Chemical synthesis of the O-antigen repeating unit of Actinobacillus actinomycetemcomitans serotype f

Herein, we report the total synthesis of the trisaccharide repeating unit of the O-antigen of Actinobacillus actinomycetemcomitans serotype f. The trisaccharide comprising of α-(1-2) and α-(1-3)-linked L-rhamnopyranosides backbone with the latter rhamnose containing a branching N-acetyl-d-galactosaminopyranoside at the C2-O via a β-glycosidic bond was synthesized by two methods. Initially, the protected trisaccharide has been synthesized by step-wise assembly of the monosaccharide building blocks and subsequently the former was synthesized by the one-pot assembly of the latter components. The synthesized trisaccharide contains an aminoethyl linker appended as an O-glycoside at the reducing end, thereby providing scope for further conjugation for different applications.

Computational modeling and druggability assessment of Aggregatibacter actinomycetemcomitans leukotoxin

The leukotoxin (LtxA) of Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is a protein exotoxin belonging to the repeat-in-toxin family (RTX). Numerous studies have demonstrated that LtxA may play a critical role in the pathogenicity of A. actinomycetemcomitans since hyper-leukotoxic strains have been associated with severe disease. Accordingly, considerable effort has been made to elucidate the mechanisms by which LtxA interacts with host cells and induce their death. However, these attempts have been hampered by the unavailability of a tertiary structure of the toxin, which limits the understanding of its molecular properties and mechanisms. In this paper, we used homology and template free modeling algorithms to build the complete tertiary model of LtxA at atomic level in its calcium-bound Holo-state. The resulting model was refined by energy minimization, validated by Molprobity and ProSA tools, and subsequently subjected to a cumulative 600ns of all-atom classical molecular dynamics simulation to evaluate its structural aspects. The druggability of the proposed model was assessed using Fpocket and FTMap tools, resulting in the identification of four putative cavities and fifteen binding hotspots that could be targeted by rational drug design tools to find new ligands to inhibit LtxA activity.

The serotype a-EmaA adhesin of Aggregatibacter actinomycetemcomitans does not require O-PS synthesis for collagen binding activity

Aggregatibacter actinomycetemcomitans, a causative agent of periodontitis and non-oral diseases, synthesizes a trimeric extracellular matrix protein adhesin A (EmaA) that mediates collagen binding and biofilm formation. EmaA is found as two molecular forms, which correlate with the serotype of the bacterium. The canonical protein (b-EmaA), associated with serotypes b and c, has a monomeric molecular mass of 202 kDa. The collagen binding activity of b-EmaA is dependent on the presence of O-polysaccharide (O-PS), whereas biofilm activity is independent of O-PS synthesis. The EmaA associated with serotype a strains (a-EmaA) has a monomeric molecular mass of 173 kDa and differs in the amino acid sequence of the functional domain of the protein. In this study, a-emaA was confirmed to encode a protein that forms antenna-like appendages on the surface of the bacterium, which were found to be important for both collagen binding and biofilm formation. In an O-PS-deficient talose biosynthetic (tld) mutant strain, the electrophoretic mobility of the a-EmaA monomers was altered and the amount of membrane-associated EmaA was decreased when compared to the parent strain. The mass of biofilm formed remained unchanged. Interestingly, the collagen binding activity of the mutant strain was similar to the activity associated with the parent strain, which differs from that observed with the canonical b-EmaA isoform. These data suggest that the properties of the a-EmaA isoform are like those of b-EmaA, with the exception that collagen binding activity is independent of the presence or absence of the O-PS.

Dispersion from Cα or NH: 4D experiments for backbone resonance assignment of intrinsically disordered proteins

Resonance assignment of intrinsically disordered proteins is remarkably challenging due to scant chemical shift dispersion arising from conformational heterogeneity. The challenge is even greater if repeating segments are present in the amino acid sequence. To forward unambiguous resonance assignment of intrinsically disordered proteins, we present iHACANCO, HACACON and (HACA)CONCAHA, three H^α-detected 4D experiments with C^α as an additional dimension. In addition, we present (HACA)CON(CA)NH and (HACA)N(CA)CONH, new 4D H^α-start, H^N-detect experiments which have two N^H dimensions to enhance peak dispersion in a sequential walk through C', N^H and H^N, and provide more accurate N^H/H^N chemical shifts than those that can be obtained from a crowded ¹H, ¹⁵N-HSQC spectrum. Application of these 4D experiments is demonstrated using BilRI (165 aa), an outer-membrane intrinsically disordered protein from the opportunistic oral pathogen Aggregatibacter actinomycetemcomitans. BilRI amino acid sequence encompasses three very similar repeats with a 13-residue identical stretch in two of them.

Membrane localization of the Repeats-in-Toxin (RTX) Leukotoxin (LtxA) produced by Aggregatibacter actinomycetemcomitans

The oral bacterium, Aggregatibacter actinomycetemcomitans, which is associated with localized aggressive periodontitis, as well as systemic infections including endocarditis, produces numerous virulence factors, including a repeats-in-toxin (RTX) protein called leukotoxin (LtxA), which kills human immune cells. The strains of A. actinomycetemcomitans most closely associated with disease have been shown to produce the most LtxA, suggesting that LtxA plays a significant role in the virulence of this organism. LtxA, like many of the RTX toxins, can be divided into four functional domains: an N-terminal hydrophobic domain, which contains a significant fraction of hydrophobic residues and has been proposed to play a role in the membrane interaction of the toxin; the central domain, which contains two lysine residues that are the sites of post-translational acylation; the repeat domain that is characteristic of the RTX toxins, and a C-terminal domain thought to be involved in secretion. In its initial interaction with the host cell, LtxA must bind to both cholesterol and an integrin receptor, lymphocyte function-associated antigen-1 (LFA-1). While both interactions are essential for toxicity, the domains of LtxA involved remain unknown. We therefore undertook a series of experiments, including tryptophan quenching and trypsin digestion, to characterize the structure of LtxA upon interaction with membranes of various lipid compositions. Our results demonstrate that LtxA adopts a U-shaped conformation in the membrane, with the N- and C-terminal domains residing outside of the membrane.

Opposite effect of supernatants from selected periopathogens and oral lactobacilli cultures on ATP levels in human gingival fibroblasts

Studies were performed on the effects of supernatants obtained from bacterial cultures, including cultures of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Prevotella intermedia and Lactobacillus acidophilus strains on ATP levels in human gingival fibroblasts (HGF-1) and on their viability. ATP levels were evaluated using luminescence test and cell viability was estimated using a fluorescence test. In control cultures mean levels of ATP in HGF-1 amounted to 4.90±0.32 mln RLU. Supernatants of P. gingivalis and A. actinomycetemcomitans cultures were found to significantly reduce ATP production in HGF-1 (mean levels of ATP amounted to 3.41±0.33 and 3.55±0.3 mln RLU respectively), which was not accompanied by an increased proportion of dead fibroblasts. Supernatants of P. intermedia induced no significant alterations in ATP level in HGF-1. In turn, supernatants of L. acidophilus H2O2 (+) and H2O2 (-) cultures significantly increased ATP levels in HGF-1 (the mean levels amounted to 5.94±0.31 mln RLU and 5.88±0.28 mln RLU respectively). The results indicate that extracellular products of P. gingivalis and A. actinomycetemcomitans most probably represent mitochondria-targeted peptides, which reduce synthesis of ATP in HGF-1. In turn, extracellular products of L. acidophilus seem to represent exopolysaccharides (EPS) with pro-oxidant activity, which stimulate synthesis of ATP in HGF-1.

The cytolethal distending toxin of Aggregatibacter actinomycetemcomitans inhibits macrophage phagocytosis and subverts cytokine production

Aggregatibacter actinomycetemcomitans is an important periodontal pathogen that can participate in periodontitis and other non-oral infections. The cytolethal distending toxin (Cdt) is among the virulence factors produced by this bacterium. The Cdt is also secreted by several mucosa-associated Gram-negative pathogens and may play a role in perpetuating the infection by modulating the immune response. Although the toxin targets a wide range of eukaryotic cell types little is known about its activity on macrophages which play a key part in alerting the rest of the immune system to the presence of pathogens and their virulence factors. In view of this, we tested the hypothesis that the A. actinomycetemcomitans Cdt (AaCdt) disrupts macrophage function by inhibiting phagocytic activity as well as affecting the production of cytokines. Murine macrophages were co-cultured with either wild-type A. actinomycetemcomitans or a Cdt(-) mutant. Viable counts and qPCR showed that phagocytosis of the wild-type strain was significantly reduced relative to that of the Cdt(-) mutant. Addition of recombinant Aa(r)Cdt to co-cultures along with the Cdt(-) mutant diminished the phagocytic activity similar to that observed with the wild type strain. High concentrations of Aa(r)Cdt resulted in decreased phagocytosis of fluorescent bioparticles. Nitric oxide production was modulated by the presence of Cdt and the levels of IL-1β, IL-12 and IL-10 were increased. Production of TNF-α did not differ in the co-culture assays but was increased by the presence of Aa(r)Cdt. These data suggest that the Cdt may modulate macrophage function in A. actinomycetemcomitans infected sites by impairing phagocytosis and modifying the pro-inflammatory/anti-inflammatory cytokine balance.

Immunostimulating Factor Isolated fromActinobacillus actinomycetemcomitansStimulates Monocytes and Inflammatory Macrophages

Immunostimulating factor (ISTF) isolated from Actinobacillus actinomycetemcomitans which has been described previously, is distinct from lipopolysaccharide and induces proliferation of B cells. This study was undertaken to investigate whether ISTF might enhance the stimulation of other immune cells. Immunohistochemically, ISTF exhibited a profound stimulating effect on macrophages and dendritic cells as well as B cells in the spleen of BALB/c mice. ISTF was also recognized for its capacity to induce direct activation of mouse macrophages to produce IL-6, TNF-alpha, and NO and MHC class II expression. Therefore, it is postulated that ISTF stimulates macrophages and possibly other cells to produce a wide variety of proinflammatory mediators, which may be involved in the chronicity and tissue destruction of periodontal disease.

Periodontal pathogen Aggregatibacter actinomycetemcomitans LPS induces mitochondria-dependent-apoptosis in human placental trophoblasts

OBJECTIVE

Increasing evidence suggests an association between periodontal disease and low birthweight (LBW); however the underlying molecular mechanisms are yet to be fully elucidated. In this study, we performed a microarray analysis to observe the human placental trophoblast-like BeWo cells response to lipopolysaccharide (LPS) from periodontopathogen Aggregatibacter actinomycetemcomitans (Aa), in order to investigate the molecular basis of mechanisms for periodontitis-associated LBW. In vivo pregnant rats were also used to confirm the in vitro results.

STUDY DESIGN

The effects of Aa-LPS on cultured human placental trophoblast-like BeWo cells were studied using a DNA microarray, Ingenuity Pathway Analysis, real-time PCR and poly-caspase staining. The in vivo effects of Aa-LPS in pregnant rats were examined using TUNEL assays.

RESULTS

In BeWo cells, Aa-LPS increased levels of cytochrome c, caspase 2, caspase 3, caspase 9 and BCL2-antagonist/killer 1 mRNA, decreased those of B-cell CLL/lymphoma 2, BCL2-like 1 and catalase mRNA and increased poly-caspase activity, all of which are consistent with activation of the mitochondria-dependent apoptotic pathway. TUNEL assays confirmed the increased incidence of apoptosis in placentas of Aa-LPS-treated rats (p < 0.001).

CONCLUSION

Aa-LPS induces apoptosis in human trophoblasts via the mitochondria-dependent pathway, and this effect may contribute to the pathogenesis of periodontitis-associated LBW.

Role of the ATM-checkpoint kinase 2 pathway in CDT-mediated apoptosis of gingival epithelial cells

The cytolethal distending toxin (CDT) of the oral pathogen Aggregatibacter actinomycetemcomitans induces cell cycle arrest and apoptosis in various cell types. Western analysis, pharmacological inhibition and siRNA silencing were performed in human immortalized gingival keratinocytes (HIGK) to dissect the functional role of the ataxia telangiectasia mutated (ATM) pathway in the signal transduction steps triggered by the CDT. Infection of HIGK was associated with a time-dependent induction of cytoplasmic histone-associated DNA fragmentation. However, in the absence of CDT, infected HIGK underwent reversible DNA strand breaks but not apoptosis, while caspase 3 activity, p21 levels, and HIGK viability were unaffected. Caspase 9 activity was attenuated in the CDT mutant-infected HIGK compared to wild-type infected cells. Pharmacological inhibition and siRNA-silencing of the ATM downstream effector, the protein kinase checkpoint kinase 2 (Chk2), significantly impacted CDT-mediated apoptosis. Together, these findings provide insight on the specificity of the ATM-Chk2 pathway in response to the CDT of A. actinomycetemcomitans in oral epithelial cells, which ultimately leads to apoptosis. We further propose the existence of an unidentified factor that is distinct from the CDT, and involved with a reversible DNA fragmentation that does not trigger terminal apoptosis in oral epithelial cells. This model potentially explains conflicting reports on the biological activity of the A. actinomycetemcomitans CDT.

Expression and biochemical characterization of the periplasmic domain of bacterial outer membrane porin TdeA

TolC is an outer membrane porin protein and an essential component of drug efflux and type-I secretion systems in Gram-negative bacteria. TolC comprises a periplasmic alpha- helical barrel domain and a membrane-embedded beta-barrel domain. TdeA, a functional and structural homolog of TolC, is required for toxin and drug export in the pathogenic oral bacterium Actinobacillus actinomycetemcomitans. Here, we report the expression of the periplasmic domain of TdeA as a soluble protein by substitution of the membraneembedded domain with short linkers, which enabled us to purify the protein in the absence of detergent. We confirmed the structural integrity of the TdeA periplasmic domain by size-exclusion chromatography, circular dichroism spectroscopy, and electron microscopy, which together showed that the periplasmic domain of the TolC protein family can fold correctly on its own. We further demonstrated that the periplasmic domain of TdeA interacts with peptidoglycans of the bacterial cell wall, which supports the idea that completely folded TolC family proteins traverse the peptidoglycan layer to interact with inner membrane transporters.

Adiponectin inhibits osteoclast formation stimulated by lipopolysaccharide fromActinobacillus actinomycetemcomitans

Previous epidemiologic studies have suggested that periodontal disease is closely related to obesity and glucose tolerance. As the level of adiponectin, an adipocyte-derived cytokine, in plasma had been reported to decrease in obese and type 2 diabetes patients, we explored the role of adiponectin in the etiology of periodontitis using the D clone of RAW264, a clone that exhibits highly efficient osteoclast formation, to determine whether adiponectin acts as a regulatory molecule in osteoclast formation stimulated by lipopolysaccharide of periodontopathic bacteria. We observed that adiponectin acted as a potent inhibitor of osteoclast formation stimulated by Toll-like receptor 4 (TLR4) ligand and receptor activator of NF-kappaB ligand (RANKL). Because NF-kappaB is an important transcription factor in osteoclast formation, we examined the effect of adiponectin on its transcriptional activity. A luciferase assay showed that adiponectin was able to inhibit the TLR4-mediated NF-kappaB activity in RAW264 cells. In addition, we observed that the cytokine was actually able to inhibit TLR4-mediated expression of the gene for inducible nitric oxide synthase and production of nitric oxide in the cells. These observations strongly suggest that adiponectin may function as a negative regulator of lipopolysaccharide/RANKL-mediated osteoclast formation in periodontal disease.

The role of cyclic-AMP on arginase activity by a murine macrophage cell line (RAW264.7) stimulated with lipopolysaccharide from Actinobacillus actinomycetemcomitans

AIMS

The aim of the present study was to determine the role of cyclic adenosine monophosphate (cAMP) on arginase activity in a murine macrophage cell line (RAW264.7 cells) stimulated with lipopolysaccharide (LPS) from Actinobacillus actinomycetemcomitans.

MATERIALS AND METHODS

The cells were treated with A. actinomycetemcomitans LPS for 24 h. The effects of SQ22536 (an adenylyl cyclase inhibitor), ODQ (a guanylyl cyclase inhibitor), dibutyryl cAMP (a cAMP analog), 8-bromo cyclic guanosine monophosphate (a cGMP analog), forskolin (an adenylyl cylase activator), and cycloheximide (a protein synthesis inhibitor) on arginase activity in A. actinomycetemcomitans LPS-stimulated RAW264.7 cells were also determined. Arginase activity was assessed in LPS-stimulated cells in the presence of 3-isobutyl-1-methylxanthine (IBMX), siguazodan and rolipram [phosphodiesterase (PDE) inhibitors] as well as KT5720 [a protein kinase A (PKA) inhibitor].

RESULTS

Arginase activity in A. actinomycetemcomitans LPS-stimulated RAW264.7 cells was suppressed by SQ22536 but not ODQ. Enhancement of arginase activity was observed in the presence of cAMP analog or forskolin but not cGMP analog. Cycloheximide blocked arginase activity in the cells in the presence of cAMP analog or forskolin with or without A. actinomycetemcomitans LPS. IBMX augmented arginase activity in A. actinomycetemcomitans LPS-stimulated cells. Rolipram (a PDE4 inhibitor) increased the levels of arginase activity higher than siguazodan (a PDE3 inhibitor) in the antigen-stimulated cells. The effect of cAMP analog or forskolin on arginase activity in the presence or absence of A. actinomycetemcomitans LPS was blocked by the PKA inhibitor (KT5720).

CONCLUSION

The results of the present study suggest that A. actinomycetemcomitans LPS may stimulate arginase activity in murine macrophages (RAW264.7 cells) in a cAMP-PKA-dependent pathway.

[Production of interleukin-11 and interleukin-6 in cultured human gingival fibroblasts with the stimulation of lipopolysaccharides]

OBJECTIVE

To observe the effects of Porphyromonas gingivalis (Pg), Actinobacillus actinomycetemcomitans (Aa), Escherichia coli (Ec) lipopolysaccharides (LPS) on the production of IL-11 and IL-6 from healthy human gingival fibroblasts (HGF), and the effects of endogenous prostaglandin on HGF IL-11 and IL-6 production stimulated with the above LPS.

METHODS

HGF were stimulated with Pg-, Aa-, Ec-LPS of different concentrations (0.1, 1, 10 mg/L) for 24 h. And HGF were also stimulated with the combinations of 10 mg/L Pg-, Aa-, Ec-LPS and 10(-6) mol/L indomethacin respectively for 24 h. Levels of IL-11 and IL-6 in the supernatants were quantitated by ELISA.

RESULTS

LPS from Aa, Ec, at the concentration of 10 mg/L and from Pg at the concentrations 1, 10 mg/L significantly augmented IL-11 production by HGF. IL-6 production was also significantly increased by stimulation with Aa-LPS at concentrations 1, 10 mg/L and with Ec-, Pg-LPS at concentrations 0.1, 1, 10 mg/L. In addition, IL-11 production was lower than IL-6 production by HGF stimulated with LPS. Indomethacin significantly inhibited IL-6 and IL-11 production in LPS-stimulated HGF.

CONCLUSIONS

Aa-, Pg-, Ec-LPS may significantly increase IL-11 and IL-6 level in the supernatants of HGF, and endogenous prostaglandin may upregulate IL-11 and IL-6 production in LPS-stimulated HGF.

Novel surface structures are associated with the adhesion of Actinobacillus actinomycetemcomitans to collagen

Actinobacillus actinomycetemcomitans is a gram-negative, facultative, anaerobic bacterium that colonizes the human oral cavity and the upper respiratory tract. This bacterium is strongly associated with localized aggressive periodontitis and adult periodontitis and is the causative agent for other serious systemic infections. Recently, we have identified a protein, EmaA (extracellular matrix protein adhesin A), that mediates the adhesion of A. actinomycetemcomitans to collagen. The conserved sequence and predicted secondary structure suggest that EmaA is an orthologue of the Yersinia enterocolitica adhesin YadA. Electron microscopy examinations of A. actinomycetemcomitans have identified antenna-like protrusions associated with the surface of the bacterium. These structures are absent on emaA mutant strains and can be restored by transformation of the mutant strain with emaA in trans. The loss of these structures is associated with a decrease in the binding of this bacterium to collagen. The antenna-like structures are composed of a long rod that terminates in an ellipsoidal head region. The analysis of these structures using image processing techniques has provided an initial estimate of the overall dimensions, which suggests that the appendages are oligomeric structures formed by either three or four subunits. Together, the data suggest that emaA is required for the expression of novel appendages on the surface of A. actinomycetemcomitans that mediate the adhesion of the bacterium to collagen.

The effects of Porphyromonas gingivalis LPS and Actinobacillus actinomycetemcomitans LPS on human dendritic cells in vitro, and in a mouse model in vivo

Interaction between different bacterial plaque pathogens and dendritic cells may induce different types of T helper (Th) cell response, which is critical in the pathogenesis of periodontitis. In this study we investigated the effects of lipopolysaccharide (LPS) from Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans on human monocyte-derived dendritic cells (Mo-DCs) with respect to co-stimulatory molecule expression, cytokine production and Th cell differentiation. Unlike Escherichia coli and A. actinomycetemcomitans LPS, P. gingivalis LPS induced only low levels of CD40, CD80, HLA-DR and CD83 expression on Mo-DCs. LPS from both bacteria induced considerably lower TNF-alpha and IL-10 than did E. coli LPS. LPS from all three bacteria induced only negligible IL-12 production. In a human mixed-leukocyte reaction, and in an ovalbumin-specific T cell response assay in mice, both types of LPS suppressed IFN-gamma production. In conclusion, stimulation by P. gingivalis LPS and A. actinomycetemcomitans LPS appears to bias Mo-DCs towards Th2 production.

Protective Effects of Grape Seed Proanthocyanidins Against Oxidative Stress Induced by Lipopolysaccharides of Periodontopathogens

BACKGROUND

During phagocytosis or stimulation with bacterial components, macrophages activate various cell processes, including the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are critical for successful defense against invading organisms. Increased levels of ROS/RNS create oxidative stress that results in tissue and bone destruction. Grape seed proanthocyanidins have been reported to possess a wide range of biologic properties against oxidative stress. In the present study, we investigated the effects of a grape seed proanthocyanidin extract (GSE) and commercial polyphenols on the production of ROS and RNS and on the protein expression of inducible nitric oxide synthase (iNOS) by murine macrophages stimulated with lipopolysaccharides (LPS) of periodontopathogens.

METHODS

Macrophages (RAW 264.7) were treated with non-toxic concentrations of either GSE or commercial polyphenols (gallic acid [GA] and [-]-epigallocatechin-3-gallate [EGCG]) and stimulated with LPS of Actinobacillus actinomycetemcomitans or Fusobacterium nucleatum, and iNOS expression was evaluated by immunoblotting. Nitric oxide (NO) production was quantified using the colorimetric Griess assay, whereas ROS production was measured with the fluorescent 123-dihydrorhodamine dye.

RESULTS

GSE strongly decreased NO and ROS production and iNOS expression by LPS-stimulated macrophages. GA also revealed a strong inhibitory effect on NO production without affecting iNOS expression but slightly increasing ROS production. EGCG showed an inhibitory effect on NO and ROS production and on iNOS expression by macrophages.

CONCLUSION

Our findings demonstrate that proanthocyanidins have potent antioxidant properties and should be considered a potential agent in the prevention of periodontal diseases.

Variation of loop sequence alters stability of cytolethal distending toxin (CDT): crystal structure of CDT from Actinobacillus actinomycetemcomitans

Cytolethal distending toxin (CDT) secreted by Actinobacillus actinomycetemcomitans induces cell cycle arrest of cultured cells in the G2 phase. The crystal structure of the natural form of A. actinomycetemcomitans DCT (aCDT) has been determined at 2.4 A resolution. aCDT is a heterotrimer consisting of the three subunits, aCdtA, aCdtB, and aCdtC. Two crystallographically independent aCDTs form a dimer through interactions of the aCdtB subunits. The primary structure of aCDT has 94.3% identity with that of Haemophilus ducreyi CDT (hCDT), and the structure of aCDT is quite similar to that of hCDT reconstituted from the three subunits determined recently. However, the molecular packings in the crystal structures of aCDT and hCDT are quite different. A careful analysis of molecular packing suggests that variation of the amino acid residues in a nonconserved loop (181TSSPSSPERRGY192 of aCdtB and 181NSSSSPPERRVY192 of hCdtB) is responsible for the different oligomerization of very similar CDTs. The loop of aCdtB has a conformation to form a dimer, while the loop conformation of hCdtB prevents hCDT from forming a dimer. Although dimerization of aCDT does not affect toxic activity, it changes the stability of protein. aCDT rapidly aggregates and loses toxic activity in the absence of sucrose in a buffered solution, while hCDT is stable and retains toxic activity. Another analysis of crystal structures of aCDT and hCDT suggests that the receptor contact area is in the deep groove between CdtA and CdtC, and the characteristic "aromatic patch" on CdtA.

Pro-atherogenic properties of lipopolysaccharide from the periodontal pathogen Actinobacillus actinomycetemcomitans

An association between cardiovascular and periodontal disease may be due to lipopolysaccharide (LPS)-promoted release of inflammatory mediators, adverse alterations of the lipoprotein profile, and an imbalance in cholesterol homeostasis. Since periodontopathogenic potential differs between serotypes of a major periodontal pathogen, Actinobacillus actinomycetemcomitans, we studied the pro-atherogenic properties of LPS preparations from serotypes b and d strains on macrophages (RAW 264.7). A. actinomycetemcomitans LPS preparations induced a time-dependent release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta). LPS induced foam cell formation and cholesteryl ester accumulation from native low density lipoprotein in the following order: A. actinomycetemcomitans strains JP2 (serotype b) > Y4 (serotype b) > IDH781 (serotype d). mRNA expression levels of scavenger receptor class B, type-I, and ATP-binding cassette transporter-1, receptors mediating cholesterol efflux from macrophages, were decreased by LPS preparations. The results suggest that the pro-atherogenic potential of A. actinomycetemcomitans LPS may depend on the infecting strain and correlate with the periodontopathogenic potential of the pathogen.

Characterization of immunoaffinity purified peptidoglycan-associated lipoprotein of Actinobacillus actinomycetemcomitans

Peptidoglycan-associated lipoprotein (PAL) is a highly conserved structural outer membrane protein among Gram-negative bacteria. In some species, it is proinflammatory and released extracellularly. We purified a newly identified PAL (AaPAL) of a periodontal pathogen Actinobacillus actinomycetemcomitans by using AaPAL antipeptide antibodies coupled to immunoaffinity chromatography column. No protein impurities originating in A. actinomycetemcomitans were found in the final product. Sera from patients infected by A. actinomycetemcomitans recognized the purified AaPAL. The present purification method seems to be suitable for isolation of AaPAL and probably PALs of other bacterial species, and applicable in studies investigating proinflammatory mechanisms of A. actinomycetemcomitans.

Characterization of leukotoxin from a clinical strain of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a Gram negative pathogen that is the etiologic agent of localized aggressive periodontitis (LAP), a rapidly progressing and severe disease of the oral cavity that affects predominantly adolescents. A. actinomycetemcomitans is also found in extraoral infections including infective endocarditis. As one of its many virulence determinants, A. actinomycetemcomitans produces the RTX (repeats in toxin) exotoxin, leukotoxin (LtxA). LtxA specifically kills leukocytes of humans and Old World Monkeys. All of our current knowledge of A. actinomycetemcomitans LtxA is based on the protein from strain JP2, a nonadherent laboratory isolate. Because laboratory isolates can lose virulence properties, we wished to examine LtxA from a clinical isolate, NJ4500. We show that localization patterns of LtxA do not differ between the strains. Subcellular localization studies with NJ4500 revealed that LtxA localizes to the outer membrane and that the interaction between LtxA and the surface of cells is specific. Surface localized LtxA was not removed with NaCl treatment and protease protection experiments revealed that approximately 10 kDa of LtxA is exposed. We purified secreted LtxA from NJ4500 and found that the specific activity of this toxin was greater than that of secreted LtxA from JP2. For other RTX toxins, fatty acid modification affects toxin activity, and A. actinomycetemcomitans LtxA is predicted to be modified. We show by two-dimensional gel electrophoresis that NJ4500 LtxA is more highly modified than JP2 LtxA, suggesting that the difference in activities could be due to differential modification. Studies of A. actinomycetemcomitans pathogenesis should therefore consider LtxA from clinical isolates.

A searchable database for proteomes of oral microorganisms

An online database of proteomes for two-dimensional electrophoresis (2DE) gel data was constructed and it is now freely accessible through a web-based interface. Proteins from three oral bacteria, Streptococcus mutans UA159, Actinobacillus actinomycetemcomitans HK1651, and Porphyromonas gingivalis W83, whose genome databases are freely available, were separated by 2DE, and protein spots were analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and identified. About 1000 spots from the gels of P. gingivalis W83 were extracted and analyzed by MALDI-TOF, and 330 proteins were identified. In addition, 160 of 240 spots of A. actinomycetemcomitans and 158 of 356 spots of S. mutans were identified. Information such as spot coordinates on the gels, protein names (predicted functions), molecular weights, isoelectroric points, and links to online databases, including Oral Pathogen Sequence Databases of the Los Alamos National Laboratory Bioscience Division (ORALGEN) and National Center for Biotechnology Information (NCBI) or The Institute Genomic Research (TIGR), were stored in tables accessible through the relational database management system MySQL on an Apache web server. To test for functionality of this database system, responses of S. mutans to environmental changes were analyzed using the database and 21 spots on the gel were identified as proteins whose expression had been increased or decreased by environmental pH change without in-gel trypsin digestion, protein extraction, or MALDI-TOF/TOF-MS (mass spectrometer) analysis. The identified proteins are agreement with those reported in previous papers on acid tolerance of S. mutans, demonstrating the usefulness of the system. This database is available at http://www.myamagu.dent.kyushu-u.ac.jp/~bioinformatics/index.html or http://www.bipos.mascat.nihon-u.ac.jp/index.html.

Differential effect of the cytolethal distending toxin of Actinobacillus actinomycetemcomitans on co-cultures of human oral cells

The periodontal pathogen Actinobacillus actinomycetemcomitans expresses a cytolethal distending toxin (CDT) that typically arrests the growth of eukaryotic cells at either the G0/G1 or G2/M phase of the cell cycle. It was previously found that CDT failed to arrest the growth of human periodontal ligament fibroblasts (HPLFs) when grown in pure culture. In contrast, proliferation of an oral epithelial cell line was rapidly inhibited by the toxin. In this study, the feasibility of using mixed-cell cultures and cell-specific markers to evaluate the response of oral cells, when in heterogeneous populations, to CDT was established. Proliferation of epithelial cells was rapidly inhibited and the cells were selectively eliminated in co-culture with HPLFs or cementoblasts by 24-48 h post-intoxication. Epithelial cells and HPLFs were detected and counted in co-cultures following cell-specific immunolabelling with antibodies against simian virus 40 large T antigen and the Ab-1 surface antigen, respectively. These results demonstrated that the activities of potential virulence factors, such as CDT, from periodontal pathogens can be successfully examined in mixed-cell cultures. This approach is especially relevant to infectious diseases that affect tissues with a diverse cellular composition, such as the periodontium.

Prevalence of periodontal pathogens in Brazilians with aggressive or chronic periodontitis

OBJECTIVES

Previous studies suggest differences between geographically and racially distinct populations in the prevalence of periodontopathic bacteria as well as greater periodontal destruction associated with infection by highly leucotoxic Actinobacillus actinomycetemcomitans. The present study examined these hypotheses in Brazilians with aggressive or chronic periodontitis.

MATERIALS AND METHODS

Clinical, radiographical, and microbiological assessments were performed on 25 aggressive periodontitis and 178 chronic periodontitis patients including 71 males and 132 females, 15-69 years of age.

RESULTS

The prevalence of Porphyromonas gingivalis was similar to that of other South American populations. The prevalence of A. actinomycetemcomitans and its highly leucotoxic subgroup was higher in Brazilians. Highly leucotoxic A. actinomycetemcomitans was more prevalent in aggressive periodontitis (chi2=27.83) and positively associated with deep pockets (>6 mm, chi2=18.26) and young age (<29 years, chi2=18.68). Greater mean attachment loss was found in subjects with highly leucotoxic A. actinomycetemcomitans than in subjects with minimally leucotoxic (p=0.0029) or subjects not infected (p=0.0001).

CONCLUSION

These data support the hypothesis of differences between populations in the prevalence of periodontopathic bacteria and of greater attachment loss in sites infected with highly leucotoxic A. actinomycetemcomitans. Detection of highly leucotoxic A. actinomycetemcomitans in children and adolescents may be a useful marker for aggressive periodontitis.

Binding of Actinobacillus actinomycetemcomitans lipopolysaccharides to Peptostreptococcus micros stimulates tumor necrosis factor alpha production by macrophage-like cells

Peptostreptococcus micros is a gram-positive bacterium that has been associated with periodontitis and endodontic infections. In this study, we hypothesized that P. micros binds the immunomodulating component lipopolysaccharide derived from gram-negative bacteria to increase its capacity to stimulate cytokine production by host cells. The ability of P. micros to bind Actinobacillus actinomycetemcomitans lipopolysaccharide was demonstrated by an enzyme-linked immunosorbent assay and by immunoelectron microscopy. Pretreatment of P. micros cells with A. actinomycetemcomitans lipopolysaccharide was associated with a 49-fold increase in tumor necrosis factor alpha production by human monocytic cells U937 differentiated into adherent macrophages, compared to the stimulation with untreated P. micros. This effect was suppressed by incorporating polymyxin B, a lipid A-binding substance, during treatment of macrophage-like cells with lipopolysaccharide-coated P. micros cells. This is the first study reporting a binding interaction between lipopolysaccharide and a gram-positive bacterium. This interaction represents a new mechanism that could promote the inflammatory response during periodontitis.

Induction of Cell Cycle Arrest in Lymphocytes byActinobacillus actinomycetemcomitansCytolethal Distending Toxin Requires Three Subunits for Maximum Activity

We have previously shown that Actinobacillus actinomycetemcomitans produces an immunosuppressive factor encoded by the cytolethal distending toxin (cdt)B gene. In this study, we used rCdt peptides to study the contribution of each subunit to toxin activity. As previously reported, CdtB is the only Cdt subunit that is capable of inducing cell cycle arrest by itself. Although CdtA and CdtC do not exhibit activity alone, each subunit is able to significantly enhance the ability of CdtB to induce G2 arrest in Jurkat cells; these effects were dependent upon protein concentration. Moreover, the combined addition of both CdtA and CdtC increased the ED50 for CdtB >7000-fold. In another series of experiments, we demonstrate that the three Cdt peptides are able to form a functional toxin unit on the cell surface. However, these interactions first require that a complex forms between the CdtA and CdtC subunits, indicating that these peptides are required for interaction between the cell and the holotoxin. This conclusion is further supported by experiments in which both Jurkat cells and normal human lymphocytes were protected from Cdt holotoxin-induced G2 arrest by pre-exposure to CdtA and CdtC. Finally, we have used optical biosensor technology to show that CdtA and CdtC have a strong affinity for one another (10(-7) M). Furthermore, although CdtB is unable to bind to either CdtA or CdtC alone, it is capable of forming a stable complex with CdtA/CdtC. The implications of our results with respect to the function and structure of the Cdt holotoxin are discussed.

Detection ofActinobacillus actinomycetemcomitansin Unstimulated Saliva of Patients With Chronic Periodontitis

BACKGROUND

The use of whole saliva has shown to be promising in detecting Actinobacillus actinomycetemcomitans out of the subgingival environment. The objective of the present study was to evaluate the use of unstimulated saliva in detecting A. actinomycetemcomitans and to compare the subgingival and extracrevicular occurrence of this pathogen in Brazilian subjects with chronic periodontitis.

METHODS

Sixty-six patients (mean age 38.01 9.28 years) with advanced generalized chronic periodontitis were sampled. Subgingival plaque samples were collected from eight sites per patient representing the two deepest sites of each quadrant. Samples of the mucous surfaces, including dorsal surface of the tongue and cheek, were collected with a sterile swab and placed in a microtube containing a reduced solution. Samples of unstimulated saliva were also collected in sterile tubes and 0.1 ml of whole saliva was diluted in 1 ml of reduced solution. The presence of A. actionomycetemcomitans was established using bacterial culture in trypticase soy bacitracin vancomycin selective media. Polymerase chain reaction (PCR) was used to differentiate highly from minimally leukotoxic strains in patients who presented A. actinomycetemcomitans in at least two sampled sites.

RESULTS

A. actinomycetemcomitans was isolated from 63.63% of subgingival samples, 56.06% of saliva samples, and 45.45% of samples from mucous surfaces. No statistical difference was observed between subgingival and salivary occurrence of the microorganism. Linear regression showed an association between subgingival plaque and saliva (r(2) = 0.897; P = 0.015) and mucous membrane and saliva (r(2) = 0.152; P = 0.024). The same A. actinomycetemcomitans leukotoxic profile was observed in all sampled sites for a given patient.

CONCLUSION

These results suggest that in advanced periodontitis, unstimulated saliva is representative of pooled subgingival plaque samples and its use is appropriate in the oral detection of A. actinomycetemcomitans.

Actinobacillus actinomycetemcomitansLipopolysaccharide Activates Matrix Metalloproteinase-2 and Increases Receptor Activator of Nuclear Factor-κB Ligand Expression in Human Periodontal Ligament Cells

BACKGROUND

The lipopolysaccharide (LPS) of A. actinomycetemcomitans is one of the major pathogenic factors in periodontal disease. It induces secretion of proinflammatory cytokines and is involved in alveolar bone destruction. We hypothesized that the LPS of A. actinomycetemcomitans could affect the activation of matrix metalloproteinase (MMP)-2 and the expression of receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin in human periodontal ligament (HPDL) cells leading to the destruction of periodontium.

METHODS

HPDL cells were cultured in serum-free medium with or without the LPS of A. actinomycetemcomitans for 36 hours. The activation of MMP-2 was analyzed by zymography. Changes of the expression of RANKL and osteoprotegerin (OPG) were examined by reverse transcription-polymerase chain reaction and supported by Western blot analysis.

RESULTS

The activation of MMP-2 could be induced by the LPS of A. actinomycetemcomitans in HPDL cells and could be inhibited by a serine protease inhibitor. This result suggested that the LPS might activate MMP-2 through a serine protease-dependent pathway. This activation was also blocked by NF-kappaB inhibitor, which indicated the involvement of NF-kappaB. The upregulation of RANKL but not OPG by the LPS was found in both transcription and translation and could be reduced by indomethacin. In addition, serine protease inhibitor also inhibited the upregulation of RANKL, suggesting the activity of serine protease.

CONCLUSIONS

The effect of the LPS of A. actinomycetemcomitans on HPDL cells is serum-independent and the induction of the activation of MMP-2 and the expression of RANKL are serine protease-dependent pathways. The results suggest the role of HPDL cells in the pathogenesis of periodontitis.

Cell cycle arrest of human gingival fibroblasts and periodontal ligament cells byActinobacillus actinomycetemcomitans: involvement of the cytolethal distending toxin

The cytolethal distending toxin (Cdt) is produced by several Gram-negative bacterial species and causes growth arrest and morphological alterations in mammalian cells. Actinobacillus actinomycetemcomitans, which is involved in the pathogenesis of localized aggressive periodontitis, also produces a Cdt that affects periodontal connective tissue cells. The aim of this study was to investigate in which phase of the cell cycle these cells are arrested and enlarged when challenged with A. actinomycetemcomitans, and to evaluate the involvement of its Cdt. Human gingival fibroblasts and periodontal ligament cells were challenged with A. actinomycetemcomitans extract, or with purified Cdt, and cell cycle analysis was performed by propidium iodide staining and flow cytometry. Cells exposed to an A. actinomycetemcomitans wild-type strain, or to purified Cdt, were arrested in both G1 and G2/M phases, and appeared enlarged compared to the corresponding controls. The cellular enlargement occurred in both G1 and G2/M arrested cells. In contrast, cells exposed to an A. actinomycetemcomitans cdt-knockout mutant strain showed cell cycle phase distribution and size similar to the controls. In conclusion, A. actinomycetemcomitans causes a combined G1 and G2/M growth arrest and enlargement in periodontal connective tissue cells, which is attributed to its Cdt.

Enzymatic detachment of Staphylococcus epidermidis biofilms

The gram-positive bacterium Staphylococcus epidermidis is the most common cause of infections associated with catheters and other indwelling medical devices. S. epidermidis produces an extracellular slime that enables it to form adherent biofilms on plastic surfaces. We found that a biofilm-releasing enzyme produced by the gram-negative periodontal pathogen Actinobacillus actinomycetemcomitans rapidly and efficiently removed S. epidermidis biofilms from plastic surfaces. The enzyme worked by releasing extracellular slime from S. epidermidis cells. Precoating surfaces with the enzyme prevented S. epidermidis biofilm formation. Our findings demonstrate that biofilm-releasing enzymes can exhibit broad-spectrum activity and that these enzymes may be useful as antibiofilm agents.

Selective blockade of voltage-gated potassium channels reduces inflammatory bone resorption in experimental periodontal disease

The effects of the potassium channel (Kv1.3) blocker kaliotoxin on T-cell-mediated periodontal bone resorption were examined in rats. Systemic administration of kaliotoxin abrogated the bone resorption in conjunction with decreased RANKL mRNA expression by T-cells in gingival tissue. This study suggests a plausible therapeutic approach for inflammatory bone resorption by targeting Kv1.3.

INTRODUCTION

Kv1.3 is a critical potassium channel to counterbalance calcium influx at T-cell receptor activation. It is not known if Kv1.3 also regulates RANKL expression by antigen-activated T-cells, and consequently affects in vivo bone resorption mediated by activated T-cells.

MATERIALS AND METHODS

Actinobacillus actinomycetemcomitans 29-kDa outer membrane protein-specific Th1-clone cells were used to evaluate the expression of Kv1.3 (using reverse transcriptase-polymerase chain reaction [RT-PCR] and Western blot analyses) and the effects of the potassium channel blocker kaliotoxin (0-100 nM) on T-cell activation parameters ([3H]thymidine incorporation assays and ELISA) and expression of RANKL and osteoprotegerin (OPG; flow cytometry, Western blot, and RT-PCR analyses). A rat periodontal disease model based on the adoptive transfer of activated 29-kDa outer membrane protein-specific Th1 clone cells was used to analyze the effects of kaliotoxin in T-cell-mediated alveolar bone resorption and RANKL and OPG mRNA expression by gingival T-cells. Stimulated 29-kDa outer membrane protein-specific Th1 clone cells were transferred intravenously on day 0 to all animals used in the study (n = 7 animals per group). Ten micrograms of kaliotoxin were injected subcutaneously twice per day on days 0, 1, 2, and 3, after adoptive transfer of the T-cells. The control group of rats was injected with saline as placebo on the same days as injections for the kaliotoxin-treated group. The MOCP-5 osteoclast precursor cell line was used in co-culture studies with fixed 29-kDa outer membrane protein-specific Th1-clone cells to measure T-cell-derived RANKL-mediated effects on osteoclastogenesis and resorption pit formation assays in vitro. Statistical significance was evaluated by Student's t-test.

RESULTS

Kaliotoxin decreased T-cell activation parameters of 29-kDa outer membrane protein-specific Th1 clone cells in vitro and in vivo. Most importantly, kaliotoxin administration resulted in an 84% decrease of the bone resorption induced in the saline-treated control group. T-cells recovered from the gingival tissue of kaliotoxin-treated rats displayed lower ratios of RANKL and OPG mRNA expression than those recovered from the control group. The ratio of RANKL and osteoprotegerin protein expression and induction of RANKL-dependent osteoclastogenesis by the activated T-cells were also markedly decreased after kaliotoxin treatments in vitro.

CONCLUSION

The use of kaliotoxin or other means to block Kv1.3 may constitute a potential intervention therapy to prevent alveolar bone loss in periodontal disease.

Actinobacillus actinomycetemcomitansCytolethal Distending Toxin (Cdt): Evidence That the Holotoxin Is Composed of Three Subunits: CdtA, CdtB, and CdtC

We have shown the Actinobacillus actinomycetemcomitans produces an immunosuppressive factor encoded by the cytolethal distending toxin (cdt)B gene, which is homologous to a family of Cdts expressed by several Gram-negative bacteria. We now report that the capacity for CdtB to induce G(2) arrest in Jurkat cells is greater in the presence of the other Cdt peptides: CdtA and CdtC. Plasmids containing the cdt operon were constructed and expressed in Escherichia coli; each plasmid contained a modified cdt gene that expressed a Cdt peptide containing a C-terminal His tag. All three Cdt peptides copurified with the His-tagged Cdt peptide. Each of the peptides associated with the complex was truncated; N-terminal amino acid analysis of CdtB and CdtC indicated that the truncation corresponds to cleavage of a previously described signal sequence. CdtA was present in two forms in crude extracts, 25 and 18 kDa; only the 18-kDa fragment copurified with the Cdt complexes. Cdt complexes were also immunoprecipitated from A. actinomycetemcomitans extracts using anti-CdtC mAb. Exposure of Jurkat cells to 40 pg resulted in >50% accumulation of G(2) cells. CdtB and CdtC were detected by immunofluorescence on the cell surface after 2-h exposure to the holotoxin. CdtA was not detected by immunofluorescence, but all three peptides were associated with Jurkat cells when analyzed by Western blot. These studies suggest that the active Cdt holotoxin is a heterotrimer composed of truncated CdtA, CdtB, and CdtC, and all three peptides appear to associate with lymphocytes.

Prostaglandin E2 downregulates interleukin-12 production through EP4 receptors in human monocytes stimulated with lipopolysaccharide from Actinobacillus actinomycetemcomitans and interferon-gamma

In the present study, we examined the effect of prostaglandin (PG) E2 on interleukin (IL) -12 production in monocytes stimulated with a combination of lipopolysaccharide (LPS) from Actinobacillus actinomycetemcomitans and interferon-gamma (A. actinomycetemcomitans-LPS/IFN-gamma). Indomethacin, a cyclooxygenase inhibitor, enhanced IL-12 production, but inhibited PGE2 generation in A. actinomycetemcomitans-LPS/IFN-gamma-stimulated monocytes. Exogenous PGE2 inhibited IL-12 release in the cells. EP2, EP3 and EP4 receptor mRNA expression was detected in monocytes by reverse transcription-polymerase chain reaction. 11-deoxy-PGE1 (an EP2/EP4 agonist) inhibited IL-12 production in A. actinomycetemcomitans-LPS/IFN-gamma-challenged monocytes, whereas butaprost (an EP2 agonist) or ONO-AP-324 (an EP3 agonist) had no effect on IL-12 production. Dibutyryl cAMP, a cAMP analogue, and forskolin, an adenylate cyclase activator, mimicked depression of IL-12 production by PGE2. From these results, we suggest that PGE2 inhibits IL-12 production via EP4 receptors by cAMP-dependent pathways in A. actinomycetemcomitans-LPS/IFN-gamma-challenged monocytes.

Lack of lipoprotein-dependent effects on the cytotoxic interactions of Actinobacillus actinomycetemcomitans leukotoxin with human neutrophils

A high odds ratio has been reported for hyperlipidemia and periodontal diseases in humans, and the severity of periodontitis seems to correlate with the hyperlipidemic status of the patients. Early studies indicated that the lipoprotein-containing fraction of the serum enhances the leukotoxic activity of the periodontopathogen Actinobacillus actinomycetemcomitans against human polymorphonuclear leukocytes (PMNL). The protease inhibitors of normal serum account for this enhancement, while delipidated serum has no effect on the leukotoxin-dependent PMNL cytolysis. No information exists for the effect of serum lipoproteins or hyperlipidemic serum. The aim of this study was to evaluate the role of serum lipoproteins in the interaction of the leukotoxin of A. actinomycetemcomitans with human PMNL. Purified leukotoxin was mixed with human PMNL prepared from venous blood of healthy subjects and various varying amounts of hyperlipidemic or delipidated serum, or purified serum lipoproteins. The cytolytic activity of leukotoxin was determined by activity of the cytosol enzyme lactate dehydrogenase released from injured PMNL. The degranulating activity of the toxin was measured through the release of the granule components elastase and lactoferrin. Normal human serum without leukotoxin-neutralizing antibodies caused a 4-fold enhancement of the leukotoxic activity when present at concentrations of 5-10% in the reaction mixture. Serum lipoproteins had no effect when added at concentrations that occur normally in serum. At high concentrations, purified low density and very low-density lipoproteins increased the leukotoxicity of the mixture. Nevertheless, hyperlipidemic serum prepared from a normal serum by the addition of autologous lipoproteins had no influence on the leukotoxin-caused cytolysis compared to the normal serum. Pre-incubation of PMNL for 1 h in hyperlipidemic or delipidated serum had no effect on the leukotoxin-induced degranulation of PMNL. The results indicate that the cytotoxic interactions of A. actinomycetemcomitans leukotoxin against human PMNL are not influenced by the presence of serum lipoproteins.

In vitro effect of laser irradiation on cementum-bound endotoxin isolated from periodontally diseased roots

BACKGROUND

In a previous study, we evaluated the in vivo effects of an Nd:YAG laser on periodontal disease by measuring crevicular interleukin (IL)-1beta levels before and after laser application. It was found that laser therapy was less effective than traditional scaling and root planing. These results might be due to incomplete removal of microbial residues and cementum-bound endotoxin on root surfaces by the laser. In this study, we explored the in vitro effectiveness of an Nd:YAG laser for the elimination of cementum-bound endotoxin by measuring IL-1beta changes in stimulated monocytes.

METHODS

Fresh human monocytes were harvested from adults without periodontitis and grown in RPMI 1640 medium. Diseased cementum particles were collected and prepared from teeth with untreated periodontitis and were irradiated with 5 levels of laser energy. Cementum particles were subjected to endotoxin testing by a limulus amebocyte lysate (LAL) assay and then were incubated with cultured monocytes. Production of IL-1beta in stimulated monocytes was measured by enzyme-linked immunosorbent assay and quantified by spectrophotometry.

RESULTS

The endotoxin unit (EU) of diseased cementum was 18.4 EU/mg, which seemed to be remarkably lower than that of common periodontal pathogens including Porphyromonas gingivalis (381) at 15,300 EU/mg/ml, Prevotella intermedia (ATCC 25611) at 227 EU/mg/ml, and Fusobacterium nucleatum (ATCC 25586) at 1,987 EU/mg/ml. Monocytes subjected to stimulation by diseased cementum particles without laser irradiation produced 124 to 145 pg/ml IL-1beta, 9- to 18-fold higher than that of unstimulated monocytes (7.07 to 15.95 pg/ml). Diseased cementum particles after irradiation with various energy levels of the Nd:YAG laser could still stimulate monocytes to secrete 89 to 129 pg/ml IL-1beta. No statistically significant difference was found in the production of IL-1beta induced by diseased-bound cementum with or without laser irradiation.

CONCLUSIONS

The Nd:YAG laser varying from 50 mJ, 10 pps to 150 mJ, 20 pps, for 2 minutes, did not seem to be effective in destroying diseased cementum endotoxin.

Reconstitution and purification of cytolethal distending toxin of Actinobacillus actinomycetemcomitans

Cytolethal distending toxin (CDT) has been found in various pathogenic bacterial species and causes a cell distending and a G2 arrest against eukaryotic cells. All the cdtABC genes, which encode CDT, are known to be required for the CDT activities although the CDT holotoxin structure has not been elucidated. We cloned the cdtABC genes of Actinobacillus actinomycetemcomitans and constructed an Escherichia coli expression system for them. We found that crude extracts from six deletion mutants (delta cdtA, delta cdtB, delta cdtC, delta cdtBC, delta cdtAC, and delta cdtAB) of recombinant E. coli, which showed very weak or no detectable CDT activities, restored the CDT activities when pre-mixing and pre-incubation of them were performed in combinations to contain all the CdtA, CdtB, and CdtC proteins. These results indicate that all the Cdt proteins are required for the CDT activities. We also found that the chimera CdtB protein, CdtB-intein-CBD (chitin binding domain) like CdtB protein itself assembled with CdtA and CdtC. The reconstituted CDT containing the chimera CdtB protein was specifically extracted by chitin beads and the only CDT portion was isolated from the chitin beads by a cleavage reaction of the intein. The purified reconstituted-CDT was found to consist of CdtA, CdtB, and CdtC proteins, and showed appreciable CDT activities, indicating that the CDT holotoxin structure is the CdtABC complex. To our knowledge, this is the first report succeeded in complete purification of an active CDT and may offer useful tools for elucidation of the toxic mechanism of CDT.

Actinobacillus actinomycetemcomitans induces lethal effects on the macrophage-like human cell line U937

We examined the cytotoxicity in culture medium of Actinobacillus actinomycetemcomitans against the human monocyte-macrophage-like cell line U937 using the trypan blue exclusion test and WST-1 test. We found that A. actinomycetemcomitans Y4 showed the highest cytotoxic activity among the three different serotype strains and the cytotoxic effects of both bacterial cells and culture supernatants in A. actinomycetemcomitans Y4 were stronger on phorbol-12-myristate 13-acetate (PMA)-induced U937 cells than uninduced U937 cells. Morphological changes in PMA-induced U937 cells treated with culture supernatants differed from those treated with leukotoxin, and a difference in the susceptibility to 56 degrees C heat treatment was found between culture supernatants and leukotoxin. The cytotoxic activity by WST-1 was determined more rapidly and strongly than that by trypan blue assay. These findings suggested that the cytotoxic effect of A. actinomycetemcomitans was influenced by the differentiation of U937 cells and may be more potent on the respiratory chain than the cell membrane.

Characterization of serum antibody to Actinobacillus actinomycetemcomitans GroEL-like protein in periodontitis patients and healthy subjects

Recent evidence suggests that molecular mimicry between bacterial and human heat shock protein 60 (hsp60) is involved in various conditions of autoimmune and infectious diseases. Many periodontopathic bacteria have been reported to express GroEL-like protein that is homologous to human hsp60. In this study, the presence of antibodies to the hsp60 of Actinobacillus actinomycetemcomitans in the sera of periodontitis patients and periodontally healthy control subjects was evaluated by enzyme-linked immunosorbent assay using a recombinant A. actinomycetemcomitans GroEL as an antigen. Furthermore, their cross-reactivity with Escherichia coli GroEL and Mycobacterium bovis BCG hsp65 was examined. The mean values of antibody were 0.624 (range 0.088-1.113) and 0.728 (range 0.217-1.296) in control subjects and periodontitis patients, respectively. The antibody levels to A. actinomycetemcomitans after absorption with E. coli GroEL and M. bovis BCG clearly decreased in both control subjects and periodontitis patients. The remaining antibody levels to A. actinomycetemcomitans GroEL after absorption with M. bovis BCG hsp65 were higher than those with E. coli GroEL, indicating higher cross-reactivity with E. coli GroEL. These results suggest that not only periodontitis patients but also periodontally healthy subjects may be infected with A. actinomycetemcomitans but that the part of the antibody could be derived from the cross-reactivity with E. coli GroEL. Any relationship of the antibody to the disease, however, remains to be determined.

Enhancement of plasminogen activator activity stimulated by LPS in gingival fibroblasts of individuals with Down syndrome

Individuals with Down syndrome (DS) have a high prevalence of periodontal disease, which develops early and progressed rapidly and extensively, in comparison with healthy controls. The severe periodontal disease in individuals with DS has been considered to result from abnormal factors in their host responses. The mechanisms involved in the periodontal inflammatory processes in individuals with DS are not fully understood. Plasminogen activators (PA) are serine proteases that are well known for their part in the initiation of the fibrinolytic cascade leading to the generation of plasmin in periodontal homeostasis, including fibrinolysis and connective tissue remodeling. The PA-plasmin system affects the progression of periodontal disease. In the present study, we examined the effects of the levels of PA activity stimulated with lipopolysaccharide (LPS) in the gingival fibroblasts from donors with DS (DGF). The levels of PA activity without LPS were low in the DGFs, the same as that in the gingival fibroblasts from donors of healthy controls (NDGF). In contrast, the levels of PA activity with LPS in DGFs were significantly higher than that in the NDGFs. These results suggested that PA plays an important role in inducing extensive and rapid inflammation in the periodontal disease in individuals with DS.

Structural and genetic analyses of O polysaccharide from Actinobacillus actinomycetemcomitans serotype f

The oral bacterium Actinobacillus actinomycetemcomitans is implicated as a causative agent of localized juvenile periodontitis (LJP). A. actinomycetemcomitans is classified into five serotypes (a to e) corresponding to five structurally and antigenically distinct O polysaccharide (O-PS) components of their respective lipopolysaccharide molecules. Serotype b has been reported to be the dominant serotype isolated from LJP patients. We determined the lipopolysaccharide O-PS structure from A. actinomycetemcomitans CU1000, a strain isolated from a 13-year-old African-American female with LJP which had previously been classified as serotype b. The O-PS of strain CU1000 consisted of a trisaccharide repeating unit composed of L-rhamnose and 2-acetamido-2-deoxy-D-galactose (molar ratio, 2:1) with the structure -->2)-alpha-L-Rhap-(1-3)-2-O-(beta-D-GalpNAc)-alpha-L-Rhap-(1-->* O-PS from strain CU1000 was structurally and antigenically distinct from the O-PS molecules of the five known A. actinomycetemcomitans serotypes. Strain CU1000 was mutagenized with transposon IS903phikan, and three mutants that were deficient in O-PS synthesis were isolated. All three transposon insertions mapped to a single 1-kb region on the chromosome. The DNA sequence of a 13.1-kb region surrounding these transposon insertions contained a cluster of 14 open reading frames that was homologous to gene clusters responsible for the synthesis of A. actinomycetemcomitans serotype b, c, and e O-PS antigens. The CU1000 gene cluster contained two genes that were not present in serotype-specific O-PS antigen clusters of the other five known A. actinomycetemcomitans serotypes. These data indicate that strain CU1000 should be assigned to a new A. actinomycetemcomitans serotype, designated serotype f. A PCR assay using serotype-specific PCR primers showed that 3 out of 20 LJP patients surveyed (15%) harbored A. actinomycetemcomitans strains carrying the serotype f gene cluster. The finding of an A. actinomycetemcomitans serotype showing serological cross-reactivity with anti-serotype b-specific antiserum suggests that a reevaluation of strains previously classified as serotype b may be warranted.

Identification of the exported proteins of the oral opportunistic pathogen Actinobacillus actinomycetemcomitans by using alkaline phosphatase fusions

A phoA fusion library of Actinobacillus actinomycetemcomitans genomic DNA has been screened to identify genes encoding exported and secreted proteins. A total of 8,000 colonies were screened, and 80 positive colonies were detected. From these, 48 genes were identified with (i) more than half having homology to known or hypothetical Haemophilus influenzae genes, (ii) 14 having no ascribed function, and (iii) 4 having very limited or no homology to known genes. The proteins encoded by these genes may, by virtue of their presence on the cell surface, be novel virulence determinants.

Heterogeneous post-translational modification of Actinobacillus actinomycetemcomitans fimbrillin

Fresh isolates of Actinobacillus actinomycetemcomitans produce bundle-forming fimbriae. The exact molecular mass of A. actinomycetemcomitans fimbrillin, a structural subunit of fimbriae, was determined by liquid chromatography-electrospray ionization mass spectrometry. Three major molecular species with 6,226.0, 6,366.0, and 6,513.0 Da were detected in a purified fimbrial fraction from the strain 310-a. These molecular masses were significantly higher than the molecular weight (5,118 Da) calculated from nucleotide sequence data of the fimbrillin gene, flp, suggesting that the fimbrial peptides were post-translationally modified. Modification of the fimbrial peptides was also suggested by an N-terminal amino acid sequence analysis of fimbrillin peptic fragments, with the modified amino acids being due to seven serine or asparagine residues located in the C-terminal region. A periodate oxidation/biotin-hydrazide labeling assay of fimbrillin suggested that it might be glycosylated.

Cell surface-associated enolase in Actinobacillus actinomycetemcomitans

Cell surface-associated materials of Actinobacillus actinomycetemcomitans were extracted by a short incubation of the cell suspension in a Tris-buffered saline in the presence and absence of a restriction enzyme, EcoRI. The supernatants (which we termed EcoRI extract and surface extract, respectively) contained a number of extracellularly released proteins. Of these proteins, four major proteins were identified by N-terminal sequencing to be the 34 and 39 kDa outer membrane proteins, the GroEL-like protein, and a 47 kDa protein homologous to Haemophilus influenzae enolase. Enolase activity was found in the extracts and its relative amount of activity in the EcoRI extract from a culture of the mid-exponential growth phase was estimated as 5.7% of total enzyme activity. In contrast, the relative amount of activity of another cytosolic enzyme, lactate dehydrogenase, was extremely low in the extracts and also in the culture supernatant. These results suggest the external localization of enolase in this bacterium.

Nonspecific adherence by Actinobacillus actinomycetemcomitans requires genes widespread in bacteria and archaea

The gram-negative coccobacillus, Actinobacillus actinomycetemcomitans, is the putative agent for localized juvenile periodontitis, a particularly destructive form of periodontal disease in adolescents. This bacterium has also been isolated from a variety of other infections, notably endocarditis. Fresh clinical isolates of A. actinomycetemcomitans form tenacious biofilms, a property likely to be critical for colonization of teeth and other surfaces. Here we report the identification of a locus of seven genes required for nonspecific adherence of A. actinomycetemcomitans to surfaces. The recently developed transposon IS903phikan was used to isolate mutants of the rough clinical isolate CU1000 that are defective in tight adherence to surfaces (Tad(-)). Unlike wild-type cells, Tad(-) mutant cells adhere poorly to surfaces, fail to form large autoaggregates, and lack long, bundled fibrils. Nucleotide sequencing and genetic complementation analysis revealed a 6.7-kb region of the genome with seven adjacent genes (tadABCDEFG) required for tight adherence. The predicted TadA polypeptide is similar to VirB11, an ATPase involved in macromolecular transport. The predicted amino acid sequences of the other Tad polypeptides indicate membrane localization but no obvious functions. We suggest that the tad genes are involved in secretion of factors required for tight adherence of A. actinomycetemcomitans. Remarkably, complete and highly conserved tad gene clusters are present in the genomes of the bubonic plague bacillus Yersinia pestis and the human and animal pathogen Pasteurella multocida. Partial tad loci also occur in strikingly diverse Bacteria and Archaea. Our results show that the tad genes are required for tight adherence of A. actinomycetemcomitans to surfaces and are therefore likely to be essential for colonization and pathogenesis. The occurrence of similar genes in a wide array of microorganisms indicates that they have important functions. We propose that tad-like genes have a significant role in microbial colonization.

A novel factor isolated from Actinobacillus actinomycetemcomitans stimulates mouse B cells and human peripheral blood mononuclear cells

A novel immunostimulating factor (ISTF) of Actinobacillus actinomycetemcomitans ATCC 29522 was isolated and characterized as inducing proliferation of mouse B cells and human peripheral blood mononuclear cells. This factor was isolated from the bacterial culture medium and purified by size exclusion chromatography, dye-ligand affinity chromatography, immunoaffinity chromatography using monoclonal antibodies, and preparative electrophoresis. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the purified ISTF migrated as a single band corresponding to a molecular mass of 13 kDa. ISTF was a proteinaceous material distinct from lipopolysaccharide; it directly induced the proliferation of B lymphocytes but had no effect on the proliferation of T lymphocytes, even in the presence of antigen-presenting cells. A B-lymphocyte-mitogenic activity of ISTF was also shown by flow cytometric analysis of responding cell subpopulations. Immunoblot analysis revealed that ISTF was a component of the outer membranes of bacteria, could exist as a soluble form, and was released by growing and/or lysed bacteria. These results suggest that ISTF produced by A. actinomycetemcomitans may play an important role in immunopathologic changes associated with A. actinomycetemcomitans infections.

Relationships between the onset of pustulosis palmaris et plantaris, periodontitis and bacterial heat shock proteins

Relationships between the onset of pustulosis palmaris et plantaris, periodontitis and heat shock proteins were studied by using enzyme-linked immunosorbent assay to examine levels of immunoglobulin G (IgG) against Escherichia coli GroEL, a recombinant DnaJ of Actinobacillus actinomycetemcomitans heat shock protein, a synthetic peptide made from the 180th to the 188th amino acids of Mycobacterium bovis BCG Hsp65, and a recombinant human Hsp60, in sera obtained from 43 pustulosis palmaris et plantaris patients judged to have chronic infectious diseases of the oral cavity. We found that the titers of IgG against E. coli GroEL and A. actinomycetemcomitans DnaJ in the sera from pustulosis palmaris et plantaris patients were significantly higher than those in the control group, whereas the titers of IgG against the synthetic M. bovis Hsp65 and the recombinant Hsp60 did not differ significantly. Periodontal therapy and extraction of teeth with periapical infectious resulted in remission of pustulosis palmaris et plantaris and a statistically significant reduction in the levels of IgG against E. coli GroEL in 9 of the 22 patients (41%) examined. We also found that the IgG levels against A. actinomycetemcomitans DnaJ in 6 serum samples of 16 (37%) were reduced, but not significantly, after the treatment. These results suggest that the IgG responses to heat shock proteins partially induced by oral bacteria may be related to the onset of pustulosis palmaris et plantaris in some patients.

Localization of heat shock proteins in clinical Actinobacillus actinomycetemcomitans strains and their effects on epithelial cell proliferation

Actinobacillus actinomycetemcomitans is an important pathogen in periodontitis. In the present study we localized the GroEL- and DnaK-like heat shock proteins (Hsp) in subcellular fractions of 12 A. actinomycetemcomitans strains of various clinical origin and compared their effects on periodontal epithelial cell proliferation and viability. In all strains, GroEL-like protein was found in the membrane, cytoplasm, and periplasm, whereas DnaK-like protein was present in the cytoplasm and periplasm. No correlation was observed between the Hsp expression and the serotype or origin of A. actinomycetemcomitans strains. The bacterial membrane fractions that expressed the GroEL-like protein moderately or strongly induced epithelial cell proliferation more strongly than strains that expressed the protein weakly. The results suggest that GroEL-like Hsp may play a role in the virulence of A. actinomycetemcomitans by increasing epithelial proliferation.

Protective effect of serum antibodies against a 110-kilodalton protein of Actinobacillus actinomycetemcomitans following periodontal therapy

Thirty-four adult patients with untreated periodontitis were randomly assigned to receive full mouth scaling alone or scaling with an adjunctive antimicrobial therapy, both followed by supportive periodontal therapy. At 24 months, specific serum immunoglobulin A (IgA), IgG and IgG subclass antibody reactivities against a 110-kDa protein of Actinobacillus actinomycetemcomitans were assessed by Western blot. In patients harboring A. actinomycetemcomitans intraorally, the IgG4 antibody reactivity against the 110-kDa protein of A. actinomycetemcomitans was associated with significantly increased survival rates of teeth and of sites not exhibiting 2 mm or more of probing attachment loss. The same trend was found for IgG3 and IgG2 antibody reactivities, but it was statistically insignificant. No association with clinical treatment outcome was observed for IgA, IgG and IgG1 antibody reactivities. The results indicated that systemic IgG4 antibody reactivity against the 110-kDa protein of A. actinomycetemcomitans may have a protective effect against periodontal disease progression in patients harboring A. actinomycetemcomitans and receiving periodontal therapy.

Paradoxical role of PGE2 and cAMP in Actinobacillus actinomycetemcomitants strain Y4-induced lymphocyte proliferation

An immune mechanism has been suggested in the pathogenesis of periodontal disease. Actinobacillus actinomycetemcomitants (Aa) has been implicated as one of the etiological agents that induces the major immune response together with a dense infiltrate of inflammatory cells. But the exact role of these immune cells in periodontal disease has not yet been clarified. In this study the T lymphocyte (TL) proliferative response was evaluated after having being exposed to free cell supernatant (SN) from Aa. Aa SN increased TL proliferation. This mitogenic effect of Aa SN was attenuated by pretreating TL with indomethacin (INDO) or acetylsalicylic acid (ASA) but not by polymyxin B. The inhibitory effect of INDO on cell proliferation was reversed by the addition of prostaglandin E2 (PGE2) to the culture assay. Moreover, when immune cells were exposed to Aa SN they were able to generate PGE2 at the same time as intracellular levels of cAMP decreased. Both, PGE2 release and decrease accumulation of cAMP in TL were blunted by treated lymphocytes with INDO. In this paper we demonstrate that cell free SN from Aa induces a mitogenic effect on murine lymphocytes. The mechanism involves the host's immunecompetent cells and the release of PGE2 and appears not to be induced by capsular-like polysaccharide antigen. Results show a paradoxical mitogenic effect of Aa SN accompanied by increased generation of PGE2 and decreased production of cAMP by lymphocytes.