron-binding protein transferrin lacked this capacity. ODN binding by lactoferrin did not require the presence of CpG motifs and was calcium independent. The process was inhibited by high salt, and the highly cationic N-terminal sequence of lactoferrin (lactoferricin B) was equivalent to lactoferrin in its ODN-binding ability, suggesting that ODN binding by lactoferrin occurs via charge-charge interaction. Heparin and bacterial LPS, known to bind to the lactoferricin component of lactoferrin, also inhibited ODN binding. Lactoferrin and lactoferricin B, but not transferrin, inhibited CpG ODN stimulation of CD86 expression in the human Ramos B cell line and decreased cellular uptake of ODN, a process required for CpG bioactivity. Lactoferrin binding of CpG-containing ODN may serve to modulate and terminate host response to these potent immunostimulatory molecules at mucosal surfaces and sites of bacterial infection.

Increased antibacterial activity of 15-residue murine lactoferricin derivatives

LFM W8 is a synthetic 15-residue lactoferricin derivative (H2N-EKCLRWQWEMRKVGG-COOH), corresponding to residues 16-30 of the mature murine lactoferrin protein except that the asparagine residue in position 8 of the native peptide is replaced with tryptophan. We have previously reported that the two tryptophan residues in positions 6 and 8 are of crucial importance for the antibacterial activity of many lactoferricin derivatives but, despite fulfilling this requirement, LFM W8 is inactive against Escherichia coli and Staphylococcus aureus. In order to solve this puzzle, a quantitative structure-antibacterial activity relationship study of synthetic LFM W8 derivatives was performed by replacing the glutamate residues in positions 1 and 9 with arginine or alanine, and the valine residue in position 13 with tyrosine. The results from the study were analyzed using multivariate data analysis. The derived mathematical model clustered the peptides into distinct groups which reflected their antibacterial activities, pointed out correlations between different structural parameters, highlighted the structural parameters that were important for antibacterial activity, and enabled us to predict the activity of a 15-residue bovine lactoferricin derivative. The results showed that net charge and micelle affinity, as determined from the ratio of alpha-helicity in sodium dodecyl sulfate micelles and in 1,1,1,3,3,3-hexafluoro-2-propanol, were the most important structural parameters affecting antibacterial activity. The most active derivative, LFM R1,9 W8 Y13, displayed a minimal inhibitory concentration of 10 and 12 microM against E. coli and S. aureus, respectively. This represented more than 50-fold and 40-fold increases in antibacterial activity, respectively, compared with LFM W8.

Diversity of antimicrobial peptides and their mechanisms of action

Antimicrobial peptides encompass a wide variety of structural motifs. Many peptides have alpha-helical structures. The majority of these peptides are cationic and amphipathic but there are also hydrophobic alpha-helical peptides which possess antimicrobial activity. In addition, some beta-sheet peptides have antimicrobial activity and even antimicrobial alpha-helical peptides which have been modified to possess a beta-structure retain part of their antimicrobial activity. There are also antimicrobial peptides which are rich in a certain specific amino acid such as Trp or His. In addition, antimicrobial peptides exist with thio-ether rings, which are lipopeptides or which have macrocyclic Cys knots. In spite of the structural diversity, a common feature of the cationic antimicrobial peptides is that they all have an amphipathic structure which allows them to bind to the membrane interface. Indeed, most antimicrobial peptides interact with membranes and may be cytotoxic as a result of disturbance of the bacterial inner or outer membranes. Alternatively, a necessary but not sufficient property of these peptides may be to be able to pass through the membrane to reach a target inside the cell. The interaction of these peptides with biological membranes is not just a function of the peptide but is also modulated by the lipid components of the membrane. It is not likely that this diverse group of peptides has a single mechanism of action, but interaction of the peptides with membranes is an important requirement for most, if not all, antimicrobial peptides.