Effects of a bacterial cell wall fragment on monocyte inflammatory function

Proinflammatory mediators related to orthodontically induced periapical root resorption in rat mandibular molars

Objectives

The early phase of orthodontic tooth movement involves acute inflammatory response that may induce bone resorption. The aim of this study was to localize and quantify cells in the periodontium expressing proinflammatory mediators during orthodontically induced periapical root resorption of the rat mandibular molars.

Materials and methods

The levels of proinflammatory cytokines interleukin-1 (IL-1) α and β, tumor necrosis factor-α (TNF-α), inflammatory enzymes cyclooxygenase (COX) 1 and 2, and their product prostaglandin E2 (PGE2) in the root resorption site were compared to those in the corresponding area of the untreated periodontal ligament (PDL) of physiologically drifting teeth. Continuous heavy orthodontic force was applied to the mandibular first molar for 8 and 15 days while in occlusion to induce root resorption. Frozen sections including root resorption lacunae were analyzed for the activity of non-specific esterase (NSE) and tartrate-resistant acid phosphatase (TRAP) by enzyme histochemistry and for the expression of IL-1α, IL-1β, TNF-α, COX-1, COX-2, and PGE2 by immunohistochemistry.

Results

The active root resorption lacunae had significantly more TRAP-positive multinucleated odontoclasts, whereas the number of NSE-positive cells of the monocyte-macrophage lineage did not differ from that in the control PDL. Several types of periodontal cells exhibited a significant increase in the expression of IL-1α, IL-1β, TNF-α, COX-2, and PGE2 in the root resorption zone, while COX-1 was rarely detected.

Conclusions

These data suggest that proinflammatory mediators expressed in periodontal cells may synergistically promote apical root resorption in response to continuous heavy mechanical force applied to teeth.

Structural Requirements of Synthetic Muropeptides to Synergize with Lipopolysaccharide in Cytokine Induction

Muropeptides contribute to the recognition of bacteria by modulating immune responses: the structural requirements for adjuvant activity were described in the seventies. During the last years, our knowledge of bacterial pattern recognition has increased dramatically and the importance of the absence of contaminations in both muropeptide preparations and other bacterial stimuli has become clear. We investigated a panel of 15 synthetic Limulus-negative muropeptides, four of them synthesized for the first time, as to their potency to synergize with lipopolysaccharide (LPS) in cytokine induction in human whole blood. No muropeptide was capable of stimulating cytokine release from human blood. However, as little as 20 nM of the muropeptides N-acetyl-muramyl-l-alanyl-d-isoglutamine (muramyl dipeptide, M(AdiQ)), N-acetyl-glucosamine-muramyl dipeptide GM(AdiQ), or C(18)M(AdiQ), which carries a non-natural additional fatty acid, sufficed to induce an up to 3 log-order shift in tumor necrosis factor alpha-release in response to 100 pg/ml LPS. The release of interleukin-1beta, interleukin-6, and interleukin-10 was also significantly enhanced although to a lesser extent. The synergistic effect was stereoselective with M(AdiQ) being the minimal active principle. Synergy was also observed on the transcriptional level by means of real-time PCR. Smaller molecules like N-acetylmuramic acid (M), aM, carrying a naturally occurring 1,6-anhydro-bound in M or M(A), containing only the amino acid l-alanine neither synergized with LPS nor influenced the synergy of other muropeptides with LPS. In conclusion, these data show that nanomolar quantities of muropeptides dramatically potentiate LPS-induced monocyte activation. This has implications for pyrogenicity testing and endotoxemia in patients.

The synergistic effect of peptidoglycan and lipopolysaccaride on osteoclast formation

PURPOSE

The purpose of this study was to investigate the mechanisms leading to periapical tissue destruction by the Gram-positive bacterial cell component, peptidoglycan (PGN) and Gram-negative bacterial cell component lipopolysaccaride (LPS).

STUDY DESIGN

Osteoclast precursor RAW 264.7 cells were cultured with 50 ng/ml receptor activator of NF-kappaB ligand (RANKL) for 72 hours. RANKL was then removed and the cells were treated with various concentrations of PGN in the presence or absence of various concentration of LPS for an additional 48 hours. RT-PCR analysis was performed to examine the presence of receptors on osteoclasts known to be involved in mediating cellular activation in response to PGN (TLR2) and LPS (TLR 4).

RESULTS

PGN dose dependently and reproducibly stimulated TRAP-positive multinucleated osteoclast-like (OCL) cell formation. PGN and LPS had synergistic effects on the induction of OCL cell formation. Both unstimulated and RANKL-stimulated RAW 264.7 cells expressed TLR2 and TLR4 mRNA.

CONCLUSION

The results underscore the importance of considering both Gram-positive and Gram-negative bacteria when interpreting findings associated with primary and secondary periapical lesions.

Evidence for a role of mitogen-activated protein kinases in proliferating and differentiating odontogenic epithelia of inflammatory and developmental cysts

OBJECTIVE

The activation of intracellular signaling cascades involving serine/threonine kinases ERK1/2 has been variably reported either to stimulate or inhibit epithelial cell differentiation in response to extracellular signals. The purpose of our study was to determine the distribution of the signaling molecule ERK1 and its activated form pERK1/2 in the epithelial components of developmental and inflammatory odontogenic cysts in relation to parameters of differentiation and proliferation.

STUDY DESIGN

Thirty samples of dental follicles, dentigerous cysts, and radicular cysts were immunostained with antibodies to ERK1, pERK1/2, and proliferating cell nuclear antigen (a marker for proliferation). The tissues were subclassified according to the pattern of histomorphological differentiation (ie, squamous differentiation) and the proliferation rate of their epithelial components. The significance of differences in the proportion of ERK1- and pERK1/2-expressing cells among the tissue groups was determined by chi-square analysis or Fisher's exact test.

RESULTS

ERK1 and pERK1/2 were found to be expressed in a significantly higher proportion of cells with differentiated and highly proliferating epithelial components, as compared with those of nondifferentiated, quiescent epithelial rests. The epithelium of radicular cysts exhibited the highest proportion of pERK1/2-positive cells. In both dentigerous and radicular cyst samples, pERK1/2 expression was significantly higher in the inflamed tissues.

CONCLUSIONS

These data demonstrate that ERK1 and its active form pERK1/2 are associated with differentiating and actively proliferating epithelia of odontogenic cysts, and are consistent with pERK1/2 involvement in the activation of odontogenic epithelia in response to inflammation.