Biological role of lactoferrin

Orally administered bovine lactoferrin inhibits bacterial translocation in mice fed bovine milk

Feeding of bovine milk to mice induced a high incidence of bacterial translocation from the intestines to the mesenteric lymph nodes, and the bacteria involved were mainly members of the family Enterobacteriaceae. Supplementation of the milk diet with bovine lactoferrin or a pepsin-generated hydrolysate of bovine lactoferrin resulted in significant suppression of bacterial translocation. Our findings suggest that this ability of lactoferrin to inhibit bacterial translocation may be due to its suppression of bacterial overgrowth in the guts of milk-fed mice.

Giardicidal activity of lactoferrin and N-terminal peptides

Human and bovine lactoferrins and their derived N-terminal peptides were giardicidal in vitro. Fe3+, but not Fe2+, protected trophozoites from both native lactoferrin and peptides, although the latter lack iron-binding sites. Other divalent metal ions protected only against native lactoferrin. Log-phase cells were more resistant to killing than stationary-phase cells. These studies suggest that lactoferrin, especially in the form of the N-terminal peptides, may be an important nonimmune component of host mucosal defenses against Giardia lamblia.

The immunologic significance of breast milk

The importance of breast milk in protecting the newborn from infection is recognized worldwide. Infant morbidity and mortality have been directly affected by a decline in breastfeeding. Health care providers are working toward meeting the national goal of increased initiation and duration of breastfeeding. This article focuses on the protective factors transferred to the infant through breast milk. A discussion of maximizing the immunologic benefits of breast milk for the high-risk infant is presented.

Characterization of lbpA, the structural gene for a lactoferrin receptor in Neisseria gonorrhoeae

Neisseria gonorrhoeae acquires iron (Fe) efficiently from lactoferrin (LF). A 103-kDa gonococcal outer membrane LF-binding protein (Lbp) was identified previously. We isolated the structural gene lbpA for Lbp1 by screening a gonococcal library for a clone that could repair an LF- receptor mutant. An mTnCm3 transposon insertion mutant of lbpA was unable to use LF-bound Fe for growth, unable to bind LF to whole cells, and unable to express Lbp1. The DNA sequence of lbpA predicted a protein that shared 94% identity with the meningococcal LF receptor protein, Lbp, and was closely related to Tbp1, one of the transferrin receptor proteins. Clinical isolates of gonococci are frequently unable to acquire Fe from LF, and LF- isolates do not have a functional LF receptor. The wild-type lbpA gene transformed most tested LF- clinical isolates to LF+, indicating that lbpA is defective in many clinical isolates.

Effect of intracellular iron depletion by picolinic acid on expression of the lactoferrin receptor in the human colon carcinoma cell subclone HT29-18-C1

A lactoferrin receptor has been found on the brush-border membrane of intestinal epithelial cells of several species, including humans. A role for this receptor in intestinal iron absorption, which is well regulated in response to body iron stores, has been proposed. We have investigated the effect of intracellular iron depletion by picolinic acid, an iron chelator, on the cell surface binding of human lactoferrin to human enterocytes and its intracellular uptake, using HT29-18-C1 cells, an enterocyte-like differentiable cell line. The confluent cells exhibited 5.8 x 10(6) specific binding sites per cell for diferric human 125I-labelled lactoferrin with relatively low affinity (Kd 8.4 x 10(-7) M). The addition of picolinic acid to the culture medium resulted in a concentration- and time-dependent increase in lactoferrin binding that was correlated with a decrease in intracellular iron content. The maximum effect of picolinic acid on lactoferrin binding (approx. 2-fold increase), which appeared between 12 and 18 h after its addition, was obtained at a picolinic acid concentration of 2 mM. Scatchard analysis showed that the enhanced lactoferrin binding resulted from an increase in the number of lactoferrin receptors rather than an alteration in the binding affinity for lactoferrin. The time-dependent effect of picolinic acid was completely abolished in the presence of 1 microM anisomycin, a protein synthesis inhibitor, indicating that ongoing protein synthesis is involved in this effect. The enhanced lactoferrin binding induced by picolinic acid produced an increase of approx. 30% in the uptake of lactoferrin-bound 59Fe, indicating the existence of functional receptors. These results suggest that biosynthesis of lactoferrin receptors in intestinal epithelial cells can be regulated in response to the levels of intracellular chelatable iron, consistent with intestinal iron absorption dependent on body iron stores.

Lactoferrin down-modulates the activity of the granulocyte macrophage colony-stimulating factor promoter in interleukin-1 beta-stimulated cells

The human neutrophil lactoferrin (Lf), a cationic iron-binding glycoprotein, has an inhibitor role on granulocyte macrophage colony-stimulating factor (GM-CSF) production via interleukin-1 (IL-1). The nuclear localization of Lf suggests that it may be involved in the transcriptional regulation of GM-CSF gene expression. To explore this possibility, the effect of Lf on GM-CSF gene expression was investigated in various cell lines and in primary cultures of fibroblasts. Down-regulation of GM-CSF mRNA level was observed in Lf-transfected embryonic fibroblasts induced to produce GM-CSF by IL-1 beta. In 5637 cell-line and in embryonic fibroblasts, co-transfection experiments, in which an Lf expression vector was used together with a vector carrying a reporter gene linked to the GM-CSF promoter, revealed that Lf reduces the activity of the GM-CSF promoter. This effect is marked in IL-1 beta-stimulated cells. These findings suggest that Lf plays a negative role in GM-CSF expression at the transcriptional level, perhaps through the mediation of IL-1 beta.

Interaction of beta-lactoglobulin with retinol and fatty acids and its role as a possible biological function for this protein: a review

beta-Lactoglobulin is the major whey protein in the milk of ruminants and some nonruminants, such as pigs and horses. Although beta-lactoglobulin was first isolated 60 yr ago, no function has been definitely ascribed to beta-lactoglobulin. Recent x-ray crystallographic studies have advanced knowledge of the structure of beta-lactoglobulin, which is homologous with that of retinol-binding protein and lipocalycins; the function of these proteins seems to be participation in the transport of small hydrophobic substances. By analogy, this protein has been suggested as having a role as a transporter of fatty acids and retinol. This review reassesses the function of beta-lactoglobulin in light of the large amount of information that has accrued in the last few years. In particular, this review concentrates upon studies of the binding of retinol and fatty acids to beta-lactoglobulin, including the binding constants and number of binding sites, the location of the binding sites, and the influence of chemical modifications in the interaction of the protein with both ligands. This study also describes studies of the influence of beta-lactoglobulin on several biological processes that may be relevant to the possible biological role of this protein.

A system for production of commercial quantities of human lactoferrin: a broad spectrum natural antibiotic

We previously reported the production of limited quantities of biologically active recombinant human lactoferrin in the filamentous fungus Aspergillus oryzae. In the present study, we report a modification of this production system combined with a classical strain improvement program that has enabled production of levels of recombinant human lactoferrin in excess of 2 g/l. The protein was expressed in Aspergillus awamori as a glucoamylase fusion polypeptide which was secreted into the growth medium and processed to mature human lactoferrin by an endogenous KEX-2 peptidase. The recombinant protein retains full biological activity in terms of its ability to bind iron and human enterocyte receptors. Furthermore, the recombinant protein functions as a potent broad spectrum antimicrobial protein.

Iron: mammalian defense systems, mechanisms of disease, and chelation therapy approaches

During the past 6 decades, much attention has been devoted to understanding the uses, metabolism and hazards of iron in living systems. A great variety of heme and non-heme iron-containing enzymes have been characterized in nearly all forms of life. The existence of both ferrous and ferric ions in low- and high-spin configuration, as well as the ability of the metal to function over a wide range of redox potentials, contributes to its unique versatility. Not surprisingly, the singular attributes of iron that permit it to be so useful to life likewise render the metal dangerous to manipulate and to sequester. All vertebrate animals are prone to tissue damage from exposure to excess iron. In order to protect them from this threat, a complex system has evolved to contain and detoxify this metal. This is known as the iron withholding defense system, which mainly serves to scavenge toxic quantities of iron and also for depriving microbial and neoplastic invaders of iron essential for their growth. Since 1970, medical scientists have become increasingly aware of the problems involved in cellular iron homeostasis and of the disease states related to its malfunctioning. Scores of studies have reported that excessive iron in specific tissue sites is associated with development of infection, neoplasia, cardiomyopathy, arthropathy and a variety of endocrine and neurologic deficits. Accordingly, several research groups have attempted to develop chemical agents that might prevent and even eliminate deposits of excess iron. A few of these drugs now are in clinical use, e.g. deferiprone (L1). In the present review, we focus on recent developments in (i) selected aspects of the iron withholding defense system, and (ii) pharmacologic methods that can assist the iron-burdened patient.

Bacteriostatic effect of orally administered bovine lactoferrin on proliferation of Clostridium species in the gut of mice fed bovine milk

When milk-fed mice were orally inoculated with Clostridium ramosum C1, this strain proliferated in the gut and became the dominant component of the fecal microflora. In this experimental model, bovine lactoferrin (bLF) administered with milk suppressed the proliferation of this strain in vivo and decreased the numbers of C. ramosum and other bacteria in the feces. This bacteriostatic effect of bLF was dependent on the concentration of bLF, the duration of feeding, and the administered dose of C. ramosum C1. Compared with bovine serum albumin, ovalbumin, bovine whey protein isolate, or bovine casein, only bLF showed this specific activity. A similar effect of bLF was observed after oral inoculation with C. ramosum JCM 1298, C. paraputrificum VPI 6372, or C. perfringens ATCC 13124. A hydrolysate prepared by digestion of bLF with porcine pepsin showed the same inhibitory effect on proliferation of C. ramosum in vivo as occurred with undigested bLF. These results indicate that ingested bLF can exert a bacteriostatic effect against clostridia in the gut even after it has been digested to some extent.

A review: the active peptide of lactoferrin

A potent antimicrobial peptide, 'lactoferricin', was found to be generated upon gastric pepsin cleavage of lactoferrin. The active peptide consists mainly of a loop of 18 amino acid residues, derived from the N-terminal region of the lactoferrin molecule. Like various other antimicrobial peptides that display membrane-disruptive properties, it contains a high proportion of basic amino acid residues. A physiologically diverse range of micro-organisms was tested and found to be susceptible to inhibition by this natural peptide including Gram-negative and Gram-positive bacteria, yeasts and filamentous fungi. Its antimicrobial effect against sensitive micro-organisms was lethal. Electron microscopy studies revealed that it induces a profound change in cell ultrastructural features and causes substantial cell damage in bacteria and fungi. These findings suggest the possibility that active peptides of lactoferrin may have a role in the host defense against microbial disease. If produced in substantial quantities in vivo such peptides could have important physiological significance, especially in nursing infants.

The bovine lactoferrin gene (LTF) maps to chromosome 22 and syntenic group U12

Five overlapping lambda EMBL-clones, containing the complete bovine lactoferrin gene (LTF), have been used to map this gene by fluorescence in situ hybridization to bovine Chromosome (Chr) band 22q24. Primers derived from promoter and exon I sequences were applied in polymerase chain reactions (PCRs) to DNA samples of a previously characterized panel of somatic cell hybrid lines, allowing the assignment of the bovine lactoferrin locus to syntenic group U12. These results permit the assignment of syntenic group U12 to bovine Chr 22.

Serotransferrin, ovotransferrin and metallothionein levels during an immune response in chickens

Extracellular iron-binding proteins function in iron transport, iron scavenging and bactericidal activity. To determine whether the levels of chicken iron-binding proteins are altered during an immune challenge, young broiler chicks and 40-week-old hens were injected with lipopolysaccharide (LPS). Serum transferrin and liver mRNA for serum transferrin increased at 24 hr after injection. Increased levels of serum transferrin and hepatic mRNA for serum transferrin define chicken serum transferrin as an acute-phase protein. Magnum mRNA for ovotransferrin decreased 24 hr after the immune challenge in hens. Hens had also stopped ovulating, suggesting that synthesis of all egg proteins was decreased.

Structure of the bovine lactoferrin-encoding gene and its promoter

Lactoferrin (Lf), a ferric ion (Fe3+)-binding glycoprotein, is found most notably in milk, probably to mediate protection against microbial infection of the mammary gland. Based on an initial isolation and sequencing of a complete cDNA of the bovine Lf gene (bLf), the complete gene was obtained from genomic libraries on five overlapping phage lambda EMBL3 clones. A detailed restriction map and the complete exon/intron structure of the gene are presented, together with 1 kb of sequence data of the promoter upstream from the proximal exon. The coding sequence is dispersed over 17 exons spanning 34.5 kb of genomic DNA. While the exons are of similar size, as in other members of the transferrin gene family (Tf), some of the intron sizes are very different. Evolutionary conservation of both exon sizes and their contribution to the various domains of the protein molecule add to the evidence that Lf originated via an internal sequence duplication. The promoter sequence lacks some of the sequence motifs for transcriptional enhancers found in the promoters of human and mouse Lf, suggesting a potential reason for the relatively weak expression of bLf.

Lactoferrin is a lipid A-binding protein

Lactoferrin (LF), a cationic 80-kDa protein present in polymorphonuclear leukocytes and in mucosal secretions, is known to have antibacterial effects on gram-negative bacteria, with a concomitant release of lipopolysaccharides (LPS, endotoxin). In addition, LF is known to decrease LPS-induced cytokine release by monocytes and LPS priming of polymorphonuclear leukocytes. Its mechanism of action is incompletely understood. We have now demonstrated by in vitro-binding studies that LF binds directly to isolated lipid A and intact LPS of clinically relevant serotypes of the species which most frequently cause bacteremia (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa), as well as to lipid A and LPS of mucosal pathogens (among others, Neisseria meningitides and Haemophilus influenzae). Binding to LPS was inhibitable by lipid A and polymyxin B but not by KDO (3-deoxy-D-manno-octulosonate), a glycoside residue present in the inner core of LPS. Binding of LF to lipid A was saturable, and an affinity constant of 2 x 10(9) M-1 was calculated for the LF-lipid A interaction. Our data may explain, in part, the mechanism whereby LF exerts its antibacterial and anti-endotoxic effects. Further studies on the ability of LF to block the detrimental effects of LPS, both in vitro and in vivo, are warranted.

Proposed mechanisms for the involvement of lactoferrin in the hydrolysis of nucleic acids

Lactoferrin has recently been proposed to have ribonuclease activity in the absence of bound iron. We and others have demonstrated previously that lactoferrin interacts with DNA and will bind a number of transition metal ions via surface-exposed histidyl residues. In the present study, we investigated the possibility that surface-bound copper ions on lactoferrin may catalyze the production of active oxygen species responsible for the hydrolysis of nucleic acids. Purified lactoferrin (apo- and holo-forms) was incubated with CuCl2 in solution to obtain lactoferrin with surface binding sites saturated by Cu(II)ions. the lactoferrin-Cu(II) complex was purified by Bio-Gel P-6 chromatography columns and tested for hydrolytic activity against DNA and RNA as analyzed by agarose gel electrophoresis. Incubation of lactoferrin-Cu(II) complexes with supercoiled plasmid Bluescript II SK DNA led to the rapid formation of relaxed open circular or linear forms of DNA characterized by changed electrophoretic mobility. Lactoferrin with bound Cu(II) also caused extensive degradation of yeast tRNA molecules in the presence of hydrogen peroxide. Covalent modification of surface-exposed histidyl residues by carboxyethylation with diethylpyrocarbonate abolished the lactoferrin-associated hydrolytic activity. These results indicate that lactoferrin-bound Cu(II) can indeed facilitate the hydrolysis of DNA and RNA molecules. Copper-binding sites on lactoferrin appear to serve as centers for repeated production of hydroxyl radicals via a Fenton-type Haber-Weiss reaction. Enhanced nuclease activity associated with elevated local concentrations of lactoferrin would promote microbial degradation.

In vitro inhibition of mammary cell growth by lactoferrin: a comparative study

The effect of lactoferrin (Lf) on mammary epithelial cell growth in culture was tested in a comparative study of bovine and human Lf. Bovine Lf was inhibitory to growth of a bovine mammary epithelial cell line, both in the presence and absence of fetal bovine serum in the medium. The growth inhibition activity of bovine Lf was not affected by iron-saturation status of the protein. In contrast with bovine Lf, human Lf had minimal inhibitory activity on bovine cell growth in the presence of serum, and cell growth was stimulated by human Lf in the absence of serum. In the latter case, human Lf may have acted as an iron-transport protein for the cells. Bovine Lf and human Lf had no effect on growth of MCF-7 human breast tumor cells and only minimal inhibitory activity toward the MDA-MB 231 human breast tumor cell line. The effect of bovine Lf on bovine mammary epithelial cells could be prevented by immunoneutralization of the Lf. These results indicate that Lf can be inhibitory to growth of mammary epithelial cells in culture, but this response to specific for the species origin of the Lf and of the mammary cell.

Lactoferrin receptors in intestinal brush border membranes

Lactoferrin from milk may have a physiological effect on the neonate by stimulating iron acquisition and/or mucosal growth. We have hypothesized that in order to achieve such an effect(s), lactoferrin will bind to a specific receptor located on the mucosal surface of the enterocyte. We have studied the presence of lactoferrin receptors in the brush border membrane from infant rhesus monkey intestine and from fetal and infant human intestine. The receptor exhibits saturation kinetics and the binding is specific for human and monkey lactoferrin--bovine lactoferrin or human transferrin do not bind to the receptor or compete with the binding of the primate lactoferrins. Enzymatic deglycosylation does not affect the binding of human lactoferrin to its receptor, suggesting that the glycan(s) is not needed for receptor recognition. Competitive binding experiments showed that holo-lactoferrin was more effective than less Fe-saturated forms of lactoferrin with regard to receptor binding. Mn-lactoferrin bound to the receptor, while we were unable to prepare Zn-lactoferrin in any physiological buffer. The human lactoferrin receptor was isolated and found to have a MW of approximately 110 kDa. This receptor has now been cloned and is being sequenced.

The developmental profile of lactoferrin in mouse epididymis

A sandwich e.l.i.s.a. method was developed to examine the distribution of lactoferrin in mouse reproductive tract. The lactoferrin concentration was found to be much higher in oviduct, uterus, vagina, vas deferens or epididymis than in serum, but the concentration in ovary, testis, seminal vesicle, prostate or coagulating gland was comparable with that in serum. The existence of lactoferrin in male sexual organs was confirmed by Western-blot analyses for tissue proteins. Lactoferrin in male sexual organs was shown to have a molecular mass similar to that of the deglycosylated form of lactoferrin purified from mouse uterine luminal fluid. Northern-blot analyses for total RNA prepared from male sexual organs indicated that only epididymis contained the lactoferrin mRNA. The lactoferrin mRNA was found in the prepubertal period and increased with the growth of epididymis. The mRNA level in prepubertal epididymis could be stimulated by 17 beta-oestradiol, but was not influenced by testosterone.

Effect of heat treatment and other milk proteins on the interaction of lactoferrin with monocytes

The interaction of lactoferrin from human and bovine milk with the human promonocytic cell line U937 has been studied. Both human and bovine Fe-lactoferrins bound to the cells. Binding of bovine lactoferrin was inhibited by excess bovine lactoferrin but not by human lactoferrin, suggesting that the binding mechanisms for the two proteins are different. Binding of human but not bovine lactoferrin was inhibited by bovine lactoperoxidase, while a 20-fold excess of human IgA inhibited binding of human but not bovine lactoferrin. Human and bovine alpha-lactalbumins, bovine beta-lactoglobulin, and human lysozyme had no effect on binding of lactoferrin from either species. Samples of bovine Fe- and apolactoferrin in capillary tubes were exposed to temperatures of 72 degrees C for 20 s, 85 degrees C for 20 min or 137 degrees C for 8 s. All the heated samples inhibited binding of native Fe- and apolactoferrin, though to a lesser extent than the native proteins. Both heated and native lactoferrins enhanced [3H]thymidine incorporation by U937 cells, except for Fe-lactoferrin heated at 85 degrees C for 20 min, which was inhibitory. These results suggest that heat treatment of lactoferrin under conditions used for industrial processing does not greatly affect its ability to interact with and stimulate monocytic cells, and that other milk proteins in general do not interfere with lactoferrin-monocyte interactions. It may thus be feasible to incorporate biologically active lactoferrin into infant formulas.