Killing of Actinobacillus actinomycetemcomitans by human lactoferrin

The gut's role in metabolism, mucosal barrier function, and gut immunology

The gastrointestinal tract functions not only to absorb nutrients, it also plays an important immunologic role during health and critical illness. Under experimental and certain clinical conditions, stimulating the gut attentuates the stress response and avoids mucosal atrophy and increases permeability. Gut stimulation prevents atrophy of the gut-associated lymphoid tissue, the body's major defender of moist mucosal surfaces. A better understanding of gut function and improved nutrient delivery has clinical implications in the treatment of critically ill patients.

The effects of different (pseudo)halide substrates on peroxidase-mediated killing of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a Gram-negative bacterium which has an important role in localized juvenile and in progressive periodontitis. It is sensitive to killing by the myeloperoxidase (MP)-hydrogen peroxide (H2O2)-chloride system which is part of the innate host defense mediated by polymorphonuclear leukocytes. Since it has been recently suggested that thiocyanate, instead of chloride, could serve as a main substrate for MP as for lactoperoxidase (LP) and salivary peroxidase, we investigated in this study the effect of both LP and MP systems on A. actinomycetemcomitans with different (pseudo)halide substrates, thiocyanate, chloride and iodide. The concentrations of the substrates were physiological for oral fluids, as was the concentration range of H2O2. Both peroxidases produced end products with identical antibacterial activity with thiocyanate and iodide. The oxidation of iodide resulted in the highest antimicrobial efficiency followed by chloride and thiocyanate. Addition of thiocyanate into either MP-H2O2-chloride or MP/LP-H2O2-iodide system abolished the bactericidal activity of the oxidized halide. However, the chloride did not affect the bactericidality of the MP-H2O2-iodide system, but when all 3 (pseudo)halide substrates were present no antimicrobial effect was recorded. Our study shows that the presence of thiocyanate in physiological amounts is able to prevent the bactericidal activity of halide-peroxidase systems in low H2O2 concentrations. These results explain why thiocyanate-peroxidase systems of either innate origin (saliva, crevicular fluid) or introduced by commercial oral hygiene products are most probably ineffective against A. actinomycetemcomitans in vivo. Further studies of halide/thiocyanate ratio are needed to develop products which are also effective against oral anaerobes.

Calprotectin and lactoferrin levels in the gingival crevicular fluid of children

The purpose of this study was to determine the levels of calprotectin and lactoferrin, 2 microbiostatic proteins, in the gingival crevicular fluid (GCF) of normal children. The children represented a population, primarily underprivileged, seeking care at a regional dental health care center. GCF was collected from Ramfjord teeth (or their deciduous equivalent). GCF volume was quantified by conductance. Calprotectin and lactoferrin levels were quantified by sandwich ELISA, and found to have a mean value of 70.8+/-94.2 microg/mL and 68.2+/-108.7 microg/mL, respectively. The levels of calprotectin and lactoferrin varied directly with one another and inversely with the amount of fluid obtained in a 20-second sampling period. The mean levels were at or above the minimum inhibitory concentration determined in vitro.

Characterization and functional analysis of the porcine lactoferrin gene promoter

Lactoferrin, a ferric binding glycoprotein found in milk, can possibly prevent microbial infection of the mammary gland and gastrointestinal tract. To define the regulation of the porcine lactoferrin gene (pLTF), we cloned its 5'-flanking region from a porcine liver genomic library and analyzed the 5' upstream region of approx. 4kb, two exons, and an intron. The transcription start site was localized by primer extension to residue G, which is 41 nucleotides upstream from the ATG start codon. The pLTF 5'-flanking region possesses several putative cis-acting regulatory elements found in both housekeeping and inducible genes; to define their function, they were inserted into a chloramphenicol acetyltransferase reporter construct. The region up to -156 sufficed for basic promoter activity, whereas the region up to -780 was required for maximal promoter activity in porcine testis cells (STcells), kidney cells (PK15 cells) and human mammary epithelial cells (HBL-100 cells). Detailed analysis of this proximal region by DNase I footprinting and electrophoretic mobility shift assays reveals that the ubiquitous factors SP1, AP2 and the mammary gland-specific factor (MGF) might play significant roles in regulating the transcription of the pLTF gene.

Expression of Human Lactoferrin cDNA Confers Resistance to Ralstonia solanacearum in Transgenic Tobacco Plants

ABSTRACT A construct containing a human lactoferrin cDNA was used to transform tobacco (Nicotiana tabacum) using an Agrobacterium-mediated DNA-transfer system to express this human protein in transgenic plants. Transformants were analyzed by Southern, Northern, and Western blots to determine integration of the cDNA into the plant genome and lactoferrin gene expression levels. Most transgenic plants demonstrated significant delays of bacterial wilt symptoms when inoculated with the bacterial pathogen Ralstonia solanacearum. Quantification of the expressed lactoferrin protein by enzyme-linked immunosorbent assay in transgenic plants indicated a significant positive relationship between lactoferrin gene expression levels and levels of disease resistance. Incorporation of the lactoferrin gene into crop plants may enhance resistance to other phytopathogenic bacteria as well.

Structure-function relationship of antibacterial synthetic peptides homologous to a helical surface region on human lactoferrin against Escherichia coli serotype O111

Lactoferricin includes an 11-amino-acid amphipathic alpha-helical region which is exhibited on the outer surface of the amino-terminal lobe of lactoferrin. Synthetic peptides homologous to this region exhibited potent antibacterial activity against a selected range of both gram-negative and gram-positive bacteria. An analog synthesized with methionine substituted for proline at position 26, which is predicted to disrupt the helical region, abolished antibacterial activity against Escherichia coli and considerably reduced antibacterial activity against Staphylococcus aureus and an Acinetobacter strain. The mode of action of human lactoferrin peptide (HLP) 2 against E. coli serotype O111 (NCTC 8007) was established by using flow cytometry, surface plasmon resonance, and transmission electron microscopy. Flow cytometry was used to monitor membrane potential, membrane integrity, and metabolic processes by using the fluorescent probes bis-1,3-(dibutylbarbituric acid)-trimethine oxonol, propidium iodide, and carbonyl cyanide m-chlorophenylhydrazone, respectively. HLP 2 was found to act at the cell membrane, causing complete loss of membrane potential after 10 min and of membrane integrity within 30 min, with irreversible damage to the cell as shown by rapid loss of viability. The number of particles, measured by light scatter on the flow cytometer, dropped significantly, showing that bacterial lysis resulted. The peptide was shown to bind to E. coli O111 lipopolysaccharide by using surface plasmon resonance. Transmission electron microscopy revealed bacterial distortion, with the outer membrane becoming detached from the inner cytoplasmic membrane. We conclude that HLP 2 causes membrane disruption of the outer membrane, resulting in lysis, and that structural considerations are important for antibacterial activity.

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.

Lactoferrin impedes epithelial cell adhesion in vitro

In the process of host defence against microbial challenge, neutrophils release granule contents with the potential side effect of damaging structural tissues. In the junctional epithelium such damage may contribute to the degeneration and renewal of the epithelial cells attached directly to the tooth (DAT cells), and subsequently to periodontal pocket formation. This study reports on lactoferrin, one of the substances released by neutrophils, and its effects on epithelial cell adhesion, growth, DNA synthesis and spreading of cell colonies at concentrations recorded in the crevicular fluid. We show that, in opposition to what has been reported on bacterial cells, lactoferrin has no effect on the DNA synthesis of attached epithelial cells in model systems attempting to simulate the DAT cells in vivo. However, both iron-saturated and unsaturated lactoferrin hampered cell adhesion, growth and spreading of cell colonies in a dose-dependent manner. These findings suggest that lactoferrin does not affect epithelial cell proliferation but it may have a role in delaying the repair of the DAT cell population during inflammation by interfering with cell adhesion.

Advances in mucosal immunology

HIV infection is likely to remain a significant medical and scientific problem well into the twenty-first century. During the first 15 years of the epidemic, much has been learned about the biology of HIV infection, but the majority of biomedical research has focused on the peripheral circulation. It is likely that the behavior of the virus within the unique immunologic environment of the intestinal mucosa differs from that which is observed in the periphery. Many clinical and epidemiologic features of HIV infection offer compelling reasons to encourage further examination of the mucosal immune system's role in AIDS pathogenesis. This article has touched on most of the significant observations concerning the mucosal immune system and HIV infection, and it is clear that much remains to be done. As mentioned earlier, the mucosal abnormalities observed in HIV infection are likely to have many causes. Careful evaluation of patients with early disease and fewer confounding variables may provide fresh insight into AIDS pathogenesis. Similarly, prospective evaluation of selected patient populations may be more informative in characterizing the progressive alterations in mucosal immune function than random cross-sectional studies of poorly defined groups. It is equally important for immunologic assessment to be correlated with nutritional and symptomatic evaluation. Finally, the success or failure of future antiretroviral therapies will be critically related to the impact of such agents on lymphoid reservoirs of HIV infection such as the gastrointestinal tract, which are at present refractory to treatment.

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.

A possible role for lysozyme in determining acute exacerbation in chronic bronchitis

The aggregation of non-serotypable Haemophilus influenzae (NTHI) by whole saliva from patients with chronic obstructive lung disease (COLD) was investigated. Significant differences were observed between salivary aggregating activity of a control and COLD population (P < 0.001). Saliva from patients less prone to acute exacerbations had a greater capacity to aggregate bacteria compared with saliva from patients with a predilection to infection. The mechanism of saliva-mediated aggregation of NTHI was investigated and shown to be related to lysozyme content. Lysozyme activity in saliva was measured by the turbidimetric technique and results showed that patients with chronic bronchitis had increased levels of salivary lysozyme, with a subpopulation within the non-infection-prone group having greater amounts. A significant difference was observed in salivary lysozyme between controls and non-infection-prone (P < 0.005) and infection-prone (P < 0.05) patients, respectively: the non-infection-prone patients having significantly (P < 0.005) more than the infection-prone patients. There was significant correlation (r = 0.742, P < 0.001) between salivary aggregation of NTHI and lysozyme activity. Chromatographically purified human lysozyme had a similar aggregation profile to that of saliva. There was no difference in serum and saliva lactoferrin concentrations between groups, but there was a significant increase (P < 0.05) in serum lysozyme concentration in the non-infection-prone group. This study suggests that the level of salivary lysozyme derived from macrophages may play an important role in determining resistance or susceptibility to acute bronchitis.

Mouse lactoferrin gene: a marker for estrogen and epidermal growth factor

Lactoferrin mRNA in the 21-day-old mouse uterus can be increased several hundredfold by estrogen. The physiological role of lactoferrin in mouse uterus is unclear; however, it can be a useful marker for the estrogen action in the uterus. The structural organization and the chromosome location of the lactoferrin gene are similar to members of the transferrin gene family. At the 5' flanking region of the lactoferrin gene, we have characterized two modules that respond to estrogen and growth factor stimulation. Each module is composed of either overlapping or multiple transcription factor-binding elements. The well-characterized estrogen and growth factor response modules in the mouse lactoferrin gene could serve as the foundation to understand the intricate molecular mechanisms of estrogen action and its relationship to growth factors.

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.

Lactoferrin interaction with Actinobacillus actinomycetemcomitans

The interaction of lactoferrin with Actinobacillus actinomycetemcomitans was examined in a 125I-labeled protein binding assay. The binding of human and bovine lactoferrins reached maximum within 1 h. Lactoferrin binding to the bacterium was pH-dependent and reversible. Scatchard analysis indicated the existence of two different types of binding sites on the bacterium, one with a high affinity constant k alpha approximately 8.8 x 10(-7) M) and the other with a low one (k alpha approximately 1.8 x 10(-6) M). Bacteria in the exponential phase of growth showed higher binding than cells in the stationary phase. Bacteria grown in medium containing serum and/or lysed erythrocytes bound lactoferrin to a lesser extent. Heat-inactivated serum, lysed erythrocytes and other proteins such as mucin and laminin inhibited lactoferrin binding to A. actinomycetemcomitans in a competitive binding assay. Sodium dodecyl sulfate polyacrylamide-gel electrophoresis and Western blot analysis of the cell envelope as well as the outer membrane of A. actinomycetemcomitans revealed lactoferrin-reactive protein bands at 29 kDa and 16.5 kDa. The 29-kDa band displayed a heat-modifiable lactoferrin-reactive form with a molecular weight of 34 kDa. Neither proteinase K-treated cell envelope nor lipopolysaccharide of this bacterium showed reactivity with lactoferrin. These data suggests a specific interaction of lactoferrin with outer membrane proteins of A. actinomycetemcomitans.

Effect of lactoferrin on interaction of Prevotella intermedia with plasma and subepithelial matrix proteins

A lactoferrin-binding protein with an estimated molecular mass of 57 kDa was identified in the cell envelope of Prevotella intermedia by gel electrophoresis and Western-blot analysis. Peroxidase-labeled bovine lactoferrin and human lactoferrin showed similar specific binding to this protein. Whole cells of P. intermedia were also examined for interactions with 5 125I-labeled plasma and subepithelial matrix proteins. A high degree of binding was found with fibronectin, collagen type I and type IV and laminin, whereas a moderate interaction was detected with fibrinogen. The ability of bovine lactoferrin to affect the interactions of the above proteins with P. intermedia was examined. In the presence of unlabeled bovine lactoferrin, a dose-dependent inhibition of binding was observed with all 5 proteins tested. Unlabeled bovine lactoferrin also dissociated the bacterial complexes with these proteins. The complexes with laminin or collagen type I were more effectively dissociated than fibronectin or fibrinogen, whereas the interaction with collagen type IV was affected to a lesser extent. A strain-dependent variation in the effect of bovine lactoferrin was observed. These data establish the presence of a specific lactoferrin-binding protein in the cell envelope of P. intermedia. The ability of lactoferrin to inhibit the binding of some plasma and subepithelial matrix proteins to P. intermedia could be a protective mechanism against the establishment of this pathogen in the periodontal pocket.

Antimicrobial peptides of lactoferrin

Lactoferrin was found to contain an antimicrobial sequence near its N-terminus which appears to function by a mechanism distinct from iron chelation. Antimicrobial peptides representing this domain were isolated following pepsin cleavage of human lactoferrin and bovine lactoferrin. The antimicrobial sequence was found to consist mainly of a loop of 18 amino acid residues formed by a disulfide bond between cysteine residues 20 and 37 of human lactoferrin, or 19 and 36 of bovine lactoferrin. The identified domain contains a high proportion of basic residues, like various other antimicrobial peptides known to target microbial membranes and it appears to be located on the surface of the folded protein allowing its interaction with surface components of microbial cells. The isolated domain, "lactoferrin", was shown to have potent broad spectrum antimicrobial properties and its effect was lethal causing a rapid loss of colony-forming capability. Such evidence points to the conclusion that this domain is the structural region responsible for the microbicidal properties of lactoferrin. The evidence also suggests the possibility that active peptides produced by enzymatic digestion of lactoferrin may contribute to the host defense against microbial disease.

The effects of lactoferrin on gram-negative bacteria

Lactoferrin is an iron-binding protein found in human mucosal secretions as well as the specific granules of polymorphonuclear leukocytes. A variety of functions have been ascribed to the protein, and it appears to contribute to antimicrobial host defense. In particular, it has been shown to have direct effects on pathogenic microorganisms including bacteriostasis and the induction of microbial iron uptake systems. Still its overall physiologic role remains to be defined. It has appeared logical that antimicrobial activity of the protein arises from sequestration of environmental iron thereby causing nutritional deprivation in susceptible organisms. This argument is buttressed by the finding that selected highly virulent pathogens have evolved techniques to subvert this effect and use the protein as an iron source. However, recent observations indicate that the protein has additional properties that contribute to host defense. Work by several groups has shown that the protein synergistically interacts with immunoglobins, complement, and neutrophil cationic proteins against Gram-negative bacteria. Further, both the whole protein and a cationic N-terminus peptide fragment directly damage the outer membrane of Gram-negative bacteria suggesting a mechanism for the supplemental effects. This review will summarize these diverse observations with a consideration of how the in vitro work relates to the physiological role of the protein.

The fungicidal effect of human lactoferrin on Candida albicans and Candida krusei

Five oral isolates each of Candida albicans and Candida krusei were studied for their sensitivity to the fungicidal effect of human lactoferrin. Significant inter- and intraspecies variations were observed and with most isolates the sensitivity of C. krusei to lactoferrin was greater than that of C. albicans. Fungicidal activity of lactoferrin was dose-dependent and observable only with the iron-free form of the molecule (apo-lactoferrin). Iron-saturated lactoferrin was ineffective against all isolates. Supernatant protein assays and scanning electron microscopy indicated cell surface alterations--leakage of proteins and formation of surface blebs--only in those Candida isolates that were sensitive to apo-lactoferrin. As lactoferrin is a common, non-immune, mucosal defence protein, its varying mode of action against C. albicans and C. krusei may be related to their different oral carriage rates.

Lactotransferrin binding to its platelet receptor inhibits platelet aggregation

A fluorescent lactotransferrin probe was prepared by coupling 5-(([2-(carbhydrazino)methyl]-thio)acetyl)amino fluorescein to aldehyde groups that were produced by a mild periodic-acid oxidation of the glycan moieties of lactotransferrin. In this manner, the receptor-binding site of the lactotransferrin remains active in contrast to the binding site of the lactotransferrin derivatized with fluorescein isothiocyanate. The fluorescent probe allowed us to characterize, by flow cytometry, the binding of lactotransferrin to non-activated human platelets. The putative lactotransferrin platelet receptor was purified and its immunological and physico-chemical properties were found to be very similar to those of the receptor previously isolated from activated human lymphocytes. Lactotransferrin inhibits ADP-induced platelet aggregation at concentrations down to 5 nM, which can be reached in the plasma after leukocyte degranulation. Inhibition of platelet aggregation was also observed with the N-terminal fragment of lactotransferrin (residues 3-281; 50% inhibition = 2 microM) and with CFQWQRNMRKVRGPPVSC synthetic octodecapeptide (residues 20-37; 50% inhibition = 20 microM) corresponding to one of the two external loops (residues 28-34 and 39-42) where we recently located the receptor-binding site. The activity (50% inhibition = 500 microM) of the tetrapeptide KRDS (residues 39-42), which has already been described, was at least 25-times and 16000-times lower than the activity of the octodecapeptide and of the lactotransferrin molecules, respectively. Finally, the inhibition was demonstrated to be mediated by a mechanism which requires the binding of lactotransferrin to its putative receptor and not to platelet glycoprotein IIb-IIIa.

COUP-TF acts as a competitive repressor for estrogen receptor-mediated activation of the mouse lactoferrin gene

We previously demonstrated that the estrogen response module (mERM) of the mouse lactoferrin gene, which contains an overlapping chicken ovalbumin upstream promoter transcription factor (COUP-TF)- and estrogen receptor-binding element, is responsible for estrogen induction. In this report we show that COUP-TF represses the mERM response to estrogen stimulation. Mutation and deletion of the COUP-TF-binding element or reduction of the endogenous COUP-TF increases mERM estrogen responsiveness. Likewise, overexpression of the COUP-TF expression vector blocked the estrogen-stimulated response of mERM in transfected cells. The molecular mechanism of this repression is due to the competition between COUP-TF and the estrogen receptor for binding at identical contact sites in the overlapping region of the mERM. Our results indicate that two members of the steroid-thyroid receptor superfamily work in concert to modulate lactoferrin gene expression.

Agglutination of Streptococcus mutans serotype C cells but inhibition of Porphyromonas gingivalis autoaggregation by human lactoferrin

The ability of various forms of human lactoferrin (LF) to agglutinate oral Streptococcus mutans, Strep. sobrinus, Strep. rattus, Strep. sanguis, Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans cells was studied spectrophotometrically. Fe3+ saturated LF was unable to agglutinate these bacteria, whereas iron-free LF (apo LF) effectively agglutinated Strep. mutans cells but not the other bacteria. The efficiency and rate of agglutination of Strep. mutans were somewhat lower with apo LF than with human whole saliva. However, secretory IgA, phosphate and whole saliva almost totally abolished the apo LF-mediated agglutination of Strep. mutans, suggesting binding to the same target sites on bacterial cell surfaces, or to each other. The presence of exogenous iron (Fe2+, Fe3+), lactoperoxidase or serum albumin did not affect the agglutination by apo LF. Low Ca2+ (50-100 microns) slightly enhanced the agglutination by apo LF but higher concentrations (0.5-1.0 mM) totally blocked the apo LF-mediated agglutination of Strep. mutans. Both saliva and apo LF significantly delayed the rapid autoaggregation of P. gingivalis cells. Aggregation of P. gingivalis is considered a potential virulence factor and a protective mechanism against the host's cellular defences in the gingival crevice. These findings show a novel, strain-specific antibacterial mechanism for LF against Strep. mutans and P. gingivalis and adds a new compound to the group of agglutinating proteins in human saliva.

COUP-TF acts as a competitive repressor for estrogen receptor-mediated activation of the mouse lactoferrin gene

We previously demonstrated that the estrogen response module (mERM) of the mouse lactoferrin gene, which contains an overlapping chicken ovalbumin upstream promoter transcription factor (COUP-TF)- and estrogen receptor-binding element, is responsible for estrogen induction. In this report we show that COUP-TF represses the mERM response to estrogen stimulation. Mutation and deletion of the COUP-TF-binding element or reduction of the endogenous COUP-TF increases mERM estrogen responsiveness. Likewise, overexpression of the COUP-TF expression vector blocked the estrogen-stimulated response of mERM in transfected cells. The molecular mechanism of this repression is due to the competition between COUP-TF and the estrogen receptor for binding at identical contact sites in the overlapping region of the mERM. Our results indicate that two members of the steroid-thyroid receptor superfamily work in concert to modulate lactoferrin gene expression.

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.

Antibacterial activity of lactoferrin and a pepsin-derived lactoferrin peptide fragment

Although the antimicrobial activity of lactoferrin has been well described, its mechanism of action has been poorly characterized. Recent work has indicated that in addition to binding iron, human lactoferrin damages the outer membrane of gram-negative bacteria. In this study, we determined whether bovine lactoferrin and a pepsin-derived bovine lactoferrin peptide (lactoferricin) fragment have similar activities. We found that both 20 microM bovine lactoferrin and 20 microM lactoferricin release intrinsically labeled [3H]lipopolysaccharide ([3H]LPS) from three bacterial strains, Escherichia coli CL99 1-2, Salmonella typhimurium SL696, and Salmonella montevideo SL5222. Under most conditions, more LPS is released by the peptide fragment than by whole bovine lactoferrin. In the presence of either lactoferrin or lactoferricin there is increased killing of E. coli CL99 1-2 by lysozyme. Like human lactoferrin, bovine lactoferrin and lactoferricin have the ability to bind to free intrinsically labeled [3H]LPS molecules. In addition to these effects, whereas bovine lactoferrin was at most bacteriostatic, lactoferricin demonstrated consistent bactericidal activity against gram-negative bacteria. This bactericidal effect is modulated by the cations Ca2+, Mg2+, and Fe3+ but is independent of the osmolarity of the medium. Transmission electron microscopy of bacterial cells exposed to lactoferricin show the immediate development of electron-dense "membrane blisters." These experiments offer evidence that bovine lactoferrin and lactoferricin damage the outer membrane of gram-negative bacteria. Moreover, the peptide fragment lactoferricin has direct bactericidal activity. As lactoferrin is exposed to proteolytic factors in vivo which could cleave the lactoferricin fragment, the effects of this peptide are of both mechanistic and physiologic relevance.

Antibacterial spectrum of lactoferricin B, a potent bactericidal peptide derived from the N-terminal region of bovine lactoferrin

A physiologically diverse range of Gram-positive and Gram-negative bacteria was found to be susceptible to inhibition and inactivation by lactoferricin B, a peptide produced by gastric pepsin digestion of bovine lactoferrin. The list of susceptible organisms includes Escherichia coli, Salmonella enteritidis, Klebsiella pneumoniae, Proteus vulgaris, Yersinia enterocolitica, Pseudomonas aeruginosa, Campylobacter jejuni, Staphylococcus aureus, Streptococcus mutans, Corynebacterium diphtheriae, Listeria monocytogenes and Clostridium perfringens. Concentrations of lactoferricin B required to cause complete inhibition of growth varied within the range of 0.3 to 150 micrograms/ml, depending on the strain and the culture medium used. The peptide showed activity against E. coli O111 over the range of pH 5.5 to 7.5 and was most effective under slightly alkaline conditions. Its antibacterial effectiveness was reduced in the presence of Na+, K+, Mg2+ or Ca2+ ions, or in the presence of various buffer salts. Lactoferricin B was lethal, causing a rapid loss of colony-forming capability in most of the species tested. Pseudomonas fluorescens, Enterococcus faecalis and Bifidobacterium bifidum strains were highly resistant to this peptide.

Susceptibility of Porphyromonas gingivalis and P. asaccharolytica to the non-oxidative killing mechanisms of human neutrophils

Neutrophils are essential for host defence against bacterial dental plaque and the pathogenic bacterial species within it, but in anaerobic environments such as the gingival crevice neutrophils can kill bacteria only with non-oxidative microbicidal compounds stored in their granules. Porphyromonas gingivalis W83, a pathogenic plaque species, and the avirulent non-oral type-strain P. asaccharolytica were incubated anaerobically with intact neutrophils and with compounds extracted from normal human neutrophil granules. The killing of bacteria and the inactivation of lysozyme, cathepsin G, elastase, bacterial-permeability increasing factor and defensins by culture supernatants were assayed. P. asaccharolytica but not P. gingivalis was killed under anaerobic conditions by intact neutrophils. P. gingivalis was also resistant to neutrophil granule compounds, its viability being reduced from a mean of 3.3 x 10(6) to 6.1 x 10(4) c.f.u/ml in 60 min by 400 micrograms/ml neutrophil granule extract, as compared to a reduction from 4.4 x 10(6) to 2.3 x 10(3) c.f.u/ml for P. asaccharolytica. P. gingivalis culture supernatant inactivated cathepsin G, elastase, bacterial-permeability increasing factor and defensins. Resistance to neutrophil non-oxidative killing mechanisms may be an important virulence factor for P. gingivalis.

The neutrophil: mechanisms of controlling periodontal bacteria

The control of potentially periodontopathic microorganisms by host neutrophils is crucial to periodontal health. Neutrophils may use oxidative or nonoxidative mechanisms and either kill bacteria, influence bacterial growth, or modify bacterial colonization in the periodontium. Delivery of antimicrobial substances by neutrophils involves respiratory burst activity, phagocytosis, secretion, or cytolysis/apoptosis. Neutrophils contain a number of antimicrobial components including calprotectin complex, lysozyme, defensins, cofactor-binding proteins, neutral serine proteases, bactericidal/permeability increasing protein, myeloperoxidase, and a NADPH oxidase system. Many of these components are multifunctional and exhibit several mechanisms of antimicrobial activity. When comparisons are made among periodontal bacteria, differences in sensitivity to different components are observed. A hypothesis of specific defense is presented: That specific periodontal diseases can result from the failure of specific aspects of the host immune system (the neutrophil, in particular) in its interaction with specific periodontal pathogens. Failure may be due to phenotypic variation (pleomorphism) within the host or bacterial evasive strategies.

Differential killing of Actinobacillus actinomycetemcomitans and Capnocytophaga spp. by human neutrophil granule components

The purpose of this study was to determine whether granule fractions of human neutrophils differentially kill Actinobacillus actinomycetemcomitans and Capnocytophaga spp. Granule extracts were subjected to gel filtration, and seven fractions (designated A through G) were obtained. Under aerobic conditions at pH 7.0, representative strains of A. actinomycetemcomitans were killed by fraction D and variably by fraction B. In contrast, the Capnocytophaga spp. were killed by fractions C, D, F, and G. Fractions A (containing lactoferrin and myeloperoxidase) and E (containing lysozyme) exerted little bactericidal activity under these conditions. Anaerobiosis had little effect on the bactericidal activity of fractions D and F but inhibited that of fractions B and C. Electrophoresis, zymography, determination of amino acid composition, and N-terminal sequence analysis revealed that fraction C contained elastase, proteinase 3, and azurocidin. Fraction D contained lysozyme, elastase, and cathepsin G. Subfractions of C and D containing elastase (subfraction C4), a mixture of elastase and azurocidin (subfraction C5), and cathepsin G (subfraction D9) were found to be bactericidal. The bactericidal effects of fraction D and subfraction D9 against A. actinomycetemcomitans was not inhibited by heat inactivation, phenylmethylsulfonyl fluoride, or N-benzyloxycarbonylglycylleucylphenylalanylchloromethyl ketone. We conclude that (i) A. actinomycetemcomitans and Capnocytophaga spp. were sensitive to the bactericidal effects of different neutrophil granule components, (ii) both were sensitive to the bactericidal effects of neutral serine proteases, and (iii) the killing of A. actinomycetemcomitans by cathepsin G-containing fractions was independent of oxygen and neutral serine protease activity.

In vitro killing of oral Capnocytophaga by granule fractions of human neutrophils is associated with cathepsin G activity

The Capnocytophaga are inhabitants of the hypoxic human gingival crevice that are normally prevented by neutrophils from causing periodontal and systemic infection. To identify potential nonoxidative bactericidal mechanisms against Capnocytophaga within human neutrophils, gel filtration chromatography was used to fractionate neutrophil granule extracts. Seven granule fractions, designated A through G, were obtained. The Capnocytophaga were most sensitive to killing by fraction D. Fraction D exhibited substantial bactericidal activity under aerobic and anaerobic conditions. The bactericidal activity associated with ion-exchange subfractions D8-D11, which contained primarily cathepsin G as assessed by enzymatic activity, amino acid composition, and NH2-terminal sequence. Heat-inactivation, diisopropylfluorophosphate, PMSF, and N-benzyloxycarbonylglycylleucylphenylalanyl-chloromethyl ketone inhibited bactericidal activity against Capnocytophaga sputigena but not Escherichia coli. We conclude that (a) human neutrophil cathepsin G is an important antimicrobial system against the Capnocytophaga, (b) the bactericidal activity of cathepsin G against Capnocytophaga is oxygen independent, and (c) an intact enzyme active site is involved in the killing of C. sputigena but not E. coli. We suggest that human neutrophil cathepsin G is an important antimicrobial system against certain oral bacteria and that cathepsin G kills bacteria by two distinct mechanisms.

Salivary defense mechanisms in juvenile periodontitis

The local, saliva-associated defense mechanisms of 28 juvenile periodontitis (JP) patients and their age- and sex-matched controls were studied. Lysozyme, lactoferrin, salivary peroxidase, myeloperoxidase, and thiocyanate concentrations were determined from both whole saliva and parotid saliva. The total concentrations of salivary IgA, IgG, and IgM were assayed. The periodontal condition and the salivary flow rates were registered. Among the JP patients, a significantly elevated concentration of IgG was found in parotid saliva but not in whole saliva. Salivary peroxidase activities were significantly low both in the whole and in the parotid saliva samples of the JP patients, and leukocyte-derived myeloperoxidase was present in significantly low amounts in whole saliva of these patients. Because both glandular (salivary peroxidase) and polymorphonuclear-cell-derived (myeloperoxidase) enzyme activities were low among the JP patients, suppressed peroxidase-mediated host defense mechanisms could be characteristic of JP.

In vitro sensitivity of oral, gram-negative, facultative bacteria to the bactericidal activity of human neutrophil defensins

Neutrophils play a major role in defending the periodontium against infection by oral, gram-negative, facultative bacteria, such as Actinobacillus actinomycetemcomitans, Eikenella corrodens, and Capnocytophaga spp. We examined the sensitivity of these bacteria to a mixture of low-molecular-weight peptides and highly purified individual defensin peptides (HNP-1, HNP-2, and HNP-3) isolated from human neutrophils. Whereas the Capnocytophaga spp. strains were killed significantly by the mixed human neutrophil peptides, the A. actinomycetemcomitans and E. corrodens strains were resistant. Killing was attributable to the defensins. The bactericidal activities of purified defensins HNP-1 and HNP-2 were equal, and both of these activities were greater than HNP-3 activity against strains of Capnocytophaga sputigena and Capnocytophaga gingivalis. The strain of Capnocytophaga ochracea was more sensitive to defensin-mediated bactericidal activity than either C. sputigena or C. gingivalis was. The three human defensins were equipotent in killing C. ochracea. C. ochracea was killed under aerobic and anaerobic conditions and over a broad pH range. Killing was most effective under hypotonic conditions but also occurred at physiologic salt concentrations. We concluded that Capnocytophaga spp. are sensitive to oxygen-independent killing by human defensins. Additional studies will be required to identify other components that may equip human neutrophils to kill A. actinomycetemcomitans, E. corrodens, and other oral gram-negative bacteria.

Prooxidant activity of transferrin and lactoferrin

Acceleration of the autoxidation of Fe2+ by apotransferrin or apolactoferrin at acid pH is indicated by the disappearance of Fe2+, the uptake of oxygen, and the binding of iron to transferrin or lactoferrin. The product(s) formed oxidize iodide to an iodinating species and are bactericidal to Escherichia coli. Toxicity to E. coli by FeSO4 (10(-5) M) and human apotransferrin (100 micrograms/ml) or human apolactoferrin (25 micrograms/ml) was optimal at acid pH (4.5-5.0) and with logarithmic phase organisms. Both the iodinating and bactericidal activities were inhibited by catalase and the hydroxyl radical (OH.) scavenger mannitol, whereas superoxide dismutase was ineffective. NaCl at 0.1 M inhibited bactericidal activity, but had little or no effect on iodination. Iodide increased the bactericidal activity of Fe2+ and apotransferrin or apolactoferrin. The formation of OH.was suggested by the formation of the OH.spin-trap adduct (5,5-dimethyl-1-pyroline N-oxide [DMPO]/OH)., with the spin trap DMPO and the formation of the methyl radical adduct on the further addition of dimethyl sulfoxide. (DMPO/OH).formation was inhibited by catalase, whereas superoxide dismutase had little or no effect. These findings suggest that Fe2+ and apotransferrin or apolactoferrin can generate OH.via an H2O2 intermediate with toxicity to microorganisms, and raise the possibility that such a mechanism may contribute to the microbicidal activity of phagocytes.