Potent bactericidal activity of bovine lactoferrin hydrolysate produced by heat treatment at acidic pH

Diverse Mechanisms of Antimicrobial Activities of Lactoferrins, Lactoferricins, and Other Lactoferrin-Derived Peptides

Lactoferrins are an iron-binding glycoprotein that have important protective roles in the mammalian body through their numerous functions, which include antimicrobial, antitumor, anti-inflammatory, immunomodulatory, and antioxidant activities. Among these, their antimicrobial activity has been the most studied, although the mechanism behind antimicrobial activities remains to be elucidated. Thirty years ago, the first lactoferrin-derived peptide was isolated and showed higher antimicrobial activity than the native lactoferrin lactoferricin. Since then, numerous studies have investigated the antimicrobial potencies of lactoferrins, lactoferricins, and other lactoferrin-derived peptides to better understand their antimicrobial activities at the molecular level. This review defines the current antibacterial, antiviral, antifungal, and antiparasitic activities of lactoferrins, lactoferricins, and lactoferrin-derived peptides. The primary focus is on their different mechanisms of activity against bacteria, viruses, fungi, and parasites. The role of their structure, amino-acid composition, conformation, charge, hydrophobicity, and other factors that affect their mechanisms of antimicrobial activity are also reviewed.

A Narrative Review on the Unexplored Potential of Colostrum as a Preventative Treatment and Therapy for Diarrhea in Neonatal Dairy Calves

Diarrhea is the leading cause of morbidity and mortality in pre-weaned dairy calves and, as such, represents a significant animal health and welfare concern. Furthermore, digestive disease early in life is associated with several long-term consequences such as reduced growth rate and decreased milk yield during the first lactation, thus generating severe economic losses. The majority of diarrheic cases in young calves are treated with antimicrobials; however, it is necessary to develop alternative treatments, as excessive antimicrobial usage can lead to antimicrobial resistance and can negatively impact the gut microflora of a calf. Bovine colostrum is abundant in immune and bioactive factors that improve immune function and development. This rich and natural combination of immunoglobulins, natural antimicrobial factors, growth factors, anti-inflammatories and nutrients may be an attractive alternative to antimicrobials in the treatment of diarrhea in young dairy calves. There is evidence that supports the use of colostrum as an early treatment for diarrhea in young calves. Future research should investigate its therapeutic and economic effectiveness.

A prospective on multiple biological activities of lactoferrin contributing to piglet welfare

Piglets, especially weaning piglets, show a lower level of immunity and higher morbidity and mortality, owing to their rapid growth, physiological immaturity, and gradual reduction of maternal antibodies, which seriously affects their growth and thus, value. It is important that piglets adapt to nutrient digestion and absorption and develop sound intestinal function and colonization with gut microbiota as soon as possible during their early life stage. Lactoferrin is a natural glycoprotein polypeptide that is part of the transferrin family. It is widely found in mucosal secretions such as saliva and tears, and most highly in milk and colostrum. As a multifunctional bioactive protein and a recommended food additive, lactoferrin is a potential alternative therapy to antibiotics and health promoting additive for piglet nutrition and development. It is expected that lactoferrin, as a natural food additive, could play an important role in maintaining pig health and development. This review examines the following known beneficial effects of lactoferrin: improves the digestion and capacity for absorption in the intestinal tract; promotes the absorption of iron and reduces the incidence of iron deficiency anemia; regulates intestinal function and helps to balance the microbial biota; and enhances the resistance to disease of the piglets via modulating and enhancing the immune system.

Antilisterial activity of dromedary lactoferrin peptic hydrolysates

The aim of this study was to explore the antibacterial peptides derived from dromedary lactoferrin (LFc). The LFc was purified from colostrum using a batch procedure with a cation exchange chromatography support and was hydrolyzed with pepsin to generate peptic digest. This peptic digest was fractionated by cation exchange chromatography, and the antilisterial activity of LFc, peptic digest, and obtained fractions was investigated using the bioscreen method. The growth of Listeria innocua ATCC 33090 and LRGIA 01 strains was not inhibited by LFc and its hydrolysates. Two fractions of dromedary lactoferrin peptic hydrolysate were active against both strains. A tandem mass spectroscopy analysis revealed that the 2 active fractions comprised at least 227 different peptides. Among these peptides, 9 found in the first fraction had at least 50% similarity with 10 known antimicrobial peptides (following sequence alignments with the antimicrobial peptide database from the University of Nebraska Medical Center, Omaha). Whereas 9 of these peptides presented homology with honeybee, frog, or amphibian peptides, the 10th peptide, F₁₅₂SASCVPCVDGKEYPNLCQLCAGTGENKCACSSQEPYFGY₁₉₂ (specifically found in 1 separated fraction), exibited 54% homology with a synthetic antibacterial peptide (AP00481) derived from human lactoferrin named kaliocin-1. Similarly, the second fraction contained 1 peptide similar to lactoferrampin B, an antibacterial peptide derived from bovine milk. This result suggests that peptic hydrolysis of LFc releases more active antimicrobial peptides than their protein source and thus provides an opportunity for their potential use to improve food safety by inhibiting undesirable and spoilage bacteria.

Bioactive Functions of Milk Proteins: a Comparative Genomics Approach

The composition of milk includes factors required to provide appropriate nutrition for the growth of the neonate. However, it is now clear that milk has many functions and comprises bioactive molecules that play a central role in regulating developmental processes in the young while providing a protective function for both the suckled young and the mammary gland during the lactation cycle. Identifying these bioactives and their physiological function in eutherians can be difficult and requires extensive screening of milk components that may function to improve well-being and options for prevention and treatment of disease. New animal models with unique reproductive strategies are now becoming increasingly relevant to search for these factors.

Serine protease PrtA from Streptococcus pneumoniae plays a role in the killing of S. pneumoniae by apolactoferrin

It is known that apolactoferrin, the iron-free form of human lactoferrin, can kill many species of bacteria, including Streptococcus pneumoniae. Lactoferricin, an N-terminal peptide of apolactoferrin, and fragments of it are even more bactericidal than apolactoferrin. In this study we found that apolactoferrin must be cleaved by a serine protease in order for it to kill pneumococci. The serine protease inhibitors were able to block killing by apolactoferrin but did not block killing by a lactoferrin-derived peptide. Thus, the killing of pneumococci by apolactoferrin appears to require a protease to release a lactoferricin-like peptide(s). Incubation of apolactoferrin with growing pneumococci resulted in a 12-kDa reduction in its molecular mass, of which about 7 to 8 kDa of the reduction was protease dependent. Capsular type 2 and 19F strains with mutations in the gene encoding the major cell wall-associated serine protease, prtA, lost much of their ability to degrade apolactoferrin and were relatively resistant to killing by apolactoferrin (P < 0.001). Recombinant PrtA was also able to cleave apolactoferrin, reducing its mass by about 8 kDa, and greatly enhance the killing activity of the solution containing the apolactoferrin and its cleavage products. Mass spectroscopy revealed that PrtA makes a major cut between amino acids 78 and 79 of human lactoferrin, removing the N-terminal end of the molecule (about 8.6 kDa). The simplest interpretation of these data is that the mechanism by which apolactoferrin kills Streptococcus pneumoniae requires the release of a lactoferricin-like peptide(s) and that it is this peptide(s), and not the intact apolactoferrin, which kills pneumococci.

Specific degradation of the mucus adhesion-promoting protein (MapA) of Lactobacillus reuteri to an antimicrobial peptide

The intestinal flora of mammals contains lactic acid bacteria (LAB) that may provide positive health effects for the host. Such bacteria are referred to as probiotic bacteria. From a pig, we have isolated a Lactobacillus reuteri strain that produces an antimicrobial peptide (AMP). The peptide was purified and characterized, and it was unequivocally shown that the AMP was a well-defined degradation product obtained from the mucus adhesion-promoting protein (MapA); it was therefore termed AP48-MapA. This finding demonstrates how large proteins might inherit unexpected pleiotropic functions by conferring antimicrobial capacities on the producer. The MapA/AP48-MapA system is the first example where a large protein of an intestinal LAB is shown to give rise to such an AMP. It is also of particular interest that the protein that provides this AMP is associated with the binding of the bacterium producing it to the surface/lining of the gut. This finding gives us new perspective on how some probiotic bacteria may successfully compete in this environment and thereby contribute to a healthy microbiota.

Lactoferrin and cancer disease prevention

Lactoferrin (LF) is an iron-binding glycoprotein that is composed of the transferrin family and is predominantly found in the products of the exocrine glands located in the gateways of the digestive, respiratory, and reproductive systems, suggesting a role in the non-specific defence against invading pathogens. Additionally, several physiological roles have been attributed to LF, namely regulation of iron homeostasis, host defence against infection and inflammation, regulation of cellular growth, and differentiation and protection against cancer development and metastasis. These findings have suggested LF's great potential therapeutic use in cancer disease prevention and/or treatment, namely as a chemopreventive agent. This review looks at the recent advances in understanding the mechanisms underlying the multifunctional roles of LF and future perspectives on its potential therapeutic applications.

IsdA protects Staphylococcus aureus against the bactericidal protease activity of apolactoferrin

An important facet of the Staphylococcus aureus host-pathogen interaction is the ability of the invading bacterium to evade host innate defenses, particularly the cocktail of host antimicrobial peptides. In this work, we showed that IsdA, a surface protein of S. aureus which is required for nasal colonization, binds to lactoferrin, the most abundant antistaphylococcal polypeptide in human nasal secretions. The presence of IsdA on the surface of S. aureus confers resistance to killing by lactoferrin. In addition, the bactericidal activity of lactoferrin was inhibited by addition of phenylmethylsulfonyl fluoride, implicating the serine protease activity of lactoferrin in the killing of S. aureus. Recombinant IsdA was a competitive inhibitor of lactoferrin protease activity. Reciprocally, antibody reactive to IsdA enhanced killing of S. aureus. Thus, IsdA can protect S. aureus against lactoferrin and acts as a protease inhibitor.

Intestinal microflora of human infants and current trends for its nutritional modulation

Diet, among other environmental and genetic factors, is currently recognised to have an important role in health and disease. There is increasing evidence that the human colonic microbiota can contribute positively towards host nutrition and health. As such, dietary modulation has been proposed as important for improved gut health, especially during the highly sensitive stage of infancy. Differences in gut microflora composition and incidence of infection occur between breast- and formula-fed infants. Human milk components that cannot be duplicated in infant formulae could possibly account for these differences. However, various functional food ingredients such as oligosaccharides, prebiotics, proteins and probiotics could effect a beneficial modification in the composition and activities of gut microflora of infants. The aim of the present review is to describe existing knowledge on the composition and metabolic activities of the gastrointestinal microflora of human infants and discuss various possibilities and opportunities for its nutritional modulation.

The effects of α-lactalbumin and glycomacropeptide on the association of CaCo-2 cells by enteropathogenicEscherichia coli, Salmonella typhimuriumandShigella flexneri

Two milk components, alpha-lactalbumin (alpha-La) and glycomacropeptide (GMP) may inhibit intestinal infection/intoxification. (3)[H] thymidine-labeled enteropathogenic Escherichia coli (EPEC), Salmonella typhimurium (ATCC 6994) or Shigella flexneri (ATCC 9199) were introduced to CaCo-2 cultures and their association with CaCo-2 cells was assessed. Undigested, pepsin-digested and pepsin- and pancreatin-digested alpha-lactalbumin and glycomacropeptide inhibited association. Thus, milk supplemented with alpha-lactalbumin and glycomacropeptide might be effective in inhibiting associations of the pathogens EPEC, Salmonella typhimurium, and Shigella flexneri to intestinal cells.

Milk biologically active components as nutraceuticals: review

Milk contains components that provide critical nutritive elements, immunological protection, and biologically active substances to both neonates and adults. Milk proteins are currently the main source of a range of biologically active peptides. Concentrates of these peptides are potential health-enhancing nutraceuticals for food and pharmaceutical applications. Several bioactive peptides may be used as nutraceuticals, for example, in the treatment of diarrhea, hypertension, thrombosis, dental diseases, as well as mineral malabsorption, and immunodeficiency. Minor whey proteins, such as lactoferrin, lactoperoxidase, lysozyme, and immunoglobulins, are considered antimicrobial proteins. Milk also contains some natural bioactive substances. These include oligosaccharides, fucosylated oligosaccharides, hormones, growth factors, mucin, gangliosides, and endogenous peptides, which are present in milk at secretion. Most of the claimed physiological properties of milk bioactive components have been carried out in vitro or in animal model systems, and these hypothesized properties remain to be proven in humans. Whether these milk bioactive components will replace drugs entirely in the immediate future is still unclear, but the increasing appreciation of "drug foods" or nutraceuticals plays a complementary rather than a substitutional role to the synthetic pharmacological drugs.

Lactoferrin—a multifunctional protein with antimicrobial properties

Lactoferrin is a member of the transferrin family of iron-binding proteins. Numerous functions have been reported and continue to be reported for the protein, some of which are related to its iron-binding properties. Its extensive antimicrobial activities were originally attributed to its ability to sequester essential iron, however, it is now established that it possesses bactericidal activities as a result of a direct interaction between the protein or lactoferrin-derived peptides. This article reviews the antimicrobial activities of lactoferrin and discusses the potential mode of action of lactoferrin-derived cationic peptides against Gram-negative bacteria in the light of recent studies.

Expression, characterization, and biologic activity of recombinant human lactoferrin in rice

BACKGROUND

Lactoferrin has been suggested to have many biologic activities, such as facilitating iron absorption and having antimicrobial and antiinflammatory effects. In humans, several of these activities are likely to only be facilitated by human lactoferrin because they depend on the binding of human lactoferrin to specific receptors. Rice may be a useful vehicle to introduce recombinant human lactoferrin to infant foods because it has low allergenicity and is likely to be safer than using microorganisms or transgenic animals.

METHODS

Recombinant human lactoferrin was expressed in the rice cell culture system, and its biologic activity was assessed by iron-binding and -releasing properties, antimicrobial activity, and binding and uptake to Caco-2 cells. The authors also compared the stability of recombinant and native human lactoferrins against heat, low pH, and in vitro digestion.

RESULTS

Biologic activity of rice-expressed recombinant human lactoferrin was similar to that of native human lactoferrin. Heat-treated proteins retained their functional activities except with severe treatment at 100 degrees C for 8 seconds, which disturbed the iron-binding capacity of recombinant human lactoferrin. Both types of proteins retained their functional activities between pH 2 and 7.4. After in vitro digestion, 50% of both proteins were detectable by enzyme linked immunosorbent assay. The remaining native and recombinant lactoferrins retained antimicrobial and Caco-2 binding and uptake activities.

CONCLUSIONS

The results indicate recombinant human lactoferrin has stability similar to native human lactoferrin when exposed to thermal treatment, pH treatment, and in vitro digestion, suggesting it may be active when added to infant formula.

Effective artificial proteases synthesized by covering silica gel with aldehyde and various other organic groups

Organic artificial proteases with broad substrate specificity were synthesized by covering the surface of silica gel with aldehyde and the functional groups present in amino acids. The artificial proteases hydrolyzed ovalbumin, albumin, hemoglobin, gamma-globulin with half-lives as short as 50 min at 25 degrees C or 7 min at 50 degrees C.

Bovine lactoferrin and lactoferricin derived from milk: production and applications

Bovine lactoferrin is produced on an industrial scale from cheese whey or skim milk. The safety of purified lactoferrin has been confirmed from the results of a reverse mutation test using bacteria, a 13-week oral repeated-dose toxicity study in rats, and clinical studies. In order to apply active lactoferrin to various products, a process for its pasteurization was developed. Subsequently, lactoferrin has been used in a wide variety of products since it was first added to infant formula in 1986. A pepsin hydrolysate of lactoferrin is also used in infant formula. This hydrolysate contains a potent antimicrobial peptide named lactoferricin that is derived from the lactoferrin molecule by pepsin digestion. Semilarge-scale purification of lactoferricin can be performed by hydrophobic interaction chromatography. Lactoferricin also exhibits several biological actions and appears to be the functional domain of lactoferrin. Recent studies have demonstrated that oral administration of lactoferrin or lactoferricin exerts a host-protective effect in various animals and in humans. The results of these studies strongly suggest that the effects of oral lactoferrin are mediated by modulation of the immune system. Further elucidation of the clinical efficacy and mechanism of action of lactoferrin will increase the value of lactoferrin-containing products.

Symposium on 'nutritional effects of new processing technologies'. New processing technologies: an overview

Most food-preservation techniques act by slowing down or completely inhibiting the growth of micro-organisms. Few techniques act by inactivating them. While heat remains the technique most extensively used for inactivation, there has been increasing interest recently in the development of alternative approaches in response to the desires of consumers for products which are less organoleptically and nutritionally damaged during processing and less reliant on additives than previously. The new approaches, therefore, mostly involve technologies that offer full or partial alternatives to heat for the inactivation of bacteria, yeasts and moulds. They include the application to foods of high hydrostatic pressure, high-voltage electric discharges, high-intensity laser and non-coherent light pulses, 'manothermosonication' (the combination of mild heating with ultrasonication and slightly-raised pressure), and high-magnetic-field pulses. In addition, a number of naturally-occurring antimicrobials, including lysozyme and low-molecular-weight products of micro-organisms are finding increasing use. High pressure is being used commercially to non-thermally pasteurize a number of foods, while the other physical procedures are in various stages of development and commercial evaluation. Possible nutritional consequences have so far been given little attention compared with microbiological ones.

Bacteriostatic activity of human lactoferrin against Staphylococcus aureus is a function of its iron-binding properties and is not influenced by antibiotic resistance

The in vitro antistaphylococcal activity of lactoferrin and the antibiotic resistance of clinical Staphylococcus aureus isolates obtained from three different sites of infection were examined. Antibiotic, but not lactoferrin resistance correlated with selective antibiotic pressure, and nosocomial and most community isolates were antibiotic resistant, whereas only a third of each group was resistant to lactoferrin. The antimicrobial activity of lactoferrin, both in defined medium and in normal human plasma serum, was dependent upon its ferrochelating properties. Therapeutic approaches based on the use of ferrochelating agents such as lactoferrin combined with antimicrobial drugs may help to counteract the reduced efficacy of current antibiotics.

Effects of milk-derived bioactives: an overview

Milk contains various components with physiological functionality. Peptides derived from caseins and whey proteins including opioid peptides, antihypertensive peptides, casein phosphopeptides, alpha- and beta-lactorphins and albutensin have been shown to possess various bioactive properties. This review considers an overview of the bioactive components in milk proteins and whey and their physiological function.

Expression of full-length bioactive antimicrobial human lactoferrin in potato plants

A cDNA fragment encoding human lactoferrin (hLF) linked to a plant microsomal retention signal peptide (SEK-DEL) was stably integrated into the Solanum tuberosum genome by Agrobacterium tumefaciens-mediated leaf disk transformation methods. The lactoferrin gene was expressed under control of both the auxin-inducible manopine synthase (mas) P2 promoter and the cauliflower mosaic virus (CaMV) 35S tandem promoter. The presence of the hLF cDNA in the genome of regenerated transformed potato plants was detected by polymerase chain reaction amplification methods. Full-length hLF protein was identified by immunoblot analysis in tuber tissue extracts from the transformed plants by immunoblot analysis. The hLF produced in transgenic plant tissues migrated during polyacrylamide gel electrophoresis as a single band with an approximate molecular mass equal to hLF. Auxin activation of the mas P2 promoter increased lactoferrin expression levels in transformed tuber and leaf tissues to approximately 0.1% of total soluble plant protein. Antimicrobial activity against four different human pathogenic bacterial strains was detected in extracts of lactoferrin-containing potato tuber tissues. This is the first report of synthesis of full length, biologically active hLF in edible plants.

The effect of alpha-lactalbumin and beta-lactoglobulin hydrolysates on the metabolic activity of Escherichia coli JM103

Bovine milk proteins alpha-lactalbumin (alpha-la) and beta-lactoglobulin (beta-lg) were hydrolysed with seven different proteolytic enzymes, and the effect of various hydrolysates on a genetically modified luminous Escherichia coli JM103 was tested in vitro with a bioluminescence assay for bacterial growth and metabolism. Undigested proteins did not inhibit the activity of tested E. coli JM103 at a concentration as high as 0.1 g ml-1. At the same concentrations, alpha-la hydrolysed with pepsin or trypsin and beta-lg hydrolysed with alcalase, pepsin or trypsin, showed a lower metabolic activity during the first 8 h of growth. The activity of E. coli JM103 in the presence of 25 mg ml-1 alpha-la or beta-lg hydrolysed with pepsin and trypsin was only 21% of the control after incubation for 6 h. The preliminary results indicated that ultrafiltration through 10 kDa and 1 kDa molecular mass cut-off membranes may be used to enrich bacteriostatic properties.

Proposing sequences for peptides derived from whey fermentation with potential bioactive sites

In fed-batch fermentation by Kluyveromyces marxianus var. marxianus, whey-soluble proteins were converted into oligopeptides. To assess whether bioactive peptides could be produced during whey fermentation, K. marxianus was cultured in batch in deproteinized media containing 5 or 15% (wt/vol) dehydrated whey for 20 h and then was in fed-batch mode for 50 h. After harvesting the biomass (25,000 x g, 15 min), at 6-h intervals, the wort was analyzed to determine protein consumption and oligopeptide production by HPLC. The proteins in the wort showed an oscillatory degradation with a constant increase in the production of oligopeptides. Four major peaks were collected and were analyzed by API mass spectroscopy. Sequences of fermented peptides were compared with sequences of known bioactive peptides. On the basis of their molecular weights, two amino acid sequences were proposed. The presence of sites containing the peptide sequence of beta-lactorphin (YLLF) suggests that these oligopeptides may have antihypertensive properties.

Relationship between antibacterial activity and cell surface binding of lactoferrin in species of genus Micrococcus

Human lactoferrin was bactericidal in vitro for Micrococcus luteus but not for other Micrococcus species (M. radiophilus, M. roseus and M. varians). A correlation between the binding of lactoferrin to the bacterial surface and the antimicrobial action was observed. Viability assays showed that ferric, but not ferrous, salts prevented binding and consequently M. luteus was not killed. The unsaturated form of lactoferrin showed a greater affinity than that of the iron-saturated molecule for lipomannan, a lipoglycan present on the cell wall of M. luteus, supporting the role for lipomannan as one of the possible binding sites of lactoferrin on M. luteus.

Antibacterial activity in bovine lactoferrin-derived peptides

Several peptides sharing high sequence homology with lactoferricin B (Lf-cin B) were generated from bovine lactoferrin (Lf) with recombinant chymosin. Two peptides were copurified, one identical to Lf-cin B and another differing from Lf-cin B by the inclusion of a C-terminal alanine (lactoferricin). Two other peptides were copurified from chymosin-hydrolyzed Lf, one differing from Lf-cin B by the inclusion of C-terminal alanyl-leucine and the other being a heterodimer linked by a disulfide bond. These peptides were isolated in a single step from chymosin-hydrolyzed Lf by membrane ion-exchange chromatography and were purified by reverse-phase high-pressure liquid chromatography (HPLC). They were characterized by N-terminal Edman sequencing, mass spectrometry, and antibacterial activity determination. Pure lactoferricin, prepared from pepsin-hydrolyzed Lf, was purified by standard chromatography techniques. This peptide was analyzed against a number of gram-positive and gram-negative bacteria before and after reduction of its disulfide bond or cleavage after its single methionine residue and was found to inhibit the growth of all the test bacteria at a concentration of 8 microM or less. Subfragments of lactoferricin were isolated from reduced and cleaved peptide by reverse-phase HPLC. Subfragment 1 (residues 1 to 10) was active against most of the test microorganisms at concentrations of 10 to 50 microM. Subfragment 2 (residues 11 to 26) was active against only a few microorganisms at concentrations up to 100 microM. These antibacterial studies indicate that the activity of lactoferricin is mainly, but not wholly, due to its N-terminal region.

Physicochemical and antibacterial properties of lactoferrin and its hydrolysate produced by heat treatment at acidic pH

In order to apply functionally active lactoferrin (Lf) to food products, the effect of pH on the heat stability of Lf was studied. Lf was easily denatured to an insoluble state by heat treatment under neutral or alkaline conditions, above pH 6. In contrast, it remained soluble after heat treatment under acidic conditions at pH 2 to 5, and the HPLC pattern of Lf heat-treated at pH 4 at 100 degrees C for 5 min was the same as that of native Lf. Lf was found to be very thermostable at pH 4, and could be pasteurized or sterilized without any significant loss of its physicochemical properties. Lf was hydrolyzed by heat treatment at pH 2 to 3 at above 100 degrees C, and its iron binding capacity and antigenicity were lost. But the antibacterial activity of the hydrolysate was found to be much stronger than that of native Lf. The antibacterial component of Lf hydrolysate produced by heat treatment at acidic pH was verified to be a peptide including the sequence of residues 1-54 from the N-terminal end of the bovine Lf molecule.

Thermal behavior of bovine lactoferrin in water and its relation to bacterial interaction and antibacterial activity

Heat-induced enthalpy changes in different forms of bovine lactoferrin in water were examined by differential scanning calorimetry. Two thermal transitions with varying enthalpies were observed, depending on the iron-binding status of the protein. Iron-saturated lactoferrin was more resistant to heat-induced changes than was the apolactoferrin. Native lactoferrin had two transitional peaks, and pasteurization affected only the low temperature transition. Iron-saturated lactoferrin revealed a single transitional peak that was resistant to pasteurization. However, both protein forms were completely denatured by UHT. The effect of pasteurization and UHT on the protein interaction capacity with bacteria was examined in a 125I-labeled lactoferrin binding-inhibition assay. The ability of native and iron-saturated lactoferrins to bind various bacterial species was unaffected by pasteurization. However, UHT treatment decreased this interaction capacity. Native lactoferrins, both unheated and pasteurized, showed similar antibacterial properties and moderately inhibited Escherichia coli. However, this inhibitory capacity was lost after UHT treatment. Finally, iron-saturated lactoferrin did not inhibit bacterial growth; neither pasteurization nor UHT could change this property. Thus, UHT seems to affect structural as well as certain biological properties of both native and iron-saturated bovine lactoferrins, and pasteurization seems to be a treatment of choice for products containing this protein.

Iron-binding properties of bovine lactoferrin in iron-rich solution

The iron-binding properties of bovine lactoferrin in iron-rich solution were investigated. Ferrous iron was not stable in solution and was easily changed to the insoluble ferric state, but solubility of ferrous iron was stabilized by the presence of lactoferrin. However, casein hydrolysate or BSA was not effective in stabilizing iron in solution. As indicated by use of cibacron blue affinity gel, iron bound to lactoferrin, and the charge of supersaturated lactoferrin was higher than that of normal iron-saturated lactoferrin according to native PAGE electrophoresis. The evidence suggests that lactoferrin can bind iron at sites other than its chelate-binding sites, thereby stabilizing iron in solution.

Relationship between antibacterial activity and porin binding of lactoferrin in Escherichia coli and Salmonella typhimurium

The effect of lactoferrin (Lf) on bacterial growth was tested by measuring conductance changes in the cultivation media by using a Malthus-AT system and was compared with the magnitude of 125I-labeled Lf binding in 15 clinical isolates of Escherichia coli. The binding property was inversely related to the change in bacterial metabolic rate (r = 0.91) and was directly related to the degree of bacteriostasis (r = 0.79). The magnitude of Lf-bacterium interaction showed no correlation with the MIC of Lf. In certain strains, Lf at supraoptimal levels reduced the bacteriostatic effect. Thus, the Lf concentration in the growth media was critical for the antibacterial effect. The cell envelopes of Salmonella typhimurium 395MS with smooth lipopolysaccharide (LPS) and its five isogenic rough mutants revealed 38-kDa porin proteins as peroxidase-labeled-Lf-reactive components in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot (ligand blot) analysis. However, in the whole cell binding assay, parent strain 395MS demonstrated a very low interaction with 125I-Lf. On the other hand, Lf interaction gradually increased in correspondence with the decrease in LPS polysaccharide moiety in the isogenic rough mutants. Conductance measurement studies revealed that the low-level-Lf-binding (low-Lf-binding) strain 395MS with smooth LPS was relatively insusceptible to Lf, while the high-Lf-binding mutant Rd was more susceptible to Lf. These data suggested a correlation between Lf binding to porins and the Lf-mediated antimicrobial effect. The polysaccharide moiety of LPS shielded porins from the Lf interaction and concomitantly decreased the antibacterial effect.