Tumor Necrosis Factor-α-converting Enzyme (TACE) Levels in Periodontal Diseases

Tumor necrosis factor-α-converting enzyme (TACE) is a metalloprotease which can shed several cytokines from the cell membrane, including receptor activator of NF-κB ligand (RANKL). This study aimed to investigate the hypothesis that TACE would be elevated in the gingival crevicular fluid (GCF) of persons with periodontitis. Total TACE amounts in GCF were higher in persons with chronic and aggressive periodontitis than in those with gingivitis or in healthy persons. TACE concentrations in GCF were higher in persons with chronic and aggressive periodontitis than in those with gingivitis, although not significantly higher than in healthy persons. Persons with chronic periodontitis receiving immunosuppressive treatment exhibited over 10-fold lower TACE levels than the other periodontitis groups. TACE was positively correlated with probing pocket depth, clinical attachment levels, and RANKL concentrations in GCF. In conclusion, the increased GCF TACE levels in persons with periodontitis and their positive correlation with RANKL may indicate an association of this enzyme with alveolar bone loss, and may warrant special attention in future therapeutic approaches.

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.

Release and activation of matrix metalloproteinase 8 from human neutrophils triggered by the leukotoxin of Actinobacillus actinomycetemcomitans

Matrix metalloproteinase 8 (MMP 8) degrades type I collagen and may be involved in the pathogenesis of periodontitis. Latent MMP 8 is stored in neutrophil granules and can be activated when released extracellularly. The periodontitis-associated bacterium Actinobacillus actinomycetemcomitans produces an RTX-toxin, leukotoxin, that degranulates and lyses human neutrophils. This study deals with the ability of leukotoxic A. actinomycetemcomitans to trigger the release and activation of MMP 8. Whole bacteria of three A. actinomycetemcomitans strains or leukotoxin purified from the highly toxic strain HK 1519 were incubated with human neutrophils. The extracellularly released latent and active forms of MMP 8 were detected by an immunoblot technique using specific antibodies against the protease. The activity of MMP 8 was determined by a collagen degradation assay. All strains induced release and activation of MMP 8. The effect was more pronounced under aerobic than anaerobic conditions and correlated with the leukotoxicity of the strains. Pure leukotoxin also induced MMP 8 release and activation in a concentration-dependent manner. Under aerobic conditions, oxidising substances formed by the neutrophils contributed to the rapid activation of the latent enzyme. Upon anaerobic incubation, the activation was slow and mainly caused by other proteases released during neutrophil degranulation. The activation was totally abolished in the presence of serum, probably due to the serum-protease inhibitors. Compared to the calcium ionophore A 23187, a well-known stimulus of neutrophil degranulation, leukotoxin was a more powerful inducer of MMP 8 release, since it triggered the process at a 1000-fold lower concentration. The present findings reveal a specific mechanism that can be induced by A. actinomycetemcomitans leukotoxin and which may contribute to the degradation of periodontal tissues under certain conditions.

The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments

AIM

The objective of the present experiment was to study the early pulpal cell response and the onset of reparative dentine formation after capping application of MTA in mechanically exposed pulps.

METHODOLOGY

Thirty-three teeth from three dogs, 12-18 months of age were mechanically exposed via class V cavities. Light pressure was applied to control haemorrhage. ProRoot MTA (Dentsply Simfra, Paris) was placed at the exposure site and light pressure was applied with a wet cotton pellet. The cavities were restored with amalgam and the pulpal tissue reactions were assessed by light and electron microscopy (transmission and scanning) after healing intervals of 1, 2 or 3 weeks.

RESULTS

A homogenous zone of crystalline structures was initially found along the pulp-MTA interface, whilst pulpal cells showing changes in their cytological and functional state were arranged in close proximity to the crystals. Deposition of hard tissue of osteotypic form was found in all teeth in direct contact with the capping material and the associated crystalline structures. Formation of reparative dentine (tubular matrix formation in a polar predentine-like pattern by elongated polarized cells) was consistently related to a firm osteodentinal zone.

CONCLUSIONS

The present experiments indicate that MTA is an effective pulp-capping material, able to stimulate reparative dentine formation by the stereotypic defensive mechanism of early pulpal wound healing.

Supragingival and subgingival microbiota of adult patients with Down's syndrome. Changes after periodontal treatment

In this longitudinal study, five adult Down's syndrome patients with periodontitis were placed on a frequent recall visit schedule (every 6 weeks) after treatment, in order to investigate: 1) the microbiological status, both supragingivally and subgingivally, and the changes that occurred after treatment and 2) the effect of frequent professional supragingival plaque control on the subgingival microbiota and clinical variables in these patients. The clinical variables recorded were probing pocket depth, probing attachment level, bleeding on probing and presence of plaque (full mouth, six surfaces per tooth). Microbiological examination was performed separately for supragingival and subgingival samples from the same site for 14 species, using whole genomic DNA probes and the "checkerboard" DNA-DNA hybridization technique. The findings indicate that, although a reduction of periodontal indices was noticed, plaque levels remained high (60%) even at the end of the experimental period. Periodontal pathogens including Porphyromonas gingivalis, Bacteroides forsythus and Actinobacillus actinomycetemcomitans were frequently detected both supragingivally and subgingivally (>30%). The presence of a species supragingivally and the presence at the same time points subgingivally were correlated. This finding suggested that supragingival plaque acts as a reservoir for reinfection of treated sites. A reduction of the percentages of detection of these species was noticed 1 month after an oral hygiene period as well as at 3 and 6 months after treatment. Inadequate oral hygiene as performed by these patients probably affected supragingival, and consequently subgingival, plaque composition.

Protease inhibitors, the responsible components for the serum-dependent enhancement of Actinobacillus actinomycetemcomitans leukotoxicity

Serum enhances the leukotoxic activity of Actinobacillus actinomycetemcomitans against human polymorphonuclear leukocytes (PMNL) by a mechanism that still is unknown. Early attempts to identify the serum components responsible for this enhancement gave no conclusive results, but indicated that the lipoprotein-containing fraction of the serum was involved in the interaction. This study aimed to clarify the role of serum lipoproteins in the leukotoxin interaction, and to identify other serum components involved. The main hypothesis examined was that the leukotoxicity enhancement might depend on serum protease inhibitors that block proteolytic cleavage of leukotoxin by enzymes released from the leukocytes. PMNL were isolated from human peripheral blood and incubated with purified leukotoxin in the presence of serum or purified serum components or lipoprotein-deficient serum. Leukotoxin was also incubated with purified elastase and cathepsin G or with enzyme mixtures from degranulated PMNL. The leukotoxic activity in these mixtures was determined as the extracellular release of lactate dehydrogenase from PMNL. Cleavage of the toxin was showed by gel electrophoresis and Western blot. Morphological changes in PMNL from the above mixtures were examined by electron microscopy. Enzymes from degranulated PMNL cleaved leukotoxin to non-cytotoxic fragments. Elastase and cathepsin G were mainly responsible for the cleavage. Inhibition of leukotoxin degradation was found in the presence of whole serum or of the serum protease inhibitors alpha2-macroglobulin and alpha1-proteinase inhibitor. Under these conditions enhanced PMNL lysis was also observed. A similar enhancement of PMNL lysis was found when PMNL degranulation was blocked by EDTA. On the other hand, lipoprotein-deficient serum had no influence on the leukotoxic activity. The results indicate that the increased leukotoxicity of A. actinomycetemcomitans observed in the presence of human serum is caused by the serum protease inhibitors that counteract proteolytic degradation of leukotoxin. The degradation is caused by enzymes from degranulated PMNL triggered by leukotoxin.

Dentin regeneration in vital pulp therapy: design principles

The nature and specificity of the mechanisms by which the amputated dentin-pulp interface is therapeutically healed determine the properties of the barrier at this site and play a critical role in the outcome of vital pulp therapy. Healing of the dentin-pulp complex proceeds either by natural repair-which results in defensive hard-tissue formation, or therapeutically regulated dentin regeneration, which aims to reconstitute the normal tissue architecture at the pulp periphery. Progress in biomedical research opens new directions for the design of biologically effective pulp therapies. Application of biocompatible and biodegradable carrier vehicles for local delivery of signaling molecules in pulp-capping situations showed induction of fibrodentin/reparative dentin formation, but often at the expense of underlying pulp tissue. An alternative pre-clinical model aiming to reconstitute normal tissue architecture directly at the dentin-pulp interface should be designed on the basis of the direct induction of odontoblast-like cell differentiation and reparative dentin formation at the pulp-capping material interface. Experimental data clearly showed that pulpal cells can differentiate directly into odontoblast-like cells in association with specific extracellular matrices (dentinal or fibrodentinal matrix) or TGF beta 1-containing artificial substrates. Dentin-induced dentinogenesis can be used as a master plan for the achievement of new therapeutic opportunities. In the present study, several short-term experimental studies on dog teeth for potential direct induction of odontoblast-like cell differentiation at the surface of rhTGF beta 1-containing artificial substrates (Millipore filters, hydroxyapatite granules, calcium hydroxide, pure titanium) failed to induce any specific reparative dentinogenic effects.