Glycans of bovine lactoferrin function as receptors for the type 1 fimbrial lectin of Escherichia coli

Interaction between Dietary Lactoferrin and Gut Microbiota in Host Health

The gut microbiota are known to play an important role in host health and disease. Alterations in the gut microbiota composition can disrupt the stability of the gut ecosystem, which may result in noncommunicable chronic diseases (NCCDs). Remodeling the gut microbiota through personalized nutrition is a novel therapeutic avenue for both disease control and prevention. However, whether there are commonly used gut microbiota-targeted diets and how gut microbiota-diet interactions combat NCCDs and improve health remain questions to be addressed. Lactoferrin (LF), which is broadly used in dietary supplements, acts not only as an antimicrobial in the defense against enteropathogenic bacteria but also as a prebiotic to propagate certain probiotics. Thus, LF-induced gut microbiota alterations can be harnessed to induce changes in host physiology, and the underpinnings of their relationships and mechanisms are beginning to unravel in studies involving humans and animal models.

Protein glycosylation: Sweet or bitter for bacterial pathogens?

Protein glycosylation systems in many bacteria are often associated with crucial biological processes like pathogenicity, immune evasion and host-pathogen interactions, implying the significance of protein-glycan linkage. Similarly, host protein glycosylation has been implicated in antimicrobial activity as well as in promoting growth of beneficial strains. In fact, few pathogens notably modulate host glycosylation machineries to facilitate their survival. To date, diverse chemical and biological strategies have been developed for conjugate vaccine production for disease control. Bioconjugate vaccines, largely being produced by glycoengineering using PglB (the N-oligosaccharyltransferase from Campylobacter jejuni) in suitable bacterial hosts, have been highly promising with respect to their effectiveness in providing protective immunity and ease of production. Recently, a novel method of glycoconjugate vaccine production involving an O-oligosaccharyltransferase, PglL from Neisseria meningitidis, has been optimized. Nevertheless, many questions on defining antigenic determinants, glycosylation markers, species-specific differences in glycosylation machineries, etc. still remain unanswered, necessitating further exploration of the glycosylation systems of important pathogens. Hence, in this review, we will discuss the impact of bacterial protein glycosylation on its pathogenesis and the interaction of pathogens with host protein glycosylation, followed by a discussion on strategies used for bioconjugate vaccine development.

Dietary N-Glycans from Bovine Lactoferrin and TLR Modulation

SCOPE

Bovine lactoferrin (bLF) is an ingredient of food supplements and infant formulas given its antimicrobial and antiviral properties. We modified bLF enzymatically to alter its N-glycosylation and to isolate the glycan chains. The aims of this study include (1) to evaluate whether such derivates induce responses via pattern recognition receptors namely Toll-like receptors (TLRs) and (2) to relate those responses to their different glycosylation profiles.

METHODS AND RESULTS

The unmodified and modified bLF fractions are incubated with reporter cell lines expressing pattern recognition receptors. Afterwards, we screen for TLRs and analyze for nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) activation. Activation of reporter cell lines show that signaling is highly dependent on TLRs. The activation pattern of bLF is reduced with the desialylated form and increased with the demannosylated form. In reporter cells for TLR, bLF activate TLR-4 and inhibit TLR-3. The isolated glycans from bLF inhibit TLR-8. TLR-2, TLR-5, TLR-7, and TLR-9 are not significantly altered.

CONCLUSION

The profile of glycosylation is key for the biological activity of bLF. By understanding how this affects the human defense responses, the bLF glycan profile can be modified to enhance its immunomodulatory effects when used as a dietary ingredient.

Exploitation of SPR to Investigate the Importance of Glycan Chains in the Interaction between Lactoferrin and Bacteria

Bovine lactoferrin (LF) has been shown to prevent adhesion to and invasion of mammalian cell lines by pathogenic bacteria, with evidence for direct bacterial binding by the milk glycoprotein. However, the glycosylation pattern of LF changes over the lactation cycle. In this study, we aim to investigate the effect that this variation has on the milk glycoprotein's ability to interact with pathogens. Surface plasmon resonance technology was employed to compare the binding of LF from colostrum (early lactation) and mature milk (late lactation) to a panel of pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Cronobacter sakazakii, Streptococcus pneumoniae, Pseudomonas aeruginosa, Listeria monocytogenes and Salmonella typhimurium). Novel interactions with LF were identified for C. sakazakii, S. pneumoniae and P. aeruginosa with the highest binding ability observed for mature milk LF in all cases, with the exception of S. typhimurium. The difference in bacterial binding observed may be as a result of the varying glycosylation profiles. This work demonstrates the potential of LF as a functional food ingredient to prevent bacterial infection.

Lactoferrin prevents invasion and inflammatory response following E. coli strain LF82 infection in experimental model of Crohn's disease

BACKGROUND

Crohn's disease is a multifactorial disease in which an aberrant immune response to commensal intestinal microbiota leads to chronic inflammation. The small intestine of patients with Crohn's disease is colonized by a group of adherent-invasive Escherichia coli strongly able to adhere and invade intestinal epithelial cells lactoferrin is an iron-binding glycoprotein known to have anti-bacterial and anti-inflammatory activities.

AIMS

We explore the ability of bovine lactoferrin to modulate the interactions between the adherent-invasive E. coli strain LF82 and intestinal epithelial cells as well as the inflammatory response.

METHODS

Bacterial adhesion and invasion assays were used to assess the antimicrobial activity of lactoferrin. Electron microscopy was used to characterize bacteria-cell interactions. The mRNA expression of pro-inflammatory cytokines was measured both in cultured cells and in biopsies taken from intestine of patients affected by Crohn's disease.

RESULTS

Lactoferrin inhibited bacterial invasion through minimally affecting adhesion. This divergence was due to a mannose-dependent lactoferrin binding to the bacterial type 1 pili and consequent bacterial aggregation on the intestinal epithelial cell surface. Expression of pro-inflammatory cytokines, such as TNF-alpha, IL-8, and IL-6, was markedly inhibited by lactoferrin both in cultured and Crohn-derived intestinal cells.

CONCLUSIONS

Bovine lactoferrin might function via an antibacterial and/or anti-inflammatory mechanism in the treatment of Crohn's disease.

Profiling temporal changes in bovine milk lactoferrin glycosylation using lectin microarrays

The bovine milk glycoprotein bovine lactoferrin (bLF) has a variety of biological activities related to its constituent glycans. However, little is known about bLF's oligosaccharide structural changes over the course of lactation. BLF was isolated at 13 time points during the first three months of lactation from three individual cows and glycosylation changes were profiled by lectin microarrays. Substantial profile differences between early and late lactation were observed and accompanying monosaccharide analysis revealed that the occurrence of the non-human sialic acid, N-glycolylneuraminic acid, was greater during early stage milk production. Overall, the data suggested that more diverse complex-type oligosaccharide structures were present on bLF during early lactation with an abundance of oligomannose type glycans in later lactation. The differences in the glycoprofiles of bLF from colostrum to mature milk suggest that these may have different functionality in vivo.

Structural and functional characteristics of bovine milk protein glycosylation

Most secreted and cell membrane proteins in mammals are glycosylated. Many of these glycoproteins are also prevalent in milk and play key roles in the biomodulatory properties of milk and ultimately in determining milk's nutritional quality. Although a significant amount of information exists on the types and roles of free oligosaccharides in milk, very little is known about the glycans associated with milk glycoproteins, in particular, the biological properties that are linked to their presence. The main glycoproteins found in bovine milk are lactoferrin, the immunoglobulins, glycomacropeptide, a glycopeptide derived from κ-casein, and the glycoproteins of the milk fat globule membrane. Here, we review the glycoproteins present in bovine milk, the information currently available on their glycosylation and the biological significance of their oligosaccharide chains.

Recognition roles of the carbohydrate glycotopes of human and bovine lactoferrins in lectin-N-glycan interactions

BACKGROUND

Lactoferrin is an iron-binding protein belonging to the transferrin family. In addition to iron homeostasis, lactoferrin is also thought to have anti-microbial, anti-inflammatory, and anticancer activities. Previous studies showed that all lactoferrins are glycosylated in the human body, but the recognition roles of their carbohydrate glycotopes have not been well addressed.

METHODS

The roles of human and bovine lactoferrins involved in lectin-N-glycan recognition processes were analyzed by enzyme-linked lectinosorbent assay with a panel of applied and microbial lectins.

RESULTS AND CONCLUSIONS

Both native and asialo human/bovine lactoferrins reacted strongly with four Man-specific lectins - Concanavalia ensiformis agglutinin, Morniga M, Pisum sativum agglutinin, and Lens culinaris lectin. They also reacted well with PA-IIL, a LFuc>Man-specific lectin isolated from Pseudomonas aeruginosa. Both human and bovine lactoferrins also recognized a sialic acid specific lectin-Sambucus nigra agglutinin, but not their asialo products. Both native and asialo bovine lactoferrins, but not the human ones, exhibited strong binding with a GalNAc>Gal-specific lectin-Wisteria floribunda agglutinin. Human native lactoferrins and its asialo products bound well with four Gal>GalNAc-specific type-2 ribosome inactivating protein family lectins-ricin, abrin-a, Ricinus communis agglutinin 1, and Abrus precatorius agglutinin (APA), while the bovine ones reacted only with APA.

GENERAL SIGNIFICANCE

This study provides essential knowledge regarding the different roles of bioactive sites of lactoferrins in lectin-N-glycan recognition processes.

The immunological components of human milk

Breast-feeding is generally accepted as the optimal method of feeding infants. However, we have yet to fully understand the complex mixture of bioactive compounds contained in human milk. Epidemiological studies have indicated that breast-feeding is associated with health benefits in the infant for many immune-related conditions. Breast milk contains various antimicrobial substances, factors that promote immune development, constituents that promote tolerance/priming of the infant immune system, as well as anti-inflammatory components. This chapter identifies and discusses the immunological compounds in human milk and the available evidence for their effect on the immune system of the infant. Current feeding regimens recommended for infants are based primarily on the current understanding of the nutritional requirements of the neonate, but perhaps will be modified to reflect the consequences on immune function both immediate and later in life.

Nippostrongylus brasiliensis: identification of intelectin-1 and -2 as Stat6-dependent genes expressed in lung and intestine during infection

Elimination of the helminth parasite Nippostrongylus brasiliensis from infected mice is mediated by IL-4 or IL-13 and dependent on the IL-4Ralpha chain and the transcription factor Stat6 in non-hematopoietic cells. However, it is not clear which Stat6-dependent effector molecules mediate worm expulsion. We identified intelectin-1 and -2 as Stat6-dependent genes that are induced during infection. Intelectins can bind galactofuranose, a sugar present only in microorganisms and might therefore serve as microbial pattern element. To analyze whether constitutive expression of intelectin-1 or -2 leads to accelerated pathogen clearance, transgenic mice were generated which express high levels of these genes selectively in the lung. Infection with N. brasiliensis or Mycobacterium tuberculosis did not result in accelerated pathogen clearance in transgenic as compared to wild-type mice. Further, no significant modulation of the immune response in lung or lymph nodes was observed. Thus, under these conditions, intelectins did not enhance pathogen clearance.

In vitro growth responses of bifidobacteria and enteropathogens to bovine and human lactoferrin

A series of in vitro experiments was performed to test the ability of bovine and human lactoferrin to influence the growth of the gram-positive probiotic bacteria, Bifidobacterium bifidum, Bifidobacterium infantis, and Lactobacillus acidophilus, as well as the gram-negative enteric bacteria, E. coli O157:H7 and Salmonella typhimurium. None of the lactoferrin preparations stimulated the growth of the tested strains. However, iron-free apo-lactoferrin (bovine and human) and 66% iron-saturated bovine lactoferrin dramatically slowed the growth of E. coli O157:H7 in single culture experiments, while 98% iron-saturated preparations had no effect. In coculture experiments of B. infantis and E. coli, the iron-limited preparations of lactoferrin also slowed the growth of the latter without inhibiting the bifidobacteria. These results suggest that lactoferrin in iron-limited forms may have the potential to be combined with probiotic bacteria in biotherapeutic products, which could help balance human gut microflora and limit the overgrowth of certain enteric microorganisms.

Characterization of glycans in a lactoferrin isoform, lactoferrin-a

The presence of glycan at Asn-281 in bovine lactoferrin-a, which has a higher molecular weight than regular lactoferrin-b, was found in our previous study. The present work was performed to clarify the structures of the glycans linked to the five N-glycosylation sites in lactoferrin-a and to compare them with those of glycans linked to lactoferrin-b. In lactoferrin-a, the glycans linked to Asn-233 and Asn-545 were of the high-mannose type, whereas those present at Asn-368 and Asn-476 were complex-type ones. These glycans possessed heterogeneous structures. A comparative study of the glycans on bovine lactoferrin-a and bovine lactoferrin-b by HPLC showed that the structures of the glycans linked to Asn-368, Asn-476, and Asn-545 were very similar, the exception being the glycan linked to Asn-233. In addition, analysis of the structure of the glycan bound to Asn-281 present only in lactoferrin-a showed it possessed the heterogeneous structure of a complex-type glycan in which the structures Man3GlcNAc2, Man3GlcNAc4, Man3GlcNAc4Fuc are suggested to be present based on HPLC retention times only.

Human lactoferrin and peptides derived from a surface-exposed helical region reduce experimental Escherichia coli urinary tract infection in mice

Lactoferrin (LF) is a multifunctional immunoregulatory protein that has been associated with host defense at mucosal surfaces through its antibacterial properties. The antibacterial and anti-inflammatory properties of LF were further explored with an animal model of experimental urinary tract infection. Bovine LF (bLF), human LF (hLF), and synthetic peptide sequences based on the antibacterial region of hLF (amino acid residues 16 to 40 [HLD1] and 18 to 40 [HLD2]) were given orally to female mice 30 min after the instillation of 10(8) Escherichia coli bacteria into the urinary bladder. The control groups received phosphate-buffered saline or water. C3H/Tif mice were treated with hLF or bLF, and C3H/HeN mice were treated with bLF only. The numbers of bacteria in the kidneys and bladder of C3H/Tif and C3H/HeN mice were significantly reduced 24 h later by the LF treatments compared to the findings for the control group. The hLF-treated group showed the strongest reduction compared with the vehicle-treated-group (P values were 0.009 and 0.0001 for the kidneys and bladder, respectively). The urinary leukocyte response was diminished in the hLF-treated group. The hLF treatment also significantly reduced the urinary interleukin-6 (IL-6) levels at 2 h and the systemic IL-6 levels at 24 h after infection (P values were 0.04 and < 0.002, respectively). In the bLF-treated animals, no such strong anti-inflammatory effects were obtained. In another series of experiments, C3H/Tif mice perorally treated with HLD1 or HLD2 also showed reduced numbers of bacteria in the kidneys compared with the vehicle-treated mice, although the results were significantly different only for HLD2 (P < 0.01). Analysis of urine from hLF-fed C3H/Tif mice showed that hLF was excreted into the urinary tract at 2 h after feeding. Testing of the in vitro bactericidal activity of LF (1 mg/ml) or the peptides (0.1 mg/ml) in mouse urine against the E. coli bacteria revealed moderate killing only by HLD2. In conclusion, these results demonstrate for the first time that oral administration of hLF or peptides thereof is effective in reducing infection and inflammation at a remote site, the urinary tract, possibly through transfer of hLF or its peptides to the site of infection via renal secretion. The antibacterial mechanism is suggested to involve bactericidal capacities of LF, fragments thereof, or its peptides.

Early nutrition and the development of immune function in the neonate

The present review will concentrate on the development of the gut-associated lymphoid tissue and the role of early nutrition in promoting immune function. The intestine is the largest immune organ in the body, and as such is the location for the majority of lymphocytes and other immune effector cells. The intestine is exposed to vast quantities of dietary and microbial antigens, and is the most common portal of entry for pathogens, some of which are potentially lethal. The development of normal immune function of the intestine is therefore vital for survival, and is dependent on appropriate antigen exposure and processing, and also an intact intestinal barrier. In early life innate mechanisms of defence are probably more important than active or adaptive mechanisms in responding to an infectious challenge, since the healthy neonate is immunologically naïve (has not seen antigen) and has not acquired immunological memory. During this period maternal colostrum and milk can significantly augment resistance to enteric infections. The mechanisms of enhancing disease resistance are thought to be passive, involving a direct supply of anti-microbial factors, and active, by promoting the development of specific immune function. A tolerance response to dietary and non-invasive antigens is generally induced in the gut. However, it must also be able to mount an adequate immune response to ensure clearance of foreign antigens. It is now recognized that regulation of tolerance and active immune responses is critical to health, and failure to regulate these responses can lead to recurrent infections, inflammatory diseases and allergies. The education of the immune system in early life is thought to be critical in minimizing the occurrence of these immune-based disorders. During this phase of development maternal milk provides signals to the immune system that generate appropriate response and memory. One factor that has been proposed to contribute to the increase in the incidence of immune-based disorders, e.g. atopic diseases in Western countries, is thought to be the increased prevalence of formula-feeding.

Lactoferrin: a multifunctional glycoprotein

Lactoferrin is an iron-binding glycoprotein found in milk, exocrine secretions of mammals, and in secondary granules from polymorphonuclear neutrophils. This review describes the wide spectrum of functions ascribed to lactoferrin, with special emphasis on the antimicrobial properties of this protein, and its derived peptides.

The therapeutic effect of bovine lactoferrin in the host infected with Helicobacter pylori

BACKGROUND

It remains unclarified whether bovine lactoferrin (bLF) can exert a therapeutic effect on the host infected with Helicobacter pylori.

METHODS

Germfree BALB/c mice were orally inoculated with H. pylori to induce infection. Three weeks after infection the mice were given bLF orally once daily for 2 or 4 weeks and were then killed to examine the bacterial number in the stomach and the serum antibody titer to H. pylori. To count the number of epithelium-bound H. pylori, the resected stomach was agitated in phosphate-buffered saline to remove non-bound H. pylori before bacterial enumeration.

RESULTS

The administration of 10 mg bLF for 3 to 4 weeks decreased the number of H. pylori in the stomach to one-tenth and also exerted a significant inhibitory effect on the attachment of H. pylori to the stomach. As a result, the serum antibody titer to H. pylori, whose level is presumed to represent the size of the immune response by the host, thereby reflecting the degree of bacterial attack, decreased to an undetectable level.

CONCLUSIONS

These findings suggest that bLF exerts an inhibitory effect on colonizing H. pylori by detaching the bacterium from the gastric epithelium and by exerting a direct anti-bacterial effect.

Structures involved in the interaction of Porphyromonas gingivalis fimbriae and human lactoferrin

The ability of laboratory and clinical strains of Porphyromonas gingivalis to bind lactoferrin has been assessed (FEMS Immunology and Medical Microbiology, 1996, 14, 135-143). Relative binding for P. gingivalis to lactoferrin varies among strains from 3.78 to 26.62%. We also observed that fimbriated strains of P. gingivalis bind more strongly to lactoferrin as compared to nonfimbriated strains of P. gingivalis. This observation led us to study fimbrial interaction with human lactoferrin and the fine structure of these interactions. Binding of iodinated purified fimbriae was studied using an overlay assay. Iodinated fimbriae bind specifically and strongly to human lactoferrin. When various sugars were used to inhibit binding, only N-acetylgalactosamine and fucose were inhibitory. To confirm further that oligosaccharide of lactoferrin is involved in the interaction, lactoferrin was chemically deglycosylated, and fimbriae failed to bind deglycosylated lactoferrin. Antifimbriae, as well as four antipeptide antibodies against different regions of the P. gingivalis fimbrillin, were used to inhibit the interaction. Antipeptide E, directed against amino acids 81-98 (AAGLIMTAEPKTIVLKAG-C), was found to be the most effective inhibitor for the lactoferrin-fimbriae interaction. These results suggest that the binding of P. gingivalis cells to lactoferrin is lectin like, directed to a oligosaccharide of lactoferrin. Furthermore, these studies suggest that the region of fimbriae that binds to lactoferrin is the N-terminus of the molecule. It is likely that binding of lactoferrin to P. gingivalis cells results in antimicrobial activity directed against these cells by virtue of its ability to deprive the bacterial cell of needed iron.

Characterization of the lactoferrin-dependent inhibition of the adhesion of Actinobacillus actinomycetemcomitans, Prevotella intermedia and Prevotella nigrescens to fibroblasts and to a reconstituted basement membrane

Lactoferrin was previously shown to inhibit the adhesion of A. actinomycetemcomitans, P. intermedia and P. nigrescens to human cells. Lactoferrin was also shown to competitively inhibit the binding of these bacteria to the basement membrane protein laminin. The present study aimed to determine the type of interactions inhibited by lactoferrin. Lactoferrin binds to fibroblast monolayers and Matrigel, a reconstituted basement membrane, through ionic interactions. The adhesion of A. actinomycetemcomitans to these substrata was mainly dependent on the ionic strength of the environment. P. intermedia and P. nigrescens also adhere to fibroblasts mainly by ionic interactions, while their adhesion to Matrigel seems to be mediated by specific mechanisms. Lectin-type interactions were not found to be involved in the binding of these bacteria to the substrata. Treatment of either A. actinomycetemcomitans or fibroblasts with lactoferrin decreased the adhesion in a dose-dependent manner, while lactoferrin treatment of Matrigel alone had no adhesion-counteracting effect. Adhesion of P. intermedia and P. nigrescens to Matrigel was not significantly affected by the ionic strength, but the presence of lactoferrin inhibited the adhesion. Lactoferrin bound to Matrigel, P. intermedia and P. nigrescens was rapidly released, while lactoferrin bound to A. actinomycetemcomitans and fibroblasts was retained. These findings indicate that lactoferrin-dependent inhibition of the adhesion of A. actinomycetemcomitans, P. intermedia and P. nigrescens to fibroblasts and Matrigel can involve binding of lactoferrin to both the bacteria and substrata. The decreased adhesion may be due to blocking of both specific adhesin-ligand as well as non-specific charge-dependent interactions.

Diversity of the Escherichia coli type 1 fimbrial lectin. Differential binding to mannosides and uroepithelial cells

Type 1 fimbriae are the most common adhesive organelles of Escherichia coli. Because of their virtual ubiquity, previous epidemiological studies have not found a correlation between the presence of type 1 fimbriae and urinary tract infections (UTIs). Recently it has become clear that type 1 fimbriae exhibit several different phenotypes, due to allelic variation of the gene for the lectin subunit, FimH, and that these phenotypes are differentially distributed among fecal and UTI isolates. In this study, we have analyzed in more detail the ability of isogenic, recombinant strains of E. coli expressing fimH genes of the predominant fecal and UTI phenotypes to adhere to glycoproteins and to uroepithelial cells. Evidence was obtained to indicate that type 1 fimbriae differ in their ability to recognize various mannosides, utilizing at least two different mechanisms. All FimH subunits studied to date are capable of mediating adhesion via trimannosyl residues, but only certain variants are capable of mediating high levels of adhesion via monomannosyl residues. The ability of the FimH lectins to interact with monomannosyl residues strongly correlates with their ability to mediate E. coli adhesion to uroepithelial cells. In this way, it would be possible for certain phenotypic variants of type 1 fimbriae to contribute more than others to virulence of E. coli in the urinary tract.

Degradation of lactoferrin by periodontitis-associated bacteria

The degradation of human lactoferrin by putative periodontopathogenic bacteria was examined. Fragments of lactoferrin were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and measured by densitometry. The degradation of lactoferrin was more extensive by Porphyromonas gingivalis and Capnocytophaga sputigena, slow by Capnocytophaga ochracea, Actinobacillus actinomycetemcomitans and Prevotella intermedia, and very slow or absent by Prevotella nigrescens, Campylobacter rectus, Campylobacter sputorum, Fusobacterium nucleatum ssp. nucleatum, Capnocytophaga gingivalis, Bacteroides forsythus and Peptostreptococcus micros. All strains of P. gingivalis tested degraded lactoferrin. The degradation was sensitive to protease inhibitors, cystatin C and albumin. The degradation by C. sputigena was not affected by the protease inhibitors and the detected lactoferrin fragments exhibited electrophoretic mobilities similar to those ascribed to deglycosylated forms of lactoferrin. Furthermore a weak or absent reactivity of these fragments with sialic acid-specific lectin suggested that they are desialylated. The present data indicate that certain bacteria colonizing the periodontal pocket can degrade lactoferrin. The presence of other human proteins as specific inhibitors and/or as substrate competitors may counteract this degradation process.